Design and Studies on a Low-Frequency Truss-Based Compressive-Mode Piezoelectric Energy Harvester

In this paper, we propose a truss-based compressive-mode piezoelectric energy harvester to harness energy from low frequency vibrations with a wide bandwidth and a high-power output. The design is an integration of mainly three modules: separated excitation mechanism from transduction mechanism for low resonant frequency, truss mechanism for magnification of the applied force onto the piezoelectric element, and amplitude limit mechanism to induce impact forces. We then formulate the harvester as a two-degrees-of-freedom system featured by superposition of harmonic and impact-induced nonlinear responses. Based on our structure design, we fabricate a prototype to conduct experimental studies. The experimental results show that the harvester is capable of harnessing energy efficiently from vibrations at the resonant frequencies of 3.3 and 6.09 Hz. The total bandwidth is expanded to 4.2 Hz owing to the structure nonlinearity and bifurcation. The open circuit voltage reaches 83.3 V and maximum power gets up to 38.2 mW with the matching impedance. Also, the harvester exhibits excellent charging performance in terms of saturated voltage and charging time.