Towards long-transmission-distance and semi-active wireless strain sensing enabled by dual-interrogation-mode RFID technology

Engineering structures are subjected to strain and deflection, due to various loads, and/or environmental effects. It is, thus, of uttermost importance to monitor the strain condition of critical structures, so as to prevent catastrophic failures, but also to minimize maintenance costs. In order to overcome limitations of existing conventional strain sensors, including extensive cabling arrangement and continuous power supply, a newly dual-interrogation-mode radio frequency identification (RFID) strain sensor is proposed in this study to achieve a longer interrogation transmission distance for wireless strain sensing, which can automatically switch between passive modes with low power consumption and active modes with ultra-high frequency (UHF). The proposed design scheme involves the RFID tag and RFID reader for wireless strain transmission module and the improved Wheatstone bridge as strain measurement module. The proposed RFID strain sensor features the following merits: (i) Wireless strain sensing characteristics with the integration of RFID technology. (ii) Long transmission distance with dual interrogation mode: RFID tag is generally in a passive dormant state with an extremely low operating current. And the tag circuit will enter the working state in ultra-high frequency to collect strain data only when the RFID reader enters the interrogation area, achieving semi-active strain sensing with low energy consumption at a long distance (up to 80 m), which is especially suitable for practical strain measurement of engineering structures. (iii) Temperature self-compensation characteristic: The developed RFID sensor includes a temperature compensation strain gauge to offset the error caused by temperature change, which will improve the measurement accuracy. Finally, extensive experiments are conducted to characterize the measurement performance, including thermal stability, tensile, and compressive strain sensing for various engineering materials.