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Keywords = solenoid modal

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15 pages, 2103 KiB  
Article
Image Registration for Visualizing Magnetic Flux Leakage Testing under Different Orientations of Magnetization
by Shengping Li, Jie Zhang, Gaofei Liu, Nanhui Chen, Lulu Tian, Libing Bai and Cong Chen
Entropy 2023, 25(1), 167; https://doi.org/10.3390/e25010167 - 13 Jan 2023
Viewed by 1785
Abstract
The Magnetic Flux Leakage (MFL) visualization technique is widely used in the surface defect inspection of ferromagnetic materials. However, the information of the images detected through the MFL method is incomplete when the defect (especially for the cracks) is complex, and some information [...] Read more.
The Magnetic Flux Leakage (MFL) visualization technique is widely used in the surface defect inspection of ferromagnetic materials. However, the information of the images detected through the MFL method is incomplete when the defect (especially for the cracks) is complex, and some information would be lost when magnetized unidirectionally. Then, the multidirectional magnetization method is proposed to fuse the images detected under different magnetization orientations. It causes a critical problem: the existing image registration methods cannot be applied to align the images because the images are different when detected under different magnetization orientations. This study presents a novel image registration method for MFL visualization to solve this problem. In order to evaluate the registration, and to fuse the information detected in different directions, the mutual information between the reference image and the MFL image calculated by the forward model is designed as a measure. Furthermore, Particle Swarm Optimization (PSO) is used to optimize the registration process. The comparative experimental results demonstrate that this method has a higher registration accuracy for the MFL images of complex cracks than the existing methods. Full article
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Figure 1

Figure 1
<p>The distribution of MFL field with DOM (Simulated by COMSOL).</p>
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<p>Registration Schematic of MFL images under DOM.</p>
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<p>Magneto-optical imaging: (<b>a</b>) Schematic of MOI, (<b>b</b>) The MOI system.</p>
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<p>Schematic of the procession.</p>
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<p>The proposed method.</p>
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<p>The comparison of graphs along the row and column directions; (<b>a</b>) Before transformation, (<b>b</b>) after transformation.</p>
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<p>The example image images. (<b>a</b>) The original image of the defect. (<b>b</b>) The first direction of magnetization. (<b>c</b>) The second direction of magnetization (the angle between c and b is about 85<math display="inline"><semantics> <msup> <mrow/> <mo>∘</mo> </msup> </semantics></math>∼90<math display="inline"><semantics> <msup> <mrow/> <mo>∘</mo> </msup> </semantics></math>).</p>
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<p>The segmentation of captured image.</p>
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<p>The solenoid in specimen.</p>
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<p>Schematic of solenoid interaction. (<b>a</b>) No interactions; (<b>b</b>) With interactions.</p>
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<p>Comparison of magnetic dipole model and solenoid model. (<b>a</b>) Magnetic dipole model, (<b>b</b>) Solenoid model, (<b>c</b>) The actual MOI image.</p>
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<p>Example of operational feasibility. (<b>a</b>) Results of registration, (<b>b</b>) Convergence of iterations.</p>
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<p>The platform of MFL image detection.</p>
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<p>The samples: (<b>a</b>) Manual t-shaped crack, (<b>b</b>) Natural one-line crack, (<b>c</b>) natural three-line crack.</p>
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<p>Comparison of correlation coefficients with manual registration results.</p>
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9 pages, 3096 KiB  
Article
Demonstration of Focusing Wolter Mirrors for Neutron Phase and Magnetic Imaging
by Daniel S. Hussey, Han Wen, Huarui Wu, Thomas R. Gentile, Wangchun Chen, David L. Jacobson, Jacob M. LaManna and Boris Khaykovich
J. Imaging 2018, 4(3), 50; https://doi.org/10.3390/jimaging4030050 - 6 Mar 2018
Cited by 11 | Viewed by 6122
Abstract
Image-forming focusing mirrors were employed to demonstrate their applicability to two different modalities of neutron imaging, phase imaging with a far-field interferometer, and magnetic-field imaging through the manipulation of the neutron beam polarization. For the magnetic imaging, the rotation of the neutron polarization [...] Read more.
Image-forming focusing mirrors were employed to demonstrate their applicability to two different modalities of neutron imaging, phase imaging with a far-field interferometer, and magnetic-field imaging through the manipulation of the neutron beam polarization. For the magnetic imaging, the rotation of the neutron polarization in the magnetic field was measured by placing a solenoid at the focus of the mirrors. The beam was polarized upstream of the solenoid, while the spin analyzer was situated between the solenoid and the mirrors. Such a polarized neutron microscope provides a path toward considerably improved spatial resolution in neutron imaging of magnetic materials. For the phase imaging, we show that the focusing mirrors preserve the beam coherence and the path-length differences that give rise to the far-field moiré pattern. We demonstrated that the visibility of the moiré pattern is modified by small angle scattering from a highly porous foam. This experiment demonstrates the feasibility of using Wolter optics to significantly improve the spatial resolution of the far-field interferometer. Full article
(This article belongs to the Special Issue Neutron Imaging)
Show Figures

Figure 1

Figure 1
<p>Schematic diagram of a Wolter type I optic composed of a confocal hyperboloid and ellipsoid.</p>
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<p>Layout sketch and two photographs of the WHIMS experiment. The beam travels left to right along the positive z-direction. Visible in the top photograph are the <sup>3</sup>He polarizer (labeled with a white A), <sup>3</sup>He analyzer (labeled with a white B), the Wolter optic inside the small aluminum box (labeled with a white D), beam-limiting aperture, and the evacuated beam tube. In the bottom photograph, the polarizer solenoid, the sample solenoid (labeled with a white C) placed in the focal plane of the Wolter optic, and the analyzer solenoid are shown. Due to the use of solenoidal holding fields, the neutron polarization axis, shown as blue arrows in the sketch, is along the z-direction. The longitudinal magnetic fields from the magnetically shielded polarizer and analyzer solenoids drop off rapidly but are sufficient to maintain the neutron’s spin direction. Since they are roughly an order of magnitude lower than that of the sample solenoid’s vertical field, they were not include in the analysis. The sample field, B<sub>s</sub>, is along the y-axis, thus causing the neutron spin vector to rotate in the x-z plane. The detector is far beyond the left edge of the photograph.</p>
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<p>Schematic and photo of the WOOFF experiment. The beam propagates from right to left. The two phase gratings are visible followed by the optics. The detector is beyond the edge of the photograph.</p>
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<p>(<b>a</b>) Transmission images of the solenoid at three different applied currents. The reduction of transmission due to neutron spin rotation by the solenoid’s field is apparent. In the three images, the black circle is the boundary of the field of view and the parallel lines show the position of the solenoid. Due to the low number of counts, there is enhanced “salt and pepper” noise. (<b>b</b>) Average grey level value within the solenoid for given applied current and the fit using the cosine function. The uncertainty is the one-sigma root mean square deviation over the solenoid region.</p>
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<p>WOOFF images showing the open beam moirė pattern, the reduction in fringe visibility for three thicknesses of insulation, 0.5 mm, 1 mm and 6 mm. The white scale bar in the open beam image is 7 mm.</p>
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