Array of chipless RFID sensor tag for wireless detection of crack on large metallic surface

In this paper, two array configurations of chipless RFID sensor tags are proposed for the detection of crack on a large metallic surface. A single sensor tag contains compass-shaped and a pair of L-shaped resonators. The metallic object under observation is identified by resonant frequencies of L-shaped resonators and crack on metallic object is observed by shift in resonant frequency of compass-shaped resonator. The unit cell tag provides read range of 120 cm and sensitivity of around 75 MHz/mm for 6 cm wide square-shaped surface. However, its performance degrades for larger surface. Therefore, a $3 \times 3$ array of sensor tag is proposed for larger surface area. The $3 \times 3$ array configuration can detect crack but can’t identify crack location due to the identical elements. To resolve the issue an idea of series array having five rectangular resonators with non-identical dimensions hence multiple resonant frequencies is presented. It helps to identify presence and position of crack on relatively large metallic surface.