Wireless charging for low-power mobile devices based on retro-reflective beamforming

This paper presents an experimental study on wireless power delivery to low-power mobile devices based on retro-reflective beamforming. In our scheme, a pilot signal comprised of an impulse train is broadcasted from a mobile device. The wireless charger analyzes the received pilot signal, and then accordingly constructs a focused power beam onto the mobile device. In our experiments, 14 mW out of the 1 Watt power transmitted from the charger is harvested by the mobile device 50-cm distance away, and the power beam is capable of tracking the device's location dynamically. In addition, since the pilot signal's spectrum covers a certain frequency range, the carrier of wireless power can be configured among multiple frequencies.