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CHAPTER 1

INTRODUCTION

1.1 Introduction

Wireless power transmission (WPT) is an efficient way for the transmission of electric

power from one point to another through vacuum or atmosphere without the use of wire or

any substance. By using WPT, power can be transmitted using inductive coupling for short

range, resonant induction for mid-range and Electromagnetic wave power transfer. By using

this technology, it is possible to supply power to places, which is hard to do using

conventional wires. Currently, the use of inductive coupling is in development and research

phases. The most common wireless power transfer technologies are the electromagnetic

induction and the microwave power transfer. For efficient midrange power transfer, the

wireless power transfer system must satisfy three conditions: (a) high efficiency, (b) large air

gap, (c) high power.

The microwave power transfer has a low efficiency. For near field power transfer this

method may be inefficient, since it involves radiation of electromagnetic waves. Wireless

power transfer can be done via electric field coupling, but electric field coupling provides an

inductively loaded electrical dipole that is an open capacitor or dielectric disk. Extraneous

objects may provide a relatively strong influence on electric field coupling. Magnetic field

coupling may be preferred, since extraneous objects in a magnetic field have the same

magnetic properties as empty space. Electromagnetic induction method has short range.

Since magnetic field coupling is a non-radiative power transfer method, it has higher

efficiency. However, power transfer range can be increased by applying magnetic coupling

with resonance phenomenon applied on. A magnetic field is generated when electric charge

moves through space or within an electrical conductor. The geometric shapes of the magnetic

flux lines produced by moving charge (electriccurrent) are similar to the shapes of the flux

lines in an electrostatic field.

1.2 OBJECTIVE

Wireless energy transfer or wireless power is the transmission of electrical

energy from a power source to electrical load without interconnecting wires. Wireless

transmission is useful in cases where interconnecting wires are inconvenient, hazardous or

impossible. Wireless power differs from wireless telecommunications, where the signal-to-

noise ratio (SNR) or the percentage of energy received becomes critical only if it is too low

for the signal to be adequately recovered. With wireless power transmission, efficiency is the

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most important parameter. The most common form of wireless power transmission is carried

out using inductive coupling followed by resonant inductive coupling. Other methods include

microwaves and lasers.

1.3 HISTORY OF WIRELESS ENERGY TRANSFER

In 1820 Andre Marie Amperes developed Ampere’s law showing that electric current

produce a magnetic field .In 1831 Michel Faraday develops Faraday’s law of induction. And

in 1888 Henrich Rodlaf Hertz confirms the existence of electromagnetic radiation .Like this

so many pioneers experimented about the characteristics of electric energy in 19 th century

In this remarkable discovery of the "True Wireless" and the principles upon which

transmission and reception, even in the present day systems, are based, Dr. Nikola Tesla

shows us that he is indeed the "Father of the Wireless."

The most well-known and famous Wardenclyffe Tower (Tesla Tower) was designed and

constructed mainly for wireless basis transmission of electrical power, rather than telegraphy.

The most popular concept known is Tesla Theory in which it was firmly believed that

Wardenclyffe (Fig.1) would permit wireless transmission and reception across large

distances with negligible losses. In spite of this he had made numerous experiments of high

quality to validate his claim of possibility of wireless transmission of electricity (Fig.2)

Recently in1998 Intel produces Tesla’s original implementation by wirelessly powering

nearby light bulb with 75% efficiency. In 2009 Texas Instruments release the first device.

In 2010 Harier group debuts the world’s first completely wireless LCD television at CES

2010 based on prof. Marin follow-up research on wireless energy transfer.

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CHAPTER 2

TECNIQUES OF ENERGY TRANSFER

2.1 Near field techniques:

Near field are wireless transmission techniques over distances comparable to, or a few times the

diameter of the device(s), and up to around a quarter of the wavelengths used. Near field energy

itself is non radiative, but some radiative losses will occur. In addition there are usually resistive

losses. Near field transfer is usually magnetic (inductive), but electric (capacitive) energy

transfer can also occur.

2.1.1 Induction technique ( Inductive coupling):

The action of an electrical transformer is the simplest instance of wireless energy transfer. The

primary and secondary circuits of a transformer are not directly connected. The transfer of

energy takes place by electromagnetic coupling through a process known as mutual induction.

The battery chargers of a mobile phone or the transformers on the street are examples of how

this principle can be used. Induction cookers and many electric toothbrushes are also powered by

this technique.

The main drawback to induction, however, is the short range. The receiver must be very close to

the transmitter or induction unit in order to inductively couple with it.

2.1.2 Electrodynamics’ induction technique (resonant energy transfer):

The "electrodynamics inductive effect" or "resonant

inductive coupling" has key implications in solving the main

problem associated with non-resonant inductive coupling for

wireless energy transfer; specifically, the dependence of

efficiency on transmission distance.

Electromagnetic induction works on the principle of a

primary coil generating apredominantly magnetic field and a

secondary coil being within that field so a current is induced in

Fig 1.Resonant induction recharging

the secondary. This results in a negligible range because most of the magnetic field misses the

secondary. Over relatively small distances the induction method is inefficient and wastes much

of the transmitted energy.

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The application of resonance improves the situation somewhat, moderately improving the

efficiency by "tunneling" the magnetic field to a receiver coil that resonates at the same

frequency.

When resonant coupling is used the two inductors are tuned to a mutual frequency and the input

current is modified from a sinusoidal into a non-sinusoidal rectangular or transient waveform so

as to more aggressively drive the system. In this way significant power may be transmitted over

a range of many meters.

Unlike the multiple-layer windings typical of non-resonant transformers, such transmitting and

receiving coils are usually single layer solenoids or flat spirals with series capacitors, which, in

combination, allow the receiving element to be tuned to the transmitter frequency and reduce

losses.

A common use of the technology is for powering contactless smartcards, and systems exist to

power and recharge laptops and cell phones.

2.1.3 Electrostatic induction technique (Capacitive coupling):

Tesla illuminating two exhausted tubes by means of a

powerful, rapidly alternating electrostatic field created

between two vertical metal sheets suspended from the

ceiling on insulating cords.

The "electrostatic induction effect" or "capacitive coupling"

is a type of high field gradient or differential capacitance

between two elevated electrodes over a conducting ground

plane for wireless energy transmission involving high

frequency alternating current potential differences transmitted

between two plates.

Fig 2: Tesla's wireless bulbs

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The electrostatic forces through natural media across a conductor situated in the changing

magnetic flux can transfer energy to a receiving device

Sometimes called "the Tesla effect" it is the application of a type of electrical displacement, i.e.,

the passage of electrical energy through space and matter, other than and in addition to the

development of a potential across a conductor

Instead of depending on [electrodynamics] induction at a distance to light the tube . . . [the] ideal

way of lighting a hall or room would . . . be to produce such a condition in it that an illuminating

device could be moved and put anywhere, and that it is lighted, no matter where it is put and

without being electrically connected to anything.

Tesla has been able to produce such a condition by creating in the room a powerful, rapidly

alternating electrostatic field. For this purpose he suspend a sheet of metal a distance from the

ceiling on insulating cords and connect it to one terminal of the induction coil, the other terminal

being preferably connected to the ground. Or else he suspends two sheets . . . each sheet being

connected with one of the terminals of the coil, and their size being carefully determined. An

exhausted tube may then be carried in the hand anywhere between the sheets or placed

anywhere, even a certain distance beyond them; it remains always luminous.

2.2Far field techniques:

Means for long conductors of electricity forming part of an electric circuit and

electrically connecting said ionized beam to an electric circuit.

Far field methods achieve longer ranges, often multiple kilometer ranges, where the distance is

much greater than the diameter of the device(s).

With radio wave and optical devices the main reason for longer ranges is the fact that

electromagnetic radiation in the far-field can be made to match the shape of the receiving area

(using high directivity antennas or well-collimated Laser Beam) thereby delivering almost all

emitted power at long ranges. The maximum directivity for antennas is physically limited by

diffraction.

2.2.1 Radio and microwave (Microwave power transmission)technique: In 1875 Thomas Edison worked on this later Guglielmo Marconi worked with a modified

form of Edison's transmitter. Nikola Tesla also investigated radio transmission and reception.

Japanese researcher Hidetsugu Yagi also investigated wireless energy transmission using a

directional array antenna that he designed. This beam antenna has been widely adopted

throughout the broadcasting and wireless telecommunications industries due to its excellent

performance characteristics.

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Figure: 3Diagram showing the transmitting & receiving circuit for the transmission & reception of electric power by

wireless

The modern ideas are dominated by microwave power transmission called Solar power satellite

to be built in high earth orbit to collect sunlight and convert that energy into microwaves, then

beamed to a very large antenna on earth, the microwaves would be converted into conventional

electrical power.

A rectenna may be used to convert the microwave energy back into electricity. Rectenna

conversion efficiencies exceeding 95% have been realized.

A block diagram of the demonstration components is shown. The primary components include a

microwave source, a transmitting antenna, and a receiving rectenna. Fig.1Microwave power

transmission. 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 2.45GHz.

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.

Figure 4:Two optical forms of wireless

antennae formed ofsearch light beam- ionised atmospheric streams

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The rectifier is a Ga As 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. 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.Power beaming by microwaves has the difficulty

that for most space applications the required aperture sizes are very large due to diffraction

limiting antenna directionality. These sizes can be somewhat decreased by using shorter

wavelengths, although short wavelengths may have difficulties with atmospheric absorption and

beam blockage by rain or water droplets.

For earthbound applications a large area 10 km diameter receiving array allows large total power

levels to be used while operating at the low power density suggested for human electromagnetic

exposure safety.

A human safe power density of 1 mW/cm2 distributed across a 10 km diameter area corresponds

to 750 megawatts total power level. This is the power level found in many modern electric power

plants.

2.2.2 Laser With a laser beam centered on its panel of photovoltaic cells, a lightweight model plane makes

the first flight of an aircraft powered by a laser beam inside a building at NASA Marshall Space

Flight Center.

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.

Fig 5. Laser power beaming

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CHAPTER 3

CONSTRUCTION OF WIRELESS ENERGY TRANSFER

3.1 CONSTRUCTION

Inductive or magnetic coupling works on the principle of electromagnetism. When a wire is

proximity to a magnetic field, it induces a magnetic field in that wire. Transferring energy

between wires through magnetic fields is inductive coupling.

Figure: 6 Magnetic coupling with four component fluxes

Magnetic resonant coupling uses the same principles as inductive coupling, but it uses resonance

to increase the range at which the energy transfer can efficiently take place.Resonance can be

two types: (a) series resonance & (b) parallel resonance. In these both types of resonance, the

principle of obtaining maximum energy is same but the methods are quite different.

Figure: 7 Equivalent circuit of Magnetic Resonant Coupling

Quality factor (Q-factor) is a dimensionless parameter that describes the characteristic of an

oscillator or resonator, or equivalently, characterizes a resonator’s band width relative to its

Centre frequency. Higher Q indicates a lower rate of energy loss relative to the stored energy of

the oscillator; the oscillations die out more slowly. Determines the qualitative behavior

oscillators

oscillators. A system with low quality factor to be over damped. Such a system does not oscillate

at all, but when displaced from its equilibrium steady state output, it returns to it by exponential

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decay, approaching the steady state value asymptotically. System with (Q> ½) is said to be under damped. Under damped systems combine oscillation at a specific frequency with decay of the

amplitude of the signal. A system with aquality factor (Q = ½) is said to be critically damped.an over damped system, the output does not oscillate, adoes not overshoot its steady-state output

(i.e., it approaches a steady-state asymptote). Like an under damped response, the output of such

a system responds quickly to a unit step input. The efficiency of the coupled system depends on

how much energy is transferred from the transmitted to the receiver circuit.

The maximum energy found on the transmitted Etransmitter.max, is the amount of energy

initially put on the input capacitor Ct by the voltage source V0.

Where Vin is the voltage of C positive pulse duration Ct acts like a voltage source and completes

a series loop with the transmitter elements, Rt, Lt , Ct .

Figure: 8 resonant wireless power transmission circuit diagrams

The maximum energy transferred to the receiver is only a fraction of input energy. The energy

found is receiver circuit is

At maximum voltage level on receiver circuit, current becomes zero and no current flows the

circuit. At this point energy stored in receiver inductor is zero because current is zero. Thus,

maximized receiver energy is:

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CHAPTER 4

DESIGN OF WIRELESS ENERGY TRANSFER

4.1 DESIGN

The following table shows the components which are used to make the oscillator.

Table 1.Oscillator Components

Our experimental realization of the scheme consists of three coils tuned at the same frequency.

An oscillation circuit is connected with a source coil S is in turn coupled resonant inductively to

a load carrying coil Q. The coils are made of an electrically conducting copper pipe of a cross-

sectional radius wound into a helix of single turn, radius r.Then a radio frequency oscillating

signal is passed through the coil S, it generates an oscillating magnetic field through the

inductance of the coil S, which is tuned at the same frequency by the inductance of the coil and a

resonating capacitor c. The load coil Q, tuned at the same resonant frequency receives the power

through the magnetic field generated by the source coil S.

Figure 9.Block diagram of wireless power transfer system

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CHAPTER 5

EXPERIMENTAL RESULTS

Introduction:

After completing the basic device we took the measurement of power efficiency of the two

receivers. For efficiency calculation, we have taken transmitting and receiving end power of the

two receivers respectively. The formula for efficiency calculation is,

We used the following formula for power calculation,

All the tables and Line chart are as follows –

Table for Receiver 1 at Receiving End:

Table 2.Power calculation receiving end (receiver 1)

Table for Receiver 1 at Sending End: Table 3.Power calculation at sending end (receiver 1)

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Table for Receiver 2 at Receiving End: Table 4.Power calculation at receiving end (receiver 2)

Table for Receiver 2 at Sending End:

Table 5.Power calculation at sending end (receiver 2)

Figure 10.Power Vs Distance chart for both receivers at receiver end

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Table for Efficiency Calculation for Receiver 1: Table 6.Efficiency calculation for receiver 1

Table for Efficiency Calculation for Receiver 2: Table 7.Efficiency calculation for receiver 2

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CONCLUSION

The goal of this project was to design and implement a wireless power transfer system via

magnetic resonant coupling. After analyzing the whole system systematically for optimization, a

system was designed and implemented. Experimental results showed that significant

improvements in terms of power-transfer efficiency have been achieved. Measured results are in

good agreement with the theoretical models.

We have described and demonstrated that magnetic resonant coupling can be used to deliver

power wirelessly from a source coil to a with a load coil with an intermediate coil placed

between the source and load coil and with capacitors at the coil terminals providing a sample

means to match resonant frequencies for the coils. This mechanism is a potentially robust means

for delivering wireless power to a receiver from a source coil.

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REFERENCES

[1] Zia A. Yamane and Juan L. Bala, Jr., “Electromechanical Energy Devices and Power

Systems”, John Wiley and Sons, 1947, p. 78

[2] Simon Ramo, John R. Whinnery and Theodore Van Duzer, “Fields and Waves in

Communication Electronics”, John Wiley & Sons, Inc.; 3rd edition (February 9, 1994)

[3] S. Kopparthi, Pratul K. Ajmera, "Power delivery for remotely located Microsystems," Proc.

of IEEE Region 5, 2004 Annual Tech. Conference, 2004 April 2, pp. 31-39.

[4] Tomohiro Yamada, Hirotaka Sugawara, Kenichi Okada, Kazuya Masu, andAkio Oki,

"Battery-less Wireless Communication System through Human Body for invivoHealthcare

Chip,"IEEE Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems”

[5] “Category: Radio spectrum -Wikipedia, the free encyclopedia,” [online document], 2004 Aug

26 [cited 12/11/04].