Ultrasonic Synthetic Aperture Imaging Algorithm For Oblique Crack In Double Layer Media

Ultrasonic synthetic aperture imaging algorithm is an ultrasonic signal post-processing method,widely used in industrial non-destructive testing because of its characteristic that its imaging resolution does not change with the location and depth.In recent years,many colleges and universities and research institutions have also joined the research of optimizing ultrasonic synthetic aperture imaging algorithm,but these studies focus on single-layer,can not be used in multi-layer media.In this paper,the improved algorithm of ultrasonic synthetic aperture imaging in the case of double-layer media was studied.The main work of this paper includes the following two points:Firstly,the theoretical principle of time domain ultrasonic synthetic aperture imaging is analyzed in detail,and the inverse thinking of the method is analyzed.In order to correspond to the positive process in the actual detection,this paper adopts the computer graphics perspective,The delay rule and the full range dynamic focus process are interpreted as the operation of drawing a circular arc on the reconstructed image.In this thesis,the circular transformation method of grating graphics is introduced,and the forward mapping algorithm of time domain synthetic aperture algorithm is studied.It is proved that the forward mapping algorithm is shorter than the traditional time domain synthetic aperture imaging algorithm,and the average speed is twice as fast as that of the former.Then,according to the synthetic focusing detection principle of double layer medium,the time-domain synthetic focusing algorithm of traditional technology with the realization process of defect detection of double layer medium ray tracing,from the view of the forward mapping process as painting double medium refraction ray trace curve between the mobile operation process in the reconstructed image,and analyzed the tracking algorithm fold the ray trajectory.The algorithm does not need to obtain the position of the refractive index of each refractive index,so as to avoid the large number of iterative operations required by traditional ray tracing technology.At the same time,the improved algorithm does not need to calculate the effective length of the synthetic aperture,so it can avoid the error caused by the imaging result of the parameter in the reconstruction process of the double layer medium.In this algorithm,the linear scan conversion algorithm in computer graphics is introduced.The experimental results show that the imaging efficiency of the proposed algorithm is 15 times higher than that of the conventional synthetic aperture focusing and ray tracing technique.