Embedded fiber Bragg grating strain sensor with enhanced sensitivity

In engineering practice, especially in the structural health monitoring (SHM) of civil engineering, the deformation of concrete is usually small, so a strain sensor don't need a large measuring range but a high sensitivity. This work presents the structural design, measuring and sensitization principle, and full test of an embedded FBG strain sensor for SHM of reinforced concrete. Two capillary steel tubes protected by a stainless steel tube and embedded with each end fiber of a FBG have been proposed, which possesses the capacity of strain sensitization and adjustment. Experimental results show that sensor provides a sensitivity of 4.2 pm/mu epsilon in measurement range of +/- 300 mu epsilon, which is 3.5 times than the bare FBG with center wavelength of 1550 nm. Test results also demonstrate that the sensor possesses good repeatability and creep resistance, which is promising for applications in civil engineering.