Quote:
Originally Posted by Penn
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Same way
passive RFID chips / cards work. The card reader emits an magnetic field (H-field), antenna in the card turns it into AC, rectifies to DC, and powers a micro-controller in the card. (Said micro-controller then does whatever the RFID / smart card is supposed to do. Often it's something very simple, such as broadcast a serial number for the reader to pick up. Weak broadcast, but you're already close to the reader or you wouldn't have power.) They're used in transit system passes and race timers. I believe SWC had me use one once, so I could run a distance and they could get an accurate time without me necessarily knowing how I did.
Nokia is supposedly developing something similar, but even more radical: instead of pulling power from a specific (and nearby) emitter, they claim to soak up ambient radiated energy (such as radio, TV, etc) and gradually recharge the cell phone.