Assessing the Efficiency of a Nonlinear Anti-phase Motion Energy Harvester Under Non-harmonic Excitation

This paper presents an approach to investigate the efficiency of a nonlinear anti-phase motion energy harvester (APMEH) when subjected to non-harmonic and harmonic excitations. Specifically, the paper aims to establish a trade-off between the device’s operational bandwidth, harvested voltage/power, and resonant operations under both harmonic and non-harmonic excitation. The repulsive force F_rep in the magnets was identified to successfully create static preloads/offsets and a pseudo-hardening effect in the linear spring as the distances between them are varied. Consequently, the spring begins to show nonlinear characteristics with a slight manifestation of hardening while increasing resonant frequencies and bandwidths over different magnet spacings. The APMEH configurations were tested with three preload distances: 12.024, 15.748, and 25.522 mm, defined as configurations 1, 2, and 3, respectively. In the harmonic/resonant application of the design, APMEH harvested much larger power, reaching 65.08, 81.28, and 90.56 mW, respectively, for configurations 1, 2, and 3 at a harmonic acceleration of 0.40 g over an external load of 200.00 Ω. Linear performance of the APMEH shows that a lower static offset distance will enhance the operational bandwidth. For instance, the bandwidth of configuration 1 improved by 12.20% and 51.22% over configurations 2 and 3, respectively, at a compromised power output measured at configuration 1 relative to 2 and 3, which was compromised by 19.93 and 28.13%. The observed increase in resonance with a smaller offset was attributed to the inertia redistribution as a result of the magnitudes and directions of repulsive forces F_rep initiating a hardening effect. In non-harmonic excitation, a larger F_rep consequently improved the harvested voltage by 21.08 and 25.41% when the horizontal distance (x) is reduced by 23.65 and 52.89%, respectively, for the same reasons as mentioned above. Therefore, a trade-off on harvested power and bandwidth is possible with the APMEH through appropriate parametric tuning of static distances.