Low-frequency coupling between eardrum and manubrium in a finite-element model.

The mechanical coupling between the eardrum and the manubrium was studied by means of a finite-element model of the cat eardrum. Previous calculations of the effect of varying the eardrum curvature were extended, demonstrating the critical role of curvature in the behavior of the eardrum. A new procedure was developed for directly studying the coupling of forces from different points on the eardrum to the manubrium, and the distribution of load-coupling values over the eardrum surface was calculated. A geometrically simplified eardrum with a circular outline was also studied. It was found that certain regions of the eardrum are more effective in driving the manubrium than can be explained on the basis of their distance from the axis of rotation. This enhanced coupling depends on the curvature of the eardrum but, unlike the mechanism hypothesized by Helmholtz, requires neither tension nor anisotropy.