A shoe-mounted frequency up-converted piezoelectric energy harvester

This study presents a shoe-mounted piezoelectric energy harvester (PEH) to harvest energy from human walking. The PEH realizes frequency up-conversion technology through the impact between ratchet and piezoelectric beam in the gait cycle. A piecewise force-electric coupling model of the PEH is established based on the different motion states of the piezoelectric beam. Three motion states of piezoelectric beam are named as “plucking”, “vibration” and “impact” and analyzed through dynamic simulation. An experimental prototype of the proposed PEH is manufactured and its performance is tested at different gait frequencies. When the gait frequency increases from 1.5 Hz to 4 Hz, the output voltage varies weakly, and the output power varies differently in the upward phase and downward phase of a gait cycle. In the upward phase, when the walking frequency varies from 1.5 Hz to 4 Hz, the peak output power and average output power increased from 9.17 mW and 0.11 mW–13.88 mW and 0.98 mW, respectively. In the downward phase, the peak output power slightly fluctuates around 8 mW, and the average output power slightly increases from 0.12 mW to 0.18 mW. The experimental results show that the proposed PEH has 8 high-power peaks in a gait cycle and provides effective energy output within the frequency range of human walking, which has the potential in the application of driving wearable devices.