FDTD Calculation of Cavity Resonant Frequencies in Case of Nonuniform Internal Magnetic Field Distribution

An improved finite difference time-domain formulation that can work with nonuniform internal magnetic field distributions is introduced and used to obtain the resonant frequencies of a rectangular cavity filled with magnetic material. The nonuniformity of the internal field should be considered when the applied field is of the same order as the saturation magnetization. Even in case of large applied fields, when the magnetic device is small, the deviation from uniform distribution is significant. The nonuniform internal field distribution is obtained by an iterative method, assuming that the magnetic medium is saturated in the direction of local internal field (the condition for equilibrium distribution of magnetization). It is shown that this solution is stable and satisfies the standard boundary value problem of electromagnetism