Receiver-Feedback-Free Cavity Resonant Wireless Power Transfer Based on In Situ S-Parameter Estimation Using a Parasitic Antenna

This letter proposes a novel cavity resonant wireless power transfer that can optimize the load condition of a parasitic antenna without receiver feedback or the need to know the S-parameter
a priori
. In this letter, it is hypothesized that the transmission efficiency to a receiver can be indirectly maximized by minimizing reflection observed at the signal source, and the proposed method is based on this. Furthermore, an
in situ
S-parameter estimation based on load modulation is proposed. This estimation provides a closed-form optimum load condition for minimizing reflection, and avoids the need for a brute force search with load sweeping. Experiments carried out in a 200 mm conductive cube cavity successfully demonstrate the effectiveness of the proposed method, which obtains a high transmission efficiency of 42.2% that is comparable to the achievable maximum.