[pt] Esta tese trata do desenvolvimento de sensores para a monitoração do fluxo de campo magnético utilizando fibras ópticas. A principal motivação reside no uso destes sensores no control da condição de hidrogeradores. Duas tecnologias de sensoriamento com fibras ópticas são exploradas. A primeira baseia-se no uso de redes de Bragg e a segunda no emprego de interferômetros modais em fibras ópticas microestruturadas que apresentam alta birefringência. Em ambos os casos as fibras são recobertas por uma camada de material compósito magnetoestrictivo, que responde ao campo magnético deformando-se. Esta deformação é transferida para a rede de Bragg ou para a fibra microestruturada, produzindo uma resposta dependente do campo magnético. Os sensores desenvolvidos são leves e compactos. O sensor baseado em redes de Bragg, de formato cilíndrico com 1,5 mm de diâmetro e 7 mm de comprimento, passou por testes estáticos em campos magnéticos de até 750 mT tendo apresentado uma resolução de 0,3 mT. Testes dinâmicos foram realizados em um rotor de bancada desbalanceado e os resultados obtidos comparados com os fornecidos por um sensor magnético de efeito Hall mostrando excelente concordância. O sensor a fibra óptica interferométrico foi caracterizado estaticamente, tendo apresentado uma sensibilidade ao campo magnético duas vezes superior à do sensor baseado em redes de Bragg. / [en] This work explores the use of optical fiber sensors for the measurement of magnetic fields. In focus are applications in the condition monitoring of hydrogenerators, in particular for the measurement of the air gap, which consists in the space between rotor and stator of the synchronous machine. Two different fiber optic sensing principles were employed to develop magnetic field sensors. The first was based on fiber Bragg gratings and the second on an in-fiber modal interferometer, where the two orthogonally polarized modes of a high birefringent microstructured fiber generate fringes over the optical spectrum of a broad band source. In both cases, the fibers are coated by a thick layer of a magnetostrictive composite that deforms due to changes in its magnetization state. Strains in the coating are transferred to the fiber and measured by the sensor. The developed sensors are light and compact. The Bragg grating magnetic field sensor is cylindrical in shape with diameter of 1.5 mm and 7 mm long. The sensor was tested at magnetic fields of up to 750 mT under static conditions. The resolution achieved with a commercial interrogator was estimated at 0.4 mT. Dynamic tests were carried out in a laboratory rotor that presented a magnetic unbalance of approximately 7 percent in one of its four poles. Results were compared with a Hall Effect sensor showing excellent agreement. The interferometric sensor was characterized and results of static tests demonstrated that its sensibility to changes in the magnetic field is twice that of the sensor based on Bragg gratings.

This master's thesis focuses on the utilization of an artificially created weak magnetic field for navigation in 3D space. The theoretical part of this work deals with the general properties of the magnetic field and with its description. The next section of the theoretical part contains an overview of measuring principles for magnetic field measurements. Based on various types of measuring principles, the thesis elaborates on commercially available miniature sensors for magnetic field measurement with a measuring range up to 10 mT. The work focuses mainly on the magnetoresistive principle and fluxgate sensors. Furthermore, the theoretical part contains descriptions of methods for modeling the magnetic field of simple permanent magnets and various magnet assemblies. Lastly, the theoretical part involves a patent search of devices used for locating magnets that are installed in an intramedullary nail, which is used in intramedullary stabilization used on fractures of human bones. By locating the magnet in the nail, it is possible to precisely determine the position of the mounting holes. The practical part of the thesis deals with the analysis of magnetic field behavior in the vicinity of various magnetic assemblies, which were modeled in COMSOL Multiphysics using the finite element method. The models were created with the aim of analysing the behaviour of the magnetic field in the vicinity of the magnets and at the same time to find possible analytical functions that could be used to determine the position of the magnet in space relative to the probe. The result of this work is an analysis of various assemblies, which contains graphs of different dependencies and prescription of polynomial functions that approximate these dependencies. Another part of the thesis is the design of a probe that serves to locate the magnetic target. The work describes two possible methods of localization. For the differential method, a user interface in LabVIEW was created. The probe based on this method is fully capable of locating the magnet in the 2D plane. The state space search method is described only in theory.