小波变换在混凝土冲击回波检测中的应用

Application of wavelet transform in detection of concrete impact echo

采用冲击回波法检测混凝土厚度或者缺陷时,采用传统快速傅里叶变换方法,由于傅里叶变换的时移性以及信号中包含表面波和结构模态振动使得特征频率的提取较为困难。要解决特征频率提取受到干扰的问题,该文提出一种小波变换结合傅里叶变换的信号处理方法。首先对回波信号进行小波变换,得到信号时频图和小波边际谱,其次将小波边际谱与傅里叶谱相乘,得到增强傅里叶谱。结果表明:信号时频图可以确定表面波和模态振动的频率范围和时间跨度,增强傅里叶谱不仅可保证频率分辨率,而且抑制由于傅里叶变换的时移性产生的多个波峰,使得特征频率在频谱中更为清晰和准确,是一种适用于冲击回波检测的信号处理方法。

When impact echo method is used to detect the thickness or defects of concrete, in the processing of echo signals using the traditional method of fast Fourier transform, due to the time shift of the Fourier transform and the surface wave and structural modal vibration contained in the signal, the extraction of feature frequencies is difficult. To solve the problem that feature frequency extraction is disturbed, this paper proposes a signal processing method which combines wavelet transform with Fourier transform. Firstly, wavelet transform is performed on the echo signal to obtain the signal time-frequency spectrum and the wavelet marginal spectrum, then the wavelet marginal spectrum is multiplied with the Fourier diagram to obtain an enhanced Fourier spectrum. The result shows that the signal time-frequency diagram can determine the frequency range and time span of the surface wave and modal vibration. In the enhanced Fourier spectrum, not only the frequency resolution is guaranteed, but also the time-shift due to the Fourier transform is suppressed. Multiple peaks make the characteristic frequencies clearer and more accurate in the spectrum which is a signal processing method suitable for impact echo detection.