Surface crack detection in metallic materials using sensitive microwave-based sensors

This paper presents a highly sensitive sensor inspired by complementary split-ring resonators (CSRRs). The resonators are electrically small and designed as a near-field sensor to detect surface cracks in metallic surfaces. The sensor is etched in the ground plane of a microstrip line and fabricated using printed circuit board technology (PCB). Compared to available microwave techniques, the sensor introduced here has key advantages including high sensitivity (increasing dynamic range of the sensor), spatial resolution, design simplicity and scalability. The sensor is able numerically to detect a crack of 10 um (equivalent to λ/3400), with 200 MHz shift in the resonance frequency. For a surface crack having 200 μm width and 2 mm depth, the numerical result showed a shift in the resonance frequency of more than 2 GHz. This resonance frequency shift exceeds what can be achieved using other sensors operating in the low GHZ frequency regime by significant margin.