Modeling of surface hairline-crack detection in metals under coatings using an open-ended rectangular waveguide
Modeling of surface hairline-crack detection in metals under coatings using an open-ended rectangular waveguide
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使用开放式矩形波导对涂层下金属的表面发丝裂纹检测进行建模
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
R. Zoughi
中科院分区：
文献类型：
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作者：
C. Huber;H. Abiri;S. Ganchev;R. Zoughi
开口矩形波导探头扫描金属试件时，如果出现表面断裂的细微裂纹或狭缝，则会影响入射主模的反射系数特性。在扫描这种表面的同时，随后记录驻波图案的变化导致所谓的裂纹特征信号。由于微波信号穿透到介质材料内部，这种方法也能够检测不同电厚度的介质涂层下的裂纹。为了模拟介质涂层下开端矩形波导与表面断裂发际线裂纹的相互作用，将介质涂层层模拟为具有大截面的波导。因此，问题被简化为三个相互作用的波导系统，同时裂纹的位置相对于探测波导孔径不断变化(动态扫描问题)。给出了将介质涂层模拟为大截面介质填充波导的分析，并与辐射进入无约束介质的情况进行了比较。为了得到主模和高阶模式的反射系数，分别分析了探测波导-介质-涂层结和介质-涂层-裂纹结的电磁特性。对于每个结，在公共孔上方引入磁流密度M。随后，将由两个相应的波导段形成的结分成两个系统。利用矩量法得到了数值解，并用它们各自的广义散射矩阵来表示结的性质。因此，可以计算整个系统的广义散射矩阵。研究了系统的收敛行为，以确定快速准确解的最优基函数集和最优高阶振型个数。最后，将理论裂纹特征信号与实测裂纹特征信号进行了比较。
A surface-breaking hairline crack or a narrow slot in a metallic specimen when scanned by an open-ended rectangular waveguide probe influences the reflection-coefficient properties of the incident dominant mode. Subsequent recording of a change in the standing-wave pattern while scanning such a surface results in what is known as the crack characteristic signal. Since microwave signals penetrate inside dielectric materials, this methodology is capable of detecting cracks under dielectric coatings of various electrical thicknesses as well. To electromagnetically model the interaction of an open-ended rectangular waveguide with a surface-breaking hairline crack under a dielectric coating, the dielectric-coating layer is modeled as a waveguide with a large cross section. Thus, the problem is reduced to a system of three waveguides interacting with each other while the location of the crack is continuously changing relative to the probing waveguide aperture (a dynamic scanning problem). An analysis of modeling the dielectric-coating layer as a dielectric-filled waveguide with a large cross section is given, and its comparison with radiation into an unbounded medium is presented. For obtaining the reflection coefficients of the dominant and higher order modes, the electromagnetic properties of the probing waveguide-dielectric-coating layer junction and the dielectric-coating layer-crack junction are separately analyzed. For each junction, a magnetic-current density M is introduced over the common aperture. Subsequently, the junction formed by the two respective waveguide sections is separated into two systems. A numerical solution employing the method of moments is obtained, and the properties of the junctions are expressed by their respective generalized scattering matrices. Consequently, the generalized scattering matrix for the total system can be evaluated. The convergence behavior of the system is studied to determine an optimal set of basis functions and the optimal number of higher order modes for a fast and accurate solution. Finally, the theoretical and measured crack characteristic signals are compared.