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Research on Electromagnetic Acoustic Transducer Detection System Based on FPGA

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Tutor: WangShuJuan;LiuGuiDong
School: Harbin Institute of Technology
Course: Power Electronics and Power Drives
Keywords: EMAT,FPGA,SOPC,FIR filter,Wavelet denoising method
CLC: TH878.2
Type: Master's thesis
Year:  2008
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Abstract:
Electromagnetic ultrasonic technology is widely used in on-line, high-speed and high-temperature nondestructive detection fields due to its high detection efficiency and adaptability of environment, while FPGA possesses unique advantages in real-time signal processing field resulted from its characteristics of flexibility and high processing speed. As a consequence, the research of an electromagnetic ultrasonic detection system based on FPGA is of great theoretical and practical value.Based on extensive study of the present researching status of electromagnetic ultrasonic technology, this paper analyzes the mechanism of the electromagnetic acoustic transducers (EMATs), and successfully develops an electromagnetic ultrasonic detection system based on FPGA. The system consists of electromagnetic ultrasonic transmitting and receiving circuits, digital signal processing module based on FPGA and defects detection module based on SOPC.Based on DDS technology, the transmitting circuit designed in this paper is able to generate tone burst signal with high frequency and large power, whose repetitive frequency, frequency, number of waves and magnitude can be continuously adjusted. The receiving circuit designed in this paper has a strong ability of weak signal detection under a strong noise environment. A second-order infinite-gain multi-feedback band-pass filter designed in this paper has a good performance in improving the signal-to-noise ratio of the EMAT received signal.Based on analyzing the components of the received signals and noise sources, this paper adopts FIR band-pass filtering and wavelet denoising algorithm to effectively denoise the received signal. Digital demodulation method is used to extract the envelope of the received signals. The flexibility and real-time quality of the detection system is greatly enhanced utilizing hardware description language realized by FPGA.Functions of data acquisition, defect detection, defect localization and display are realized based on SOPC technology. Experiments of steel plate defect detection, sound field directivity measurement and train wheel detection implemented by the designed system have verified the validity of the system. The design of this system establishes a solid foundation for practical application of the electromagnetic ultrasonic online detection.
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