Microwave near-field and far-field imaging of composite plate with hat stiffeners

Composite stiffened structures that are widely used in engineering inevitably produce various defects in manufacturing and service. In order to detect them, a microwave nondestructive testing platform is built in this paper, which simply combines near-field and far-field microwave scanning imaging. 0.4 mm metal hole, 0.5 mm and 1 mm inclusions and 0.1 mm thick debonding are detected by high resolution microwave near-field imaging. Internal poor resin infusions defects in 39 mm thick hat stiffener are detected by high penetration microwave far-field imaging. Far-field microwave images the shape and internal structure of stiffener by adjusting stand-off distance. Detection of the fiber wrinkling defects demonstrates the effectiveness of combining near-field and far-field imaging methods, saving 95% of the scan imaging time. Feature-based image stitching technique is adopted to obtain the full-size image of the large stiffened composite structure.