Mechanical modeling and dynamical behavior of the human middle ear

Very serious injuries may result from impulse noise applied to the human ea r. To assess the hazard of a given impulse, its effects on the displacement s 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 app lied pressure and the resulting temporal response of the ossicular displace ments and velocities, These investigations have to be carried out in the ti me domain because the relations in the frequency domain known from steady-s tate motion do not hold. Mechanical models based on the finite-element appr oach 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 al l points of the ossicular chain can be calculated using these models. The f ree vibrations as well as the general solution of the excited system, consi sting of a transient and a steady-state part, are analyzed. Three different sound pressure sources are considered and the dynamical response of the os sicular chain evaluated. It is not sufficient to assess a particular impuls e only by its peak pressure and a characteristic time duration since the te mporal 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 fi rst negative part of the pressure waveform is expected to cause the worst d amage.