Array Waveguide Probe Loaded with Split-Ring Resonators for Sizing the Cracks in Metal Surface

Microwave nondestructive testing (NDT) technology developed rapidly, but crack detection in metal surface is facing many troubles, such as hard quantitation and low sensitivity. To solve these problems, this letter proposes a two-cell array waveguide microwave NDT probe with an array of split-ring resonators which operates at 12.5 GHz. It detects quantitatively tiny crack (as low as 0.5 mm) in metal surface. Maximum difference between simulation and experimental results is just 9%. Result shows that the peak distance of $S-{21}$ has a sensitive and quantitative link with the width and depth of crack. It is shown that the probe is capable of determining the location and dimension of surface cracks of a few millimeter depths and widths.