Electrical Air Waves

The tangled knot of electrical cables that recharge our laptops, mobile phones and PDAs could soon disappear. A team of U.S. physicists led by Martin Soljacic at the Massachusetts Institute of Technology (MIT) has demonstrated wireless power transmission. The method uses “resonant” antennas to send power through the air, and it is being called WiTricity.

Transmitting electricity wirelessly, however, is not a new achievement. It can be traced back to Nikola Tesla, who achieved this in the early 1900s. At that time, the technology was dangerous because the necessary electromagnetic energy would have to go off in all directions. Last year, Soljacic proposed a way to avoid these problems by employing nonradiative “evanescent” electromagnetic waves. But, this new technology did not work because the waves decayed very quickly.

This year, however, Soljacic’s team has developed its theory to create a pair of ring-shaped copper antennas. They connected one of the antennas to an electricity supply, while they connected the other to a 60-watt light bulb placed 7 feet away. When they ran an oscillating current through the first, it produced a magnetic field that “resonantly coupled” to the second, thus inducing a current. This current, the MIT team claims, fully lit the bulb with a transmission efficiency of 40 percent, just as their theory predicted.

Although the antennas demonstrated were over half a meter in diameter, Soljacic and co-workers say scaled-down versions of the system could be made for portable devices without sacrificing efficiency. They also stated this might enable the design of electronic medical implants that do not need cumbersome wiring.

However, the implications for the electrical contractor are obvious and endless.  EC



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