Sensors

Editorial

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5 pages, 158 KiB

Open AccessEditorial

Special Issue “Fibre Optic Sensors for Structural and Geotechnical Monitoring”

by Michele Arturo Caponero

Sensors 2020, 20(8), 2415; https://doi.org/10.3390/s20082415 - 24 Apr 2020

Cited by 5 | Viewed by 2448

Abstract

In this editorial on the special issue “Fibre Optic Sensors for Structural and Geotechnical Monitoring” a review of the contribution papers selected for publication is given. Each paper is briefly summarized, presenting its objective and methods, then a comment is given about the [...] Read more.

In this editorial on the special issue “Fibre Optic Sensors for Structural and Geotechnical Monitoring” a review of the contribution papers selected for publication is given. Each paper is briefly summarized, presenting its objective and methods, then a comment is given about the relevance of the work with respect to the advance and the spreading of the fibre optic technology for monitoring applications. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

Research

Jump to: Editorial, Other

27 pages, 15050 KiB

Open AccessArticle

Monitoring of Strain and Temperature in an Open Pit Using Brillouin Distributed Optical Fiber Sensors

by Chiara Lanciano and Riccardo Salvini

Sensors 2020, 20(7), 1924; https://doi.org/10.3390/s20071924 - 30 Mar 2020

Cited by 26 | Viewed by 4824

Abstract

Marble quarries are quite dangerous environments in which rock falls may occur. As many workers operate in these sites, it is necessary to deal with the matter of safety at work, checking and monitoring the stability conditions of the rock mass. In this [...] Read more.

Marble quarries are quite dangerous environments in which rock falls may occur. As many workers operate in these sites, it is necessary to deal with the matter of safety at work, checking and monitoring the stability conditions of the rock mass. In this paper, some results of an innovative analysis method are shown. It is based on the combination of Distributed Optical Fiber Sensors (DOFS), digital photogrammetry through Unmanned Aerial Vehicle (UAV), topographic, and geotechnical monitoring systems. Although DOFS are currently widely used for studying infrastructures, buildings and landslides, their use in rock marble quarries represents an element of peculiarity. The complex morphologies and the intense temperature range that characterize this environment make this application original. The selected test site is the Lorano open pit which is located in the Apuan Alps (Italy); here, a monitoring system consisting of extensometers, crackmeters, clinometers and a Robotic Total Station has been operating since 2012. From DOFS measurements, strain and temperature values were obtained and validated with displacement data from topographic and geotechnical instruments. These results may provide useful fundamental indications about the rock mass stability for the safety at work and the long-term planning of mining activities. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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18 pages, 6540 KiB

Open AccessArticle

Detection of Crack Initiation and Growth Using Fiber Bragg Grating Sensors Embedded into Metal Structures through Ultrasonic Additive Manufacturing

by Sean K. Chilelli, John J. Schomer and Marcelo J. Dapino

Sensors 2019, 19(22), 4917; https://doi.org/10.3390/s19224917 - 12 Nov 2019

Cited by 24 | Viewed by 5343

Abstract

Structural health monitoring (SHM) is a rapidly growing field focused on detecting damage in complex systems before catastrophic failure occurs. Advanced sensor technologies are necessary to fully harness SHM in applications involving harsh or remote environments, life-critical systems, mass-production vehicles, robotic systems, and [...] Read more.

Structural health monitoring (SHM) is a rapidly growing field focused on detecting damage in complex systems before catastrophic failure occurs. Advanced sensor technologies are necessary to fully harness SHM in applications involving harsh or remote environments, life-critical systems, mass-production vehicles, robotic systems, and others. Fiber Bragg Grating (FBG) sensors are attractive for in-situ health monitoring due to their resistance to electromagnetic noise, ability to be multiplexed, and accurate real-time operation. Ultrasonic additive manufacturing (UAM) has been demonstrated for solid-state fabrication of 3D structures with embedded FBG sensors. In this paper, UAM-embedded FBG sensors are investigated with a focus on SHM applications. FBG sensors embedded in an aluminum matrix 3 mm from the initiation site are shown to resolve a minimum crack length of 0.286 ± 0.033 mm and track crack growth until near failure. Accurate crack detection is also demonstrated from FBGs placed 6 mm and 9 mm from the crack initiation site. Regular acrylate-coated FBG sensors are shown to repeatably work at temperatures up to 300

^{\circ}

C once embedded with the UAM process. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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14 pages, 1740 KiB

Open AccessArticle

Evaluation of Horizontal Stresses in Soil during Direct Simple Shear by High-Resolution Distributed Fiber Optic Sensing

by Assaf Klar, Michael Roed, Irene Rocchi and Ieva Paegle

Sensors 2019, 19(17), 3684; https://doi.org/10.3390/s19173684 - 24 Aug 2019

Cited by 7 | Viewed by 5012

Abstract

This paper presents an approach for evaluating the horizontal stresses that develop in geotechnical Direct Simple Shear (DSS) tests through the use of high-resolution distributed fiber optic sensing. For this aim, fiber optics were embedded in 3D printed rings used for confining the [...] Read more.

This paper presents an approach for evaluating the horizontal stresses that develop in geotechnical Direct Simple Shear (DSS) tests through the use of high-resolution distributed fiber optic sensing. For this aim, fiber optics were embedded in 3D printed rings used for confining the soil in the test procedure. An analytical approach linking the measured spatially-distributed strain profile and the internal soil-ring contact stresses is developed in the paper. The method is based on representation of the contact stresses by a Fourier series expansion, and determining the coefficients of the series by minimizing the difference between the measured strain and the analytical strain within the linear elastic ring. The minimization problem results in a linear set of equations that can easily be solved for a given measurement. The approach is demonstrated on a set of drained DSS tests on clean sand specimens. Stress paths using the evaluated horizontal stresses are plotted together with Mohr circles at failure. These illustrate how, in these specific tests, the horizontal stress increases and principal stress direction rotates, until failure occurs along horizontal planes. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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15 pages, 1239 KiB

Open AccessArticle

Load-Independent Characterization of Plate Foundation Support Using High-Resolution Distributed Fiber-Optic Sensing

by Asmus Skar, Assaf Klar and Eyal Levenberg

Sensors 2019, 19(16), 3518; https://doi.org/10.3390/s19163518 - 11 Aug 2019

Cited by 4 | Viewed by 3285

Abstract

The evaluation of soil reaction in geotechnical foundation systems such as concrete pavements, mat- and raft foundations is a challenging task, as the process involves both the selection of a representative mechanical model (e.g., Winkler, Continuum, Pasternak, etc.) and identify its prevailing parameters. [...] Read more.

The evaluation of soil reaction in geotechnical foundation systems such as concrete pavements, mat- and raft foundations is a challenging task, as the process involves both the selection of a representative mechanical model (e.g., Winkler, Continuum, Pasternak, etc.) and identify its prevailing parameters. Moreover, the support characteristics may change with time and environmental situation. This paper presents a new method for the characterization of plate foundation support using high-resolution fiber-optic distributed strain sensing. The approach involves tracking the location of distinct points of zero and maximum strains, and relating the shift in their location to the changes in soil reaction. The approach may allow the determination of the most suited mechanical model of soil representation as well as model parameters. Routine monitoring using this approach may help to asses the degradation of the subsoil with time as part of structural health monitoring strategies. In this paper, fundamental expressions that relate between the location of distinct strain points and the variation of soil parameters were developed based on various analytical foundation support models. Finally, as an initial validation step and to underpin the idea basics, the proposed method was successfully demonstrated on a simple mechanical setup. It is shown that the approach allows for load-independent characterization of the soil response and, in that sense, it is superior to common identification methods. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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13 pages, 3552 KiB

Open AccessArticle

Strain Monitoring of a Composite Drag Strut in Aircraft Landing Gear by Fiber Bragg Grating Sensors

by Agostino Iadicicco, Daniele Natale, Pasquale Di Palma, Francesco Spinaci, Antonio Apicella and Stefania Campopiano

Sensors 2019, 19(10), 2239; https://doi.org/10.3390/s19102239 - 15 May 2019

Cited by 29 | Viewed by 5738

Abstract

This work reports on the use of Fiber Bragg Grating (FBG) sensors integrated with innovative composite items of aircraft landing gear for strain/stress monitoring. Recently, the introduction of innovative structures in aeronautical applications is appealing with two main goals: (i) to decrease the [...] Read more.

This work reports on the use of Fiber Bragg Grating (FBG) sensors integrated with innovative composite items of aircraft landing gear for strain/stress monitoring. Recently, the introduction of innovative structures in aeronautical applications is appealing with two main goals: (i) to decrease the weight and cost of current items; and (ii) to increase the mechanical resistance, if possible. However, the introduction of novel structures in the aeronautical field demands experimentation and certification regarding their mechanical resistance. In this work, we successfully investigate the possibility to use Fiber Bragg Grating sensors for the structural health monitoring of innovative composite items for the landing gear. Several FBG strain sensors have been integrated in different locations of the composite item including region with high bending radius. To optimize the localization of the FBG sensors, load condition was studied by Finite Element Method (FEM) numerical analysis. Several experimental tests have been done in range 0–70 kN by means of a hydraulic press. Obtained results are in very good agreement with the numerical ones and demonstrate the great potentialities of FBG sensor technology to be employed for remote and real-time load measurements on aircraft landing gears and to act as early warning systems. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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12 pages, 6749 KiB

Open AccessArticle

Identification of Ground Intrusion in Underground Structures Based on Distributed Structural Vibration Detected by Ultra-Weak FBG Sensing Technology

by Weibing Gan, Sheng Li, Zhengying Li and Lizhi Sun

Sensors 2019, 19(9), 2160; https://doi.org/10.3390/s19092160 - 9 May 2019

Cited by 43 | Viewed by 6110

Abstract

It is challenging for engineers to timely identify illegal ground intrusions in underground systems such as subways. In order to prevent the catastrophic collapse of subway tunnels from intrusion events, this paper investigated the capability of detecting the ground intrusion of underground structures [...] Read more.

It is challenging for engineers to timely identify illegal ground intrusions in underground systems such as subways. In order to prevent the catastrophic collapse of subway tunnels from intrusion events, this paper investigated the capability of detecting the ground intrusion of underground structures based on dynamic measurement of distributed fiber optic sensing. For an actual subway tunnel monitored by the ultra-weak fiber optic Bragg grating (FBG) sensing fiber with a spatial resolution of five meters, a simulated experiment of the ground intrusion along the selected path was designed and implemented, in which a hydraulic excavator was chosen to exert intrusion perturbations with different strengths and modes at five selected intrusion sites. For each intrusion place, the distributed vibration responses of sensing fibers mounted on the tunnel wall and the track bed were detected to identify the occurrence and characteristics of the intrusion event simulated by the discrete and continuous pulses of the excavator under two loading postures. By checking the on-site records of critical moments in the intrusion process, the proposed detection approach based on distributed structural vibration responses for the ground intrusion can detect the occurrence of intrusion events, locate the intrusion ground area, and distinguish intrusion strength and typical perturbation modes. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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18 pages, 10186 KiB

Open AccessArticle

Research on the Earth Pressure and Internal Force of a High-Fill Open-Cut Tunnel Using a Bilayer Lining Design: A Field Test Using an FBG Automatic Data Acquisition System

by Tianyuan Xu, Mingnian Wang, Li Yu, Cheng Lv, Yucang Dong and Yuan Tian

Sensors 2019, 19(7), 1487; https://doi.org/10.3390/s19071487 - 27 Mar 2019

Cited by 11 | Viewed by 3456

Abstract

When there are railway tunnels on both sides of a valley, a bridge is usually built to let trains pass. However, if the valley is very close to an urban area, building an open-cut tunnel at the portal and then backfilling it to [...] Read more.

When there are railway tunnels on both sides of a valley, a bridge is usually built to let trains pass. However, if the valley is very close to an urban area, building an open-cut tunnel at the portal and then backfilling it to create available land resources for the city and to prevent excavation slag from polluting the environment would be a wise choice. This has led to the emergence of a new type of structure, namely, the high-fill open-cut tunnel. In this paper, by performing an automatic long-term field test on the first high-fill open-cut tunnel using a bilayer design in China, the variations of earth pressure and structural internal force during the backfilling process were obtained, and different tunnel foundation types were studied. The results showed that the earth pressure significantly exceeded the soil column weight, with a maximum earth pressure coefficient between 1.341 and 2.278. During the backfilling process, the earth pressure coefficient increased at first and then decreased slowly to a relatively stable value, and a stiffer foundation would make the structure bear higher earth pressure (1.69 times the normal one observed during monitoring). The change of internal force had two stages during backfilling: before the backfill soil reached the arch crown, the internal force of the lining changed slowly and then grew linearly as the backfill process continued. Moreover, the axial force ratio of the inner and outer linings was close to their thickness proportion, and the interaction mode between the two layers was very similar to the composite beam. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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13 pages, 3720 KiB

Open AccessArticle

Research on Optical Fiber Sensor Based on Underwater Deformation Measurement

by Jiawang Chen, Chen Cao, Yue Huang, Yonglei Zhang and Yongqiang Ge

Sensors 2019, 19(5), 1115; https://doi.org/10.3390/s19051115 - 5 Mar 2019

Cited by 4 | Viewed by 3455

Abstract

With the increase in the scale and complexity of underwater engineering, safety problems caused by underwater deformation have become increasingly prominent. Although the intensity fiber curvature sensor can be used for curvature monitoring on the ground, its sensing mechanism is still under investigation. [...] Read more.

With the increase in the scale and complexity of underwater engineering, safety problems caused by underwater deformation have become increasingly prominent. Although the intensity fiber curvature sensor can be used for curvature monitoring on the ground, its sensing mechanism is still under investigation. This paper establishes the mathematical model of optical power relative loss and bending radius during deformation of the fiber sensitive region and uses the optical power meter to measure light intensity loss in the sensitive region, which verifies the correctness of the model and reveals the sensing mechanism of the intensity fiber curvature sensor, then optimizes the sensor signal conditioning circuit, applies the sensor to the single-point deformation curvature measurement, and analyzes its measurement error and accuracy. It is proved that the linear measurement range of the sensor is improved when compared with existing similar products. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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18 pages, 4816 KiB

Open AccessArticle

Application of a Novel Long-Gauge Fiber Bragg Grating Sensor for Corrosion Detection via a Two-level Strategy

by Yuyao Cheng, Chenyang Zhao, Jian Zhang and Zhishen Wu

Sensors 2019, 19(4), 954; https://doi.org/10.3390/s19040954 - 23 Feb 2019

Cited by 12 | Viewed by 4395

Abstract

Corrosion of main steel reinforcement is one of the most significant causes of structural
deterioration and durability reduction. This research proposes a two-level detection strategy to
locate and quantify corrosion damage via a new kind of long-gauge fiber Bragg grating (FBG) sensor.
Compared [...] Read more.

Corrosion of main steel reinforcement is one of the most significant causes of structural
deterioration and durability reduction. This research proposes a two-level detection strategy to
locate and quantify corrosion damage via a new kind of long-gauge fiber Bragg grating (FBG) sensor.
Compared with the traditional point strain gauges, this new sensor has been developed for both
local and global structural monitoring by measuring the averaged strain within a long gauge length.
Based on the dynamic macrostrain responses of FBG sensors, the strain flexibility of structures are
identified for corrosion locating (Level 1), and then the corrosion is quantified (Level 2) in terms of
reduction of sectional stiffness of reinforcement through the sensitivity analysis of strain flexibility.
The two-level strategy has the merit of reducing the number of unknown structural parameters
through corrosion damage location (Level 1), which guarantees that the corrosion quantification
(Level 2) can be performed efficiently in a reduced domain. Both numerical and experimental
examples have been studied to reveal the ability of distributed long-gauge FBG sensors for corrosion
localization and quantification. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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14 pages, 5740 KiB

Open AccessArticle

Comparative Analysis of Deformation Determination by Applying Fiber-optic 2D Deflection Sensors and Geodetic Measurements

by Marko Z. Marković, Jovan S. Bajić, Mehmed Batilović, Zoran Sušić, Ana Joža and Goran M. Stojanović

Sensors 2019, 19(4), 844; https://doi.org/10.3390/s19040844 - 18 Feb 2019

Cited by 13 | Viewed by 4168

Abstract

In the paper the description of an experiment for a comparative analysis of two different methods for deformation determination, geodetic and 2D deflection sensors based on fiber-optic curvature sensors (FOCSs) is given. The experiment is performed by a using specially designed assembly which [...] Read more.

In the paper the description of an experiment for a comparative analysis of two different methods for deformation determination, geodetic and 2D deflection sensors based on fiber-optic curvature sensors (FOCSs) is given. The experiment is performed by a using specially designed assembly which makes it possible to apply both methods. For performing geodetic measurements, a geodetic micro-network is established. Measurements by applying a 2D deflection sensor and three total stations are carried out for comparison. The data processing comprises graphical and numerical analysis of the results. Based on the presented results the potential of 2D deflection sensor application in structural health monitoring (SHM) procedures is indicated. The analysis of the measurement results also indicates the importance of integrating various types of sensors for obtaining more accurate and more reliable deformation measurements results. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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20 pages, 7171 KiB

Open AccessArticle

Distributed Temperature Sensing Monitoring of Well Completion Processes in a CO₂ Geological Storage Demonstration Site

by Dasom Sharon Lee, Kwon Gyu Park, Changhyun Lee and Sang-Jin Choi

Sensors 2018, 18(12), 4239; https://doi.org/10.3390/s18124239 - 3 Dec 2018

Cited by 13 | Viewed by 4212

Abstract

The Distributed Temperature Sensing (DTS) profiles obtained during well completion of a CO₂ monitoring well were analyzed to characterize each well completion process in terms of temperature anomalies. Before analysis, we corrected the depth by redistributing the discrepancy, and then explored three [...] Read more.

The Distributed Temperature Sensing (DTS) profiles obtained during well completion of a CO₂ monitoring well were analyzed to characterize each well completion process in terms of temperature anomalies. Before analysis, we corrected the depth by redistributing the discrepancy, and then explored three temperature calibration methods. Consequently, we confirmed the depth discrepancy could be well corrected with conventional error redistribution techniques. Among three temperature calibration methods, the conventional method shows the best results. However, pointwise methods using heat coil or in-well divers also showed reliable accuracy, which allows them to be alternatives when the conventional method is not affordable. The DTS data revealed that each well completion processes can be characterized by their own distinctive temperature anomaly patterns. During gravel packing, the sand progression was monitorable with clear step-like temperature change due to the thermal bridge effect of sand. The DTS data during the cementing operation, also, clearly showed the progression up of the cement slurry and the exothermic reaction associated with curing of cement. During gas lift operations, we could observe the effect of casing transition as well as typical highly oscillating thermal response to gas lifting. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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19 pages, 4784 KiB

Open AccessArticle

Field Performance of Open-Ended Prestressed High-Strength Concrete Pipe Piles Jacked into Clay

by Hai-Lei Kou, Wen-Zhou Diao, Tao Liu, Dan-Liang Yang and Suksun Horpibulsuk

Sensors 2018, 18(12), 4216; https://doi.org/10.3390/s18124216 - 1 Dec 2018

Cited by 14 | Viewed by 3934

Abstract

The behavior of open-ended pipe piles is different from that of closed-ended pipe piles due to the soil plugging effect. In this study, a series of field tests were conducted to investigate the behavior of open-ended prestressed high-strength concrete (PHC) pipe piles installed [...] Read more.

The behavior of open-ended pipe piles is different from that of closed-ended pipe piles due to the soil plugging effect. In this study, a series of field tests were conducted to investigate the behavior of open-ended prestressed high-strength concrete (PHC) pipe piles installed into clay. Two open-ended PHC pipe piles were instrumented with Fiber Bragg Grating (FBG) sensors and jacked into clay for subsequent static loading tests. Soil plug length of the test piles was continuously measured during installation, allowing for calculation of the incremental filling ratio. The recorded data in static loading test were reported and analyzed. The distribution of residual forces after installation and the effect on the bearing capacity were also discussed in detail. The test piles were observed to be in partially plugged condition during installation. The measured ultimate shaft resistance and total resistance of the test piles were 639 and 1180 kN, respectively. The residual forces locked in the test piles after installation significantly affected the evaluation of the axial forces, and thus the shaft and end resistances. It tended to underestimate the end resistances and overestimate the shaft resistances if the residual forces were not considered in the loading test. However, the residual forces did not affect the total bearing capacity of open-ended PHC pipe piles in this study. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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19 pages, 8290 KiB

Open AccessArticle

Twisted Dual-Cycle Fiber Optic Bending Loss Characteristics for Strain Measurement

by Sang-Jin Choi, Seong-Yong Jeong, Changhyun Lee, Kwon Gyu Park and Jae-Kyung Pan

Sensors 2018, 18(11), 4009; https://doi.org/10.3390/s18114009 - 16 Nov 2018

Cited by 8 | Viewed by 3819

Abstract

The intensity-based fiber optic sensor (FOS) head using twisted dual-cycle bending loss is proposed and experimentally demonstrate. The bending loss characteristics depend on the steel wire radius, number, and distance. To determine the effects of these parameters, two samples in each of seven [...] Read more.

The intensity-based fiber optic sensor (FOS) head using twisted dual-cycle bending loss is proposed and experimentally demonstrate. The bending loss characteristics depend on the steel wire radius, number, and distance. To determine the effects of these parameters, two samples in each of seven configuration cases of the proposed FOS head were bonded to fiber reinforced plastics coupons, and tensile and flexural strain tests were repeated five times for each coupon. The bending loss of the manufactured FOS heads was measured and converted to the tensile and flexural strain as a function of configuration cases. The measurement range, sensitivity, and average measurement errors of the tensile load and flexural strain were 4.5 kN and 1760 με, 0.70 to 3.99 dB/kN and 0.930 to 6.554 dB/mm, and 57.7 N, and 42.6 με, respectively. The sensing range of FOS head were 82 to 138 mm according to configuration cases. These results indicate that it is possible to measure load, tensile strain, and flexural strain using the proposed FOS head, and demonstrate that the sensitivities, the operating ranges, and the sensing range can be adjusted depending on the deformation characteristics of the measurement target. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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16 pages, 3535 KiB

Open AccessArticle

Localization and Discrimination of the Perturbation Signals in Fiber Distributed Acoustic Sensing Systems Using Spatial Average Kurtosis

by Fei Jiang, Honglang Li, Zhenhai Zhang, Yixin Zhang and Xuping Zhang

Sensors 2018, 18(9), 2839; https://doi.org/10.3390/s18092839 - 28 Aug 2018

Cited by 32 | Viewed by 4280

Abstract

Location error and false alarm are noticeable problems in fiber distributed acoustic sensing systems based on phase-sensitive optical time-domain reflectometry (Φ-OTDR). A novel method based on signal kurtosis is proposed to locate and discriminate perturbations in Φ-OTDR systems. The spatial kurtosis (SK) along [...] Read more.

Location error and false alarm are noticeable problems in fiber distributed acoustic sensing systems based on phase-sensitive optical time-domain reflectometry (Φ-OTDR). A novel method based on signal kurtosis is proposed to locate and discriminate perturbations in Φ-OTDR systems. The spatial kurtosis (SK) along the fiber is firstly obtained by calculating the kurtosis of acoustic signals at each position of the fiber in a short time period. After the moving average on the spatial dimension, the spatial average kurtosis (SAK) is then obtained, whose peak can accurately locate the center of the vibration segment. By comparing the SAK value with a certain threshold, we may to some degree discriminate the instantaneous destructive perturbations from the system noise and certain ambient environmental interferences. The experimental results show that, comparing with the average of the previous localization methods, the SAK method improves the pencil-break and digging locating signal-to-noise ratio (SNR) by 16.6 dB and 17.3 dB, respectively; and decreases the location standard deviation by 7.3 m and 9.1 m, respectively. For the instantaneous destructive perturbation (pencil-break and digging) detection, the false alarm rate can be as low as 1.02%, while the detection probability is maintained as high as 95.57%. In addition, the time consumption of the SAK method is adequate for a real-time Φ-OTDR system. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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13 pages, 8252 KiB

Open AccessArticle

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

by Yongxing Guo, Wenlong Liu, Li Xiong, Yi Kuang, Heng Wu and Honghai Liu

Sensors 2018, 18(6), 1899; https://doi.org/10.3390/s18061899 - 11 Jun 2018

Cited by 21 | Viewed by 4655

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Fiber Optic Sensors for Structural and Geotechnical Monitoring)

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