Combined Effect of Bistability and Mechanical Impact on the Performance of a Nonlinear Electromagnetic Vibration Energy Harvester

This paper presents the design, modeling, fabrication, and characterization of a nonlinear bistable electromagnetic vibrational energy harvesting device. A folded cantilever structure based on low Young's modulus FR4 material reduces the operating frequency, while keeping the device footprint relatively small. The bistability is introduced into the system by a pair of repulsively oriented Nd-FeB permanent magnets. A second nonlinear mechanism, i.e., mechanical impact between the oscillator and the base, is also taken into account. Analytical expressions are derived to obtain the restoring force and potential energy for such a system. The model was further numerically simulated and validated with experimental results of the fabricated device. The device generated maximum power of 19.3 mu W at 1.5-g acceleration across an optimum resistive load of 1 k Omega, which was further improved by almost 70% with an optimized prototype. Both the numerical simulation and experimental results show broadening of the operational frequency range of the nonlinear bistable device by up to 4.35 Hz at 0.6-g acceleration with respect to the linear counterpart. At higher input vibration, the harvester oscillates with large amplitude and collides with the base, which abruptly changes the system dynamics. At an acceleration of 1.5 g, this impact induced change in dynamics increases the peak power frequency and widens the bandwidth even further up to 8 Hz (22% of the peak power frequency). Thus, the effects of both bistability and mechanical impact are incorporated into a single device to obtain a fairly wideband operation.