Definition[edit]
Relative permittivity is typically denoted as εr(ω) (sometimes κ or K) and is defined as
varepsilon _{r}(omega )={frac {varepsilon (omega )}{varepsilon _{0}}},
where ε(ω) is the complex frequency-dependent absolute permittivity of the material, and ε0 is the vacuum permittivity.
Relative permittivity is a dimensionless number that is in general complex-valued; its real and imaginary parts are denoted as:[11]
varepsilon _{r}(omega )=varepsilon _{r}'(omega )-ivarepsilon _{r}''(omega ).
The relative permittivity of a medium is related to its electric susceptibility, χe, as εr(ω) = 1 + χe.
In anisotropic media (such as non cubic crystals) the relative permittivity is a second rank tensor.
The relative permittivity of a material for a frequency of zero is known as its static relative permittivity.