Remote imaging of plate-like structures with E-camera

Thin walled large structures are widely used for pipes, bridges, wings and body of aircrafts, and automobile bodies. To maintain such large structures, in addition to visual inspection, non-destructive testing with X-ray and ultrasonic is periodically implemented for essential parts. In ultrasonic non-destructive testing, ultrasonic pulse echo technique is generally used, in which plate thickness is measured using a contact ultrasonic transducer by the flight time of pulse echo signal. Although the conventional widely-used technique is reliable and highly accurate in thickness measurements, it is not suitable to inspect whole areas of large structures due to its small measurement area underneath a transducer. Guided wave inspection has been considered recently as an effective inspection technique for such large platelike structures. Guided waves are ultrasonic modes propagating along such waveguides as plates, pipes, bars, and railway rails. Guided wave inspection has been highly expected as an efficient technique for long range inspection. However, there still have some issues, one of which is that defect echoes cannot be obtained for a defect in a desired size due to the use of low -frequency range for long-range propagation. Therefore, the authors have developed defect imaging for plate-like structures using a scanning laser source technique [1-3]. Because the imaging technique is established with a non-contact and fast measurement and has a potential to be a very easy imaging technique like optical and infrared cameras, we call it E-camera. This paper describes the principle of defect imaging with E-camera first and introduces some results of the defect imaging.