Elastic wave harvesting in piezoelectric-defect-introduced phononic crystal microplates

Abstract

The localization of elastic wave at defect in phononic crystals (PnCs) has been applied to design piezoelectric energy harvesting (PEH) devices. However, the earlier researches were based on classical linear elasticity theory, which failed to predict the structural behavior at the micron scale. Based on a modified couple stress theory (MCST) and a mixed finite element method, the physics builder in COMSOL® Multiphysics is used to develop a novel interface that can capture the microstructure-dependent size effect and be applied in the simulation of a PnC-based PEH device. Size dependence of the newly developed model is demonstrated by three sets of models at different sizes. Numerical results show that when the size effect is considered in the model, the frequencies of the bandgap and defect bands increase with decreasing model size compared to the classical theory. Furthermore, the size reduction changes the internal stiffness ratio in the model, which affects the displacement amplitude, output voltage and output electrical power of the PEH device. Therefore, size effects are inevitable in micron-level models. These discoveries would help the design of small-scale PnC-based PEH devices for enhanced energy collection.