Modeling and experimental investigation of an AA-sized electromagnetic generator for harvesting energy from human motion

Human body mechanical motion is considered as an ideal energy resource for portable or wearable devices. This paper presents an AA-sized electromagnetic energy harvester to convert the motion of human limbs motion into electrical energy. A cylindrical permanent magnet is freely moved in a 3D-printed tube wholly wrapped with coils. The outer dimensions of the device are 14 mm in diameter and 44 mm in height. Based on Faraday's law a theoretical model was derived and the device size was optimized. The influence of the magnet and coil dimensions on the output power was analyzed by theoretical calculations and proved by experiment following. The optimized dimensions from two separate methods agrees well with each other. When the harvester prototypes are driven by hand shaking at 5 Hz, the average output power reaches to 63.9 mW with power density of 9.42 mW cm(-3), which is 51% larger than that of the conventional tube electromagnetic energy harvester. While when the harvester is worn on ankle, a power of 4.2 mW can be obtained even at normal walking frequency of 1 Hz, corresponding to a power density of 0.62 mW cm(-3), which is considerably higher compared with other devices of human energy harvesting. Furthermore, the new developed device is simple without needing any restoring spring and is easy to be fabricated.