Strongly coupled piezoelectric energy harvesters: Finite element modelling and experimental validation

Abstract

Piezoelectric energy harvesters (PEHs) are usually connected to a load resistor 𝑅𝐿 matching to the impedance of their internal capacitance 𝐶𝑃 𝑇 to characterise the power generation during transducer design and optimisation. For strongly-coupled PEHs operating near resonance, this simple RC matching method underestimates the power output and fails to characterise the dual power peaks but are still often used in both simulation and experiment. This study analysed the internal impedance network and the power output characteristics of PEHs. Based on the analysis, a novel and efficient finite element model (FEM) for strongly coupled PEHs was developed and applied to a pre-stressed piezoelectric stack energy harvester (PSEH). A stationary analysis was first performed to simulate the pre-stressed state of the PSEH. The FEM then analysed the internal impedance of the pre-stressed PSEH, which was used as the optimal load resistance to simulate the electric power output. The simulated internal impedance and electric power output of the PSEH were validated by the experiment with good agreement. The FEM developed precisely predicted the electric power output, including the two identical power peaks, of the strongly coupled PSEH operating near resonance and outside resonance. In contrast, the FEM with the traditional RC matching showed only one power peak and significantly underestimated the power output near resonance, although it was still valid outside resonance. The developed FEM was also able to predict the effects of the static pre-stress and coupling efficiency figure of merit on the PSEH. The coupling efficiency figure of merit was found to increase the power output.