Дисертації з теми "Mechanical Waveguides"
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Cockrell, Kevin L. "Understanding and utilizing waveguide invariant range-frequency striations in ocean acoustic waveguides." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/65275.
Повний текст джерелаCataloged from PDF version of thesis.
Includes bibliographical references (p. 163-170).
Much of the recent research in ocean acoustics has focused on developing methods to exploit the effects that the sea surface and seafloor have on acoustic propagation. Many of those methods require detailed knowledge of the acoustic properties of the seafloor and the sound speed profile (SSP), which limits their applicability. The range-frequency waveguide invariant describes striations that often appear in plots of acoustic intensity versus range and frequency. These range-frequency striations have properties that depend strongly on the frequency of the acoustic source and on distance between the acoustic source and receiver, but that depend mildly on the SSP and seafloor properties. Because of this dependence, the waveguide invariant can be utilized for applications such as passive and active sonar, time-reversal mirrors, and array processing, even when the SSP or the seafloor properties are not well known. This thesis develops a framework for understanding and calculating the waveguide invariant, and uses that framework to develop signal processing techniques for the waveguide invariant. A method for passively estimating the range from an acoustic source to a receiver is developed, and tested on experimental data. Heuristics are developed to estimate the minimum source bandwidth and minimum horizontal aperture required for range estimation. A semi-analytic formula for the waveguide invariant is derived using WKB approximation along with a normal mode description of the acoustic field in a rangeindependent waveguide. This formula is applicable to waveguides with arbitrary SSPs, and reveals precisely how the SSP and the seafloor reflection coefficient affect the value of the waveguide invariant. Previous research has shown that the waveguide invariant range-frequency striations can be observed using a single hydrophone or a horizontal line array (HLA) of hydrophones. This thesis shows that traditional array processing techniques are sometimes inadequate for the purpose of observing range-frequency striations using a HLA. Array processing techniques designed specifically for observing range-frequency striations are developed and demonstrated. Finally, a relationship between the waveguide invariant and wavenumber integrations is derived, which may be useful for studying range-frequency striations in elastic environments such as ice-covered waveguides.
by Kevin L. Cockrell.
Ph.D.
Chen, Tianrun. "Mean, variance, and temporal coherence of the 3D acoustic field forward propagated through random inhomogeneities in continental-shelf and deep ocean waveguides." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/46621.
Повний текст джерелаIncludes bibliographical references (p. 165-175).
When an acoustic field propagates through a multimodal waveguide, the effect of variations in medium properties induced by 3D random inhomogeneities accumulates by multiple forward scattering over range. This causes significant random fluctuations in the received field and greatly affects underwater acoustic sensing and communication systems, such as Ocean Acoustic Waveguide Remote Sensing(OAWRS). In order to characterize this effect, analytical expressions are derived for the mean, variance and temporal covariance of the acoustic field forward propagated through an ocean waveguide containing internal waves, fish shoals, wind-generated bubble clouds and krill. These expressions account for the accumulated effects of multiple forward scattering through temporally and spatially varying scatter function densities of the 3D inhomogeneities. In order to quantify the statistics of the scatter function densities, physical models and statistical descriptions of these inhomogeneities are developed.Acoustic field transmission through internal waves in both continental shelf and deep ocean waveguides is investigated. Stratified ocean models are used to describe physical and statistical internal waves properties. Simulations for a typical continental-shelf environment show that when the standard deviation of the internal wave displacement exceeds the acoustic wavelength, the acoustic forward field becomes so randomized that the expected total intensity is dominated by the variance field and lacks a the coherent interference structure beyond moderate ranges. This leads to an effectively saturated field that decays monotonically. It is found that 3D scattering effects become pronounced when the acoustic Fresnel width exceeds the cross-range coherence length of the internal waves. This leads to frequency and range-dependent power losses in the forward field that explains some of the attenuation observed in acoustic transmission through typical continental shelf and deep ocean waveguides.
(cont.) A general analytical expression is derived for the temporal coherence of an acoustic signal propagating through an ocean waveguide with random 3D inhomogeneities.Advance knowledge of this coherence time scale is often essential in the design of ocean acoustic experiments and subsequent data analysis. This is because it determines the number of fluctuations in a given measurement period and the time window within which the coherent processing techniques essential to ocean acoustic data reduction and analysis can be applied. The analytic approach is found to explain the time scale of acoustic field fluctuations observed both at mega meters ranges in the deep ocean, as well as at kilometer ranges in continental shelf environments. The acoustic time scale is found to be much shorter than the coherence time scale of ocean internal waves. This is shown to be a consequence of multiple forward scattering of the acoustic waves through the internal waves. Analytical expressions are derived for the attenuation and dispersion of the acoustic field forward propagated through fish shoals and wind-generated bubble clouds in an ocean waveguide. It is found that at swim bladder resonance, fish shoals may sometimes lead to measurable attenuation in the forward field. The attenuation at off-resonant OAWRS frequencies, however, is typically negligible as shown both by the present theory and experimental data. The modeled attenuation due to random wind-generated bubble clouds is found to be highly sensitive to the choice of cutoff radius, which determines whether resonant bubbles are included in the bubble spectra. It is also found that bubble clouds generated under high wind speeds lead to additional dispersion and attention of the transmitted signal. These expected distortions can significantly degrade standard coherent processing techniques in ocean acoustics, such as the match filter, if not taken into account.
(cont.) Antarctic krill play a key role in the marine food chain as the primary source of sustenance for many species of whales, seals, birds, squid and fish. This makes knowledge of the distribution and abundance of krill essential to ecological research in the southern oceans. It is shown that swarms of Antarctic krill with typical packing densities can be instantaneously imaged by OAWRS over thousands of square kilometers in both deep and shallow water environments given properly designed experiments.
by Tianrun Chen.
Ph.D.
Pearson, Stephen Herbert. "Nonlinear Ball Chain Waveguides For Acoustic Emission And Ultrasound Sensing Of Ablation." ScholarWorks @ UVM, 2014. http://scholarworks.uvm.edu/graddis/256.
Повний текст джерелаLiu, Jinghao. "ADVANCED STUDIES ON SERIES IMPEDANCE IN WAVEGUIDES WITH AN EMPHASIS ON SOURCE AND TRANSFER IMPEDANCE." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/821.
Повний текст джерелаAlbertson, Nicholas James. "Mechanical and Electromagnetic Optimization of Structurally Embedded Waveguide Antennas." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/81959.
Повний текст джерелаMaster of Science
Martinez, Jose Antonio. "A Micro-Opto-Electro-Mechanical System (MOEMS) for Microstructure Manipulation." FIU Digital Commons, 2008. http://digitalcommons.fiu.edu/etd/206.
Повний текст джерелаMehrotra, Sandeep. "Analysis of optical waveguide fabrication processes." Ohio : Ohio University, 1986. http://www.ohiolink.edu/etd/view.cgi?ohiou1183140884.
Повний текст джерелаLee, Sunwoong. "Efficient localization in a dispersive waveguide : applications in terrestrial continental shelves and on Europa." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36197.
Повний текст джерелаIncludes bibliographical references (p. 211-225).
Methods are developed for passive source localization and environmental parameter estimation in seismo-acoustic waveguides by exploiting the dispersive behavior of guided wave propagation. The methods developed are applied to the terrestrial continental shelf environment and the Jovian icy satellite Europa. The thesis is composed of two parts. First, a method is derived for instantaneous source-range estimation in a horizontally-stratified ocean waveguide from passive beam-time intensity data obtained after conventional plane-wave beamforming of acoustic array measurements. The method is advantageous over existing source localization methods, since (1) no knowledge of the environment is required except that the received field should not be dominated by purely waterborne propagation, (2) range can be estimated in real time with little computational effort beyond plane-wave beamforming, and (3) array gain is fully exploited. Second, source range estimation and environmental parameter inversion using passive echo-sounding techniques are discussed and applied to Europa. We show that Europa's interior structure may be determined by seismo-acoustic echo sounding techniques by exploiting natural ice fracturing events or impacts as sources of opportunity.
(cont.) A single passive seismic sensor on Europa's surface may then be used to estimate the thickness of its ice shell and the depth of its subsurface ocean. To further understand the seismo-acoustic characteristics of natural sources on Europa, a fracture mechanics model is developed for the initiation and propagation of a crack through a porous ice layer of finite thickness under gravitational overburden. It is found that surface cracks generated in response to a tidally induced stress field may penetrate through the entire outer brittle layer if a subsurface ocean is present on Europa. While Europa's ice is likely highly porous and fractured, our current caculations show that porosity-induced scattering loss of ice-penetrating radar waves should not be significant.
by Sunwoong Lee.
Ph.D.
Jain, Ankita Deepak. "Instantaneous continental-shelf scale sensing of cod with Ocean Acoustic Waveguide Remote Sensing (OAWRS)." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100125.
Повний текст джерелаCataloged from PDF version of thesis.
Includes bibliographical references (pages 259-278).
Reported declines in the population of Atlantic cod have a potential to affect long-term ecological balance and the sustainability of the cod fishery along the US northeast coast. These assessments have led to severe fishing cuts over the past few years, have consequently threatened the centuries-old Atlantic cod fishery along the New England coast and put the livelihood of thousands of fishermen at risk. Amidst this fisheries crisis, calls by elected officials, environmental groups and fishing consortiums were made for an Ocean Acoustic Waveguide Remote Sensing (OAWRS) survey of the Gulf of Maine cod stock. Typically, cod stock assessments incorporate data collected from conventional acoustic and trawl line transect surveys that highly undersample the marine environment in space and time and lead to ambiguities in population estimates. The combination of conventional methods and OAWRS techniques, however, has been demonstrated to provide rapid and accurate fish stock assessments over ecosystem-scale areas for other species. In this thesis, the feasibility of accurately surveying cod stocks with OAWRS is theoretically assessed. These theoretical predictions are then experimentally verified by successfully sensing cod with OAWRS over ecosystem scales in the Nordic Seas. Following direct requests by Massachusetts state officials to determine if OAWRS could be used to detect and survey the reported waning cod populations in coastal New England waters, we obtained measurements of typical aggregation densities and occupancy depths of spawning cod in Ipswich Bay from conventional echosounder surveys conducted in Spring 2011. Cod length distributions were also measured from which we estimated the swimbladder resonance frequencies of local cod via a harmonic oscillator model that includes the effects of damping, the cod's swim bladder air volume at a given neutral buoyancy depth as well as changes to this volume for deviations from neutral buoyancy depth. The optimal frequency for OAWRS detection typically corresponds to that where the resonance peak is found. We showed that our theoretical estimates of cod swimbladder resonance matched very well with independent measurements of caged cod resonance from decades old Norwegian data. Using parabolic equation modeling of ocean waveguide propagation, the scattered level of typical spawning cod aggregations was estimated and compared with that from seafloor scattering, which is a typical limiting factor in long range active sensing. Seafloor scattering was estimated via a Rayleigh-Born approach we developed, where the magnitude squared of seafloor scattering amplitude was empirically determined from thousands of measurements made during major OAWRS experiments along the US Northeast coast. It was found that near cod swimbladder resonance (roughly 150-600 Hz), determined from the New England length and depth distribution data, OAWRS was capable of robustly detecting spawning cod aggregations from many tens of kilometers in range with high signal-to- noise ratios (SNRs) greater than 20 dB for typical spawning cod configurations in New England waters. Above the resonance frequency peak, it is possible to detect cod for typical shoaling densities because cod scattering reaches a plateau due to geometric scattering that is above the seafloor scattering trend for typical OAWRS frequencies. Well below the resonance peak, scattering from cod is expected to fall off rapidly and faster than seafloor scattering, and so provides important information about resonance behavior but can be difficult to probe given the very low frequencies involved. This theoretical feasibility study emphasized the need for a low frequency source that spans cod swimbladder resonance and helped demonstrate the potential for use of OAWRS for cod assessments over ecosystem scales. To confirm our theoretical predictions on the OAWRS detection of cod and other keystone fish species, we designed, prepared and conducted a major oceanographic experiment in the Nordic Seas in the Arctic in the winter (February-March) of 2014 using three major research vessels, the US RV Knorr, the Norwegian RV Johan Hjort and the Norwegian FV Artus. The Nordic Seas 2014 experiment was conducted in difficult gale and hurricane force weather conditions along most of Norway's western and northern coast. MIT's OAWRS Source, obtained through a NSF-Sloan MRI grant, spanned the 800-1600 Hz range, and the receiver was ONR's Five Octave Receiver Array (FORA). Unlike the declining trend of cod population in New England waters, cod population in the Nordic Seas has been thriving for many years and is currently at its healthiest recorded state. The experiment period was chosen such that it coincided with the peak spawning period of cod along the coastal Lofoten region in Norway where they congregate in high densities, as well as other keystone species that migrate from the ice-edge to spawn in some of the world's largest mass migrations. In planning, we determined likely spawning grounds for cod, and other keystone species such as capelin, herring, and haddock using historic survey data collected along the Norwegian coast. With our calibrated model of fish swimbladder resonance and historic length distribution data from Norway, swimbladder resonance frequencies and target strengths of these fish species were estimated. We also determined optimal OAWRS ship tracks for remote detection of these species above seafloor scattering using waveguide propagation modeling. While the OAWRS frequencies were greater than those expected for cod swimbladder resonance, cod shoals over ten kilometers in length were robustly detected and successfully imaged from tens of kilometer ranges during the experiment. This produced the first instantaneous images of a vast cod shoal. It also confirmed our predictions that OAWRS can be used to remotely sense and survey cod populations. Our theoretical predictions suggest that the use of lower OAWRS frequencies near cod swimbladder resonance would lead to greater dynamic range in population density estimates. The Nordic Seas experiment provided the first look revealing the entire horizontal morphology of vast cod, capelin, haddock and Norwegian herring shoals. This was done with instantaneous OAWRS imaging. The presence of multiple shoaling fish species during the Nordic Seas experiment provided us with a unique opportunity to study general shoaling behavior across species over ecosystem scales with OAWRS. For example, many pelagic and demersal fish species are known to undergo distant migrations for feeding, spawning and overwintering year after year. This suggests that migrating populations have an ability to efficiently sense their environment. By combining OAWRS estimates of fish scattering strength and population density obtained from simultaneous depth echo-sounding along line transects, areal population densities over entire shoals were determined. This enabled estimation of total shoal population, shoal aspect ratio, and shoal migration speed via cross correlation of population density over time. It was shown that across several species, as shoal population increased (tens of thousands to hundreds of millions of individuals), shoal aspect ratio also increased (roughly from one to ten). Single-celled organisms with higher aspect ratios have been shown to more efficiently and accurately detect chemical gradients at microscopic scales. The high-aspect ratio or elongated morphology of a large migrating fish shoal is consistent with the entire shoal serving the function of a biological antenna for efficient spatial and temporal sensing of mesoscale processes in the environment. We also studied the evolution of air resonance power efficiency in the violin and its ancestors. We collected historical data, including samples from roughly 500 classical Cremonese violins from the renowned workshops of Amati, Stradivari and Guarneri, to establish historic time series of key design traits. We determined the primary physical mechanisms governing radiated air resonance power in the violin and its ancestors and used this knowledge to explain the evolutionary trends we discovered.
by Ankita Deepak Jain.
Ph. D.
Puckett, Anthony. "An Experimental and Theoretical Investigation fo Axially Symmetric Wave Propagation In Thick Cylindrical Waveguides." Fogler Library, University of Maine, 2004. http://www.library.umaine.edu/theses/pdf/PuckettA2004.pdf.
Повний текст джерелаMirza, Imran. "Storage, Interference and Mechanical Effects of Single Photons in Coupled Optical Cavities." Thesis, University of Oregon, 2014. http://hdl.handle.net/1794/18525.
Повний текст джерела10000-01-01
Ignisca, Anamaria. "Analytic model for matched-filtered scattered intensity of volume inhomogeneities in an ocean waveguide calibrated to measured seabed reverberation." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67615.
Повний текст джерелаCataloged from PDF version of thesis.
Includes bibliographical references (p. 117-119).
In this thesis, we derive full theoretical expressions for the moments of the matched filtered scattered field due to volume inhomogeneities in an ocean waveguide and provide a computationally efficient time harmonic approximation to the matched filtered model. Following the approach developed by Galinde et al 16], the expressions are derived from first principles, by applying Green's theorem and the Born approximation. The scattered field and the total moment expressions are in terms of the fractional changes in the bottom compressibility and density, as well as the waveguide Green function and its gradients. The volume inhomogeneities are assumed to be statistically stationary, and assumed to be correlated in all three directions following a delta correlation function. Sound propagation in the ocean is modeled using the parabolic equation model and actual measurements of bathymetry and sound speed at the experimental locations. Monte Carlo simulations are used to account for the sound speed variability in the ocean waveguide due to internal waves or other sources of acoustic field randomization. The computationally efficient time-harmonic model is shown to provide a good approximation to the full broadband matched filtered model for a standard Pekeris waveguide. The time-harmonic model is then calibrated for ocean bottom reverberation at several frequencies in the 415-1325 Hz band, with data collected during the 2003 and 2006 ONR Geoclutter Experiments on the New Jersey continental shelf and on the northern flank of Georges Bank in the Gulf of Maine, respectively. The statistics for the inverted bottom parameters are summarized for all frequencies and experimental locations considered. The acoustically determined bottom parameters are shown to vary with approximately the wavelength cubed, suggesting that, by different frequencies selecting the scale of the acoustic inhomogeneities, the acoustic effects dominate over the geophysical effects.
by Anamaria Ignisca.
S.M.
Fitzmaurice, Michael G. "A new finite-difference time-domain method applied to an open waveguide structure." Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/7950.
Повний текст джерелаKaklamanis, Eleftherios. "Spectral discrimination of fish shoals from seafloor in the Gulf of Maine during the ocean acoustic waveguide remote sensing (OAWRS) 2006 experiment." Thesis, Massachusetts Institute of Technology, 2021. https://hdl.handle.net/1721.1/130860.
Повний текст джерелаCataloged from the official PDF version of thesis.
Includes bibliographical references (pages 87-91).
In this thesis, we perform a spectral discrimination of fish shoals from background returns using statistical techniques. Classification of fish species requires an efficient and solid approach to distinguish fish scattering from seafloor returns. Neyman-Pearson Hypothesis Testing, Kullback-Leibler divergence, Matched Filter and discriminating based on the shape of the spectral dependence, methods originated from Detection theory, are applied in well documented cases from Gulf of Maine during spawning season to distinguish seafloor returns from fish scattering across frequency domain. The discrimination of fish shoals from seafloor returns is achieved by analyzing the absolute levels of scattered returns and the pattern of their frequency response. A generalization of the statistical techniques is developed that enables all frequencies to be tested at once, allowing the spectral discrimination and echolocation of fish shoals from regions dominated by background returns. Conclusions derived from statistical techniques are consistent with physical evidences, such as in situ echosounder measurements and frequency responses. Fish shoals are distinguished from background regions by evaluating the likelihood ratio test, matched filter and analyzing the slope of the frequency dependence of all pixels in an examined ocean acoustic waveguide remote sensing (OAWRS) image.
by Eleftherios Kaklamanis.
S.M.
S.M. Massachusetts Institute of Technology, Department of Mechanical Engineering
Wilkinson, Peter John. "Novel mechanical alignment and component fabrication for wavelength-selective optical switches." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277801.
Повний текст джерелаRunyon, Matthew. "Experimental Design and Implementation of Two Dimensional Transformations of Light in Waveguides and Polarization." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36881.
Повний текст джерелаDeng, Jie. "Vibroacoustic modeling of acoustic blackhole applications in flat, curved andcomplex mechanical structures." Doctoral thesis, Universitat Ramon Llull, 2020. http://hdl.handle.net/10803/670666.
Повний текст джерелаLos agujeros negros acústicos en mecánica (conocidos por las siglas ABHs, del inglés Acoustic Black Holes) suelen estar formados por muescas en vigas y placas, el grueso de las cuales decae según una ley potencial. El efecto del ABH es el de ralentizar las velocidades de fase y de grupo de las ondas de flexión incidentes de tal modo que, en teoría, haría falta un tiempo infinito para que las ondas alcanzaran el centro del ABH, si el grueso de este último fuera exactamente cero. Sin embargo, en la práctica esto no es posible, aunque se puede conseguir una fuerte disipación colocando una capa de material amortiguador en el centro del ABH, donde se concentra la mayor parte de la energía de las ondas. En los últimos años, los ABHs no sólo se han explotado como método pasivo para reducir vibraciones estructurales y la consecuente emisión de ruido, sino que también se ha explorado su potencial para otras aplicaciones como la manipulación de ondas o la captación de energía. Esta tesis tiene tres objetivos principales. Así pues, tras una introducción general a los ABHs, el trabajo se ha dividido en tres grandes secciones. La primera aborda aplicaciones de los ABHs en vigas rectas y placas planas. Para empezar, se propone y analiza un voladizo piezoeléctrico con un acabado de ABH para capturar energía. A continuación, se presentan ABHs en forma de anillo para aislar puntos de excitación externos en placas planas y así evitar la transmisión de vibraciones. Finalmente, se contemplan configuraciones periódicas de matrices de ABHs para colimar haces de ondas de flexión y concentrar su energía en zonas predeterminadas de una placa. La segunda parte de la tesis propone nuevos diseños de ABHs para estructuras con curvatura. Estas son muy habituales en los sectores naval, aeronáutico e industrial, por lo que merece la pena investigar si los ABH pueden dar buenos resultados en algunos casos. La sección comienza analizando la inclusión de ABHs en vigas circulares y se ve como estos dan pie a la aparición de fenómenos típicos de sistemas periódicos. Seguidamente se propone un ABH anular para reducir las vibraciones en conductos cilíndricos. En concreto, se tratan los casos de un conducto simplemente soportado con un ABH anular, y el de un conducto con ABH, soportes periódicos y rigidificadores. Para finalizar la sección, se investigan los efectos de los ABH anulares en la radiación acústica del conducto teniendo en cuenta el nivel de potencia acústica, la eficiencia de radiación y la intensidad supersónica. La tercera parte de la tesis es más corta que las anteriores y simula el aislamiento de una placa con múltiples ABHs, en el rango de media y alta frecuencia. A tal efecto se emplea el método del análisis estadístico de distribución modal de energía (SmEdA: statistical modal energy distribution analysis). En esta sección, la estructura con ABHs ya no se analiza como un elemento individual, sino que se acopla a dos cavidades de aire formando parte de un sistema mecánico más complejo. A lo largo de la tesis se utiliza repetidamente el método de expansión gaussiana (GEM: Gaussian expansión method). Por GEM entendemos tomar funciones gaussianas como base para resolver ecuaciones diferenciales en derivadas parciales en el marco del método de Rayleigh-Ritz. El GEM se parece mucho a los enfoques de ondículas, pero ofrece algunas ventajas en el caso de condiciones de contorno periódicas. Al principio de la tesis se expone un breve repaso del GEM y, cuando es necesario, se aborda su reformulación para un problema particular en el capítulo correspondiente.
Acoustic black holes (ABHs) in mechanics usually consist of geometrical indentations on beams and plates having a power-law decreasing thickness profile. An ABH slows down the phase and group velocity of incident flexural waves in such a way that, ideally, it would take an infinite amount of time for them to reach the ABH center, if the latter had an exact zero thickness. Though this is not possible in practice, strong wave dissipation can be achieved by placing a damping layer at the central region of the ABH, where most vibration energy concentrates. In recent years, ABHs have been not only exploited as a passive means for structural vibration and noise reduction, but its potential for other applications like wave manipulation or energy harvesting have been also explored. The objective of this thesis is threefold. Therefore, after an initial overview the work is divided into three main parts. The first one deals with ABH applications on straight beams and flat plates. To start with, an ABH piezoelectric bimorph cantilever for energy harvesting is proposed and analyzed. Then, ring-shaped ABH indentations are suggested as a means of isolating external excitation points in flat plates and prevent vibration transmission. Finally, periodic ABH array configurations are contemplated to collimate flexural wave beams and focus energy at desired plate locations. The second part of the thesis proposes new ABH designs for curved structures. The latter are very common in the naval, aeronautical and industrial sectors so it is worth investigating if ABHs could function for them. The section starts analyzing the embedding of ABHs on circular beams and how this results in the appearance of typical phenomena of periodic systems. After that, an annular ABH is proposed to reduce vibrations in cylindrical shells. The cases of a simply supported shell with an annular ABH indentation and of a periodic simply supported ABH shell with stiffeners are considered. To finish the section, the effects of annular ABHs on sound radiation are investigated in terms of sound power level, radiation efficiency and supersonic intensity. The third part of the thesis is shorter than the previous ones and is devoted to analyzing the transmission loss of a plate with multiple ABH indentations, in the mid-high frequency range. Statistical modal energy distribution analysis is used for that purpose. Here, the ABH plate is not taken as an individual structure but coupled to two air cavities, thus being part of a more complex mechanical system. Throughout the thesis repeated use is made of the Gaussian expansion method (GEM). The GEM refers to taking Gaussian functions as the basis for solving partial differential equations in the framework of the Rayleigh-Ritz method. The GEM closely resembles wavelet approaches but offers some advantages in the case of periodic boundary conditions. A brief overview of the GEM is exposed at the beginning of the thesis and, when necessary, its reformulation for a particular problem is tackled in its corresponding chapter.
Atanazio, Paulo Filipe Braghetto. "Chaves MEMS aplicadas a dispositivos de RF e micro-ondas : projeto, tecnologia e implementação fisica de deslocador de fase e filtro sintonizavel." [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/259494.
Повний текст джерелаDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
Made available in DSpace on 2018-08-13T08:18:49Z (GMT). No. of bitstreams: 1 Atanazio_PauloFilipeBraghetto_M.pdf: 6727187 bytes, checksum: 90bbbbf904ffcce6757eeaeefe4abd96 (MD5) Previous issue date: 2009
Resumo: O propósito deste trabalho é, a partir dos conceitos de linhas de transmissão, teoria de filtros e o conhecimento pioneiro deste grupo acerca das chaves MEMS de RF, propor duas aplicações reais baseadas nesta estrutura singular: um deslocador de fase e um filtro sintonizável na faixa de 0,1-35GHz e banda Ku (12,4-18GHz) respectivamente. Uma abordagem puramente eletromecânica é realizada na etapa inicial, observando a tensão de ativação da chave para diferentes formas estruturais, desmistificando a histerese mecânica, fenômeno intrínseco a este tipo de dispositivo. Na segunda fase do trabalho é feito um detalhamento do comportamento eletromagnético da chave MEMS, explorando fortemente a extração dos parâmetros elétricos e sua inserção em outros circuitos. Por fim, a implementação do filtro sintonizável e do deslocador de fase realizouse baseada nos conceitos de DMTL - Distributed MEMS Trasmission Lines - onde tanto a seleção da frequência central de passagem do filtro, quanto o comprimento elétrico total do deslocador são controladas pela capacitância variável da chave MEMS, de acordo com uma tensão de controle DC aplicada.
Abstract: The purpose of this work is, based on transmission line concepts, filter theory and the pioneer knowledge of this group about RF MEMS Switches, propose two physical applications employing this singular structure: a phase shifter and a tunable filter at 0.1 - 35GHz range and Ku band respectively. A purely electromechanical approach is done at the initial step, observing the switch pull-in voltages for several structural geometries, demystifying the mechanical hysteresis, intrinsic phenomena of this kind of device. On the second phase of the work, the MEMS switch electromagnetic behavior is detailed, strongly exploring the electrical parameters extraction and its application on other types of circuits. Finally, the tunable filter and phase shifter are implemented through DMTL - Distributed MEMS Transmission Lines - concepts, where frequency selection and the amount of phase shifting are controlled by the variable switch capacitance according to the applied DC control voltage.
Mestrado
Telecomunicações e Telemática
Mestre em Engenharia Elétrica
Oldham, Jonathan Reed. "Development of a Multiple Microphone Probe Calibrator." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2042.pdf.
Повний текст джерелаWang, Zhechao. "Investigation of New Concepts and Solutions for Silicon Nanophotonics." Doctoral thesis, KTH, Mikroelektronik och tillämpad fysik, MAP, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-13029.
Повний текст джерелаQC20100705
Coja, Michael. "Effective vibro-acoustical modelling of rubber isolators." Doctoral thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-266.
Повний текст джерелаBelon, Rémy. "Céramiques transparentes de YAGNd pour applications laser : mise en forme et densification de pièces de grandes dimensions, élaboration d'architectures complexes par coulage en bande." Thesis, Limoges, 2019. http://www.theses.fr/2019LIMO0058.
Повний текст джерелаThe first step of this work was focused on the shaping and sintering of large sized Nd:YAG transparent ceramics. The choice of the pressure casting and cold isostatic pressing parameters allowed to control the thickness and the microstructure of the green bodies. However, vacuum sintering of these parts led to a microstructural heterogeneity between the core and the edge of the samples. More particularly, residual pores have been detected in the core of the ceramics, decreasing the optical properties. Then, HIP (Hot Isostatic Pressing) post-treatments were implemented to control the ceramics microstructure. This route helped to reduce the number and size of residual pores. But limitations appeared, especially concerning the large ceramics. Finally, the obtained ceramics showed laser performances close to those of the single crystals of same composition.The second part was devoted to the development of a tape casting process for the elaboration of YAG multilayered transparent ceramics. More particularly, the influence of the slurry formulation on the mechanical properties of the green tapes was studied. This original work allowed the shaping of green tapes with good mechanical properties and a controlled organic content. Then, a multilayered ceramic with a central Nd-doped layer could be elaborated by thermolamination of layers with different compositions (YAG and YAG: Nd). After debinding and sintering, a transparent ceramic planar waveguide was finally obtained
Yeo, Inah. "A quantum dot in a photonic wire : spectroscopy and optomechanics." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENY076/document.
Повний текст джерелаIn the framework of this thesis, single InAs/GaAs quantum dot devices were studied by optical means. Starting with a general description of self-assembled InAs QDs, two types of single QD devices were presented. The first approach was a tapered GaAs photonic wire embedding single InAs QDs whose efficiency as a single photon source was previously shown to be 90%. We investigated several optical properties of the single QDs. The charged and neutral states of the QD were identified and selectively excited using quasi-resonant excitation.The first original result of this thesis is the observation of a continuous temporal blue-drift of the QD emission energy. We attributed this blue drift to oxygen adsorption onto the sidewall of the wire, which modified the surface charge and hence the electric field seen by the QD. Moreover, we demonstrated that a proper coating of the GaAs photonic nanowire surface suppressed the drift. The temperature effect on this phenomenon revealed an adsorption peak around 20K, which corresponds to the adsorption of oxygen on GaAs. This observation is in good agreement with previous temperature studies with a tapered photonic wire. This was the first study of the spectral stability of photonic wires embedding QDs, crucial for resonant quantum optics experiments. As an alternative, we took advantage of this temporal drift to tune QD emission energies. In a controlled way, we tuned into resonance two different QDs which were embedded in the same photonic nanowire. In the last part of this work, we studied the influence of the stress on single QDs contained in a trumpet-like GaAs photonic wire. The main effect of stress is to shift the luminescence lines of a QD. We applied the stress by exciting mechanical vibration modes of the wire. When the wire is driven at its the mechanical resonance the time-integrated photoluminescence spectrum is broaden up to 1 meV owing to the oscillating stress, The measured spectral modulation is a first signature of strain-mediated coupling between a mechanical resonator and embedded QD single light emitter. With a stroboscopic technique, we isolated a certain phase of the oscillating wire and thereby selected a value of QD emission energies. As a highlight of our study, we managed to bring two different QDs contained in the same wire into resonance by controlling their relative phase. In addition, we could extract the 2D spatial positioning of embedded QDs from the spectral shifts observed for two orthogonal mechanical polarizations.. The investigation of the strain-mediated tuning of QDs can, therefore, be an effective tool to explore the QD positions without destroying the sample
Arunbabu, A. V. "Optical, Structural and Mechanical Characterization of Ultrafast Laser Inscribed Chalcogenide Waveguides." Thesis, 2017. http://etd.iisc.ac.in/handle/2005/4220.
Повний текст джерелаSun, Yue. "Opto-mechanical interactions in nanowire waveguides." Phd thesis, 2015. http://hdl.handle.net/1885/150777.
Повний текст джерелаChang, Chung-Che, and 張宗哲. "Optical Phase Shifters Using Micro-Electro-Mechanical-System Actuated Deformable Silicon Wire Waveguides." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/13244181703274487411.
Повний текст джерела國立清華大學
光電工程研究所
99
An optical phase shifter for integrated optics is proposed and demonstrated in a single SOI chip. By monolithic integration of deformable silicon wire waveguides and micro-electro-mechanical- system (MEMS) actuators, the optical phase shifter for a guided wave can be realized by mechanically stretching the waveguide length using the electrostatic force. Besides, in order to realize highly compact photonic integrated circuits based on silicon photonic wires, multimode interference (MMI) couplers were introduced for performing light splitting and combing due to the advantages of wide optical bandwidth(about 20nm), polarization independence and large fabrication tolerance. In experimental measurement, the maximum phase shift of 0.35? is attained at 200V around the wavelength 1550nm for the TM-polarized light. The dynamic actuation speed is also verified to be near 103?酨 for the proposed device.
Vijay, Prakash S. "Analytical Investigations on Linear And Nonlinear Wave Propagation in Structural-acoustic Waveguides." Thesis, 2016. http://etd.iisc.ac.in/handle/2005/2679.
Повний текст джерелаVijay, Prakash S. "Analytical Investigations on Linear And Nonlinear Wave Propagation in Structural-acoustic Waveguides." Thesis, 2016. http://etd.iisc.ernet.in/handle/2005/2679.
Повний текст джерелаSingh, Prem Prakash. "Fabrication and Characterization of Optomechanical Devices." Thesis, 2019. https://etd.iisc.ac.in/handle/2005/4695.
Повний текст джерелаCSIR
Chellappan, Vinita. "Spectral Methods for different classes of Partial Differential Equations." Thesis, 2015. https://etd.iisc.ac.in/handle/2005/4501.
Повний текст джерелаYang, Chin-Hao, and 楊青浩. "Design of W-band Substrate Integrated Waveguide Mechanical Switch." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/45376716125954154978.
Повний текст джерела國立交通大學
電信工程研究所
102
In this thesis, W-band mechanical switches are proposed using the substrate integrated waveguide (SIW). The substrate integrated waveguiude is manufactured on a Rogers RT-Duroid 5880® low loss substrate with a dielectric constant of 2.2, and a thickness of 10mil. The first step to design the proposed single-pole-double-throw (SPDT) switch is to design a SIW single-pole-single-throw (SPST) switch with a center frequency of 90GHz. Then decide the size of the SIW by the formula of rectangular waveguide. Four different kind of SPST SIW switch structures are designed based on these rules. The on and off of the SPST switch is mechanically controlled by a piece of conducting material to lift or contact the specified area of the switch. Based on the design of SPST SIW switch, the same concept is applied to design the SPDT SIW switch. All the circuits are H-plane SIW circuits that they could be easily measured by a network analyzer with the W-band (WR-10) waveguide extenders through the newly developed SIW to rectangular waveguide transitions.
Wei, Shih-Chiang, and 魏士強. "Design of V-band Substrate Integrated Waveguide Phase Shifter and Mechanical Switch." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/89798602740891697228.
Повний текст джерела國立交通大學
電信工程研究所
104
In this thesis, a V-band phase shifters and a V-band mechanical switches are proposed using the substrate integrated waveguide (SIW). The substrate integrated waveguide is manufactured on a Rogers RT-Duroid 5880® low loss substrate with a dielectric constant of 2.2 and a thickness of 10 mil. The single-pole-single-throw (SPST) and single-pole-double-throw (SPDT) switches are proposed with a center frequency of 60 GHz where the so-called cross centered copper ring structure are adopted. The on and off of the switches are mechanically controlled by a piece of conducting material to lift or contact the specified area of the switch. On the other hand, the proposed phase shifter cascades three different phase shifters which include a 90 degree digital phase shifter, a 180 degree digital phase shifter and a 90 degree tunable phase shifter. Finally, the proposed switches and the proposed phase shifter are measured by a network analyzer with the V-band (WR-15) waveguide extenders through the newly developed SIW to rectangular waveguide transition. The advantage of this newly developed transition is no electrical contact with the metal of the rectangular waveguide.
Ramabathiran, Amuthan Arunkumar. "Wave Propagation In Hyperelastic Waveguides." Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2327.
Повний текст джерелаRamabathiran, Amuthan Arunkumar. "Wave Propagation In Hyperelastic Waveguides." Thesis, 2012. http://etd.iisc.ernet.in/handle/2005/2327.
Повний текст джерелаLee, Hoshik 1975. "Quantum chaos and electron transport properties in a quantum waveguide." Thesis, 2008. http://hdl.handle.net/2152/3914.
Повний текст джерелаtext
Mitra, Mira. "Wavelet Based Spectral Finite Elements For Wave Propagation Analysis In Isotropic, Composite And Nano-Composite Structures." Thesis, 2006. https://etd.iisc.ac.in/handle/2005/448.
Повний текст джерелаMitra, Mira. "Wavelet Based Spectral Finite Elements For Wave Propagation Analysis In Isotropic, Composite And Nano-Composite Structures." Thesis, 2006. http://hdl.handle.net/2005/448.
Повний текст джерелаBendix, Oliver. "Transport in nicht-hermiteschen niedrigdimensionalen Systemen." Doctoral thesis, 2011. http://hdl.handle.net/11858/00-1735-0000-0006-B542-6.
Повний текст джерела