A “33” mode (mechanical stress being in parallel to the electric dipole moment direction) piezoelectric lead zirconate titanate (PZT) multilayer stack-based piezoelectric flextensional energy harvester (PZT-Stacked-FEH) has been developed. Interdisciplinary approaches had been taken to increase the performance of the PZT-Stacked-FEH. First, an elastic flextensional frame for force amplification has been optimally designed to capture more mechanical energy with high energy transition efficiency into the PZT-Stacked-FEH. Second, a “33” mode piezoelectric PZT multilayer stack (PZT-Stack) was employed instead of “31” mode (stress being in perpendicular to the dipole moment direction) single layer piezoelectric component to increase mechanical to electrical energy conversion efficiency and to generate more electrical charges in order to improve energy storage efficiency. With these approaches, the PZT-Stacked-FEH demonstrates excellent performance: 1) a 19% of overall mechanical to electrical energy conversion efficiency was achieved, 2) 48.6 times more mechanical energy was transited into PZT-Stacked-FEH and 26.5 times more electrical power was generated than directly applying force to the PZT-stack, and 3) energy storage efficiency was significantly improved. In this paper, we are focusing on the investigations for the off-resonance mode performance of the PZT-Stacked-FEH through theoretical modeling, prototype development, and experimental studies. A prototype PZT-Stacked-FEH of weight 18 grams was able to generate 666 mW electrical power under 52 N rms force at 250 Hz, which is much lower than the resonant frequency (936 Hz). At this condition, a 6,600 μF super-capacitor was charged from 0 to 7 V in 1.6 second, at an average rate of 100 mW. Furthermore, 70% of generated appear electrical powers were delivered to matched resistive loads in the investigated regime of frequencies. Finally, the experimental results matched well with theoretical predictions which verified the developed theoretical models.

This paper developed an analytical model for a frequency-up-conversion <b>piezoelectric</b> <b>energy</b> <b>harvester</b> (PEH) composed of a piezoelectric bimorph and a stopper as shown in Fig.1. The whole system was subjected to a harmonic excitation. A bimodal approach was adopted to animate the beam stopper reaction. When the tip of the bimorph vibrates in free space or impacts with the stopper, a cantilever beam function was adopted. On the other hand, if the tip of the bimorph sticks with the stopper, a clamped-pinned beam function was applied to model the piezoelectric bimorph. To exam the effect of backward mechanical-electric coupling on power output, the dynamics and output energies are compared for two cases: 1) neglecting the backward mechanical-electric coupling effect in the model; 2) including the backward mechanical-electric coupling effect in the model. To obtain maximum output energy, the steady-state analytical solutions were studied to obtain the optimum gap between the piezoelectric beam and the stopper. From the results, we found that if the beam impacts and&#x2F;or sticks with the stopper, the PEH model without the backward mechanical-electric coupling will exaggerate the output energy.