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In this work, we propose a variation of Miura origami which, different from the existing out-of-plane bending Miura origami, has an in-plane bent configuration due to its graded crease pattern. By combining with the one-way shape memory alloy spring, we show that the proposed graded Miura origami can serve as a smart actuator and can be applied to drive crawling robots or grippers. First, we constructed a physical model of the graded Miura origami, from which a curvature-programmable geometric equation is proposed. Then, in addition to providing a mechanical model that can capture the mechanical behavior of the initial force–displacement relationship of the curved beam, we show that the proposed curved origami has a different mechanical behavior compared to the corresponding simple flexible arch, specifically if realized by silicon rubbers. By arranging anisotropic friction to the feet, the origami robot can crawl with an omega-elongation/compression motion like an inchworm. With a closed-loop current source control system using a high-frequency pulse width modulation-based topology, where the strain state of the arched origami is detected by a demodulator-free fiber Bragg grating sensor, the average speed of the origami crawling robot can reach 2.72 mm/s. In addition, by arranging three graded Miura origami, a gripper capable of lifting a weight of 518.5 g can be formed, where the carried load is over 4.5 times its own weight. [ABSTRACT FROM AUTHOR]

Coaxial cables and optical fibers are two types of cylindrical waveguides used in telecommunications. Fiber Bragg gratings (FBGs) have found successful applications in various fields, such as optical communications, fiber lasers, and fiber-optic sensing. In this paper, we propose and numerically investigate the implementations of various fiber Bragg configurations, including uniform, chirped, apodized, and phase-shifted configurations, on coaxial cables to generate the corresponding special types of coaxial cable Bragg gratings (CCBGs). The simulation results of different CCBGs match well with the well-known FBG theories. It is demonstrated that the reflection spectrum of a CCBG can be flexibly tailored by introducing various quasi-periodic perturbations in the permittivity of the dielectric layer along the coaxial cable. The proposed special types of CCBGs with unique characteristics could find potential applications in radio frequency signal processing, communication, and sensing fields. [ABSTRACT FROM AUTHOR]

The normal operation of various superconducting magnets is greatly influenced by the thermal stress of the insulating system, commonly made of epoxy resins with vacuum pressure impregnation (VPI) technology, throughout the curing and cooling processes. In this work, we developed a Fiber Bragg Grating (FBG) strain measurement method to monitor the real-time strain responses of an epoxy resin IR-3 and its glass fiber-reinforced composite during both curing and cooling processes. Then, we also monitored the same process of a Nb–Ti superconducting magnet coil prepared by VPI technology. With the help of FBG strain sensors, the residual strains of the coil at various positions and directions were investigated. The results show that the large residual strain occurred near the end of the coil in the axial direction. In addition, the interlaminar shear stress properties were measured at both room temperature and liquid nitrogen temperature. The strain characteristics of the epoxy resin IR-3 and the insulating system can provide useful guidance for the design and construction of high-field Nb–Ti superconducting magnets. [ABSTRACT FROM AUTHOR]

In open Radio access network (oRAN) 5G networks, a fronthaul segment between virtual Distribution unit (vDU) edge cloud and other external Remote radio units (RRUs) sites is very important to transmit high data rate to achieve 5G requirements. Performance parameters such as Quality factor (Q-factor) and Bit error rate (BER) of an optical fiber fronthaul segment are the main important parameters to enhance latency and bit rate. An Apodized fiber bragg grating (AFBG) is utilized with different apodization profiles to optimize linewidth of an optical signal leading to enhance performance. The designed AFBG is used with a data rate of 25 Gb/s optical Ethernet module at the vDU edge cloud to optimize the linewidth of the optical signal between the vDU and the RRU in the fronthaul optical fiber segment. The AFBG is investigated at different connections pre, post, and symmetrical connections, where different apodization functions are used in the AFBG design. It is found that the best results for the maximum Q-factor and minimum BER are 9.2 and 2.72e− 21, respectively, obtained from uniform function in the symmetrical connection. Finally, the proposed model linewidth is 0.408 nm, which is better than 1.56 nm that is evaluated by related work. [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 paper examines the acquisition of the measurement data of the spatial distribution of unsteady pressure on a ship advancing in waves. The purpose of the study is to investigate the reliability of the pressure data obtained by the unprecedented experiment and to provide experimental data of unsteady pressure which can be used for validation of arbitrary computation methods. The optical fiber sensing technology, so-called FBG (fiber Bragg gratings) sensing, is employed as the pressure sensors. In the experiment, 379 FBG pressure sensors (version 7; the latest version) in total are attached to the port side surface of ship model and also ordinary strain-type pressure sensors are embedded in the starboard side for validating reliability of FBG pressure sensors by comparing both results. In addition to the pressure distribution, measurement is made for unsteady hydrodynamic forces such as added mass, damping coefficients, and wave exciting forces, and also for ship motions and added resistance. Most of the measurement is repeated at least five times for each condition, and results of measured pressures are evaluated with mean value and standard deviation. Regarding the added resistance, the distribution for estimating added resistance is also extracted from obtained pressure distribution and its pressure contour is illustrated to show visually which hull region affects the added resistance significantly. Validation of the measured pressure with FBG pressure sensors is carried out also by integrating measured pressures over the ship model surface and comparing it with forces directly measured with load cells. The measured pressure distribution is compared with typical calculation results with the Rankine panel method in frequency domain to demonstrate usefulness of the spatial pressure data for validating the calculation method. Through these studies, it is confirmed that the measured unsteady pressures with FBG pressure sensors are accurate enough and valuable as the validation data for any calculation method. [ABSTRACT FROM AUTHOR]

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]

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]

This research work is based on a previous study by the authors that characterized the behavior of FBG sensors with a polyimide coating in a structural monitoring system. Sensors applied to structural health monitoring are affected by the presence of simultaneous multidirectional strains. The previous study observed the influence of the transverse strain ( ε y ) while keeping the longitudinal strain constant ( ε x ), where the x direction is the direction of the optical fiber. The present study develops an experimental methodology consisting of a biaxial test plan on cruciform specimens with three embedded FBG sensors coated with polyimide, acrylate, and ORMOCER®. Applying the Strain–Optic Theory as a reference, a comparison of the experimental values obtained with the different coatings was studied. This experimental work made it possible to study the influence of the transverse strain ( ε y ) on the longitudinal measurements of each FBGS and the influence of the coating material. Finally, the calibration procedure was defined as well as K (strain sensitivity factor) for each sensor. [ABSTRACT FROM AUTHOR]

Simultaneous measurement of strain and temperature is crucial for various applications that operate in diverse environments. Fiber Bragg gratings, known for their sensitivity to both strain and temperature, can serve as effective sensors for such simultaneous measurements. However, achieving discrimination between strain and temperature in FBG sensors requires the incorporation of a distinct mechanism in their design. This present a novel approach to dual sensing by exploring the impact of modulation depth of refractive index in cascaded FBGs. Modulation depth of refractive index is a significant spectral parameter of FBGs, influencing the grating's strength. By cascading two gratings with different modulation depths, the reflection spectrum exhibits two peaks, and their amplitudes are influenced by the modulation depth. Notably, the proposed sensor design eliminates the need for complicated packaging, which is often time-consuming and expensive. The study includes a simulation analysis of the proposed sensor, consisting of two FBGs with distinct modulation depths of refractive index. This technique demonstrates a linear variation in both Bragg wavelength and normalized peak difference (M) in response to changes in strain and temperature. The obtained strain and temperature sensitivities in this study were 1.19 pm/με and 11.4 pm/°C, respectively. [ABSTRACT FROM AUTHOR]

The temperature and strain fields monitoring during the preparation process of buoyancy materials, as well as the health status after molding, are important for mastering the mechanical properties of buoyancy materials and ensuring the safety of operators and equipment. This paper proposes a short and high-density femtosecond fiber Bragg grating (fs-FBG) array based on different temperature coefficients fibers. By optimizing the parameters of femtosecond laser point-by-point writing technology, high-performance fs-FBG arrays with millimeter level gating length and millimeter level spatial resolution were prepared on two types of fibers. These were successfully embedded in buoyancy materials to achieve in-situ online monitoring of the curing process and after molding. The experimental results show that the fs-FBG array sensor has good anti-chirp performance and achieves online monitoring of millimeter-level spatial resolution. Intelligent buoyancy materials can provide real-time feedback on the health status of equipment in harsh underwater environments. The system can achieve temperature monitoring with an accuracy of 0.56 °C and deformation monitoring with sub-millimeter accuracy; the error is in the order of micrometers, which is of great significance in the field of deep-sea exploration. [ABSTRACT FROM AUTHOR]

Intelligent compaction (IC) has emerged as a breakthrough technology that utilizes advanced sensing, data transmission, and control systems to optimize asphalt pavement compaction quality and efficiency. However, accurate assessment of compaction status remains challenging under real construction conditions. This paper reviewed recent progress and applications of smart sensors and machine learning (ML) to address existing limitations in IC. The principles and components of various advanced sensors deployed in IC systems were introduced, including SmartRock, fiber Bragg grating, and integrated circuit piezoelectric acceleration sensors. Case studies on utilizing these sensors for particle behavior monitoring, strain measurement, and impact data collection were reviewed. Meanwhile, common ML algorithms including regression, classification, clustering, and artificial neural networks were discussed. Practical examples of applying ML to estimate mechanical properties, evaluate overall compaction quality, and predict soil firmness through supervised and unsupervised models were examined. Results indicated smart sensors have enhanced compaction monitoring capabilities but require robustness improvements. ML provides a data-driven approach to complement traditional empirical methods but necessitates extensive field validation. Potential integration with digital construction technologies such as building information modeling and augmented reality was also explored. In conclusion, leveraging emerging sensing and artificial intelligence presents opportunities to optimize the IC process and address key challenges. However, cooperation across disciplines will be vital to test and refine technologies under real-world conditions. This study serves to advance understanding and highlight priority areas for future research toward the realization of IC's full potential. [ABSTRACT FROM AUTHOR]

A two-stage decoupling model based on an artificial neural network with polynomial regression is proposed for the six-component force sensor load decoupling problem in the case of multidimensional mixed loading. The six-dimensional load categorization stage model constructed in the first stage combines 63 load category label sets with a deep BP neural network. The six-dimensional load regression stage model was constructed by combining polynomial regression with a BP neural network in the second stage. Meanwhile, the six-component force sensor with a fiber Bragg grating (FBG) sensor as the sensitive element was designed, and the elastomer simulation and calibration experimental dataset was established to realize the validation of the two-stage decoupling model. The results based on the simulation data show that the accuracy of the classification stage is 93.65%. The MAPE for the force channel in the regression stage is 6.29%, and 3.24% for the moment channel. The results based on experimental data show that the accuracy of the classification stage is 87.80%. The MAPE for the force channel in the regression phase is 5.63%, and 4.82% for the moment channel. [ABSTRACT FROM AUTHOR]

Background: The interest of using fiber Bragg gratings (FBGs) dosimeters in radiotherapy (RT) lies in their (i) microliter detection volume, (ii) customizable spatial resolution, (iii) multi‐point dose measurement, (iv) real‐time data acquisition and (v) insensitivity to Cherenkov light. These characteristics could prove very useful for characterizing dose distributions of small and nonstandard fields with high spatial resolution. Purpose: We developed a multi‐point FBGs dosimeter customized for small field RT dosimetry with a spatial resolution of ∼$\sim$1 mm. Methods: The 3 cm‐long multi‐point dosimeter is made by embedding a 80 μm$\umu{\rm {m}}$ silica fiber containing an array of thirty (30) co‐located ∼$\sim$ 1 mm‐long fs‐written FBGs inside a plastic cylinder with an UV curing optical adhesive. With its higher thermal expansion coefficient, the plastic cylinder increases the sensitivity of the dosimeter by stretching the fiber containing the FBGs when the temperature rises slightly due to radiation energy deposition. Irradiations (2000 MU at 600 MU/min) were performed with a Varian TrueBeam linear accelerator. Results: The dose profile of a 2 ×$ \times$ 2 cm2$^{2}$ 6 MV beam was measured with a mean relative difference of 1.8% (excluding the penumbra region). The measured output factors for a 6 MV beam are in general agreement with the expected values within the experimental uncertainty (except for the 2 ×$\,\times $ 2 cm2$^{2}$ field). The detector response to different energy of photon and electron beams is within 5% of the mean response (0.068±0.002$0.068\pm 0.002$ pm/Gy). The calorimeter's post‐irradiation thermal decay is in agreement with the theory. Conclusions: An energy‐independent small field calorimeter that allows dose profile and output factor measurements for RT using FBGs was developed, which, to our knowledge, has never been done before. This type of detector could prove really useful for small field dosimetry, but also potentially for MRI‐LINAC since FBGs are insensitive to magnetic fields and for FLASH since FBGs have been used to measure doses up to 100 kGy. [ABSTRACT FROM AUTHOR]

Multimode interference of light is an optical interference phenomenon based on waveguides, which has broad applications in optical communication, lasers, and optical fiber sensing. Since optical fiber has become the most widely used optical waveguide in modern society, multimode interference in optical fibers is an ideal candidate for projects in university teaching laboratories. Here, we implement an in-fiber Mach–Zehnder strain sensor-based experiment to study multimode interference in optical fibers. The sensor is fabricated by fusion splicing a piece of thin core fiber between two single mode fibers. One end of the thin core fiber is spliced without a core offset, while the other end is spliced with a core offset. Due to the mode field diameter mismatch and core offset, cladding modes are excited and interfere with the core mode in thin core fiber. Students can observe the sensor fabrication demonstration and perform a strain test with an optical spectrum analyzer. The wavelength spectra captured by the optical spectrum analyzer under different strains are analyzed with the signal processing tools of fast Fourier transform and fast Fourier transform filter. Students then find characteristics of the multimode interference in the sensor from the analysis. The experiment extends undergraduates' knowledge of light interference and is an instructive exercise for them in modern coherence theory. This paper reports the development of an advanced instructional laboratory experiment aimed at teaching undergraduates about the physics and applications of multimode interference effects in optical fibers. The experiment is based on an in-fiber Mach-Zehnder strain sensor, which is fabricated by fusion-splicing a thin core fiber between two single-mode fiber leads. The experiment introduces students to optical fiber sensing in a cost-effective way and applies theoretical concepts they have learned in courses in the areas of wave guides, optical interference, and spectral analysis. Experimental results are presented for the sensor's output optical interference spectrum as well as the spectral response to strain. This experiment will be of interest to advanced laboratory and upper-level optics course instructors. [ABSTRACT FROM AUTHOR]

Optical cross-correlation is a technique that can achieve both high specificity and high sensitivity when deployed as the basis for a sensing technology. Offering significant gains in cost, size and complexity, it can also deliver significantly higher signal-to-noise ratios than traditional approaches such as absorption methodologies. In this paper, we present an optical cross-correlation technology constructed around a bespoke customised Fiber Bragg Grating (FBG). Exploiting the remarkable flexibility in design enabled by multiple aperiodic Bragg gratings, optical filters are devised that exactly mimic the absorption features of a target gas species (for this paper, acetylene C 2 H 2 ) over some waveband of interest. This grating forms the heart of the sensor architecture described here that employs modulated optical cross-correlation for gas detection. An experimental demonstration of this approach is presented, and shown to be capable of differentiating between different concentrations of the C 2 H 2 target gas. Furthermore these measurements are shown to be robust against interloper species, with minimal impact on the detection signal-to-noise arising from the introduction of contaminant gases. This represents is a significant step toward the use of customised FBGs as low-cost, compact, and highly customisable photonic devices for deployment in gas detection. [ABSTRACT FROM AUTHOR]

Hollow-core photonic crystal fibers (HC-PCFs) provide an ideal transmission medium and experimental platform for laser–matter interaction. Here, we report a cascaded all-fiber gas Raman laser based on deuterium (D2)-filled HC-PCFs. D2 is sealed into a gas cavity formed by a 49 m-long HC-PCF and solid-core fibers, and two homemade fiber Bragg gratings (FBGs) with the Raman and pump wavelength, respectively, are further introduced. When pumped by a pulsed fiber amplifier at 1540 nm, the pure rotational stimulated Raman scattering of D2 occurs inside the cavity. The first-order Raman laser at 1645 nm can be obtained, realizing a maximum power of ~0.8 W. An all-fiber cascaded gas Raman laser oscillator is achieved by adding another 1645 nm high-reflectivity FBG at the output end of the cavity, reducing the peak power of the cascaded Raman threshold by 11.4%. The maximum cascaded Raman power of ~0.5 W is obtained when the pump source is at its maximum, and the corresponding conversion efficiency inside the cavity is 21.4%, which is 1.8 times that of the previous configuration. Moreover, the characteristics of the second-order Raman lasers at 1695 nm and 1730 nm are also studied thoroughly. This work provides a significant method for realizing all-fiber cascaded gas Raman lasers, which is beneficial for expanding the output wavelength of fiber gas lasers with a good stability and compactivity. [ABSTRACT FROM AUTHOR]

A novel method to generate and two frequency 16-tupling millimeter wave (MMW) and distribute the generated MMW over fiber system (MMOF) with two base stations (BS) by the remodulation with Mach–Zehnder modulators (MZM) is proposed. At the central station(CS), the ± 4th order optical sidebands generated by a dual parallel MZM (DPMZM) are split into two branches, one of which is injected into a photodetector (PD) to generate the 8th harmonic of the RF drive signal of the MZM, which acts as the RF driving signal for the remodulation, and the other acts as the carrier for the remodulation. The remodulation is realized by injecting the outputs of the two branches into an MZM. After remodulation, the signal which contains mainly the ± 20th, ± 12th and ± 4th order optical sidebands is divided into two branches, in which the positive and negative sidebands are filtered out by two optical band-pass filters (OBPF) first and the 4th and − 4th order sidebands are filtered by two fiber Bragg gratings (FBG) later, with which the data of the downlink are modulated on it. At the two BSs, the 12th and − 12th order sidebands in the downlink optical signal are first filtered out by two FBGs, with which the data of the uplink are modulated onto it and transmitted to the CS via optical fibers for carrier reuse; the output signals of the FBGs are injected into two PDs to produce two 16-tupling frequency MMWs with the data of downlinks. The feasibility of our scheme is verified by theoretical analysis and simulation experiments. The main innovations of our designed scheme are that the modulation index of MZM is greatly reduced by using the remodulation method, the power utilization rate is greatly improved by using all the main sidebands and the cost of the system is reduced by using the two BSs structures with carrier reuse. [ABSTRACT FROM AUTHOR]

Many techniques have been studied for recovering information from shared media such as optical fiber that carries different types of communication, sensing, and data streaming. This article focuses on a simple method for retrieving the targeted information with the least necessary number of significant samples when using statistical population sampling. Here, the focus is on the statistical denoising and detection of the fiber Bragg grating (FBG) power spectra. The impact of the two-sided and one-sided sliding window technique is investigated. The size of the window is varied up to one-half of the symmetrical FBG power spectra bandwidth. Both, two- and one-sided small population sampling techniques were experimentally investigated. We found that the shorter sliding window delivered less processing latency, which would benefit real-time applications. The calculated detection thresholds were used for in-depth analysis of the data we obtained. It was found that the normality three-sigma rule does not need to be followed when a small population sampling is used. Experimental demonstrations and analyses also showed that novel denoising and statistical threshold detection do not depend on prior knowledge of the probability distribution functions that describe the FBG power spectra peaks and background noise. We have demonstrated that the detection thresholds' adaptability strongly depends on the mean and standard deviation values of the small population sampling. [ABSTRACT FROM AUTHOR]

The constant monitoring and control of various health, infrastructure, and natural factors have led to the design and development of technological devices in a wide range of fields. This has resulted in the creation of different types of sensors that can be used to monitor and control different environments, such as fire, water, temperature, and movement, among others. These sensors detect anomalies in the input data to the system, allowing alerts to be generated for early risk detection. The advancement of artificial intelligence has led to improved sensor systems and networks, resulting in devices with better performance and more precise results by incorporating various features. The aim of this work is to conduct a bibliometric analysis using the PRISMA 2020 set to identify research trends in the development of machine learning applications in fiber optic sensors. This methodology facilitates the analysis of a dataset comprised of documents obtained from Scopus and Web of Science databases. It enables the evaluation of both the quantity and quality of publications in the study area based on specific criteria, such as trends, key concepts, and advances in concepts over time. The study found that deep learning techniques and fiber Bragg gratings have been extensively researched in infrastructure, with a focus on using fiber optic sensors for structural health monitoring in future research. One of the main limitations is the lack of research on the use of novel materials, such as graphite, for designing fiber optic sensors. One of the main limitations is the lack of research on the use of novel materials, such as graphite, for designing fiber optic sensors. This presents an opportunity for future studies. [ABSTRACT FROM AUTHOR]

Batteries play a crucial role as energy storage devices across various industries. However, achieving high performance often comes at the cost of safety. Continuous monitoring is essential to ensure the safety and reliability of batteries. This paper investigates the advancements in battery monitoring technology, focusing on fiber Bragg gratings (FBGs). By examining the factors contributing to battery degradation and the principles of FBGs, this study discusses key aspects of FBG sensing, including mounting locations, monitoring targets, and their correlation with optical signals. While current FBG battery sensing can achieve high measurement accuracies for temperature (0.1 °C), strain (0.1 μ ε ), pressure (0.14 bar), and refractive index (6 × 10−5 RIU), with corresponding sensitivities of 40 pm/°C, 2.2 pm/ μ ε , −0.3 pm/bar, and −18 nm/RIU, respectively, accurately assessing battery health in real time remains a challenge. Traditional methods struggle to provide real-time and precise evaluations by analyzing the microstructure of battery materials or physical phenomena during chemical reactions. Therefore, by summarizing the current state of FBG battery sensing research, it is evident that monitoring battery material properties (e.g., refractive index and gas properties) through FBGs offers a promising solution for real-time and accurate battery health assessment. This paper also delves into the obstacles of battery monitoring, such as standardizing the FBG encapsulation process, decoupling multiple parameters, and controlling costs. Ultimately, the paper highlights the potential of FBG monitoring technology in driving advancements in battery development. [ABSTRACT FROM AUTHOR]

This paper presents a study about the integration of Piezoelectric Energy Harvesting Systems (PE-EHSs) into building envelopes for powering Fiber Bragg Grating (FBG) sensors, enabling efficient and low-consumption monitoring with the objective of leveraging structural health monitoring (SHM). The research includes preliminary tests conducted in a real environment to validate the PE-EHS when fully integrated into a ventilated façade, capturing mechanical vibrations generated mainly by wind loads. Based on these activities, the final configuration of PE-EHSs is defined to provide a complete system for façade monitoring. This integrated system includes the piezoelectric generator (PEG), supercapacitor (SC), Power Conditioner Circuit (PCC), Fiber Optic Sensing (FOS) interrogator, and the IoT gateway transmitting measurement data within an Internet of Things (IoT) monitoring platform. This configuration is tailored to address the challenges related to the structural integrity of building envelopes. Results demonstrate a potential for a stand-alone solution in the façade sector but raise issues for certain limitations, requiring further investigation. In particular, the study emphasizes constraints related to the energy production of PE-EHSs for façade integration. It highlights the necessity to carefully consider these limitations within the broader context of their applicability, providing insights for the informed deployment of piezoelectric energy harvesting technology in building envelope monitoring. [ABSTRACT FROM AUTHOR]

A low-velocity impact event can produce undetectable damages inside laminated composite structures. Such damages have been introduced as one of the main causes of catastrophic failure of whole structure, thus impact event detection and localization should be essential for many kinds of composite structures. In this study, low-velocity impact localization method was proposed using six multiplexed fiber Bragg grating (FBG) sensors on the composite wingbox structure. The principle is to find the location which has the most similar set of reference signals from the database. Firstly, the required reference signals were measured to construct the database for the test section which is located on the upper skin of the wingbox. Then, the localization was implemented with the process of detecting the time of arrival (TOA) and finding the impact location. The similarities between the impact-induced signals and reference signals are assessed by calculating the root mean squared (RMS) values. Through the impact localizations on the non-reference locations, this method was validated. Also, this method was applied to the impact localizations when the wingbox structure was under static loads. From the acceptable results of such experiments under static loading conditions, the practicality of this method was successfully verified. [ABSTRACT FROM AUTHOR]

Temperature is one of the most important physical quantities in the field of earthquake precursor observation. Aiming at the problem of low sensitivity in the Fiber Bragg Grating (FBG) temperature sensor, the sensitized FBG temperature sensor based on bimetal three-substrates is proposed. Through theoretical analysis of the bimetallic model, the structural parameters of the sensor are optimized, and the sensor is simulated and analyzed with ANSYS. Then, the sensor is developed according to the simulation results, and the temperature test system is built to test the performance of the sensor. The results show that the sensitivity of the temperature sensor is 49.3 pm/°C, which is about 4.9 times that of the bare FBG sensor, and the linearity is over 0.999. The research results provide a reference for developing the same type of sensors and further improving the sensitivity of FBG temperature sensors. [ABSTRACT FROM AUTHOR]

In this work, we have demonstrated the use of a fiber Bragg grating (FBG) sensor to measure the pressure profile of blast waves generated inside a vertical shock tube (VST). An FBG pressure sensor probe has been designed and developed that can be incorporated into the wall of the VST. The VST facility is used to generate blast waves with decay times of the order of a few milliseconds to simulate explosive events. Pressure measurement experiments have been carried out at different incident blast wave peak pressures inside the VST. The FBG pressure sensor measurements are validated against a standard piezoelectric pressure transducer at an acquisition rate of 1 MHz. The pressure signals of both sensors are found to match well with similar rise times and decay profiles. The validated FBG pressure sensor is then incorporated into a sand column mounted in the test section of the VST to measure the pressure profile of blast wave-induced stress waves in granular media. The FBG and piezoelectric pressure sensor data are compared using fast Fourier transform analysis and continuous wavelet transform. The feasibility of FBG sensors for blast pressure measurement under harsh conditions imposed inside shock tube environments is established. [ABSTRACT FROM AUTHOR]

Photonic Crystal Fiber (PCF) constructions, controlled light propagation for measuring amplitude, phase, polarization and wavelength of the spectrum, and PCF-incorporated interferometry techniques are the foundations upon which sensors operate. But the existing PCF techniques have very large stretching that tends to be difficult to align due to the cross-polarization mode of the optical fiber structure. Hence, the novel Polymer graphene-based Hexagonal cladding is designed by using a hexagonal hollowed core and a cladding material of Polymethyl methacrylate reinforced with gyroidal graphene which increases confinement strength. Once the crystal structure is designed, normally the presence of substrate the Q-factors is degraded. On substrates, Q-factors are enhanced by fine-tuning the position of the neighboring holes. Hence, the novel Bilayer Grating Stratum solves the degrading issues in Q-factors, which utilizes a Silicon polyamide-coated FBG in the crystal that is incorporated using the Femto-laser technique thereby increasing the wavelength tenability. To identify the electric field pattern, the designed structure is simulated in COMSOL software. Thus, the proposed system has a high sensitivity of 22 with a low material loss of 0.1% and a low response time of 0.2 s. [ABSTRACT FROM AUTHOR]

[Display omitted] An all-fiber-optic system for rapid detection of antibiotic concentration, based on an optical enzyme biosensor with microfiber interferometer (MFI) and fiber gratings (FBGs) power variation, is proposed and experimentally validated. During the experiment, β-lactamase(β-LS) is fixed on the polyaniline (PANI)-coated optical fiber by cross-linking through glutaraldehyde (GA) covalent bonding. β-LS can hydrolyze β-lactam antibiotics to generate acidic by-products that transform polyaniline from the form of the emerald base to emerald salt, which results in the surface refractive index (RI) variation of MFI, to convert MFI wavelength and FBGs power macroscopic change for feedbackingly detecting the concentration of β-lactam antibiotics. The detection of amoxicillin (AMX) in deionized water at concentrations in the range of 0.01–100 nM resulted in a wavelength change sensitivity of 0.6 nm/nM, and FBGs power difference change sensitivity of 1.3 dB/nM, with a detection limit LOD = 0.04 nM in real food and urine samples. The sensing system by the same calibration technique can detect antibiotic concentrations in different substances (tap water, milk and artificial urine). This developed all-fiber-optic system can be used as a rapid solution for the measurement of β-lactam antibiotic residues in food and the environment. [ABSTRACT FROM AUTHOR]

Tunnel excavation induces the stress redistribution of surrounding rock. In this excavation process, the elastic strain in the rock is quickly released. When the maximum stress on the tunnel lining exceeds the concrete's load-bearing capacity, it causes cracking of the lining. Comprehensive geophysical exploration methods, including seismic computerized tomography, the high-density electrical method, and the ultrasonic single-plane test, indicated the presence of incomplete distribution of broken rock along the tunnel axis. Based on the geophysical exploration results, a carbon-fiber-strengthened tunnel simulation model was established to analyze the mechanical characteristics of the structure and provide a theoretical basis for sensor deployment. Fiber Bragg grating (FBG) strain sensors were used to measure the stress and strain changes in the second lining concrete after carbon reinforcement. Meanwhile, one temperature sensor was installed in each section to enable temperature compensation. The monitoring results demonstrated that the stress–strain of the second lining fluctuated within a small range, and the lining did not show any crack expansion behavior, which indicated that carbon-fiber-reinforced polymer (CFRP) played an effective role in controlling the structural deformation. Therefore, the combined detection of physical exploration and FBG sensors for the structure provided an effective monitoring method for evaluating tunnel stability. [ABSTRACT FROM AUTHOR]

In optical fiber sensing systems based on fiber Bragg gratings (FBGs), there are numerous parameters that significantly limit the overall sensing performance. In this study, the effects of FBG parameters such as grating length, Bragg wavelength, and reflection rate on temperature sensitivity have been investigated considering there are no strain effects along the length of the grating. For this purpose, the OptiSystem program has been utilized to design an FBG-based sensing system, which is a relevant approach for simulating and analyzing the performance of FBGs. For temperature variations in the range of 1–120 °C, variations of wavelength shift and grating length have been obtained between 14 and 1680 pm and between 0.1 and 100 mm, respectively. It has been observed that the grating length changes have no direct impact on the temperature sensitivity. On the other hand, a 1 °C variation in temperature causes a wavelength change of ~ 14 pm. Furthermore, temperature sensitivities have been found to be 3.66 pm/°C, 4.58 pm/°C, 5.50 pm/°C, 9.2 pm/°C, 14 pm/°C and 18.4 pm/°C for the Bragg wavelengths of 400 nm, 500 nm, 600 nm, 1000 nm, 1550 nm and 2000 nm, respectively. Moreover, the change in temperature sensitivity depending on Bragg wavelength has been computed as ~ 9.15 × 10–3 pm/°C(nm)−1. For the reflection rate variations in the range of 0.001–0.99%, temperature sensitivity has taken the value of ~ 14 pm/°C at 100 °C whilst the reflected powers have varied from 11.1 to 42 dBm. Moreover, a change in temperature sensitivity with reflection rate has been acquired as ~ 0.021 pm/°C(%)−1. [ABSTRACT FROM AUTHOR]

An optical fiber pH sensor based on a long-period fiber grating (LPFG) is reported. Two oppositely charged polymers, polyethylenimine (PEI) and polyacrylic acid (PAA), were alternately deposited on the sensing structure through a layer-by-layer (LbL) electrostatic self-assembly technique. Since the polymers are pH sensitive, their refractive index (RI) varies when the pH of the solution changes due to swelling/deswelling phenomena. The fabricated multilayer coating retained a similar property, enabling its use in pH-sensing applications. The pH of the PAA dipping solution was tuned so that a coated LPFG achieved a pH sensitivity of (6.3 ± 0.2) nm/pH in the 5.92–9.23 pH range. Only two bilayers of PEI/PAA were used as an overlay, which reduces the fabrication time and increases the reproducibility of the sensor, and its reversibility and repeatability were demonstrated by tracking the resonance band position throughout multiple cycles between different pH solutions. With simulation work and experimental results from a low-finesse Fabry–Perot (FP) cavity on a fiber tip, the coating properties were estimated. When saturated at low pH, it has a thickness of 200 nm and 1.53 ± 0.01 RI, expanding up to 310 nm with a 1.35 ± 0.01 RI at higher pH values, mostly due to the structural changes in the PAA. [ABSTRACT FROM AUTHOR]

At present, most of the damage detection techniques based on global vibration and local guided wave have obvious limitations, which brings difficulties to the safety assessment of structures. To solve this problem, a damage location identification method based on micro-dynamic balance and inverse finite element is proposed. Firstly, the vibration frequency, measuring point density and damage magnitude were determined by using finite simulation composite plate structure. Secondly, a fiber grating sensor is attached to the surface of the laminate to receive the strain response signal of the structure under steady-state vibration, and the global displacement of the structure is constructed by inverse finite element method. Finally, the inverse finite element listing is introduced into the theoretical framework of the dynamic response of the micro-element, and the structural damage identification experiment based on the measured strain data is realized. The experimental results show that this method can effectively identify the structural damage area and has a special sensitivity to structural damage, and the identification accuracy and efficiency are high. [ABSTRACT FROM AUTHOR]

The operating temperature of integrated magnetic components can be critical. Excessively high temperature can significantly modify the properties of components, especially those of magnetic material, such as saturation magnetization and magnetic permeability. This article introduces an experimental characterization method using two different sensors. We compare the results obtained from these sensors. Initially, the method is validated using a "meander component, and subsequently, it is applied to planar spiral inductors, both with and without magnetic material. [ABSTRACT FROM AUTHOR]

The nonlinear coupled Schrödinger equation in fiber Bragg gratings is studied in this paper. The existence of soliton solutions and periodic solutions are proved by qualitative analysis, and exact solutions are given, as well as the parameter condition of each solution is described. Then the modulation instability (MI) analysis is carried out and the linear stability criterion is given. In particular, external perturbation terms are introduced to prove that the equation exists chaotic behaviors. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced composites (CFRP) are susceptible to hidden damage from low velocity external impacts during their service life. To ensure the proper monitoring of the state of the composites, it is crucial to predict the location of an impact event. In this paper, fiber Bragg grating (FBG) sensors are affixed to the surface of a carbon fiber composite tube, and an optical sensing interrogator is used to capture the central wavelength shift of the FBG sensors due to low-velocity impacts. A discrete wavelet transform is used for noise reduction in the response signals. Then, the differences in the captured response signals of the FBG sensors at different locations of the impact were analyzed. Moreover, two methods were implemented to predict the location of low-velocity impacts, according to the differences in the captured response signals. The BP neural network-based method utilized three data sets to train the neural network, resulting in an average localization error of 20.68 mm. In contrast, the method based on error outliers selected a specific data set as the reference dataset, achieving an average localization error of 13.98 mm. The comparison of the predicted results shows that the latter approach has a higher predictive accuracy and does not require a significant amount of data. [ABSTRACT FROM AUTHOR]

Recently, many researches have been conducted on a Taper Fiber Bragg Grating (TFBG) as a temperature sensor in a wide range of applications due to its significant merits. Besides, the majority of these researches have been focused on improving the sensor performance. In this work, the temperature sensitivity is enhanced by coating the sensor with four different materials Polymer, In, Zn and TiN with different coated layer thicknesses. This study presents the impact of the thickness layers of these materials on the overall performance of the TFBG temperature sensor. Different coating techniques are carried out which gave a uniform crystalline structure of the coated layer. Optical spectrum analyzer is used to monitor the Bragg wavelength shift of the TFBG sensor under different temperature values (25–150 °C). The results approve that the coating materials could enhance the temperature sensitivity depending on the material type and coating thickness, additionally, these coating layers sever as a protect layers for the grating area from the external environmental factors. For further investigation, simulation work is carried out using MATLAB; and there are good agreement between experimental and simulation studies. The results show that the layers with thickness of 50 µm, 15 µm, 7.5 µm and 12 µm were optimum thicknesses that gave a higher wavelength shift; hence higher temperature sensitivity for Polymer, Zn, TiN and In coating layers, respectively. Within these values, the temperature sensitivities were estimated to be 1.793 pm/°C, 2.351 pm/°C, 2.893 pm/°C and 3.547 pm/°C which enhanced approximately by factor 2, 3, 4 and 6 for Polymer, Zn, TiN and In coating layers respectively compared with sensitivity of bare TFBG sensor. This work will significantly enrich the knowledge of enhancing the sensor performance by polymer or metal coating approach. [ABSTRACT FROM AUTHOR]

Temperature and refractive index are two important parameters for many fields, where their accurate measurement is crucial. This review discusses the development of refractive index and temperature dual-parameter fiber sensors based on different interferometric structures in recent years, such as the Mach–Zehnder, Michelson or Fabry–Perot interferometers, which are composited by the grating reflectors, and multi-separated-region based on thin film layers and special structures. The working principle and performance of different types of sensors are analyzed. This review can provide the technical references for the development of novel dual-parameter sensors with practical potential and high performance. [ABSTRACT FROM AUTHOR]

A scheme for the compensation of chromatic dispersion in Radio over Fiber systems with enhanced performance is proposed and demonstrated. The system implements a cascade of an Ideal Dispersion Compensation Filter and a tanh apodized, linearly chirped Fiber Bragg Grating for mitigating the degradation caused by chromatic dispersion. The analysis probes variations in transmission distance and channel spacing while investigating vital performance parameters like the Q factor and Bit Error Rate. Two-channel spacings of 100 GHz and 50 GHz, transmission distances ranging between 70 and 120 km and effective refractive index of the apodized and linearly chirped FBG extending between 1.3 and 1.5 are considered for the study. The analysis also covers the analysis of optical signal to noise ratio as the fiber length is varied. Additionally, the system performance is evaluated when the transmitted power of the continuous wave Laser in the transmitter segment is altered. The simulation results demonstrate that the system provides acceptable Q factor and BER values even at a transmission distance of 120 km. The comparative analysis with the formerly published results validates the performance enhancement achieved by the proposed system. [ABSTRACT FROM AUTHOR]

In this paper, the damage monitoring investigation based on the remote bonding fiber Bragg grating sensing is performed on the aerospace aluminum alloy thin-walled structure with prefabricated damage. Firstly, an ultrasonic excitation-fiber Bragg gratings (UE-FBGs) sensing experimental platform is established for the simulation of defects monitoring, in which the sensors are placed at a certain distance from the bonding area. Secondly, different arrangements of exciters and receivers are utilized for the original signals and the damage signals. Subsequently, the raw signals are processed by filter and feature extraction in order to denoise the signals and acquire the parameters sensitive to the damage. Finally, an improved Reconstruction for Image Defects (RAPID) algorithm is used to locate and reconstruct the pre-existing damage. The results show that the proposed system improves the sensitivity of the FBG receiver signal and the accuracy of the damage imaging. [ABSTRACT FROM AUTHOR]

Background: Needle‐based procedures, such as fine needle aspiration and thermal ablation, are often applied for thyroid nodule diagnosis and therapeutic purposes, respectively. With blood vessels and nerves nearby, these procedures can pose risks in damaging surrounding critical structures. Purpose: The development and validation of innovative strategies to manage these risks require a test object with well‐characterized physical properties. For this work, we focus on the application of ultrasound‐guided thermal radiofrequency ablation. Methods: We have developed a single‐use anthropomorphic phantom mimicking the thyroid and surrounding anatomical and physiological structures that are relevant to ultrasound‐guided thermal ablation. The phantom was composed of a mixture of polyacrylamide, water, and egg white extract and was cast using molds in multiple steps. The thermal, acoustical, and electrical characteristics were experimentally validated. The ablation zones were analyzed via non‐destructive T2‐weighted magnetic resonance imaging scans utilizing the relaxometry changes of coagulated egg albumen, and the temperature distribution was monitored using an array of fiber Bragg grating sensors. Results: The physical properties of the phantom were verified both on ultrasound as well as in terms of the phantom response to thermal ablation. The final temperature achieved (92°C), the median percentage of the nodule ablated (82.1%), the median volume ablated outside the nodule (0.8 mL), and the median number of critical structures affected (0) were quantified. Conclusion: An anthropomorphic phantom that can provide a realistic model for development and training in ultrasound‐guided needle‐based thermal interventions for thyroid nodules has been presented. [ABSTRACT FROM AUTHOR]

Sulfurized polyacrylonitrile (SPAN) is a very stable and promising sulfur‐based cathode material for high energy density lithium–sulfur (Li–S) batteries, which can circumvent the polysulfides dissolution issue. However, the stress concentration caused by volume change in SPAN cathodes is relatively significant but is rarely focused on. It is widely reckoned that the binder plays a key role in buffering the stress induced by electrode materials and hence maintains the integrity of electrodes. Nevertheless, the understanding of the actual effect of binders to SPAN cathodes from the aspect of mechanics remains to be deepened. Here, the optical fiber Bragg grating (FBG) is implanted into SPAN cathode films to in situ evaluate the electrochemo‐mechanical behaviors by using four different binders. The internal strain evolution of SPAN cathodes is affected by multiple factors of adhesion and mechanical properties of different binders. It is found that the SPAN cathode using poly(acrylic acid) (PAA) binder with outstanding mechanical properties experiences the largest strain change but the electrochemical performance is even better under high sulfur loading. Furthermore, the strain evolution is monitored under high sulfur loading condition and how the sulfur loading affects the signals of the built‐in FBG sensors is tried to figure out. [ABSTRACT FROM AUTHOR]

Recent earthquakes in several developing countries have shown that reinforced concrete (RC) buildings with improper structural detailing experience severe damage under seismic motions. Using low-quality construction materials such as brick aggregates, resulting in low-strength concrete, significantly impacts the bond between rebar and concrete. Accurate evaluation of the bond performance of such low-strength concrete is one of the key issues for seismic safety assessment of RC buildings, especially in Bangladesh; thus, the bond performance is usually evaluated through laboratory tests. However, conventional measurements of bond stress based on rebar strains measured by electrical resistance strain gauges are likely to negatively impact the bond behavior/performance because of the reduced total contact area between rebar and concrete as well as the changing rebar surface boundary conditions. Under the above social and academic backgrounds, in this study, a new measurement technique that applies fiber Bragg grating (FBG) sensors embedded in optical fiber to rebar strain measurements is developed, and its effectiveness is investigated to realize more accurate measurements of the bond stress between rebar and concrete. Two 70% scaled RC beam-column joint specimens in which the beam rebar was anchored in a straight manner were constructed with identical detailing, except for the beam rebar strain measuring methods. The specimens were then subjected to cyclic lateral loading until failure. By comparing the experimental data acquired by the above two different devices (the FBG sensors and conventional strain gauges), it was found that the experimental bond strength on the beam rebar based on the strain data measured by the FBG sensors was much higher than that from the data measured using conventional strain gauges. Which negatively impacted the test data on the beam-column joint's capacity in the specimen applied the conventional measuring method, indicating the necessity of the presented method not only for accurate evaluation of the bond stress between rebar and concrete but also for seismic safety assessments of RC buildings. [ABSTRACT FROM AUTHOR]

A novel fiber-optic hydrogen sensor including Pt/WO 3 sensing material with a microporous structure is proposed and experimentally demonstrated with improved performance. The proposed Pt/WO 3 sensing material is realized by introducing metal-organic frameworks (MOFs) as templates. The mesoporous structure of the ZIF-8 template improves the reactive sites of hydrogen sensitive materials with hydrogen. Hydrogen sensors were fabricated by combining the synthesized material with Fiber Bragg Gratings (FBGs) and the performance of hydrogen sensors was investigated. The experimental results show that the hydrogen sensitivity of the FBG with ZIF-8 synthesized Pt/WO 3 has been increased to 0.075 pm/ppm, which is twice that without ZIF-8 synthetization. The stability and the response speed are also significantly improved. The introduction of microporous MOFs templates into Pt/WO 3 sensing material will greatly accelerate the wide application of Pt/WO 3 -based fiber optic hydrogen sensors on hydrogen leakage detection. • A promising porous Pt/WO 3 synthesized based on ZIF-8 is proposed and demonstrated. • The porous structure provides more active sites and diffusion channels for H 2. • The sensor coated with the porous Pt/WO 3 showed excellent response sensitivity. • The porous Pt/WO 3 sensor exhibited excellent response efficiency and stability. [ABSTRACT FROM AUTHOR]

Accurately mapping the temperature during ablation is crucial for improving clinical outcomes. While various sensor configurations have been suggested in the literature, depending on the sensors' type, number, and size, a comprehensive understanding of optimizing these parameters for precise temperature reconstruction is still lacking. This study addresses this gap by introducing a tool based on a theoretical model to optimize the placement of fiber Bragg grating sensors (FBG) within the organ undergoing ablation. The theoretical model serves as a general framework, allowing for adaptation to various situations. In practical application, the model provides a foundational structure, with the flexibility to tailor specific optimal solutions by adjusting problem-specific data. We propose a nonlinear and nonconvex (and, thus, only solvable in an approximated manner) optimization formulation to determine the optimal distribution and three-dimensional placement of FBG arrays. The optimization aims to find a trade-off among two objectives: maximizing the variance of the expected temperatures measured by the sensors, which can be obtained from a predictive simulation that considers both the type of applicator used and the specific organ involved, and maximizing the squared sum of the distances between the sensor pairs. The proposed approach provides a trade-off between collecting diverse temperatures and not having all the sensors concentrated in a single area. We address the optimization problem through the utilization of approximation schemes in programming. We then substantiate the efficacy of this approach through simulations. This study tackles optimizing the FBGs' sensor placement for precise temperature monitoring during tumor ablation. Optimizing the FBG placement enhances temperature mapping, aiding in tumor cell eradication while minimizing damage to surrounding tissues. [ABSTRACT FROM AUTHOR]

This document is a review of recent advancements in Fiber Bragg Grating (FBG) sensing technology. It explores the fabrication techniques, applications, and future trends of FBGs and optical fiber sensors. The review includes summaries of specific research articles that focus on topics such as enhancing FBG sensors, using smaller-diameter optical fibers, and developing FBG force sensors. The articles highlight the potential advantages and advancements in these areas of FBG sensing technology. The review serves as a guide to the evolving field of FBGs and optical fiber sensor technologies, showcasing their potential for precision measurement and real-time monitoring. [Extracted from the article]

The additive noise in the condition monitoring system using fiber Bragg grating (FBG) sensors, including white Gaussian noise and multifrequency interference, has a significantly negative influence on the fault diagnosis of rotating machinery. Spectral subtraction (SS) is an effective method for handling white Gaussian noise. However, the SS method exhibits poor performance in eliminating multifrequency interference because estimating the noise spectrum accurately is difficult, and it significantly weakens the useful information components in measured signals. In this study, an improved spectral subtraction (ISS) method is proposed to enhance its denoising performance. In the ISS method, a reference noise signal measured by the same sensing system without working loads is considered the estimated noise, the same sliding window is used to divide the power spectrums of the measured and reference noise signals into multiple frequency bands, and the formula of spectral subtraction in the standard SS method is modified. A simulation analysis and an experiment are executed by using simulated signals and establishing a vibration test rig based on the FBG sensor, respectively. The statistical results demonstrate the effectiveness and feasibility of the ISS method in simultaneously eliminating white Gaussian noise and multifrequency interference while well maintaining the useful information components. [ABSTRACT FROM AUTHOR]

Li-ion batteries are expected to become the mainstream devices for green energy storage or power supply in the future due to their advantages of high energy and power density and long cycle life. Monitoring the temperature and strain change characteristics of Li-ion batteries during operation is conducive to judging their safety performance. The hinged differential lever sensitization structure was used for strain sensitization in the design of an FBG sensor, which also allowed the simultaneous measurement of strain and temperature. The temperature and strain variation characteristics on the surface of a Li-ion soft-packed battery were measured using the des.igned sensor. This report found that the charging and discharging processes of Li-ion batteries are both exothermic processes, and exothermic heat release is greater when discharging than when charging. The strain on the surface of Li-ion batteries depends on electrochemical changes and thermal expansion effects during the charge and discharge processes. The charging process showed an increasing strain, and the discharging process showed a decreasing strain. Thermal expansion was found to be the primary cause of strain at high rates. [ABSTRACT FROM AUTHOR]

We propose a humidity sensor using an excessively tilted fiber grating (Ex-TFG) coated with agarose fabricated using femtosecond laser processing. The processed grating showcases remarkable differentiation between TE and TM modes, achieving an exceptionally narrow bandwidth of approximately 1.5 nm and an impressive modulation depth of up to 15 dB for both modes. We exposed the agarose-coated TFG sensor to various relative humidity levels and monitored the resonance wavelength to test its humidity sensing capability. Our findings demonstrated that the sensor exhibited a rapid response time (2–4 s) and showed a high response sensitivity (18.5 pm/%RH) between the humidity changes and the resonant wavelength shifts. The high sensitivity, linearity, repeatability, low hysteresis, and excellent long-term stability of the TFG humidity sensor, as demonstrated in our experimental results, make it an attractive option for environmental monitoring or biomedical diagnosis. [ABSTRACT FROM AUTHOR]

This paper describes design, theoretical analysis, and experimental evaluation of a π-Phase-Shifted Fiber Bragg Grating (π-PSFBG) inscribed in the standard telecom fiber for slow light generation. At first, the grating was designed for its use in the reflection mode with a central wavelength of 1552 nm and a pass band width of less than 100 pm. The impact of fabrication imperfections was experimentally investigated and compared to model predictions. The optical spectra obtained experimentally show that the spectral region used for slow light generation is narrower (less than 10 pm), thus allowing for too-low levels of slow light optical-output power. In the next step, the optimization of the grating design was conducted to account for fabrication errors, to improve the grating's spectral behavior and its temporal performance, and to widen the spectral interval for slow light generation in the grating's transmission mode. The targeted central wavelength was 1553 nm. The π-PSFBG was then commercially fabricated, and the achieved parameters were experimentally investigated. For the region of (1551–1554) nm, a 15-fold increase in the grating's pass band width was achieved. We have shown that a pair of retarded optical pulses were generated. The measured group delay was found to be ~10.5 ps (compared to 19 ps predicted by the model). The π-PSFBG operating in its transmission mode has the potential to operate as tunable delay line for applications in RF photonics, ultra-fast signal processing, and optical communications, where tunable high precision delay lines are highly desirable. The π-PSFBG can be designed and used for the generation of variable group delays from tens to hundreds of ps, depending on application needs. [ABSTRACT FROM AUTHOR]

Pressure determination is an essential measure for safety assessment in modern applications. Conventional methods for measuring pressure have been replaced by fiber Bragg grating (FBG) sensors owing to inherent benefits. However, enhancing pressure sensitivity at the low-pressure range (< 10 kPa) is still a challenge for FBG sensors. Low pressure fails to induce significant strain on FBG, reducing the sensor's sensitivity. Therefore, a sensitizing mechanism must be incorporated into the sensor design along with a proper selection of materials. This paper presents mathematical modeling and simulation analysis of an FBG pressure sensor that uses a circular diaphragm and a flexure hinge-based beam made of acrylonitrile butadiene styrene as a sensing mechanism unit. A cascaded FBG is fixed on the notch surface of the flexure hinge beam which provides the measuring signal is based on Bragg wavelength. The sensor also eliminates the effect of temperature cross-sensitivity using cascade FBG. This mechanical configuration amplifies the low pressure to strain on the FBG. This design has the advantage of high sensitivity, compact size and high linearity. Here, the analysis of circular diaphragm and circular flexure hinge-based beam structure through finite element analysis and theoretical calculation has been carried out. Comparative analysis with the stainless steel sensor indicates the sensitivity of 80 pm/kPa for the ABS sensor which is 16 times greater than that of the stainless steel sensor. Such a sensor can be widely used for low-pressure measurements such as gas and oil pipelines, aircraft wall pressure, and heating, ventilation and air-conditioning. [ABSTRACT FROM AUTHOR]