中文摘要：

超声检测粗晶材料时,结构噪声会严重降低检测信号的信噪比,造成缺陷反射波很难分辨出来。为提高检测信号的信噪比,增加粗晶材料超声检测的可靠性,本研究采用希尔伯特-黄变换（HHT）对检测信号进行分析处理。用超声检测系统对材料进行检测,采集粗晶材料测试数据;通过经验模态分解获得组成信号的本征模态函数,并经过希尔伯特变换得到不同模特对应的边际谱;分析信号的时频信息,去除噪声信号,提高了信噪比,使缺陷反射更加明显。实验结果表明：HHT能够有效去除无效的结构噪声,提高信噪比,缺陷反射更加突出。

英文摘要：

In ultrasonic testing of coarse grain materials, signal to noise ratio （SNR） is so poor because of the serious structure noise, and reflected wave from defects is difficult to be identified. In order to improve SNR and increase the reliability of ultrasonic testing for coarse grain materials, Hilbert-Huang Transform （HHT） is introduced to analyze and process the testing signal here. Firstly, detected signals from the coarse grain material can be collected by using ultrasonic test system. And then many Intrinsic Mode Function （IMF） can be obtained according to Empirical Mode Decomposition （ EMD）, and marginal spectrum of different mode can be gotten by Hilbert transform. And finally, the noise should be removed after analyzing the time- frequency information, and SNR is able to be enhanced and the reflection wave from defect is being more obvious. It was shown from the experimental result that the ineffective structure noise could be removed after HHT, and SNR could be improved and the defect reflection is more outstanding.