Time Domain Computation of a Nonlinear Nonlocal Cochlear Model with Applications to Multitone Interaction in Hearing

A nonlinear nonlocal cochlear model of the transmission line type is studied in order to capture the multitone interactions and resulting tonal suppression effects. The model can serve as a module for voice signal processing, it is a one dimensional (in space) damped dispersive nonlinear PDE based on mechanics and phenomenology of hearing. It describes the motion of basilar membrane (BM) in the cochlea driven by input pressure waves. Both elastic damping and selective longitudinal fluid damping are present. The former is nonlinear and nonlocal in BM displacement, and plays a key role in capturing tonal interactions. The latter is active only near the exit boundary (helicotrema), and is built in to damp out the remaining long waves. The initial boundary value problem is numerically solved with a semi-implicit second order finite difference method. Solutions reach a multi-frequency quasi-steady state. Numerical results are shown on two tone suppression from both high-frequency and low-frequency sides, consistent with known behavior of two tone suppression. Suppression effects among three tones are demonstrated by showing how the response magnitudes of the fixed two tones are reduced as we vary the third tone in frequency and amplitude. We observe qualitative agreement of our model solutions with existing cat auditory neural data. The model is thus simple and efficient as a processing tool for voice signals.Comment: 23 pages,7 figures; added reference

Numerical Analysis of a Nonlinear Mechanical-Electrical-Acoustical Model of the Cochlea

The overarching goal of my research project is to develop a computational model of the mammalian auditory system and compare the results with the experimental data. This model describes the response of the cochlea to both external acoustic and internal electrical stimulations. The cochlea is the spiral-shaped part of the inner ear where the fluid-borne vibrations are detected by the auditory sensors and then the information, in the form of neural signals, are transferred to the brain by the auditory nerves. The cochlear model will enhance our understanding of failure mechanisms in the cochlea, answering important questions as to the morphological elements of the cochlea that fail and why. A mathematical model of the cochlear response to sound over the entire spectrum will help us understand how important classes of signals are processed in the cochlea (such as speech and music) which can lead to better speech processing algorithms or cochlear implant electrical stimulation paradigms. One important question of biophysics of the cochlea is the underlying mechanism of the cochlear active process which enables sound processing over a broad range of frequencies and intensities. Two mechanisms are hypothesized as the main active processes: outer hair cell (OHC) somatic electromotility and hair bundle (HB) motility. The proposed active mechanisms are implemented into our model and their relative contribution on the cochlear nonlinear amplifier is investigated. It is shown that somatic based activity plays a fundamental role in amplification while the HB motility contribution remains elusive. Two distinct mechanisms are identified through which the HB activity affects the cochlear dynamics. The extracellular voltage is shown to undergo a phase shift at frequencies slightly below the peak, that coincides with the onset of the nonlinear amplification. It is hypothesized that this phase difference between the electrical and mechanical responses gives rise to effective power generation of the OHC somatic force. A three-dimensional model of the cochlea is utilized along with experimental data and it is shown that the electro-mechanical phase transition, generated by the tectorial membrane (TM) shear mechanics, activates the cochlear nonlinear amplifier. The cochlear computational model is also used to simulate a series of active in vitro experiments and interpret the results. It is shown that our model of the electrical, mechanical, and acoustical conditions of the experimental configuration is able to replicate the important findings of the experiments while our interpretation of the results contradicts conclusion of the experiments. It is shown that the OHC somatic electromotility, rather that HB motility, is sufficient to predict the nonlinearities observed in the experiments.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144086/1/nankali_1.pd

Design of Bio-Inspired Multifrequency Acoustic Sensors and Metamaterial Energy Harvesting Smart Structures

Due to the limited availability and high depletion rates of nonrenewable sources of energy as well as environmental concerns, the scientific community has started to explore many alternative clean sources of energies. It is identified that civil, mechanical and Aerospace structures are always subjected to acoustic noises and vibration which could potentially be used as renewable source of energy. Roads and Industrial noise barriers are used inside industrial facilities alongside the walls, around construction pillars, nearby machinery and other equipment to separate quite work zones, protect walls, deliver extra safety and precautions while diminish sound and vibrational pressure. We hypothesized if these noise barriers/structures could serve dual purposes, while harvest energies from the filtered noises and vibrations, significant energies could be renewed. Such renewable energies could be then used for different purposes, like charging cell phones, wearable devices, powering small electronics and remote sensors etc. Additionally, due to gravity, it is natural that our heavy mechanical equipment runs, operates, walks on the ground which are covered by cosmetic materials. Such materials encounter continuously changing pressure on the surface which is otherwise waisted if not harvested. Keeping these applications in mind for walls/ barriers/ tiles, oin this dissertation, utilizing one unique physics, two different type of renewable energy harvesting technologies are proposed. While proposing the application of harvesting and noise filtering, similar physics/mechanics prevalent in cochlea of human inner ear, further motivated this dissertation to device bio-inspired acoustic bandpass sensor. The harvesting and sensing devices that are conceptualized, analytically modeled, numerically simulated via COMSOL Multiphysics software, optimized, fabricated and tested to present the proof of concept are presented below. All models are numerically 1) A novel three-dimensional piezoelectric energy harvester based on a metamaterial structure is proposed, which is capable of scavenging energy at very low frequencies (\u3c~1kHz) from multi-axial ambient vibrations. The proposed structure and its unit cell exploit the negative mass at local resonance frequencies and entraps the vibration energy as dynamic strain. The captured kinetic energy is then transformed to electric potential using three Lead Zirconate Titanate wafers, optimally embedded in the cell\u27s soft constituent. 2) In the second design, a multi-frequency vibration-based energy harvester unit cell which is inspired from the design of human inner-ear, i.e. a snail-shaped model to enhance differential shear deformation of a membrane is proposed. Next an array of the proposed cell in the form of metamaterial bricks in a wall or a metamaterial tiles on the ground (Meta-tile) are modeled and fabricated to experimentally validated the concept. A spiral snail shaped PVDF membrane is embedded inside a Polydimethylsiloxane (PDMS) matrix that entraps the kinetic energy of the vibration within its structure. Numerical and experimental studies show that the unit cell and the Meta-tiles can harvest electrical power of up to ~1.8 mW and 11 mW against a 10KΩ resistive load, respectively. 3) Concurrent to the development of electronic processing of frequencies, mechanical sensors capable of selecting, processing, filtering specific single or a distinct band of frequencies are contributing an essential role in many sciences, technologies and industrial applications. After developing the energy harvester devices, the next objective of this PhD dissertation is to present a scalable numerical model along with a fabricated proof of concept of a bio-inspired acoustic bandpass sensor with a user-defined range of frequencies. In the proposed sensor, the geometric structure of a human’s basilar membrane is adopted as the main model to capture the sonic waves with a target frequency ranges. Human’s basilar membrane in the inner ear could be investigated in two ways, a) plate type and b) beam type. Both models are numerically and experimentally validated. In the first step, a predictive mathematical model of the proposed bandpass sensor is developed based on a plate type model. Next, the dynamic behavior of beam-type basilar membrane with 100 Zinc-Oxide electrodes is modeled and numerically verified. A sensor array is fabricated with using photolithography techniques with Polyvinylidene Difluoride (PVDF) piezoelectric material as a proof-of-concept. The fabricated plate-type sensor is experimentally tested, and its effective performance is validated in the frequency range of ~3 kHz-8 kHz. Similarly, in beam model the longest electrode is near the Apex region (8 mm x 300 μm x 20 μm thick) and the shortest electrode is near the Base side of the sensor with (3 mm x 300 μm x 110 μm thick) are proposed. Eventually, the effective performances of the proposed acoustic sensors are verified using COMSOL Multiphysics Software and the functionality of the proposed sensor appeared in the frequency range of ~ 0.5 kHz near Apex and to ~ 20 kHz near base side. To run all the required experiments on the fabricated energy harvesters and acoustic sensors in this dissertation, a novel three-dimensional exciter is developed as a miscellaneous work. A high percentage of failures in sensors and devices employed in harsh industrial environments and airborne electronics is due to mechanical vibrations and shocks. Therefore, it is important to test the equipment reliability and ensure its survival in long missions in the presence of physical fluctuations. Traditional vibration testbeds employ unidirectional acoustic or mechanical excitations. However, in reality, equipment may encounter uncoupled (unidirectional) and/or coupled (multidirectional) loading conditions during operation. Hence, to systematically characterize and fully understand the proposed energy harvesters’ and acoustic sensors’ behaviors, a testbed capable of simulating a wide variety of vibration conditions is required which is designed, and fabricated. The developed testbed is an acousto electrodynamic three-dimensional (3-D) vibration exciter (AEVE 3-D), which simulates coupled and decoupled (with unpowered arms) 3-D acoustic and/or 3-D mechanical vibration environments. AEVE 3-D consists of three electromagnetic shakers (for mechanical excitation) and three loudspeakers (for acoustic excitation) as well as a main control unit that accurately calculates and sets the actuators\u27 input signals in order to generate optimal coupled and decoupled vibrations at desired frequencies. In this paper, the system\u27s architecture, its mechanical structure, and electrical components are described. In addition, to verify AEVE 3-D\u27s performance, various experiments are carried out using a 3-D piezoelectric energy harvester and a custom-made piezoelectric beam

Cochlear models

The intention of the research activity described in this thesis is to contribute to the dynamical theory of the cochlea of the human inner ear. The Science of Hearing, being disseminated in a wide range of frequently independent or unco-ordinated disciplines, is advancing far in the fields of subjective human acoustics, middle ear restorative surgery, medical diagnostic electro-encephalography and cochlear-nucleus-to-thalamus neural communications research. At the same time, exploitation, in auditory research, of the techniques and resources of modern engineering science, which may be particularly appropriately applied to analyses of the peripheral hearing system, has not been manifest to any great degree. It was therefore hoped that a first-principles engineering approach to the subject of cochlear action would demonstrate the need for a mathematical and quantitative type of analysis of the response of this key organ of hearing and also indicate the extent to which cochlear science is at present to be found in a state of disarray. The writer's principal thesis is that a considerably greater potential for discrimination of the frequencies and intensities of pure and complex tones is attributable to the mechanical action of the cochlea than is generally supposed. That thesis will be more fully proven (it is expected) when current research is considerably extended and improved to permit the computation of spatial arrays of cochlear hair cell cilia shearing force patterns and electrical responses. The studies reported herein are relevant and fundamental to this aim and are limited to considerations of the dynamical response of the cochlear partition as a whole. This research has included approximately equal parts of review, physical cochlear model experimentation and mathematical analysis. The first two chapters end sections of most of the other chapters concentrate on defining the system and reviewing the literature. Chapters 3 and 4 estimate the order and ranges of the physical properties of mass and stiffness of the scala media (or cochlear partition), these properties being essential to the subsequent design of both physical and mathematical models of the cochlea in Chapters 5 and 6 respectively. The final chapter adds to the comments in other chapters on the credibility of the physical constants previously deduced in the thesis and tested in the models, the performance of the models, the particular problems clearly requiring further research effort and the relevance of the work to a more complete comprehension of human auditory theory

Frequency Selectivity of Synaptic Exocytosis in Hair Cells of the Bullfrog\u27s Amphibian Papilla

Auditory organs act as spectral analyzers by decomposing acoustic stimuli into their frequency constituents. Individual auditory afferent neurons of the VIIIth cranial nerve respond best to a particular frequency of stimulation, and are thus frequency-tuned. Much of the tuning in the inner ears of mammals is ascribed to the frequency dependence of the traveling waves on the basilar membrane, the flexible structure that houses hair cells, the auditory receptors. However, in non-mammalian vertebrates, the basilar membrane does not conduct a traveling wave. In some animals, the membrane is absent entirely. Yet auditory fibers from these animals display comparable sharpness of tuning. Though other tuning mechanisms have been characterized in these animals, they do not account for the observed sharpness found in auditory-nerve recordings. Hence, we explored the frequency response of the hair cell’s synapse in the bullfrog’s amphibian papilla, an auditory organ that lacks a basilar membrane. We monitored the synaptic output of hair cells by measuring changes in their membrane capacitance in response to sinusoidal electrical stimulation. Using perforated-patch recordings, we found that individual hair cells display frequency selectivity in synaptic exocytosis over the range of frequencies sensed by the organ. Moreover, this tuning varies from cell to cell in accordance with the cells’ tonotopic position. Using confocal imaging, we determined that hair cells tuned to high frequencies have a greater expression of the Ca 2+ buffers parvalbumin 3 and calbindin-D28k than those tuned to low frequencies. We then used an extension of an existing model for synaptic release to explore how this gradient might influence the frequency response of the synapse. Increasing buffer concentration in the absence of other changes quenches free Ca 2+ and thereby reduces the synaptic output. However, adjusting just one other release rate in conjunction could keep the system poised near a Hopf bifurcation, thereby keeping the system tuned with exquisite sensitivity to small stimuli at a particular frequency. Furthermore, the frequency range afforded by the model matched the hearing range of the organ. Thus, hair cells of the bullfrog’s amphibian papilla use synaptic tuning as an additional mechanism by which to sharpen their frequency selectivity, and a conspicuous gradient in Ca 2+ buffering may help to keep the system poised near maximal sensitivity

Bio-Inspired Compressive Sensing based on Auditory Neural Circuits for Real-time Monitoring and Control of Civil Structures using Resource Constrained Sensor Networks.

Recent natural hazard disasters including Hurricane Sandy (2012) and the Tohoku Earthquake (2011) have called public attention to the vulnerability of civil infrastructure systems. To enhance the resiliency of urban communities, arrays of wireless sensors and actuators have been proposed to monitor and control infrastructure systems in order to limit damage, speed emergency response, and make post-disaster decisions more efficiently. While great advances in the use of wireless sensor networks (WSNs) for the purposes of monitoring and control of civil infrastructure have been made, significant technological barriers have hindered their ability to be reliably used in the field for long durations. Some of these limitations include: reliance on finite, portable power supplies, limited radio bandwidth for data communication, and limited computational capacity. To resolve current bottlenecks, paradigm-altering approaches to the design of wireless monitoring and control systems are required. Through the process of evolution, biological central nervous systems (CNS) have evolved into highly adaptive and robust systems whose sensing and actuation capabilities far surpass the current capabilities of engineered (i.e., man-made) monitoring and control systems. In this dissertation, the mechanisms employed by biological sensory systems serve as sources of inspiration for overcoming the current challenges faced by wireless nodes for structural monitoring and control. The basic, yet elegant, methods of signal processing and data transmission used by the CNS are mimicked in this thesis to enable highly compressed communication with real-time data processing for WSNs engaged in infrastructure monitoring. Specifically, the parallelized time-frequency decomposition of the mammalian cochlea is studied, modeled, and recreated in an ultra-low power analog circuit. In lieu of transmitting data, the cochlea-inspired wireless sensors emulate the neurons by encoding filtered outputs into binary electrical spike trains for highly efficient wireless transmission. These transmitted spike train signals are processed for pattern classification of sensor data to identify structural damage and to perform feedback control in real-time. A key contribution of this thesis is the development and experimental validation of a bio-inspired wireless sensor node that exhibits large energy savings while employing real-time processing techniques, thus overcoming many of the current challenges of traditional wireless sensor nodes.PHDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107302/1/cpeckens_1.pd