Design Of Lamb Wave Detection System Based On FPGA

Metal materials are widely used in the construction of large-scale projects and major projects in China.But in the production process,metal components are inevitably damaged by external forces,and once damaged metal components are applied,there will be safety hazards.Therefore,it is essential to detect the damaged components in time for the production,processing and service of the metal components.Electromagnetic ultrasonic Lamb detection technology has the advantages of no coupling agent,simple excitation,high detection sensitivity,and is widely used for non-destructive testing of metal layered,plate-shaped,pipeline-type components.However,the current electromagnetic ultrasonic Lamb wave detection device is large in volume,and Lamb wave has multi-mode,dispersion,complex wave structure and other issues.Moreover,time-frequency analysis of electromagnetic ultrasonic non-stationary non-linear signals is difficult,which makes Lamb wave detection technology has many shortcomings.Therefore,this paper has carried out research on the Lamb wave detection system based on FPGA.The main research work is as follows:1)The generation mechanism and detection method of Lamb wave are studied.The wave characteristics of Lamb wave(dispersion,multi-mode,complex wave structure)and its influencing factors are analyzed.The single-mode EMAT coil and magnet structure with high rejection ratio are designed.2)Aiming at the problem of large volume and inconvenience to carry of high-energy pulse power supply,the hardware circuit of Lamb wave detection system is designed and manufactured,including excitation device and receiving device.The excitation device is mainly composed of the Boost circuit,power amplifier circuit,driving circuit,etc.The receiving device is mainly composed of low-noise preamplifier circuit,low-pass filter circuit,analog-to-digital conversion circuit and data acquisition circuit of FPGA.3)A data acquisition and processing system based on FPGA is designed to solve the problems of weak signal and noise stripping and time-frequency extraction of non-linear ultrasonic signals.A data processing method based on the combination of adaptive filtering and the Empirical Mode Decomposition(EMD)is proposed to realize the adaptive noise reduction of electromagnetic ultrasonic signals.The main modal components of the signals are obtained under the energy accumulation effect,and the time-frequency features are extracted,which lays a foundation for the recognition,location and non-linear analysis of the signals.4)The electromagnetic ultrasonic Lamb wave detection platform is built,and the hardware system and software system designed in this paper are combined,and the defect detection experiment is carried out,which can effectively filter out the noise,extract the time-frequency characteristics of the signal,and realize the location of the crack and the plastic damage.The detection waveform and frequency information are displayed on the screen.