超声干涉法薄层厚度测量声阻抗匹配判据及其应用

Acoustic Impedance Matching Criteria and Their Applications for Layer Thickness Measurement by Ultrasonic Interferometry

针对超声干涉法测量薄层厚度的原理,讨论了薄层及与其相邻介质声阻抗匹配分别满足界面声压反射系数|R1|<1/2或|R1|>1/2时回波信号的选取原则,并以薄层声压反射系数谱为依据,分析了上述两种声阻抗匹配条件下谱线分别出现次生极大或极小值的规律,在此基础上提出了薄层厚度测量时谱线极值的选择方法。以航空雷达罩蒙皮GFRP(Glass Fiber Reinforced Plastic)层板外表面复合涂层以及钢基体表面ZrO2陶瓷涂层样品为例进行了薄层厚度测量实验研究及信号分析。研究表明,超声干涉法薄层厚度实验结果与SEM(Scanning Electron Mi-croscope)测量结果相符。由此可知,薄层及与其相邻介质声阻抗匹配判据对于超声干涉法薄层厚度测量具有很强的理论指导意义及工程应用价值。

Based on the fundamental principles of ultrasonic interferometry of thin layer thickness measurement, criteria are proposed when the interfacial reflection coefficient between the layer and its adjacent medium meets ｜R1｜ 〈 1/√2 or ｜R1｜〉 1/√2, respectively. And a choice between the minima and maxima used in thickness measurement is made by investigating secondary extreme of the reflection coefficient spectrum under two conditions. Using the above principles, the thickness of Airborne Radome Skin coating and ZrO2 ceramic coating sprayed on steel substrate are experimentally studied. Comparing with the SEM （Scanning Electron Microscope）results, the experimental error ε1≤ 12% for Airborne Radome Skin coating and ε2 ≤ 11% for ZrO2 ceramic coating, both meet the need of engineering. It is concluded that the acoustic impedance matching criteria are of great value in layer thickness measurement using ultrasonic interferometry.