Wireless power: Parking Transponder (Score 1)

Wireless power is already used in some types of parking transponders. These are the things that people have in their cars that open the gates when they drive up. Although most parking transponders still use a small battery (watch battery), batteryless transponders are becomming more common. I'm an EE student and the parking permits at the university that I go to use this technology. Basically it operates on RF energy. The transponder has an antenna that picks up RF energy from a transmitter at the gate. A capacitor charges (quickly) and then the transponder sends out a signal which the receiver decodes and (depending on authorization) opens the gate.