Image Reconstruction of Defects in Metallic Plates Using a Multi-Frequency Detector System and a Discrete Geometric Approach

This work presents an inversion procedure for the image reconstruction of defects in metallic plates using eddy current testing. We performed a minimization technique based on a discrete geometric approach for eddy currents, and an iteration procedure driven by sensitivity data. In particular we propose a multi-probe detector system excited with multi-frequency signal, in order to increase the number of sensitivity data. In this way we improve the accuracy and efficiency of the inverse procedure

I. Multi-Frequencies Detector System

In general the image reconstruction of defects in a material has been derived by means of suitable detector systems with several probe-coils [1] [2]. The multi-probes systems provide many sensitivity data, but in some cases they are insufficient for an accurate resolution of the inverse problem. In this work we used a multi-frequency excitation for each probe-coil. In particular we used an input current for a suitable number of frequencies and we calculated for each frequency the voltage output. So the number of sensitivity data is the product between the number of the probe-coils and the number of the frequencies considered.