Overcoming Efficiency Degradation in Wireless Power Transfer Systems: A Supply Voltage Modulation Method Empowered by 5.64-GHz 256-Element Antenna Array Receiving 10.6-Watt

This paper proposes a supply voltage switching method for a 16 $\times$ 16 large-scale array system operating at 5.64 GHz to efficiently receive radio frequency power, considering transmitter hardware efficiency—a factor not extensively addressed in previous wireless power transfer (WPT) research. This study focuses on improving both transmitter efficiency ($\eta_{tx}$) and free-space efficiency ($\eta_{air}$). We optimize $\eta_{air}$ by determining each element's transmission amplitude and phase through convex optimization. However, this requires amplitude tapering of approximately 50 dB or more, negatively affecting $\eta_{tx}$. To address this degradation, we propose techniques to enhance the product of the two efficiencies and conduct experiments using an implemented system. Comparing the commonly used time-reversal pattern in WPT with the proposed convex pattern, we demonstrate that the proposed method improves $\eta_{air}$ from 62 \% to 78 \% ideally. Additionally, the measured received power was 10.6 W for 5 $\times$ 5 array configuration at 0.5 m distance.