Pressure sensitivity response of polymeric ferroelectret foam films

The modification in the properties of polypropylene ferroelectret films when they are subjected to hydrostatic pressure variations (1-8 bar) is studied by analyzing the variations in the spectral response of the film thickness resonance and in their electromechanical response as ultrasonic receiver. Thickness resonances in the transmission coefficient are measured using wide-band air-coupled piezoelectric transducers. Film density, thickness, ultrasound velocity and attenuation and C₃₃, are extracted from the spectral analysis of the transmission coefficient. These data are used to explain the observed behavior. Film response comprises an immediate (elastic) response that is strongly non-linear with a C₃₃ that depends on the film strain (pore shape) and a delayed one due to viscoelastic and creep effects.