PPT Report

A Seminar Report

on

“WITRICITY”

(Wireless Power Transmission)

Submitted for partial fulfillment

of

Bachelor of Engineering

in

Electronics & Communication Engineering

Submitted to Submitted by

Ms. Shruti Kalra Supreet Kumar SinghAssistant Professor Roll # 118

VIII Semester

Jaipur Engineering College & Research Centre, Jaipur

Session : 2011 – 12

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ABSTRACT

The technology used for wireless power transmission is known as witricity. Wireless

power transmission is not a new idea, Nikola Tesla proposed theories of wireless

power transmission in the late 1800s and early 1900s. Tesla's work was impressive,

but it did not immediately lead to wide spread practical methods for wireless power

transmission. Since then many 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. In 2006 researchers at Massachusetts

Institute of Technology led by Marine Soijacic discovered an efficient way to transfer

power between coils separated by a few meters. They have dubbed this technology as

witricity. Witricity is based upon coupled resonant objects. Two resonant objects of

the same resonant frequency tend to exchange energy efficiently, while not

interchanging the surroundings. The researchers demonstrate the ability to transfer

60W with approximately 40% efficiency over distance in excess of 2 meters.

Currently the project is looking for power transmission in the range of 100watts. As

witricity is in the development stage, lots of work is to be done in improving the

range of power transmission and efficiency.

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CONTENTS

Sr.no . Content Pg no.

1 Introduction 4

2 Principle of working 5

3 Circuit and its component 11

4 Advantages and Disadvantages 15

5 Application 17

6 Conclusion 20

7 Bibliography 21

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1. INTRODUCTION

If we are particularly organized and good with tie wrap then also a few dusty power

cord tangles around our home. We have even had to follow one particular cord

through the seemingly impossible snarl to the outlet hoping that the plug pull will be

the right one. This is one of the downfalls of electricity. While it can make people's

lives easier, it can add a lot of clutter in the process. For these reasons, scientists have

tried to develop methods of wireless power transmission that could cut the clutter or

lead to clean sources of electricity. Wireless power transmission is not a new idea.

Many researchers developed several methods for wireless power transmission. But

witricity is a new technology used for wireless power transmission. By the use of this

technology transmission of electrical energy to remote objects without wires can be

possible. The inventors of witricity are the researchers from Massachusetts Institute

of Technology (MIT). They developed a new technology for wireless electricity

transmission and this is based upon the coupled resonant objects. In this resonant

magnetic fields are used. So the wastage of power is reduced. The system consists of

witricity transmitters and receivers. The transmitters and receivers contain magnetic

loop antennas made of copper coils and they are tuned to the same frequency.

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2. PRINCIPLE OF WORKING

A transformer is an example of wireless energy transfer, although it does not seem to

be so, due to the close proximity of the primary and secondary coils. If the coils are

moved further apart and have different cores, instead of a common core, you have

wireless energy transfer, due to the induction effect. However, the important issue

here is the efficiency with which energy is transferred. The farther apart the coils are

from each other, the less the transfer efficiency. If this figure can be improved to

reach e.g. 70% or 80% then we could have a practical way to transfer energy without

wires over long distances. If efficiency is ignored (or not important), as is the case of

supplying small appliances, wireless energy transfer can be a very practical way of

supply. However, if you are to supply thousands of watts to a circuit, things look a lot

more difficult.

2.1 Inductive Coupling

Inductive coupling uses magnetic fields that are a natural part of current's movement

through wire. Any time electrical current moves through a wire, it creates a circular

magnetic field around the wire. Bending the wire into a coil amplifies the magnetic

field. The more loops the coil makes, the bigger the field will be.

If you place a second coil of wire in the magnetic field you've created, the field can

induce a current in the wire. This is essentially how a transformer works, and it's how

an electric toothbrush recharges. It takes three basic steps:

1. Current from the wall outlet flows through a coil inside the charger, creating a

magnetic field. In a transformer, this coil is called the primary winding.

2. When you place your toothbrush in the charger, the magnetic field induces a

current in another coil, or secondary winding, which connects to the battery.

3. This current recharges the battery.

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You can use the same principle to recharge several devices at once. For example, the

Splash power recharging mat and Edison Electric's Power desk both use coils to

create a magnetic field. Electronic devices use corresponding built-in or plug-in

receivers to recharge while resting on the mat. These receivers contain compatible

coils and the circuitry necessary to deliver electricity to devices' batteries.

2.2 Resonance and Wireless Power

Household devices produce relatively small magnetic fields. For this reason, chargers

hold devices at the distance necessary to induce a current, which can only happen if

the coils are close together. A larger, stronger field could induce current from farther

away, but the process would be extremely inefficient. Since a magnetic field spreads

in all directions, making a larger one would waste a lot of energy.

Research at MIT indicates that induction can take place a little differently if the

electromagnetic fields around the coils resonate at the same frequency. The theory

uses a curved coil of wire as an inductor. A capacitance plate, which can hold a

charge, attaches to each end of the coil. As electricity travels through this coil, the

coil begins to resonate. Its resonant frequency is a product of the inductance of the

coil and the capacitance of the plates.

Resonant transfer works by making a coil ring with an oscillating current.  This

generates an oscillating magnetic field. Because the coil is highly resonant any energy

placed in the coil dies away relatively slowly over very many cycles; but if a second

coil is brought near to it, the coil can pick up most of the energy before it is lost, even

if it is some distance away.  The fields used are predominately non- radiative, near

field (sometimes called evanescent waves), as all hardware is kept well within the 1/4

wavelength distance they radiate little energy from the transmitter to infinity.

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FIG 2.1 The MIT wireless power project uses a curved coil and capacitive plates.

The wireless power transfer system involves resonating two identical coils with a

high frequency power source. The power is transmitted through magnetic resonance

coupling in between the two coils at the resonance frequencies. The power

transmitted to the receiving antenna is then utilized in the load Electromagnetic

resonance coupling involves creating an LC resonance, and transferring the power

with electromagnetic couplings without radiating electromagnetic waves. Hence, the

magnetic coupling and electric coupling can be represented as mutual inductance and

mutual capacitance respectively as shown in Fig. 2.

Zsource in Fig. 2 represents the characteristic impedance, and Zload is the impedance

of the load. In this system, they are both considered to be the same at Z0, 50_ the

default characteristic of most high frequency systems. The ohm loss and the radiation

loss of the antennas are represented by R. In this paper, the power is transferred via

magnetic coupling. Therefore the coupling can be represented by mutual induction

Lm. Next the resonance frequency is calculated based on the equivalent circuit. To

satisfy the resonance condition, the reactance of Fig.2 must be 0, as in equation (1).

The condition in equation (1) can be satisfied by two resonant frequencies as

calculated in equation (2) and (3).

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2.2.1 Energy transfer and efficiency

The general principle is that if a given oscillating amount of energy (for example

alternating current from a wall outlet) is placed into a primary coil which is capacitive

loaded, the coil will 'ring', and form an oscillating magnetic field. The energy will

transfer back and forth between the magnetic field in the inductor and the electric

field across the capacitor at the resonant frequency. This oscillation will die away at a

rate determined by the Q factor, mainly due to resistive and radiative losses.

However, provided the secondary coil cuts enough of the field that it absorbs more

energy than is lost in each cycle of the primary, then most of the energy can still be

transferred.

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The primary coil forms a series RLC circuit, and the Q factor for such a coil is:

,

Because the Q factor can be very high, (experimentally around a thousand has been

demonstrated with air cored coils) only a small percentage of the field has to be

coupled from one coil to the other to achieve high efficiency, even though the field

dies quickly with distance from a coil, the primary and secondary can be several

diameters apart.

2.2.2 Coupling coefficient

The coupling coefficient is the fraction of the flux of the primary that cuts the

secondary coil, and is a function of the geometry of the system. The coupling

coefficient is between 0 and 1.

Systems are said to be tightly coupled, loosely coupled, critically coupled or over

coupled. Tight coupling is when the coupling coefficient is around 1 as with

conventional transformers. Over coupling is when the secondary coil is close enough

that it tends to collapse the primary's field, and critical coupling is when the transfer

in the pass band is optimal. Loose coupling is when the coils are distant from each

other, so that most of the flux misses the secondary, in Tesla coils around 0.2 is used,

and at greater distances, for example for wireless power transmission, it may be lower

than 0.01.

2.2.3 Power transfer

Because the Q can be very high, even when low power is fed into the transmitter coil,

a relatively intense field builds up over multiple cycles, which increases the power

that can be received—at resonance far more power is in the oscillating field than is

being fed into the coil, and the receiver coil receives a percentage of that.

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2.2.4 Voltage gain

The voltage gain of resonantly coupled coils is proportional to the square root of the

ratio of secondary and primary inductances

2.2.5 Transmitter coils and circuitry

Unlike the multiple-layer secondary of a non-resonant transformer, coils for this

purpose are often single layer solenoids (to minimize skin effect and give improved

Q) in parallel with a suitable capacitor, or they may be other shapes such as wave-

wound lit wire. Insulation is either absent, with spacers, or low permittivity, low loss

materials such as silk to minimize dielectric losses.

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3. CIRCUIT AND ITS COMPONENETS

The various components in making the circuit for the project- Wireless transmission

of electric power using resonance circuit can be explained as:

1. Bifilar enhanced coil: 22 gauge copper wire

2. Capacitors 10. ‘1 µF’ capacitors are connected to give ‘.01 µf’capacitor.

3. LED

4. Function generator

3.1 Primary and Secondary coils

Both primary and secondary circuit consists of bifilar enhanced coils. These coils are

of copper wire of 22 gauge and have 41 turns on either side i.e. both primary and

secondary coils consists of 41 turns of 22 gauge copper wire each. The inductance of

both the coils is 2.788 micro Henry

3.2 Capacitors

A capacitor is a passive electronic component consisting of a pair of conductors

separated by a dielectric (insulator). When there is a potential difference (voltage)

across the conductors, a static electric field develops in the dielectric that stores

energy and produces a mechanical force between the conductors. An ideal capacitor

is characterized by a single constant value, capacitance, measured in farads. This is

the ratio of the electric charge on each conductor to the potential difference betwee

them.

Fig 3.1 A capacitor

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Capacitors are widely used in electronic circuits for blocking direct current while

allowing alternating current to pass, in filter networks, for smoothing the output of

power supplies, in the resonant circuits that tune radios to particular frequencies and

for many other purposes.

In the circuit 10 – 0.1 micro Farad capacitors are connected in series to give a 0.01

micro farad capacitor on both secondary and primary circuit.

FIG 3.2 Series connection of Capacitors

3.3 Function Generator

A function generator is a piece of electronic test equipment or software used to

generate electrical waveforms. These waveforms can be either repetitive or single-

shot, in which case some kind of triggering source is required (internal or external).

Function Generators are used in development, testing and repair of electronic

equipment, e.g. as a signal source to test amplifiers, or to introduce an error signal

into a control loop.

Analog function generators usually generate a triangle waveform as the basis for all

of its other outputs. The triangle is generated by repeatedly charging and discharging

a capacitor from a constant current source. This produces a linearly ascending or

descending voltage ramp. As the output voltage reaches upper and lower limits, the

charging and discharging is reversed using a comparator, producing the linear triangle

wave. By varying the current and the size of the capacitor, different frequencies may

be obtained. Saw tooth waves can be produced by charging the capacitor slowly,

using a current, but using a diode over the current source to discharge quickly - the

polarity of the diode changes the polarity of the resulting saw tooth, i.e. slow rise and

fast fall, or fast rise and slow fall.

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A typical function generator can provide frequencies up to 20 MHz RF generators for

higher frequencies are not function generators in the strict sense since typically

produce pure or modulated sine signals only.

In the project we have supplied a sinusoidal waveform of 30 V and 40kHz.

FIG 3.3 A picture of Function Generator

3.4 Light Emitting Diode

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as

indicator lamps in many devices, and are increasingly used for lighting. Introduced as

a practical electronic component in 1962, early LEDs emitted low-intensity red light,

but modern versions are available across the visible, ultraviolet and infrared

wavelengths, with very high brightness.

When a light-emitting diode is forward biased (switched on), electrons are able to

recombine with electron holes within the device, releasing energy in the form of

photons. This effect is called electroluminescence and the color of the light

(corresponding to the energy of the photon) is determined by the energy gap of the

semiconductor. An LED is often small in area (less than 1 mm2), and integrated

optical components may be used shape its radiation pattern. LEDs present many

advantages over incandescent light sources including lower energy consumption,

longer lifetime, improved robustness, smaller size, faster switching, and greater

durability and reliability. LEDs powerful enough for room lighting are relatively

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expensive and require more precise current and heat management than compact

fluorescent lamp sources of comparable output.

In the circuit LED is being used as an indicating device in the circuit of our project.

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4. ADVANTAGES AND DISADVANTAGES

4.1 Advantages

Wireless Power Transmission system would completely eliminates the existing high-

tension power transmission line cables, towers and sub stations between the

generating station and consumers and facilitates the interconnection of electrical

generation plants on a global scale. It has more freedom of choice of both receiver

and transmitters. Even mobile transmitters and receivers can be chosen for the WPT

system. The cost of transmission and distribution become less and the cost of

electrical energy for the consumer also would be reduced. The power could be

transmitted to the places where the wired transmission is not possible. Loss of

transmission is negligible level in the Wireless Power Transmission; therefore, the

efficiency of this method is very much higher than the wired transmission. Power is

available at the rectenna as long as the WPT is operating. 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.

Eliminates the use of power transmission lines, cables and substations, thus

reducing the cost of electrical energy.

More freedom of choice of both receiver and transmitter.

Power can be transferred to the places where wired transmission is not

possible.

Low transmission loss, thus increasing the efficiency.

To make the recharge of electronic devices more convenient for consumer

especially for the elderly and the disabled

To reduce the Faults because of Short Circuit of wires and cables

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4.2 Disadvantages

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.

4.3 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 higher

than 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.

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5. APPLICATION

Generating power by placing satellites with giant solar

arrays in Geosynchronous Earth Orbit and transmitting

the power as microwaves to the earth known as Solar

Power Satellites (SPS) is the largest application of WPT.

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).

Direct Wireless Power—when all the power a device needs is provided wirelessly,

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.

Consumer Electronics

Automatic wireless charging of mobile electronics (phones, laptops, game

controllers, etc.) in home, car, office, Wi-Fi hotspots while devices are in use

and mobile.

Direct wireless powering of stationary devices (flat screen TV’s, digital

picture frames, home theater

accessories, wireless loud … eliminating expensive custom wiring, unsightly

cables and “wall-wart” power supplies.

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FIG 5.1 Electronics Application

Direct wireless powering of desktop PC peripherals: wireless mouse,

keyboard, printer, speakers, display, etc … eliminating disposable batteries

and awkward cabling.

Industrial

Direct wireless power and communication

interconnections across rotating and moving

“joints” (robots, packaging machinery,

assembly machinery, machine tools) …

eliminating costly and failure-prone wiring.

Direct wireless power and communication

interconnections at points of use in harsh

environments (drilling, mining, underwater, etc.)

where it is impractical or impossible to run wires.

Direct wireless power for wireless sensors and actuators, eliminating the need

for power wiring or battery replacement

and disposal.

Transportation

Automatic wireless charging for existing

electric vehicle classes: golf carts,

industrial vehicles.

Automatic wireless charging for future

hybrid and all-electric passenger and

commercial

Vehicles, at home, in parking garages, at

fleet depots, and at remote kiosks.

Direct wireless power interconnections to replace costly vehicle wiring

harnesses and slip rings.

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FIG 5.2 Industrial Application

FIG 5.3 Transportation Application

Other Applications

Direct wireless power interconnections and

automatic wireless charging for implantable

medical devices (ventricular assist devices,

pacemaker, defibrillator, etc.).

Automatic wireless charging and for high

tech military systems (battery powered

mobile devices, covert sensors, unmanned

mobile robots and aircraft, etc.).

Direct wireless powering and automatic

wireless charging of smart cards.

FIG 5.4 other application

wireless charging of consumer appliances, mobile robots, etc.

6. CONCLUSION

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FIG 4.4 Othen

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.

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.

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. Nikola 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 anywhere 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.

7. BIBLIOGRAPHY

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en.wikipedia.org/wiki/Wireless_energy_transfer

http://electronics.howstuffworks.com/wireless-power.htm

http://www.instructables.com/id/Wireless-Power-Transmission-Over-Short-Distances-U/

www.tfcbooks.com/articles/tws8c.htm

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