Fiber Temperature Research Articles

Research on spatial resolution improvement of distributed optical fiber temperature measurement based on Raman signal segmentation and reconstruction

Research on spatial resolution improvement of distributed optical fiber temperature measurement based on Raman signal segmentation and reconstruction

Study on the Performance of In-Line Closed-Loop Polarization Maintaining Fiber Temperature Sensor

Study on the Performance of In-Line Closed-Loop Polarization Maintaining Fiber Temperature Sensor

Temperature Monitoring in the Refractory Lining of a Continuous Casting Tundish Using Distributed Optical Fiber Sensors

This article explores the prospects of using spatially distributed optical fiber temperature sensors based on Rayleigh optical frequency domain reflectometry (OFDR) technology in the continuous casting of molten steel. The measurement capability of the optical fiber sensors in a simulated steelmaking environment was demonstrated using a mock refractory-lined tundish, which was fabricated in-house. Single-mode optical fibers, contained in protective stainless-steel tubing, were embedded in the refractory lining of the mock tundish. The instrumented tundish was preheated up to a temperature of 960 °C (recorded at the surface of the working lining) before the molten steel pour. A low-alloy steel (AISI 4140 grade) was melted in a 200 lb (90.7 kg) coreless induction furnace and was poured into the instrumented preheated tundish. The embedded optical fiber sensors were used to measure the temperature distribution in the castable lining during the preheating process of the tundish and during its contact with molten steel. Temperatures were metered with a spatial resolution of 0.65 mm along the embedded optical fibers. The measurements were recorded with an update rate of 1 Hz. The maximum temperature recorded by the optical fiber sensors in the castable lining after the steel pour was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$591^{\circ }\text{C}$ </tex-math></inline-formula> . The spatially continuous optical fiber sensors provided useful information on thermal gradients in the castable lining. Real-time monitoring of spatially distributed thermal profiles in the refractory lining can improve superheat control, reduce energy losses, detect refractory wear, and improve the quality of the cast.

Optical Fiber Temperature Sensor Based on PDMS-Filled Air-Cavity Fabry–Perot Structure

Optical Fiber Temperature Sensor Based on PDMS-Filled Air-Cavity Fabry–Perot Structure

Development of a Highly Sensitive and Low Hysteresis Temperature Sensing System With PEDOT:PSS Containing Polymer Sensing Membrane

In our study, we have designed and developed a side-polished optical fiber (SPOF) pulsewidth modulation (PWM)-based sensing system that can detect temperatures from 21 °C (room temperature) to 70 °C. According to the proposed SPOF PWM system, the received sensing signal pulsewidth changes if the optical fiber temperature sensing element (TSE) gets heat. The pulsewidth changes due to a change in the refractive index (RI) of the heat-sensitive polymer membrane of the SPOF TSE. We applied poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) as the primary temperature-sensitive sensing material to make the heat-sensitive polymer sensing membrane of the designed TSE. To the best of our knowledge, it is the first temperature sensing system/device where the optical sensing element uses PEDOT:PSS containing polymer sensing membrane and the optical PWM technique. The sensitivity and linearity of the designed TSE were approximately 960 ns/°C and 0.997, respectively. A microcontroller ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{C}$ </tex-math></inline-formula> ) and readily available electronic component-based light detection and signal processing unit were designed to process the received sensing signal. The proposed temperature sensing system has different features: low cost, susceptibility, excellent hysteresis response, good reproducibility, highly stable performance, and others. The proposed SPOF TSE offers first response and recovery times of approximately 2.59 and 3.14 s, respectively. Finally, in our study, we compared the sensing performance of the proposed TSE with other temperature sensors in terms of the temperature measurement range, linearity, and response/recovery time. We found that the overall sensing performance of the proposed TSE is better than the other temperature sensors.

Electrospinning of Softwood Organosolv Lignin without Polymer Addition

Due to its nature and structure, lignin is a very difficult polymer to electrospin without any additives as only a few studies reported on the successful electrospinning of lignins in general and even more limited for softwood lignins to date. This paper highlights the possibility to use softwood organosolv lignin as a precursor for fiber electrospinning without any polymer addition. We have successfully electrospun pure organosolv softwood lignin into uniform, bead-free fibers. A concentration of 57 wt % of lignin in dimethyl formamide was determined as optimal, while other processing parameters (voltage, needle–collector distance, flow rate, and humidity) were studied to improve the fiber uniformity. We also studied the effects of minimum FeCl3 addition and demonstrated its efficiency in improving the processability. Thus, the addition of 2 wt % FeCl3 allowed decreasing the minimum fiber diameter from 400 to 200 nm. The addition of FeCl3 also resolved the problem of fiber fusion on the collector, and it also allowed increasing the glass transition temperature of lignin fibers. These results open a way to new applications of lignin, such as 100% biosourced carbon fiber since no petroleum-sourced molecules were used in this study.

Experimental Study on Mechanical Properties of Basalt Fiber Concrete after Cryogenic Freeze-Thaw Cycles.

Basalt fiber (BF) has received much attention in recent years for engineering practice and scientific research related to basalt fiber reinforced concrete (BFRC) due to its advantageous mechanical properties and cost-effectiveness. By researching its performance characteristics after cryogenic freeze-thaw cycles, the advantages of BFRC's mechanical properties can be further exploited in order to expand its application scope. The effects of the fiber volume fraction, temperature gradient, and number of freeze-thaw cycles on the compressive strength, toughness index, splitting tensile strength, flexural strength, etc., of BFRC were investigated. Additionally, the damage mechanism of BFRC after freeze-thaw cycles was analyzed via scanning electron microscopy (SEM). The results show that the compressive strength of BFRC reaches its peak value when the fraction reaches 0.1% under the conditions of freezing and thawing cycles from room temperature to -80 °C. When the fraction of BFRC is 0.1%, and the maximum reduction is 17.1%, the splitting tensile strength decreased most sharply when the fraction was 0.1%, and the decrease amplitude was 40.9%, and the flexural strength decreased most acutely when the fraction was 0.3%, and the maximum decrease was 44.62%. The addition of basalt fibers can reduce the damage to the microstructure of concrete and improve its plastic degradation characteristics to a certain extent. With a decrease in the minimum temperature of the cryogenic freeze-thaw cycle, the optimal fiber content for compressive strength increases. Nevertheless, the splitting tensile strength and flexural strength of BFRC is improved as the fiber content increases under the cryogenic freeze-thaw environment.

Initiation and propagation fracture toughness of injection-moulded short fibre composites under different environmental conditions

Injection-moulded short-fibre composites combine lightweight and manufacturability; however, their fracture behaviour and how it is affected by the microstructure and environmental conditions are yet to be fully characterised. The initiation and propagation fracture toughnesses of injection-moulded short glass-fibre reinforced polyamide 6.6 composites were characterised through compact tension testing under the combined effect of fibre orientation, moisture level and temperature. Full R-curves were calculated using either an FE-based compliance calibration method, or the J-integral method based on full-field measurements from Digital Image Correlation; both data reduction methods provided consistent propagation values for the fracture toughness, although only the J-integral method can characterise the initiation toughness and the shape of R-curves reliably. This work revealed that the material became tougher with increasing fibre orientation along the loading direction, increasing moisture content, and/or increasing temperature; the corresponding increase in toughness was related to changes in failure and toughening mechanisms, identified through fractography. FE simulations of the compact tension tests have demonstrated the need to consider both initiation and propagation values of fracture toughness to accurately predict the response of notched specimens. The thorough characterisation of fracture toughness presented in this paper can contribute to design safer and more efficient damage-tolerant IM-SFRP components.

Stationary Random Vibration Analysis of Composite Laminated Shell Structures of Revolution in Thermal Environment

Currently, few studies are focused on the stationary random vibration for composite laminated shell structures of revolution (CLSSR), including composite laminated cylindrical shell (CLCY), composite laminated conical shells (CLCO), and composite laminated annular plates (CLAP). To fill this void corresponding to the above research in the literatures, a combination of the spectro-geometric method (SGM) and pseudo-excitation method (PEM) was developed to construct the theoretical model within the first-order shear deformation theory (FSDT). The different boundary restraints and coupling conditions were achieved by taking the appropriate stiffness values of artificial springs, and the thermal effect induced by thermal load was considered. Moreover, the Rayleigh–Ritz method was employed to deduce the governing differential equation. Further, the solution accuracy of the established model was assessed by comparing the obtained results with those from the literatures and the finite element method (FEM). Finally, the effect of specific parameters (i.e. fiber angle, temperature value and ply number) on the stationary random response of CLSSR was explored. According to the results, the proposed method proved effective for predicting the stationary random response characteristics of CLCY, CLCO, and CLAP in a thermal environment.

Fiber Temperature Sensor Based on Vernier Effect and Optical Time Stretching Method.

A novel method for ultra-sensitive and ultra-fast temperature sensing has been successfully implemented by cascading Saganc rings to generate the Vernier effect and doing the same dispersive fibers to achieve the optical time-stretching effect. This is different from the traditional point fiber sensor demodulated by optical spectrum analyzer (OSA) whose demodulation speed is usually at the second level. The designed system maps the wavelength domain to the time domain through the dispersive fiber, which can realize the ultra-fast temperature monitoring at the nanosecond level. The cascaded Sagnac ring is composed of polarization maintaining fiber (PMF) which is significantly affected by the thermal-optical coefficient. When the temperature changes, the variation is as high as -6.228 nm/°C, which is 8.5 times higher than the sensitivity based on the single Sagnac ring system. Furthermore, through the optical time stretching scheme, the corresponding response sensitivity is increased from 0.997 ns/°C to 7.333 ns/°C, and the magnification is increased 7.4 times with a response speed of 50 MHz.

Quad core gold coated photonic crystal fiber temperature sensor based on surface plasmon resonance

This paper shows a simple quad core Photonic Crystal Fiber (PCF) temperature sensor based on Surface Plasmon Resonance (SPR) which has very high sensitivity and sensor resolution. For evaluating the sensing performance Finite Element Method (FEM) is used. In this design, gold is used as plasmonic material and the outer layer of the designed PCF has to be filled by it for making the fabrication easier than any other model. Besides, the Chloroform is used as the temperature sensitive liquid (analyte). The designed temperature sensor has the maximum wavelength sensitivities which are 7.5 nm/°C and 10.5 nm/°C for x and y-polarization respectively. The sensor shows the resolution of 13.33 × 10−3 RIU for x-polarization and 9.52 × 10−3 RIU for y-polarization. Core diameter, radius of air hole, thickness of gold and pitch are the structural parameters which are adjusted to their optimized value for getting higher sensitivity. Easy fabrication and simplicity are the major aspects of this proposed model which makes it applicable to various applications such as medical science, power plant, engineering sector, environment monitoring etc.

The research on improving the spatial resolution of radiant optical fiber temperature sensor

A method to improve the spatial resolution of the radiant optical fiber temperature sensor is proposed in this paper. The front lens of the sensor is designed to limit the diameter of the thermometry target. In order to avoid limiting the influence of the thermometry target diameter on the sensor radiation-light coupling ability, a mathematical model of the radiation-light coupling of the sensor is established, and the relationship between the radiation-light coupling ability of the sensor and the diameter of the thermometry target is analyzed. Furthermore, an aspheric lens is applied to reduce the influence of aberration on the diameter of the thermometry target. The experimental results show that the deviation between the actual temperature measuring target diameter and the theoretical design value is less than 0.2 mm. The radiation received by the sensor outside the temperature measuring target is less than 10% of its total received radiation. Moreover, when there is radiated light interference outside the temperature measurement target, the temperature measurement error of the sensor is only 0.21%–2.61%, indicating that the proposed method has practical significance in improving the spatial resolution of the temperature measurement.

A calibration-free fiber sensor based on CdZnSe/ZnSe/ZnS quantum dots for real-time monitoring of human thermal activities

A calibration-free fiber sensor based on CdZnSe/ZnSe/ZnS quantum dots (QDs) was proposed. The sensor was fabricated by filling fully a thick hollow core fiber (HCF) with QDs solutions and fused tapering to seal the micro-cavity subsequently. Results showed that sensors with different cavity lengths can provide a similar temperature sensitivity of 0.12 nm/°C with an excellent linearity. Compared with sensors based on the interference and grating, the temperature demodulation function is universal due to a fact that fluorescence wavelengths changed by temperatures are only related to QDs materials, independent of the cavity length and the excitation power, so the sensor can be calibration-free, providing an idea and the technology for the calibration-free work of optical fiber temperature sensor in the future. Furthermore, the sensor exhibiting an excellent stability and repeatability can monitor thermal signals generated by human activity in real-time.

Sensitivity-enhanced temperature sensor utilizing core offset and hollow core Bragg fiber

A novel sensitivity-enhanced optical fiber temperature sensor (OFTS) utilizing core offset and hollow core Bragg fiber (HCBF) is proposed and experimentally investigated. The OFTS was fabricated by sandwiching the HCBF between two single-mode fibers (SMFs). The operation principle of temperature sensitivity enhancement is to excite inter-modal interference by lateral offset splicing fibers. The four-cladding structure unique to HCBF induces periodic interference envelopes in the transmission spectrum, which can be used to monitor changes in the external environment. The experimental results show that the temperature and strain sensitivities of OFTS is 10.27 pm/°C and −4.03 × 10−4 nm/με, respectively. After introducing different core offsets, the temperature sensitivities are improved to 16.29 pm/°C, 18.29 pm/°C, and 30.03 pm/°C, respectively. The strain sensitivities are −1.98 × 10−4 nm/με, −4.33 × 10−4 nm/με, and −4.96 × 10−4 nm/με, respectively. Moreover, due to the high-temperature sensitivity, strain insensitivity, and compact structure, the proposed sensor has broad application prospects in complex environments such as aerospace.

Improved wavelet modulus maximum method for distributed optical fiber temperature sensing

The temperature measurement accuracy of the Raman distributed optical fiber temperature sensing system is an important metric. Aimed at the reduction of the temperature measurement error, which is caused by the noises in the sensor system, an improved wavelet modulus maximum method, which combine the 3sigm criterion with the traditional wavelet modulus maximum algorithm is proposed. In this proposed algorithm, the 3sigm value is used as the threshold for the highest decomposition layer of the wavelet modulus maximum method to judge whether it is a signal or noise, instead of using the ratio of the modulus maximum of the highest decomposition level to the number of decomposition levels to determine the threshold. We conduct distributed temperature measurement on a 10-km long multimode fiber, and analyze the experimental data by using the improved algorithm. The results show that the temperature measurement fluctuation obtained by improved method is 0.497°C on average. It is better than the 1.13°C that is obtained by the traditional wavelet modulus maximum algorithm. Compared with the traditional algorithms, the 3sigm criterion algorithm has improved the temperature measurement accuracy significantly. The improved algorithm provides a new idea for the selection of the threshold value, which makes the threshold selection more statistically.

Influence of Different Heat Loads and Durations on the Field Thermal Response Test

Geothermal energy exhibits considerable development potential in space heating. Shallow geothermal energy stored in the soil in the form of low-grade energy is mainly extracted via the ground source heat pump (GSHP) system. GSHP systems use the subsoil as a heat source, typically involving a vertical borehole heat exchanger (BHE) to extract heat from the formation. Accurate measurement of the thermal properties of the formation is very important for the design of BHEs. At present, the most common and effective method to measure the thermal conductivity of the formation in the field is the thermal response test (TRT). However, the test conditions (heat load, test time) during the thermal response test can impact the test results. Therefore, in this study, a borehole with a depth of 130 m was evaluated in the field. The TRT module and the distributed thermal response test (DTRT) module based on distributed optical fiber temperature sensor (DOFTS) technology were used to monitor the test with different working conditions in real-time. In the field tests, geothermal conditions and the evolution of the formation temperature with time and depth were determined. Based on the test results under different heat loads and test times, the influence of the test conditions on the thermal conductivity results was analyzed and described. A constant temperature zone was located at a depth from 25 m to 50 m, and an increasing temperature zone was located at a depth from 50 m to 130 m, with a geothermal gradient of 3 °C/100 m. The results showed that the heat load slightly influenced the thermal conductivity test results. At the initial stage of the test, the temperature significantly increased from 0 to 12 h. After reaching the quasi-stable state, the test time slightly influenced the thermal conductivity test results. The characteristics of the formation thermal recovery stage after the test stage were studied. The heat load decreased, which could shorten the time for the formation to recover the initial temperature. The results could provide a basis for the optimization of thermal response test conditions.

A hybrid distributed optical fiber vibration and temperature sensor based on optical Rayleigh and Raman scattering

A hybrid distributed optical fiber vibration and temperature sensing system is proposed and experimentally demonstrated. By the system structure of optical time domain reflectometer (OTDR) and wavelength division method, the Rayleigh and Raman scattering light in multi-mode fiber (MMF) are extracted respectively for fiber vibration event detection and hot spot monitoring. The vibration event causes the polarization state and phase of the optical signal propagating in MMF to change, which makes the OTDR trace become smooth from the vibration position to the fiber end, so that it provides a reliable way to locate the vibration events. And then, a data processing method that averages the data within the vibration position and at least 50 continuous positions behind is proposed to improve the signal to noise ratio (SNR) of the vibration signal and finally by fast Fourier transform (FFT), the vibration spectrum is accurately obtained. In addition, the backscattered Raman Stokes and anti-Stokes signals are separated by the wavelength division multiplexer (WDM) and then they are converted into voltage signals. By conventional temperature demodulation algorithm, the temperature information along the MMF is obtained with measurement accuracy of about 1.5 °C. The experimental results show that the proposed hybrid distributed vibration and temperature sensing system possess good performance and as it is compatible with MMF that has been laid on the power cable, it is of great significance for engineering application.

Optical fiber temperature sensor based on Fabry-Perot interferometer with photopolymer material

We propose and demonstrate a new method for fabricating a Fabry-Perot interferometer sensor. This work uses photopolymerizable materials to construct Fabry-Perot interference structures, making the fabrication process more straightforward and less expensive than other methods. We put a 532 nm laser into the single-mode fiber (SMF) to fabricate photopolymer probes on the face of the fiber. The end face of the probe and the end face of the SMF will form a Fabry-Perot interferometer (FPI). At the same time, to demonstrate its ability to be easily fabricated for sensing various parameters, we incorporated PDMS into the photopolymer material and conducted temperature sensing experiments. The relationship between the concentration of the PDMS and the temperature sensitivity is studied. The experimental results show that the higher the concentration of PDMS, the higher the temperature sensitivity. In the case of ensuring other capabilities, the sensitivity has reached − 1.18 nm/°C in the temperature range of 20–110 °C. We propose and demonstrate a new method for fabricating a Fabry-Perot interferometer sensor. This work uses photopolymerizable materials to construct Fabry-Perot interference structures, making the fabrication process more straightforward and less expensive than other methods. We put a 532 nm laser into the single-mode fiber (SMF) to fabricate photopolymer probes on the face of the fiber. The end face of the probe and the end face of the SMF will form a Fabry-Perot interferometer (FPI). At the same time, to demonstrate its ability to be easily fabricated for sensing various parameters, we incorporated PDMS into the photopolymer material and conducted temperature sensing experiments. The relationship between the concentration of the PDMS and the testing sensitivity is studied. The experimental results show that the higher the concentration of PDMS, the higher the testing sensitivity. In the case of ensuring other capabilities, the sensitivity has reached − 1.20507 nm/°C in the temperature range of 20–80 °C. • This work uses a free-radical photopolymerizable formulation is sensitive between 450 and 550 nm and converted through a free-radical cross-linking polymerization under green light irradiation, which can easily fabricate waveguide structure on the fiber end face. • This photopolymeriazble formulation allows us to add different sensitive materials for the purpose of making different sensors. • We add PDMS into the photopolymeriazble formulation to measure the temperature. In the temperature range of 20–80 °C, the sensitivity reached − 1.20507 nm/°C and demonstrates good stability.

Influence of thermal moisture impact on the structure and properties of polyimide carbon fiber

The article studies influence of laboratory-simulated external influencing operational factors – water and moisture saturation, combined effect of elevated temperature and humidity, exposure in a tropical climate chamber on the properties of high-temperature carbon fiber based on a melted thermosetting polyimide binder. Studies of the structure, glass transition temperature and elastic-strength characteristics of carbon fiber after exposure were carried out, the change in the mass of carbon fiber samples during long-term exposure to water and moisture was estimated.

A Case Study of Field Thermal Response Test and Laboratory Test Based on Distributed Optical Fiber Temperature Sensor

To design an efficient ground source heat pump (GSHP) system, it is important to accurately measure the thermophysical parameters of the geotechnical layer. In the current study, a borehole is tested in detail using a combined thermal response test system (CTRTS) based on a distributed optical fiber temperature sensor (DOFTS) and a laboratory test. Real-time monitoring of the stratum temperature according to depth and operation time and the geothermal profile and thermal conductivity of each stratum are obtained. The results show that the undisturbed ground temperature is 10.0 °C, and the formation temperature field within 130 m can be divided into variable temperature formation, constant temperature formation (9.13 °C), and warming formation (geothermal gradient is 3.0 °C/100 m). The comprehensive thermal conductivity of the region is 1.862 W/m·K. From top to bottom, the average thermal conductivity of silty clay, mudstone, argillaceous siltstone, and mudstone is 1.631 W/m·K, 1.888 W/m·K, 1.862 W/m·K, and 2.144 W/m·K, respectively. By comparing the measurement results, the accuracy and effectiveness of the CTRTS are verified. Therefore, it is recommended to use the thermal conductivity obtained by the CTRTS to optimize the design of the borehole heat exchanger (BHE). This study provides a case for establishing a standard distributed thermal response test (DTRT).