NOTE 1 – For sinusoidal conditions in an isotropic medium, the medium is dielectric if the following relation is satisfied:

${\displaystyle \frac{\gamma }{{\epsilon }_0\omega }\gg {{\epsilon }^{\prime }}_{\text{r}}}$

where γ is the conductivity, ε₀ the electric constant, ω the angular frequency and ε′_r the real relative permittivity.

NOTE 2 – An anisotropic medium may be dielectric only in certain directions.