Scavenging energy from human limb motions

Abstract

This paper proposes a nonlinear piezoelectric energy harvester (PEH) to scavenge energy from human limb motions. The proposed PEH is composed of a ferromagnetic ball, a sleeve, and two piezoelectric cantilever beams each with a magnetic tip mass. The ball is used to sense the swing motions of human limbs and excite the beams to vibrate. The two beams, which are sensitive to the excitation along the radialis or tibial axis, generate electrical outputs. Theoretical and experimental studies are carried out to examine the performance of the proposed PEH when it is fixed at the wrist, thigh and ankle of a male who travels at constant velocities of 2 km/h, 4 km/h, 6 km/h, and 8 km/h on a treadmill. The results indicate that the low-frequency swing motions of human limbs are converted to higher-frequency vibrations of piezoelectric beams. During each gait cycle, different excitations produced by human limbs can be superposed and multiple peaks in the voltage output can be generated by the proposed PEH. Moreover, the voltage outputs of the PEH increase monotonously with the walking speed, and the maximum effective voltage is obtained when the PEH is mounted at the ankle under the walking speed of 8 km/h.