Abstract

The anisotropy and phonon focusing of MgS are investigated through continuously elastic medium theory and physical acoustics theory in the solid state. The anisotropy and phonon propagation are theoretically researched in three–dimensional figures and their projections. The contours of three dimensional slowness surfaces give insights into the mixing of longitudinal modes and transverse modes, and show the origin of the phonon caustics due to the fact that the phonon phase velocity and group velocity are generally not collinear in elastically anisotropic crystals. The comparative investigations between anisotropy and slowness show that the propagation of elastic wave is affected by the elastic anisotropy of the lattice, and the phonon caustics “walk along” the extreme direction of elastic anisotropy.

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