A Novel 4-Bit U-Shaped Chipless Flexible Substrate RFID Sensor Sensing Characterization Study

Technical method for strain detection using radio frequency identification (RFID) technology is characterized by flexibility, low cost and high intelligence. The traditional planar-based rigid sensing antennas are basically made of rigid substrates, which have the disadvantages of poor surface fit and flexibility, so flexible electronics are gradually applied in the field of structural health monitoring (SHM) to solve the challenge of non-planar deformation monitoring. In this paper, we propose a flexible reconfigurable strain-gauge RFID sensor with an encoding capability of 4 bits. The encoding structure is based on a coupled U-shaped resonator with strain resonance in the UHF RFID frequency band from 0–4 GHz. Reconfigurability is achieved by introducing a diode with modulated bandstop filtering in the resonator. The proposed antenna uses an FPCB board with total dimensions of 100 mm
$\times71.4$
mm
$\times0.508$
mm. It is subjected to thermal stability experiments, four-point bending strain and strain monitoring inside concrete, and the simulation and measurement results verify the feasibility of the design. This is important for realizing high-performance integrated strain monitoring in structural health monitoring using RFID technology.