Research And Design Of High-speed Railway Bridge Crack Detection Technology Based On Ultrasonic Phased Array

As a hub of transportation,the safety of bridges is of utmost importance.However,with the intensification of transportation tasks and the coupling of complex factors such as earthquakes and environmental erosion,bridges are prone to damage during operation.Among them,bridge cracks induced by fatigue damage,steel wire corrosion,and concrete cracking are the most common.Therefore,it is particularly important to efficiently detect and repair bridge cracks.This research topic has been going on for many years.Scholars at home and abroad have put forward many methods for evaluating the safety of contact and non-contact bridge structures such as ray method,infrared method,but there are common problems of high cost and low efficiency.Ultrasonic phased array technology has the advantages of sound beam deflection and dynamic focusing.The technology has high detection efficiency and reliable test results.Besides,the image is intuitive.Therefore,this paper finally chooses to use phased array technology as a means of detecting cracks.By analyzing the data requirements of the phased array imager,we found that the most important data is the amplitude and time of the echo signal,because these are the cores of the A-scan image,and other forms of images are formed on the superposition of multiple sets of A-scan data.When performing image processing in the later stage,we only need to label different amplitudes with different colors.Based on the above analysis,this thesis uses FPGA as the control core to build a phased array transceiver system.The key transceiver circuits and received signal processing algorithms are researched and designed in this paper.Finally,this paper completes the extraction of the amplitude information of the echo signal in order to provide it to the phased array imager.The main works are as follows:1.Study the related theory of ultrasonic acoustics and the principle of ultrasonic phased array technology.To lay a solid theoretical foundation for the design of the follow-up detection system,the principle of phased array emission reception,the process of sound beam deflection and focusing,basic scanning methods and imaging forms were studied.Besides,the influence of array element parameters on sound beam pattern also was emphatically analyzed.2.A detection system with FPGA as the control core is designed.After repeated selection,the paper designs a phased array front-end transmitting and receiving circuit,and uses the FPGA internal phase-locked loop(PLL,Phase-Locked Loop)to achieve a delay accuracy of 2.5ns.The front-end circuit includes a high-voltage excitation generating circuit,a limiting circuit,a preamplifier circuit with the LMH6629 chip as the core,a filter circuit,and a gain amplifier circuit with the AD603 chip as the core.Finally,each circuit module has been simulated and verified.We find that the circuits achieve the expected effects.3.The key algorithms for echo signal processing are researched and designed.In the beamforming algorithm,This thesis compares the difference between the weighting of constant coefficients and the weighting of covariance coefficients.And simulation shows that the MVDR(Minimum Variance Distortionless Response)algorithm can suppress incoming interference and noise more effectively.In the process of moving the signal from high frequency to low frequency,This thesis uses FPGA to realize the digital quadrature demodulation algorithm,and better extracts the signal amplitude envelope for subsequent sampling and storage.Demodulation maximizes the use of FPGA built-in IP core and increases processing speed.Since MATLAB has powerful computing and processing capabilities,this paper uses ZYNQ7020 chip and MATLAB to design and simulate the algorithm in detail.