Capturing energy through a shoe-mounted piezoelectric energy harvester

This paper presents a shoe-mounted piezoelectric energy harvester (PEH) with intent to scavenge energy from human walking. The proposed PEH comprises of four piezoelectric cantilever beams magnetically coupled with a spring-mass system. Theoretical design and analysis were carried out using the standard accelerations obtained by fitting the experimental data. A prototype was also fabricated and its feasibility was verified by experimental tests. The results indicate that the four beams can be triggered multiple times by the spring-mass system within one step when the PEH is subjected to accelerations along the tibial axis. This operating principle realizes frequency up-conversion and brings about higher conversion efficiency. The superposition of voltage outputs generated by accelerations coming from two orthogonal directions is also achieved with the proposed design, endowing the proposed PEH with better functionality. The peak voltage output from each beam is as large as 10 V when the walking speed ranges from 2 km/h to 8 km/h.