Increasing the robustness of electrodynamic WPT systems with hybrid electromechanical transduction

Abstract In this paper, we compare the electrical damping capability of low-frequency electrodynamic wireless power transmission (EWPT) systems based on a resonant electromechanical receiver in the context of increasing their mechanical robustness. This study is carried out for piezoelectric (PE) and electrodynamic (ED) transducers. The receiver studied, excited by a distant transmitter coil, consists of a magnet and a resonant cantilever beam, and both ED and PE transducers (hybrid system). A strategy based on dual energy conversion is proposed that takes advantage of each transduction characteristic: the receiver with high-quality-factor is sufficiently sensitive to very weak excitation fields far from the transmitter, while it is robust to strong magnetic fields close to the transmitter by damping its motion. This approach is particularly relevant to increase the robustness of resonant receivers powering moving sensor nodes as the field strength seen by the receiver can vary greatly. 
This paper aims to evaluate three energy transduction strategies (PE-only, ED-only and hybrid) to both harvest more power and increase EWPT systems robustness by overdamping. An analytical model of the system is presented along with comparison with experimental results from a 71.7 cm3 prototype. When the motion amplitude is limited to 0.7 mm to limit aging, the receiver output 19 mW which outperforms the PE and ED modes alone by a factor of 1.5 and 1.8, respectively. Furthermore, the hybrid receiver can limit the amplitude of motion to 0.7 mm under a magnetic field up to 3.6 mT, which is 2.5 and 1.2 times higher than PE and ED alone, respectively.