Electrical time domain reflectometry sensing cables as distributed stress/strain sensors in smart material systems

Electrical time domain reflectometry (ETDR) stress/strain sensing technique has been successfully demonstrated in geotechnical applications to detect rock deformation and longwall movement. The ETDR sensing method appears to be practical for health monitoring applications of civil engineering structures since durable sensor media can be used. To use the ETDR sensing technique for structural stress/strain measurements, the coupling mechanism between applied loads and TDR signal response of the sensors need to be understood and modeled accurately. In this paper a theoretical model capable of describing the relation between applied loads and TDR signal response of a coaxial cable was developed. The accuracy of the model was verified by comparing theoretical results with those of finite element analyses. Parametric study to investigate the effects of the physical and structural parameters of the cable was also performed using the theoretical model.