Dielectric materials are non-conductors of electricity (electrical insulators) that are able to be highly polarized by an electrical field(this is expressed as the material’s dielectric constant).

Charges within dielectric materials can be displaced from an equilibrium position by an electric field, and in some cases the charges may also be aligned to the applied field, but do not pass through the material. On removal of the electric field, the material returns to its original state and the time taken to do this is referred to as the relaxation period which is a characteristic of the dielectric material. Typical tests involve applying a varying electrical field (AC waveform), and monitoring the relaxation of the material as a function of its permittivity (capacitance and conductance) vs. the applied AC frequency.