Experimental Research On High Sensitivity Ultrasonic Guided Wave Receiving Transducer

Ultrasonic guided wave testing technique has been the research hotspot in the field of pipe nondestructive testing. As an important component of the ultrasonic guided wave testing system, relative sensitivity of receiving type transducer is directly related to the defect detection rate. Because of matching layer and backing layer, Relative sensitivity of receiving transducer change during the process of packing piezoelectric ceramic, which are usually pasted to pipe’s outer surface in the laboratory environment, into receiving transducer. So, it’s very importance to study the matching layer and backing layer to develop high relative sensitivity receiving transducer.In order to get high relative sensitivity receiving transducer, whose relative sensitivity will be equal to or higher than piezoelectric wafer, experimental study method will be used in this paper to study how the matching layer and backing layer affect the receiving transducer’s receiving performance parameters such as relative sensitivity. Experiments have been conducted to detect artificial simulated defect in pipe using receiving transducer developed in this paper, compared with the piezoelectric, ceramic PZT-5 transducer showed higher relative sensitivity. In this paper, the main work and research content are as follows:1) The method of transmission line has been proposed to evaluate receiving performance of transducer, transmission method of test system have been established. By applying the method of transmission line, receiving performance of piezoelectric ceramic piece (PZT-5 type) and new type of ferroelectric relaxation-magnesite niobate single crystal lead acid crystals (PMN-PT) have been compared.2) On the basis of analyzing the classical matching layer design theory, the ultrasonic guided wave transducer matching layer design method have been put forward, and through the experimental method, with different thickness of the stainless steel sheet and organic glass, receiving performance of PZT-5 have been studied, the results show that when the thickness of 0.15 mm stainless steel act as the PZT-5’s matching layer, receiving performance parameters such as relative sensitivity and signal-to-noise ratio could meet the standard parameters.3) Through experimental method, the influence of backing layer with different proportions of silicon carbide, epoxy resin and thiokol on receiving performance have been studied, simple transducer with matching layer and backing layer have been made, through the transmission line method the simple transducer’s receiving performance has been assessed. Experimental results showed that with the increase of the proportion of silicon carbide, lowering the relative sensitivity of simple transducer; the lower proportion of silicon carbide, the smaller the noise amplitude value was and the lower signal to noise ratio was; When the silicon carbide, epoxy resin, and the proportion of thiokol reaches 3:2:1, simple transducer’s receiving performance meet the requirements of standard parameters.4) Through experimental method, detection capability of PZT-5 piezoelectric ceramics and piezoelectric ultrasonic guided wave transducer have been compared via detecting section area defect rate 20% artificial simulated defect in an 18m pipe, the results showed that the transducer’s relative sensitivity to artificial simulation was higher than the piezoelectric ceramic piece.Conclusion:Receiving transducer’s matching layer material and thickness and backing layer material have been confirmed to get high relative sensitivity, and ultrasonic guided wave high relative receiving transducer have been made; experiment have been conducted to detect artificial simulated defects and it turned out that the receiving transducer’s relative sensitivity was higher than piezoelectric ceramic.