Finite-element and experimental analyses of the response of the cat eardrum to large static pressures

Currently available mathematical models of the eardrum are limited to low pressure levels owing to the assumption of linearity between stimulus (applied pressure) and response (eardrum displacement). In this work, the response of the cat eardrum to large static pressures is measured with a moire interferometer, and the data are modelled using the finite-element method. Experimental data indicate that eardrum response with a normal mobile malleus is nonlinear, asymmetric and hysteretic. Measurements with a fixed malleus permit investigation of eardrum behaviour without the confounding effects of the middle-ear ossicles.Artifactual banding in measured displacement patterns is investigated by means of numerical simulations. Artifacts in moire interferometry arise from ignoring height-dependent fringe-plane spacing, modulation, reflectivity and magnification when reconstructing surface shape. Systematic errors induced by these assumptions are small: their effects are not apparent in shape measurements, but do show up as bands in displacement images.The fixed-malleus data are modelled using the finite-element method to assess the importance of geometric nonlinearities at high pressure levels. Individualized finite-element models are created from shape data for each eardrum. Results indicate that geometric nonlinearity combined with nonuniform mechanical properties shows promise in describing eardrum response at high pressures