Scientists have known for nearly two centuries how to transmit electricity without wires, and the phenomenon has been demonstrated several times before. But it wasn't until the rise of personal electronic devices that the demand for wireless power materialized. In the past few years, at least three companies have debuted prototypes of wireless power devices, though their distance range is relatively limited [see "Power Brokers," next page]. Then last year, a team at the Massachusetts Institute of Technology set the stage for wireless power that works from across a room.
The key to wireless power is resonance. Think of a wineglass that shatters when an opera singer hits just the right note. When the voice matches the glass's resonant frequency—the tone you hear when you tap the glass—the glass efficiently absorbs the singer's energy and cracks. Using magnetic induction and two identical copper coils that resonate at the same frequency, the MIT scientists successfully powered a 60-watt lightbulb from a power source seven feet away. The team called their invention WiTricity, short for "wireless electricity." Next up: sending the juice even farther and more efficiently.single page
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.