An FBG Displacement Sensor in Deformation Monitoring of Subway Floating Slab

In order to monitoring vibration-reduction and vibration-isolation effects of subway floating slab, an FBG displacement sensor was developed to monitor the deformation of the subway floating slab. The proposed sensor mainly consists of an FBG, a thin-walled ring, a steel-spring, connecting rod probe, linear bearing, sleeve, and other auxiliary unit. The connecting rod probe transmits the external displacement to the steel-spring and elastic thin-walled ring, and then leads to the wavelength shift of the FBG pasted in the reserved groove of the thin-walled ring. Meanwhile, the linear bearing can reduce the friction loss and increase the sensor stability. Lots of sensing tests showed that, the sensor has a sensitivity of 36.36 pm/mm and a precision of 8.25×10-2 mm in the displacement range of 0-20 mm, and also has good micro-displacement measurement capabilities. The theoretically calculated data for the vertical displacement of the floating slab are consistent with the actual measured data, which verifies the feasibility of the proposed displacement sensor in the monitoring of the subway floating slab.