A toroidal inductor is a resonator, though it can be approximated as a simple inductor at frequences well below its self resonant frequency (SRF). Lets take a simple example, a ferrite toroid of rectangular cross section.

From the basic definition \(\mu=B/H\) we can derive the relationship that the flux density in the core with current I flowing through N turns is given by \(B=\frac{\mu_0 \mu_r N I}{2 \pi r}\). Continue reading Calculation of impedance of a ferrite toroidal inductor – from first principles