Designs and evaluations of thin film piezoelectric vibration energy harvesters based on an equivalent circuit model

Abstract

For the purpose of realizing flexible and lightweight battery-less systems, we are developing piezoelectric vibration energy harvesters (PVEHs) with piezoelectric thin-films. We have optimized structures of PVEHs by theoretical models of equivalent circuit based on the lumped parameter model and the piezoelectric constitutive equations. The mechanical systems consist of a metallic cantilever beam with piezoelectric films, while the electrical ones are composed of electrode capacitances and a transformer connecting these two systems. Based on these equations, we have made an equivalent circuit model of the PVEH with trapezoidal cantilevers. We can calculate not only sine wave responses but also impulse ones. We have calculated formula Pout and shows electrode length and substrate SUS thickness-dependences of output power. We can maximize the output power by making the electrode length to 2/3 of cantilever length, and also by the substrate thickness thicker, where we have to balance with the substrate rigidity.