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Wireless power

How WiTricity transfers energy using resonance, and where the company sees the tech going

By , Network World
January 12, 2010 03:30 PM ET

Network World - Despite the fact that the company's name is short for wireless electricity, Eric Giler, CEO of WiTricity, is quick to point out that isn't exactly what the company does. It only looks like that. Giler is the first business exec brought into this 16-person company, which is trying to commercialize the tech developed by Massachusetts Institute of Technology professor Marin Soljacic. Giler was founder and former CEO of Brooktrout, a provider of telecom software and hardware platforms, and the guy who invented how to get faxes into e-mail. Network World Editor in Chief John Dix caught up with Giler in his Watertown, Mass. Office.

If you don't put electricity in the air, what do you do?

 Electricity in the air is lightning, right, so by definition, it wouldn't be safe. We don't put electricity in the air, we utilize a very low density magnetic field to move energy through the air. The magnetic field we create is on the order of the earth's magnetic field. The difference is that we use an oscillating magnetic field, while the earth's field is static. By designing a power source and power capture device to oscillate at the same exact frequency, we can achieve what is called "Highly Resonant Magnetic Coupling."

Resonance exists in many physical systems, and is a very efficient way to exchange energy between two devices. Probably the most famous example is Ella Fitzgerald on the Memorex commercial where she sings and the glass breaks on the other side of the room. That is acoustic resonance. The glass resonated at the same frequency as her voice and the glass picked up that energy. Note it didn't break anybody else's eardrum in the room. It was safe to everybody because the glass was the only object that had the exact same resonant frequency as the note that Ella sang..

So resonance exists in nature and Dr. Marin Soljacic was thinking, "Can we get two magnetic devices to resonate and exchange energy over distance?" Magnetic fields don't interact with living organisms very much at all. You look like air to a magnet. You don't interfere with it and it doesn't interfere with you at the levels we're talking about.

If you were to look inside a transformer that takes AC current and transforms it to a low a voltage for your cell phone or laptop, you'd find two coils of wire placed very, very close to each other. One coil creates a magnetic field and it induces one on the other. But if you pull the coils apart just a little bit they stop working because the inductions phenomenon only works over a very short distance.

For example, you can can buy an electric toothbrush that has a coil in it and there is another one in the base and the power is transferred wirelessly, but if you pull the toothbrush out of the base more than just a little bit it stops charging. What Dr. Soljacic figured out was how to separate the coils to a distance greater than the size of the coils.

He published a paper that said, "This is theoretically possible to do and here's the mathematical theory." And nobody believed him. They said, "That's impossible."

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