【作者】 潘伟才；

【导师】 王淑娟； 刘贵栋；

【作者基本信息】 哈尔滨工业大学 ， 电力电子及电力传动， 2008， 硕士

【摘要】 由于电磁超声技术检测效率高、环境适应性强,因此被广泛应用于无损在线检测研究领域。FPGA灵活性强、处理速度高,在实时信号处理中具有独特优势。本文研究基于FPGA的电磁超声检测系统具有重要的理论意义和实用价值。本文在深入研究国内外电磁超声检测方法的基础上,分析了电磁超声换能器(electromagnetic acoustic transducers,EMAT)的工作机理,成功研制了基于FPGA的电磁超声检测系统。该系统包括电磁超声发射、接收电路、基于FPGA的数字信号处理和基于SOPC的缺陷检测部分。基于DDS技术的电磁超声发射电路能够产生高频、大功率正弦电流脉冲串,脉冲串的频率、重复频率、波数及幅度均连续可调。本文设计的电磁超声接收电路具备强噪声背景下的微弱信号检测能力,采用2级级联的二阶无限增益多路反馈带通滤波电路能够显著提高接收信号的信噪比。本文在分析电磁超声接收信号成分及噪声来源的基础上,采用FIR带通滤波与小波消噪算法有效地降低了电磁超声接收信号中的噪声含量,并利用数字检波方法提取了接收信号的包络。上述算法通过硬件描述语言编程,并由FPGA实现,提高了检测系统的灵活性与实时性。本文基于SOPC技术实现了对消噪后接收信号的采集、缺陷判断、缺陷定位与显示。采用所研制的基于FPGA的电磁超声检测系统进行了钢板缺陷检测、声场指向性测量和列车轮对检测实验。实验结果验证了检测方法的有效性与正确性。该系统的研制为电磁超声在线检测技术的工程应用奠定了良好的基础。更多还原

【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.更多还原