SBIR-STTR Award

A continuing theme in shipboard monitoring is the need to inspect hulls of boats and submarines for signs of metal fatigue, typically manifesting as weld breaks, corrosion, and for submarines, metal-polymer debonding. Visual inspection remains the most reliable diagnostic, but is cumbersome if paint or plastic must be removed to reach the metal. Non-invasive diagnostics have problems too: eddy-current monitoring is reliable for weld fatigue, but not for corrosion onset or debonding, and polymers are opaque to ultrasound. Because missing a defect is unacceptable, existing non-visual methods are inherently slow. SARA proposes a millimeter-wave (MMW) imaging system, based on the science used for airport body scanners, to inspect welds without needing to remove the insulating layer. Because structural polymers typically have windows of transparency in the MMW domain, this technology provides rapid “see-thru” imaging of metal and associated defects in steel (such as those in butt/fillet welds, and corrosion onset). Stand-off scanning of a MMW imager will enable the Navy to localize weld joints and corrosion on quarter-wave scales (1mm or less), and will detect hairline cracks of even smaller scale. Debonding will be measured by phase rotation of multipath reflection, which only occurs when an air/water gap is present.

Keywords:
Millimeter Wave, Polymer Transparency, Imaging, Weld Inspection, Ndt.,

SARA’s PolyUrethane Millimeter-wave Imaging System (PUMIS) will image surface-metal defects through optically and acoustically “thick” coatings, such as those found on submarine exteriors, without needing to compromise the insulating layer. The device will be built in the form of a hand-scanner, imaging rust formations, de-bonding, and hairline metal cracks on the submarine. Image interpretation will be intuitive, enabling the operator to reject false positives due to changes in the submarine structure, such as metal curvature, thickness variation in the polymer, and mounting bolts. In-wire processing of the millimeter-wave backscatter caused by such defects will enable real-time imaging of the area under test, by way of a mobile PC or tablet, smartphone, or the monocle of a personal media viewer such as a MyVu. Nominal surface area coverage using the envisioned scan methodology will be 25-50 square feet per minute (end of Phase II), encumbered only by the operator’s ability to maneuver around the area under test. Because the system noise and background clutter is low, SARA’s long-term expectation is that, for coarse assessment, linear sweeps across submarine material may be executed as quickly as an individual can operate a squeegee, with coverage areas up to 30-50 square meters per minute.

Keywords:
Weld Inspection, Weld Inspection, Polymer Transparency, Millimeter Wave, Ndt., Imaging