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Lorentz force evaluation: novel forward solution and inverse methods
The development of new materials, as well as the increasing standards for quality and safety, require high-resolution, nondestructive evaluation methods for manufacturing and maintenance. In a novel method, referred to as Lorentz force evaluation, a permanent magnet is moved relative to a conducting specimen. Owing to this movement, eddy currents are induced inside the conductor. The interaction of the eddy currents with the magnetic field leads to the Lorentz force acting on the conductor. A force of the same magnitude but in opposite direction acts on the permanent magnet, where it is measured. In the presence of a defect, the eddy currents are perturbed. Consequently, the Lorentz force components are also perturbed. The defect properties are determined from the measured Lorentz force components by solving an ill-posed inverse problem. The thesis aims to develop a novel forward solution, compare different forward solutions, develop new inverse calculation methods and create a method for improving defect depth estimation for Lorentz force evaluation. Further, a qualitative comparison to classical eddy current evaluation was realized. The existing forward solutions in Lorentz force evaluation: approximate forward solution and the computational more demanding extended area approach were compared regarding their defect reconstruction performance. A goal function scanning method was used as inverse method in order to directly compare the influence of both forward solutions on the defect reconstruction result avoiding the bias of tuning parameters of the inverse methods. The use of the extended area approach as forward solution yielded more accurate defect depth and extensions estimations compared to the approximate forward solution. However, both forward solutions are limited to defects of regular geometry. Thus, a novel forward solution referred to as single voxel approach was developed. It is based on the superposition of force perturbation signals of small elementary defects. For numerical simulations of various ...
Lorentz force evaluation: novel forward solution and inverse methods
The development of new materials, as well as the increasing standards for quality and safety, require high-resolution, nondestructive evaluation methods for manufacturing and maintenance. In a novel method, referred to as Lorentz force evaluation, a permanent magnet is moved relative to a conducting specimen. Owing to this movement, eddy currents are induced inside the conductor. The interaction of the eddy currents with the magnetic field leads to the Lorentz force acting on the conductor. A force of the same magnitude but in opposite direction acts on the permanent magnet, where it is measured. In the presence of a defect, the eddy currents are perturbed. Consequently, the Lorentz force components are also perturbed. The defect properties are determined from the measured Lorentz force components by solving an ill-posed inverse problem. The thesis aims to develop a novel forward solution, compare different forward solutions, develop new inverse calculation methods and create a method for improving defect depth estimation for Lorentz force evaluation. Further, a qualitative comparison to classical eddy current evaluation was realized. The existing forward solutions in Lorentz force evaluation: approximate forward solution and the computational more demanding extended area approach were compared regarding their defect reconstruction performance. A goal function scanning method was used as inverse method in order to directly compare the influence of both forward solutions on the defect reconstruction result avoiding the bias of tuning parameters of the inverse methods. The use of the extended area approach as forward solution yielded more accurate defect depth and extensions estimations compared to the approximate forward solution. However, both forward solutions are limited to defects of regular geometry. Thus, a novel forward solution referred to as single voxel approach was developed. It is based on the superposition of force perturbation signals of small elementary defects. For numerical simulations of various ...
Lorentz force evaluation: novel forward solution and inverse methods
Dölker, Eva-Maria (Autor:in) / Haueisen, Jens / Formisano, Alessandro / Baumgarten, Daniel
17.03.2020
Hochschulschrift
Elektronische Ressource
Englisch
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