Detection of Metallic Surface Cracks Based on Multiunit Periodic Resonant Structure

A novel sensor based on a multiunit periodic resonant structure is proposed to detect slender cracks on a metallic surface. The detection is based on the variation of the resonance frequency of the sensor, which is caused by metallic surface cracks. By etching rectangular stripes in the ring to reduce the surface area of the resonant structure and increase the current flow path, it can achieve higher detection sensitivity and can detect metallic surface cracks with 0.02-mm width. Periodic expansion of a single-unit structure can increase the concentration area of the electromagnetic field of the sensor and make it more sensitive to slender cracks. By simulation and experiment, when detecting cracks of the same size, the resonance frequency shift of the multiunit periodic structure is higher than that of the single-unit structure, indicating that the multiunit periodic structure has better detection ability. The multiunit periodic structure sensor has a frequency shift of more than 300 MHz for a slender crack with a 0.02-mm width.