Repulsive-Torque-Enhanced Wrist-Worn Rotational Electret Energy Harvester

In this report, we propose a frequency tuning method using repulsive torque for rotational electret energy harvester (REEH) to enhance the output power from arm swing during human walking at different speeds. With the repulsive torque, the natural frequency is decoupled from the excitation torque by the inertia force, thereby the excitation torque can be increased without changing the natural frequency. The proposed repulsive torque is implemented to the REEH prototype by integrating a pair of c-shaped permanent magnet. Up to 10 times higher output power has been obtained with the REEH prototype at the low walking speed below 4 km/h.