High-Sensitivity RFID Tag Sensor With Coupled Ring Resonators for Multiposition Crack Monitoring

Wireless monitoring of cracks is a critical task in evaluating the state of metal structure. Radio frequency identification (RFID) antenna sensors have been intensively investigated for crack detection. Nevertheless, the development of RFID antenna sensors satisfying the requirements of high sensitivity and coverage remains a challenge. In this article, an ultrahigh frequency (UHF) RFID antenna sensor with coupled ring resonators has been proposed, where the outer ring is designed for radiation and sensing, and the inner ring is utilized for impedance matching. The sensor is directly placed on metallic surface, forming an electromagnetically induced transparency-like (EIT-like) effect to enhance sensing capabilities. Due to a relatively uniform electromagnetic field constrained under the outer ring, surface cracks can be detected in different positions and directions. The sensor is sensitive to both depth and width of crack, with a sensitivity of −5.46 MHz/mm in crack depth and −10 MHz/mm in crack width detection. According to the results of this investigation, a potential sensing technique for practical applications is demonstrated.