Theoretical and experimental study on the fiber Bragg grating-based inclinometer for slope displacement monitoring

We demonstrate a new concept for an all-fiber inclinometer based on a tapered fiber Bragg grating (tFBG) in a fiber ring laser (FRL) with the capability of measuring the tilt angle and temperature simultaneously. The sensor performance is analyzed theoretically and investigated experimentally. The dependence of tilt angle on the spectral response in variable temperature conditions was measured. Two inclinometers with different lengths have been fabricated and characterized in FRL. The sensitivity is 0.583 dB/° and 0.849 dB/°, respectively, in the range of 0° to 90°. Thanks to the FRL system, narrow 3-dB bandwidth (<0.1 nm) and high optical signal-to-noise ratio (~60 dB) are achieved. The tFBG in the FRL system can be used for working as a temperature insensitive inclinometer. The results suggested that the proposed inclinometer has the advantages of compact size and convenient manufacture, enhancing its potential for application prospect.

Section: Discussionmentioning

confidence: 99%

A Temperature Independent Inclinometer Based on a Tapered Fiber Bragg Grating in a Fiber Ring Laser

Lin

Zhou

Shao

et al. 2021

“…Then, the outer periphery of the casing is grouted with cement mortar. Next, the FBG flexible sensor is placed in the casing [36,37]. With the protection of the casing, even if the shear strains around the FBG flexible sensor are large, this will not cause the plastic deformation of the whole sensor structure.…”

Section: Methodsmentioning

confidence: 99%

Design, Optimization and Improvement of FBG Flexible Sensor for Slope Displacement Profiles Measurement

Tian

Wang

Sui

et al. 2019

The accurate measurement of slope displacement profiles using a fiber Bragg grating flexible sensor is limited due to the influence of accumulative measurement errors. The measurement errors vary with the deformation forms of the sensor, which dramatically affects the measurement accuracy of the slope displacement profiles. To tackle the limitations and improve the measurement precision of displacement profiles, a segmental correction method based on strain increments clustering was proposed. A K-means clustering algorithm was used to automatically identify the deformation segments of a flexible sensor with different bending shapes. Then, the particle swarm optimization method was adopted to determine the correction coefficients corresponding to different deformation segments. Both finite element simulations and experiments were performed to validate the superiority of the proposed method. The experimental results indicated that the mean absolute errors (MAEs) percentages of the reconstructed displacements using the proposed method for six different bending shapes were 1.87%, 5.28%, 6.98%, 7.62%, 4.16% and 8.31%, respectively, which had improved the accuracy by 26.83%, 18.94%, 29.49%, 26.35%, 7.39%, and 19.65%, respectively. Therefore, it was confirmed that the proposed correction method was competent for effectively mitigating the measurement errors and improving the measurement accuracy of slope displacement profiles, and it presented a vital significance and application promotion value.

“…Equations (11) and (12) are the contour curve fitting equations of mutual inductance voltage and Hall voltage, respectively. y r = 0.000000014x 6 − 0.0000016x 5 + 0.000068x 4 − 0.0013x 3 + 0.033x 2 − 0.00398x + 10.8 (11) y h = −0.00000026x 6 + 0.000014x 5 − 0.000286x 4 + 0.00248x 3 − 0.0264x 2 + 0.015x + 11.73 (12) Figure 13 shows the voltage contour drawn by MATLAB when the measured mutual inductance voltage is 1.858 V, Hall voltage is 1.559 V and the horizontal displacement and vertical displacement are both 10 mm under 0 degree of tilt angle. The fitted contour curve and the original contour discrete points of the mutual inductance voltage and Hall voltage are shown in Figure 14.…”

Section: Data Modelingmentioning

confidence: 99%

“…At present, the global monitoring of deep displacement of rock and soil mass mainly includes borehole inclinometer, time domain reflection technology, Brillouin Optical Time Domain Reflection (BOTDR) technology, borehole extensometer and sedimentation instrument.Borehole inclinometer is the most mature and widely used deep displacement monitoring technology for rock and soil mass due to its simple structure, high reliability and ability to measure the deep horizontal displacement and velocity of rock and soil mass. However, there are still many shortcomings in the development of this technology [10,11]. Each measuring unit of the inclinometer has strong coupling and rigidity, which leads to the insensitivity to small displacement in the deep displacement measurement of the soft soil, that is, the sensitivity of the inclinometer is limited.…”

mentioning

confidence: 99%

Research on Structure Optimization and Measurement Method of a Large-Range Deep Displacement 3D Measuring Sensor

Shentu

Wang

et al. 2020

Deep displacement monitoring of rock and soil mass is the focus of current geological hazard research. In the previous works, we proposed a geophysical deep displacement characteristic information detection method by implanting magneto-electric sensing arrays in boreholes, and preliminarily designed the sensor prototype and algorithm of deep displacement three-dimensional (3D) measurement. On this basis, we optimized the structure of the sensing unit through 3D printing and other technologies, and improved the shape and material parameters of the permanent magnet after extensive experiments. Through in-depth analysis of the experimental data, based on the data query algorithm and the polynomial least square curve fitting theory, a new mathematical model for 3D measurement of deep displacement has been proposed. By virtue of it, the output values of mutual inductance voltage, Hall voltage and tilt measuring voltage measured by the sensing units can be converted into the variations of relative horizontal displacement, vertical displacement and axial tilt angle between any two adjacent sensing units in real time, and the measuring errors of horizontal and vertical displacement are tested to be 0-1.5 mm. The combination of structural optimization and measurement method upgrading extends the measurement range of the sensing unit from 0-30 mm to 0-50 mm. It shows that our revised deep displacement 3D measuring sensor can better meet the needs of high-precision monitoring at the initial stage of rock and soil deformation and large deformation monitoring at the rapid change and imminent-sliding stage. stage is characterized by cracks in the surface layer of rock and soil mass, followed by collapse [9]. Therefore, studying the deep displacement of rock and soil mass is more in line with the needs of disaster prevention and mitigation than the study of surface displacement. The deep displacement of rock and soil mass can reflect the dynamic stability of rock and soil mass more accurately and quickly, therefore it provides accurate, powerful data and theoretical support for early warning of landslides.However, the deep displacement measuring device must be buried deep underground, requiring the instrument to be strong, anticorrosive, convenient for installation, operation, long-distance signal transmission and so on. At the same time, the deep displacement monitoring environment is harsh and complicated, and there are problems such as no light, water seepage, corrosion, geotechnical shearing and extrusion, which can easily cause damage to the buried instruments. Therefore, compared with surface displacement monitoring, the development of deep displacement monitoring technology is relatively slow, and the types of deep displacement monitoring instruments that can be practically applied are obviously less and have poorer performance. At present, the global monitoring of deep displacement of rock and soil mass mainly includes borehole inclinometer, time domain reflection technology, Brillouin Optical Time Domain Reflection (BO...