Enhanced Subsurface Analysis Using Proper Orthogonal Decomposition in Nonstationary Thermal Wave Imaging

Active infrared thermography (AT) has been evolved as a prominent nondestructive testing technique for in-situ monitoring of defect-free composite material manufacturing. The recent past witnessed the growth of low peak power nonstationary thermal wave imaging schemes to provide a promising axial and spatial resolution to cater for these requirements. The present article employs a proper orthogonal decomposition (POD) for the processing of quadratic frequency modulated thermal waves intended to enhance the detection of subsurface anomalies by using selective mode consideration. The performance of POD is experimentally validated over carbon fiber and glass fiber reinforced plastic specimens with artificially created flat bottom holes and Teflon inclusions considered to be the subsurface anomalies. Further, the enhanced defect detection capabilities of POD are qualitatively assessed using signal-to-noise ratio and size of defects as a figure of merit.