A vibrating cantilever footfall energy harvesting device

Human footfall is an attractive source of energy for harvesting for low-power applications. However, the nature of footfall is poorly matched to electromagnetic generators. Footfall motion is characterised by high forces and low speeds, while electromagnetic generators are normally most efficient at relatively high speed. This article proposes a novel mechanism for converting the low-speed motion of footfall to a higher speed oscillating motion suitable for electromagnetic power generation. The conversion is achieved using a cantilever beam which is deflected by the footfall motion using a special 'striker' mechanism which then allows the cantilever to oscillate freely at a relatively high speed. An arrangement of permanent magnets attached to the cantilever causes an alternating magnetic field, and a stationary coil converts this to a usable voltage. This article describes the mechanism and provides a mathematical model of its behaviour which allows the system parameters to be optimised and its performance predicted. The performance of a prototype device is presented, and it is shown that this is capable of generating up to 60 mJ/step and that the conversion efficiency is up to 55%.