MODE SHAPES OF A DAMAGED AND REPAIRED TYMPANIC MEMBRANE AS ANALYZED BY THE FINITE-ELEMENT METHOD

This work makes use of recent finite element discretization of the hum an tympanic membrane where the known anisotropy of the tympanic membra ne is implemented by a series of thin beam elements superimposed on th in shell membrane elements. These thin beam elements were introduced i n order to simulate the fibre structure of the tympanic membrane. The onset of tympanosclerosis has been modelled as a gradual increase in t ympanic membrane density and modulus in the affected area. This increa sed density results in a fall of 55% of the first natural frequency fo r only a 16% area of drum sclerosis. Additionally the amplitude respon se is significantly reduced. Repair of the membrane was simulated by r emoval-of the fibre system from the affected area. Under these circums tances the natural frequencies virtually return to the healthy state b ut the mode shapes of vibration do not. The repair to tile membrane, a lthough not significantly altering frequency values, has resulted in a disruption to the normal mode shape patterns with consequences in the movements conveyed to the stapes and cochlear fluids.