= Complex permittivity
{title2=$\epsilon^*(\omega)=\epsilon'(\omega)-i\epsilon''(\omega)$}
For harmonic <electric fields> with time convention $e^{i\omega t}$, write $\mathbf D=\epsilon^*(\omega)\mathbf E$ for their complex amplitudes, where $\omega$ is <angular frequency>. The <real part> $\epsilon'$ describes the in-phase <electric displacement field>; the minus <imaginary part> $\epsilon''$ describes the loss component. The sign reverses with the opposite time convention. <Complex permittivity> can also be a <tensor> in a <linear anisotropic dielectric>.
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