MIT demonstrates wireless power

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Wireless power transfer over two-meter distance, from the coil on the left to the coil on the right, where it powers a 60W light bulb. Members of the team that performed the experiment are obstructing the direct line of sight between the coils; front row:

June 9, 2007 The possibility of wireless power transfer came much closer this week when a team of scientists at MIT demonstrated an important step toward accomplishing this vision of the future. The breakthrough moved us one step closer to the point where devices such as cell phones, mp3 players and laptop computers might not even need their bulky batteries to operate.

A team from MIT's Department of Physics, Department of Electrical Engineering and Computer Science, and Institute for Soldier Nanotechnologies (ISN) has experimentally demonstrated an important step toward accomplishing this vision of the future.

The team members are Andre Kurs, Aristeidis Karalis, Robert Moffatt, Prof. Peter Fisher, and Prof. John Joannopoulos (Francis Wright Davis Chair and director of ISN), led by Prof. Marin Soljacic.

Realizing their recent theoretical prediction, they were able to light a 60W light bulb from a power source seven feet (more than two meters) away; there was no physical connection between the source and the appliance. The MIT team refers to its concept as "WiTricity" (as in wireless electricity). The work will be reported in the June 7 issue of Science Express, the advance online publication of the journal Science. Late-night beeps

The story starts one late night a few years ago, with Soljacic (pronounced Soul-ya-cheech) standing in his pajamas, staring at his cell phone on the kitchen counter. "It was probably the sixth time that month that I was awakened by my cell phone beeping to let me know that I had forgotten to charge it. It occurred to me that it would be so great if the thing took care of its own charging." To make this possible, one would have to have a way to transmit power wirelessly, so Soljacic started thinking about which physical phenomena could help make this wish a reality. Radiation methods

Various methods of transmitting power wirelessly have been known for centuries. Perhaps the best known example is electromagnetic radiation, such as radio waves. While such radiation is excellent for wireless transmission of information, it is not feasible to use it for power transmission. Since radiation spreads in all directions, a vast majority of power would end up being wasted into free space.

One can envision using directed electromagnetic radiation, such as lasers, but this is not very practical and can even be dangerous. It requires an uninterrupted line of sight between the source and the device, as well as a sophisticated tracking mechanism when the device is mobile.

The key: Magnetically coupled resonance

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