Measurement of dielectric and magnetic properties of ferromagnetic materials at microwave frequencies

Some experimental techniques are discussed which permit measurement of the magnetic and dielectric properties of ferrite materials in the microwave region by observing the perturbation in a cylindrical cavity due to insertion of a small ferrite sample. A comparison of the properties of thin disc samples with those of small spheres shows that discs yield more accurate results in the region below ferromagnetic resonance whereas spheres are preferable for the study of ferrite properties near resonance. A short description of instrumentation for cavity measurements at 9,200 mc is given and experimental results of disc measurements are reported for a low-loss BTL ferrite and several disc diameters. A comparison of experimental results with Polder's theory indicates that the loss of polycrystalline ferrites below resonance is considerably lower than that predicted from an evaluation of the width of the resonance absorption line.