underestimation of emf/nir exposure for children for mobile telephones and for electronic article...

Underestimation of EMF/NIR Exposure for Children for Mobile

Telephones and for Electronic Article Survellance(EAS) Systems

Om P. Gandhi

Department of Electrical & Computer EngineeringUniversity of Utah

Salt Lake City, UT 84112 U.S.A.

Invited paper presented at the International NIR and Health Workshop- Brazil, May 18,19,2009.

Some Pertinent Publications1. O. P. Gandhi, G. Lazzi and C. M. Furse,

“Electromagnetic Absorption in the Human Head and Neck for Mobile Phones at 835 & 1900 MHz,” IEEE Trans on Microwave Theory & Techniques, Vol. 44(10), pp. 1884-1897, 1996.

2. O. P. Gandhi and G. Kang, “Some Present Problems and a Proposed Experimental Phantom for SAR Compliance Testing of Cellular Telephones at 835 and 1900 MHz,” Physics in Medicine & Biology, Vol. 47, pp. 1501-1518, 2002.

3. O. P. Gandhi and G. Kang, “Inaccuracies of a Plastic “Pinna” SAM for SAR Testing of Cellular Telephones Against IEEE and ICNIRP Safety Guidelines,” IEEE Trans. On Microwave Theory & Techniques, Vol. 52(8), pp. 2004-2012, 2004.

Pertinent Publications - Continued

4. O. P. Gandhi, “Electromagnetic Fields: Human Safety Issues,” Annual Review of Biomedical Engineering, Vol. 4, pp. 211-234, 2002.

5. O. P. Gandhi and G. Kang,” “Calculation of Induced Current Densities for Humans by Magnetic Fields from Electronic Article Surveillance Devices,” Physics in Medicine & Biology, Vol. 46, pp. 2759-2771, 2001.

6. G. Kang and O. P. Gandhi, “SARs for Pocket-Mounted Mobile Telephones at 835 and 1900 MHz,” Physics in Medicine & Biology, Vol. 47, pp. 4301-4313, 2002.

• Two different anatomic models of the head (The Utah Model and the Visible Man Model), and

• +11.1% larger and -9.1% smaller versions of the above two models i.e. a total of six anatomical models.

• The smaller versions of the head models were used to correspond to the smaller heads of the adults as well as the children.

In order to study the effect of head size and pinna thickness on the absorption of electro-magnetic energy radiated by cell phones, we have used:

Continued ….

• Different thicknesses of pinnas of the head models (20, 14, 10, and 6 mm) to correspond to the various individuals as well as thinner pinnas of children.

• Different sizes/tilt angles of cell phone antennas and handsets (2 types of antennas, three sizes of handsets).

• Two frequencies: 1900 and 835 MHz.

Gandhi & Kang, Phys. Med. Biol., 47, 1501-18, 2002.Gandhi & Kang, IEEE Trans. MTT, 52(8), 2004-12, 2004.

(b) The "Visible Man" model(a) The Utah Model

Gandhi & Kang, Phys. Med. Biol., 47, 1501-18, 2002.

Fig. 1. A visualization of the two anatomically-based 30º-tilted head models used for SAR calculations.

Body tissues Brain Body tissues Brain Body tissues Brain Body tissues Brain Body tissues Brain

Peak 1-g SAR (W/kg)

Tissue Larger Head Model

Average Head Model

Smaller Head Model

Utah Visible man Utah Visible man Utah

Model

Helix 20 mm length Helix 20 mm length Helix 20 mm length Monopole 40 mm length Monopole 40 mm length

AntennaHandset

Dimensions mm

22 x 42 x 122 22 x 42 x 122 22 x 42 x 82 22 x 42 x 122 22 x 42 x 122

0.96 0.22 1.16 0.09 0.89 0.22 0.95 0.13 0.76 0.25

1.32 0.31 1.22 0.13 1.23 0.33 1.00 0.14 1.02 0.33

1.45 0.45 1.61 0.18 1.390.48 1.21 0.25 1.13 0.45

Table 1. The calculated peak 1-g SARs for two models of the human head for an irradiated power of 125 mW at 1900 MHz.

Gandhi & Kang, Physics in Med & Biol., 47, 1501-18, 2002.

Calculated peak 1-g SARs for two models of the head at 835 MHz

Body tissues Brain Body tissues Brain Body tissues Brain Body tissues Brain Body tissues Brain

Peak 1-g SAR (W/kg)

Tissue Larger Head Model

Average Head Model

Smaller Head Model

Utah Visible man Utah Visible man Utah

Model

Helix 20 mm length Helix 20 mm length Monopole 80 mm length Monopole 80 mm length Monopole 80 mm length

AntennaHandset

Dimensions mm

22 x 42 x 122 22 x 42 x 122 22 x 42 x 122 22 x 42 x 122 22 x 42 x 102

3.84 0.83 3.88 0.37 2.92 1.04 3.01 0.64 2.65 1.08

3.91 1.03 4.29 0.49 3.20 1.24 3.29 0.80 2.81 1.28

4.20 1.20 4.36 0.56 3.47 1.38 3.43 0.97 2.86 1.43

Table 2. The calculated peak 1-g SARs for two models of the human head for an irradiated power of 600 mW at 835 MHz.

Gandhi & Kang, Physics in Med & Biol., 47, 1501-18, 2002.

Note that the peak 1-g SARs for both the body tissue and the brain increase monotonically with the reducing head size (and pinna thickness) for both of the head models (Utah and “Visible Man”), all handset dimensions and the antennas i.e. monopoles as well as helices.

Fig. 2. SAR distribution of Utah head model at 1900 MHz. (a) 11.1% larger, (b) average, and (c) smaller.

Gandhi & Kang, Phys. Med. Biol., 47, 1501-18, 2002.

Fig. 3. SAR distribution of Utah head model at 835 MHz. (a) 11.1% larger, (b) average, and (c) 9.09 % smaller.

Gandhi & Kang, Phys. Med. Biol., 47, 1501-18, 2002.

These figures calculated for the human heads of various sizes are consistent with the results reported for head models of adults and children (Gandhi et al., IEEE MTT, 44, 1884-97, 1996) in that there is a deeper penetration of absorbed energy for the smaller heads compared to that for the larger heads, both for 1900 and 835 MHz of radiated fields.

Effect of the pinna thickness on the brain and body tissue SAR is given in the following table:

Frequency (MHz)

(irradiated power in mW)

Antenna length (mm)

Tissue

Pinna thickness (mm)

20 14 10 6

Peak 1-g SAR

1900 (125 mW) 40Body tissue

Brain

0.51

0.20

0.83

0.27

1.02

0.33

1.29

0.46

835 (600 mW) 80Body tissue

Brain

2.44

0.85

2.95

1.06

3.20

1.24

3.50

1.37

Table 3. The calculated peak 1-g body tissue and brain SARs for the Utah Model of the head. Assumed is a handset of dimensions 22 x 42 x 122 mm held at an angle of 30º relative to the head.

Gandhi & Kang, Physics in Med & Biol., 47, 1501-18, 2002.

As expected, both the body tissue and brain SARs increase monotonically with the reducing pinna thickness (e.g. for the children). This is due to the closer placement of the radiating antenna to the body tissues and to the brain.

We have also reported [Gandhi & Kang, IEEE Trans. MTT, 52, 2004-12, 2004] that use of a plastic “pinna” for the specific anthropomorphic mannequin (SAM) head model used for SAR compliance testing of cell phones underestimates both the peak 1-g SAR as well as the 10-g SAR required for ICNIRP Guidelines by a factor of 1.6-2.0 or more, even for adults.

We have also reported that use of the so-called “Visible Man” Model based on the CT scans of a fairly husky (105 kg) man’s cadaver tends to underestimate both the peak 1- and 10-g SARs.

This problem is further compounded by the fact that SARs are higher for children as compared to adults.

LERE

M

Fig. 4. SAM head model with three cross-sectional cuts defining the 5-10 mm thickness of the plastic shell. (Source: IEEE Std., 1528, 2005)

(a) Side view. (b) Cut through reference plane R passing through mouth M.

(c) A cut 30 mm below plane R.

Gandhi, IEEE Trans. on Microwave Theory & Techniques, 52(8), 2004.

Table 4. Comparison of peak 1- and 10-g SARs obtained for SAM and Anatomic Models for the “cheek” and “15º-tilted” positions of the 22 x 42 x 122 mm handsets with different antennas. The SARs are normalized to a radiated power of 600 mW at 835 MHz.

AntennaAxial

Length mm

Peak 1-g SAR (W/kg)

SAM 5-10 mm plastic pinna

Utah Model,6 mm-thick pinna

Utah Model, 14 mm-thick pinna

Visible Man,6 mm-thick pinna

Cheek Position

80 mmmonopole 3.30 10.82 9.58 6.43

20 mm helix 4.18 14.40 14.51 9.07

15-Tilted position

80 mmmonopole 2.49 10.90 8.80 7.12

20 mm helix 2.65 14.96 12.96 9.95

Peak 10-g SAR (W/kg)

Cheek Position

80 mmmonopole 2.36 3.67 4.55 2.34

20 mm helix 3.03 4.79 6.61 3.21

15-Tilted position

80 mmmonopole 1.69 3.83 4.46 3.17

20 mm helix 1.77 5.06 5.94 4.15Gandhi, IEEE Trans. on Microwave Theory & Techniques, 52(8), 2004-12, 2004.

Table 5. Comparison of peak 1- and 10-g SARs obtained for SAM and anatomic models for the “cheek” and “15º-tilted” positions of the 22 x 42 x 122 mm handsets with different antennas. The SARs are normalized to a radiated power of 125 mW at 1900 MHz.

AntennaAxial

Length mm

Peak 1-g SAR (W/kg)

SAM 5-10 mm plastic pinna

Utah Model,6 mm-thick pinna

Utah Model, 14 mm-thick pinna

Visible Man,6 mm-thick pinna

Cheek Position

80 mmmonopole 0.73 2.05 2.31 1.97

20 mm helix 0.93 2.24 2.54 2.66

15-Tilted position

80 mmmonopole 1.13 3.06 3.00 3.06

20 mm helix 1.30 3.52 3.45 3.96

Peak 10-g SAR (W/kg)

Cheek Position

80 mmmonopole 0.49 0.85 1.04 0.90

20 mm helix 0.59 0.94 1.16 1.02

15-Tilted position

80 mmmonopole 0.74 1.16 1.33 1.36

20 mm helix 0.82 1.34 1.52 1.61Gandhi, IEEE Trans. on Microwave Theory & Techniques, 52(8), 2004-12, 2004.

10-g SAR, “Visible Man” Model, cheek position, frequency = 1900 MHz Radiated power = 125 mW

Fig. 5. Variation of peak 10-g SAR as a function of separation from the absorptive tissues. Handset of dimensions 22 x 42 x 122 mm.

10-g SAR, Utah Model, 15º-tilted position, frequency = 1900 MHz Radiated power = 125 mW

Fig. 6. Variation of peak 10-g SAR as a function of separation from the absorptive tissues. Handset of dimensions 22 x 42 x 122 mm.

1-g SAR, Utah Model, 15º-tilted position, frequency = 835 MHz Radiated power = 600 mW

Fig. 7. Variation of peak 1-g SAR as a function of separation from the absorptive tissues. Handset of dimensions 22 x 42 x 122 mm.

The underestimation of SAR by SAM is due to the fact that the cell phone under test is physically separated from the tissue-simulant head model of SAM by several millimeters.

It has been repeatedly shown both computationally and experimentally* that each additional millimeter of physical separation of the radiating source from the tissue-simulant model results in an underestimation of SAR by 13-15%. Thus, a factor of 2 or more underestimation of SAR by the SAM SAR com-pliance model is understandable because of the 6-10 mm thickness of the plastic “pinna” used for SAM.

*Kang and Gandhi, Phys. Med. Biol., 47, 4301-13, 2002. Gandhi & Kang, IEEE-MTT, 52, 2004-12, 2004.

Electronic Article Surveillance (EAS) Systems

• Being introduced into stores, libraries, and hospitals to prevent theft of items.

• Use alternating magnetic fields (at frequencies of several kHz to several MHz.

• May take the form of one- or two-sided panels of current-carrying loops near the exit door, loops hidden in the floor or under the checkout counters.

• We have used the impedance method to calculate induced current densities for 1mm resolution anatomical models of adult and scaled models of 10- and 5-year old children.

Gandhi & Kang, Phys. Med. Biology, 46, 2759-71, 2001.

Fig. 8. A few representative EAS systems.

Adult Male 10-Year Old Boy 5-Year Old Boy

Head circumference (cm) Body weight (kg) Height (cm) Body surface area Head surface area Voxel size for head (mm) Voxel size for arms, torso, and legs (mm)

(cm2 )

(cm2 )

53.8

71.7

176

17,400

1305

52.3

30.5

138

9610

1048

51.0

18.9

112

7510

984

1.974 1.974 2.930

1.974 1.974 2.930

1.974 1.974 2.352

1.400 1.400 2.282

1.871 1.8712.330

1.196 1.196 1.782

C. Lentner, “Geigy Scientific Tables”.

1

1

1

1

1

1

Table 6. Some typical external dimensions and derived voxel sizes used for the anatomic models of the male adult and 10- and 5-year old boys.

Gandhi & Kang, Phys. Med. Biol., 47, 2759-71, 2001.

(a) Adult male (b) 10-year old boy (c) 5-year old boy

Fig. 9. The three anatomic models used for calculations of induced electric fields and current densities.

Gandhi & Kang, Phys. Med. Biol., 47, 2759-71, 2001.

Fig. 10. Top view of the schematic of an assumed magnetic deactivator coil and the placement of the human model relative to it. All dimensions are in cm.

From: Gandhi & Kang, Phys. Med. Biol., 46, 2759-71, 2001.

x m x m

Coil I

Coil II

x

y z

(b) Top view

(a) Perspective view.

Model in the assumed central

position

10

50.0

60.0

20

120

Fig. 11. An assumed EAS system using a pair of rectangular coils with an overlap of 10 cm. The lower rung of the bottom coil is assumed to be 20 cm off the ground plane. The marked dimensions are in cm.

From: Gandhi & Kang, Phys. Med. Biol., 46, 2759-71, 2001.

Fig. 12. The calculated variations of the magnetic fields with distance y from the center of the deactivator solenoid and for the vertical z-axis passing through the front of the human model (y = 40 cm) at the edge of the table.

Along the y-axis from y = 40 cm (frontal plane of the body) to y = 70 cm.

From: Gandhi & Kang, Phys. Med. Biol., 46, 2759-71, 2001.

Fig. 13. The calculated variations of the magnetic fields with distance y from the center of the deactivator solenoid and for the vertical z-axis passing through the front of the human model (y = 40 cm) at the edge of the table.

Along the vertical z-axis passing through the front of the model.

From: Gandhi & Kang, Phys. Med. Biol., 46, 2759-71, 2001.

Fig. 14. The calculated variations of the magnetic fields with distance y along line passing through the center of the EAS coils and for a vertical line at a distance x = 20 cm (y = 0) from the plane of the EAS panel.

Along line passing through the center of the coils of the EAS system.

m mx x

m mx x

11

From: Gandhi & Kang, Phys. Med. Biol., 46, 2759-71, 2001.

Fig. 15. The calculated variations of the magnetic fields with distance y along line passing through the center of the EAS coils and for a vertical line at a distance x = 20 cm (y = 0) from the plane of the EAS panel.

Along the vertical line at a distance x = 20 cm (y = 0) from the plane

m mx x11

11

From: Gandhi & Kang, Phys. Med. Biol., 46, 2759-71, 2001.

Assumed for the calculation of induced current densities for the various parts of the body is:

Frequency (F) of 1 kHz, 50,000 A turns rms for the 85 cm high table top deactivator, and

Frequency of 30 kHz, 100 A turns for a second panel type EAS system.

ICNIRP Basic Restriction for max area-averaged current density J for CNS tissues (brain and spinal cord)

2max

2

J 2mA / m at F 1 kHz

60 mA / m at F 30 kHz

21cm

OrganAdult

10-year old child

5-year old child

J(mA m-2) J(mA m-2) J(mA m-2)

Brain

Pineal gland

Organ-averaged

Maximum (1 cm-2)

Organ-averaged

Maximum (1 cm-2)

0.15

0.48

0.02

---

0.66

2.02

0.10

---

1.77

4.46

0.51

---

Table 7. The calculated organ-averaged and maximum 1 cm2 area-averaged current densities (J) for the CNS tissues for the models of the adult and 10- and 5-year old children for the 1 kHz magnetic deactivator.

Gandhi & Kang, Phys. Med. Biol., 47, 2759-71, 2001.

OrganAdult

10-year old child

5-year old child

J(mA m-2) J(mA m-2) J(mA m-2)

Brain

Pineal gland

Organ-averaged

Maximum (1 cm-2)

Organ-averaged

Maximum (1 cm-2)

4.75

17.63

0.92

---

23.20

64.64

17.42

---

40.70

98.93

36.27

---

Table 8. The calculated organ-averaged and maximum 1 cm2 area-averaged current density (J) for the CNS tissues for the models of the adult and 10- and 5-year old children for the 30 kHz EAS pass-by system.

Gandhi & Kang, Phys. Med. Biol., 47, 2759-71, 2001.

The point to note is that higher current densities are induced for the CNS tissues of the 10- and 5-year old children for both of the assumed EAS systems.

This is due to the fact that the head of the taller adult is considerably above the deactivator or the pass-by EAS panel and is thus in the weaker magnetic field region.

The heads of the shorter children, on the other hand, are in higher magnetic fields. The maximum induced J for the children may exceed ICNIRP basic restrictions if sufficiently strong magnetic fields are used.

Conclusions – for Mobile Telephones

• Use of six different anatomical models (two different head shapes and three different scaled versions i.e. average, larger, and smaller versions of each, shows that the peak 1-g SAR for the brain for the smaller models representative of children may be up to 220% at 1900 MHz and 144% at 835 MHz of the SARs of the larger models.

• This is due to the thinner pinna and the skull for the smaller models which results in closer placement of the mobile telephones to the brain of children.

Conclusions -- Continued

• Use of the SAM (“standard anthropomorphic mannequin”) model with a 5-10 mm thick plastic spacer in the shape of “pinna” chosen by industry for SAR compliance testing results in an artificial, more distant placement of the mobile telephone from the tissue-simulating fluid of SAM. This gives an SAR that is up to two or more times smaller than for the anatomic models of the adult head, and an even larger underestimation of the SAR for the heads of children.

Conclusions -- Continued• In Europe, compliance of the maximum

magnetic fields induced current densities for the CNS tissues (brain and the spinal cord) against ICNIRP guidelines is required for all EAS systems.

• Because of the larger height, the adult head is generally in the weaker magnetic field region resulting in lower induced current densities for the brain for adults.

• The heads of children, on the other hand, are in the stronger magnetic field regions resulting in higher induced currents for the brain as compared to adults.