Research On Ultrasonic Testing Technology Based On Linear FM Signal

Since the beginning of the21century, modern industry towards the rapid development ofsophisticated direction in which the ultrasonic testing technology plays an extremelyimportant role, and countries in the world are focus on UT research as the crucial technology.Ultrasonic testing as most widely used non-destructive testing means, basically is to useultrasonic sound propagation in the medium of subjects and attenuation characteristics todetect whether there are the internal defects in the target, and to make a location, qualitativeand quantitative analysis. Ultrasonic testing not only has an important meaning in the modernindustrial development, and in transportation, medical, oil exploration domain has theory andapplication value, also has broad application prospects in the military and civilian. On theother hand, the rapid development of the modern digital signal processing technology andintegrated electronic technology provide more research and development space for ultrasonictesting technology.For now, the pulse echo method is the most widely used method of ultrasonic testing;however, quantitative testing cannot achieve high precision through this method, as well ashigh missing rate of special defects and difficulty of blind spot detection. These disadvantageslimit the application of ultrasonic testing in many high-tech and sophisticated fields. Thus,this thesis research for the deficiencies of the traditional ultrasonic testing methods and makesome improvements, mainly including the following two aspects:1. Ultrasonic testing method based on distributed multi-probe: Using multiple distributedultrasonic probes to capture ultrasonic echo signals from different propagation paths, andestablishing the mathematical model of the target’s defect location through ultrasonic echosignals’ time of flight (TOF) from different propagation paths as parameters. At last,according to the delay of each path of ultrasonic signals, we can estimate the quantitativeinformation of the defect.2. Ultrasonic signal detection method based on linear frequency modulation (LFM)signal and its high-precision frequency estimation: No longer dependent on the characteristicsof the sound pressure which be used in the traditional ultrasonic testing method.Comparatively, the new method use linear frequency modulated ultrasonic signal as emission source, and make a coherent processing for ultrasonic echo signal; afterwards, estimate thefrequency of low-frequency sine part of the echo signal through the frequency estimationalgorithm of rational combination of spectrum lines. This method estimate ultrasonic echodelay through frequency characteristics of the echo signal, resulting in higher reliability andaccuracy of detection.Finally, combining these two aspects of the research content, I designed a completeultrasonic testing system which based on linear FM signal and distributed multi-probe at theend of this paper. Simulation results show that the ultrasonic signal detection method based onlinear FM signal and its high-precision frequency estimation can work reliably in thedetection environment as low as-20dB SNR, and the precision is far superior to traditionaltesting methods. In the design of the complete system solution, the simulation results alsoconfirms the performance advantages of the new method in the reliability and accuracy; onthe other hand, the designed system has excellent performance on the aspect of special defectsdetection such as transverse defects and longitudinal defects.