The Dielectric Properties of Insulating Materials

HE development of dielectric theory in recent years has been along such specialized lines that there is need of some correlation between the newer and the older theories of dielectric behavior to keep clear what is common to both, though sometimes expressed in different terms. The purpose of the present paper is to outline in qualitative terms the way in which the dielectric constant varies with frequency and temperature and to indicate the type of information regarding the structure of materials which can be obtained from the study of the dielectric constant. The important dielectric properties include dielectric constant (or specific inductive capacity), dielectric loss, loss factor, power factor, a.c. conductivity, d.c. conductivity, electrical breakdown strength and other equivalent or similar properties. The term dielectric behavior usually refers to the variation of these properties with frequency, temperature, voltage, and composition. In discussing the dielectric properties and behavior of insulating materials it will be necessary to use some kind of model to represent the dielectric. The success of wave-mechanics in explaining why some materials are conductors and others dielectrics suggests that it might be desirable to use a quantum-mechanical model even in a general outline of the characteristics of dielectrics, but for the aspects of the theory of dielectric behavior with which we are immediately concerned here the behavior predicted is essentially the same as that derived on the basis of classical mechanics.