A Multiscale Unconditionally Stable Time-Domain (MUST) Solver Unifying Electrodynamics and Micromagnetics

A rigorous yet computationally efficient 3-D numerical method has been proposed based on modified alternatingdirection-implicit finite-difference time-domain (ADI FDTD) methods. It has the capability of modeling the anisotropic and dispersive properties of magnetic material. The proposed algorithm solves Maxwell's equations and Landau-Lifshitz-Gilbert equation jointly and simultaneously, requiring only tridiagonal matrix inversion as in ADI FDTD. The accuracy of the modeling has been validated by: 1) the nonreciprocity of an X-band ferrite resonance isolator; 2) the attenuation constant of a magnetically tunable waveguide filter; and 3) the dispersive permeability of a 2-μm-thick magnetic thin film. Time steps that are up to 5000 times larger than the Courant-Friedrichs-Lewy limit have been used in these simulations without encountering stability issues. The simulation results agree with the predictions made from the theory, the commercial software or the experiments. Moreover, the algorithm has been applied to predict the effect of high permeability thin films in platform effect reduction. An electric current sheet close to a perfect electrically conducting plane coated with a 2-μm-thick magnetic thin film is simulated, which exhibits an enhanced surface resistance by three orders of magnitude higher than that without the magnetic thin film.