Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 70-73).

Thesis (M.Eng.)(Bioengineering)--University of Pretoria, 2005. / Title from opening screen (Viewed March 20, 2006). Summaries in English and Afrikaans. Includes bibliographical references.

A cochlear implant is a prosthetic device that can provide severe-to-profoundly deaf individuals with partially restored hearing. It emulates the function of a normal cochlea through combined functioning of externally situated electronics and an electrode array surgically implanted into the cochlea. Speech coding strategies implemented in speech processors aim to stimulate the auditory nerve in a way similar to that of a normal working cochlea by modelling the way the cochlea processes sound. Current speech processing strategies rely on the tonotopicity of the cochlea, i.e. the relation between distance from the base of the cochlea and the specific frequency that causes the highest amplitude of deflection at the specific point. The phenomenon of the travelling wave on the basilar membrane is thus reduced to its point or points of maximal deflection. In this study, the behaviour along the full length of the basilar membrane will be investigated in the time domain, i.e. the deflection along the whole membrane for any point in time, in order to evaluate the relevance of the travelling wave in coding sound in a cochlear implant system. The additional information acquired by emulating the motion of the fluid and the basilar membrane in the cochlea, will be transmitted to the recipient in electrical stimulus patterns, to assess whether it provides recipients of cochlear implants with better pitch perception. It will be shown that for the individuals that partook in the experiments, improvement of discrimination around 100 Hz were obtained when compared to current speech coding strategies like the advanced combination encoder (ACE) speech coding strategy in the same recipient. / Dissertation (MEng (Bio-Engineering))--University of Pretoria, 2007. / Electrical, Electronic and Computer Engineering / unrestricted

Verification of basilar mebrane function as frequency analyser in the case of pressure wave excitation. Calculate the transfer function of sound signals to the inner ear in case of interruption of the chain of ear bone. Computational modeling of the system ANSYS.

Current technology used to diagnose hearing disorders is limited. This is mostly due to the fact that the auditory structures are very small and not easily accessible with existing imaging technologies. The objective of this dissertation was to investigate the potential of high-frequency ultrasound as a tool for exploring the anatomy of the auditory system. Three studies were conducted in order to demonstrate the feasibility of high-frequency ultrasound as a diagnostic technology for hearing disorders. In the first study, an in-house developed 50 MHz annular array-based ultrasound system was used to provide ex-vivo images of auditory structures in cadaveric temporal bones. It was shown that the spatial resolution was sufficient to visualize a high level of detail of the ossicular bones of the middle ear as well as intra-cochlear structures of the inner ear. In the second study, a 50 MHz 1.26? pitch phased array ultrasound transducer was designed for imaging intra-cochlear structures through the round window membrane. As this element pitch results in large grating lobe artifacts, novel transmit beamforming techniques were developed to suppress grating lobes resulting from this large-pitch array. Theoretical techniques using the impulse-response simulation method and experimental verification using high-frequency linear array ultrasound system (Vevo 2100, VisualSonics, Canada) showed that these techniques were able to suppress grating lobe levels up to 40 dB. In the third study, a needle mounted 45 MHz single-element ultrasound probe was fabricated in order to measure the vibrations of intra-cochlear structures on human cadavers. Basilar membrane velocimetry measurements were successfully performed using pulsed-wave Doppler ultrasound in the frequency range between 100 Hz-2 KHz. The measured velocity of the basilar membrane and the round window membrane showed that the middle ear resonance frequency near 1 KHz was present over multiple temporal bones. This is the first work that has explored the human auditory system with high resolution ultrasonic visualization and Doppler velocimetry.

No description available.

This thesis aims to verify the function of the cochlea as a spectrum analyzer based on computational modeling of macro-mechanics of the cochlea using FEM. I aim to identify the spectrum of the basilar membrane, which is dependent on the variability of geometry, material characteristics and the presence of liquid environments. Interactions between liquid and solid phases is described by fluid-structure interaction in the system ANSYS. The model is linear and does not pursue an active policy of metabolic processes. Further the work focuses on the decomposition of the sound and check of two best known hypotheses about the transmission frequency of the sound to the brain.