Design of a linearized magnetic spring for body-worn inertial energy harvesters

A potential method for powering body-worn sensors is that of inertial energy harvesting; extracting energy from the movement of the human body. However, the frequencies typically present are <;5 Hz, hence requiring physically large devices. A promising solution utilizes a magnetic spring, but these exhibit a non-linear relationship between force (and hence resonant frequency) and displacement. This paper describes a design for implementing a linearized magnetic spring. Finite element analysis is used to model this device and compare against those reported in the literature. Simulation results indicate that, compared to the state-of-the-art, this design exhibits improved linearity (2%) across a wider displacement range (±25 mm). A prototype has been fabricated, and the simulation results experimentally validated.