Study On Ultrasonic Imaging Based On Two-dimensional Planar Array In Air

Ultrasonic imaging has the advantages of non-ionizing radiation,good repeatability,economy and practicality,so it is widely used in medical diagnosis,nondestructive testing,sonar detection and other fields.Compared with optical imaging,ultrasonic imaging is a good detecting method in smoke,dark and other environments,which overcomes the shortcomings and defects of optical detection in this environment,and provides a new detecting method for scene perception and reconstruction as well.At present,the ultrasonic imaging in air mainly depends on few ultrasonic transducers or a one-dimensional array.However,this sensing method is difficult to obtain threedimensional information of the detecting object,and has poor real-time performance.In contrast,the two-dimensional ultrasonic array can ensure the real-time imaging and obtain more accurate information of reflected waves.It is a powerful,efficient and accurate detecting tool for ultrasonic three-dimensional imaging.Therefore,the study of ultrasonic array imaging is of great significance.In view of the increasingly mature technology of linear array imaging,a scanning detecting system based on a two-dimensional array of 16 × 16 with good synchronization is set up in this study.By the law of ultrasonic array imaging under solid and liquid,a reconstruction scheme of a two-dimensional image based on timedomain amplitude signals in air is proposed.The main contents of this research are as follows:1.According to the law of time-lapse focusing,a mathematical model of a 16 × 16 receiving array and a 2 × 2 synchronous transmitting array are established in this study.At the same time,the characteristics of the sound field in air are simulated by Field II and COMSOL software,which confirms that the focus lateral resolution of the receiving array in the range of 1 m is less than ± 5 °,and theoretically,the features with a diameter more than 8.4 mm can be accurately identified.2.A PC-based ultrasonic imaging detecting system with a host program for parameter setting and human-computer interaction is built,and the usability of the system by a synchronization testing is verified.Then,an experiment of the twodimensional imaging based on planar scanning is designed,and the experiment of the measured objects with different spatial positions for each testing group are carried out.3.A data processing scheme based on the back-projection(BP)analytical reconstruction algorithm is proposed,which can restore higher-resolution twodimensional images based on the original time-domain amplitude signals,with a pixel resolution of 640 × 640.The reconstructed images can be identified by the features of reflected waves of basic geometries or simple geometric combinations.By the comparative analysis between the experimental results and the simulation,the results of the experiment demonstrate a good ability of two-dimensional imaging in the range of 1 m away and deflecting angle of 30 °.The proposed scheme is effective and feasible,which has certain reference value for the research of the ultrasonic imaging in air.