Mechanical modeling and dynamical behavior of the human middle ear.

Very serious injuries may result from impulse noise applied to the human ear. To assess the hazard of a given impulse, its effects on the displacements and the velocities of the structures in the middle and inner ear have to be evaluated. Thus, it is necessary to consider the temporal pattern of applied pressure and the resulting temporal response of the ossicular displacements and velocities. These investigations have to be carried out in the time domain because the relations in the frequency domain known from steady-state motion do not hold. Mechanical models based on the finite-element approach and the multibody system method are presented to describe the spatial motions of the eardrum and the ossicles in the middle ear. The motion of all points of the ossicular chain can be calculated using these models. The free vibrations as well as the general solution of the excited system, consisting of a transient and a steady-state part, are analyzed. Three different sound pressure sources are considered and the dynamical response of the ossicular chain evaluated. It is not sufficient to assess a particular impulse only by its peak pressure and a characteristic time duration since the temporal response of the middle ear is strongly dependent on the waveform of sound pressure. In particular, it is shown that in most of the cases the first negative part of the pressure waveform is expected to cause the worst damage.