Charging of cellular space-charge electret films in various gas atmospheres

A strong electromechanical transducer effect is achieved in cellular polymer films e.g. by corona charging, which initiates charge separation inside the film. In order to create an effective charge separation, a high electric field is required. The electromechanical effect can be further enhanced by corona charging in high-pressure atmospheres or in various dielectric gases that have high, electrical breakdown strengths. The effect of the gas inside the cellular structure has also been studied. A higher electric field most likely causes more complete charging throughout the cellular film. The electromechanical effect corresponding to the piezoelectric d/sub 33/ coefficient was enhanced after corona charging at 100-450 kPa or at 100-140 kPa in ambient nitrogen or in nitrous oxide, respectively, with corona voltages of up to 60 kV. The highest d/sub 33/ coefficient of about 790 pCN/sup -1/ was achieved after replacing air with nitrogen gas inside the cellular structure through consecutive low and high-pressure treatments at 293 or at 313 K.