Research On The Technique Of Ultrasonic Guided Wave With Arbitrary Waveform Excitation

High efficiency and accurate seamless rail temperature stress detection and flaw detection is an important technology to ensure the safe operation of high speed railway. Because the ultrasonic guided waves can get far transmission distance and cause the whole particle vibration of rail cross section, the online monitoring technique for rail condition based on ultrasonic guided wave is getting more and more attention. A key to the application of ultrasonic guided waves is to control the guided waveform in the rail accurately, then the change in shape and speed can be measured, the critical condition of rail such as temperature stress and defect can be detected. In this paper, the control method of guided wave was studied from two aspects:the structure of the guided wave transducer and the excitation signal. With the ANSYS finite element simulation and the experiments, the strategy of direct coupling of piezoelectric crystal and time reversal waveform control were proposed which led to good results.First of all, the propagation of ultrasonic guided waves in flat plate and rail was simulated using the finite element method. The experiment was setup at the same time. The simulation results and experimental results have excellent similarity. That verified the feasibility of the finite element simulation method.The 35kHz optimal excitation frequency and excitation position in ANSYS simulation were confirmed by theory analysis, and then theory results was verified by simulation. In the paper, the model of variable amplitude bar transducer, sandwich transducer and piezoelectric transduce were setup. According to the simulated results, the piezoelectric transduce was finally used in the subsequent research.The influence of the damping to the lamb wave propagation in tablet was analyzed through simulation analysis. The optimal damping value was determined. The results obtained in the simulation are in agreement with the curves obtained in the experiments. Based on this, the feasibility of time reversal was verified. In the end of the paper, through the use of time reversal method and the finite element simulation of ultrasonic guided wave transducer, the arbitrary waveform excitation was obtained, which take the 5 cycles Harming window modulated sine signal with an amplitude of 1 as an example, improving the precision of the received waveform.