Understanding the role of the gas in the voids during corona charging of cellular electret films - a way to enhance their piezoelectricity

The influence of the corona-charging process on the piezoelectric transducer coefficient d₃₃ of a cellular electret film has been investigated. An increased corona voltage can be considered as a way to enhance the charge density and thus also the resulting piezoelectric effect. Higher corona-charging voltages are possible with increased ambient pressure or in suitable dielectric gases. The effect of the gas inside the voids has also been studied. Enhanced transducer coefficients were obtained by corona charging in N₂ or N₂O gas atmospheres at 100-450 or 100-140 kPa pressures, respectively. The highest transducer coefficients of about 790 pCN^-1 were obtained when N₂ gas was filled into the voids of a cellular polymer film by means of consecutive vacuum and high-pressure treatments at 295 or 313 K.