Fiber Bragg Grating Technology Research Articles

Enhancing FBG Sensing in the Industrial Application by Optimizing the Grating Parameters Based on NSGA-II.

Fiber Bragg grating (FBG) technology has shown a mutation in developing fiber optic-based sensors because of their tiny size, high dielectric strength, distributed sensing, and immunity to high voltage and magnetic field interference. Therefore, FBG sensors significantly improve performance and accuracy in the world of measurements. The reflectivity and bandwidth are the main parameters that can dramatically affect the sensing performance and accuracy. Each industrial application has its requirements regarding the reflectivity and bandwidth of the reflected wavelength. Optimizing such problems with multi-objective functions that might t with each other based on applications' needs is a big challenge. Therefore, this paper presents an optimization method based on the nondominated sorting genetic algorithm II (NSGA-II), aiming at determining the optimum grating parameters to suit applications' needs. To sum up, the optimization process aims to convert industrial applications' requirements, including bandwidth and reflectivity, into the manufacturing setting of FBG sensors, including grating length and modulation refractive index. The method has been implemented using MATLAB and validated with other research work in the literature. Results proved the capability of the new way to determine the optimum grating parameters for fulfilling application requirements.

The Effect of Infill Pattern and Density on the Response of 3-D-Printed Sensors Based on FBG Technology

Fiber Bragg gratings (FBGs) are known for their uses in applications ranging from civil engineering to medicine. A bare FBG is small and light; hence, it can be easily embedded into hosting materials. However, conventional fabrication methods are generally time-consuming with reproducibility issues. A more recent strategy has been proposed to develop novel FBG-based systems by encapsulating the grating within 3-D-printed structures. This process, known as 3-D printing, is characterized by several advantages like rapid prototyping, printing precision, and high customization. The possibility of quickly personalizing the 3-D-printed sensors by customizing the infill settings makes this technique very appealing for medical purposes, especially for developing smart systems. However, the influence of printing settings on the sensor response has not been yet systematically addressed. This work aimed at combining FBG with the most popular 3-D printing technique (the fused deposition modeling [FDM]) to develop four 3-D-printed sensors with different printing profiles. We chose two patterns (triangle and gyroid) and two infill densities (30% and 60%) to investigate their influence on the sensors’ response to strain, temperature, and relative humidity (RH), and on the hysteresis behavior. Then, we preliminary assess the sensor performance in a potential application scenario for FBG-based 3-D printing technology: the cardiorespiratory monitoring. The promising results confirm that our analysis can be considered the first effort to improve the knowledge about the influence of printing profiles on sensor performance and, consequently, pave the way to develop highly performant 3-D-printed sensors customized for specific applications.

Leveraging internal curing effect of fly ash cenosphere for alleviating autogenous shrinkage in 3D printing

• Perforated fly ash cenospheres (PFACs) were used as an internal curing agent for developing printable cement-based materials. • Internal curing effect of PFACs can alleviates autogenous shrinkage strain by 81% in 3D printing component. • Effect of PFACs on the rheology of limestone calcined clay cement (LC3) was evaluated. • Fiber Bragg Grating technology was adopted to study autogenous shrinkage by monitoring the interlayer strain. • Incorporating 15 vol% PFAC to replace sand gives LC3 exceptional resistance to autogenous shrinkage and printability. The development of three-dimensional (3D) printing technology in the construction industry has coincided with growing attention on the investigation of printable cement-based composite. Meanwhile, the exploitation of high-performance and environmentally friendly printable cement-based composite is an inevitable path for the sustainable development of 3D printing in the construction industry. This study proposes the use of perforated fly ash cenospheres (PFACs) as internal curing (IC) agent into limestone calcined clay cement (LC3) mortar to develop a novel green printable cement-based composite. Rheological behavior of LC3 mortar containing PFACs has been shown to meet the requirements of 3D printing. The internal curing effect on autogenous shrinkage of mortar was studied by employing Fiber Bragg Grating (FBG) technology. Compressive and flexural strengths of LC3 mortar containing PFACs were evaluated. Additionally, microstructural investigation was analyzed through SEM, and the hydration products were studied by XRD and TG tests. Results suggest that shrinkage strain of LC3 mortar containing 15% PFAC was approximately 80% lower than that of mortar without PFAC, which indicates that PFAC in LC3 mortar can be effective in holding the mixing water for IC that can reduce the autogenous shrinkage. Furthermore, additional mechanical strength of mortar containing PFAC was generated through IC effect and the pozzolanic activity of PFAC, which can effectively compensate the strength loss caused by the PFAC. However, microstructural investigation indicated that the pozzolanic activity of PFAC has limited effect on cement hydration compared with the introduction of additional IC water. Consequently, this study reveals that it is effective to adopt PFAC as IC agent into LC3 mortar to develop high-performance and sustainable printable cement-based composite.

Monitoring Evolution of Temperature and Strain in Cement Sheath Using Embedded Optical Fiber Bragg Gratings

Summary In the full life cycle of a well, thermal and mechanical loads may yield serious issues for the cement sheath integrity. However, the information for the integrity assessment, such as temperature and strain, is difficult to acquire underground. In this study, a full-scale experimental facility is used, allowing us to mimic the casing-cement sheath-formation (CCSF) system of a well. The system is monitored by fiber Bragg grating (FBG), enabling a real-time, high-accuracy, nondestructive measurement of temperature and strain inside the cement sheath in the sequence of setting and completion stage. Our observation reveals that the temperature of the cement sample cured in the mold is 22.3°C higher than the curing temperature; however, this temperature difference is not observed in the cement sheath cured in the CCSF system. This implies that the data obtained from the cement sample may overestimate the early-age performance of the cement sheath. Besides, the FBG measures a free strain of the tested cement during the hydration to be −370 με. This shrinkage can yield an internal stress in the CCSF system, which leads the cement sheath to swell circumferentially during the setting stage. During the completion stage, when the cement sheath is subjected to cyclic loading at three casing pressure levels, (i i.e., 10, 20, and 50 MPa), the maximum increment of circumferential strain reaches 160, 270, and 850 με, respectively. A plastic strain is observed for the 50 MPa pressure level, but not for the two other pressure levels (10 and 20 MPa). Unlike the observations in cyclic loading tests on cement samples, the plastic strain in the CCSF system accumulates linearly in the first 10 cycles and then increases slowly afterward. This difference is suggested to be attributed to the redistribution of internal stress along with the accumulation of plastic strain. Finally, the strains measured by the FBG are validated by the simulation, demonstrating the promising applicability of the FBG technology for monitoring the integrity of cement sheath.

Deformation and Damage Characteristics of Deep Rock Specimens Based on 3D-DIC and FBG

Abstract Specimen-scale testing of loaded rock parameters is an important research component of rock mechanics testing. In this paper, a method combining 3D-DIC and FBG (fiber Bragg grating) technology is proposed and applied to the study of deformation and damage characteristics of deep limestone and sandstone specimens under uniaxial loading conditions in the Panxie mine area of Huainan coalfield. The selection of optical fiber, the bonding method, and the process of rock specimen fabrication are introduced in detail. Two different fiber Bragg grating sensor arrays were constructed by using both multi-inclination type and orthogonal type deployment of fiber grating to dynamically monitor the strain response of rock specimens throughout the whole process. The results show that both 3D-DIC displacement monitoring and fiber Bragg grating strain captured the rock deformation and failure process well with identical outcomes. Under a continuous load of 0.3 kN/s, the local cracks of the rock specimen and the damage to the rock specimen resulted in different degrees of sudden changes in the fiber strain value. According to the differences in the degrees of brittleness and texture densities of the rock specimens, the local cracks evolution to transfixion of the limestone registered a certain time accumulation and produced more local cracks, while the sandstone at the same stage produced fewer local cracks within a shorter duration. The effective combination of regional noncontact testing and high-precision point contact can dynamically and accurately capture the rock deformation and damage characteristics at the specimen scale. In addition, the combined monitoring method of 3D-DIC and fiber grating can provide assistance in the prediction of rock crack expansion and potential fracture surfaces.

New shapemeter roll technology based on Fiber Bragg Grating technology for on-line flatness monitoring of thin cold rolled metal sheets

The shape of laminated products is a crucial parameter in high-speed and high-volume finishing lines where they must fulfill tight tolerances. Latent defects are detected by flatness rolls (or shapemeter rolls) inserted in the manufacturing line for online flatness control. A prototype of flatness roll has been developed with high spatial resolution (5 mm) and measurement capability over a thickness range of 0.1–1 mm to evaluate flatness and residual stresses of flat metal strip products manufactured by continuous cold rolling (ultra-thin sheets for packaging and automotive markets). The flatness roll prototype relies on pressure-induced strain sensing on segmented blades using Fiber Bragg Grating technology. Synchronous measurement of the flatness profile across strip width rejects disturbances of strip tension during rolling. We provide a proof-of-concept on pilot lines in both static and dynamic conditions (e.g., roll in rotation and in contact with a strip under tension) and the sensing mechanism shows a capability above 3. This combination of performances remains unique up to now. Interblade crosstalk appears to be an important issue. We propose a crosstalk model that agrees with experimental coupling coefficients. A crosstalk matrix inversion yields the distribution in contact pressure from strain data measured on the reverse side. Additional work will be required to use the flatness roll in industrial conditions.

Smart Manufacturing in Rolling Process Based on Thermal Safety Monitoring by Fiber Optics Sensors Equipping Mill Bearings

The steel rolling process is critical for safety and maintenance because of loading and thermal operating conditions. Machinery condition monitoring (MCM) increases the system’s safety, preventing the risk of fire, failure, and rupture. Equipping the mill bearings with sensors allows monitoring of the system in service and controls the heating of mill components. Fiber optic sensors detect loading condition, vibration, and irregular heating. In several systems, access to machinery is rather limited. Therefore, this paper preliminarily investigates how fiber optics can be effectively embedded within the mill cage to set up a smart manufacturing system. The fiber Bragg gratings (FBG) technology allows embedding sensors inside the pins of backup bearings and performing some prognosis and diagnosis activities. The study starts from the rolling mill layout and defines its accessibility, considering some real industrial cases. Testing of an FBG sensor prototype checks thermal monitoring capability inside a closed cavity, obtained on the surface of either the fixed pin of the backup bearing or the stator surrounding the outer ring. Results encourage the development of the whole prototype of the MCM system to be tested on a real mill cage in full operation.

Respiratory and heart rate monitoring using an FBG 3D-printed wearable system.

This work proposes a 3D-printed sensor based on fiber Bragg grating (FBG) technology for respiratory rate (RR) and heart rate (HR) monitoring. Each sensor is composed of a single FBG fully encapsulated into a 3D-printable Flexible, during the printing process. Sensors with different material thicknesses and infill densities were tested. The sensor with the best metrological properties was selected and preliminary assessed in terms of capability of monitoring RR and HR on three users. Preliminary results proved that the developed sensor can be a valuable easy-to-fabricate solution, with high reproducibility and high strain sensitivity to chest wall deformations due to breathing and heart beating.

Structure optimization of electrical penetration assemblies: Experimental facts and stress field analysis by the finite element method

Thermal-mechanical induced stress in glass is critical for the performance of glass-to-metal-type electrical penetration assemblies (EPAs) used in nuclear reactors and is mainly determined by the thermal expansion mismatch between glass and metal and the structural design of the EPAs. Here, from the perspective of structural design, a new strategy for optimizing thermal stress in EPA glass is proposed. A flexible structure is designed to act as a stress buffer layer between glass and metal. The stress field of the EPA is analysed in detail using an improved finite element (FE) model, and the fidelity is verified by stress measurements based on fibre Bragg grating (FBG) technology. The results show that the designed buffer structure can effectively reduce the concentration of von Mises stress and tangential stress in glass. Moreover, the effect of the geometric dimension on the stress field of the EPA is limited. In addition, compression tests and thermal shock tests are employed to evaluate the mechanical strength and service performance, respectively. The flexible structure can enhance the mechanical properties and accident-tolerant capability of EPAs. The findings of this study have important technical implications for the optimization of seal configurations in EPAs.

A Wearable System Composed of FBG-Based Soft Sensors for Trunk Compensatory Movements Detection in Post-Stroke Hemiplegic Patients.

In this study, a novel wearable system for the identification of compensatory trunk movements (CTMs) in post-stroke hemiplegic patients is presented. The device is composed of seven soft sensing elements (SSEs) based on fiber Bragg grating (FBG) technology. Each SSE consists of a single FBG encapsulated into a flexible matrix to enhance the sensor’s robustness and improve its compliance with the human body. The FBG’s small size, light weight, multiplexing capability, and biocompatibility make the proposed wearable system suitable for multi-point measurements without any movement restriction. Firstly, its manufacturing process is presented, together with the SSEs’ mechanical characterization to strain. Results of the metrological characterization showed a linear response of each SSE in the operating range. Then, the feasibility assessment of the proposed system is described. In particular, the device’s capability of detecting CTMs was assessed on 10 healthy volunteers and eight hemiplegic patients while performing three tasks which are representative of typical everyday life actions. The wearable system showed good potential in detecting CTMs. This promising result may foster the use of the proposed device on post-stroke patients, aiming at assessing the proper course of the rehabilitation process both in clinical and domestic settings. Moreover, its use may aid in defining tailored strategies to improve post-stoke patients’ motor recovery and quality of life.

Strain Sensor Based on Embedded Fiber Bragg Grating in Thermoplastic Polyurethane Using the 3D Printing Technology for Improved Sensitivity

A new and easy-to-fabricate strain sensor has been developed, based on fiber Bragg grating (FBG) technology embedded into a thermoplastic polyurethane filament using a 3-dimensional (3D) printer. Taking advantage of the flexibility and elastic properties of the thermoplastic polyurethane material, the embedding of the FBG provides durable protection with enhanced flexibility and sensitivity, as compared to the use of a bare FBG. Results of an evaluation of its performance have shown that the FBG sensors embedded in this way can be applied effectively in the measurement of strain, with an average wavelength responsivity of 0.013 5 nm/cm of displacement for tensile strain and −0.014 2 nm/cm for compressive strain, both showing a linearity value of up to 99%. Furthermore, such an embedded FBG-based strain sensor has a sensitivity of ∼1.74 times greater than that of a bare FBG used for strain measurement and is well protected and suitable for in-the-field use. It is also observed that the thermoplastic polyurethane based (TPU-based) FBG strain sensor carries a sensitivity value of ∼2.05 times higher than that of the polylactic acid based (PLA-based) FBG strain sensor proving that TPU material can be made as the material of choice as a “sensing” pad for the FBG.

Development and Application of Fiber-Optic Sensing Technology for Monitoring Soil Moisture Field

Accurate acquisition of the moisture field distribution in in situ soil is of great significance to prevent geological disasters and protect the soil ecological environment. In recent years, rapidly developed fiber-optic sensing technology has shown outstanding advantages, such as distributed measurement, long-distance monitoring, and good durability, which provides a new technical means for soil moisture field monitoring. After several years of technical research, the authors’ group has made a number of new achievements in the development of fiber-optic sensing technology for the soil moisture field, that is, two new fiber-optic sensing technologies for soil moisture content, including the actively heated fiber Bragg grating (AH-FBG) technology and the actively heated distributed temperature sensing (AH-DTS) technology, and a new fiber-optic sensing technology for soil pore gas humidity are developed. This paper systematically summarizes the three fiber-optic sensing technologies for soil moisture field, including sensing principle, sensor development and calibration test. Moreover, the practical application cases of three fiber-optic sensing technologies are introduced. Finally, the development trend of fiber-optic sensing technology for soil moisture field in the future is summarized and prospected.

Stress Monitoring of Roadway with Bolt Sensor Based on Fiber Bragg Grating Technology

Stress Monitoring of Roadway with Bolt Sensor Based on Fiber Bragg Grating Technology

Stress Monitoring of Roadway with Bolt Sensor Based on Fiber Bragg Grating Technology

Stress Monitoring of Roadway with Bolt Sensor Based on Fiber Bragg Grating Technology

Mechanical Strain Measurements in High-Field Low-Temperature Superconducting Magnets

Optical fiber sensors based on Fiber Bragg Grating (FBG) technology are used to monitor the mechanical behavior of the magnet's coils from its assembly at room temperature to its powering at cryogenic temperatures. The development of this instrumentation required several years of research and development effort to validate the precision and accuracy of FBGs based measurements in cryogenic conditions. FBGs are bonded on the coils in different locations along with the longitudinal and azimuthal directions that allow studying the average stress levels. The stainless-steel shells of the magnets and each extremity of the four rods are equipped with resistive strain gauges (RSG). This paper provides a description of the instrumentation used to monitor the strain profile of superconducting magnets. Strain measurements during magnet assembly, cool-down, and powering are presented to confirm the agreement between electrical and optical sensors.

Discussion of Fiber Bragg Grating Technology Applicability on Diagnostic Field Testing of Steel Girder Bridges

Discussion of Fiber Bragg Grating Technology Applicability on Diagnostic Field Testing of Steel Girder Bridges

Experimental study on cement sheath integrity based on fiber Bragg grating technology

Fiber Bragg grating (FBG) sensing technology is a new structure monitoring technology. Aiming at the influence of hydration and cyclic casing pressure on cement sheath integrity in real wellbore conditions, firstly, the temperature and strain variation regularities of cement sheath in setting stage are investigated by FBG and a test device for evaluating cement sheath integrity. Then the circumferential strains of cement sheath and casing under cyclic casing pressure are studied. Furthermore, the applicability of FBG technology is verified. The results show that the temperature and strain of cement slurry change rapidly in 5 hours after pouring. In cyclic casing pressure stage, circumferential strains of cement sheath and casing are both tensile strains. In addition, circumferential strain of cement sheath and casing increases with the increase of casing pressure. The FBG sensors have high sensitivity that can reflect the change of casing pressure in time. The FBG technology is a scientific temperature and strain monitoring method for cement sheath. The results of this study are of great significance to the application of FBG technology for cement sheath integrity.

Experimental study on a new method to forecasting goaf pressure based key strata deformation detected using optic fiber sensors

The spatial distribution of rock mass stress in goaf seriously affects the stable operation of underground reservoir. Measurement of stress distribution in the goaf of coal mines is difficult due to the complex internal environment and other restrictive conditions of goaf. This paper presents a new method of monitoring the deformation of key stratum in overburden by optical fiber sensing, and then characterizing the pressure of goaf. The internal mechanism of key stratum breakage and the variation of goaf stress is investigated by physical model with the geometric dimension of 3 (length) × 1.3 (height) × 0.4 (width) m), in which the Brillouin Optical Time Domain Analysis (BOTDA) fiber-optic sensing technology and Fiber Bragg Grating (FBG) technology are used to monitor the stability of key stratum and the non-contact Digital Image Correlation (DIC) technique is employed to provide real-time deformation measurements. Combining the fracture mechanics model of key strata with the parabolic function model of subsidence trajectory, the stress evolution model of coal seam mining space is established for the first time, the goaf pressure change and the corresponding relation between the key layer breakage was quantitatively characterized. The research results show that: The fracture location of the key strata is consistent with the peak stress location of the goaf. The breaking limit strain threshold value of the key strata based on optical fiber sensing detection is 4000 με. Through the inversion of optical fiber monitoring results, the fracture degree and range of overburden rock in goaf are obtained, thus reflecting the position and change of the peak pressure in goaf. The consistency between key layer deformation and goaf pressure variation is verified.

Plant Wearable Sensors Based on FBG Technology for Growth and Microclimate Monitoring.

Plants are primary resources for oxygen and foods whose production is fundamental for our life. However, diseases and pests may interfere with plant growth and cause a significant reduction of both the quality and quantity of agriculture products. Increasing agricultural productivity is crucial for poverty reduction and food security improvements. For this reason, the 2030 Agenda for Sustainable Development gives a central role to agriculture by promoting a strong technological innovation for advancing sustainable practices at the plant level. To accomplish this aim, recently, wearable sensors and flexible electronics have been extended from humans to plants for measuring elongation, microclimate, and stressing factors that may affect the plant’s healthy growth. Unexpectedly, fiber Bragg gratings (FBGs), which are very popular in health monitoring applications ranging from civil infrastructures to the human body, are still overlooked for the agriculture sector. In this work, for the first time, plant wearables based on FBG technology are proposed for the continuous and simultaneous monitoring of plant growth and environmental parameters (i.e., temperature and humidity) in real settings. The promising results demonstrated the feasibility of FBG-based sensors to work in real situations by holding the promise to advance continuous and accurate plant health growth monitoring techniques.

Deep displacement monitoring and foundation base boundary reconstruction analysis of diaphragm wall based on ultra-weak FBG

The instability or destruction of diaphragm walls in underground engineering will cause significant economic losses and casualties. The distributed and high-precision monitoring of diaphragm wall deformation can provide reliable and detail data for disaster early-warning as well as economical design. However, recording continuous deformation of the diaphragm wall using traditional monitoring technologies remain challenging. Moreover, the basement movement of diaphragm wall is rarely considered in previous studies. In order to overcome the shortcomings of the current displacement monitoring methods and deal with the basement boundary issues, a new base boundary reconstruction (BR) was proposed and the ultra-weak Fiber Bragg grating (UWFBG) technology was adopted to monitor the displacement of the diaphragm wall. For validation, a laboratory test based on ultra-weak FBG was carried out and the feasibility of the BR method was demonstrated. Subsequently, the ultra-weak FBG and the BR method were applied to Shanghai metro line 18. The results showed that the monitoring technology and analysis method proposed in this paper can obtain detailed deformation information of the diaphragm wall in real-time, which not only provides an advanced monitoring method for the deep deformation of diaphragm wall, but also solves the deformation calculation issue with the base boundary condition changes involved.