A tunable nonlinear vibration energy harvester based on a magnetically-sprung resonator using ring magnets

Abstract

This paper presents a novel design of a magnetically-sprung mechanical resonator for electromagnetic vibration energy harvesting. The proposed resonator consists of a plastic cylinder, a moving magnet encapsulated in the cylinder, and two fixed ring magnets fitted on the cylinder suspending the moving magnet between them. The magnetic poles of the ring magnets are arranged so that the face opposed to the moving magnet has the opposite polarity. Thanks to this arrangement, the ring magnet attracts the moving magnet when it is far, but repels it when it comes close. This means that a single ring magnet can stably hold the moving magnet at its equilibrium, and the magnetic force between them is highly nonlinear. As a result, the overall restoring force-displacement relationship shows variety of nonlinear characteristics, from high-stiffness monostability to low-stiffness essential nonlinearity and even bistability, depending on the distance between the ring magnets. Simplified and detailed mathematical models of the proposed magnetic spring are presented to understand the dependence of the force-displacement characteristics on the design parameters. The numerical model of a prototype harvester is investigated to demonstrate the tunability of the resonance frequency by adjusting the axial position of the ring magnets.