Frequency Shifts in Cavities with Longitudinally Magnetized Small Ferrite Discs

Abstract

Values of the tensor permeability components of a magnetized ferrite at microwave frequencies may be determined from the frequency shift that a sample produces in a resonant cavity. In this paper mathematical expressions are obtained relating this frequency shift to the diagonal and off-diagonal permeability tensor values and to the cavity geometry and ferrite geometry for any TE, TM or TEM mode natural to the empty cavity. The cavities considered are axial and have generalized cross section. The expressions are valid for ferrite discs whose volume is small compared with the cavity volume; it is assumed that the ferrite sample does not perturb the fields outside the ferrite from their empty cavity values. The cross section of the ferrite disc is arbitrary in shape and is perpendicular to the axis of the cavity. Examples are given in which the frequency shifts in a circular coaxial cavity, circular cylindrical cavity and rectangular cavity containing thin ferrite discs are derived for general TE and TM modes. The TEM-type cavity is also considered.