Optimization of beam profiles for improved piezoelectric energy harvesting efficiency

Abstract

Piezoelectric cantilever beams are among the most popular vibration energy harvesting devices. Homogenization of the spatial distribution of axial strain along those beams increases harvesting efficiency. The general approach to minimize axial strain variation is to use triangular or trapezoidal width profiles. In this study, a width profile function that includes curved shapes is proposed and a finite element–based optimization scheme is constructed to maximize harvesting efficiency. A distribution parameter is defined for quantifying the strain uniformity. Optimization is performed for various tip mass values, using this parameter as the objective function. It is shown that curved beam profiles exhibit less variation in axial strain, compared to triangular and rectangular beams. Optimized shapes for minimal strain variation at resonance are determined. Experimental results also validate the findings of the optimization. At least 22% increase in strain uniformity is obtained with the optimized-shaped beam, compared to a triangular beam when no tip mass is used. The increase in strain uniformity becomes 29% when the tip mass is increased to 5 g. The results indicate the potential of employing beam-type piezoelectric energy harvesters with optimized width profiles.