Cutoff Conditions in an Acoustic Fiber with Infinitely Thick Cladding

Absfmcf-Exact cutoff conditions for all modes in a fiber acoustic waveguide with infinitely thick cladding are derived. The cutoff conditions for radial-axial and flexural modes with circumferential orders equal to and grealer than unity (n 2 I) are presented in compact determinant forms. Special attention is paid to the cutoff analysis of the first flexural mode F, ,. It is proved analytically that this mode always exhibits a zero cutoff frequency and is therefore an all-pass mode. The analysis presented here is sufficiently general to cover such rare cases as Stoneley waves. Cutoff frequencies for the first ten lower order modes in several fiber samples are also provided.