Wireless power presentation

Wireless Power

By Jenna Rock and Loren Schwappach

For Jing Guo – Electromagentics

March 2010

Overview

History

Recent Developments

Technical Details

Demonstration

Advantages and Disadvantages

Variants and Evolution of Technology

History

Nikola Tesla’s experiments (1900s)

Experiments conducted by Nikola Tesla over 100 years ago.

The Chicago World’s Fair Demonstration in 1893.

Required a clear line-of-site.

Second proposed system used the earth’s ionosphere.

Investors could not see a way to manage and profit from Tesla’s ideas.

Wireless power via highly elliptical antennas (1970s)

June 5, 1975 NASA JPL Goldstone demonstration.

34kw of power at a distance of 1.5km; 82% efficiency.

Seen as impractical due to atmospheric absorption and free space loss.

Wireless power in the Twentieth Century (2000s)

Today the most popular approach to wireless power uses inductive charging.

Considered a type of short distance wireless energy transfer.

Impractical for separation of more than a few inches.

Massachusetts Institute of Technology (MIT) Experiment

Project Lead: Marin Soljačić

Solution: wireless power transfer via strongly coupled magnetic resonances.

Recent Developments

Concept: “WiTricity” (Wireless Electricity)

Overcomes several major drawbacks Free space loss and atmospheric absorption.

Requirement for unobstructed line-of-sight (Lasers & HDAs).

Close-range and very low-power energy transfer limitations.

“WiTricity” concept 106 times better than magnetic induction.

Technical Details

Faraday's law of electromagnetic induction:

E= -dφB/dt E = electromotive force.φB = magnetic flux.

Magnetic Induction Loop or coil of conductive material like copper, carrying

an AC current, to generate an oscillating magnetic field.

When second conducting loop (receiver) is brought close enough to the first, it captures a portion of the oscillating magnetic field, inducing an electric current in the second coil.

The current it drives around the circuit opposes the change in magnetic flux (Lenz’s Law).

When the current reverses direction, the magnetic field also reverses its direction.

Coupling Conductors are referred to as inductively or

magnetically coupled when they are configured such that change in current flow through one induces a voltage across the ends of the other through electromagnetic induction.

A simple example is a locomotive pulling a train car.

Technical Details (Continued)

Resonance: The tendency of a system to oscillate at larger amplitude at

some frequencies than at others.

These are known as the system's resonant frequencies.

At these frequencies, even small periodic driving forces can produce large amplitude oscillations.

Opera singer example, swing example.

Resonant Magnetic Coupling: Magnetic coupling occurs when two objects exchange energy

through their oscillating magnetic fields.

All resonators have a Q (Quality) factor characterizes a resonator's bandwidth relative to its center frequency, a tuning fork has a resonance of approx 1000.

The transmitting coil output a 9.9MHz resonating magnetic field.

The resulting resonant frequency is:

Both coils were separated by a distance of 2m with a 60W light connected to the receiving coil.

Technical Details (Continued)

The MIT Experiment Used two self-resonant coils, single copper loops (r =25 cm).

One coil (the source coil) is coupled inductively to an oscillating

circuit; the other (the device coil) is coupled inductively to a resistive

load.

LCf

2

10

Demonstration

Advantages and Disadvantages Pros

No negative effect on humans.

“WiTricity” is using higher frequencies than pacemakers use,

for example.

Efficient power transfer is only received by like resonant

devices.

“WiTricity” magnetic field is << than earths.

No negative effects on the environment.

No more batteries ending up in landfills.

“WiTricity” is several thousand times more efficient than

batteries and a million times more efficient than induction.

Cons

Small power transmission waste due to coils (thermal

energy).

Products and Applications Consumer: phones, laptops, flat screen TV’s, digital pictures, home

theater systems, speakers, and desktop PC’s and peripherals for use in home and “WiTricity” enabled hot spots.

Industrial: power interconnections across rotating and moving “joints” (think robotics, packing machinery, assembly machinery, machine tools), power interconnections in harsh environments (drilling, mining, underwater), robotics, and automatic guided vehicles.

Transportation: Automatic wireless powering for personal and commercial hybrid and future all electric vehicles and high tech military systems (mobile robotics, aircrafts, etc).

Evolution of “WiTricity” technology Smaller scale WiTricity fixed receivers, capable of enabling the WiTricity

transmitters within an area.

WiTricity on a larger scale (street “WiTricity” transmitters), recreational use.

Variants and Evolution of the

Technology

Conclusion

Wireless power transfer is quickly

becoming a viable reality. “WiTricity”

products expected in 2011

“WiTricity” offers an extremely efficient

alternative to previous attempts at

providing wireless power.

Future improvements in wireless power

technology offer world changing

implications.

References

F. Hadley,. (2007). “Goodbye wires”. (PDF)

“MIT_WiTricity_Press_Release.pdf”

J. Dix. (2010). “Wireless power” Retrieved March 17, 2010, from

http://www.networkworld.com/news/2010/011210-

witricity.html?page=1

A. Kurs., A. Karalis., R. Moffatt., P. Fisher., & M. Soljacic. (2007). “Wireless

power transfer via strongly coupled magnetic resonances”. Science

Express. (n.d.).

A. Kurs. (2007). “Wireless power transfer via strongly coupled magnetic

resonances. Science. 317(7), 83,

A. Karalis., J. Joannopoulos., & Marin Soljacic. (2007). Efficient wireless non-

radiative mid-range energy transfer. Annals of Physics. 323(2008),

34-48.

Questions?