Group velocity and power flow relations for surface waves in plane-stratified anisotropic media

Two aspects of power flow associated with electromagnetic waves in plane-stratified, dispersive, anisotropic media that are also lossless and linear are considered. One aspect is the relation between group velocity and the velocity of energy transport of surface waves in such media. It is shown that the group velocity of surface waves is equal to the ratio of the real part of the complex Poynting vector, integrated over the coordinate of stratification, to the corresponding integral of the stored energy density. The second aspect is the relation between the dyadic surface impedance representing either a slab of plane-stratified medium above a perfectly conducting plane or a semi-infinite region, the latter for the case of evanescent fields, and the power flow in the respective structures. The significance of the surface impedance and power relations for surface waves is discussed.