Wireless power technology transmits electricity to devices without the use of cables

Impact: Any low-power device, such as a cell phone, iPod, or laptop, could recharge automatically simply by coming within range of a wireless power source, eliminating the need for multiple cables—and perhaps, eventually, for batteries.

Context: Eliminating the power cord would make today’s ubiquitous portable electronics truly wireless. A number of researchers and startups are making headway in this growing field.

The researchers built two resonant copper coils and hung them from the ceiling, about two meters apart. When they plugged one coil into the wall, alternating current flowed through it, creating a magnetic field. The second coil, tuned to the same frequency and hooked to a light bulb, reso­nated with the magnetic field, generating an electric current that lit up the bulb--even with a thin wall between the coils.

So far, the most effective setup consists of 60-centimeter copper coils and a 10-megahertz magnetic field; this transfers power over a distance of two meters with about 50 percent efficiency. The team is looking at silver and other materials to decrease coil size and boost efficiency. "While ideally it would be nice to have efficiencies at 100 percent, realistically, 70 to 80 percent could be possible for a typical application," says Soljačić.