Is Wireless Power Closer Than We Think?

May 2nd, 2008 by Timothy B. Hurst

Tesla Would Be Proud

A few years back, Marin Soljačić was driven from bed by the insistent beeping of his mobile phone. But it wasn’t beeping for him to answer it, it was beeping for him to plug it in. Since that night, the assistant professor of physics at MIT, has been thinking about ways to start his phone charging as soon as he enters his home – without the need for plugs or wires.

Jennifer Chu at Technology Review writes that Soljačić considered using radio waves, but found that most of their energy would be lost in transmission. Targeted methods like lasers require a clear line-of-sight and could be dangerous for anything in their way. According to Chu, he eventually settled on a phenomenon called magnetic resonance coupling, in which two objects tuned to the same frequency exchange energy strongly but interact only weakly with other objects.

“A classic example is a set of wine glasses, each filled to a different level so that it vibrates at a different sound frequency. If a singer hits a pitch that matches the frequency of one glass, the glass might absorb so much acoustic energy that it will shatter; the other glasses remain unaffected.”

Now, Soljačić and his team have successfully demonstrated the use of magnetic resonance coupling to power a 60 watt light bulb from a distance of roughly two meters – and through a thin wall.

The most effective setup, thus far, transfers power over a distance of two meters with about 50 percent efficiency. The team is looking at other materials to decrease coil size and boost efficiency. “While ideally it would be nice to have efficiencies at 100 percent,” says Soljačić. “So realistically, 70 to 80 percent could be possible for a typical application.”

While some wireless power technologies have emerged in the marketplace, Soljačić’s technique differs in that it might one day enable devices to recharge automatically, whenever they come within range of a wireless transmitter.

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