A new embeddable FBG sensor system to measure and decouple moisture swelling, thermal expansion, and mechanical strain

This paper introduces an innovative Fiber Bragg Grating (FBG) sensor system designed to measure and decouple the simultaneous effects of temperature, humidity, and mechanical strain within a host material. The system uniquely integrates a novel theoretical framework and a specific sensor configuration to accurately isolate these parameters. The proposed sensor system consists of three FBG sensors: one dedicated to temperature measurement, a second sensitive to both temperature and humidity, and a third influenced by temperature, humidity, and strain. A theoretical framework, based on linear strain superposition and constitutive laws, is developed to separate each factor's contribution. Experimental validation, conducted under controlled hygrothermal conditions, demonstrates the system's ability to detect and decouple these effects accurately, enabling precise monitoring. The described system provides a reliable, compact, and effective solution, suitable for long-term monitoring. It further enables enhancements in predictive maintenance through improved accuracy of health and usage monitoring systems (HUMS).