For characterizing the flaw, we calculate the impulse response of the system by using a deconvolution method (conjugate gradient)(2) associated with an exponential weighting function to remove the measurement noise on impulse response. We can see Figure 2 impulse responses for different flaws at two depths.
Such responses can be used for characterizing the flaws.
In the full paper, we will present in detail the numerical method, and all the experimental results (different sizes and depths for the flaws, influence of the lift off).
 Figure 1: experimental system |  Figure 2: impulse response for different flaws. |
References.
1. T.KSARKAR, F.I.TSENG, S.M.RAO,S.A.DIANAT,B.Z.HOLLMANN: "Deconvolution of impulse response from time-limited input and output: theory and experiment", I.E.E.E Transactions on instrumentation and mesurement, vol 34 no 4, pp 541-546, December 1985.
2. F.THOLLON:" Conception et optimization de capteurs a courant de Foucault pour la detection de defauts profonds dans des materioux amagnetiques" Ph D Thesis, Ecole Centrale de Lyon, France, Janvier 1995.
Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00
Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:
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