According to this MIT Technology Review article, researchers at the University of Washington have developed prototype devices that communicate using just ambient radio waves — no batteries needed. The devices achieve this trick by varying how much they reflect and absorb radio waves, and scavenge power from those same radio waves. Bandwidth is low — only about 1 kilobit per second — and range is currently less than 1 meter, though that can reportedly be extended to about 6 meters easily. By eliminating batteries, such devices can become significantly smaller and cheaper, and could appear in a wide variety of scenarios, from contactless payments to warehouse item tracking, plus the killer app of locating your glasses and keys. follow link
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Researchers Demo Devices Powered by TV Signals