Ultrasonic imaging for appearance of vertical slot by reverse time migration

The problem in traditional industrial ultrasonic imaging methods is the difficulty to obtain the appearance or the shape of defects inside solid materials although the methods have the ability to detect and determine the position and lateral dimensions. These special defects, like the vertical slot or crack, are typical examples. Based on the multi-element array ultrasonic technique, the numerical and experimental studies on reverse time migration (RTM) ultrasonic imaging for metalic materials are carried out. In this paper, the objects in detecting and imaging experiments are aluminum samples with slot intersecting the bottom or interior slot, which cannot be effectively detected by traditional ultrasonic methods. First the single component ultrasonic field for RTM imaging is studied to obtain RTM ultrasonic imaging results based on numerical simulation and experimental measurements using a multi-element array ultrasonic testing system. Then, the RTM imaging techniques based on multi-component ultrasonic displacement field detection and converted shear wave separation are further studied, and a new approach using a multi-component laser interferometer is proposed. Numerical simulation results verify that the multi-component RTM imaging reconstructive method can overcome the shortcomings of single component method, and obtain better image quality.