Research On The Defect Detection Technology For Plate Structure Based On The Electromagnetic Ultrasonic Guided Waves

Safe operation of power station has been the focus of the electric power industry, the safety of power station equipment depends on the integrity of its structure, so it is very important to detect the defects of power station equipment. Compared with the traditional piezoelectric ultrasonic detection technology, electromagnetic ultrasonic guided wave detection technology was an emerging defect detection techniques with the advantages of coupling agent free, high detection precision, surface detection without pretreatment etc. which has broad development prospects.The purpose of this paper is to design electromagnetic ultrasonic transducer for detection of plate and to do experimental study of the influence of parameters on its performance based on the propagation characteristic of ultrasonic guided wave and the work mechanism of electromagnetic ultrasonic transducer. Then, experimental study on the defect imaging detection technology of plate is carried out based on the array of transducers. The main research work is as follows:Firstly, the generation and propagation characteristics of the electromagnetic ultrasonic guided waves were studied, and the group velocity dispersion curves of the ultrasonic guided wave modes were calculated. The mechanism of the electromagnetic ultrasonic transducer was analyzed, and the electromagnetic acoustic transducer was designed, which adopts the structure of spiral coil to excited circumferential consistent single SO mode Lamb wave.Secondly, a complete defect detection experiment system was built, and the effect of frequency on the transducer was researched, then an experimental research on effects of the helical coil electromagnetic ultrasonic transducer’s parameters on its performance was carried out; Directional experiment for the electromagnetic ultrasonic transducer was done in this paper to verify its circumferential consistency.Finally, according to the theory of phase controlled virtual focus, experimental study of the defect imaging detection technology in plate was carried out, and the influence of one dimensional linear array in different number and element spacing on the imaging effect was analyzed, then the 2 d L array’s imaging effect was studied, because of the linear array have mirror effect.