Fiber Bragg Grating-based Temperature Research Articles

Enhancing Sensitivity of Fiber Bragg Grating-Based Temperature Sensors through Teflon Coating

As global warming and climate change persistently threaten our planet, especially in developing countries, environmental monitoring becomes more and more imperative. One of the key parameters in estimating ecological disturbance due to climate change is temperature. In this work, we design a temperature sensor based on a fiber Bragg grating (FBG) and investigate the effect on its sensitivity upon applying a polymeric coating, and contrast it with different metal coatings. The reflected spectrum of an FBG has a narrow peak, corresponding to the Bragg wavelength, which is contingent on the grating period, grating length and effective refractive index. We simulate an outdoor ambient environment and examine the change in the peak reflected wavelength on variation in temperature. The shift in the peak for a unit change in temperature can be defined as the sensitivity of the FBG sensor. To enhance the sensitivity, we apply a uniform coating of Polytetrafluoroethylene (PTFE), more popularly known as Teflon. We also compare the sensitivity obtained on using PTFE coating with that through other materials, such as zinc, aluminum and stainless steel. It is visibly evident from this assessment that the coefficient of thermal expansion (CTE) has a significant effect on the sensitivity, when other physical and mechanical parameters are maintained constant. Since the CTE value is much higher for polymers than it is for metals, PTFE is able to provide a sensitivity of 0.3 nm/ °C, which is impressive when compared to zinc, the metal offering the highest sensitivity of around 0.079 nm/ °C. However, the CTE of PTFE itself varies with temperature, which is why we predict a sudden nonlinearity in the temperature dependence of the reflected wavelength, in an experimental scenario. Investigating this deviation leads us to the conclusion that, in the temperature range of 19–25 °C, PTFE undergoes two phase transitions from a triclinic to a hexagonal crystal phase, and subsequently to a pseudo-hexagonal phase. We calculate the sensitivities for the various phases of PTFE, and conclude that the high numerical and simulated values make this technology a promising application for futuristic purely optical sensors.

Machine Learning Assisted Fiber Bragg Grating-Based Temperature Sensing

This letter proposes an alternative approach to the signal processing of temperature measurements based on fiber Bragg gratings (FBGs) using the machine learning tool Gaussian process regression (GPR). The experimental results show that for a majority of the cases under consideration, the reported technique provides a more accurate calculation of the temperature than the conventional methods. Furthermore, the GPR can give the uncertainty of an estimate together with the estimate itself, which for example is useful when it is important to know the worst-case scenario of a measurand. The GPR also has the potential to improve the measurement speed of FBG-based temperature sensing compared to current standards.

A Novel Wireless Mobile Platform to Locate and Gather Data From Optical Fiber SensorsIntegrated Into a WSN

This paper presents a novel design for a wireless mobile platform to locate and gather data from different types of optical fiber sensors, thereby enabling the more effective integration of a number of such optical fiber sensors with an advanced mobile wireless sensor network (WSN). This then more readily permits potential applications, such as monitoring in remote and harsh environments and tracking, exploiting fully the combined advantages offered both by the mobile WSN and the advanced optical fiber sensing technologies. The platform which was designed and implemented consists of an optical fiber sensor module and a smart mobile WSN module, which shows important advantages for mobile sensing and tracking and mesh networking. In this paper, a fiber Bragg grating-based temperature sensor and an intrinsic pH optical fiber sensor were specially designed and integrated successfully into the optical fiber sensor module as an exemplar to investigate the performance of the integrated system based on the mobile WSN platform. The positive experimental results obtained have confirmed the functionality of the platform designed and demonstrated its capacity for real-time optical fiber sensor data monitoring, processing, and wireless transmission. The successful creation of this type of wireless mobile platform with optical fiber sensors can thus be expected to make an important impact on a number of sectors, where either conventional optical sensor designs or WSNs alone cannot meet the systems requirements.

Fiber Bragg Grating Cryosensors for Superconducting Accelerator Magnets

The design, fabrication, and tests of the new generation of superconducting magnets for the High Luminosity upgrade of the Large Hadron Collider (HL-LHC) require the support of an adequate sensing technology able to assure the integrity of the strain-sensitive and brittle superconducting cables through the whole service life of the magnet: assembly up to 150 MPa, cool down to 1.9 K, and powering up to about 16 kA. A precise temperature monitoring is also needed, in order to guarantee the safe working condition of the superconducting cables in the power transmission lines (SC-Link) designed to feed the magnet over long distance. Fiber Bragg Grating-based temperature and strain monitoring systems have been implemented in the first SC-Link prototype and in two subscale dipole magnets and tested in the cryogenic test facility at CERN, at 30 K, 77 K, and 1.9 K.

Characterization of Encapsulating Materials for Fiber Bragg Grating-Based Temperature Sensors

An experimental study has been carried out for the characterization of encapsulating materials for fiber Bragg grating-based temperature sensors to prevent the formation of micro-cracks and devitrification on the fiber surface at elevated temperatures by making use of a rigid probe. The developed sensor probe was configured by encapsulating a type 1 fiber Bragg grating with an aluminum nitride tube and is used to measure temperatures from 20°C to 500°C. The adapted encapsulation technique validated the sensor to achieve linearity of 99.979%, sensitivity of 14.03 ± 0.02 pm/°C, and good repeatability; its practical use in harsh environments is predicted.

Study of the nonuniform behavior of temperature sensitivity in bare and embedded fiber Bragg gratings: experimental results and analysis

This paper presents an experiment and analysis on the factors affecting nonlinear evolution of Bragg wavelength with change in temperature in typical bare and embedded fiber Bragg grating-based (FBG) temperature sensors. The purpose of the study was to find the constants in the function required to evaluate temperature from Bragg wavelength shift. The temperature sensitivity of bare FBGs was found to increase with temperature elevation, and is different for FBGs written in different fiber types. The average temperature sensitivity increased by about 20% when the bare FBG temperature was elevated from 25°C to 525°C. The average temperature sensitivity of the embedded FBG sensor, investigated in the temperature range of 30°C-90°C, was a factor of 2-3 times larger than for bare FBG, depending on its fastened length with the substrate. Analytically, it is shown that the nonuniform behavior of temperature sensitivity in bare FBGs is the result of both the thermal expansion effect of the fiber and the temperature derivatives of the effective refractive index. The strain transfer and temperature coefficients of thermal expansion of the substrate affect the nonuniform behavior of temperature sensitivity in embedded FBG sensors.

Non-terminal miniature fiber Bragg grating temperature probe based in a u-shape lossless taper

A novel miniature fiber Bragg grating-based temperature probe is presented. The sensor design integrates a u-shape lossless taper, thus offering the advantages of a terminal temperature probe while enabling effective serial multiplexing. We report on the experimental validation of the temperature probe design, demonstrating lossless operation and effective elimination of strain cross-sensitivity.

Miniature High-Temperature Fiber Bragg Grating Sensor Design Based on U-Shaped Lossless Taper for Thermal Mapping Applications

A novel design for a miniature fiber Bragg grating-based temperature probe is presented. The sensor integrates a u-shaped lossless taper thus offering the advantages of a terminal temperature probe free from of strain cross-sensitivity and showing installation flexibility while enabling effective serial multiplexing. The experimental validation of the probe design is reported, being demonstrated lossless operation and effective elimination of strain cross-sensitivity up to 400°C.