Witricity

WITRICITY (WIRELESS ELECTRICITY)

FUTURE OF ELECTRICITY

WHAT IS WPT?

• Wireless energy transfer means transmission of energy

from one place to another without using wires

• Also known as “WiTricity”.

• Power source (transmitter) provides power to the devices

whereas capture device (receiver) captures it.

• Wireless transmission is useful in cases where

interconnecting wires are inconvenient, hazardous or

impossible.

WHY NOT WIRES ?

• The percentage of loss of power during transmission and

distribution is approximated as 26-40%. In India, it

exceeds 40%

• Eliminates the use of cables for transmission of power.

• More secure, no risk of getting shock.

• Need for battery is eliminated.

• E-waste is eliminated.

• The main reason for power loss during transmission and

distribution is the resistance of wires used in grid.

HISTORY

• 1899: Sir NICOLAI TESLA was the first one to propose

and research the idea of wireless transmission. He

managed to light 200 lamps from a distance of 40km.

• 1961: William C. Brown publishes an article exploring

possibilities of microwave power transmission

• 2009: Sony shows a wireless electrodynamics-

induction powered TV set, 60 W over 50 cm

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HOW WIRELESS POWER WORKS

• Magnetic coil is housed in a box

and can be set in wall or ceiling.

• Antenna A is powered by mains

which resonates at a particular

frequency.

• Electromagnetic waves are

transmitted through the air

• Second magnetic coil, antenna B

fitted in laptop or TV resonates

with the same frequency as first

coil and absorbs energy.

• Energy charges the device.

TYPES AND TECHNOLOGIES OF WPT

• Near-field techniques

1. Inductive Coupling

2. Resonant Inductive Coupling

3. Air Ionization

• Far-field techniques

4. Microwave Power Transmission (MPT)

5. LASER power transmission

1. INDUCTIVE COUPLING

• Primary and secondary coils are not connected with

wires. Energy transfer is due to Mutual Induction.

some examples:

• electric brushes.

• Wireless Charging Pad(WCP).The devices are to be

kept on a WCP or very near to each other and the

battery will be automatically charged. It is preferred

because it is comfortable, uses less wires and is shock

proof.

2. RESONANCE INDUCTIVE COUPLING(RIC)

• Combination of inductive coupling and resonance.

Resonance makes two objects interact very strongly

and inductance induces current.

HOW RESONANCE IN RIC?

• Coil provides the inductance

• Capacitor is connected parallel to the coil

• Energy will be shifting back and forth between

magnetic field surrounding the coil and electric field

around the capacitor

• Radiation loss will be negligible

WITRICITY (A GLIMPSE)

At source:

Electricity =>

Magnetic waves

At device:

Magnetic waves =>

Electricity

WITRICITY… SOME STATISTICS

• Used frequencies are 1MHz and

10MHz

• At 1Mhz, field strengths were safe

for human

• At 10MHz, Field strengths were

more than ICNIRP standards

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RIC VS. INDUCTIVE COUPLING

• RIC is highly efficient

• RIC has much greater range than inductive coupling

• RIC is directional when compared to inductive

coupling

• RIC can be one-to-many. But usually inductive

coupling is one-to-one

• Devices using RIC technique are highly portable

3. Atmospheric conduction method

In this method a closed circuit is made using transmitter,

ionized path between upper atmosphere and transmitter,

second ionized path connecting receiver. The circuit back to

the transmitter is completed through the earth.

High potential is maintained at transmitter and receiver end.

A high potential transmitter transmits an “electromotive

impulse” through the ionized path to the upper atmosphere

where it ionizes the air, and this air between the transmitter

and receiver would conduct like a neon tube .

ADVANTAGES OF NEAR-FIELD TECHNIQUES

• No wires

• No e-waste

• Need for battery is

eliminated

• Efficient energy transfer

using RIC

• Harmless, if field strengths

under safety levels

• Maintenance cost is less

DISADVANTAGES OF NEAR-FIELD TECHNIQUES

• Distance constraint

• Field strengths have to be under safety levels

• Initial cost is high

• In RIC, tuning is difficult

• High frequency signals must be the supply

• Air ionization technique is not feasible

4. MICROWAVE POWER TRANSFER (MPT)Power transmission via radio waves can be made more

directional, allowing longer distance power beaming, with

shorter wavelengths of electromagnetic radiation, typically in

the microwave range.

A rectenna may be used to convert the microwave energy

back into electricity which has an efficiency of 95%.

Transmitted waves are received at rectenna which

rectifies, gives DC as the output. Power beaming using

microwaves has been proposed for the transmission of

energy from orbiting solar power satellites to Earth.

5. LASER TRANSMISSION

• LASER is highly directional, coherent

• Not dispersed for very long but gets attenuated when

it propagates through atmosphere

• Simple receiver

• Photovoltaic cell

• Cost-efficient

ADVANTAGES OF FAR-FIELD ENERGY TRANSFER

• Efficient

• Easy

• Need for grids, substations etc are eliminated

• Low maintenance cost

• More effective when the transmitting and receiving points

are along a line-of-sight

• Can reach the places which are remote

DISADVANTAGES OF FAR-FIELD ENERGY TRANSFER

• Radiative

• Needs line-of-sight

• Initial cost is high

• When LASERs are used,

• conversion is inefficient

• Absorption loss is high

• When microwaves are used,

• interference may arise

APPLICATIONS

• Near-field energy transfer

• Electric automobile charging

• Static and moving

• Consumer electronics

• Industrial purposes

• Harsh environment

• Far-field energy transfer

• Solar Power Satellites

• Energy to remote areas

• Can broadcast energy globally (in future)

CONCLUSION

• Transmission without wires- a reality

• Efficient

• Low maintenance cost. But, high initial cost

• Better than conventional wired transfer

• Energy crisis can be decreased

• Low loss

• In near future, world will be completely wireless

REFERENCES• André Kurs, Aristeidis Karalis, Robert Moffatt, J. D. Joannopoulos, Peter

Fisher and Marin Soljačić, “Wireless Power Transfer via Strongly Coupled

Magnetic Resonances”, Science, June 2007

• Peter Vaessen,” Wireless Power Transmission”, Leonardo Energy,

September 2009

• C.C. Leung, T.P. Chan, K.C. Lit, K.W. Tam and Lee Yi Chow, “Wireless Power

Transmission and Charging Pad”

• David Schneider, “Electrons unplugged”, IEEE Spectrum, May 2010

• White Paper on Solar Power Satellite (SPS) Systems, URSI, September

2006

• Richard M. Dickinson, and Jerry Grey, “Lasers for Wireless Power

Transmission”

THANK YOU!