Broadband Power Generation from Arm Swing During Walking by Repulsive-Torque-Enhanced Rotational Electret Energy Harvester

In this report, a broadband wrist-worn repulsive-torque-enhanced rotational electret energy harvester has been presented. By introducing the repulsive torque against the gravity direction, the natural frequency is tuned to 1 Hz, a typical frequency of arm swing during walking, while the excitation torque is enhanced, thereby both the bandwidth and the output power have been increased. In addition, the output power and the 3-axis wrist acceleration were measured for seven subjects wearing a wireless measurement system on their wrists. The cut-off walking speed is noticeably reduced by the repulsive torque, with average output power as high as 0.2-0.3 mW even at a low walking speed of 3 km/h.