Ring resonator based signal and power transfer at UHF frequencies

We present low-cost, high-efficient electromagnetic coupling between open ring geometry and a so-called butterfly structure on standard printed circuit boards (FR4) for the purpose of short range wireless data and power transfer at an UHF resonance frequency of 868 MHz. The components of the transfer system are characterized by simulation and experiments in terms of associated scattering parameters. Characterizing the efficiency of the coupled resonators, RF signal power transmission is examined for high power transfer as well as for low power DC supply utilizing a voltage doubler rectifier. With an enhanced butterfly structure coupler, unmodulated RF power transmission of 17.3 W is achieved with an efficiency of more than 95%. Furthermore, signal transmission of Pulse-Width-Modulated (PWM) signals with frequencies up to 5 MHz is demonstrated.