A Nonresonant and Frequency Up-Conversion Motion Converter for Footstep Energy Harvesting

Abstract

Insufficient power output and poor wearability present significant challenges to the real-world implementation of existing footwear energy harvesters. Herein, we propose a leaf-spring-based motion converter that converts the low-frequency linear motion from footstep activity into the high-speed rotation of the electromagnetic generator and achieves high-performance power output and wearability. The motion converter employs a moderate stiffness leaf spring coupled with bearings to transfer vertical displacement of the heel into horizontal deformation and absorb shock at the footstep touchdown moment. A ratchet clutch is utilized to switch the working modes of the generator between the stance and swing phases. We characterized the dynamic response of the motion converter and developed an analytical model to predict the power output of the system. Furthermore, we fabricated a lightweight and compact prototype and tested it under pseudo and natural walking conditions. The prototype achieves a displacement amplification ratio of up to 2.2 and reduces acceleration amplitude at touchdown by 10.7% compared with walking without the device. At a stride frequency of 1 Hz, our prototype shows an open-circuit voltage of 20 V, short-circuit current of 0.4 A, a peak power of 1.88 W, and a power density of 15.2 mW/cm3, higher than the previously reported footwear energy harvester.