Omnidirectional Multi-Transmitter Wireless Power Transfer System With Integrated Coupling Coefficient Sensor

A 6.78-MHz multi-transmitter wireless power transfer (WPT) system that allows relaxed alignment power transfer is proposed. The coupling coefficient (k) between each transmitting coil and the receiving coil is analyzed. By using a novel integrated coupling coefficient sensor (k-sensor), transmitteri(TXᵢ) is selectively activated based on the magnitude ofkᵢ, and the phase of the received current is duly adjusted to avoid current cancellation to increase the system power transfer efficiency (η SYS). Power control is implemented on an integrated circuit (IC) fabricated using a 0.18-μm CMOS process with 3.3-V devices. The WPT system consists of one receiver (RX) coil and a2~× ~2transmitter (TX) coil array driven by the proposed IC. Eight RX coil positions were evaluated to assess the performance of the WPT system. Experimental results show that, compared with the multi-TX WPT system without using thek-sensor, the best improvement occurred when the RX coil was positioned perpendicular to the TX coils, withη SYSincreased from 0.3% to 63.7%, and delivered power rose from 3 mW to 2 W. Performance enhancement was observed for most cases.