Electromagnetic Resonator based Passive Wireless Sensor for Bolt Preload Monitoring

The progressive attenuation of bolt preload in tower cranes, caused by long-term exposure to transverse alternating loads, temperature fluctuations, and material fatigue, represents a universal structural degradation challenge for high-risk special equipment in dynamic environments. This implies the critical importance of real-time preload monitoring for ensuring the safety of such critical equipment. Addressing the limitations of conventional intrusive installation and wired measurement technologies, this study proposes a non-invasive integrated sensing-communication electromagnetic resonator based sensor that enables wireless passive monitoring of bolt preload. The sensor employs an inter-digital capacitor structure as a pressure-sensitive element, which combines with a planar spiral inductor to form an LC resonant circuit. Through the mapping between mechanical stress and capacitance, variations in preload are effectively translated into measurable frequency changes accessible through wireless interrogation. Simulation results demonstrate the sensor's capability to resolve pressure variations of 9 MPa in a range of 54 MPa. This research validates the feasibility of wireless and non-invasive bolt preload detection, offering a potential solution for enhancing safety and reliability in engineering systems.