Vibration characteristics of the tympanoperiotic complex in the bottlenose dolphin, Tursiops truncatus.

Abstract

Modal finite + boundary element analysis of a bottlenose dolphin’s bony tympanoperiotic complex, including the ossicles, was performed to determine the mode shapes and natural frequencies. The goal was to gain insight into the transmission of sound pressure waves arriving through the soft tissues and transmitted across the bony components into the oval window of the inner ear. The finite element model of the bones was derived from CT scans with a 360 μm voxel resolution. In the first approximation the soft tissue was considered to be acoustically equivalent to an incompressible inviscid liquid, taken as infinite in extent. The added mass terms were computed with a boundary element model. The computed frequencies cover the range up to 160 kHz. The capacity of the natural vibration modes to excite motion of the stapes footplate was assessed by measuring the relative motion of the incudostapedial joint normalized by the normal displacement of the wet‐surface of the ear bones. In addition to a quantitative assessment a number of qualitative observations may be made that could explain the function of the dolphin’s ear complex. For example, the vibrational patterns are nontrivial and frequency dependent. [Work supported by the U.S. Navy CNO45.]