Electret research — Stages in its development

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 the 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 induction plate method, and the superposition of free surface charge and dielectric volume polarisation. 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 hand of simple experiments most of them performed with Carnauba wax. Recent research has added a wealth of detailed information, but still leaves open many important questions.