Detuning piezoelectric receivers by resistive load adjustment for electrodynamic wireless power transfer

This article investigates electrical detuning techniques for low-frequency electrodynamic wireless power transfer (EWPT) systems. This study focuses on protecting the receiver from potential damage when quick increases in magnetic fields occur due to transmitter–receiver distance variation or in-rush transmitter coil currents. In the case of such event, to avoid damaging the mechanical receiver, the solution investigated in this article is to adjust the electrical load connected to the receiver. This adjustment enables precise tuning and detuning of the receiver’s resonant frequency and damping characteristics, thereby allowing to reduce its mechanical displacement amplitude and protecting it from damage. Based on well-known models of EWPT systems, we develop an analysis of two key operational modes of the proposed tuning/detuning approach: maximum transmitted power (MTP) mode, where the receiver circuitry’s input impedance is optimized for peak power transfer, and minimum displacement (MD) mode, which involves electrically detuning the receiver’s resonant frequency to limit its mechanical displacement. We establish transition conditions between MD and MTP modes based on the receiver voltage amplitude, enabling automated monitoring and adjustment of the receiver’s detuning. Experimental validation has been conducted with an EWPT experimental setup and a custom piezoelectric receiver. The results, in good agreement with the proposed analytical model predictions, confirm the effectiveness of the proposed detuning algorithm, which successfully reduces the receiver displacement by 60% in response to sudden magnetic field increases.