Electrodynamic Wireless Power Transfer Using Rotating Resonant Receiver With Highly Nonlinear Behavior

This paper reports an experimental study of a compact electrodynamic wireless power transfer (EWPT) receiver operating in an oscillating rotating mode. The receiver is fabricated with a diametrically-magnetized magnet and an electromechanical transducer (receiver coil) by modifying a commercial off-the-shelf coreless DC motor. In our system, the main oscillating magnet is accompanied by a fixed magnet creating a magnetic stiffness and thus a restoring torque. Various stiffness strengths are obtained by tuning the gap between the main rotating magnet and the fixed one. Three designs are characterized under time-varying magnetic field excitation, demonstrating their highly nonlinear behavior. The $0.58 \mathrm{~cm}^{3}$ generator outputs up to 14.0 mW at 53 Hz for a $1.4 \mathrm{mT}_{\text {PEAK }}$ input field. The resulting maximum power density is $24.0 \mathrm{~mW} / \mathrm{cm}^{3}$ with the $1.8-\mathrm{mm}$-gap design achieving the best power density for an oscillating rotating operating mode system. The maximum normalized power density of $35.0 \mathrm{~mW} / \mathrm{cm}^{3} / \mathrm{mT}^{2}$ was achieved at 0.5 mT using the $2.8-\mathrm{mm}$-gap design.