Piezoelectric and acoustic behavior of polypropylene piezoelectret films

Abstract

Piezoelectrets are made from cellular polypropylene(pp)foam sheets by using a pressed-gas expansion followed by corona charging process. The elastic modulus, piezoelectricity and the acoustic response of such fabricated films are investigated. The results show that the Youngs modulus in the thickness direction is more than two orders of magnitude higher than those in the transverse directions. The d33 coefficient remains linear in an applied pressure range from 15 to 35 kPa. As measuring frequency increases from 2 to 300 Hz, d33 coefficient decreases to 81%, which is probably associated with the enhancement of elastic modulus of the film with pressure increasing. In a range from 100 Hz to 100 kHz, the PP piezoelectric films exhibit flat frequency response curves. The open circuit voltage sensitivity and d33 coefficient at 1 kHz are 0.84 mV/Pa and 164 pC/N, respectively.