Wireless strain and crack sensing using a folded patch antenna

In this research, folded patch antennas are investigated as low-cost and wireless smart-skin sensors that monitor the strain and crack in metallic structures. A radio frequency identification (RFID) chip is used for signal modulation. When the antenna is under strain/deformation, its resonance frequency varies accordingly. The variation can be easily interrogated and recorded by a reader that wirelessly delivers power for the antenna operation. Therefore, the antenna sensor can measure strain/crack. This paper reports latest test results on the strain and crack sensing performance of the antenna. In particular, tensile tests show that the wireless antenna sensor can detect small strain changes lower than 20 με, and can perform well at large strains higher than 10,000 με. In the crack test, a growing sub-millimeter crack is successfully detected by the antenna sensor.