A novel microwave method for surface crack detection using higher order waveguide modes

Abstract

A novel microwave nondestructive testing method for fatigue/surface crack detection on metal surfaces is described. This technique uses an open-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 presence 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 and theoretical foundation of this technique is given, along with several examples. It is shown that fatigue/surface cracks with widths less than 5 mm can be detected at 38 GHz. The optimum measurement parameters are theoretically predicted and confirmed by experiments.