Extraction of crack indications from ECT signals by using signal phase characteristics

This paper shows phase characteristics of crack indications obtained with a multi-coil ECT probe, and proposes a method to reduce noise and extract crack indications from the detection signals of this multi-coil ECT probe based on these phase characteristics. Because this multi-coil ECT probe performs two kinds of scanning patterns: U-scan and T-scan, and obtains two sets of signal distributions for one scanning area simultaneously, the proposed method uses a two-stage process that includes so-called a main filter and a sub filter. While the main filter uses the phase information of the same scanning pattern by which the target signals are obtained, the sub filter uses the phase information of the other scanning pattern for the target signals. Using these two filters imposes more strict conditions on extracting crack indications so as to reduce more noise. (author)