This thesis deals with design of an eddy current transducer which enables non-destructive inspection of composite aircraft structures primarily carbon fiber reinforced plastic (CFRP) in areas of manufacture and maintenance. The design of the transducer is based on analytical-experimental approach and its electrical and mechanical parameters were optimized to ensure a good signal to noise ratio at the six composite samples. These samples contain artificial discontinuities in the form of various types of defects. These defects are simulating the various types of damage created in the aircraft structure, especially delamination or thickness changes of composite materials. The experimental measurements, data collection and non-destructive evaluation were performed during the period. The result of this work is functional eddy current probe, which is reliably able to detect some damage of the carbon composite structures to the depth of 3,9 mm.

We consider the problem of extracting a specific feature from a noisy signal generated by a multi-channels Remote Field Eddy Current Sensor. The sensor is installed on a mobile robot whose mission is the detection of anomalous regions in metal pipelines. Given the presence of noise that characterizes the data series, anomaly signals could be masked by noise and therefore difficult to identify in some instances. In order to enhance signal peaks that potentially identify anomalies we consider an entropy filter built on a-posteriori probability density functions associated with data series. Thresholds based on the Neyman-Pearson criterion for hypothesis testing are derived. The algorithmic tool is applied to the analysis of data from a portion of pipeline with a set of anomalies introduced at predetermined locations. Critical areas identifying anomalies capture the set of damaged locations, demonstrating the effectiveness of the filter in detection with Remote Field Eddy Current Sensor.

Superligas à base de níquel vêm sendo extensivamente utilizadas em diversas aplicações nas indústrias devido ao excelente comportamento mecânico e anticorrosivo. No entanto, essas ligas possuem certas particularidades que levam à necessidade de desenvolvimento de técnicas de inspeção e caracterização metalúrgica, como forma de garantir a integridade estrutural dos componentes fabricados com essas ligas. Neste trabalho, a técnica de correntes parasitas foi aplicada à superligas à base de níquel com duas propostas distintas: 1) Em um primeiro momento foi realizado o estudo da evolução microestrutural da liga Inconel 718 durante o processo de envelhecimento através da combinação do ensaio por correntes parasitas, análise de difração de raios-X, análise metalográfica, medidas de dureza e tamanho de grão. As medidas foram realizadas em amostras submetidas a diferentes ciclos de tratamentos térmicos variando entre 620-1035°C. Os resultados mostraram que as diferentes microestruturas do Inconel 718 têm efeitos distintos na condutividade elétrica quando medidos através da técnica de correntes parasitas. A influência da microestrutura na condutividade pode ser mostrada sendo devido à competição de dois efeitos sobre o espalhamento de elétrons: a purificação da matriz e a morfologia, distribuição e tamanho dos precipitados. A combinação dos valores de dureza e condutividade elétrica provou ser uma forma rápida e prática de determinar o nível de envelhecimento da liga; 2) Em um segundo momento foi desenvolvido um processo de otimização de sensores através de modelagem por elementos finitos (MEF). Através de uma metodologia de otimização, os parâmetros de construção e operação de um sensor foram otimizados para inspeção de defeitos superficiais e subsuperficiais esperados em materiais cladeados com Inconel 625. O sensor com a geometria ótima foi construído e testado a fim de verificar a eficiência do processo de otimização. Uma ótima correlação entre os resultados numéricos e experimentais foi encontrada e o sensor ótimo se mostrou eficiente na inspeção de pequenos defeitos superficiais e subsuperficiais na liga Inconel 625 quando operado nas frequências apropriadas. / Nickel-based superalloys have been extensively used in various industries due to its unique mechanical and corrosion behavior. However, these alloys show particular characteristics which lead to the need for specific inspection and metallurgical characterization techniques in order to ensure the structural integrity of components manufactured from these alloys. In this work , the eddy current technique was applied to nickel-base superalloys with two aims: 1 ) Firstly, the microstructural evolution of Inconel 718 during aging processes has been studied through a combination of eddy current testing, X-ray diffraction analysis, metallography, hardness and grain size measurements. Measurements were carried out in samples subjected to different heat treatment cycles between 620-1035°C. Results show that different microstructures of Inconel 718 have a distinguishable effect on electrical conductivity when this is measured through an appropriately sensitive technique (i.e. eddy current testing). The influence of microstructure on conductivity could be shown to be due to the competition between two effects on the scattering of electrons: matrix purification and precipitate size, distribution and morphology. A combination of hardness values and electrical properties proved to be a fast and practical way of determining the stage of aging of the alloy; 2) An optimization method of eddy current sensor design was developed through finite element modeling (FEM). Through a methodology of optimization, the construction and operation parameters of the sensor were optimized for inspection of superficial and subsuperficial defect, commonly found in weld overlay Inconel 625 claddings. A prototype of this sensor with the optimum geometry was built and tested on blocks identical to those considered in the models in order to verify the efficiency of the optimization process. A very good agreement between numerical and experimental results was found. Moreover, the optimal sensor was efficient to detect small surface and subsurface defects in Inconel 625 when operated at appropriate frequencies.

This thesis deals with design of an eddy current transducer which enables non-destructive inspection of composite aircraft structures primarily carbon fiber reinforced plastic (CFRP) in areas of manufacture and maintenance. The design of the transducer is based on analytical-experimental approach and its electrical and mechanical parameters were optimized to ensure a good signal to noise ratio at the six composite samples. These samples contain artificial discontinuities in the form of various types of defects. These defects are simulating the various types of damage created in the aircraft structure, especially delamination or thickness changes of composite materials. The experimental measurements, data collection and non-destructive evaluation were performed during the period. The result of this work is functional eddy current probe, which is reliably able to detect some damage of the carbon composite structures to the depth of 3,9 mm.

The aim of the diploma thesis is to clarify the topic of calibration samples used in eddy current testing on equipment in nuclear energy. The theoretical part of the diploma thesis is focused on the eddy current testing method, which belongs to the technology of non-destructive defectoscopy. This part of the work describes the principle of the method, its scope, limitations and dividing of sensors used in this test method. The work briefly describes the physical principle of the laser, its types and operating modes. The practical part of the work is focused on the production of a calibration samples by laser. Another point of the work is the comparison of data obtained from eddy current measurements on samples made by laser and on calibration samples used in practice.

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The optical power of satellites such as the Hubble telescope is directly related to the size of the primary mirror. However, due to the limited capacity of the shuttle bay, progress towards the development of more powerful satellites using traditional construction methods has come to a standstill. Therefore, to allow larger satellites to be launched into space significant interest has been shown in the development of ultra large inflatable structures that can be packaged inside the shuttle bay and then deployed once in space. To facilitate the packaging of the inflated device in its launch configuration, most structures utilize a thin film membrane as the optical or antenna surface. Once the inflated structure is deployed in space, it is subject to vibrations induced mechanically by guidance systems and space debris as well as thermally induced vibrations from variable amounts of direct sunlight. For the optimal performance of the satellite, it is crucial that the vibration of the membrane be quickly suppressed. However, due to the extremely flexible nature of the membrane structure, few actuation methods exist that avoid local deformation and surface aberrations. One potential method of applying damping to the membrane structure is to use magnetic damping. Magnetic dampers function through the eddy currents that are generated in a conductive material that experiences a time varying magnetic field. However, following the generation of these currents, the internal resistance of the conductor causes them to dissipate into heat. Because a portion of the moving conductor's kinetic energy is used to generate the eddy currents, which are then dissipated, a damping effect occurs. This damping force can be described as a viscous force due to the dependence on the velocity of the conductor. While eddy currents form an effective method of applying damping, they have normally been used for magnetic braking applications. Furthermore, the dampers that have been designed for vibration suppression have typically been ineffective at suppressing structural vibration, incompatible with practical systems, and cumbersome to the structure resulting in significant mass loading and changes to the dynamic response. To alleviate these issues, three previously unrealized damping mechanisms that function through eddy currents have been developed, modeled and tested. The dampers do not contact the structure, thus, allowing them to add damping to the system without inducing the mass loading and added stiffness that are typically common with other forms of damping. The first damping concept is completely passive and functions solely due to the conductor's motion in a static magnetic field. The second damping system is semi-active and improves the passive damper by allowing the magnet's position to be actively controlled, thus, maximizing the magnet's velocity relative to the beam and enhancing the damping force. The final system is completely active using an electromagnet, through which the current can be actively modified to induce a time changing magnetic flux on the structure and a damping effect. The three innovative damping mechanisms that have resulted from this research apply control forces to the structure without contacting it, which cannot be done by any other passive vibration control system. Furthermore, the non-contact nature of these dampers makes them compatible with the flexible membranes needed to advance the performance of optical satellites. / Ph. D.

Recently planar magnetic technologies have been widely used in power electronics, due to good cooling and ease of fabrication. High frequency operation of magnetic components is a key to achieve high power density and miniaturization. However, at high frequencies, skin and proximity effect losses in the planar windings become significant, and parasitics cannot be ignored. This piece of work deals with the modeling and design of planar integrated magnetic component for power electronics applications. First, one-dimensional eddy current analysis in some simple winding strategies is discussed. Two factors are defined in order to quantify the skin and proximity effect contributions as a function of frequency. For complicated structures, 2D and 3D finite element analysis (FEA) is adopted and the accuracy of the simulation results is evaluated against exact analytical solutions. Then, a planar litz structure is presented. Some definitions and guidelines are established, which form the basis to design a planar litz conductor. It can be constructed by dividing the wide planar conductor into multiple lengthwise strands and weaving these strands in much the same manner as one would use to construct a conventional round litz wire. Each strand is subjected to the magnetic field everywhere in the winding window, thereby equalizing the flux linkage. 3D FEA is utilized to investigate the impact of the parameters on the litz performance. The experimental results verify that the planar litz structure can reduce the AC resistance of the planar windings in a specific frequency range. After that, some important issues related to the planar boost inductor design are described, including core selection, winding configuration, losses estimation, and thermal modeling. Two complete design examples targeting at volume optimization and winding parasitic capacitance minimization are provided, respectively. This work demonstrates that planar litz conductors are very promising for high frequency planar magnetic components. The optimization of a planar inductor involves a tradeoff between volumetric efficiency and low value of winding capacitance. Throughout, 2D and 3D FEA was indispensable for thermal & electromagnetic modeling. / Master of Science