Microwave Detection of Finite Surface Cracks in Metals using Rectangular Waveguides

An electromagnetic model for finite surface crack detection is developed and its results are compared with those of the existing long crack model and some experimental results to verify its integrity. An open-ended waveguide sensor is used to scan a metal surface with a crack in it. The crack is then modelled as a small waveguide being fed by a larger one. The presence of the crack causes higher order modes to be generated, which in turn influence the properties of the standing wave set up inside the waveguide. Strategic probing of the standing wave properties is used to indicate the presence of a crack (detection). The distribution of the tangential electric field on a metal surface is investigated. This is done to check whether the boundary conditions have been properly forced. The behavior of crack characteristic signals as a function of varying crack length and location within the sensor aperture is also studied. The possibility of using the phase of the reflection coefficient for crack detection is investigated by a numerical simulation. A finite fatigue crack is finally detected at 38 GHz to demonstrate the practical feasibility and potential of this technique