A NOVEL MICROWAVE METHOD FOR DETECTION OF LONG SURFACE CRACKS IN METALS

A novel microwave technique for detecting long surface cracks in metal s is described. This technique utilizes an open-ended waveguide tb pro be the surface of a metal. In the absence of a crack the metal surface is seen as a relatively good short-circuit load. However, in the pres ence of a crack higher order modes are generated which in turn change the reflection properties at the waveguide aperture. This change bring s about a perturbation in the standing wave characteristics which is t hen probed by a diode detector. The experimental and theoretical found ations of this technique are given, along with several examples. It is shown that cracks a fraction of a millimeter in width are easily dete cted at around 20 GHz or lower. Smaller cracks can be detected at high er microwave frequencies.