Reliable Crack Monitoring Based on Guided Wave Through Periodically Loaded Transmission Line

Cracks are commonly occurring defects in metal. Crack monitoring in large-area infrastructures requires numerous sensors and thus increases the weight, complexity, and integrity problem for wire deployment. The electromagnetic (EM) resonator-based sensor enjoys good sensitivity but suffers limited coverage. The perturbation theory governing crack detection for EM resonator-based sensors indicates that the uneven field distribution inside the resonator is the bottleneck behind the sensitivity and coverage. In this article, the EM energy is confined underneath the resonator but evenly distributed along the transmission line through periodically loading interleaved step impedance resonators (SIRs) on the two sides of a microstrip line. In this way, the sensitivity can be maintained and the coverage can be extended. An averaged attenuation constant is studied and extracted as a feature for crack characterization. The measurement normalized sensitivity is −0.057 N.U./mm2. This article provides a paradigm to bridge the gap between local and global monitoring. The proposed sensor can be used for monitoring potential cracks of in-service complex components.