A comparison of polymer piezoelectrets with open and closed tubular channels: Pressure dependence, resonance frequency, and behavior under humidity

Piezoelectrets with open or closed tubular channels were produced by a lamination process around a template. Closed channels were obtained by additional sealing in a hot press. When the channels are closed, a more rigid structure is formed, leading to lower piezoelectric d₃₃ coefficients. However, for small stresses, the sealing does not significantly affect the electromechanical properties of the sample, as observed in the dielectric resonance spectroscopy. The samples were also investigated in different humidities at 25 °C, and the results show that the humidity has no influence on the piezoelectric effect, at least for the exposure periods analyzed here. The main interest in having samples with closed channels is that different gases could be used to fill the channels, which may provide distinct electrical properties without interfering too much with the mechanical properties.