The Measurement of the Permeability of Low-conductivity Ferromagnetic Materials at Centimetre Wavelengths

A waveguide impedance method for the measurement of the permeability of low-conductivity ferromagnetic materials at centimetre wavelengths is described. The method avoids the difficulties and anomalies present in earlier measurements. The complex magnetic and dielectric properties of a specimen filling a section of waveguide are derived from standing-wave measurements of the short-circuit and open-circuit impedances of the section. The experimental apparatus and techniques which have been employed at wavelengths of 60-20 cm., 15-6 cm., 3 cm. and 1¼ cm. are described, and some typical results of measurements on γ-ferric oxide are given. It is shown that the observed magnetic dispersion is an inherent property of the material, and is not attributable to skin-effect.