Fiber Bragg Grating Temperature Sensor Research Articles

Fiber Bragg Grating Temperature Sensor by the Wavelength Tuning Using the Temperature Dependence of VCSEL

Fiber Bragg Grating Temperature Sensor by the Wavelength Tuning Using the Temperature Dependence of VCSEL

Application of Additive Layer Manufacturing Technique on the Development of High Sensitive Fiber Bragg Grating Temperature Sensors

This paper presents the development of temperature sensors based on fiber Bragg gratings (FBGs) embedded in 3D-printed structures made of different materials, namely polylatic acid (PLA) and thermoplastic polyurethane (TPU). A numerical analysis of the material behavior and its interaction with the FBG sensor was performed through the finite element method. A simple, fast and prone to automation process is presented for the FBG embedment in both PLA and TPU structures. The temperature tests were made using both PLA- and TPU-embedded FBGs as well as an unembedded FBG as reference. Results show an outstanding temperature sensitivity of 139 pm/°C for the FBG-embedded PLA structure, which is one of the highest temperature sensitivities reported for FBG-based temperature sensors in silica fibers. The sensor also shows almost negligible hysteresis (highest hysteresis below 0.5%). In addition, both PLA- and TPU-embedded structures present high linearity and response time below 2 s. The results presented in this work not only demonstrate the feasibility of developing fully embedded temperature sensors with high resolution and in compliance with soft robot application requirements, but also show that the FBG embedment in such structures is capable of enhancing the sensor performance.

Simultaneous interrogation of multiple fiber Bragg grating temperature sensors using a microwave photonic approach

In this paper, we demonstrate a microwave photonic (MWP) approach for interrogating multiple linearly chirped fiber Bragg grating (LCFBG) temperature sensors. The MWP interrogation system is based on an arrayed waveguide grating Sagnac interferometer, incorporating multiple LCFBG sensors, that is used to generate multiple chirped microwave waveforms whose characteristics are uniquely related to those of the LCFBGs. Compressing the generated microwave signals allows monitoring simultaneously and independently the shifts associated with applying temperature changes to each LCFBG in real time.

Study on the characteristics of GDL with different PTFE content and its effect on the performance of PEMFC

The content of Polytetrafluoroethylene (PTFE) is the key factor to determine the hydrophobicity and heat transfer characteristics of the gas diffusion layer (GDL), which directly affects the performance of the proton exchange membrane fuel cell (PEMFC). The PTFE content of GDL materials changes due to the complex and variable working conditions and the accumulation of working hours in fuel cells. In order to study the effect of PTFE content and external load on the thermal conductivity of GDL materials, a new method based on Fiber Bragg Grating (FBG) sensing technology was proposed to measure the thermal conductivity of GDL materials. The thermal conductivity of GDL materials with different PTFE content was measured by FBG temperature sensor, and the effect of different PTFE content on the performance of fuel cell was studied. The experimental results show that the hydrophobicity of GDL material increases with the increase of PTFE content, and different PTFE content of GDL materials have different effects on the performance of PEMFC. The difference of thermal conductivity of GDL material with different PTFE content can be measured by using FBG sensing measurement technology, which reflects the change of GDL material properties due to the difference of PTFE content in the GDL material. The results of this study provide guidance for the method of detecting the change of internal material characteristics of PEMFC.

Calibration Experiment for Seepage Monitoring Using Fiber Bragg Grating Hydrothermal Cycling Integration System

Abstract Seepage monitoring is an important element in geotechnical engineering. This article proposed a new integrated system for seepage monitoring composed of a fiber Bragg grating (FBG) sensing system and a water-heating cycling system. The boiler is used as the heating equipment in the integrated system. The heated water is distributed to each heating pipeline for cyclic heating through the water separator and water collector. The FBG temperature sensors are preburied in the heating pipeline to monitor the water temperature in real time. Recognizing the correlation between the temperature field and the seepage field, we proposed to fit coefficient ξv according to the cooling curve and used it as an index to identify the seepage state. We conducted this numerical simulation to analyze the heat transfer process of the heat source in the porous media. We carried out the calibration experiments of seepage velocity using the FBG-sensing heating system in the porous medium with four different gradations. Our results showed that the temperature gradient decreased over time, indicating that the primary way the heat source was transferred was through the convective heat transfer caused by the seepage. Therefore, the coefficient ξv could be used as the seepage identification index. On the basis of our calibration experiments, we obtained the fitting formulas of ξv and the seepage velocity in four kinds of porous mediums. The formulas can be used for the inversion of seepage velocity. The experimental results proved that ξv was unrelated to the initial cooling temperature. This finding showed that the influence of an uneven temperature distribution along the heating pipeline on monitoring results could be ignored.

High-resolution slow-light fiber Bragg grating temperature sensor with phase-sensitive detection

This Letter reports a slow-light fiber Bragg grating (FBG) temperature sensor with a record temperature resolution of ∼0.3 m°C/√Hz, a drift of only ∼1 m°C over the typical duration of a measurement (∼30 s), and negligible self-heating. This sensor is particularly useful for applications requiring the detection of very small temperature changes, such as radiation-balanced lasers and the measurement of small absorptive losses using calorimetry. The sensor performance is demonstrated by measuring the heat generated in a pumped Yb-doped fiber. The sensor is also used to measure the slow-light FBG's very weak internal absorption loss (0.02 m-1), which is found to be only ∼2% of the total loss.

Integration of fiber Bragg grating temperature sensors in plasma facing components of the WEST tokamak.

Plasma Facing Components (PFC) temperature measurement is mandatory to ensure safe high power and long pulse tokamak operation. IR thermography systems which are widely used in magnetic fusions devices become challenged with the choice of tungsten as a PFC material in the ITER tokamak, mainly due to emissivity uncertainties and reflection issues in a hot environment. Embedded temperature measurements are foreseen to cross-check the IR thermography measurements. Fiber Bragg grating sensors are potentially of great interest for this application because they are immune to electromagnetic interference and allow the measurement of a large number of temperature spots on a single fiber. Four optical fiber temperature sensing probes, each of them including 11 regenerated fiber Bragg gratings equally spaced by 12.5 mm (equivalent to one ITER-like tungsten monoblock), have been specifically designed and manufactured for the WEST project (W-tungsten Environment and Steady State Tokamak). The four probes are embedded in W-coated graphite components at two different distances from the surface, 3.5 mm and 7 mm, to cover a wide range of temperatures up to 900 °C. This paper addresses the design and integration issues and the qualification and performance assessment performed in the laboratory. It also shows the first measurements of this new diagnostic achieved in a tokamak environment during baking of the machine and during early diverted plasma exposure.

Selecting of FBG Coatings for Quench Detection in HTS Coils

Fiber Bragg grating (FBG) temperature sensors are now regarded as a relatively mature sensing technology for temperature measurement in ambient conditions, and may offer potential as a cryogenic temperature sensor for quench detection. In this paper, the temperature response of three different coated FBG sensors from 77 to 293 K was studied; bare (silica) FBG, acrylic coated, and polyimide coated FBG sensors. We examine the effect of fiber coatings on the temperature sensitivity of an embedded FBG sensor down to cryogenic temperatures. Measurements were repeated with sensors from two FBG suppliers. The measured temperature response was then compared and contrasted with the predicted sensor response. In order to assess the sensor sensitivity, repeatability, and any hysteresis, these sensors were then subjected to repeated cool-down / warm-up cycles (77–293 K). The effect of epoxy resin impregnation on the temperature response characteristics was analyzed by comparing the sensor response characteristics before and after embedding into a 10 mm × 2 mm × 4 mm epoxy block. We compare this to the uncoated fiber for embedment in HTS coils. Finally, we recommend the optimum low-cost sensor construction for use in quench detection in coils.

Temperature dependence of microhole-based fiber Fabry–Perot interferometric sensors fabricated by excimer laser

A miniature in-fiber Fabry–Perot interferometric (FPI) sensor is demonstrated. Through manufacturing microhole in a single-mode fiber with excimer laser, a single microhole FPI sensor and a dual microhole FPI sensor are fabricated, and the temperature sensing characteristics of them are investigated experimentally. The results show that the spectra of two sensors shift to short wavelength with an increase in the temperature, and the relationships between wavelength shift and temperature change have better linearity in temperature range of 30°C to 85°C. The temperature sensitivity of single microhole FPI sensor is 0.160 nm / ° C, and the dual microholes FPI sensor has two temperature sensitivities corresponding to different FP cavities. Furthermore, the temperature sensitivity can be adjusted by changing the distance between two microholes. When increasing the distance from 1 to 2 mm, the higher temperature sensitivity can be changed from 0.176 to 0.192 nm / ° C, and the temperature-dependent wavelength shift still keeps a good linearity. Compared with conventional fiber Bragg grating temperature sensor, this kind of FPI sensor has not only different dual temperature sensitivities but also higher sensitivity and stability, so that this kind of microhole FPI sensor can be used in many fields.

Metallic-packaging fiber Bragg grating sensor based on ultrasonic welding for strain-insensitive temperature measurement

In this paper, a metallic-packaging fiber Bragg grating temperature sensor characterized by a strain insensitive design is demonstrated. The sensor is fabricated by the one-step ultrasonic welding technique using type-II fiber Bragg grating combined with an aluminum alloy substrate. Finite element analysis is used to perform theoretical evaluation. The result of the experiment illustrates that the metallic-packaging temperature sensor is insensitive to longitudinal strain. The sensor's temperature sensitivity is 36 pm/°C over the range of 50-110 °C, with the correlation coefficient (R2) being 0.999. The sensor's temporal response is 40 s at a sudden temperature change from 21 °C to 100 °C. The proposed sensor can be applied on reliable and precise temperature measurement.

Combined distributed Raman and Bragg fiber temperature sensing using incoherent optical frequency domain reflectometry

Abstract. Optical temperature sensors offer unique features which make them indispensable for key industries such as the energy sector. However, commercially available systems are usually designed to perform either distributed or distinct hot spot temperature measurements since they are restricted to one measurement principle. We have combined two concepts, fiber Bragg grating (FBG) temperature sensors and Raman-based distributed temperature sensing (DTS), to overcome these limitations. Using a technique called incoherent optical frequency domain reflectometry (IOFDR), it is possible to cascade several FBGs with the same Bragg wavelength in one fiber and simultaneously perform truly distributed Raman temperature measurements. In our lab we have achieved a standard deviation of 2.5 K or better at a spatial resolution in the order of 1 m with the Raman DTS. We have also carried out a field test in a high-voltage environment with strong magnetic fields where we performed simultaneous Raman and FBG temperature measurements using a single sensor fiber only.

Power Capacitor Temperature Measurement System Using FBG Sensors and Its Validation

It is difficult to accurately measure internal temperature of power capacitor. To accurately measure internal and external temperatures of an operating capacitor, a capacitor temperature measurement system based on fiber Bragg grating (FBG) temperature sensors is developed. First, technical parameters of the sensors and the optical sensing interrogator are determined according to the practical situations. Second, the sensors are calibrated using a highly accurate thermostatic bath, and their reproducibility is checked. Third, in combination with ENLIGHT software, the temperature measurement system based on FBG sensors is set up. Finally, three BAM6.56-556-1W high-voltage film capacitors are manufactured, and the FBG sensors are put into a high-voltage film capacitor and placed on its shell, the temperature distribution of the capacitor in the thermal stability test is measured. The corresponding temperature field model of the capacitor under the same conditions is created and solved in Fluent. The simulation results are consistent with the measured results, which validates the temperature measurement system. This paper fixes the problem of internal temperature measurement for high-voltage film capacitor which can be taken as a reference to online monitoring of power capacitor temperature.

Disilicate Dental Ceramic Surface Preparation by 1070 nm Fiber Laser: Thermal and Ultrastructural Analysis.

Lithium disilicate dental ceramic bonding, realized by using different resins, is strictly dependent on micro-mechanical retention and chemical adhesion. The aim of this in vitro study was to investigate the capability of a 1070 nm fiber laser for their surface treatment. Samples were irradiated by a pulsed fiber laser at 1070 nm with different parameters (peak power of 5, 7.5 and 10 kW, repetition rate (RR) 20 kHz, speed of 10 and 50 mm/s, and total energy density from 1.3 to 27 kW/cm2) and the thermal elevation during the experiment was recorded by a fiber Bragg grating (FBG) temperature sensor. Subsequently, the surface modifications were analyzed by optical microscope, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS). With a peak power of 5 kW, RR of 20 kHz, and speed of 50 mm/s, the microscopic observation of the irradiated surface showed increased roughness with small areas of melting and carbonization. EDS analysis revealed that, with these parameters, there are no evident differences between laser-processed samples and controls. Thermal elevation during laser irradiation ranged between 5 °C and 9 °C. A 1070 nm fiber laser can be considered as a good device to increase the adhesion of lithium disilicate ceramics when optimum parameters are considered.

Resolution enhancement of fiber Bragg grating temperature sensor using a cavity ring-down technique

A new technique for enhancing the measurement resolution of a fiber Bragg grating (FBG) temperature sensor is proposed. This technique uses a cavity ring-down approach to amplify optical intensity by accumulating unremarkable intensity changes. A wavelength-stabilized optical pulse with a width of 10 ns rotates several times inside an optical fiber loop that contains a FBG sensor. In other words, the loop system functions as an integrator of slight intensity transition. A temperature resolution of at least 0.02 °C was achieved at 20.0 °C. Resolution with this technique is at least five times higher than previous techniques.

Ionic Conductive Polyurethane-Graphene Nanocomposite for Performance Enhancement of Optical Fiber Bragg Grating Temperature Sensor

Polyurethane-graphene (PU-graphene) nanocomposite was utilized as the sensing material for a fiber Bragg grating (FBG) temperature sensor. The nanocomposite was characterized using a Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS) to study the morphology and physical properties of the materials for FBG temperature sensing application. The physical, chemical, and conductivity of PU-graphene improve after graphene was introduced in pristine PU. The FTIR shows that the strong intermolecular interaction between–O–C = O (ester) and hydrogen in graphene in the PU-graphene was indicated by the shift to lower wavenumber of ether (C–O–C) peak at ~1220 cm−1 to ~1218 cm−1. TGA shows the thermal stability of PU increases to 217 °C due to the strong intermolecular interaction with the presence of graphene flakes. EIS shows a good electrical conductivity of $1.39\times 10^{-9}$ Scm−1 in the PU-graphene due to the electron transfer provided by the graphene. The SEM shows a rough and uneven texture on the surface of FBG coated by PU-graphene nanocomposite which shows that the graphene flakes are completely coated by polyurethane polymer. The PU-graphene was then dip-coated on the optical fiber-based Bragg grating, and the sensor performance for a temperature sensor was evaluated, where a good linearity with the sensitivity of 6 pm/°C was achieved.

Experimental study on fibre Bragg grating temperature sensor and its pressure sensitivity

At present, ocean temperature almost depends on electric signal inspection, but the sensor is not safe in the water. In order to overcome this shortage and improve measurement veracity and safety, the temperature sensing theory of Bragg grating was analysed and a new ocean temperature sensor was presented with advantages of all optic elements, underwater safety and feasibility of sensor network, etc. By setting a spring in the metal tube, the temperature was measured with pressure isolation encapsulation. Multiple plus-minus temperature tests were carried out. Results show that the sensor under the condition of no pressure and the temperature of 0~35°C has an excellent repeatability, hysteresis and linearity. Temperature sensitivity is 29.9 pm/°C, which is close to the theoretical value. Pressure sensitivity tests were executed under the condition of 0~5 MPa. Results show that the wavelength has no change and is not affected by pressure.

Experimental study on fibre Bragg grating temperature sensor and its pressure sensitivity

At present, ocean temperature almost depends on electric signal inspection, but the sensor is not safe in the water. In order to overcome this shortage and improve measurement veracity and safety, the temperature sensing theory of Bragg grating was analysed and a new ocean temperature sensor was presented with advantages of all optic elements, underwater safety and feasibility of sensor network, etc. By setting a spring in the metal tube, the temperature was measured with pressure isolation encapsulation. Multiple plus-minus temperature tests were carried out. Results show that the sensor under the condition of no pressure and the temperature of 0~35°C has an excellent repeatability, hysteresis and linearity. Temperature sensitivity is 29.9 pm/°C, which is close to the theoretical value. Pressure sensitivity tests were executed under the condition of 0~5 MPa. Results show that the wavelength has no change and is not affected by pressure.

Meta-clay geopolymer as encapsulator of FBG temperature sensor

A study about design of temperature sensor system based on Fiber Bragg Grating (FBG) with encapsulation method has been conducted. Encapsulation of FBG used meta-clay geopolymer ceramic-tube. The results of the measurement showed that the coefficient of thermal expansion of the material was (α)-54.91 × 10−6 K−1. Chemical composition, crystallinity as well as surface morphology of ceramic-geopolymers were examined by using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). FBG sensor measurement performed at temperature from 50 °C to 250 °C. Characteristics of the FBG temperature sensor that used encapsulation method is obtained sensitivity 11 pm °C −1, linearity of 99,31% and good repeatability.

Structural health monitoring of a newly built high-piled wharf in a harbor with fiber Bragg grating sensor technology: design and deployment

Structural health monitoring (SHM) of civil infrastructure using fiber Bragg grating sensor networks (FBGSNs) has received significant public attention in recent years. However, there is currently little research on the health-monitoring technology of high-piled wharfs in coastal ports using the fiber Bragg grating (FBG) sensor technique. The benefits of FBG sensors are their small size, light weight, lack of conductivity, resistance corrosion, multiplexing ability and immunity to electromagnetic interference. Based on the properties of high-piled wharfs in coastal ports and servicing seawater environment and the benefits of FBG sensors, the SHM system for a high-piled wharf in the Tianjin Port of China is devised and deployed partly using the FBG sensor technique. In addition, the health-monitoring parameters are proposed. The system can monitor the structural mechanical properties and durability, which provides a state-of-the-art mean to monitor the health conditions of the wharf and display the monitored data with the BIM technique. In total, 289 FBG stain sensors, 87 FBG temperature sensors, 20 FBG obliquity sensors, 16 FBG pressure sensors, 8 FBG acceleration sensors and 4 anode ladders are installed in the components of the back platform and front platform. After the installation of some components in the wharf construction site, the good signal that each sensor measures demonstrates the suitability of the sensor setup methods, and it is proper for the full-scale, continuous, autonomous SHM deployment for the high-piled wharf in the costal port. The South 27# Wharf SHM system constitutes the largest deployment of FBG sensors for wharf structures in costal ports to date. This deployment demonstrates the strong potential of FBGSNs to monitor the health of large-scale coastal wharf structures. This study can provide a reference to the long-term health-monitoring system deployment for high-piled wharf structures in coastal ports.

Laboratory investigations of the thermal strain of frozen soils, using fiber-optic strain gauges based on Bragg gratings

Measurements of the thermal deformations of frozen soil samples were performed in the cold laboratory in temperature range from 0 °C to −12 °C. Fiber Bragg Gratings strain and temperature sensors were used to measure the deformation and temperature inside the samples. A number of tests with the samples prepared from Kaolin and Cambrian clay saturated with fresh water, and prepared from fine and silt sand saturated with fresh or saline water, are performed. Thermal deformations of the samples are analyzed depending on the cyclic changes of their temperature.