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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
421

Algoritmos para o problema da cobertura por sensores / Algorithms for the sensor cover problem

Rafael da Ponte Barbosa 12 December 2011 (has links)
Neste trabalho estudamos aspectos algorítmicos do Problema da Cobertura por Sensores. Em linhas gerais, este problema a entrada consiste em uma região a ser monitorada por um conjunto de sensores previamente posicionados, cada qual dotado de bateria com duração limitada, e o objetivo é atribuir a cada sensor um tempo de início, de modo que toda a região seja coberta o maior tempo possível. Focamos nosso estudo no caso unidimensional do problema, chamado Problema da Cobertura de Faixa Restrita, no qual a região a ser monitorada é um intervalo (da reta real). Estudamos diversas variantes, de acordo com os subintervalos que os sensores cobrem (se de tamanhos fixos ou variados), e de acordo com a duração das baterias (se uniformes ou não). Estudamos também o caso preemptivo: quando os sensores podem ser ligados mais de uma vez. Para este último caso, projetamos um algoritmo polinomial bem simples. O Problema da Cobertura de Faixa Restrita é NP-difícil no caso não-preemptivo em que os sensores têm bateria de duração variável. Para este caso, em 2009 Gibson e Varadarajan apresentaram um algoritmo polinomial que provaram ser uma 5-aproximação. Provamos que este algoritmo tem fator de aproximação 4, e mostramos que este fator é justo. Apresentamos também formulações lineares inteiras para este caso, e os resultados computacionais obtidos. / We study the algorithmic aspects of the Sensor Cover Problem. Broadly speaking, in this problem the input consists of a region to be covered by a set of sensors previously positioned, each one powered with a battery of limited duration, and the objective is to assign to each sensor an initial time, so as to cover the given region for as long as possible. We focus our study on the one-dimensional case of the problem, called Restricted Strip Cover Problem, in which the region to be covered is an interval (of the real line). We study several variants, according to the type of the subintervals the sensors cover (if they have fixed length or not), to the duration of the batteries (if uniform or not). We also study the preemptive case: when the sensors can be turned on and off more than once. For this case, we designed a simple polynomial-time algorithm. The Restricted Strip Cover Problem is NP-hard in the non-preemptive case in which the sensors have non-uniform duration batteries. For this case, in 2009 Gibson and Varadarajan designed a polynomial-time algorithm which they proved to be a 5-aproximation. We prove that this algorithm has approximation ratio 4, and show that this ratio is tight. We also present two integer linear formulations for this case, and report on the computational results obtained with this approach.
422

Imagens da guerra: Brasil, Palestina e Portugal / War images: Brazil, Palestina and Portugal.

Maranhão, Cristina 02 October 2013 (has links)
Made available in DSpace on 2016-04-26T14:54:30Z (GMT). No. of bitstreams: 1 Cristina Maranhao.pdf: 11708246 bytes, checksum: a0bee347f82f275fe29d92e5d9847d6b (MD5) Previous issue date: 2013-10-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This thesis seeks to comprehend the imagetic construction of contemporary wars transmitted by national and international media, through the case study of two current conflicts: the war between police and drug dealers at Rio de Janeiro´s favelas of Complexo do Alemão, and the armed conflict between israelis and palestinians in the Gaza Strip, involving the Palestine Question. Devided in two parts, war and image, this work shows how significative changes occurred in the form of the warfare, associated to new global economic formula, originated from globalization and mundialization. These changes reflected in the form of representing the armed conflicts and therefore in the current photojournalism. . From the observation of significative diferences in the field of images, we focus in two aspects: the image as an action of imagination, and the image as excessive production of clichés from the society of the spectacle . This thesis proposes the construction of a western imagery catalog, elaborated from the relationship between the analysed images of conflicts and the images collected from paints, engraving or photographs. This proposition occured because we realised that there is an imagetic construction of war, wich is responsable for the imaginary of the warrior and of conflicts. Images of war today have changed along with changes of the armed conflict universe, demonstrating a reverberation of images and specific subjects turned into simple pictural clichés, wich in many cases do not represent the violence experienced by the population envolved. This reverberation expresses the generalization of images of war today / Esta tese procura compreender a construção imagética das guerras contemporâneas veiculadas pela mídia nacional e internacional por meio do estudo de caso de dois conflitos atuais: a guerra travada entre policiais e traficantes nas favelas cariocas do Complexo do Alemão e o conflito armado entre israelenses e palestinos na Faixa de Gaza que envolve a Questão Palestina. Dividido em duas partes, guerra e imagem, o trabalho mostra como ocorreram mudanças significativas na forma de guerrear associadas a nova formulação econômica global proveniente da globalização e da mundialização. Estas mudanças refletiram-se na forma de representar os conflitos armados e consequentemente no fotojornalismo atual. A partir da constatação de diferenças significativas no campo da imagem, nos concentramos dois aspectos: a imagem como uma ação do imaginar e a imagem como produção excessiva e formadora de clichês provenientes da sociedade do espetáculo . A tese propõe a construção de um catálogo imagético ocidental elaborado a partir da relação entre as imagens analisadas dos conflitos e imagens coletadas seja na pintura, em gravuras ou na fotografia. A proposta deste ocorreu, pois percebemos que existe uma construção imagética da guerra esta que é responsável pela elaboração do imaginário do guerreiro e dos conflitos. As imagens de guerra na atualidade se modificaram juntamente com as alterações do universo dos conflitos armados, demonstrando uma reverberação de imagens e de temas específicos transformando em meros clichês imagéticos que em muitos casos não representa a violência vivenciada pela população que está envolvida. Reverberação, esta, que expressa a generalização das imagens de guerra na atualidade
423

Fatigue crack growth assessment and fatigue resistance enhancement of aluminium alloys

Mohin, Ma January 2018 (has links)
Fatigue damage of aluminium alloys is one of the key concerns in transport industries, particularly in the aerospace industry. The purpose of the project is to develop new knowledge and techniques against fatigue failure for these industries through a systematic investigation of fatigue resistance and crack growth behaviours of aluminium alloys. Fatigue and fracture mechanics have been investigated analytically, numerically and experimentally in this project. Overload transient effect on fatigue crack growth has been examined by considering various parameters including crack closure, overload ratio (OLR), load ratio (R ratio), baseline stress intensity factor range, (∆K)_BL and geometry. It was found that crack closure can be correlated qualitatively and quantitatively to all other parameters associated with overload transient behaviour. It is proposed that the effect of crack tip plasticity on the non-linearity of the compliance curve can be separated to obtain reliable crack closure measurement. In this project, different methods are used to better understand the transient retardation process so that the damage tolerance design (DTD) of the components made of aluminium alloys can be enhanced. Another important parameter for fatigue and damage tolerance design (DTD) of engineering components is the threshold stress intensity factor range for fatigue crack growth, ∆K_th. A small variation in identification of ∆K_th can lead to a big change in overall estimation of fatigue life. In this project, an analytical model has been developed for aluminium alloys by fitting an analytical curve with raw crack growth data in order to identify the ∆K_th. This model has the capacity to identify ∆K_th for different aluminium alloys at various R ratios. There is a great demand for enhanced fatigue life of aluminium alloys in the transport industry. This project has carried out a detailed investigation of electromagnetic treatment (ET) in the form of electropulsing treatment to develop an efficient technique for fatigue resistance enhancement. ET parameters including the treatment intensity, treatment time and the number of applications have been optimised. It is suggested that the duration of ET treatment can be used as the main parameter among all these to control the fatigue resistance of the aluminium alloy. The improvement in fatigue resistance has been explained by the change in microhardness and conductivity of aluminium alloy due to ET. Additionally, the fracture morphology was analysed using scanning electron microscopy (SEM). The precipitates and dislocation characteristics were also studied using transmission electron microscopy (TEM). The outcomes of this investigation will help improve structural integrity by enhancing fatigue resistance of aluminium alloys.
424

Lateral Resistance of H-Piles and Square Piles Behind an MSE Wall with Ribbed Strip and Welded Wire Reinforcements

Luna, Andrew I. 01 May 2016 (has links)
Bridges often use pile foundations behind MSE walls to help resist lateral loading from seismic and thermal expansion and contraction loads. Overdesign of pile spacing and sizes occur owing to a lack of design code guidance for piles behind an MSE wall. However, space constraints necessitate the installation of piles near the wall. Full scale lateral load tests were conducted on piles behind an MSE wall. This study involves the testing of four HP12X74 H-piles and four HSS12X12X5/16 square piles. The H-piles were tested with ribbed strip soil reinforcement at a wall height of 15 feet, and the square piles were tested with welded wire reinforcement at a wall height of 20 feet. The H-piles were spaced from the back face of the MSE wall at pile diameters 4.5, 3.2, 2.5, and 2.2. The square piles were spaced at pile diameters 5.7, 4.2, 3.1, and 2.1. Testing was based on a displacement control method where load increments were applied every 0.25 inches up to three inches of pile deflection. It was concluded that piles placed closer than 3.9 pile diameters have a reduction in their lateral resistance. P-multipliers were back-calculated in LPILE from the load-deflection curves obtained from the tests. The p-multipliers were found to be 1.0, 0.85, 0.60, and 0.73 for the H-piles spaced at 4.5, 3.2, 2.5, and 2.2 pile diameters, respectively. The p-multipliers for the square piles were found to be 1.0, 0.77, 0.63, and 0.57 for piles spaced at 5.7, 4.2, 3.1, and 2.1 pile diameters, respectively. An equation was developed to estimate p-multipliers versus pile distance behind the wall. These p-multipliers account for reduced soil resistance, and decrease linearly with distance for piles placed closer than 3.9 pile diameters. Measurements were also taken of the force induced in the soil reinforcement. A statistical analysis was performed to develop an equation that could predict the maximum induced reinforcement load. The main parameters that went into this equation were the lateral pile load, transverse distance from the reinforcement to the pile center normalized by the pile diameter, spacing from the pile center to the wall normalized by the pile diameter, vertical stress, and reinforcement length to height ratio where the height included the equivalent height of the surcharge. The multiple regression equations account for 76% of the variation in observed tensile force for the ribbed strip reinforcement, and 77% of the variation for the welded wire reinforcement. The tensile force was found to increase in the reinforcement as the pile spacing decreased, transverse spacing from the pile decreased, and as the lateral load increased.
425

A Multiple Coupled Microstrip Transmission Line Model for High-Speed VLSI Interconnect Simulation

Uzelac, Lawrence Stevan 11 December 1991 (has links)
A model is presented which incorporates the advantages of a mixed mode simulation to characterize transmission line behavior in multiple coupled Transmission line systems. The model is intended for use by digital circuit designers who wish to be able to obtain accurate transmission line behavior for complex digital systems for which continuous time simulation tools such as SPICE would time prohibitive. The model uses a transverse electromagnetic wave approximation to obtain solutions to the basic transmission line equations. A modal analysis technique is used to solve for the attenuation and propagation constants for the transmission lines. Modal analysis done in the frequency domain after a Fast Fourier Transform of the time-domain input signals. Boundary conditions are obtained from the Thevinized transmission line input equivalent circuit and the transmission line output load impedance. The model uses a unique solution queue system that allows n-line coupled transmission lines to be solved without resorting to large order matrix methods or the need to diagonals larger matrices using linear transformations. This solution queue system is based on the method of solution superposition. As a result, the CPU time required for the model is primarily a function of the number of transitions and not the number of lines modeled. Incorporation of the model into event driven circuit simulators such as Network C is discussed. It will be shown that the solution queue methods used in this model make it ideally suited for incorporation into a event-driven simulation network. The model presented in this thesis can be scaled to incorporate direct electromagnetic coupling between first, second, or third lines adjacent to the line transitioning. It is shown that modeling strictly adjacent line coupling is adequate for typical digital technologies. It is shown that the model accurately reproduces the transmission line behavior of systems modeled by previous authors. Example transitions on a 8-line system are reviewed. Finally, future model improvements are discussed.
426

Solutions For Plane Strain And Axisymmetric Geomechanics Problems With Lower Bound Finite Elements Limit Analysis

Khatri, Vishwas N 03 1900 (has links)
The present thesis illustrates the application of the lower bound limit analysis in combination with finite elements and linear programming for obtaining the numerical solutions for various plane strain and axisymmetric stability problems in geomechanics. For the different plane strain problems dealt in the thesis, the existing formulation from the literature with suitable amendments, wherever required, was used. On the other hand for various axisymmetric problems, the available plane strain methodology was modified and a new formulation is proposed. In comparison to the plane strain analysis, the proposed axisymmetric formulation requires only three additional linear constraints to incorporate the presence of the hoop/circumferential stress (σθ). Several axisymmetric geotechnical stability problems are solved successfully to demonstrate the applicability of the proposed formulation. In the entire thesis, three noded triangular elements are used for carrying out the analysis. The nodal stresses are treated as basic unknowns and the stress discontinuities are employed along the interfaces of all the elements. To ensure that the finite element formulation leads to a linear programming problem, the Mohr-Coulomb yield surface is approximated by a polygon inscribed to the parent yield surface. For solving different problems, computer programs are developed in ‘MATLAB’. The variation of the bearing capacity factor Nγ with footing-soil interface roughness angle δ is obtained for different soil friction angles. The magnitude of Nγ is found to increase extensively with an increase in δ. With respect to variation in δ, the obtained values of Nγ were found to be generally smaller than the results available in literature. The effect of the footing width on the magnitude of Nγ has been examined for both smooth and rough strip footings. An iterative computational procedure is introduced to account for the dependency of φ on the mean normal stress ( σm). Two well defined φ- σm curves from literature, associated with two different relative densities, are being chosen for performing the computational analysis. The magnitude of Nγ is obtained for different footing widths, covering almost the entire range of model and field footing sizes. For a value of the footing width greater than approximately 0.2 m and 0.4 m, for a rough and smooth footing, respectively, the magnitude of Nγ varies almost linearly on a log-log scale. The bearing capacity factors Nc, Nq and Nγ are computed for a circular footing both with smooth and rough footing interface. The bearing capacity factors for a rough footing are found to be consistently greater than those with a smooth interface, especially with grater values of soil friction angle (φ). An encouraging comparison between the obtained results and those available from the literature is noted. Bearing capacity factor Nc for axially loaded piles in clays whose cohesion increases linearly with depth has been estimated numerically under undrained (φ = 0) condition. The variation of Nc with embedment ratio is obtained for several rates of the increase of soil cohesion with depth; a special case is also examined when the pile base was placed in the stiff clay stratum overlaid by a soft clay layer. It has been noticed that the magnitude of Nc reaches almost a constant value for embedment ratio approximately greater than unity. The bearing capacity factor Nγ has been computed for a rough conical footing placed over horizontal ground surface. The variation of Nγ with the cone apex (interior) angle (β), in a range of 30º - 180º, is obtained for different values of friction angle ( φ). For φ< 30º, the magnitude of Nγ is found to decrease continuously with an increase in β from 30º to 180º. On the other hand, for φ > 30º , the minimum magnitude of Nγ is found to occur generally between β = 120 and β = 150º. In all the cases, it has been noticed that the magnitude of Nγ becomes maximum for β = 30o. The vertical uplift resistance of circular plate anchors, embedded horizontally in a clayey stratum whose cohesion increases linearly with depth, has been obtained under undrained ( φ = 0) condition. The variation of the uplift factor (Fc) with changes in the embedment ratio (H/B) has been computed for several rates of the increase of soil cohesion with depth. It has been noted that in all the cases, the magnitude of Fc increases continuously with H/B up to a certain value of Hcr/B beyond which the uplift factor becomes essentially constant. The results obtained from the analysis are noted to compare quite well with those published in literature. From the investigation reported in this thesis, it is expected that the proposed axisymmetric formulation will be quite useful for solving various axisymmetric geotechnical stability problem in a rapid manner. The available plane strain formulation has also been found to yield quite satisfactory solutions even for a problem where the soil friction angle depends on the state of stress at a point.
427

Process Control and Simulation of Ferromagnetic Strip in the Power Transformers and Electrical Machines Applications : Electric power systems

Mousavi Takami, Kourosh January 2009 (has links)
This thesis investigates optimization of the control of electrical and thermal equipment by using FEM and CFD modeling in combination with dynamic simulation models. The thesis focuses on the production of electrical strips and the control system with the aim of reducing losses and improving magnetic properties. Several parameters and factors contribute to core losses. Thickness deviations in strip production, high levels of impurities in the core, orientation, ageing, surface oxidation, overloading, and hot spot temperature are among the reasons for losses in the core. Some of the losses occur during strip cutting and core assembly. This dissertation focuses on the reduction of losses in the cold rolling, annealing and manufacturing stages. The cold rolling process has a direct influence on the accuracy of the strip thickness and magnetic ageing of sheets. Some disturbances such as eccentricity, working rolls gap deviation, shape and edge deflections have to be removed in order to achieve accurate thickness. Thickness measurement makes up an important portion of loss evaluation in electrical equipment. Impurities and dirty strip surfaces in the cold rolling step can increase the carbon content of strips that pass through the annealing furnaces after cold rolling. The slab should be cleaned before reeling and rewinding. As the strip passes through the annealing furnaces, the temperature should be homogenous over the entire strip. According to simulations of furnace and strip temperature computed in the COMSOL environment, homogenous temperatures may be achieved using high electrical power reflectors which are equipped with molybdenum disilicide (MoSi2) electrical heating elements to replace the gas fired burners that are currently used. Modelling of the cold rolling process is conducted in order to find the correlation between control system parameters. A multivariable mathematical model for the rolling process is derived here, which reveals the interactions of the influencing variables. This approach provides numerically efficient algorithms, which are necessary for running in a real-time environment. A control model is applied in the MATLAB environment in order to determine the strip thickness at online-offline state using a robust algorithm. The critical problem in the thickness control loop is analysed, and an adaptive control algorithm is proposed. A number of control methods are investigated to improve the final strip properties. Cold rolled strip thickness deviations, eccentricities and shape defects are compensated for. The simulation results are verified with measurement data and the most significant sources of disturbances are detected. Finally, to solve the hottest spot problem in large scale electric power transformer, a new apparatus, oil spraying, is proposed and analysed. / Denna avhandling behandlar optimering och kontroll av elektrisk och termisk utrustning med hjälp av FEM och CFD-modellering i kombination med dynamiska simuleringsmodeller. Avhandlingen fokuserar på produktion av remsor och styrsystemet i syfte att minska förluster och ge bättre magnetiska egenskaper. Flera parametrar och faktorer bidrar till förluster i kärnan. Tjockleksavvikelser i remsor, höga nivåer av föroreningar i kärnan, orientering, åldrande, yta oxidation, överbelastning och temperaturer i heta punkter finns bland orsakerna till förlusterna i kärnan. Några av de förluster som uppstår under klippning av remsor och ihopsättningen av kärnan. Denna avhandling fokuserar på att minska förlusterna i produktionsstegen för kallvalsning och  glödgning. Kallvalsningen har ett direkt inflytande på riktigheten av remsornas tjocklek och magnetiska åldrande. Vissa störningar i till exempel excentriciteten, gapet mellan valsarna, form och kanter måste minimeras för att uppnå korrekt tjocklek. Tjockleksmätningar utgör en viktig del av utvärderingen av förluster  i elektrisk utrustning. Föroreningar och smutsiga bandytor i kallvalsningssteget kan öka kolhalten i band som passerar genom ugnar efter kallvalsning. Valsämnet bör rengöras innan avhaspling och upprullning. När bandet passerar genom glödgningsugnar bör temperaturen vara homogen över hela remsan. Enligt simuleringar av ugnen och remsans temperatur kan homogen temperatur uppnås med elektriska värmeelement (Molybden disilikat, MoSi2) insatta i reflektorer. De kan ersätta den gaseldade brännare som för närvarande används. Modellering av kallvalsningsprocessen sker i syfte att hitta korrelation mellan styrsystemparametrar. En multivariabel matematisk modell för valsningsprocessen har tagits fram som använder korrelation mellan variabler. Denna metod ger numeriskt effektiva algoritmer som behövs för att köra i en realtids-miljö. En modell har tagits fram för att bestämma remsornas med tjocklek för kontinuerlig och icke-kontinuerligt tillstånd med hjälp av en robust algoritm. Det kritiska problemet i reglerloopen för tjocklek har analyserats, och en adaptiv regleralgoritm föreslås. Ett antal metoder har undersökts för att förbättra de slutliga bandegenskaperna. Avvikelser i kallvalsade band med avseende på tjocklek, excentriciteter och form kompenseras. Simuleringsresultaten har verifierats med mätdata och de viktigaste källorna till störningar upptäckts.   Slutligen, för att lösa problemet med heta punkter i stora transformatorer föreslås en ny metod för oljesprutning, vilken också analyseras i avhandlingen.
428

Application of FLAC in bearing capacity analyses of layered clays

Bhardwaj, Vivek 08 January 2007 (has links)
Understanding the bearing response of the footings on layered soils has always been a challenge for researchers. Due to the limitations of analytical and empirical solutions it had been difficult to understand the true bearing behavior. Some researchers have tried solving this problem by numerical analysis and have found some success. In this study the numerical analysis approach has been applied using a commercial tool FLAC (Fast Lagrangian Analysis of Continua) to study the bearing response of surface footings on layered clays. First, small deformation analyses were taken up to study the undrained bearing response of strip and circular footings resting on a horizontally layered strong over a soft clay foundation, and then over soft over strong clay foundation. In the end application of large strain mode of FLAC was explored to investigate the large deformation behavior of the strip footing resting on the surface of a strong over soft clay foundation. All models were run by applying velocity loading and a elastic-perfectly plastic Tresca yield criterion has been used. The results are compared with published Finite Element Method (FEM) results, and with analytical, empirical and semi-empirical solutions. It was found that bearing capacity results from the present small-strain FLAC analyses agree well with the FEM results. However, these results in most of the cases tend to differ (as much as 49% for certain layered clay foundations) from those predicted with analytical, empirical and semi-empirical solutions, mainly due to the assumptions made in these solutions. Since no such assumptions are made in the present FLAC analyses, the results and the methodology of this thesis can be applied to predict the bearing capacity of the practical problems. Application of the large-strain mode of FLAC to study the large deformation of shallow foundations has pointed out a limitation of FLAC in completing such analyses. However, it is observed from the early trends of these analyses that whereas the small deformation analysis may under estimate the ultimate bearing capacity for certain cases of layered foundations where the upper clay is moderately stiffer than the lower clay layer, it might also over predict the ultimate bearing capacity for other cases when the upper clay is very stiff in comparison to the lower clay layer. / February 2007
429

Theory, Design and Development of Resonance Based Biosensors in Terahertz and Millimeter-wave

Neshat, Mohammad January 2009 (has links)
Recent advances in molecular biology and nanotechnology have enabled scientists to study biological systems at molecular and atomic scales. This level of sophistication demands for new technologies to emerge for providing the necessary sensing tools and equipment. Recent studies have shown that terahertz technology can provide revolutionary sensing techniques for organic and non-organic materials with unprecedented accuracy and sensitivity. This is due to the fact that most of the macromolecules have vibrational and/or rotational resonance signatures in terahertz range. To further increase the sensitivity, terahertz radiation is generated and interacted with the bio-sample on a miniaturized test site or the so-called biochip. From the view point of generation and manipulation of terahertz radiation, the biochip is designed based on the same rules as in high frequency electronic chips or integrated circuits (IC). By increasing the frequency toward terahertz range, the conventional IC design methodologies and analysis tools fail to perform accurately. Therefore, development of new design methodologies and analysis tools is of paramount importance for future terahertz integrated circuits (TIC) in general and terahertz biochips in particular. In this thesis, several advancements are made in design methodology, analysis tool and architecture of terahertz and millimeter-wave integrated circuits when used as a biochip. A global and geometry independent approach for design and analysis of the travelling-wave terahertz photomixer sources, as the core component in a TIC, is discussed in details. Three solvers based on photonic, semiconductor and electromagnetic theories are developed and combined as a unified analysis tool. Using the developed terahertz photomixer source, a resonance-based biochip structure is proposed, and its operation principle, based on resonance perturbation method, is explained. A planar metallic resonator acting as a sample holder and transducer is designed, and its performance in terms of sensitivity and selectivity is studied through simulations. The concept of surface impedance for electromagnetic modeling of DNA self-assembled monolayer on a metal surface is proposed, and its effectiveness is discussed based on the available data in the literature. To overcome the loss challenge, Whispering Gallery Mode (WGM) dielectric resonators with high Q factor are studied as an alternative for metallic resonator. The metallic loss becomes very high at terahertz frequencies, and as a result of that planar metallic resonators do not exhibit high Q factor. Reduced Q factor results in a low sensitivity for any sensor using such resonators. Theoretical models for axially and radially layered dielectric resonators acting on WGM are presented, and the analytical results are compared with the measured data. Excitation of WGM through dielectric waveguide is proposed, and the critical coupling condition is explained through analytical formulation. The possibility of selecting one resonance among many for sensing application is also studied both theoretically and experimentally. A high sensitivity sensor based on WGM resonance in mm-wave and terahertz is proposed, and its sensitivity is studied in details. The performance of the proposed sensor is tested for sensing drug tablets and also liquid droplets through various measurements in mm-wave range. The comprehensive sensitivity analysis shows the ability of the proposed sensor to detect small changes in the order of 10−4 in the sample dielectric constant. The results of various experiments carried out on drug tablets are reported to demonstrate the potential multifunctional capabilities of the sensor in moisture sensing, counterfeit drug detection, and contamination screening. The measurement and simulation results obtained in mm-wave hold promise for WGM to be used for sensing biological solutions in terahertz range with very high sensitivity.
430

Theory, Design and Development of Resonance Based Biosensors in Terahertz and Millimeter-wave

Neshat, Mohammad January 2009 (has links)
Recent advances in molecular biology and nanotechnology have enabled scientists to study biological systems at molecular and atomic scales. This level of sophistication demands for new technologies to emerge for providing the necessary sensing tools and equipment. Recent studies have shown that terahertz technology can provide revolutionary sensing techniques for organic and non-organic materials with unprecedented accuracy and sensitivity. This is due to the fact that most of the macromolecules have vibrational and/or rotational resonance signatures in terahertz range. To further increase the sensitivity, terahertz radiation is generated and interacted with the bio-sample on a miniaturized test site or the so-called biochip. From the view point of generation and manipulation of terahertz radiation, the biochip is designed based on the same rules as in high frequency electronic chips or integrated circuits (IC). By increasing the frequency toward terahertz range, the conventional IC design methodologies and analysis tools fail to perform accurately. Therefore, development of new design methodologies and analysis tools is of paramount importance for future terahertz integrated circuits (TIC) in general and terahertz biochips in particular. In this thesis, several advancements are made in design methodology, analysis tool and architecture of terahertz and millimeter-wave integrated circuits when used as a biochip. A global and geometry independent approach for design and analysis of the travelling-wave terahertz photomixer sources, as the core component in a TIC, is discussed in details. Three solvers based on photonic, semiconductor and electromagnetic theories are developed and combined as a unified analysis tool. Using the developed terahertz photomixer source, a resonance-based biochip structure is proposed, and its operation principle, based on resonance perturbation method, is explained. A planar metallic resonator acting as a sample holder and transducer is designed, and its performance in terms of sensitivity and selectivity is studied through simulations. The concept of surface impedance for electromagnetic modeling of DNA self-assembled monolayer on a metal surface is proposed, and its effectiveness is discussed based on the available data in the literature. To overcome the loss challenge, Whispering Gallery Mode (WGM) dielectric resonators with high Q factor are studied as an alternative for metallic resonator. The metallic loss becomes very high at terahertz frequencies, and as a result of that planar metallic resonators do not exhibit high Q factor. Reduced Q factor results in a low sensitivity for any sensor using such resonators. Theoretical models for axially and radially layered dielectric resonators acting on WGM are presented, and the analytical results are compared with the measured data. Excitation of WGM through dielectric waveguide is proposed, and the critical coupling condition is explained through analytical formulation. The possibility of selecting one resonance among many for sensing application is also studied both theoretically and experimentally. A high sensitivity sensor based on WGM resonance in mm-wave and terahertz is proposed, and its sensitivity is studied in details. The performance of the proposed sensor is tested for sensing drug tablets and also liquid droplets through various measurements in mm-wave range. The comprehensive sensitivity analysis shows the ability of the proposed sensor to detect small changes in the order of 10−4 in the sample dielectric constant. The results of various experiments carried out on drug tablets are reported to demonstrate the potential multifunctional capabilities of the sensor in moisture sensing, counterfeit drug detection, and contamination screening. The measurement and simulation results obtained in mm-wave hold promise for WGM to be used for sensing biological solutions in terahertz range with very high sensitivity.

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