On the damped frequency response of a finite-element model of thecat eardrum

This article presents frequency responses calculated using a three‐dimensional finite‐element model of the cat eardrum that includes damping. The damping is represented by both mass‐proportional and stiffness‐proportional terms. With light damping, the frequency responses of points on the eardrum away from the manubrium display numerous narrow minima and maxima, the frequencies and amplitudes of which are different for different positions on the eardrum. The frequency response on the manubrium is smoother than that on the eardrum away from the manubrium. Increasing the degree of damping smooths the frequency responses both on the manubrium and on the eardrum away from the manubrium. The overall displacement magnitudes are not significantly reduced even when the damping is heavy enough to smooth out all but the largest variations. Experimentally observed frequency responses of the cat eardrum are presented for comparison with the model results

On the degree of rigidity of the manubrium in a finite-element model of the cat eardrum

It has always been assumed that the manubrium is in effect perfectly rigid. In this paper, a more realistic model of the manubrium is incorporated into an existing finite‐element model of the cat eardrum. The manubrial thickness is based on a three‐dimensional reconstruction from serial histological sections. After a review of the literature, a value of 2×1011 dyn cm−2 is adopted for the Young’s modulus of the bone. The mode of vibration of the model is investigated for different manubrial‐thickness values and it is found that a significant degree of manubrial bending occurs in the model for realistic values of manubrial thickness. As a result of the bending, the frequency response at the umbo at high frequencies displays much higher amplitudes and larger phase lags than when the manubrium is rigid. The bending will also affect the displacements transmitted to the ossicular load, and introduce significant errors into estimates of such displacements based on measurements of umbo displacement even at frequencies as low as a few kHz. Recent measurements of manubrium vibrations in the cat ear provide experimental evidence of bending

Response of the cat eardrum to static pressures: Mobile versus immobile malleus

A phase-shift shadow moiré interferometer was used to measure the shape of the cat eardrum with a normal mobile malleus and with an immobile malleus as it was cyclically loaded with static middle-ear pressures up to ±2.2 kPa. The shape was monitored throughout the loading and unloading phases, and three complete cycles were observed. The mobile-manubrium measurements were made in five ears. In three ears, the malleus was then immobilized with a drop of glue placed on the head of the malleus. Eardrum displacements were calculated by subtracting shape images pixel by pixel. The measurements are presented in the form of gray-level full-field shape and displacement images, of displacement profiles, and of pressure-displacement curves for selected points. Displacement patterns with a mobile malleus show that pars-tensa displacements are larger than manubrial displacements, with the maximum pars-tensa displacement occurring in the posterior region in all cats except one. Displacements vary from cycle to cycle and display hysteresis. For both the mobile-malleus and immobile-malleus cases, the eardrum response is nonlinear. The response is asymmetric, with lateral displacements being larger than medial displacements. With a mobile malleus, manubrial displacements exhibit more pronounced asymmetry than do pars-tensa displacements

Measurement and modelling of the response of the cat eardrum to large static pressures

A study was carried out to observe the effect of inclusion of geometric nonlinearity in an FE model. The inclusion allows simulation of the stiffening behavior of the eardrum with increasing pressure. The eardrum is modelled as being isotropic, homogeneous throughout its thickness, and uniform across its surface. The results show that the by increasing the stiffness of the superior third of the posterior pars tensa in the model has the effect of shifting the maximum inferiorly and of decreasing its magnitude