Surface impedance of saturating iron in travelling fields

The step-function approximation to the B-H curve for saturating iron is used here to examine the behaviour of the surface impedance in the presence of travelling surface fields. The method is an extension of that employed by other authors for pulsating fields and uses the concept of a wavefront which sweeps into the medium twice every cycle. The magnitude and phase of the surface impedance is computed for both sinusoidal electric and magnetic surface fields, from which it is found that, over the permissible range of wavelengths, the change in both surface impedance magnitude and penetration is small. The surface impedance angle increases from its value for pulsating fields, although, for most practical situations, this increase will not be more than a few degrees.