Wireless power transfer (WPT), also known as WiTricity, allows transmission of energy without wires. There are two main types - near-field techniques which work over short distances using induction or resonance between coils, and far-field techniques using microwaves or lasers over longer distances. Near-field techniques include inductive coupling used in wireless charging pads and resonant inductive coupling which improves efficiency. Far-field techniques transfer power through the air as radio waves or laser beams and require line-of-sight. WPT could eliminate wires and enable applications like charging electric vehicles on the go and powering devices remotely without batteries.

1. WITRICITY (WIRELESS ELECTRICITY)
FUTURE OF ELECTRICITY

2. 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.

3. 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.

4. 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
4

5. 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.

6. 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

7. 1. INDUCTIVE COUPLING
• Primary and secondary coils are not connected with
wires. Energy transfer is due to Mutual Induction.

8. 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.

9. 2. RESONANCE INDUCTIVE
COUPLING(RIC)
• Combination of inductive coupling and resonance.
Resonance makes two objects interact very strongly
and inductance induces current.

10. 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

11. WITRICITY (A GLIMPSE)
At source:
Electricity =>
Magnetic waves
At device:
Magnetic waves =>
Electricity

12. 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
12

13. 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

14. 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 .

15. 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

16. 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

17. 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.


18. 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

19. 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

20. 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

21. 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)

22. 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

23. 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”

24. THANK YOU!