Fluid motion in the cochlea resulting from bone conducted stimulation

Fluid motion in the cochlea resulting from bone conduction is analyzed in this thesis. Bone conduction is a method of sound transmission to the cochlea through the vibration of bones in the skull. These vibrations deform the shape of the cochlear capsule and give rise to the fluid motion. A three-dimensional channel is used to model the cochlea. Motion of the basilar membrane resulting from the cochlear fluid motion will be of particular interest. Asymmetry in the impedance of the oval window and round window is shown to give rise to a pressure gradient across the basilar membrane resulting in fluid motion and basilar membrane displacement. The cochlear pressure is expressed in terms of an integral equation in the basilar membrane velocity. In the analysis, the ratio of the height to the length of the channel epsilon is considered to have a magnitude that is much less than one. In this limit, rapid spatial variation in the velocity of the basilar membrane requires one to treat the higher order fluid modes within the cochlear fluid. Thus, asymptotic expansions in epsilon are used to treat the evanescent pressure modes. It will be shown that the asymptotic expansions lead to the simplification of the analysis and improved accuracy of the solution. A complete solution for the pressure within the cochlea is obtained and basilar membrane response at various frequencies is shown.