Asynchronous phase shifted electromagnetic energy harvester

A vibration-based energy harvester is built upon the idea of transforming mechanical vibration of an inertial frame into electrical power. When the excitation frequency matches the natural frequency of the harvester, the energy generated by mechanical vibration is maximized. However, the reliance on resonance inevitably poses a robustness issue, in that power production drops significantly when the excitation frequency is slightly off from the tuned natural frequency of the harvester. To reduce the sensitivity of power output on the resonance, this paper proposes a novel concept of vibration based energy harvester in which both the magnets and the coils are attached to the vibrating cantilevers whose natural frequencies are separated with an optimally chosen frequency band. Due to the relative motions between the coil and the magnet cantilevers, the proposed energy harvester generates higher power over a wider range of excitation frequency compared to a conventional inertial frame based energy harvester. The improvements in the power output and the robustness are validated by experiments in the laboratory and on a bridge.