Multi-magnet coupled bistable piezoelectric energy harvesters for performance enhancement

This paper utilizes a multi-magnet configuration to form nonlinear magnetic negative stiffness and to construct a multi-magnet coupled bistable piezoelectric energy harvester (MC-BPEH). By adjusting the distance between adjustable magnets and fixed magnets and increasing the number of adjustable magnets, the MC-BPEH achieves high output voltage and power and wide bandwidth for energy collection. The effect of magnetic distances and quantities on the magnetic force, nonlinear magnetic negative stiffness, potential energy well, and magnetic flux density of the system is scrutinized. The dynamic responses and energy harvesting performance of the MC-BPEH are characterized by frequency-sweep and fixed-frequency experiments. The maximum power output and power density of the MC-BPEH with four adjustable magnets is 12 mW and 1.17 mW/cm3 3 at the optimal resistance of 300 k Omega, approximately 78 % and 72 % higher than the counterparts with two adjustable magnets under 0.5g excitation level, respectively. The device is also demonstrated to light up 93 LEDs. These results show that the introduction of multiple magnets into a piezoelectric energy harvester brings the redistribution of magnetic flux density and improves the energy harvesting performance of the proposed MC-BPEH. The optimized method proposed in this study is beneficial for developing high-performance and broadband energy harvesters for low- frequency and large-amplitude application scenarios.