Frequency up-conversion electromagnetic energy harvester for generating electrical power from vibration of beams under moving load

This paper studies a single-resonator electromagnetic energy harvester that employs an impact-driven frequency up-conversion mechanism to convert low-frequency vibrations of a multi-span beam, subjected to successive moving loads, into electrical power. The harvester consists of a cantilever beam made of plastic, serving as the resonator, with a thick square copper coil attached to its free end. This coil moves relative to two stationary cubic neodymium permanent magnets, each positioned on one side of the coil. To expand the harvester’s operational bandwidth, a stopper is positioned beneath the resonator, inducing controlled mechanical impacts as the cantilever beam vibrates. These impacts effectively increase the system’s stiffness, introducing nonlinear dynamic effects that widen the resonance frequency range, thereby enhancing energy harvesting efficiency. To evaluate the effectiveness of the energy harvester with the proposed impact mechanism, a finite element (FE) model of a multi-span beam subjected to successive moving loads is developed in COMSOL Multiphysics (version 6.2) to analyze its acceleration at varying speeds of the load. Subsequently, an analytical model of the energy harvester with impact effects is developed to analyze the induced voltage under measured acceleration signals of the multi-span beam, both with and without impact. An experimental prototype is also fabricated to validate the effect of impact on widening the harvester’s frequency response across different acceleration intensities. The numerical and experimental results demonstrate the effectiveness of the proposed impact mechanism in both increasing the induced voltage and widening the energy harvester’s operational bandwidth. It was found that, for the given materials properties and geometrical dimensions, the fabricated prototype with an impact gap of 7 mm increases the maximum induced voltage from 32 mV (no impact) to 43 mV (with impact) at a peak acceleration of 0.20g while also widening the frequency bandwidth by 1 Hz.