Waveguide probe loaded with split-ring resonators for crack detection in metallic surfaces

We present a near-field waveguide probe with an embedded array of split-ring resonators (SRRs) that operate at 16.65 GHz. When the probe scans a metal surface, the magnetic flux generated from the currents on the metallic surface strongly affects the equivalent lumped parameters of the SRRs. This, in turn, affects the reflection coefficient of the feeding port leading to high sensitivity in detecting anomalies such as cracks in the surface. Experimental results indicated the feasibility of detecting cracks, as small as 25 μm in width, in metallic surfaces. Additionally, the probe achieves good resolution in detecting closely spaced cracks.