Through-thickness inductive imaging for monitoring of features in thin-ply CFRP unidirectional tapes
Abstract
Thin-ply unidirectional (UD) carbon-fibre reinforced polymer (CFRP) tapes enable improved mechanical performance in advanced aerospace structures but remain highly sensitive to manufacturing-induced defects. Reliable monitoring at the tape level is therefore essential to ensure consistent fibre distribution and prevent defect propagation into subsequent laminate assemblies. This study evaluates the feasibility of high-frequency Eddy-Current (EC) sensing for through-thickness inspection of individual carbon-fibre thermoplastic (CFTP) tapes. A differential transmit–receive coil pair was designed, manufactured, and optimised for the constrained geometry of UD tapes, enabling through-thickness interrogation in high resolution. UD-CFRP tapes were produced using a controlled powder-based dispersion slurry and calandering process, in which fibre tension, calander pressure, and line speed were varied, from which representative fibre-distribution anomalies could be detected. Twenty-one samples were scanned using a motorised system operating near a 50 MHz resonance, and spatially resolved maps of transfer magnitude and phase were obtained. The sensor exhibited sensitivity to variations in fibre packing density, tow spacing and structure, and local conductivity, with signal-to-noise ratios reaching up to 30 dB for the most distinct features. While some defect classes produced lower contrast, the results indicate that the through-thickness measurement configuration can detect prominent tape-level structural variations. These findings demonstrate the feasibility of inductive EC sensing as an evaluation tool for thin-ply tape production. The approach provides a foundational step toward developing future process monitoring strategies and improving the reliability of next-generation composite manufacturing.
