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Electromagnetic pulse

Small electronic devices could be powered by wireless resonant electromagnetic energy, physicists say

Wednesday, November 15, 2006 by: Ben Kage
Tags: electromagnetic pulse, battery recharging, electromagnetic pollution

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(NewsTarget) A group of researchers from the Massachusetts Institute of Technology have outlined a system that could power devices such as laptop computers and MP3 players from a remote location, without wires.

Renowned physicist and engineer Nikola Tesla theorized a similar device in the 19th century, even going so far as to build a 95-foot antenna known as Wardenclyffe Tower in New York, but he ran out of money before it could be used.

A working model of the MIT system has yet to be built, but the researchers said that it should work if their computer models and mathematical calculations are correct.

"There are so many autonomous devices such as cell phones and laptops that have emerged in the last few years," said researcher and MIT assistant professor Marin Soljacic. "We started thinking, 'It would be really convenient if you didn't have to recharge these things,' and because we're physicists we asked, 'What kind of physical phenomenon can we use to do this wireless energy transfer?'"

The team decided that the best way was to incorporate "resonance," which occurs when energy of a certain frequency is sent to the object in question. Soljacic noted that two objects resonating at the same frequency "tend to couple very strongly." The phenomenon can be observed in the case of musical instruments.

"When you play a tune on one, then another instrument with the same acoustic resonance will pick up that tune, it will visibly vibrate," he said.

The team is considering electromagnetic waves instead of acoustic vibrations, but such waves -- which include radio waves, infrared and X-rays -- tend to scatter in all directions, wasting energy into open space. As a solution, the team is looking at a special class of "non-radiative" objects with "long-lived resonances." These objects bind energy that is applied to them, turning it into "tails" of energy and preventing its escape.

"If you bring another resonant object with the same frequency close enough to these tails then it turns out that the energy can tunnel from one object to another," Soljacic said.

Along with Tesla, other scientists have attempted wireless energy transfer. One method tested was the use of lasers, but they require uninterrupted line of sight, making them impractical for use around the home. A U.K.-based company called Splashpower has been developing recharging pads that use electromagnetic induction -- a process currently used for electric toothbrushes -- to charge devices.

Splashpower co-founder James Hay said that wireless power was something that consumers would love to have, but noted that the transfer of power was only half the battle.

"There are a number of other aspects that need to be addressed to ensure efficient conversion of power to a form useful to input to devices," he said.

"The question in all this, though, is what are the health consequences of being in the same field as a resonant wireless energy field?" said Mike Adams, a consumer health advocate. "With mobile phone radiation already known to reduce the sperm count of otherwise healthy men, we have an obligation to look more closely at the health implications of wireless technologies before unleashing them onto consumers."

The MIT work conducted by Soljacic and his colleagues Aristeidis Karalis and John Joannopoulos will be presented at the Physics Forum of the American Institute of Physics in San Francisco on Nov. 14.


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