Sensing and Transmission of Mechanical Deformation Data in the GHz Range from Chipless Printed Graphene Sensor

Chipless radio-frequency identification (RFID) sensors are a promising technology for real-time, wireless monitoring of the structural health of infrastructures in complex environments; however, they have not seen wide-scale adaptation in deformation sensing because of performance and cost limitations. We have designed, manufactured, and prototyped a complementary U-shaped chipless RFID sensor using routine printing methods and an ink prepared from highly conductive and processable nitrogen-doped thermally reduced graphene oxide (N-TrGO) materials. The sensor is printed on a low-cost, flexible, plastic substrate. The electromagnetic performance of the sensor is evaluated under different mechanical deformation conditions, including bending, torsion, and linear strain. The assessment is based on key backscattered signal parameters such as the reflected intensity, resonance frequency, and quality (Q) factor. Under bending deformation, the sensor exhibits a linear negative correlation in reflected signal intensity and an exponential decay in the Q-factor. In contrast, torsional loading results in a linear reduction in both the reflected intensity and Q-factor. During strain sensing, the sensor exhibits a linear shift in resonance toward lower frequencies as strain increases, confirming its capability to detect tensile deformations effectively. Aside from being rather easy to manufacture, microscopic surface analysis and sheet resistance of the film before and after cyclic deformation confirm the mechanical robustness and electrical stability of graphene-based tags. The sensor's performance was further evaluated under varying environmental conditions, including changes in relative humidity and temperature, to assess its operational stability in realistic settings. Overall, the sensor addresses reading range limitations of printed chipless RFID devices reported so far, reaching reading distances in excess of 80 cm while facilitating the quantification of multimodal deformations. These results highlight the potential of graphene materials as a realistic substitute for metal-based inks for more mechanically robust, cost-effective, and tailored solutions for wireless deformation sensing in emerging applications.