Anisotropy-aware phase–frequency coherence imaging (PFCI) for guided-wave damage localization in composite structures

Guided-wave damage imaging in realistic composite aircraft structures is difficult because anisotropic propagation, multimodal dispersion, internal interfaces, and boundary reflections distort wave packets and generate coherent clutter. Delay correction alone may still accumulate non-damage components and produce high-amplitude pseudo-foci. This study proposes an anisotropy-aware phase–frequency coherence imaging (PFCI) method for damage localization in a locally planar region selected from an Airbus A380 composite flap track fairing. Direction-dependent dispersion information is extracted from experimental guided-wave measurements to reconstruct a continuous anisotropy-aware wavenumber model for propagation compensation. After compensation, PFCI evaluates each trial point through a joint packet-level coherence test combining envelope-phase alignment and local instantaneous-frequency consistency near the focusing instant. This criterion enhances damage-consistent responses and suppresses pseudo-indications caused by reflections, direct-wave residue, and imperfect focusing. Experiments using a piezoelectric transducer network and full-matrix guided-wave measurements show that, for the representative single-defect case at 60 kHz with a 5-cycle tone burst, PFCI achieved a localization error of 5.831 mm, a peak-to-background ratio of 13.507 dB, and a contrast-to-noise ratio of 6.956. In the dual-defect case, two defect-related indications were identified, with a mean localization error of 7.697 mm. The results show that PFCI provides an effective feature-level imaging criterion for guided-wave damage localization in the tested composite aircraft structure under a healthy-baseline condition.