On the propagation of pure plane waves in anisotropic media

Abstract

In this letter it is shown that, for plane longitudinal waves propagating in generally anisotropic media, any direction in which the polarization vector is collinear with the propagation direction is also a direction in which the energy flux vector is collinear with the propagation direction. For transverse waves, the condition that the polarization vector is perpendicular to the propagation direction is shown to imply that the energy flux vector is collinear with the propagation direction only if the anisotropic media satisfies certain implicit symmetry conditions. Possible applications of these results to the determination of the elastic moduli of anisotropic media are discussed.