Nonlinear resonance-type electromagnetic vibration energy harvester excited by an impact ball

抄録

Nonlinear resonance of a cantilever beam under mechanical impacts is investigated experimentally for energy harvesting from human induced low-frequency vibration. In the prototype of this study, a metal ball is used to yield impulsive forces acting upon the cantilever installed in an electromagnetic type vibration energy harvester. A multipole magnet array attached on the cantilever moves above a planar coil fixed on the baseplate of the device, leading to power generation through electromagnetic induction. Due to the nonlinear excitation force arising from ball impacts, superharmonic resonance occurs at integer fractional frequencies of the cantilever’s natural frequency. Nonlinear response amplitudes of the cantilever and resulting induced voltage are measured under continuous sinusoidal excitation at 1-20 Hz. To explore resonance characteristic, we examine three cantilevers with different natural frequencies: 21, 34 and 76 Hz. In addition, the travelling distance of the ball is altered to realize maximum induced voltage. It is found that the travelling distance needs to be tuned depending on the natural frequency of the cantilever because there is an optimal distance for power generation. For a larger travelling distance, the induced voltage decreases. The critical distance can be numerically estimated by using the analytical model based on a single DOF damped mass-spring system. Combination of the frequency up-conversion technique and tuning strategy developed in this study offers a fundamental advantage for low-frequency vibration energy harvesting with compact device dimensions compared to the commonly used on-resonance harvesters.