Xu Bai Yu. / "August 22, 2000." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (p. [164]-169). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Lee Wai Ming. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 177-181). / List of Figures and Tables --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Photonic Band Gap materials --- p.1 / Chapter 1.2 --- Theoretical Calculation on PBG materials --- p.5 / Chapter 2 --- Plane Wave Expansion --- p.13 / Chapter 2.1 --- Plane Wave Expansion within Scalar Wave Approximation --- p.14 / Chapter 2.2 --- Plane Wave Expansion to Scalar I and II Equations --- p.21 / Chapter 3 --- Formalism of Photonic k.p Theory --- p.33 / Chapter 3.1 --- Vectorial k.p formulation --- p.33 / Chapter 3.2 --- Scalar k. p formulations --- p.36 / Chapter 4 --- Implementation and k.p Band Structures --- p.38 / Chapter 4.1 --- Evaluation of Integrals plj and qlj --- p.38 / Chapter 4.2 --- k.p Band Models --- p.47 / Chapter 5 --- Dependence of k .p Parameters on Dielectric Contrast and Fill- ing Ratio --- p.57 / Chapter 5.1 --- Accuracy of Integrals plj and qlj --- p.57 / Chapter 5.2 --- Sensitivity of k.p Parameters to System Parameters --- p.71 / Chapter 6 --- Empirical Tight-binding Scheme --- p.99 / Chapter 6.1 --- Electronic Tight Binding Approximation --- p.99 / Chapter 6.2 --- Empirical Tight-binding Scheme --- p.101 / Chapter 7 --- Summary --- p.137 / Chapter A --- Preprint of Ref. [36] --- p.144 / Chapter B --- The Coefficients in Eq. (2.22) --- p.161 / Chapter C --- Formalism of Photonic k.p Theory --- p.163 / Chapter D --- The Coefficients in Eq. (5.2) --- p.166 / Chapter E --- The Coefficients in Eq. (5.3) --- p.168 / Chapter F --- The Coefficients in Eq. (6.15) --- p.170

No description available.

Louis Stark. / "This report is based on a thesis submitted to the Department of Electrical Engineering, M.I.T., in partial fulfillment of the requirements for the degree of Master of Science, May 1952." / Bibliography: p. 41. / Signal Corps Contract No. DA36-039 sc-100, Project 8-102B-0. Dept.of the Army Project 3-99-10-022.

by Leung, Kwok Kong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 67). / Text in English; abstracts in English and Chinese. / by Leung, Kwok Kong. / Abstract --- p.ii / Acknowledgement --- p.iii / Contents --- p.iv / List of Figures --- p.vi / Chapter Chapter 1. --- Introduction --- p.1 / Chapter Chapter 2. --- Transmittance in Metal-Dielectric Multilayers --- p.4 / Chapter 2.1 --- Introduction --- p.4 / Chapter 2.2 --- Transfer matrix approach --- p.5 / Chapter 2.3 --- Transfer matrix simulation --- p.7 / Chapter 2.4 --- Physical explanation --- p.14 / Chapter Chapter 3. --- Optical Nonlinear Response of Composite Layer --- p.17 / Chapter 3.1 --- Transfer matrix formalism for oblique incidence --- p.18 / Chapter 3.1.1 --- Transfer matrix method in nonlinear region --- p.18 / Chapter 3.1.2 --- S-polarization --- p.19 / Chapter 3.1.3 --- P-polarization --- p.19 / Chapter 3.1.4 --- Backward propagation technique --- p.22 / Chapter 3.2 --- Nonlinear phase shift --- p.22 / Chapter 3.3 --- Transfer matrix method approach --- p.24 / Chapter 3.4 --- Analytic solution formalism --- p.26 / Chapter Chapter 4. --- Study of Photonic Band Gap of Nonlinear Dielectrics --- p.33 / Chapter 4.1 --- Introduction --- p.33 / Chapter 4.2 --- Nonlinear response of single thin nonlinear layer --- p.34 / Chapter 4.3 --- Nonlinear response of δ-function between two linear dielectric --- p.37 / Chapter 4.4 --- Photonic band structure --- p.41 / Chapter 4.4.1 --- Photonic band structure of linear thin films --- p.41 / Chapter 4.4.2 --- Photonic band structure of linear layers --- p.42 / Chapter 4.5 --- Photonic band gap of nonlinear dielectric multilayers --- p.46 / Chapter Chapter 5. --- Optical Limiting of Composite Material --- p.49 / Chapter 5.1 --- Transmittance of periodic multilayer structures --- p.50 / Chapter 5.1.1 --- Transmittance properties at low intensity --- p.50 / Chapter 5.1.2 --- Transmittance at high intensity: optical limiting effect --- p.52 / Chapter 5.2 --- The effect of layer thickness on optical limiting --- p.53 / Chapter 5.3 --- Optical limiting property of PBG materials --- p.55 / Chapter Chapter 6. --- Conclusion --- p.63 / Chapter Appendix A. --- Effective dielectric function --- p.64 / Bibliography --- p.67

L'évolution continue des systèmes de communications sans fil en indoor rend nécessaire le développement des outils de caractérisation et de modélisation de la propagation des ondes électromagnétiques; afin de répondre aux problématiques et besoins d'ingénieur et de garantir une meilleure planification et un fonctionnement optimal des systèmes communicants. Les travaux effectués dans le cadre de cette thèse portent sur la modélisation du rayonnement des antennes en tenant compte de la complexité environnementale. La méthode de modélisation basée sur la FDTD, détaillée au cours de ce manuscrit, permet d'obtenir d'une manière efficace et précise les niveaux de champs, en tenant compte des phénomènes de propagation et d'interaction des ondes radioélectriques dans un environnement quelconque. Des améliorations ayant deux objectifs essentiels, ont été apportées à ce code. Le premier s'est consacré à améliorer ses performances, et le deuxième s'est intéressé à l'intégration d'un modèle de corps humain et d'autres sources d'émission, dans le but d'assurer plus de réalisme à la modélisation effectuée avec ce code. La validation du code FDTD a été menée par des études comparatives réalisées dans trois environnements différents. La première étude a porté sur une communication sans fil à travers des portes étanches métalliques à bord d'un navire. Une bonne précision du code FDTD a été relevée en comparant les résultats obtenus par ce code avec ceux obtenus par des mesures. La deuxième a porté sur la caractérisation du rayonnement d'antennes dans un bureau universitaire. Les résultats obtenus par des mesures effectuées dans cet environnement ont été confrontés aux ceux obtenus par le code FDTD et par d'autres outils de simulation (HFSS et un outil de tracé de rayons "Wireless lnsite"). Ils ont permis de montrer la capacité du code FDTD à fournir les résultats les plus proches des mesures avec un temps de calcul acceptable et sans avoir besoin de grandes ressources informatiques. La dernière étude a porté sur l'effet de la présence humaine dans une chambre en acier. Une comparaison entre les résultats fournis par le code FDTD et ceux obtenus expérimentalement a été réalisée et un bon accord a été observé. / He continuous evolution of wireless communication systems in indoor environments requires the development of characterization and modeling tools for electromagnetic waves propagation, in order to answer the engineer's issues and needs and to ensure the best planning and an optimal operation of the communicating systems. The work carried out during this thesis concerns antenna radiation modeling, taking into account the environment complexity. The modeling method based on FDTD, detailed in this manuscript, provides efficiently and accurately the fields' strengths, taking account of propagation and radio waves interactions phenomena in any environment. Two main objectives of improvement were brought to this code. The first focused on improving its performance, and the second concerned the emission of multi-sources and the integration of a human body model in order to ensure more realism to modeling realized with this code. The validation of the FDTD code was done by comparative studies in three different environments. The first study concerned a wireless communication through metallic watertight doors on ship board. Good accuracy of the FDTD code was noticed by comparing the code's and measurements' results. The second study concerned the antenna radiation within a typical office environment. The results obtained by measurements were compared to those obtained by the FDTD code and other simulation tools (HFSS and the raytracing tool "Wireless lnsite"). They have shown that the FDTD code provides the most accurate results with an acceptable computational time and without big computer resources. The last study examined the human presence effect in a steel room. Measurements' and FDTD code's results were compared and a qood aqreement was obtained.

CAPES / Devido a crescente demanda por conectividade, um maior número de APs tendem a ser utilizados para que, em todo um ambiente, os clientes de uma rede sem fio possam receber o sinal de rádio. Contudo, a distribuição desorganizada destes APs no ambiente pode reduzir a qualidade do sinal. Esta qualidade é influenciada pelo aumento da interferência que os APs exercem entre si. Por este motivo, encontrar uma forma de reduzi-la vem sendo motivo de pesquisas. Dentre as soluções encontradas, a otimização de canal e potência estão entre as mais eficientes. Neste trabalho, é proposto um algoritmo heurístico para otimizar a configuração de canal e potência para APs pertencentes a rede. Este algoritmo realiza uma avaliação da rede, utilizando modelos analíticos de propagação e técnicas para otimização de canal e potência a fim de encontrar uma solução que aumente a qualidade da rede. Nos resultados obtidos, o algoritmo proposto teve um desempenho muito próximo da melhor solução encontrada com o método exaustivo. / With the crescent demand for connectivity, a large number of access points may be used to cover the entire environment, of a wireless network, with radio signal. But, the disorganized distribution of these access points may reduce the quality of the signal. This quality is influenced by the interference of nearby access points, and therefore many researchers are seeking a method to reduce it. The channel and power optimization are efficient methods to reduce interference. In this work, an heuristic algorithm to find a better configuration of channel and transmission power for those access points in the network is proposed. This algorithm evaluates the network, using analytical models, and techniques to optimize the channel and the transmission power to increase the quality of the signal in the environment. In the results, the algorithm arrives at solution close to the optimal.

In this thesis, we study some aspects of the transmission of a monochromatic electromagnectic plane wave inciding into some configurations of multilayered films. Using a transfer matrix formalism, we firstly investigate the case of a binary sequence of N dielectric layers distributed in a random way, where the layer parameters follow the Bragg condition (nAdA = nBdB). We could observe that the mode for which the optical thickness of the layers corresponds to half-wavelength is insensitive to disorder and fully transparent. The average transmission in a frequency range around this resonance decays as 1/N1/2, and the localization length diverges quadratically as this resonance mode is approached. In the vicinity of the quarter-wavelength, the localization length diverges logarithmically and the frequency averaged transmission exhibits an stretched exponential dependence on the total thickness. At the quarter-wavelength resonance, the Lyapunov exponent for different realizations of disorder has a Gaussian distribution leading to distinct scaling laws for the geometric and arithmetic averages of the transmission. The scaling laws for the half-and quarter-wavelength modes are analogous to those found in electronic onedimensional Anderson models with random dimers and pure off-diagonal disorder, respectively, which are known to display similar violations of the usual exponential Anderson localization. These scale behavior were compared with the case of a disordered structure where one kind of constituint material is a metamaterial. We observe that the spectrally averaged transmission in a frequency range around the fully transparent resonant mode is shown to decay faster as the number of layer increases (1/N). The interplay of strong localization and the emergence of resonant modes within the gap leads to a non-monotonous disorder dependence of the transmission that reaches a minimum at an intermediate disorder strength. Using the same layer parameters of the first case, we investigate the influence of a binary aperiodic incommensurated sequence of layers. The aperiodicity is introduced by considering the sequence of refractive indices to follow a sinusoidal function whose phase ϕ varies as a power-law of the layer index (ϕ ∝ jν). For ν > 1 the resulting sequence is effectivelly uncorrelated leading to the usual Anderson localization of light. The crossover from a uniform structure at ν = 0 to a quasi-periodic structure at ν = 1 is signaled by a minimum at the spectrally averaged transmission. We perform a spectral analysis of the refractive index sequence to show its close connection to the main features exhibited by the averaged optical transmittance. The last case studied is about the inclusion of a cholesteric liquid crystal (ChLC) in the film composition. We considered a single-pitched ChLC multilayered system with quasiperiodic Fibonaccian phase defects as well as an alternate sequence of single-pitched ChLC and isotropic dielectric layers. Using the Berreman 4 × 4 matrix formalism, we numerically obtain the reflection spectrum and the chromaticity diagram of these structures. The associated chromaticity is shown to depend on the incidence angle. However, for the ChLC Fibonaccian phase defect system, the color shift can be controlled by the defect angle α. For the F4 generation and α = π/3, the chromaticity of the reflected light remains close to the white color region for a wide range of incidence angles, followed by a blue-shift at intermediate incidence angles. This is the setup that produces the nearest omnidirectional red-green-blue condition for the reflection spectrum. On the other hand, the structure with alternate ChLC and isotropic layers exhibits a complex sequence of color shifts when the incidence angle is increased. / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Nesta tese, estudamos vários aspectos da transmissividade de uma onda eletromagn ética plana monocromática incidindo sobre algumas configurações de filmes de multicamadas. Aplicando o formalismo de matriz de transferência, inicialmente tratamos o caso de uma sequencia binária de N camadas dielétricas distribuidas aleatoriamente, cujas características das camadas obedecem à condição de Bragg (nAdA = nBdB). Vemos que o modo para o qual o caminho óptico das camadas corresponde a meio comprimento de onda da luz incidente é insensível à desordem e completamente transparente. A média da transmissão na região de frequência ao redor desta ressonância cai com 1/N1/2 e o comprimento de localização diverge quadraticamente à medida que a frequência da luz se aproxima desta ressonância. Na vizinhança dos modos de quarto de onda, o comprimento de localização diverge logaritmicamente e a média espectral da transmissão apresenta uma dependência com N do tipo exponencial alongada. Ainda neste modo, o expoente de Lyapunov para diferentes realizações de desordem apresenta uma distribuição Gaussiana, levando a leis de escala distintas para as médias geométrica e aritmética da transmissão. As leis de escala para os modos de meio e quarto de onda apresentam-se análogas às obtidas no modelo eletrônico 1D de Anderson com dímeros aleatórios e com desordem nos termos de hopping do hamiltoniano respectivamente. Estes sistemas são conhecidos por apresentarem uma violação similar para a localização exponencial de Anderson usual. Estes comportamentos de escala foram comparados ao caso de uma estrutura desordenada onde uma das camadas é constituida por metamaterial. Vimos que a média espectral da transmissão ao redor do modo completamente transmissível decai de maneira mais rápida com o aumento do número de camadas (1/N). A ação conjunta da forte localização e do surgimento de modos ressonantes dentro da banda proibida leva a uma dependência não-monotônica da transmissão com o grau de desordem, que atinge um mínimo para um grau de desordem intermediário. Utilizando os mesmos parâmetros de construção do primeiro caso, investigamos a influência de uma distribuição binária de camadas aperiódica incomensurável. A aperiodicidade é introduzida baseando-se em uma lei senoidal cuja fase ϕ varia como uma lei de potência do índice das camadas (ϕ ∝ jν). Para ν > 1, a sequência resultante é efetivamente descorrelacionada, levando à localização de Anderson usual da luz. A transição de uma estrutura uniforme em ν = 0 para uma estrutura quasi-periódica em ν = 1 é assinalada por um mínino na média espectral da transmissão. Realizamos uma análise espectral do sequência de índices de refração para mostrar sua íntima relação com o comportamento encontrado para a média da transmissão. O último caso de multicamada estudado trata-se da utilização de cristal líquido colestérico (ChLC) na composição do filme. Consideramos uma estrutura de ChLC com ângulos de defeito que obedecem uma sequência quasi-periódica de Fibonacci assim como uma estrutura formada por camadas alternadas de ChLC e dielétrico isotrópico. Utilizando o formalismo matricial de Berreman, obtivemos o espectro de reflexão e o diagrama cromático destas estruturas. A cromaticidade associada apresentou dependência com o ângulo de incidência. No entanto, para o caso com ângulo de defeito Fibonnaciano, o deslocamento cromático pode ser controlado pelo ângulo de defeito α. Para a geração F4 com α = π/3, a cromaticidade da luz refletida se mantém próxima à região do branco para um largo intervalo de ângulos de incidência, seguido por um deslocamento para o azul em incidências intermediários. Esta configuração se aproxima de um refletor RGB omnidirecional. Por outro lado, a estrutura com camadas alternadas exibe uma sequência complexa de deslocamentos cromáticos com o aumento do ângulo e incidência.

Le cadre général de cette thèse porte sur les communications véhicule à véhicule (V2V). L'objectif principal de ce type de communication est d'améliorer la sécurité routière et d'optimiser la fluidité du trafic. Les performances de systèmes de communication embarqués dépendent principalement de la configuration des antennes, du type de récepteurs utilisés (modem) et du canal de propagation. Le sujet de la thèse se concentre précisément sur l'élaboration d'un outil de simulation robuste et fiable pour optimiser les choix technologiques d'antennes et leurs implantations à bord. Il permettra de limiter ainsi le recours aux prototypes et aux essais de roulage. Dans un premier temps, nous avons proposé une méthode de type géométrique-stochastique pour modéliser des canaux de propagation d'un système de communication V2V. Cette méthode permet de définir des scénarios dynamiques et sa flexibilité nous offre l'opportunité de paramétrer les caractéristiques d'un canal de propagation. Nous montrons pour l'essentiel de quelle manière l'agencement et le nombre de diffuseurs de forme simple peuvent contribuer à influencer les statistiques de l'étalement des retards, la distribution des angles d'arrivée et les spectres Doppler. Dans la deuxième partie de ces travaux, nous nous focalisons sur la problématique d'intégration d'antenne. Il a été constaté qu'il est particulièrement utile de simplifier la maquette numérique du véhicule complet lors d'une simulation électromagnétique de l'antenne intégrée à bord de ce véhicule. De plus, dans cette section, nous avons étudié la limite de la validité de substitution d'une antenne intégrée à bord par son seul diagramme de rayonnement dans les modèles de canaux de propagation. A partir de cette étude, nous en avons déduit, que les interactions électromagnétiques avec les éléments se situant dans le champ-proche n'étaient plus valides. Ainsi, une stratégie de correction a été trouvée en considérant l'élément en champ proche dans la simulation initiale de l'antenne intégrée sur le véhicule. L'évaluation des performances d'antennes, en termes de taux d'erreurs paquet, après l'implémentation de la couche physique du standard 802. 11 p, est au cœur de la troisième partie de cette thèse. Des résultats de simulation, pour chaque configuration d'antenne, ont été donnés pour plusieurs combinaisons de paramètres de couche PHY tels que le débit et la longueur de paquet. La dernière partie de ce manuscrit traite de la présentation d'une campagne de mesure qui a été réalisée principalement dans un environnement de type rural. Les essais de roulage avaient pour but de démontrer la capacité des méthodes de simulation à faire un choix approprié d'installation d'antenne. Nous avons constaté que les tendances attendues des performances de communication en termes de PER sont globalement prévisibles à partir de notre modèle bien que nous ayons obtenu des résultats surprenants dans certains cas. Ce qui nécessitera une enquête plus approfondie. / The general framework of this Ph.D. thesis deals with Vehicle to Vehicle (V2V) communications. This communication is principally dedicated to reinforce security through exchange of information between vehicles in case of unexpected events. The development of V2V solutions requires the understanding and merging of a number of techniques from several communication technology areas. Indeed, the performance of these systems are related to three main blocks: the implementation of the modems, the antenna configuration and the fast varying electromagnetic environment surrounding the transmitter and the receiver. The purpose of this PhD thesis is precisely to elaborate a design strategy to investigate all the different blocks constituting the communication chain. The ultimate goal is to optimize antenna selection and location on board the vehicle. In the first place, we proposed a geometry-based stochastic channel modelling approach to develop virtual dynamic scenarios. It was shown that the most common propagation environments such as rural, highway or urban-like propagation channels are reached through adjustment or numbers and location of simple metallic plates. Using this method, we are able to emulate the characteristics, such as the delay spread, angles of arrival distribution and the Doppler spectrum, of these typical driving scenarios. Moreover, we dealt with antenna integration problems in the second part of this work. A study on the simplification of numerical models of vehicles was carried out. Furthermore in this section, we investigated the limit of validity of representing the integrated antenna on board vehicle solely by its radiation pattern. We deduced from this study that the interactions with the elements present in the near-field is no longer valid. Thus, a strategy to alleviate the degree of error was found upon consideration of the near-field scatter in the a-priori simulation of the antenna integrated on the vehicle. In the third part of this thesis, we evaluated the performance of different antenna configurations in terms of packet error rate after the embodiment of the PHY layer of the LEEE 802.11p standard. Simulation results, for each antenna configurations, was given for several combinations of PHY layer parameters such as data rate and packet length. The last part of this manuscript is dedicated to the presentation of a measurement campaign that was carried out in a rural driving environment. Results obtained from these functional tests were confronted with simulation results to demonstrate the strength of the latter. We found that the expected trends in communication performance in terms of PER are globally predictable from our model though we obtained surprising results in some cases, needing further investigation.