TABLE OF CONTENTS It is important, before we set out to measure our dielectric materials, that we know something about the physics of dielectric response behaviour. The most relevant physical processes here are those that give rise to power loss in bulk dielectrics. In the RF and MW region of the spectrum such power losses arise largely from four different physical processes - see [22 24] or [5] for details and [12] for an introduction. These four physical processes are associated with mechanisms for generating loss - that is, conversion of EM energy into other forms of energy - and so are commonly called 'loss processes'. They are (1) Electrical Conduction, (2) Dielectric Relaxation, (3) Dielectric Resonance and (4) Loss from Non-Linear Processes.
Electrical Conduction in which charge carriers (electrons, ions or holes) in a material medium are relatively free to move physically through the medium under the influence of an electric field. The ease of conduction is quantified by the conductivity of the medium, ?, measuredinsiemenspermetre(Sm -1). In general, ? will depend on frequency, temperature, concentration of carriers, etc., though in many materials ? will change only slowly with frequency in the RF and MW range. In metals the effective conductivity depends on the physical properties of the metal surface (e.g. scratches, machining or grinding marks or debris) and so ? will depend on frequency because the skin-depth [18] is a function of frequency.
Dielectric Relaxation refers to the...
