Development and Characterization of a Novel Interdigitated Capacitive Strain Sensor for Structural Health Monitoring

Monitoring of structural health plays a crucial role in condition-based maintenance and degradation prediction of infrastructures. In this paper, we developed a novel interdigitated capacitive (IDC) strain sensor which could be integrated in a wireless monitoring system for structural health monitoring (SHM) applications. The IDC sensors were fabricated by laser-micromachining a 127-mu m-thick brass sheet followed by encapsulation in deformable thermoset polymers. The wireless monitoring system was implemented using a commercial wireless module (eZ430-RF2500 from Texas Instruments) which could provide multi-modality monitoring simultaneously. A graphical user interface was developed to display and store data as well as perform real-time analysis remotely. The wireless communication distance was up to 35 m inside buildings. The sensitivity of the sensor was characterized in both stretching and bending aspects, yielding a limit of detection with respect to strain of 0.025%. The gauge factor was found in the range of 6-9 which is much higher than those of commercially available strain gauges. The bending detection is reliable up to 20 degrees. Hysteresis and temperature dependence were also investigated, revealing predictable responses. Finally, the entire system was demonstrated with both single and multiple sensors for a real-time SHM case.