On a Measurement Method of the Tensor Permeability of Ferrite Using Faraday Rotation

A new measuring technique of the tensor permeability of ferrite in the microwave frequencies based on Faraday rotation is proposed. A circular cylindrical waveguide containing a longitudinally magnetized ferrite rod is used. A plane polarized TE11 wave is incident upon the section where the ferrite cylinder is placed. One end of the circular waveguide is short-circuited by a movable short-circuit plunger, which holds the ferrite cylinder through a hole drilled at the center. The angle of Faraday rotation and the position of the minimum voltage point of the elliptically polarized standing wave are measured far from the ferrite section. In addition to the measurement theory, several discussions are given: i) the relationship between a diameter of the specimen and the cutoff wavelengths of modes in the waveguide, ii) the extent of unwanted reflections due to the impedance mismatch at the end of the rod. As an experimental example, the tensor permeabilities of a polycrystalline rod of YIG are measured at the frequency 3.75 GHz with some dc magnetic field intensities.