Flaw Inspection of Aluminum Plates with a Non-contact Ultrasound Visualization System Using Laser Ultrasound Generation and an Air-coupled Sensor

Our group had previously proposed a defect visualization technique in which the animation of ultrasound propagation is created even on non-flat surfaces from the waveforms recorded using a generation laser scanning system. Recently, we developed the system to be completely non-contact by employing an air-coupled ultrasound transducer as a receiver instead of the conventionally used contact piezoelectric transducer. In this research, we used this non-contact ultrasound visualization system to inspect aluminum plates with such flaws as slits or thinning. Several visualized images of guided waves propagating on the specimens were obtained, including those visualized after eliminating the forward traveling wave using a synchronizing differential method; the flaws were successfully detected visually in the images.