In the industrial fields, many high temperature structures that require a non-destructive inspection\nexist. However, there are currently few sensors that can carry out non-destructive testing in a\nhigh temperature environment. In particular, the ultrasonic sensor is normally not used at over 50\ndegrees Celsius. Also, a special sensor for high temperature is currently available, but there are\nvarious constraints; it has not yet reached a level that is useful in industry. Therefore, we have\nbeen developing a new sensor system using a long waveguide which can transmit an ultrasonic\nwave from a long distance. Especially, this study focuses on applying the developed technique to a\npipe which is used in a nuclear power plant. Therefore, the best rectangular-shaped waveguide\nwas studied and attempted to be wound around a pipe to be driven by an acoustic source of a\nguide wave. Finally, the L (0, 2) and T (0, 1)-mode guide waves were successfully detected by optimizing\nthe shape of the opposite edge of the rectangular-shaped waveguide that could detect the\nreflected signal from an artificial defect machined into a test pipe.
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