${\displaystyle {\delta }_M=\text{arctan}\frac{{\mu }_{\text{r}}^{″}}{{\mu }_{\text{r}}^{\prime }}}$

where ${\mu }_{\text{r}}^{\prime }$ and ${\mu }_{\text{r}}^{″}$ are the negative imaginary part and the real part, respectively, of the relative complex permeability μ_r

${\displaystyle {\delta }_M=\text{arctan}\frac{{\mu }_{\text{r}}^{″}}{{\mu }_{\text{r}}^{\prime }}}$

${\mu }_{\text{r}}^{\prime }$ et ${\mu }_{\text{r}}^{″}$ étant respectivement l'opposé de la partie imaginaire et la partie réelle de la perméabilité relative complexe μ_r