Description:
<jats:p> Polarization properties of acoustic waves propagating in a symmetry plane m may be characterized by the aggregate rotation 2πp (p = 0,±1), which is gained by the polarization vector with respect to its initial orientation as the propagation direction turns through 2π in m. The criterion is deduced, which reveals the value of the rotation index p depending on elastic coefficients of a given monoclinic medium. It is shown that knowledge ofp delivers conclusions, not attainable by direct algebraic analysis, about the number of longitudinal normals existing in m and the distribution of pure 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. </jats:p>