Research On Encoding And Decoding Technology And Application Of Orthogonal Complementary Golay Sequence For Ultrasonic Inspection

During the ultrasonic inspection process,coded excitation is the key technology for improving detection range and measurement resolution.Among all types of coed sequence,the ideal decoding performance of coded excitation appears only by orthogonal complementary Golay code.This paper is entitled by ‘research on encoding and decoding technology and application of orthogonal complementary Golay sequence for ultrasonic inspection',in which the followings are studied: basic theory of orthogonal complementary Golay code,multiple orthogonal complementary Golay sequence(MOCGS)coding and decoding technology,and single-transmitted MOCGS coding and decoding technology and implementation.The research,which is funded by Scientific Instruments Development Program of NSFC(2013YQ23057),is valued by its study on improvement of coding efficiency,SNR,flexibility and its practicability.This paper research on encoding and decoding technology and application of orthogonal complementary Golay code for ultrasonic testing.Based on binary and multielement coded excitation methods,the progress of the study is summarized and the content is confirmed.The detailed content includes the followings:(1)Excitation approaches of orthogonal complementary Golay sequence.Based on the very property of orthogonal complementary Golay code and the correlation of sequence A and B,general term recurrence method and cross-interpolation method are put forward since these two methods can be easily carried out by FPGA.Hardware structures are analyzed and built in terms of generation,transmission and reception modules,respectively.Then code gain and excitation efficiency are analyzed in order to give a foundation to the multiple code excitation technique of orthogonal complementary Golay sequence.(2)MOCGS coding and decoding technology based on orthogonal complementary Golay sequence.In terms of coding principles,transmission module is studied including fundamental wave generation,code element R-times interpolator and convolution modulator.In terms of decoding principles and approaches,matched filtering and unmatched filtering are studied respectively.Decoding performance is analyzed for the designed matched filtering on pulse compression,with valuing the relation between echo side lobe and main lobe.The study result indicates that smaller PSNL is,higher SNR is.(3)Single-transmitted MOCGS coding and decoding technology.MOCGS excitation modularization implementation process is studied including MOCGS generation,amplitude & phase modulation and code excitation,the algorithm of which is carry out by simulation.Both time domain deconvolution method and frequency domain decoding method are put forward in order to switch double-transmission excitation to single-transmission excitation,which results in decoding SNR improvement.Parameters as PNSL,HDL language and process time are applied synthetically to evaluate the decoding performance.(4)Single-transmitted MOCGS based ultrasonic coded excitation system design and RTL level simulation implementation by means of Field II and ModelSim.Experimental platform is built for defect detection of FRP sample in order to verify the feasibility of the very ultrasonic coded excitation approach.The results show high definition of the scanned image by singletransmitted MOCGS based ultrasonic coded excitation,along with clear defect feature and realistically matched hole image(2:5:10),the SNR of which is relatively high to provide a criterion for sample defect detection assessment.