A Piezoelectric Heterostructure Scavenging Mechanical Energy from Human Foot Strikes

This paper presents a piezoelectric heterostructure for extracting mechanical energy from human foot strikes based on the impact of a moving block on the tips of the piezoelectric unimorph cantilevers. The use of the magnetic springs allows low-frequency and high-amplitude movements of the device. The piezoelectric unimorph cantilevers deform under a human foot strike on the pedal, and the piezoelectric elements in d(31)-mode produce output voltages. An analysis was conducted, and the working principle was stated. A prototype was fabricated to validate the feasibility of the proposed design. The experimental results show that the generated RMS voltage increases with human walking (running) speed. At the walking speed of 6 km/h, an average power of 36.26 μW is produced across a matching resistive load of 4 MΩ with an initial separating distance of 9 mm. Improvements of the device are possible, allowing an increase in the average power by increasing the number of piezoelectric unimorph cantilevers and using the piezoelectric materials with higher piezoelectric constants.