Дисертації з теми "Focusing wave"
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Jendrej, Jacek. "On the dynamics of energy-critical focusing wave equations." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX029/document.
Повний текст джерелаIn this thesis we study the global behavior of solutions of the energy-criticalfocusing nonlinear wave equation, with a special emphasis on the description of the dynamics in the energy space. We develop a new approach, based on the energy method, to constructing unstable type II blow-up solutions. Next, we give the first example of a radial two-bubble solution of the energy-critical wave equation. By implementing this construction in the case of the equivariant wave map equation, we obtain bubble-antibubble solutions in equivariance classes k > 2. We also study the relationship between the speed of a type II blow-up and the weak limit of the solution at the blow-up time. Finally, we prove that there are no pure radial two-bubbles with opposite signs for the energy-critical wave equation
Joubert, J. R. "An investigation of the wave energy resource on the South African Coast, focusing on the spatial distribution of the South West coast." Thesis, Link to the Internet, 2008. http://hdl.handle.net/10019.1/351.
Повний текст джерелаAydin, Baran. "Analytical Solutions Of Shallow-water Wave Equations." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613349/index.pdf.
Повний текст джерелаlong waves&ndash
over one- and two-dimensional bathymetries. In one-dimensional case, the nonlinear equations are solved for a plane beach using the hodograph transformation with eigenfunction expansion or integral transform methods under different initial conditions, i.e., earthquake-generated waves, wind set-down relaxation, and landslide-generated waves. In two-dimensional case, the linear shallow-water wave equation is solved for a flat ocean bottom for initial waves having finite-crest length. Analytical verification of source focusing is presented. The role of focusing in unexpectedly high tsunami runup observations for the 17 July 1998 Papua New Guinea and 17 July 2006 Java Island, Indonesia tsunamis are investigated. Analytical models developed here can serve as benchmark solutions for numerical studies.
Kälvegren, Christian, and Tobias Sjölin. "Wave power - The future of energy supply? Focusing on its sealing solutions." Thesis, KTH, Maskinkonstruktion (Inst.), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209547.
Повний текст джерелаEtt nytt koncept för att utvinna förnyelsebar energi har framtagits på KTH Elkraftteknik, denna gång handlar det om vågkraft. Till skillnad från flera andra vågkraftverk så öppnar detta koncepts nyframtagna generator upp för möjligheten att vara verksamt även vid låga hastigheter samtidigt som det bibehåller hög krafttäthet samt verkningsgrad. Denna lösning av generatorn är i behov av att tätas då dess ingående komponenter inte tål den omgivande havsmiljön, detta är därför syftet med projektet som genomförts. Flertalet problem existerar med de lösningar som för nuvarande finns att tillgå, varför det finns behov av att ta fram en skräddarsydd tätningslösning till detta koncept. Dessa problem är exempelvis läckage och utmattningsbrott vilka leder till att livslängden hos tätningarna blir oacceptabelt kort. De frågeställningar vilka i rapporten och projektet behandlas är ifall det finns några belastningar verkande på tätningen som är specifikt kritiska, ifall det finns något enkelt sätt att reducera just dessa, ifall det finns några lösningar som är tätare än de som finns att tillgå idag (som också har godkända egenskaper gällande hållfasthet och livslängd till följd av de krav som ställs på dem), ifall dessa lösningar skulle vara applicerbara i alla hav och ifall dessa lösningar är ekonomiskt tillämpbara. För att besvara detta har flertalet konceptgenereringar utförts med hjälp av brainstorming där potentiella lösningar utvärderats baserat på en omfattande informationssökning, för att till sist komma fram till och skissera upp de mest lovande slutkoncepten. Dessa modellerades därefter upp med hjälp av 3D-modelleringsprogrammet Solid Edge för att slutligen analyseras med programvaran Ansys. Resultaten och slutsatserna från både informationssökningen och de utförliga analyserna var att de kritiska belastningarna är de spänningar vilka uppstår till följd av kompression, expansion och böjning av bojen, vilka kan reduceras genom att skapa en inre struktur i tätningen som leder till att belastningarna sker mer jämnt. Det finns även tätningslösningar vilka är helt täta då de inkapslar den del av vågkraftskonceptet som behöver tätas, så kallade damasklösningar. Dessa lösningar är dessutom applicerbara i alla hav både ur ett perspektiv gällande material men också ett dimensioneringsmässigt sådant, där möjligheten finns att justera tätningens längd vid tillverkningen utefter den varierande våghöjden där denna ska appliceras. Gällande den sista frågan vilken behandlar den ekonomiska tillämpbarheten kunde inga tillräckligt träffsäkra resultat genereras och därav inga slutsatser dras.
Brouzet, Christophe. "Internal wave attractors : from geometrical focusing to non-linear energy cascade and mixing." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEN012/document.
Повний текст джерелаA question of paramount importance in the dynamics of oceans is related to the energy cascade from large to small scales and its contribution to mixing. Internal wave attractors may be one of the possible mechanisms responsible for such a cascade. In this manuscript, we study experimentally internal wave attractors in a trapezoidal test tank filled with linearly stratified fluid. In such a geometry, the waves can form closed loops called attractors. We show that the attractor formation is purely linear: small scales are thus created by wave focusing. The attractor characteristics are found to only depend on the trapezoidal geometry of the tank. At the ocean scale, we show that attractors are very likely to be unstable. Indeed, internal wave attractors are prone to a triadic resonance instability, which transfers energy from the attractor to a pair of secondary waves. This instability and its main characteristics are described as a function of the geometry of the basin. For long-term experiments, the instability produces several pairs of secondary waves, creating a cascade of triadic interactions and transferring energy from large-scale monochromatic input to multi-scale internal-wave motion. We reveal, for the first time, experimental convincing signatures of internal wave turbulence. Beyond this cascade, we have a mixing regime, which appears to be independent of the trapezoidal geometry and, thus, universal. This manuscript is completed by a study on added mass and wave damping coefficient of bodies oscillating horizontally in a stratified fluid, with applications to tidal conversion
Zhao, Ningxiner. "Design and Analysis of Piecewise Assembled, Reconfigurable Acoustic Arrays for Sound Wave Focusing." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586188427835977.
Повний текст джерелаAnthony, Brian W. 1972. "Anisotropic wave guides-- propagation, focusing and dispersive phenomena with applications for non-destructive testing." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50067.
Повний текст джерелаIncludes bibliographical references (p. 60).
Acoustic Non-Destructive Testing (NDT) has a long history of applications in fatigue monitoring, fault testing, and more recently production control. A very large family of manufactured and raw materials consist of thin layers. Some examples include rolled aluminum, window glass, plywood, automobile bodies, plane wings, silicon wafers, bridge support beams, and paper. These layers can be viewed and modeled as acoustic waveguides. This thesis will present the framework in which to analyze such layers. To this end, analytic solutions to the plane wave displacement and stress fields in a single layer monoclinic material will be presented The propagation, frequency, and dispersive characteristics of transmitted signals can be analyzed to determine various elastic properties of the layer or to identify faults. Wavelet (time-frequency), Fourier (frequency), and signal matching (time) techniques will be developed to analyze and extract features and properties of signals. Several experimental examples will be presented.
S.M.
Blackhurst, Tyler D. "Numerical Investigation of Internal Wave-Vortex Dipole Interactions." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3133.
Повний текст джерелаSrinivas, Vivek. "Adaptive, Wave Guiding Acoustic Arrays using Circularly Symmetric Reconfigurable Structures." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587130205893861.
Повний текст джерелаCajko, Frantisek. "Nano-Focusing of Light: Electromagnetic Analysis and Simulation." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1249331504.
Повний текст джерелаAugello, Elisa. "Precise Near-Field Focusing exploiting Bessel Beam Launchers for Wireless Power Transfer at millimeter waves." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amslaurea.unibo.it/25774/.
Повний текст джерелаJouadé, Antoine. "Millimeter-wave radar imaging systems : focusing antennas, passive compressive devicefor MIMO configurations and high resolution signal processing." Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S154/document.
Повний текст джерелаThe broad topic of the presented Ph.D. thesis consists in the contribution to the study of Radar imaging systems at millimeter-wave and more specifically to the antennas and signal processing. These works have been carried out during a partnership between Canon Research Center France and IETR. A first study on focusing antennas, particularly on Fresnel lens antennas, thanks to a technological process to manufacture inhomogeneous materials, has allowed to improve the efficiency and the frequency bandwidth. The antenna has been mounted on a rotary system to image a real outdoor scene. Then, the study has been focused on the realization of a Multiple-Input Multiple-Output (MIMO) configuration notably using a 4 × 1 passive compressive device allowing to reduce, by compression, the number of radiofrequency (RF) chains. The chains are decompressed by post-processing. The device, used at the transmitting part, is associated with a scanner that synthetizes a receiving array of antennas. This configuration allows to generate a large virtual array, to improve the azimutal resolution of the system while maintaining acceptable the number of RF chains. This configuration has been used to image a scene in an anechoid chamber to validate the concept. To further improve the spatial resolution of the system for a given number of RF chains, the study of high resolution algorithms, or spectral estimation methods, are used to image scenes in near field and wide-band configurations. The combination of MIMO configurations, the passive compressive device and the spectral estimation methods have allowed to drastically improve the spatial resolution of the radar imaging system while limiting the number of RF chains
Piskarskas, Rimtautas. "Spatio-temporal characterization of propagation of intense femtosecond light wave packets in Kerr media." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20090901_074534-46464.
Повний текст джерелаDisertacijoje nagrinėjamas intensyvių femtosekundinių šviesos impulsų fokusavimosi reiškinys kubinio netiesiškumo terpėse bei atskleidžiama šviesos gijų formavimosi prigimtis. Darbe yra pasiūlytos ir eksperimentiškai realizuotos šviesos bangų paketų registravimo metodikos, kurios leidžia su didele skyra fiksuoti laikinę, erdvinę bei spektrinę šviesos bangų paketų dinamiką netiesinio sklidimo metu, taip pat stebėti bei itin tiksliai kiekybiškai įvertinti terpės savybių sparčius pokyčius. Pasitelkus didelės laikinės (20 fs) ir erdvinės (1 μm) skyros lazerinės tomografijos metodiką, parodyta, kad pradinio Gauso formos bangų paketo energija saviveikos Kero terpėje metu persiskirsto taip, kad erdvėlaikyje jis įgauna sudėtingą X tipo intensyvumo skirstinį. Ši transformacija yra universali, ir ją nulemia laikinis ir erdvinis spektro plitimas (dėl fokusavimosi ir fazės moduliavimosi), kūginė spinduliuotė (dėl keturbangio maišymosi) bei nuostoliai dėl daugiafotonės sugerties. Remiantis atvaizduojančio spektrometro metodika parodyta, kad formuojantis šviesos gijai normalios grupinių greičių dispersijos terpėje bangų paketo tolimojo lauko kampinis spektrinis skirstinys yra X formos, o anomalios grupinių greičių dispersijos terpės atveju – O formos. Abiem atvejais stebima bangų paketo lokalizacija, tačiau kiekybinius kampinių spektrinių skirstinių skirtumus nulemia keturbangio dažnių maišymo fazinio sinchronizmo sąlygos. Ir galiausiai, naudojant didelės laikinės (23 fs) ir erdvinės (1,5... [toliau žr. visą tekstą]
Brath, Alexander J. "Advanced techniques for ultrasonic imaging in the presence of material and geometrical complexity." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1510053440115292.
Повний текст джерелаGiammarinaro, Bruno. "Focalisation non linéaire des ondes de choc de cisaillement dans les solides incompressibles." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066054/document.
Повний текст джерелаShear shock waves in quasi-incompressible soft solids have been observed experimentally only twelve years ago. They differ from compression shock waves because their nonlinearity is cubic instead of quadratic. Velocities of shear waves are small, of the order of the meter per second, and thus induce a strong nonlinear behavior over small distances. This allows to counter-balance the quite strong absorption in such media. To our knowledge, these shear shock waves have been studied only for plane waves. However, focusing is a fundamental phenomenon in the wave physics and its applications. This is why our objective is to investigate the focusing of shear waves theoretically, numerically, and experimentally. This work was in particular motivated by a potential application in biomechanics. We have hypothesized that shear shock waves could play a role in the formation of some traumatic brain injuries, the geometry of the skull producing the focusing effect. These hypotheses have governed our studies for the choice of the different parameters such as the frequency, the amplitude and the geometry. The focusing has been demonstrated in a biological tissue-mimicking gel. Comparisons with the theoretical and numerical model have shown a good agreement. Further studies should concern the possible formation of lesions by shear shock waves
Sanguinet, William Charles. "Various extensions in the theory of dynamic materials with a specific focus on the checkerboard geometry." Digital WPI, 2017. https://digitalcommons.wpi.edu/etd-dissertations/243.
Повний текст джерелаOsterhoff, Markus Verfasser], Tim [Akademischer Betreuer] [Salditt, and Rainer G. [Akademischer Betreuer] Ulbrich. "Wave optical simulations for x-ray nano-focusing optics / Markus Osterhoff. Gutachter: Tim Salditt ; Rainer G. Ulbrich. Betreuer: Tim Salditt." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://d-nb.info/1044073888/34.
Повний текст джерелаCassier, Maxence. "Analysis of two wave propagation phenomena: 1) Space-time focusing in acoustics; 2) Transmission between a dielectric and a metamaterial." Palaiseau, Ecole polytechnique, 2014. https://theses.hal.science/pastel-01023289/document.
Повний текст джерелаThis thesis consists of two independent parts. In the first one, we consider a reference medium, containing some scatterers whose positions are unknown. Using an array of transducers, our goal is to generate an acoustic wave that would focus in space and in time near one of these scatterers. The technique proposed here is based on DORT method (French acronym for Decomposition of the Time Reversal Operator) which leads to space focusing properties in the frequency domain. It consists in a singular value decomposition (SVD) of the scattering operator, that is, the operator which maps the input signals sent to the transducers to the measure of the scattered wave. In the context of the Foldy-Lax approximation (which is justified here in 2D), by introducing a particular SVD related to the symmetry of the scattering operator, we show how to synchronize the time-harmonic signals derived from the DORT method to achieve space-time focusing. Theoretical properties and a numerical study justify our approach. The second part is devoted to a transmission problem between a dielectric and a metamaterial. The question we consider is the following : does the limiting amplitude principle hold in such a medium? This principle defines the stationary regime as the large time asymptotic behavior of a system subject to a periodic excitation. An answer is proposed here in the case of a two-layered medium composed of a dielectric and a particular metamaterial (Drude model). In this context, we reformulate the time-dependent Maxwell's equations as a Schrödinger equation and perform its complete spectral analysis. As an application of this study, we show finally that the limiting amplitude principle holds except for a particular fequency, called the plasmonic frequency, characterised by a ratio of permittivities and permeabilities equal to -1 across the interface. This frequency is a resonance of the system and the response to this excitation blows up linearly in time
Giuliani, Chiara. "Alteration of ocean waves by periodic submerged structures for renewable energy extraction." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
Знайти повний текст джерелаZhang, Jie. "Intéractions vagues-fond marin et mécanismes de formation des vagues scélérates en zone côtière Wave-bottom interaction and extreme wave statistics due to shoaling and de-shoaling of irregular long-crested wave trains over steep seabed changes." Thesis, Ecole centrale de Marseille, 2020. http://www.theses.fr/2020ECDM0003.
Повний текст джерелаIn the maritime community, the term "rogue wave" or “freak wave” is used for waves whose wave height exceeds twice the significant wave height of the ambient sea state, and which appear more frequently than predicted by the Rayleigh distribution for wave height based on a Gaussian sea state hypothesis. In the oceanic domain, rogue waves that have caused loss of lives and severe damage have been widely reported in recent decades. In coastal areas, irregular bathymetry can also trigger such high extreme waves due to seabed-wave interactions. In this thesis, we focus on three mechanisms or scenarios of wave-bottom interactions that can lead to the formation of high waves.The first scenario is a resonance phenomenon, known as Fabry-Perot resonance, which can develop when monochromatic waves propagate over a bathymetry with two areas of sinusoidal undulations on an otherwise flat bottom. In the resonator zone located between the two areas of ripples, a significant increase in the height of the incident wave can be obtained if the resonance condition is met. By comparing numerical simulations with either exact or approximated bottom boundary condition and an asymptotic linear analytical solution, we observe a shift of the resonance frequency at the resonance condition for cases where the ratio between the amplitude of the ripples and the water depth is large: resonance occurs for a smaller wave number than predicted by the approximate analytical theory. This downshift effect of resonance frequency plays a secondary role for Bragg resonance, but it is very important and sensitive for Fabry-Perot resonance.The second scenario corresponds to the instabilities of amplitude modulated wave trains, commonly called "breathers", which propagate over irregular bottoms. Three types of bathymetric profiles are studied experimentally and numerically with a fully nonlinear model and with nonlinear (cubic) Schrödinger equation. This study has shown that for shallow depths and for certain conditions, the amplitude of the modulation can reach twice the amplitude of the initial train. This shallow depth amplification results from mechanisms that do not exist at constant depth. The influences of parameters that can affect the dynamics of breathers, including the Akhmediev breather parameter, water depth, steepness of the carrier wave, wave period and bottom slopes are analysed.The third scenario corresponds to unidirectional irregular wave trains propagating on variable coastal bottom profiles. When an incident sea state in equilibrium condition passes over a submerged bar or step, non-equilibrium dynamics appear and force the sea state to a new equilibrium compatible with the finite depth, characterized by highly non-Gaussian statistics and an increased probability of extreme wave occurrence. The combination of large-scale experiments and fully nonlinear simulations allows a better understanding of the dynamic response of the wave train. The resulting data were analysed in depth using a combination of spectral, bispectral and statistical approaches
Piskarskas, Rimtautas. "Intensyvių femtosekundinių šviesos bangų paketų sklidimo Kero terpėse laikinis ir erdvinis charakterizavimas." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20090901_074558-11811.
Повний текст джерелаIn the disertation, the self-focusing phenomenon of intense femtosecond light pulses in media with cubic nonlinearity is investigated and the origin of formation of light filaments is revealed. In this work, new measurement techniques are introduced and applied experimentally, which allowed high resolution temporal, spatial and spectral mapping of light wave-packet dynamics during the nonlinear propagation in transparent media, and enabled to observe and make accurate quantitative evaluation of the ultrafast change of medium properties. By means of high temporal (20 fs) and spatial (1 μm) resolution laser 3D mapping technique, it was shown that the initial Gaussian wave packet during self-action in Kerr media redistributes its energy in a way that in spatio-temporal domain the wave packet takes a complex X-type intensity distribution. This transformation is universal and is determined by temporal and spatial spectral broadening (as a consequence of self-focusing and self phase modulation), conical emission (as a consequence of four-wave mixing) and nonlinear losses caused by multiphoton absorption. By means of imaging spectrometer technique it was shown that in the medium with normal group velocity dispersion the far-field angular spectrum of the wave packet takes a characteristic X shape, whereas in anomalous group velocity dispersion regime – a characteristic O shape. In both cases the localization of the wave packet is observed, however the quantitative differences of the... [to full text]
Aliyar, Sithik. "Extreme wave interaction with fixed and floating structures using hybrid coupling approach." Electronic Thesis or Diss., Ecole centrale de Nantes, 2022. http://www.theses.fr/2022ECDN0047.
Повний текст джерелаThe thesis aims to study the effectiveness and accuracy of the NS and SWENSEbased solvers for simulating fixed and floating structures. Both solvers are OpenFOAM-based and are independently coupled with HOS for wave generation in terms of domain and functional decomposition approach. The solvers are tested for three applications. The first and second applications present the focusing wave interaction with fixed and moving cylinders and the third is the interaction of regular and irregular waves with the OC3 Hywind SPAR type substructure. The wave generating methods and parametersfor NS and SWENSE solvers are discussed in detail for regular, irregular, and focused waves. For verification, the case’s uncertainty is quantified using the Richardson extrapolation approach and validated with the experimental measurements.A significant reduction in the mesh size is predicted in both approaches. For the floating body wave interaction study, the moorings are modelled in two ways: by considering the mooring lines as a linear spring with defined spring stiffnessand coupling with a dynamic mooring model (MoorDyn). The numerical results of surface elevation, body motions, and mooring tensions are validated against the experiments carried out in the SOFTWIND project, and the efficiency andaccuracy of the two solvers are compared
Bobinski, Tomasz. "Métamatériaux pour les ondes à la surface de l'eau." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066125/document.
Повний текст джерелаThis thesis presents numerical and experimental results concerning usage of metamaterials for water waves control. Two applications were considered. Firstly, we showed how to focus water waves using analogy to a group of metamaterials called epsilon-near-zero. This allowed to tailor phase pattern at the circular interface between two domains with high contrast in water depth. The analogy resulted in highly nonlinear behaviour of waves, manifested by sub-wavelength cascade of focal spots with respect to the incident wave. The second considered application of metamaterials for water waves was hiding (cloaking) defects in a waveguide from the far-field observer. In the first project, related to cloaking, waveguide with varying cross-sections was analyzed. The efficiency of bathymetry, rendered by conformal mapping, was evaluated in terms of scattering properties. The influence of water waves dispersivity on the cancellation of scattering was also determined. Cloaking properties of the obtained bathymetry were experimentally confirmed using a wave packet characterized by broadband spectrum. In the second project, we showed how to cloak a cylinder that is shifted from the centreline of a waveguide. Smooth cloaking bathymetry surrounding a cylinder was able to significantly reduce the scattering in broad range of frequencies. The experimental counterparts confirmed increase in transmission with respect to a reference case with flat bathymetry. The remainder of the thesis presents novel method for the analysis of fringe profilometry images. Performance of the new method was compared to the Fourier Transform Profilometry. We obtained significant enhancement in spectral capabilities
PERIGO, ELIO A. "Desenvolvimento de um focalizador magnético utilizando um arranjo periódico de ímãs permanentes para aplicaçãao em dispositivos de microondas de potência." reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11338.
Повний текст джерелаMade available in DSpace on 2014-10-09T13:58:24Z (GMT). No. of bitstreams: 1 11097.pdf: 8468953 bytes, checksum: 884442a7a2e945eacad452d3697f2149 (MD5)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
Mazzoccoli, Jason Paul. "Properties of poly(ethylene glycol) diacrylate blends and acoustically focused multilayered biocomposites developed for tissue engineering applications." online version, 2008. http://rave.ohiolink.edu/etdc/view.cgi?acc%5Fnum=case1212612650.
Повний текст джерелаPaković, Srdan. "Contributions to the theory of non diffractive waves and synthesis of metallic Bessel beam/X-wave launchers." Thesis, Rennes 1, 2021. http://www.theses.fr/2021REN1S128.
Повний текст джерелаThis thesis present the author’s contributions to the field of non-diffractive waves. Essentially, non-diffractive waves are electromagnetic beams that radiate localized energy with a variety of potential practical applications. The work presented in this thesis can be divided into two parts. In the first part, a novel concept of synthesizing metallic spline profiled Bessel beam/X-wave launchers has been proposed. First, an ad-hoc tool based on mode matching is presented. The tool is capable of evaluating the S parameters, near-, and far-field radiation patterns of metallic structures with azimuthal symmetry. Then, metallic Bessel beam/X-wave launchers are synthesized using the ad-hoc tool. The concept has been experimentally validated by manufacturing and measuring an X-wave launcher operating in a 75-105 GHz frequency range. The fabricated launcher is the first experimental demonstration of an X-wave launcher at such frequencies. In the second part, we have investigated the use of non-diffractive waves for wireless power transfer. First, the use of Bessel-Gauss beams for WPT is investigated. The superior performance of Bessel-Gauss beams compared to Bessel beams is demonstrated. A Bessel-Gauss launcher has been designed for validating this claim. The power transfer coefficient of the launcher exceeds 50% for distances exceeding its non-diffractive range
Zaukevičius, Audrius. "Kampinės dispersijos panaudojimas galingų ir ultratrumpų impulsinių šviesos pluoštų formavimui netiesinių sąveikų metu." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20121227_090243-44723.
Повний текст джерелаThis thesis is aimed to provide an extensive picture of the phenomena encountered in optical parametric amplification of pulsed light beams. The particular attention is paid for the spatio-temporal dynamics of the pulsed light beams being amplified. All the research has been done by means of numerical methods. The equations used in the model were derived from the Maxwell’s equations and the assumptions made along the derivation of equations were discussed. Using the presented model it has been numerically demonstrated, that in noncollinear optical parametric amplifier, when pulse fronts of pump and signal are not matched, the signal pulse becomes tilted and aside from angular dispersion acquires a spatial chirp. It has been shown, that the magnitudes of the induced spatial and angular dispersions decrease at different rates with the increase of the signal pulse temporal chirp. The main results of this study were verified experimentally. Additionally, in this thesis we have proposed a novel and versatile method for pulsed conical wave parametric amplification with subsequent spatio-temporal compression during propagation in free space. It allows to form ultra-intense and propagation invariant wave-packets capable to propagate over many Rayleigh range in the desired material. In contrast to ordinary chirped-pulse amplification technique it does not require a pulse compressor, thus greatly facilitates the parametric amplification of few-cycle light pulses.
Zaukevičius, Audrius. "The use of angular dispersion for formation of high peak power and ultrashort pulsed light beams in nonlinear interactions." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20121227_090300-84220.
Повний текст джерелаDisertacija yra skirta išnagrinėti ir paaiškinti impulsinių šviesos pluoštų parametrinio stiprinimo metu vykstančius reiškinius. Ypatingas dėmesys yra skiriamas erdvinei-laikinei impulsinio šviesos pluošto dinamikai stiprinimo metu. Visi nagrinėjamų reiškinių tyrimai buvo atliekami taikant skaitmeninio modeliavimo metodus. Modelyje panaudotos lygtys buvo išvestos iš Maksvelo lygčių, išsamiai aptariant lygčių išvedimo metu daromas prielaidas. Naudojantis pateiktu modeliu buvo gauti skaitmeniniai rezultatai, kurie parodė, jog nekolineariame parametriniame stiprintuve, kuomet kaupinimo ir signalinio impulsų frontai nėra sutapatinti, signalinis impulsas tampa pakrypęs ir be kampinės dispersijos taip pat įgyja ir erdvinį čirpą. Nustatyta, kad indukuotų erdvinės ir kampinės dispersijų mažėjimo sparta, didinant signalinio impulso laikinį čirpą, yra skirtinga. Pagrindiniai šio teorinio tyrimo rezultatai buvo patvirtinti eksperimentiškai. Taip pat šioje disertacijoje yra pristatomas naujas ir universalus impulsinių kūginių bangų parametrinio stiprinimo metodas, kuriame sustiprinti impulsai patys susispaudžia laike ir erdvėje paprasčiausiai sklisdami laisvoje erdvėje. Šis metodas leidžia formuoti didelio smailinio intensyvumo invariantiškus bangų paketus, galinčius nusklisti daugelį Relėjaus nuotolių norimoje medžiagoje. Priešingai nei įprastame čirpuotų impulsų stiprinimo metode, šis metodas nereikalauja impulsų spaustuvo, o tai žymiai palengvina parametrinį kelių optinių ciklų... [toliau žr. visą tekstą]
Ibrahim, Rony. "Focalisation des ondes électromagnétiques pour la transmission d'énergie sans fil." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI109.
Повний текст джерелаMost recent developments in Wireless Energy Transmission (WET) using electromagnetic (EM) waves focus on designing systems to recover the electromagnetic energy lost by common wireless systems such as Wi-Fi networks. However, the intermittent and unpredictable nature of these ambient sources makes harvesting energy critical for some applications. Hence, the WET over considerable distances using microwaves appears in this context allowing the remote wake-up and wireless powering of electronic devices in a myriad of applications that are a part of the constantly evolution of the way of life. Wireless powering of an electronic device eliminates the need of the battery, which reduces its size and cost. The work presented in this thesis belong to the WET in indoor environments field. When energy is voluntarily transmitted by microwaves, systems using continuous waves are not necessarily the most efficient. The aim of this research project is to achieve a complete WET system by focusing of EM waves at the receiver in order to increase the overall energy transfer efficiency. The studies presented during this thesis show that the time reversal technique (TR) is optimal for the focusing of EM waves. The procedure is carried out in two stages. In the first stage called \textit{learning stage}, a low energy pulse is transmitted by an emitting antenna. Another antenna placed in other location in the medium receives and records a signal made of a succession of delayed pulses, more or less attenuated, and related to reflections on the environment. In a second stage called \textit{focusing stage}, a high-energy signal constructed from the time reversal of the recorded signal is transmitted by one of the antennas. Using this technique, it results that the temporally inverted signal focuses spatio-temporally on the receiving antenna in the form of a Pulsed Wave (PW). These properties are particularly important for the WET. At the receiver circuit, the \textit{rectenna} (rectifying antenna) is the device for capturing and converting focused PW to DC voltage. In this research project, we introduce a novel rectenna design based on Schottky diodes with a current-doubler topology designed, developed and optimized to ensure optimum conversion performance of PW. Experimental measurements demonstrate good performance predicted by the design procedure. Moreover, the performances obtained are perfectly distinct from those found in the state of the art, making this work an innovation in WET domain
Eliasson, Veronica. "On focusing of shock waves." Doctoral thesis, Stockholm : Mekanik, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4479.
Повний текст джерелаYi, Kaijun. "Controlling guided elastic waves using adaptive gradient-index structures." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC044/document.
Повний текст джерелаGRadient INdex (GRIN) media are those whose properties smoothly vary in space or/and time. They have shown promising effects in many engineering applications, such as Structural Health Monitoring (SHM), vibration and noise control, energy harvesting, etc. On the other hand, piezoelectric materials provide the possibility to build unit cells, whose mechanical properties can be controlled on-line. Motivated by these two facts, adaptive GRIN structures, which can be realized using shunted piezoelectric materials, are explored in this dissertation to control guided elastic waves. Two types of adaptive GRIN structures are studied in this work. The first type is a piezo-lens. It is composed of shunted piezoelectric patches bonded on the surfaces of plates. To control the mechanical properties of the piezoelectric composite, the piezoelectric patches are shunted with Negative Capacitance (NC). By tuning the shunting NC values, refractive indexes inside the piezo-lens are designed to satisfy a hyperbolic secant function in space. Numerical results show that the piezo-lens can focus waves by smoothly bending them toward the designated focal point. The piezo-lens is effective in a large frequency band and is efficient in many different working conditions. Also the same piezo-lens can focus waves at different locations by tuning the shunting NC values. The focusing effect and tunable feature of piezo-lens make it useful in many applications like energy harvesting and SHM. The former application is fully discussed in this thesis. The focusing effect at the focal point results in a known point with high energy density, therefore harvesting at the focal point can yield more energy. Besides, the tunable ability makes the harvesting system adaptive to environment changes. The second type is the time-space modulated structure. Its properties are modulated periodically both in time and space. Particularly, the modulation works like a traveling wave in the structure. Due to the time-varying feature, time-space modulated structures break the reciprocity theorem, i.e., the wave propagation in them is nonreciprocal. Many unusual phenomena are observed during the interaction between waves and time-space modulated structures: frequency splitting, frequency conversion and one-way wave transmission. Two types of frequency conversion are demonstrated and explained. The first type is caused by energy transmission between different orders Bloch modes. The second type is due to the Bragg scattering effect inside the modulated structures. The one-way wave transmission could be exploited to realize one-way energy insulation in equivalent infinite or semi-inffnite systems. However, the one-way energy insulation fails in finite systems due to the frequency conversion phenomenon
Eliasson, Veronica. "On focusing of strong shock waves." Licentiate thesis, Stockholm : Department of Mechanics, Royal Institute of Technology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-565.
Повний текст джерелаVallon, Henri. "Focusing high-power electromagnetic waves using time-reversal." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC006/document.
Повний текст джерелаA main aspect of this work has been to develop analytical and statistical models of the power efficiency of a time-reversal amplification system (TRAS).It is also important to evaluate the efficiency of a reverberation chamber. This allows quantifying the power received by one or more antenna when the reverberation chamber is excited. This factor is important when considering construction of the most efficient chamber for time-reversal amplification.Measurements assessing the loading effect of antennas in reverberation chambers when the field can be considered diffused were also undertaken. The study focuses on the evaluation of the varying quality factor when adding loaded antennas in the chamber.Another focus of this work is to evaluate the ratios between signals during calibration and focusing phase. An important aspect of the studies presented in this work thus concerns evaluation of the maximum value of the impulse response in a complex propagation system.We also present the power gain of time-reversal techniques and its statistical advantages compared to a classic use of a reverberation chamber.The development of a prototype required the design and implementation of each of the branches of the complete systems.The first measurement campaigns allowed the complete validation of the models
Bor, Jonathan. "Focusing antennas and associated technology in millimeter waves and sub-millimeter waves." Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S169.
Повний текст джерелаWith the increase of wireless communications and the required bite rate of data, it needs to increase the working frequency up to the millimeter wave range. For that purpose, the 60 GHz bandwidth (57-66GHz) has been unlicensed all over the world. Because of the loss and possible non-line-of-sight communication, the antennas should have beam scanning properties. Therefore, the Canon Research Center France and the IETR have run a study (PhD) to fulfill this project. A new technological process has been developed in order to manufacture inhomogeneous materials. By pressing a composite foam material sample, it will expel the air from the sample and so, increase its density and its relative permittivity. Using this process, several antennas and components have been manufactured. A particular focus has been done on the Luneburg lens antenna. This one has a radial index law and has infinity of focal points around the lens. This lens has been manufactured with a smooth gradient index law and first fed by an open-ended waveguide to validate the technological process. Secondly, integrated sources have been studied in order to place them side by side and to allow scanning the main beam direction. Thus, the use of Radiating Substrate Integrated Waveguide (RSIW) appears to be the solution. Two passives sources have been realized. The first one is a RSIW fed by a coupling slot from a microstrip line and the second one is a RSIW fed by a coaxial probe from a first thin SIW. A thirdly RSIW has been studied fed by a coplanar line and a coaxial probe and to simplify the manufacturing. Finally, two active antennas prototypes have been realized to perform a complete communication at 60 GHz. Complete integrated chips from the Hittite company have been used to feed the RSIW which illuminate the Luneburg lens. The objective was to implement a beam scanning antennas with three distinct beam directions. Lastly, a preliminary contribution to the sub-millimeter antennas has been performed with the manufacturing of a horn, a circular polarization antenna and a near-field focusing antenna
McGregor, A. "Periodic magnet focussing of electron beams in travelling wave tubes." Thesis, Lancaster University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376707.
Повний текст джерелаAl, Durra Ahmed Abad. "DORT method and selective focusing of UWB electromagnetic waves." Connect to resource, 2005. http://hdl.handle.net/1811/5864.
Повний текст джерелаTitle from first page of PDF file. Document formattted into pages: contains 23 p.; also includes graphics. Includes bibliographical references (p. 22-23). Available online via Ohio State University's Knowledge Bank.
Chernukha, Yevheniia. "Investigation of phase transitions triggered by laser-induced focusing shock waves." Thesis, Le Mans, 2019. http://www.theses.fr/2019LEMA1038.
Повний текст джерелаThe ability of certain materials to change its ground state due to laser excitation has arisen a lot of opportunities for light-control of material properties. The field of photo-induced phase transitions counts a rich variety of chemical and physical processes triggered by light-matter interactions involved during the phase transition process. Recently it was reported that elastically driven cooperativity leads to the amplification of spin state in molecular crystals and prolonged the lifetime of the transient state with an ultra-short laser pulse. The cooperative response appears during the propagation of non-linear coherent strain waves, in other words shock waves, coupled with the order parameter field. Shock waves can be seen as a new challenging pathway to achieve a permanently switched state with appropriate excitations.First, we introduce time-resolved single-shot imaging combined with the laser shock focusing technique that makes it possible to generate, acoustically focus, and directly visualize under a microscope shock waves propagating and focusing along the sample surface. The spatial separation of the laser-influenced and strain-influenced regions makes it possible to disentangle the material changes produced solely by the shock waves. Second, we present experimental results involving the shock-focusing technique to materials undergoing phase transitions linked with a macroscopic change of their volume (spin-crossover systems, Mott insulators). Post-mortem analyses of the samples confirm permanent phase transition under specific experimental conditions. These innovative results open doors for a generic elastically driven cooperativity
Scarfe, Bradley Edward. "Oceanographic Considerations for the Management and Protection of Surfing Breaks." The University of Waikato, 2008. http://hdl.handle.net/10289/2668.
Повний текст джерелаJenkins, Robert M. "Semiclassical Asymptotics of the Focusing Nonlinear Schrodinger Equation for Square Barrier Initial Data." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/193553.
Повний текст джерелаMacNeil, John Michael Larratt. "Solitary waves in focussing and defocussing nonlinear, nonlocal optical media." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/20951.
Повний текст джерелаSun, Ruoci. "Comportement en grand temps et intégrabilité de certaines équations dispersives sur l'espace de Hardy Long time behavior of the NLS-Szegö equation Traveling waves of the quintic focusing NLS-Szegö equation Complete integrability of the Benjamin-Ono equation on the multi-soliton manifolds." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS111.
Повний текст джерелаWe are interested in three non linear dispersive Hamiltonian equations: the defocusing cubic Schrödinger equation filtered by the Szegö projector on the torus that cancels every negative Fourier modes, leading to the cubic NLS--Szegö equation on the torus; the focusing quintic Schrödinger equation, which is filtered by the Szegö projector on the line, leading to the quintic NLS--Szegö equation on the line and the Benjamin--Ono (BO) equation on the line. Similarly to the other two models, the BO equation on the line can be written as a quadratic Schrödinger-type equation that is filtered by the Szegö projector on the line. These three models allow us to study their qualitative properties of some traveling waves, the phenomenon of the growth of Sobolev norms, the phenomenon of non linear scattering and some properties about the complete integrability of Hamiltonian dynamical systems. The goal of this thesis is to investigate the influence of the Szegö projector on some one-dimensional Schrödinger-type equations and to adapt the tools of the Hardy space on the torus and on the line. We also use the Birkhoff normal form transform, the concentration--compactness argument, refined as the profile decomposition theorem, and the inverse spectral transform in order to solve these problems. In the third model, the integrability theory allows to establish the connection with some algebraic and geometric aspects
Tabak, Esteban Gregorio. "Focusing of weak shock waves and the von Neumann paradox of oblique shock reflection." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/108868.
Повний текст джерелаSullivan, Brendan. "Delayed triggering of early aftershocks by multiple surface waves circling the earth." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45827.
Повний текст джерелаDegueldre, Henri-Philippe Verfasser], Theo [Akademischer Betreuer] [Geisel, Ragnar Akademischer Betreuer] Fleischmann, and Eberhard [Akademischer Betreuer] [Bodenschatz. "Random Focusing of Tsunami Waves / Henri-Philippe Degueldre. Betreuer: Theo Geisel. Gutachter: Ragnar Fleischmann ; Eberhard Bodenschatz." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://d-nb.info/1078774277/34.
Повний текст джерелаBarnard, M. E. "The surface acoustic wave focussing slanted chirped transducer and its assessment as the basis of a spectrum analyser." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355726.
Повний текст джерелаIliopoulos, Ioannis. "Engineering the near field of radiating systems at millimeter waves : from theory to applications." Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S165.
Повний текст джерелаWith the demand for near-field antennas continuously growing, the antenna engineer is charged with the development of new concepts and design procedures for this regime. From the microwave and up to terahertz frequencies, a vast number of applications, especially in the biomedical domain, are in need for focused or shaped fields in the antenna proximity. This work proposes new theoretical methods for near-field shaping based on different optimization schemes. Continuous radiating planar apertures are optimized to radiate a near field with required characteristics. In particular, a versatile optimization technique based on the alternating projection scheme is proposed. It is demonstrated that, based on this scheme, it is feasible to achieve 3-D control of focal spots generated by planar apertures. Additionally, with the same setup, also the vectorial problem (shaping the norm of the field) is addressed. Convex optimization is additionally introduced for near-field shaping of continuous aperture sources. The capabilities of this scheme are demonstrated in the context of different shaping scenarios. Additionally, the discussion is extended to shaping the field in lossy stratified media, based on a spectral Green's functions approach. Besides, the biomedical applications of wireless power transfer to implants and breast cancer imaging are addressed. For the latter, an extensive study is included here, which delivers an outstanding improvement on the penetration depth at higher frequencies. The thesis is completed by several prototypes used for validation. Four different antennas have been designed, based either on the radial line slot array topology or on metasurfaces. The prototypes have been manufactured and measured, validating the overall approach of the thesis
Hernández, Cubero Óscar Rubén. "Méthodes optiques innovantes pour le contrôle rapide et tridimensionnel de l’activité neuronale." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCB005.
Повний текст джерелаThe ongoing revolution of optogenetic tools – genetically encoded light-sensitive proteins that can activate, silence and monitor neural activity – has opened a new pathway to bridge the gap between neuronal activity and cognition. However, to take full advantage of these tools we need optical methods that can deliver complex light patterns in the brain. During my doctorate, I worked on two novel and complementary optical systems for complex spatiotemporally neural activity stimulation. The first system combined acousto-optic deflectors and low numerical aperture Gaussian beam illumination for fast photoactivation of optogenetic tools. The random-access capabilities of the system allowed to deliver complex spatiotemporal illumination sequences that successfully emulated physiological patterns of cerebellar mossy fiber activity in acute slices. These results demonstrate that patterned optogenetic stimulation can be used to recreate ongoing activity and study brain microcircuits in a physiological activity context. Alternatively, Computer Generated Holography (CGH) can powerfully enhance optogenetic stimulation by efficiently shaping light onto multiple cellular targets simultaneously. Nonetheless, the axial confinement degrades for laterally extended illumination patterns. To address this issue, CGH can be combined with temporal focusing that axially confines fluorescence regardless of lateral extent. However, previous configurations restricted nonlinear excitation to a single spatiotemporal focal plane. In this thesis, I describe two alternative methods to overcome this limitation and enable three-dimensional spatiotemporal focused pattern generation
Cebrecos, Ruiz Alejandro. "Transmission, reflection and absorption in Sonic and Phononic Crystals." Doctoral thesis, Universitat Politècnica de València, 2015. http://hdl.handle.net/10251/56463.
Повний текст джерела[ES] Los cristales fonónicos son materiales artificiales formados por una disposición periódica de inclusiones en un medio, pudiendo ambos ser de carácter sólido o fluido. Controlando la geometría y el contraste de impedancias entre los materiales constituyentes se pueden controlar las propiedades dispersivas de las ondas. Cuando una onda propagante se encuentra un medio con diferentes propiedades físicas puede ser transmitida y reflejada, en medios sin pérdidas, pero también absorbida, si la disipación es tenida en cuenta. La presente tesis está dedicada al estudio de diferentes efectos presentes en cristales sónicos y fonónicos relacionados con la transmisión, reflexión y absorción de ondas, así como el desarrollo de una técnica para la caracterización de sus propiedades dispersivas, descritas por la estructura de bandas. En primer lugar, se estudia el control de la propagación de ondas en transmisión en sistemas conservativos. Específicamente, nuestro interés se centra en mostrar cómo los cristales sónicos son capaces de modificar la dispersión espacial de las ondas propagantes, dando lugar al control del ensanchamiento de haces de sonido. Haciendo uso de las curvas de dispersión espacial extraídas del análisis de la estructura de bandas, se predice primero la difracción nula y negativa de ondas a frecuencias cercanas al borde de la banda, resultando en la colimación y focalización de haces acústicos en el interior y detrás de un cristal sónico 3D, y posteriormente se demuestra mediante medidas experimentales. La eficiencia de focalización de un cristal sónico 3D está limitada debido a las múltiples reflexiones existentes en el interior del cristal. Para superar esta limitación se consideran estructuras axisimétricas trabajando en el régimen de longitud de onda larga, como lentes de gradiente de índice. En este régimen, las reflexiones internas se reducen fuertemente y, en configuración axisimétrica, la adaptación de simetría con fuentes acústicas radiando haces de sonido incrementa la eficiencia drásticamente. Además, la teoría de homogenización puede ser empleada para modelar la estructura como un medio efectivo con propiedades físicas efectivas, permitiendo el estudio del frente de ondas en términos refractivos. Se mostrará el modelado, diseño y caracterización de un dispositivo de focalización eficiente basado en los conceptos anteriores. Considérese ahora una estructura periódica en la que uno de los parámetros de la red, sea el paso de red o el factor de llenado, cambia gradualmente a lo largo de la dirección de propagación. Los cristales chirp representan este concepto y son empleados aquí para demostrar un mecanismo novedoso de incremento de la intensidad de la onda sonora basado en un fenómeno conocido como reflexión "suave". Este incremento está relacionado con una ralentización progresiva de la onda conforme se propaga a través del material, asociado con la velocidad de grupo de la relación de dispersión local en los planos del cristal. Un modelo basado en la teoría de modos acoplados es propuesto para predecir e interpretar este efecto. Se observan dos fenómenos diferentes al considerar pérdidas en estructuras periódicas. Por un lado, si se considera la propagación de ondas sonoras en un array periódico de capas absorbentes, cuyo frente de ondas es paralelo a los planos del cristal, se produce una reducción anómala en la absorción combinada con un incremento simultáneo de la reflexión y transmisión a las frecuencias de Bragg, de forma contraria a la habitual reducción de la transmisión, característica de sistemas periódicos conservativos a estas frecuencias. En el caso de la misma estructura laminada en la que se cubre uno de sus lados mediante un reflector rígido, la incidencia de ondas sonoras desde un medio homogéneo, cuyo frente de ondas es perpendicular a los planos del cristal, produce un gran incremento de la fuerza de
[CAT] Els cristalls fonònics són materials artificials formats per una disposició d'inclusions en un medi, ambdós poden ser sòlids o fluids. Controlant la geometría i el contrast d'impedàncies dels seus materials constituents, és poden controlar les propietats dispersives de les ondes, permetent una gran varietatde fenòmens fonamentals interessants en el context de la propagació d'ones. Quan una ona propagant troba un medi amb pèrdues amb propietats físiques diferents es pot transmetre i reflectir, però també absorbida si la dissipació es té en compte. Aquests fenòmens fonamentals s'han explicat clàssicament en el context de medis homogenis, però també ha sigut un tema de creixent interés en el context d'estructures periòdiques en els últims anys. Aquesta tesi doctoral tracta de l'estudi de diferents efectes en cristalls fonònics i sònics lligats a la transmissió, reflexió i absorció d'ones, així com del desenvolupament d'una tècnica de caracterització de les propietats dispersives, descrites mitjançant la estructura de bandes. En primer lloc, s'estudia el control de la propagació ondulatori en transmissió en sistemes conservatius. Més específicament, el nostre interés és mostrar com els cristalls sonors poden modificar la dispersió espacial d'ones propagants donant lloc al control de l'amplària per difracció dels feixos sonors. Mitjançant les corbes dispersió espacial obtingudes de l'anàlisi de l'estructura de bandes, es prediu, en primer lloc, la difracció d'ones zero i negativa a freqüències próximes al final de banda. El resultat és la collimació i focalització de feixos sonors dins i darrere de cristalls de so. Després es mostra amb mesures experimentals. L'eficiència de focalització d'un cristall de so 3D està limitada per la gran dispersió d'ones dins del cristall, que és característic del règim difractiu. Per a superar aquesta limitació, estructures axisimètriques que treballen en el règim de llargues longituds d'ona, i es comporten com a lents de gradient d'índex. En aquest règim, la dispersió es redueix enormement i, en una configuració axisimètrica, a causa de l'acoblament de la simetría amb les fonts acústiques que radien feixos sonors, l'eficiència de radiació s'incrementa significativament. D'altra banda, la teoria d'homogeneïtzació es pot utilitzar per a modelar, dissenyar i caracteritzar un dispositiu eficient de focalització basat en aquests conceptes. Considerem ara una estructura periòdica en la qual un dels seus paràmetres de xarxa, com ara la constant de xarxa o el factor d'ompliment canvia gradualment al llarg de la direcció de propagació. Els cristalls chirped representen aquest concepte i s'utilitzen ací per a demostrar un mecanisme nou d'intensificació d'ones sonores basat en el fenòmen conegut com a reflexió "suau". La intensificació està relacionada amb la alentiment progressiva de l'ona conforme propaga al llarg del material, que està associada amb la velocitat de grup de la relació de dispersió local en els diferents plànols del cristall. Es proposa un model basat en la teoria de modes acoblats per a predir i interpretar este efecte. Dos fenòmens diferents cal destacar quan es tracta d'estructures periòdiques amb dissipació. Per un costat, al considerar la propagació d'ones sonores en el plànol en un array periòdic de capes absorbents, s'observa una disminució anòmala de l'absorció i es combina amb un augment simultani de reflexió i transmissió en les freqüències de Bragg que contrasta amb la usual disminució de transmissió, característica dels sistemes conservatius a eixes freqüències. Per a un medi similar de capes, amb un reflector rígid darrere, les ones fora del pla incidint l'estructura des de un medi homogeni, augmentaran considerablement la interacció. En altres paraules, el retràs temporal de les ones sonores dins del sistema periòdic augmentarà significativament produint un augmen
Cebrecos Ruiz, A. (2015). Transmission, reflection and absorption in Sonic and Phononic Crystals [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/56463
TESIS
Premiado
Perfetti, Claire. "Particle manipulation in minichannels for enhanced digital holographic microscopy observation." Doctoral thesis, Universite Libre de Bruxelles, 2014. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209283.
Повний текст джерелаsizes - mostly in the nano to millimeter scale - when dispersed in a carrier medium, is an increasingly important topic in many fields such as biotechnology,nanotechnology, medicine, biophysics and environmental monitoring and remediation. The underlying rationale for using such techniques stands in the sometimes compelling requirements of avoiding clogging as in micro/nano channel flows, of limiting sedimentation and wall interactions in particle/cell counting, of enhancing particle-surface interaction as in bio-sensing or of facilitating characterization and sorting as in bio-physical applications. Being developed in the frame of a Belgian national project devoted to the characterization and counting of pollutant in water media by digital holographic microscopy, this thesis tackles a peculiar class of particle manipulation techniques, commonly known as Focusing. The main goal of focusing is to avoid at best wall particle interactions and sedimentation, prevalent issues for dispersions owing in micro/mini-channels especially for applications such as optical characterization and counting.
The main attention was given to two flow focusing techniques - Hydrodynamic and Acoustic Focusing - for their wide range applicability and cost effectiveness. Hydrodynamic Focusing consists in controlling the position and spreading of the sample under investigation by means of a so-called sheath flow. A low-cost, nevertheless effective, prototype has been conceived, designed, manufactured and tested. It allowed for controlling the spreading of the sample stream and achieving a focusing ratio accounting for only 4% of the original stream width.
Acoustic Focusing takes advantage of the time-averaged pressure fields induced by the creation of standing waves in channels to manipulate and focus the dispersed particles. In the frame of this thesis, several devices have been developed using square cross section glass mini-channels. Aside from the cost-effectiveness, particles where focused in a somehow unexpected but high reproducible 3D matrix-like structure. A novel numerical model has also been implemented in order to study the conditions leading to the 3D structure formation. A good agreement between experimental and numerical results was found./Ce projet de thèse portant sur la manipulation de micro-particules dans des minicanaux s'inscrit dans le développement de cellules de flux pour des applications biologiques, qui est l'une des problématiques du projet HOLOFLOW, soutenu par
la région de Bruxelles Capitale. Les cellules de flux doivent permettre l'observation et la reconnaissance des micro-organismes vivants dans une large gamme de dimensions (de quelques microns à 1mm) avec la microscopie holographie digitale.
La problématique d'observation et de manipulation des microorganismes en flux est liée au clogging (bouchage) et à la sédimentation qui limitent la durée de vie des cellules d'observation. Ce projet de thèse s'inscrit dans cette problématique et propose deux axes d'étude pour limiter l'interaction entre organismes et canaux, la focalisation hydrodynamique, basée sur le guidage de flux, et la focalisation acoustique, basée sur la manipulation des particules.
La focalisation hydrodynamique est une technique basée sur l'injection différentiée de l'échantillon à observer et d'un fluide support. La différence des vitesses d'injection des flux permet de contrôler la dispersion des particules afin d'optimiser leur observation. Dans le cadre de cette thèse, un prototype à bas-coût a été développé et construit, permettant de focaliser les particules dans un faisceau jusqu'à 4% de leur faisceau incident.
La focalisation acoustique utilise la création d'une onde acoustique stationnaire afin de regrouper les particules en suspension au centre du canal. Au cours de cette thèse, plusieurs prototypes ont été réalisés, mettant en évidence la formation de motifs tridimensionnaux. Un model numérique a été spécialement développé afin d'étudier les conditions de génération de ces motifs, et de nombreuses expériences ont été menées afin de s'assurer de leur reproductibilité. Une bonne adéquation entre la position des particules mesurée et calculée numériquement a été démontrée.
Doctorat en Sciences de l'ingénieur
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PILLAI, Vinoshene. "Intravital two photon clcium imaging of glioblastoma mouse models." Doctoral thesis, Scuola Normale Superiore, 2021. http://hdl.handle.net/11384/109211.
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