Fiber Bragg Grating Displacement Sensor Research Articles

Fiber Bragg grating displacement sensor based on synchronous deformation sensing for real-time monitoring of a tunnel lining.

A fiber Bragg grating (FBG) displacement sensor based on synchronous sensing is developed for real-time monitoring of a tunnel lining. The sensing principle and mechanical structure of the proposed sensor are analyzed and simulated, and its sensitization effectiveness and temperature compensation are verified. Equivalent model tests show that the sensor has a good linear sensitivity of 19.48pm/mm and an excellent precision of 5.13×10-2 m m in the displacement range of 0-25mm, which is basically consistent with the simulation results. The key traffic parameters of the train were successfully obtained by real-time monitoring of the tunnel lining in a field trial, which shows the superior capability of micro-displacement measurement of the sensor. Furthermore, good stability and excellent creep resistance have also been demonstrated. Our results provide theoretical guidance for the fabrication and package of the FBG displacement sensor, which is valuable for structure health monitoring (SHM) in civil engineering applications.

FBG displacement sensor with hyperbolic flexible hinge structure

This paper proposes a design method for a fiber Bragg grating (FBG) displacement sensor with a hyperbolic flexible hinge structure. A compact FBG displacement sensor with strong micro displacement measurement capability was fabricated. The final assembly testing showed that the sensor achieved good linearity with a linearity of 0.53%F·S at a range of 50 mm. The sensitivity was measured as 24.45 pm mm−1, hysteresis error as 1.1%FS, and repeatability error as 0.659%. The testing results demonstrated that the fabricated FBG displacement sensor exhibited strong practicality and good stability, making it suitable for long-term displacement monitoring of slope safety.

A high-sensitivity fiber Bragg grating sensor for displacement measurement in structural health monitoring.

Displacement measurement is of great significance to monitor the crack variation and ensure the health of building structures. Aiming at the problems of low sensitivity and high temperature error of fiber Bragg grating (FBG) displacement sensors in displacement monitoring, this paper presents an adjustable cantilever beam displacement sensor with the FBGs as the sensing element. The sensor adds double FBGs on the relative surfaces of the equal-strength cantilever beam, which increases the bending deformation on the FBG of the beam surface to improve the sensitivity and realize the temperature compensation of the sensor. By adding an adjustable external rod structure between a flexible spring and a fixed foot stand, the sensor can regulate the range of initial crack width for different occasions. A theoretical analysis of the displacement sensor is performed, and the simulation analysis and optimization design for the structural parameters of the cantilever beam elastic sensitive element are implemented by adopting SolidWorks and ANSYS software. Finally, a displacement testing platform is constructed to test its performance. Experimental results show that this design has a high sensitivity coefficient of 39.47 pm/mm and a temperature coefficient of 1.04 pm/°C in the range of initial crack width from 0 to 110mm or from 0 to 130mm depending on different monitoring situations. Furthermore, good linearity, hysteresis delay, repeatability, and temperature compensation performance have also been demonstrated.

Coiling an optical fiber for long-range dynamic displacement and force sensing

Optical fiber sensors have been applied on detecting various physical parameters. In this work, inspired by the mechanism of tendril coiling, we designed a spring-like sensor using optical fibers based on macro bending loss. The proposed optical-fiber spring has good elasticity like a mechanical spring and thus can be used to measure large displacement. As a contact-type sensor, the fabricated optical-fiber spring can measure dynamic displacement, whose range is 4 orders of magnitude higher than that of the point-wise fiber Bragg grating displacement sensor. In addition to the point-wise displacement sensing, we further integrated the optical-fiber spring with a Kresling origami to form a force sensor.

A Double FBGs Temperature Self-Compensating Displacement Sensor and Its Application in Subway Monitoring.

In order to ensure the effective vibration–reduction and vibration–isolation of the steel spring floating plate rail and meet the safe operation requirements of the subway, a Fiber Bragg Grating (FBG) displacement sensor for the deformation monitoring of the subway floating plate is proposed. The sensor adopts double FBGs to realize temperature self-compensation. The elastic ring is used as the elastic conversion structure after the fiber grating is pre-stretched; the two ends are pasted and fixed in the groove in the diameter direction of the ring, which avoids the waveform distortion caused by the full pasting of the fiber grating. The combination of linear bearing and displacement probe rods can increase stability and reduce friction loss so that the sensor has the advantages of high sensitivity and accurate measurement results. The test results and error analysis show that in the range of 0~20 mm, the sensitivity of the sensor is 164.2 pm/mm, the accuracy reaches 0.09% F.S, and the repeatability error and hysteresis error are only 1.86% and 0.99%, respectively. The thermal displacement coupling experiment proves that the sensor has good temperature self-compensation performance. It provides a new technical scheme for the effective monitoring and condition assessment of the built-in steel spring floating plate rail.

Fiber-Bragg-Grating-Based Displacement Sensors: Review of Recent Advances.

With the development of fiber optical technologies, fiber Bragg grating (FBG) sensors are frequently utilized in structural health monitoring due to their considerable advantages, including fast response, electrical passivity, corrosion resistance, multi-point sensing capability and low-cost production, as well as high accuracy and resolution over a long period. These characteristics allow FBG to be a proper alternative sensing element for displacement measurements. In this article, the recent sensing advances and principles of detection of FBG-based displacement sensors are illustrated. Specifically, the latest FBG-based displacement technologies are examined from three principles of detection, i.e., wavelength, intensity and phase signal demodulation. Regarding wavelength detection methods, the problem related to the cross-sensitivity can significantly be reduced depending on the new type of cantilever–FBG-based sensing developed. Vice versa, only the packaging method of FBG prestressed between two fixed ends can still avoid the chirp phenomenon in the reflection spectrum. Moreover, to attenuate the influence of temperature variations on the accuracy of FBG displacement sensors, specific temperature self-compensation structures were successfully designed according to the concepts of phase signal demodulation. In future investigations, different elastic structures and gratings manufactured through special fibers and new methodologies for temperature compensation will still highly refine the efficiency of FBG-based displacement sensors.

A Fiber Bragg Grating Sensor for Positive and Negative Displacement Measurement

This work presents a fiber Bragg grating (FBG) displacement sensor suitable for alternate positive and negative displacement measurement. When measuring alternating displacements, existing FBG displacement sensors need to pre-stretch to a certain state, thus the elastic element of the sensor will in a state of large deformation instead of the working “zero deformation point”. The elastic element is easy to creep and lose its resilience, which will lead to inaccurate measurement. The FBG displacement sensor proposed in this work can overcome the above shortcomings. Through ingenious design, two pairs of “FBG - cantilever - wedge shaped slider” structure are used for positive and negative displacement detecting respectively. When measuring the positive displacement, one cantilever beam with FBG is in a deformed state, while the other one is not deformed and provides temperature compensation. For negative displacement measurement, the situation is just reversed. Comprehensive performance tests have been carried out, and the experimental results demonstrate that the sensor possesses a measurement range of ±50mm and a sensitivity of 29.373 pm/mm. Furthermore, good micro-displacement measurement capability, creep resistance, and temperature compensation performance have also been demonstrated.

Study of landslide geological hazard prediction method based on probability migration

Based on construction of landslide displacement field detection system in Heifangtai (Lanzhou, China), landslide geological hazard prediction method based on probability migration is proposed and verified in this paper. In the hardware of landslide displacement field detection system, there are five diction points which contain 15 fiber Bragg grating (FBG) displacement sensors, and the data of detection point 1 m1 m2 and m3 are chosen as sample to complete data analyses. After data analyses, the future trend state of m1 is ‘S’ due to that state transition probability Pm111 > Pm113 > Pm112, m2 is ‘S’ due to that Pm211 > Pm212 > Pm213, and m3 is ‘S’ due to that Pm311 > Pm312 = Pm313. The future trend state prediction is highly consistent with the actual measured data and field observation results. These results of data analyses show that the proposed prediction method in this paper can realize effective prediction of landslide state and has important practical value for landslide prediction.

Experimental Investigation and Error Analysis of High Precision FBG Displacement Sensor for Structural Health Monitoring

High precision structural displacement monitoring is challenging, but an effective method for structural health monitoring and particularly damage evaluation. In this paper, a high precision fiber Bragg grating (FBG) displacement sensor with embedded spring is developed to monitor structural displacement variation even at very small ranges. The principle of such monitoring is based on the central wavelength shifts in accordance with the displacement between measuring points. Calibration experiments are conducted to examine the performance of the innovative displacement sensor. The result indicates that the sensor has excellent linearity and repeatability, with the sensitivity coefficient being 23.96[Formula: see text]pm/mm, and the static relative error is 4.94% after three loading and unloading cycles. The displacement sensor therefore shows an excellent sensitivity and high precision for application. Moreover, it has been verified that this sensor is suitable and applicable for displacement monitoring in quasi-static experiment of structures.

Temperature Compensated FBG Displacement Sensor for Long-Range Applications

This letter presents an improved fiber Bragg grating (FBG) displacement sensor for long-range measurements. A mechanical transfer structure is designed and developed, which converts the displacement of a measurement wire to the elastic deflection of a sensing arm. The wavelength shift difference between two FBGs symmetrically pasted on the sensing arm is found to be proportional to the displacement. The experimental results show that this design has a displacement sensitivity of 23.80 pm/mm within a measurement range of 0–150 mm. This improved displacement sensor shows good temperature compensation with the very low temperature sensitivity of 0.076 pm/°C for a temperature range of −40–120 °C. This sensor can be utilized for long-range and high endurance displacement measurement applications in harsh industrial environment.

Fiber Bragg Grating Displacement Sensor With High Measurement Accuracy for Crack Monitoring

This paper presents a fiber Bragg grating (FBG) displacement sensor for crack monitoring in high-speed railway tunnels. Two FBGs placed in a single-mode optical fiber around two cylindrical rods are employed and configured in a prestretched and suspended status with the two ends fixed to two beams. This design can effectively avoid the pasting process of the grating area and the concomitant problem of chirp phenomenon in the reflection spectrum and promises a high sensitivity and resolution. The mechanical structure, operation principle, and corresponding theoretical model are presented in detail in sequence. Full-scale tests including the accuracy of this sensing system have been performed. The experimental results show that the sensor possesses a high sensitivity of 3304.7 pm/mm, a high accuracy of 20 $\mu$ m within a range of 0–2 mm, and a low repeatability error of 2.71%. Furthermore, excellent creep resistance (fluctuant value is within 2 pm) and good temperature compensation capacity (maximum value is 27 pm) have also been verified. The proposed sensor shows good performance that satisfies the actual requirements of long-term crack monitoring.

Extracting torsional band gaps and transient waves in phononic crystal beams: Method and validation

Due to an absence of proper measuring techniques, torsional waves/vibrations in one-dimensional phononic crystals (PCs) or elastic metamaterials are usually theoretically or numerically studied without experimental validations. This work proposes a measurement method capable of extracting torsional band gaps and transient torsional waves from the total responses of PC and metamaterial beams. Specifically, a pair of point-wise self-demodulated fiber Bragg grating (SFBG) displacement sensors, which can be arranged at points very close to each other on a thin PC beam, is utilized along with the proposed extraction method. The SFBGs are symmetrically set up at two locations about the central line on the surface of the PC beam. The torsional band gaps and the transient torsional waves are extracted from the differential responses of the two SFBGs, in which the common bending waves are cancelled out. In addition to the torsional behaviors, the bending waves can also be extracted from the summation responses of the two SFBGs. We first examine the dynamic linearity of the SFBGs. Then, steady-state detection of the torsional and bending band gaps of a PC beam is performed. Finally, a cantilever PC beam subjected to an eccentric steel ball impact, whose loading history is recorded by a pair of polyvinylidene fluoride (PVDF) films, is investigated to demonstrate the extraction of the torsional/bending bandgaps and waves from the early short time transient responses. The feasibility of the proposed torsional (or bending) extraction method is justified by the method of reverberation-ray matrix (MRRM), which is capable of providing “pure” torsional (or bending) behaviors of the PC beam. With the proposed extraction method, we also observe surface localized modes in the transmission of the PC beam, which are strongly related to the arrangement of the constituent components with different impedances in the unit cells. We believe that the proposed extraction method for torsional wave, along with the SFBG sensing technique and the MRRM, can provide future researchers with measurement and analysis method to validate their designs of torsional phononic crystals or metamaterials.

Analysis of Mechanical Response for a Reinforced Bedded Rock Slope under Rainfall

This paper has the objective to reveal real-time responses at several locations in reinforced bedded rock slopes under different rainfall conditions. Four scaled model tests have been conducted by varying rainfall patterns and slope inclinations, while several sensors, including fiber Bragg grating (FBG) displacement sensors, pore pressure sensors, and miniature pressure gauges, were instrumented in layers to capture corresponding responses during and after rainfall. The results show that the the slide of a reinforced bedded rock slope has a locking section, and the ultimate displacement under long-term medium rainfall was about three times larger than that under short-term storm rainfall. Meanwhile, the short-term storm rainfall generated little influence on the deeper pore pressure for reinforced bedded rock slope. The pore pressure at the surface layer was initially larger and then smaller than that at the intermediate layer for the same slope. For the slope under long-term medium rainfall, the shift moment was at 11.5 hours after testing started, while for the slope under short-term storm rainfall, the shift moment was at 3.5 hours after testing started. The thrust pressure ascended with the rainfall persisting and descended a little after rainfall. The descending in thrust pressure was mainly due to the fact that the strength of slope mass recovered partially with water flowing out of the slope from the frontal portion and the slide tendency was weakened. These results can provide engineers with more acquaintance with response characteristics for these kinds of rock slope.

Fiber optic displacement sensor used in railway turnout contact monitoring system

Railway turnout contact monitoring is very important in high-speed rail operation systems. In order to measure the distance between the sharp rail and the basic rail in a switch system, a wide-range, high-precision fiber Bragg grating (FBG) displacement sensor was designed. Because the distance between the sharp and basic rails is always greater than 14 cm, the measurement range width and accuracy of the proposed sensor system are ensured through the use of a long spring and a beam of constant strength. A differential compensation method is used to eliminate temperature effects. Test results show that the resolution of the proposed sensor is 0.040 mm and the measuring range is 0–170 mm. A field test was also carried out to evaluate the performance of the sensors.

Superwide-Range Fiber Bragg Grating Displacement Sensor Based on an Eccentric Gear: Principles and Experiments

AbstractAiming at the large displacement monitoring needs of slope, road, and bridge engineering, a new method concerning the superwide-range fiber Bragg grating (FBG) displacement sensor based on ...

Study on fiber Bragg grating displacement sensor with angle steel structure

In this paper, two fiber reinforced polymer/plastic (FRP) encapsulated fiber Bragg grating (FBG) sensors were installed on the two sides of the angle steel beam, which was used to measure the displacement and direction of the diagonal steel beam, so as to realize the health inspection of the angle steel structure. The sensors were re-spectively installed on the different positions of angle steel beam, and the relationship between displacement and strain transmission of angle steel beam was simulated by the finite element analysis. The optimum design of sensors installation were discussed and the experimental verification was carried out. The simulation and experimental results show that the sensor has the capacity to discriminate the direction and measure the size of one side of the angle steel beam displacement when installed in a reasonable position. To realize the health monitoring by using optical fiber sensors on the structures composed by angle steel, such as bridges, electric towers and cranes, and so on, a basic research was provided.

Fiber Bragg Grating Displacement Sensor with High Abrasion Resistance for a Steel Spring Floating Slab Damping Track.

This paper presents a fiber Bragg grating (FBG) displacement sensor with high abrasion resistance for displacement monitoring of a steel spring floating slab damping track. A wedge-shaped sliding block and an equal-strength beam form a conversion mechanism to transfer displacement to the deflection of the beam, and the deflection-induced strain is exerted on two FBGs. A special linear guide rail-slider and a precision rolling bearing have been adopted onto the conversion mechanism, which turned sliding friction into rolling friction and thus significantly reduced the friction during frequent alternating displacement measuring. Sensing principle and the corresponding theoretical derivation have been demonstrated. Experiment results show that the sensor has a sensitivity of 34.32 pm/mm and a high resolution of 0.0029 mm within a measurement range of 0~90 mm. Besides, the sensor has also a good measurement capability for micro-displacement within a range of 0~3 mm. The repeatability error and hysteresis error are 1.416% and 0.323%, respectively. Good creep resistance and high abrasion resistance for alternating displacement measurement have also been presented by a performance test. These excellent performances satisfy the requirements of high precision and long-term stability in structural health monitoring for machinery equipment and civil engineering, especially in the displacement monitoring of a floating slab damping track.

Fiber Bragg grating based displacement sensors: state of the art and trends

PurposeThe purpose of this paper is to present the latest sensing structure designs and principles of information detection of fiber Bragg grating (FBG) displacement sensors. Research advance and the future work in this field have been described, with the background that displacement and deformation measurements are universal and crucial for structural health monitoring.Design/methodology/approachThis paper analyzes and summarizes the existing FBG displacement sensing technologies from two aspects principle of information detection (wavelength detection, spectral bandwidth detection, light intensity detection, among others) and principle of the sensing elastomer structure design (cantilever beam type, spring type, elastic ring type and other composite structures).FindingsThe current research on developing FBG displacement sensors is mainly focused on the sensing method, the construction and design of the elastic structure and the design of new information detection method. The authors hypothesize that the following research trends will be strengthened in future: temperature compensation technology for FBG displacement sensors based on wavelength detection; a study of more diverse elastic structures; and fiber gratings manufactured with special fibers will greatly improve the performance of sensors.Originality/valueThe latest sensing structure designs and principles of information detection of FBG displacement sensors have been proposed, which could provide important reference for research group.

A hybrid FBG displacement and force sensor with a suspended and bent optical fiber configuration

This paper has proposed a novel fiber Bragg grating (FBG)-based hybrid displacement and force sensor with a compact structure and excellent resolution by using the transverse property of a tightly suspended and slightly bent optical fiber. The optical fiber, embedded with an FBG element, has been suspended with its ends fixed on the sensor frame and implemented with a pre-tension force by the displacement loading along its vertical direction to form a bent shape. A conversion mechanism has been designed to convert the displacement and force inputs into the transverse movement of different points along the suspended fiber. Experimental results show that the displacement sensitivity and force sensitivity are −219.69pm/mm within the range of 0–2.5mm and −345.2pm/N with a high calculated resolution of 2.9mN, respectively. Results from both the displacement and force experiments have illustrated a close agreement with values from commercial sensors.

A High-Sensitivity Fiber Bragg Grating Displacement Sensor Based on Transverse Property of a Tensioned Optical Fiber Configuration and Its Dynamic Performance Improvement

This paper presents a high-sensitivity fiber Bragg grating (FBG) displacement sensor with a novel configuration for structural health monitoring. The transverse movement of an optical fiber that has been configured as a tight suspension status with its two ends fixed has been utilized to measure displacement. The theoretical models for both static and dynamic displacements have been derived. The corresponding simulations have been conducted to determine the relationship between the model parameters and the sensor performance. This approach supports the sensor design improvement and structural optimization. Two small working ranges have been selected to determine the simplified linear model according to Taylor series. The sensitivity of this sensor can reach up to 490.1 pm/mm with a high resolution of $2.04~\mu \text{m}$ in a range of 1.4~2.0 mm. The introduction of the supporting spring unit has significantly enhanced the sensor’s resonant frequency without sacrificing the sensitivity. The application of the stiffer spring unit has enlarged the working bandwidth from 0~8 Hz to exceed 50 Hz. Enhancing the damping ratio unit can effectively improve the flatness of the dynamic response within the working bandwidth, while it does not affect other dynamic properties of the sensor. These improvements and design guidelines have been validated by both dynamic experiments and theoretical modeling.