Measurement of polarization charge density at the interface between PET-film and electrode with a thin air layer by PEA method

Surface charge density on a 25 /spl mu/m PET film due to polarization was measured by a PEA method. In order to separate a pressure wave due to charges on the film from that due to charges on the adjacent electrode, a very thin air layer less than 1 /spl mu/m at the interface was utilized as an acoustic barrier. A linear relationship between the charge density due to polarization of the film and the applied voltage below 3 kV was observed. When the applied voltage exceeded 4 kV, the charge density on the film was saturated because the opposite polarity charges were injected from an adjacent electrode. The value of 4 kV gave a critical field strength across the interface for the charge injection up to 5/spl times/10/sup 8/ V/m.