Transient response of the eardrum excited by localized mechanical forces

Abstract

The Tympanic Membrane (TM, eardrum) is the interface between the middle and outer ear and helps transform the variations in sound pressure in the ear canal into vibrations of the ossicles. However, the transient acoustic response of TM due to the complexity of wave interference, hinders the understanding of the motions. Therefore, to reduce this effect, local (<1 mm2 area) mechanical excitation rather than entire-surface acoustic loading is proposed. To focus on the initial stages of the evolution of motion, we have developed a high-speed digital holographic system based on local phase correlation method, enabling the acquisition of full-field displacements of the TM up to 10 μs temporal and 150 k points spatial resolution. A piezoelectric plunger equipped with a feedback load sensor excites the TM by a 50 μs click and the mechanical contact is guaranteed during the experiment by >100 μm indentation of TM surface towards the camera. The results include characterization of wave travelling speed versus input force and localized mechanical properties, such as damping ratio, modal frequencies, and time constants. We expect that the results will lead to an improved understanding of the TM’s localized material properties and modeling of the eardrum behavior.