Permeability Tensor Values from Waveguide Measurements

Measurements of the components of the microwave permeability tensor of ferrites are usually made on very small specimens, such as spheres, discs, or rods, placed in cavities. Using degenerate modes, one can relate the frequency shifts of these modes to the real parts, and the changes in Q to the imaginary parts, of the tensor components. The technique herein described makes use of measurements performed on a ferrite rod placed along the axis of a circular waveguide. Exciting the specimen successively with the two senses of circular polarization, one obtains phase and attenuation information for each of these modes which can then be related by a perturbation treatment back to the real and imaginary parts, respectively, of the tensor components. The variation of phase and attenuation are recorded continuously (but on successive runs) as functions of the changing applied magnetic field. The apparatus used for these purposes will be described and certain novel features pointed out. While this method lacks the advantage of cavity techniques to separate out the dielectric contributions to the phase and attenuation shifts, it does offer a means whereby a fairly large specimen can be examined for its basic parameters in a geometrical configuration often used in applications.