Abstract
Eddy-current testing (ECT) has been widely applied in manufacturing to the inspection of defects inside conducting materials. It, however, is still difficult to obtain accurate depth information on deep cracks and to detect cracks on the reverse sides of thick structures by using the technique. We conducted a theoretical analysis based on 3-D solutions of Maxwell equations to determine the optimum exciting frequencies and suitable positions of a sensor for both depth detection and reverse-side detection. An ECT probe consisting of a single-direction exciting coil with a spin-valve-type giant magnetoresistive (SV-GMR) sensor was employed in experimental inspection of 12-mm-and 22-mm-thick stainless steel (SUS) plates with 67% deep and 77% deep cracks, respectively. The experimental results show good agreement with our theoretical analysis. Thus it is confirmed that both the ECT probe and the theoretical analysis proposed in this paper are capable of detecting defects in a thick SUS plate.
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