[pt] A utilização de transformadores de impedância banda larga possibilita o acoplamento de forma eficiente das linhas convencionais de 50 (ômegas) dos sistemas de alta freqüência aos componentes optoeletrônicos de alta velocidade de baixa impedância, tais como lasers semicondutores (tipicamente com 3 a 5 (ômegas) de resistência de entrada). Uma das principais restrições para a realização de um transformador de impedância planar para uso em sistemas de comunicações ópticas é a sua dimensão física. A fim de se obter um transformador de impedância compacto, de dimensões compatíveis com às dos dispositivos optoeletrônicos, foram analisadas diferentes configurações. Inicialmente foi analisada a configuração coplanar (CPW) utilizando substrato de altíssima constante dielétrica. Devido às limitações encontradas nesta configuração, são propostas, aqui, duas outras soluções. As duas novas configurações propostas associam ao substrato bulk convencional de alumina, filmes de elevada constante dielétrica. Foi desenvolvida uma técnica para caracterizar a constante dielétrica e as perdas dos filmes especialmente fabricados para este trabalho. As análises teóricas mostraram que as configurações propostas apresentam desempenho muito superior ao desempenho das configurações convencionais CPW. Foi implementado o transformador de impedância utilizando uma das soluções propostas e seu desempenho foi avaliado experimentalmente. / [en] Wide-band transmission line impedance transformer enables efficient coupling of 50 (ômegas) transmission line circuits to low impedance high-speed optoelectronic components such as semiconductor lasers (typically with input resistance of 3 to 5 [ômegas]). The physical dimensions of the planar transmission line transformer have to be properly chosen to allow its use in optical communication systems. In order to design a high performance impedance transformer with physical dimensions compatible with optoelectronic components, several possibilities were investigated. A CPW configuration with very high dielectric constant bulk substrate has been analyzed. Simulations have shown some limitations in the performance of this configuration. Then, two new configurations were introduced. Both configurations are obtained using high dielectric constant films and alumina bulk substrate. A new technique has been developed in order to characterize the dielectric constant and the losses of the films specially made for this thesis. Simulations have shown that the performance of both new configurations is much better than the conventional CPW configuration performance. The planar transmission line impedance transformer has been constructed using a new configuration and its performance has been experimentally evaluated.

The thesis represents the design for dual-band quarter wavelength and half wavelength microstrip transmission line. Chapter 2 proposed the design of a novel dual-band asymmetric pi-shaped short-circuited quarter wavelength microstrip transmission line working at frequencies 1GHz and 1.55 GHz for 50Ω transmission line and at frequencies 1GHz and 1.43GHz for 60Ω transmission line. Chapter 3 proposed the design of a novel dual-band quarter wavelength microstrip transmission line with asymmetrically allocated open stubs and short-circuited stubs working at frequencies 1GHz and 1.32GHz. Chapter 4 proposed the design of dual-band pi-shaped open stub half wavelength microstrip transmission line working at frequencies 1GHz and 2.07GHz. Numerical simulations are performed both in HyperLynx 3D EM and in circuit simulator ADS for all of the proposed designs to measure the return loss (S11) and insertion loss (S12) in dB and phase response for S12 in degree.

The use of electromagnetic waves as a nondestructive evaluation technique to evaluate Portland cement concrete (PCC) structures is based on the principle that a change in the structure, composition, or properties of PCC results in a change in its dielectric properties. The coaxial transmission line is one of the few devices that can measure the dielectric properties of PCC at a frequency range of 100-1000 MHz. A coaxial transmission line developed at Virginia Tech was used to study the effect of moisture, type of aggregate, water/cement ratio, curing period, admixture type (microsilica, superplasticizer, and shrinkage admixture), and chloride content on the dielectric properties of PCC. Measurements were conducted in the time domain and converted to the frequency domain using Fast Fourier Transform. The research found that an increase in the moisture content of PCC resulted in an increase in the dielectric constant. Mixes containing limestone aggregate had a greater dielectric constant than those containing granite. The dielectric constant decreased with curing period due to the reduction in free water availability. Mixes containing higher water/cement ratios exhibited a higher dielectric constant, especially in the initial curing period. The admixtures did not significantly affect the dielectric constant after one day of curing. After 28 days of curing, however, all three admixtures had an effect on the measured dielectric constant as compared to control mixes. Chloride content had a significant effect on the loss part of the dielectric constant especially during early curing. A relationship was also established between the chloride permeability (based on conductance measurements) of PCC and its dielectric constant after 75 days of moist curing. / Master of Science

Detta projekt undersöker olika alternativ av design utav transmissionskedja för ett vågkraftverk. Designen av koncepten kan delas in i två grupper, en grupp med styva länkar och rörliga leder och en annan grupp med stela leder och böjflexibla länkar. Analysen genomförs genom att undersöka olika tvärsnitt och olika material. De material som länkarna undersöks för är kolstål, rostfritt stål, aluminium, glas- och kolfiberkomposit. Analyserna utförs analytiskt för transmissioner med stela leder och böjflexibla länkar och för styva länkar med rörliga leder används Solidworks tillsammans med Ansys Workbench. En transmission med rörliga leder togs fram och idén baserades på en rullkedja. Denna design klarar de ställda kraven men det skapas problem i kontakteringen mellan kedjelederna där det blir koncentrationsspänningar och mycket slitage. I nuläget finns det inte några bussningar eller lager som klarar kraven som ställs på kedjan. I den andra gruppen med stela leder och böjflexibla länkar togs det fram två koncept. Den första har ett rektangulärt tvärsnitt och den andra ett runt. Den med det runda tvärsnittet klarar inte kraven då både böj- och dragspänningarna inte kan hållas tillräckligt låga samtidigt.Konceptet med det rektangulära tvärsnittet, som liknar ett band, klarar alla krav förutom utmattningskravet. Då bandet är tillverkat i stål blir bandets bredd för stor för bojen. Då bandet är tillverkat i aluminium uppfylls inte utmattningskravet. Fiberkompositer tappar mer än 50 % av sin styrka efter 10 miljoner repetitioner vilket gör att de måste bytas ut med jämna mellanrum för att undvika brott. / This project examines different options of designs of transmission chains for a wave power plant. The different designs can be divided into two groups, one group that contains chains with stiff links and moving joints and another group with stiff joints and bend flexible links. The analysis is carried out by examining different cross sections and different materials. The links are evaluated with carbon steel, stainless steel, aluminum, glass and carbon fiber composite. The analyses are preformed analytically for the group with stiff joints and bend flexible links and the group with stiff links and moving joints are examined with Solidworks together with Ansys workbench. One transmission with stiff links and moving joints was made inspired by a roller chain. This design meets the requirements, but problems occur in the contact between the links, where it appears concentration stresses and a lot of wear. At present there are no bearings that meet the demands on the chain.In the second group with stiff joints and bend flexible links, two designs were developed. The first one has a rectangular cross section and the other one has a round. The circular cross section does not meet the requirements, since both bending and tensile stresses cannot be kept low enough at the same time. The design with the rectangular cross section meets all the requirements except the fatigue requirement. After 10 million repetitions the fiber composites loses more than 50 % of its strength, which means that they needs to be replaced periodically to avoid fracture.

We propose an efficient wideband theory for adjoint variable sensitivity analysis of problems with general anisotropic materials. The method is formulated based on the transmission line numerical modeling technique. The anisotropic material properties of potential interest are the full tensors of permittivity, permeability, electrical conductivity, magnetic resistivity, magnetoelectric coupling, and electromagnetic coupling. The tensors may contain non-diagonal elements. Our method estimates the gradients of the desired response with respect to all designable parameters using at most one extra simulation, regardless of their number. In contrast, in the conventional sensitivity analysis method using central finite differences, the number of the required simulations scales linearly with the number of designable parameters. The theory has been implemented for sensitivity analysis of the two and three-dimensional structures. The available adjoint variable method (AVM) sensitivities enable the optimization-based design of anisotropic and dispersive anisotropic structures. We apply our AVM technique to optimization-based wideband invisibility cloak design of arbitrary-shape objects. Our method optimizes the voxel-by-voxel constitutive parameters of an anisotropic cloak. This results in a large number of optimizable parameters. The associated sensitivities of a wideband cloaking objective function are efficiently estimated using our anisotropic adjoint variable method technique. A gradient-based optimization algorithm utilizes the available sensitivity information to iteratively minimize the visibility objective function and to determine the constitutive parameters of the optimal cloak. / Thesis / Doctor of Philosophy (PhD)

Partial discharge (PD) is a micro discharge that occurs in defected regions within the insulating media. As these discharges are the main culprits that cause dielectric material aging, PD measurements have been used for assessing insulating materials, including solids, liquids, and gases for power applications. There are various methods and sensors available for measuring PD sensitive to specific characteristics and operable over a wide range of frequencies. Most PD measurement techniques provide patterns that enable PD interpretation more comfortable for users. For example, in AC applications, the phase-resolved partial discharge (PRPD) technique provides identifiable patterns for distinguishing various types of PDs. However, the establishment of meaningful patterns to multiple types of PD in DC systems requires more sensitive and accurate measurements of individual PD pulses with noise rejection functionality due to the lack of phase-resolved information. Investigating of the transient phenomena such as individual PD pulses requires well-designed circuits with sufficiently large bandwidths. Waveshapes can be easily disturbed by background noise and deformed by the frequency response of measuring circuits and data acquisition systems (DAQ). Noises are unwanted disturbances that could be suppressed by suitable filters or mathematical methods. Measurement circuits and DAQ systems consist of transmission lines, sensors, cables, connectors, DAQ hardware, and oscilloscopes. Therefore, matching the impedance of all components guarantees a reflectionree path for traveling signals and addresses most of the challenges relevant to transient measurements. In this dissertation, we proposed and designed an appropriate testbed equipped with high bandwidth transmission line and electromagnetic field sensors suitable for investigating PD under DC electrical stresses. We comprehensively used finite element analysis simulations through the COMSOL Multiphysics software to design the dimensions and evaluate the frequency response of the testbed, transmission line, and electromagnetic sensors. Furthermore, based on the new testbed, DC PD measurements were performed using conventional and non-conventional sensors. Finally, various types of DC PD were statistically classified based on the proposed testbed.

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Detta examensarbete syftar sig till att undersöka olika konceptuella lösningar utav en transmissionslina för ett vågkraftverk. De tre olika konceptuella lösningarna är; ett rep av materialet HMPE (High Modulus Polyethylene), en transmissionslina baserad på KONE Ultrarope samt en transmissionskedja baserad på elastomera lager. Dessa har indelats i nämnd följd enligt koncept A, koncept B och koncept C. Analysen av dessa grundar sig i befintlig information och kunskap. Från dessa koncept har sedan koncept A valts att studeras vidare för optimering, vilket gjordes genom bedömning enligt Pughmetoden. Verktyget Solid Edge har använts vid framtagandet av koncept A och B. Vid optimeringen för koncept A så konstruerades en trumma för att minimera nötning, maximera repets livslängd samt för att uppnå de satta kraven. / This bachelor’s thesis aims to examine different conceptual solutions of transmission lines for a winch-based wave power plant. The different concepts are; a rope of the material HMPE (High Modulus Polyethylene), a transmission line based on KONE Ultrarope and a transmission chain based on elastomeric bearings. These have then been divided in that order into concept A, concept B and concept C. The analyses of these are based on existing information and knowledge. From these concepts, concept A has been chosen to be further analyzed and optimized. Concept A was chosen by following the method of a Pugh matrix. The modeling software Solid Edge has been used when developing concepts, A and B. Concept A was optimized by designing a drum that minimize abrasion, maximize the life of the rope and was also adjusted for reaching the specific requirements.