The electromagnetic behavior of magnetic devices used in power electronics circuitry, is studied in order to predict their performance within a context of desirable circuit parameters. Past efforts have focused on simplifications widely used in electric machinery applications. Due to the greatly increased operating frequencies of today's circuits (in the upper kHz and lower MHz region), the operation and design of magnetic components greatly differs from those of 60 Hz machinery. A set of models based on assumptions that are unique to the these devices used in power electronics are put forth. The entire approach is based on deriving models from solutions of the field equations, rather than using older, less accurate circuit analogies. More importantly, models are needed for accurate design and optimization processes of complete power electronic systems, in which the magnetic components form a small part. Solutions are sought without using the popular simplifications at very low and very high frequencies, since they are not accurate at intermediate frequencies encountered in power electronics. The conductors used in transformers and inductors are modelled in these high frequency regions. / Ph. D.

Silicon magnetic sensors based on the Hall effect have proven to be an excellent sensor choice for many applications, such as position sensing, gear-tooth sensing, contact-less switching and linear sensing. Although a sensor can be trimmed over temperature before it is shipped to the customer, little can be done about the sensitivity's stability once the sensor has been installed in its final application. The goal of this project is to propose and implement mechanisms to stabilize the Hall sensor's sensitivity through the use of mechanical stress feedback and magnetic feedback.

Orientador: Evandro Conforti / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e Computação / Made available in DSpace on 2018-08-06T03:26:36Z (GMT). No. of bitstreams: 1 Tosin_Giancarlo_D.pdf: 3627033 bytes, checksum: 259c4fdcd684f17b9b0a0dbe346d2342 (MD5) Previous issue date: 2005 / Resumo: As medições acuradas e precisas do campo magnético dos dispositivos de inserção (DIs) são essenciais para garantir que suas instalações no Anel de Armazenamento de Elétrons do Laboratório Nacional de Luz Síncrotron (LNLS) alcançarão o desempenho desejado e não comprometerão a estabilidade do feixe de elétrons estocado. Tais dispositivos são versáteis fontes de radiação introduzidas nos Anéis de Armazenamento onde, a partir dos seus perfis de campos, promovem a emissão de intensos fluxos de fótons, de largo espectro ou monocromáticos, cuja polarização também pode ser controlada. Devido às características do feixe de elétrons do Anel de Armazenamento do LNLS, tais como energia de operação, energia de injeção e abertura dinâmica (região onde o feixe é estável), severas restrições na qualidade do campo são impostas para garantir o tempo de vida e a estabilidade da órbita. Para a verificação dessas especificações e do perfil do campo, que é fundamental para a determinação do espectro emitido, construiu-se uma bancada de caracterização com alcance útil de 4,2 m. Duas técnicas foram nela instaladas: bobina girante, para a medida de campos médios (ou integrados), e sensores Hall, para a medição de campos locais. Ambas as técnicas foram exploradas nos seus conceitos, e aperfeiçoadas, a fim de assegurar a confiabilidade dos valores medidos, dentro de suas especificações. O aperfeiçoamento das técnicas aqui proposto permitiu melhorar substancialmente a precisão apresentada na literatura especializada / Abstract: This Thesis was a consequence of the need for an accurate and precise magnetic field measurement bench for insertion devices characterization (IDs). Such devices are versatile radiation sources installed in Electron Storage Rings. From their magnetic field profile, they provide high photon fluxes, with broad or monochromatic spectrum, being possible, depending on the ID geometry, to control also the radiation polarization. Due to some features of the LNLS electron beam, such as injection energy, operation energy and dynamic aperture, severe restrictions are imposed on the magnetic field quality to assure a long life time and a stable beam orbit. A characterization bench, 4.2 m in length, was built to verify such specifications and to determine the field profile, which is correlated to the emission spectrum. Two techniques were implemented in this bench: rotating coil, for average (or integrated) field measurements, and Hall probes, for local field measurements. Both techniques were conceptually explored and improved to guarantee the reliability of the measured values within their specifications. The results showed a considerable increasing in the precision with respect to values presented in the scientific literature / Doutorado / Eletrônica, Microeletrônica e Optoeletrônica / Doutor em Engenharia Elétrica

The subject of this thesis is to study the interaction between carbon nanotubes (CNTs) and antiferromagnetic tetrametallic molecules attached to them. By employing quantum transport measurements, the sensitivity to sense the interactions is greatly increased, because the quantum dot is very susceptible to changes in its environment. The properties of carbon nanotubes can be altered by chemical functionalization with the aforementioned molecules, where the attachment is performed covalently via a ligand exchange with the CNT. The thesis is partitioned into two main parts: the first part presents experiments performed on tetramanganese functionalized CNTs, whereas for the second similar studies are conducted, except manganese is replaced by cobalt. Both complexes exhibit an antiferromagnetic ground state, yet the metal spin of manganese (S=5/2) is reduced to S=3/2 for cobalt. Additionally, an altered device preparation has been employed during the second part, leading to a strong suppression of the background signal. Quantum transport measurements at T=4K on manganese-functionalized CNTs show a very regular pattern of Coulomb diamonds, indicating only a mild disturbance of the quantum dot's electron system by the covalent bond. Moreover, the charging energy reveals a wave function extending over the entire device dimensions. However, at T=30mK in the tunneling current a strong noise emerges, when repeatedly measuring over an hour while keeping external biases constant. Additionally, these time traces are superimposed by a long-term background, which is removed by a correction algorithm plus a subsequent digitization. The remaining signal reveals a random telegraph signal (RTS) which is extensively studied and from its statistics the equivalent temperature of T=654mK for the excitation of the system is extracted. The quantum transport experiments conducted on cobalt-functionalized CNTs show a much better data quality of the coulomb diamonds, which is ascribed to the alteration in the device's preparation. From the line shape of the Coulomb oscillations as well as from the Coulomb staircases an electron temperature of about T=500mK is extracted. Moreover, a magnetic field dependence of the stability diagrams is apparent, attributable to Zeeman splitting. The respective Landé factor of g=1.73 is, compared to similar CNT quantum dot systems, unusually low. It is as attributed to an increased spin-orbit interaction between the conduction electrons and the cobalt's nuclei. The respective time traces exhibit or lack an RTS signal, depending on their external biases. Regarding the Coulomb diamonds, an essential prerequisite for the occurrence of an RTS is the proximity to a resonance, which is equatable to a high sensitivity of the quantum dot detector. Considering the available energy, the underlying process that is the cause for the emergence of the RTS is ascertained to be an internal excitation of the antiferromagnetic states of the metallic core.