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Boffins demo wireless electricity

Switching on lightbulbs from a distance

By Lucy Sherriff, 8 Jun 2007

Researchers in the US have demonstrated an experimental wireless energy transfer system that could pave the way for truly wireless computing. The team has already successfully made a 60W light bulb light up from a distance of 2 metres.

This might be very early days, but the work has been described as "truly pioneering" by Professor Moti Segev of the Israel Institute of Technology.

The group of researchers, from the Massachusetts Institute of Technology (MIT), outlined their ideas in a paper in 2006. But this experiment (the details of which have been published in the Journal Science), is the first time it has been made to work.

The experiment exploits the phenomenon of resonant coupling. It involves two copper coils of two feet in diameter. One, the transmitter, is connected to a power source and the other is connected to a light bulb. The two coils are set up two metres apart, and when the transmitter is switched on, the light bulb (attached to the receiver) lights up.

MIT explains how resonant coupling can add energy to a system by drawing a parallel with a child on a swing. The child can, by pumping his or her legs at the resonant frequency of the swing, add energy to the system and swing higher. Similarly, an opera singer can, by sustaining a powerful enough note for long enough, cause a wine glass to shatter, so long as the note matches the resonant frequency of the glass.

In the experiment, the transmitter generates a non-radiative magnetic field oscillating at MHz frequencies. This field mediates the power exchange with the other coil, which has been specifically designed to resonate with it.

The researchers explain that the crucial advantage of using the non-radiative field lies in the fact that most of the power not picked up by the receiving coil remains bound to the vicinity of the sending unit, instead of being radiated into the environment and lost.

This design does limit the range of the power transfer, but is much more efficient. The team adds that it is about a million times more efficient than non-resonance based induction.

"We had a strong faith in our theory but experiments are the ultimate test," said assistant professor Marin Soljacic, who worked on the research. "So we went ahead and sure enough we were successful, the experiments behave very much like the theory."

Happily for lovers of neologisms everywhere, they have dubbed their discovery: WiTricity. Nikola Tesla, who first proposed radiant energy around the turn of the last century, would be proud, we are sure.

The team suggests the system could be modified to create power hotspots for laptops so mobile users wouldn't need to run down their batteries when they are out and about.

The wider scientific community is keen to stress the safety of using magnetic fields and resonance to transfer power.

"The body really responds strongly to electric fields, which is why you can cook a chicken in a microwave," Professor Sir John Pendry of Imperial College London told the BBC. "But it doesn't respond to magnetic fields. As far as we know the body has almost zero response to magnetic fields in terms of the amount of power it absorbs."

This, we are sure, will not stop someone from claiming that their WiTricity has given them a headache/nausea/caused them to be bed ridden. A friend of El Reg recently reported meeting someone who claimed her LCD screen made her sneeze. We'll make no further comment. ®

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