Simulation of space charge deposition by barrier discharges in piezoelectric polymer foams

Ferroelectrets (electrically charged voided polymers) have been studied intensively in recent years due to their high piezoelectric coefficients (typical d33 coefficients reach several hundred pC/N), their mechanical flexibility and their capability to cover large areas, making them ideal candidates for a wide range of sensor and actuator applications. The piezoelectric activity of ferroelectrets results from engineered electric dipoles, formed by space charges deposited on the inner surfaces of the lens-like or box-shaped voids. The voids are electrically charged by applying a high electric field to the foam in the direction perpendicular to the film surface. As the electric field in the gas-filled voids reaches the critical field E_c for Paschen breakdown, a dielectric barrier discharge occurs, generating charge pairs that are separated and trapped at the internal surfaces of the voids. In the present work, this model was used to evaluate the dependence of the piezoelectric d33 coefficient on the gas pressure during the charging process, with the aim of predicting optimum charging parameters.