WIRELESS TRANSMISSION OF POWER Submitted in partial fulfillment of the requirements for the award of

Degree of

BACHELOR OF TECHNOLOGY

In

ELECTRICAL AND ELECTRONICS ENGINEERING

Submitted By

N.MAHESH (09261A0240)

Department Electrical and Electronics EngineeringMAHATMA GANDHI INSTITUTE OF TECHNOLOGY

(Affiliated to Jawaharlal Nehru Technological University,Hyderabad,A.P)ChaitanyaBharathi P.O., Gandipet, Hyderabad-500 075

2012

Department of Electrical and Electronics Engineering

Mahatma Gandhi Institute of Technology

(Affiliated to JNTU, Hyderabad, A.P)

ChaitanyaBharathi P.O, Gandipet, Hyderabad-75

CERTIFICATE

This is to certify that the seminar work entitled WIRELESS TRANSMISSION OF POWER is

being submitted by N.MAHESH (09261A0240) in partial fulfillment for the award of Degree

of BACHELOR OF TECHNOLOGY in ELECTRICAL & ELCTRONICS ENGINEERING to

theJawaharlal Nehru Technological University, Hyderabad during the academic year 2012-13

is a record of bonafide work carried out by her under our guidance and supervision.

The results embodied in this report have not been submitted by the student to any other

University or Institution for the award of any degree or diploma.

Seminar Coordinator Head Of Department

B.NARASIMHA REDDY Dr. P Ram Kishore Kumar Reddy

Assosiate Professor Assosiate Professor

Dept.of EEE Dept. of EEE

MGIT, MGIT,

Hyderabad Hyderbad

ACKNOWLEDGEMENT

The satisfaction and euphoria that accompany the successful completion of any task

would be incomplete without the mentioning of the people whose constant guidance and

encouragement made it possible. I take pleasure in presenting before you, my seminar,

which is result of studied blend of both research and knowledge.

I express our earnest gratitude to seminar Coordinator B.NARASIMHA REDDY,

Associate professor, Department of EEE, for his constant support, encouragement and

guidance. We are grateful for his cooperation and his valuable suggestions.

With Gratitude,

N.MAHESH

CONTENTSS.NO LIST OF CONTENTS PAGE NO

ABSTRACT i

LIST OF FIGURES ii

1 INTRODUCTION 1

2 BACKGROUND OF THE INVENTION 3

3 PRINCIPLE OF WPT 5

4 COMPONENTS OF WPT 16

a. MAGNETRON 10

b. KLYSTRON 12

c. SEMICONDUCTOR AMPLIFIER 13

d. RECTENNA 13

5 SOLAR POWER SATELLITES (SPS) 15

6 MERITS, DEMERITS of WPT 20

7 BIOLOGICAL & ECONOMIC IMPACT 23

8 CONCLUSION 24

9 REFERENCES 24

ABSTRACT

Among all the available sources of energy electrical energy is most cheapest, and easy to

generate while compared to other sources of energy. Many of the energy sources in nature

produce the waste products that contaminate the environment, But the electrical energy is only

one of the source that does not produce any waste product while it is consumed. The electrical

energy produced must be transferred to the substations for the distribution through cables during

this process most of the energy around 30% is wasted during the transmission due to the

resistance of the wire this shows that our transmission system is only 70 % efficient .Due to this

drop we are in need to set up boosters and take measurements to see that the voltage dropped is

not more than 6 volts. This process increase the cost for transmission. So, the concept of wire

less transmission have came its existence so has to reduce the transmission losses and cost per

unit of electric energy. This report mainly discuss about various technologies available so far for

wireless transmission of electricity and the need for a Wireless System of Energy Transmission,

their advantages, disadvantages and economical consideration.

The principle involved in WPT is conversion of electrical energy to the microwaves and

transmitting them, these transmitted waves will be received by a receiving rectenna and will be

converted back into electrical energy. The economical methods are being materialized on this

concept of transmission. This concept can be applied for various applications like charges with

out cables, this concept can be applied to the transportation system replacing the fuel like diesel

petrol with the electrical energy so that we can also reduce the pollution. This method of

transmission is also useful in cases where the transmission of energy is not possible example like

in deserts, islands. In spite of advantages it has some disadvantages like biological impact, and it

cannot be used every were because the rectenna can’t be used in every case. The report also

discusses the possible ways to get useful and practical results out of all research carried out so

far.

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LIST OF FIGURES

Fig No. Description Pg No

1 Block diagram of WPT 6

2 Wave guide 8

3 Circulator 8

4 Rectenna 8

5 Block diagram of efficiency of WPT 9

6 Magnetron 11

7 Klystron amplifier schematic diagram 12

8 Schematic of rectenna circuit. 14

9 Rectenna Array 15

10 Beam Control using Pilot signal 18

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1. INTRODUCTION

In our present electricity generation system we waste more than half of its resources. Especially

the transmission and distribution losses are the main concern of the present power technology.

Much of this power is wasted during transmission from power plant generators to the consumer.

The resistance of the wire used in the electrical grid distribution system causes a loss of 26-30%

of the energy generated. This loss implies that our present system of electrical distribution is only

70-74% efficient. The main reason for power loss during transmission and distribution is the

resistance of wires used for grid. The efficiency of power transmission can be improved to

certain level by using high strength Composite over head conductors and underground cables

that use high temperature super conductor. But, the transmission is still inefficient. According to

the World Resources Institute (WRI), India’s electricity grid has the highest transmission and

distribution losses in the world – a whopping 27%. Numbers published by various Indian

government agencies put that number at 30%, 40% and greater than 40%.The above discussed

problem can be solved by choose an alternative option for power transmission which could

provide much higher efficiency, low transmission cost and avoid power theft. Microwave Power

Transmission is one of the promising technologies and may be the righteous alternative for

efficient power transmission. The discussion of wireless power transmission as an alternative to

transmission line power distribution started in the late 19th century. Both Heinrich Hertz and

Nicolai Tesla theorized the possibility of wireless power transmission. Tesla demonstrated it in

1899 by powering fluorescent lamps 25 miles from the power source without using wires.

Despite the novelty of Tesla’s demonstration and his personal efforts to commercialize wireless

power transmission, he soon ran out of finding because it was much less expensive to lay copper

than to build the equipment necessary to transmit power through radio waves.

William C. Brown contributed much to the modern development of microwave power

transmission which for many reasons dominates research and development of wireless

transmission today. In the early 1960s brown invented the rectenna which directly converts

microwaves to DC current. He demonstrated its ability in 1964 by powering a helicopter from

the solely through microwaves.

“In 1982, Brown (Raytheon) and James F. Trimer (NASA) announced the development of a thin-

film plastic rectenna using printed-circuit technology that weighed only one-tenth as much as

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any previous rectenna”. This new, lighter weight rectenna led to the development of the

Stationary High Altitude Relay Platform (SHARP). The purpose of the sharp program, as its

name suggests, was to develop unmanned aircraft that would maintain a circular trajectory above

a microwave antenna field for the purpose of relaying communications from various ground

terminals. No commercial development past the prototype stage has been funded.

Despite these advances wireless power transmission has not been adopted for commercial use

except for the sole exception of pacemakers and electric toothbrush rechargers. However,

research is ongoing because of the many promising applications suited for wireless power

transmission.

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2. BACKGROUND OF THE INVENTION

It is known to use wireless power transmission in situations where physical wiring or cabling

between a power source and a power consumption point is difficult, if not impossible, to

implement. Electromechanical devices conventionally employ inductive elements for power

transmission e.g. between rotating or otherwise separated components. Inductive power

transmission is also used for recharging low-power batteries, for example. In inductive power

transmission, the power source and the power consumption or recharging point must be located

close to each other, and it is often necessary to isolate them galvanically from the environment,

because the electromagnetic radiation caused by induction may interfere with the operation of

adjacent devices

Solutions are also known wherein power transmission is carried out as radio frequency

transmission from a transmitter to one or more receivers, such as radio-frequency identification

and key cards. Such a solution is only suitable for power transmission of a very low level,

because it is difficult to direct the total power to be used for the transmission at specific receiving

antennas, and in practice transmission losses are extremely large. In addition, the efficiency of

radio frequency power transmission degrades rapidly as a function of distance.

A possibility to carry out wireless power transmission is to use a light source as the power

transmitter, the transmitted light then being received by a photo-detector and converted into

electric current. A light source is easier to direct towards a receiver, and this enables a better

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efficiency than that achieved e.g. in radio frequency power transmission to be achieved.

Publications EP 734 110 and U.S. Pat. No. 4,078,747, for example, describe solutions wherein

high power lasers are used for wireless transmission of high currents in the power supply of

electric trains and, similarly, for transferring solar energy generated in space.

A problem with the above-described solutions is that they are not suitable for efficient wireless

power transmission in environments occupied by people since the intensity of the laser to be

used is substantially life-threatening. Even if significantly reduced, the power levels required for

a sufficiently good efficiency would be so high that the laser would at least severely damage

vision in case of ocular exposure. The aforementioned safety problems further present the

disadvantage that although optical data transmission is known per se, such transmission is

difficult to implement wirelessly in a safe manner; therefore, an optical fibre is typically used for

optical data transmission

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3.PRINCIPLE OF WIRELESS TRANSMISSION OF POWER

There many methods to transmit the power without wires among the best methods for long range transmission is by

1.Microwave transmission

2. Laser Method

MICROWAVE TRANSMISSION:

In this methods the DC electrical energy is converted into microwave energy at large frequency in the range of 2.45Ghz by using microwave source and there are fed to the antenna . This microwaves are captured by the rectenna(rectifying Device) and is converted back to the DC electrical energy.

Wireless high power transmission using microwaves is well proven. Experiments in the tens of kilowatts have been performed at Goldstone in California in 1975 and more recently (1997) at Grand Bassin on Reunion Island. These methods achieve distances on the order of a kilometer.

LASER METHOD:

In the case of electromagnetic radiation closer to visible region of spectrum (10s of microns (um) to 10s of nm), power can be transmitted by converting electricity into a laser beam that is then pointed at a solar cell receiver This mechanism is generally known as "power beaming" because the power is beamed at a receiver that can convert it to usable electrical energy

NASA's Dryden Flight Research Center has demonstrated flight of a lightweight unmanned model plane powered by a laser beam.[58] This proof-of-concept demonstrates the feasibility of periodic recharging using the laser beam system and the lack of need to return to ground

LASER technology is limited due to its drawbacks of public safety and less efficiency

So in this report we concentrate on the microwave transmission

The next chapter deals with the components of WPT

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4. COMPONENTS OF WPT

William C. Brown, the leading authority on wireless power transmission technology, has loaned

this demonstration unit to the Texas Space Grant Consortium to show how power can be

transferred through free space by microwaves. A block diagram of the demonstration

components is shown below.

Fig 1 :Block diagram of WPT

The Primary components of Wireless Power Transmission are

1. Microwave Generator,

2. Transmitting antenna and

3. Receiving antenna (Rectenna).

1. Microwave Generator: The microwave transmitting devices are classified as Microwave

Vacuum Tubes (magnetron, klystron, Travelling Wave Tube (TWT), and Microwave

Power Module (MPM) and Semiconductor Microwave transmitters (GAAS

MESFET,GAN PHEMT, SIC MESFET, ALGAN/GAN HFET, and INGAAS).

Magnetron is widely used for experimentation of WPT. The microwave transmission

often uses 2.45GHz or5.8GHz of ISM band. The other choices of frequencies are

8.5GHz, 10 GHz and 35 GHz . The highest efficiency over 90% is achieved at 2.45 GHz

among all the frequencies.

2. Transmitting Antenna : The slotted wave guide antenna, microstrip patch antenna, and

parabolic dish antenna are the most popular type of transmitting antenna. The slotted

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waveguide antenna is ideal for power transmission because of its high aperture efficiency

(> 95%) and high power handling capability.

3. Rectenna: The concept, the name „rectenna‟ and the rectenna was conceived by W.C.

Brown of Raytheon Company in the early of 1960s [5]. The rectenna is a passive element

consists of antenna, rectifying circuit with a low pass filter between the antenna and

rectifying diode. The antenna used in rectenna may be dipole, Yagi – Uda, microstrip or

parabolic dish antenna. The patch dipole antenna achieved the highest efficiency among

the all. Schottky barrier diodes (GaAs W, Si, and GaAs) are usually used in the rectifying

circuit due to the faster reverse recovery time and much lower forward voltage drop

The microwave source consists of a microwave oven magnetron with electronics to control the

output power. The output microwave power ranges from 50 W to 200 W at 2.45 GHz. A coaxial

cable connects the output of the microwave source to a coax-to-waveguide adapter. This adapter

is connected to a waveguide ferrite circulator which protects the microwave source from

reflected power.

The circulator is connected to a tuning waveguide section to match the waveguide impedance to

the antenna input impedance. The slotted waveguide antenna consists of 8 waveguide sections

with 8 slots on each section. These 64 slots radiate the power uniformly through free space to the

rectenna. The slotted waveguide antenna is ideal for power transmission because of its high

aperture efficiency (> 95%) and high power handling capability. A rectifying antenna called a

rectenna receives the transmitted power and converts the microwave power to direct current

(DC) power. This demonstration rectenna consists of 6 rows of dipoles antennas where 8 dipoles

belong to each row. Each row is connected to a rectifying circuit which consists of low pass

filters and a rectifier. The rectifier is a GaAs Schottky barrier diode that is impedance matched to

the dipoles by a low pass filter. The 6 rectifying diodes are connected to light bulbs for indicating

that the power is received.

Magnetron is widely used for experimentation of WPT. The microwave transmission often uses

2.45GHz or 5.8GHz of ISM band. The other choices of frequencies are 8.5GHz, 10 GHz and 35

GHz . The highest efficiency over 90% is achieved at 2.45 GHz among all the frequencies

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BASIC DIAGRAMS OF ITS COMPONENTS:

Fig 2:Wave guide Fig 3:Circulator

Fig 4:Rectenna

The light bulbs also dissipated the received power. This rectenna has a 25% collection and

conversion efficiency, but rectennas have been tested with greater than 90% efficiency at 2.45

GHz.

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The below figure shows the Block diagram of Microwave Wireless Power Transmission

Fig 5:Block diagram of efficiency of WPT

The overall efficiency of the WPT system can be improved by Increasing directivity of the

antenna array Using schottky diode with higher ratings.

The Transmission efficiency is defined as as the function of “τ”

τ=√A t A rλD

Where At = transmitter aperture area

Ar = Receiver aperture area

λ =wave length of the microwave

D = Distance between transitter and reciever

The efficiency can approach 100 if τ is maintained greate than 2. For example the efficiency is 99.63% at τ =2.4

TRANSMITTER:

The key requirement of a transmitter is its ability to convert dc power to RF power

efficiently and radiate the power to a controlled manner with low loss. The transmitter’s

efficiency drives the end-to-end efficiency as well as thermal management system i.e., any heat

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generated from inefficiencies in the dc-RF conversion, should be removed from the transmitter

as it reduces the life time of RF devices and control electronics. Passive inter modulation is

another field which requires critical attention. Filtering of noise and suppression of harmonics

will be required to meet the regulatory requirement.

The main components of a transmitter include dc-to-RF converter and transmitting

antenna. The complexity of the transmitter depends on the WPT application. For the large scale

WPT application such as SPS, phased array antennas are required to distribute the RF power

sources across the aperture and electronically control the power beam. Power distribution at the

transmitting antenna=√ (1-r²), where r is the radius of antenna.

There are mainly three dc-to-RF power converters: magnetrons, klystrons and solid state

amplifiers. let us discuss about them

4.1 MAGNETRON:

The microwave radiation of microwave ovens and some radar applications is produced by a

device called a magnetron

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The magnetron is called a "crossed-field" device in the industry because both magnetic and

electric fields are employed in its operation, and they are produced in perpendicular directions so

that they cross. The applied magnetic field is constant and applied along the axis of the circular

device illustrated. The power to the device is applied to the center cathode which is heated to

supply energetic electrons which would, in the absence of the magnetic field, tend to move

radially outward to the ring anode which surrounds it.

Fig 6:Magnetron

Electrons are released at the center hot cathode by the process of thermionic emission and have

an accelerating field which moves them outward toward the anode. The axial magnetic field

exerts a magnetic force on these charges which is perpendicular to their initially radial motion,

and they tend to be swept around the circle. In this way, work is done on the charges and

therefore energy from the power supply is given to them. As these electrons sweep toward a

point where there is excess negative charge, that charge tends to be pushed back around the

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cavity, imparting energy to the oscillation at the natural frequency of the cavity. This driven

oscillation of the charges around the cavities leads to radiation of electromagnetic waves, the

output of the magnetron.

4.2 KLYSTRON:

The below fig shows the schematic diagram of a klystron amplifier

Fig 7 Klystron amplifier schematic diagram

Here a high velocity electron beam is formed, focused and send down a glass tube to a collector

electrode which is at high positive potential with respect to the cathode. As the electron beam

having constant velocity approaches gap A, they are velocity modulated by the RF voltage

existing across this gap. Thus as the beam progress further down the drift tube, bunching of

electrons takes place. Eventually the current pass the catcher gap in quite pronounce bunches and

therefore varies cyclically with time. This variation in current enables the klystron to have

significant gain. Thus the catcher cavity is excited into oscillations at its resonant frequency and

a large output is obtained.

The tube body and solenoid operate at 300°C and the collector operates at 500°C. The overall

efficiency is 83%. The microwave power density at the transmitting array will be 1 kW/m² for a

typical 1 GW SPS with a transmitting antenna aperture of 1 km diameter. If we use 2.45 GHz for

WPT, the number of antenna elements per square meter is on the order of 100. Therefore the

power allotted to the individual antenna element is of the order of 10 W/element. So we must

distribute the high power to individual antenna through a power divider .

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4.3 SEMICONDUCTOR AMPLIFIER

After 1980s, semiconductor device plays the lead in microwave world instead of the microwave

tubes. It causes by advance of mobile phone network. The semiconductor device is expected to

expand microwave applications, for instance, phased array and Active integrated antenna (AIA),

because of its manageability and mass productivity. After 1990s, some MPT experiments were

carried out in Japan with phased array of semiconductor amplifiers. Typical semiconductor

device for microwave circuits are FET (Field Effect Transistor), HBT (Heterojunction Bipolar

Transistor), and HEMT (High Electron Mobility Transistor). Present materials for the

semiconductor device are Si for lower frequency below a few GHz and GaAs for higher

frequency. We design microwave circuits with these semiconductor devices. It is easy to control

a phase and amplitude through the microwave circuits with semiconductor devices, for example,

amplifiers, phase shifters, modulators, and so on. For the microwave amplifiers, circuit design

theoretically determines efficiency and gain. A, B, C class amplifiers are classified in bias

voltage in device. These classes are also applied in kHz systems. In D, E, F class amplifiers for

microwave frequency, higher harmonics are used effectively to increase efficiency, theoretically

100%. Especially F class amplifier is expected as high efficient amplifier for the MPT system.

4.4 RECETENNA:

Brown was the pioneer in developing the first 2.45GHz rectenna.

Rectenna is the microwave to dc converting device and is mainly composed of a receiving

antenna and a rectifying circuit. Fig shows the schematic of rectenna circuit. It consists of a

receiving antenna, an input low pass filter, a rectifying circuit and an output smoothing filter.

The input filter is needed to suppress re radiation of high harmonics that are generated by the non

linear characteristics of rectifying circuit. Because it is a highly non linear circuit, harmonic

power levels must be suppressed. One method of suppressing harmonics is by placing a

frequency selective surface in front of the rectenna circuit that passes the operating frequency

and attenuates the harmonics.

Fig 8: Schematic of rectenna circuit.

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For rectifying Schottky barrier diodes utilizing silicon and gallium arsenide are

employed. In rectenna arrays, the diode is the most critical component to achieve higher

efficiencies because it is the main source of loss. Diode selection is dependent on the input

power levels. The breakdown voltage limits the power handling capacity and is directly related

to series resistance and junction capacitance through the intrinsic properties of diode junction

and material .For efficient rectification the diode cut off frequency should be approximately ten

times the operating frequency.

Diode cut off frequency is given by ƒ=1/ [2πRsCj], where ƒ is the cut off frequency, Rs is

the diode series resistance, Cj is the zero-bias junction capacitance.

The input low pass filter between the antenna and the rectifier is used

(i) to prevent re-radiation by the antenna of harmonic waves produced by the rectifier,

(ii) for impedance matching purposes between the antenna and circuit and

(iii) to ensure a continuous current pass from the antenna to the rectifier.

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5.Solar Power Satellites (SPS):

The concept of a large SPS that would be placed in geostationary orbit was invented by Peter

Glaser in 1968 .The SPS concept was examined extensively during the late 1970s by the U.S

Department of Energy (DOE) and the National Aeronautics and Space Administration (NASA).

Solar Power Satellites would be located in the geosynchronous orbit. The difference between

existing satellites and SPS is that an SPS would generate more power-much more power than it

requires for its own operation.

The solar energy collected by an SPS would be converted into electricity, then into

microwaves. The microwaves would be beamed to the Earth’s surface, where they would be

received and converted back into electricity by a large array of devices known as rectifying

antenna or rectenna(Rectification is the process by which alternating electrical current ,such as

that induced by a microwave beam , is converted to direct current). This direct current can then

be converted to 50 or 60 Hz alternating current.

Each SPS would have been massive measuring 10.5 km long and 5.3 km wide or with an

average area of 56 sq.km.The surface of each satellite would have been covered with 400 million

solar cells. The transmitting antenna on the satellite would have been about 1 km in diameter and

the receiving antenna on the Earth’s surface would have been about 10 km in diameter .The SPS

would weigh more than 50,000 tons.

Fig 9: Rectenna Array

The reason that the SPS must be so large has to do with the physics of power beaming.

The smaller the transmitter array, the larger the angle of divergence of the transmitted beam. A

highly divergent beam will spread out over a large area, and may be too weak to activate the

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rectenna. In order to obtain a sufficiently concentrated beam a great deal of power must be

collected and fed into a large transmitter array.

Configuration of SPS in space:

The day-night cycle, cloud coverage, atmospheric attenuation etc, reduces the amount of solar

energy received on Earth’s surface. SPS being placed in the space overcomes this .Another

important feature of the SPS is its continuous operation i.e, 24 hours a day, 365 days a year basis.

Only for ma total of 22 in a year would the SPS would be eclipsed for a period of time to a

maximum of 72 min. If the SPS and the ground antenna are located at the same longitude, the

eclipse period will centre around midnight.

The power would be beamed to the Earth in the form of microwaves at a frequency of

2.45 GHz. Microwaves can pass unimpeded through clouds and rain .Microwaves have other

features such as larger band width , smaller antenna size, sharp radiated beams and they

propagate along straight lines. Because of competing factors such as increasing atmospheric

attenuation but reducing size for the transmitting antenna and the other components at higher

frequency, microwave frequency in the range of 2-3 GHz are considered optimal for the

transmission of power from SPS to the ground rectenna site. A microwave frequency of 2.45

GHz is considered particularly desirable because of its present uses for ISM band and

consequently probable lack of interference with current radar and communication systems. The

rectenna arrays would be designed to let light through, so that crops or even solar panels could be

placed underneath it.

The amount of power available to the consumers from one SPS is 5 GW. The

peak intensity of microwave beam would be 23 mW/cm².So far, no non thermal health effects of

low level microwave exposure have been proved, although the issue remains controversial . SPS

has all the advantage of ground solar, plus an additional advantage; it generates power during

cloudy weather and at night. In other words SPS receiver operates just like a solar array. Like a

solar array, it receives power from space and converts it into electricity. If the satellite position is

selected such that the Earth and the Sun are in the same location in the sky, when viewed from

the satellite, same dish could be used both as solar power collector and the microwave antenna.

This reduces the size and complexity of satellite.

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However, the main barrier to the development of SPS is social, not technological. The

initial development cost for SPS is enormous and the construction time required is very long.

Possible risks for such a large project are very large, pay-off is uncertain. Lower cost technology

may be developed during the time required to construct the system. So such a large program

requires a step by step path with immediate pay-off at each step and the experience gained at

each step refine and improve the risk in evolutionary steps.

The SPS satellites would be put in high earth orbit at geosynchronous locations. The high orbit

would allow them to receive light 99% of the year . A large rectenna array facility will be built

on the Earth to collect the incoming microwaves. In order to maintain a good lock on the

rectenna the satellite will need to be built with a retrodirective transmitter which locks on to a

pilot beam emanated from the ground station. Since most of the research is done in the 2.4 GHz

to 5.8 GHz range there are some spectrum regulatory issues to deal with. Also since the

retrodirective antenna system is unproven. There is the health concern that the microwave beam

could veer off target and microwave some unsuspecting family. However, a Japanese

government agency is planning to send up 10 to 100 kW low earth orbit satellite to prove its

feasibility.

BEAM CONTROL:

A key system and safety aspect of WPT in its ability to control the power beam. Retro directive

beam control systems have been the preferred method of achieving accurate beam pointing. As

shown in fig.7 a coded pilot signal is emitted from the rectenna towards the SPS transmitter to

provide a phase reference for forming and pointing the power beams . To form the power beam

and point it back forwards the rectenna, the phase of the pilot signal is captured by the receiver

located at each sub array is compared to an onboard reference frequency distributed equally

throughout the array. If a phase difference exists between the two signals, the received signal is

phase conjugated and fed back to earth dc-RF converted. In the absence of the pilot signal, the

transmitter will automatically diphase its power beam, and the peak power density decreases by

the ratio of the number of transmitter elements.

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Fig 10: Beam Control using Pilot signal

ADVANTAGES AND DISADVANTAGES:

ADVANTAGES:

The idea collecting solar energy in space and returning it to earth using microwave beam has

many attractions.

1. The full solar irradiation would be available at all times expect when the sun is eclipsed by

the earth . Thus about five times energy could be collected, compared with the best

terrestrial sites

2. The power could be directed to any point on the earth’s surface.

3. The zero gravity and high vacuum condition in space would allow much lighter, low

maintenance structures and collectors

4. The power density would be uninterrupted by darkness, clouds, or precipitation, which are

the problems encountered with earth based solar arrays.

5. The realization of the SPS concept holds great promises for solving energy crisis

6. No moving parts.

7. No fuel required.

8. No waste product.

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DISADVANTAGES:

1. The main draw back of solar energy transfer from orbit is the storage of electricity during

off peak demand hours

2. The frequency of beamed radiation is planned to be at 2.45 GHz and this frequency is used

by communication satellites also.

3. The entire structure is massive.

4. High cost and require much time for construction.

5. Radiation hazards associated with the system.

6. Risks involved with malfunction.

7. High power microwave source and high gain antenna can be used to deliver an intense

burst of energy to a target and thus used as a weapon.

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6.Merits & Demerits Wireless Technologies:

Merits

1.An electrical distribution system, based on this method would eliminate the need for an

inefficient, costly, and capital intensive grid of cables, towers, and substations.

2.The system would reduce the cost of electrical energy used by the consumer and rid the

landscape of wires, cables, and transmission towers. There are areas of the world where the need

for electrical power exists, yet there is no method for delivering power. Africa is in need of

power to run pumps to tap into the vast resources of water under the Sahara Desert. Rural areas,

such as those in China, require the electrical power necessary to bring them into the 20th century

and to equal standing with western nations.

3.The wireless transmission will solve many of these problems The electrical energy can be

economically transmitted without wires to any terrestrial distance, so there will be no

transmission and distribution loss. More efficient energy distribution systems and sources are

needed by both developed and under developed nations. In regards to the new systems, the

market for wireless power transmission is enormous

4.High Transmission Integrity and Low Loss: - To transmit wireless power to any distance

without limit. It makes no difference what the distance is. The efficiency of the transmission can

be as high as 96 or 97 per cent, and there are practically no losses.

5.  Wireless energy transfer can potentially recharge laptops, cell phones without chords.

6.  No need of the wires to transfer the electricity.

7.No Waste Products

8.The power failure due to short circuit and fault on cables would never exist in the transmission

and power theft would be not possible at all.

9.Another application of WPT is moving targets such as fuel free airplanes, fuel free electric

vehicles, moving robots and fuel free rockets. The other applications of WPT are Ubiquitous

Power Source (or) Wireless Power Source, Wireless sensors and RF Power Adaptive Rectifying

Circuits (PARC).

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10.This concept can be used for electrifying the Transportation facility. The fallowing pictures

illustrate this in detail

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If we are able to materialize this technology we could achieve a pollution free world.

Demerits:

(1) The frequency of beamed radiation is planned to be at 2.45 GHz and this frequency is used

by communication satellites also.

(2)   The transmitter and receiver also should be very powerful devices as the distance increases.

(3)    Wireless transmission of the energy causes some drastic effects to human body, because of

its radiation.

(4)    Practical possibilities are not yet applicable as there is no much advancement in this field.

(5)    Initially, the procedure will be very expensive.

(6)    All the present appliances can’t be attached with a transmitter and receiver.

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7.Biological & Economic impact

Biological Impacts

Common beliefs fear the effect of microwave radiation. But the studies in this domain repeatedly proves that the microwave radiation level would be never higher than the dose received while opening the microwave oven door, meaning it is slightly higherthan the emissions created by cellular telephones. Cellular telephones operate with power densities at or below the ANSI/IEEE exposure standards . Thus public exposure to WPT fields would also be below existing safety guidelines.

Economic Impact

The concept looks to be costly initially. The investment cost of Tesla Tower was $150,000

(1905). In terms of economic theory, many countries will benefit from this service. Only

private, dispersed receiving stations will be needed. Just like television and radio, a single

resonant energy receiver is required, which may eventually be built into appliances, so no power

cord will be necessary! Monthly electric utility bills from old-fashioned, fossil-fuelled, loss

prone electrified wire-grid delivery services will be optional, much like “cable TV” of today. In

the 21st century, “Direct TV” is the rage, which is an exact parallel of Tesla’s “Direct

Electricity.”

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8.CONCLUSION:

The transmission of power without wires is not a theory or a mere possibility, it is now a reality.

The electrical energy can be economically transmitted without wires to any terrestrial distance.

Many researchers have established in numerous observations, experiments and measurements,

qualitative and quantitative. Dr.N.Tesla is the pioneer of this invention. Wireless transmission of

electricity have tremendous merits like high transmission integrity and Low Loss (90 efficient)

and can be transmitted to any where in the globe and eliminate the need for an inefficient, costly,

and capital intensive grid of cables, towers, and substations. The system would reduce the cost of

electrical energy used by the consumer and get rid of the landscape of wires, cables, and

transmission towers. It has negligible demerits like reactive power which was found insignificant

and biologically compatible. It has a tremendous economic impact to human society. Many

countries will benefit from this service. Monthly electric utility bills from old-fashioned, fossil-

fuelled, loss prone electrified wire-grid delivery services will be optional, much like “cable TV”

of today.

9.REFERENCES

1. http://www.wikipedia.com

2. http://hyperphysics.phy-astr.gsu.edu/hbase/waves/magnetron.html

3. Wireless Power Transmission for Solar Power Satellite (SPS) (Second Draft by N. Shinohara), Space Solar Power Workshop, Georgia Institute of Technology.

4. "Goodbye wires…". MIT News. 2007-06-07.

http://web.mit.edu/newsoffice/2007/wireless-0607.html.

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