Study of two-dimensional inspection of thin sheets using Lamb wave

The Lamb wave inspection technique with a tire transducer has been used for the on-line defect inspection of steel sheets. However, the conventional Lamb wave inspection process has the following two problems. One is the existence of wide dead zones that appear in the near and far positions for the tire transducer. The other is misdetection due to parasitic echoes or electrical noises. Therefore, we have developed a method that could solve these problems using the two-dimensional signal characteristics. As a result, the dead zone and the misdetections can be reduced. This paper describes the measurement principle, the algorithm of the signal processing and the distinction logic. The results showed that the dead zone was reduced to 100 mm from the strip edge and the misdetection was eliminated.