Exact analysis of acoustic wave propagation in piezoelectric fibers of hexagonal crystal symmetry

An exact analysis is presented for acoustic wave propagation in a cladded acoustic fiber having a core and an infinite thick cladding both made of piezoelectric hexagonal crystal of 6-mm point group symmetry. The crystalline Z axes of both the core and cladding coincide with the fiber axis. A general dispersion equation is derived for all the acoustic modes propagating along the fiber axis. Two simpler and independent equations which represent the dispersion relations for torsional and radial-axial modes can be separated from the general dispersion equation. It is found that the radial-axial and general flexural modes are piezoelectrically active, while the torsional modes are not. Numerical results for the dispersion curves of a few lower-order pure guided flexural, radial-axial, and torsional modes for a ZnS fiber are given