ACOUSTIC-WAVE PROPAGATION IN PIEZOELECTRIC FIBERS OF HEXAGONAL CRYSTAL SYMMETRY

An exact analysis is presented for acoustic wave propagation in cladde d acoustic fibers having a core and an infinite thick cladding both ma de of piezoelectric hexagonal crystal of 6 mm point group symmetry. Th e crystalline Z axes of both the core and cladding coincide with the f iber axis. A general dispersion equation is derived for all the acoust ic modes propagating along the fiber axis. Two simpler and independent equations which represent the dispersion relations of torsional and r adial-axial modes can be separated from the general dispersion equatio n. It has been found that the radial-axial and general flexural modes are piezoelectrically active while the torsional modes are not. Approx imate dispersion relations for pure guided modes in weakly guiding wea kly piezoelectric fibers which are much simpler than the exact ones ar e also given. Numerical results are only presented for pure guided mod es. Exact and approximate dispersion curves of several lower order pur e guided flexural, radial-axial and torsional modes in a weakly guidin g ZnS fiber are compared and they are in good agreement.