Complex Resonances of Anisotropic Spherical Resonators

In this paper, we report the complex resonant frequencies of inhomogeneous anisotropic spherical resonators. The anisotropy can be of gyroelectric or gyromagnetic type, having one isotropic axis. Two kinds of configurations are considered: an anisotropic sphere and an anisotropic spherical shell coating a concentric perfect electric conducting core. Two full-wave methods are employed for the calculation and verification of the resonances. The first is a method based on the weak form of the coupled-field surface-volume integral equation (CFSVIE), which is solved using entire domain basis functions of Dini-type. The second is the discrete eigenfunction method (DEM) that allows the expansion of the unknown fields in the region of anisotropy in terms of spherical vector wave functions. Both the CFSVIE and the DEM are validated by comparisons with separation of variables method, regarding isotropic and metallic-isotropic resonators. It is shown that commercial packages, such as HFSS, cannot address the full spectrum of such open structures. Numerical results for complex resonances, verified by both the CFSVIE and the DEM, are given for various anisotropic configurations. Finally, magnetic plasmon resonances are particularly examined in ferromagnetic resonators.