【作者】 李秋锋；

【导师】 梁大开； 石立华；

【作者基本信息】 南京航空航天大学 ， 测试计量技术及仪器， 2008， 博士

【摘要】 超声检测方法具有穿透能力强,检测设备简单,操作方便,检测成本低廉等优点,在工程上已经得到广泛应用,尤其在混凝土大坝、桥梁、道路和房屋等大体积混凝土质量检测中应用更广。超声成像技术在现代工业无损检测中具有重要地位,已成为定量检测的重要手段。本文旨在进行混凝土结构内部异常的超声成像技术研究,致力于提高这项技术的成像分辨率,使其更加可靠、实用。在分析超声成像理论的基础上,应用合成孔径技术(SAFT)的一般原理,从多个方面进行了混凝土结构超声成像技术的研究,总结出了一些能够有效提高成像分辨率的方法,文中主要研究工作内容有以下几个方面:(1)对本文的研究背景和研究方向进行概述,通过比较各种成像方法,确定了本文的研究方向;(2)根据合成孔径聚焦技术思想编写了SAFT成像算法,为了解决低频检测信号在聚焦时出现的波包变形问题和减少成像算法的运算量,引入波包分解技术(WDT),对SAFT成像算法进行改进,能够有效的解决上述问题,并采用数值仿真验证了成像算法的使用效果;(3)应用成像算法进行了水浸探测成像实验,通过所建立的超声探测系统对三种超声激励信号的检测效果进行了研究;(4)针对超声传感器的窄带频响特性,提出了一种数字补偿滤波方法。通过建立传感器系统模型求得数字补偿滤波器,对探测信号进行矫正和恢复,可以有效提高图像的时空分辨率;(5)根据探测要求建立了混凝土超声探测系统,并浇铸了几块混凝土试件供实验系统做实际混凝土探测实验;在实验中,提出了一整套对检测信号进行预处理的方案,能够有效抑制和消除实际B扫描探测信号中的各种噪声和一些干扰信号,从而改善信噪比,提高成像分辨率;(6)最后应用上述的各种方法对各混凝土试件进行成像显示,对成像结果逐个进行了分析和解释。通过对成像结果的对比,可以看出改进的SAFT成像算法的实际使用效果最佳,经过使用本文研究的检测数据处理方法后,能够有效提高成像分辨率。更多还原

【Abstract】 Ultrasonic test method has many advantages, such as strong penetrability, compact devices, low cost, and has been wildly used in engineering test, and especially in quality measurement of large concrete structures, for instance concrete dam, bridge, road and building.Ultrasonic imaging technology has significant status in current NDT, and is an important method for quantitative test. This dissertation aim to research on ultrasonic imaging technology for abnormity inside concrete structures and enhance the imaging resolution and reliability and practicability. On the base of analysis of ultrasonic imaging theory and Synthetic Aperture Focusing Technique (SAFT), and several aspects have been studied and some approaches have been concluded to improve imaging resolution effectively. And main contents are as follow:(1)Firstly, it has been summarized research background and significance of this dissertation, and research direction has been confirmed by comparison of several imaging methods;(2)The algorithm has been programmed according to SAFT. To resolve the wavepacket distortion and decrease calculation, Wavepacket Decomposition Technique (WDT) is introduced here to improve the SAFT algorithm and solve these problems. And the effect of imaging algorithm is verified by numerical simulation.(3)Imaging experiment of water- immerging detection has been achieved with the algorithm, and the measurement effects of three excitation waveforms are researched through establishing ultrasonic detecting system;(4)A method based on digital compensation filtering is proposed for narrow-band frequency response characteristic of ultrasonic transducers. The digital compensation filter is designed by modeling the transducers system, which can correct and recover the received signals and enhance the spatiotemporal resolution of image effectively.(5)The ultrasonic test system for detection of concrete elements is built according to requirement and several concrete specimens is casted for experiment. In experiment, a set of methods are presented for preprocessing the detecting signals, which can restrain and remove the noise and some disturbing signals in B-scan data and improve the signal-to-noise ratio (SNR) and imaging resolution.(6)At last, the upper methods are applied to image the concrete specimens, and the results are been analyzed and explained. By comparison of imaging results, it can be found that the effect of SAFT algorithm is the best. After processing test data researched in this dissertation, the imaging resolution is enhanced effectively.更多还原