Fluid coupling between the elements in a discrete model of cochlear mechanics

When analysing the coupled mechanics of the cochlea, due to the interaction between fluid coupling and basilar membrane motion, it is convenient to divide the cochlea longitudinally into a discrete number of sections. This report considers the fluid coupling in such a discrete model. The fluid coupling is analysed using a wavenumber formulation and is separated into long wavelength and short wavelength components. The short wavelength components are then seen as one of a number of sources of additional longitudinal coupling that could be incorporated into a modified model of basilar membrane dynamics. The effects of non-uniformity and asymmetry in the fluid chamber areas can then be taken into account to predict both the pressure difference between the chambers and the mean pressure. The results from the analytic formulation, in which the fluid is assumed to be incompressible, are also compared with those of an acoustic finite element model for the fluid coupling. Although the agreement is good at low frequencies, a resonance is observed at about 11 kHz due to the compressibility of the fluid, although this does not appear to affect the coupled cochlear response