Visualization of defects in high-attenuation billet using back propagation of scattered waves

Defects in billet are inspected nondestructively by ultrasonic testing. Ultrasonic pulse-echo method is currently used. From the viewpoint of inspection capability, a method using time-of-Hight (TOF) and computerized tomography (CT) was proposed, but it needs a lot of transmissions to visualize defects. Then, we proposed a method using time-reversal (TR) waves which needs a few transmissions. However, the time-reversal method was not evaluated by high-attenuation specimen. The computerized tomography method can visualize defects in a specimen of stainless, which has high-attenuation. It is necessary to evaluate the time-reversal method by the specimen to study the capability. In this paper, we conducted an experiment of defect visualization using a specimen of stainless, which has a defect. As a result, the defect is visualized by the time-reversal method. To make the visualized image clearer, minor improvements are conducted in the algorithm. Improved image depicts the defect better. As a conclusion, it is found that the time-reversal method can visualize defects in high-attenuation billet.