Wireless Power Delivery to Low-Power Mobile Devices Based on Retro-Reflective Beamforming

This letter presents an experimental study on wireless power delivery to low-power mobile devices based on retro-reflective beamforming. In our scheme, a pilot signal composed of an impulse train is broadcast from a mobile device. The pilot signal is received and analyzed by a wireless charger that includes four antenna elements. Then, according to the analysis outcome, the wireless charger constructs a focused power beam onto the mobile device. In our experiments, the total power transmitted from the wireless charger is approximately 1 Watt; 14 mW of power is harvested by the mobile device 50-cm distance away. Our experimental results successfully demonstrate that the power beam in reaction to the pilot signal is capable of tracking the mobile device's location dynamically. In addition, since the pilot signal's spectrum covers a certain frequency range, the carrier of wireless power in our scheme can be configured among multiple frequencies.