A stacked electromagnetic energy harvester with frequency up-conversion for swing motion

This paper undertakes theoretical and experimental investigations of a stacked magnetic modulation harvester with frequency up-conversion for energy harvesting performance enhancement from swing motion. The harvester includes stacked rings including a coil ring, an energy harvesting magnetic ring, a ferromagnetic ring, and a frequency up-conversion magnetic ring with a proof mass, which are axially designed in the same rotating axis to increase the rotation speed of the magnetic field due to swing excitations from human motion. The magnetic flux density produced by frequency up-conversion mechanisms is calculated to derive the governing theoretical model for harvester performance prediction. The rotation speeds and inductive voltages of theoretical results show good agreement with the experimental results in a range of rotational speeds. A range of motion speed tests on a treadmill are performed to demonstrate the advantage of the stacked electromagnetic harvesters on harvested energy from human motion. The average output power improves from approximately 1.5 mW to 11.8 mW when motion speed increases from 4 km/h to 8 km/h. The maximum power density under human motion is 61.9 μW·g−1, with a total weight of 190.7 g.