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Free-space optics communication (FSO) can be used as a transmission medium for fiber optic sensing signals to make fiber optic sensing easier to implement; however, interference with the sensing signals caused by the optical turbulence and scattering of airborne particles in the FSO path is a potential problem. This work aims to deep denoise sensed signals from fiber Bragg grating (FBG) sensors based on FSO link transmission using advanced denoising deep learning techniques, such as stacked denoising autoencoders (SDAE). Furthermore, it will demodulate the sensed wavelength of FBGs by applying the deep belief network (DBN) technique. This is the first time the real FBG sensing experiment has utilized the actual noise interference caused by the environmental turbulence from an FSO link rather than adding noise through numerical processing. Consequently, the spectrum of the FBG sensors is clearly modulated by the noise and the issue with peak power variation. This complicates the determination of the center wavelengths of multiple stacked FBG spectra, requiring the use of machine learning techniques to predict these wavelengths. The results indicate that SDAE is efficient in denoising from the FBG spectrum, and DBN is effective in demodulating the central wavelength of the overlapped FBG spectrum. Thus, it is beneficial to implement an FSO link-based FBG sensing system in adverse weather conditions or atmospheric turbulence. [ABSTRACT FROM AUTHOR]

A fiber Bragg grating (FBG) pulse and systolic blood pressure (SBP) measurement system based on the edge-filtering method is proposed. The edge filter is the Mach–Zehnder interferometer (MZI) fabricated by two fiber couplers with a linear slope of 52.45 dBm/nm. The developed system consists of a broadband light source, an edge filter, fiber Bragg gratings (FBGs), a coarse wavelength-division multiplexer (CWDM), and signal-processing circuits based on a field-programmable gate array (FPGA). It can simultaneously measure pulse pulsations of the radial artery in the wrist at three positions: Cun, Guan and Chi. The SBP can be calculated based on the pulse transit time (PTT) principle. The measurement results compared to a standard blood pressure monitor showed the mean absolute error (MAE) and standard deviation (STD) of the SBP were 0.93 ± 3.13 mmHg. The system meets the requirements of the Association for the Advancement of Medical Instrumentation (AAMI) equipment standards. The proposed system can achieve continuous real-time measurement of pulse and SBP and has the advantages of fast detection speed, stable performance, and no compression sensation for subjects. The system has important application value in the fields of human health monitoring and medical device development. [ABSTRACT FROM AUTHOR]

The work is devoted to the consideration of methods for determining the strain of objects using fiber Bragg gratings under a high-frequency vibration or pulsed mechanical action, which is difficult to perform using widespread methods and devices. The methods are based on numerical processing of the time dependence of the radiation power reflected from the fiber Bragg grating at various wavelengths, which makes it possible to measure strain parameters in a wide range of magnitude and frequencies. The efficiency of the proposed methods is demonstrated by numerical simulation. It is shown that it is possible to restore the strain dependence on time in the range ± 1000   μ ϵ or more from simultaneously measured power dependencies reflected by the fiber Bragg grating using common fiber-optic components. The case of sequential registration of reflected radiation power at different wavelengths to determine the probability density of the distribution of the strain values is also considered. The results of signal processing obtained both by numerical simulation and experimentally for the case of a linear vibration are presented. The technical problems of using the proposed methods are discussed. [ABSTRACT FROM AUTHOR]

Embedded fiber Bragg gratings are increasingly applied for in-situ strain measurement in fiber-reinforced plastics, integral to high-end aerospace equipment. Existing research primarily focuses on in-plane strain measurement, limited by the fact that fiber Bragg gratings are mainly sensitive to axial strain. However, out-of-plane strain measurement is equally important for comprehending structural deformation. The birefringence of fiber Bragg gratings shows promise for addressing this problem; yet, the strain transfer relationship between composites and optical fibers, along with the decoupling method for multi-directional strains, remains inadequately explored. This study introduces an innovative method for multi-directional strain measurement in fiber-reinforced plastics using the birefringence of a single-fiber Bragg grating. The strain transfer relationship between composites and embedded optical fibers was derived based on Kollar's analytical model, leading to the development of a multi-directional strain decoupling methodology. This method was experimentally validated on carbon fiber/polyetherimide laminates under thermo-mechanical loading. Its reliability was confirmed by comparing experimental results and finite element simulations. These findings significantly broaden the application scenarios of fiber Bragg gratings, advancing the in-situ measurement technology crucial for the next generation of high-end aerospace equipment. [ABSTRACT FROM AUTHOR]

A compact gain-switched all-fiber ytterbium laser operating at a wavelength of 1127 nm with the ability to control pulsed radiation parameters has been investigated. Gain switching was carried out by modulating the current of a semiconductor pump diode. With pumping energy ranging from 197.6 to 263.5 μJ, there was one generation pulse per each pump pulse with a duration of 0.43 to 1.1 μs, energy of 5.3 to 8.8 μJ, and a repetition rate of 100 Hz. Increasing the pumping energy above 265 μJ led to a change in the shape of generated pulses and to their energy rising up to 70 μJ. [ABSTRACT FROM AUTHOR]

In this article, we discuss the scientific research we conducted to ensure information security on concrete structures using the fiber Bragg grating method. As a result, guided by the experiences of other researchers and their results in our studies, the main hazards were identified, and the influence of temperature and deformation sensors in concrete was studied. The work determines the dependence of temperature on the optical cable and its effect on concrete deformation. It also studies the change in the internal structure of the optical fiber when exposed to concrete, and in comparison, with non-concrete optical fiber. In the experimental chapter, conducted on laboratory bench, we consider and study the signal transmission structure of an optical sensor that experiences deformation upon impact with concrete and such fibers. Graphic data was obtained using the OptiSystem program. During the process of determining the optical power of the sensors, we discovered that the higher the vibration during signal transmission, the higher the power of the optical data acquisition system unit. The results presented in this paper show the promise of fiber optics in other environments, as well as new discoveries in the construction industry and the successful use of electrical laser sensors to maintain temperature and stress in a variety of concrete structures, including cooling towers in nuclear and thermal power plants. [ABSTRACT FROM AUTHOR]

We designed a novel elliptical topology fiber‐optic sensing network to improve the coverage and reliability of fiber‐optic sensing networks. A sensitive area model detection experiment of fiber Bragg‐grating sensors was conducted, and a fiber‐optic sensing network based on an elliptical topology model was established based on the optimal coverage. To further optimize the network performance, the graph theory's adjacency matrix, coupled with the shortest‐path algorithm, efficiently uncovers and establishes the demodulation pathway for failed sensors in the fiber‐optic sensing network at a higher rate, thereby improving the response speed of self‐repair. Floyd's algorithm demonstrated a significant improvement in repair time compared with the standard practice, specifically reducing the repair time by approximately 88.25%. [ABSTRACT FROM AUTHOR]

To address the issue of harsh marine background noise impacting the monitoring signal of fiber-optic hydrophones, we propose a low-noise fiber Bragg grating (FBG) hydroacoustic monitoring system with a reference sensor based on genetic algorithm backpropagation (GA-BP). Through theoretical analysis, we deduce the noise suppression steps of the GA-BP algorithm based on the reference sensor and construct train and test sets based on the data from the reference sensor and monitoring sensor at different times, optimizing the GA-BP algorithm to find the best fitting results and thereby obtaining the low-noise monitoring signal. Experimental results from the anechoic tank show that the proposed method can suppress background noise interference on effective signals and that the suppression effect improves as the background noise increases. The sound pressure sensitivity ranges from −173.76 dB to −171.33 dB at frequencies of 8 kHz to 12 kHz, with a response flatness of less than 2.43 dB. The noise suppression effect is obvious under the condition of poor signal-to-noise ratio (SNR), which can reach more than 18.3 dB. The advantages of the proposed algorithm in array signal processing are further demonstrated by the directivity experiment, which proves that the algorithm has a great potential for engineering applications in harsh marine environment. [ABSTRACT FROM AUTHOR]

We demonstrate a low latency delay of a radio frequency (RF)–linear frequency-modulated (LFM) pulse by modulating it onto optical carriers from a Kerr comb and sending the signal through a concatenation of off-the-shelf linearly chirped fiber Bragg gratings (LC-FBGs) and chirped-and-sampled FBG (CS-FBG). We characterize the frequency response and latency of the LC-FBG and CS-FBG. Then, experimentally, the LFM pulse performance is characterized by measuring the peak sidelobe level (PSL) at the output of the tunable delay system. The experiment, performed with an LFM pulse of 1 GHz bandwidth at a 10 GHz center frequency, shows a PSL better than 34.4 dB, attesting to the high quality of the buffer RF transfer function. Thus, the proposed optical memory buffer architecture, utilizing compact devices based on a Kerr comb and FBGs, offers several benefits for delaying LFM pulses, including (i) a larger tunable delay range, (ii) low latency, (iii) wide bandwidth, and (iv) high PSL. [ABSTRACT FROM AUTHOR]

Shield tunnels' structural stability is challenged due to the fact that they are often built under rivers, lakes, and oceans. It is crucial to execute the structural deformation perception of the shield tunnel. Fiber Bragg grating (FBG) sensing technology is sensitive to deformation information, making it one of the greatest options for shield tunnels to perceive structural deformation. In this study, a 1:20 scale model test was carried out to investigate the deformation perception of the shield tunnel structure under three different layouts of surface-mounted FBG sensors. The deformation law of the tunnel is discussed, under the condition of two-factor cross fusion and especially under the condition of constant water pressure and soil pressure change. The results indicate that, under the combined action of water and soil pressure, the uniform water pressure of 0.33 MPa has a stabilizing effect on the segment strain under the vertical load of 0.4 MPa. The traditional four-point layout and the 18° uniform layout are more effective in detecting changes in local tunnel curvature and strain, respectively, compared to the 36° uniform layout mode. It is advised that the traditional four-point layout be used to collect information for other sections' monitoring and that the 18° uniform layout is for harsh terrain conditions. [ABSTRACT FROM AUTHOR]

Abstract Temperature changes during the chemical corrosion of stone cultural relics affect the condensation and evaporation of water and chemical reactions between soluble substances and corrosive solutions. This ultimately leads to changes in the internal structure and composition of the artifacts, which in turn lead to changes in the microstrain of cultural relics. To obtain in-situ real-time information on changes in the temperature and microstrain of stone cultural relics during chemical corrosion damage, a fiber Bragg grating (FBG) detection system was developed. The detection principle for the temperature and microstrain of sandstone was provided. Thermal field emission scanning electron microscopy, X-ray diffraction, and mercury intrusion porosimetry were used to characterize the surface morphology, composition, and pore structure of the sandstone samples, respectively. The temperature and microstrain changes of the sandstone samples under deionized water with different acidic/alkaline and salt solutions and at different temperatures were examined online in situ using the FBG measurement system. The results indicate that the dissolution of sandstone in the acidic solution (H2SO4 and NaHSO4) resulted in an exothermic chemical reaction as well as the dissolution of sandstone in the neutral salt solution (Na2SO4) and alkaline solution (NaOH and Na2CO3) led to material conversion and exothermic chemical reaction; the deionization reaction belongs to the dissolution reaction. The NaHSO4 solution caused the most serious corrosive disease on the sandstone surface. When the temperature of the NaHSO4 solution was 60 °C, the temperature and microstrain of the sandstone reached 63.9 °C and 253.6 με, respectively. The results of this study can support the research of revealing the corrosion mechanism of sandstone in different environments.

Abstract A large number of slopes appear along the line during railway construction, which will pose a threat to railway safety operation. Slope monitoring plays an important role in ensuring the safety of railway operation. Aiming at the difficulties of sensor multiplexing, low accuracy, and large disturbance by trains, this paper proposes a railway slope monitoring method based on integrated fusion detection of inclination and vibration. Instability and failure characteristics of the K3 slope in Shuohuang Railway and dynamic characteristics under the excitation of the train load are analyzed by the finite element method (FEM) analysis. Based on the above analysis, a slope monitoring system is established utilizing the self-developed dual-parameter fiber Bragg grating (FBG) sensor. The monitoring data of the past four years show that the slope is in a relatively stable state at present. The monitoring data are consistent with the results of the FEM. The feasibility of the damage identification method based on inclination and vibration characteristics is verified, which provides a new method for railway slope monitoring.

This article outlines the development of a Fiber Bragg Grating (FBG) intended for use as a sensor for CH4 and CO2 gases. Following fabrication, the FBG was effectively treated with a layer of Graphene Material through a modified RF Sputtering process. This coating procedure involved introducing argon gas into the chamber and subjecting the FBG, securely held by two vacuum stages, to a temperature range of 27°C to 600°C by adjusting the power supplied to the cathode and anode, ranging from 0 to 125 Watts. Subsequently, the FBG was employed as a key sensing element within an experimental setup aimed at measuring gas concentrations within a confined space. The assessment involved analyzing the reflected signal of the FBG using an Optical Interrogator System, which demonstrated a shift in the Bragg wavelength of the reflected signal corresponding to varying gas concentrations. This study indicates promising outcomes for the Graphene-coated FBG as a gas sensor. The sensor’s sensitivity was evaluated based on the Bragg wavelength shift resulting from gas presence within the chamber. The Graphene-coated FBG exhibited sensitivities of 3.3 ppm for CH4 and 3.7 ppm for CO2, surpassing those reported in prior research efforts.

Objective FBG (fiber bragg grating) monitoring technology features fast dynamic response, strong anti-interference, high precision and strong durability, and can realize long-distance real-time monitoring. The feedback circumferential deformation monitoring data from FBG is of great significance to the parameter adjustment in the process of shield tunneling. Therefore, it is necessary to conduct an in-depth research on the circumferential deformation law of the segments based on FBG technology. Method With a metro tunnel project as the example, the fiber optic sensors are used for real-time monitoring of the segments during metro tunnel construction. Through analysis of the monitoring data, the changing law of the circumferential strain in the segment construction environment is studied, and the correlation between the relative convergence displacement and the shield tunneling parameters is analyzed. Result & Conclusion The monitoring data indicates that the circumferential deformation mainly occurs within one week after the installation of the tunnel segments and within a 50 m range of the adjacent tunnel excavation. In condition of unfavorable stratum and small buried depth, the effect of the subsequent tunnel excavation on the convergence of the already constructed segments is about 50%. When the stratum is favorable and the buried depth is large, the effect of subsequent tunnel excavation on the above convergence is approximately 65% to 83%. The strain of the segments is affected significantly by the stratum and the adjacent tunnel construction under different buried depths. The segments in a shallow buried depth and poor soil stratum have large deformation, while those in the larger buried depth exhibit better constraint and unnoticeable deformation. There is a clear correlation between the relative convergence displacement and the shield tunneling parameters. The total thrust of the subsequent shield tunneling is negatively correlated with the relative convergence displacement of the previously constructed segments, while the excavation speed of the subsequent shield tunneling is positively correlated with the above relative convergence displacement. The real-time monitoring data obtained through FBG monitoring technology can serve as a basis for adjusting the shield tunneling parameters.

This work presents a technique to obtain wavelength tuning for a fiber laser with a nonthermal plasma‐based temperature regulator system and a fiber Bragg grating (FBG). The plasma effect was generated in a dielectric barrier discharge (DBD) reactor filled with helium as the carrier gas for plasma generation. The temperature characterization of the DBD reactor had shown that the nonthermal heating mechanism of plasma could manipulate gas temperature from 25°C to around 145°C in ~10 min. By exploiting the rapid temperature change of plasma, the reflected wavelength of the FBG can be tuned accordingly. At a discharge voltage of 3 kV, the fiber laser was tuned within a range of 2 nm with 11.9 pm/°C tuning resolution. The fiber laser exhibits a thermally stable emission with very low shifting at a constant temperature value. [ABSTRACT FROM AUTHOR]

Fiber dispersion is a severe constraint to be addressed in high speed optical communication, as it restricts the transmission capacity and reach of fiber optics link. This work presents an effective dispersion compensation technique in the optical domain with minimal hardware complexity. Here, we integrated a single linearly chirped fiber Bragg grating (CFBG) with tanh apodization for Chromatic Dispersion (CD) compensation and a second-order optical FIR filter for Polarization Mode Dispersion (PMD) compensation. Adaptive PMD compensation is obtained by updating the filter parameters using Least Mean Square (LMS) error algorithm, which enables the system to adjust and mitigate PMD effects dynamically, enhancing overall efficiency. The performance of the proposed system with different modulation schemes such as NRZ, RZ, and duo-binary schemes are experimented. A WDM link of 16 channels over 100 km is designed with the proposed model, with each channel transmitting data at 40 Gbps. Simulation results reveal that the presented model performed well with reduced hardware complexity, keeping BER value below 10 - 9 and Q-Factor above 6. [ABSTRACT FROM AUTHOR]

Laser direct writing (LDW) is versatile in structuring fibers with micro‐sized functional elements such as fiber Bragg grating (FBG) and backscattering centers by finely manipulating back and side scattering from laser‐induced refractive index modified (RIM) points. However, the side‐scattering is a lesser‐explored property in laser‐structured fibers. In this work, a concise physical model is established to understand the side‐scattering as a combined effect of microstructure and geometry of RIM points. Based on a single‐pulsed LDW method, the parametric decoupling between scattering loss (α) and coupling strength (κ) coefficients of FBGs is reported, whose cross‐section is customized to have a flattened ellipse with thoroughly positive RIM, enabling controllable reflectivity from −21.33 dB to −0.0018 dB while maintaining narrow bandwidth and low loss. Exemplarily, a designed FBG realizes ultra‐low loss of 0.008 dB with a resonance attenuation of 10.81 dB, exhibiting a record‐breaking κ/α of 2083. Using this FBG as the high‐reflective mirror of a home‐made bismuth‐doped fiber laser, narrow‐band lasing with a high optical signal‐to‐noise ratio of ≈43 dB is achieved, demonstrating flexibilities of the proposed approach in customizing both back‐ and side‐scattering in fibers and opening up wide opportunities for combining multifunctional components into optical fibers and realizing all‐fiber networks. [ABSTRACT FROM AUTHOR]

Modern power grids are undergoing a significant transformation with the massive integration of renewable, decentralized, and electronically interfaced energy sources, alongside new digital and wireless communication technologies. This transition necessitates the widespread adoption of robust online diagnostic and monitoring tools. Sensors, known for their intuitive and smart capabilities, play a crucial role in efficient condition monitoring, aiding in the prediction of power outages and facilitating the digital twinning of power equipment. This review comprehensively analyzes various sensor technologies used for monitoring power transformers, focusing on the critical need for reliable and efficient fault detection. The study explores the application of fiber Bragg grating (FBG) sensors, optical fiber sensors, wireless sensing networks, chemical sensors, ultra-high-frequency (UHF) sensors, and piezoelectric sensors in detecting parameters such as partial discharges, core condition, temperature, and dissolved gases. Through an extensive literature review, the sensitivity, accuracy, and practical implementation challenges of these sensor technologies are evaluated. Significant advances in real-time monitoring capabilities and improved diagnostic precision are highlighted in the review. It also identifies key challenges such as environmental susceptibility and the long-term stability of sensors. By synthesizing the current research and methodologies, this paper provides valuable insights into the integration and optimization of sensor technologies for enhancing transformer condition monitoring and reliability in modern power systems. [ABSTRACT FROM AUTHOR]

With the increase in the demand for large-capacity optical communication capacity, multi-core optical fiber (MCF) communication technology has developed, and both the types of MCFs and related devices have become increasingly mature. The application of MCFs in the field of sensing has also received more and more attention, among which MCF fiber Bragg grating (FBG) devices have received more and more attention and have been widely used in various fields. In this paper, the main writing methods of MCF FBGs and their sensing applications are reviewed. The future development of the MCF FBG is also prospected. [ABSTRACT FROM AUTHOR]

Shape recognition plays a significant role in the field of robot perception. In view of the low efficiency and few types of shape recognition of the fiber tactile sensor applied to flexible skin, a convolutional-neural-network-based FBG tactile sensing array shape recognition method was proposed. Firstly, a sensing array was fabricated using flexible resin and 3D printing technology. Secondly, a shape recognition system based on the tactile sensing array was constructed to collect shape data. Finally, shape classification recognition was performed using convolutional neural network, random forest, support vector machine, and k-nearest neighbor. The results indicate that the tactile sensing array exhibits good sensitivity and perception capability. The shape recognition accuracy of convolutional neural network is 96.58%, which is 6.11%, 9.44%, and 12.01% higher than that of random forest, k-nearest neighbor, and support vector machine. Its F1 is 96.95%, which is 6.3%, 8.73%, and 11.94% higher than random forest, k-nearest neighbor, and support vector machine. The research of FBG shape sensing array based on convolutional neural network provides an experimental basis for shape perception of flexible tactile sensing. [ABSTRACT FROM AUTHOR]

Optical fiber interconnects are playing a vital role in satisfying the demand for high-speed data transmission for long-range applications. The primary goal of the work presented here is to design an optical fiber communications system suitable for use at distances of up to 100 km. In this work, an intensity-modulated scheme at the transmitter and direct reception at the detector are employed to lower the overall system cost. Single-mode fiber (SMF) with nonlinearities is used as a transmission medium, connecting both transmitting and receiving sections. In order to get rid of the distortion brought on by the fiber, Bragg grating is used at the SMF's output. A Gaussian LPF is included in the receiver to eliminate the APD noise induced in the process of optical-to-electrical signal conversion. The performance of the system at 10 Gbps is assessed by examining the BER, Q-factor, and eye diagrams. The theoretical description of a Bragg grating is provided, and this work employs Optisystem softwarebased simulation. The results obtained reveal a BER value below 10-13 in the entire range of 100 km, in addition to the eye-opening factor of 0.85. [ABSTRACT FROM AUTHOR]

This paper proposes a flexible sensor made of fiber Bragg gratings (FBGs) package that can effectively recognize the direction and velocity of relative sliding on its surface. The measurement principle and structural design of the sensor are introduced, and the sensor is analyzed by finite element simulation software to verify that the sensor can detect the shear deformation of relative sliding on its surface. On this basis, an experimental platform is built to test the relative sliding direction and velocity, the feature values are extracted after the initial signal is processed with noise reduction, and the recognition prediction is carried out by using back-propagation neural network (BPNN) and GA-BP neural network optimized by Genetic Algorithm (GA). The experimental results show that GA-BP neural network has better recognition accuracy, and the correlation coefficients R2 in the recognition of the sliding direction and velocity parameters are 0.9851 and 0.9819, respectively, which are able to recognize the sliding sensation parameters effectively. [ABSTRACT FROM AUTHOR]

The creep behavior of composite wing leading edges resulting from nonequilibrium residual stresses and material viscoelasticity needs to be evaluated comprehensively as it significantly affects assembly. In this study, long-term creep monitoring of a composite wing leading edge used in an actual airplane for 710 h is conducted using embedded fiber Bragg grating arrays and a creep extraction algorithm. The spectra and Bragg wavelength shifts of two embedded arrays, which involve temperature, thermal expansion, and creep, are recorded and analyzed. The creep curve of the composite wing leading edge is reconstructed and further predicted using the creep extraction algorithm based on multiparameter decoupling and the Burgers model. This study elucidates the enlargement of the opening size in the composite wing leading edge by measuring the tensile strain above the neutral axis. The predicted creep time serves as a valuable reference for determining the appropriate assembly timing. [ABSTRACT FROM AUTHOR]

We demonstrate fast writing of strong fiber Bragg grating (FBG) without hydrogen loading using 343 nm femtosecond pulses of only 7 μ J energy at 60 kHz repetition rates and a two-mask interferometer. The beam was focused to a 30–50 μ m diameter along the fiber axis, greatly enhancing the peak power while avoiding damage to the masks. A refractive index modulation of more than 10 − 3 could be obtained in less than one minute exposure. To avoid the observed strong temperature gradient observed in the SMF-28 fiber, a galvo scanner was used to rapidly move the beam back and forth laterally up to 1 mm. FBG were written in SMF-28, as well as 20/400 μ m fiber. In the latter fiber, better heat dissipation allowed us to write the FBG with the standard phase mask scanning technique, and a 0.28 mm Gaussian apodized FBG could be written. [ABSTRACT FROM AUTHOR]

There has been a growing interest in using Fiber Bragg Grating (FBG) sensors for the detection of humidity and water content due to their high sensitivity, ease of installation, multiplexing capability, reliability, and resistance to electromagnetic interference. Although, several studies and papers have been published on FBG sensors and their applications in various fields such as construction, geophysical, there is a lack of a consolidated review that specifically focuses on recent developments in agriculture with particular reference soil humidity and water content. Therefore, a comprehensive and up-to-date analysis of the advances, detection mechanisms, challenges, and potential future directions in this field is needed. This paper provides an in-depth analysis and summarizes the fundamental principles, advancements, methodologies, and recent research findings, highlighting the potential application in agriculture, development, challenges, and prospects for FBG-based humidity and water content detection. By utilizing the changes in FBG wavelength or amplitude caused by the presence of humidity, they provide an effective means for real-time monitoring and control of water content. However, challenges remain to be addressed, such as the need for accurate calibration and the potential for drift over time. In this review, we further discuss the strategies and techniques proposed to overcome the highlighted challenges, such as sensor packaging, signal processing algorithms, and calibration procedures, and suggest that further studies could be done to investigates the novel materials with enhanced sensitivity and selectivity, development of miniaturized and wireless FBG sensor system, as well as investigating multiplexing techniques for simultaneous measurement of multiple parameters. [ABSTRACT FROM AUTHOR]

A dual short period fiber Bragg grating (D-FBG) device was devised, whereby one FBG was inscribed inside the core and the other within the cladding, enabling the reflection of two distinct wavelengths. The design presented in this study demonstrates versatility by using both core and cladding FBGs to provide multi-sensing capabilities. COMSOL was used to realize the proposed design in this work. The core grating had a reflected frequency of 199.345 THz, while that of the cladding was at 199.47 THz. The heterodyne technique for terahertz and gigahertz frequencies in these designs is very promising. The generated frequency is 0.125 THz, this suggests that the proposed design can be used for beat frequency generation and multi-sensing application. [ABSTRACT FROM AUTHOR]

Fiber Bragg Grating sensors are playing decisive role in clinical decisions, where its ability to show chemical-inertness, small in size and high-sensitivity makes it superior over the electric-sensors for both in vivo as well as ex vivo examinations. In the recent years, different FBG sensors are proposed for biosensing task(s); yet, ensuring high-resolution, accurate and high-sensitive sensing under complex operating environment remains challenge. The fiber Bragg grating coating or grating-encapsulation(s) by using metals or polymers enables better spectral efficiency; yet, inappropriate coating and allied grating might cause varied spectral-responses or reflectivity, causing multiple peaks over response. Demodulating such ambiguous spectral responses might be difficult and can cause false positive result. Its severity can be more frequent over biosensing involving viscous analytes-antibody or aqueous (test)-solutions. The local conditions like viscosity-strain and temperature caused noises too give rise to the different peaks over fiber Bragg grating spectra response that might impose wrong clinical diagnosis decisions. With such inference, this research proposes a robust self-compensating gold-encapsulated tilted fiber Bragg grating structure for peak-tracking-based biosensing. It involves two sequential phases, where initially a gold-encapsulated tilted fiber Bragg grating is designed with grating's tilt angle of 9°. Simulating the sensor, the spectral responses are obtained for the different Bragg wavelengths, which are subsequently processed for cross-correlation-based matched filtering for peak identification to make clinical decisions. Toward self-compensation, cross-correlation was performed between the reference spectra and the measured fiber Bragg grating responses. Employing Mexican-Hat wavelet response as the reference signal and measured spectra, zero-crossing points and correlation-vectors were obtained signifying the peak locations. Thus, retaining the correlation vectors with higher peak intensity over the Bragg wavelength, the target peak for the tilted fiber Bragg grating was tracked. Simulation results confirmed that the proposed tilted fiber Bragg grating with self-compensation ability can achieve 0.9 nm/refractive index unit sensitivity while suppressing noise elements and false-peaks caused due to local artefacts like viscosity, strain, temperature, etc. Such abilities make the proposed gold-encapsulated sensor suitable for both biosensing as well as physio-mechanical sensing tasks, and hence can be suitable for in vivo and/or ex vivo biosensing tasks. [ABSTRACT FROM AUTHOR]

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Self-compacting concrete (SCC) is the most flowable concrete type that exerts high pressure on formwork. SCC is the most commonly used concrete globally for construction applications due to its cost-effectiveness. However, to make a formwork resist the exerted lateral pressure of SCC, it is required to have a suitable design for formwork. This paper presents a novel approach on how could create and prepare the Fiber Bragg Grating (FBG) optics using as a sensor to measure lateral pressure and temperature of SCC. To ensure the FBG sensor works properly a validated methodology is conducted. In the first stage, FBG sensors are calibrated with temperature sensitivity and then are calibrated with water pressure. The latter calibration is used to verify lateral pressure with SCC. However, this is not the only sensor used to record the result, a genuine sensor such as a transducer sensor has been positioned close to the FBG sensor to validate the results of the FBG sensor. The created FBG sensor demonstrates highly promising results, effectively validating the outcomes of the transducer sensor, while also reducing costs and enhancing usability for construction applications. [ABSTRACT FROM AUTHOR]

A hybrid enhanced inverse finite element method (E-iFEM) is proposed for real-time intelligent sensing of discontinuous aerospace structures. The method can improve the flight performance of intelligent aircrafts by feeding back the structural shape information to the control system. Initially, the presented algorithm combines rigid kinematics with the classical iFEM to discretize the aerospace structures into elastic parts and rigid parts, which will effectively overcome structural complexity due to fluctuating bending stiffness and a special aerodynamic section. Subsequently, the rigid parts provide geometric constraints for the iFEM in the shape reconstruction method. Meanwhile, utilizing the Fiber Bragg grating (FBG) strain sensor to obtain real-time strain information ensures lightweight and anti-interference of the monitoring system. Next, the strain data and the geometric constraints are processed by the iFEM for monitoring the full-field elastic deformation of the aerospace structures. The whole procedure can be interpreted as a piecewise sensing technology. Overall, the effectiveness and reliability of the proposed method are validated by employing a comprehensive numerical simulation and experiment. [ABSTRACT FROM AUTHOR]

To address the constraints associated with conventional fitting techniques for temperature demodulation in the context of subway tunnel fires, a new method of demodulation grating sensing spectrum using long short‐term memory convolutional neural network (LSTM‐CNN) is proposed in this paper. Build the monitoring platform based on LSTM‐CNN ultra‐weak fiber grating temperature measurement system, predict its sensing signals by LSTM‐CNN algorithm, select 18000 spectra as sample data for training, use AdamW stochastic optimization algorithm for training, and carry out the temperature calibration and demodulation error analysis of the Fiber Bragg Grating within the temperature range of 25–75°C. Compared with GRU algorithm, LSTM algorithm and traditional maximum peak method, the algorithm of this paper is good and can effectively improve the measurement accuracy, the experimental results show that: the demodulation accuracy of temperature wavelength prediction in this paper can be up to 99.27%, and the root mean square deviation is 0.08528°C, through the experiments, it is verified that the method proposed in this paper has a certain reference and support in terms of theories and technology significance. It is suitable for the identification and monitoring of fire hazards in underground tunnels, and also has application value in the signal processing of grating array sensing demodulation system. [ABSTRACT FROM AUTHOR]

In this paper, fiber Bragg grating (FBG) sensors were applied to investigate the frost resistance of C60 concrete. First, the growth of both the static and dynamic elastic modulus of C60 concrete with curing age was investigated using an FBG, the standard method, and the resonance method, respectively. Second, to simulate the freezing and thawing conditions in cold regions, the concrete specimens were subjected to air freezing and water thawing using the slow freezing method. The authors explored the effect of freeze–thaw cycles on the mechanical properties of concrete and established a mathematical model relating its mechanical properties to freeze–thaw cycles based on an FBG sensor. Meanwhile, its compressive strength, dynamic elastic modulus, and mass loss rate were tested. Finally, the interface morphology and hydration products of concrete were observed using a scanning electron microscope (SEM) after freeze–thaw cycles. The results indicate that both the static and dynamic elastic modulus of C60 concrete increase with curing age. Its elastic modulus measured by FBG is approximately the same as that measured by the standard method, confirming the viability of using an FBG sensor to measure its elastic modulus. Furthermore, the authors highlighted the dependence of its compressive strength on the freeze–thaw cycles. The relationship of the static elastic modulus to freeze–thaw cycles is similar to that of the dynamic elastic modulus and mass loss rate. A static elastic modulus achieved from an FBG is proposed here to characterize the frost resistance of C60 concrete. [ABSTRACT FROM AUTHOR]

This study presents a technique for implementing all-optical Full Adder (FA) and Full Subtractor (FS) functionalities utilizing a Fiber Bragg Grating (FBG) structure. The proposed method exploits the cross-phase modulation (XPM) mechanism within a phase-shifted FBG (PSFBG) configuration. An analysis of basic gate operations and corresponding switching phenomena is provided, along with the optimization and implementation of FA and FS circuits using the PSFBG structure. Extensive simulations, validated against conventional circuits and truth tables, demonstrate the efficacy of the proposed approach. The coupled-mode theory governing FBG behavior as an optical switching element is elucidated, along with mathematical descriptions of FBG and PSFBG functionalities for switching applications. MATLAB simulations are employed for comprehensive analysis and validation of the proposed all-optical FA and FS schemes. This work contributes to the advancement of all-optical computing techniques, facilitating efficient high-speed data processing with notable optical communication benefits. [ABSTRACT FROM AUTHOR]

Throughout the central nervous system, the spinal cord plays a very important role, namely, transmitting sensory and motor information inwardly so that it can be processed by the brain. There are many different ways this structure can be damaged, such as through traumatic injury or surgery, such as scoliosis correction, for instance. Consequently, damage may be caused to the nervous system as a result of this. There is no doubt that optical devices such as microscopes and cameras can have a significant impact on research, diagnosis, and treatment planning for patients with spinal cord injuries (SCIs). Additionally, these technologies contribute a great deal to our understanding of these injuries, and they are also essential in enhancing the quality of life of individuals with spinal cord injuries. Through increasingly powerful, accurate, and minimally invasive technologies that have been developed over the last decade or so, several new optical devices have been introduced that are capable of improving the accuracy of SCI diagnosis and treatment and promoting a better quality of life after surgery. We aim in this paper to present a timely overview of the various research fields that have been conducted on optical devices that can be used to diagnose spinal cord injuries as well as to manage the associated health complications that affected individuals may experience. [ABSTRACT FROM AUTHOR]

Copyright of Urban Mass Transit is the property of Urban Mass Transit 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 Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny 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.)

In situ monitoring of the temporal and spatial distribution of soil moisture and thermal properties are important for studying the water and energy transport in the vadose zone. The single-probe heat-pulse method based on fiber Bragg grating technology (SPHP-FBG) has become a research focus in field monitoring because of its capability to realize quasi-distributed and real-time monitoring. However, the SPHP-FBG method can only obtain thermal conductivity. This study developed a dual-probe heat-pulse method based on FBG (DPHP-FBG). The DPHP-FBG method can measure thermal conductivity (λ), volumetric heat capacity (Cv), and thermal diffusivity (k). Consequently, volumetric soil water content (θ) can be estimated from its linear relationship with Cv. The accuracy of the DPHP-FBG method in the estimation of Cv, λ, and θ was tested under different heating duration and various soil moisture conditions. In addition, Monte Carlo simulation was performed to investigate the impact of FBG measurement errors on accuracy. Finally, a field test was conducted to verify the effectiveness of the developed DPHP-FBG system. The results show that the DPHP-FBG method allows accurate soil moisture and thermal properties estimation without soil-specific calibration. The mean errors of the Cv and θ decrease with the extended heating duration. When the heating lasts 20 s, the measured Cv and θ have mean errors of 0.02 MJ m−3 K−1 and 0.01 m3/m3, respectively, for various moisture conditions. In the field test, the spatio-temporal distribution of soil moisture and thermal properties can be obtained in real time. Thereby, the proposed DPHP-FBG monitoring system is potential to conduct in situ coupled heat and soil moisture measurements at a large scale.

Abstract The illegal water injection into meat not only breaks the market equity, but also deteriorates the meat quality and produces harmful substances. In this work, we proposed a fiber Bragg grating (FBG) sensor that enabled fast, quantitative, and in-situ detection of the moisture content of water-injected meat. The FBG was written in the erbium-ytterbium (Er/Yb) co-doped fiber, which could perform the self-photothermal effect by injecting the near infrared laser into the fiber. As the heated fiber sensor probe was inserted into the meat sample, the temperature decreased due to the heat dissipation mediated by moisture. The intracore Bragg grating could monitor the temperature loss by recording the Bragg wavelength shift, which reflected the water content quantitatively. The results revealed that the sensor could complete the detection within 15 s. The sensor’s sensitivity to detect changes in the pork water content was theoretically calculated to be 0.090847%. The proposed sensor is expected to provide a novel approach for examination of the meat moisture.

This paper reports on the testing and evaluation of a passive autoranging (AR) method designed to dynamically extend the measurement range of a photonic current transducer (PCT) to pave the way toward a realization of a combined metering- and protection-class current sensor. The PCT utilizes a current transformer (CT), a piezoelectric transducer (PZT), and a fiber Bragg grating (FBG) to enable current measurement at multiple points in an electrical power network whereby multiple sensors are deployed and interrogated serially using a single optical fiber. The autoranging technique relies on incorporating static MOSFET switches to instantaneously short individual serially connected CT burdens in response to a measured current magnitude exceeding pre-set thresholds. The AR circuit switching events produce distinctive signal features that are used by the proposed switching algorithm to apply appropriate scaling factors to reconstruct the measured current from the optical signal. It is shown through laboratory experiments that the AR circuit correctly reacts to pre-set burden current thresholds of 130% of the nominal value and 22 times the nominal value, signifying its "metering" and "protection" range boundaries. The circuit reaction time is below 4 ms, rendering it suitable for standard power system protection purposes. Moreover, the operation of the AR circuit is demonstrated for burden currents of up to 100 A for over 1 s, satisfying a test procedure for the secondary CT circuit, as required by some power system operators. It is demonstrated that the proposed switching algorithm allows for a correct reconstruction of the burden currents from the optical signal acquired by the FBG interrogator, offering the potential to realize a dual-class optical current sensor. [ABSTRACT FROM AUTHOR]

To measure vibration signals, a low-frequency fiber Bragg grating (FBG) acceleration sensor featuring a flexible hinge with a spring support and symmetric compensation structure has been designed. Based on the mechanical model of the sensor's structure, the expressions for sensitivity and resonant frequency of the sensor are derived. The structural parameters of the sensor are optimized, and a simulation analysis is conducted using ANSYS 19.2 software. According to the results of simulation analysis and size optimization, the sensor prototype is constructed. Subsequently, its amplitude-frequency response, sensitivity, and temperature characteristics are investigated through vibration experiments. The experimental results show that the resonant frequency of the sensor is 73 Hz, the operating frequency range is 0~60 Hz, and the sensitivity measures 24.24 pm/g. This design meets the requirements for measuring vibration signals at low frequencies. [ABSTRACT FROM AUTHOR]

Induction motors are widely applied in motor drive systems. Effective temperature monitoring is one of the keys to ensuring the reliability and optimal performance of the motors. Therefore, this paper introduces a multiplexed optical temperature sensing system for induction motors based on few-mode fiber (FMF) spatial mode diversity. By using the spatial mode dimension of FMF, fiber Bragg grating (FBG) carried by different spatial modes of optical paths is embedded in different positions of the motor to realize multipoint synchronous multiplexing temperature monitoring. The paper establishes and demonstrates a photonic lantern-based mode division sensing system for motor temperature monitoring. As a proof of concept, the system demonstrates experiments in multiplexed temperature sensing for motor stators using the fundamental mode LP01 and high-order spatial modes LP11, LP21, and LP02. The FBG sensitivity carried by the above mode is 0.0107 nm/°C, 0.0106 nm/°C, 0.0097 nm/°C, and 0.0116 nm/°C, respectively. The dynamic temperature changes in the stator at different positions of the motor under speeds of 1k rpm, 1.5k rpm, 2k rpm with no load, 3 kg load, and 5 kg load, as well as at three specific speed–load combinations of 1.5k rpm_3 kg, 1k rpm_0kg, 2k rpm_5 kg and so on are measured, and the measured results of different spatial modes are compared and analyzed. The findings indicate that different spatial modes can accurately reflect temperature variations at various positions in motor stator winding. [ABSTRACT FROM AUTHOR]