Circuit Design and Implementation for Non-Destructive Detection of Metal Surface Defects

Metallic materials are widely used in critical components such as aerospace structures, nuclear power plant steam generators, and steel bridges. However, operational loads (e.g., bending, torsion) induce localized stress accumulation, leading to crack initiation and performance degradation. Surface defects in metals are often concealed beneath protective coatings, complicating their detection. Microwave non-destructive testing (NDT) addresses this challenge by penetrating non-metallic coatings to interrogate subsurface flaws. Conventional microwave NDT systems integrate sensors with vector network analyzers (VNAs), yet suffer from high cost, bulky footprints, and slow scan rates, rendering them impractical for modern manufacturing. To overcome these limitations, this work proposes a novel Complementary Split-Ring Resonator (CSRR)-based electromagnetic sensing method, implementing a compact surface defect detection system. To validate the feasibility of the proposed testing system, an experimental platform was constructed. The test results demonstrate a linear relationship between the resonant frequency shift and crack width within the range of $0.6-1.4 \mathrm{~mm}$. With a detection speed of 7 seconds per measurement, this system offers advantages such as low cost, portability, and rapid inspection compared to conventional testing methods. These characteristics make it highly suitable for widespread applications in aerospace, automotive manufacturing, and related fields.