Moment Method Solution for Modeling the Interaction of Open Ended Coaxial Probes and Surface Cracks in Metals

摘要

Surface discontinuities, such as surface fatigue cracks, constitute a large proportion of metal discontinuities which can affect the integrity of metallic structures. Therefore, nondestructive detection of tight surface cracks in metals has always been an important issue when one is concerned with in service testing and condition monitoring of critical metallic structures. Although there are several conventional nondestructive testing (NDT) methods available for this purpose, microwave techniques using open ended probes have also been receiving an increased level of attention for this application. This paper presents an efficient electromagnetic model for simulating the interaction of open ended coaxial probes with surface cracks in metals. The model is based on the equivalence principle and the moment method, by which the reflection coefficient of the dominant mode in the coaxial probe is calculated as a function of the location and size of the crack within the coaxial aperture. The results of the model are then compared to an earlier model which predicted the experimental results well. Several issues regarding the convergence of the method and the situation where the crack and the center conductor of the coaxial probe coincide are also discussed.