Fiber Bragg Grating Displacement 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.

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.

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.

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.

A FBG based displacement transducer for small soil deformation measurement

A small soil deformation measurement system based on fiber Bragg grating (FBG) has been developed for underground displacement monitoring. This new displacement transducer consists of two anchorage plates for the fixation of displacement sensor in soil, a single FBG sensor for sensing the occurred deformation, and a PolyVinyl Chloride (PVC) tube for the protection of inner FBG sensor. The two anchorage plates were fabricated and fixed on the PVC tube surface by FDM process. Gauge length, maximum measurement displacement, and displacement resolution of the proposed FBG displacement transducer were 90 mm, 0.9 mm, and 0.0747 mm, respectively. Raw material of the anchorage plates was Polylactic Acid (PLA) material. An embankment model was established and installed with multiplexed four FBG displacement transducers for the measurement of internal horizontal displacement in laboratory. Both static load and movable load were applied on the top surface of the embankment model. It is found that maximum error of the four sensors under different static load was less than 6%. The monitored strains of four different FBG displacement transducers under movable load were highly consistent, indicating that the smart FBG based small deformation monitoring system can be used to monitor vehicle flow in future. All monitored displacement values were less than 0.03 mm. Therefore the FBG displacement transducer characterized by high resolution can be used to monitor small displacement occurred underground.

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 ...

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.

Development of a Cloud Computing-Based Pier Type Port Structure Stability Evaluation Platform Using Fiber Bragg Grating Sensors.

Structure Health Monitoring is a topic of great interest in port structures due to the ageing of structures and the limitations of evaluating structures. This paper presents a cloud computing-based stability evaluation platform for a pier type port structure using Fiber Bragg Grating (FBG) sensors in a system consisting of a FBG strain sensor, FBG displacement gauge, FBG angle meter, gateway, and cloud computing-based web server. The sensors were installed on core components of the structure and measurements were taken to evaluate the structures. The measurement values were transmitted to the web server via the gateway to analyze and visualize them. All data were analyzed and visualized in the web server to evaluate the structure based on the safety evaluation index (SEI). The stability evaluation platform for pier type port structures involves the efficient monitoring of the structures which can be carried out easily anytime and anywhere by converging new technologies such as cloud computing and FBG sensors. In addition, the platform has been successfully implemented at “Maryang Harbor” situated in Maryang-Meyon of Korea to test its durability.

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.

A Novel Fiber Bragg Grating Displacement Sensor With a Sub-Micrometer Resolution

This letter has proposed a novel fiber Bragg grating (FBG) displacement sensor with a sub-micrometer resolution through the use of the transverse property of a suspended optical fiber with a pre-tension force. A wedge-shaped sliding block and a T-shaped cantilever beam formed a conversion mechanism to transfer the horizontal measured-displacement into the transverse movement of the optical fiber midpoint. Compared with existing FBG displacement sensors, this design does not only avoid the FBG-pasting process and its associated issues, such as the chirping failure and low repeatability, but also achieves a high resolution. The sensing principle has been presented, and the corresponding theoretical model has been derived and validated. Experiments show that this design has an excellent sensitivity of 2086.27 pm/mm and a high resolution of $0.48~\mu \text{m}$ within a range of 1.0~2.0 mm. The displacement results from the proposed sensor closely agree with the values detected from the commercial laser displacement sensor, validating its effectiveness. Therefore, the proposed sensor can be directly utilized to measure the sub-micrometer displacement, and also support multi-point distributed detection.

A novel wide measuring range FBG displacement sensor with variable measurement precision based on helical bevel gear

A novel fiber Bragg grating (FBG) displacement sensor is proposed, which can achieve wide measuring range displacement detection with variable measurement precision due to its mechanical transfer structure of helical bevel gear. A prototype is designed and fabricated. The maximum detection displacement of this prototype is 1.751 m, and the precision grade changes from 0.2% to 6.7%. Through analyzing the experiment data which is obtained in the calibration experiment, the measuring range of this sensor is from 0 m to 1.532 m, and the wavelength shift errors between experiment data and theory calculation are all less than 5%.

Improved design of slow light interferometer and its application in FBG displacement sensor

An optical fiber Mach–Zehnder interferometer (MZI) based on slow light in polymer-infiltrated PCW (PI-PCW) was proposed to enhance the demodulation sensitivity of fiber Bragg grating (FBG) displacement sensor. By optimizing the structure of PI-PCW, slow light with high group index of 110 was realized, which is advantageous to develop high-sensitive MZI. And thanks to electro-optic effect of the infiltrated polymer, the working wavelength of flat band slow light, as well as the demodulation range of MZI, could be flexibility changed and enlarged by tuning external driving voltage. At last, differential and orthogonal method was used to demodulate the interference spectrum of MZI with high stability and good linearity. The FBG was pasted on an Omega-like beam, thus the displacement variation of the free end of the Omega-like beam could be measured by monitoring the output phase of MZI. Finally, the proposed displacement sensor demonstrated a high sensitivity of 1.035rad/mm with good linearity and wide measurement range of 55.6mm.

Fiber Bragg Grating Sensor Package for Submicron Level Displacement Measurements

In this article, the design and development of a Fiber Bragg Grating (FBG) based displacement sensor package for submicron level displacement measurements are presented. A linear shift of 12.12 nm in Bragg wavelength of the FBG sensor is obtained for a displacement of 6 mm with a calibration factor of 0.495 mu m/pm. Field trials have also been conducted by comparing the FBG displacement sensor package against a conventional dial gauge, on a five block masonry prism specimen loaded using three-point bending technique. The responses from both the sensors are in good agreement, up to the failure of the masonry prism. Furthermore, from the real-time displacement data recorded using FBG, it is possible to detect the time at which early creaks generated inside the body of the specimen which then prorogate to the surface to develop visible surface cracks; the respective load from the load cell can be obtained from the inflection (stress release point) in the displacement curve. Thus the developed FBG displacement sensor package can be used to detect failures in structures much earlier and to provide an adequate time to exercise necessary action, thereby avoiding the possible disaster.

Application of a Fiber Bragg Grating-Based Sensing System on Investigating Dynamic Behaviors of a Cantilever Beam Under Impact or Moving Mass Loadings

By setting up a fiber Bragg grating (FBG) displacement and strain sensing system, this paper experimentally investigates dynamic behaviors of a cantilever beam under impact or moving mass loadings. Dynamic sensing ability of the FBG displacement sensor is demonstrated by simultaneously measuring with a noncontact Fotonic sensor. Responses obtained from the FBG strain sensor are compared with those obtained from polyvinylidene fluoride film sensors and a strain gauge. First, an impact loading is generated by an impact hammer, and transient out-of-plane displacement responses obtained from the proposed FBG displacement sensor are compared with finite element simulations. Then, vibrations of the cantilever beam subjected to impact loadings by a steel ball are investigated. Finally, with a high-speed camera to detect the moving speed, experimental study of the cantilever beam under a moving mass is performed. By using the FBG displacement and strain sensing system, three kinds of modes of the cantilever beam (i.e., bending modes, lateral bending modes, and torsional modes) are detected under impact or moving mass loadings. With the high sensitivity of the proposed FBG sensing system, relationships between the transient responses induced by impact or moving mass loading and the vibration modes are discussed.

Active suppression of a beam under a moving mass using a pointwise fiber bragg grating displacement sensing system

This paper investigates active vibration control of a beam under a moving mass using a pointwise fiber Bragg grating (FBG) displacement sensing system. Dynamic responses of the proposed FBG displacement sensor are demodulated with an FBG filter and verified with measurement results obtained from a noncontact fiber-optic displacement sensor. System identification of the beam is first performed with a piezoceramic actuator and positive position feedback (PPF) controllers are designed based on the identified results. Then, transient responses of the beam under a moving mass with different moving conditions are measured using the FBG displacement sensor. A high-speed camera is used to detect the speed of the moving mass for further discussions about its influence on the transient response. Finally, active vibration control of the beam under the moving mass is performed and fast Fourier transform (FFT) as well as short-time Fourier transform (STFT) are employed to demonstrate control performances. For the case in which a rolling steel ball is directed from a slide to the beam to generate the moving mass, reductions of the vibration up to 50% and 60% are achieved in the frequency domain for the first and second modes of the beam, respectively. Based on the control experiments on the smallscale beam, results in this work show that the proposed FBG displacement sensing system can be used in research on the moving mass problem.

A point-wise fiber Bragg grating displacement sensing system and its application for active vibration suppression of a smart cantilever beam subjected to multiple impact loadings

In this work, active vibration suppression of a smart cantilever beam subjected to disturbances from multiple impact loadings is investigated with a point-wise fiber Bragg grating (FBG) displacement sensing system. An FBG demodulator is employed in the proposed fiber sensing system to dynamically demodulate the responses obtained by the FBG displacement sensor with high sensitivity. To investigate the ability of the proposed FBG displacement sensor as a feedback sensor, velocity feedback control and delay control are employed to suppress the vibrations of the first three bending modes of the smart cantilever beam. To improve the control performance for the first bending mode when the cantilever beam is subjected to an impact loading, we improve the conventional velocity feedback controller by tuning the control gain online with the aid of information from a higher vibration mode. Finally, active control of vibrations induced by multiple impact loadings due to a plastic ball is performed with the improved velocity feedback control. The experimental results show that active vibration control of smart structures subjected to disturbances such as impact loadings can be achieved by employing the proposed FBG sensing system to feed back out-of-plane point-wise displacement responses with high sensitivity.