Electret Research - Stages in Its Development

Part 1 of this paper describes aspects of research on dielectrics and electrets carried out by the author over the last 50 years, in an attempt to show the systematics of its development and logical relation between its successive steps. Starting with dielectric absorption, it covers open-circuit behavior of dielectrics, thermally stimulated currents, Paschen breakdown and its effects on the performance of the inductionplate method, and the superposition of free surface charge and dielectric volume polarization. The two-charge theory appears as the result of a straightforward application of the basic charge-and-field equations of electrostatics, without the introduction of a specific model. Theoretical results are developed on the basis of simple experiments, most of them performed with Carnauba wax. Part 2 reviews theoretical aspects of isothermal and thermally activated dielectric relaxation. It includes the theory of the dielectric relaxation function and its interpretation in terms of distributions of natural frequencies or of activation energies, establishment of universal expressions for the relaxation function related with the theory of cooperative processes, theories based on the diffusion equation and normal modes, and the failure of the theory of equivalence during thermally stimulated transients.