太赫兹脉冲光谱法测量微米级多层油漆涂层厚度技术

在汽车工业、飞机、船舶等领域中，油漆的涂层厚度管理对产品防水、防锈功能和颜色效果有着重要影响，但是目前采用的商业化涂层测厚仪都是接触式，并且很难直接获得多层涂层中的各层厚度。利用反射式太赫兹时域光谱(THz-TDS)系统探测样品的太赫兹脉冲光谱，基于脉冲回波的飞行时间建立简易的单点漆膜厚度提取模型。并通过最小二乘法拟合油漆样品的光学厚度与几何厚度之间的线性关系计算出12种涂覆在铝板上的油漆样品的测量折射率，发现金属油漆与非金属油漆在太赫兹波段的折射率存在较大的差异，闪光银色油漆样品的测量折射率为5.15，而白色油漆样品的测量折射率仅为2.64。在单层白色油漆样品厚度分布均匀的区域内测量50个点的膜厚，以磁/涡流感应涂层测厚仪的测量数据为参考标准，得到的厚度平均值为71.7 μm，测量误差为3.5 μm。对双层油漆样品进行二维扫描，测得白色油漆和底漆的厚度分布分别是(233±13)和(130±11) μm。同样，通过黑色三层油漆样品和银色三层油漆样品的二维分布图，分析了各层的漆膜厚度及其分布的均匀性。结果表明，太赫兹脉冲光谱法实现了1～3层漆膜的厚度测量及其分布均匀性评估，该方法对金属油漆的厚度分辨力较高，并且可通过非接触探测样品的太赫兹脉冲光谱，获得多层油漆的各层厚度及厚度的二维分布信息，易于实现喷涂质量的评估。

Study on Terahertz Pulse Spectra Technology to Measure the Thickness of Micro-Scale Multilayer Coatings

Paint thickness management has a significant impact on waterproofing,rust-proof function and color effects of prod-ucts in the field of automotive,aircraft,ships,etc.However,commercially available coating thickness meters are contact-type, and it is difficult to determine the individual paint thickness for each layer of the multilayer coating directly.In this paper,the terahertz pulse waveforms of samples were detected with reflection terahertz time-domain spectroscopy (THz-TDS)system,and the simple single-point thickness measurement model was established based on the time-of-flight measurement of the pulse echo. Besides,the refractive indexes of 12 kinds of paint samples coated on aluminum panels were calculated from the linear relation-ship between the optical thickness and geometrical thickness,which was fitted by the least squares method.It was found that there was a big difference of refractive index between the metallic paint and nonmetallic paint in the terahertz band,and the measuring refractive index was 5.15 for shining silver paint and 2.64 for white paint.The thickness of monolayer white paint sample was measured by detecting the thickness of 50 points in the region that the thickness distribution was uniform,and the average value of thickness was 72 μm with an error of 4 μm when the reference standard was the data measured by the electro-magnetic/eddy current thickness meter.By two-dimensional (2-D)scanning,the observed uniformity of the thickness distribu-tion of two-layer paint sample was (233±13)μm for white paint and (130±11)μm for primer.Similarly,the individual paint thickness for each layer and the distribution uniformity of the three-layer paint black samples or silver samples was determined by analyzing the thickness 2-D map.The results showed that terahertz pulse spectroscopy provided a feasible method of measuring film thickness and assessing uniformity of 1～3 layer paint,and the method could provide a higher thickness resolution for metal-lic paint.It was easy to assess the quality of the multilayer paint with the thickness data and 2-D distribution information extrac-ted from terahertz pulsed waveforms detected in non-contact way.