Electromagnetic propagation through dielectric medium

Before we consider the behaviour of polymers, it is helpful to define the basic quantities which occur in dielectric and electrical studies. The relative dielectric permittivity, which is also known as the dielectric constant, or specific inductive capacity, of a material occurs naturally in Maxwell s equations for the propagation of electromagnetic radiation through a medium. However it is perhaps simpler to define it in relation to low frequency ( lumped circuit ) measurements as the factor of proportionality between the dielectric displacement D and the applied electric field E when the field is applied to a capacitor filled with the dielectric. 

Exercise. Show that a monochromatic electromagnetic plane wave, propagating in the x-direction through a medium whose dielectric constant varies with x, obeys an equation of the form (1.3). 

Propagation Delay of Lossless Lines. The minimum propagation delay (Tpd expressed in picoseconds per centimeter) for a unit length of lossless line is the inverse of the phase velocity (op) of the electromagnetic waves propagating through the dielectric medium surrounding the conductor line ... 

The properties of a dielectric medium through which an electromagnetic (optical) wave propagates are completely described by the relation between the polarization density vector P(r, t) and the electric-field vector E r, t). It was suggested that P(r, t) could be regarded as the output of a system whose input was E(r, t). The mathematical relation between the vector functions P(r, t) and E(r, t) defines the system and is governed by the characteristics of the medium. The medium is said to be nonlinear if this relation is nonlinear. 

---