The discharge of charged dipolar insulating materials

The separation of space charge and polarization effects in acoustic pulse observations of dielectrics requires some reliable theoretical models for reference purposes. In the present paper, we have numerically analyzed the behavior of the fields and the space charge during the discharge of a material containing both space charge and fictitious (dipolar) charge in comparable amounts. We show that the relevant time constant is the dipolar relaxation time, and that the two types of charge follow different histories if the sample were initially carrying a space-charge-limited current. This variation may be sufficient for the two sorts of charge to be distinguished experimentally. A system in which the initial fields vary linearly with distance can be worked out by an alternate numerical route. This example serves to confirm the accuracy of our computation, although it would not be useful for comparison with experiment.