Thesis (Ph.D.)--University of Wollongong, 2006. / Typescript. Includes bibliographical references: leaf 199-216.

Thesis (Ph.D.)--University of Wollongong, 2008. / Typescript. Includes bibliographical references: leaf [162]-180.

Thesis (M.S.)--Florida State University, 2006. / Advisor: Justin Schwartz, Florida State University, College of Engineering, Dept. of Mechanical Engineering. Title and description from dissertation home page (viewed Sept. 19, 2006). Document formatted into pages; contains xii, 43 pages. Includes bibliographical references.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: High Temperature Superconductors (HTS) exhibit exceptional electrical properties that make them attractive candidates for numerous electronic devices and applications. However, constructing working devices can be challenging due to fabrication difficulties of these brittle ceramics. This thesis investigates new methods to make the fabrication of high quality YBa2Cu3O7 (YBCO) thin films easier and compatible with more materials. We present the development of a universal add-on method that can be used in situ to improve the quality of superconducting thin films deposited by Pulsed Laser deposition (PLD). We investigate the in situ application of electric fields and voltage biasing to improve the thin film growth. Considering various electrode configurations, we have developed a final electrode design that is stable and produces reproducible results. By introducing an insulated high voltage (HV) electrode into the chamber during deposition, the quality of the deposited thin films can be modulated depending on the polarity of the voltage applied. Applying a positive voltage improves the film quality obtained. Applying a negative voltage degrades the superconducting properties of the films. A simple proof-of-concept HTS dual-mode microwave filter was designed, fabricated and tested. Only the filter produced using our novel PLD technique displayed the correct filtering action upon cooling to 77K. This is attributed to the thin films better superconducting properties due to our developed technique. / AFRIKAANSE OPSOMMING: Hoë Temperatuur Supergeleiers (HTS) vertoon aantreklike elektriese eienskappe wat hulle goeie kandidate maak vir verskeie elektroniese toepassings. Om werkende toestelle te ontwikkel kan 'n uitdaging wees, as gevolg van die vervaardigings probleme wat bestaan vir hierdie bros keramiek materiaal. Hierdie tesis ondersoek nuwe metodes om die vervaardiging van 'n hoë gehalte YBa2Cu3O7 (YBCO) dun films makliker en versoenbaar te maak met verskeie materiale. Ons toon die ontwikkeling van 'n algemene metode wat maklik bygevoeg kan word om in situ die gehalte van supergeleidende dun films, wat deur gepulseerde laser deponering (PLD) gedeponeer is, te verbeter. Ons ondersoek die in situ toepassing van elektriese velde en spannings om die dun film groei te verbeter. Verder oorweeg ons verskeie elektrode konfigurasies en ontwikkel 'n finale elektrode ontwerp wat stabiel is en herhaalbare resultate produseer. Die kwaliteit van die gedeponeerde dun films kan gemoduleer word deur die byvoeging van 'n geïsoleerde hoogspannings (HV) elektrode tydens deponering, afhangende van die polariteit van die aangelegde spanning. 'n Positiewe spanning verhoog die film kwaliteit, terwyl 'n negatiewe spanning die supergeleidende eienskappe van die films verlaag. 'n Eenvoudige HTS dubbele-modus mikrogolffilter is ontwerp, vervaardig en getoets, om as toepassings voorbeeld te dien. Slegs die filter wat geproduseer was met behulp van ons nuwe PLD tegniek, vertoon die beste filter oordrag by 77K. Dit word toegeskryf aan die beter supergeleidende eienskappe van die dun film, as gevolg van die toepassing van ons ontwikkelde tegniek.

Nesta tese investigamos o estado normal (T > Tc) dos Yba2Cu3O6+x supercondutores de alto Tc. As técnicas da RMN e RQN foram empregadas para estudar as respostas estática e dinâmica do sistema de spins eletrônicos em função da temperatura, para diversas concentrações de oxigênio: x = 0.5 (cristal 1), 0.92 (cristal 2), 0.94 (cristal 3) e 1.0 (cristais 4 e 5). Focalizando diferentes sítios nucleares a RMN pode fornecer uma informação mais rica da susceptibilidade dinâmica, X (q.w), abrangendo diferentes regiões da Zona de Brillouin (ZB). Com os sítios do 17O(2,3) e do 89Y sensoreamos a região próxima ao centro do ZB, q == 0, enquanto que com o sitio do Cu(2) exploramos o extremo do ZB, (q == QAF). Foi realizado um estudo comparativo da RMN dos sítios do Cu(2), do O(2,3) e do Y sobre o cristal 1. Da comparação entre os deslocamentos hiperfinos magnéticos do Y e do O(2,3) extraímos as contribuições orbitais e as constantes de acoplamento hiperfino do Y. A razão entre as relaxações spin-rede do O(2,3) e do Y mostrou-se independente da temperatura, e próxima do esperado teoricamente a partir das constantes hiperfinas no cenário do hamiltoniano de Mila e Rice. Questões como a dependência da taxa de relaxação spin-rede (T1-1) com a intensidade do campo e a anisotropia da susceptibilidade estática de spin foram estudadas sobre o cristal 2. Acima de Tc, para o Cu(2), não foi encontrada nenhuma dependência de T1 com a intensidade do campo. Os resultados sobre o Y indicam uma anisotropia da susceptibilidade e do tensor de acoplamento hiperfino. Uma extensa comparação entre os resultados da RMN e da Difusão Inelástica de Nêutrons (DIN) foi realizada sobre as mesmas amostras (cristais 4 e 5), fato inédito ate então. Propõe-se um modelo gaussiano para X\"~q,o», compatível com as experiências de nêutrons, no qual o comprimento de correlação ~ foi fixado pelos resultados da DIN sobre o cristal 2. Analisando a relaxação spin-spin do Cu(2), 63(T2g)-1, em função deste modelo, extraímos a susceptibilidade estática X\'(q=QAF) em unidades absolutas e encontramos um fator de Stoner X\'(q=QAF) / X\'(q=O) ~ 10. Da análise conjunta de 63(T1T)-1 e 63 (T2g)-1 obtivemos a energia característica das flutuações AF, rAF::::3:0meV, em excelente acordo com a DIN. Estes mesmos resultados permitiram evidenciar, exclusivamente através do RMN, quando ocorre a abertura de um gap de spin. Neste trabalho mostramos que resultados da DIN são compatíveis com a RMN para o sitio do Cu(2), porem, sérias dificuldades são encontradas para explicar os resultados sobre os sítios do Y e, principalmente, do O(2,3). As alternativas para este problema são discutidas. Os resultados obtidos nesta tese levaram ao estabelecimento de um diagrama de fase, segundo a RMN, do estado normal dos Yba2Cu3O6+x supercondutores, cobrindo do regime sub-dopado ao regime sobre-dopado, passando pela composição de dopagem ótima. / The normal state(T > Tc) of the high Te superconducting Yba2Cu3O6+x was studied. The NMR and NQR techniques were employed in order to investigate the static and dynamic responses of the electronic spin system as function of temperature, for the following oxygen contents: x = 0.5 (crystal 1), 0.92 (crystal 2), 0.94 (crystal 3) e 1.0 (crystals 4 and 5). Focusing various nuclear sites the NMR could give a more rich information of the dynamical susceptibility, X(q,ffi), probing different regions of the Brillouin Zone (ZB). With 17O(2,3) and 89Y sites the BZ center, q:: 0, was studied, while with the Cu(2) site it was the BZ extreme, (q:: QAF) that was investigated. In crystal 1 we have compared the NMR of the Cu(2), O(2,3) and Y sites. From the comparison between the Y and O(2,3) magnetic hyperfine shift we have extracted the orbital contributions and the Y hyperfine coupling tensor. The ratio between the O(2,3) and Y nuclear spin lattice relaxation rate was found to be temperature independent, and its value was in fair agreement with what it was expected theoretically from the coupling constants within the picture of the Mila-Rice Hamiltonian. Problems such as the field intensity dependence of the spin-lattice -relaxation rate (T1-1) and the anisotropy of the static susceptibility where investigated in crystal 2. Above Tc, for the Cu(2) site, we have not found any field dependence of T1. Our results on the Y site indicate an anisotropy of both the static susceptibility and the Y coupling tensor. An extensive comparison between the NMR and the Inelastic Neutron Diffusion (IND) results was done in the very same samples, crystals 2 and 4. In accordance to neutron data a Gaussian model for X\"AF( q,ro) is proposed, in which the coherence length ~ was fixed by the IND results in crystal 2. Analyzing the Cu(2) nuclear spin-spin relaxation rate, 63(T2g)-1, as function of this model, we have extracted the staggered susceptibility X\'(q=QAF) in absolute units, finding a Stoner factor X \'( q=QAF) / X\'( q=O) ~ 10. From the analysis of 63(T1T)-1 together with 63(T2g)-1 we have obtained the AF characteristic energy, rAF ::::l 30meV, in excellent agreement with IND. These results provided us a powerful method to evidence the opening of a spin pseudo gap, exclusively from the NMR results. A consistent picture arise from the comparison between IND and the Cu(2) NMR. In contrast, it is hard to explain the Y and, specially, the O(2,3) results within this same picture. The theoretical alternatives to this puzzle are discussed. The whole set of results we have obtained led us to propose a NMR based phenomenological phase diagram for the normal state of the superconducting Yba2Cu3O6+x, covering from the under doped regime to the over doped regime, passing through the optimal doping.

Orientadores: Ernesto Ruppert Filho, Carlos Alberto Baldan / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-13T08:37:22Z (GMT). No. of bitstreams: 1 Freitas_RafaelCassiolatode_M.pdf: 4732668 bytes, checksum: 0819e8d6aca546a3c44b407acd86b0a9 (MD5) Previous issue date: 2008 / Resumo: O crescimento da demanda de energia elétrica nos centros urbanos e industriais tem levado à necessidade de expansão dos sistemas de energia elétrica o que tem causado aumento nos níveis de curto-circuito, atingindo o limite da capacidade dos sistemas de proteção existentes exigindo sua substituição por outros de maior capacidade. Nessa situação nem sempre a recapacitação dos sistemas de proteção resolve o problema sendo necessário duplicar circuitos. Para postergar investimentos ou para funcionar na rede juntamente com o disjuntor ou ainda, para proteger os circuitos existentes quando conectados a geradores distribuídos, os limitadores de corrente instalados em série com os disjuntores atuais permitem limitar a corrente de falta, principalmente nos primeiros 100ms até a atuação do sistema de proteção. Dentre os diversos tipos de dispositivos limitadores de corrente elétrica existentes no mercado e também ainda em pesquisa atualmente, os construídos a partir de materiais supercondutores possuem a vantagem de proporcionar limitação de corrente elétrica praticamente instantânea causando mínima interferência no funcionamento normal dos sistemas de energia elétrica. Neste trabalho foram estudadas diversas configurações de limitadores de corrente elétrica utilizando fitas de materiais cerâmicos supercondutores de alta temperatura crítica (HTS), de modo especial os limitadores resistivos em forma de bobinas helicoidais enroladas com fita supercondutora BSCCO. Foi desenvolvida metodologia para o cálculo eletromagnético, projeto, construção e ensaio das bobinas supercondutoras do limitador de corrente, bem como se procurou caracterizar eletricamente a fita HTS sob influência de campo magnético externo com o objetivo de determinar as condições de corrente elétrica e de campo magnético sobre ela aplicado para a transição do estado supercondutor para o estado condutor normal do material ("quench"). Ao final do trabalho foram construídos e ensaiados dois protótipos limitadores de corrente elétrica supercondutores mostrando que, apesar da fita HTS de BSCCO ainda não possuir características adequadas para aplicação em limitadores de corrente, com a esperada evolução destes materiais já existe disponível a técnica para projetá-los e construí-los. / Abstract: The growth in demand of electric energy in urban and industrial centers has lead to the need of expansion of the electrical systems which has caused increase in short circuit levels, reaching the limit capacity of the existing protection systems requiring its replacement by others of greater capacity. In these situations the upgrade of protection systems does not always solve the problem being necessary the circuit's duplication. To postpone investments, to operate together in the electrical system with the circuit breakers or even to protect the existing circuits when connected to distributed generators, fault current limiters should be installed in series with the circuit breakers allowing to limit fault currents, specially in the first 100m until the protection system is triggered. Among the many different types of fault current limiter devices existing in the market and which are under development, the ones made of superconducting materials have the advantage of providing practically instantaneous fault current limitation causing minimum interference in the normal operation of the electrical systems. In this work many configurations of electric fault current limiters were studied using superconducting ceramic materials of high transition temperature (HTS), specially the resistive superconducting fault current limiters in form of helical coils with BSCCO superconducting tapes. The methodology for the electromagnetic calculation, project, construction and tests of the superconducting coils of the fault current limiter was carried out along with the HTS tape characterization under external magnetic field influence in order to determine the conditions of electric current and magnetic field for the transition from superconducting state to normal conducting state (quench). At the end of this work two fault current limiters were built and tested showing that, although BSCCO HTS tapes yet do not have good characteristics for fault current limiters application, when these materials which tend to be developed reach applicability level, the technique to design and built them is already available. / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

Orientadores: Ernesto Ruppert Filho, Carlos Alberto Baldan / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-19T21:08:53Z (GMT). No. of bitstreams: 1 EliasJunior_Antonio_M.pdf: 3083167 bytes, checksum: f6bea29b3a45a17156c136bda7644b30 (MD5) Previous issue date: 2011 / Resumo: Esta dissertação apresenta um estudo sobre limitadores de corrente elétrica supercondutores que funcionam com um transformador e com material supercondutor de alta temperatura crítica (HTS) em forma de fita. Neste caso utilizou-se a fita supercondutora do composto de YBCO. Neste trabalho é apresentado um resumo da evolução da supercondutividade desde a origem dos materiais supercondutores de baixa temperatura crítica (LTS) até os de alta temperatura crítica (HTS), as fitas supercondutoras de segunda geração (2G), seus processos de produção, suas composições e suas propriedades. Também faz parte desta dissertação um estudo sobre diferentes equipamentos utilizados para limitar a corrente elétrica em sistemas de energia elétrica aprofundando o estudo sobre limitadores de corrente elétrica supercondutores que funcionam usando transformador. Por fim, simulou-se a operação do limitador de corrente elétrica em questão acoplado ao sistema elétrico usando o pacote MATLAB/Simulink/SimPowerSystems. A simulação foi baseada em características reais dos elementos do sistema, como transformador de distribuição e no comportamento resistivo do material supercondutor de alta temperatura crítica de YBCO / Abstract: This work presents a study about transformer type superconductive fault current limiter using high critical temperature (HTS) tape. In this case the YBCO superconductive tape was used. The history of superconductivity since the beginning of low temperature (LTS) superconductive materials until the high critical temperature superconductive second generation (2G) tapes is presented, also their production process and their compositions are studied. It is part of this work a study about different equipments used to limit the electrical current in electrical power systems going deeply in the transformer type superconductive fault current limiter. Finally, the operation of superconductive electrical current limiter coupled to the electrical power system using MATLAB/Simulink/ SimPowerSystems was simulated. The simulation was based on the real characteristics of power system elements, as distribution transformer and on the resistive behavior of high critical temperature superconductive material of YBCO type / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19720号 / 工博第4175号 / 新制||工||1644(附属図書館) / 32756 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 川上 養一, 教授 田中 勝久, 准教授 掛谷 一弘 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

High Temperature Superconductors (HTS) materials are ideal for many electrical applications. These applications include high speed interconnects, microwave structures and transmission lines, as well as electronic devices that utilize the unique electrical and magnetic properties of these materials. To date, the use of high temperature superconductors has been limited to a narrow range of substrate materials, due to the reactive nature of these superconductors. Chemical reactions between the substrate and the superconductor cause decomposition of the superconductor into an insulator. The researcher has developed a thick film system that allows the production of high quality HTS films on reactive substrates, such as alumina (Al203). This system utilizes a thick film buffer layer of pure silver in combination with thick film superconductors composed of Y1Ba2~CU30X. The silver buffer layer is designed to prevent contact between the substrate and the superconductor, thereby eliminating chemical reactions between the two materials. The development as well as the comprehensive characterization of these films is described in this work. / Master of Science

The field of superconductivity has recently begun to grow in an exponential fashion. This thesis has briefly described a history of superconductivity discoveries, provided the brief literature review about the superconductors. The superconductor material realization and characterization are provided. The delay line design method is presented and various printed delay lines are constructed. The experimental results are presented and discussed. / Master of Science