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Eddy Current Interaction With An Ideal Crack, Part I: The Forward Problem, John R. Bowler
Eddy Current Interaction With An Ideal Crack, Part I: The Forward Problem, John R. Bowler
John R. Bowler
The impedance of an eddy-current probe changes when the current it induces in an electrical conductor is perturbed by a flaw such as a crack. In predicting the probe signals, it is expedient to introduce idealizations about the nature of the flaw. Eddy-current interaction is considered with an ideal crack having a negligible opening and acting as a impenetrable barrier to electric current. The barrier gives rise to a discontinuity in the electromagnetic field that has been calculated by finding an equivalent electrical source distribution that produces the same effect. The choice of source is between a current dipole layer …
Eddy-Current Interaction With An Ideal Crack. Ii. The Inverse Problem, John R. Bowler, David Harrison, Steve Norton
Eddy-Current Interaction With An Ideal Crack. Ii. The Inverse Problem, John R. Bowler, David Harrison, Steve Norton
John R. Bowler
Eddy-current inversion is the process whereby the geometry of a flaw in a metal is derived from electromagnetic probe measurements. An inversion scheme is described for finding the shape and size of cracks from eddy-current probe impedance measurements. The approach is based on an optimization scheme that seeks to minimize a global error function quantifying the difference between predicted and observed probe impedances. The error minimum is sought using a standard descent algorithm that requires a knowledge of the gradient of the error with respect to a variation of the flaw geometry. Computation of the gradient is based on a …