On the definiteness of the constitutive parameters of a moving anisotropic medium

Using coordinate independent dyadic notation the constitutive parameters of a moving medium are derived in a form that is more concise than what is obtained if the conventional matrix methods are used. The result allows a study on the definite character of the constitutive parameters. It is found that if a medium with positive definite symmetric dyadics ε and μ is set in a uniform motion, these dyadics remain positive definite if and only if the velocity does not exceed the ray velocity of the medium.