Wireless recharging one step closer to reality

August 25, 2008

SAN FRANCISCO, California (AP) -- Imagine juicing up your laptop computer or cell phone without plugging it into an electrical socket.

That's a luxury that could be provided by wireless power transmission, a concept that has been bandied about for decades but is creeping closer to becoming viable.

Building off work unveiled last year by Massachusetts Institute of Technology researchers, Intel Corp. demonstrated Thursday how to make a 60-watt light bulb glow from an energy source 3 feet away.

The Intel team did it with relatively high efficiency, losing only a quarter of the energy the researchers started with.

"That, to me, is the most striking part about it: transmitting 60 watts at 75 percent efficiency over several feet," said Intel's chief technology officer, Justin Rattner.

"The power pack for your laptop isn't that efficient. ... It's one of those things that's almost too good to be true."

Wireless transmission of electricity makes use of some basic physics. Electric coils that resonate at the same frequency can transmit energy to each other at a distance.

But this technology has a long way to evolve before it becomes a commercial product. In both the MIT and the Intel work, researchers used charging coils far too large for wide-scale use.

Even so, Rattner said Intel is in the early stages of trying to modify a laptop to accept wireless power. One challenge is figuring out how to prevent the electromagnetic field from interfering with the computer's other parts, he said.

Eventually, a homeowner could attach a large transmitter to a wall -- or even bury it inside the wall -- and plant many smaller receivers inside nearby tables and chairs and other pieces of furniture, creating the ultimate in recharging convenience.

MIT physics professor Marin Soljacic said researchers have proposed many intriguing ideas for real-world applications since his group disclosed its breakthrough last year in a scientific journal. Those include the possibility of wirelessly powering pacemakers and artificial hearts.

One of the big challenges in transmitting wireless power is preventing too much energy from escaping while in transit.

The MIT researchers, who call the technology WiTricity, a combination of "wireless" and "electricity," had lit their bulb from 7 feet away with larger charging coils and between 40 percent to 45 percent efficiency.

That means most of the energy didn't make it to the light bulb.

But Soljacic said his group has been able to get up to 90 percent efficiency when the devices were moved to about 3 feet apart, better than the Intel demo.

Soljacic, who didn't work with Intel, said Thursday that he was pleased the world's largest computer chip maker is getting behind the technology and helping push the envelope.

"For me, it's like a confirmation that it's so exciting, it's something people would like to have," Soljacic said. "Now, the question is if it's feasible or not. It's exciting that they're also inspired, and it seems closer to reality every day."

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