ULTRASOUND COMPUTED TOMOGRAPHY BY LINEAR ARRAYS WITH USED THROUGH TRANSMISSION TESTING METHOD

The article describes few view through-transmission ultrasound tomography using linear gratings. Obtaining initial data is based on alternate radiation by each element of the emitting antenna array and simultaneous reception by all elements of the receiving antenna array. This results in a set of shadow images from different angles, the number of which is equal to the number of elements of the radiating array. The tomogram reconstruction process consists in calculating the signal amplitude in each pixel of the monitoring zone as the sum of signals from several sources passing to a specific receiver through this pixel. The defect decreases the signal amplitude at the receiver, which is linearly related to the area of the shadow at the receiver. To assess the magnitude of the signal attenuation, the defect detection coefficient was used, calculated as the ratio of the signal amplitude at the receiver that passed through the defect to the signal amplitude at the receiver in the absence of a defect. The use of a limited set of angles leads to a deterioration in the quality of the tomogram and, as a result, errors appear in the form of lines from emitters to receivers intersecting at the location of the defect. To improve the quality of the tomogram, a Gaussian filter was applied, after which the manifestation of artifacts was reduced, which made it possible to more accurately determine the coordinates and dimensions of the defect. In the article, a model study was carried out and the use of a filter with different parameters was tested on experimental data. The theoretical range of variation of the filter parameters is calculated and the optimal parameters are determined, at which the best tomogram quality is obtained. The simulation results are given for one and two reflectors located in the control zone. The resolving power of the system consisting of receiving and transmitting antenna arrays with 16 elements is determined. The resolution was 12 mm for arrays of circular piezoelectric elements 3 mm thick and 6 mm in diameter with a 10 mm distance between the centers of neighboring piezoelectric elements and 400 mm between the receiving and emitting gratings.