Super-resolution detection of high-contrast embedded objects in structures using differential X-band sensor array

We describe a non-ionizing imaging technique to detect highly conductive embedded objects inside of a poorly conducting structural material. We have constructed an array with four differential dasiapixelspsila each consisting of a pair of tuned, cross-polarized resonant microwave probes. The probes were individually tuned using dielectric loading and spatial tuning screws. The probes interact with the embedded wires in the structure causing a secondary resonance to form as detected using a network analyzer. The orthogonal polarization of the probes was used to perform differential measurements and to eliminate the effect of probe stand-off variations and surface non-uniformities. The experimental results demonstrated sensitivity to different diameters of embedded wires (with a minimum detectable signal of 1 mum at 100 mum depth) in a rubber structure. Individual broken wires could also be distinguished from a background of unbroken ones.