Dynamic behavior of the human tympanic membrane using a viscoelastic model

The human tympanic membrane (TM) plays a key role in driving sound from the air to the fluid inside the cochlea. It transforms the acoustic energy into mechanical vibratory energy. The mechanism involved in this transformation is currently under study, being numerical modeling one of the common strategies. The proper knowledge of the mechanical properties for the different components is the main limitation for the validity of these models. It is especially relevant the dynamic response in the frequency range of audible sound. This becomes especially critical for the case of the TM where the properties for this thin biological tissue are commonly simplified and represented by means of a static mechanical elastic modulus and damping properties. In this study, a viscoelastic model is used to simulate the dynamic behavior of the TM. The tissue is characterized assuming viscoelastic linear behaviour based in the Wiechert model, which is composed of simple mechanical elements (springs, dashpots). Experimental measurements of complex modulus on samples of the TM are used to determine the parameters of the viscoelastic model. Once the constitutive equation of the material has been determined it is implemented into a complete middle ear finite element model (FEM), composed of the TM, the ossicular chain and the suspensory ligaments and tendons. The middle ear transfer function is obtained by means of a harmonic analysis and it is used to evaluate the viscoelastic model. Finally, numerical results are compared with other experimental results. The viscoelastic model provides a better agreement with the experimental data than the previous approach.