No batteries! Wireless tech recycles airborne radio waves

A world full of Internet-connected devices is a giant step closer to reality thanks to a new communications system that works without batteries or wires for power.

Just as we use mirrors to reflect light, or turbines to catch the wind, this technique — known as "ambient backscatter"— co-opts transmissions from TV and cellular towers and reflects them to exchange information between wireless devices. These waves serve as both a source of power and carriers of information.

"We just use existing signals all around us," Shyam Gollakota, an assistant professor of computer science and engineering at the University of Washington in Seattle, explained to NBC News.

He and colleagues built a proof-of-concept system consisting of credit-card-size electronic devices that use antennas to detect, harness and reflect a TV signal, which is then picked up by similar devices.

Since TV signals are reflected off buildings, cars, trees and everything else in a city as it travels from a transmission tower to a TV set, the extra reflection doesn't degrade the signal. "Our reflection is yet just another reflection," Gollakota said.

The prototype devices communicate with each other over a distance of several feet. They flash little LED lights when they receive a signal from another device.

The applications of the technology are limitless: a keychain that sends out a text message to its owner's mobile phone when it falls out of a pocket, for instance; or an array of pad-like sensors embedded in a roof that relay a message to a homeowner when a water leak is detected.

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