Automated ultrasonic inspection of curved composite structures remains a challenge, especially when surface geometries involve small and/or changing radii as found in stringers, leading edges, or double-curved CFRP panels. Existing water-coupled or contact-based solutions are effective for flat panels but are poorly suited for complex geometries. As a result, inspection of such components often relies on manual procedures, where probe heads must be frequently changed to match varying curvatures.

This contribution presents an UT inspection setup based on laser-generated ultrasound in combination with an optical microphone (OM) as the receiver. The OM is a broadband, air-coupled sensor that allows stand-off measurements without physical contact or couplant. The probe's small form factor (matchbox-sized) and non-contact nature make it well suited for robotic integration and for navigating tight radii or irregular contours, including trailing edge radii as low as 5 mm, and the interior of confined spaces with dimensions as small as 30 mm x 30 mm.

The capabilities of this setup are demonstrated through inspection trials on representative structures, including curved panels and stringers, covering both through-thickness (pulse-echo, through-transmission) inspection and bond integrity assessment. EFIT-based ultrasonic simulations support the analysis by providing deeper insight into wave propagation and defect interaction in these complex structures. Results show that the presented method maintains reliable signal quality as well as the capability of detecting defects, even for complex geometries.

This approach offers a viable path toward the automation of ultrasonic inspection for complex geometries that are still often inspected by hand—bridging a key gap in aerospace NDT workflows with improved reliability and long-term cost efficiency.