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Regularization methods to assess the eddy current density inside conductive non-ferromagnetic media

Ribeiro, A. L. ; Pasadas, D. ; Ramos, H. ; Rocha, T.

Regularization methods to assess the eddy current density inside conductive non-ferromagnetic media, Proc Review of Progress in Quantitative Nondestructive Evaluation - QNDE, Baltimore, United States, Vol. 0, pp. 0 - 0, July, 2013.

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Abstract
This presentation describes two regularization methods that were applied to preview the current density induced in an aluminum plate. The images that resulted from the measurement of one magnetic field component by scanning the plate were used to determine the current density. The maps of the measured magnetic field were disturbed by the presence of some defects that had been previously machined. The scanning was performed using a constant field eddy current probe and a rectangular area including the defect was covered. With the constant field probe a sinusoidal excitation was imposed to the plate, being the amplitude and phase invariant under a limited space translation. The secondary magnetic field created by the eddy currents was measured using a giant magneto-resistance sensor that increased the sensitivity.
The inversion problem was solved using discrete Fourier transform methods with Tikhonov regularization and the total-variation method. Both methods produced equivalent results, but the Tikhonov regularization algorithm is very fast while the total-variation iterative method is quite slow. We conclude that Tikhonov method is appropriate to be programmed either using software or using hardware directly.