Properties of acoustic polarization in a symmetry plane of monoclinic and higher symmetry media

Polarization properties of acoustic waves propagating in a symmetry plane m may be characterized by the aggregate rotation 2 pi p (p = 0, +/-1), which is gained by the polarization vector with respect to its initial orientati on as the propagation direction turns through 2 pi in m. The criterion is d educed, which reveals the value of the rotation index p depending on elasti c coefficients of a given monoclinic medium. It is shown that knowledge of p delivers conclusions, not attainable by direct algebraic analysis, about the number of longitudinal normals existing in m and the distribution of pu re longitudinal modes between the in-plane polarized wave branches. Results for the general case of monoclinic symmetry are further specified for the cases of higher symmetry.