A NOVEL MICROWAVE METHOD FOR SURFACE CRACK DETECTION USING HIGHER-ORDER WAVE-GUIDE MODES

A novel microwave nondestructive testing method for fatigue/surface cr ack detection on metal surfaces is described. This technique uses an o pen-ended waveguide to probe the surface of a metal. In the absence of a crack, the metal surface is seen as a relatively good short circuit load that will not generate any higher order modes. However, in the p resence of a crack higher order modes are generated, and subsequently the transverse electric field components of these modes are used as a qualitative indication of the existence of a crack. The experimental a nd theoretical foundation of this technique are given, along with seve ral examples. It is shown that fatigue/surface cracks with widths less than 5 mm can be detected at 38 GHz. The optimum measurement paramete rs are theoretically predicted and confirmed by experiments.