An Electromagnetically Induced Transparency Inspired Antenna Sensor for Crack Monitoring

The simultaneous communication and sensing based on antenna sensors are receiving increasing attention for pervasive monitoring in the internet of things (IoT). The open structure for high radiation limits the antenna’s sensitivity and resolution when it functions as an electromagnetic sensor. In this article, an antenna sensor operated in the ultra-high frequency (UHF) radio frequency identification (RFID) band is reported for structural health monitoring (SHM) applications. A loaded split-ring resonator (SRR) renders a low Q-factor bright mode for communication and two back-sited U-shaped strip resonators are embedded among high dielectric material, confining the near-field and yielding a high Q-factor dark mode for sensing. The two modes are proximity coupled and form an electromagnetically induced transparency (EIT)-like effect to achieve simultaneous communication and sensing in the narrow UHF RFID band. An enhancement around five times in the sensitivity can be observed resulting from the trapped field in the dark mode. The simulated sensitivity and the maximum peak realized gain of the proposed antenna sensor are around 3.0 MHz/mm
²
and 3.77 dBi respectively. A prototype antenna sensor in a size of 42.0 mm
$\times42.0$
mm
$\times9.0$
mm is fabricated and measured. The detectability of surface crack using the proposed antenna sensor is experimentally validated by two case studies. The measured results demonstrate a sensitivity of 2.73 MHz/mm
²
for crack depth characterization and a sensitivity of 2.75 MHz/mm
²
for crack width characterization.