WASHINGTON  There may be hope — however distant — for recharging nearly drained cell phone, laptop and other batteries without plugging them into the wall, a scientist said.
Although he hasn't built a device yet, Massachusetts Institute of Technology physics professor Marin Soljacic said he has figured out how to wirelessly recharge batteries, much like the way people can surf the Web untethered.
In a presentation Tuesday at an American Institute of Physics forum in San Francisco, Soljacic made the case for using specially tuned waves of electromagnetism that don't radiate like normal waves.
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The idea is that the recharge device and the receiver would be on the same acoustic frequency, similar to how a radio picks up only one channel at a time, so that the energy would mostly go straight to the intended battery, Soljacic said.
Some of the electromagnetic energy would go elsewhere, but Sojacic doesn't believe it would harm people, noting that humans can endure strong magnetic fields with magnetic resonance imaging machines.
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Soljacic envisions a device with wiring loops mounted on the ceiling of a room. He even sees this as a way of recharging electric buses on the go if there's a large "pipe" with recharging energy above a highway.
The concept of wirelessly recharging batteries has been dismissed before, deemed as far too inefficient with too much energy put out into the air and little where it's supposed to go.
But Soljacic said using special resonating frequencies could theoretically cut energy loss to only half of the energy produced, making the technology usable.
Soljacic said he is about to start experiments on his theory, which he believes would take at least a year to prove.
"It's too early to tell people 'why don't you take your battery and throw it away,'" Soljacic said.
Wednesday at the American Institute of Physics Industrial Physics Forum meeting in San Francisco, a group of researchers proposed new research into an old way, invented by Nikola Tesla,  to transfer power wirelessly. Marin Soljacic and his MIT colleagues revived an idea which involves a source that creates a short range oscillating field. Nearby circuits that resonate at the frequency of the source absorb some of the energy. The system would operate in much the same way as the coils inside a transformer, except that the researchers believe they can develop sources that transfer energy over much longer distances than is typical in transformers. Technology based on this proposal could mean wireless gadgets such as cell phones and iPods never have to be plugged into a wall outlet. The researchers also propose that it could power micro-robots or other machines that are too small to carry their own batteries. Eventually it might enable electric transportation such as buses to recharge wirelessly through power sources near the roadway. One potential problem with the system could be its inefficiency. Soljacic's calculations show that it is at best 60% efficient.