How Porosity Affects the Performance of Piezoelectric Energy Harvesters and Sensors

Porosity has been experimentally employed to enhance the power output of piezoelectric energy harvesters. However, porosity lowers the breakdown voltage of the piezoelectric layer and hampers the pre-poling of the piezoelectric, which is needed to achieve enhanced performance. Furthermore, the effect of fractional porosity and pore size on the poling conditions and the enhanced power output of the comprising piezoelectric harvesters is not yet known. Here, through finite-element method simulations, it is shown that the enhanced performance of the porous piezoelectric harvesters is independent of the size and distribution of the pores and only depends on the fractional porosity. Moreover, it is shown that the presence of pores yields the emergence of local stress hot spots that are mainly responsible for improved performance. Moreover, it is suggested that the breakdown issue of the porous piezoelectric layers can be mitigated by poling the structures in a vacuum using electric fields below the threshold field for electron field emission from the piezoelectric layer.