Multi-layers fluoroethylenepropylene (FEP) films bounded with adhesive tape to create piezoelectrets with controlled cavities

Multi-layer piezoelectrets of fluoropolymers prepared by thermal fusing processes have been already reported in different techniques. In this work, we present new piezoelectrets prepared without any heating procedure. The method used to produce these structures consists of bonding at least two films of fluoroethylenepropylene (FEP) with an adhesive tape between then. The cavities, necessary for the piezoelectric effect, are created pre-molding at least one of the films over a template in a press. Latter, the films are metalized with aluminum electrodes, arranged into a FEP-adhesive-FEP stack and charged. This process does not only allows a good control of the void geometry but also does not affect any previous treatment that can be performed on the surface of the fluoropolymer films to enhance piezoelectric activity. In this paper we also present previous results of the piezoelectric d₃₃ coefficients over time and temperature exposure.