Electrical systems have become ubiquitous, and with them come the need to accurately monitor electric current. The aerospace industry is no exception. Modern aircraft may contain more than one hundred current sensors, each one critical to a properly functioning vehicle. While these sensors function acceptably, several areas have been identified for improvement: size, weight, and cost. Each sensor is bulky, taking up valuable space. They are also costly to manufacture. The existing design is based on the Hall effect, and has remained fundamentally unchanged for decades. With the recent progress in manufacturing techniques and materials, it would be beneficial to reexamine these sensors and determine if improvements can be made using the accomplishments of recent years. Of particular interest are microelectromechanical systems, also known as MEMS. Using a sensor based on MEMS technologies in which design, function, and fabrication are closely intertwined would automatically meet two of the three goals: reducing size and weight. MEMS additionally have the potential to allow existing systems to be miniaturized. Also of interest are advanced materials, some of which can behave as transducers, linking different physical phenomenon. The goal of this dissertation is to use advances in manufacturing techniques and materials, specifically those discussed above, to design a better current sensor. As part of this goal, several potential solutions were studied and optimized. Finally, proof-of-concept prototypes were fabricated and tested to validate the feasibility of the designs and offer insight into continued sensor development.

This work is comprised of the study of two magneto-optical phenomena: the Kerr effect and the Faraday effect. Neutron physics experiments often utilize polarized neutrons, and one method to generate or guide polarized neutrons involves the use of a system of magnetic super-mirrors. Experience shows that the magnetization of the super-mirror may decay with time; therefore, we implemented the surface magneto-optical Kerr effect (SMOKE) to study the temporal behavior of the magnetization of a magnetized remnant super-mirror sample, where a sensitivity of 0.1 mrad was obtained. Unique to our set-up was the method in which the various magnetization directions were probed. The sample was magnetized prior to insertion into the set-up, and a high precision rotational stage was used to manually rotate the sample to effectively generate a reversal of the magnetic field. Multiple samples from a larger super-mirror specimen were tested, in which no change in the magnetization was detected for one month after sample magnetization. Further studies could increase the sensitivity of the experiment, potentially rendering the method as an application for real-time magnetization monitoring. Polarized 3He nuclei are often used as an effective polarized neutron target at various laboratories, including Jefferson Lab, through the use of spin-exchange optical pumping in a glass cell constructed of GE-180. Utilizing the nuclear spin optical rotation to measure the Faraday effect of polarized 3He would develop a new procedure for polarization monitoring, establish a powerful tool to diagnose the wall properties and thicknesses of the cells used, and the determination of the frequency independent magnetic component of the polarizability would ultimately lead to the extraction of the spin polarizability of 3He. Furthermore, this study has the future implications of being the pioneer experiment for terrestrial dark matter studies. A new triple modulation technique was devised, where a sensitivity of 60 nrad was obtained, and the first ever extraction of the Verdet constant of GE-180 was recorded, an important factor in wall thicknesses and diagnostic investigations for Jefferson Lab. However, a measurement of the nuclear spin optical rotation of a polarized 3He target was not realized, as the measured polarization suggests a Faraday rotation just below the 60 nrad threshold. Nevertheless, the devised triple modulation method proves to be a very sensitive probe in Faraday effect studies, and additional examination of the polarized target for the production of a larger polarization, should yield a measurement of the nuclear spin optical rotation of polarized 3He.

Thesis (M.S.)--University of North Texas, Dec., 2008. / Title from title page display. Includes bibliographical references.

Este trabalho é dedicado à investigação de diferentes aspectos da física de monocamadas de grafeno suspenso e epitaxial. A descrição do grafeno é baseada no modelo quase-relativístico de Dirac. Isso permite a aplicação dos métodos da Teoria Quântica de Campos (TQC) na investigação dos efeitos de interação entre o grafeno e o campo eletromagnético (EM). Usando o formalismo de integral de trajetória, nós formulamos uma teoria efetiva do campo EM na presença de monocamadas de grafeno. Esta teoria é governada pelo operador de polarização das quase-partículas de Dirac. Dois fenômenos importantes são investigados: as propriedades óticas do grafeno (o efeito Faraday em particular) e a interação de Casimir entre uma camada de grafeno e um metal paralelo. Em primeiro lugar, estudamos a propagação de ondas eletromagnéticas na presença de camadas de grafeno. A dinâmica de ondas é governada pelas equações modificadas de Maxwell obtidas a partir da teoria efetiva para o campo EM. Nós calculamos os coeficientes de reflexão e transmissão de luz polarizada linearmente e investigamos detalhadamente o efeito quântico de Faraday no campo magnético externo. Em particular, mostramos que as previsões do modelo de Dirac estão em boa concordância com os recentes resultados experimentais sobre a transmissão de luz e rotação de Faraday gigante em regime de ressonância cíclotron. Novos regimes também são previstos. Em segundo lugar, investigamos a interação de Casimir entre filmes suspensos de grafeno com um condutor ideal. O efeito é investigado tanto no caso ideal (temperatura nula, amostras ideais) quanto para configurações mais realistas (temperatura não nula e a presença de potencial químico). No caso de temperatura nula, a força de Casimir entre grafeno e condutor ideal é aproximadamente 2.6% da força entre dois condutores ideais. Ao mesmo tempo, no limite de temperatura elevada, o efeito mostra-se ser muito forte cerca de 50% de efeito entre metais ideais. / This research is devoted to investigation of several aspects of the physics of suspended and epitaxial graphene monolayers. The description of graphene is based on the quasi--relativistic Dirac model which permits application of the methods of the Quantum Field Theory to investigation of the interaction of graphene with electromagnetic field. Basing on the path integral formalism we formulate the effective theory for EM field in presence of graphene monolayers which is governed by the polarization operator of the Dirac quasi-particles in graphene. The two main phenomena in the interaction of graphene with electromagnetic field are studied: the optical properties of graphene (the Faraday rotation in particular), and Casimir interaction between graphene samples and parallel metal. First, we study the propagation of electromagnetic waves in presence of suspended and epitaxial graphene layers. Their dynamics is governed by the modified Maxwell equations obtained from the effective theory for EM field. We calculate the reflection and transmission coefficient for linearly polarized light and investigate in detail the quantum Faraday effect in external magnetic field. In particular it is showed that the prediction of the Dirac model are in good agreement with recent experimental results on transmission and giant Faraday rotation in cyclotron resonance. New regimes are also predicted Secondly, we investigate Casimir interaction between suspended graphene films with ideal conductor. The effect is investigated both in the idealistic case (zero temperature, ideal samples) and for realistic configurations (non zero temperature and/or presence of impurities and chemical potential). For zero temperature the Casimir force between graphene and a conductor is about 2.7% of that between two ideal conductors. At the same time in the high temperature limit the effect is showed to be greatly enhanced being about 50% of that between ideal metals.

Orientador: Edmundo Capelas de Oliveira / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-15T07:12:57Z (GMT). No. of bitstreams: 1 Rodrigues_FabioGrangeiro_M.pdf: 2473878 bytes, checksum: edf9dfdf8d0b07b971df24b68798f67f (MD5) Previous issue date: 2010 / Resumo: Neste trabalho é dada uma prova de equivalência entre diferentes formas de se escrever a lei de Faraday. a forma integral e a diferencial. Nosso objetivo é esclarecer alguns pontos relevantes da prova dessas equivalências que são normalmente apresentadas nos livros textos de Física apenas para casos muito particulares. Aqui apresentamos a derivação das ditas equivalências para uma situação geral. Incluímos também as ferramentas matemáticas necessárias para o tratamento rigoroso do nosso problema / Abstract: In this work we give a rigorous proof of the equivalence of some different forms of Faraday's law of induction clarifying some misconceptions on the subject and emphasizing that many derivations of this law appearing in textbooks and papers are only valid under very special circunstances and not satisfactory under a mathematical point of view. We include also the mathematical apparatus necessary for a rigorous presentation of our subject / Mestrado / Fisica-Matematica / Mestre em Matemática Universitária

Commutated N-path networks have seen a resurgence in the past decade in the context of modern integrated circuits. N-path circuits have been used to implement high-quality tunable band-pass and notch filters with just switches and capacitors. Recently, nonreciprocal circuits such as circulators and isolators have also been reported as other applications of Linear Periodically-Time-Varying (LPTV) networks. In this dissertation, high performance filters and inductorless nonreciprocal components based on novel LPTV networks are introduced. We proposed a concept called Negative Transresistance (NTR) in phase-shifted N-path structures. The rejection of the conventional N-path notch filters is limited to the number of paths used; however, by using our proposed NTR concept, we were able to achieve more than 50dB rejection regardless of the number of paths. Using the same concept, we introduced the first prototype of N-path Low-Pass Filter (LPF). The resulting components can find application in blocker-tolerant systems, to select closely-spaced frequency channels, and also in the analog Baseband (BB). Nonreciprocal components such as circulators and isolators have traditionally relied on ferrites that offer nonreciprocal behavior based on Faraday Effect (by applying an external magnetic field). Recent efforts to eliminate the need for magnetic materials, despite being a huge success involve the usage of transmission lines (and/or inductors). In this dissertation, a novel concept called Nonreciprocal Transresistance (NRTR) is introduced. This led to the first ever inductorless RF isolator. Furthermore, we expanded the idea to the first inductorless circulator consisting of only switches and capacitors. The resulting isolator can find application in base stations to prevent back reflections (e.g. to protect the Power Amplifier (PA)). Also, in superconducting quantum systems, an isolator is necessary to separate the noise and reflections at the interface of different blocks. The introduced circulator can find applications in wireless communication systems as an antenna interface connecting the Transmitter (TX) and the Receiver (RX) to a shared antenna. This is crucial, especially for Full-Duplex (FD) applications where high isolation between RX and TX is necessary as they are operating at the same frequency. Finally, we enhanced the performance of the conventional N-path Band-Pass Filter (BPF). We first introduced a second-order N-path BPF with passive gain called impedance-transforming N-path filter. We then proposed a concept called rotary-clock-path in N-path filters which enables passive frequency shifting of N-path filters of any kind without the need for a separate clock frequency or active circuitries. Then by combining the impedance-transforming BPF and rotary-clock-path ideas, we implemented the first ever inductorless passive higher-order N-path BPF with voltage gain. The resulting BPFs can find applications in matching networks and also in a Surface Acoustic Wave (SAW)-less mixer-first receivers.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19728号 / 工博第4183号 / 新制||工||1645(附属図書館) / 32764 / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 田中 勝久, 教授 平尾 一之, 教授 三浦 清貴 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20044号 / 理博第4229号 / 新制||理||1609(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 高橋 義朗, 教授 田中 耕一郎, 教授 川上 則雄 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20386号 / 工博第4323号 / 新制||工||1670(附属図書館) / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 田中 勝久, 教授 平尾 一之, 教授 三浦 清貴 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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