Power over the air

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LOOK, MA! NO WIRES: MIT has demonstrated wireless power transmission from the coil on the left to the coil on the right, where it powers a 60W light bulb. Members of the team are (from left) front row: Peter Fisher and Robert Moffatt; middle row: Marin Soljacic; back row: Andre Kurs, John Joannopoulos and Aristeidis Karalis.

Imagine one day no longer needing to plug in your cell phone or laptop to charge it up. Simply walk into a room, and all your electronic devices will recharge automatically, drawing electricity seemingly from the air itself.

Massachusetts Institute of Technology researchers have sussed out a way to transmit power wirelessly. The work was funded by the Army Research Office 'through the Institute for Soldier Nanotechnologies ' the National Science Foundation and the Energy Department.

Transmitting electricity sans wires has been done before, but such methods leaked so much power in transit as to make it useless for practical applications. The new work promises a dramatic improvement. In the June 7 issue of Science, the researchers reported transmitting 60 watts over a distance of 2 meters with 40 percent efficiency.

The trick? Something called magnetically coupled resonance.

The researchers used two large copper coils. One was attached to a power source and radiated the power in a specific frequency. The other coil, the receiving unit, was tuned to pick up power at that frequency. Because the two units were in resonance, much more power could be transferred ' and transferred over greater distances ' than by standard induction.

'Two resonant objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with extraneous off-resonant objects,' the article states.

Evidently, this approach works best over short distances, say the length of a single room or so. And the prototype used bulky coils ' too large to be placed in rooms, much less squeezed into your BlackBerry. But the proof of concept has been laid out, and if this technique can be scaled to workable proportions, we can all feel a little foolish for not thinking of this simple form of power conveyance sooner.

About the Author

Joab Jackson is the senior technology editor for Government Computer News.


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