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Purpose: The aging and deterioration of engineering building structures present significant risks to both life and property. Fiber Bragg grating (FBG) sensors, acclaimed for their outstanding reusability, compact form factor, lightweight construction, heightened sensitivity, immunity to electromagnetic interference and exceptional precision, are increasingly being adopted for structural health monitoring in engineering buildings. This research paper aims to evaluate the current challenges faced by FBG sensors in the engineering building industry. It also anticipates future advancements and trends in their development within this field. Design/methodology/approach: This study centers on five pivotal sectors within the field of structural engineering: bridges, tunnels, pipelines, highways and housing construction. The research delves into the challenges encountered and synthesizes the prospective advancements in each of these areas. Findings: The exceptional performance of FBG sensors provides an ideal solution for comprehensive monitoring of potential structural damages, deformations and settlements in engineering buildings. However, FBG sensors are challenged by issues such as limited monitoring accuracy, underdeveloped packaging techniques, intricate and time-intensive embedding processes, low survival rates and an indeterminate lifespan. Originality/value: This introduces an entirely novel perspective. Addressing the current limitations of FBG sensors, this paper envisions their future evolution. FBG sensors are anticipated to advance into sophisticated multi-layer fiber optic sensing networks, each layer encompassing numerous channels. Data integration technologies will consolidate the acquired information, while big data analytics will identify intricate correlations within the datasets. Concurrently, the combination of finite element modeling and neural networks will enable a comprehensive simulation of the adaptability and longevity of FBG sensors in their operational environments. [ABSTRACT FROM AUTHOR]

The current situation with prestressed structures raises questions about the ways how to determine residual prestressing which is the crucial factor for the evaluation of the prestressed structure. Therefore, this study aims to enhance existing knowledge of the so‐called Saw‐cut method which is considered a non‐destructive indirect technique. The presented study focuses on the determination of various factors which could influence the applicability and accuracy of this method such as both compressive and tensile normal stress release, the type of measuring instrument (linear foil strain gauge or newly developed FBG sensor), and the length of the normal stress release recording (up to almost 9 h). The obtained results suggest that tensile normal stress release could be more problematic for the evaluation than compressive normal stress release. Moreover, the application of FBG sensors seems to be more precise but also more complicated regarding the installation, recording and costs. Finally, the time span of the measurement can influence the residual normal stress release. For practical reasons, 60 min after the performance of the final sawing should be sufficient. Finally, when used at locations with adequate compressive normal stress, the Saw‐cut method seems to be a promising tool for prestressing evaluation. [ABSTRACT FROM AUTHOR]

The anisotropic and irreversible expansion properties of polymer‐bonded explosives (PBX) can significantly influence the utility and reliability of associated equipment. The physical state of PBX under temperature cycling affects the strain distribution across the surface of cylindrical specimens. This strain is indicative of the irreversible growth and anisotropic expansion of the specimens. In this study, fiber Bragg grating sensors are employed to monitor the strain of PBX throughout the temperature cycling process, and our focus was on analyzing the changes in anisotropy and strain distribution during the cycle. The relationships between strain, temperature, material properties, and differences among various materials are examined. Experimental results indicate that the strain along the height and radial directions of the PBX specimens displayed a monotonic gradient distribution, increasing progressively in areas of higher density. TATB‐based PBX exhibited anisotropic expansion throughout the temperature cycling, with the degree of anisotropy increasing during heating and decreasing upon cooling. Conversely, HMX‐based PBX showed greater expansion in the height direction during both the heating and cooling phases, but it did not display noticeable anisotropy following the temperature cycling. At the highest temperature‐holding stage (100°C), the HMX‐based PBX was isotropic. The extent of strain in PBX was correlated with the thermal expansion coefficient of the crystal, although the final degree of expansion was not dependent on the initial range of strain. The ratchet growth of TATB‐based PBX was approximately 31 μϵ greater than that of HMX‐based PBX. [ABSTRACT FROM AUTHOR]

Pipes are the main structures serving as the lifeline for oil and gas transportation. However, they are prone to cracks, holes and other damages due to harsh working environments, which can lead to leakage incidents and result in significant economic losses. Therefore, the development of structural health monitoring systems with advanced online diagnostic methods is of great importance for identifying local damages and assessing the safety state of pipe structures. These efforts can guide rapid repairs and ensure the continuous, efficient and cost-effective transportation of oil and gas resources. To address this problem, this paper proposes the development of a pipe monitoring system based on quasi-distributed fiber Bragg grating (FBG) sensing technology. The SSI-COV method is employed to process the sensor responses and extract the modal parameters of the structure. Based on this foundation, an enhanced damage identification index is proposed, which mitigates the effects of support and excitation positions on damage identification. The pipe structure can be regarded as a continuous super-statical beam, and based on its structural symmetry, a unit structure, specifically a stainless-steel pipe with fixed ends, is regarded as the experimental subject. Impact experiments have been conducted to analyze its behavior in both undamaged and damaged states. The research indicates that by using the proposed modal parameter identification method and the A S M D I damage index, A S M D I exhibits peak values at damage locations of the pipe structure. This allows for the identification of structural damage with high accuracy, fast processing efficiency and strong robustness. The study provides an effective and reliable damage diagnosis method, which can contribute to the refinement and visualization of pipe structural health monitoring systems. [ABSTRACT FROM AUTHOR]

Predictive maintenance (PM) is a data-driven approach to performing proactive maintenance by analyzing the condition of the equipment in any industrial setting. The high-precision sensors are widely adapted to meticulously analyze critical maintenance conditions using such a datadriven approach. In a similar context, a fiber brag grating (FBG) sensor is a passive and high-precision sensor that is widely used in industries where conventional sensors are not preferred. Broadly, this article presents four sub elements of the proposed integrated system such as the design of the sensor element, signal processing scheme (SPS), machine learning (ML) model for predicting anomalies, and decision support system (DSS) to suggest maintenance actions. Also, this article highlights an experimental case study on vibration monitoring and analysis of real-time signals for making proactive maintenance decisions. An FBG vibration sensor of center wavelength 1,550 nm is designed and utilized to acquire real-time vibration signatures of a rotating machine under test. A piezoelectric vibration sensor is used with the FBG sensor to compare the vibration response obtained during the test. Pre-processing of raw signals is performed using a moving average filter (MAV) followed by a low pass filter to nullify the effect of noise. To obtain proactive maintenance decisions, a DSS model is prepared by considering the processed vibration signatures. Various maintenance conditions are tested during the experimental analysis and detailed results analysis are presented. [ABSTRACT FROM AUTHOR]

The construction of buildings and infrastructure on marine deposits is challenging. The impact of the horizontal behavior of structures on reclaimed areas is critical. This study investigated the behavior of laterally loaded drilled shafts in marine deposits through a comprehensive analysis and full-scale lateral load test conducted in Songdo, South Korea. It identified various critical pile characteristics for designing and constructing architectural and civil structures in marine environments, focusing on a 2.5 m diameter, 40 m long drilled shaft. At a 900 kN design load, the test pile experienced a maximum moment of 3520.2 kN·m and a lateral deflection of 2.32 mm, with anticipated failure at a load of 1710 kN and 11.30 mm displacement. Fiber Bragg Grating (FBG) sensors enabled precise displacement and strain measurements, essential for constructing accurate load–displacement curves and understanding lateral load responses. Inverse analysis with validated data from a commercial software (LPILE) showed good alignment of maximum moment and displacement but highlighted challenges at failure loads. The study developed depth-dependent p-y curves for marine deposits, crucial for predicting soil–pile interaction and optimizing shaft design. Practical implications include using derived p-y curves and an empirical equation using Standard Penetration Test (SPT) results to predict the coefficient of horizontal subgrade reaction (kh) with high accuracy. Overall, this research emphasizes the importance of advanced instrumentation and analytical techniques for optimizing drilled shaft design and ensuring structural stability in challenging marine geological conditions. [ABSTRACT FROM AUTHOR]

Because of the sensitivity enhancement of the fiber Bragg grating (FBG) sensor is still matter of challenge, and it is very important in different field of study, this paper proposes a new approach to enhance the humidity and temperature sensitivities of FBG sensors based on Levenberg–Marquardt algorithm by utilizing artificial neural networks (ANNs). The ANN's usage yield a more precise model that considered uncertainties and nonlinearities in the response of the FBG sensor, leading to a significant humidity and temperature measurements with higher sensitivity and accuracy. Compared to traditional sensors, the presented FBG sensor based on ANNs reflects a significant enhancement in both humidity and temperature sensitivity. The current work also illustrates the ANNs potential as a tool to improve the performance of FBG fiber-optic sensors, which could be utilized to other kinds of fiber optic sensors, leading to better accuracy and sensitivity for a wide range of applications. According to sensitivity of humidity, the FBG sensor based on the ANNs exhibited a good enhancement estimated by 20.13 pm/%RH. The linearity performance of the current FBG sensor based on the ANNs approach referred a significant behavior under different surrounding factors and conditions of humidity with estimated R square value of 0.95328. Moreover, in terms of percentage errors for humidity sensitivity, the values were estimated to be 1%, 1.3%, 1%, 1%, and 1.2% for 30, 40, 55, 75, and 95%RH, respectively. According to sensitivity of temperature, the FBG sensor based on ANN method showed a significant improvement calculated to be 0.8625 pm/°C. Additionally, the linearity performance of the proposed approach refers to a good FBG sensor performance under wide range of applied temperatures with calculated R square value of 0.98199. Furthermore, in terms of percentage errors for temperature sensitivity, the values were estimated to be 1%, 1.1%, 1.2%, 1%, and 1.1% for 25, 35, 55, 75, and 95 °C, respectively. The contribution of the current work is to develop more reliable and advanced fiber optic based on FBG humidity and temperature sensors, which could have an essential influence on structure health monitoring systems and related applications. The current work impact is essential, because it proposes a promising solution for conventional FBG limitations in terms of humidity and temperature sensors, leading to more reliable and accurate measurements in different applications, for example, structural health monitoring systems, automation of building, and processing of food. [ABSTRACT FROM AUTHOR]

This research presents a comprehensive study focused on the design, implementation, and analysis of an innovative fiber Bragg grating (FBG) based foot pressure assessment system. FBG sensors strategically placed on the great toe, metatarsal 1, metatarsal 2, and heel provided distinct peak resonant wavelengths, strains, and pressures during experimental cycles. Participant 1 exhibited peak resonant wavelength of 1537.745 nm for great toe, 1537.792 nm for metatarsal 1, 1537.812 nm for metatarsal 2, and 1537.824 nm for heel. Participant 2 showcased distinct graphical representations with peak resonant wavelengths ranging from 1537.903 to 1537.917 nm. In a fracture patient condition, the FBG‐based system monitored weight‐bearing capacity, integrated with real‐time X‐ray imaging for dynamic insights of rehabilitation as distinct approach. The strains and pressures at each position exhibited notable variations along with the sensitivity of 1.31με obtained across all positions, underscoring the FBG‐based system's reliability in capturing subtle foot pressure. [ABSTRACT FROM AUTHOR]

Smart composites embedded with Fiber Bragg Grating (FBG) sensors are getting increasingly popular in aircraft structures due to their self‐sensing and monitoring capability. However, a resin pocket around the FBG sensor would be formed in the manufacturing process, which strongly impacts the mechanical properties of the composite host. Therefore, the influence of primary processing parameters (FBG orientation angle, preforming temperature, and preforming pressure) on the formation of resin pockets was investigated in this work. It is found that there is a sinusoidal relation between the resin pocket geometry and the FBG orientation angle. A negative linear relation is noted between the resin pocket geometry and the preforming temperature and pressure. A prediction model based on the backpropagation neural network (BPNN) was established, which was able to quickly and accurately predict resin pocket geometry subjected to given processing parameters. This work provides useful guidance for the processing control of smart composites embedded with FBG sensors. Highlights: Resin pocket geometry was formed primarily in the preforming stage.Effect of processing parameters on resin pocket geometry was characterized.A BPNN model was established for the fast prediction of resin pocket geometry. [ABSTRACT FROM AUTHOR]

In recent years, due to the changing climate conditions and the continuous deepening of water resource conservation measures, the groundwater level in northern China has gradually risen, leading to the increasingly prominent issue of anti-floating in existing buildings and structures. The development and adoption of reliable anti-floating reinforcement techniques for existing structures are crucial for ensuring the quality of such reinforcements. Therefore, focusing on the limitations of the anchor method for anti-floating reinforcement, this paper proposes a new type of anti-floating prestressed compression anchor that features a full-length anti-compressive steel pipe with a bearing body at the end and uses non-bonding tendons throughout its length. Firstly, the structural form of this pressure-type anchor is introduced; subsequently, combined with the results of on-site pull-out tests of the anchor, an analysis is conducted on the working principle, lateral resistance distribution, and internal force transfer mechanism of the new anti-floating anchor, and its load-bearing characteristics are elucidated. Finally, relying on actual anti-floating reinforcement projects and through numerical calculations, the changes in internal forces under different anti-floating conditions of existing structures reinforced with the new anchor compared to conventional anchors are contrasted. Research findings and engineering practice indicate that this new anti-floating anchor improves the mechanical performance of the grout body of the anchor, solves the water seepage problem at the anchor location of the waterproof slab, effectively suppresses cracking of the foundation waterproof slab after reinforcement, and enhances the anti-floating and durability of existing structures. [ABSTRACT FROM AUTHOR]

The construction of buildings and infrastructure on marine deposits is challenging. The impact of the horizontal behavior of structures on reclaimed areas is critical. This study investigated the behavior of laterally loaded drilled shafts in marine deposits through a comprehensive analysis and full-scale lateral load test conducted in Songdo, South Korea. It identified various critical pile characteristics for designing and constructing architectural and civil structures in marine environments, focusing on a 2.5 m diameter, 40 m long drilled shaft. At a 900 kN design load, the test pile experienced a maximum moment of 3520.2 kN·m and a lateral deflection of 2.32 mm, with anticipated failure at a load of 1710 kN and 11.30 mm displacement. Fiber Bragg Grating (FBG) sensors enabled precise displacement and strain measurements, essential for constructing accurate load–displacement curves and understanding lateral load responses. Inverse analysis with validated data from a commercial software (LPILE) showed good alignment of maximum moment and displacement but highlighted challenges at failure loads. The study developed depth-dependent p-y curves for marine deposits, crucial for predicting soil–pile interaction and optimizing shaft design. Practical implications include using derived p-y curves and an empirical equation using Standard Penetration Test (SPT) results to predict the coefficient of horizontal subgrade reaction (kh) with high accuracy. Overall, this research emphasizes the importance of advanced instrumentation and analytical techniques for optimizing drilled shaft design and ensuring structural stability in challenging marine geological conditions.

In this simulation study, the response of fiber Bragg grating (FBG) sensors is investigated and optimized. Uniform and nonuniform FBG spectra with new component are suggested by fine selection with (COMSUL program) and compared theoretically under the effect of several external strain values (0.005, 0.006, 0.007, 0.008, 0.009 and 0.01). These two types operation have been examined by the Optisystem programmer. The measured sensitivity was based on VCSEL laser source with operation wavelengths of 1650, 1600, and 1550 nm via non-uniform and uniform configuration. The achieved sensitivity was found to have different values; 5.7, 2.6, and 1.77, while the highest observed sensitivity value is recorded at a wavelength of 1550 nm. Accordingly, this wavelength was chosen to advance the study. Temperatures of 20, 30, 40, 50, and 60 degrees Celsius were applied. Measured sensitivity between them varied, and satisfied the following functions: sine, Gauss, and Boltzmann indicating altering in sensor responses.

In recent years, due to the changing climate conditions and the continuous deepening of water resource conservation measures, the groundwater level in northern China has gradually risen, leading to the increasingly prominent issue of anti-floating in existing buildings and structures. The development and adoption of reliable anti-floating reinforcement techniques for existing structures are crucial for ensuring the quality of such reinforcements. Therefore, focusing on the limitations of the anchor method for anti-floating reinforcement, this paper proposes a new type of anti-floating prestressed compression anchor that features a full-length anti-compressive steel pipe with a bearing body at the end and uses non-bonding tendons throughout its length. Firstly, the structural form of this pressure-type anchor is introduced; subsequently, combined with the results of on-site pull-out tests of the anchor, an analysis is conducted on the working principle, lateral resistance distribution, and internal force transfer mechanism of the new anti-floating anchor, and its load-bearing characteristics are elucidated. Finally, relying on actual anti-floating reinforcement projects and through numerical calculations, the changes in internal forces under different anti-floating conditions of existing structures reinforced with the new anchor compared to conventional anchors are contrasted. Research findings and engineering practice indicate that this new anti-floating anchor improves the mechanical performance of the grout body of the anchor, solves the water seepage problem at the anchor location of the waterproof slab, effectively suppresses cracking of the foundation waterproof slab after reinforcement, and enhances the anti-floating and durability of existing structures.

Carbon-fiber-reinforced polymer (CFRP) composites have many advantages, and have been widely used in aerospace structures, buildings, bridges, etc. The analysis of dynamic response characteristics of CFRP composite structures is of great significance for promoting the development of smart composite structures. For this reason, vibration experiments of CFRP laminates with surface-attached fiber Bragg grating (FBG) sensors under various dynamic loading conditions were carried out. Time- and frequency-domain analyses were conducted on the FBG testing signals to check the dynamic characteristics of the CFRP structure and the sensing performance of the installed sensors. The results show that the FBG sensors attached to the surface of the CFRP laminates can accurately measure the dynamic response and determine the excited position of the CFRP laminates, as well as invert the strain distribution of the CFRP laminates through the FBG sensors at different positions. By performing Fourier transform, short-time Fourier transform, and frequency domain decomposition (FDD) on the FBG sensing signals, the time–frequency information and the first eight modal frequencies of the excited CFRP structure can be obtained. The modal frequencies obtained by different excitation types are similar, which can be used for structural damage identification. The research in this paper clarifies the effectiveness and accuracy of FBG sensors in sensing the dynamic characteristics of CFRP structures, which can be used for performance evaluation of CFRP structures and will effectively promote the design and development of intelligent composite material structures. [ABSTRACT FROM AUTHOR]

Pipelines provide an economical mode of transportation for hauling gas and liquids such as oil over long distances. Pipeline explosions cause massive loss of lives, and adversely impact both the environment and the economy. Accurate and automated detection of the arrival times of negative pressure waves (NPW) because of leakages is the key parameter in many pipeline leakage detection approaches. The method introduced here uses the absolute maximum difference in the slopes of NPW time-domain signals for accurate determination of the time of signal arrivals at the sensors. The proposed method involves Fiber Bragg Grating (FBG) sensor-based detection of the leakages, and determination of the arrival of NPW signals for accurate detection of the knee-points in the signals. The main advantage in using the proposed approach is determination of exact arrival time of NPW for accurate detection of leakage point locations along the lengths of pipelines. The experimental program includes construction of two separate gas and liquid pipelines for evaluation of the absolute maximum slope difference (AMSD) method. The study includes evaluation of the differences between the proposed method and conventional visual determination of the NPW arrival times, and the actual locations of the leakage sources in the experiments. The numerical approach introduced herein enables direct integration of the proposed method, for automated real-time monitoring of pipeline leakage locations. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Rolling Stock (1002-7602) is the property of Rolling Stock Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Lithium-ion batteries (LiBs) are well-known power sources due to their higher power and energy densities, longer cycle life and lower self-discharge rate features. Hence, these batteries have been widely used in various portable electronic devices, electric vehicles and energy storage systems. The primary challenge in applying a Lithium-ion battery (LiB) system is to guarantee its operation safety under both normal and abnormal operating conditions. To achieve this, temperature management of batteries should be placed as a priority for the purpose of achieving better lifetime performance and preventing thermal failures. In this paper, fibre Bragg Grating (FBG) sensor technology coupling with machine learning (ML) has been explored for battery temperature monitoring. The results based on linear and nonlinear models have confirmed that the novel methods can estimate temperature variations reliably and accurately. [ABSTRACT FROM AUTHOR]

Model tests are carried out on the jacked single piles of different diameters and pile lengths under the model pile of different diameters and pile lengths in clayey soil, which aims to investigate the penetration mechanical mechanism. How to accurately test the pile end resistance and pile side resistance during jacked pile sinking is particularly important. In this paper, a full-section spoke-type pressure sensor, a double diaphragm temperature self-compensating fiber Bragg grating (FBG) earth pressure sensor and a sensitized miniature FBG strain sensor are jointly applied to a single pile penetration model test to test a single pile driving force, pile end resistance and pile body stress during penetration. The test results show that the load transfer performance of test piles will be affected by different diameters, and the axial force transfer capability of a large diameter in the depth direction is better than that of a small diameter since the compacting effect is more obvious. The unit skin friction of the pile increases gradually as the depth increases, which is larger due to the lateral extrusion force increasing as the diameter increases. At the same depth, the unit skin friction of two different diameter piles demonstrates "friction fatigue", which also decreases obviously as the depth increases. Under the conditions of this test, the maximum frictional resistance of the pile TP1 pile side is about 27.7% higher than that of the test pile TP2. In the static pile sinking process of three test piles in cohesive soil, 50% is end bearing; therefore, there is 50% friction, and the diameter influences the end bearing and the length influences the friction. [ABSTRACT FROM AUTHOR]

In conventional rock mechanics testing, radial strain measuring devices are usually attached to the sample's surface at its mid-height. Although this procedure provides a realistic picture of the lateral deformation undergone by homogeneous samples, however, this assumption may not be accurate if the tested rock has significant heterogeneity. Fibre Bragg Grating (FBG) sensors have recently been introduced to various rock testing applications due to their versatility over conventional strain gauges and radial cantilevers. FBG sensors have small size, multiplexing capability, and immunity to magnetic interference. The main objective of this study is to explore and understand the capabilities of FBG sensing for strain measurement during rock mechanics testing, including under confining. To do so, two limestone plugs (Savonnières limestone) and one acrylic Poly Methyl Methacrylate (PMMA) plug, all of 38 mm diameter, were prepared. The acrylic plug and one of the Savonnières samples plugs were subjected to Unconfined Compressive Strength (UCS) tests. The second Savonnières plug was subjected to a hydrostatic test up to 20 MPa confining at room temperature. FBG sensors of 125 μm cladding diameter with ceramics (Ormocer) coating were glued on the surface of each sample, spreading across the entire sample's height. Strain gauges and cantilever-type radial gauges were used on the samples submitted to UCS for comparison. Results show that radial strain measurements and calculated elastic properties derived from the FBG readings for samples are comparable to readings from the conventional strain gauges and cantilever-type devices. Apparent bulk moduli based on volumetric strain computed from FBG radial strain readings during the hydrostatic test on the Savonnières sample was consistent with benchtop measurements conducted on the Savonnières sample and another plug extracted from the same parental block, as well as published literature data. Moreover, variations in the calculated elastic properties are interpreted as evidence that the FBG sensors detected heterogeneities in the samples' inner structure, which can be seen in the density profiles computed from x-ray CT images. Such observation confirms the potential of the presented FBG sensors configuration for 3D strain mapping in rock mechanics tests.

Freeze-thaw (F-T) damage is one of the common types of damage in concrete durability problems. The use of sensors to monitor the health of concrete during freeze-thaw conditions can offer real-time information about the status of concrete. In this study, fiber Bragg grating (FBG) sensors were used to record the strain and temperature histories of concrete specimens under F-T cycles. The results of the experiments demonstrated that during the F-T process, the concrete specimen exhibited different extremes on the temperature at the center and the top position. By calculating the cumulative residual strain, it is found that the cumulative residual strain at top position of the top-exposed specimen stops growing after 50 freeze-thaw cycles, while that of the top-sealed specimen keeps growing slowly within 200 freeze-thaw cycles. After 100 freeze-thaw cycles, the cumulative residual strain at the center position of both coating regimes began to increase, although the rate of increase was larger for the top exposed specimens than for the top sealed specimens. High water saturation of pores caused by internal water migration is the main factor leading to residual strain in concrete during freeze-thaw. The X-ray computed tomography (CT) analysis revealed that both the number of pores and the average pore size progressively decreased from the surface to the center.

Abstract The strain-temperature cross-sensitivity problem easily occurs in the engineering strain monitoring of the self-sensing embedded with fiber Bragg grating (FBG) sensors. In this work, a theoretical investigation of the strain-temperature cross-sensitivity has been performed using the temperature reference grating method. To experimentally observe and theoretically verify the problem, the substrate materials, the preloading technique, and the FBG initial central wavelength were taken as main parameters. And a series of sensitivity coefficients calibration tests and temperature compensation tests have been designed and carried out. It was found that when the FBG sensors were embedded on different substrates, their coefficients of the temperature sensitivity were significantly changed. Besides, the larger the coefficients of thermal expansion (CTE) of substrates were, the higher the temperature sensitivity coefficients would be. On the other hand, the effect of the preloading technique and FBG initial wavelength was negligible on both the strain monitoring and temperature compensation. In the case of similar substrates, we did not observe any difference between temperature sensitivity coefficients of the temperature compensation FBG with one free end or two free ends. The curves of the force along with temperature were almost overlapped with minor differences (less than 1%) gained by FBG sensors and pressure sensors, which verified the accuracy of the temperature compensation method. We suggest that this work can provide efficient solutions to the strain-temperature cross-sensitivity for engineering strain monitoring with the self-sensing element embedded with FBG sensors.

The strain-temperature cross-sensitivity problem easily occurs in the engineering strain monitoring of the self-sensing embedded with fiber Bragg grating (FBG) sensors. In this work, a theoretical investigation of the strain-temperature cross-sensitivity has been performed using the temperature reference grating method. To experimentally observe and theoretically verify the problem, the substrate materials, the preloading technique, and the FBG initial central wavelength were taken as main parameters. And a series of sensitivity coefficients calibration tests and temperature compensation tests have been designed and carried out. It was found that when the FBG sensors were embedded on different substrates, their coefficients of the temperature sensitivity were significantly changed. Besides, the larger the coefficients of thermal expansion (CTE) of substrates were, the higher the temperature sensitivity coefficients would be. On the other hand, the effect of the preloading technique and FBG initial wavelength was negligible on both the strain monitoring and temperature compensation. In the case of similar substrates, we did not observe any difference between temperature sensitivity coefficients of the temperature compensation FBG with one free end or two free ends. The curves of the force along with temperature were almost overlapped with minor differences (less than 1%) gained by FBG sensors and pressure sensors, which verified the accuracy of the temperature compensation method. We suggest that this work can provide efficient solutions to the strain-temperature cross-sensitivity for engineering strain monitoring with the self-sensing element embedded with FBG sensors. [ABSTRACT FROM AUTHOR]

Among the optical fiber sensors, fiber Bragg grating (FBG) has found remarkable attraction and many applications due to its ability to measure all environmental parameters, high accuracy and sensitivity, easy installation, and low price. The sensor's ability to simultaneous measurement of two environmental (physical) parameters, especially strain and temperature, has made it even more demanding. Recently, two techniques based on full width at half maximum (FWHM) and peak power changes of FBG spectrum have been proposed for simultaneous measurement of temperature and strain that use a uniform FBG on a tilted cantilever beam. In this article, we evaluate and compare both techniques and demonstrate that both are equivalent and have almost similar behaviour but do not have the same applications. We find that at the low strain range the peak power technique is more accurate while at the high strain range the FWHM technique has better accuracy. Therefore, in applications such as monitoring civil structures that have a high strain range, it is better to use the FWHM technique and in some delicate industrial applications with a low strain range, the peak power technique is used. [ABSTRACT FROM AUTHOR]

• This study proposes the design of a Fiber Bragg Grating (FBG) sensor system to monitor cardiac and respiratory activities in numerous body positions including Fowler's, Orthostasis and Supine positions. The system integrates advanced signal processing techniques to extract information from the FBG sensor output. A custom-designed software platform is used to analyze and visualize the collected data efficiently. The FBG sensor's placement and sensitivity are optimized to accurately capture cardiac and respiratory parameters across changed body postures, ensuring a holistic understanding of the examinee's physiological responses. The strain sensitivity of FBG Sensor inscribed in a Germania-doped silica fiber is approximately 1.20 pm (µɛ)−1. This innovative approach enhances the potential for remote health monitoring and provides valuable insights into the dynamic relationship between body position and physiological parameters, paving way for personalized healthcare solutions. The study also incorporates the use of a smartwatch to conveniently display and evaluate the obtained results in real-time, offering a user-friendly interface for both healthcare professionals and individuals monitoring their own health. This study proposes the design of a Fiber Bragg Grating (FBG) sensor system to monitor cardiac and respiratory activities in numerous body positions including Fowler's, Orthostasis and Supine positions. The system integrates advanced signal processing techniques to extract information from the FBG sensor output. A custom-designed software platform is used to analyze and visualize the collected data efficiently. The FBG sensor's placement and sensitivity are optimized to accurately capture cardiac and respiratory parameters across changed body postures, ensuring a holistic understanding of the examinee's physiological responses. The strain sensitivity of FBG Sensor inscribed in a Germania-doped silica fiber is approximately 1.20 pm (µɛ)−1. This innovative approach enhances the potential for remote health monitoring and provides valuable insights into the dynamic relationship between body position and physiological parameters, paving way for personalized healthcare solutions. The study also incorporates the use of a smartwatch to conveniently display and evaluate the obtained results in real-time, offering a user-friendly interface for both healthcare professionals and individuals monitoring their own health. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced plastic (CFRP) structures are vulnerable to low-speed impacts, which will lead to almost invisible impact damage. Therefore, the timely localization of impact is of great significance to damage detection and maintenance of the structure. In this article, a low velocity impact supervisory and testing system based on fiber Bragg grating (FBG) sensors was built up for CFRP laminates to obtain the low velocity impact strain sensitivity model. Meanwhile, genetic algorithm was applied to optimize the configuration of the FBG sensing network. The eigenvectors of the impact signals were extracted by applying fast Fourier transform (FFT) transform and principal component analysis (PCA) technology used as the input of the back propagation (BP) neural network model, while the corresponding impact coordinates were used as the output, to train the model. After training, the impact position prediction model based on BP neural network was obtained, thereby achieving the impact localization for CFRP laminates successfully with an average localization error of 2.1 cm. [ABSTRACT FROM AUTHOR]

Fiber Bragg Gratings (FBGs) are one of the most preferred high technology sensors in the sensor market. Although, FBG based strain sensors are widely used they are most likely to get affected by climate changes such as temperature. Thereby, most of the time they have to be used along with a reference temperature sensor. Otherwise, one should be ensuring that the FBG sensor is isolated from the climate changes which requires more effort and is a less reliable approach as compared to using an additional temperature sensor. In this study, a novel design of temperature compensated FBG sensor package, manufacturing of polyimide coated FBG sensors, and finally montaging of the manufactured FBG sensors to the corresponding package with an appropriate adhesive is presented. In addition, the designed package has been tested under discrete and continuous loading conditions. Obtained results showed that with the designed package it is possible to measure the strain change in terms of sensing capability of 1.2 microstrains (με) up to 80 with an extensive compensation ratio. [ABSTRACT FROM AUTHOR]

A fiber Bragg grating (FBG) sensor includes three main parts, an FBG, a sensor substrate, and a packaging material. The most commonly used packaging material is epoxy resin adhesive, which is prone to aging and failure, which further affects the performance and life of a sensor. This research provides an innovative approach that enables all-silicon sensor fabrication, where the substrate and packaging material are prepared by silicon glass, which is consistent with silicon optical fiber. In the packaging process, there are three main bottleneck problems, which are considered in this study: 1) highly elastic processing of glass used in the sensor elastic element; 2) thermal fixation between the silicon packaging material and substrate; and 3) selecting appropriate FBG parameters and fixing methods. In the proposed approach, an elastic glass cantilever beam and an FBG are packaged with molten glass powder. The proposed approach is verified by tests, and the test results show that the packaged FBG has good package quality and sensing performance. The theoretical analysis of the wavelength drift phenomenon during the packaging is presented. Finally, the introduced packaging method is applied to the fabrication of an FBG tilt sensor. The sensor shell, cantilever beam, temperature compensation beam, mass block, and other components are designed and made of silicon glass. The sensing principle and performance tests of the tilt sensor have been described in detail. The tilt sensor shows good linearity and repeatability. The presented packaging technology shows good applicability and has promising applications in the fabrication of high-performance FBG sensors. [ABSTRACT FROM AUTHOR]

This article studies the influence of fiber Bragg grating (FBG) head length on insulated gate bipolar transistor (IGBT) direct on-chip thermal sensing performance of FBG sensors. To this end, the surface of a commercial IGBT chip is thermally simulated and experimentally characterized. Uniform FBG sensors with three head sizes are then tested in two promising thermal sensing locations. The study has found that the large thermal gradients in this application create an additional constraint when using longer head lengths. A distortion in the reflected spectrum of the 5-mm FBG sensor is used to illustrate the underlying physical effect, which causes this limitation for IGBT junction temperature measurement. This additionally affects the length of head sizes providing accurate temperature readings of the IGBT surface hotspots, and significantly, this limit is location-dependent in a given IGBT geometry. [ABSTRACT FROM AUTHOR]

Aiming at the problem of large measurement errors in the current stress-strain monitoring methods of transmission tower, this study was carried out to improve the accuracy of strain measurement of transmission pole and tower angle steel. Based on fiber bragg grating (FBG) sensor, an accurate online monitoring method for angle steel strain of transmission towers was proposed considering the position and mode of sensor installation on the surface of angle steel. Firstly, the transmission tower angle steel surface strain distribution characteristics of different positions were analized based on the finite element simulation, and then according to the transmission tower structure in L shape characteristics of angle steel, a removable hand ring type L-type joint angle sensor was designed on the surface of the fixed clamp. The comparison and analysis of different sensor installation methods and their influence on the angle steel strain measurement accuracy were examined. Finally, this method was used to design an accurate online monitoring system of transmission pole tower angle steel strain based on fiber bragg grating sensor. The strain data of angle steel in weak position of pole tower of a 220 kV transmission line was measured and analyzed. The results show that the strain measurement error of the measured data and the finite element simulation data was less than 1. 5x10 -5 ; and the relative error was less than 6. 28%, which could effectively improve the measurement accuracy of the Angle steel strain of transmission tower. The finding of this study showed extra light on the accurate online monitoring of transmission tower structure. [ABSTRACT FROM AUTHOR]

Carbon-fiber-reinforced polymer (CFRP) composites have many advantages, and have been widely used in aerospace structures, buildings, bridges, etc. The analysis of dynamic response characteristics of CFRP composite structures is of great significance for promoting the development of smart composite structures. For this reason, vibration experiments of CFRP laminates with surface-attached fiber Bragg grating (FBG) sensors under various dynamic loading conditions were carried out. Time- and frequency-domain analyses were conducted on the FBG testing signals to check the dynamic characteristics of the CFRP structure and the sensing performance of the installed sensors. The results show that the FBG sensors attached to the surface of the CFRP laminates can accurately measure the dynamic response and determine the excited position of the CFRP laminates, as well as invert the strain distribution of the CFRP laminates through the FBG sensors at different positions. By performing Fourier transform, short-time Fourier transform, and frequency domain decomposition (FDD) on the FBG sensing signals, the time–frequency information and the first eight modal frequencies of the excited CFRP structure can be obtained. The modal frequencies obtained by different excitation types are similar, which can be used for structural damage identification. The research in this paper clarifies the effectiveness and accuracy of FBG sensors in sensing the dynamic characteristics of CFRP structures, which can be used for performance evaluation of CFRP structures and will effectively promote the design and development of intelligent composite material structures.

Carbon Fiber Reinforced Plastic (CFRP) shaft tube structure is widely applied in different fields, including aerospace, automotive, and wind power. Since CFRP shaft tube is often subjected to bending fatigue loads, it is of great significance to research its bending fatigue characteristics. Because of its unique advantages, such as a smaller size, lighter weight, and the outstanding ability to form a sensor network, the Fiber Bragg Grating (FBG) sensor is very applicable for health monitoring research of composite material structures. Taking the CFRP shaft tube under bending load as the research object, based on the theory of composite material mechanics and applying the research idea of combining simulation analysis and experiment, the fatigue life, residual stiffness, and fatigue damage evolution of CFRP tubes under three-point bending fatigue loading were studied. Moreover, the fatigue characteristics of CFRP tubes under different fatigue loading were analyzed. At the same time, the ultrasonic phased array was used to obtain the fatigue damage evolution rule by scanning and analyzing the damage to the CFRP shaft tube after different fatigue loading times. Through the application of the FBG sensors, the whole process of fatigue evolution of the CFRP shaft tube was fully monitored. [ABSTRACT FROM AUTHOR]

The in-situ health condition of carbon fiber reinforced polymer (CFRP) reinforced structures has become an important topic, which can reflect the structural performance of the retrofitted structures and judge the design theory. An optical fiber-based structural health monitoring technique is thus suggested. To check the effectiveness of the proposed method, experimental testing on smart CFRP reinforced steel beams under impact action has been performed, and the dynamic response of the structure has been measured by the packaged FBG sensors attached to the surface of the beam and the FBG sensors inserted in the CFRP plates. Time and frequency domain analysis has been conducted to check the structural feature of the structures and the performance of the installed sensors. Results indicate that the packaged Fiber Bragg Grating (FBG) sensors show better sensing performance than the bare FBG sensors in perceiving the impact response of the beam. The sensors embedded in the CFRP plate show good measurement accuracy in sensing the external excitation and can replace the surface-attached FBG sensors. The dynamic performance of the reinforced structures subjected to the impact action can be straightforwardly read from the signals of FBG sensors. The larger impact energies bring about stronger impact signals. [ABSTRACT FROM AUTHOR]

This article focuses on the development of a carbon composite bicycle frame using various experimental methods of structural analysis. Two types of frame specimen were used. The complete frame specimen was tested in accordance with ISO test load cases with the addition of an ergometer test in order to refine the operational strain envelope of such a frame. Resistive strain gauges and optical Fiber Bragg Grating (FBG) sensors were used for this analysis. The FBG sensors were embedded inside the head tube joints during the manufacturing process. The head connection was designed as a geometrically precise form–connection of wound composite tubes, reinforced with a wrap of high-strength unidirectional carbon tapes and carbon fabrics. Additional structural strength laboratory tests were conducted using simplified frame specimens, in order to evaluate the range of the limit case strain ranges. The digital image correlation method was used for the evaluation of the strain distribution in the head tube area. Resistive strain gauges were used for local strain analysis in critical areas. The acoustic emission method was used to detect structural defects before they could influence the stiffness response of the frame. It was found that the joints of the frame tubes are crucial for the strength and safety of the frame. Therefore, attention was also focused on the strengthening of the head tube joint, and on its experimental verification. A positive effect on the strength of the reinforced frame was found by doubling the thickness of the carbon fabric in the head tube joint area. [ABSTRACT FROM AUTHOR]

The FBG sensors, embedded in triangle region of composite T-stiffened panels, were used to monitor the strain change during curing process and quasi-static compression real-timely. The results show that the compression load of stiffened panels with the FBG sensor embedded along the stiffener is the same as that without the FBG sensor. The FBG sensor embedded in the triangular area of the stiffened panels can effectively monitor during the curing process, and it can also be used to monitor the temperature and strain changes real-timely after curing process. In the quasi-static compression process, the strain curve measured by the FBG sensor is the same as the force-displacement curve. The FBG sensors can monitor accurately the damage such as lamination and cracking in the stiffened panels without affecting the property of the stiffened panels.

This study proposes a fiber Bragg grating (FBG) tactile sensing system utilizing a cross-modal Transformer architecture. Human tactile perception relies not only on single modalities but also on multimodal perception. Therefore, we decode the collected FBG tactile signals into dynamic vibration and static stress signals, and perform cross-modal perception to enable a robotic hand to perceive tactile properties of touched objects for precise manipulation. Experimental results demonstrate accuracy rates exceeding 87% for identifying the hardness and roughness properties of objects. Furthermore, the system occupies only 2.4 MB of storage space and achieves a recognition time of only 0.92 s per instance. Due to its lightweight and low-latency characteristics, the system holds wide application prospects in the field of tactile perception, including smart manufacturing, virtual reality, and online healthcare. [Display omitted] • A cross-modal tactile perception method is proposed • A multimodal tactile sensing platform is built. • Tactile Multimodal Transformer network is constructed. • The sensor system has the advantages of low delay and high accuracy. [ABSTRACT FROM AUTHOR]

• Thermoplastic automated tape layup is prone to residual stress. • Composite fatigue damage complexity causes a need for constant monitoring. • Both issues tackled with application of HB FBG sensors. • HB FBG sensors measuring multiaxial residual strain during manufacturing process. • HB FBG used for strain measurement and composite monitoring during fatigue. Monitoring of thermoplastic carbon reinforced composites is critical for the safe operation and optimization of composite structures. Strain measurement during their manufacturing and operation is often achieved with embedded Fiber Bragg Gratings (FBG). However, conventional FBGs can only measure axial strain. To measure multiaxial strain in thermoplastic composites, FBGs inscribed in highly-birefringent side-hole elliptical core optical fiber (SH2 FBG) are proposed. SH2 FBG were used to monitor composite produced by automated tape laying process, first − to measure residual in-plane and out-of-plane strain during the manufacturing stage, second − in plane transverse strain during cyclic loading. It was demonstrated that the sensors can be used to measure multiaxial residual strain, observe changes in material stiffness, and calculate the area of the mechanical hysteresis loop. As a result − it was shown that embedding SH2 FBG can be an effective and robust method for monitoring the carbon fiber reinforced thermoplastic composite. [ABSTRACT FROM AUTHOR]

Model tests are carried out on the jacked single piles of different diameters and pile lengths under the model pile of different diameters and pile lengths in clayey soil, which aims to investigate the penetration mechanical mechanism. How to accurately test the pile end resistance and pile side resistance during jacked pile sinking is particularly important. In this paper, a full-section spoke-type pressure sensor, a double diaphragm temperature self-compensating fiber Bragg grating (FBG) earth pressure sensor and a sensitized miniature FBG strain sensor are jointly applied to a single pile penetration model test to test a single pile driving force, pile end resistance and pile body stress during penetration. The test results show that the load transfer performance of test piles will be affected by different diameters, and the axial force transfer capability of a large diameter in the depth direction is better than that of a small diameter since the compacting effect is more obvious. The unit skin friction of the pile increases gradually as the depth increases, which is larger due to the lateral extrusion force increasing as the diameter increases. At the same depth, the unit skin friction of two different diameter piles demonstrates “friction fatigue”, which also decreases obviously as the depth increases. Under the conditions of this test, the maximum frictional resistance of the pile TP1 pile side is about 27.7% higher than that of the test pile TP2. In the static pile sinking process of three test piles in cohesive soil, 50% is end bearing; therefore, there is 50% friction, and the diameter influences the end bearing and the length influences the friction.

• The sensor consists of a single-mode fiber, a four-core fiber with fiber Bragg gratings inscribed on its side cores, and a hollow-core fiber filled with Polydimethylsiloxane (PDMS). • The sensor's signal is measured through a single-mode fiber, offering the advantage of high integration. • Fiber Bragg gratings and Fabry-Perot Interferometer exhibit distinct responses to pressure, vector bending, and temperature, enabling simultaneous measurement of multi-parameter. A multi-parameter sensor based on cascaded multi-core fiber Bragg grating (FBG) and Fabry-Perot interferometer (FPI) is proposed. The sensor consists of a single-mode fiber (SMF), a four-core fiber (FCF), and a hollow fiber (HCF) filled with polydimethylsiloxane. The HCF is fused at the end of the FCF to form an FPI. Through thermal diffusion technology (TDT), the all-fiber single-channel measurement of the sensor is realized. The FCF FBGs have a maximum sensitivity of 96.33 pm/m−1 for vector bending and 9.8 pm/°C for temperature. The FPI is capable of measuring temperature and pressure with sensitivities of 1621.2 pm/°C and 6500.0 pm/MPa, respectively. Consequently, a set of wavelength shift equations is derived to simultaneously measure vector bending, temperature, and pressure. The proposed multi-parameter sensor offers the advantages of high integration and reduced cross-talk, making it a promising candidate for applications such as environmental monitoring, structural health monitoring, and wearable artificial electronics. [ABSTRACT FROM AUTHOR]

To locate the impact source of a composite material structure with a series of fiber Bragg grating (FBG) sensors, a hybrid correlation interpolation method is proposed, in this paper, based on a weighted correlation analysis and a unidirectional cubic spline interpolation. First, the signals collected by FBG sensors are preprocessed on the frequency domain to reduce noise interference. Second, the impact similarity map is built by using the weighted cross-correlation value to estimate the location of the impact roughly. Third, the similarity map is further subdivided by the unidirectional cubic spline interpolation to increase the impact localization. Fourth, the FBG sensor network is experimental analyzed to optimize the layout and the structure of the FBG sensor network. The validity of the multi FBG sensor-based impact localization method is verified on a carbon fiber composite plate with a size of 650 Ă— 500 (mm). The experimental result shows that the mean absolute error is 9.74 mm for our suggested method and 15.51 mm for the bicubic polynomial interpolation (BPI) algorithm, which is reduced by 5.77 mm. The maximum errors are 36.40 mm for the BPI algorithm while are reduced to 21.55 mm for our suggested method. Furthermore, the effect of FBG sensor combination layout and number on impact location accuracy is analyzed and compared. It shows that the sensor network layout of rectangular structure using four FBG sensors is a better choice after the comprehensive consideration of economic benefits, localization accuracy, and error rate. [ABSTRACT FROM AUTHOR]

Summary: As the deployment of fiber‐based broadband networks continues to accelerate, the number of network facilities too is increasing exponentially. The network of optical fiber cables keeps growing as the number of passive optical network (PON) customers increases, eventually leading to unforeseen faults. Several solutions are offered for monitoring the optical link in PON with the optical time‐domain reflectometer (OTDR) as the most common for point‐to‐point optical link characterization. However, the OTDR approach has been found to be inadequate for point to multipoint network fault characterizations due to numerous back‐reflected signals converging at the power splitter that cannot be identified simultaneously by the OTDR detector. Several machine learning (ML) methods have recently been introduced for successful monitoring of optical communication links, but much of the ML technique depends on data from network transceivers to train ML algorithms to identify and detect faults. However, the use of data information for monitoring purposes can have an impact on the consistency of the services offered. In this article, we consider the deployment of the fiber Bragg grating sensor to acquire the monitoring data samples used to train the ML technique for effective link characterization. The proposed solution has the advantage of having a separate monitoring source that is independent of the data transmission signal and guarantees transparent transmission of information. The proposed ML‐based technique shows up to 99% precision for the identification of fiber defect in the PON optical distribution network. [ABSTRACT FROM AUTHOR]

Most of the tragedies on any bridge structure have been the cause of high‐density crowd behavior as a response to trampling as well as the crushing scenario. Therefore, it is most important to monitor such unforeseen situations by sensing the load imposed on the bridge structures. This scenario may arise where crowd movement is huge on these types of bridges. Similarly, the fiber Bragg grating (FBG) is a promising technology for structural health monitoring applications. In this work, an Internet of Things based FBG optical sensing scheme is proposed to monitor real‐time strain distribution throughout the bridge structures and localization of load imposed on the structure from a central control room. A suspension bridge model is designed by referring to a real bridge scenario and these FBG sensors are deployed to validate the proposed machine learning models. In this article, the performances of two machine learning strategies are discussed for the accurate estimation of load and its position by acquiring high sensitive FBG sensors signals at a very high data rate. The algorithms include K‐nearest neighbor (KNN) and random forest (RF); which are applied on each sensing data source, and then validated using a prototype suspension bridge model integrated with three FBG sensors (1532 nm, 1538 nm, and1541 nm) on a single optical fiber cable. [ABSTRACT FROM AUTHOR]