Investigating the Impact of Substrate Defects on the Operational Performance of a Silicon-Substrate Bimorph Piezoelectric Energy Harvester

Abstract

Cracks are prevalent defects found in micro-electromechanical systems, influencing both the operational dynamics and performance of these structures. These cracks have the potential to alter the stiffness of the structure and impact various parameters such as resonance frequency, voltage, and output power. This transformation may eventually result in structural failure over a defined period. Hence, it is imperative to diagnose and detect structural cracks. In this study, we introduce a semi-analytical method to examine transverse cracks occurring within the mid-layer of a bimorph piezoelectric energy harvester. The investigation encompasses reductions in stiffness and variations in capacitance resulting from mid-layer transverse cracks. From a microscale perspective, we employ a stress transfer technique based on crack density to quantify stiffness reduction caused by mid-layer cracks. Analytical outcomes concerning the influence of cracks in the mid-layer of the bimorph are obtained using assumptions derived from the Euler-Bernoulli beam theory and substantiated through finite element analysis. The consequences of these imperfections on mechanical parameters such as resonance frequency, as well as electrical parameters like output electrical power, are deliberated upon. It is observed that the existence of cracks in the mid-layer of the bimorph piezoelectric energy harvester leads to a decline in its resonance frequency, accompanied by an increase in voltage and output power, indicative of impending device malfunction. This research facilitates the identification of defects in MEMS by monitoring the harvester's operational performance.