Lockin-speckle-interferometry for non-destructive testing
Lockin-speckle-interferometry for non-destructive testing
复制标题
用于无损检测的锁定散斑干涉测量法
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
G. Busse
中科院分区：
文献类型：
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作者：
P. Menner;H. Gerhard;G. Busse
像剪切照相术或电子散斑干涉术（ESPI）这样的干涉测量方法正在用于远程变形测量。对于无损检测，通常不关心整个被检物体的变形，而只关心由隐藏缺陷引起的变形场的变化。通过应用锁定技术，即使在大的背景变形上也可以监测小的局部不连续性。动态激发是通过调制吸收光强度进行的，同时连续记录物体变形以给出条纹图像的堆叠。而不是只使用图像中包含的信息与最佳对比度，我们的技术评估整个图像堆栈相对于本地响应的编码输入。通过对每个像素处的时间相关信号进行傅立叶变换来提取变形的周期性分量。通过这种方式，图像堆栈中包含的相关信息被压缩为幅度和相位角图像。由于只有缺陷对相位图像中的信号变化有贡献，因此该方法是缺陷选择性的。此外，相变取决于缺陷所在的深度，因为涉及热波。另一个优点是信噪比的显著改善。
Interferometrical methods like Shearography or Electronic-Speckle-Pattern-Interferometry (ESPI) are being used for remote deformation measurements. For non-destructive testing, usually not the deformation of the whole inspected object is of interest, but only the changes in the deformation field that are caused by hidden defects. By applying the lockin technique, small local discontinuities can be monitored even on a large background deformation. Dynamic excitation is performed by modulation of absorbed light intensity while object deformation is continuously recorded to give a stack of fringe images. Instead of using only the information contained in the image with the best contrast, our technique evaluates the whole image stack with respect to the local response to the coded input. The periodical component of the deformation is extracted by Fourier transformation for the time dependent signal at each pixel. This way the relevant information contained in the image stack is compressed to an amplitude- and a phase angle image. As only defects contribute to a signal change in the phase image, the method is defect selective. Furthermore, the phase change depends on depth where the defect is located since thermal waves are involved. One more advantage is the substantial improvement of the signal-to-noise ratio.