A generalized differential effective medium model of piezoelectret foams.

Abstract

Piezoelectrets are closed‐cell foams consisting of a continuous polymer matrix containing preferentially oriented and electrically polarized ellipsoidal voids. These materials display low density, low characteristic impedance, thicknesses on the order of 100 μm, and potential to act as conformal transducers on complex geometries. They therefore provide an intriguing alternative to piezoelectric ceramics and piezopolymers for applications such as air‐coupled ultrasonics or underwater receive elements. Unfortunately, some fundamental attributes of piezoelectret behavior, such as their nonmonotonic change in receive sensitivity with increasing ambient pressure, remain unexplained by physical modeling or experiment. To explain this and other behavior, this work develops a fully coupled multiscale microelectromechanical model which captures the void‐scale physics and predicts macroscopically observed piezoelectric properties. The model employs volume averaged Green’s function solutions of the three‐dimensional...