The mechanical properties of the non-sticky spiral in Nephila orb webs (Araneae, Nephilidae).

STRUCTURAL-ENGINEERING OF AN ORB-SPIDERS WEB

Author(s): LIN, LH (LIN, LH); EDMONDS, DT (EDMONDS, DT); VOLLRATH, F (VOLLRATH, F)

Source: NATURE  Volume: 373   Issue: 6510   Pages: 146-148   DOI: 10.1038/373146a0   Published: JAN 12 1995

Times Cited: 52 (from Web of Science)

Cited References: 17      

Abstract: THE silk of spiders first evolved 400 million years ago and orb webs emerged 180 million years ago(1,2); present-day spiders' webs are structures efficiently engineered by nature. The planar orb web of the garden spider Araneus diadematus has evolved with the prime function of capturing fast-moving and, on a relative scale, massive insects. We have now analysed the structural engineering of a complete web, using computer modelling, to incorporate the measured time-dependent stress-strain characteristics of the two chief types of web silk. With this model we unexpectedly discovered that aerodynamic damping plays a crucial role in prey capture, an observation that we confirmed in laboratory experiments on real webs.

Comparative study of the internal structures of Kevlar and spider

silk by atomic force microscopyS. F. Y. Li, A. J. McGhie, and S. L. Tang

Atomic force microscopy was used to study the internal structures of Kevlar(R) 49 fibers and spider dragline silk from the microtomed sections of the fibers. Both fibers exhibited fibrillar structures. For Kevlar(R), the fibrils were aligned along the fiber axial direction, tightly packed and braided. In addition, a prominent skin layer was present. For the dragline silk, pleated fibrils that were unfolded upon extension were observed in the core region. The skin appeared to be very thin. These structural features correspond well with the mechanical properties of these high‐strength fibers.

Spider orb webs rely on radial threads to absorb prey kinetic energy

1. Andrew T. Sensenig 1 ,*, 2. Kimberly A. Lorentz 2 , 3. Sean P. Kelly 2  and 4. Todd A. Blackledge 2

+Author Affiliations1. 1Department of Biology, Tabor College, Hillsboro, KS 67063-1799, USA

2. 2Department of Biology and Integrated Bioscience Program, University of Akron, Akron, OH 44325-3908, USA

1. ↵ *Author for correspondence (andrews@tabor.edu). 

Next Section

Abstract

The kinetic energy of flying insect prey is a formidable challenge for orb-weaving spiders. These spiders construct two-dimensional, round webs from a combination of stiff, strong radial silk and highly elastic, glue-coated capture spirals. Orb webs must first stop the flight of insect prey and then retain those insects long enough to be subdued by the spiders. Consequently, spider silks rank among the toughest known biomaterials. The large number of silk threads composing a web suggests that aerodynamic dissipation may also play an important role in stopping prey. Here, we quantify energy dissipation in orb webs spun by diverse species of spiders using data derived from high-speed videos of web deformation under prey impact. By integrating video data with material testing of silks, we compare the relative contributions of radial silk, the capture spiral and aerodynamic dissipation. Radial silk dominated energy absorption in all webs, with the potential to account for approximately 100 per cent of the work of stopping prey in larger webs. The most generous estimates for the roles of capture spirals and aerodynamic dissipation show that they rarely contribute more than 30 per cent and 10 per cent of the total work of stopping prey, respectively, and then only for smaller orb webs. The reliance of spider orb webs upon internal energy absorption by radial threads for prey capture suggests that the material properties of the capture spirals are largely unconstrained by the selective pressures of stopping prey and can instead evolve freely in response to alternative functional constraints such as adhering to prey.

1. Introduction

More than 3000 species of spiders rely on silk orb webs to capture flying insect prey [1,2]. The ability of orb webs to stop insects in midflight helps make these spiders dominant predators of insects in many ecosystems [3,4]. Orb webs are spun from some of the toughest known biological materials—spider silks, which can exceed even synthetic fibres such as Kevlar in their capacity to absorb energy without breaking [5–7]. The exceptional performances of the dragline silk, which composes the supporting radial threads and frames of orb webs, and the elastic capture spiral silk, are hypothesized to result from strong selection of their role in absorbing the tremendous kinetic energy of flying insect prey. However, these silks are combined together into complex, composite structures—orb webs, which undergo strong deformation during prey impact. Thus, the work performed by an orb web during prey capture may be determined not only by the intrinsic material properties of silk threads, but also by how those threads are interconnected and even by the aerodynamic drag of the web moving through the air [8,9]. While many studies measure and compare the material properties of discrete spider silk threads [8,10–12], the actual process by which orb webs absorb prey energy is largely uninvestigated [9,13].As the threads in an orb web are stretched by an insect, the kinetic energy of flight is transferred to the silk. Some of that energy is stored in the molecular deformation of the silk and will be returned to the insect as the web oscillates. However, much of the

energy is permanently removed from the prey through viscous dissipation as flight energy is converted to heat [7]. The fraction of energy lost to viscous dissipation within a silk fibre as the thread is stretched is the damping capacity (or hysteresis) of the silk and is critical for preventing insects from ‘catapulting’ back out of the web after prey impact [7,14]. In contrast to other energy absorbing, tough biomaterials like rubber or mammalian hamstring that lose less than 5 per cent of energy in a cycle, spider silks exhibit damping capacities as high as 70 per

cent [7,14]. This suggests that internal dissipation of energy by silk threads may dominate the prey-stopping function of orb webs.However, spider silk stretches substantially during prey strikes so that aerodynamic damping could account for a significant proportion of the energy dissipated by orb webs [14]. Reynolds number (Re) describes the ratio of inertial to viscous force on an object moving through a fluid, such as air [15]. Spider silk moves through the air during prey impact at velocities of up to 5 m s –1, so that its interaction with the air occurs at intermediate Re numbers typically defined as Re ∼ 1 [15]. At intermediate Re numbers, the drag force on an object moving through fluid is taken from empirical measurements, because the importance of inertial and viscous forces complicates an analytical solution. Aerodynamic drag on spider silk is supported by the ‘ballooning’ of juvenile spiders as they float through the air on silk threads [16]. However, the importance of aerodynamic dissipation for the function of orb webs is unclear, with some studies suggesting that it is crucial for stopping flying insects [9] while others ignore aerodynamic dissipation entirely when describing web mechanics [17–19].

Energy dissipation by orb webs can be partitioned into three components: (i) internal dissipation within the radial silk, (ii) internal dissipation within the capture spiral silk, and (iii) aerodynamic drag as the web moves or oscillates during prey impact. Our study is the first to quantify and compare the importance of each of the three potential routes for viscous dissipation of flight energy during prey capture. In particular, we test the hypothesis that orb webs depend upon aerodynamic dissipation as a vital component for stopping flying insects. We also consider how energy dissipation is partitioned among these three routes for different sizes of orb webs and its implications for the evolution of spider orb webs.

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2. Methods

2.1. Spiders

We collected penultimate and adult female spiders at the University of Akron's Field Station at the Bath Nature Preserve, OH and nearby localities. Spiders were housed in either 40 × 40 × 10 cm or 80 × 80 × 20 cm screen cages with removable Plexiglass sides, depending upon the spider's size [20]. Spiders were held in a 23°C room and misted with tap water daily. Humidifiers were used to keep humidity above 60 per cent to stimulate web spinning and ensure that the glue droplets of the capture spiral were well hydrated, maximizing their stickiness [21]. Only freshly spun orb webs were included in the study. Eight orb webs were analysed in detail to determine how prey energy was dissipated by webs, one web each from Argiope aurantia, Neoscona domiciliorum, Araneus trifolium, Araneus bicentenarius, Larinioides cornutusand Verrucosa arenata, and two webs from two different individual Argiope trifasciata (table 1). Adult spiders in these species spin threads and webs that are sufficiently large (more than 19 cm width) to be measured in our study, although significantly smaller, ‘miniature’ orb webs are common in nature [2].Table 1.

Spider taxa and energy parameters of reconstructed impacts. Web diameter is the horizontal span of the web. Uncertainty intervals are computed using the method of propagation of error.

View this table:

taxa

body weight (mg)

projectile weight (mg)

relative impact energy (μJ mg−1)

projectile mass/spider mass

energy absorbed by radials ± uncertainty (μJ)

energy absorbed by spirals ± uncertainty (μJ)

energy absorbed by aerodynamic drag ± uncertainty (μJ)

web diameter (cm)

total input energy (μJ)

Araneus bicentenarius 800 30 0.04 0.04 28 ± 65 1.7 ± 1.8 1.2 ± 0.5 29 40

taxa

body weight (mg)

projectile weight (mg)

relative impact energy (μJ mg−1)

projectile mass/spider mass

energy absorbed by radials ± uncertainty (μJ)

energy absorbed by spirals ± uncertainty (μJ)

energy absorbed by aerodynamic drag ± uncertainty (μJ)

web diameter (cm)

total input energy (μJ)

Araneus trifolium 1270 98 0.18 0.08 207 ± 244 11 ± 10 9 ± 1 21 180

Argiope aurantia 375 500 3.2 1.33

1067 ± 497 60 ± 30 85 ± 13 19 1245

Argiope trifasciata 100 30 0.38 0.30 32 ± 31 1.5 ± 1.9 4 ± 0.6 27 19

Argiope trifasciata 172 98 3.3 0.57 526 ± 365 9 ± 4 39 ± 1.9 25 466

Larinioides cornutusa 121 500 7.2 4.13 421 ± 310 214 ± 107 241 ± 3.7 33 1707

Neoscona sp. 50 30 3.4 0.60 80 ± 75 88 ± 76 4 ± 0.7 20 33

Verrucosa arenataa 56 30 0.4 0.54 9 ± 15 7.5 ± 8.6 3.2 ± 0.2 21 43

aBreaking impacts.

An additional 45 orb webs from 45 individual spiders of seven species were examined to study how the numbers of threads contacting prey affected capture. These webs included a Metepeira species, in addition to those listed above (table 2).

View this table:

taxan (number of webs)

body weight (mg) mean ± s.d.

total energy absorbed (μJ) mean ± s.d.

Metepeira sp. 6 130 ± 20 545 ± 220

Verrucosa arenata 3 56 ± 1 759 ± 960

Larinioides cornutus 29 144 ± 66 718 ± 443

Argiope trifasciata 3 136 ± 1 1919 ± 948

Neoscona domiciliorum 1 47 ± 0 835 ± 0

Araneus trifolium 2 1162 ± 153 1161 ± 977

Araneus bicentenarius 1 800 ± 0 133 ± 0

all groups 45 183 ± 226 787 ± 591

 

Table 2.

Descriptive statistics for an escaping 300 mg projectile. The energy absorbed by webs during impact by this relatively high energy projectile was measured by tracking the deceleration of the projectile in 500 fps video. Energy measurements were taken from a total of 45 different webs spun by different

spiders, and regressed against the number of spiral and radial threads contacted during the impact (figure 8).

2.2. Projectiles simulating flying prey

We used rectangular blocks of balsam wood to simulate insect prey because their densities allowed us to make projectiles of similar sizes and masses as real insects. Blocks of 30, 98, 300 or 500 mg balsam wood were launched into the middle of the capture areas of orb webs with velocities between 1 and 3 m s–1 using a spring actuated ‘gun’ constructed from PVC pipe. Projectiles were fired at a distance of 0.5 m from the webs so that ‘prey’ impacted webs with kinetic energies very similar to typical insect prey of spiders, flies (30 μJ) and large grasshoppers (1100 μJ) [22]. A range of prey sizes relative to spider masses were used in order to measure web performance under both easy and extreme conditions. For example, the relative size of prey versus spider body mass varied from just 4 per cent of the spider mass for an Araneus bicentenarius web up to a 500 mg prey that was 400 per cent the mass of the Larinioides cornutus web builder.2.3. Imaging methods

Images were captured using a single Fastech Troubleshooter 1268 × 1024 pixel camera (17150 Via Del Campo Suite 301, San Diego, CA, USA) at 500 fps. The camera was fitted with a 15 f lens and positioned at a 45° angle to the web at a distance of 2 m. Webs were then back-illuminated using two 250 W lights positioned at 90° from each other, about 20 cm from the webs, and just out of the frame of view. A 15 × 15 cm Rosco Roscolux Super Heat Shield was placed between each light and the web. PROANALYST motion analysis software (Xcitex, Inc., Cambridge, MA, USA) was then used to digitize up to 64 silk junctions between capture spirals and radial threads.2.4. Web discretization

The prey position was tracked beginning at 16 frames (32 µs) before contact with silk. To track web motion after impact, we digitized up to 64 points (figures 1–3), representing the inner, middle and outermost capture spiral junctions with each radius in the web. The autotracking feature of PROANALYST then measured the position of each point for every subsequent frame of video. This marking scheme designated two regions within each radius—an inner and outer segment, whose extensions could be tracked independently over time. It also defined inner, mid and outer sectors of capture silk, with the length of each row of capture spiral within a sector defined by the distance between the adjacent radial threads. Because not all the capture spiral junctions were tracked, we approximated the behaviour of some capture spiral threads within a sector from their nearest tracked neighbour. To do this, the number of rows of capture spiral within a sector was calculated as one-third of the total rows of capture spiral:

2.1

 

Figure 1.

Discretization of web segments in a simplified spider orb web. The inner, middle and outermost junctions with the capture spiral were designated for each radius. Only points from 08.00 h inside to 09.00 h outside are depicted here. The radial segment 9 mid–9 out is illustrated in bold and the spiral segment group 8 mid–9 mid is illustrated with two dotted lines. The load of a single spiral segment is multiplied twofold in this simplified web because it represents two of the six total rows of the capture spiral. Actual webs used in the study had many more rows of capture spiral than this, with up to 39 rows in Argiope trifasciata. Radii are approximately three orders of magnitude stiffer than capture spirals and are therefore stretched to much lower extensions during most impacts.

 

Figure 2.

Web of Araneus trifolium (body weight 1270 mg, web width 21 cm) broken by a 300 mg balsam wood projectile. Note the high displacement of threads around the local area of impact when compared with the rest of the web. Frames are separated by 10 ms.

View larger version:

 

Figure 3.

Energy absorption colour scale is normalized to the web region absorbing the highest energy. Aerodynamic dissipation for each segment was less than 0.1 relative energy, and is therefore not depicted. The inner-, middle and outer-most rows of capture spiral are summarized together. (a) Large web of A. trifolium (21 cm wide, spider weight 1270 mg) catching a balsam block (98 mg) shows that radii far from the impact site absorbed significant energy. (b) A slightly smaller web of Verrucosa arenata (21 cm wide, spider weight 56 mg) slowing, but not stopping, a balsam wood block (30 mg) shows that radial and capture spiral silk absorbed equivalent amounts of energy, with little role played by aerodynamic drag. The block broke through the web but was slowed from 2 to 0.3 m s−1.

The total length of capture spiral within each discrete region was then calculated as 2.2where Sli, the single spiral segment length (m), was computed as the distance between the two adjacent radial thread points that defined that spiral sector. In conclusion, our digitization constructed a digital web ‘skeleton’ that directly measured some of the threads and approximated the remaining threads (figure 3).2.5. Spatial calibration

Orb webs are approximately planar structures that are distorted into conical shapes during insect impact. We used a single video camera and performed spatial calibration in two planes: parallel and perpendicular to the web plane. Neither calibration correctly captured all of the motion of the points on the three-dimensional cone, but instead provided exact measurements only for points in the specified calibration plane and then approximated the rest of the points.

A planar grid with 2.54 cm squares served as the calibration object. Perspective transformation was accomplished internally by PROANALYST. First, the two-dimensional space was calibrated in the plane parallel to the web surface. This calibrated all motion in that two-dimensional space, assuming no motion out of this plane. Perpendicular plane calibration was also accomplished within PROANALYST. This perspective calibration quantified motion of those points residing entirely on the plane perpendicular to the web surface and that intersected the web hub. In order to quantify the error

introduced by the single plane assumption, we compared the strain values from each calibration. The difference in velocities, strains and segmental distances between these calibrations provided measures of spatial uncertainty owing to the calibration error (see electronic supplementary material) [23]. Together, the experimental error in measuring each of these variables produces a range in the energy that we compute to be absorbed by the web. We used the most extreme differences between estimates to calculate the maximum error in our measures of thread displacement.

2.6. Kinetic energy of projectiles

The pre-impact kinetic energy (KEinitial) of each projectile was calculated from the projectile's positions in the video frames for 16 frames prior to impact. Projectiles were launched at the web so that flight trajectories deviated from the normal vector of the web by less than 10° horizontally. The plane of the flight trajectory was parallel to the perpendicular calibration plane. Total energy input to the web was calculated as the sum of the changes in kinetic and gravitational potential energies in this calibration plane as the prey came to rest in the web. Gravitational energy change was computed from the difference in height between initial impact and rest.

2.7. Tensile testing of silk threads

Internal energy absorption by the radial and capture spiral silks was calculated by combining the video-derived strain data with mechanical testing data on energy absorption and damping by the capture spiral and radial silk. Tensile tests were performed using a Nano Bionix test system (Agilent Technologies, TN, USA), previously described in Blackledge et al. [24]. Our goal was to measure the load (i.e. force) versus strain curve at various relevant extension–retraction cycles, in order to characterize the work performed by threads within the capture areas of webs as they stretched to different distances [14]. Damping capacity, or the fraction of energy lost in viscous dissipation within the silk in a loading–unloading cycle, was calculated from the area under the load–strain curve during each extension–relaxation cycle [14]. It was important to separate the amount of energy lost versus stored during thread extension because prey oscillate in webs, repeatedly straining and then relaxing threads. Damping capacity was measured for three capture spirals and three radial threads from each web. The median tensile strength fibre was then chosen as representative of the performance of the rest of the fibres in the web for the reconstruction of energy absorption.

2.8. Modelling energy absorbed by thread strain

Internal silk strain energy was estimated separately for capture spiral and radial threads. For the capture spiral, the load measured for a single thread was multiplied by the number of capture spiral rows in that discretized region to compute the total load for that region. Strain energy for a time increment (frame interval of 0.002 s) was set to zero except when a thread segment was extending at positive strain beyond the native tension necessary to hold a stationary web taut. Energy dissipation owing to silk strain was then summed across web regions for each time increment separately for each silk type.

Damping capacity of 0.50 ± 0.30% was measured for both capture spiral and radial threads close to breaking strains (figure 4b,c) such that we used a damping capacity of 0.5 for all webs to reconstruct energy dissipation [14]. We measured much lower dampening capacities in silk at low strain, but they were associated with such low force that they were largely irrelevant to the overall calculation of impact energy absorption. For instance, damping capacity was less than 0.2 for radial threads stretched less than 5 per cent strain, and were subject to proportionally large experimental error owing to the low forces involved. Capture spiral threads exhibited nearly perfect elastic energy return (0 damping capacity) at strains less than 20 per cent (figure 4c). At higher strains (greater than 100%), the damping capacity of capture spiral silk was equivalent to radial threads. Thus, 0.50 of the loading energy was assumed to be lost instantaneously at each increasing strain increment for all webs. Variation in the loading force curve across spiders was far more significant for computing energy absorption than was the small variation in damping capacity (e.g. 20 times increase in radial thread energy absorption was computed using high loading force radial threads instead of low-force threads

compared with only four times increase in radial thread energy absorption when modelling 70% instead of 20% damping).

 

Figure 4.

(a) Damping capacity testing of a single thread of radial silk. A radial thread from a Larinioidesweb is strained and relaxed in 5% strain increments, with energy damping indicated by the shading under each stress–strain curve. The thread was first pulled to 5%, followed by 10%, then 15%, and so on until break. The dotted line indicates the final cycle where the radius broke. The force at a given strain in subsequent stretch cycles was always lower than the previous cycle. (b) Radial thread tensile test from an Araneus web. Radius load climbs rapidly with extension, and typically breaks at approximately 0.3 engineering strain (30% extension). The force versus strain was fitted with a third-order polynomial for the loading region of the curve (top arrow). Energy absorbed by the thread is the area inside the loading and unloading curves. (c) Capture spiral thread tensile test from the same web as (b). (d) The loading cycles of (b) and (c) shown to scale. Radii are much stiffer than capture spiral, and hence absorb significant energy at very small strains. Both radii (red line) and capture spiral (blue line) are shown in cycles close to breaking strain.The energy (R) dissipated by radius segment j at each time increment i was calculated as

2.3where HR is the damping capacity of 0.5, ΔLR the incremental change in length and FR the instantaneous load on the thread segment.2.8.1. Aerodynamic drag estimation

The ratio of inertial to viscous force on an object moving through a fluid defines the Reynolds number (Re). Spider silk moves through the air during prey impact at velocities resulting in an intermediate  Re. For example, maximum speeds of targeted flying insects are about 3 m s –1and maximum diameters of

threads are 6 µm, producing a maximal Re of approximately 1: 2.4for spiral segment j in time increment i, where u = speed of thread, d = thread diameter (between 1 and 6 µm), and γ is the kinematic viscosity of air at room temperature, 16 × 10–6 m2 s–1.Empirical formulae for the drag coefficient (Cd) on a cylinder moving normal to flow are derived from wind or water tunnel experiments at intermediate Re [25]. Such studies show that Cd is a function

of Re and the classic approximation by Tritton is [25] 2.5The velocity of each thread of the discretized web was input to Tritton's approximation to derive a drag coefficient appropriate for that

thread in that time interval. Drag force (D) on spiral j in time increment i was calculated as

2.6where u is the speed of thread, ρ the density of the fluid, d the diameter of the thread, Sl is the spiral length associated with that discretized web point and Cd the drag coefficient [25]. Note that thread diameter (d) cancels with the thread diameter implicit in Cd. Thus, drag force is independent of thread diameter, as noted in the study of Lin et al. [9].

Total length of capture spiral silk in discrete region j was computed as 2.7where Sli is the single spiral segment length (m), and Sn the average number of capture spirals within the region.The energy dissipation by aerodynamics (A) on region j in time increment i was calculated as

2.8where the increment of the capture spiral region displacement in the calibration plane was calculated

as 2.9where f is the camera frame rate of 500 frames s–1.

The dissipation owing to air resistance was then summed across web regions at each time increment, and a cumulative sum then taken over time to estimate the total aerodynamic dissipation.

By conservation of energy, total energy dissipated by the web should be equivalent to the total change in projectile energy, both for successful capture events and for escapes at the moment projectiles lost contact with the silk. We refer to the total change in projectile energy as the total energy input to the web and define the total absorbed energy as the sum of the energy dissipated internally by radial threads, internally by capture spirals and through aerodynamic drag. The congruence of the independent measures of energy input and energy absorption served as a check on the assumptions intrinsic to the dissipation calculations (electronic supplementary material, figure S9). Oscillations decay so that after two oscillations, negligible energy remains, although the web can visibly oscillate more than six times.

Spider weight correlates highly with the total silk volume used in a web [20], which itself strongly influences prey capture. Therefore, in order to standardize impact energy and to rank impacts by ‘ease of capture’, we divided the total absorbed energy by the spider weight. Hereafter, we refer to this parameter as relative impact energy. While this ignores variation in silk toughness across species, the simplification is justified in that silk toughness varies fourfold across species, while spider weight varies by 25-fold in the current study, so that it plays a significantly greater role in determining inter-individual variation in our experiment. The energy absorbed by each of the three dissipation routes was divided by the total input energy to derive a fraction of total work. We then asked, using a univariate linear regression, whether any of these work fractions changed with relative impact energy or spider body weight [26].Finally, we calculated two parameters to measure how the contribution of capture spiral silk and radial silk to stopping projectiles varied across the entire orb web surface. The first parameter, ‘fraction of web at high strain’, measured the area of web containing silk stretched to our pre-defined high level of strain, where energy damping becomes significant. We defined high strain for radial threads as greater than 5 per cent because this meant that the silk had clearly yielded, thereby influencing its future performance in the web and resulting in significant damping. High strain for capture spiral was defined as strain greater than 20 per cent. This was near the strain in which the recovery force was not equivalent to the extension force, and therefore damping capacity became measurable. The second parameter, ‘90 per cent energy threshold’, measured the minimal area of the web accounting for 90 per cent of the total energy dissipation. Each of these parameters was computed separately for radial and spiral silk. The discretized segments meeting each criterion were normalized by total number of segments in the web, creating a ratio that was essentially the length of highly strained silk to the total length of silk in the web. We then asked whether any of the ‘area’ parameters for each of the silk types changed with relative impact energy by using univariate linear regression [26].2.9. Influence of thread contact area

Finally, we measured the details of how threads contacted prey blocks related to energy absorption for a larger set of web impacts (table 2). The total energy input to orb webs from a 300 mg block was measured by the change in mechanical energy of the projectile. The goal here was to relate the number of radial and capture spiral threads directly in contact with the block to the performance of the

web, in terms of energy removed by the web. While about half of the projectiles were caught by the web, these events can underestimate potential performance of the web. Therefore, we selected only breaking impacts for this analysis because they represent events where webs clearly performed to their maximum potential. We used a multiple regression technique to ask whether radial and/or capture spiral thread contact number had predictive value for the log-transformed energy absorbance [26]. The multiple regression technique was able to quantify the effect of one type of thread contact while controlling for the other thread type.Previous Section Next Section

3. Results

As an insect was decelerated by an orb web, its kinetic and gravitational energies were transferred along three routes—internal strain energies of the radial and capture spiral silks within the web and to the air around the moving threads. For many impacts, most of this transfer occurred within 0.1 s, even though the prey oscillated as it was brought to rest. Approximately 50 per cent of the remaining prey energy was absorbed at each subsequent oscillation (figure 5). For most impacts, internal dissipation by capture spirals and aerodynamic dampening was negligible compared with internal dissipation by radii. Radial threads could account for 100 per cent of the absorbed prey energy in six of eight trials (figure 6a,b), when measurement error was propagated to predict maximal radii dissipation. The capture spiral potentially accounted for 100 per cent of the work in only one instance. Aerodynamic damping never accounted for more than 30 per cent of the work, even under the most generous assumptions. Error propagation produced very large uncertainty intervals for some energy routes (figure 6) so that radii energy absorption intervals were often large enough that more energy was predicted to be absorbed than was originally available. This condition applies to the range greater than 1 on the y-axis (figure 6). For the internal capture spiral dissipation and aerodynamic dissipation, the upper uncertainty never overlapped with 100 per cent, indicating that those routes were always insufficient to account for web function. Our goal here was not to predict the precise energy dissipated through each route, but rather to show the potential of each route to account for spider orb web function.

 

Figure 5.

Energy budget for a web of A. trifolium (spider weight 1270 mg) capturing a 98 mg projectile that impacted with about 180 μJ of kinetic energy. Impact is at time 0 s, and several oscillations are shown as the prey comes to rest in the web. The time-dependent energy input was calculated as the sum of kinetic energy and gravitational potential energy change as the prey came to rest in the web. Total energy absorption was calculated as the sum of the three routes of energy dissipation after the prey came to rest—dissipation through radii, dissipation through the capture spiral and aerodynamic damping. Red solid line, total energy input; yellow solid line, prey kinetic energy; black solid line, total

energy absorbed; blue dashed line, radii internal; red dashed line, capture spiral internal; green dashed line, aerodynamic.

View larger version:

Figure 6.

(a) Partitioning of the relative work of prey stopping by orb webs. The fraction of work performed by each route was independent of relative impact energy (aerodynamic damping F= 2.99, p = 0.17, radii F = 1.37, p = 0.29, capture spiral silk F = 0.13, p = 0.73). Fraction of work was calculated as the total energy absorbed by that specific route divided by the total energy input to the web. Relative impact energy was calculated as (total energy absorbed (μJ)/spider body weight (mg)) to account for differences in web sizes. Relative impact energy is a measure of the ‘difficulty’ of the catch. Symbols indicate the mean and bars indicate the confidence intervals of each estimate as calculated from propagation of error, with the capture spiral and aerodynamic bars shifted slightly to the right, respectively, so as not to overlap. Internal dissipation by radii was sufficient to account for all energy absorption in six of eight trials, indicated by a fraction of work that included unity (1) in the confidence interval for that estimate. Boxes and dotted line indicate the two impacts in which the projectile broke through the web. (b) Fraction of work by each of the three energy dissipation routes did not depend on spider body weight (radii F = 0.08, p = 0.78, capture spiral F = 0.69, p = 0.44, aerodynamic F = 0.46, p = 0.53). Capture spiral and aerodynamic work were only important in some smaller spiders. However, aerodynamic work was always rather low, and never exceeded 30% of total energy input to the web. Blue diamond, radii; red square, capture spiral; green triangle, aerodynamic dissipation.The fraction of work performed by the various energy dissipation routes did not depend on relative impact energy (aerodynamic route, nsample size = 8, F statistic = 2.99, p probability = 0.17; dissipation in radial threads F = 1.37, p = 0.29; dissipation in spiral threads F = 0.13, p= 0.73; figure 6a) or on spider body weight (aerodynamic F = 0.46, p = 0.53; radial F = 0.08, p = 0.78; spiral F = 0.69, p = 0.44; figure 6b). Capture spirals and aerodynamic damping only played a significant role in webs spun by relatively small species of spiders (Neoscona domiciliorum, Larinioides cornutus, and Verrucosa arenata; figure 6b).

Fraction of highly strained radial threads did not depend on relative impact energy (fraction regressed onto log relative impact energy, y = 0.31 + 0.18x, n = 8, r = 0.56, p = 0.14) but fraction of high-strained capture spiral threads did increase (y = 0.18 + 0.17x, n = 8, r = 0.82, p = 0.01; figure 7a). The fraction of the capture spiral in the orb web strained beyond 20 per cent (i.e. contributing measurably to energy transfer) increased from about 3 per cent up to 50 per cent as the relative work performed by webs increased (figure 7a). The area of orb web recruited for 90 per cent of the total energy dissipated decreased with relative energy of impact for radial threads (fraction regressed onto log relative impact energy, y = 0.36 − 0.15x, n = 8, r = −0.73, p = 0.04). However, the area of the orb accounting for 90 per cent of the energy dissipated by capture spirals did not change with relative energy of impact (y = 0.28 + 0.028x, n = 8, r = 0.23, p = 0.59; figure 7b). Webs typically used about 30 per cent of their silk to absorb 90 per cent of prey energy (figures 3 and 7b), with radial threads far from the impact site absorbing significant energy (figure 3a,b).

 

Figure 7.

Two measures of web surface area recruitment. The x-axis can be interpreted as the relative difficulty of prey capture. (a) Proportion of silk reaching high strain during prey impact. High strain was defined as 5% for radial silk and 20% for capture spiral because this approximated the minimal strain at which significant energy damping occurs. The total fraction of silk pulled to high strain under prey impact was independent of relative impact energy for radial threads (y = 0.31 + 0.18x, n = 8, r = 0.56, p = 0.14) but increased for capture spiral threads (y = 0.18 +0.17x, n = 8, r = 0.82, p = 0.01). The ratios were calculated as the total number of segments of each type of silk pulled to high strain divided by the total number of segments of each type of silk. (b) Web area required to absorb prey energy. They-axis indicates the minimal area of the web required for 90% of the total work performed by a particular type of silk and is a measure of how well the impact was distributed through the web. The fraction of web area recruited decreased with relative impact energy for radii (blue diamonds: y = 0.36 − 0.15x, n = 8, r = −0.73, p = 0.04) but not for capture spirals (red squares: y = 0.28 + 0.028x, n = 8, r = 0.23, p = 0.59). Between 20 and 40% of capture spirals and radii are recruited for difficult prey.

The lower energy of easy prey is broadly distributed among the radii of a web while the increased energy of difficult impacts is concentrated in a smaller area of the web. Radii are recruited at greater distances from the impact site than are capture spirals.In a separate dataset in which 45 escaping projectiles were tracked, the total work performed by the orb web increased with the number of radial threads contacting the projectile but total work was independent of the number of capture spiral rows (multiple regression of natural log of absorbed energy onto number of radial and capture spiral threads, n = 45 webs, radii F = 6.7, p = 0.01, capture spiral F = 0.7, p = 0.41;table 2 and figure 8).

Figure 8.

(a) The energy absorbed by webs increased with increasing number of radii that were in direct contact with a 300 mg balsam block projectile. Forty-five breaking (escape) events were analysed (p = 0.01, multiple regression of natural log of absorbed energy onto both spiral and radial thread number). The number of contacting threads varied owing to orientation of projectile, differences in impact location on the web and differences in thread density. The analysis of escape events ensured that webs were functioning at a maximal capacity. (b) The energy absorbed by webs did not change with the number of spiral threads in direct contact with the projectile as it broke through the web (p = 0.41, multiple regression).Previous Section Next Section

4. Discussion

Spider orb webs evolved under selection to dissipate the tremendous kinetic energy of flying insects [2,20]. Consequently, the silk threads used to spin those webs are among the strongest and toughest known biomaterials [2]. Spider silk threads are also very thin, ranging from tens of nanometres up to a few micrometres in diameter, resulting in intermediate Reynolds numbers. Prior modelling argued that aerodynamic damping played a crucial role in energy absorption by orb webs [9], but did not directly

quantify damping in realistic prey capture scenarios. Subsequently, other studies argued against a significant role for aerodynamic work performed by orb webs [19,27], but again without empirical measurement. We directly measured the strain of silk in whole orb webs during simulated prey impacts and calculated the work performed internally by both the radial threads and the capture spiral silks, as well as the work done by aerodynamic resistance to silk motion. We found that both aerodynamic damping and the capture spiral silk usually play only a minor role in energy dissipation during prey capture. Orb webs instead rely upon internal dissipation of prey energy by radial silk for up to 98 per cent of the work of stopping flying insects (figures 5 and 6). Further evidence for the primary importance of radial silk compared with capture spirals comes from the increase in web performance as more radial threads, but not capture spiral rows, contact prey (figure 8).Orb webs are not simply passive sieves that strain insects from the air [28–30]. Instead, multiple threads within webs work together in absorbing prey energy and adhering to insects. Thus, the degree to which web architecture facilitates recruitment of additional silk during prey impact may be as important as the material properties of individual threads for energy absorption. We quantified silk recruitment for each prey impact, defined as radial threads that clearly extended past yield (5% strain) or capture spiral that stretched at least 20 per cent (where energy damping became measureable) to determine the fraction of silk in a web involved in energy dissipation. For radial silk, the area of web recruited during prey impact varied widely and was unrelated to relative impact energy (figure 7a). However, the recruitment of the capture spiral increased from less than 10 per cent for ‘easy’ captures of slower, lighter projectiles in larger spiders’ webs to up to 50 per cent under the highest energy impacts (figure 7a). In contrast, the fraction of radial silk responsible for 90 per cent of the work of stopping prey decreased under more challenging impacts, from 60 to 20 per cent (figure 7b). This means that as more kinetic energy is imparted to orb webs by increasingly larger or faster prey, orb webs depend more on the radial silk in the local area of impact. Work becomes increasingly concentrated in webs under higher impact due in part to the nonlinear material properties of radial silk, wherein it initially softens after yield but then stiffens substantially prior to failure [13]. In contrast, the fraction of capture spiral silk responsible for 90 per cent of all the work performed by the capture spiral remained constant at 20–40%, regardless of relative impact energy (figure 7b). In summary, while large amounts of silk are strained during extreme prey impacts, less of that silk is responsible for the bulk of the work. While this could indicate a failure of orb webs to effectively distribute energy under more difficult prey impacts, it could also be interpreted as a mechanism to enhance the robustness of the structure [13] because partial, damaged orb webs can continue to function as very effective traps (A. T. Sensenig 2009, unpublished data).Both aerodynamic damping and internal energy dissipation by the capture spiral play a larger role for some smaller orb webs spun byVerrucosa arenata, Neoscona domiciliorum and Larinioides cornutus (figures 3 and 6b). The use of relatively small, immature spiders in prior studies may partially explain the report of significant aerodynamic effects [9]. Several factors may explain why dissipation through capture spirals and aerodynamic damping are more important for smaller orb webs. The architectures of smaller webs enhance these two routes because smaller species of spiders, and even smaller individuals within a species, typically spin webs with larger numbers of radial threads and more rows of capture spiral [20,31]. This may allow radial threads to distribute energy more effectively to numerous rows of capture spirals. The higher numbers of threads overall in the web may also then provide proportionally greater aerodynamic drag. Non-intuitively, however, the drag does not change as a result of silk diameter owing to the inverse dependence of the drag coefficient on diameter in the intermediate Re regime. The material properties of silk also vary with spider size. The capture spirals of smaller spiders are also stiffer, increasing their contribution to dissipating prey energy at lower extensions [20]. Regardless of the mechanism, our data suggest changes in how orb webs function across both ontogenetic and evolutionary shifts in spider body size. In particular, large spiders spin webs that are capable of capturing prey by relying almost entirely on radial silk to absorb impact energy. The material properties of capture spiral silks contrast strongly with the major ampullate silks that comprise the supporting radial threads. Capture spiral silks are highly compliant and up to an order of magnitude more extensible than radial silk [32,33]. Yet, capture spiral silks achieve similarly impressive toughness, suggesting that they too have been shaped by selection for energy dissipation during prey impact [12,20]. However, we found little evidence for a significant role of capture spirals in energy dissipation during most prey impacts, especially for larger spiders’ webs. At best, capture spirals account for only 20 per cent of total energy dissipation at spider sizes larger than 100 mg. Thus, we argue that the material properties of capture spiral silk may have evolved primarily under selection for adhering to and retaining prey. For instance, high extensibility facilitates adhesion of capture spiral at both the whole thread [34] and individual glue droplet levels [35]. Moreover, there is a close evolutionary relationship between capture spiral extensibility and stickiness [36]. We even

suggest that the prey-retaining function of the capture spiral may select for properties that decrease its contribution to energy absorption during prey impact. For example, low stiffness promotes wrapping of struggling prey, so that more spirals can be incorporated in the wrapping [32]. But, that low stiffness also means that capture spiral silk contributes little to energy dissipation until it is extended to strains well beyond those typical of prey impacts.Orb webs overcome the daunting challenge of stopping the flight of insects by using a combination of different silks that are among the toughest known materials [32]. Despite the small diameters of these silk threads, and their correspondingly low Re, aerodynamic damping plays only a minor role in prey energy absorption for many orb webs. The elastic capture spiral of orb webs is also so compliant that it also usually dissipates little energy. Instead, orb webs rely primarily upon major ampullate silk in radial threads to dissipate most of the prey's flight energy, particularly for larger webs. This suggests that the material properties of capture spiral silk are ‘freed’ to respond to selection on alternative functions, in particular how the capture spiral retains prey through adhesion long enough to be subdued by spiders. While increasingly larger amounts of silk in orb webs become strained under higher energy prey impacts, most of the prey's energy is still dissipated by a relatively constant fraction of silk (approx. 30% of the total web), suggesting that orb webs may have evolved in part to maintain their functionality even under moderate to high levels of damage. Our findings provide new insight into how orb webs function and help identify different mechanistic pathways by which natural selection has operated on the evolutionary diversification of the spider silk toolkit.Previous Section Next Section

Acknowledgements

The authors thank Kenneth Kiger from the University of Maryland for some comments on early drafts of the manuscript. Brittany Lesher of the University of Akron assisted in collection of data. This work was supported by NSF award IOS-0745379 to T.A.B. and a Tabor College Hope Scholarship Grant to A.T.S. This is publication no. 30 of the University of Akron Field Station.

Received December 5, 2011. Accepted January 27, 2012. This journal is © 2012 The Royal Society

Previous Section

 

References

1. ↵

 

1. Blackledge T. A., 2. Scharff N., 3. Coddington J. A., 4. Szüts T., 5. Wenzel J. W., 6. Hayashi C. Y., 7. Agnarsson I.

 2009 Reconstructing web evolution and spider diversification in the molecular era. Proc. Natl Acad. Sci. USA 106, 5229–5234. (doi:10.1073/pnas.0901377106)

Abstract / FREE   Full Text

2. ↵

 

1. Blackledge T. A., 2. Kuntner M., 3. Agnarsson I.

 2011 The form and function of spider orb webs: evolution from silk to ecosystems. Adv. Insect Physiol. 41, 175–262. (doi:10.1016/B978-0-12-415919-8.00004-5)

 

CrossRef Web of Science

3. ↵

 

1. Foelix R. F. 1996 Biology of spiders, 2nd edn, p. 330. New York, NY: Oxford University Press.

 

Search Google Scholar

4. ↵

 

1. Turnbull A. L. 1973 Ecology of the true spiders (Araneomorphae). Annu. Rev. Entomol. 18, 305–348.(doi:10.1146/annurev.en.18.010173.001513)

 

CrossRef Web of Science

5. ↵

 

1. Work R. W. 1976 Force-elongation behavior of web fibers and silks forcibly obtained from orb-web-spinning spiders. Textile Res. J. 46,485–492.

 

Web of Science

6.1. Li S. F. Y., 2. McGhie A. J., 3. Tang S. L.

 1994 Comparative study of the internal structures of Kevlar and spider silk by atomic force microscopy. J. Vac. Sci. Technol. A 12, 1891–1894. (doi:10.1116/1.578978)

 

CrossRef

7. ↵

 

1. Denny M. 1976 Physical properties of spider's silks and their role in design of orb-webs. J. Exp. Biol. 65, 483–506.

Abstract / FREE   Full Text

8. ↵

 

1. Craig C. L. 1987 The ecological and evolutionary interdependence between web architecture and web silk spun by orb web weaving spiders. Biol. J. Linn. Soc. 30, 135–162. (doi:10.1111/j.1095-8312.1987.tb00294.x)

 

CrossRef Web of Science

9. ↵

 

1. Lin L. H., 2. Edmonds D. T., 3. Vollrath F.

 1995 Structural engineering of an orb-spider's web. Nature 373, 146–148.(doi:10.1038/373146a0)

 

CrossRef Web of Science

10. ↵

 

1. Opell B. D. 1996 Functional similarities of spider webs with diverse architectures. Am. Nat. 148, 630–648. (doi:10.1086/285944)

CrossRef Web of Science

11.1. Swanson B. O., 2. Blackledge T. A., 3. Summers A. P., 4. Hayashi C. Y.

 2006 Spider dragline silk: correlated and mosaic evolution in high performance biological materials. Evolution 60, 2539–2551. (doi:10.1554/06-267.1)

 

CrossRef Medline Web of Science

12. ↵

 

1. Swanson B. O., 2. Blackledge T. A., 3. Hayashi C. Y.

 2007 Spider capture silk: performance implications of variation in an exceptional biomaterial. J. Exp. Zool. A Ecol. Genet. Physiol. 307A, 654–666. (doi:10.1002/jez.420)

 

CrossRef

13. ↵

 

1. Cranford S. W., 2. Tarakanova A., 3. Pugno N. M., 4. Buehler M. J.

 2012 Nonlinear material behaviour of spider silk yields robust webs. Nature482, 72–76. (doi:10.1038/nature10739)

 

CrossRef Medline Web of Science

14. ↵

 

1. Kelly S. P., 2. Sensenig A., 3. Lorentz K. A., 4. Blackledge T. A.

 2011 Damping capacity is evolutionarily conserved in the radial silk of orb weaving spiders. Zoology 114, 233–238. (doi:10.1016/j.zool.2011.02.001)

 

CrossRef Medline Web of Science

15. ↵

 

1. Suter R. B. 1991 Ballooning in spiders: results of wind-tunnel experiments. Ethol. Ecol. Evol. 3, 13–25.(doi:10.1080/08927014.1991.9525385)

 

CrossRef Web of Science

16. ↵

 

1. Nachtigall W. 2001 Some aspects of Reynolds number effects in animals. Math. Methods Appl. Sci. 24, 1401–1408.(doi:10.1002/mma.188)

 

CrossRef

17. ↵

 

1. Aoyanagi Y., 2. Okumura K.

 2010 Simple model for the mechanics of spider webs. Phys. Rev. Lett. 104, 038102.(doi:10.1103/PhysRevLett.104.038102)

 

CrossRef Medline

18.1. Alam M. S., 2. Wahab M. A., 3. Jenkins C. H.

 2007 Mechanics in naturally compliant structures. J. Mech. Mater. 39, 145–160.(doi:10.1016/j.mechmat.2006.04.005)

 

CrossRef

19. ↵

 

1. Ko F. K., 2. Jovicic J.

 2004 Modeling of mechanical properties and structural design of spider web. Biomacromolecules 5, 780–785.(doi:10.1021/bm0345099)

 

CrossRef Medline Web of Science

20. ↵

 

1. Sensenig A., 2. Agnarsson I., 3. Blackledge T. A.

 2010 Behavioural and biomaterial coevolution in spider orb webs. J. Evol. Biol. 23,1839–1856. (doi:10.1111/j.1420-9101.2010.02048.x)

 

CrossRef Medline Web of Science

21. ↵

 

1. Opell B. D. 2002 Estimating the stickiness of individual adhesive capture threads in spider orb webs. J. Arachnol. 30, 494–502.(doi:10.1636/0161-8202(2002)030[0494:ETSOIA]2.0.CO;2)

 

CrossRef Web of Science

22. ↵

 

1. Blackledge T. A., 2. Zevenbergen J. M.

 2006 Mesh width influences prey retention in spider orb webs. Ethology 112, 1194–1201.(doi:10.1111/j.1439-0310.2006.01277.x)

 

CrossRef Web of Science

23. ↵

 

1. Kline S. J., 2. McClintock F. A.

 1953 Describing uncertainties in single-sample experiments. Mech. Eng. 75, 3–8.

 

Search Google Scholar

24. ↵

 

1. Blackledge T. A., 2. Swindeman J. E., 3. Hayashi C. Y.

 2005 Quasistatic and continuous dynamic characterization of the mechanical properties of silk from the cobweb of the black widow spider Latrodectus hesperus. J. Exp. Biol. 208, 1937–1949. (doi:10.1242/jeb.01597)

Abstract / FREE   Full Text

25. ↵

 

1. Tritton D. J. 1988 Physical fluid dynamics, 2nd edn. Oxford, UK: Oxford University Press.

 

Search Google Scholar

26. ↵

 

StatSoft. 2009 STATISTICA (data analysis software system). See http://www.statsoft.com/#.

27. ↵

 

1. Alam M. S., 2. Wahab M. A., 3. Jenkins C. H.

 2007 Mechanics in naturally compliant structures. Mech. Mater. 39, 145–160.(doi:10.1016/j.mechmat.2006.04.005)

 

CrossRef Web of Science

28. ↵

 

1. Diaz-Fleischer F. 2005 Predatory behaviour and prey-capture decision-making by the web-weaving spider Micrathena sagittata. Can. J. Zool. 83, 268–273. (doi:10.1139/z04-176)

 

CrossRef Web of Science

29.1. Uetz G. W., 2. Johnson A. D., 3. Schemske D. W.

 1978 Web placement, web structure and prey capture in orb-weaving spiders. Bull. Br. Arachnol. Soc. 4, 141–148.

 

Search Google Scholar

30. ↵

 

1. Nentwig W. 1983 The non-filter function of orb webs in spiders. Oecologia 58, 418–420. (doi:10.1007/BF00385246)

 

CrossRef Web of Science

31. ↵

 

1. Craig C. L. 1987 The significance of spider size to the diversification of spider-web architectures and spider reproductive modes. Am. Nat. 129, 47–68. (doi:10.1086/284622)

 

CrossRef Web of Science

32. ↵

 

1. Blackledge T. A., 2. Hayashi C. Y.

 2006 Silken toolkits: biomechanics of silk fibers spun by the orb web spider Argiope argentata. J. Exp. Biol.209, 2452–2461. (doi:10.1242/jeb.02275)

 

Abstract / FREE   Full Text

33. ↵

 

1. Gosline J. M., 2. Guerette P. A., 3. Ortlepp C. S., 4. Savage K. N.

 1999 The mechanical design of spider silks: from fibroin sequence to mechanical function. J. Exp. Biol. 202, 3295–3303.

 

Abstract / FREE   Full Text

34. ↵

 

1. Opell B. D., 2. Hendricks M. L.

 2007 Adhesive recruitment by the viscous capture threads of araneoid orb-weaving spiders. J. Exp. Biol.210, 553–560. (doi:10.1242/jeb.02682)

 

Abstract / FREE   Full Text

35. ↵

 

1. Sahni V., 2. Blackledge T. A., 3. Dhinojwala A.

 2010 Viscoelastic solids explain spider web stickiness. Nat. Commun. 1, 19.(doi:10.1038/ncomms1019)

 

Medline

36. ↵

 

1. Agnarsson I., 2. Blackledge T. A.

 2009 Can a spider web be too sticky? Tensile mechanics constrains the evolution of capture spiral stickiness in orb weaving spiders. J. Zool. (London) 278, 134–140. (doi:10.1111/j.1469-7998.2009.00558.x)

را   کافی رشد آنها با مقابله های فناوری ایجاد متاسفانه ، تهاجمی تجیهزات ساخت زمینه در گسترده پیشرفتهای رغم علی . سند هزاران با کنون تا تجربه با متخصص یک عنوان به است بوده کشورها از معدودی به محدود آنها توسعه یا و نداشته

، ام کرده برخورد آنها به مربوط مسائل و مهمات و سالح انواع ساخت ارزشی درباره با و مفید اطالعات ندرت به اما . ام دیده هوایی تهاجم برابر در جامع دفاع درباره

زیر نابودی در کننده تعیین عاملی عنوان به سنگین هوایی حمالت که اخیر های دهه در بخصوص هوایی پدافند اهمیت . بر عالوه جامع دفاع یک است حیاتی و روشن بسیار است گرفته قرار نظر مورد منظم جنگ در کشور یک های ساخت

. است کشور یک بنایی زیر امکانات و ها جان حفظ به قادر متجاوز به سنگین خسارت و هزینه تحمیل

In recent decays that heavy airstrikes are accepted as a determining factor to win a war with destruction of the infrastructure of a country, the importance of air defense seems so vital. In addition to protecting people and infrastructure, Comprehensive defense will increase the cost and damage for invading enemy and makes advanced technologies inefficient.

. بر دانشی است ضعیف و قدرتمند کشورهای بین قوا توازن نوعی ایجاد به قادر نامتعارف جنگ و بازدارنده دفاع ترکیبطبیعت پایه بر شده بهینه فناوری اساس

Improvised defense and unconventional warfare could able to create a balance between powerful and weak countries.

The other serious problem, also common to explosive weapons is unexploded ordnance (UXO) of cluster

bomblets left behind after a strike. These bomblets may be duds or in some cases the weapons are

designed to detonate at a later stage. In both cases, the surviving bomblets are live and can explode

when handled, making them a serious threat to civilians and military personnel entering the area. In

effect, the UXOs can function like land mines.

Even though cluster bombs are designed to explode prior to or on impact, there are always some

individual submunitions that do not explode on impact. The US-made MLRS with M26 warhead and M77

submunitions are supposed to have a 5% dud rate but studies have shown that some have a much higher

rate.[49] The rate in acceptance tests prior to the Gulf War for this type ranged from 2% to a high of 23%

for rockets cooled to −25 °F(−32 °C) before testing.[50] The M483A1 DPICM artillery-delivered cluster

bombs have a reported dud rate of 14%.[51]

Given that each cluster bomb can contain hundreds of bomblets and be fired in volleys, even a small

failure rate can lead each strike to leave behind hundreds or thousands of UXOs scattered randomly

across the strike area. For example, after the 2006 Israel-Lebanon conflict, UN experts have estimated

that as many as one million unexploded bomblets may contaminate the hundreds of cluster munition

strike sites in Lebanon.[52]

M77 submunition of type fired against Lebanon in 1986. Each MLRS rocket has 644 M77 packed in the warhead

In addition, some cluster bomblets, such as the BLU-97/B used in the CBU-87, are brightly colored to

increase their visibility and warn off civilians. However, the yellow color, coupled with their small and

nonthreatening appearance, is attractive to young children who wrongly believe them to be toys. This

problem was exacerbated in the War in Afghanistan (2001–present), when US forces dropped

humanitarian rations from airplanes with similar yellow-colored packaging as the BLU-97/B, yellow being

the NATO standard colour for high explosive filler in air weapons. The rations packaging was later

changed first to blue and then to clear in the hope of avoiding such hazardous confusion.

The US military is developing new cluster bombs that it claims could have a much lower (less than 1%)

dud rate

UHPC is based—like its quotidian cousins—on sand and cement. In addition, though, it is doped with powdered quartz (the pure stuff, rather than the tainted variety that makes up most sand) and various reinforcing metals and fibres.

UHPC can withstand more compression than other forms of concrete. Ductal, a French version of the material which is commercially available, can withstand pressure many times higher than normal concrete can. UHPC is also more flexible and durable than conventional concrete. It can therefore be used to make lighter and more slender structures.

For this reason, Iranian civil engineers are interested in using it in structures as diverse as dams and sewage pipes and are working on improving it. Mahmoud Nili of Bu-Ali Sina University in Hamadan for example, is using polypropylene fibres and quartz flour, known as fume, in his

mix. It has the flexibility to absorb far heavier blows than regular concrete. Rouhollah Alizadeh may do better still. Dr Alizadeh, a graduate of the University of Tehran, is currently working at Ottawa University in Canada on the molecular structure of cement. Once again, this research is for civilian purposes and could pave the way for a new generation of UHPC with precisely engineered properties and outstanding performance.

One way to tamper with the internal structure of concrete is to use nanoparticles. Ali Nazari and his colleagues at Islamic Azad University in Saveh have published several papers on how to do that with different types of metal-oxide nanoparticles. They have worked with oxides of iron, aluminium, zirconium, titanium and copper. At the nanoscale materials can take on extraordinary properties. Although it has been demonstrated only in small samples, it might be possible, using such nanoparticles, to produce concrete that is four times stronger than Ductal.

All of which is fine and dandy for safer dams and better sewers, which threaten no one. But UHPC's potential military applications are more intriguing—and for many, more worrying. A study published by the University of Tehran in 2008 looked at the ability of UHPC to withstand the impact of steel projectiles. These are not normally a problem during earthquakes. This study found that concrete which contained a high proportion of long steel fibres in its structure worked best. Another study, published back in 1995, showed that although the compressive strength of concrete was enhanced only slightly by the addition of polymer fibres, its impact resistance improved sevenfold.

Western countries, too, have been looking at the military uses of UHPC. An Australian study carried out between 2004 and 2006 confirmed that UHPC resists blasts as well

as direct hits. The tests, carried out at Woomera (once the British empire's equivalent of Cape Canaveral), involved a charge equivalent to six tonnes of TNT. This fractured panels made of UHPC, but did not shatter them. Nor did it shake free and throw out fragments, as would have happened had the test been carried out on normal concrete. In a military context, such shards flying around inside a bunker are a definite plus from the attackers' point of view, but obviously not from the defenders'.

Those people who design bunker-busters no doubt understand these points and have their own secret data to work with. Nevertheless, during the Gulf war in 1991 the American air force found that its 2,000lb (about a tonne) bunker-busters were incapable of piercing some Iraqi bunkers. The bomb designers went back to the drawing board and after two generations of development the result, all 13 tonnes of it, is the MOP. So heavy is it that the weapon bays of B-2 stealth bombers have had to be strengthened to carry it. It can, reportedly, break through over 60 metres of ordinary concrete. However, the bomb it is less effective against harder stuff, penetrating only eight metres into concrete that is just twice as strong. It is therefore anyone's guess (at least, anyone without access to classified information) how the MOP might perform against one of Iran's ultra-strong concretes.

Deep bunkers can be tackled in other ways. The DTRA has looked at what is known in the jargon as functional defeat, in other words bombing their entrances shut or destroying their electrical systems with electromagnetic pulses. They are also working on active penetrators—bombs which can tunnel through hundreds of metres of earth, rock and concrete. Development work is also under way on esoteric devices such as robot snakes, carrying warheads, which can infiltrate via air ducts and cable runs.

In the meantime, though, the Pentagon is stuck with the “big hammer” approach. The question is how reliably that hammer would work if the order were given to attack Iran's underground nuclear facilities. It would be embarrassing if the bunkers were still intact when the smoke cleared.

The United States may use a new 13,600-kilogram bunker-buster bomb against Iran, DefenseNews.com reported on Thursday, March 8, 2012, quoting the U.S. Air Force Lt. Gen. Herbert Carlisle as saying.

General

The Massive Ordnance Penetrator (MOP) bomb has been developed by Boeing for use against hardened, reinforced targets up to 200 feet underground. The bomb is GPS guided and carried by the B-2 bomber. The bomb is so large and heavy the B-2 bomber can only carry two at a time. The bomb weighs 30,000 pounds and carries 6,000 pounds of explosives. The nose and body are designed for ground penetration and made of a cobalt alloy material. The explosives detonate after ground penetration rather than upon initial impact delivering the explosive power to the underground target. The bomb has small wings and tail constructed link a trellis for guidance. The Air Force has less than 10 of these bombs.

Specifications

Length: 20 feet

Diameter: 31 ½”

Overall Weight: 30,000 pounds

Explosives: 6,000 pounds

Reinforced concrete penetration: up to 200 feet

Hard rock penetration: 125 feet

10 Formidable Predatory   Insects

by TyB | August 9, 2010

The most advanced bomb , the most vulnerable to defeat

Warning: ugly bugs We are used to seeing insects as prey animals; everyone eats them, from birds and spiders, to

humans. But there are predators among insects as well, and some of them are among Nature’s most perfect killers. I

give you ten of the most formidable predatory insects… and be grateful that they don’t come in large sizes!

10

Robber fly

We are all familiar with the house fly, which feeds on decaying organic matter (among other disgusting things), and is

pretty much harmless to other insects. However, there are around 120,000 species of flies in the world (many are yet

to be discovered) and some of them are accomplished predators. Robber flies are among these; they have extremely

sharp eyesight and can fly at high speed, catching other insects in mid air. They have stabbing mouthparts

(proboscis) which inject a powerful neurotoxic venom and digestive juices into the victim, liquifying its innards, which

the fly sucks afterwards.

Due to this formidable weapon and the robber fly’s devastating attack speed, not even wasps, bees or spiders in their

webs are safe from these aerial killers. Robber fly venom is usually harmless to humans, but if captured they can give

an extremely painful bite.

9

Water scorpion

Despite their fearsome appearance and alarming name, water scorpions are actually insects, belonging to the true

bug (Hemiptera) group, and completely harmless to humans. However, they are the scourge of small aquatic

animals, which they capture with their strong, modified forelegs. Water scorpions are sort of the insect equivalent of a

crocodile; they are slow moving ambush predators that snatch any small animal that comes close; mostly, they feed

on other aquatic insects such as mosquito larvae and diving beetles, but they have been known to dine on small fish

and frogs once in a while.

Although they have wings, their flight muscles are poorly developed and they fly rarely, usually when the ponds or

lakes where they live start to dry up and they must find a new residence. As for the long, tail-like projection at the end

of their abdomen, it is actually a breathing tube; the water scorpion uses it to collect oxygen from the surface, and can

subsequently remain underwater for up to half an hour before it has to breathe again.

8

Arachnocampa luminosa

Arachnocampa is a kind of gnat from New Zealand; as an adult, its only goal in life is to mate, and it doesn’t feed at

all. However, its larvae are accomplished predators with a most unusual hunting method, which gives the animal its

name (Arachnocampa means “spider worm”). They usually live in the ceiling of dark, secluded caves, away from wind

currents and sunlight. The larvae spin a nest of silk (produced by themselves) and hang several silk threads from the

cave ceiling, around the nest.

Each one of these threads is covered on sticky droplets of mucus, sometimes loaded with venom. The

Arachnocampa larva can glow like a firefly, which attracts flying insects such as moths to the sticky threads and to a

horrible end. Once the unfortunate insect is caught, the larva tones down its glow, pulls the silk thread up and starts

feeding voraciously on the entangled prey, whether it is alive or dead.

7

Tiger Beetle

Everyone knows that the fastest land predator is the cheetah, which can reach speeds of 115 kms (71 mph) per hour.

Compared to this, a Tiger Beetle is a slowpoke; it can only run at a speed of 8 kms (5 mph) per hour. But if we take

its size into account, it is actually the fastest animal in the world! If we could run as fast as the tiger beetle,

proportionally to our size, we could reach speeds of almost 500 kms (311 mph) per hour! This speed is so extreme

that a running Tiger Beetle must stop constantly to locate prey, since its eyes are unable to process visual information

at such high speed.

Tiger Beetles feed on whatever small animal they can subdue; they hunt mostly on land, but are also skilled flyers

and have been known to catch other insects in the air too. Their sharp mandibles can easily sever the limbs and body

parts of other insects, sometimes bigger than the Tiger Beetle itself. There are many species of Tiger Beetle and they

are among the most abundant insect predators, being extremely useful to humans as they help control pests. The

larvae of these beetles are also fearsome predators, but instead of chasing their prey, they prefer to wait in ambush,

hidden underground, and capture any passing insect with their enormous jaws.

6

Antlion

Adult antlions look rather like damselflies, and although some species hunt smaller flying insects, most of them prefer

to feed on pollen and nectar. Antlion larvae, on the other hand, are deadly insect predators, and just like

Arachnocampa, they have developed a most amazing trick to capture prey. They live in sandy places, where they dig

a funnel-shaped pit, cleverly designed so that no insect can climb its steep walls. The antlion then buries itself in the

bottom of the pit. Whenever an unfortunate insect (usually an ant) steps on the edge of the pit, the sand collapses

and the victim falls to the bottom, and into the antlion larva’s deadly jaws.

Sometimes, an ant will escape the larva and attempt to climb the walls of the pit; in this case, the antlion has another

trick up its sleeve; it throws jets of sand to the ant, so that it slips back into the pit’s bottom. Once the antlion larva has

secured its prey, it sucks its body fluid with the tooth-like projections of its jaws, and then throws the dry carcass out

of the pit.

5

Assassin bug

Assassin bugs are among Nature’s most ingenious killers. There are plenty of species, and most of them are

harmless to man (although some have excruciatingly painful bites). Often, a species of assassin bug will specialize in

a certain kind of prey; for example, some of them feed only on spiders, others prefer ants, etc. They are armed with

needle-like mouthparts, which they use to inject lethal saliva into their prey; this saliva liquifies the victim’s innards.

(Like many other insects, assassin bugs are unable to feed on solid matter). However, most assassin bugs aren’t fast

flyers or runners, so they use trickery to hunt. Some of them cover their bodies with bark, dust, or even dead insects

to disguise their appearance and scent, and sneak up on unsuspecting prey.

Spider-hunting assassin bugs often mimic the vibrations produced by insects entangled in a spider web; the spider

attacks, thinking that it has caught a tasty meal, only to be killed and devoured itself. Perhaps the most amazing

assassin bug is a certain species that feeds on ants. It produces a sugary substance through its abdomen, which

serves as bait for the sweet-loving ants. But the sugary substance is also loaded with a powerful tranquilizer; soon,

the ant collapses, paralyzed, and the assassin bug can suck its innards without any resistance.

4

Dragonfly

The Dragonfly is the ultimate aerial killer of the insect world; its design is so perfect, that it has remained almost

unchanged for the last 300 million years. It is among the fastest flying insects, reaching almost 90 kms (56 miles) per

hour (which is even more amazing if we consider its small size and apparent fragility). It can dive-bomb, hover like a

helicopter, and even fly backwards, and its enormous eyes, which cover almost all of its head, give it near-360

degree vision, so that no insect escapes its attention.

Dragonflies feed on any flying insects they can catch, and also on spiders, which they capture from their webs.

Although they usually hunt and devour prey at high speed in the air, they can also snatch spiders and insects from

exposed surfaces. Dragonfly larvae are also formidable predators; they are aquatic, and use their protractile, sharp

mouthparts to stab other small animals to death, including small fish, frogs and other dragonfly larvae.

3

Siafu ant

Also known as the driver, safari or army ant, this African species if the only insect known to attack and devour

humans, although this happens only very rarely. Siafu ants have very large, sharp jaws and venomous stings, which

they use to subdue small animals such as lizards, worms and other insects. However, there have been reports of

cows, goats and other domestic animals that were tied to trees or poles by their owners, and, unable to get out of the

way, were killed by the Siafu ants. Wild animals avoid ant armies on the move, and some naturalists have claimed

that even lions and elephants flee away from them.

There have been reports of attacks on people who couldn’t run away on time, such as unattended babies, sleeping or

injured people and at least one drunken man. Also, one tourist that was reported as missing in Tanzania was later

found to have been killed by Siafu ants. It is said that these larger victims may not die of envenomation after being

stung, but rather of asphyxia, since the attacking ants will go into any body orifice and crawl into the lungs.

2

Praying mantis

Possibly the best known predatory insect. There are many species of praying mantis, or mantids, around the world,

but they are all perfect ambush hunters, armed with long, modified forelegs armed with sharp hooks to capture prey.

These forelegs are usually called the “raptorial legs”.

These insects usually stand still, camouflaged, until a smaller insect or animal gets close; then they capture with a

lightning fast movement, and start feeding whether the victim is alive or dead.

They are extremely voracious and any kind of prey is good to them; they have been known to capture and devour

spiders (including the deadly black widow spider), lizards, small snakes and even birds. They are also infamously

prone to cannibalism; females often bite off the head of the male during sex, and feed on the rest of him afterwards.

Baby mantids are also known to feed on their siblings when food is scarce. Mantids are skilled flyers but they usually

only fly at night, to avoid birds and other larger predators.

1

Japanese hornet

Known as “tiger hornets” in some parts of Asia, these large wasps are relentless hunters that kill any insect they can

capture, including other predators such as the praying mantis. They are armed with an incredibly potent venom, and

inject great amounts of it; like other hornets, they can sting repeatedly. This venom is strong enough to cause serious

illness, and even death, to humans; indeed, they are the most dangerous wild animal in Japan, killing around 40

people per year (more than venomous snakes and bears combined). But the Japanese hornet uses its sting as a

defensive weapon only; to kill prey, it uses its sharp jaws to decapitate the victim, and cut its body in small pieces. It

then carries the carcass back to the nest, where it chews the dead insect into a soft paste to feed the larvae. The

larvae then produce a sugary fluid which is the adult hornet’s main food.

To give you an idea of the destructive power of Japanese hornets, let us only say that a few of them can completely

devastate a honey bee colony in a couple of hours, decapitating every single bee in the nest (up to 30,000) one by

one. When all the bees are dead, the hornets feed on the honey and then carry the bee larvae, and parts of the adult

bee bodies, back to their own nest to feed their larvae. This is the horrible end met by European honeybees

(introduced to Japan to increase honey production) when confronted with the “tiger hornet”. But Japanese honey

bees are different; they evolved along with the hornet, and have developed an incredible trick to kill the hornet scouts

as soon as they find their hive.

Up to 500 bees form a tight ball that engulfs the scout hornet(s) and start vibrating their wing muscles until their body

temperature increases up to 47°C. Honey bees can survive this temperature, but hornets cannot; they are basically

fried alive by the bees. With the scouts dead, the hornet colony never finds out about the location of the honey bee

nest. Even the most formidable predatory insect has to meet its match one day…

The Electromagnetic Bomb - a Weapon of Electrical Mass DestructionCarlo Kopp

Defence Analyst

Melbourne, Australia

Carlo.Kopp@aus.net

http://www.cs.monash.edu.au/~carlo/

ABSTRACT

High Power Electromagnetic Pulse generation techniques and High Power Microwave technology have matured to the point where practical E-bombs (Electromagnetic bombs) are becoming technically feasible, with new applications in both Strategic and Tactical Information Warfare. The development of conventional E-bomb devices allows their use in non-nuclear confrontations. This paper discusses aspects of the technology base, weapon delivery techniques and proposes a doctrinal foundation for the use of such devices in warhead and bomb applications.

1. Introduction

The prosecution of a successful Information Warfare (IW) campaign against an industrialised or post industrial opponent will require a suitable set of tools. As demonstrated in the Desert Storm air campaign, air power has proven to be a most

effective means of inhibiting the functions of an opponent's vital information processing infrastructure. This is because air power allows concurrent or parallel engagement of a large number of targets over geographically significant areas [SZAFRANSKI95].

While Desert Storm demonstrated that the application of air power was the most practical means of crushing an opponent's information processing and transmission nodes, the need to physically destroy these with guided munitions absorbed a substantial proportion of available air assets in the early phase of the air campaign. Indeed, the aircraft capable of delivery laser guided bombs were largely occupied with this very target set during the first nights of the air battle.

The efficient execution of an IW campaign against a modern industrial or post-industrial opponent will require the use of specialised tools designed to destroy information systems. Electromagnetic bombs built for this purpose can provide, where delivered by suitable means, a very effective tool for this purpose.

2.The EMP Effect

The ElectroMagnetic Pulse (EMP) effect [1] was first observed during the early testing of high altitude airburst nuclear weapons [GLASSTONE64]. The effect is characterised by the production of a very short (hundreds of nanoseconds) but intense electromagnetic pulse, which propagates away from its source with ever diminishing intensity, governed by the theory of electromagnetism. The ElectroMagnetic Pulse is in effect an electromagnetic shock wave.

This pulse of energy produces a powerful electromagnetic field, particularly within the vicinity of the weapon burst. The field can be sufficiently strong to produce short lived transient voltages of thousands of Volts (ie kiloVolts) on exposed electrical conductors, such as wires, or conductive tracks on printed circuit boards, where exposed.

It is this aspect of the EMP effect which is of military significance, as it can result in irreversible damage to a wide range of electrical and electronic equipment, particularly computers and radio or radar receivers. Subject to the electromagnetic hardness of the electronics, a measure of the equipment's resilience to this effect, and the intensity of the field produced by the weapon, the equipment can be irreversibly damaged or in effect electrically destroyed. The damage inflicted is not unlike that experienced through exposure to close proximity lightning strikes, and may require complete replacement of the equipment, or at least substantial portions thereof.

Commercial computer equipment is particularly vulnerable to EMP effects, as it is largely built up of high density Metal Oxide Semiconductor (MOS) devices, which are very sensitive to exposure to high voltage transients. What is significant about MOS devices is that very little energy is required to permanently wound or destroy them, any voltage in typically in excess of tens of Volts can produce an effect termed gate breakdown which effectively destroys the device. Even if the pulse is not powerful enough to produce thermal damage, the power supply in the equipment will readily supply enough energy to complete the destructive process. Wounded devices may still function, but their reliability will be seriously impaired. Shielding electronics by equipment chassis provides only limited protection, as any cables running in and out of the equipment will behave very much like antennae, in effect guiding the high voltage transients into the equipment.

Computers used in data processing systems, communications systems, displays, industrial control applications, including road and rail signalling, and those embedded in military equipment, such as signal processors, electronic flight controls and digital engine control systems, are all potentially vulnerable to the EMP effect.

Other electronic devices and electrical equipment may also be destroyed by the EMP effect. Telecommunications equipment can be highly vulnerable, due to the presence of lengthy copper cables between devices. Receivers of all varieties are particularly sensitive to EMP, as the highly sensitive miniature high frequency transistors and diodes in such equipment are easily destroyed by exposure to high voltage electrical transients. Therefore radar and electronic warfare equipment, satellite, microwave, UHF, VHF, HF and low band communications equipment and television equipment are all potentially vulnerable to the EMP effect.

It is significant that modern military platforms are densely packed with electronic equipment, and unless these platforms are well hardened, an EMP device can substantially reduce their function or render them unusable.

3. The Technology Base for Conventional Electromagnetic Bombs

The technology base which may be applied to the design of electromagnetic bombs is both diverse, and in many areas quite mature. Key technologies which are extant in the area are explosively pumped Flux Compression Generators (FCG), explosive or propellant driven Magneto-Hydrodynamic (MHD) generators and a range of HPM devices, the foremost of which is the Virtual Cathode Oscillator or Vircator. A wide range of experimental designs have been tested in these technology areas, and a considerable volume of work has been published in unclassified literature.

This paper will review the basic principles and attributes of these technologies, in relation to bomb and warhead applications. It is stressed that this treatment is not exhaustive, and is only intended to illustrate how the technology base can be adapted to an operationally deployable capability.

3.1. Explosively Pumped Flux Compression Generators

The explosively pumped FCG is the most mature technology applicable to bomb designs. The FCG was first demonstrated by Clarence Fowler at Los Alamos National Laboratories (LANL) in the late fifties [FOWLER60]. Since that time a wide range of FCG configurations has been built and tested, both in the US and the USSR, and more recently CIS.

The FCG is a device capable of producing electrical energies of tens of MegaJoules in tens to hundreds of microseconds of time, in a relatively compact package. With peak power levels of the order of TeraWatts to tens of TeraWatts, FCGs may be used directly, or as one shot pulse power supplies for microwave tubes. To place this in

perspective, the current produced by a large FCG is between ten to a thousand times greater than that produced by a typical lightning stroke [WHITE78].

The central idea behind the construction of FCGs is that of using a fast explosive to rapidly compress a magnetic field, transferring much energy from the explosive into the magnetic field.

The initial magnetic field in the FCG prior to explosive initiation is produced by a start current. The start current is supplied by an external source, such a a high voltage capacitor bank (Marx bank), a smaller FCG or an MHD device. In principle, any device capable of producing a pulse of electrical current of the order of tens of kiloAmperes to MegaAmperes will be suitable.

A number of geometrical configurations for FCGs have been published (for examples see REINOVSKY85, CAIRD85, FOWLER89) The most commonly used arrangement is that of the coaxial FCG. The coaxial arrangement is of particular interest in this context, as its essentially cylindrical form factor lends itself to packaging into munitions.

In a typical coaxial FCG , a cylindrical copper tube forms the armature. This tube is filled with a fast high energy explosive. A number of explosive types have been used, ranging from B and C-type compositions to machined blocks of PBX-9501. The

armature is surrounded by a helical coil of heavy wire, typically copper, which forms the FCG stator. The stator winding is in some designs split into segments, with wires bifurcating at the boundaries of the segments, to optimise the electromagnetic inductance of the armature coil.

The intense magnetic forces produced during the operation of the FCG could potentially cause the device to disintegrate prematurely if not dealt with. This is typically accomplished by the addition of a structural jacket of a non-magnetic material. Materials such as concrete or Fibreglass in an Epoxy matrix have been used. In principle, any material with suitable electrical and mechanical properties could be used. In applications where weight is an issue, such as air delivered bombs or missile warheads, a glass or Kevlar Epoxy composite would be a viable candidate.

It is typical that the explosive is initiated when the start current peaks. This is usually accomplished with a explosive lense plane wave generator which produces a uniform plane wave burn (or detonation) front in the explosive. Once initiated, the front propagates through the explosive in the armature, distorting it into a conical shape (typically 12 to 14 degrees of arc). Where the armature has expanded to the full diameter of the stator, it forms a short circuit between the ends of the stator coil, shorting and thus isolating the start current source and trapping the current within the device. The propagating short has the effect of compressing the magnetic field, whilst reducing the inductance of the stator winding. The result is that such generators will producing a ramping current pulse, which peaks before the final disintegration of the device. Published results suggest ramp times of tens to hundreds of microseconds, specific to the characteristics of the device, for peak currents of tens of MegaAmperes and peak energies of tens of MegaJoules.

The current multiplication (ie ratio of output current to start current) achieved varies with designs, but numbers as high as 60 have been demonstrated. In a munition application, where space and weight are at a premium, the smallest possible start current source is desirable. These applications can exploit cascading of FCGs, where a small FCG is used to prime a larger FCG with a start current. Experiments conducted by LANL and AFWL have demonstrated the viability of this technique [KIRTLAND94, REINOVSKY85].

The principal technical issues in adapting the FCG to weapons applications lie in packaging, the supply of start current, and matching the device to the intended load. Interfacing to a load is simplified by the coaxial geometry of coaxial and conical FCG designs. Significantly, this geometry is convenient for weapons applications, where FCGs may be stacked axially with devices such a microwave Vircators. The demands of a load such as a Vircator, in terms of waveform shape and timing, can be satisfied

by inserting pulse shaping networks, transformers and explosive high current switches.

3.2. Explosive and Propellant Driven MHD Generators

The design of explosive and propellant driven Magneto-Hydrodynamic generators is a much less mature art that that of FCG design. Technical issues such as the size and weight of magnetic field generating devices required for the operation of MHD generators suggest that MHD devices will play a minor role in the near term. In the context of this paper, their potential lies in areas such as start current generation for FCG devices.

The fundamental principle behind the design of MHD devices is that a conductor moving through a magnetic field will produce an electrical current transverse to the direction of the field and the conductor motion. In an explosive or propellant driven MHD device, the conductor is a plasma of ionised explosive or propellant gas, which travels through the magnetic field. Current is collected by electrodes which are in contact with the plasma jet [FANTHOME89].

The electrical properties of the plasma are optimised by seeding the explosive or propellant with with suitable additives, which ionise during the burn [FANTHOME89, FLANAGAN81]. Published experiments suggest that a typical arrangement uses a solid propellant gas generator, often using conventional ammunition propellant as a base. Cartridges of such propellant can be loaded much like artillery rounds, for multiple shot operation.

3.3. High Power Microwave Sources - The Vircator

Whilst FCGs are potent technology base for the generation of large electrical power pulses, the output of the FCG is by its basic physics constrained to the frequency band below 1 MHz. Many target sets will be difficult to attack even with very high power levels at such frequencies, moreover focussing the energy output from such a device will be problematic. A HPM device overcomes both of the problems, as its output power may be tightly focussed and it has a much better ability to couple energy into many target types.

A wide range of HPM devices exist. Relativistic Klystrons, Magnetrons, Slow Wave Devices, Reflex triodes, Spark Gap Devices and Vircators are all examples of the available technology base [GRANATSTEIN87, HOEBERLING92]. From the perspective of a bomb or warhead designer, the device of choice will be at this time the Vircator, or in the nearer term a Spark Gap source. The Vircator is of interest because it is a one shot device capable of producing a very powerful single pulse of

radiation, yet it is mechanically simple, small and robust, and can operate over a relatively broad band of microwave frequencies.

The physics of the Vircator tube are substantially more complex than those of the preceding devices. The fundamental idea behind the Vircator is that of accelerating a high current electron beam against a mesh (or foil) anode. Many electrons will pass through the anode, forming a bubble of space charge behind the anode. Under the proper conditions, this space charge region will oscillate at microwave frequencies. If the space charge region is placed into a resonant cavity which is appropriately tuned, very high peak powers may be achieved. Conventional microwave engineering techniques may then be used to extract microwave power from the resonant cavity. Because the frequency of oscillation is dependent upon the electron beam parameters, Vircators may be tuned or chirped in frequency, where the microwave cavity will support appropriate modes. Power levels achieved in Vircator experiments range from 170 kiloWatts to 40 GigaWatts over frequencies spanning the decimetric and centimetric bands [THODE87].

The two most commonly described configurations for the Vircator are the Axial Vircator (AV) (Fig.3), and the Transverse Vircator (TV). The Axial Vircator is the simplest by design, and has generally produced the best power output in experiments. It is typically built into a cylindrical waveguide structure. Power is most often extracted by transitioning the waveguide into a conical horn structure, which functions as an antenna. AVs typically oscillate in Transverse Magnetic (TM) modes. The

Transverse Vircator injects cathode current from the side of the cavity and will typically oscillate in a Transverse Electric (TE) mode.

Technical issues in Vircator design are output pulse duration, which is typically of the order of a microsecond and is limited by anode melting, stability of oscillation frequency, often compromised by cavity mode hopping, conversion efficiency and total power output. Coupling power efficiently from the Vircator cavity in modes suitable for a chosen antenna type may also be an issue, given the high power levels involved and thus the potential for electrical breakdown in insulators.

4. The Lethality of Electromagnetic Warheads

The issue of electromagnetic weapon lethality is complex. Unlike the technology base for weapon construction, which has been widely published in the open literature, lethality related issues have been published much less frequently.

While the calculation of electromagnetic field strengths achievable at a given radius for a given device design is a straightforward task, determining a kill probability for a given class of target under such conditions is not.

This is for good reasons. The first is that target types are very diverse in their electromagnetic hardness, or ability to resist damage. Equipment which has been intentionally shielded and hardened against electromagnetic attack will withstand orders of magnitude greater field strengths than standard commercially rated equipment. Moreover, various manufacturer's implementations of like types of equipment may vary significantly in hardness due the idiosyncrasies of specific electrical designs, cabling schemes and chassis/shielding designs used.

The second major problem area in determining lethality is that of coupling efficiency, which is a measure of how much power is transferred from the field produced by the weapon into the target. Only power coupled into the target can cause useful damage.

4.1. Coupling Modes

In assessing how power is coupled into targets, two principal coupling modes are recognised in the literature:

Front Door Coupling occurs typically when power from a electromagnetic weapon is coupled into an antenna associated with radar or communications equipment. The antenna subsystem is designed to couple power in and out of the equipment, and thus provides an efficient path for the power flow from the electromagnetic weapon to enter the equipment and cause damage.

Back Door Coupling occurs when the electromagnetic field from a weapon produces large transient currents (termed spikes, when produced by a low frequency weapon ) or electrical standing waves (when produced by a HPM weapon) on fixed electrical wiring and cables interconnecting equipment, or providing connections to mains power or the telephone network [TAYLOR92, WHITE78]. Equipment connected to exposed cables or wiring will experience either high voltage transient spikes or standing waves which can damage power supplies and communications interfaces if these are not hardened. Moreover, should the transient penetrate into the equipment, damage can be done to other devices inside.

A low frequency weapon will couple well into a typical wiring infrastructure, as most telephone lines, networking cables and power lines follow streets, building risers and corridors. In most instances any particular cable run will comprise multiple linear segments joined at approximately right angles. Whatever the relative orientation of the weapons field, more than one linear segment of the cable run is likely to be oriented such that a good coupling efficiency can be achieved.

It is worth noting at this point the safe operating envelopes of some typical types of semiconductor devices. Manufacturer's guaranteed breakdown voltage ratings for Silicon high frequency bipolar transistors, widely used in communications equipment, typically vary between 15 V and 65 V. Gallium Arsenide Field Effect Transistors are usually rated at about 10V. High density Dynamic Random Access Memories (DRAM), an essential part of any computer, are usually rated to 7 V against earth. Generic CMOS logic is rated between 7 V and 15 V, and microprocessors running off 3.3 V or 5 V power supplies are usually rated very closely to that voltage. Whilst many modern devices are equipped with additional protection circuits at each pin, to sink electrostatic discharges, sustained or repeated application of a high voltage will often defeat these [MOTO3, MICRON92, NATSEMI86].

Communications interfaces and power supplies must typically meet electrical safety requirements imposed by regulators. Such interfaces are usually protected by isolation transformers with ratings from hundreds of Volts to about 2 to 3 kV [NPI93].

It is clearly evident that once the defence provided by a transformer, cable pulse arrestor or shielding is breached, voltages even as low as 50 V can inflict substantial damage upon computer and communications equipment. The author has seen a number of equipment items (computers, consumer electronics) exposed to low frequency high voltage spikes (near lightning strikes, electrical power transients), and in every instance the damage was extensive, often requiring replacement of most semiconductors in the equipment [2].

HPM weapons operating in the centimetric and millimetric bands however offer an additional coupling mechanism to Back Door Coupling. This is the ability to directly couple into equipment through ventilation holes, gaps between panels and poorly shielded interfaces. Under these conditions, any aperture into the equipment behaves much like a slot in a microwave cavity, allowing microwave radiation to directly excite or enter the cavity. The microwave radiation will form a spatial standing wave pattern within the equipment. Components situated within the anti-nodes within the standing wave pattern will be exposed to potentially high electromagnetic fields.

Because microwave weapons can couple more readily than low frequency weapons, and can in many instances bypass protection devices designed to stop low frequency coupling, microwave weapons have the potential to be significantly more lethal than low frequency weapons.

What research has been done in this area illustrates the difficulty in producing workable models for predicting equipment vulnerability. It does however provide a solid basis for shielding strategies and hardening of equipment.

The diversity of likely target types and the unknown geometrical layout and electrical characteristics of the wiring and cabling infrastructure surrounding a target makes the exact prediction of lethality impossible.

A general approach for dealing with wiring and cabling related back door coupling is to determine a known lethal voltage level, and then use this to find the required field strength to generate this voltage. Once the field strength is known, the lethal radius for a given weapon configuration can be calculated.

A trivial example is that of a 10 GW 5 GHz HPM device illuminating a footprint of 400 to 500 metres diameter, from a distance of several hundred metres. This will result in field strengths of several kiloVolts per metre within the device footprint, in turn capable of producing voltages of hundreds of volts to kiloVolts on exposed wires or cables [KRAUS88, TAYLOR92]. This suggests lethal radii of the order of hundreds of metres, subject to weapon performance and target set electrical hardness.

4.2. Maximising Electromagnetic Bomb Lethality

To maximise the lethality of an electromagnetic bomb it is necessary to maximise the power coupled into the target set.

The first step in maximising bomb lethality is is to maximise the peak power and duration of the radiation of the weapon. For a given bomb size, this is accomplished by using the most powerful flux compression generator (and Vircator in a HPM bomb) which will fit the weapon size, and by maximising the efficiency of internal

power transfers in the weapon. Energy which is not emitted is energy wasted at the expense of lethality.

The second step is to maximise the coupling efficiency into the target set. A good strategy for dealing with a complex and diverse target set is to exploit every coupling opportunity available within the bandwidth of the weapon.

A low frequency bomb built around an FCG will require a large antenna to provide good coupling of power from the weapon into the surrounding environment. Whilst weapons built this way are inherently wide band, as most of the power produced lies in the frequency band below 1 MHz compact antennas are not an option. One possible scheme is for a bomb approaching its programmed firing altitude to deploy five linear antenna elements. These are produced by firing off cable spools which unwind several hundred metres of cable. Four radial antenna elements form a "virtual" earth plane around the bomb, while an axial antenna element is used to radiate the power from the FCG. The choice of element lengths would need to be carefully matched to the frequency characteristics of the weapon, to produce the desired field strength. A high power coupling pulse transformer is used to match the low impedance FCG output to the much higher impedance of the antenna, and ensure that the current pulse does not vapourise the cable prematurely.

Other alternatives are possible. One is to simply guide the bomb very close to the target, and rely upon the near field produced by the FCG winding, which is in effect a loop antenna of very small diameter relative to the wavelength. Whilst coupling efficiency is inherently poor, the use of a guided bomb would allow the warhead to be positioned accurately within metres of a target. An area worth further investigation in this context is the use of low frequency bombs to damage or destroy magnetic tape libraries, as the near fields in the vicinity of a flux generator are of the order of magnitude of the coercivity of most modern magnetic materials.

Microwave bombs have a broader range of coupling modes and given the small wavelength in comparison with bomb dimensions, can be readily focussed against targets with a compact antenna assembly. Assuming that the antenna provides the required weapon footprint, there are at least two mechanisms which can be employed to further maximise lethality.

The first is sweeping the frequency or chirping the Vircator. This can improve coupling efficiency in comparison with a single frequency weapon, by enabling the radiation to couple into apertures and resonances over a range of frequencies. In this fashion, a larger number of coupling opportunities are exploited.

The second mechanism which can be exploited to improve coupling is the polarisation of the weapon's emission. If we assume that the orientations of possible coupling

apertures and resonances in the target set are random in relation to the weapon's antenna orientation, a linearly polarised emission will only exploit half of the opportunities available. A circularly polarised emission will exploit all coupling opportunities.

The practical constraint is that it may be difficult to produce an efficient high power circularly polarised antenna design which is compact and performs over a wide band. Some work therefore needs to be done on tapered helix or conical spiral type antennas capable of handling high power levels, and a suitable interface to a Vircator with

multiple extraction ports must devised. A possible implementation is depicted in Fig.5. In this arrangement, power is coupled from the tube by stubs which directly feed a multi-filar conical helix antenna. An implementation of this scheme would need to address the specific requirements of bandwidth, beamwidth, efficiency of coupling from the tube, while delivering circularly polarised radiation.

Another aspect of electromagnetic bomb lethality is its detonation altitude, and by varying the detonation altitude, a tradeoff may be achieved between the size of the lethal footprint and the intensity of the electromagnetic field in that footprint. This provides the option of sacrificing weapon coverage to achieve kills against targets of greater electromagnetic hardness, for a given bomb size (Fig.7, 8). This is not unlike the use of airburst explosive devices.

In summary, lethality is maximised by maximising power output and the efficiency of energy transfer from the weapon to the target set. Microwave weapons offer the ability to focus nearly all of their energy output into the lethal footprint, and offer the ability to exploit a wider range of coupling modes. Therefore, microwave bombs are the preferred choice.

5. Targeting Electromagnetic Bombs

The task of identifying targets for attack with electromagnetic bombs can be complex. Certain categories of target will be very easy to identify and engage. Buildings housing government offices and thus computer equipment, production facilities, military bases and known radar sites and communications nodes are all targets which can be readily identified through conventional photographic, satellite, imaging radar, electronic reconnaissance and humint operations. These targets are typically geographically fixed and thus may be attacked providing that the aircraft can penetrate to weapon release range. With the accuracy inherent in GPS/inertially guided weapons, the electromagnetic bomb can be programmed to detonate at the optimal position to inflict a maximum of electrical damage.

Mobile and camouflaged targets which radiate overtly can also be readily engaged. Mobile and relocatable air defence equipment, mobile communications nodes and naval vessels are all good examples of this category of target. While radiating, their positions can be precisely tracked with suitable Electronic Support Measures (ESM) and Emitter Locating Systems (ELS) carried either by the launch platform or a remote surveillance platform. In the latter instance target coordinates can be continuously datalinked to the launch platform. As most such targets move relatively slowly, they are unlikely to escape the footprint of the electromagnetic bomb during the weapon's flight time.

Mobile or hidden targets which do not overtly radiate may present a problem, particularly should conventional means of targeting be employed. A technical solution to this problem does however exist, for many types of target. This solution is the detection and tracking of Unintentional Emission (UE) [HERSKOWITZ96]. UE has attracted most attention in the context of TEMPEST [3]   surveillance, where transient emanations leaking out from equipment due poor shielding can be detected and in many instances demodulated to recover useful intelligence. Termed Van Eck radiation [VECK85], such emissions can only be suppressed by rigorous shielding and emission control techniques, such as are employed in TEMPEST rated equipment.

Whilst the demodulation of UE can be a technically difficult task to perform well, in the context of targeting electromagnetic bombs this problem does not arise. To target such an emitter for attack requires only the ability to identify the type of emission and thus target type, and to isolate its position with sufficient accuracy to deliver the bomb. Because the emissions from computer monitors, peripherals, processor equipment, switchmode power supplies, electrical motors, internal combustion engine ignition systems, variable duty cycle electrical power controllers (thyristor or triac based), superheterodyne receiver local oscillators and computer networking cables are all distinct in their frequencies and modulations, a suitable Emitter Locating System can be designed to detect, identify and track such sources of emission.

A good precedent for this targeting paradigm exists. During the SEA (Vietnam) conflict the United States Air Force (USAF) operated a number of night interdiction gunships which used direction finding receivers to track the emissions from vehicle ignition systems. Once a truck was identified and tracked, the gunship would engage it [4].

Because UE occurs at relatively low power levels, the use of this detection method prior to the outbreak of hostilities can be difficult, as it may be necessary to overfly hostile territory to find signals of usable intensity [5]. The use of stealthy reconnaissance aircraft or long range, stealthy Unmanned Aerial Vehicles (UAV) may be required. The latter also raises the possibility of autonomous electromagnetic warhead armed expendable UAVs, fitted with appropriate homing receivers. These would be programmed to loiter in a target area until a suitable emitter is detected, upon which the UAV would home in and expend itself against the target.

6. The Delivery of Conventional Electromagnetic Bombs

As with explosive warheads, electromagnetic warheads will occupy a volume of physical space and will also have some given mass (weight) determined by the density of the internal hardware. Like explosive warheads, electromagnetic warheads may be fitted to a range of delivery vehicles.

Known existing applications [6] involve fitting an electromagnetic warhead to a cruise missile airframe. The choice of a cruise missile airframe will restrict the weight of the weapon to about 340 kg (750 lb), although some sacrifice in airframe fuel capacity could see this size increased. A limitation in all such applications is the need to carry an electrical energy storage device, eg a battery, to provide the current used to charge the capacitors used to prime the FCG prior to its discharge. Therefore the available payload capacity will be split between the electrical storage and the weapon itself.

In wholly autonomous weapons such as cruise missiles, the size of the priming current source and its battery may well impose important limitations on weapon capability. Air delivered bombs, which have a flight time between tens of seconds to minutes, could be built to exploit the launch aircraft's power systems. In such a bomb design, the bomb's capacitor bank can be charged by the launch aircraft enroute to target, and after release a much smaller onboard power supply could be used to maintain the charge in the priming source prior to weapon initiation.

An electromagnetic bomb delivered by a conventional aircraft [7] can offer a much better ratio of electromagnetic device mass to total bomb mass, as most of the bomb mass can be dedicated to the electromagnetic device installation itself. It follows therefore, that for a given technology an electromagnetic bomb of identical mass to a electromagnetic warhead equipped missile can have a much greater lethality, assuming equal accuracy of delivery and technologically similar electromagnetic device design.

A missile borne electromagnetic warhead installation will comprise the electromagnetic device, an electrical energy converter, and an onboard storage device such as a battery. As the weapon is pumped, the battery is drained. The electromagnetic device will be detonated by the missile's onboard fusing system. In a cruise missile, this will be tied to the navigation system; in an anti-shipping missile the radar seeker and in an air-to-air missile, the proximity fusing system. The warhead fraction (ie ratio of total payload (warhead) mass to launch mass of the weapon) will be between 15% and 30%  [8] .

An electromagnetic bomb warhead will comprise an electromagnetic device, an electrical energy converter and a energy storage device to pump and sustain the electromagnetic device charge after separation from the delivery platform. Fusing could be provided by a radar altimeter fuse to airburst the bomb, a barometric fuse or in GPS/inertially guided bombs, the navigation system. The warhead fraction could be as high as 85%, with most of the usable mass occupied by the electromagnetic device and its supporting hardware.

Due to the potentially large lethal radius of an electromagnetic device, compared to an explosive device of similar mass, standoff delivery would be prudent. Whilst this is an inherent characteristic of weapons such as cruise missiles, potential applications of these devices to glidebombs, anti-shipping missiles and air-to-air missiles would dictate fire and forget guidance of the appropriate variety, to allow the launching aircraft to gain adequate separation of several miles before warhead detonation.

The recent advent of GPS satellite navigation guidance kits for conventional bombs and glidebombs has provided the optimal means for cheaply delivering such weapons. While GPS guided weapons without differential GPS enhancements may lack the pinpoint accuracy of laser or television guided munitions, they are still quite accurate (CEP \(~~ 40 ft) and importantly, cheap, autonomous all weather weapons.

The USAF has recently deployed the Northrop GAM (GPS Aided Munition) on the B-2 bomber [NORTHROP95], and will by the end of the decade deploy the GPS/inertially guided GBU-29/30 JDAM (Joint Direct Attack Munition)[MDC95] and the AGM-154 JSOW (Joint Stand Off Weapon) [PERGLER94] glidebomb. Other countries are also developing this technology, the Australian BAeA AGW (Agile Glide Weapon) glidebomb achieving a glide range of about 140 km (75 nmi) when launched from altitude [KOPP96].

The importance of glidebombs as delivery means for HPM warheads is threefold. Firstly, the glidebomb can be released from outside effective radius of target air defences, therefore minimising the risk to the launch aircraft. Secondly, the large

standoff range means that the aircraft can remain well clear of the bomb's effects. Finally the bomb's autopilot may be programmed to shape the terminal trajectory of the weapon, such that a target may be engaged from the most suitable altitude and aspect.

A major advantage of using electromagnetic bombs is that they may be delivered by any tactical aircraft with a nav-attack system capable of delivering GPS guided munitions. As we can expect GPS guided munitions to be become the standard weapon in use by Western air forces by the end of this decade, every aircraft capable of delivering a standard guided munition also becomes a potential delivery vehicle for a electromagnetic bomb. Should weapon ballistic properties be identical to the standard weapon, no software changes to the aircraft would be required.

Because of the simplicity of electromagnetic bombs in comparison with weapons such as Anti Radiation Missiles (ARM), it is not unreasonable to expect that these should be both cheaper to manufacture, and easier to support in the field, thus allowing for more substantial weapon stocks. In turn this makes saturation attacks a much more viable proposition.

In this context it is worth noting that the USAF's possesion of the JDAM capable F-117A and B-2A will provide the capability to deliver E-bombs against arbitrary high value targets with virtual impunity. The ability of a B-2A to deliver up to sixteen GAM/JDAM fitted E-bomb warheads with a 20 ft class CEP would allow a small number of such aircraft to deliver a decisive blow against key strategic, air defence and theatre targets. A strike and electronic combat capable derivative of the F-22 would also be a viable delivery platform for an E-bomb/JDAM. With its superb radius, low signature and supersonic cruise capability an RFB-22 could attack air defence sites, C3I sites, airbases and strategic targets with E-bombs, achieving a significant shock effect. A good case may be argued for the whole F-22 build to be JDAM/E-bomb capable, as this would allow the USAF to apply the maximum concentration of force against arbitrary air and surface targets during the opening phase of an air campaign.

7. Defence Against Electromagnetic Bombs

The most effective defence against electromagnetic bombs is to prevent their delivery by destroying the launch platform or delivery vehicle, as is the case with nuclear weapons. This however may not always be possible, and therefore systems which can be expected to suffer exposure to the electromagnetic weapons effects must be electromagnetically hardened.

The most effective method is to wholly contain the equipment in an electrically conductive enclosure, termed a Faraday cage, which prevents the electromagnetic field from gaining access to the protected equipment. However, most such equipment must communicate with and be fed with power from the outside world, and this can provide entry points via which electrical transients may enter the enclosure and effect damage. While optical fibres address this requirement for transferring data in and out, electrical power feeds remain an ongoing vulnerability.

Where an electrically conductive channel must enter the enclosure, electromagnetic arresting devices must be fitted. A range of devices exist, however care must be taken in determining their parameters to ensure that they can deal with the rise time and strength of electrical transients produced by electromagnetic devices. Reports from the US [9] indicate that hardening measures attuned to the behaviour of nuclear EMP bombs do not perform well when dealing with some conventional microwave electromagnetic device designs.

It is significant that hardening of systems must be carried out at a system level, as electromagnetic damage to any single element of a complex system could inhibit the function of the whole system. Hardening new build equipment and systems will add a substantial cost burden. Older equipment and systems may be impossible to harden properly and may require complete replacement. In simple terms, hardening by design is significantly easier than attempting to harden existing equipment.

An interesting aspect of electrical damage to targets is the possibility of wounding semiconductor devices thereby causing equipment to suffer repetitive intermittent faults rather than complete failures. Such faults would tie down considerable maintenance resources while also diminishing the confidence of the operators in the equipment's reliability. Intermittent faults may not be possible to repair economically, thereby causing equipment in this state to be removed from service permanently, with considerable loss in maintenance hours during damage diagnosis. This factor must also be considered when assessing the hardness of equipment against electromagnetic attack, as partial or incomplete hardening may in this fashion cause more difficulties than it would solve. Indeed, shielding which is incomplete may resonate when excited by radiation and thus contribute to damage inflicted upon the equipment contained within it.

Other than hardening against attack, facilities which are concealed should not radiate readily detectable emissions. Where radio frequency communications must be used, low probability of intercept (ie spread spectrum) techniques should be employed exclusively to preclude the use of site emissions for electromagnetic targeting purposes [DIXON84]. Appropriate suppression of UE is also mandatory.

Communications networks for voice, data and services should employ topologies with sufficient redundancy and failover mechanisms to allow operation with multiple nodes and links inoperative. This will deny a user of electromagnetic bombs the option of disabling large portions if not the whole of the network by taking down one or more key nodes or links with a single or small number of attacks.

8. Limitations of Electromagnetic Bombs

The limitations of electromagnetic weapons are determined by weapon implementation and means of delivery. Weapon implementation will determine the electromagnetic field strength achievable at a given radius, and its spectral distribution. Means of delivery will constrain the accuracy with which the weapon can be positioned in relation to the intended target. Both constrain lethality.

In the context of targeting military equipment, it must be noted that thermionic technology (ie vacuum tube equipment) is substantially more resilient to the electromagnetic weapons effects than solid state (ie transistor) technology. Therefore a weapon optimised to destroy solid state computers and receivers may cause little or no damage to a thermionic technology device, for instance early 1960s Soviet military equipment. Therefore a hard electrical kill may not be achieved against such targets unless a suitable weapon is used.

This underscores another limitation of electromagnetic weapons, which is the difficulty in kill assessment. Radiating targets such as radars or communications equipment may continue to radiate after an attack even though their receivers and data processing systems have been damaged or destroyed. This means that equipment which has been successfully attacked may still appear to operate. Conversely an opponent may shut down an emitter if attack is imminent and the absence of emissions means that the success or failure of the attack may not be immediately apparent.

Assessing whether an attack on a non radiating emitter has been successful is more problematic. A good case can be made for developing tools specifically for the purpose of analysing unintended emissions, not only for targeting purposes, but also for kill assessment.

An important factor in assessing the lethal coverage of an electromagnetic weapon is atmospheric propagation. While the relationship between electromagnetic field strength and distance from the weapon is one of an inverse square law in free space, the decay in lethal effect with increasing distance within the atmosphere will be greater due quantum physical absorption effects [10]. This is particularly so at higher frequencies, and significant absorption peaks due water vapour and oxygen exist at frequencies above 20 GHz. These will therefore contain the effect of HPM weapons to shorter radii than are ideally achievable in the K and L frequency bands.

Means of delivery will limit the lethality of an electromagnetic bomb by introducing limits to the weapon's size and the accuracy of its delivery. Should the delivery error be of the order of the weapon's lethal radius for a given detonation altitude, lethality will be significantly diminished. This is of particular importance when assessing the

lethality of unguided electromagnetic bombs, as delivery errors will be more substantial than those experienced with guided weapons such as GPS guided bombs.

Therefore accuracy of delivery and achievable lethal radius must be considered against the allowable collateral damage for the chosen target. Where collateral electrical damage is a consideration, accuracy of delivery and lethal radius are key parameters. An inaccurately delivered weapon of large lethal radius may be unusable against a target should the likely collateral electrical damage be beyond acceptable limits. This can be a major issue for users constrained by treaty provisions on collateral damage [AAP1003].

9. The Proliferation of Electromagnetic Bombs

At the time of writing, the United States and the CIS are the only two nations with the established technology base and the depth of specific experience to design weapons based upon this technology. However, the relative simplicity of the FCG and the Vircator suggests that any nation with even a 1940s technology base, once in possession of engineering drawings and specifications for such weapons, could manufacture them.

As an example, the fabrication of an effective FCG can be accomplished with basic electrical materials, common plastic explosives such as C-4 or Semtex, and readily available machine tools such as lathes and suitable mandrels for forming coils. Disregarding the overheads of design, which do not apply in this context, a two stage FCG could be fabricated for a cost as low as $1,000-2,000, at Western labour rates [REINOVSKY85]. This cost could be even lower in a Third World or newly industrialised economy.

While the relative simplicity and thus low cost of such weapons can be considered of benefit to First World nations intending to build viable war stocks or maintain production in wartime, the possibility of less developed nations mass producing such weapons is alarming. The dependence of modern economies upon their information technology infrastructure makes them highly vulnerable to attack with such weapons, providing that these can be delivered to their targets.

Of major concern is the vulnerability resulting from increasing use of communications and data communications schemes based upon copper cable media. If the copper medium were to be replaced en masse with optical fibre in order to achieve higher bandwidths, the communications infrastructure would become significantly more robust against electromagnetic attack as a result. However, the current trend is to exploit existing distribution media such as cable TV and telephone wiring to provide multiple Megabit/s data distribution (eg cable modems, ADSL/HDSL/VDSL) to

premises. Moreover, the gradual replacement of coaxial Ethernet networking with 10-Base-T twisted pair equipment has further increased the vulnerability of wiring systems inside buildings. It is not unreasonable to assume that the data and services communications infrastructure in the West will remain a "soft" electromagnetic target in the forseeable future.

At this time no counter-proliferation regimes exist. Should treaties be agreed to limit the proliferation of electromagnetic weapons, they would be virtually impossible to enforce given the common availability of suitable materials and tools.

With the former CIS suffering significant economic difficulties, the possibility of CIS designed microwave and pulse power technology leaking out to Third World nations or terrorist organisations should not be discounted. The threat of electromagnetic bomb proliferation is very real.

10. A Doctrine for the Use of Conventional Electromagnetic Bombs

A fundamental tenet of IW is that complex organisational systems such as governments, industries and military forces cannot function without the flow of information through their structures. Information flows within these structures in several directions, under typical conditions of function. A trivial model for this function would see commands and directives flowing outward from a central decisionmaking element, with information about the state of the system flowing in the opposite direction. Real systems are substantially more complex.

This is of military significance because stopping this flow of information will severely debilitate the function of any such system. Stopping the outward flow of information produces paralysis, as commands cannot reach the elements which are to execute them. Stopping the inward flow of information isolates the decisionmaking element from reality, and thus severely inhibits its capacity to make rational decisions which are sensitive to the currency of information at hand.

The recent evolution of strategic (air) warfare indicates a growing trend toward targeting strategies which exploit this most fundamental vulnerability of any large and organised system [11]. The Desert Storm air war of 1991 is a good instance, with a substantial effort expended against such targets. Indeed, the model used for modern strategic air attack places leadership and its supporting communications in the position of highest targeting priority [WARDEN95]. No less importantly, modern Electronic Combat concentrates upon the disruption and destruction of communications and information gathering sensors used to support military operations. Again the Desert Storm air war provides a good illustration of the application of this method.

A strategy which stresses attack upon the information processing and communications elements of the systems which it is targeting offers a very high payoff, as it will introduce an increasing level of paralysis and disorientation within its target. Electromagnetic bombs are a powerful tool in the implementation of such a strategy.

10.1 Electronic Combat Operations using Electromagnetic Bombs

The central objective of Electronic Combat (EC) operations is the command of the electromagnetic spectrum, achieved by soft and hard kill means [12] against the opponent's electronic assets. The underlying objective of commanding the electromagnetic spectrum is to interrupt or substantially reduce the flow of information through the opponent's air defence system, air operations environment and between functional elements of weapon systems.

In this context the ability of electromagnetic bombs to achieve kills against a wide range of target types allows their general application to the task of inflicting attrition upon an opponent's electronic assets, be they specialised air defence assets or more general Command-Control-Communications (C3) and other military assets.

Electromagnetic bombs can be a means of both soft and hard electrical kill, subject to the lethality of the weapon and the hardness of its target. A hard electrical kill by means of an electromagnetic device will be achieved in those instances where such severe electrical damage is achieved against a target so as to require the replacement of most if not all of its internal electronics.

Electronic combat operations using electromagnetic devices involve the use of these to attack radar, C3 and air defence weapon systems. These should always be attacked initially with an electromagnetic weapon to achieve soft or hard electrical kills, followed up by attack with conventional munitions to preclude possible repair of disabled assets at a later time. As with conventional SEAD operations, the greatest payoff will be achieved by using electromagnetic weapons against systems of strategic importance first, followed in turn by those of operational and tactical importance [KOPP92].

In comparison with an AntiRadiation Missile (ARM - a missile which homes on the emissions from a threat radar), the established and specialised tool in the conduct of SEAD operations, an electromagnetic bomb can achieve kills against multiple targets of diverse types within its lethal footprint. In this respect an electromagnetic device may be described as a Weapon of Electrical Mass Destruction (WEMD). Therefore electromagnetic weapons are a significant force multiplier in electronic combat operations.

A conventional electronic combat campaign, or intensive electronic combat operations, will initially concentrate on saturating the opponent's electronic defences, denying information and inflicting maximum attrition upon electronic assets. The force multiplication offered by electromagnetic weapons vastly reduces the number of air assets required to inflict substantial attrition, and where proper electronic reconnaissance has been carried out beforehand, also reduces the need for specialised assets such as ARM firing aircraft equipped with costly emitter locating systems.

The massed application of electromagnetic bombs in the opening phase of an electronic battle will allow much faster attainment of command of the electromagnetic spectrum, as it will inflict attrition upon electronic assets at a much faster rate than possible with conventional means.

Whilst the immaturity of conventional electromagnetic weapons precludes an exact analysis of the scale of force multiplication achievable, it is evident that a single aircraft carrying an electromagnetic bomb capable of concurrently disabling a SAM site with its colocated acquisition radar and supporting radar directed AAA weapons, will have the potency of the several ARM firing and support jamming aircraft required to accomplish the same result by conventional means. This and the ability of multirole tactical aircraft to perform this task allows for a much greater concentration of force in the opening phase of the battle, for a given force size.

In summary the massed application of electromagnetic weapons to Electronic Combat operations will provide for a much faster rate of attrition against hostile electronic assets, achievable with a significantly reduced number of specialised and multirole air assets [13]. This will allow even a modestly sized force to apply overwhelming pressure in the initial phase of an electronic battle, and therefore achieve command of the electromagnetic spectrum in a significantly shorter time than by conventional means.

10.2. Strategic Air Attack Operations using Electromagnetic Bombs

The modern approach to strategic air warfare reflects in many respects aspects of the IW model, in that much effort is expended in disabling an opponent's fundamental information processing infrastructure. Since we however are yet to see a systematic IW doctrine which has been tested in combat, this paper will approach the subject from a more conservative viewpoint and use established strategic doctrine.

Modern strategic air attack theory is based upon Warden's Five Rings model [WARDEN95], which identifies five centres of gravity in a nation's warfighting capability. In descending order of importance, these are the nation's leadership and supporting C3 system, its essential economic infrastructure, its transportation network, its population and its fielded military forces.

Electromagnetic weapons may be productively used against all elements in this model, and provide a particularly high payoff when applied against a highly industrialised and geographically concentrated opponent. Of particular importance in the context of strategic air attack, is that while electromagnetic weapons are lethal to electronics, they have little if any effect on humans. This is a characteristic which is not shared with established conventional and nuclear weapons.

This selectivity in lethal effect makes electromagnetic weapons far more readily applicable to a strategic air attack campaign, and reduces the internal political pressure which is experienced by the leadership of any democracy which must commit to warfare. An opponent may be rendered militarily, politically and economically ineffective with little if any loss in human life.

The innermost ring in the Warden model essentially comprises government bureaucracies and civilian and military C3 systems. In any modern nation these are heavily dependent upon the use of computer equipment and communications equipment. What is of key importance at this time is an ongoing change in the structure of computing facilities used in such applications, as these are becoming increasingly decentralised. A modern office environment relies upon a large number of small computers, networked to interchange information, in which respect it differs from the traditional model of using a small number of powerful central machines.

This decentralisation and networking of information technology systems produces a major vulnerability to electromagnetic attack. Whereas a small number of larger computers could be defended against electromagnetic attack by the use of electromagnetic hardened computer rooms, a large distributed network cannot. Moreover, unless optical fibre networking is used, the networking cables are themselves a medium via which electromagnetic effects can be efficiently propagated throughout the network, to destroy machines. Whilst the use of distributed computer

networks reduces vulnerability to attack by conventional munitions, it increases vulnerability to attack by electromagnetic weapons.

Selective targeting of government buildings with electromagnetic weapons will result in a substantial reduction in a government's ability to handle and process information. The damage inflicted upon information records may be permanent, should inappropriate backup strategies have been used to protect stored data. It is reasonable to expect most data stored on machines which are affected will perish with the host machine, or become extremely difficult to recover from damaged storage devices.

The cost of hardening existing computer networks is prohibitive, as is the cost of replacement with hardened equipment. Whilst the use of hardened equipment for critical tasks would provide some measure of resilience, the required discipline in the handling of information required to implement such a scheme renders its utility outside of military organisations questionable. Therefore the use of electromagnetic weapons against government facilities offers an exceptionally high payoff.

Other targets which fall into the innermost ring may also be profitably attacked. Satellite link and importantly control facilities are vital means of communication as well as the primary interface to military and commercial reconnaissance satellites. Television and radio broadcasting stations, one of the most powerful tools of any government, are also vulnerable to electromagnetic attack due the very high concentration of electronic equipment in such sites. Telephone exchanges, particularly later generation digital switching systems, are also highly vulnerable to appropriate electromagnetic attack.

In summary the use of electromagnetic weapons against leadership and C3 targets is highly profitable, in that a modest number of weapons appropriately used can introduce the sought state of strategic paralysis, without the substantial costs incurred by the use of conventional munitions to achieve the same effect.

Essential economic infrastructure is also vulnerable to electromagnetic attack. The finance industry and stock markets are almost wholly dependent upon computers and their supporting communications. Manufacturing, chemical, petroleum product industries and metallurgical industries rely heavily upon automation which is almost universally implemented with electronic PLC (Programmable Logic Controller) systems or digital computers. Furthermore, most sensors and telemetry devices used are electrical or electronic.

Attacking such economic targets with electromagnetic weapons will halt operations for the time required to either repair the destroyed equipment, or to reconfigure for manual operation. Some production processes however require automated operation,

either because hazardous conditions prevent human intervention, or the complexity of the control process required cannot be carried out by a human operator in real time. A good instance are larger chemical, petrochemical and oil/gas production facilities. Destroying automated control facilities will therefore result in substantial loss of production, causing shortages of these vital materials.

Manufacturing industries which rely heavily upon robotic and semiautomatic machinery, such as the electronics, computer and electrical industry, precision machine industry and aerospace industries, are all key assets in supporting a military capability. They are all highly vulnerable to electromagnetic attack. Whilst material processing industries may in some instances be capable of function with manual process control, the manufacturing industries are almost wholly dependent upon their automated machines to achieve any useful production output.

Historical experience  [14]  suggests that manufacturing industries are highly resilient to air attack as production machinery is inherently mechanically robust and thus a very high blast overpressure is required to destroy it. The proliferation of electronic and computer controlled machinery has produced a major vulnerability, for which historical precedent does not exist. Therefore it will be necessary to reevaluate this orthodoxy in targeting strategy.

The finance industry and stock markets are a special case in this context, as the destruction of their electronic infrastructure can yield, unlike manufacturing industries, much faster economic dislocation. This can in turn produce large systemic effects across a whole economy, including elements which are not vulnerable to direct electromagnetic attack. This may be of particular relevance when dealing with an opponent which does not have a large and thus vulnerable manufacturing economy. Nations which rely on agriculture, mining or trade for a large proportion of the their gross domestic product are prime candidates for electromagnetic attack on their finance industry and stock markets. Since the latter are usually geographically concentrated and typically electromagnetically "soft" targets, they are highly vulnerable.

In summary there is a large payoff in striking at economic essentials with electromagnetic weapons, particularly in the opening phase of a strategic air attack campaign, as economic activity may be halted or reduced with modest expenditure of the attacker's resources. An important caveat is that centres of gravity within the target economy must be properly identified and prioritised for strikes to ensure that maximum effect is achieved as quickly as possible.

Transport infrastructure is the third ring in the Warden model, and also offers some useful opportunities for the application of electromagnetic weapons. Unlike the

innermost rings, the concentration of electronic and computer equipment is typically much lower, and therefore considerable care must be taken in the selection of targets.

Railway and road signalling systems, where automated, are most vulnerable to electromagnetic attack on their control centres. This could be used to produce traffic congestion by preventing the proper scheduling of rail traffic, and disabling road traffic signalling, although the latter may not yield particularly useful results.

Significantly, most modern automobiles and trucks use electronic ignition systems which are known to be vulnerable to electromagnetic weapons effects, although opportunities to find such concentrations so as to allow the profitable use of an electromagnetic bomb may be scarce.

The population of the target nation is the fourth ring in the Warden model, and its morale is the object of attack. The morale of the population will be affected significantly by the quality and quantity of the government propaganda it is subjected to, as will it be affected by living conditions.

Using electromagnetic weapons against urban areas provides the opportunity to prevent government propaganda from reaching the population via means of mass media, through the damaging or destruction of all television and radio receivers within the footprint of the weapon. Whether this is necessary, given that broadcast facilities may have already been destroyed, is open to discussion. Arguably it may be counterproductive, as it will prevent the target population from being subjected to friendly means of psychological warfare such as propaganda broadcasts.

The use of electromagnetic weapons against a target population is therefore an area which requires requires careful consideration in the context of the overall IW campaign strategy. If useful objectives can be achieved by isolating the population from government propaganda, then the population is a valid target for electromagnetic attack. Forces constrained by treaty obligations will have to reconcile this against the applicable regulations relating to denial of services to non-combatants [AAP1003].

The outermost and last ring in the Warden model are the fielded military forces. These are by all means a target vulnerable to electromagnetic attack, and C3 nodes, fixed support bases as well as deployed forces should be attacked with electromagnetic devices. Fixed support bases which carry out depot level maintenance on military equipment offer a substantial payoff, as the concentration of computers in both automatic test equipment and administrative and logistic support functions offers a good return per expended weapon.

Any site where more complex military equipment is concentrated should be attacked with electromagnetic weapons to render the equipment unservicable and hence reduce the fighting capability, and where possible also mobility of the targeted force. As discussed earlier in the context of Electronic Combat, the ability of an electromagnetic weapon to achieve hard electrical kills against any non-hardened targets within its lethal footprint suggests that some target sites may only require electromagnetic attack to render them both undefended and non-operational. Whether to expend conventional munitions on targets in this state would depend on the immediate military situation.

In summary the use of electromagnetic weapons in strategic air attack campaign offers a potentially high payoff, particularly when applied to leadership, C3 and vital economic targets, all of which may be deprived of much of their function for substantial periods of time. The massed application of electromagnetic weapons in the opening phase of the campaign would introduce paralysis within the government, deprived of much of its information processing infrastructure, as well as paralysis in most vital industries. This would greatly reduce the capability of the target nation to conduct military operations of any substantial intensity.

Because conventional electromagnetic weapons produce negligible collateral damage, in comparison with conventional explosive munitions, they allow the conduct of an effective and high tempo campaign without the loss of life which is typical of conventional campaigns. This will make the option of a strategic bombing campaign more attractive to a Western democracy, where mass media coverage of the results of conventional strategic strike operations will adversely affect domestic civilian morale.

The long term effects of a sustained and concentrated strategic bombing campaign using a combination of conventional and electromagnetic weapons will be important. The cost of computer and communications infrastructure is substantial, and its massed destruction would be a major economic burden for any industrialised nation. In addition it is likely that poor protection of stored data will add to further economic losses, as much data will be lost with the destroyed machines.

From the perspective of conducting an IW campaign, this method of attack achieves many of the central objectives sought. Importantly, the massed application of electromagnetic weapons would inflict attrition on an opponent's information processing infrastructure very rapidly, and this would arguably add a further psychological dimension to the potency of the attack. Unlike the classical IW model of Gibsonian CyberWar, in which the opponent can arguably isolate his infrastructure from hostile penetration, parallel or hyperwar style massed attack with electromagnetic bombs will be be extremely difficult to defend against.

10.3. Offensive Counter Air (OCA) Operations using Electromagnetic Bombs

Electromagnetic bombs may be usefully applied to OCA operations. Modern aircraft are densely packed with electronics, and unless properly hardened, are highly vulnerable targets for electromagnetic weapons.

The cost of the onboard electronics represents a substantial fraction of the total cost of a modern military aircraft, and therefore stock levels of spares will in most instances be limited to what is deemed necessary to cover operational usage at some nominal sortie rate. Therefore electromagnetic damage could render aircraft unusable for substantial periods of time.

Attacking airfields with electromagnetic weapons will disable communications, air traffic control facilities, navigational aids and operational support equipment, if these items are not suitably electromagnetic hardened. Conventional blast hardening measures will not be effective, as electrical power and fixed communications cabling will carry electromagnetic induced transients into most buildings. Hardened aircraft shelters may provide some measure of protection due electrically conductive reinforcement embedded in the concrete, but conventional revetments will not.

Therefore OCA operations against airfields and aircraft on the ground should include the use of electromagnetic weapons as they offer the potential to substantially reduce hostile sortie rates.

10.4. Maritime Air Operations using Electromagnetic Bombs

As with modern military aircraft, naval surface combatants are fitted with a substantial volume of electronic equipment, performing similar functions in detecting and engaging targets and warning of attack. As such they are vulnerable to electromagnetic attack, if not suitably hardened. Should they be hardened, volumetric, weight and cost penalties will be incurred.

Conventional methods for attacking surface combatants involve the use of saturation attacks by anti-ship missiles or coordinated attacks using a combination of ARMs and anti-ship missiles. The latter instance is where disabling the target electronically by stripping its antennae precedes lethal attack with specialised anti-ship weapons.

An electromagnetic warhead detonated within lethal radius of a surface combatant will render its air defence system inoperable, as well as damaging other electronic equipment such as electronic countermeasures, electronic support measures and communications. This leaves the vessel undefended until these systems can be restored, which may or may not be possible on the high seas. Therefore launching an electromagnetic glidebomb on to a surface combatant, and then reducing it with laser or television guided weapons is an alternate strategy for dealing with such targets.

10.5. Battlefield Air Interdiction Operations using Electromagnetic Bombs

Modern land warfare doctrine emphasises mobility, and manoeuvre warfare methods are typical for contemporary land warfare. Coordination and control are essential to the successful conduct of manoeuvre operations, and this provides another opportunity to apply electromagnetic weapons. Communications and command sites are key elements in the structure of such a land army, and these concentrate communications and computer equipment. Therefore they should be attacked with electromagnetic weapons, to disrupt the command and control of land operations.

Should concentrations of armoured vehicles be found, these are also profitable targets for electromagnetic attack, as their communications and fire control systems may be substantially damaged or disabled as a result. A useful tactic would be initial attack with electromagnetic weapons to create a maximum of confusion, followed by attack with conventional weapons to take advantage of the immediate situation.

10.6. Defensive Counter-Air (DCA) and Air Defence Operations using Electromagnetic Warheads

Providing that compact electromagnetic warheads can be built with useful lethality performance, then a number of other potential applications become viable. One is to equip an Air-Air Missile (AAM) with such a warhead. A weapon with datalink midcourse guidance, such as the AIM-120, could be used to break up inbound raids by causing soft or hard electrical kills in a formation (raid) of hostile aircraft. Should this be achieved, the defending fighter will have the advantage in any following engagement as the hostile aircraft may not be fully mission capable. Loss of air intercept or nav attack radar, EW equipment, mission computers, digital engine controls, communications and electronic flight controls, where fitted, could render the victim aircraft defenceless against attack with conventional missiles.

This paradigm may also be applied to air defence operations using area defence SAMs. Large SAMs such as the MIM-104 Patriot, RIM-66E/M and RIM-67A Standard, 5V55/48N6 (SA-10) and 9M82/9M83 (SA-12) could accommodate an electromagnetic warhead comparable in size to a bomb warhead. A SAM site subjected to jamming by inbound bombers could launch a first round under datalink control with an electromagnetic warhead to disable the bombers, and then follow with conventional rounds against targets which may not be able to defend themselves electronically. This has obvious implications for the electromagnetic hardness of combat aircraft systems.

10.7. A Strategy of Graduated Response

The introduction of non-nuclear electromagnetic bombs into the arsenal of a modern air force considerably broadens the options for conducting strategic campaigns. Clearly such weapons are potent force multipliers in conducting a conventional war, particularly when applied to Electronic Combat, OCA and strategic air attack operations.

The massed use of such weapons would provide a decisive advantage to any nation with the capability to effectively target and deliver them. The qualitative advantage in capability so gained would provide a significant advantage even against a much stronger opponent not in the possession of this capability.

Electromagnetic weapons however open up less conventional alternatives for the conduct of a strategic campaign, which derive from their ability to inflict significant material damage without inflicting visible collateral damage and loss of life. Western governments have been traditionally reluctant to commit to strategic campaigns, as the expectation of a lengthy and costly battle, with mass media coverage of its highly visible results, will quickly produce domestic political pressure to cease the conflict.

An alternative is a Strategy of Graduated Response (SGR). In this strategy, an opponent who threatens escalation to a full scale war is preemptively attacked with electromagnetic weapons, to gain command of the electromagnetic spectrum and command of the air. Selective attacks with electromagnetic weapons may then be applied against chosen strategic targets, to force concession. Should these fail to produce results, more targets may be disabled by electromagnetic attack. Escalation would be sustained and graduated, to produce steadily increasing pressure to concede the dispute. Air and sea blockade are complementary means via which pressure may be applied.

Because electromagnetic weapons can cause damage on a large scale very quickly, the rate at which damage can be inflicted can be very rapid, in which respect such a campaign will differ from the conventional, where the rate at which damage is inflicted is limited by the usable sortie rate of strategic air attack capable assets [15].

Should blockade and the total disabling of vital economic assets fail to yield results, these may then be systematically reduced by conventional weapons, to further escalate the pressure. Finally, a full scale conventional strategic air attack campaign would follow, to wholly destroy the hostile nation's warfighting capability.

Another situation where electromagnetic bombs may find useful application is in dealing with governments which actively implement a policy of state sponsored terrorism or info-terrorism, or alternately choose to conduct a sustained low intensity land warfare campaign. Again the Strategy of Graduated Response, using

electromagnetic bombs in the initial phases, would place the government under significant pressure to concede.

Importantly, high value targets such as R&D and production sites for Weapons of Mass Destruction (nuclear, biological, chemical) and many vital economic sites, such as petrochemical production facilities, are critically dependent upon high technology electronic equipment. The proliferation of WMD into developing nations has been greatly assisted by the availability of high quality test and measurement equipment commercially available from First World nations, as well as modern electronic process control equipment. Selectively destroying such equipment can not only paralyse R&D effort, but also significantly impair revenue generating production effort. A Middle Eastern nation sponsoring terrorism will use oil revenue to support such activity. Crippling its primary source of revenue without widespread environmental pollution may be an effective and politically acceptable punitive measure.

As a punitive weapon electromagnetic devices are attractive for dealing with belligerent governments. Substantial economic, military and political damage may be inflicted with a modest commitment of resources by their users, and without politically damaging loss of life.

11. Conclusions

Electromagnetic bombs are Weapons of Electrical Mass Destruction with applications across a broad spectrum of targets, spanning both the strategic and tactical. As such their use offers a very high payoff in attacking the fundamental information processing and communication facilities of a target system. The massed application of these weapons will produce substantial paralysis in any target system, thus providing a decisive advantage in the conduct of Electronic Combat, Offensive Counter Air and Strategic Air Attack.

Because E-bombs can cause hard electrical kills over larger areas than conventional explosive weapons of similar mass, they offer substantial economies in force size for a given level of inflicted damage, and are thus a potent force multiplier for appropriate target sets.

The non-lethal nature of electromagnetic weapons makes their use far less politically damaging than that of conventional munitions, and therefore broadens the range of military options available.

This paper has included a discussion of the technical, operational and targeting aspects of using such weapons, as no historical experience exists as yet upon which to

build a doctrinal model. The immaturity of this weapons technology limits the scope of this discussion, and many potential areas of application have intentionally not been discussed. The ongoing technological evolution of this family of weapons will clarify the relationship between weapon size and lethality, thus producing further applications and areas for study.

E-bombs can be an affordable force multiplier for military forces which are under post Cold War pressures to reduce force sizes, increasing both their combat potential and political utility in resolving disputes. Given the potentially high payoff deriving from the use of these devices, it is incumbent upon such military forces to appreciate both the offensive and defensive implications of this technology. It is also incumbent upon governments and private industry to consider the implications of the proliferation of this technology, and take measures to safeguard their vital assets from possible future attack. Those who choose not to may become losers in any future wars.

12. Acknowledgements

Thanks to Dr D.H. Steven for his insightful comment on microwave coupling and propagation, and to Professor C.S. Wallace, Dr Ronald Pose and Dr Peter Leigh-Jones for their most helpful critique of the drafts. Thanks also to the RAAF Air Power Studies Centre and its then Director, Group Captain Gary Waters, for encouraging the author to investigate this subject in 1993. Some material in this paper is derived from RAAF APSC Working Paper 15, "A Doctrine for the Use of Electromagnetic Pulse Bombs", published in 1993 [KOPP93], and is posted with permission.

An earlier version of this paper was presented at InfoWarCon V and first published in "Information Warfare - Cyberterrorism: Protecting Your Personal Security In the Electronic Age", 1996, Thunder's Mouth Press, 632 Broadway 7th FL, New York, NY, ISBN: 1-56025-132-8, http://www.infowar.com, posted with permission.

13. References

AAP1000 - RAAF, DI(AF) AAP1000, The Air Power Manual, Second Edition, RAAF APSC, Canberra, 1994

AAP1003 - RAAF, DI(AF) AAP1003, Ch.8 The Law of Aerial Targeting, Operations Law for RAAF Commanders, First Edition, RAAF APSC, Canberra, 1994

AFM1-1 - Basic Aerospace Doctrine of the United States Air Force, Air Force Manual 1-1, Volume 1, March 1992.

CAIRD85 - Caird R.S. et al, Tests of an Explosive Driven Coaxial Generator, Digest of Technical Papers, 5th IEEE Pulsed Power Conference, pp.220, IEEE, New York, 1985.

DIXON84 - Dixon R.C., Spread Spectrum Systems, John Wiley and Sons, New York, 1984.

FANTHOME89 - Fanthome B.A., MHD Pulsed Power Generation, Digest of Technical Papers, 7th IEEE Pulsed Power Conference, pp.483, IEEE, New York, 1989.

FLANAGAN81 - Flanagan J., High-Performance MHD Solid Gas Generator, Naval Research Lab, Patent Application 4269637, May 1981.

FOWLER60 - C. M. Fowler, W. B. Garn, and R. S. Caird, Production of Very High Magnetic Fields by Implosion, Journal of Applied Physics, Vol. 31, No. 3, 588-594, March, 1960.

FOWLER89 - C. M. Fowler,R. S. Caird, The Mark IX Generator, Digest of Technical Papers, Seventh IEEE Pulsed Power Conference, 475, IEEE, New York, 1989.

FULGHUM93 - Fulghum, D.A., ALCMs Given Non Lethal Role, Aviation Week & Space Technology, February 22, 1993.

GLASSTONE64 - S. Glasstone, Editor, The Effects of Nuclear Weapons, US AEC, April, 1962, Revised Edition February, 1964.

GOFORTH89 - Goforth J.H. et al, Experiments with Explosively Formed Fuse Opening Switches in Higher Efficiency Circuits, Digest of Technical Papers, 7th IEEE Pulsed Power Conference, pp.479, IEEE, New York, 1989.

GRANATSTEIN87 - Granatstein V.L., Alexeff I., High Power Microwave Sources, Artech House, Boston, London, 1987

HERSKOVITZ96 - Herskowitz D., The Other SIGINT/ELINT, Journal of Electronic Defence, April, 1996.

HOEBERLING92 - Heoberling R.F., Fazio M.V., Advances in Virtual Cathode Microwave Sources, IEEE Transactions on Electromagnetic Compatibility, Vol. 34, No. 3, 252, August 1992.

ICH10 - EW Systems: AN/ Designated Hardware, pp.86, International Countermeasures Handbook, 10th Edition, Cardiff Publishing, Colorado, 1985.

ICH14 - International Countermeasures Handbook, 14th Edition, Cardiff Publishing, Colorado, 1989.

JED95 - USAF Looks for HPM SEAD Solution, pp.36, Journal of Electronic Defence, September, 1995.

JED96 - Hughes to Build HPM SEAD Demonstrator, pp.29, Journal of Electronic Defence, February, 1996.

KIRTLAND94 - High Energy Microwave Laboratory, Fact Sheet, USAF AFMC, Phillips Laboratory, Kirtland AFB, 1994.

KOPP92 - Kopp C., Command of the Electromagnetic Spectrum - An Electronic Combat Doctrine for the RAAF, Working Paper No.8, Air Power Studies Centre, Royal Australian Air Force, Canberra, November 1992.

KOPP93 - Kopp C., A Doctrine for the Use of Electromagnetic Pulse Bombs, Working Paper No.15, Air Power Studies Centre, Royal Australian Air Force, Canberra, July 1993.

KOPP96 - Kopp C., Australia's Kerkanya Based Agile Gliding Weapon, pp.28, Australian Aviation, Aerospace Publications, Canberra, June 1996.

KRAUS88 - Kraus J.D., Antennas, Second Edition, McGraw-Hill, 1988.

MDC95 - Joint Direct Attack Munition (JDAM), unclassified briefing, McDonnell Douglas Corporation, 1995, unpublished material.

MICRON92 - Micron DRAM Data Book, Micron Technology Inc, Idaho, 1992.

MOTO3 - Motorola RF Device Data, Motorola Semiconductor Products Inc, Arizona, 1983.

NATSEMI78 - CMOS Databook, National Semiconductor Corporation, Santa Clara, 1978

NORTHROP95 - B-2 Precision Weapons, unclassified briefing, Northrop-Grumman Corporation, September, 1995, unpublished material.

NPI93 - NPI Local Area Network Products, SMD Transformers, Nano Pulse Industries, Brea, 1993.

PERGLER94 - Pergler R., Joint Standoff Weapon System (JSOW), unclassified briefing, Texas Instruments, Inc., December 1994, unpublished material.

RAMO65 - Ramo S. et al, Fields and Waves in Communications Electronics, New York, John Wiley & Sons, 1965

REINOVSKY85 - Reinovsky R.E., Levi P.S. and Welby J.M., An Economical, 2 Stage Flux Compression Generator System, Digest of Technical Papers, 5th IEEE Pulsed Power Conference, pp.216, IEEE, New York, 1985.

SANDER86 - Sander K. F. and G.A.L. Reed, Transmission and Propagation of Electromagnetic Waves, Cambridge University Press, 1986.

STAINES93 - Staines, G.W., High Power Microwave Technology - Part IV, Military Applications of High Power Microwaves, Salisbury, DSTO ERL, EWD, 1993, draft paper.

SZAFRANSKI95 - Szafranski R., Col USAF, Parallel War and Hyperwar, Chapter 5 in Schneider B.R, Grinter L.E., Battlefield of the Future, 21st Century Warfare Issues, Air University Press, Maxwell AFB, September 1995.

TAYLOR92 - Taylor C.D., Harrison C.W., On the Coupling of Microwave Radiation to Wire Structures, IEEE Transactions on Electromagnetic Compatibility, Vol. 34, No. 3, 183, August 1992.

THODE87 - Thode L.E., Virtual-Cathode Microwave Device Research: Experiment and Simulation, Chapter 14 in High Power Microwave Sources, 1987.

VECK85 - van Eck W., "Electromagnetic Radiation from Video Display Units: An Eavesdropping Risk", Computers and Security, 1985, pp. 269.

WARDEN95 - Warden J.A. III, Col USAF, Air Theory for the Twenty-first Century, Chapter 4 in Schneider B.R, Grinter L.E., Battlefield of the Future, 21st Century Warfare Issues, Air University Press, Maxwell AFB, September 1995.

WATERS92 - Waters Gary, Gulf Lesson One, Canberra, Air Power Studies Centre, 1992

WHITE78 - The EMP - A Triangular Impulse, 2.29, A Handbook Series on Electromagnetic Interference and Compatibility, Don White Consultants, Maryland, 1978.

Carlo Kopp Born in Perth, Western Australia, the author graduated with first class honours in Electrical Engineering in 1984, from the University of Western Australia. In 1996 he completed an MSc in Computer Science and is currently working on a PhD in the same discipline, at Monash University in Melbourne, Australia. He has over a decade of diverse industry experience, including the design of high speed communications equipment, optical fibre receivers and transmitters, communications equipment including embedded code, Unix computer workstation motherboards, graphics adaptors and chassis. More recently, he has consulted in Unix systems programming, performance engineering and system administration. Actively publishing as a defence analyst in Australia's leading aviation trade journal, Australian Aviation, since 1980, he has become a locally recognised authority on the application of modern military technology to operations and strategy. His work on electronic combat doctrine, electromagnetic weapons doctrine, laser remote sensing and signature reduction has been published by the Royal Australian Air Force's Air Power Studies Centre since 1992, and he has previously contributed to CADRE Air Chronicles.

1 - Electromagnetic pulse or EMP device is a generic term applied to any device, nuclear or conventional, which is capable of generating a very intense but short electromagnetic field transient. For weapons applications, this transient must be sufficiently intense to produce electromagnetic power densities which are lethal to electronic and electrical equipment. Electromagnetic weapons are electromagnetic devices specifically designed as weapons. Whilst the terms 'conventional EMP weapon' and 'High Power Microwave or HPM weapon' have been used interchangeably in trade journals (see FULGHUM93), this paper will distinguish between microwave band and low frequency weapons. The term 'electromagnetic bomb' or 'E-bomb' will be used to describe both microwave and low frequency non-nuclear bombs. This paper will not address the use of nuclear EMP, or alternate uses of HPM technology. HPM technology has a broad range of potential applications in EW, radar and directed energy weapons (DEW). The general conclusions of this paper in the areas of infrastructure vulnerability and hardening are also true for microwave directed energy weapons. This paper extends the scope of earlier work by the author on this subject [KOPP93].

2 - One bizzare instance of lightning strike electrical damage was described to the author by an eyewitness technician, tasked with assessing the damage on the site. A lightning bolt impacted in the close vicinity of a transmitter shed. RF and power

cables ran from the transmitter shed to a transmission tower through a rectangular, metal shielded tunnel. The effect of the lightning strike was to produce an electromagnetic standing wave in the tunnel, much like in a microwave waveguide. All cables within the tunnel were burned through at regular spacings along the tunnel, corresponding precisely to the half wavelength of the standing wave in the tunnel.

3 - The NACSIM 5100A standard specifies acceptable emission levels for TEMPEST (Transient ElectroMagnetic Pulse Emanation Standard) rated equipment.

4 - The Northrop/Lockheed ASD-5 Black Crow DF receiver was fitted to the AC-130A Pave Pronto gunships, rebuilt from obsoleted C-130 transports [ICH10].

5 - A noteworthy technical issue in this context is that even equipment not-rated to TEMPEST standards will radiate energy at very low power levels, in comparison with intentional transmissions by radar or communications equipment. A receiver designed to detect, identify and locate sources of UE radiation will either need to be highly sensitive, or deployed very close to the emitter. It is worth noting that UE from computer monitors and networks exhibit known regular patterns, and correlation techniques could be used to significantly improve receiver sensitivity [DIXON84].

6 - Fulghum D.A., ALCMs Given Non Lethal Role, AW&ST, Feb 22, 1993. This recent report indicates that the US has progressed significantly with its development work on electromagnetic warhead technology. An electromagnetic warhead was fitted to the USAF AGM-86 Air Launched Cruise Missile airframe, involving both structural and guidance system modifications. The description in this report suggests the use of an explosive pumped flux generator feeding a device such as a Vircator. References to magnetic coils almost certainly relate to the flux compression generator hardware.

7 - The Journal of Electronic Defence [JED96] recently reported on the USAF Phillips Laboratory at Kirtland awarding a $6.6M HPM SEAD weapon technology demonstration program contract to Hughes Missile Systems Co. This contract will see Hughes conduct design studies in order to define design goals, and then fabricate brassboard demonstration hardware using government developed technology. JED speculate that the weapon will be a FCG driven microwave tube, which is most likely the case given the USAF's prior research activities in this area [REINOVSKY85]. An earlier report [JED95] indicated the existence of a related program which addresses command and control warfare and counter-air capabilities. In any event, the devices produced by these programs are likely to become the first operationally fielded HPM electromagnetic bombs for delivery by combat aircraft.

8 - This may be readily determined by calculating the ratio of warhead mass to total weapon launch mass, for representative missile types. Taking the AGM-78 Standard as a lower limit yields 15.9%, whereas taking the AGM/BGM-109 Tomahawk as an upper limit yields about 28%. Figures are derived from manufacturers' brochures and reference publications eg Jane's Air-Launched Weapons.

9 - Staines, Fulghum. This is entirely consistent with theoretical expectations, as the different spectral characteristics of microwave electromagnetic warheads, compared to nuclear electromagnetic weapons, will significantly affect the effectiveness of protective filters. What is important from an electrical engineering viewpoint is that a filter designed to stop signals in the lower frequency bands may perform very poorly at microwave frequencies.

10 - See International Countermeasures Handbook, 14th Edition, pp 104.

11 - Gary Waters, Gulf Lesson One. Chapter 16 of this reference provides a good discussion of both the rationale and implementation of this strategy.

12 - Soft kill means will inhibit or degrade the function of a target system during their application, leaving the target system electrically and physically intact upon the cessation of their application. Hard kill means will damage or destroy the target system, and are thus a means of inflicting attrition.

13 - This is also the stated intent of the USAF HPM SEAD technology demonstration program. The fact that the first application of a HPM bomb is electronic combat underscores the tactical, operational and strategic importance of first defeating an air defence system when prosecuting a strategic air war.

14 - The classical argument here is centred upon Allied experience in bombing Germany during WW2, where even repeated raids on industrial targets were unable to wholly stop production, and in many instances only served to reduce the rate of increase in production. What must not be overlooked is that both the accuracy and lethality of weapons in this period bore little comparison to what is available today, and automation of production facilities was almost non-existent.

15- This constraint primarily results from limitations in numbers. Strategic air attack requires precision delivery of substantial payloads, and is thus most effectively performed with specialised bomber assets, such as the B-52, B-1, B-2, F-111, F-15E, F-117A, Tornado or Su-24. These are typically more maintenance intensive than less complex multirole fighters, and this will become a constraint to the sortie rate achievable with a finite number of aircraft, assuming the availability of aircrew. Whilst multirole fighters may be applied to strategic air attack, their typically lesser

payload radius performance and lesser accuracy will reduce their effectiveness. In the doctrinal context, this can be directly related to existing USAF aerospace doctrine [AFM1-1], in several areas.

A version of this article was first published in: "Information Warfare - Cyberterroism: Protecting Your Personal Security in the Electronic Age" by Winn Schwartau, 1996 Thunder's Mouth Press, 632 Broadway 7th Fl, New York, New York, ISBN: 1-56025-132-8, http://www.infowar.com

The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, and academic environment of Air University. They do not reflect the official position of the US Government, Department of Defense, the United States Air Force or the Air University.

congruence)=congruency(موافقت ،تناسب ،تجانس

tautسفت ،شق ،محکم کشيدن ،کشيده ،مات کردن ،درهم پيچيدن ،محکم بسته شده( مثل طناب دور يک بسته

Braided; woven together

Dragline; excavator; rope or cable used to pull things; type of dredging حفار با جام کابل دار

scaffolding سکوب بندى ،چوب بست سازى ،داربست

canopy طاقه چتر،روکش قايق ،خيمه ،کروک اتومبيل ،سايبان گذاشتن

drogue parachute لنگر چترى

culminate به اوج رسيدن ،بحد اکثر ارتفاع رسيدن ،بحد اعلى رسيدن

duds رخت کهنه ،رخت وپخت ،ژنده ،پاره

hedgerowرديف بوته هاى پرچين ،سياج بند،رديف خاربن

scaffoldingسکوب بندى ،چوب بست سازى ،داربست

sutureبخيه( در پزشکى)،درز،بخيه ،شکاف ،چاک ،دوختنclose a wound

intricacyپيچيدگى ،بغرنجى ،تودرتويى ،ريزه کارى

Arguably بطور مشکوک ،بطور نامعلومdebatably, disputably

Willing مايل ،راضى ،حاضر،خواهان ،راغب

constituent ماده متشکله ،جزء متشکله ،سازه ،جزء ترکيب کننده ،سازا،جزء اصلى ،انتخاب کننده ،موکل ،سازنده

exodus مهاجرت بنى اسرائيل از مصر به کنعان ،خروج ،مهاجرت دسته جمعى

Destitute (با)غير ملى ،بينوا،بيچاره ،خالى ،تهىof ،نيازمند

needy نيازمند

political clout : influence in the political arena

conform to همنوايى کردن ،مطابقت کردن ،وفق دادن ،پيروى کردن

envision خيال بافى کردن ،رويايى بودن ،دررويا ديدن

farfetched شبيه بعيد،بعيد،غير ميسر

anticipate پيش بينى کردن ،انتظار داشتن ،پيشدستى کردن ،جلوانداختن ،پيش گرفتن بر،سبقت جستن بر

indispensable واجب ،حتمى ،چاره نا پذير،ضرورى ،ناگزير،صرفنظر نکردنى ،الزم االجرا

impediment بار و بنه ،مانع ،عايق ،رادع ،محظور،اشکال ،گير

vacant خالى ،اشغال نشده ،بى متصدى ،بالتصدى ،بيکار

Dome of the Rock: Muslim mosque in Jerusalem famous for its large golden dome

Deter: بازداشتن ،ترساندن ،تحذير کردن

eagerness اشتياق ،ارزومندى

Temple Mount: mount in Jerusalem on which the Jewish Holy Temple was built

divine خدايى ،يزدانى ،الهى ،کشيش ،استنباط کردن ،غيب گويى کردن

shrine جاى مقدس ،زيارتگاه ،درمعبد قرار دادن

redemption فک ،از گرو دراوردن ،معادلransom استهالک ،مبادله اوراق بهادار با پول ،بازخريد،بازپرداخت ،بازخريد،خريدارى و ازاد سازى ،رستگارى

clientele ارباب رجوع ،مشتريان ،پيروان ،موکلين

pious Jew: ديندار،پرهيزگار،زاهد،متقى ،پارسا،وارسته

revenues : درامدهاى بودجه اىبازرگانى

veteran کهنه سرباز،سرباز قديمى يا سرباز شرکت کننده در جنگهاى گذشته ،ثابت استوار،کهنه کار،کهنهسرباز،سرباز سابق ،کارازموده

infuriate اتشى کردن ،بسيار خشمگين کردن

expedition تسريع ،سفر،اردوکشى ،هيئت اعزامى

Passover sacrifice: sacrifice offered for the Passover holiday during the time of the Jewish temple and symbolized by the lamb bone during the Seder ritual

Thou shalt not kill: you will not murder

Condemned: محکوم

tempt بطمع انداختن ،تطميع کردن ،شيفتن: allure: اغوا کردن ،فريفتن ،دچار وسوسه کردن

priest کشيش ،مجتهد،روحانى ،کشيشى کردن

fervent باحرارت ،باحميت ،پرشور وشعف ،ملتهب

Heifer گوساله ماده ،ماده گوساله

Sentiments: feeling, emotion; attitude, opinion; tender emotion

Compromise: تسالم ،خطر کشف رمز،امکان کشف داشتن به خطر افتادن ،تراضى ،توافق ،مصالحه کردن ،تسويه کردن

Quarrelsome: ستيزه جو،جنگار،ستيزگر

Striving: strenuous effort made to attain a goal, effortful attempt to accomplish a task

pursuit تعاقب کردن ،تعقيب ،پيگرد،تعاقب ،حرفه ،پيشه ،دنبال ،پيگيرى

bloodletting phlebotomy, draining of blood for medical purposes; killing, bloodshed

his descendants: his offspring, his issue, his progeny, his seed: : اوالدقانون ـ فقه

advocate دفاع کردن ،طرفدارى کردن ،حامى ،طرفدار،وکيل مدافع

solidarity تضامن ،اتحاد،انسجام ،بهم پيوستگى ،مسئوليت مشترک ،همکارى ،همبستگى

contempt اخالل در نظم دادگاه ،تحقير،اهانت ،خفت ،خوارى

complicity (حق ).همدستى درجرم ،شرکت در جرم

infamy اشتهار،شهرت ،نام ،اوازه ،مشهور کردن

fame اشتهار،شهرت ،نام ،اوازه ،مشهور کردن

accusation (حق )تهمت ،اتهام

forgery صورت سازى ،سند سازى ،جعل اسناد،امضاء سازى ،سند جعلى

Vicious بدسگال ،بدکار،شرير،تباهکار،فاسد،بدطينت ،نادرست

hatredدشمنى ،کينه ،عداوت ،بغض ،بيزارى ،تنفر،نفرت

the Israelitesبنى اسرائيل ،اسرائيليان

ghettoized: a part of a city, especially a slum area, occupied by a minority group: the Jewish quarter in a city.

Sectفرقه ،مسلک ،حزب ،دسته مذهبى ،مکتب فلسفى ،بخش ،بريدن ،قسمت کردن

Exodusمهاجرت بنى اسرائيل از مصر به کنعان ،خروج ،مهاجرت دسته جمعى

malevolentبدخواه ،بدنهاد،(درموردستاره بخت )نحس

mightier; strong; powerful; great

covenantشرط،عقد منجز،منشور عقد بستن ،تعهد کردن ،در CL عبارت است از عقدى که بر مبناى قرارداد کتبىمهر و امضا شده ،که بين طرفين مبادله مى گردد،عهد،پيمان بستن ،ميثاق بستن

altarsقربان گاه ،قربانگاه ،مذبح ،محراب ،مجمره

in the wake ofدر دنبال ،بتقليد،بتاسى

enslavementبنده سازى ،غالمى ،اسارت ،بردگى

edictفرمان ،حکم ،قانون

misfortuneبدبختى ،بيچارگى ،بدشانسى

strayedاواره ،سرگردان ،راه گذر،تک توک ،جانور ولگرد

compendiumخالصه ،زبده ،مختصر،کوتاهى ،اختصار

lore اموزش ،معرفت ،دانش ،مجموعه معارف وفرهنگ يک قوم ونژاد،فرهنگ نژادى ،افسانه هاورواياتقومى ،فاصله بين چشم ومنقار( يا دماغ )حيوانات

Rabbis; Jewish teacher or scholar, Jewish religious leader

allusionsگريز،اشاره ،کنايه ،اغفال

casteطبقه منفصل ،طبقه ،صنف ،قبيله ،طبقات مختلف مردم هند

exterminatedقلع و قمع کردن ،برانداختن ،بکلى نابودکردن ،منهدم کردن ،منقرض کردن ،دفع افات کردن

intimatelyصميمانه

masterwork شاهکار،کار مهم ،برجسته

reluctantبى ميل

unprecedentedبى سابقه ،بى مانند،جديد،بى نظير

pleaپاسخ دعوى ،دادخواست ،منازعه ،مشاجره ،مدافعه ،عذر،بهانه ،تقاضا،استدعا،پيشنهاد،وعده مشروط،ادعا

expulsionاخراج ،دفع ،راندگى ،بيرون شدگى ،تبعيد

enduringپرطاقت ،بادوام

Satraps; governor of a province in ancient Persia

Obliges; obligate, compel; do something as a favor, accommodate; در محظور قرار دادن ،متعهد وملتزم کردن ،ضامن سپردن ،ضرورى

synagogues)synagog(کنيسه ،پرستشگاه يهود

clericsکشيش

vexationازردگى ،رنجش ،ازار،تغيير،حالت تحريک

avengedکينه جويى کردن( از)،تالفى کردن ،انتقام کشيدن( از)،دادگيرى کردن ،خونخواهى کردن

yoke)قسمتى از سيستم انحراف پرتو الکترونى که براى ادرس دهى يک نمايش تصويرى بکار مى رود،قيد،يوخ ،يوغ زرده تخم مرغ ،(زيست شناسى ))yolk( ،سکان)،دهانه ،دوشاخه استقرار

swerveمنحرف شدن ،عدول کردن ،طفره زدن ،کج شدن ،منحرف کردن

Humiliated; made to feel shameful; mortified, ashamed; abashed

occultistعارف ،عرفانى ،متصوف ،اهل تصوف ،اهل سر،رمزى

Heed: pay attention; listen: پروا،توجه ،رعايت ،مراعات ،اعتناکردن( به)،محل گذاشتن به ،مالحظه کردن

Grand Inquisitorرئيس دادگاه رسيدگى در برخى کشورها

the Jesuit; Society of Jesus, Roman Catholic religious order for men founded by Saint Ignatius of Loyola in 1534

inconceivableتصور نکردنى ،غير قابل ادراک ،باور نکردنى

descent توارث ،وراثت ،نسب ،نژاد،نزول ،هبوط

tenets اصول مسلم

despoil(بيشتر با )غارت کردن ،ربودن loot, take spoils, plunder; rob, steal

incestuousزانى با محارم ،وابسته به جفت گيرى جانوران از يک جنس

appointedانتصابى

reignسلطنت کردن ،حکومت ،حکمفرمايى ،سلطنت يا حکمرانى کردن ،حکمفرما بودن

West Indies; group of islands located in the Caribbean Sea between North and South America

retaliateتالفى کردن ،تاوان دادن ،عين چيزى را بکسى برگرداندن

wrathخشم ،غضب ،غيظ،اوقات تلخى زياد،قهر

sanctityتقدس ،پرهيز کارى ،حرمت ،علو مقام

emissaryجاسوس ،مامور سرى ،فرستاده

subsistزيست کردن ،ماندن ،گذران کردن

Swarmدسته زياد،گروه زنبوران ،ازدحام کردن ،هجوم اوردن

devourبلعيدن ،فرو بردن ،حريصانه خوردن

curseدشنام ،لعنت ،بال،مصيبت ،نفرين کردن ،ناسزا گفتن ،فحش دادن

Jeopardized; endangered, placed in danger, imperiled, at risk بخطر انداختن

furnishانجام دادن ،تهيه ديدن ،مبله کردن ،داراى اثاثه کردن ،مجهز کردن ،مزين کردن ،تهيه کردن

descendantsنسل ، زاده (در جمع) اوالد ، زادگان

House of Commonsمجلس مبعوثان ،مجلس عوام انگليس

abrogationالغاء،بطالن ،نسخ

proclaimed اعالن کردن ، علنا اظهار داشتن ، جار زدن

en masse; together, as a group, in one mass

closely-knit; united by strong relationships and common interests.

Ghetto; part of a city, especially a slum area, occupied by a minority group.

Ordainedترتيب دادن ، مقدر کردن ، وضع کردن ، امر کردن ، فرمان دادن

testimonyگواهى ،شهادت ،تصديق ،مدرک ،دليل ،اظهار

stark خشن ،زبر،شجاع ،خشک وسرد( در موردزمين)،شاق ،قوى ،کامل ،سرراست ،رک ،صرف ،مطلق ،حساس ،سفت ،سرسخت ،پاک ،تماما

envyرشک ،حسادت ،حسد بردن به ،غبطه خوردن

bettermentترميم ،بهترى ،بهبودى ،اصالح ،بهبود

upright; vertical, perpendicular, erect; just, honorable, principled

consciences; sense of right and wrong(.n): وجدان ، ضمير ، ذمه ، باطن ، دل

harbourلنگرگاه ،بندرگاه ،پناهگاه ،پناه دادن ،پناه بردن ،لنگر انداختن ،پروردن

Pursuit; chase, hunt; quest, search; occupation, pastime

judiciousداراى قوه قضاوت سليم

exploitationاستفاده از موفقيت ،بهره کشى کردن سوء استفاده ،بهره بردارى ،انتفاع ،استخراج ،استثمار

assureاطمينان دادن ،بيمه کردن ،مجاب کردن

oratorsسخن پرداز ، سخنران ، ناطق ، خطيب ، مستدعي

feigning(.): وانمود کردن ، به خود بستن ، جعل کردن

enthusiasm(.): هواخواهي با حرارت ، شوروذوق ، غيرت ، جديت ، (م.م) الهام ، وجد و سرور ، اشتياق

flatteryچاپلوسى ،تملق

Proletariat رطبقه زحمتکش ،طبقه رنجبر،کارگر ورنجبر،طبقه کارگ

daredيارا بودن ، جرات کردن ، مبادرت به کار دليرانه کردن ، به مبارزه طلبيدن ، شهامت ، يارايي

odiousکراهت اور،نفرت انگيز

piousديندار ، پرهيزگار ، زاهد ، متقي ، پارسا ، وارسته

bearsبردن ، حمل کردن ، دربرداشتن ، داشتن ، زائيدن ، ميوه دادن ، (مج.) تاب آوردن ، تحمل کردن

righteousنيکو کار،عادل ،درست کار،صالح ،پرهيزکار

blatantپرسروصدا،شلوغ کننده ،خودنما،خشن ،رسوا

onslaughtيورش ،حمله

courageousدلير،باجرات

deafکر،فاقد قوه شنوايى

condemnمحکوم کردن ،محکوم شدن

awashمماس با سطح اب ،سرگردان بر روى امواج دريا،لبريز

Coerced; forced, compelled to do something brought about through force or other forms of compulsion

bribedرشوه پردازى ،پرداخت نامشروع ،رشوه دادن ،تطميع کردن ،رشوه ،بدکند

conform to; مطابق بودن با

predecessorاسبق ،سابق ،قبلى ،اجداد،(درجمع )پيشنيان ،ماقبل ،سلف

ferment ترش شدن ،مخمرشدن ،ور امدن ،(مج ).برانگيزاندن ،تهييج کردن ،مادهتخمير،مايه ،جوش ،خروش ،اضطراب

surrender پس گرفتن و تبديل کردن ،صرفنظر کردن ،واگذار کردن ،سپردن ،رهاکردن ،تسليم شدن ،تحويلدادن ،تسليم ،واگذارى ،صرفنظر

intrinsicبيواسطه ،ذاتى ،اصلى ،باطنى ،طبيعى ،ذهنى ،روحى ،حقيقى ،مرتب ،شايسته

parasiticپارازيتى ،انگلى

self-assuredمطمئن بنفس خود

parade; lineup; procession; display, exhibit

apatheticبى احساس ،بى تفاوت ،بى روح

gullibilityساده لوحى ،گول خورى ،فريب خورى ،زود باورى

gloatنگاه از روى کينه و بغض ،نگاه عاشقانه و حاکى از عالقه ،نگاه حسرت اميز کردن ،خيره نگاه کردن

swaggerخود فروشانه گام زدن ،با تکبر راه رفتن ،کبر فروشى ،خودستايى ،مغرور،(انگليس)شيک

deceitتقلب ،گول ،فريب ،حيله ،خدعه

dreadfulوحشتناک ،بد

impositionتحميل ،تکليف ،وضع ،باج ،ماليات ،عوارض

destinyسرنوشت( تقدير)،سرنوشت ،ابشخور،تقدير،نصيب و قسمت

played havoc with; made a mess of

a long way offبسياردور

tear asunder(:)n.(معموال بصورت جمع )اشک ،سرشک ،گريه ، :)n.vt.& vi.(دراندن ،گسيختن ،گسستن ،پارگى ،پاره کردن ،دريدن ،چاک دادن

cling toصداى جرنگ( مثل صداى افتادن پول خرد )چسبيدن ،پيوستن ،(مج ).وفادار بودن

keynote speech; important speech (as at a conference or political rally)

recapitulate; summarize, conclude, sum upرئوس مطالب را تکرار کردن ،(زيست شناسى )صفات ارثى را در طى چند نسل تکرارى کردن

disposal; getting rid of; act of disposing, arranging; device that grinds up garbage

dispossessخلع يد کردن ،ازتصرف محروم کردن ،بى بهره کردن ،محروم کردن ،دورکردن ،بيرون کردن ،رهاکردن

incessantالينقطع ،پيوسته ،پى در پى ،بى پايان

postpone به تاخير انداختن ،بتعويق افتادن ،عقب انداختن ،بتعويق انداختن ،موکول کردن ،پست تر دانستن ،دردرجه دوم گذاشتن

undisputedبى چون وچرابى ،بحث ناپذيرى ،مسلم بودن

cohabitباهم زندگى کردن( زن ومرد)،رابطه جنسى داشتن

grimترسناک ،شوم ،عبوس ،سخت ،ظالم

Devastated; destroyed, demolished; upset, crushed; hopeless

Exhausted; خسته ،تمام شده ،مصرف شده ،تحليل رفته;

arbitrateداورى کردن ،حکميت کردن( در)،فيصل دادن ،فتوى دادن

mouthpieceلثه ،دهانه ،لبه ،دهن گير،سخنگو،عامل

backward به عقب ،عقب افتاده ،به پشت ،ازپشت ،وارونه ،عقب مانده ،کودن

defamation توهين ،افترا،بدگويى ،تهمت ،بدنامى و رسوايى

Anti-Defamation League: organization opposed to and taking action against racial slander and libel, ADL

sympathy همدمى ،همدردى ،دلسوى ،رقت ،همفکرى ،موافقت

ample فراخ ،پهناور،وسيع ،فراوان ،مفصل ،پر،بيش از اندازه

nonsensical مزخرف ،چرند

authorship تاليف و تصنيف ،نويسندگى ،احداث ،ايجاد،ابداع ،ابتکار،اصل ،اغاز

banished; expel; send away, dismiss

in exile تغريب ،شخص تبعيد شده ،نفى بلد،جالى وظن ،تبعيد کردن

thence از انجا،از ان زمان ،پس از ان ،از ان جهت ،ديگر

manuscript دستخط،کتاب خطى ،نسخه خطى ،نوشته

acquaintance اشنايى ،سابقه ،اگاهى ،اشنايان

mimeograph ماشين تکثير،تکثير کردن ،استنسيل ،دستگاه تکثير

Synod شوراى کليسايى ،مجلس مناظره مذهبى

Procurator کفيل ،معاون ،رئيس کالنترى يا دادستان ،مامور مالى ،وکيل ،عامل ،گماشته ،ناظر هزينه ،نايب

Chamberlain خزانه دار،رئيس خلوت ،پيشکار،ناظر،پرده دار،حاجب

deliberate دانسته ،عمليات با فرصت ،تعمد کردن ،عمدا انجام دادن ،عمدى ،تعمدا،تعمق کردن ،سنجيدن ،انديشه کردن ،کنکاش کردن

fraudulent شياد،کالهبردار،متقلب ،کاله بردار،گول زن ،حيله گر،فريب اميز

faux; French) false; artificial, fake

pas; step in a dance; movement in a dance; dance

filthچرک ،کثافت ،پليدى ،الودگى ،(مج ).هرزه

ascertain معلوم کردن ،ثابت کردن ،معين کردن

Assholes; idiot, stupid person, ass (Slang)

pull no punches; not hold anything back, not withhold anything; give as much effort as possible

applaud افرين گفتن ،تحسين کردن ،کف زدن ،ستودن

Wannabe; want-to-be", person who imitates another person, one who dresses and acts like someone else

Burdens; load; weigh down زير بار خم شدن يا کردن