Electromechanical response of piezoelectric foams

Abstract

A three-dimensional finite element model is developed to completely characterize the elastic, dielectric, and piezoelectric properties of piezoelectric foam structures. Three kinds of 3-3 type piezoelectric foam structures (i.e. with asymmetric interconnects, with symmetric interconnects, and without any interconnects) are identified and their electromechanical properties are characterized as a function of the interconnect geometry and architecture and benchmarked with that of long porous 3-1 type piezoelectric materials over a range of volume fractions/foam densities. In general, at a particular volume fraction a majority of the elasticity constants (with the exception of C55 and C13) of the 3-3 type open foam structures are lower than that of the 3-1 type long porous structure. Amongst the 3-3 type foam structures the sparsely packed foam structures (with longer and thicker interconnects) display higher coupling constants and acoustic impedance as compared to close-packed foam structures (with shorter and thinner interconnects). The piezoelectric charge coefficients (dh), the hydrostatic voltage coefficients (gh) and the hydrostatic figures of merit (dhgh) are observed to be significantly higher for the 3-3 type (PZT-7A) piezoelectric foam structures as compared with that of the 3-1 type (PZT-7A) long porous materials. For example, at about 3% volume fraction, the dh, gh, and dhgh figures of merit are 360%, 1000% and 5000% higher, respectively, for the interconnect-free foam structure compared with the 3-1 type long porous materials. Amongst the 3-3 type piezoelectric foam structures those that are close packed exhibit higher piezoelectric charge coefficients, while the sparsely packed structures exhibit higher hydrostatic voltage coefficients and hydrostatic figures of merit.