Image Enhancement in Transient Lock-In Thermography Through Time Series Reconstruction and Spatial Slope Correction
Image Enhancement in Transient Lock-In Thermography Through Time Series Reconstruction and Spatial Slope Correction
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DOI：
10.1109/tim.2011.2174095
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发表时间：
2012-04
影响因子：
5.6
通讯作者：
K. Chatterjee;S. Tuli
中科院分区：
文献类型：
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作者：
K. Chatterjee;S. Tuli
锁定（LI）热成像是一种流行的热无损检测技术，它像其他主动热成像技术一样，需要外部加热刺激，最好是在变黑的表面上。然而，它并不能避免非理想情况，如不均匀加热和表面发射率变化。相位图像在某种程度上有助于减少这些伪影的影响，但如果变化很大，则是不够的。例如，由于表面的直接反射，表面上具有反射斑点的黑色不佳的金属样品非常难以主动热成像。本文提出了一种图像重建算法，离线消除这种伪影。此外，所提出的算法使LI热成像测试在瞬态制度，并消除由于不均匀加热的温度梯度。该算法进行了测试，具有20毫米直径的回钻孔在不同的深度范围从0.2至7.7毫米，刺激在20-，40-，50-，60-，和80-兆赫的激励频率的低碳钢样品。还介绍了加热循环总数的影响。
Lock-in (LI) thermography is a popular thermal-nondestructive-testing technique which, like other active thermographic techniques, requires an external heating stimulus, preferably on a blackened surface. It is not, however, immune to nonideal situations like nonuniform heating and surface emissivity variation. The phase image, to some extent, helps to reduce the effect of these artifacts but is inadequate if the variations are large. For example, a poorly blackened metallic sample with reflecting patches on its surface is very difficult to actively thermograph because of direct reflection from the surface. This paper proposes an image reconstruction algorithm for offline removal of such artifacts. In addition, the proposed algorithm enables LI thermography tests in the transient regime and removes temperature gradients due to nonuniform heating. The algorithm was tested with a mild-steel sample having 20-mm-diameter back-drilled holes at various depths ranging from 0.2 to 7.7 mm, stimulated at 20-, 40-, 50-, 60-, and 80-mHz excitation frequencies. The effect of the total number of heating cycles is also presented.