Nonlinear multi-modal energy harvester and vibration absorber using magnetic softening spring

This paper presents a nonlinear multi-modal energy harvester and vibration absorber (EHVA) for both energy harvesting and vibration suppressing in low-medium frequency band. Two different methods are applied to broaden the effective bandwidth. Not only the multi-modal shapes of EHVA are designed, but also the hysteresis property of nonlinear softening spring is realized by a novel permanent magnets structure proposed in this paper. The simulation results illustrate that the magnetic repelling force reduces significantly when the oscillator magnet is close to the stator magnet, causing the nonlinearity of the softening spring. The linear and nonlinear stiffness parameters, natural frequencies and damping values of the oscillator are experimentally identified. The analytical model of flux density in the space is established to obtain the induced voltage. Then, the identified parameters are used to obtain the analytical nonlinear frequency response. It indicates that the effective bandwidth is widened by the nonlinear softening spring. The experiments demonstrate that the designed EHVA can help attenuate the vibration more than 15 dB and harvest 47 mV maximum voltage in the bandwidth from 11 Hz to 24 Hz. Comparing with the harvester using hard spring, the size of EHVA proposed in this paper can be decreased theoretically. (C) 2020 Elsevier Ltd. All rights reserved.