Millimeter-Wave Imaging of Surface-Breaking Cracks in Steel With Severe Surface Corrosion

Robust detection of surface-breaking (fatigue) cracks in metals with severe surface corrosion (rust) and pitting is of great practical interest. Detection of surface-breaking cracks in the millimeter-wave frequency range (30-300 GHz) has received considerable attention in the past two decades. At these frequencies, corrosion byproducts (rust) are in the family of dielectric materials allowing millimeter-wave signals to penetrate through and interact with a visually masked crack. When using open-ended rectangular waveguides, no contact is required, and the crack signal characteristics are significantly different than those from corrosion and pitting, which renders a crack detectable even in the presence of severe corrosion. Moreover, synthetic aperture radar images of cracks masked by corrosion can be rapidly generated providing additional geometrical information. This paper presents the results of uniquely combining these two methods for detecting cracks in severely corroded steel plates and for other similar applications where a crack is visually masked by a dielectric layer.