Large Strain Fiber Bragg Grating Sensor

A fiber Bragg grating is a periodic perturbation of the refractive index along the optical fiber which is formed by exposure of the core to an intense optical interference pattern. The fiber Bragg grating sensors have many advantages for sensing applications, such as immunity to electromagnetic interference, resistance to chemical corrosion, low dissipation, small size,etc. However, the long-term stain is less than 3000μεin fiber. The wavelength shift of fiber Bragg grating is always less than 3000 pm, when the stain sensitivity of FBG is around 1.2 pm/με. The fiber Bragg grating sensor with the stain of 0～3000μεis frequently used and unable to meet the actul measurement such as cast zinc alloy, zaluminum, concrete structure with the stain of 5000με～10000μεin an optimal situation.In order to expand the range of stain,the fiber Bragg grating sensor with the stain of 0～6000μεis developed, which is the desensitization mechanical structure that is the distance between two fixed pivots less than the length of fiber between two adjusting tubes. The ends of the fiber Bragg grating is fixed at two adjusting tubes.They are fixed in the ends of desensitization tubes by screw thread.The other end of the desensitization tube is fixed at the fastening tube. Two fastening tubes connects with the stain tube.Two fixed pivots are mounted on two fastening tubes.By the external forces, the relative position of the fixed pivots are changed, which causes the axial deformation of the strain tube leading to the Bragg wavelengths shift in proportion of fiber Bragg grating attached at two ends of the adjusting tubes. The main completed work as follows:(1) The model of fiber Bragg grating sensor with large strain is established and the mathematical is deduced.(2) The materials of the fiber Bragg grating sensor are selected, and the material selection parameters of the s sensor are calculated theoretically. When the tubes material is chosen as steel, adjusting tubes with the length of 15mm, stain tubes with outer diameter of 7mm, inter diameter of 5mm and the length of 70mm, desensitization tube with the length of 50 mm, fastening tube with the length of 20mm.The theory response sensitivity of the sensor is 1.58 pm/kg, and the theory stain sensitivity is 0.607 pm/με. (3) Through loading, the sensor is stretched. The experimental results show that the response sensitivity of the sensor is 1.783 pm/kg, the stain sensitivity is 0.685 pm/με, and the maximum stain range could be 5250με.