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Understanding functioning and evolution of bird middle ear mechanics through high-realism finite element modelling and system identification (FWOAL736)

When life evolved from aquatic to terrestrial animals, a biomechanical system developed which bridges the difference in acoustic impedance between air and fluid: the middle ear (ME). If this structure would not be present, the major part of sound energy in air would reflect at the interface with the fluid-filled inner ear. In mammals, this mechanical system consists of the eardrum and three ossicles, (and two muscles and some ligaments) which act as a lever system to transform sound waves in air to sound waves with higher pressure but smaller amplitude in the fluid of the inner ear (where sound energy is transformed to electric impulses going to the brain). In birds the ME is far simpler, mainly consisting of just an eardrum and one muscle and ossicle (yet partly cartilaginous), the so called columella, directly connecting the eardrum to the oval window in the inner ear. The system is enclosed in a cavity which connects to the outside world with the Eustachian tube. Under normal circumstances this tube is closed so quasi-static pressure differences exist between the ME and the outside world, e.g. due to altitude changes, meteorology circumstances etc. Acoustic information is of primary importance to birds, so it is fascinating to see that such a relatively simple middle ear developed. Moreover, birds are typically subject to sudden height changes and the single ossicle ear does not have the same flexibility to cope with large eardrum deformations as has the mammal three ossicle ear. These fundamental questions have held the attention of many researchers in the past, but up till now no in depth model based quantitative analysis is available. In this project we will measure the necessary input parameters for such a model (elasticity of eardrum and bones, vibration pattern of the eardrum and the ossicle, high resolution anatomical shape model) and use these to develop a highly realistic finite element model of the bird middle ear. We will develop new techniques to investigate how sound energy is transported from the eardrum to the inner ear, based on transfer path and power flow analysis. This will be done for two commercially available species (e.g. pigeon or duck, and chicken), representative for birds who adapted to a life upon the ground or a life facing fast pressure changes. We will measure how pressure change influences the system, and we will investigate how pressure varies in the bird ear, another question which remained unanswered up till now. Then we will use our model to reveal the functional evolution using less common species (e.g. falcons). Finally we will use the model to investigate new designs of an artificial ME ossicle which moves like in birds, and test it in our models of the mammal ear. When in humans the ossicles are blocked or missing, a prosthesis is used to connect the eardrum to the inner ear, but such prosthesis has no flexibility to deal with static pressure changes. We want to learn from nature to see which other single ossicle designs can solve this fundamental problem.
Date:1 Jan 2014 →  31 Dec 2017
Keywords:vibrations, acoustics, fluid dynamics, combustion
Disciplines:Acoustics, noise and vibration engineering, Other engineering and technology