Vibrational Energy Harvesting From Human Gait

Driven by the necessity to provide energy to wearable computing devices, the conversion of human movement into useful electrical energy has become a topic of extensive study. This paper presents a framework of calculating the maximal energy conversion from a resonant vibrational harvester during human gait. Acceleration measurements from both recreational and elite athletes are used to estimate power output for various gait speeds. Significant power density was found to occur at the harmonics of the gait cadence with the maximum power density occurring at twice the gait frequency. Though relatively large output power can occur at the first and second harmonics of the gait cadence, the resulting generator displacements are too large for practical use. Constraining the generator displacement to a root-mean-square magnitude of 25 mm provides approximately 28 mW of power for a 30-g device at optimal generator tuning conditions. As expected, the maximum power output increases with increasing electromechanical coupling and decreases with increasing damping.