Les plasmons de surface sont des modes non-radiatifs qui vivent à l'interface d'un diélectrique et d'un métal. Ils peuvent confiner la lumière à des échelles sub-longueur d'onde. Néanmoins, leur propagation reste limitée par les pertes inhérentes au métal qui entraînent une absorption rapide du mode. L'objet de cette thèse est l'étude du couplage des plasmons de surface dans des structures planes métallo-diélectriques. L'obtention des propriétés des différents modes nécessite le prolongement des solutions dans le plan complexe définissant la constante de propagation. La méthode mise en œuvre consiste à déterminer les pôles de la matrice de diffusion en utilisant les intégrales de Cauchy. Une première solution pour résoudre le problème de propagation des plasmons de surface consiste à coupler ces modes entre eux. Dans un milieu symétrique, lorsque l'épaisseur d'un film métallique devient suffisamment faible, le couplage entre les modes plasmons existants sur chaque surface devient possible. L'un des deux modes couplés ainsi créé, dit plasmon longue portée, a une longueur de propagation supérieure à celle du plasmon de surface usuel tandis que l'autre, dit plasmon à courte portée, se propage moins. Nous présentons une configuration permettant l'excitation du mode longue portée sans le mode courte portée grâce à une couche métallique déposée sur un substrat infiniment conducteur. Cette excitation peut alors être effectuée dans l'air et permettre des applications comme la détection et la caractérisation de molécules. Ensuite, nous présentons le couplage entre deux guides d'ondes diélectriques, et plus particulièrement la théorie des modes couplés, étendue au cas de la polarisation transverse magnétique. Nous considérons aussi le cas de la PT symétrie. La dernière partie de ce mémoire présente la démonstration du régime de couplage fort entre un plasmon de surface et un mode guidé. Nous mettons alors en évidence une augmentation de la longueur de propagation pour le mode hybride plasmon dont le confinement reste celui d'un mode de surface. Un gain linéaire est ensuite ajouté dans les différentes couches de la structure pour en étudier l'effet. L'ajout de gain dans la couche intermédiaire entre les deux modes couplés a pour conséquence l'exaltation de la longueur de propagation des modes et plus particulièrement du mode hybride plasmon qui peut alors se propager au-delà du millimètre. / Surface plasmon polaritons are non radiative modes which exist at the interface between a dielectric and a metal. They can confine light at sub-wavelength scales. However, their propagation is restricted by the intrinsic losses of the metal which imply a rapid absorption of the mode. The aim of this thesis is the study of the coupling of surface plasmons in metallo-dielectric planar structures. Obtaining the properties of the modes implies the extension of the solutions to the complex plane of propagation constants. The method used consists in determining the poles of the scattering matrix by means of Cauchy's integrals. The first solution to solve the problem of propagation of the surface plasmons consists in coupling these modes to one another. In a symmetric medium, when the thickness of the metallic film becomes thin enough, the coupling between the plasmon modes which exist on each side becomes possible. One of the coupled modes which is created, the so-called long range surface plasmon, has a bigger propagation length than the usual plasmon whereas the other coupled mode, named short range surface plasmon, has a smaller propagation length. We present a configuration which allows the excitation of the long range surface plasmon without the short range mode with a metallic layer deposited on a perfect electric conductor substrate. This excitation can be done in air and allows applications, such as the detection and the characterisation of molecules. Then, we present the coupling between dielectric waveguides, and, in particular, the coupled-mode theory in the case of the transverse magnetic polarisation. We consider also the case of PT symmetric structure. The last part of this work presents the demonstration of the strong coupling regime between a surface plasmon and a guided mode. We demonstrate an increase of the propagation length of the hybrid surface plasmon, which still has the confinement of a surface mode. A linear gain is added in the different layers of the structure. When the gain is added in the layer between both coupled modes allows an enhancement of the propagation lengths of the modes, and more precisely of the hybrid surface plasmon mode, which can propagate at the millimeter scale.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The scientific advances we have experienced in recent decades have enabled us to produce systems in the mesoscopic scale. These systems have become very useful as research tools in various areas of science. In mesoscopic physics the ondulatory characteristic of electrons is more evident than in classical physics and the electron conduction process is better represented by the wave function that describes it. Examples of application of mesoscopic systems are quantum dots which are open cavities where electrons are limited to flow through. Thus, the objective of this work is to study the effects of decoherence in the transport of electrons in two systems: i) quantum dot with a fictitious guide and ii) quantum dot with stub, where we take into account ondulatory properties of electrons. The formalism that we use is the scattering matrix, which relates the incoming and outgoing amplitudes in the scattering of waves coming in and out of the scattering region. Since the studied systems are chaotic, the scattering matrices can be treated as random. These matrices were generated by computational simulation and then the conductance values were computed. The conductance distribution was obtained by means of probabilistic analysis. / Os avanços científicos que temos experimentado nas últimas décadas proporcionaram a construção de sistemas em escala mesoscópica. Esses sistemas tornaram-se muito úteis como ferramentas de investigação em diversas áreas da ciência. Na física mesoscópica a característica ondulatória dos elétrons é mais evidente do que na física clássica e o processo de condução dos elétrons é melhor representado pela função de onda que os descreve. Exemplos da aplicação de sistemas mesoscópicos são os pontos quânticos que são cavidades abertas por onde os elétrons são limitados a fluirem. Dessa forma, o objetivo deste trabalho é estudar os efeitos da decoerência no transporte de elétrons em dois sistemas: i) ponto quântico com guia fictício e ii) ponto quântico com estube, onde levamos em consideração as propriedades ondulatórias dos elétrons. O formalismo que utilizamos é o da matriz de espalhamento, a qual relaciona as amplitudes das ondas que entram e saem da região de espalhamento. Como os sistemas estudados são caóticos, as matrizes de espalhamento podem ser tratadas como aleatórias. Geramos estas matrizes por meio de simulação computacional e delas extraímos a condutância do sistema. A distribuição da condutância foi obtida por meio de uma análise probabilística.

Surface plasmon polaritons are non radiative modes which exist at the interface between a dielectric and a metal. They can confine light at sub-wavelength scales. However, their propagation is restricted by the intrinsic losses of the metal which imply a rapid absorption of the mode. The aim of this thesis is the study of the coupling of surface plasmons in metallo-dielectric planar structures. Obtaining the properties of the modes implies the extension of the solutions to the complex plane of propagation constants. The method used consists in determining the poles of the scattering matrix by means of Cauchy's integrals. The first solution to solve the problem of propagation of the surface plasmons consists in coupling these modes to one another. In a symmetric medium, when the thickness of the metallic film becomes thin enough, the coupling between the plasmon modes which exist on each side becomes possible. One of the coupled modes which is created, the so-called long range surface plasmon, has a bigger propagation length than the usual plasmon whereas the other coupled mode, named short range surface plasmon, has a smaller propagation length. We present a configuration which allows the excitation of the long range surface plasmon without the short range mode with a metallic layer deposited on a perfect electric conductor substrate. This excitation can be done in air and allows applications, such as the detection and the characterisation of molecules. Then, we present the coupling between dielectric waveguides, and, in particular, the coupled-mode theory in the case of the transverse magnetic polarisation. We consider also the case of PT symmetric structure. The last part of this work presents the demonstration of the strong coupling regime between a surface plasmon and a guided mode. We demonstrate an increase of the propagation length of the hybrid surface plasmon, which still has the confinement of a surface mode. A linear gain is added in the different layers of the structure. When the gain is added in the layer between both coupled modes allows an enhancement of the propagation lengths of the modes, and more precisely of the hybrid surface plasmon mode, which can propagate at the millimeter scale.

In this thesis, the in-duct experimental methods for determining aeroacoustic N-ports of in-duct elements are discussed and improved. The scattering matrix determination methods and the related wave decomposition methods are evaluated from measurements in an empty duct carrying a mean flow. The improvements of a new over-determination method for the source part of the N-port is studied using simulations and measurements; in quiescent air as well as measurements of the flow associated noise of a mixer plate, here a triangular plate inserted at an angle in a duct. The new method is shown to improve suppression of random errors while no improvement is achieved for bias errors.   Further, the methods are applied in the study of two different aeroacoustic phenomena; one is the effect on the flow associated noise of the triangular plate achieved by varying the bending stiffness. For the most resilient plate tested, it is observed that when the Strouhal number of the flow noise coalesce with the Helmholtz number of a specific eigen-mode of the plate, the noise is drastically dampened. There is also a weaker broad band effect.   The other phenomena studied is the amplification and attenuation obtained for sound waves propagating in a T-junction of rectangular ducts. It is found that by adding only 10% of inflow in the side branch relative to that in the main branch, the amplification is heavily increased. By adding another 10% the amplification is again similar to that of no side branch flow. Adding further flow lessens the effects still. / QC 20101118 / Experimental characterization of aero-acoustic sources

[pt] Neste presente trabalho, o Método do Casamento de Modos é aplicado na análise e no projeto de estruturas coaxiais. A estrutura de excitação é um dos pontos críticos do projeto de antenas do tipo discone quando se pretende explorar suas características de banda larga. Seções não uniformes de guias de ondas coaxiais são usualmente utilizadas como elementos dessa estrutura de excitação sendo, eventualmente, necessária a inclusão de anéis dielétricos para garantir a rigidez mecânica da antena. Devido a essas não uniformidades encontradas nas dimensões e no meio dielétrico desse dispositivo de microondas, métodos numéricos serão utilizados na predição do seu comportamento eletromagnético. O correto dimensionamento desses anéis e das descontinuidades de guias de onda coaxiais que compõe a estrutura de alimentação, permite estabelecer um compromisso entre minimização das perdas, alargamento da banda passante e rigidez mecânica. Associados ao Método do Casamento de Modos serão utilizados algoritmos de otimização que farão o ajuste das dimensões dessas seções de guias de onda coaxiais não uniformes, visando à minimização da perda de retorno e o aumento da banda de operação da antena. Finalmente, será feito o estudo de algumas estruturas de excitação, onde serão otimizados seus desempenhos para a perda de retorno. / [en] In this present work, the Mode Matching technique is applied in the analysis and project of coaxial structures. The feed junction is one of the critical points of the project of discone antennas when broadband performance is expected. Usually, these junctions are composed of nonuniform sections of coaxial waveguide and, to guarantee the necessary mechanical rigidity of the structure, some sections are filled with dielectric material. The project of these feed junctions requires a compromise between frequency band, compact structure, minimal losses, and mechanical rigidity. Due to the discontinuities, numerical methods are used to predict the electromagnetic behavior. Here, Mode Matching technique associated with an optimization algorithm is employed in the adjustment of the dimensions of the coaxial waveguide sections, seeking the minimization of the return loss and the enlargement of the antenna bandwidth. Several types of junctions are explored and their performance is compared.

This thesis discusses the aero-acoustic characterisation of a perforate sample using a three-port technique. A rectangular T-junction with a flush mounted perforated sample at the intersection form the acoustical three-port. Under acoustic excitation from three different directions a direct method of impedance determination is incorporated to experimentally determine the passive acoustic properties of the perforate. The three-port scattering matrix and the normalised transfer impedance are calculated in the presence of grazing flow and for high-level excitation and the behaviour of these characteristics is studied. Validation of the determined results in the linear range is carried out by comparing it with existing models. Moreover, based on the experimental results for low grazing flow velocities the dependence of the real part of the transfer impedance on the grazing flow parameters as well as dimensionless numbers is described, and a semi-empirical model quantifying the behaviour is proposed. Furthermore, the thesis explains some experimental errors pertaining to standing wave patterns and operating conditions, and corrections are suggested to reduce the errors. / <p>QC 221007</p>

Submitted by Viviane Lima da Cunha (viviane@biblioteca.ufpb.br) on 2016-05-02T10:49:21Z No. of bitstreams: 1 arquivototal.pdf: 1791577 bytes, checksum: ecd7a6eb8a18230d0145c24932d9e248 (MD5) / Made available in DSpace on 2016-05-02T10:49:22Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1791577 bytes, checksum: ecd7a6eb8a18230d0145c24932d9e248 (MD5) Previous issue date: 2015-08-03 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The Hanbury Brown-Twiss experiment is very well established in quantum optics literature, so we devoted this dissertation in order to embed the parity and temporal reversal symmetry in the former experiment. Therefore, we developed the scattering matrix formalism which allow us use some techniques such as the scattering matrices' concatenation of di erent sections in terms of one matrix and the scattering problem of a parity and temporal reverse symmetric system. In this manner, we could derive the scattering matrix of a parity and temporal reverse symmetric Hanbury Brown- Twiss experiment(HBT-PT). With the possession of this matrix, we proposed a theoretical model which provides how to measure the symmetry of this system, which we called correlation functions formalism. In order to stablish the former formalism, we studied B uttiker formalism, which we veri ed how the correlation between 2 incident particles in a system relates to the noise due transport of this particles and what kind of noise we are treating in a given regime which the system is operating. Then, we found the input states in terms of the output states of two particles inciding in a multiterminal system, which we used it's scattering matrix to stablish the relation between the states. Thereat, we derived all the possibles correlations(therefore, the noise) of two incident particles in the former system. Thereby, we analysed the extreme cases of a barrier coupled to the HBT-PT experiment for the purpose of stablish which regime the experiment is symmetric adjusted, so, demonstrating the Hanbury Brown-Twiss E ect with parity and temporal reverse symmetries. / Sendo o experimento Hanbury Brown-Twiss bem estabelecido na literatura da otica quântica, dedicamos esta dissertação a embutir no mesmo experimento a questão da simetria por paridade e reversão temporal. Para tanto, abrimos mão do formalismo da matriz de espalhamento que permitiu nos utilizar tecnicas como a concatenação de matrizes de espalhamento de sec ções diferentes em termos de apenas uma matriz e o problema do espalhamento em um sistema simétrico por paridade e reversão temporal. Dessa forma, pudemos derivar a matriz de espalhamento para o experimento Hanbury Brown-Twiss com simetria de paridade e revers~ao temporal(HBT-PT). De posse dessa matriz, propusemos um modelo teórico que propicia a medição experimental a simetria desse sistema, o qual chamamos de formalismo das fun c~oes de correla c~ao. Para estabelecermos o formalismo supracitado, estudamos o formalismo de Buttiker, onde veri case como a correlaçãao entre 2 partículas incidentes em um sistema relaciona-se com o ru do devido ao transporte dessas part culas e que tipo de ru do estamos tratando, dado o regime em que o sistema está operando. Em seguida, encontramos os estados de entrada em termos dos estados de saída de 2 partículas incidindo em um sistema multiterminal, onde utilizamos a sua matriz de espalhamento para estabelecer a rela c~ao entre os estados. Com isso, derivamos todas as possíveis correlações (e, por conseguinte, o ruído) de 2 partículas incidentes nesse sistema. Assim, analisamos os casos extremos de uma barreira acoplada ao experimento HBT-PT, a m de estabelecer o regime em que o experimento está simetricamente ajustado e demonstramos o Efeito Hanbury Brown-Twiss por paridade e reversão temporal.