Painting-Type Passive Loose-Bolt Sensing Based on Abnormality-Induced Changes in Waveguide Resonance

The ability to detect abnormalities in infrastructure automatically and remotely with a small number of sensors would greatly contribute to efficient and timely infrastructure inspection. Here, we propose a passive sensor that can be installed by painting. The painted waveguide-based sensor detects abnormalities in infrastructure from abnormality-induced changes in the resonance frequency of electromagnetic waves resonating inside the sensor. In this paper, the principle of detecting loose bolts with the painted waveguide-based sensor is demonstrated by simulation and experiment. The sensor is designed and fabricated as a resonator with resonance frequencies from 100 kHz to 2.5 GHz, which includes the UHF radio-frequency identification band, and the measurement frequency was set within this range. The fabricated sensor is capable of detecting not only a single loose bolt but also two or more loose bolts on the waveguide of the sensor to monitor.