Two-layer Medium Ultrasonic Phased Array Total Focusing Method Imaging Based on Sparse Matrix

Ultrasonic phased array total focusing method has the advantages of high accuracy and dynamic focusing in all regions, but the problem of long imaging time limits of the actual industrial application. In order to improve the imaging efficiency of phased array total focusing method, taking commonly used wedge coupling detection for example, the delay time of all array elements are calculated in two-layer medium based on Fermat principle, a two-layer medium phased array total focusing method is built. By reducing the number of transmitting/receiving elements, with the same effective aperture as the whole array, the weighting function of transmitting/receiving elements distribution is studied, and a two-layer medium corrected sparse total focusing method is proposed. Taking the side-drilled holes with arc distribution for example, two images of total focusing method and sparse total focusing method in the two-layer medium are formed, and the effects on defect quantitative precision and calculation efficiency are discussed when the transmitter array is sparse. The results show that the corrected sparse total focusing method can improve the imaging efficiency obviously in the meanwhile the imaging accuracy is kept. 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.