Subwavelength microwave near-field imaging enabled by a novel dielectric-loaded waveguide probe for high-resolution nondestructive evaluation of multiscale defects in aerospace composites

Microwave imaging technology has garnered significant attention in aerospace non-destructive testing (NDT) due to its advantages in detecting defects in metallic and composite materials. However, the practical application of conventional rectangular waveguides is constrained by image distortion caused by their inherent characteristics. To enhance the resolution and sensitivity of near-field imaging, a dielectric-loaded rectangular aperture probe based on an X-band rectangular waveguide was proposed. The probe was designed and optimized through three-dimensional electromagnetic simulations, with a systematic analysis of the effects of various design parameters on its performance. Simulation results demonstrated that the proposed probe exhibits superior impedance matching, higher gain, and narrower beam width, leading to significant improvements in detection resolution and sensitivity, achieving a lateral resolution of λ/4.4 with a 46.36% improvement and an axial resolution of λ/64.6. Experimental validation confirmed that the designed probe outperforms traditional rectangular waveguides in spatial resolution for aerospace composite defect detection, enabling the detection of deeper defects and clearer imaging quality. The detection depth has increased by approximately 30.77%. This study demonstrates the potential advantages of the proposed probe in composite material defect detection and provides a novel solution for advancing aerospace NDT technologies.