Closed loop?
In a state called magnetic resonance, one device wirelessly transmits electrical power to another.

MIT Center for Materials Science and Engineering

Outlets Are Out

Imagine recharging your cell phone without plugging it in. Or powering your iPod while you walk around the house with it. Researchers at the Massachusetts Institute of Technology (MIT) have taken the first steps towards such wireless energy transfer by conceptualizing a way to transmit electricity over room-size distances. One day, they say, the technology could power whole households or even motor vehicles wirelessly.

The MIT team calls the concept a nonradiative electromagnetic field. It involves two simple ring-shaped devices made of copper. One, connected to a conventional power source, would generate magnetic fields similar to those that power electric motors. These fields would stretch outward a few meters and would only affect the receiving--or companion device--which would be outfitted with a second copper ring tuned to a specific frequency. Team leader Marin Soljačić says he began working on the concept because he wanted to find a better alternative to having to recharge his laptop computer and cell phone so frequently. He presented the team's findings today at an American Institute of Physics forum in San Francisco, California.

The technology shouldn't harm other electronics or humans, says team member John Joannopoulos. Computer simulations, he says, have shown that the essential mechanism--magnetic resonance--means little or no power is transferred to extraneous objects, such as computer hard drives or even magnetic stripes on credit cards. Joannopoulos says that "for certain designs, the effect on a person is weaker than the Earth's own magnetic field."

Although the concept has yet to be verified--the team is preparing prototypes that will be tested sometime next year--Joannopoulos says he is confident the tests will be successful. "Our computational experiments have been as close to reality as they can be," he says. In principle, he adds, "you could power everything in the room," and looking much farther into the future, he predicts that someday this technology could power motor vehicles down highways, using transmitters buried in the pavement.

It's an "extremely original" and "extremely exciting" idea, says physicist Mordechai Segev of the Technion-Israel Institute of Technology in Haifa. If the concept is found to be reasonably efficient, he says, it "could revolutionize technology by making many battery-powered products lighter and smaller."