Design of Displacement Sensor Based on the Bending Loss of U-Type Wingding Fiber

In view of the nonlinear relationship between displacement and bending loss in traditional fiber bending loss displacement sensor, and the problem that high sensitivity and large scale cannot be obtained at the same time, we design a novel displacement sensor based on the bending loss of U-type winding fiber. The fiber consists of a U-type turning and a spiral winding around the shaft, which of them arc called U-type winding. It is proved theoretically that there is a linear relationship between the measured displacement and the bending loss. We deduce the expression of them, discuss the effect of spiral winding on the bending radius of fiber and the effect of U-type turning on the accuracy of the sensor, and carry out a series of experimental studies and performance tests. Experimental results demonstrate that displacement sensitivity of the sensor is 0.14 dB/mm in the range from 0 to 120 mm, and the linear correlation coefficient is greater than 0.99. There is no stress relaxation of the optical fiber in the winding process. It is suggested that the radius of curvature of the U-type turning fiber should be larger than 6 mm. The displacement sensor based on the bending loss of U-type winding fiber has good measurement precision and large scale. It can realize the monitoring of concrete structure cracks and continuous monitoring of the displacement of large structure.