Assigning viscoelastic and hyperelastic properties to the middle-ear soft tissues for sound transmission

A finite element model of the human ear considering viscoelasticity and hyperelasticity of the middle-ear (ME) soft tissues is developed in this paper. The present model is validated by comparing the static and dynamic responses to experimental data. The model-derived results are in good agreement with existing measurements. On this basis, the dynamic response of the ME under static pressure is re-evaluated. The results show that the static pressure mainly affects the low-frequency responses of the ME below 1000 Hz. In the case of static pressure preloading, the low-frequency displacement of the tympanic membrane and the stapes footplate (SF) and the ME gain are decreased, while the reverse ME impedance is increased. This is because the effective stiffness of the ME is increased due to large deformation and material nonlinearity, resulting in a decrease in the forward response of the ME at frequencies below 1000 Hz. Furthermore, the contribution of viscoelasticity to the ME sound transmission is also discussed. With the consideration of viscoelasticity, the magnitude of the SF displacement increases at frequencies above 3000 Hz, and the phase is mainly increased in the frequency band of 2000-5000 Hz. Moreover, viscoelasticity is more important for the SF displacement under static pressure. Given that only one type of material property (hyperelasticity or viscoelasticity) is considered in most published models, the consideration of both viscoelasticity and hyperelasticity helps to establish an accurate human ear model.