Wave packets, the Poynting vector, and energy flow: 1. Non-dissipative (anisotropic) homogeneous media

Two methods for finding the energy velocity in electromagnetic propagation are in common use, the one employing wave packets and the other involving the Poynting vector. However, there appear to have been few attempts to correlate the results, especially for propagation through media of complex natures. The present paper, which is the first of a series, deals only with non-dissipative media, in which the effective permittivity matrix, ∈pq, is Hermitian, that is, . For such media, it is shown that the directions given by the two methods are the same, and hence either may be used for the direction of energy flow.