Ce travail de thèse adresse les phénomènes en jeux dans les interfaces tactiles par ondes de Lamb avec, d’une part, l’influence des perturbations engendrées par les touchers d’utilisateurs et, d’autre part, l’influence des conditions environnementales sur les matériaux et l’algorithme de localisation.Dans une première partie, des mesures expérimentales du comportement viscoélastique de l’index ont été réalisées et relient l’effort et l’angle d’appui à la superficie de contact elliptique par une loi en puissance. Les impédances acoustiques caractéristiques du doigt et de divers matériaux ont été mesurées pour les ondes longitudinales et transversales. Ces paramètres sont représentatifs de la capacité à perturber la propagation d’ondes dans une cavité acoustique. En s’appuyant sur ces résultats, un doigt artificiel a été conçu, permettant des mesures automatisées ou des calibrations répétables de surfaces tactiles.Dans une seconde partie, l’influence des conditions de température et d’humidité relative sur les propriétés mécaniques a été étudiée par l’analyse des vitesses et des atténuations des ondes de volumes dans deux thermoplastiques différents. Alors que l’ABS injecté présente des vitesses de propagation linéairement dépendantes avec la température, elles ont une dépendance quadratique dans le cas d’un polyamide fritté. La sensibilité des ondes de Lamb aux conditions climatiques est estimée à partir des propriétés des matériaux et permet de déduire les modifications des spectres de réponse d’un toucher sur une coque, autorisant une compensation de l’algorithme de localisation. Enfin, différentes pistes d’amélioration du contrôle des ondes guidées et de l’algorithme sont proposées en s’appuyant sur l’utilisation de matériaux viscoélastiques et de représentations temps-fréquence. / This work addresses the phenomena taking place in Lamb wave tactile interfaces by studying the perturbation due to a user touch, and the influence of environmental conditions on materials and localization algorithm.In the first part, viscoelastic measurements of the index finger show a power law relation between force, angle and elliptic area of the contact. The acoustic impedances of index finger and different materials have been measured for longitudinal and transversal waves. These parameters are representatives of the ability to perturb the propagation of waves in the acoustic cavity. From these results, an artificial finger has been designed and allows automated measurements and repeatable calibration of tactile surfaces to be carried out.In the second part, the influence of temperature and humidity on mechanical properties is investigated by analyzing velocities and attenuations of bulk waves in two different thermoplastics. While velocities are linearly dependent on temperature for injected ABS, they are quadratically dependent for the sintered polyamide. Sensibility of Lamb waves to the environmental conditions is estimated with material properties and allows the modifications of the spectral response of a touch to be calculated. That enables compensations in the localization algorithm.Finally, various improvements in the control of guided waves and localization algorithm are proposed. They rely on viscoelastic materials and time-frequency representations.

<div>Global warming is considered to result from excessive emission of CO₂ caused by human activity. The security of long term CO₂ capture and sequestration on the subsurface depends on the integrity of caprocks. Natural and engineered subsurface activities can generate fractures in caprocks that can lead to CO₂ leakage. Reactive fluids that flow through a fracture may seal a fracture through mineral precipitation or open a fracture through dissolution. It is extremely useful to CO₂ storage to understand the behavior of reactive fluids that generates mineral precipitation that can seal a fracture. Experiments on non-reactive and reactive fluid mixing were performed to explore gravity-driven chemical dynamics that control the mixing and spatial distribution of mineral precipitates. Fracture inclination, fracture apertures, fluid pumping rates, and density contrasts between fluids were studied for their effects on fluid mixing. From non-reactive fluid mixing experiments, a less dense fluid was found to be confined to a narrow path (runlet) by the denser fluid under the influence of gravity. Fracture inclination angle affected the shape of the less dense fluid runlet. As the angle of inclination decreased, the area of the less dense runlet increased. Improved mixing and a potentially larger area of precipitation formation will occur during reactive fluid mixing when the fracture plane is perpendicular to gravity. Fracture aperture affected the time evolution of the mixing of the fluids, while pumping rate affected fluid mixing by controlling the relative velocities between the two fluids. The fact that the spatial distribution of the two fluids, instead of the fracture roughness, dominated the fluid mixing sheds light on the potential behaviors of reactive fluids mixing in fractures. The location for the majority of precipitation formation and the transport of precipitates can be accordingly predicted from knowledge of the properties of the two reactive fluids and the orientation of the fracture.</div><div>From a small study on wave propagation across fractures with precipitates, simulation results showed that the impedance difference between the matrix material and the precipitate affects the transmitted signal amplitude. Both the aperture and fraction of aperture filled with precipitates affect signal amplitude.</div><div><br></div>

<p>Proton beam therapy has shown great promise for cancer treatment due to its high precision in irradiating tumor volumes. However, due to the massive size and expense of the cyclotrons/synchrotrons needed to accelerate the protons, the widespread use of proton therapy is limited. Laser plasma accelerated (LPA) proton beams may be a potential alternative to conventional proton beams: by shooting an ultraintense, ultrashort pulsed laser at a thin target, a plasma sheath electric field may be formed with the capability of accelerating protons to potentially therapeutic energies in very short distances. In addition to accessibility, there is significant uncertainty in proton range in heterogeneous tissues. Thermoacoustic computed tomographic (TACT) imaging has the potential to provide <em>in vivo</em> dose imaging and range verification to address these uncertainties. TACT measures thermoacoustic waves generated from the absorbed dose and implements a 3D filtered backprojection to reconstruct volumetric images of the dose. The purpose of this thesis is to determine the feasibility of integrating LPA proton beams with thermoacoustic imaging into a novel image-guided small animal therapy platform as an early step towards clinical  translation to address the issues of accessibility and dosimetric spatial uncertainty. A Monte Carlo (MC) method is used to simulate an LPA proton beam with characteristics based on literature, thermoacoustic waves are simulated on a voxel-wise basis of the MC dose, and 3D filtered backprojection is used to reconstruct a volumetric image of the dose. In Specific Aim 1, the dependence of image accuracy on transducer array angular coverage is investigated; in Specific Aim 2, an iterative reconstruction algorithm is implemented to improve image accuracy through increased sampling of projection space when transducer array angular coverage is insufficient; and in Specific Aim 3, the detector sensitivity to dose is determined for several therapeutic endpoints. The work presented in this thesis not only demonstrates the feasibility of integrating LPA and thermoacoustic technologies but necessary design changes to realize a functional small animal platform.</p>

Small-signal moving-coil loudspeaker driver parameters are traditionally derived through electrical impedance measurement techniques. These parameters are commonly called Thiele/Small parameters, after Neville Thiele and Richard Small who are credited with developing industry-standard loudspeaker modeling techniques. However, because loudspeaker drivers are electro-mechano-acoustical transducers, it should be possible to measure their parameters in physical domains other than the electrical domain. A method of measuring loudspeaker parameters from the acoustical domain will be developed. The technique uses a plane wave tube to measure acoustical properties of a baffled driver under test. Quantities such as the transmission loss through the driver are measured for a driver placed in the tube using the two-microphone transfer-function technique. Models have been developed to curve fit the resulting data, from which small-signal loudspeaker parameters are subsequently derived. This thesis discusses the acoustical measurement theory, apparatus, and system modeling methods (via equivalent circuits). It also compares measured parameters to those derived using electrical techniques. Parameters derived from both approaches are compared with reference values to establish bias errors. Sequential measurements are also compared to reveal random errors in the derivation processes.

Near-field acoustical holography (NAH) has been used extensively for acoustical imaging of infinitesimal-amplitude (or small-amplitude) sources. However, recent interests are in the application of NAH to image finite-amplitude (or high-amplitude) sources such as jets and rockets. Since NAH is based on linear equations and finite-amplitude sources imply nonlinear effects, which cause shock formation and consequently an altered spectral shape, a feasibility study is carried out to determine the effect of nonlinear propagation on NAH. Jet and rocket sources typically have a distinct spectral shape resembling a ‘haystack’ and center frequencies varying from 30 to 300 Hz. To test the effect of nonlinear propagation on jet or rocket noise, several waveforms with varying spectral shapes and center frequencies were created and numerically propagated in one dimension using a nonlinear propagation algorithm. Bispectral methods were used to determine the amount and effect of nonlinearity, showing that higher center frequencies lead to more nonlinearities for a given amplitude. Also, higher-order statistical analysis of the time derivative of the waveforms was used to determine information about the relative amount of waveform steepening and shock coalescence occurring. NAH was then used to reconstruct the original waveform magnitude and the errors were determined. It was found that the ‘haystack’ spectral shape can be preserved by the nonlinear effects leading to low amplitude-reconstruction errors, whereas a narrow-band spectral shape will become altered and reconstruct very poorly. However, if nonlinear effects become strong due to higher center frequencies, longer propagation distances or higher amplitudes, even the ‘haystack’ shape will become altered enough to cause poor reconstruction. Two-dimensional propagation studies were also performed from two point sources, showing differences between linear and nonlinear propagation.

<p>The capability of manipulation of the flow of mechanical energy in the form of mechanical waves (including acoustic and elastic waves) has always been a challenge and a critical part in various areas of engineering. The recent advances in topological acoustic/elastic metamaterials certainly open a new pathway to the manipulation of mechanical waves, especially for the novel scattering-immune wave-guiding capability, even in the presence of defects, disorders or sharp bends along the waveguide. In this Dissertation, the theoretical background and experimental evidence of various types of elastic-wave topological metamaterials including analogues to 2D quantum valley Hall effect (QVHE) materials, 2D quantum spin Hall effect (QSHE) topological insulators are presented. First, the formulation the elastic-wave analogue to QVHE materials in a general continuous elastic phononic structure (not limited to local resonant lattices, filling the gap in the literature) is proposed, and a strategy using pressurized cells to actively control the phononic lattice is presented. By finite prestrain and geometric nonlinear effect, the space inversion symmetry of the original hexagonal lattice is broken, resulting in distinct QVHE phases (characterized by valley Chern numbers) in lattice domains with opposite pressurization. With such mechanism, the edge-state path, i.e., the domain wall connecting lattices with distinct QVHE phases, can be real-time configured. Further more, edge states with tunable frequency-wavenumber dispersion can be created at the external boundaries of the lattice by appropriate pressurization of the outermost cells. An aluminum reticular sheet built with water-jet cutting is machined in the pre-deformed pattern with a Z-shape domain wall at the center, which spatially divides the sheet into two domains with opposite QVHE phases. Using piezoelectric transducers and laser Doppler vibrometry, the measured harmonic and transient responses confirm the back-scattering-immunity of the topological edge states, and the frequency-wavenumber dispersion matches the numerical prediction. A strategy is proposed for unidirectionally generating edge states along the domain wall using two off-phase transducers, which is also experimentally demonstrated. For elastic-wave analogue to QSHE topological insulators, we focus on the ``zone-folding'' method and propose a honeycomb 2D elastic beam network with periodically altered thickness with a generalized Kekule distortion pattern. Such framework provides a parametric space with exhaustive control in the topological phase diagram of waves in the lattice compared to earlier works in the literature. The effective Hamiltonian as well as the characterized topological phase are gauge dependent, particularly they change with different reference frames. This lead to ambiguity in the topological phase of such phononic crystal. Based on this argument, it is predicted that edge states could exist at a dislocation interface connecting two piece of phononic structures of the same pattern with relative displacement. Following the same idea, but considering the available fabrication options, a phononic plate with honeycomb groove pattern engraved on both sides is built, which the depth varied according to the Kekule pattern. With proper tuning of the parameters, it realizes an analogue to the QSHE topological insulator. With <em>ab initio</em> calculation of the Berry curvature (without involving any approximations such as the perturbative approach), a new topological invariant <em>local topological charge</em> is defined and evaluated as the counterpart of the Z₂ invariant in the classical-wave-zone-folding analogue. The local topological charge has intrinsic ambiguity and its value depends on the selected reference frame. However, its <em>change </em>according to changes in the parameters, under a consistent reference frame, is well-defined. Given the fact that shifting the reference frame by certain fractions of a lattice constant was equivalent to changing one of the parameters by a certain amount, it also lead to a well-defined change in the local topological charge, which indicates topological phase transition, and one can predict the existence of edge states at the displacement-dislocation interface between two neighboring lattices having the same pattern up to a rigid-body shifting. The phononic plate is machined by a CNC mill, and the experiment is carried out using piezoelectric transducers and laser Doppler vibrometry, which confirms the existence and robustness of the topological edge states at such dislocation interface connecting identical pattern, which was unprecedented in both quantum and classical systems. The final part of this Dissertation focuses on creating classical mechanical analogues to the 1D Kitaev superconducting model and Majorana-like bound states aimed at future acoustic-wave based computation.</p>

State and federal agencies spend considerable time and resources to enhance and create habitat for wildlife. Understanding how target and non-target species respond to these efforts can help direct the allocation of limited conservation resources. However, monitoring species response to habitat management comes with several logistical challenges that are exacerbated as the area of geographic focus increases. I used autonomous recording units (ARUs) to mitigate these challenges when assessing Eastern Whip-poor-will (Antrostomus vociferus) response to forest management. I deployed 1,265 ARUs across managed and unmanaged public and private forests from western North Carolina to southern Maine. I then applied a machine learned classifier to all recordings to create whip-poor-will daily detection histories for each survey location. I used detection data and generalized linear models to examine regional, landscape, and site factors that influenced whip-poor-will occurrence. Whip-poor-wills were detected at 399 (35%) survey locations. At the regional scale, occupancy decreased with latitude and elevation. At the landscape scale, occupancy was negatively associated with the amount of impervious cover within 500m, and was positively associated with the amount of oak forest and evergreen forest cover within 1,750m. Additionally, whip-poor-will occupancy exhibited a quadratic relationship with the amount of shrub/scrub cover within 1,500m. At the site-level, occupancy was negatively associated with increased basal area and exhibited a quadratic relationship with woody stem density. Whip-poor-will populations can benefit from the implementation of forestry practices that create and sustain early successional forests within forested landscapes, especially those dominated by oak forest types. The use of ARUs helped overcome several challenges associated with intensive broad-scale monitoring efforts for a species with a limited survey window, but also presented new challenges associated with data management, storage, and analyses.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Cette thèse a pour but d‘estimer la position et la puissance de sources sonores ponctuelles à l'aide d‘une antenne acoustique. Nous nous intéressons d‘abord à la directivité des antennes acoustiques pondérées. On montre qu‘une telle antenne, appelée antenne conventionnelle, même si elle est à directivité optimale, est inutilisable pour localiser plusieurs sources sonores. Des traitements adaptatifs d‘antenne sont donc exigés et les méthodes dites à haute résolution sont introduites. Elles sont basées sur l‘estimation de la matrice de covariance des signaux issus des capteurs et présentent l‘avantage de s‘affranchir des limitations naturelles du traitement d‘antenne conventionnel. Cependant, ces méthodes nécessitent l‘emploi d‘un modèle de propagation et sont donc par nature peu robustes aux erreurs de modèle, ce qui peut être parfois un handicap et dégrader leurs performances. Par la suite, nous présentons une nouvelle méthode de séparation des sources utilisant une représentation parcimonieuse des signaux. Nous montrons que ses performances sont meilleures que celles obtenues par les méthodes à haute résolution et notre algorithme parvient à une bonne résolution spatiale, même sous des conditions défavorables. Cette méthode est appliquée aux sources corrélées et décorrélées, à bande étroite et à large bande, en champ proche et en champ lointain. Pour finir, nous présentons des méthodes pour estimer la puissance des sources sonores. Des simulations numériques et des expérimentations en chambre anéchoïque sont effectuées afin de vérifier et de valider les analyses et les résultats théoriques / This thesis concerns the problem of sensor array source localization and power estimation by an acoustical array of sensors. In first the acoustical array directivity is treated. It is shown that such array is not useful for the localization of multiple sources. Adaptive arrays and high resolution methods are then introduced. They are based on the estimation of the sensor output covariance matrix and their performances overcome the natural limitations of the weighted beamforming processing. However, these methods require the use of a propagation model and are not robust to model errors. We present a new method which is an application of sparse regularization methodology to acoustical source localization using an acoustical array. Its performances are better than high-resolution methods and this method works very well in the case of correlated or uncorrelated signals, narrow band or wideband signals, near field or far field environments. Finally, a power estimation of sound sources by an acoustical array is presented. Numerical and experimental results in an anechoic room are presented showing the effectiveness of theoretical results

Finite amplitude perturbations in compressible media are ubiquitous in scientific and engineering applications such as gas-turbine engines, rocket propulsion systems, combustion instabilities, inhomogeneous solids, and traffic flow prediction models, to name a few. Small amplitude waves in compressible fluids propagate as sound and are very well described by linear theory. On the other hand, the theory of nonlinear acoustics, concerning high-amplitude wave propagation (Mach<2) is relatively underdeveloped. Most of the theoretical development in nonlinear acoustics has focused on wave steepening and has been centered around the Burgers' equation, which can be extended to nonlinear acoustics only for purely one-way traveling waves. In this dissertation, theoretical and computational developments are discussed with the objective of advancing the multi-fidelity modeling of nonlinear acoustics, ranging from quasi one-dimensional high-amplitude waves to combustion-induced detonation waves. <br> <br> We begin with the theoretical study of spectral energy cascade due to the propagation of high amplitude sound in the absence of thermal sources. To this end, a first-principles-based system of governing equations, correct up to second order in perturbation variables is derived. The exact energy corollary of such second-order system of equations is then formulated and used to elucidate the spectral energy dynamics of nonlinear acoustic waves. We then extend this analysis to thermoacoustically unstable waves -- i.e. amplified as a result of thermoacoustic instability. We drive such instability up until the generation of shock waves. We further study the nonlinear wave propagation in geometrically complex case of waves induced by the spark plasma between the electrodes. This case adds the geometrical complexity of a curved, three-dimensional shock, yielding vorticity production due to baroclinic torque. Finally, detonation waves are simulated by using a low-order approach, in a periodic setup subjected to high pressure inlet and exhaust of combustible gaseous mixture. An order adaptive fully compressible and unstructured Navier Stokes solver is currently under development to enable higher fidelity studies of both the spark plasma and detonation wave problem in the future. <br>