改进的希尔伯特-黄变换(HHT)在多模式Lamb波检测中的应用

Lamb波的主要特点在于它的多模式和频散,在任一给定的激发频率下,至少存在两种Lamb波模式。各模式的频散特性使Lamb波检测变得非常复杂,所以,Lamb波检测的关键在于缺陷信号特征参数的提取和精确的信号解释。首先采用HHT直接对多模式Lamb波检测信号进行了分析,通过分析,得出了直接对多模式Lamb波信号进行EMD分解来得到信号的瞬时频率和瞬时幅值的方法是不适合的结论。采用改进后的HHT方法进行分析,有效消除了噪声干扰和各模式Lamb波的相互干扰,得到的信号时频集聚性较好,有利于特征参数的提取和进一步分析。针对不同大小和深度的孔型人工缺陷的检测试验,分别提取了信号瞬时幅值的峰值和瞬时频率的均值作为检测信号的特征参数进行线性回归分析,发现采用瞬时幅值的峰值作为孔型缺陷检测的特征参数比采用瞬时频率的均值这一参数要好。同时提出可采用瞬时幅值的峰值回归直线的斜率K来标定特征参数对缺陷孔径变化的敏感性,从而可对未知缺陷的大小进行预判。

Applied Research for Improved Hilbert-Huang Transform（HHT） in the Multi-Mode Lamb Wave Detection

The main characteristics of Lamb waves are multi-mode and dispersion, in any given excitation frequency, there are at least two Lamb Wave modes. The dispersion characteristics of each mode make Lamb wave detection become very complex, so extraction for characteristic parameters of the signal and accurate signal interpretation is the key of Lamb wave detection. The signal of multi-mode Lamb wave detection was analyzed directly by HHT, and the conclusion was obtained that the approach of using multi-mode Lamb waves signal by EMD decomposition to extract the instantaneous frequency and instantaneous amplitude directly was not suitable. The noise and the mutual interference of Lamb wave modes was effectively eliminated by improved HHT, and the time-frequency clustering of the signal was good, and it was of benefit to characteristic parameters extraction and further analysis. Testing for different size and depth of the hole type artificial defects, the peak of instantaneous amplitude and the mean of instantaneous frequency were extracted respectively for linear regression analysis, it was discovered that the peak of instantaneous amplitude was a better characteristic parameter than the mean of instantaneous frequency for the detection of hole type defect. And the sensitivity of the change of the defect diameter could be calibrated by the regression line slope K of the peak of instantaneous amplitude, which could be used to predict the size of unknown defects.