Wireless power has come a long way from Nikola Tesla's early ruminations on the matter, and it looks like some researchers from Duke and Georgia Tech are now taking the idea to its logical, robot-powering conclusion. While their setup (thankfully) isn't yet able to power robots beyond the confines of the Q L-C resonator-equipped table, it does appear to work remarkably well in that limited proof-of-concept, with five bots each equipped with a non-resonant pickup coil able to follow a path around the table, or simply sit still to recharge their batteries. They were even able to power an LED light with the system for good measure. Natually, they eventually hope to expand the system to power larger swarms of robots and do away with the need for batteries altogether. Yeah, that's a good idea.
This paper from ICRA 2008 details the construction of the 60cm x 60 cm surface that provides wireless power and bidirectional communication to an initial swarm consisting of five line-following robots, each consuming 200 mW. Power transmission in the system was achieved through magnetic flux coupling between a high Q L-C resonator placed beneath the operating surface and a non-resonant pickup coil on each robot. The average power density demonstrated was 4.1mW/cm2 for a static load, and the paper demonstrates much greater peak power for dynamic loads via capacitor storage and power conditioning circuitry (PDF)(Powerpoint Slides).