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M.Ing. (Electrical and Electronic Engineering) / This dissertation presents a comprehensive electrical model of the human auditory periphery. The model focuses on the generation and transmission of otoacoustic emissions (OAEs) under biometric conditions. The auditory system model was divided and studied in three sections, namely the outer, middle and inner ear sections. Existing models were used and improved for the study. The outer ear model was derived using electroacoustic analogies. The middle ear model was derived empirically. The inner ear model was derived by relating the mechanical properties of the inner ear to electrical principles. The outer ear model includes an analog diffraction circuit and a linear transmission line representation of the auditory canal and the concha. The variation of the radius of the auditory canal along its length was incorporated when computing the model of the outer ear. A pair of second order polynomials were used to create a new radius-length function which approximates the relationship between the radius of the auditory canal and its length. The frequency response of the outer ear model obtained using the radius-length function gave a wide frequency range representation of the outer ear characteristics. The middle ear is modelled using an analog network. Only the linear operation region of the middle ear was considered, thus excluding its reflex nonlinear mechanisms, namely; the stapedius muscle action and the stapes clipping displacement. The influence of the middle ear on the transmission of OAEs was evaluated by considering both the forward and reverse transmission characteristics/path of the middle ear. The middle ear response demonstrated great sensitivity to changes in the terminal loads connected to the middle ear as well as the transformer ratio. The inner ear behavior is represented by means of a nonlinear transmission line model. The nonlinear mechanism of the outer hair cells, which are taken as the primary sources of OAEs, are modelled using nonlinear voltage sources. The inner ear model was evaluated for conditions of both the active and inactive outer hair cells voltage sources. Due to limitations in the simulation software, a reduced active inner ear model was computed.The influence of the number of segments of the inner ear was explored. A reduced inner ear model having 40 segments was found to be sufficient in representing the frequency characteristics of the inner ear, whilst preserving the frequency-latency relationship of OAEs. The study not only improved the model of the auditory periphery, but also suggested several factors that can be incorporated in future research in order to better design signal acquisition and processing methods for OAE biometric applications.

<p>This thesis addresses the biomechanics of the human middle ear, that part of the auditory system which converts sound pressure waves in air to fluid pressure waves in the cochlea. The middle ear's mechanism is analysed in four papers, three main and one supporting; in the main papers the middle ear is treated as a multi-particle, multi-rigid body ensemble possessing a variable number of degrees of freedom depending upon the case being investigated.</p><p>It is confirmed, using the standard representation of a single fused incudo-malleal block, that the middle ear's motion is linear, but when this fused block restriction is lifted nonlinearity is present which significantly affects the mechanism's behaviour. In view of the linearity of the chain under the fused block conditions, the explanatory veracity of the conventionally accepted `fixed axis hypothesis' of ossicular motion is examined and found to be wanting as a realistic description of the chain's physical movement.</p><p>The nonlinear behaviour of the ossicular chain centres around the action of the incudo-malleal joint. This joint is shown to have preferential planes of operation, principally the pitch or longitudinal plane and in general to act as an efficient energy dissipator at high driving pressures and low frequencies. Providing the pressure is high enough, it is shown this energy dissipator effect eventually becomes independent of frequency.</p><p>The supporting paper discusses the dynamics of the imposition and removal of equation constraints justifying methods used to investigate the functioning of the incudo-malleal joint.</p>

This thesis addresses the biomechanics of the human middle ear, that part of the auditory system which converts sound pressure waves in air to fluid pressure waves in the cochlea. The middle ear's mechanism is analysed in four papers, three main and one supporting; in the main papers the middle ear is treated as a multi-particle, multi-rigid body ensemble possessing a variable number of degrees of freedom depending upon the case being investigated. It is confirmed, using the standard representation of a single fused incudo-malleal block, that the middle ear's motion is linear, but when this fused block restriction is lifted nonlinearity is present which significantly affects the mechanism's behaviour. In view of the linearity of the chain under the fused block conditions, the explanatory veracity of the conventionally accepted `fixed axis hypothesis' of ossicular motion is examined and found to be wanting as a realistic description of the chain's physical movement. The nonlinear behaviour of the ossicular chain centres around the action of the incudo-malleal joint. This joint is shown to have preferential planes of operation, principally the pitch or longitudinal plane and in general to act as an efficient energy dissipator at high driving pressures and low frequencies. Providing the pressure is high enough, it is shown this energy dissipator effect eventually becomes independent of frequency. The supporting paper discusses the dynamics of the imposition and removal of equation constraints justifying methods used to investigate the functioning of the incudo-malleal joint.