about the new technology related to wireless

1. A COST-EFFECTIVE SYSTEM FOR WIRELESS POWER
TRANSMISSION
SEMINAR REPORT
Submitted in partial fulfillment of the requirements for the award of B.tech degree in Electrical and
Electronics Engineering by the University of Kerala
Submitted By
NABEEL.PM
S7 EEE
ROLL NO: 33
University NO: 08401017
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
GOVERNMENT ENGINEERING COLLEGE BARTON HILL
TRIVANDRUM
2011

2. DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING
GOVERNMENT ENGINEERING COLLEGE
BARTON HILL
THIRUVANANTHAPURAM
CERTIFICATE
This is to certify that this report titled “A COST-EFFECTIVE SYSTEM FOR WIRELESS
POWER TRANSMISSION” is a bonafide record of the seminar presented by NABEEL.PM
towards the fulfillment of the requirements for the award of B-Tech Degree in Electrical &
Electronics Engineering of the University of Kerala during the year 2011.
Guided by
Prof.Jayaprakash Prof. Sheela.S
Professor and Head Asst. Professor
Dept. of EEE Dept. of EEE
Prof.B.Mayadevi Prof.K.L.Sreekumar
Asst. Professor Asst. Professor
Dept. of EEE Dept. of EEE

3. INDEX OF CONTENTS
1. INTRODUCTION 06
2.WITRICITYTECHNOLOGY 10
2.1 ELECTRICITY 10
2.2MAGNETISM 10
2.3ELECTROMAGNETISM 10
2.4MAGNETICINDUCTION 10
2.5 RESONANCE 10
2.6RESONANTMAGNETICCOUPLING 11
3. WITRICITY TECHNOLOGY 12
4. HOW WIRELESS POWER COULD WORK 13
4.1 SHORT RANGE WIRELESS POWER TRANSMISSION 13
4.2 LONG DISTANCE WIRELESS POWER TRANSMISSION 14
5. WIRELESS POWER TRANSMISSION SYSTEM 16
6. COMPONENTS OF WPT SYSTEM 17
6.1 MICROWAVE GENERATOR 17
6.2 TRANSMITTING ANTENNAT 17
6.3 RECTENNA 17
7. A COST EFFECTIVE SYSTEM DESIGN 19
7.1 SYSTEM DESIGN 20
7.2 DESIGN OF CONTROL SIGNAL WAVEFORMS 20
7.3 PHYSICAL ISOLATION 22

4. 7.4 INVERTER CIRCUIT 24
7.5 LOAD DESIGN 26
i) Induction Coil Design: 26
(ii) Snubber circuit 27
8. DIFFERENT WAVEFORMS IN THE CIRCUIT 29
9. ADVANTAGES OF WITRICITY 33
10. DISADVANTAGES OF WITRICITY 34
11. BIOLOGICAL IMPACT OF WITRICITY 35
12. WITIRICITY APPLICATIONS 36
13. FREQUENTLY ASKING QUESTIONS 37
14. WHAT IS THE FUTURE OF WITRICITY 38
15. CONCLUSION 39
16. REFERENCES 40

5. ABSTRACT
In this paper, we present the concept of transmitting power without using wires i.e., transmitting
power as microwaves from one place to another is in order to reduce the transmission and
distribution losses. This concept is known as Microwave Power transmission (MPT). We also
discussed the technological developments in Wireless Power Transmission (WPT). The
advantages, disadvantages, biological impacts and applications of WPT are also presented.
In recent years, the notion of transfer of power using wireless techniques has attracted many
researchers. Transfer of power by wireless means has been recently demonstrated in the
Massachusetts Institute of Technology (MIT). This system operates at 9.9 MHz. In this paper, we
have discussed the design of a simple and cost-effective system which can enable transmission of
power over short distances. We have employed the H – Bridge Inverter configuration to convert
DC power to high frequency (100 kHz) which is then radiated with the help of a suitable loop
antenna. It is observed that this system can also be used as a induction heating unit. In this form
it can be used to replace conventional convection heating based electric stoves.

6. ACKNOWLEDGEMENT
I express my sincere gratitude to Prof.Jayaprakash, Professor and Head, Prof.Sheela.S, Staff
Advisor, Department of Electrical & Electronics Engineering, Government Engineering College,
Barton Hill, Thiruvananthapuram, for their expert advice and timely guidance in preparation of
the seminar.
I express my heartfelt thanks to Prof.K.L.Sreekumar, Assistant Professor, Prof.B.Mayadevi,
Professor, Smt.Arlene Davidson, Lecturer, Smt.Anu, Lecturer, Mr. Vinod, Lecturer, Guest
Lecturer Mr.Vinith, Department of Electrical & Electronics Engineering, Government
Engineering College, Barton Hill, Thiruvananthapuram, for their kind co-operation,
encouragement and help.
I thank God Almighty for showering his blessings on me without which this report would have
been impossible.
Last but not the least, I wish to place on record my gratefulness to my parents and friends for
their suggestions, criticisms and assistance towards the improvement and successful completion
of the report.
NABEEL.PM

7. NOMENCLATURE
 PRU: Power Reciving Unit
 PTU: Power Transmission Unit.
 Fig (1) Nikola Tesla
 Fig (2): Magnetic lines from a coil
 Fig (3): Nikola Tesla‘s Wardenclyffe tower built on Long Island
 Fig (4): A Schematic arrangement of Short range power transmission and reception
 Fig (5): A Schematic arrangement of Long distance Wireless power transmission and
reception
 Fig (6): Functional Block Diagram of Wireless Power Transmission System
 Fig (7): Functional Diagram.
 Fig (8): Control Signal Pulse Generator
 Fig (9): Pulse Transformer Arrangement
 Fig (10): Driver Circuit
 Fig (11): H-Bridge Inverter
 Fig (12): MOSFET IRFPG50
 Fig (13): PCB Design of H-Bridge inverter.
 Fig (15): Pancake Induction coil
 Fig (16): Turn- OFF Snubber Circuit.
 Fig (17): Waveform across the load without snubber circuits
 Fig (18): Waveform across the load with the snubber circuits
 Fig (19): Waveform at A
 Fig (20): Waveform at B
 Table 1. Performance of Printed Rectenna
 Table2. Rectenna Efficiency for Various Diodes at Different Frequency

8. 1. INTRODUCTION
In this era of modernization, electricity has become the cup of life. A moment without electricity
makes your thinking go dry. The major source of conventional form of electricity is through
wires. The continuous research and development has brought forward a major breakthrough,
which provides electricity without the medium of wires. This wonder baby is called WiTricity.
There are certain small but very useful discoveries made in history, which changed the world
forever, Newton‘s gravitational law, Watt‘s steam engine, Thomson‘s bulb and many more. But
a renaissance occurred with the invention of Electromagnetic Waves by Maxwell. Sir Jagdish
Chandra Bose successfully generated electromagnetic waves having wavelength in the range of
5mm to 25 mm. Thereafter an Italian scientist named Marconi succeeded in transmitting
electromagnetic waves up to a distance of several miles and with this there started a new era
called WIRELESS TECHNOLOGY. Today, as we can see the word ‗wireless‘ is common in day
– to – day life. Wireless communication has made the world smaller. Almost each and
everything is wireless or cordless. Cordless mouse, cordless keyboard, satellite communication,
mobiles, cordless microphones and headphones, wireless internet service i.e. WI-FI, etc. And
these have definitely increased the standard of living. In fact it dates back to the 19th century,
when Nikola Tesla used conduction-based systems instead of resonance magnetic fields to
transfer wireless power. As it is in Radiative mode, most of the Power was wasted and has less
efficiency. Further, in 2005, Dave Gerding coined the term WiTricity which is being used by the
MIT researchers today.

9. Fig (1) Nikola Tesla was the first to experiment with wireless electricity, butultimatelyfailedafterlosing his key
financial backing in the late 1800's
Moreover, we all are aware of the use of electromagnetic radiation (radio waves) which
is quite well known for wireless transfer of information. In addition, lasers have also been used
to transmit energy without wires. However, radio waves are not feasible for power transmissions
because the nature of the radiation is such that it spreads across the place, resulting into a
largeamount of radiations being wasted. And in the case of lasers, apart fromrequirement
of uninterrupted line of sight (obstacles hinders the transmission process). It is also very
dangerous. WiTricity is nothing but wireless electricity. Transmission of electrical energy from
one object to another without the use of wires is called as WiTricity.
WiTricity will ensure that the cellphones, laptops, iPods and other power hungry devices get
charged on their own, eliminating the need of plugging them in. Even better, because of
WiTricity some of the devices won't require batteries to operate. Nikola Tesla was the first to
experiment with wireless electricity, but ultimatelyfailedafter losing his key financial backing in the
late 1800's.

10. 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 – 97 % 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.

11. 2.WITRICITYTECHNOLOGY
WiTricity Technology is transferring electric energy or power over distance without wires, with
the basics of electricity and magnetism, and work our way up to the WiTricity Technology.
2.1 ELECTRICITY
The flow of electrons (current) through a conductor (like a wire), or charges through the
atmosphere (like lightning). A convenient way for energy to get from one place to another!
2.2MAGNETISM
A fundamental force of nature, which causes certain types of materials to attract or repel each
other. Permanent magnets, like the ones on your refrigerator and the earth‘s magnetic field, are
examples of objects having constant magnetic fields. Oscillating magnetic fields vary with time,
and can be generated by alternating current (AC) flowing on a wire. The strength, direction, and
extent of magnetic fields are often represented and visualized by drawings of the magnetic field
lines.
2.3ELECTROMAGNETISM
A term for the interdependence of time-varying electric and magnetic fields. For example, it
turns out that an oscillating magnetic field produces an electric field and an oscillating electric
field produces a magnetic field.
2.4MAGNETICINDUCTION
A loop or coil of conductive material like copper, carrying an alternating current (AC), is a very
efficient structure for generating or capturing a magnetic field. If a conductive loop is connected
to an AC power source, it will generate an oscillating magnetic field in the vicinity of the loop. A
second conducting loop, brought close enough to the first, may ―capture‖ some portion of that

12. oscillating magnetic field,which in turn, generates or induces an electric current in the second
coil. The current generated in the second coil may be used to power devices. This type of
electricalpower transfer from one loop or coil to another is well known and referred to
asmagnetic induction. Some common examples of devices based on magnetic inductionare
electric transformers and electric generators.
Fig (2): Magnetic lines from a coil.
2.5 RESONANCE
Resonance is a property that exists in many different physical systems. It can be thought of as the
natural frequency at which energy can most efficiently be added to an oscillating system. A
playground swing is an example of an oscillating system involving potential energy and kinetic
energy. The child swings back and forth at a rate that is determined by the length of the swing.
The child can make the swing go higher if she properly coordinates her arm and leg action with
the motion of the swing. The swing is oscillating at its resonant frequency and the simple
movements of the child efficiently transfer energy to the system. Another example of resonance
is the way in which a singer can shatter a wine glass by singing a single loud, clear note. In this
example, the wine glass is the resonant oscillating system. Sound waves traveling through the air
are captured by the glass, and the sound energy is converted to mechanical vibrations of the glass

13. itself. Whenthe singer hits the note that matches the resonant frequency of the glass, the glass
absorbs energy, begins vibrating, and can eventually even shatter. The resonant frequency of the
glass depends on the size, shape, thickness of the glass, and how much wine is in it.
2.6RESONANTMAGNETICCOUPLING
Magnetic coupling occurs when two objects exchange energy through their varying or oscillating
magnetic fields. Resonant coupling occurs when the natural frequencies of the two objects are
approximately the same.
WiTricity power sources and capture devices are specially designed magnetic resonators that
efficiently transfer power over large distances via the magnetic near-field. The proprietary source
and device designs and the electronic systems the control them support efficient
energy transfer over distances that are many times the size of the sources/devices themselves.
At first glance, WiTricity technology for power transfer appears to be traditional magnetic
induction, such as is used in power transformers, where conductive coils transmit power to each
other wirelessly, over very short distances. In a transformer, an electric current running in a
sending coil (or ―primary winding‖) induces another current in a receiving coil (or ―secondary
winding‖). The two coils must be very close together, and may even overlap, but the coils do not
make direct electrical contact with each other. However, the efficiency of the power exchange in
traditional magnetic induction systems drops by orders of magnitude when the distance between
the coils becomes larger than their sizes. In addition to electric transformers, other devices based
on traditional magnetic induction include rechargeable electric toothbrushes, and inductive
―charging pads‖ which require that the object being charged be placed directly on top of, or very
close to, the base or pad supplying the power.

14. 3. WITRICITY TECHNOLOGY
In the late 1800‘s and early 1900‘s, at the dawn of the electrification of the modern world, some
scientists and engineers believed that using wires to transfer electricity from every place it was
generated to every place that it could be used would be too expensive to be practical. Nikola
Tesla, one of the most well-known of these scientists, had a vision for a wireless world in which
wireless electric power and communications would reach around the world, delivering
information and power toships at sea, factories, and every home on the planet. Tesla contributed
significantly toour understanding of electricity and electrical systems and is credited with
inventingthree-phase AC power systems, induction motors, fluorescent lamps, radio
transmission, and various modes of wireless electric power transfer.
WiTricity mode of wireless power transfer is highly efficient over distances ranging from
centimeters to several meters. Efficiency may be defined as the amount of usable electrical
energy that is available to the device being powered, divided by the amount of energy that is
drawn by the WiTricity source. In many applications, efficiency can exceed 90%. And
WiTricity sources only transfer energy when it is needed. When WiTricity powered device no
longer needs to capture additional energy, the WiTricity power source will automatically reduce
its power consumption to a power saving ―idle‖ state.
Fig (3): Nikola Tesla’s Wardenclyffe tower built on Long Island

15. 4. HOW WIRELESS POWER COULD WORK
Researchers have developed several techniques for moving electricity over long distances
without wires. Some exist only as theories or prototypes, but others are already in use. Magnetic
resonance was found a promising means of electricity transfer because magnetic fields travel
freely through air yet have little effect on the environment or, at the appropriate frequencies, on
living beings and hence is a leading technology for developing WiTricity.
4.1 SHORT RANGE WIRELESS POWER TRANSMISSION
Power supply for portable electronic devices is considered, which receives ambient radio
frequency radiation (typically in an urban environment) and converts it to DC electricity that is
stored in a battery for use by the portable device. A Power transmission unit (PTU) is connected
to the electrical utility, typically in a domestic and office environment, and uses the electricity to
generate a beam of electromagnetic radiation. This beam can take the form of visible light,
microwave radiation, near infrared radiation or any appropriate frequency or frequencies,
depending on the technology chosen. The beam can be focused and shaped using a focusing
mechanism: for example, a parabola shape may be chosen to focus light waves at a certain
distance from the PTU. A Power reception unit (PRU) receives power from one or several
PTU's, and converts the total power received to electricity, which is used to trickle charge a
storage unit such as a battery or transferred directly to the appliance for use, or both. If
transferred to the storage unit, the output of the storage unit can power the appliance. Similarly to
the focusing of the transmitted power, it is possible to concentrate the received power for
conversion, using receiving arrays, antennas, reflectors or similar means.

16. It is possible to construct power "relay units", consisting of PRU's powering PTU's, whose
function is to make the transmitted power available at further distances than would normally be
possible.
Fig (4): A Schematic arrangement of Short range power transmission and reception
4.2 LONG DISTANCE WIRELESS POWER TRANSMISSION
Some plans for wireless power involve moving electricity over a span of miles. A few proposals
even involve sending power to the Earth from space. The Stationary High Altitude Relay
Platform (SHARP) unmanned plane could run off power beamed from the Earth. The secret to
the SHARP's long flight time was a large, ground-based microwave transmitter. A large, disc-
shaped rectifying antenna, or rectenna, near the system changed the microwave energy from the
transmitter into direct-current (DC) electricity. Because of the microwaves' interaction with the
rectenna, the system had a constant power supply as long as it was in range of a functioning
microwave array. Rectifying antennae are central to many wireless power transmission theories.
They are usually made of an array of dipole antennae, which have positive and negative poles.
These antennae connect to semiconductor diodes. Here's what happens:

17. 1. Microwaves, which are part of the electromagnetic spectrum, reach the dipole antennae.
2. The antennae collect the microwave energy and transmit it to the diodes.
3. The diodes act like switches that are open or closed as well as turnstiles that let electrons flow
in only one direction. They direct the electrons to the rectenna circuitry.
4. The circuitry routes the electrons to the parts and systems that need them.
Fig (5): A Schematic arrangement of Long distance Wireless power transmission and reception

18. 5. WIRELESS POWER TRANSMISSION SYSTEM
William C. Brown, the pioneer in wireless power transmission technology, has designed,
developed a unit and demonstrated to show how power can be transferred through free space by
microwaves. The concept of Wireless Power Transmission System is explained with functional
block diagram shown in Fig (6). In the transmission side, the microwave power source generates
microwave power and the output power is controlled by electronic control circuits. The wave
guide ferrite circulator which protects the microwave source from reflected power is connected
with the microwave power source through the Coax – Waveguide Adaptor. The tuner matches
the impedance between the transmitting antenna and the microwave source. The attenuated
signals will be then separated based on the direction of signal propagation by Directional
Coupler. The transmitting antenna radiates the power uniformly through free space to the
rectenna. In the receiving side, a rectenna receives the transmitted power and converts the
microwave power into DC power. The impedance matching circuit and filter is provided to
setting the output impedance of a signal source equal to the rectifying circuit. The rectifying
circuit consists of Schottky barrier diodes converts the received microwave power into DC
power.
Fig (6): Functional Block Diagram of Wireless Power Transmission System

19. 6. COMPONENTS OF WPT SYSTEM
The Primary components of Wireless Power Transmission are Microwave Generator,
Transmitting antenna and Receiving antenna (Rectenna). Refer the figure Fig (6).
6.1 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 or 5.8GHz of ISM band. The other choices of
frequencies are 8.5 GHz , 10 GHz and 35 GHz . The highest efficiency over 90% is achieved at
2.45 GHz among all the frequencies.
6.2 TRANSMITTING ANTENNAT
The slotted wave guide antenna, micro strip patch antenna, and parabolic dish antenna are the
most popular type of transmitting antenna. The slotted waveguide antenna is ideal for power
transmission because of its high aperture efficiency (> 95%) and high power handling capability.
6.3 RECTENNA
The concept, the name ‗rectenna‘ and the rectenna was conceived by W.C. Brown of Raytheon
Company in the early of 1960s . 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. The performance of various printed
rectenna is shown in Table I. 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

20. drop and good RF characteristics. The rectenna efficiency for various diodes at different
frequency is shown inTable II.
Table 1. Performance of Printed Rectenna
Table 2. Rectenna Efficiency for Various Diodes at Different Frequency

21. 7. A COST EFFECTIVE SYSTEM DESIGN
Wireless power transmission is still in its infancy as a topic. Although devices and applications
have been designed that transmit power over short distances, their price and design complexity
keep them out of the reach of ordinary users. There is a need for a simple, efficient and cost-
effective system which can create the changing electromagnetic field required to initiate wireless
power transfer. In addition, this can be used to heat vessels as an induction coil based stove. By
suitably replacing the induction coil element with an efficient antenna, the system can be applied
to deliver limited amounts of power wirelessly, for small applications like the charging of mobile
handsets, or laptops.
The aim is to design a system that can be constructed from easily available and low cost
electronic components, thus facilitating the transfer of this technology for the benefit of
humanity. The fundamental principle guiding this system is the use of a suitable inverter circuit
to convert D.C voltage into an alternating supply. Such an alternating voltage would create a
rapidly changing magnetic flux, as per the equation: φ = B * A * Cosθ
Where ‗φ‘ is the magnetic flux,
‗B‘ is the magnetic field density,
‗A‘ is the cross sectional area of the loop and
‗θ‘ is the angle between the magnetic field density and the surface of the loop.
This flux change induces an e.m.f (electromotive force) in any wire loop or metal surface that
cuts the magnetic flux lines. Such an e.m.f, if suitably tapped, can be used either wireless power
transfer

22. 7.1 SYSTEM DESIGN
The goal is to develop a system capable of operating at a frequency of 100 KHz, with an inverter
supply voltage of 300V DC. This frequency is chosen because efficient low cost power
MOSFET switches can be operated efficiently at these frequencies. If the frequency of operation
is further increased, we will have to use expensive power devices which would not be readily
available and would increase the cost of the system. The system as designed by us can be
partitioned into 4 functional blocks, as described in Figure 6.
Fig (7): Functional Diagram.
7.2 DESIGN OF CONTROL SIGNAL WAVEFORMS
It is required to produce two sets of non-overlapping pulses to drive the inverter circuit. The
SG3524 circuit manufactured by Philips semiconductor is ideal for this purpose. It allows for
duty ratio variation up to a maximum of 40%. In addition, a blanking pulse to both outputs rules
out the possibility of pulse overlap. The SG3524 is connected as shown in figure 2 with the
output pulses seen at pins 11 and 14.

23. Fig (8): Control Signal Pulse Generator
The SG2524 and SG3524 incorporate on a single monolithic chip all the function required for
the construction of regulating power supplies inverters or switching regulators. They can also be
used as the control element for high power-output applications. The SG3524 family was
designed for switching regulators of either polarity, transformer- coupled dc-to-dc converters,
transformer less voltage doubles and polarity converter applications employing fixed-frequency,
pulse-width modulation techniques. The dual alternating outputs allows either single-ended or
push-pull applications. Each device includes an on-ship reference, error amplifier, programmable
oscillator, pulse-steering flip flop, two uncommitted output transistors, a high-gain comparator,
and current limiting and shut-down circuitry.

24. 7.3 PHYSICAL ISOLATION
The H-bridge inverter employs high side and low side switches (four switches in all). The pulses
used to drive the high side switches are derived from the pulses used to drive the low side
switches. However, physical isolation using a suitable isolating technique needs to be
implemented before these pulses are used to drive the high side MOSFETs. This precaution is
essential, for if the same signal is used to drive both the high side and low side MOSFETs in the
circuit without physical isolation, a short circuit will result due to creation of a parasitic path
between the ground and the source of the high side MOSFET. This can result in serious damage
to the MOSFET switches. Physical isolation of the high side drive waveforms can be
implemented using several methods. One such method is to use a high side driver which is
available from several manufacturers. However, we have used pulse transformers to realize this
function in the interests of simplicity, ease of availability and low cost. A 1:1:1 pulse transformer
is used. The output of the SG3524 is used to drive the primary winding of the transformer after
suitable current amplification. Current amplification becomes necessary because the outputs of
the SG3524 are not designed to drive inductive loads directly. The drive waveform is replicated
at the two secondary windings which are physically isolated from the primary windings. A
freewheeling diode (BA 159) is connected across the primary winding of the transformer. A
combination of a resistor and a zener diode is used across the secondary windings of the
transformer to obtain pulses suitable for driving the MOSFET switches. These details are
described in Fig (9).

25. Fig (9): Pulse Transformer Arrangement
Fig (10): Driver Circuit

26. 7.4 INVERTER CIRCUIT
The outputs from the secondary windings of the pulse transformers are sent to the H-bridge
inverter circuit detailed in Fig (11). One of the advantages of using an H-bridge inverter is that
the load experiences a peak-to-peak voltage of 2Vcc. The inverter works in the required manner
i.e. when Q is high, M1 and M2 are turned ON and current flows from Vcc to Gnd via the path
M1- - A -- Load -- B -- M2. At this stage, the Other two MOSFETs will not be conducting
because their input Q' will be low. When Q becomes low turning Off M1 and M2, Q' becomes
high after sometime, which turns on M3 and M4. Now, the current flows from Vcc to Gnd via
the path M3 -- B - - Load -- A -- M4. The power MOSFETs used to build the inverter are of type
IRFPG50. The VDS=1000 V, ID (max) = 6.1 Amp and on resistance Ron =2 ohms.
Fig (11): H-Bridge Inverter

27. MOSFET, N, 1000V, 6.1A, TO-247AC; Transistor Type:MOSFET; Transistor Polarity; Voltage,
Vds Typ:1000V; Current, Id Cont:6A; Resistance, Rds On:2ohm; Voltage, Vgs Rds on
Measurement:10V; Voltage, Vgs th Typ:4V; Case Style:TO-247AC; Termination Type:Through
Hole; Current, Idm Pulse:24A; Lead Spacing:5.45mm; No. of Pins:3; Power Dissipation:180W;
Power, Pd:180W; Temperature, Current:25°C; Temperature, Full Power Rating:25°C; Thermal
Resistance, Junction to Case A:0.65°C/W; Transistors, No. of:1; Voltage, Vds:1000V;
Voltage, Vds Max:1000V
Fig (12): MOSFET IRFPG50
Fig (13): PCB Design of H-Bridge inverter.

28. 7.5 LOAD DESIGN
(i) Induction Coil Design:
A wide variety of coil designs are available for several applications. The choice of shape depends
on the nature of radiation pattern to be established (if the application is wireless power transfer)
and the shape of the vessel to be heated (if the system is also to be employed as an induction
cooking unit). We have found the pancake design to be most suitable for a wide range of
applications. Hence, we have designed and fabricated a pancake coil shown in Fig (13) for use in
this system. As a result of the pancake coil design, the energy is focused in the region of space
immediately above the surface of the coil. It is well known that the coupling efficiency increases
with frequency. The coupling efficiency of pancake coil with magnetic steel is 0.35 at a
frequency of 10 Hz and this figure increases to 0.5 at a frequency of 450 kHz. It is for this reason
that we have chosen an operating frequency of 100 kHz. The pancake coil is constructed out of
enamel-coated copper of size SWG 22. Giving a clearance of approx. 1.5 cm on each side, and
the gap between subsequent turns at 3mm, the length of wire required is estimated to be 20m
before braiding. Nails are placed on the board in perpendicular directions at the specified interval
to keep the coil in place while winding. After winding is completed, further nails are driven in to
ensure no two consecutive turns are touching each other. In order to make the coil permanent, the
gaps are filled with Araldite adhesive and allowed to set overnight, after which the nails are
removed. On analyzing the coil characteristics, its parameters were found to be: L = 60.2 μH.R =
0 .790 Ω.
.

29. Fig (15): Pancake Induction coil
(ii) Snubber circuit
Due to the high speed switching coupled with the presence of an inductive load, the switch
experiences a huge amount of back e.m.f during the turn off stage described by the equation:
E = -L*(di/dt).
Where ‗E‘ is the induced e.m.f, ‗L‘ is the inductance of the coil, and ‗di/dt‘ is the change in
current with respect to time. This leads to the spikes in voltage across the switches, which can
damage the device in the long term. In order to combat these spikes, turn-off snubber circuits
have been designed and put in place across every switch to absorb the back e.m.f and protect the
device. The value of Capacitance and Resistance are given by the following equations:
C = iL * tf / (2Vcc)
Vcc/ (Icm-iL) < R < Ton-min/5C

30. Where iL is the load current at the collector, if is the fall time of the signal, Icm is the maximum
collector current rating of the MOSFET, and Ton-min is the minimum time during which the
MOSFET should remain ON so that the capacitor can fully discharge. Assuming iL to be 3A and
tf to be 0.12 μSec and since we are operating at a Vcc of 200V, C is found to be 1nF with 1 kV
rating. As per device characteristics, Icm and Ton-min were found to be 8A and 4 μSec
respectively since the duty ratio is 40%. From these, we choose the resistance value to be 470Ω.
The addition of snubber circuits lead to signification suppression of spikes across the switching
devices as shown in fig (17) and Fig (18). On connecting the circuit to the Induction Coil in
series with a 60W bulb at an operating voltage of 60V, the waveforms listed in Fig 19, 20 and 21
were observed. We increased the operating voltage to 120 V. When a coil of wire (closed wire
loop) connected to a 6V bulb was brought close to the Induction coil, it was observed to light up.
This is shown in Fig (20).
Fig (16): Turn- OFF Snubber Circuit.

31. 8. DIFFERENT WAVEFORMS IN THE CIRCUIT
Fig (17): Waveform across the load without snubber circuits
Fig (18): Waveform across the load with the snubber circuits

32. Fig (19): Waveform at A in Fig(11)
Fig (20): Waveform at B in Fig (11)

33. Fig (21): Waveform across the LOAD in Fig (11).

34. A few observations were noted
 On increasing the distance between the loop and the coil, the glow of the bulb gradually
diminishes.
 For a given distance, the intensity of the bulb‘s glow is maximum when the surface of the
wire loop is parallel to the surface of the coil. The intensity reduces when the loop is
placed at an angle to the coil.
 For a given distance, the intensity of the bulb‘s glow is maximum when the loop is placed
near the center of the coil, and reduces as the loop is moved away from the coil.
Thus, it is demonstrated that wireless power transmission is practically possible on such a
system. The system provides conclusive evidence that despite the absence of an antenna of
suitable directivity, a sizeable amount of power can be wirelessly transmitted over short
distances. The next step in the development of this system is to design and build a helical
transmitter and receiver antenna system of suitable dimensions, which can increase the distance
of transmission by improving directivity and gain. By increasing the operating voltage through
repeated testing, the Coil can be applied for use as a heating stove.

35. 9. ADVANTAGES OF WITRICITY
1. Completely eliminates the existing high-power transmission line cables, towers etc…
2. The cost of transmission and distribution become less
3. WiTricity uses resonant magnetic fields to reduce wastage of power.
4. So efficiency of this method is very much higher than wired transmission.
5. The power failure due to short circuit and fault o cables would never exist.
6. The power could be transmitted to the places where the wired transmission is not
possible.
7. Do not interfere with radio waves.
8. No need of power cables and batteries - WiTricity replaces the use of power cables and
batteries

36. 10. DISADVANTAGES OF WITRICITY
1. The resonance condition should be satisfied and if any error exists, there is no
possibility of power transfer.
2. If there is any possibility of very strong ferromagnetic material presence causes low
power transfer due to radiation.
3. The Capital Cost for practical implementation of WPT seems to be very high and the
other disadvantage of the concept is interference of microwave with present
communication systems

37. 11. BIOLOGICAL IMPACT OF WITRICITY
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 higher than the emissions created by
cellular telephones. Cellular telephones operate with power densities at or below the ANSI/IEEE
exposure standards [18]. Thus public exposure to WPT fields would also be below existing
safety guidelines.

38. 12. WITIRICITY APPLICATIONS
WiTricity wireless power transfer technology can be applied in a wide variety of applications
and environments. The ability of our technology to transfer power safely, efficiently, and over
distance can improve products by making them more convenient, reliable, and environmentally
friendly. WiTricity technology can be used to provide:
DirectWirelessPower—whenallthepoweradeviceneedsisprovidedwirelessly and no batteries are
required. This mode is for a device that is always used within range of its WiTricity power
source.
Automatic Wireless Charging —when a device with rechargeable batteries charges itself while
still in use or at rest, without requiring a power cord or battery replacement. This mode is for a
mobile device that may be used both in and out of range of its WiTricity power source.
WiTricity technology is designed for Original Equipment Manufacturers (OEM‘s) to embed
directly in their products and systems.
WiTricitytechnologywillmakeyourproducts:
MoreConvenient
No manual recharging or changing batteries.
Eliminate unsightly, unwieldy and costly power cords.
MoreReliable
Never run out of battery power.
Reduce product failure rates by fixing the ‗weakest link‘: flexing wiring.
MoreEnvironmentallyFriendly
Reduce use of disposable batteries.
Use efficient electric ‗grid power‘ directly instead of inefficient battery charging.

39. 13. FREQUENTLY ASKING QUESTIONS
The concept being so new and innovative brings in so many questions. Hereafter, some questions
are being answered on the basis of study done on the topic and relevant topics.
Is WiTricity technology safe?
Human beings or other objects placed between the transmitter and receiver do not hinder thetrans
mission of power. WiTricity technology is a non-radiative mode of energy transfer, relying
instead on the magnetic near field. Magnetic fields interact very weakly with biological
organisms—people and animals—and are scientifically regarded to be safe.
WiTricity products are being designed to comply with applicable safety standards and regulations.
Howmuchpowercanbetransferred?
Till now, Scientists has been able to transfer more than 60W power. The technology by itself is
capable of scaling from applications requiring mill watts to those requiring several kilowatts of
power.
Over what distance can WiTricitytechnology transfer power?
WiTricity technology is designed for ―mid-range‖ distances, which we consider to be anywhere
from a centimeter to several meters. The actual operating range for a given application is
determined by many factors, including power source and capture device sizes, desired efficiency,
and the amount of power to be transferred.
HowefficientisWiTricitytechnology?
The power transfer efficiency of a WiTricity solution depends on the relative sizes of the power
source andcapture devices, and on the distance between the devices. Maximum efficiency is
achieved when the devicesare relatively close to one another, and can exceed 95%.

40. 14. WHAT IS THE FUTURE OF WITRICITY
MIT's WiTricit is only 40 to 45% efficient and according to
Soljacic, they have to be twice as efficient tocompete with the traditional chemical batteries. The
team's next aim is to get a robotic vacuum or a
laptopworking, charging devices placed anywhere in the room and even robots on factory floors.
Theresearchers are also currently working on the health issues related to this concept
and have said that in another three to five years‘ time, they will come up with a WiTricity system
for commercial use.
“WiTricity, if successful will definitely change the way we live.
Imagine cellphones, laptops, digital camera’s getting self-charged! Engineers have got job on
hand to research and commercialize the technology. Till then, it is a wait in anticipation”
9rfrff

41. 15. CONCLUSION
The concept of Wireless Power Transmission system is presented. The technological
developments in Wireless Power Transmission (WPT), the advantages, disadvantages, biological
impacts and applications of WPT are also discussed. The system provides conclusive evidence
that despite the absence of an antenna of suitable directivity, a sizeable amount of power can be
wirelessly transmitted over short distances. The next step in the development of this system is to
design and build a helical transmitter and receiver antenna system of suitable dimensions, which
can increase the distance of transmission by improving directivity and gain.
This concept offers greater possibilities for transmitting power with negligible losses and ease of
transmission than any invention or discovery heretofore made. Dr. Neville of NASA states ―You
don‘t need cables, pipes, or copper wires to receive power. We can send it to you like a cell
phone call – where you want it, when you want it, in real time‖. We can expect with certitude
that in next few years‘ wonders will be wrought by its applications if all the conditions are
favorable.

42. 16. REFERENCES
[1] Nikola Tesla, ―The Transmission of Electrical Energy Without Wires as a Means for
Furthering Peace,‖ Electrical World and Engineer. Jan. 7, p. 21, 1905.
[2] Nikola Tesla, My Inventions, Ben Johnston, Ed., Austin, Hart Brothers, p. 91,1982.
[3] Thomas F. Valone, ― Tesla‘s Wireless Energy... For the 21st
Century!!! One Step Beyond
Direct TV!!!‖ Extra Ordinary Technology, 1, no. 4, Oct / Nov / Dec 2003.
[4] James O. McSpadden, ― Wireless Power Transmission Demonstration‖, Texas A&M
University, June, 1997.
[5] Thomas W. Benson , ― Wireless transmission of power now possible‖, News Letter, pp1118 –
9, March , 1920.
[6] Charych Arthur (Setauket, NY), ― System and method for wireless electrical power
transmission‖, Patent No. 6,798,716, September 28, 2004.
[7] Joe T. Howell, et. al , ―Advanced receiver / converter experiments for laser wireless power
transmission‖5th. Wireless transmission conference, pp 1-8, Garanda, Spain,2004.
[8] Nikola Tesla, ― The true wireless‖, Electrical Experiments ,May, 1919.
[9] Toby Grotz,‖ Wireless transmission of power‖, Courtesy of the Tesla BBS at 719 486-2775,
August 28, 1990.
[10] L.Umanand and S.R.Bhat, ―Design of Magnetic Components for Switched Mode Power
Converters‖, Wiley Eastern Limited, 1992.
[11] Zinn and Semiatin, "Coil Design and fabrication", Heat Treating, p. 32- 36, June 1988.
[12] IRF840 datasheet, Fairchild Semiconductor, p. 1-2, January 2002.
[13] IRFPG50 datasheet, International Rectifier, p. 1-2, October 1997.
[14] SG3524 datasheet, Philips Semiconductors, p.1-2, August 1994.