Performance Improvement in Implicit Cavity Resonant Wireless Power Transfer Using Dual Parasitic Antennas

Abstract

This study proposed an implicit CRWPT method to improve the transfer efficiency at blind spots caused by standing-wave nodes. The method uses the diversity effect of dual Pxs. Based on the fluctuation of the reflected signal observed at a transmitting port during load modulation of the dual Pxs (minimum seven load combinations), the reflection characteristics for arbitrary load conditions of the Pxs were predicted through the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -parameter estimation among the antennas. Then, considering the principle of “transmission maximization via reflection minimization” established in an electromagnetically shielded space, the load condition maximizing transfer efficiency was implicitly identified in the absence of feedback from the receiver by identifying the minimum point of the estimated reflection surface. Further, through an experiment conducted in a 200 mm metal cavity at a 2.4 GHz frequency, it was confirmed that the proposed method improved the transfer efficiency by up to 14.4 times compared with the use of a single Px; the method achieved spatial uniformity with a transfer efficiency of approximately 50% or more at most measurement points.