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Spherical, rolling magnet generators for passive energy harvesting from human motion

In this work, non-resonant, vibrational energy harvester architectures intended for human-motion energy scavenging are researched. The basic design employs a spherical, unidirectionally magnetized permanent magnet (NdFeB) ball that is allowed to move arbitrarily in a spherical cavity wrapped with copper coil windings. As the ball rotates and translates within the cage, the time-varying magnetic flux induces a voltage in the coil according to Faraday's Law. Devices ranging from 1.5 cm3 to 4 cm3 in size were tested under human activity scenarios—held in the user's hand or placed in the user's pocket while walking (4 km h−1) and running (14.5 km h−1). These harvesters have demonstrated rms voltages ranging from ∼80 mV to 700 mV and time-averaged power densities up to 0.5 mW cm−3.