Classification of dispersion equations for homogeneous   dielectric-magnetic uniaxial materials
  The geometric representation at a fixed frequency of the wavevector (or dispersion) surface $\omega(\vec k)$ for lossless, homogeneous dielectric--magnetic uniaxial materials is explored, when the elements of the relative permittivity and permeability tensors of the material can have any sign. Electromagnetic plane waves propagating inside the material can exhibit dispersion surfaces in the form of ellipsoids of revolution, hyperboloids of one sheet, or hyperboloids of two sheets. Furthermore, depending on the relative orientation of the optic axis, the intersections of these surfaces with fixed planes of propagation can be circles, ellipses, hyperbolas, or straight lines. The obtained understanding is used to study the reflection and refraction of electromagnetic plane waves due to a planar interface with an isotropic medium. 
Ricardo A. Depine, Marina E. Inchaussandague, and Akhlesh Lakhtakia