Research On Ultrasonic Sparse TFM Phase Weighted Imaging Method Based On Virtual Source

Ultrasonic phased array testing,as the most widely used method in the field of non-destructive testing,plays an important role in the industrial field.Total focus method(TFM)is an ultrasonic phased array imaging method.Compared with the traditional phased array imaging method,TFM has a larger dynamic focus range and higher spatial resolution,and has become one of the mainstream methods of phased array detection.However,TFM imaging needs to process a large amount of full matrix data,which leads to a relatively long imaging time,and greatly limits its application and development in the industrial field.The sparse method can improve the computational efficiency by reducing the amount of data,but the resolution and intensity of the sparse image are very low.To solve this problem,this paper proposes a sparse TFM phaseweighted imaging of ultrasonic phased array based on virtual source,which can greatly improve the calculation efficiency and provide better imaging quality than conventional TFM.First,the array radiated sound field is used as the optimization objective function,and the phased array sparse array is optimized by genetic algorithm(GA)to perform sparse imaging.The sparse method can greatly reduce the amount of data and improve the calculation efficiency,but the reduction of the amount of data will also cause the resolution and signal-to-noise ratio of the sparse image to decrease,which affects the quality of the detected image.Aiming at the problem of quality degradation of sparse images,virtual source theory is used to enhance sparse images and improve image resolution.The virtual source array is composed of multiple virtual sources,and the location of each virtual source is determined by the specific layout of the sparse array.Although the quality of the sparse TFM image of the virtual source is greatly improved compared to the sparse image,it is still lower than the quality of the conventional TFM image.In order to solve this problem,according to the phase distribution characteristics of the defect signal and noise signal in the ultrasonic detection signal,a phase coherence factor is constructed to weight the sparse TFM image of the virtual source.This method can enhance the defect information while weakening the signals of other imaging areas,and eliminate the artifacts around the defect.And greatly improve the signal-to-noise ratio of sparse images and improve image quality.Through the detection experiments on standard phased array test blocks,train wheels and rail defects,the adaptability and imaging effect of the optimization method to different scenarios and types of defects are analyzed.Experimental results show that the sparse TFM phase-weighted imaging of ultrasonic phased array based on virtual source proposed in this paper can improve the quality of sparse images and eliminate artifacts around defects.Compared with conventional TFM,this optimization method can not only greatly improve imaging efficiency,but also provides better imaging quality than TFM.