At the Darnell nanoPower Forum on May 18th, Powercast and CAP-XX presented a battery-free wireless power module for wireless sensors. The module uses the Powercast P2100 Powerharvester receiver, a CAP-XX GZ 115 supercapacitor, and the Texas Instruments eZ430-RF2500 wireless board. The modules work by receiving radio waves and converting them into DC, which is then stored in the supercap. When a charge threshold is reached on the supercap, the output to the wireless sensor is turned on which activates the sensor. The sensor can have zero stand-by power instead of using a sleep mode, and power can be sent on demand, o na scheduled basis, or continuously.
The joint press release by Powercast and CAP-XX contains additional details.