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No / A compact-size asymmetrical linearly tapered slot antenna required for portable ultra-wideband (UWB) imaging systems is presented. The total antenna size is reduced compared with the conventional linearly tapered slot antenna by using a triangular slot on the left-hand side of the tapered-shaped radiator, whereas introducing a corrugated pattern of cuts on the right side. The antenna operates over a wide bandwidth extending from 3.1 to 10.6 GHz with a maximum gain of 8.5 dBi. Stable radiation patterns are observed across the operational bandwidth, with cross-polarization levels below 20 dB. The realized antenna structure occupies a volume of 35 x 36 x 0.8 mm3, and possesses the essential time domain fidelity needed for UWB imaging applications. (c) 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

<p dir="ltr">The thermal efficiency of gas turbines improves with higher turbine inlet temperatures (TIT) or compressor outlet pressure. Nowadays, gas turbines achieve TITs up to 1600 °C for power generation and 2000 °C for aircraft. These temperatures far exceed the limits where structural integrity can be maintained. For Ni-based superalloys with thermal barrier coatings, that limit is about 1200 °C. Gas turbines can operate at these high temperatures because all parts of the turbine component that contact the hot gases are cooled so that material temperatures never exceed those limits. </p><p dir="ltr">Gas-turbine vanes and blades are cooled by internal and film cooling with the cooling air extracted from the compressor. Since the extracted air could be used to generate power or thrust, the amount of cooling air used must be minimized. Thus, numerous researchers have investigated fluid flow and heat transfer in internal and film cooling to enable effective cooling with less cooling flow. For internal cooling, significant knowledge gaps persist, notably in ducts with varying cross sections. Reviews of existing literature indicate a lack of studies on flow and heat transfer in cooling ducts that account for the taper in the blade geometry from root to tip for both power-generation and aircraft gas turbines.</p><p dir="ltr">This study investigates the flow and heat transfer in ribbed and smooth tapered U-ducts, under conditions relevant to turbine cooling by using computational fluid dynamics (CFD) and a reduced-order model (ROM) developed in this study. The CFD analysis was based on steady Reynolds-Averaged Navier-Stokes (RANS) equations with the Shear Stress Transport (SST) turbulence model. The CFD analysis examined the effects of rotation number (Ro = 0, 0.0219, 0.0336, 0.0731), Reynolds number (Re = 46,000, 100,000, 154,000), and taper angle (α = 0°, 1.41°) under conditions that are relevant to electric-power-generation gas turbines. CFD results obtained showed increasing the taper angle significantly increases both the friction coefficient and the Nusselt number, regardless of rotation. With rotation at Ro = 0.0336 and Re = 100,000, the maximum increase in the average friction coefficient and Nusselt number due to taper was found to be 41.7% and 36.6% respectively. Without rotation at Re = 46,000, those increases were 11.5% and 14.7% respectively. </p><p dir="ltr">The ROM was derived from the integral continuity, momentum, and energy equations for a thermally and calorically perfect gas to provide rapid assessments of radially outward flow in tapered ducts subjected to constant heat flux. The ROM was used to study the effects of taper angle (α = 0°, 1.5°, 3.0°), ratio of mean radius to hydraulic diameter (Rm/Dh = 45, 150), rotation number (Ro = 0, 0.025, 0.25), Reynolds number (Re = 37,000, 154,000), and thermal loadings (q" = 5×104, 105 W/m2) on the mean density, velocity, temperature, and pressure along the duct. The parameters studied are relevant to both electric-power-generation and aircraft gas turbines. Results obtained show density and pressure variations to be most affected by the rotation number, while velocity along the duct is most affected by the duct’s taper angle. Additionally, it was found that if the taper angle is sufficiently large (α = 3°), then the temperature could reduce along the duct despite being heated because the thermal energy is converted to mechanical energy. When compared to a duct without taper, the mass flow rate of the cooling air could be reduced by up to 44% to achieve the same temperature distribution of the cooling flow along the duct.</p><p dir="ltr">The ROM developed was assessed by comparing against grid-converged CFD results for both ribbed and smooth sections of the duct. The validation study showed the maximum relative errors for density, velocity, temperature, and pressure distributions to be 0.6%, 3.3%, 0.4%, and 0.3% for smooth sections, and 3.2%, 5.6%, 0.9%, and 3.0% for ribbed sections, respectively. Thus, the ROM developed has accuracy comparable to CFD based on steady RANS but is order of magnitude more efficient computationally, making it a valuable tool for preliminary design. </p><p><br></p>

Motivados pelas atuais tendências e suportados pelo grande interesse de indústrias do segmento aeronáutico, estudos e desenvolvimentos vêm sendo conduzidos na área de análise estrutural de materiais compósitos. Todavia, mesmo havendo várias contribuições científicas e tecnológicas nesta área, este assunto continua sendo um campo aberto e bastante promissor para novas pesquisas, devido a sua extensa complexidade e imediata aplicação. A ausência de um modelo capaz de projetar com elevada precisão uma estrutura aeronáutica com presença de escalonamento fabricada em material compósito, que pode sofrer modo de falha translaminar, motivou o presente trabalho. É sabido que o método de elementos finitos estendidos (XFEM - eXtendend Finite Element Method, do Inglês) vem sendo usado de maneira robusta para análise de propagação de trincas em elementos estruturais tridimensionais isotrópicos durante os últimos anos, mas não em compósitos. De forma a contribuir com a pequena quantidade de trabalhos científicos referentes a métodos XFEM 3D para análise de estruturas fabricadas em materiais compósitos não convencionais, como estruturas com escalonamento de camadas e laminados espessos, é apresentada uma nova metodologia implementada como uma ferramenta computacional para analisar quase estaticamente este tipo de estrutura. O modelo é baseado no aprimoramento do \"Método da Seção de Ouro\" que é aplicado em conjunto com uma versão aprimorada do critério de falha de Puck, permitindo assim definir com precisão e baixo custo computacional a iniciação e direção de uma trinca. Esta informação é utilizada para iniciar uma rotina baseada em XFEM, que é usada para o enriquecimento dos elementos finitos que vão falhando progressivamente durante a análise. A nova metodologia (implementada computacionalmente) apresenta convergência uma ordem de grandeza maior quando comparada com o algoritmo tradicional, sendo aproximadamente 20 vezes mais eficiente em termos computacionais. O modelo é ainda avaliado quanto a seus resultados em comparação com dados provenientes de ensaios experimentais, demonstrando uma boa convergência entre as previsões computacionais e os resultados obtidos em laboratório. / Supported by current trends and by the great interest of aeronautic industries, studies and developments have been made in the field of high performance composite materials. Nonetheless, even with the scientific and technological contributions, the matter is still a field wide open and promising for new research due to its high complexity and immediate application. The absence of a model capable of universally reproducing mechanical behavior of composite materials tapered structures, which can suffer translaminar failure mode, motivated the present work. It is well known that the eXtended Finite Elements Method (XFEM) has been used robustly for analysis of crack propagation in isotropic tri-dimensional structural elements lately but not for composites. In order to contribute with the scares amount of available works on 3D XFEM application on non-conventional composite material structures, such as tapered structures and thick laminates, a new methodology is presented as a computational tool for quasi-static analysis of this type of component. The model derives from \"Golden Section Method\" that is applied along with an enhanced version of Puck\'s failure criterion, which allows a low computational cost and high precision estimation of crack initiation and direction of propagation. This information is used to trigger an XFEM based routine that is applied for enriching the elements progressively during analysis. The new methodology (computationally implemented) has a convergence rate one order of magnitude greater than traditional implementation, roughly 20 times more efficient in terms of computational processing. Finally, to assure robustness, the model is validated against standardized and specifically developed experiments, showing good convergence between numerical predictions and results obtained in the laboratory.

Conventional construction of Jointed Plain Concrete Pavements (JPCP) in Canada consists of placing a round steel epoxy-coated dowel at the mid height of the pavement. Steel dowels reduce stepping at the joint to improve comfort and reduce the stress concentration on the support layer beneath the pavement. Most importantly they transfer load and are commonly referred to as load transfer devices. Problems with dowel bar deterioration, including corrosion causes the slab joint to lock and cause stress concentrations as the slab expands and or contracts and curls due to thermal and shrinkage straining occurring in the concrete. In this research, alternative joint load transfer devices are presented and compared to conventional steel dowels. Four device alternatives are developed and evaluated: a Glass Fibre Reinforced Polymer (GFRP) I-beam placed directly on the base material; GFRP tapered plates; a continuous horizontal V device; and a continuous horizontal pipe device both placed directly on the support layer. The two devices that are continuous run the length of the joint similar to a shear key. The GFRP tapered plate and I-beam, as well as conventional steel dowels, were analyzed in a wheel path sized three dimensional finite element model for wheel loading and static loading applied to either side of the joint. An experimental testing program was developed to test joint load transfer capabilities of each device when subjected to a static wheel load applied to either side of the joint. The GFRP tapered plates and I-beams were shown to transfer load based on the results from the wheel path finite element model and experimental testing program. The differential joint deflection, stress concentrations and plastic straining occurring in the concrete is not reduced with either the tapered plate or I-beam compared to a dowel under wheel loading. In addition, a similar plastic straining area identified in the finite element models were noticed as an area of damage in the experimental testing program. All of the devices developed are analyzed in a quarter slab three dimensional finite element model with shrinkage and thermal strains as well as wheel loading applied to the slab to simulate service loading. A detailed investigation into the stress distribution around the devices and the differential deflection at the joint through the service loading applied is presented in this paper. Similarly to the wheel path investigation the stress concentration in the tapered plate and I-beams are greater than conventional dowels and also have greater differential deflection occurring at the joint. Both the continuous Horizontal V and Horizontal Pipe device reduce stress and plastic straining in the concrete during the service load analysis compared to dowels. During daytime wheel loading the differential deflection in the joint is the lowest with no noticeable stepping occurring at the joint with the Horizontal V device; however is greater than conventional steel dowels under nighttime wheel load application. The differential deflection with the Horizontal Pipe during day and night straining and wheel loading is similar to conventional steel dowels.

Conventional construction of Jointed Plain Concrete Pavements (JPCP) in Canada consists of placing a round steel epoxy-coated dowel at the mid height of the pavement. Steel dowels reduce stepping at the joint to improve comfort and reduce the stress concentration on the support layer beneath the pavement. Most importantly they transfer load and are commonly referred to as load transfer devices. Problems with dowel bar deterioration, including corrosion causes the slab joint to lock and cause stress concentrations as the slab expands and or contracts and curls due to thermal and shrinkage straining occurring in the concrete. In this research, alternative joint load transfer devices are presented and compared to conventional steel dowels. Four device alternatives are developed and evaluated: a Glass Fibre Reinforced Polymer (GFRP) I-beam placed directly on the base material; GFRP tapered plates; a continuous horizontal V device; and a continuous horizontal pipe device both placed directly on the support layer. The two devices that are continuous run the length of the joint similar to a shear key. The GFRP tapered plate and I-beam, as well as conventional steel dowels, were analyzed in a wheel path sized three dimensional finite element model for wheel loading and static loading applied to either side of the joint. An experimental testing program was developed to test joint load transfer capabilities of each device when subjected to a static wheel load applied to either side of the joint. The GFRP tapered plates and I-beams were shown to transfer load based on the results from the wheel path finite element model and experimental testing program. The differential joint deflection, stress concentrations and plastic straining occurring in the concrete is not reduced with either the tapered plate or I-beam compared to a dowel under wheel loading. In addition, a similar plastic straining area identified in the finite element models were noticed as an area of damage in the experimental testing program. All of the devices developed are analyzed in a quarter slab three dimensional finite element model with shrinkage and thermal strains as well as wheel loading applied to the slab to simulate service loading. A detailed investigation into the stress distribution around the devices and the differential deflection at the joint through the service loading applied is presented in this paper. Similarly to the wheel path investigation the stress concentration in the tapered plate and I-beams are greater than conventional dowels and also have greater differential deflection occurring at the joint. Both the continuous Horizontal V and Horizontal Pipe device reduce stress and plastic straining in the concrete during the service load analysis compared to dowels. During daytime wheel loading the differential deflection in the joint is the lowest with no noticeable stepping occurring at the joint with the Horizontal V device; however is greater than conventional steel dowels under nighttime wheel load application. The differential deflection with the Horizontal Pipe during day and night straining and wheel loading is similar to conventional steel dowels.

Effective focusing of electromagnetic (EM) energy to nanoscale regions is one of the major challenges in nano-photonics and plasmonics. The strong localization of the optical energy into regions much smaller than allowed by the diffraction limit, also called nanofocusing, offers promising applications in nano-sensor technology, nanofabrication, near-field optics or spectroscopy. One of the most promising solutions to the problem of efficient nanofocusing is related to surface plasmon propagation in metallic structures. Metallic tapered rods, commonly used as probes in near field microscopy and spectroscopy, are of a particular interest. They can provide very strong EM field enhancement at the tip due to surface plasmons (SP’s) propagating towards the tip of the tapered metal rod. A large number of studies have been devoted to the manufacturing process of tapered rods or tapered fibers coated by a metal film. On the other hand, structures such as metallic V-grooves or metal wedges can also provide strong electric field enhancements but manufacturing of these structures is still a challenge. It has been shown, however, that the attainable electric field enhancement at the apex in the V-groove is higher than at the tip of a metal tapered rod when the dissipation level in the metal is strong. Metallic V-grooves also have very promising characteristics as plasmonic waveguides. This thesis will present a thorough theoretical and numerical investigation of nanofocusing during plasmon propagation along a metal tapered rod and into a metallic V-groove. Optimal structural parameters including optimal taper angle, taper length and shape of the taper are determined in order to achieve maximum field enhancement factors at the tip of the nanofocusing structure. An analytical investigation of plasmon nanofocusing by metal tapered rods is carried out by means of the geometric optics approximation (GOA), which is also called adiabatic nanofocusing. However, GOA is applicable only for analysing tapered structures with small taper angles and without considering a terminating tip structure in order to neglect reflections. Rigorous numerical methods are employed for analysing non-adiabatic nanofocusing, by tapered rod and V-grooves with larger taper angles and with a rounded tip. These structures cannot be studied by analytical methods due to the presence of reflected waves from the taper section, the tip and also from (artificial) computational boundaries. A new method is introduced to combine the advantages of GOA and rigorous numerical methods in order to reduce significantly the use of computational resources and yet achieve accurate results for the analysis of large tapered structures, within reasonable calculation time. Detailed comparison between GOA and rigorous numerical methods will be carried out in order to find the critical taper angle of the tapered structures at which GOA is still applicable. It will be demonstrated that optimal taper angles, at which maximum field enhancements occur, coincide with the critical angles, at which GOA is still applicable. It will be shown that the applicability of GOA can be substantially expanded to include structures which could be analysed previously by numerical methods only. The influence of the rounded tip, the taper angle and the role of dissipation onto the plasmon field distribution along the tapered rod and near the tip will be analysed analytically and numerically in detail. It will be demonstrated that electric field enhancement factors of up to ~ 2500 within nanoscale regions are predicted. These are sufficient, for instance, to detect single molecules using surface enhanced Raman spectroscopy (SERS) with the tip of a tapered rod, an approach also known as tip enhanced Raman spectroscopy or TERS. The results obtained in this project will be important for applications for which strong local field enhancement factors are crucial for the performance of devices such as near field microscopes or spectroscopy. The optimal design of nanofocusing structures, at which the delivery of electromagnetic energy to the nanometer region is most efficient, will lead to new applications in near field sensors, near field measuring technology, or generation of nanometer sized energy sources. This includes: applications in tip enhanced Raman spectroscopy (TERS); manipulation of nanoparticles and molecules; efficient coupling of optical energy into and out of plasmonic circuits; second harmonic generation in non-linear optics; or delivery of energy to quantum dots, for instance, for quantum computations.

The aim of this master’s thesis is familiar with the problems of optical fibers and possi- bilities creating functional optical structures in optical fibers. first section focuses on the optical fibers and their properties. Another chapter deals with the functional structures of optical fiber and their production. Next section is devoted to the analysis of combinations of these functional structures and their potential applications in sensors. Subsequently, a combined structure is proposed, which is later produced, measured and evaluated for possible use in the sensors

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