Improved vibration-based energy harvesting using piezoelectric circular diaphragm with stepped substrate

Abstract Piezoelectric energy harvesting is a promising solution for low-power applications, yet traditional piezoelectric circular diaphragm (PCD) energy harvesters often suffer from non-uniform charge density (defined as the charge generated per unit area) distribution, limiting output power. This study introduces a PCD structure with stepped substrate for vibration-based energy harvesters, aimed at improved charge density uniformity and overall output power. Finite element (FE) method simulations presented that increasing the number of brass substrate layers (from 1-layer to 4-layer) results in more uniform effective strain distribution, with maximum effective strain shifted from the center to the edges of the piezoelectric element. The coefficient of variation ( C v ) of effective strain decreases by 38.7% (from 0.421 to 0.258) as layers increase from 1 to 4, confirming strain uniformity. Experimental validation demonstrates significant improvements in charge density uniformity, with C v for voltage and charge density reduced by 76.5% (from 0.268 to 0.063) and 30.4% (from 0.319 to 0.222), respectively, for 1-layer to 3-layer substrates. The 3-layer stepped substrate, for example, generates 3.72 mW at a resonant frequency of 138 Hz, a 70.6% increase compared with the non-stepped substrate. Further application experiments confirm the practical potential of the stepped substrate in powering low-power sensors and illuminating 80 LEDs. These results highlight the potential of the stepped structure to enhance the output performance of piezoelectric energy harvesters.