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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$16 \times 16$</tex> 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 (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\eta_{t x}$</tex>) and free-space efficiency (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\eta_{\text {air }}$</tex>). We optimize <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\eta_{\text {air }}$</tex> 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\eta_{t x}$</tex>. 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\eta_{\text {air }}$</tex> from 62 % to 78 % ideally. Additionally, the measured received power was 10.6 W for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5 \times 5$</tex> array configuration at 0.5 m distance.