Research On Phased Array Ultrasonic Sparse Total Focusing Method Imaging Technique

Ultrasonic phased array total focus imaging method(TFM)is used to analyze the array echo data and realize the detection and evaluation of the defects by the way of off-line calculation.Compared with the conventional ultrasonic phased array testing technology,the image is more clear and the defect characterization ability is stronger,but its practical industrial application is limited with the problem of the large amount of full matrix data and long imaging time.In this paper,the sparse array was optimized by the almost difference set and genetic algorithm,and the sparse total focus imaging based on the virtual source was realized by constructing the virtual source.The two-layer medium total focus imaging algorithm was built based on the one-layer medium total focus imaging algorithm,the imaging quality of a variety of sparse total focus methods were analyzed by experiment.The main work is as follows:(1)Ultrasonic phased array imaging simulation was performed,the influence of element directivity function on the image quality of the full focus method was studied.And the post-processing imaging algorithms of the conventional ultrasonic phased array testing technology and TFM were discussed based on the full matrix data model.The imaging simulation of the conventional ultrasonic phased array testing technology and TFM was studied using Field Ⅱ,and the imaging performance was quantitatively analyzed by array performance index.Finally,the influence of element directivity function on the image quality of the full focus method was studied.(2)The sparse total focus imaging model based on the virtual source was built.The sparse array was optimized by ADSGA,and the sparse total focus imaging model based on the virtual source was built by constructing the virtual source instead of the array element in the actual sparse array.The full matrix data of one-layer medium were collected and analyzed,then the defect imaging amplitude and detection accuracy of the sparse total focus method,the sparse total focus method based on virtual source and TFM were discussed.(3)The corrected sparse total focus imaging model of two-layer medium was built.The propagation path and propagation time of ultrasonic in two layers were calculated based on Fermat principle,and a TFM model of two-layer medium was built.What’s more,with the same effective aperture as the whole array,the sparse total focus imaging model of two-layer medium was built by the sparse array design technique.Finally,with the experimental analysis,it was verified that for a 32-element transducer,when the number of the sparse transmitting elements reaches 8,the error between sparse matrix and full matrix is less than 5.2%,while the computational efficiency is nearly fourfold improved.In this paper,the number and layout of elements were optimized by sparse array design techniques,the sparse total focused method is developed.The efficiency of total focus methods is improved,and the sparse total focuse imaging of two-medium was studied.The results provide a theoretical basis for the indusrial application of ultrasonic phased array total focus imaging technology.