<p>A fiber Bragg grating (FBG) pressure sensor using a composite structure comprising a square diaphragm, steel trusses, and vertical beams is proposed and studied. The deflection of the square diaphragm due to the applied pressure is transferred as an axial force on the FBG mounted at the end of the vertical beams. Measurement principle and stress analysis of the pressure sensor are introduced. The experimental results indicate that the pressure sensitivity of the sensor is 622.71 pm / MPa across the range of 0 to 2 MPa with a good linearity recorded at 99.996%, and the hysteresis and repeatability of the pressure sensor are calculated to be 0.6639% full-scale output (FSO) and 0.2773% FSO, respectively. In addition, the relative error of the sensor after temperature compensation was found to be 1.46%, which indicates an effective elimination of the effect of the temperature on pressure measurement.</p>
We proposed a fiber-optic sensor implanted with helical seven-core structure based on Mach–Zehnder interference, which can be used for the measurement of tensile strain and extrusion bending. The sensor consisted of a section of seven-core optical fiber with helical structure, which can be described as the SMF-Taper-HSCF-Taper-SMF (HSCF, helical seven-core fiber) sensor. When stretching or bending is applied, the sensor will undergo certain deformation, which will lead to the changes of interference modes in the optical fiber. The tensile strain and extrusion bending can be measured accurately according to the response of transmission spectrum to mode change. The helical seven-core structure can effectively stimulate higher order modes and induced deformation changes. In the experiment, three sensors with different helical periods were fabricated and their spectral characteristics were analyzed. Finally, we selected the sensor with a helical period of 190 μm to conduct a strain and bending test. The results show that the strain sensitivity of the sensor is −21.31 pm / με in the range of 0 to 500 με, and the curvature sensitivity of the sensor is −6.36 nm / m − 1 in the range of 0.16 to 1.6 m − 1. This sensor can detect strain and bending and has stable sensing performance and high sensitivity.
The random error model for evaluating FBG dynamic sensing system is proposed and established by using Allan variance, and the error recognition is experimentally demonstrated. The composition of the FBG sensing system, the characteristic of random error and error source for FBG acceleration sensing system are analyzed. The random error theoretical model based on the FBG acceleration sensing system is proposed and analyzed. In order to experimentally perform stability characterization of the system, the static output signal is achieved, and Allan variance curve is obtained by data processing, and the main coefficients of the error source can be further obtained. The model based on the Allan variance adequately demonstrates that it is feasible to evaluate the FBG system, which provides the basis for further designing, improvements and developing.