Wireless radio frequency sensors for structural health monitoring

Structural health monitoring (SHM) is fundamentally important in civil engineering. Sensing transient changes in strain build-up of a construction is essential for determining and assessing mechanical health of its structure. To date different types of strain sensors have been reported to monitor strain. However, it is technically challenging to design and operate a strain sensor at a reduced complexity and cost, while also achieving strain assessment in plastic deformation. In this study, to address this challenge, we propose a new class of wireless radio frequency (RF) strain sensors based on metamaterial-inspired architectures that allow for real-time SHM including the plastic deformation of steel rods. Such a capability is vitally critical especially in geographical locations where earthquakes frequently occur. To enable telemetric strain sensing for SHM, we developed cost-effective, easy-to-make, passive RF sensors composed of comb-like split ring resonators, each with a cut between the two halves making the splits and a wire jumper on one end making the ring. By externally applying loads on standard steel rods, which are used in buildings, we demonstrated that the frequency shift in S11 changes with the gap width and the applied load, and that the displacement on the steel rods can be monitored telemetrically. Our results indicate that these wireless sensors hold great promise for real-time remote SHM.