Development And Receiver Test Of Piezoelectric Guided Wave Transducer Based On Relaxed Single Crystal

Pipeline ultrasonic guided wave detection has the advantages of far propagation distance,high detection efficiency and no need of large area to remove cladding layer,and has become a hotspot in the pipeline nondestructive testing field.Ultrasonic transducer as the main component of the detection system,its performance directly affect the detection results.At present,piezoelectric ceramics are usually used as actuators for ultrasonic transducers,but the new type of relaxation monocrystalline materials have higher piezoelectric properties and have great potential for development.Therefore,the development of relaxation single crystal ultrasonic transducer for improving the detection rate of pipeline defects and detection efficiency has great practical significance.This paper mainly through the experimental to study the influence of the matching layer material and thickness,the acoustic impedance of the backing layer and the encapsulation method on the echo coefficient,the signal-to-noise ratio and the tailing time of the transducer.The relationship between the input impedance of the transducer and the frequency is studied by Matlab numerical simulation.The main research work and achievements of this paper include:(1)Established the guided wave detection system.According to the dispersion curve,determined the guided wave mode of the transducer excitation.The evaluation standard of the performance of the relaxation single crystal transducer is established.The received amplitudes of the single-wafer with different sizes were studied by Ansys simulation.The simulation results show that the amplitude of the received signal increases slowly with the increase of the length of the relaxation single crystal after reaching 20 mm,and the 20 mm relaxation single crystal is used as the final size after comprehensive analysis.(2)According to the formula of sound intensity transmittance,studied the variation law of sound intensity transmittance in different matching materials acoustic impedance and different matching material thickness.The results show that the transmittance of sound intensity increases with the increase of the acoustic impedance of the matching layer,and changes with the thickness of the matching layer.When the thickness of the matching layer is small(<1mm)and the acoustic impedance is more than 5×106Pa·s/m,the material and thickness of the matching layer have little effect on the transmittance of sound intensity.Considering the attenuation of sound waves in the matching layer,the influence of different matching layer thickness on the weld echo coefficient,signal-to-noise ratio and tailing time is studied by experiment.The results show that the increase of the matching layer thickness in the low frequency region is beneficial to the improvement of the echo coefficient;In the high frequency region,the echo coefficient increases first and then decreases with the increase of the matching layer;The increase of the matching layer will reduce the signal-to-noise ratio;But had no significant effect on tailing time.(3)Four different matching layer materials were fabricated by different ratios of silicon carbide,epoxy resin and polysulfide rubber.The acoustic impedance of four kinds of backing was measured by pulse echo method.The effects of different acoustic impedance materials on the echo coefficient,signal-to-noise ratio and tailing time were studied experimentally.The results show that when the acoustic impedance of the backing layer is small,the echo coefficient increases with the increase of the acoustic impedance of the backing layer,and the signal-tonoise ratio is improved and the tailing time is not changed obviously.(4)According to the equivalent network model of the relaxation single crystal and the equivalent network model of the passive device,and the equivalent circuit of the relaxation single crystal,the numerical calculation method of the input impedance of the transducer is deduced,and studied the the input impedance of the transducer by Matlab software.The results show that the input impedance is less affected by the thickness of the matching layer and the backing layer,but decreases with the change of the excitation frequency.This paper through theoretical analysis and experiment researched the design of the relaxation single crystal transducer,and the overall detection performance of the relaxation single crystal transducer is verified by experiments.The research work has played a useful reference for the development of high performance relaxation single crystal transducers.