Space charge distribution in multilayer dielectrics

Three-layer PP (polypropylene) film shows some unexpected dielectric behavior, possibly related to the existence of film-film interfaces in such systems. An experimental technique for studying the space charge distribution in multilayer structures has been developed. Depolarization currents and space charge distribution were measured in the model samples of 25- mu m-thick biaxially stretched PP film. A record of the charge distribution after poling with 2 kV (corresponding to 27 MV/m) for 20 hours at 295 K is shown. The scan shows heterocharge at both electrodes, and the middle layer is also charged positively. There is a large variation parallel to the electrodes.<>