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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Needle-probe techniques for local magnetic flux measurements

Marc De Wulf, Luc Dupré, Dimitre Makaveev, and Jan Melkebeek

J. Appl. Phys. 93, 8271 (2003); http://dx.doi.org/10.1063/1.1544485 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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Numerical two-dimensional field investigations in the cross section of laminated nonoriented electrical steel sheet are performed in order to verify the possibilities and limitations of the two needle-probe technique for the measurement of local magnetic flux near the cutting edge. If one of the needles approaches the lamination edge or when inhomogeneities are present in the flux distribution along the strip width due to magnetic properties altered by the cutting procedure, then the signal from the needle probes no longer represents the flux through a rectangular surface under the needles because of E-field components perpendicular to the lamination surface. The flux calculated from the needles is compared to the actual flux passing through the rectangular surface under the needles and corresponding correction factors as a function of the needle position away from the cutting edge are computed. Depending on the positioning method, the needle probes can give an under- or overestimation of the actual flux. Corrections from 15% to 80% are necessary if distances of about the lamination thickness are considered. This work suggests an iterative numerical procedure for the interpretation of experimental data obtained from local flux needle-probe measurements. © 2003 American Institute of Physics.
Show PACS
07.55.Ge Magnetometers for magnetic field measurements
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Bb Fe and its alloys

Neural network-based inversion algorithms in magnetic flux leakage nondestructive evaluation

Pradeep Ramuhalli, Lalita Udpa, and Satish S. Udpa

J. Appl. Phys. 93, 8274 (2003); http://dx.doi.org/10.1063/1.1558693 (3 pages) | Cited 16 times

Online Publication Date: 9 May 2003

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Magnetic flux leakage (MFL) methods are commonly used in the nondestructive evaluation (NDE) of ferromagnetic materials. An important problem in MFL NDE is the determination of flaw parameters such as the flaw length, depth, and shape (profile) from the measured values of the flux density B. Commonly used methods use a forward model in a loop to determine B for a given set of flaw parameters. This approach iteratively adjusts the flaw parameters to minimize the error between the measured and predicted values of B. This article proposes the use of neural networks as forward models. The proposed approach uses two neural networks in feedback configuration—a forward network and an inverse network. The second network is used to predict the profile given the measured value of B, and acts to constrain the solution space. Results of applying these methods to MFL data obtained from a two-dimensional finite-element model, with rectangular flaws of various dimensions, are presented. © 2003 American Institute of Physics.
Show PACS
07.55.Ge Magnetometers for magnetic field measurements
81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing
07.05.Mh Neural networks, fuzzy logic, artificial intelligence
02.30.Zz Inverse problems
02.70.Dh Finite-element and Galerkin methods
02.60.Gf Algorithms for functional approximation

Detection of flaws in ferromagnetic samples based on low frequency eddy current imaging

Y. Fujita and I. Sasada

J. Appl. Phys. 93, 8277 (2003); http://dx.doi.org/10.1063/1.1556975 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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We report a nondestructive method to detect flaws in a ferromagnetic plate based on eddy current imaging. The inductive pickup in our previous Dahle-type probe is replaced by a thin orthogonal flux gate driven by a 1 MHz ac current. Samples are 2-mm-thick steel plates (SS400) having a 0.4-mm-wide EDM slot on the backside with various slot depths (0.4, 1.0, 1.2, and 1.6 mm). These samples were line scanned by the probe with the lift-off about 0.01 mm. The excitation field inducing the eddy current in the sample was 40 Hz–2 kHz. An interesting thing to note is the relationship between the slot depth and the excitation frequency at which peaks in the phase response locate, that is, the deeper the flaw position is, the lower the excitation frequency of peak locates. The resolution in depth profiling is evaluated to be better than 0.2 mm. © 2003 American Institute of Physics.
Show PACS
81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing
75.50.Bb Fe and its alloys
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