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Abstracts and keywords
Hearing plays an indispensable role in human communication and environmental awareness, necessitating continuous research into auditory biomechanics to better understand sound transmission processes. This dissertation investigates novel aspects of human middle ear modeling, focusing on the mechanics of ossicle chain e.g. with relaxation effect. By examining both intact and implanted middle ear conditions through experimental research and computational modeling, this study advances the current understanding of middle ear mechanics, particularly in the context of ligament relaxation, nonlinear mechanical behaviors, and double excitation phenomena in implanted ears. The research problem centers on the vibrational dynamics of the middle ear, particularly in relation to the relaxation effects of ligaments and tendons, the behavior of a Floating Mass Transducer (FMT) within an implanted system, and the impact of double excitation on the ossicular chain. The fundamental scientific questions addressed include: (1) How does ligament relaxation affect sound transfer through the middle ear? (2) What role do nonlinear mechanical properties of an FMT play in altering the vibrational response of the implanted middle ear? (3) How does double excitation, coupled with the delay in implant signal processing, influence sound transmission? To explore these issues, the study employs a combination of experimental and numerical approaches, integrating umped parameter models with computational analysis of sound wave propagation. A comprehensive literature review underscores the significance of modeling the auditory system, delineating the anatomy and mechanics of the middle ear. The human ear comprises three main parts: the outer ear, the middle ear, and the inner ear. The middle ear is of particular interest due to its role in sound transmission via three tiny bones—malleus, incus, and stapes—which form a mechanical bridge between the eardrum and cochlea. The study explores existing models and identifies gaps, particularly in the representation of viscoelastic ligament relaxation nonlinear stiffness effects, and bistable behavior in middle ear implants. To address these limitations, the research develops lumped parameter models (LPMs) of the middle ear, employing both Kelvin-Voigt and Maxwell viscoelastic models to simulate ligament relaxation effects. The study presents a three-degree-of-freedom (3-DOF) model for an intact middle ear and two five-degree-of-freedom (5-DOF) models for an implanted middle ear, one incorporating single excitation and the other incorporating double excitation with time delay effects. The Maxwell viscoelastic model introduces a modified representation of tissue elasticity, incorporating relaxation effects into the mechanical response of ligaments and tendons. The developed models demonstrate that relaxation phenomena significantly influence stapes vibration and, consequently, auditory signal transmission. Experimental research plays a crucial role in validating the numerical models. The study employs human temporal bones to examine middle ear vibrations under different excitation conditions. Bistability emerges in implanted middle ear models, indicating that multiple stable states of vibration can exist within the system. This finding has significant implications for the design and optimization of middle ear implants, as bistability can lead to variations in auditory perception. The dissertation further explores the effects of double excitation, wherein the implanted middle ear receives stimulation both from the eardrum and from the mechanical input of the FMT. Numerical simulations indicate that double excitation leads to complex vibrational interactions, with significant implications for implant performance. Additionally, time delay in the implant’s electrical processing introduces phase shifts that alter stapes footplate vibration. These results highlight the importance of accounting for double excitation and time delay effects when designing middle ear prostheses. Key findings from the study include: 1. Relaxation Effects: The viscoelastic properties of ligaments and tendons significantly influence sound transmission, with time-dependent elasticity affecting ossicular chain dynamics. 2. Bistability in Implants: The nonlinear mechanical behavior of FMTs introduces bistable states, which must be carefully managed to optimize implant performance. 3. Double Excitation and Time Delay: The interaction between natural sound conduction and implant-generated mechanical input creates complex vibrational patterns, requiring careful calibration of implant signal processing. The study makes several contributions to the field of auditory biomechanics. First, it extends existing middle ear models by incorporating ligament relaxation effects, providing a more accurate representation of physiological behavior. Second, it identifies bistability as a critical factor in middle ear implants, emphasizing the need for further research into nonlinear vibrational dynamics. Third, it highlights the significance of double excitation and time delay effects, offering practical insights for improving implant design and auditory prostheses. In conclusion, this dissertation advances the understanding of human middle ear mechanics through a combination of experimental and computational approaches. By integrating viscoelastic models, nonlinear dynamics, and implant signal processing considerations, the study provides a comprehensive framework for analyzing middle ear function in both natural and surgically altered states. These findings have far-reaching implications for the diagnosis, treatment, and rehabilitation of hearing disorders, contributing to the development of more effective middle ear implants and auditory prostheses. Future research should further refine these models by incorporating three-dimensional finite element simulations and expanding experimental studies to include a broader range of middle ear conditions. Through continued innovation in middle ear modeling, the field of auditory biomechanics can move closer to developing optimal solutions for individuals with hearing impairments. Additionally, expanding the research into real-world clinical applications can pave the way for improved auditory prosthetic devices, including next-generation cochlear implants and middle ear implants that account for personalized anatomical variations. The integration of machine learning and artificial intelligence in computational modeling may further enhance predictive accuracy, enabling medical professionals to tailor interventions with unprecedented precision. The significance of this research extends beyond the laboratory, offering potential breakthroughs in audiology, otolaryngology, and biomedical engineering. By fostering interdisciplinary collaboration, this study serves as a foundation for future advancements in auditory science, ultimately improving the quality of life for millions of individuals affected by hearing impairments worldwide. Further exploration of bio-compatible materials and real-time adaptive prosthetics could revolutionize hearing aid technology, leading to more responsive and natural auditory experiences for users. These advancements will be pivotal in bridging the gap between theoretical research and practical implementation, ensuring that cutting-edge developments reach those in need effectively and efficiently.
