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Malyarenko, Eugene V. "Lamb wave diffraction tomography." W&M ScholarWorks, 2000. https://scholarworks.wm.edu/etd/1539623991.
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As the worldwide aviation fleet continues to age, methods for accurately predicting the presence of structural flaws, such as hidden corrosion and disbonds, that compromise air worthiness become increasingly necessary. Ultrasonic guided waves, Lamb waves, allow large sections of aircraft structures to be rapidly inspected. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. In addition, human inspection process tends to be highly subjective, slow and prone to errors. The only practical alternative to traditional inspection routine is a software expert system capable of interpreting data with minimum error and maximum speed and reliability. Such a system would use the laws of guided wave propagation and material parameters to help signal processing algorithms automatically extract information from digitized waveforms. This work discusses several practical approaches to building such an expert system.;The next step in the inspection process is data interpretation, and imaging is the most natural way to represent two-dimensional structures. Unlike conventional ultrasonic C-scan imaging that requires access to the whole inspected area, tomographic algorithms work with data collected over the perimeter of the sample. Combined with the ability of Lamb waves to travel over large distances, tomography becomes the method of choice for solving NDE problems. This work explores different tomographic reconstruction techniques to graphically represent the Lamb wave data in quantitative maps that can be easily interpreted by technicians. Because the velocity of Lamb waves depends on the thickness, the traveltimes of the fundamental modes can be converted into a thickness map of the inspected region. Lamb waves cannot penetrate through holes and other strongly scattering defects and the assumption of straight wave paths, essential for many tomographic algorithms, fails. Diffraction tomography is a way to incorporate scattering effects into tomographic algorithms in order to improve image quality and resolution. This work describes the iterative reconstruction procedure developed for the Lamb Wave tomography and allowing for ray bending correction for imaging of moderately scattering objects.
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Shi, Yijun 1970. "Analysis of optimum Lamb wave tuning." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8296.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2002.Includes bibliographical references (p. 243-251).
Guided waves are of enormous interest in the nondestructive evaluation of thin-walled structures and layered media. Due to their dispersive and multi-modal nature, it is desirable to tune the waves by discriminating one mode from the others. The objectives of this thesis are (1) to develop schemes and procedures for Lamb wave tuning, (2) to develop tools for understanding and analyzing the mechanism of various tuning techniques, and (3) to provide suggestions and guidelines for selecting optimum tuning parameters. In order to remedy the inherent problems of traditional tuning techniques using angle wedge and comb transducers (such as the inability to tune the modes with low phase velocities, and the inability to control the propagation direction of tuned waves), a novel dynamic phase tuning concept using phased arrays is proposed. In this approach, the constructive interference of desired modes is achieved by properly adjusting the time delays. As an extension to this concept, the synthetic phase tuning (SPT) scheme is introduced, in which the tuning effect is achieved by constructing virtual waves. The effectiveness of SPT against other techniques is experimentally demonstrated, which shows its feasibility. To understand the mechanism of tuning, an analytical model is developed to study transient waves, based on the Fourier integral transform method. The excitation conditions for both angle wedge and array transducers are taken into account. The surface displacements of individual modes and their temporal and spatial Fourier spectrum are derived and used to study the tuning behavior. The analytical results are compared with the experimental results as well as the numerical results obtained from the finite element simulation studies.
(cont.) In dealing with broadband signals, laser generated Lamb waves are investigated. Both line and circular source loading models are developed to study the behavior in the ablation regime. The predicted waveforms and dispersion curves are in good agreement with the experimental results. Based on the same SPT scheme, virtually-tuned waves are constructed by processing a set of broadband signals. Finally, Lamb waves in a transversely isotropic composite plate are investigated. Although the analysis is limited only to the waves propagating in the principal directions, it could serve as the basis for future work on tuning of Lamb waves in composites. It is concluded from this thesis that the SPT method enjoys advantages over other methods including its low operation cost, ability to tune the. modes of low phase velocities, and capability to control the propagation direction of tuned waves. The analysis of transient waves allows us to examine various tuning scenarios. The investigation of the tuning effectiveness enables us to select optimum modes for the given conditions.
by Yijun Shi.
Ph.D.
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Chen, Liling. "Lamb wave propagation in multilayered pipes." Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/290123.
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In this dissertation a characteristic equation has been obtained, in the framework of the linear theory of elasticity, for multilayered pipes; individual layers are made of isotropic elastic solids. A theoretical study of the Lamb wave propagation in multilayered pipes for both axisymmetric and nonaxisymmetric loading is presented. The stress and displacement variations inside the multilayered pipe are theoretically calculated for a number of propagating Lamb modes. The Lamb wave dispersion curves and the curves of frequency versus the ratio of wall thickness to half wave length have been computed for different Lamb modes inside a homogeneous pipe and have been compared with published results. These computations are extended to multilayered pipes.
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Gandhi, Navneet. "Determination of dispersion curves for acoustoelastic lamb wave propagation." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37158.
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The effect of stress on Lamb wave propagation is relevant to both nondestructive evaluation and structural health monitoring because of changes in received signals due to both the associated strain and the acoustoelastic effect. A homogeneous plate that is initially isotropic becomes anisotropic under biaxial stress, and dispersion of propagating waves becomes directionally dependent. The problem is similar to Lamb wave propagation in an anisotropic plate, except the fourth order tensor in the resulting wave equation does not have the same symmetry as that for the unstressed anisotropic plate, and the constitutive equation relating incremental stress to incremental strain is more complicated. Here we review the theory of acoustoelastic and develop theory for acoustoelastic Lamb wave propagation and show how dispersion curves shift anisotropically for an aluminum plate under biaxial tension. We also develop an approximate method using the effective elastic constants (EECs) and show that existing commercial tools to generate dispersion curves can be used under restricted conditions to describe wave propagation in biaxially stressed plates. Predictions of changes in phase velocity as a function of propagation direction using theory and the EEC method are compared to experimental results for a single wave mode.
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Tang, Bruce S. "Lamb wave propagation in laminated composite plates." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/80194.
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Low frequency Lamb waves in composite laminates were investigated theoretically and experimentally. To have a general solution for Lamb wave propagation in multilayered composite laminates is not practical due to a large number of boundary conditions needed to be satisfied at the interlaminar interfaces. Various approximate theories have been proposed to model low frequency Lamb wave propagation in composite laminates. In the present study, an approximate solution was derived from an elementary shear deformation plate theory and was shown to work well in the low frequency, long wavelength region.
A simple method, similar in configuration to the acousto-ultrasonic technique, was used to measure Lamb wave phase velocities. Low frequency Lamb waves, usually in the range of 10 kHz to 1 MHz, were generated. Dispersion curves of the lowest symmetric Lamb mode and the lowest antisymmetric Lamb mode were obtained. The experimental data were compared with the results obtained from the approximate solution for the lowest Lamb modes in the low frequency, long wavelength region for a unidirectional laminate, a symmetric cross-ply laminate, a symmetric quasi-isotropic laminate and an aluminum plate. There is good correlation between the data and the results obtained from the approximate solution, which suggests that the lowest Lamb modes are modeled adequately by the present theory in these cases. This experimental procedure of measuring phase velocities can be used to characterize laminated composite plates with and without damage since each material and stacking sequence gives distinct lowest symmetric and antisymmetric curves.
Stiffness reduction of composite laminates caused by damage can be related to the change in Lamb wave propagation speed. Damage in the form of transverse cracks in the 90° plies of a [90/90/90/0], graphite/epoxy laminate reduced the phase velocities of the Lamb modes. The lowest antisymmetric mode is sensitive to stiffness reduction in composite plates. Consequently, axial stiffness reduction in [0/45/0/45/0/45], and [0]₁₂ woven graphite/polyimide composite laminates was monitored by the lowest antisymmetric Lamb mode.Ph. D.
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Prego, Borges Jose Luis. "Lamb: a simulation tool for air-coupled lamb wave based ultrasonic NDE systems." Doctoral thesis, Universitat Politècnica de Catalunya, 2010. http://hdl.handle.net/10803/6376.
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La técnica de las ondas de Lamb acopladas por aire representa un importante avance en el área de los Ensayos No Destructivos (END) de materiales laminares.Sin embargo la compleja naturaleza de las vibraciones mecánicas encontradas en acústica, hacen que el análisis y el estudio de esta área del conocimiento sea un tema muy complejo. De allí que la posibilidad de contar con una herramienta de simulación de software que permita la evaluación y prueba de diferentes configuraciones de excitación y recepción acústica utilizando la flexibilidad de un modelo de computadora sea de una gran utilidad y ayuda.
El objetivo de la presente tesis es proveer al área de los END con un software de simulación gratuito: The LAMB Matlab® toolbox basado en el modelo del software libre de la GNU.
El software es capaz de simular el comportamiento de sistemas de END basados en ondas de Lamb acopladas por aire en láminas isótropas simples utilizando transductores tipo array.
El programa se basa en un arreglo tipo C-scan de un sistema de END y está compuesto por tres bloques principales: 1) Excitación, 2) Propagación y 3) Recepción.
La verificación individual del funcionamiento de dichos módulos se presenta a lo largo de la tesis mediante una serie de comparaciones entre simulaciones y datos experimentales provenientes de diferentes pruebas. Por otro lado, la validación del programa completo se llevo a cabo por medio de experimentos en láminas de cobre y aluminio; utilizando un sistema real de END por ondas de Lamb acopladas en aire mediante arrays cóncavos.
La influencia negativa en el desempeño general de dicho sistema de END real basado en este tipo de transductores se comprobó efectivamente mediante el simulador desarrollado. Esto se debió fundamentalmente al efecto de directividad de los sensores individuales en los transductores y a la simetría cóncava de los arrays.
Para emular este comportamiento la tesis presenta un modelo geométrico bidimensional simple de un filtro espacial, junto a las simulaciones de un nuevo tipo de array plano propuesto.
El programa desarrollado comprobó así mismo la naturaleza coherente de los campos acústicos emitidos en aire por las láminas sujetas a vibraciones de Lamb. Esto se realizó mediante la implementación de un conformador de haz simple de suma y demora; constituyéndose así la etapa inicial de procesamiento de señal del bloque de recepción del programa.
El objetivo principal del presente trabajo fue contribuir con un modelo operativo de simulación y prueba de nuevos diseños de arrays e implementación de estrategias de procesado de señal útiles en sistemas de END basados en ondas de Lamb acopladas por aire.
Finalmente, si bien el objetivo de la calibración del programa no se pudo conseguir; si se logró efectivamente un notable grado de similitud con un sistema de END real.
Air-coupled ultrasonic Lamb waves represent an important advance in Non- Destructive Testing and Evaluation (NDT & NDE) techniques of plate materials and structures. Examples of these advances are the characterization and quality assessment of laminate materials in manufacturing processes, the location of damaged parts in aircrafts and structure monitoring in the aerospace industry.
However the rich and complex nature of mechanical vibrations encountered in acoustics make the subject of analysis and study of these systems a very complex task. Therefore a simulation tool that permits the evaluation and testing of different configuration scenarios using the flexibility of a computer model is an invaluable aid and advantage.
The objective of this thesis is to provide the field of NDT with free open source software i.e. the LAMB Matlabrtoolbox. The toolbox is capable of simulating the behaviour of Lamb wave based NDE systems for single ideal isotropic laminates using air-coupled ultrasonic arrays. The programme usesa pitch-catch type of a Cscan NDE arrangement and is composed of three integrated sections each individually modelling a feature in the system: 1) Excitation, 2) Propagation, and 3) Reception.
For assessment of the individual modules of the toolbox the thesis presents comparisons between each section simulations and the data obtained from different acoustic experiments. The validation of the complete simulator was carried out by evaluation tests on the copper and aluminium plates by use of a real hardware prototype of a Lamb wave based NDE system with aircoupled concave arrays.
The negative impact on the performance of the real air-coupled NDE systembased on concave arrays was effectively confirmed by the programme. This was produced by the inherent directivity of the individual sensors as well as their concave arrangement. To emulate this behaviour the thesis introduces a simple two-dimensional geometric model for the inclusion of the spatial filtering effect of the sensors plus a group of simulations for a new proposed air-coupled plane array transducer.
The software also verified the spatial coherent nature of the Lamb wave fields emitted by a plate in air. This was demonstrated by the implementation of a delay and sum beamformer to constitute an initial signal processing stage in the reception section.
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Rainisch, Uri. "Detection of Ultrasonic Lamb Waves in Paper Using an Optical MEMS Microphone." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4779.
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Laser ultrasonics has been used to measure the bending stiffness of paper products by measuring the dispersion of ultrasonic plate waves. In laser ultrasonics, ultrasound can be generated by absorption of pulsed laser spot while detection can be carried out by Laser Doppler Interferometry. The research presented in this paper describes a new method to detect ultrasonic plate waves using a recently developed acoustic transducer, more specifically an optical Micro ElectroMechanical System (MEMS) microphone with broadband capability. The MEMS device operates as a non-contact proximity probe placed less than ¼ a millimeter away from the plate. The signals are detected with a capacitive micromachined ultrasonic transducer (cMUT) in which the back electrode of the capacitive transducer on a transparent substrate is shaped as an optical diffraction grating. The displacement of the transducer membrane is determined using an optical interferometer. By applying voltage to deflect the membrane electrostatically, the detection sensitivity is kept at an optimum level.
The main purpose of the research presented herein was to test this MEMSs ability to detect ultrasonic waves propagating through paper, to increase the signal-to-noise ratio (SNR), and to calibrate the device in order to quantify the limitations on sensitivity in the context of the detection of ultrasound in paper. Similar tests were conducted for comparison with a modified Mach-Zehnder Interferometer, a more traditional method used for laser ultrasonic detection, and its results are presented in this paper.
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Rimal, Nischal. "Impact Localization Using Lamb Wave and Spiral FSAT." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1388672483.
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Kotte, Timo Oliver. "Application of Image Processing Techniques for Lamb Wave Characterization." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4787.
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Characterization of dispersion curves in plate-like structures is possible with guided Lamb waves. In this research, experimental development of dispersion curves relies on the spectrogram, which suffers from the Heisenberg Uncertainty Principle. Reassignment is capable of localizing ill--defined dispersion curves. Unfortunately, reassignment also introduces spurious components, which reduce reassignment performance. This research develops an algorithm that provides both localization of dispersion curves and elimination of spurious components. To achieve this, an alternative formulation
of reassignment called differential reassignment is modified and superimposed with nonlinear anisotropic diffusion. This study first examines reassignment and diffusion components individually. Three different versions of differential reassignment are considered, two of which are modifications explicitly derived in
this research. The combined algorithm is then applied to reassign experimentally measured spectrograms, leading to a significant increase in clarity and notch detection performance.
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McKeon, James Christopher P. "Tomography applied to Lamb wave contact scanning nondestructive evaluation." W&M ScholarWorks, 1998. https://scholarworks.wm.edu/etd/1539623370.
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The aging world-wide aviation fleet requires methods for accurately predicting the presence of structural flaws that compromise airworthiness in aircraft structures. Nondestructive Evaluation (NDE) provides the means to assess these structures quickly, quantitatively, and noninvasively. Ultrasonic guided waves, Lamb waves, are useful for evaluating the plate and shell structures common in aerospace applications. The amplitude and time-of-flight of Lamb waves depend on the material properties and thickness of a medium, and so they can be used to detect any areas of differing thickness or material properties which indicate flaws. By scanning sending and receiving transducers over an aircraft, large sections can be evaluated after a single pass. However, while this technique enables the detection of areas of structural deterioration, it does not allow for the quantification of the extent of that deterioration. Tomographic reconstruction with Lamb waves allows for the accurate reconstruction of the variation of quantities of interest, such as thickness, throughout the investigated region, and it presents the data as a quantitative map. The location, shape, and extent of any flaw region can then be easily extracted from this Tomographic image. Two Lamb wave tomography techniques using Parallel Projection tomography (PPT) and Cross Borehole tomography (CBT), are shown to accurately reconstruct flaws of interest to the aircraft industry. A comparison of the quality of reconstruction and practicality is then made between these two methods, and their limitations are discussed and shown experimentally. Higher order plate theory is used to derive analytical solutions for the scattering of the lowest order symmetric Lamb wave from a circular inclusion, and these solutions are used to explain the scattering effects seen in the Tomographic reconstructions. Finally, the means by which this scattering theory can be used to develop Lamb wave Tomographic algorithms that are more generally applicable in-the-field, is presented.
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Li, Feng. "Innovative detection methods in liquid for a lamb wave biosensor." Besançon, 2008. http://www.theses.fr/2008BESA2019.
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The fields of health care and environment control have an ever increasing demand for sensors which are able to detect low concentrations of particIes such as molecular agents, warfare agents, or solid particIes contained in gaseous or liquid samples. The acoustic sensors, with rapid response, portability, ease of use, and small size are promising typically to be used in recognition of antigens by specific antibodies, absorption of proteins on chemical tailored surfaces, etc. Among the acoustic sensors, Lamb wave sensor is more attractive in biochemical applications for its higher sensitivity and ability to work in liquid. Further more, in the thesis it is found that Lamb wave sensor has the potential for multi parameters measurement at the same time. In this thesis, the Lamb membrane is modeled and the numerical simulations of Lamb wave are realized by FEM. These methods can be applied to Lamb wave simulation on complex geometries with complicated boundary conditions. The simulation results will help to design and optimize Lamb wave sensor for us. The design and fabricating for stable and reproducible Lamb wave sensor is investigated. The first improvement to the Lamb wave devices is using Mo/Ti/Si as AIN deposition substrate rather than Al/Si. Secondly, the problem of fragility of high sensitive Lamb wave sensor has been successfully solved by minimizing the inner stress. After the Lamb wave devices are fabricated out, the performances of Lamb wave devices are investigated comprehensively, including the frequency response, the delay of Lamb wave and the vibration of the membrane. .Les domaines de la santé et du contrôle de l'environnement ont une demande croissante de capteurs capables de détecter de faible quantité d'agents toxiques ou de particules solides dans des gaz ou des liquides. Les capteurs acoustiques, avec leur réponse rapide, leur portabilité, leur utilisation aisée et leurs petites tailles sont typiquement prometteurs pour la reconnaissance d'anticorps par des antigènes spécifiques ou l'absorption de protéines sur des surfaces préparées. Le principe de détection de ces capteurs utilise la variation de fréquence de la résonance d'une onde. Parmi les capteurs acoustiques, le capteur à ondes de Lamb semble le mieux placé pour les applications biochimiques, en raison de sa sensibilité et de son aptitude à fonctionner dans un liquide. De plus, dans cette thèse, nous montrerons que les capteurs à ondes de Lamb ont la possibilité de mesurer plusieurs paramètres simultanément. Dans cette thèse, l'onde de Lamb a été modélisée et des simulations numériques ont été effectuées par la méthode des éléments finis. Ces méthodes peuvent être appliquées aux ondes de Lamb pour des géométries et des conditions aux limites complexes. Les résultats de la simulation nous aident à concevoir et optimiser les capteurs à ondes de Lamb. Nous avons développé la conception et la fabrication de capteur à ondes de Lamb. La première amélioration a été d'utiliser pour le dépôt d'AIN des couches Mo/Ti/Si plutôt que Al/Si. La seconde a porté sur la réduction des contraintes internes de la membrane. Après sa fabrication, le capteur à ondes de Lamb a été étudié complètement, y compris la réponse en fréquence, la durée de propagation des ondes et la vibration de la membrane. .
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Wilcox, Paul David. "Lamb wave inspection of large structures using permanently attached transducers." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/8087.
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Banks, Robert. "A frequency agile approach to air-coupled Lamb wave inspection." Thesis, University of Strathclyde, 1999. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=23370.
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This Thesis describes the design, manufacture and evaluation of a single sided through-air Lamb wave scanner for Non-Destructive Evaluation (NDE). The new scanning system utilises novel wideband piezocomposite transducers and specialised receive electronics to detect and monitor the thickness of faults within the structure under investigation using a frequency agile approach. Based upon the superheterodyne principle, this frequency agility dispenses with the costly requirement for precision manipulation of the transducer alignment, by effectively tuning the system for the thickness of the sample. Several important applications are identified, including defect detection on samples with tapered thicknesses and defect depth characterisation on plates with thickness erosion, in addition to conventional defect evaluation. Through the application of finite element modelling and practical analysis, a new range of wideband composite transducer have been developed which offer a considerable improvement in operational bandwidth in comparison to conventional piezocomposites. Moreover, a specialised ultra low noise heterodyning amplifier was designed and constructed to provide sufficient gain and selectivity to detect the Lamb waves generated in the various structures under examination. Experimental results obtained from the prototype system illustrate a capability to distinguish defects within test specimens of differing materials and determine the thickness of the given defect. The current system is capable of resolving defects down to less than 2mm in diameter or 20% thinning in a 1mm thick aluminium plate for a Lamb wave with a wavelength of 3mm. Moreover, the handheld nature of the scanning head employed within this system has facilitated the examination of practical NDE examples, such as disbonds between vehicle support structures and outer panelling over curved structures.
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Ramsey, James Jehiel. "Effects of Wind on Piezoelectric Lamb Wave-based Health Monitoring." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1164917033.
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Zhou, Lianqun. "Study of the membrane-fluid interaction in micro lamb wave sensor." Besançon, 2010. http://www.theses.fr/2010BESA2041.
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Micro lamb wave sensor is one of useful tools to study the membrane-fluid interaction, especially in interdisciplinary and not yet explored areas, such as gas sensing, aerodynamics, the multi-parameter decoupling and so on. This is because micro Lamb wave sensor holds high sensitivity, low losses and multi-modes. This thesis deals with the membrane-fluid interaction with micro lamb wave sensor is investigated, and the potential function method is used to analyze the dispersion curves, the displacements, the stress curves, etc. A model is built to analyze the modes distribution in micro Lamb wave sensor. The gase effects on lamb wave propagations are investigated. The applications of Lamb wave in aerodynamics and multi-parameters decoupling are discussed. The details are described as follows. In theory, combinations of the potential function method and the boundary conditions at all interfaces are used to analyze the membrane-fluid interaction. Compared with traditional plate shell theory, the particle movements in the membrane and fluid are taken into account in this method. Several aspects of the problem can be addressed, including the displacement, the stress, velocity dispersion curve, pointing vector, group velocity, energy velocity and so on. All of these are available to investigate the interaction at the membrane-fluid interface. In the case of micro Lamb wave sensor, the resonant modes can be excited and work simultaneously with the travelling modes, as the membrane is width limited and not large enough comparing with the wavelength of Lamb waves. The established model car reveal the mode distributions in micro Lamb wave device clearly and accurately. These works provide insight into the understandings of the modes in micro Lamb wave device, which is useful for further experiments. In literatures, little attention has been paid on the Lamb wavesۥ propagation near the membrane-gas interface, as both the density and sound velocity of gas are low. We aim to provide more studies of gases effects on the evanescent wave the leaky wave near the membrane-gas interface. It is shown that the relative frequency shifts in the low frequency range of the A0 mode (evanescent wave, EW) is rather important and the shape of the curve looks like ۥUۥ shape; in the high frequency range of this mode (leaky Lamb wave, LLW), the quality factor decreases rapidly when the Lamb wave phase velocity approaches the gas sound velocity. The Sº mode shows immune to gas loading, which is a good choice for a reference mode. This provides theoretical and experimental work for related fields in gas sensing. The application of membrane-gas interaction in aerodynamics in investigated theoretically and experimentally. The interaction between the gas flow boundary layer and the acoustic sound field (EW and LLW) at the membrane-gas interface can give out the parameter in the gas flow. The parameters in gas flow can be obtained from the measuring the interaction, which happens between the gas flow boundary layer and the acoustic sound field (EW and LLW) at the membrane gas interface. In the EW case, the thicknesss of the gas flow boundary layer and the penetration depth of the evanescent wave combined determine this interaction. When the Lamb wave phase velocity approaches the gas sound velocity, this effect is clearly observed. In the LLW case, it is shown experimentally that the gas flow has not evident effects on Lamb wave’s propagations. It suggests that Lamb wave is promising for applications in wind tunnel experiments, micro channels characterization, and can lead to multi-parameters measurements. The effects of the different physical parameters (density, sound velocity, viscosity, etc) on the modesۥ propagations at he membrane-liquid interface are studied. Combination of the relative frequency shifts of the A01 mode (he fundamental mode of low frequency A0 mode) and the A03 mode (the third harmonic wave of the A01 mode), the density and the sound velocity of liquid, but is amplitude changes with the viscosity. This work makes Lamb wave have promising applications in the investigation of the molecular thermodynamics, molecular labels free detection,etcCette thèse traite, théoriquement et expérimentalement, de l’interaction fluide-membrane dans un capteur a onde de Lamb. Un modèle est utilisé pour calculer les courbes de dispersion, le déplacement, les contraintes. Un autre modèle est utilisé pour analyser la distribution des modes. L’effet des gaz est étudié théoriquement et expérimentalement. Les applications des ondes de Lamb à l’aérodynamique et aux mesures multiparamétriques sont présentées. Voici quelques détails. Le premier modèle utilise les fonctions potentielles et recherche les fonctions solution des équations de propagation qui remplissent les conditions aux limites avec ou sans la présence d’un liquide. Ce modèle permet d’obtenir de nombreux paramètres, le déplacement des particules, les contraintes, le vecteur de Poynting, les vitesses de groupe et d’énergie etc. La membrane étant limitée dans le sens latéral il y a coexistence dans la membrane de modes stationnaires et d’ondes progressives. Un modèle donne la position et l’intensité relatives des modes. Le but est d’apporter des connaissances complémentaires sur l’action des gaz sur la propagation des ondes de Lamb. On montre que pour les basses fréquences de A0 (ondes évanescentes dans le gaz) l’action est principalement un changement de fréquence , tandis aux plus hautes fréquences de A0 (Ondes «fuyantes» l’action est principalement une atténuation. Le S0 mode étant très peu modifié par la présence de gaz. L’application de l’interaction gaz-membrane en aérodynamique est étudiée théoriquement et expérimentalement. Le principal effet ce produit quand la vitesse de phase de l’onde de Lamb est proche de la vitesse du son dans le gaz. Les résultats suggèrent que les applications dans ce domaine seront très prometteuses. Les effets sur l’onde de Lamb de différents paramètres (densité, vitesse du son viscosité) d’une solution liquide sont étudiés. On montre que l’utilisation conjointe de A01 mode (fondamental du A0 mode) et du A03 mode (harmonique 3 DU A0 mode) permet de mesurer la densité et la vitesse du son. La densité étant connue, le S0 mode permet d’obtenir la viscosité
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Bruhschwein, Taylor John. "Identification of Delamination Defects in CFRP Materials through Lamb Wave Responses." Thesis, North Dakota State University, 2014. https://hdl.handle.net/10365/27328.
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Delamination is currently a largely undetectable form of damage in composite laminate materials. This thesis will develop a method to more easily detect delamination damage within composite materials. Using finite element analysis modeling and lab testing, a new method from interpreting the results obtained from existing structural health monitoring techniques is developed. Lamb waves were introduced and recorded through an actuator and sensors made of piezoelectric material. The data was then analyzed through a novel data reduction method using the Fast Fourier Transform (FFT). Using the data from FFT, the idea of covariance of energy change was developed. By comparing the covariance of energy change in beams with differing delamination size, thickness and depth, correlations were able to be developed. With these correlations, the severity and of damage was able to be detected.
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Mueller, Martin Fritz. "Analytical investigation of internally resonant second harmonic lamb waves in nonlinear elastic isotropic plates." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31827.
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Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010.Committee Chair: Laurence J. Jacobs; Committee Member: Jianmin Qu; Committee Member: Jin-Yeon Kim. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Kural, Aleksander. "Ultrasonic lamb wave energy transmission system for aircraft structural health monitoring applications." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/58395/.
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In this project an investigation of a wireless power transmission method utilising ultrasonic Lamb waves travelling along plates was performed. To the author’s knowledge, this is the first time such a system was investigated. The primary application for this method is the supply of power to wireless structural health monitoring (SHM) sensor nodes located in remote areas of the aircraft structure. A vibration generator is placed in a location where electricity supply is readily available. Ultrasonic waves generated by this device travel through the aircraft structure to a receiver in a remote wireless sensor node. The receiver converts the mechanical vibration of the ultrasonic waves back to electricity, which is used to power the sensor node. An experimental setup comprising a 1000 × 821 × 1.5 mm aluminium plate was designed to model an aircraft skin panel. Pairs of piezoelectric transducers were positioned along the longer edges of the plate. The electric impedance characteristics of three transducer types were measured. A circuit simulation MATLAB code was written. An input and output power measurement system was developed. The MFC M8528-P1 transducer type was identified as providing the best performance. The use of inductors to compensate for the capacitive characteristics of transducers was shown to provide up to 170-fold power throughput increase. The propagation of Lamb waves in the experimental plate was mapped using a scanning laser vibrometer and simulated using LISA finite difference method software. An optimised laboratory system transmitted 17 mW of power across a distance of 54 cm while being driven by a 20 V, 224 kHz signal. This figure can be easily increased by using a higher drive voltage. This shows that the system is capable of supplying sufficient power to wireless SHM sensor nodes, which currently have a maximum power requirement of approximately 200 mW.
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Jolly, Prateek. "Lamb wave based active damage identification in adhesively bonded composite lap joints." Thesis, Mississippi State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10100288.
Full textAbstract:
Bonding composite structures using adhesives offers several advantages over mechanical fastening such as better flow stress, weight saving, improved fatigue resistance and the ability to join dissimilar structures. The hesitation to adopt adhesively bonded composite joints stems from the lack of knowledge regarding damage initiation and propagation mechanisms within the joint. A means of overcoming this hesitation is to continuously monitor damage in the joint. This study proposes a methodology to conduct structural health monitoring (SHM) of an adhesively bonded composite lap joint using acoustic, guided Lamb waves by detecting, locating and predicting the size of damage. Finite element modeling of a joint in both 2D and 3D is used to test the feasibility of the proposed damage triangulation technique. Experimental validation of the methodology is conducted by detecting the presence, location and size of inflicted damage with the use of tuned guided Lamb waves.
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Ha, Sungwon. "Modeling Lamb wave propagation induced by adhesively bonded PZTs on thin plates /." May be available electronically:, 2009. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Matthews, Glenn Ian, and gimatthews@ieee org. "Investigation of Flexural Plate Wave Devices for Sensing Applications in Liquid Media." RMIT University. Electrical and Computer Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20090219.120815.
Full textAbstract:
In this thesis, the author proposes and presents a novel simulation technique for the analysis of multilayered Flexural Plate Wave (FPW) devices based on the convergence of the Finite Element method (FEM) with classical Surface Acoustic Wave (SAW) analysis techniques and related procedures. Excellent agreement has been obtained between the author's approach and other more conventional modelling techniques. Utilisation of the FEM allows the performance characteristics of a FPW structure to be critically investigated and refined before undertaking the costly task of fabrication. Based on a series of guidelines developed by the author, it is believed the proposed technique can also be applied to other acoustic wave devices. The modelling process developed is quite unique as it is independent of the problem geometry as verified by both two and three dimensional simulations. A critical review of FEM simulation parameters is presented and their effect on the frequency domain response of a FPW transducer given. The technique is also capable of simultaneously modelling various second-order effects, such as triple transit, diffraction and electromagnetic feedthrough, which often requires the application of several different analysis methodologies. To verify the results obtained by the author's novel approach, several commonly used numerical techniques are discussed and their limitations investigated. The author initially considers the Transmission Matrix method, where it is shown that an inherent numerical instability prevents solution convergence when applied to large frequency-thickness products and complex material properties which are characteristic of liquids. In addition the Stiffness Matrix method is investigated, which is shown to be unconditionally stable. Based on this technique, particle displacement profiles and mass sensitivity are presented for multilayered FPW structures and compared against simpler single layer devices commonly quoted in literature. Significant differences are found in mass sensitivity between single layer and multilayered structures. Frequency response characteristics of a FPW device are then explored via a spectral domain Green's function, which serves as a further verification technique of the author's novel analysi s procedure. Modifications to the spectral domain Green's function are discussed and implemented due to the change in solution geometry from SAW to FPW structures. Using the developed techniques, an analysis is undertaken on the applicability of FPW devices for sensing applications in liquid media. Additions are made to both the Stiffness Matrix method and FEM to allow these techniques to accurately incorporate the influence of a liquid layer. The FEM based approach is then applied to obtain the frequency domain characteristics of a liquid loaded FPW structure, where promising results have been obtained. Displacement profiles are considered in liquid media, where it is shown that a tightly coupled Scholte wave exists that is deemed responsible for most reported liquid sensing results. The author concludes the theoretical analysis with an in-depth analysis of a FPW device when applied to density, viscosity and mass sensing applications in liquid media. It is shown that a single FPW device is potentially capable of discriminating between density and viscosity effects, which is typically a task that requires a complex and costly sensor array.
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Bermes, Christian. "Generation and detection of nonlinear Lamb waves for the characterization of material nonlinearities." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/13986.
Full textAbstract:
An understanding of the generation of higher harmonics in Lamb waves is of critical importance for applications such as remaining life prediction of plate-like structural components. The objective of this work is to use nonlinear Lamb waves to experimentally investigate inherent material nonlinearities in aluminum plates. These nonlinearities, e.g. lattice anharmonicities, precipitates or vacancies, cause higher harmonics to form in propagating Lamb waves. The amplitudes of the higher harmonics increase with increasing
propagation distance due to the accumulation of nonlinearity while the Lamb wave travels along its path. Special focus is laid on the second harmonic, and a relative nonlinearity parameter is defined as a function of the fundamental and
second harmonic amplitude. The experimental setup uses an ultrasonic transducer and a wedge for the Lamb wave generation and laser interferometry for detection. The experimentally measured Lamb wave
signals are processed with a short-time Fourier transformation (STFT) and a chirplet transformation-based algorithm, which yield
the amplitudes of the frequency spectrum as functions of time,
allowing the observation of the nonlinear behavior of the material. The increase of the relative nonlinearity parameter with propagation distance as an indicator of cumulative second harmonic generation is shown in the results for two different aluminum alloys. The difference in
inherent nonlinearity between both alloys as determined from longitudinal wave measurements can be observed for the Lamb wave measurements, too.
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Dodson, Jacob Christopher. "Guided Wave Structural Health Monitoring with Environmental Considerations." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/27070.
Full textAbstract:
Damage detection in mechanical and aerospace structures is critical to maintaining safe
and optimal performance. The early detection of damage increases safety and reduces cost
of maintenance and repair. Structural Health Monitoring (SHM) integrates sensor networks
and structures to autonomously interrogate the structure and detect damage. The
development of robust SHM systems is becoming more vital as aerospace structures are
becoming more complex. New SHM methods that can determine the health of the structure
without using traditional non-destructive evaluation techniques will decrease the cost
and time associated with these investigations. The primary SHM method uses the signals
recorded on a pristine structure as a reference and compares operational signals to the
baseline measurement. One of the current limitations of baseline SHM is that environmental
factors, such as temperature and stress, can change the system response so the
algorithm indicates damage when there is none. Many structures which can benefit from
SHM have multiple components and often have connections and interfaces that also can
change under environmental conditions, thus changing the dynamics of the system.
This dissertation addresses some of the current limitations of SHM. First the changes
that temperature variations and applied stress create on Lamb wave propagation velocity
in plates is analytically modeled and validated. Two methods are developed for the
analytical derivative of the Lamb wave velocity; the first uses assumes a thermoelastic material
while the second expands thermoelastic theory to include thermal expansion and
the associated stresses. A model is developed so the baseline measurement can be compensated
to eliminate the false positives due to environmental conditions without storage
of dispersion curves or baseline signals at each environmental state. Next, a wave based
instantaneous baseline method is presented which uses the comparison of simultaneously
captured real time signals and can be used to eliminate the influence of environmental effects
on damage detection. Finally, wave transmission and conversion across interfaces in
prestressed bars is modeled to provide a better understanding of how the coupled axial
and flexural dynamics of a non-ideal preloaded interface change with applied load.Ph. D.
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Oliveira, Aline Emy Takiy de [UNESP]. "Uso das ondas de Lamb e Scholte para caracterização de líquidos." Universidade Estadual Paulista (UNESP), 2015. http://hdl.handle.net/11449/132242.
Full textAbstract:
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000853520.pdf: 2749056 bytes, checksum: aeead8823ebd2b93063ca4406bc23b07 (MD5)O estudo da interação de ondas elásticas em sólidos imersos em um fluido tem sido reconhe- cido como um meio viável para caracterização de líquidos. As ondas guiadas em estruturas tipo placa possuem a característica de serem multimodais e dispersivas. Estas características introduzem mais informação ao processo de medição, além de tornar a análise teórica e a inter- pretação física dos resultados experimentais mais envolventes. Quando a placa está em contato com o fluido, há uma forte atenuação devido às ondas de fuga e perdas viscosas no fluido. Esta característica pode ser explorada para a caracterização de líquidos, devido à alta sensibilidade associada à interação entre a onda e o fluido. Pensando nesta particularidade estudou-se o modo quase Scholte, que é um tipo de onda de interface cuja energia está confinada perto da região da superfície da placa. A análise deste modo propagante é uma alternativa atraente para se determinar a velocidade volumétrica longitudinal e a atenuação no líquido, o que proporciona valiosas informações sobre as propriedades do fluido. Neste trabalho, as ondas guiadas (mo- dos de Lamb e quase Scholte) são teoricamente descritas por um sistema de equações obtido do modelamento de uma placa sólida homogênea em contato com um fluido viscoso, o qual é descrito usando a equação de Navier-Stokes. As curvas de dispersão e atenuação das ondas de Lamb e do modo quase Scholte são obtidos numericamente como soluções das equações carac- terísticas. Experimentos foram realizados visando mensurar a velocidade de fase e a atenuação para os modos de Lamb e quase Scholte, mostrando a existência de bandas de frequências de baixa atenuação. Estas medições foram obtidas usando transdutores longitudinais de banda larga acoplados a prismas de acrílico, excitados com pulsos senoidais e posteriormente analisa- dos em tempo-frequência
The study of the interaction of elastic waves in solids immersed in a fluid has been recognized as a suitable method for fluid characterization. Guided waves in plate-like structures, are mul- timodal and dispersive. These characteristics provides more information in the measurement process. In addition, the theoretical analysis and physical interpretation of the experimental results become more involved. When the plate is in contact with a fluid, there is strong attenu- ation due to Leaky waves and viscous losses in the fluid. This characteristic can be explored for the fluid characterization, due to the high sensitivity associated to the interaction between the wave and fluid. From this feature a study about the quasi-Scholte mode was done, which is a kind of interface wave and its wave energy in the fluid is confined in the region close to the surface of the plate. The analysis of this propagating mode is an attractive alternative to determine the bulk longitudinal velocity and attenuation in the liquid, which provide valuable information about the liquid properties. In this work, guided waves (Lamb and quasi-Scholte modes) are theoretically described by a system of equations obtained by modeling a homo- genous solid plate in contact with a viscous fluid, which is modeled using the Navier-Stokes equation. The dispersion and attenuation curves of Lamb waves and quasi Scholte mode are numerically calculated from the characteristic equations. Experimental measurements were conducted in order to obtain the phase velocity and attenuation for the Lamb waves and quasi Scholte mode showing the existence of low attenuation frequencies bands. These measurements were obtained by using longitudinal wide band transducers coupled to acrylic wedges, excited with senoidal pulses and then time-frequency analysed. In order to evaluate the potential use of this result in NDT applications ultrasonic images were also ...
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Oliveira, Aline Emy Takiy de. "Uso das ondas de Lamb e Scholte para caracterização de líquidos /." Ilha Solteira, 2015. http://hdl.handle.net/11449/132242.
Full textAbstract:
Orientador: Cláudio KitanoCo-orientador: Luis Elvira Segura
Banca: Aparecido Augusto de Carvalho
Banca: Ricardo Toquio Higuti
Banca: Flávio Buiochi
Banca: Nicolás Leoardo Pérez Alvarez
Resumo: O estudo da interação de ondas elásticas em sólidos imersos em um fluido tem sido reconhe- cido como um meio viável para caracterização de líquidos. As ondas guiadas em estruturas tipo placa possuem a característica de serem multimodais e dispersivas. Estas características introduzem mais informação ao processo de medição, além de tornar a análise teórica e a inter- pretação física dos resultados experimentais mais envolventes. Quando a placa está em contato com o fluido, há uma forte atenuação devido às ondas de fuga e perdas viscosas no fluido. Esta característica pode ser explorada para a caracterização de líquidos, devido à alta sensibilidade associada à interação entre a onda e o fluido. Pensando nesta particularidade estudou-se o modo quase Scholte, que é um tipo de onda de interface cuja energia está confinada perto da região da superfície da placa. A análise deste modo propagante é uma alternativa atraente para se determinar a velocidade volumétrica longitudinal e a atenuação no líquido, o que proporciona valiosas informações sobre as propriedades do fluido. Neste trabalho, as ondas guiadas (mo- dos de Lamb e quase Scholte) são teoricamente descritas por um sistema de equações obtido do modelamento de uma placa sólida homogênea em contato com um fluido viscoso, o qual é descrito usando a equação de Navier-Stokes. As curvas de dispersão e atenuação das ondas de Lamb e do modo quase Scholte são obtidos numericamente como soluções das equações carac- terísticas. Experimentos foram realizados visando mensurar a velocidade de fase e a atenuação para os modos de Lamb e quase Scholte, mostrando a existência de bandas de frequências de baixa atenuação. Estas medições foram obtidas usando transdutores longitudinais de banda larga acoplados a prismas de acrílico, excitados com pulsos senoidais e posteriormente analisa- dos em tempo-frequência
Abstract: The study of the interaction of elastic waves in solids immersed in a fluid has been recognized as a suitable method for fluid characterization. Guided waves in plate-like structures, are mul- timodal and dispersive. These characteristics provides more information in the measurement process. In addition, the theoretical analysis and physical interpretation of the experimental results become more involved. When the plate is in contact with a fluid, there is strong attenu- ation due to Leaky waves and viscous losses in the fluid. This characteristic can be explored for the fluid characterization, due to the high sensitivity associated to the interaction between the wave and fluid. From this feature a study about the quasi-Scholte mode was done, which is a kind of interface wave and its wave energy in the fluid is confined in the region close to the surface of the plate. The analysis of this propagating mode is an attractive alternative to determine the bulk longitudinal velocity and attenuation in the liquid, which provide valuable information about the liquid properties. In this work, guided waves (Lamb and quasi-Scholte modes) are theoretically described by a system of equations obtained by modeling a homo- genous solid plate in contact with a viscous fluid, which is modeled using the Navier-Stokes equation. The dispersion and attenuation curves of Lamb waves and quasi Scholte mode are numerically calculated from the characteristic equations. Experimental measurements were conducted in order to obtain the phase velocity and attenuation for the Lamb waves and quasi Scholte mode showing the existence of low attenuation frequencies bands. These measurements were obtained by using longitudinal wide band transducers coupled to acrylic wedges, excited with senoidal pulses and then time-frequency analysed. In order to evaluate the potential use of this result in NDT applications ultrasonic images were also ...
Doutor
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Karmazin, Alexander [Verfasser]. "Time-efficient Simulation of Surface-excited Guided Lamb Wave Propagation in Composites / Alexander Karmazin." Karlsruhe : KIT Scientific Publishing, 2013. http://www.ksp.kit.edu.
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Jang, Jun-keun. "Study on the Application of Shear-wave Elastography to Thin-layered Media and Tubular Structure: Finite-element Analysis and Experiment Verification." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/217145.
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Chen, Xin. "Load-enhanced lamb wave methods for the in situ detection, localization and characterization of damage." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54859.
Full textAbstract:
A load-enhanced methodology has been proposed to enable the in situ detection, localization, and characterization of damage in metallic plate-like structures using Lamb waves. A baseline-free load-differential method using the delay-and-sum imaging algorithm is proposed for defect detection and localization. The term “load-differential” refers to the comparison of recorded ultrasonic signals at various levels of stress. Defect characterization is achieved by incorporating expected scattering information of guided waves interacting with defects into the minimum variance imaging algorithm, and a method for estimating such scattering patterns from the measurements of a sparse transducer array is developed. The estimation method includes signal preprocessing, extracting initial scattering values from baseline subtraction results, and obtaining the complete scattering matrix by applying radial basis function interpolation. The factors that cause estimation errors, such as the shape parameter used to form the basis function and the filling distance used in the interpolation, are discussed.
The estimated scattering patterns from sparse array measurements agree reasonably well with laser wavefield data and are further used in the load-enhanced method. The results from fatigue tests show that the load-enhanced method is capable of detecting cracks, providing reasonable estimates of their localizations and orientations, and discriminating them from drilled holes, disbonds, and fastener tightness variations.
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Ayers, James Thomas. "Structural damage diagnostics via wave propagation-based filtering techniques." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34723.
Full textAbstract:
Structural health monitoring (SHM) of aerospace components is a rapidly emerging
field due in part to commercial and military transport vehicles remaining in operation
beyond their designed life cycles. Damage detection strategies are sought
that provide real-time information of the structure's integrity. One approach that
has shown promise to accurately identify and quantify structural defects is based on
guided ultrasonic wave (GUW) inspections, where low amplitude attenuation properties
allow for long range and large specimen evaluation. One drawback to GUWs
is that they exhibit a complex multi-modal response, such that each frequency corresponds
to at least two excited modes, and thus intelligent signal processing is required
for even the simplest of structures. In addition, GUWs are dispersive, whereby the
wave velocity is a function of frequency, and the shape of the wave packet changes
over the spatial domain, requiring sophisticated detection algorithms. Moreover, existing
damage quantification measures are typically formulated as a comparison of the
damaged to undamaged response, which has proven to be highly sensitive to changes
in environment, and therefore often unreliable.
As a response to these challenges inherent to GUW inspections, this research develops
techniques to locate and estimate the severity of the damage. Specifically, a
phase gradient based localization algorithm is introduced to identify the defect position
independent of excitation frequency and damage size. Mode separation through
the filtering technique is central in isolating and extracting single mode components,
such as reflected, converted, and transmitted modes that may arise from the incident
wave impacting a damage. Spatially-integrated single and multiple component mode coefficients are also formulated with the intent to better characterize wave reflections
and conversions and to increase the signal to noise ratios. The techniques are
applied to damaged isotropic finite element plate models and experimental data obtained
from Scanning Laser Doppler Vibrometry tests. Numerical and experimental
parametric studies are conducted, and the current strengths and weaknesses of the
proposed approaches are discussed. In particular, limitations to the damage profiling
characterization are shown for low ultrasonic frequency regimes, whereas the multiple
component mode conversion coefficients provide excellent noise mitigation. Multiple
component estimation relies on an experimental technique developed for the estimation
of Lamb wave polarization using a 1D Laser Vibrometer. Lastly, suggestions are
made to apply the techniques to more structurally complex geometries.
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Bjurström, Henrik. "Non-contact surface wave measurements on pavements." Doctoral thesis, KTH, Jord- och bergmekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-201147.
Full textAbstract:
In this thesis, nondestructive surface wave measurements are presented for characterization of dynamic modulus and layer thickness on different pavements and cement concrete slabs. Air-coupled microphones enable rapid data acquisition without physical contact with the pavement surface. Quality control of asphalt concrete pavements is crucial to verify the specified properties and to prevent premature failure. Testing today is primarily based on destructive testing and the evaluation of core samples to verify the degree of compaction through determination of density and air void content. However, mechanical properties are generally not evaluated since conventional testing is time-consuming, expensive, and complicated to perform. Recent developments demonstrate the ability to accurately determine the complex modulus as a function of loading time (frequency) and temperature using seismic laboratory testing. Therefore, there is an increasing interest for faster, continuous field data evaluation methods that can be linked to the results obtained in the laboratory, for future quality control of pavements based on mechanical properties. Surface wave data acquisition using accelerometers has successfully been used to determine dynamic modulus and thickness of the top asphalt concrete layer in the field. However, accelerometers require a new setup for each individual measurement and are therefore slow when testing is performed in multiple positions. Non-contact sensors, such as air-coupled microphones, are in this thesis established to enable faster surface wave testing performed on-the-fly. For this project, a new data acquisition system is designed and built to enable rapid surface wave measurements while rolling a data acquisition trolley. A series of 48 air-coupled micro-electro-mechanical sensor (MEMS) microphones are mounted on a straight array to realize instant collection of multichannel data records from a single impact. The data acquisition and evaluation is shown to provide robust, high resolution results comparable to conventional accelerometer measurements. The importance of a perfect alignment between the tested structure’s surface and the microphone array is investigated by numerical analyses. Evaluated multichannel measurements collected in the field are compared to resonance testing on core specimens extracted from the same positions, indicating small differences. Rolling surface wave measurements obtained in the field at different temperatures also demonstrate the strong temperature dependency of asphalt concrete. A new innovative method is also presented to determine the thickness of plate like structures. The Impact Echo (IE) method, commonly applied to determine thickness of cement concrete slabs using an accelerometer, is not ideal when air-coupled microphones are employed due to low signal-to-noise ratio. Instead, it is established how non-contact receivers are able to identify the frequency of propagating waves with counter-directed phase velocity and group velocity, directly linked to the IE thickness resonance frequency. The presented non-contact surface wave testing indicates good potential for future rolling quality control of asphalt concrete pavements.QC 20170209
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Blackhurst, Tyler D. "Numerical Investigation of Internal Wave-Vortex Dipole Interactions." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3133.
Full textAbstract:
Three-dimensional linear ray theory is used to investigate internal waves interacting with a Lamb-Chaplygin pancake vortex dipole. These interactions involve waves propagating in the same (co-propagating) and opposite (counter-propagating) horizontal directions as the dipole translation. Co-propagating internal waves in the vertical symmetry plane between the vortices of the dipole can approach critical levels where the wave energy is absorbed by the dipole or where the waves are overturned and possibly break. As wave breaking cannot be simulated with this linear model, changes in wave steepness are calculated to aid in estimating the onset of breaking. Counter-propagating internal waves in the vertical symmetry plane can experience horizontal and vertical reflections, including turning points similar to waves in two-dimensional steady shear. Wave capture is also a possible effect of either type of interaction, depending on initial wave properties and positioning relative to the vortex dipole. Away from the vertical symmetry plane, a spanwise converging (focusing) and diverging (defocusing) of wave energy is observed in co- and counter-propagating interactions as symmetric off-center rays interact with the dipole's individual vortices. Some off-center rays experience multiple horizontal refractions similar to wave trapping.
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Haig, Alexander George. "The use of macro fiber composite transducers for ultrasonic guided wave based inspection." Thesis, Brunel University, 2013. http://bura.brunel.ac.uk/handle/2438/12840.
Full textAbstract:
Sound can propagate for long distances with a low loss of intensity in objects whose geometry acts as a guide for the sound waves; a phenomenon that can be utilised for long range testing of structures. The guided sound waves can be used to conduct materials evaluation or to detect flaws, which can be done for a relatively large region of coverage from a relatively small region of access. In particular this technology can be used to inspect or monitor large engineering structures whose structural integrity is critical for safety and the environment, such as wind turbine towers, ship hulls, and pipelines. The use of guided waves for structural inspection is complicated by the existence of many wave modes. In this thesis, the Macro Fiber Composite (MFC) is characterised for its frequency, wavelength, wave mode and direction dependent sensitivity. These devices are flexible, light and thin, and, here have been shown to have wave mode sensitivity characteristics that are favourable for some applications. The MFC is a piezoelectric actuator that can be used to excite and sense in-plane vibrations at a structures surface. The surface area of an MFC is significantly large with respect to typical wavelengths used in ultrasonic guided wave applications, which combined with their in-plane extensional nature gives rise to a significantly wave mode, frequency and direction dependent sensitivity. This can limit their application, but can also potentially be exploited for greater wave mode control. A method for simulating the output from hypothesised transducer behaviour is shown and validated for the MFC. This allows their behaviour to be predicted for new structures. It is shown that their frequency response can depend on the waveguide and can vary with direction, which can lead to wave mode transmission and reception characteristics that may be advantageous for some methods of application and detrimental to others. A novel method of adapting a flexible transducer, such as the MFC, has been developed and its characterisation is given. It is shown that through the use of a decoupling membrane, an MFC can be caused to have very different wave mode sensitivity characteristics whilst retaining their light and flexible nature. These altered characteristics are favourable for applications where shear horizontal wave modes are required. Both fully coupled MFC transducers and the adapted MFC transducers are considered for application to pipeline testing. Fully coupled MFC transducers are used for inspection using longitudinal waves, whilst the adapted MFC transducers are used with torsional waves. These arrays are compared to a current commercial tool.
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Le, Guennec Yves. "Transient dynamics of beam trusses under impulse loads." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2013. http://www.theses.fr/2013ECAP0016/document.
Full textAbstract:
Ce travail de recherche est dédié à la simulation de la réponse transitoire des assemblages de poutres soumis à des chocs. De tels chargements entraînent la propagation d’ondes haute fréquence dans l’ensemble de la structure. L’énergie qu’elles transportent peut être dommageable pour son fonctionnement ou celui des équipements embarqués. Dans des études précédentes, il a été observé sur des structures expérimentales qu’un régime vibratoire diffusif tend à s’installer pour des temps longs. Le but de cette étude est donc de développer un modèle robuste de la réponse transitoire des assemblages de poutres soumis à des chocs permettant de simuler, entre autres, cet état diffusif. Les champs de déplacement étant très oscillants et la densité modale élevée, la simulation numérique de la réponse transitoire à des chocs peut difficilement être menée par une méthode d’éléments finis classique. Une approche utilisant un estimateur de la densité d’énergie de chaque mode de propagation a donc été mise en œuvre. Elle permet d’accéder à des informations locales sur les états vibratoires, et de contourner certaines limitations intrinsèques aux longueurs d’onde courtes. Après avoir comparé plusieurs modèles de réduction cinématique de poutre à un modèle de Lamb de propagation dans un guide d’ondes circulaire, la cinématique de Timoshenko a été retenue afin de modéliser le comportement mécanique haute fréquence des poutres. En utilisant ce modèle dans le cadre de l’approche énergétique évoquée plus haut, deux groupes de modes de propagation de la densité d’énergie vibratoire dans une poutre ont été isolés : des modes longitudinaux regroupant un mode de compression et des modes de flexion, et des modes transversaux regroupant des modes de cisaillement et un mode de torsion. Il peut être également montré que l’´evolution en temps des densités d’énergie associées obéit à des lois de transport. Pour des assemblages de poutres, les phénomènes de réflexion/transmission aux jonctions ont du être pris en compte. Les opérateurs permettant de les décrire en termes de flux d’´energie ont été obtenus grâce aux équations de continuité des déplacements et des efforts aux jonctions. Quelques caractéristiques typiques d’un régime haute fréquence ont été mises en évidence, tel que le découplage entre les modes de rotation et les modes de translation. En revanche, les champs de densité d’énergie sont quant à eux discontinus aux jonctions. Une méthode d’éléments finis discontinus a donc été développée afin de les simuler numériquement comme solutions d’´equations de transport. Si l’on souhaite atteindre le régime diffusif aux temps longs, le schéma numérique doit être peu dissipatif et peu dispersif. La discrétisation spatiale a été faite avec des fonctions d’approximation de type spectrales, et l’intégration temporelle avec des schémas de Runge-Kutta d’ordre élevé du type ”strong stability preserving”. Les simulations numériques ont donné des résultats concluants car elles permettent d’exhiber le régime de diffusion. Il a été remarqué qu’il existait en fait deux limites diffusives différentes : (i) la diffusion spatiale de l’´energie sur l’ensemble de la structure, et (ii) l’équirépartition des densités d’énergie entre les différents modes de propagation. Enfin, une technique de renversement temporel a été développée. Elle pourra être utile dans de futurs travaux sur le contrôle non destructif des assemblages complexes et de grandes taillesThis research is dedicated to the simulation of the transient response of beam trusses under impulse loads. The latter lead to the propagation of high-frequency waves in such built up structures. In the aerospace industry, that phenomenon may penalize the functioning of the structures or the equipments attached to them on account of the vibrational energy carried by the waves. It is also observed experimentally that high-frequency wave propagation evolves into a diffusive vibrational state at late times. The goal of this study is then to develop a robust model of high-frequency wave propagation within three-dimensional beam trusses in order to be able to recover, for example, this diffusion regime. On account of the small wavelengths and the high modal density, the modelling of high-frequency wave propagation is hardly feasible by classical finite elements or other methods describing the displacement fields directly. Thus, an approach dealing with the evolution of an estimator of the energy density of each propagating mode in a Timoshenko beam has been used. It provides information on the local behavior of the structures while avoiding some limitations related to the small wavelengths of high-frequency waves. After a comparison between some reduced-order beam kinematics and the Lamb model of wave propagation in a circular waveguide, the Timoshenko kinematics has been selected for the mechanical modelling of the beams. It may be shown that the energy densities of the propagating modes in a Timoshenko beam obey transport equations. Two groups of energy modes have been isolated: the longitudinal group that gathers the compressional and the bending energetic modes, and the transverse group that gathers the shear and torsional energetic modes. The reflection/transmission phenomena taking place at the junctions between beams have also been investigated. For this purpose, the power flow reflection/transmission operators have been derived from the continuity of the displacements and efforts at the junctions. Some characteristic features of a high-frequency behavior at beam junctions have been highlighted such as the decoupling between the rotational and translational motions. It is also observed that the energy densities are discontinuous at the junctions on account of the power flow reflection/transmission phenomena. Thus a discontinuous finite element method has been implemented, in order to solve the transport equations they satisfy. The numerical scheme has to be weakly dissipative and dispersive in order to exhibit the aforementioned diffusive regime arising at late times. That is the reason why spectral-like approximation functions for spatial discretization, and strong-stability preserving Runge-Kutta schemes for time integration have been used. Numerical simulations give satisfactory results because they indeed highlight the outbreak of such a diffusion state. The latter is characterized by the following: (i) the spatial spread of the energy over the truss, and (ii) the equipartition of the energy between the different modes. The last part of the thesis has been devoted to the development of a time reversal processing, that could be useful for future works on structural health monitoring of complex, multi-bay trusses
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Anton, Steven Robert. "Baseline-Free and Self-Powered Structural Health Monitoring." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/33731.
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The research presented in this thesis is based on improving current structural health monitoring (SHM) technology. Structural health monitoring is a damage detection technique that involves placing intelligent sensors on a structure, periodically recording data from the sensors, and using statistical methods to analyze the data in order to assess the condition of the structure. This work focuses on improving two areas of SHM; baseline management and energy supplies. Several successful SHM methods have been developed in which prerecorded baseline measurements are compared to current measurements in order to identify damage. The need to compare new data to a prerecorded baseline can present several complications including data management issues and difficulty in controlling the effects of varying environmental conditions on the data. Another potential area for improvement in SHM systems deals with their energy supplies. Many SHM systems currently require wired power supplies or batteries to operate. Practical SHM applications often require inexpensive, stand alone sensors, data acquisition, and processing hardware that does not require maintenance.
To address the issue of baseline management, a novel SHM technique is developed. This new method accomplishes instantaneous baseline measurements by deploying an array of piezoelectric sensors/actuators used for Lamb wave propagation-based SHM such that data recorded from equidistant sensor-actuator paths can be used to instantaneously identify several common features of undamaged paths. Once identified, features from these undamaged paths can be used to form a baseline for real-time damage detection. This method utilizes the concept of sensor diagnostics, a recently developed technique that minimizes false damage identification and measurement distortion caused by faulty sensors. Several aspects of the instantaneous baseline damage detection method are explored in this work including the implementation of sensor diagnostics, determination of the features best used to identify damage, development of signal processing algorithms used to analyze data, and the comparison of two sensor/actuator deployment schemes.
The ultimate goal in the development of practical SHM systems is to create autonomous damage detection systems. A limiting factor in current SHM technology is the energy supply required to operate the system. Many existing SHM systems utilize wired power supplies or batteries to power sensors, data transmission, data acquisition, and data processing hardware. Although batteries eliminate the need to run wires to SHM hardware, their periodic replacement requires components to be placed in easily accessible locations which is not always practical, especially in embedded applications. Additionally, there is a high cost associated with battery monitoring and replacement. In an effort to eliminate replaceable energy supplies in SHM systems, the concept of energy harvesting is investigated. Energy harvesting devices are designed to capture surrounding ambient energy and convert it into usable electrical energy. Several types of energy harvesting exist, including vibration, thermal, and solar harvesting. A solar energy harvesting system is developed for use in powering SHM hardware. Integrating energy harvesting technology into SHM systems can provide autonomous health monitoring of structures.
Master of Science
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Autrusson, Thibaut Bernard. "Nonlinear ultrasonic guided waves for quantitative life prediction of structures with complex geometries." Thesis, Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/37103.
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Material damage such as dislocations and microcracks are characteristic of early stages of fatigue. Accumulation of these nascent cracks leads to non-linear elastic response of the material. These non-linearities can be detected from harmonic generation for propagating elastic waves. The long term goal of this study is to investigate the non-linear elastic propagation in parts with complex geometry. Cellular Automata is introduced as a new simulation method, in order to develop new analysis on quadratic non-linearities. An existing linear code was progressively modified to take into account a different constitutive law. Also the boundary conditions need to be reviewed to ensure free stress with the non-linear behavior. The propagation of the longitudinal wave is investigated in detail. Numerical accuracy is validated from comparison with a closed, for both linear and non-linear code. The reflection of the non-linear P-wave gives confirmation for the correct treatment of the boundary condition. Finally the capabilities of the Cellular Automata code are underlined for reflection of Lamb waves for various boundary conditions.
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Ahmed, Mustofa N. "A Study of Guided Ultrasonic Wave Propagation Characteristics in Thin Aluminum Plate for Damage Detection." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1387732124.
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Kuechler, Sebastian. "Wave Propagation in an Elastic Half-Space with Quadratic Nonlinearity." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19823.
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This study investigates wave propagation in an elastic half-space with quadratic nonlinearity due to a line load on the surface. The consideration of this problem is one of the well known Lamb problems. Even since Lamb's original solution, numerous investigators have obtained solutions to many different variants of the Lamb problem. However, most of the solutions existing in the current literature are limited to wave propagation in a linear elastic half-space. In this work, the Lamb problem in an elastic half-space with quadratic nonlinearity is considered. For this, the problem is first formulated as a hyperbolic system of conservation laws, which is then solved numerically using a semi-discrete central scheme. The numerical method is implemented using the package CentPack. The accuracy of the numerical method is first studied by comparing the numerical solution with the analytical solution for a half-space with linear response (the original Lamb's problem). The numerical results for the half-space with quadratic nonlinearity are than studied using signal-processing tools such as the fast Fourier transform (FFT) in order to analyze and interpret any nonlinear effects. This in particular gives the possibility to evaluate the excitation of higher order harmonics whose amplitude is used to infer material properties. To quantify and compare the nonlinearity of different materials, two parameters are introduced; these parameters are similar to the acoustical nonlinearity parameter for plane waves.
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Blanquet, Pierrick. "Etude de l'endommagement des matériaux composites aéronautiques à partir de techniques ultrasonores." Valenciennes, 1997. https://ged.uphf.fr/nuxeo/site/esupversions/e46499c3-09ff-4aab-84aa-fc4e6b32ad80.
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Du fait de leurs caractéristiques mécaniques, les matériaux composites ont suscité un intérêt dans de nombreux secteurs industriels (aéronautique, naval, ou automobile). Cet intérêt a aussi engendré le développement de nouvelles techniques de contrôle non destructif. En effet, les techniques classiques de contrôle non-destructif par ultrasons, telles que le c-scan, demeurent longues pour des pièces de grande surface (telles que les plaques). C’est pourquoi, l'utilisation des ondes de Lamb, qui se propagent sur de grandes distances parallèlement à la surface de la plaque, permet de contrôler rapidement une plaque. Le but de cette étude est de déterminer l'existence d'un endommagement sur une ligne de propagation d'une onde de Lamb en utilisant, non pas des transducteurs collés a la surface, mais intégrés au sein de la structure afin de générer et de recevoir des ondes de Lamb. Les grands points présentés lors de ce travail sont : - l'étude de la propagation des ondes de Lamb dans des matériaux isotropes et composites. Un modèle théorique a été développé, et permet de déterminer les courbes de dispersion des ondes de Lamb dans un matériau anisotrope stratifié. - l'étude de l'intégration d'un transducteur dans une plaque de matériau composite. On déterminera alors les effets de l'intégration d'un capteur sur le comportement mécanique d'une plaque, mais aussi les variations d'impédance électrique d'un élément piézo-électrique intégré dans une plaque de composite. - les différents résultats expérimentaux obtenus au cours de ce travail. On y présente les résultats de génération et de réception d'ondes de Lamb à partir d'un capteur intégré. L’interaction d'une onde avec un défaut est étudiée à partir de l'utilisation de l'atténuation, mais aussi à partir d'une méthode d'analyse des signaux reçus basée sur la transformée de Hilbert.
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Anderås, Emil. "Advanced MEMS Pressure Sensors Operating in Fluids." Doctoral thesis, Uppsala universitet, Fasta tillståndets elektronik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-173182.
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Today’s MEMS technology allows manufacturing of miniaturized, low power sensors that sometimes exceeds the performance of conventional sensors. The pressure sensor market today is dominated by MEMS pressure sensors. In this thesis two different pressure sensor techniques are studied. The first concerns ways to improve the sensitivity in the most commonly occurring pressure sensor, namely such based on the piezoresistive technique. Since the giant piezoresistive effect was observed in silicon nanowires, it was assumed that a similar effect could be expected in nano-thin silicon films. However, it turned out that the conductivity was extremely sensitive to substrate bias and could therefore be controlled by varying the backside potential. Another important parameter was the resistivity time drift. Long time measurements showed a drastic variation in the resistance. Not even after several hours of measurement was steady state reached. The drift is explained by hole injection into the buried oxide as well as existence of mobile charges. The piezoresistive effect was studied and shown to be of the same magnitude as in bulk silicon. Later research has shown the existence of such an effect where the film thickness has to be less than around 20 nm. The second area that has been studied is the pressure sensitivity of in acoustic resonators. Aluminium nitride thin film plate acoustic resonators (FPAR) operating at the lowest-order symmetric (S0), the first-order asymmetric (A1) as well as the first-order symmetric (S1) Lamb modes have been theoretically and experimentally studied in a comparative manner. The S0 Lamb mode is identified as the most pressure sensitive FPAR mode. The theoretical predictions were found to be in good agreement with the experiments. Additionally, the Lamb modes have been tested for their sensitivities to mass loading and their ability to operate in liquids, where the S0 mode showed good results. Finally, the pressure sensitivity in aluminium nitride thin film bulk wave resonators employing c- and tilted c-axis texture has been studied. The c-axis tilted FBAR demonstrates a substantially higher pressure sensitivity compared to its c-axis oriented counterpart.
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Levine, Ross M. "Ultrasonic guided wave imaging via sparse reconstruction." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51829.
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Structural health monitoring (SHM) is concerned with the continuous, long-term assessment of structural integrity. One commonly investigated SHM technique uses guided ultrasonic waves, which travel through the structure and interact with damage. Measured signals are then analyzed in software for detection, estimation, and characterization of damage. One common configuration for such a system uses a spatially-distributed array of fixed piezoelectric transducers, which is inexpensive and can cover large areas. Typically, one or more sets of prerecorded baseline signals are measured when the structure is in a known state, with imaging methods operating on differences between follow-up measurements and these baselines. Presented here is a new class of SHM spatially-distributed array algorithms that rely on sparse reconstruction. For this problem, damage over a region of interest (ROI) is considered to be sparse. Two different techniques are demonstrated here. The first, which relies on sparse reconstruction, uses an a priori assumption of scattering behavior to generate a redundant dictionary where each column corresponds to a pixel in the ROI. The second method extends this concept by using multidimensional models for each pixel, with each pixel corresponding to a "block" in the dictionary matrix; this method does not require advance knowledge of scattering behavior. Analysis and experimental results presented demonstrate the validity of the sparsity assumption. Experiments show that images generated with sparse methods are superior to those created with delay-and-sum methods; the techniques here are shown to be tolerant of propagation model mismatch. The block-sparse method described here also allows the extraction of scattering patterns, which can be used for damage characterization.
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Chambon, Hugo. "Simulation and characterization of multi-layered surface acoustic wave devices for filtering and sensing applications." Thesis, Compiègne, 2019. http://www.theses.fr/2019COMP2512.
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Cette thèse porte sur la conception et la caractérisation de micro-dispositifs à ondes acoustiques multicouches. La cinquième génération de communication (5G) nécessite des résonateurs acoustiques plus performants (fréquences > 3GHz, bande passante plus large). Dans ce contexte, nous avons conçu et optimisé par simulation FEM la géométrie de résonateurs à ondes de Lamb à base d’AlScN. Le dispositif final, constitué d’une couche composée de 30% de Sc et déposée sur un miroir de Bragg W/SiO2, montre d’excellentes performances (coefficient de couplage de 5% et facteur de qualité de 768) et un bon accord avec la simulation. Pour caractériser la surface de BAW et SAW sur la gamme de fréquence 5G, nous avons également conçu et développé un interféromètre hétérodyne. Ce dernier a été utilisé avec succès pour caractériser des vibrations de surface d'une amplitude comprise entre 1 et 10 pm à 5,95 GHz. Par ailleurs, grâce à leur robustesse et leur capacité à être interrogé sans-fil, les capteurs SAW sont utilisés dans des environnements difficiles et suscitent un grand intérêt pour les applications médicales et de contrôle de santé intégré. Récemment, l’introduction d’empilements multi-matériaux offre de nouvelles opportunités de développements. Nous avons ainsi étudié un capteur de pression composé de deux couches complémentaires, ainsi qu'un capteur dit package-less utilisant des couches d’impédances acoustiques différentes. Pour concevoir ces nouveaux capteurs, nous avons développé un outil de simulation reposant sur l'extraction de paramètres de couplage de modes et tenant compte des effets de la température, des contraintes et des déformations pour estimer leur sensibilitéThis thesis deals with the design and characterization of multilayer acoustic wave micro-devices. The fifth generation of communication (5G) requires more efficient acoustic resonators (frequencies > 3GHz, wider bandwidth). In this context, we have designed and optimized using FEM simulation, the geometry of Lamb wave resonator based on AlScN. The final device, consisting of a layer composed of 30% Sc and deposited on a Bragg W/SiO2 mirror, shows excellent performance (coupling coefficient of 5% and quality factor of 768) as well as a good agreement with the simulation. To characterize the surface of BAW and SAW over the 5G frequency range, we also designed and developed a heterodyne interferometer. The latter has been used successfully to characterize surface vibrations with amplitudes between 1 and 10 pm at 5.95 GHz. Furthermore, thanks to their robustness and ability to be wirelessly interrogated,SAW sensors are used in harsh environments and are of great interest for medical applications and structural health monitoring. Recently, the introduction of multi-material stacks offers new development opportunities. We thus studied a pressure sensor composed of two complementary layers, as well as a so-called package- less sensor using different acoustic impedance layers. To design these new sensors, we have developed a simulation tool based on the extraction of mode coupling parameters and taking into account the effects of temperature, stresses and strains to estimate their sensitivity
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Willberg, Christian Verfasser], and Ulrich [Akademischer Betreuer] [Gabbert. "Development of a new isogeometric finite element and its application for Lamb wave based structural health monitoring / Christian Willberg. Betreuer: Ulrich Gabbert." Magdeburg : Universitätsbibliothek, 2012. http://d-nb.info/1054135924/34.
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Singh, Gurjashan. "Health Monitoring of Round Objects using Multiple Structural Health Monitoring Techniques." FIU Digital Commons, 2010. http://digitalcommons.fiu.edu/etd/330.
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Structural Health Monitoring (SHM) techniques are widely used in a number of Non – destructive Evaluation (NDE) applications. There is a need to develop effective techniques for SHM, so that the safety and integrity of the structures can be improved. Two most widely used SHM methods for plates and rods use either the spectrum of the impedances or monitor the propagation of lamb waves. Piezoelectric wafer – active sensors (PWAS) were used for excitation and sensing. In this study, surface response to excitation (SuRE) and Lamb wave propagation was monitored to estimate the integrity of the round objects including the pipes, tubes and cutting tools. SuRE obtained the frequency response by applying sweep sine wave to surface. The envelope of the received signal was used to detect the arrival of lamb waves to the sensor. Both approaches detect the structural defects of the pipes and tubes and the wear of the cutting tool.
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Molinero, Inès. "Contribution a l'etude de la diffusion acoustique par des plaques et des fils en incidence oblique : generation d'ondes de surface et d'ondes guidees." Paris 7, 1987. http://www.theses.fr/1987PA077136.
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Les solutions des equations de dispersion peuvent etre associees respectivement aux modes de lamb symetriques et antisymetriques dans le cas d'une plaque et aux modes longitudinaux et de flexion dans le cas d'un cylindre. Presentation d'une analyse experimentale approfondie du comportement non speculaire d'un faisceau borne incident sur une plaque
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Vedantham, Vikram. "In-situ temperature and thickness characterization for silicon wafers undergoing thermal annealing." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/1181.
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Nano scale processing of IC chips has become the prime production technique as the microelectronic industry aims towards scaling down product dimensions while increasing accuracy and performance. Accurate control of temperature and a good monitoring mechanism for thickness of the deposition layers during epitaxial growth are critical parameters influencing a good yield. The two-fold objective of this thesis is to establish the feasibility of an alternative to the current pyrometric and ellipsometric techniques to simultaneously measure temperature and thickness during wafer processing. TAP-NDE is a non-contact, non-invasive, laser-based ultrasound technique that is employed in this study to contemporarily profile the thermal and spatial characteristics of the wafer. The Gabor wavelet transform allows the wave dispersion to be unraveled and the group velocity of individual frequency components to be extracted from the experimentally acquired time waveform. The thesis illustrates the formulation of a theoretical model that is used to identify the frequencies sensitive to temperature and thickness changes. The group velocity of the corresponding frequency components is determined and their corresponding changes with respect to temperature for different thickness are analytically modeled. TAP-NDE is then used to perform an experimental analysis on Silicon wafers of different thickness to determine the maximum possible resolution of TAP-NDE towards temperature sensitivity, and to demonstrate the ability to differentiate between wafers of different deposition layer thickness at temperatures up to 600?C. Temperature resolution is demonstrated for ?10?C resolution and for ?5?C resolution; while thickness differentiation is carried out with wafers carrying 4000? and 8000? of aluminum deposition layer. The experimental group velocities of a set of selected frequency components extracted using the Gabor Wavelet time-frequency analysis as compared to their corresponding theoretical group velocities show satisfactory agreement. As a result of this work, it is seen that TAP-NDE is a suitable tool to identify and characterize thickness and temperature changes simultaneously during thermal annealing that can replace the current need for separate characterization of these two important parameters in semiconductor manufacturing.
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Javidan, Mohammad. "Conception des modulateurs sigma-delta d'ordre élévé pour des convertisseurs analogique-numérique en parallèle." Phd thesis, Université Paris Sud - Paris XI, 2009. http://tel.archives-ouvertes.fr/tel-00469483.
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Dans ce travail intitulé « Conception de modulateurs Sigma-Delta d'ordre élevé pour convertisseurs analogique-numérique en parallèle », les travaux ont été menés dans le contexte de la radio logicielle. La voie proposée pour la réalisation du convertisseur analogique-numérique, élément clé et bloquant de la radio logicielle, est une structure composée de plusieurs modulateurs sigma-delta passe-bande à temps continu mis en parallèle. Après avoir énuméré les différentes spécifications auxquelles le modulateur doit satisfaire, une nouvelle méthodologie de design à été proposé. Un état de l'art des différentes technologies de réalisation des filtres du modulateur a été réalisé, aboutissant à l'utilisation de résonateurs à filtres à ondes d'onde de Lamb. Les caractéristiques de ce résonateur ont été présentées ainsi qu'un circuit de commande permettant la compensation des inconvénients. Après avoir défini une novelle topologie et le résonateur, une méthode pour optimiser les performances de chaque modulateur en fonction des imperfections de l'électronique utilisée pour l'implémentation en fonction de la fréquence centrale de chacun d'entre eux a été proposé. Un travail d'analyse permettant de mettre en évidence l'influence de chacun des défauts électroniques importants sur les performances globales du modulateur, que ce soit en termes de résolution ou de stabilité, a été développé. Le comportement de la fonction de transfert de signal (STF) du système optimisé ne correspond pas à un filtre sélecteur de bande. Une modification originale de la topologie du modulateur permettant l'amélioration de la réponse en fréquence de la STF sans modifier la fonction de transfert du bruit (NTF) a été proposée. Enfin, la réalisation d'un modulateur sigma-delta à temps continu du deuxième ordre au niveau layout a été effectuée. La réduction de l'ordre est justifiée par le fait que l'intégration d'un filtre à onde de Lamb n'est pas encore un processus bien maitrisé et que son utilisation dans un sixième ordre pourrait aboutir à un circuit inexploitable en termes d'analyse.
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Bjurström, Johan. "Advanced Thin Film Electroacoustic Devices." Doctoral thesis, Uppsala universitet, Fasta tillståndets elektronik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7672.
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The explosive development of the telecom industry and in particular wireless and mobile communications in recent years has lead to a rapid development of new component and fabrication technologies to continually satisfy the mutually exclusive requirements for better performance and miniaturization on the one hand and low cost on the other. A fundamental element in radio communications is time and frequency control, which in turn is achieved by high performance electro-acoustic components made on piezoelectric single crystalline substrates. The latter, however, reach their practical limits in terms of performance and cost as the frequency of operation reaches the microwave range. Thus, the thin film electro-acoustic technology, which uses thin piezoelectric films instead, has been recently developed to alleviate these deficiencies. This thesis explores and addresses a number of issues related to thin film synthesis on the one hand as well as component design and fabrication on other. Specifically, the growth of highly c-axis textured AlN thin films has been studied and optimized for achieving high device performance. Perhaps, one of the biggest achievements of the work is the development of a unique process for the deposition of AlN films with a mean c-axis tilt, which is of vital importance for the fabrication of resonators operating in contact with liquids, i.e. biochemical sensors. This opens the way for the development of a whole range of sensors and bio-analytical tools. Further, high frequency Lamb wave resonators have been designed, fabricated and evaluated. Performance enhancement of FBAR devices is also addressed, e.g. spurious mode suppression, temperature compensation, etc. It has been demonstrated, that even without temperature compensation, shear mode resonators operating in a liquid still exhibit an excellent performance in terms of Q (200) and coupling (~1.8%) at 1.2 GHz, resulting in a mass resolution better than 2 ng cm-2 in water, which excels that of today’s quartz sensors.
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Moutaouekkil, Mohammed. "Etude de la propagation des ondes élastiques de Lamb dans les matériaux composites micro/nano structurés : Application pour l’ingénierie des propriétés physiques des résonateurs électromécaniques." Thesis, Ecole centrale de Lille, 2018. http://www.theses.fr/2018ECLI0011/document.
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Le contrôle de la propagation des ondes élastiques repose principalement sur la conception de milieu artificiel à base de matériaux structurés pour obtenir une ingénierie avancée de la dispersion de la propagation. Au cours de la thèse, la dispersion du mode (S0) dans des membranes micro-structurées à base d’AlN a été numériquement investiguée et les applications qui en découlent explorées. Il est mis en évidence le lien fort entre la dispersion du mode et la sensibilité aux perturbations externes en combinant la membrane d’AlN avec une couche de SiO2 structurée en rubans. En particulier, il est montré qu’il est possible d’obtenir un TCF=0 pour les résonateurs sans presque aucune dégradation du coefficient K2. Il est montré qu’il est possible d’ouvrir des bandes interdites avec une largeur de l’ordre de 50% en structurant l’AlN sous forme de rubans ou en utilisant des piliers pour former un PhnC. Sur cette base, des designs de cavités et de guides d’ondes sont proposés et leurs performances sont étudiées en fonction des paramètres géométriques. Il est également proposé un nouveau design de cavité basé sur l’introduction d’un défaut résonant dans le PhnC sous forme de disque de dimension très petite par-rapport à la taille de la cellule élémentaire. Le défaut permet d’introduire des modes quasi-plats dans le diagramme de bande et permet en conséquence la conception d’une nouvelle génération de dispositifs phononiques robustes pour des applications en traitement du signal et capteurs. Les structures optimales sont utilisées pour la conception de capteur de champs magnétiques, une sensibilité de 5% est obtenue pour le mode localisé dans le cas d’un disque magnéto-élastiqueThe control of elastic wave propagation relies mainly on the design of artificial media based on structured materials to achieve advanced propagation dispersion engineering. During the thesis, the dispersion of the mode (S0) in micro-structured membranes based on AlN was numerically investigated and the resulting applications explored. The strong link between mode dispersion and sensitivity to external disturbances is highlighted by combining the AlN membrane with a layer of SiO2 structured into strips. In particular, it is shown that it is possible to obtain a TCF = 0 for the resonators without any degradation of the K2 coefficient. It is shown that it is possible to open wide band-gaps of 50% by structuring the AlN in the shape of strips or using pillars to form a PhnC. On this basis, designs of cavities and waveguides are proposed and their performances are studied according to the geometrical parameters. It is also proposed a new cavity design based on the introduction of a resonant defect with a disc shape in the PhnC and presenting very small size in comparison to the unit cell. The defect makes it possible to introduce quasi-flat modes in the band diagram and consequently allows the design of a new generation of phononic devices for signal processing and sensor applications. The optimal structures are used to design a magnetic field sensor design, a sensitivity of 5% is obtained for the localized mode in the case of defect based on magneto-elastic thin film
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Talmant, Maryline. "Retrodiffusion d'une impulsion ultrasonore breve par une coque cylindrique a paroi mince." Paris 7, 1987. http://www.theses.fr/1987PA077164.
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Une comparaison peut etre etablie entre les ondes circonferentielles se propageant a la surface du tube et les ondes de surface se propageant sur une plaque plane. L'analyse experimentale est fondee sur l'obtention des variations de la vitesse de groupe en fonction de la frequence des ondes circonferentielles ainsi que de leur reemission
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Benjamin, Rishon Robert. "Silence of the lamb waves." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111503.
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Thesis: S.M., Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 101-104).
Roll-to-Roll (R2R) manufacturing has seen great interest in the recent decade due to the proliferation of personalized and wearable devices for monitoring a variety of biometrics. Given the sensitive nature of the potential applications of these sensors, the throughput of manufacturing due to increased demand, and the scale of the electrical components being manufactured, R2R flexible electronics manufacturing technologies require new sensing and measurement capabilities for defect detection and process control. The work presented herein investigates the use of ultrasound, specifically Lamb and longitudinal waves, as a sensing modality and measurement technique for thin film R2R manufacturing substrates. Contact (transducer-based) and non-contact (photoacoustic) generation methods along with deterministic and probabilistic tomographic reconstruction algorithms were implemented evaluate their suitability for non-destructive evaluation (NDE) and in-line control of surface additions of 76[mu]m aluminum and polyethylene terephthalate (PET) films. The ultrasonic waves were used to ascertain properties of these substrates such as the thickness of substrate, applied load, presence of defects (holes/cracks), size of defects, presence of surface features (fluid drops, multi-layer structures), and nature of surface features (differing chemistries). In addition, surface features alter the behavior of sound waves in the presence of such features. These surface features may then be imaged to create tomographic maps. The results presented show that, currently, a quasi-contact acoustic generation scheme can be used to successfully image defects and surface features on the order of -1mm. Furthermore, the algorithm is able to distinguish qualitatively between surface features of differing physiochemical properties. The authors hope that the information collected from this thesis will be part of a rich data set that can contribute to advanced machine-learning frameworks for predictive maintenance, failure, and process control analysis for the R2R process.
by Rishon Robert Benjamin.
S.M.