An RFID Tag Sensor for Bolt Preload Monitoring

As a core component of mechanical connections, the preload state of bolts directly affects the reliability and safety of structures. The detection of bolt preload is an important engineering issue in the field of Structural Health Monitoring (SHM). Traditional detection methods have limitations such as dependence on external power supply, wired connection, inconvenient disassembly and assembly, which are not suitable for equipment like tower cranes that require frequent assembly and disassembly with many bolts distributed separately. To address these challenges, a passive wireless strain-sensing node based on Radio Frequency Identification (RFID) technology is proposed in this paper. The proposed sensing node has a potential to enable collaborative but independent preload detection for multiple bolts, thereby facilitating efficient integrity connection monitoring of connection components. By integrating a Wheatstone bridge strain measurement module, a hardware architecture comprising a tag antenna, a tag chip, a low-power micro-controller unit (MCU), and a piezoresistive sensing signal-reading chip is designed to form a tag sensing node. An adjacent-bridge-arm temperature-compensation strategy is also incorporated and studied to enhance practical reliability. Experiments show that at a reading distance of 0.60 m, the tag achieves a strain resolution of 7.01 με and good linearity. The distributed sensing experiments on cantilever beams demonstrate its ability to accurately capture strain distribution. For an M30 bolt, the resolutions of the bolt head and the bolt shank are 3.72 kN and 0.21 kN, respectively. The proposed sensor features cost-effective, passive, wireless, and easy to install in a non invasive manner, making it suitable for frequent disassembly scenarios such as tower cranes and providing a reliable solution for real-time monitoring of bolt connection status.