Study On Performance Optimization Of Piezoelectric Ultrasonic Transducer In Condition Monitoring Of In-service Rail

With the improvement of railway mileage,traffic density and train volume in China,it is urgent to optimize and upgrade the real-time rail condition monitoring technology.Piezoelectric ultrasonic transducer is the core component of the monitoring system,and its performance will directly affect the monitoring results.This paper aims to improve the technical level of rail condition monitoring,and studies on three aspects of ultrasonic transducer’s "trailing" signal suppression,broadband impedance matching and high-voltage pulse driving,and strives to optimize the performance of piezoelectric ultrasonic transducer in rail condition monitoring in service.1.In order to suppress the "trailing" signal caused by the characteristics of the ultrasonic transducer,a new method of fitting and optimizing the BVD model parameters of ultrasonic transducer is explored,and the accurate BVD equivalent mode is established.Secondly,the transmitting response of ultrasonic transducer under different excitation signals is studied,and the optimal excitation signal is obtained.Based on the principle of wave superposition,a phase-locked amplification method that doubles the amplitude of the "trailing" suppression out-of-phase signal is proposed,and the optimal number of signal superposition periods is determined.and then a fivelevel excitation signal combining excitation signal and out-of-phase signal is designed.The simulation and experimental results show that the five-level combined excitation signal can better suppress the "tailing" effect of ultrasonic transducer and improve the damage detection performance of ultrasonic transducer.2.In response to impedance mismatch between the ultrasonic transducer and excitation source,as well as frequency deviation caused by loading,the broadband impedance matching network is studied in this paper.Four matching networks are designed based on the impedance matching principle,and by analyzing the performance of different networks,the second-order L-type network is determined to be the optimal network.Based on the transfer function of the matching network,the realization process of broadband matching is studied and the optimal parameters of the network are determined.The results from experimental platform of pitch-catch show that the broadband impedance matching network designed in this paper can significantly improve the active power,working bandwidth and transmitting intensity of the ultrasonic transducer at the transmitting end,and the ultrasonic transducer can achieve good transmitting state within the working bandwidth.3.In order to realize the emission of the five-level excitation signal designed in this paper and improve the performance of ultrasonic transducer for long-distance rail monitoring,a high-voltage driving circuit is designed.The design of inverter circuit refers to the multilevel inverter technology in the industrial field,and selects cascaded H-bridge topology to achieve five-level output.High-voltage output abandons the design scheme of pulse transformer,and directly inverts the high-voltage power supply to realize high-voltage output,so that the driving circuit is easy to combine with the impedance matching circuit.In addition,the design process of other peripheral circuits is also described in detail.Finally,the feasibility of the design scheme is verified through simulation,and the PCB circuit board of the driving circuit is trial-produced,which lays the hardware foundation for the follow-up work.