Commutated N-path networks have seen a resurgence in the past decade in the context of modern integrated circuits. N-path circuits have been used to implement high-quality tunable band-pass and notch filters with just switches and capacitors. Recently, nonreciprocal circuits such as circulators and isolators have also been reported as other applications of Linear Periodically-Time-Varying (LPTV) networks. In this dissertation, high performance filters and inductorless nonreciprocal components based on novel LPTV networks are introduced. We proposed a concept called Negative Transresistance (NTR) in phase-shifted N-path structures. The rejection of the conventional N-path notch filters is limited to the number of paths used; however, by using our proposed NTR concept, we were able to achieve more than 50dB rejection regardless of the number of paths. Using the same concept, we introduced the first prototype of N-path Low-Pass Filter (LPF). The resulting components can find application in blocker-tolerant systems, to select closely-spaced frequency channels, and also in the analog Baseband (BB). Nonreciprocal components such as circulators and isolators have traditionally relied on ferrites that offer nonreciprocal behavior based on Faraday Effect (by applying an external magnetic field). Recent efforts to eliminate the need for magnetic materials, despite being a huge success involve the usage of transmission lines (and/or inductors). In this dissertation, a novel concept called Nonreciprocal Transresistance (NRTR) is introduced. This led to the first ever inductorless RF isolator. Furthermore, we expanded the idea to the first inductorless circulator consisting of only switches and capacitors. The resulting isolator can find application in base stations to prevent back reflections (e.g. to protect the Power Amplifier (PA)). Also, in superconducting quantum systems, an isolator is necessary to separate the noise and reflections at the interface of different blocks. The introduced circulator can find applications in wireless communication systems as an antenna interface connecting the Transmitter (TX) and the Receiver (RX) to a shared antenna. This is crucial, especially for Full-Duplex (FD) applications where high isolation between RX and TX is necessary as they are operating at the same frequency. Finally, we enhanced the performance of the conventional N-path Band-Pass Filter (BPF). We first introduced a second-order N-path BPF with passive gain called impedance-transforming N-path filter. We then proposed a concept called rotary-clock-path in N-path filters which enables passive frequency shifting of N-path filters of any kind without the need for a separate clock frequency or active circuitries. Then by combining the impedance-transforming BPF and rotary-clock-path ideas, we implemented the first ever inductorless passive higher-order N-path BPF with voltage gain. The resulting BPFs can find applications in matching networks and also in a Surface Acoustic Wave (SAW)-less mixer-first receivers.

Le but de cette thèse a été de construire un modèle haute résolutionde la vitesse des ondes Sau sein la croûte et du manteau supérieur de l'arc alpin et del'Europe, à partir de corrélations de bruit. Dans ce cadre, nous avonsconstruit plusieurs modèle tomographiques à partir d'un jeu de donnéecomposé de 4 années de bruit ambiant enregistré par 1293 stationsréparties à travers l'Europe.Nous avons tout d'abord réalisé une tomographie par corrélation debruit "classique". Desmesures de vitesse de groupe des ondes de Rayleigh entre 5 et 150s depériode ont été inversées pour construire des cartes de vitesse degroupe. Elles ont été inversées avec une approche bayésienne afind'établir un modèle probabiliste de la vitesse des onde S et d'évaluerla probabilité d'avoir une interface en chaque point du modèle. Ceci apermis d'établir un modèle tomographique haute résolution del'ensemble de l'Europe en bon accord avec des études antérieursciblées sur des zones spécifiques.La forte densité de station au niveau de l'arc alpin nous a permisd'établir des cartes de vitesse de phase avec la méthode Eikonal entre7 et 25s de période. Celles-ci sont en accord avec les cartes devitesse de groupe précédemment établies. De plus nous avons pu aveccette méthode étudier l'anisotropie de la croûte à l'échelle desAlpes.Nous avons continué à affiner notre modèle de la lithosphère alpine enréalisant une tomographie basée sur l'équation d'onde ("wave equationtomography", WET) s'appuyant sur des simulationsnumériques de la propagation des ondes elastiques en 3D.Nous avons ainsi itérativement amélioré le modèle en minimisant ladifférence de vitesse de phase des ondes de Rayleigh mesurée sur descorrélations observées et simulées numériquement entre 10 et 55s depériode. Le modèle final a été obtenu après 15 itérations avec uneréduction du misift de ~65%. Au sein de la croûte, et àl'interface croûte/manteau, ce modèle présente de nouvelles structureset des contraste de vitesse plus important. Ceci illustre que cetteapproche permet d’améliorer significativement les modèlestomographiques obtenus par corrélations de bruit. / The primary goal of the thesis is to build high-resolution shear-wave velocity models of the Alpine crust and uppermost mantle using ambient noise based tomography.In this framework, we performed a series of tomographic applications using a large cross-correlation dataset computed from 4 years of noise recorded at 1293 broadband seismic stations across Europe.We first applied a 'classical' ambient noise group velocity tomography.Rayleigh wave group velocity measurements in the period band 5-150 s were inverted to construct group velocity maps.With a Bayesian 1-D depth inversion approach, we determined both the shear-wave velocity and probability of interfaces at each cell of the model.This has allowed to finally establish a high-resolution model of the European crust and uppermost mantle in good agreement with previous localized geophysical studies.Taking advantage of the dense seismic array in the Alpine region, we performed ambient noise Eikonal tomography using Rayleigh wave phase velocity measurements in the period band 7-25 s.With this method, we were able to study the anisotropy of the Alpine crust.We refined the shear wave velocity model of the Alpine crust and uppermost mantle using wave-equation tomography (WET) based on the numerical simulation of 3-D elastic wave propagation.We iteratively improved the initial model by minimizing the phase traveltime differences between the observed and synthetic Rayleigh waves in the period band 10-55 s.We obtained the final model after 15 iterations with a reduction of total misfit ~65%.At crustal and Moho depths, the final model displays several new features and much stronger velocity contrasts, which indicates that this approach can significantly improves the model obtained by classical ambient noise tomography.

Thesis (S.M.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 117-119). / The Acoustic Doppler Current Profiler (ADCP) is a proven technology which is capable of measuring surface wave height and directional information, however it is generally limited to rigid, bottom mounted applications which limit its capabilities for measuring deep water waves. By employing an upward looking ADCP on a moving platform, such as an autonomous underwater vehicle or submerged float, we show that it is possible to remove the wave induced motion of the platform and accurately measure surface ocean wave information. The platform selected for testing was a REMUS-100 vehicle equipped with an upward and downward looking ADCP and high accuracy Kearfott inertial navigation unit. Additionally, a Microstrain 3DM-GX3-25 Attitude Heading Reference System was tested as a low cost alternative to the Kearfott system. An experiment consisting of multiple REMUS deployments was conducted near the Martha's Vineyard Coastal Observatory (MVCO). The wave induced motion was measured by various inertial and acoustic sensors and removed from the ADCP data record. The surface wave height and mean directional estimates were compared against a Datawell MKIII directional Waverider buoy and bottom mounted 1200 kHz upward looking ADCP at the MVCO. Results demonstrate that the non-directional spectrum of wave height and the mean wave direction as a function of frequency can be accurately measured from an underway autonomous underwater vehicle in coastal depth waters using an ADCP. / by Scott Haven. / S.M.

Surface waves exist along the interfaces between two different media and are known to display properties that have no analogue in continuous systems. In years past, they have been the subject of many studies in a diverse collection of scientific disciplines. In optics, one of the mechanisms through which optical surface waves can exist is material nonlinearity. Until recently, most of the activity in this area was focused on interfaces between continuous media but no successful experiments have been reported. However, the growing interest that nonlinear discrete optics has attracted in the last two decades has raised the question of whether nonlinear surface waves can exist in discrete optical systems. In this work, a detailed experimental study of linear and nonlinear optical wave propagation at the interface between a discrete one-dimensional Kerr-nonlinear system and a continuous medium (slab waveguide) as well as at the interface between two dissimilar waveguide lattices is presented. The major part of this dissertation is devoted to the first experimental observation of discrete surface solitons in AlGaAs Kerr-nonlinear arrays of weakly coupled waveguides. These nonlinear surface waves are found to localize in the channels at and near the boundary of the waveguide array. The key unique property of discrete surface solitons, namely the existence of a power threshold, is investigated in detail. The second part of this work deals with the linear light propagation properties at the interface between two dissimilar waveguide arrays (so-called waveguide array hetero-junction). The possibility of three different types of linear interface modes is theoretically predicted and the existence of one of them, namely the staggered/staggered mode, is confirmed experimentally. The last part of the dissertation is dedicated to the investigation of the nonlinear properties of AlGaAs waveguide array hetero-junctions. The predicted three different types of discrete hybrid surface solitons are analyzed theoretically. The experimental results on observation of in-phase/in-phase hybrid surface solitons localized at channels on either side of the interface are presented and different nature of their formation is discussed.

Yes / This work presents new water surface elevation data including evidence of the spatial correlation of water surface waves generated in shallow water flows over a gravel bed without appreciable bed forms. Careful laboratory experiments have shown that these water surface waves are not well-known gravity or capillary waves but are caused by a different physical phenomenon. In the flow conditions studied, the shear present in shallow flows generates flow structures, which rise and impact on the water-air interface. It is shown that the spatial correlation function observed for these water surface waves can be approximated by the following analytical expression W(rho) = e(-rho 2/2 sigma w2)COS(2 pi L-0(-1)rho). The proposed approximation depends on the spatial correlation radius, sigma(w), characteristic spatial period, L-0, and spatial lag, . This approximation holds for all the hydraulic conditions examined in this study. It is shown that L-0 relates to the depth-averaged flow velocity and carries information on the shape of the vertical velocity profile and bed roughness. It is also shown that sigma(w) is related to the hydraulic roughness and the flow Reynolds number.

No description available.

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

Mathematical modeling of ocean waves is based on the formulation and solution of the appropriate equations of continuity, momentum and the choice of proper initial and boundary conditions. Under the influence of gravity, many free surface water waves can be modeled by the shallow water equations (SWE) with the assumption that the horizontal length scale of the wave is much greater than the depth scale and the wave height is much less than the fluid's mean depth. Furthermore, to describe three dimensional flows in the hydrostatic and Boussinesq limits, the multilayer SWE model is used, where the fluid is discretized horizontally into a set of vertical layers, each having its own height, density, horizontal velocity and geopotential. In this study, we used an explicit staggered finite volume method to solve single and multilayer SWE, with and without density stratification and bathymetry, to understand the dynamic of surface waves and internal waves. We implemented a two-dimensional version of the incompressible DYNAMICO method and compare it with a one-dimensional SWE. For multilayer SWE, we considered both two layer and a linear stratification of density, with very small density gradient, consistent with Boussinesq approximation. We used Lagrangian vertical coordinate which doesn't allow mass to flow across vertical layers. Numerical examples are presented to verify multilayer SWE model against single layer SWE, in terms of the phase speed and the steepness criteria of wave profile. In addition, the phase speed of the barotropic and baroclinic mode of two-layer SWE also verified our multilayer SWE model. We found that, for multilayer SWE, waves move slower than single layer SWE and get steeper than normal when they flow across bathymetry. A series of numerical experiment were carried out to compare 1-D shallow water solutions to 2-D solutions with and without density as well as to explain the dynamics of surface wave and internal wave. We found that, a positive fluctuations on free surface causes water to rise above surface level, gravity pulls it back and the forces that acquired during the falling movement causes the water to penetrate beneath it's equilibrium level, influences the generation of internal waves. Internal waves travel considerably more slowly than surface waves. On the other hand, a bumpy or a slicky formation of surface waves is associated with the propagation of internal waves. The interaction between these two waves is therefore demonstrated and discussed. / Thesis / Master of Science (MSc) / In the modelling of ocean wave, the formulation and solution of appropriate equations and proper initial and boundary conditions are required. The shallow water equations (SWE) are derived from the conservation of mass and momentum equations, in the case where the horizontal length scale of the wave is much greater than the depth scale and the wave height is much less than the fluid's mean depth. In multilayer SWE, the fluid is discretized horizontally into a set of vertical layers, each having its own height, density, horizontal velocity and geopotential. In this study, we used an explicit staggered finite volume method to solve single and multilayer SWE, with and without density stratification and bathymetry, to understand the dynamic of surface waves and internal waves. A series of numerical experiments were carried out to validate our multilayer model. It is found that, in the presence of density differences, surface waves for the multilayer SWE move slowly and get more steep than normal when they flow across bathymetry. Also, a positive fluctuations on free surface generates internal waves at the interior of ocean which propagate along the line of density gradient.

Lateral perturbations in anelasticity (Q) and wave speed together provide important constraints on thermal and chemical structures in the mantle. In present-day tomography studies of global wave speed and anelasticity, the significance of 3-D wave speed and 3-D Q structures on surface wave travel times and amplitudes has not been well understood. In this dissertation, the effects of lateral perturbations in anelasticity (Q) and wave speed on surface wave observables are quantified based upon wave propagation simulations in 3-D earth models using a Spectral Element Method. Comparison between phase delays caused by 3-D wave speed structures and those caused by 3-D Q variations show that anelastic dispersion due to lateral perturbation in Q is important in long-period surface wave and can account for 15-20% observed phase delays. For amplitude perturbations, elastic focusing/defocusing effects associated with 3-D wave speed structures are dominant while energy dissipation is important in short-period (~ 50 s) surface waves but decreases quickly with increasing wave period. Anelastic focusing/defocusing associated with 3-D anelastic dispersion becomes more important than wave attenuation in longer period surface waves. In tomography studies, ray theory breaks down and finite frequency effects become important when the length scale of heterogenities are smaller than seismic wavelength. Finite frequency effects in 3-D earth models are investigated by comparing theoretical predictions of travel times and amplitudes with "ground truth" measurements made on synthetic seismograms generated in SEM simulations. The comparisons show that finite frequency effects are stronger in amplitudes than in phases, especially at long periods. / Ph. D.

Several techniques for measuring high frequency vibrations are presented. The goal of the study is to develop a sensor for detecting acoustic emissions (AE) inside composite structures. The basics of wave propagation inside of materials has been presented along with an overview of typical acoustic emission testing. Surface acoustic waves (SAWs) were studied first and a novel, noncontact optical interferometric technique for measuring absolute amplitudes is presented. This technique has the added advantages in that it does not require that the interferometer be stabilized or phase biased. It is insensitive to laser fluctuations, random phase drifts, polarization changes and changes in mixing efficiency of the interferometer. SAW amplitudes between 7 and 2.5 angstroms were measured with the described technique. An intrinsic Fabry-Perot type interferometer was demonstrated for detecting SAW's and was then embedded into carbon fiber composite panels which were then put through tensile tests. AE's were captured, centered around 300 KHz, as is expected of a composite. These tests were repeatable and indicate that qualitative measurements of AE can be made. This sensor configuration was also used for detecting a variety of taps on the composite panel as well as pencil lead breaks, a standard calibration procedure for AE testing. / Master of Science