Whispering gallery method of measuring complex permittivity in highly anisotropic materials: discovery of a new type of mode in anisotropic dielectric resonators

The whispering gallery (WG) mode method to measure complex permittivity is applied to the highly anisotropic material rutile. In an isotropic or slightly anisotropic material standard WG mode families exist and may be measured to accurately determine the complex permittivity tensor components. In this paper, we show that the standard WG mode families in general do not always exist in an anisotropic material. This phenomenon limits the applicability of the WG mode method. However, we identify a new type of WG mode, and show that it may be used to help determine the tensor components of the complex permittivity in some instances.