Optical techniques as validation tools for finite element modeling of biomechanical structures, demonstrated in bird ear research

• Main Authors: Muyshondt Pieter, De Greef Daniël, Soons Joris, Dirckx Joris J J
• Format: Conference Proceeding
• Language: English
• Subjects: Atmospheric models; Biomechanics; Birds; Computer simulation; Damping; Dynamic models; Dynamic response; Ear; Eardrum; Finite element method; Hearing; Holography; Internal energy; Mammals; Middle ear; Optical measurement; Optical properties; Optics; Prostheses; Sound waves; Vibration measurement; Viscoelasticity
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/1.4879599

In this paper we demonstrate the potential of stroboscopic digital holography and laser vibrometry as tools to gather vibration data and validate modelling results in complex biomechanical systems, in this case the avian middle ear. Whereas the middle ear of all mammal species contains three ossicles, birds only feature one ossicle, the columella. Despite this far simpler design, the hearing range of most birds is comparable to mammals, and is adapted to operate under very diverse atmospheric circumstances. This makes the investigation of the avian middle ear potentially very meaningful, since it could provide knowledge that can improve the design of prosthetic ossicle replacements in humans such as a TORP (Total Ossicle Replacement Prosthesis). In order to better understand the mechanics of the bird's hearing, we developed a finite element model that simulates the transmission of an incident acoustic wave on the eardrum via the middle ear structures to the fluid of the inner ear. The model is based on geometry extracted from stained μCT data and is validated using results from stroboscopic digital holography measurements on the eardrum and LDV measurements on the columella footplate. This technique uses very short high-power laser pulses that are synchronized to the membrane's vibration phase to measure the dynamic response of the bird's eardrum to an incident acoustic stimulus. Vibration magnitude as well as phase relative to the sound wave can be deduced from the results, the latter being of great importance in the elastic characterization of the tympanic membrane. In this work, the setup and results from the optical measurements, as well as the properties and optimization of the finite element model are presented. Observed phase variations across the eardrum's surface on the holography results strongly suggest the presence of internal energy losses in the membrane due to damping. Therefore, a viscoelastic characterisation of the model based on a complex modulus with a loss factor is chosen. Optimal values for a number of essential material parameters are determined by applying inverse analysis techniques using the experimental results. The result is a realistic dynamic model of the avian middle ear that will be used in the future to enhance treatment of middle ear pathologies in humans.