Optical Fiber Bragg Grating Research Articles

Detection of matrix cracks in composite laminates using embedded fiber-optic distributed strain sensing

We used an optical frequency-domain reflectometry fiber Bragg grating (FBG) distributed strain measurement system to detect matrix cracks in carbon fiber-reinforced plastics. Load/unload tests were performed on cross-ply laminates under ambient-, high-, and low-temperature conditions using embedded 100mm gauge FBG sensors. We measured the strain distributed along the gauge and examined the crack initiation using optical microscopy and soft X-ray inspection. A peak appeared in the distributed strain corresponding to the occurrence of cracks. The strain distribution during crack initiation was calculated in each temperature range via finite element analysis and compared with the measurement results. We determined that the number and location of cracks can be determined by extracting the peaks from the distributed strain. However, the peaks in the distributed strain do not correspond to the occurrence of cracks that are close to each other, warranting a measurement method with a higher strain resolution.

Quantum weak measurement enhanced distributed acoustic sensing.

An enhanced distributed acoustic sensing (DAS) is proposed based on an extended Mach-Zehnder interferometer utilizing quantum weak measurement. The acoustic signals are encoded as the relative phase of the polarized light in several channels by fibers between optical fiber Bragg gratings (FBGs). With appropriate preselection and postselection, the acoustic signal can be extracted by performing the Fourier transform on the contrast ratio of the detected light intensity. Theoretical analysis shows that the scheme can achieve a spatial resolution of 1 m, and the system noise can be decreased by three orders of magnitude compared to classical distributed acoustic sensing. Moreover, this scheme might have potential application in long-distance acoustic source localization.

Inscription and Thermal Stability of Fiber Bragg Gratings in Hydrogen-Loaded Optical Fibers Using a 266 nm Pulsed Laser

Fiber Bragg gratings (FBGs) have gained substantial research interest due to their exceptional sensing capabilities. Traditionally, FBG fabrication has required the use of pre-hydrogenated fibers and high-cost laser systems such as excimer lasers at 193 nm or femtosecond lasers. In this study, we present the first instance of FBG inscription in hydrogen-loaded, standard single-mode silica optical fibers using a more affordable 266 nm solid-state pulsed laser combined with a scanning phase mask lithography technique. We systematically explored the effects of pulse energy and scanning speed on the quality and spectral characteristics of the gratings, achieving reflectivities as high as 99.81%. Additionally, we tracked the spectral evolution during the FBG inscription process, demonstrating uniform growth of the core mode. We also investigated the stability of the core mode during a 24-h thermal annealing process up to 150 °C. The sensitivity was 10.7 pm/°C in the range of 0 to 130 °C. Furthermore, strain measurement was conducted based on the FBG annealed at 100 °C, showing a sensitivity of 0.943 pm/µε in the range of 0 to 1667 µε.

Experimental studies of sensors based on fiber Bragg gratings embedded in the internal structure of composite plates

The main purpose of this article is to study the structural characteristics of carbon fiber samples printed on a 3D printer, including embedded sensors, during 3D printing, through numerical and experimental studies. There is a widespread tendency to replace metals with modern composite materials. Various methods can be used to measure the destruction of the composite structure. Fiber Bragg array sensors are known as intelligent localized and global structural condition prediction devices for all kinds of structural applications, especially those using composite materials. In this work, we created control plates by impregnating a selected number of layers of carbon fabric with epoxy resin. Fiber-optic Bragg sensors were additionally located between the layers of carbon fabric. In the course of experimental studies, a fiber Bragg grating sensor was embedded in the middle of the sample, and a second sensor was attached to the finished surface of the sample. We conducted environmental tests to examine the durability of the additively manufactured standard’s components and the impact of integrated sensors on the composite sample. We applied the concept of equations, known as conjugate modes, and used the transition matrix method to solve them numerically. The scientific novelty of the work is the development of a new method and technology for measuring spatial deformation in composite materials using fiber-optic Bragg gratings.

Optical Fiber Bragg Grating as a Strain Sensor

Abstract: The sensor technology industry has come to recognize and value the optical fibre sensor (OFS). It is frequently used to detect changes in the environment and to respond to outputs from other systems, such as those in industrial, monitoring, and chemical analysis applications. While a brief segment of optical fiber with a particular wavelength is reflected with light in a device known as a Fibre Bragg Grating, a Bragg reflector begins to grow and transmit all other wavelengths. Through software modeling, the current study focuses on the changing traits and behaviors of temperature and strain sensors that are used with fiber bragg gratings (FBG). The main objective of this work is to study the properties and behavior of strain sensors utilized in conjunction with fiber bragg gratings. A strain sensor can be used to determine the strain in an object whose resistance changes when force is applied

Optical Fiber Bragg Grating As A Temperature Sensor

The optical fibre sensor (OFS) has become quite well-known and prominent in the sensor technology industry. It is often used to react to outputs from other systems, like those in industrial, monitoring, and chemical analysis applications, and to detect changes in the environment. A Fibre Bragg Grating (FBG) is a device that allows light to be reflected from a short section of optical fiber at a specific wavelength, while the Bragg reflector expands and transmits all other wavelengths. The current effort focuses on the evolving characteristics and behaviors of strain and temperature sensors operating on fiber bragg gratings through computer modeling. The temperature sensor is employed to detect and quantify any variations in temperature on the Fiber Bragg Grating that could result in accidents or fires. This will show how the Fibre Bragg Grating may be used to showcase temperature sensors.

Sensor Systems for Measuring Force and Temperature with Fiber-Optic Bragg Gratings Embedded in Composite Materials

Currently, there is a lot of interest in smart sensors and integrated composite materials in various industries such as construction, aviation, automobile, medical, information technology, communication, and manufacturing. Here, a new conceptual design for a force and temperature sensor system is developed using fiber-optic Bragg grating sensors embedded within composite materials, and a mathematical model is proposed that allows one to estimate strain and temperature based on signals obtained from the optical Bragg gratings. This is important for understanding the behaviors of sensors under different conditions and for creating effective monitoring systems. Describing the strain gradient distribution, especially considering different materials with different Young’s modulus values, provides insight into how different materials respond to applied forces and temperature changes. The shape of the strain gradient distribution was obtained, which is a quadratic function with a maximum value of 1500 µ, with a maximum value at the center of the lattice and a symmetrically decreasing strain value with distance from the central part of the fiber Bragg grating. With the axial strain at the installation site of the Bragg grating sensor under applied force values ranging from 10 to 11 N, the change in strain was linear. As a result of theoretical research, it was found that the developed system with fiber-optic sensors based on Bragg gratings embedded in composite materials is resistant to external influences and temperature changes.

Refractive Index Determination and Air-Void Characterization of BNNT Assembly Using Optical Fiber Bragg Grating Sensors

Refractive Index Determination and Air-Void Characterization of BNNT Assembly Using Optical Fiber Bragg Grating Sensors

Embedded passive guided wave tomography. Application to corrosion monitoring in multilayered pipes

Guided wave tomography techniques have been studied in the last decade to quantitatively image defects in waveguides such as plates or pipes. Recent developments based on the use of an autocalibration method, removing the need of a reference acquisition, enabled the absolute imaging of the structure and drastically reducing the sensitivity to environmental and operational conditions. Another interesting feat for the structural health monitoring (SHM) is the use of passive methods relying on the measurement of the ambient noise, related to the use of the structure and its environment, and signal processing based on a cross-correlation to recover signals equivalent to the ones measured when a sensor is emitting. Such system prevents from the need of cumbersome circuitry and energy consumption related to wave emission. It also enables the sole use of sensors that cannot emit waves or only with a poor actuation such as optical fiber sensors. A SHM system relying solely on Fiber Bragg Gratings (FBGs) in optical fibers can then be designed. Several FBGs can be enscribed in a single optical fibers, reducing further the size and weight of the system. The optical fibers being resistant to harsh environments such as extreme temperatures or ionizing environments and having a good integration capability, such a system meets the needs for an industrial application. This talk will hence show the principle of the passive guided wave tomography with embedded sensors in a structure. It will be exemplified in the case of a multi-layered structure, showing the possibility to apply this system in a large panel of cases.

In-situ monitoring of an offshore wind turbine blade using acceleration and strain measurements

One of the most critical components of wind turbines is the blades. As blades are constantly exposed to weather and high loads, they can wear and become damaged. Performing in-situ continuous monitoring can help detect sudden damages and prevent further degradation, which is imperative to avoid economic losses and fatal accidents. However, monitoring a rotating rotor blade presents some challenges. One challenge is the consideration of lightning protection. Hence, a non-conductor measurement system must be used. Another challenge is system identification and modal tracking considering environmental and operational conditions (EOCs). Furthermore, vibration-based monitoring results from actual and operational rotor blades are scarce in the existing literature. This study centres on operational modal analysis (OMA) using covariance- driven stochastic subspace identification (SSI-COV) of an offshore wind turbine blade in operation employing eight months of data from fibre optic accelerometers (FOA) and fibre Bragg grating (FBG) strain gauges. The identification focuses on the first two bending modes in flapwise and edgewise directions and the first torsional mode. The study aims to determine which fibre optic sensor delivers better results. Furthermore, it addresses the effect of EOCs on the modal parameters, where system identification and modal tracking are discussed. It was found that tracked modes showed similar trends with respect to time, and a high connection was observed between wind speed, rotor speed, and pitch angle with frequency and damping. Additionally, acceleration and strain measurements deliver the same frequency and damping values. FBG better identified the first flapwise mode. On the other hand, FOA was superior in almost all other modes. This study points towards employing FOA for vibration-based monitoring of wind turbine blades using modal parameters.

Simulation and on-line monitoring using optical fiber Bragg grating sensors of temperature history during laser-assisted automated fiber placement

Automated fiber placement (AFP) in situ consolidation (ISC) of thermoplastic composite possess the potential to reduce manufacturing costs and improve manufacturing efficiency. The properties of composite manufactured by the ISC are affected by several mechanisms including polymer degradation, crystallization, intimate contact, polymer healing and void dynamics. All these mechanisms are directly affected by the temperature history. Consequently, the control and accurate measurement of temperature history during ISC are particularly important for improving the properties of composite. In this study, a simplified three-dimensional transient heat transfer model was established. The effect of tool temperature and placement speed on the temperature history and peak temperature were predicted. Simultaneously, an online temperature monitoring system was built and the optical Fiber Bragg Grating sensors (FBGS) was used to measure the temperature history. The results indicated that the predicted results of the model were consistent with the measured results, the error was below 8%. In addition, the temperature history of layers was significantly affected by the tool temperature and placement speed. The temperature of the layers decreased to near the tool temperature after cooling, and a higher tool temperature increasing its peak temperature because of the reduce of the cooling rate. On the contrary, an increase in placement speed will reduce the peak temperature of the layers.

Artificial Skin Based on Polymer Optical Fiber Bragg Grating Arrays for Robotic Tactile Perception

Artificial Skin Based on Polymer Optical Fiber Bragg Grating Arrays for Robotic Tactile Perception

Fiber-Optic Bragg Grating Sensor for Photothermally Examinating Moisture of Meat

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.

In Operando Monitoring the Stress Evolution of Silicon Anode Electrodes during Battery Operation via Optical Fiber Sensors.

Silicon (Si) anode has attracted broad attention because of its high theoretical specific capacity and low working potential. However, the severe volumetric changes of Si particles during the lithiation process cause expansion and contraction of the electrodes, which induces a repeatedly repair of solid electrolyte interphase, resulting in an excessive consuming of electrolyte and rapid capacity decay. Clearly known the deformation and stress changing at µε resolution in the Si-based electrode during battery operation provides invaluable information for the battery research and development. Here, an in operando approach is developed to monitor the stress evolution of Si anode electrodes via optical fiber Bragg grating (FBG) sensors. By implanting FBG sensor at specific locations in the pouch cells with different Si anodes, the stress evolution of Si electrodes has been systematically investigated, and Δσ/areal capacity is proposed for stress assessment. The results indicate that the differences in stress evolution are nested in the morphological changes of Si particles and the evolution characteristics of electrode structures. The proposed technique provides a brand-new view for understanding the electrochemical mechanics of Si electrodes during battery operation.

Contactor Fault Detection and Classification System Using Optical Fiber Bragg Grating Sensors

Contactor Fault Detection and Classification System Using Optical Fiber Bragg Grating Sensors

Sensor-Based Structural Health Monitoring of Asphalt Pavements with Semi-Rigid Bases Combining Accelerated Pavement Testing and a Falling Weight Deflectometer Test

The Structural Health Monitoring (SHM) of pavement infrastructures holds paramount significance in the assessment and prognostication of the remaining service life of roadways. In response to this imperative, a methodology for surveilling the surface and internal mechanical responses of pavements was devised through the amalgamation of Accelerated Pavement Testing (APT) and Falling Weight Deflectometer (FWD) examinations. An experimental road segment, characterized by a conventional asphalt pavement structure with semi-rigid bases, was meticulously established in Jiangsu, China. Considering nine distinct influencing factors, including loading speed, loading weight, and temperature, innovative buried and layout configurations for Resistive Sensors and Fiber-optic Bragg Grating (FBG) sensors were devised. These configurations facilitated the comprehensive assessment of stress and strain within the road structure across diverse APT conditions. The methodology encompassed the formulation of response baselines, the conversion of electrical signals to stress and strain signals, and the proposition of a signal processing approach involving partial filtering and noise reduction. In experimental findings, the asphalt bottom layer was observed to undergo alternate tensile strains under dynamic loads (the peak strain was ten με). Simultaneously, the horizontal transverse sensor exhibited compressive strains peaking at 66.5 με. The horizontal longitudinal strain within the base and subbase ranged between 3 and 5 με, with the base registering a higher strain value than the subbase. When subjected to FWD, the sensor indicated a diminishing peak pulse signal, with the most pronounced peak response occurring when the load plate was situated atop the sensor. In summary, a comprehensive suite of monitoring schemes for road structures has been formulated, delineating guidelines for the deployment of road sensors and facilitating sustained performance observation over extended durations.

Highly sensitive optical fibre Bragg grating contact pressure sensor embedded in a polymer layer: Modelling and experimental validation

This paper discusses mathematical modelling and experimental validation of a highly sensitive optical fibre Bragg grating (FBG) contact pressure sensor developed for healthcare applications. Bare FBGs are not very sensitive to pressure (∼3 × 10−3 nm/MPa) but this can be increased by embedding the FBG in a polymer layer which acts as transducer to convert transverse load (pressure) applied to an axial strain, measured by the FBG sensor. The pressure sensitivity of the FBG sensor depends on the mechanical and physical properties such as Young’s modulus, shape and size of the polymer. A finite element analysis (FEA) model is developed to optimise the design parameters of the FBG sensor in order to achieve a high sensitivity. A transfer matrix mathematical formulism is then used to relate the reflection spectrum of the FBG to the strain experienced. Three different shapes, three different sizes and three different polymer materials with different Young’s moduli have been simulated and their wavelength sensitivities related to the transverse pressure. According to the simulation results, the pressure sensitivity of a bare FBG can be increased ∼ 270 times (0.8179 nm/MPa) by selecting an FBG of 3 mm length, embedding it at the horizontal centre of a polymer layer of Young’s modulus of 20 MPa, in the shape of a circular disc with a diameter 5.5 mm and thickness of 1 mm.

A single passband microwave photonic filter with enhanced flat top and shape factor based on tunable optical bandpass filter and fiber Bragg gratings

A single passband microwave photonic filter with enhanced flat top and shape factor based on tunable optical bandpass filter and fiber Bragg gratings

Optical fiber Bragg grating (FBG)-based strain sensor embedded in different 3D-printed materials: A comparison of performance

A compact fiber Bragg grating (FBG)-based strain sensor has been developed by embedding an FBG inside a 3D-printed structure, allowing the comparison of FBG responses across different filaments such as polylactic acid (PLA), thermoplastic polyurethane (TPU), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), and nylon. Results have shown that FBG embedded in TPU can be effective in the measurements of mechanical strain, giving a responsivity value of 17.70 pm/cm with outstanding linearity of 98 %. Furthermore, small-scale field testing conducted in below-ground environments has shown that strain sensors based on FBG embedded in TPU are the most effective. They offer a responsivity of 13.9 pm/kg with a small standard deviation and high linearity. Additionally, they have the highest temperature sensitivity value of 15.4 pm/°C compared to the other embedded FBGs. Therefore, for most industrial applications, the FBG embedded in TPU can be considered as an alternative to existing embedment methods for strain sensing applications.

Optical Fiber Bragg Grating Filter for Wavelength Division Multiplexing (WDM) Applications

A Fiber Bragg grating is an aperiodic or periodic disorder of the effective index of refraction in the optical fiber core, having nanometres range period. For short periods of the index modulation, the disorder in index of refraction perturbation induces the light reflection in a limited wavelength range, for which condition of Bragg is satisfied. Incidence of a broad-spectrum light onto one fiber end containing a fiber Bragg grating, induces reflection of the portion of the light corresponding to wavelength of the Bragg grating to the input end, while the remaining light reaches the other end. Optical wavelength division multiplexing (WDM) networks employed in long distance and metro areas; several nodes are present to distribute the signal. The optical add-drop multiplexer (OADM) is the significant equipment which is responsible for separation of distinct wavelengths and redirection of the linked signals across the network to the corresponding users. The operating principle of the optical add-drop multiplexer deems an accurate filtering operation, provided by Bragg gratings. In this paper, optical fiber Bragg grating filter is designed and analysed for Wavelength Division Multiplexing (WDM) application.