Thesis--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution. / Includes bibliographical references (leaves 220-233).

The Multichannel Analysis of Surface Waves (MASW) method has been widely used to evaluate the subsurface in engineering applications since late 1990’s. In MASW, surface waves are introduced into the subsurface and recorded by sensors along the ground surface. The characteristics of the propagating surface wave are influenced by the subsurface stratification, the manner in which the surface waves are input into the ground, and the survey parameters to acquire data. Rayleigh waves are typically generated by vertical strikes on a metallic plate which serves as a coupler between the active input source (e.g., a sledgehammer) and the ground surface. It has been suggested that plastic-type base plates can improve the low-frequency energy of Rayleigh waves and therefore, can increase the depth of investigation among other potential improvements. However, very little studies exist in the literature that evaluate the role of base plate material, especially plastic materials. In addition to Rayleigh surface waves, seismic surface waves can also be generated with horizontal impacts (i.e., Love waves) using specialized base plates. In this regard, much less is available in the literature regarding Love waves as sources in MASW testing which means that optimum field survey parameters, the effects of near-field, and the role of seismic source have not been thoroughly investigated yet for Love waves. Given the aforementioned gaps in the literature, two aspects of MASW have been investigated. First, the role of base plate material, specifically plastic-type plates, has been studied. Field data collected from six sites along with the data from laboratory experiments and numerical simulations of hammer-plate impact were studied. The results showed that softer base plates improve the energy transfer by as much 20% and lead to minor improvements, typically one-digit numbers in relative changes, in other signal characteristics such as signal bandwidth and signal-to-noise ratio. These results were corroborated with laboratory testing and numerical models of wave propagation with different base plate materials. The second goal was to improve understanding of Love wave propagation, particularly as related to resolution capabilities from survey parameters. Rayleigh and Love waveforms were collected with multiple active seismic sources at three sites and a systematic comparison was made between the two types of waves. Also, seismic wave propagation was simulated using the research community code SPECFEM2D to further investigate their differences. The results revealed critical new information about the depth of investigation, the effects of bedrock location on near-field effects, and the role of the different survey parameters on Rayleigh and Love wave data. The depth of investigation of Love wave MASW was deeper by about 2-9 m than that of Rayleigh MASW as a result of improved minimum frequency. The minimum source offset to avoid near-field effects was comparable for both Rayleigh and Love waves (0.3-0.4 of maximum wavelength). At closer source offset locations, Rayleigh waves were more affected by near-field effects and showed an additional 10% underestimation of planar phase velocities. Overall, the results from both parts of this study provides new practical insights about some of the unexplored aspects of surface wave testing using MASW. / Civil Engineering

Seismic records contain information that allows geoscientists to make inferences about the structure and properties of the Earth’s interior. Traditionally, seismic imaging and tomography methods require wavefields to be generated and recorded by identifiable sources and receivers, and use these directly-recorded signals to create models of the Earth’s subsurface. However, in recent years the method of seismic interferometry has revolutionised earthquake seismology by allowing unrecorded signals between pairs of receivers, pairs of sources, and source-receiver pairs to be constructed as Green’s functions using either cross-correlation, convolution or deconvolution of wavefields. In all of these formulations, seismic energy is recorded and emitted by surrounding boundaries of receivers and sources, which need not be active and impulsive but may even constitute continuous, naturally-occurring seismic ambient noise. In the first part of this thesis, I provide a comprehensive overview of seismic interferometry, its background theory, and examples of its application. I then test the theory and evaluate the effects of approximations that are commonly made when the interferometric formulae are applied to real datasets. Since errors resulting from some approximations can be subtle, these tests must be performed using almost error-free synthetic data produced with an exact waveform modelling method. To make such tests challenging the method and associated code must be applicable to multiply-scattering media. I developed such a modelling code specifically for interferometric tests and applications. Since virtually no errors are introduced into the results from modelling, any difference between the true and interferometric waveforms can safely be attributed to specific origins in interferometric theory. I show that this is not possible when using other, previously available methods: for example, the errors introduced into waveforms synthesised by finite-difference methods due to the modelling method itself, are larger than the errors incurred due to some (still significant) interferometric approximations; hence that modelling method can not be used to test these commonly-applied approximations. I then discuss the ability of interferometry to redatum seismic energy in both space and time, allowing virtual seismograms to be constructed at new locations where receivers may not have been present at the time of occurrence of the associated seismic source. I present the first successful application of this method to real datasets at multiple length scales. Although the results are restricted to limited bandwidths, this study demonstrates that the technique is a powerful tool in seismologists’ arsenal, paving the way for a new type of ‘retrospective’ seismology where sensors may be installed at any desired location at any time, and recordings of seismic events occurring at any other time can be constructed retrospectively – even long after their energy has dissipated. Within crustal seismology, a very common application of seismic interferometry is ambient-noise tomography (ANT). ANT is an Earth imaging method which makes use of inter-station Green’s functions constructed from cross-correlation of seismic ambient noise records. It is particularly useful in seismically quiescent areas where traditional tomography methods that rely on local earthquake sources would fail to produce interpretable results due to the lack of available data. Once constructed, interferometric Green’s functions can be analysed using standard waveform analysis techniques, and inverted for subsurface structure using more or less traditional imaging methods. In the second part of this thesis, I discuss the development and implementation of a fully non-linear inversion method which I use to perform Love-wave ANT across the British Isles. Full non-linearity is achieved by allowing both raypaths and model parametrisation to vary freely during inversion in Bayesian, Markov chain Monte Carlo tomography, the first time that this has been attempted. Since the inversion produces not only one, but a large ensemble of models, all of which fit the data to within the noise level, statistical moments of different order such as the mean or average model, or the standard deviation of seismic velocity structures across the ensemble, may be calculated: while the ensemble average map provides a smooth representation of the velocity field, a measure of model uncertainty can be obtained from the standard deviation map. In a number of real-data and synthetic examples, I show that the combination of variable raypaths and model parametrisation is key to the emergence of previously-unobserved, loop-like uncertainty topologies in the standard deviation maps. These uncertainty loops surround low- or high-velocity anomalies. They indicate that, while the velocity of each anomaly may be fairly well reconstructed, its exact location and size tend to remain uncertain; loops parametrise this location uncertainty, and hence constitute a fully non-linearised, Bayesian measure of spatial resolution. The uncertainty in anomaly location is shown to be due mainly to the location of the raypaths that were used to constrain the anomaly also only being known approximately. The emergence of loops is therefore related to the variation in raypaths with velocity structure, and hence to 2nd and higher order wave-physics. Thus, loops can only be observed using non-linear inversion methods such as the one described herein, explaining why these topologies have never been observed previously. I then present the results of fully non-linearised Love-wave group-velocity tomography of the British Isles in different frequency bands. At all of the analysed periods, the group-velocity maps show a good correlation with known geology of the region, and also robustly detect novel features. The shear-velocity structure with depth across the Irish Sea sedimentary basin is then investigated by inverting the Love-wave group-velocity maps, again fully non-linearly using Markov chain Monte Carlo inversion, showing an approximate depth to basement of 5 km. Finally, I discuss the advantages and current limitations of the fully non-linear tomography method implemented in this project, and provide guidelines and suggestions for its improvement.

Este trabalho teve como objetivo a realização de um estudo sobre o método MASW (Análise Multicanal de Ondas de Superfície) avaliando-se comparativamente resultados obtidos por diferentes fontes (ativas e passivas), ondas Rayleigh e Love e diferentes modos de propagação das ondas de superfície. Dois ensaios sísmicos foram executados: com geometria de aquisição bidimensional e geofones triaxiais de 10Hz, e com geometria linear e geofones de componente vertical de 4,5Hz. Foram realizados estudos com as fontes marreta, compactador de solo, ruído ambiental e com o tráfego de veículos, a última através da técnica Passive Roadside MASW. Resultados de inversões com dados da componente vertical (ondas Rayleigh) das ondas de superfície foram avaliados com os de inversões conjuntas com a componente radial (ondas Rayleigh) e transversal (ondas Love). Analisou-se também os produtos de inversões da curva de dispersão do modo fundamental com os de inversões conjuntas com o primeiro modo superior. Os estudos foram realizados em frente ao Instituto de Astronomia, Geofísica e Ciência Atmosféricas (IAG) localizado no interior do campus Cidade Universitária Armando de Salles Oliveira (CUASO) da Universidade de São Paulo (USP) no bairro do Butantã, São Paulo. A área de estudo possui informações de sondagem mista com descrição geológica do material e valores SPT (Standard Penetration Test) que foram utilizados para validação dos resultados. O compactador de solo demonstrou ser uma melhor fonte ativa em relação a marreta através de diferentes aspectos: geração de maior energia tanto na componente vertical quanto na transversal; espectros (V,f) de melhor qualidade; os dados apresentam a vantagem de poderem ser processados através da técnica f-k beamforming. A aquisição com o ruído ambiental não possibilitou a interpretação de curvas de dispersão devido ao pouco tempo de aquisição utilizado. Os dados obtidos pela técnica Passive Roadside MASW contribuíram com os dados de ativa através do registro de frequências mais baixas. Além disso, devido a clara identificação do 1° modo superior em seu espectro (V,f) foi possível a identificação do mesmo modo no espectro (V,f) dos dados de ativa, interpretação até então duvidosa. No entanto, a inversão conjunta das curvas de dispersão dos dados Passive Roadside com as dos dados de ativa não resultou em uma melhor inversão comparada com a inversão obtida apenas pelas curvas de ativa. A inversão conjunta de curvas das componentes radial (ondas Rayleigh) e transversal (ondas Love) com as curvas obtidas da componente vertical (ondas Rayleigh) também não trouxe um melhor resultado quando comparada com a inversão alcançada apenas com as curvas da componente vertical. A utilização do primeiro modo superior com o modo fundamental, no entanto, mostrou trazer melhoras significativas nos resultados das inversões em comparação com inversões apenas da curva do modo fundamental. Considerando as incertezas envolvidas os melhores resultados deste trabalho são convergentes com os dados de sondagem da área de estudo. No atual estágio de desenvolvimento do método MASW diversas etapas são bastante dependentes do operador. Neste sentido os estudos realizados neste trabalho contribuem para um melhor entendimento do método nos seus fundamentos, parâmetros de aquisição e processamento. / This work aim to study the MASW (Multichannel Analysis of Surface Waves) method by comparing results obtained with different sources (active and passive), Rayleigh and Love waves and different modes of surface waves propagation. Two seismic tests were performed: one with two-dimensional acquisition geometry and 10Hz triaxial geophones, and the other with linear geometry and 4.5 Hz vertical component geophones. Studies were carried out with the following sources: sledgehammer, rammer compactor, ambient noise and vehicular traffic, the last through the Passive Roadside MASW technique. Inversions results with vertical component data (Rayleigh waves) were evaluated through joint inversions with the radial (Rayleigh waves) and transversal (Love waves) components. It were also analyzed the inversions results of the fundamental mode of the dispersion curve with the results of joint inversions with the first higher mode. The studies were carried out in front of the Instituto de Astronomia, Geofísica e Ciência Atmosféricas (IAG) (Institute of Astronomy, Geophysics and Atmospheric Science) located inside the university campus Cidade Universitária Armando de Salles Oliveira (CUASO) of Universidade de São Paulo (USP) (University of São Paulo) in the neighborhood of Butantã, São Paulo. The study area has information with a geological material description and SPT (Standard Penetration Test) values that were used to validate the results. The rammer compactor showed to be a better active source in relation to sledgehammer through different aspects: generation of greater energy in vertical and transverse components; better quality of (V,f) spectrum; the data have the advantage that they can be processed using the f-k beamforming technique. The acquisition with ambient noise did not allow the dispersion curves interpretation due to the short acquisition time used. Passive Roadside MASW data contributed to the active data through the lower frequency. Besides that, due to the clear identification of the 1st higher mode in its (V,f) spectrum it was possible to identify the same mode in the (V,f) spectrum of the active data, interpretation that was, until then, doubtful. However, the joint inversion of the Passive Roadside dispersion curves with the active curves did not produce better results compared to the inversion obtained only by the active curves. The joint inversion of dispersion curves from radial (Rayleigh) and transversal (Love waves) components with the curves obtained by the vertical component (Rayleigh waves) also did not bring a better result when compared with the inversion achieved only by the vertical component curves. The use of the first higher mode with the fundamental mode, however, showed significant improvements in the joint inversions results compared to inversions only of the fundamental mode curve. Considering the uncertainties involved, the best results of this work converge with the a priori information of the study area. At the current MASW method stage of development, several steps are quite dependent on the operator. Therefore, the studies carried out in this work contribute to a better understanding of the method in its fundamentals, acquisition parameters and processing.

Este trabalho teve como objetivo a realização de um estudo sobre o método MASW (Análise Multicanal de Ondas de Superfície) avaliando-se comparativamente resultados obtidos por diferentes fontes (ativas e passivas), ondas Rayleigh e Love e diferentes modos de propagação das ondas de superfície. Dois ensaios sísmicos foram executados: com geometria de aquisição bidimensional e geofones triaxiais de 10Hz, e com geometria linear e geofones de componente vertical de 4,5Hz. Foram realizados estudos com as fontes marreta, compactador de solo, ruído ambiental e com o tráfego de veículos, a última através da técnica Passive Roadside MASW. Resultados de inversões com dados da componente vertical (ondas Rayleigh) das ondas de superfície foram avaliados com os de inversões conjuntas com a componente radial (ondas Rayleigh) e transversal (ondas Love). Analisou-se também os produtos de inversões da curva de dispersão do modo fundamental com os de inversões conjuntas com o primeiro modo superior. Os estudos foram realizados em frente ao Instituto de Astronomia, Geofísica e Ciência Atmosféricas (IAG) localizado no interior do campus Cidade Universitária Armando de Salles Oliveira (CUASO) da Universidade de São Paulo (USP) no bairro do Butantã, São Paulo. A área de estudo possui informações de sondagem mista com descrição geológica do material e valores SPT (Standard Penetration Test) que foram utilizados para validação dos resultados. O compactador de solo demonstrou ser uma melhor fonte ativa em relação a marreta através de diferentes aspectos: geração de maior energia tanto na componente vertical quanto na transversal; espectros (V,f) de melhor qualidade; os dados apresentam a vantagem de poderem ser processados através da técnica f-k beamforming. A aquisição com o ruído ambiental não possibilitou a interpretação de curvas de dispersão devido ao pouco tempo de aquisição utilizado. Os dados obtidos pela técnica Passive Roadside MASW contribuíram com os dados de ativa através do registro de frequências mais baixas. Além disso, devido a clara identificação do 1° modo superior em seu espectro (V,f) foi possível a identificação do mesmo modo no espectro (V,f) dos dados de ativa, interpretação até então duvidosa. No entanto, a inversão conjunta das curvas de dispersão dos dados Passive Roadside com as dos dados de ativa não resultou em uma melhor inversão comparada com a inversão obtida apenas pelas curvas de ativa. A inversão conjunta de curvas das componentes radial (ondas Rayleigh) e transversal (ondas Love) com as curvas obtidas da componente vertical (ondas Rayleigh) também não trouxe um melhor resultado quando comparada com a inversão alcançada apenas com as curvas da componente vertical. A utilização do primeiro modo superior com o modo fundamental, no entanto, mostrou trazer melhoras significativas nos resultados das inversões em comparação com inversões apenas da curva do modo fundamental. Considerando as incertezas envolvidas os melhores resultados deste trabalho são convergentes com os dados de sondagem da área de estudo. No atual estágio de desenvolvimento do método MASW diversas etapas são bastante dependentes do operador. Neste sentido os estudos realizados neste trabalho contribuem para um melhor entendimento do método nos seus fundamentos, parâmetros de aquisição e processamento. / This work aim to study the MASW (Multichannel Analysis of Surface Waves) method by comparing results obtained with different sources (active and passive), Rayleigh and Love waves and different modes of surface waves propagation. Two seismic tests were performed: one with two-dimensional acquisition geometry and 10Hz triaxial geophones, and the other with linear geometry and 4.5 Hz vertical component geophones. Studies were carried out with the following sources: sledgehammer, rammer compactor, ambient noise and vehicular traffic, the last through the Passive Roadside MASW technique. Inversions results with vertical component data (Rayleigh waves) were evaluated through joint inversions with the radial (Rayleigh waves) and transversal (Love waves) components. It were also analyzed the inversions results of the fundamental mode of the dispersion curve with the results of joint inversions with the first higher mode. The studies were carried out in front of the Instituto de Astronomia, Geofísica e Ciência Atmosféricas (IAG) (Institute of Astronomy, Geophysics and Atmospheric Science) located inside the university campus Cidade Universitária Armando de Salles Oliveira (CUASO) of Universidade de São Paulo (USP) (University of São Paulo) in the neighborhood of Butantã, São Paulo. The study area has information with a geological material description and SPT (Standard Penetration Test) values that were used to validate the results. The rammer compactor showed to be a better active source in relation to sledgehammer through different aspects: generation of greater energy in vertical and transverse components; better quality of (V,f) spectrum; the data have the advantage that they can be processed using the f-k beamforming technique. The acquisition with ambient noise did not allow the dispersion curves interpretation due to the short acquisition time used. Passive Roadside MASW data contributed to the active data through the lower frequency. Besides that, due to the clear identification of the 1st higher mode in its (V,f) spectrum it was possible to identify the same mode in the (V,f) spectrum of the active data, interpretation that was, until then, doubtful. However, the joint inversion of the Passive Roadside dispersion curves with the active curves did not produce better results compared to the inversion obtained only by the active curves. The joint inversion of dispersion curves from radial (Rayleigh) and transversal (Love waves) components with the curves obtained by the vertical component (Rayleigh waves) also did not bring a better result when compared with the inversion achieved only by the vertical component curves. The use of the first higher mode with the fundamental mode, however, showed significant improvements in the joint inversions results compared to inversions only of the fundamental mode curve. Considering the uncertainties involved, the best results of this work converge with the a priori information of the study area. At the current MASW method stage of development, several steps are quite dependent on the operator. Therefore, the studies carried out in this work contribute to a better understanding of the method in its fundamentals, acquisition parameters and processing.

The fields of health care and environment control have an increasing demand for sensors able to detect low concentrations of specific molecules in gaseous or liquid samples. The recent introduction of microfabricated devices in these fields gave rise to sensors with attractive properties. A cutting edge technology is based on guided acoustic waves, which are perturbed by events occurring at the nanometer scale. A first part of the thesis investigates the Love mode waveguide, a versatile structure in which a thin film is guiding the acoustic wave generated in a piezoelectric substrate. A systematic analysis of its sensitivity was obtained using a transmission line model generalized to discriminate the rigid or viscous nature of the probed layers. We developed a novel integrated combination of the Love mode device with a Surface Plasmon Resonance optical sensor to quantify the thickness and the composition of soft layers. The electromagnetic interferences in the recorded signal were modeled to determine the phase velocity in the sensing area and to provide new mechanisms for an enhanced sensitivity. The experimental aspects of this work deal with the fabrication, the important issue of the packaging and the sensitivity calibration of the Love mode biosensor. A second part of the thesis investigates nanocrystalline diamond under the form of a thin film membrane suspended to a rigid silicon frame. The high mechanical and chemical resistance of nanocrystalline diamond, close to single-crystal diamond, open ways to membrane based acoustic sensors such as Flexural Plate Wave and thin Film Bulk Acoustic Resonators (FBAR). A novel dynamic characterization of the thin film is reported and the properties of composite FBAR devices including a diamond thin film membrane and a piezoelectric aluminum nitride layer are assessed using the perturbation theory. This study is applied to evaluate the high sensing potential of the first prototype of an actual diamond-based composite FBAR.

The fields of health care and environment control have an increasing demand for sensors able to detect low concentrations of specific molecules in gaseous or liquid samples. The recent introduction of microfabricated devices in these fields gave rise to sensors with attractive properties. A cutting edge technology is based on guided acoustic waves, which are perturbed by events occurring at the nanometer scale. A first part of the thesis investigates the Love mode waveguide, a versatile structure in which a thin film is guiding the acoustic wave generated in a piezoelectric substrate. A systematic analysis of its sensitivity was obtained using a transmission line model generalized to discriminate the rigid or viscous nature of the probed layers. We developed a novel integrated combination of the Love mode device with a Surface Plasmon Resonance optical sensor to quantify the thickness and the composition of soft layers. The electromagnetic interferences in the recorded signal were modeled to determine the phase velocity in the sensing area and to provide new mechanisms for an enhanced sensitivity. The experimental aspects of this work deal with the fabrication, the important issue of the packaging and the sensitivity calibration of the Love mode biosensor. A second part of the thesis investigates nanocrystalline diamond under the form of a thin film membrane suspended to a rigid silicon frame. The high mechanical and chemical resistance of nanocrystalline diamond, close to single-crystal diamond, open ways to membrane based acoustic sensors such as Flexural Plate Wave and thin Film Bulk Acoustic Resonators (FBAR). A novel dynamic characterization of the thin film is reported and the properties of composite FBAR devices including a diamond thin film membrane and a piezoelectric aluminum nitride layer are assessed using the perturbation theory. This study is applied to evaluate the high sensing potential of the first prototype of an actual diamond-based composite FBAR.

Le contexte de cette thèse est la théorie de l'élasticité non linéaire, appelée également "élasticité finie". On y présente des résultats concernant la propagation d'ondes d'amplitude finie dans des matériaux élastiques non linéaires soumis à une grande déformation statique homogène. Bien que les matériaux considérés soient isotropes, lors de la propagation d'ondes un comportement anisotrope dû à la déformation statique se manifeste. Après un rappel des équations de base de l'élasticité non linéaire (Chapitre 1), on considère tout d'abord la classe générale des matériaux incompressibles. Pour ces matériaux, on montre que la propagation d'ondes transversales polarisées linéairement est possible pour des choix appropriés des directions de polarisation et de propagation. De plus, on propose des généralisations des modèles classiques de "Mooney-Rivlin" et "néo-Hookéen" qui conduisent à de nouvelles solutions. Bien que le contexte soit tri-dimensionnel, il s'avère que toutes ces ondes sont régies par des équations d'ondes scalaires non linéaires uni-dimensionelles. Dans le cas de solutions du type ondes simples, on met en évidence une propriété remarquable du flux et de la densité d'énergie. Dans les Chapitres 3 et 4, on se limite à un modèle particulier de matériaux compressibles appelé "modèle restreint de Blatz-Ko", qui est une version compressible du modèle néo-Hookéen. En milieu infini (Chapitre 3), on montre que des ondes transversales polarisées linéairement, faisant intervenir deux variables spatiales, peuvent se propager. Bien que la théorie soit non linéaire, le champ de déplacement de ces ondes est régi par une version anisotrope de l'équation d'onde bi-dimensionnelle classique. En particulier, on présente des solutions à symétrie "cylindrique elliptique" analogues aux ondes cylindriques. Comme cas particulier, on obtient aussi des ondes planes inhomogènes atténuées à la fois dans l'espace et dans le temps. De plus, on montre que diverses superpositions appropriées de solutions sont possibles. Dans chaque cas, on étudie les propriétés du flux et de la densité d'énergie. En particulier, dans le cas de superpositions il s'avère que des termes d'interactions interviennent dans les expressions de la densité et du flux d'énergie. Finalement (Chapitre 4), on présente une solution exacte qui constitue une généralisation non linéaire de l'onde de Love classique. On considère ici un espace semi-infini, appelé "substrat" recouvert par une couche. Le substrat et la couche sont constitués de deux matériaux restreints de Blatz-Ko pré-déformés. L'onde non linéaire de Love est constituée d'un mouvement non atténué dans la couche et d'une onde plane inhomogène dans le substrat, choisies de manière à satisfaire aux conditions aux limites. La relation de dispersion qui en résulte est analysée en détail. On présente de plus des propriétés générales du flux et de la densité d'énergie dans le substrat et dans la couche. The context of this thesis is the non linear elasticity theory, also called "finite elasticity". Results are obtained for finite-amplitude waves in non linear elastic materials which are first subjected to a large homogeneous static deformation. Although the materials are assumed to be isotropic, anisotropic behaviour for wave propagation is induced by the static deformation. After recalling the basic equations of the non linear elasticity theory (Chapter 1), we first consider general incompressible materials. For such materials, linearly polarized transverse plane waves solutions are obtained for adequate choices of the polarization and propagation directions (Chapter 2). Also, extensions of the classical Mooney-Rivlin and neo-Hookean models are introduced, for which more solutions are obtained. Although we use the full three dimensional elasticity theory, it turns out that all these waves are governed by scalar one-dimensional non linear wave equations. In the case of simple wave solutions of these equations, a remarkable property of the energy flux and energy density is exhibited. In Chapter 3 and 4, a special model of compressible material is considered: the special Blatz-Ko model, which is a compressible counterpart of the incompressible neo-Hookean model. In unbounded media (Chapter 3), linearly polarized two-dimensional transverse waves are obtained. Although the theory is non linear, the displacement field of these waves is governed by a linear equation which may be seen as an anisotropic version of the classical two-dimensional wave equation. In particular, solutions analogous to cylindrical waves, but with an "elliptic cylindrical symmetry" are presented. Special solutions representing "damped inhomogeneous plane waves" are also derived: such waves are attenuated both in space and time. Moreover, various appropriate superpositions of solutions are shown to be possible. In each case, the properties of the energy density and the energy flux are investigated. In particular, in the case of superpositions, it is seen that interaction terms enter the expressions for the energy density and the energy flux. Finally (Chapter 4), an exact finite-amplitude Love wave solution is presented. Here, an half-space, called "substrate", is assumed to be covered by a layer, both made of different prestrained special Blatz-Ko materials. The Love surface wave solution consists of an unattenuated wave motion in the layer and an inhomogeneous plane wave in the substrate, which are combined to satisfy the exact boundary conditions. A dispersion relation is obtained and analysed. General properties of the energy flux and the energy density in the substrate and the layer are exhibited.

La détection de gaz potentiellement dangereux représente une problématique d’actualité pour la protectiondes personnes mais aussi un enjeu d’avenir pour le stockage des énergies renouvelables. Les outils desimulations développés au sein du Département Temps-Fréquence de l’Institut FEMTO-ST, associés aux outilstechnologiques proposés par la centrale MIMENTO ont permis la mise au point de capteurs SAW apportantdes réponses à ces problématiques. Ces derniers fondés sur les propriétés des ondes de Love ont ainsi permis ladétection du monoxyde de carbone dans la gamme du ppm. De même, la mesure de concentration d’hydrogènede l’ordre du pourcent a pu être réalisée par le biais de dispositifs s’appuyant sur les ondes Rayleigh. Les effortsfournis pour l’optimisation des dispositifs électro-acoustiques ont aboutis à la réalisation de lignes à retard surquartz affchant des pertes d’insertion de 16 dB. La limitation de ces pertes, généralement de l’ordre de 25 dB à30 dB sur quartz, augmente les potentialités de nos capteurs en terme d’autonomie et de fonctionnalisation desurface. La connaissance des phénomènes physiques gouvernant leur fonctionnement représente, à notre sens,la base de leur développement futur. De cette idée découle notre démarche d’identification et de compréhensionde ces derniers par le biais des différentes techniques de caractérisations et d’analyses disponible au sein denotre l’institut. Des pistes, telles que le recours à un alliage métallique pour la fonctionnalisation des surfacessensibles et la mise en œuvre d’une méthode de séparation des puces limitant les perturbations du signal directdes dispositifs électro-acoustiques, ont été explorées et ont permis d’améliorer la réponse des capteurs. Lepotentiel des composants à ondes élastiques guidée pour la détection de grandeurs chimiques en phase gazeusea pu être établi sur la base des résultats expérimentaux obtenus au cours de cette thèse. Dans la continuité decette dernière, deux projets de recherche (P-AIR et SMARTY) visant le contrôle de la qualité de l’air en milieuurbain ont d’ors et déjà été engagés. / The detection of hazardous gas is a topical issue for the protection of persons. Besides, it represents a challenge linked to the storage of renewable energy. Simulation tools developed within the Time and Frequency Department attached to the FEMTO-ST Institute together with technological facilities available at MIMENTO center have enabled the development of SAW sensors providing answers to these issues. These Love wave’sbased sensors properties have enabled the detection of carbon monoxide in the ppm range. Similarly, hydrogen concentrations of the percent order has been measured by mean of Rayleigh wave’s based sensors. The efforts to optimize electro-acoustic devices have led to achieve delay lines built on quartz with insertion losses of 16 dB.Usually around 25 dB to 30 dB, the reduction of the insertion losses improves the potential of these sensorsin terms of autonomy and surface functionalization. Knowledge of the physical phenomena governing theoperation of these sensors represent the basis of their future development. Thus, different characterization and analysis techniques available in our institute have been carried out to reveal these phenomena. From there, the functionalization of sensor’s sensitives surfaces with metallic alloys and implementation of a chip separation method limiting the disturbance of the direct signal of the electro-acoustic devices, have been explored to improve the performance of the sensors. Based on the experimental results obtained in this thesis, the potential of elastic guided wave’s sensors applied to the detection of chemical quantities in gas phase can be established.In continuation of this study, two projects (P-AIR and SMARTY) dedicated to the control of the urban air quality have already been engaged.

Nous avons développé, et évalué en détail, un nouveau prototype d'inclinomètre longue base à niveaux hydrostatiques appelé " wth2o ". Ce système, aux principes particulièrement simples grâce à l'absence de pièces mécaniques mobiles, présente une grande fiabilité et une excellente stabilité (dérive linéaire de 0.05 µrad par mois). Sa haute résolution jusque dans la gamme des ondes sismiques longues périodes (où, par exemple, la résolution est meilleure que 0.001 masec, soit 5. 10-12 rad), et son niveau de bruit très bas, ont permis d'obtenir des résultats d'analyses harmoniques de marées terrestres (5 ans d'enregistrements) en excellent accord avec les modèles, et dont les écarts quadratiques moyens sont les plus bas de toutes les mesures inclinométriques réalisées au Laboratoire de Géodynamique de Walferdange (Luxembourg). A titre d'exemple, l'amplitude de l'onde M2 est déterminée avec une incertitude de seulement 0.003 masec, tandis que sa phase est déterminée avec un EQM de 0.028°, ce qui correspond à une incertitude de seulement 3.3 secondes. Cet instrument permit également d'observer des phénomènes rarement mesurés avec ce type d'appareil, tel les modes sphéroïdaux et toroïdaux les plus graves des oscillations libres de la Terre excitées par le séisme du Dénali (Mw 7.9) en novembre 2002, ou les passages successifs des ondes de Love jusqu'à G7, correspondant à 3 révolutions de ces ondes de surface autour du globe. Il fut également possible de séparer pour la première fois dans une analyse harmonique de marée terrestre inclinométrique, les constituants des groupes ter- et quater-diurnes. Ces très petites ondes enregistrées sont vraisemblablement liées aux ondes de marées océaniques propres aux eaux peu profondes présentes en Mer du Nord. Les modèles théoriques détaillés de cet appareil (comprenant des composantes relatives à l'amortissement produit par l'écoulement des fluides entre les électrodes des capteurs capacitifs) ont permis de dériver les solutions des équations du mouvement en composante inclinométrique et accélérométrique. De ces solutions furent tirées les formes théoriques des fonctions de transfert de l'appareil. Ces fonctions de transferts furent comparées avec succès aux mesures expérimentales de la réponse en fréquence. Grâce aux formes analytiques des fonctions de transfert en composante inclinométrique et accélérométrique qui sont données dans le présent travail, il est possible de calculer les caractéristiques géométriques optimales pour la construction d'un prototype devant répondre aux besoins particuliers d'une nouvelle application. Une étude originale des effets de ménisques (déformations de l'interface des fluides au contact de la paroi solide des pots) a montré que, s'ils n'ont pas d'influence sur les mesures en mode différentiel, ils peuvent par contre introduire des erreurs de plusieurs pour-cent sur l'estimation de la sensibilité par déplacement d'une quantité de liquide supposée connue. Cette erreur, ne dépendant que des propriétés physico-chimiques des fluides et matériaux en contacts, provient des variations de volumes de liquide contenu dans les ménisques lors des mouvements des interfaces. Si ces mouvements sont effectués lors des étalonnages sans que la ligne de contact ne se déplace, ces erreurs [en %] seront indépendantes du volume déplacé. Ces erreurs ne sont pas particulières à notre instrument mais peuvent affecter les étalonnages réalisés de la sorte pour tout inclinomètre à niveaux hydrostatiques, quel que soit le principe de mesure de l'instrument (mesures différentielles de pression, positionnement de flotteurs etc…). / We developed and evaluated a new prototype of long base water-tube tiltmeter named "wth2o". This system, particularly simple by the absence of moving parts, showed a great reliability and a fairly high stability (linear drift rate of 0.05 µrad/month). We analyzed a 5 years-long data set of Earth tides measurements performed in the Underground Laboratory for Geodynamics in Walferdange (Luxemburg). Its high resolution up to the long-period seismic band (where for instance the resolution is better than 0.001 masec, or 5. 10-12 rad) and its very low noise rate enabled us to obtain results in excellent accordance with the models, with the lowest root mean squares among all the results obtained with other tiltmeters in Walferdange. For instance, the amplitude of the M2 wave is estimated with a RMS as small as 0.003 masec and its phase is determined with an uncertainty below 0.028°, which represents 3.3 seconds only. With the "wth2o" we have also observed some events rarely measured with a water-tube, such as the gravest toroidal and spheroidal modes of the Earth free oscillations excited by the Mw 7.9 Denali earthquake or the successive passages of Love waves (up to G7) circling the globe. For the first time in an analysis of tilt Earth tide measurements, it was possible to separate the small constituents of the ter- and quater-diurnal band. The presence of these very small waves is most likely due to the effects of the shallow-water tides known to be remarkable in the North Sea. Theoretical models of this instrument (taking into account the damping produced by the liquids' flow between the plates of the capacitive sensors) allowed to obtain the solutions of the equations of motion for tilt as well as for acceleration. From these solutions we were able to produce very accurate theoretical transfer functions, as confirmed by the successful comparison with observed frequency responses. Thanks to the analytical tilt and acceleration transfer functions given in the present document it is possible to calculate the best geometrical characteristics for the construction of a new prototype having to respond to specific requirements of a new application. A new extended study of the menisci effects (deformations of the interface of the fluids in contact with the solid wall of the end vessels) showed that they do not influence the differential measurements but they could introduce errors of a few percents in the calibration factor when this factor is evaluated by the displacement of a "known" volume of liquid. This error depends only on the physical and chemical properties of the fluids and solids put in contact. It is due to the variation of volume of liquid trapped in the menisci while the interface is moving up- or downwards. If these interface movements are made without displacing the contact line, the errors [in %] will remain the same whatever the displaced volume of liquid could be. These errors can not only affect our results but can also be found in the calibration procedure of any kind of water-tube (central differential pressure, float positioned etc…).