Chipless passive RFID sensor for structural health monitoring

Mechanical structures experience deformation and develop cracks over time, often due to factors like fatigue, stress, or environmental conditions. Therefore, it is crucial to continuously monitor the mechanical health of critical structures which not only helps prevent potentially disastrous failures but also serves to reduce maintenance expenses by avoiding unnecessary inspections. Conventional tools that are widely used for deformation detection are strain gauges and fiber optic sensors due to their low cost and efficiency. However, since these techniques require cabling or battery-driven electronics, they have certain limitations in hard to reach areas. Wireless battery-free radio frequency identification sensors provide solutions to such limitations. In this paper, we introduce a novel low-cost chipless RFID sensor tag designed for determining the dielectric properties of materials. Our sensor utilizes a depolarizing resonator loaded with printed capacitors, where the capacitance varies according to the permittivity of the material that comes in contact with the tag, which causes a shift in resonant frequency. By analyzing the shift in resonance frequency, we can accurately determine the permittivity of the material. This configuration enhances the cross-polar radar cross-section, thereby improving tag detection.