Mechanics of a single-ossicle ear: optical measurements and finite-element modeling of the avian middle ear
18 April 2018
Campus Middelheim, A.143 - Middelheimlaan 1 - 2020 Antwerpen (route: UAntwerpen, Campus Middelheim
Organization / co-organization:
Department of Physics
Joris Dirckx & Peter Aerts
PhD defence Pieter Muyshondt - Faculty of Science, Department of Physics
In contrast to the human ear that contains three bones or ossicles, birds only have a single ossicle in their middle ears, which is called the columella. Despite the fact that birds are able to hear sounds of a certain intensity about equally well as humans, it is unclear how birds achieve this by using only a single ossicle. This mystery originates from a lack of understanding of the mechanical properties of the avian middle ear. When in humans the ossicles are blocked or damaged, the bones are sometimes replaced by a rigid single-ossicle prosthesis. However, the surgical intervention is met with varying success. By investigating how nature was able to develop a well-functioning ear with only a single ossicle that can conduct sound signals from the eardrum to the inner ear, but that is also able to handle large external pressure variations, we hope to improve the design and functioning of single-ossicle prostheses.
This work investigates the mechanical functioning of the middle ear of birds by means of optical measurement techniques and computational modeling. Acoustic vibrations of the eardrum and the columella in duck were measured with digital stroboscopic holography and laser Doppler vibrometry, and the mechanics of the system was modeled by means of the finite-element method. The motions of the columella are influenced by the fluids in the inner ear. Therefore, the impedance of the inner ear was measured with laser vibrometry in the ostrich. Subsequently, the motion of the columella caused by slow pressure changes was obtained with X-ray tomography. The dynamic motion due to incident sound waves was assessed with laser vibrometry. In a finite-element model, the influence of the inner-ear impedance on these motions was examined. Another study investigated the potential effect of beak opening on sound transmission in the middle ear of roosters by using laser vibrometry.
The observed attenuation indicates the existence of a protective mechanism of the rooster’s hearing against its own crowing. In a final study, the implantation of ossicular prostheses was tested by in-vitro vibration experiments on human ears with a fracture in the malleus, the first ossicle in the middle-ear chain. In summary, the insights in the mechanical principles of the bird ear gathered with this work form an important step in the improvement of the design of single-ossicle prostheses.