Efficient energy beamforming for multi-device microwave wireless power transfer under Tx/Rx power constraints

This paper proposes an efficient energy beamforming technique for microwave wireless power transfer (WPT) feeding multiple devices simultaneously. The key feature of the proposed technique is the utilization of an optimal weight generated by synthesizing orthogonal bases of a channel matrix that are effective for power transfer, so that total power transfer efficiency in the system is maximized satisfying both transmitting (Tx) power limit and required receiving (Rx) power. This algorithm is beneficial in terms of both efficiencies of (i) power transfer for the whole system and (ii) computation for weight generation. By numerical simulation using a geometry-based channel model, the mechanism of the proposed technique is elucidated by a qualitative analysis of radiation patterns. Furthermore, its effectiveness is verified by a quantitative evaluation from the viewpoints of constraint satisfaction and power transfer efficiency.