LOFTS: Liquid core capillary based optical fiber fluorescence temperature sensor

PDMS-based liquid-core optical fiber fluorescence pressure sensor

PurposeThere are various temperature measuring systems presented in the literature and on the market today. Over the past number of years a range of luminescent‐based optical fibre sensors have been reported and developed which include fluorescence and optical scattering. These temperature sensors incorporate materials that emit wavelength shifted light when excited by an optical source. The majority of commercially available systems are based on fluorescent properties.Design/methodology/approach– Many published journal articles and conference papers were investigated and existing temperature sensors in the market were examined.Findings– In optical thermometry, the light is used to carry temperature information. In many cases optical fibres are used to transmit and receive this light. Optical fibres are immune to electromagnetic interference and are small in size, which allows them to make very localized measurements. A temperature sensitive material forms a sensor and the subsequent optical data are transmitted via optical fibres to electronic detection systems. Two keys areas were investigated namely fluorescence based temperature sensors and temperature sensors involving optical scattering.Originality/value– An overview of optical fibre temperature sensors based on luminescence is presented. This review provides a summary of optical temperature sensors, old and new which exist in today's world of sensing.

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.

A dual spherical single-mode-multimode-single-mode (DSSMS) optical fiber temperature sensor based on a Mach–Zehnder interferometer (MZI) was designed and implemented in this paper. Theoretical and experimental results indicated that the LP01 mode in the core and the LP09 mode excited by the spherical structure were maintained and transmitted via multimode fiber and interfered at the second spherical structure, resulting in the interference spectrum. An increase or decrease in temperature can cause significant red-shift or blue-shift of the spectrum, respectively. The linearity of the spectral shift due to the temperature change is ~0.999, the sensitivity at 30 °C–540 °C is ~37.372 pm °C−3, and at −25 °C–25 °C is ~37.28 pm °C−1. The reproducibility error of this all-fiber temperature sensor at 30 °C–540 °C is less than 0.15%. Compared with the optical fiber sensor with a tapered structure and fiber core offset structure, this MZI-based DSSMS optical fiber temperature sensor has higher mechanical strength. Moreover, benefiting from low-cost and environmentally friendly materials, it is expected to be a novel micro-nano all-fiber sensor.

Photothermal sensing is crucial for the creation of smart wearable devices. However, the discovery of luminescent materials with suitable dual-wavelength emissions is a great challenge for the construction of stable wearable optical fibre temperature sensors. Benefiting from the Mn2+-Mn2+ superexchange interactions, a dual-wavelength (530/650 nm)-emitting material Li2ZnSiO4:Mn2+ is presented via simple increasing the Mn2+ concentration, wherein the two emission bands have different temperature-dependent emission behaviours, but exhibit quite similar excitation spectra. Density functional theory calculations, coupled with extended X-ray absorption fine structure and electron-diffraction analyses reveal the origins of the two emission bands in this material. A wearable optical temperature sensor is fabricated by incorporating Li2ZnSiO4:Mn2+ in stretchable elastomer-based optical fibres, which can provide thermal-sensitive emissions at dual- wavelengths for stable ratiometric temperature sensing with good precision and repeatability. More importantly, a wearable mask integrated with this stretchable fibre sensor is demonstrated for the detection of physiological thermal changes, showing great potential for use as a wearable health monitor. This study also provides a framework for creating transition-metal-activated luminescence materials.

In this study, we have prepared the optical fiber temperature sensor using CdSe/ZnS Quantum Dots (QDs) as sensing media. QDs have been immobilized on the surface of tapered fiber tip, and the dependence of fluorescence intensity on ambient temperature has been investigated. The surface of the optical fiber has been silanized using 3-aminopropyltriethoxysilane (APTES) which has amine functional group. QDs with carboxyl functional group have been immobilized by EDC/NHS coupling reaction. After drying with nitrogen blowing, QDs immobilization has been confirmed by photoluminescence spectroscopy (PL) and fluorescence microscope. Green, yellow, and red emission was observed depending on the size of QDs. The photoluminescence (PL) spectra were obtained with ambient temperature in the range of 25–125°C. Linear dependence of PL intensity on temperature has been observed from optical fibers where CdSe/ZnS QDs with green and yellow emission are immobilized. This shows that optical fiber temperature sensor can be fabricated using QDs as sensing media.

The chemistry of sol-gel derived silica and refractive metal oxide has been systematically studied. Sol-gel processes have been developed for preparing porous silica and semiconductor metal oxide materials. Micelle/reversed micelle techniques have been developed for preparing nanometer sized semiconductor metal oxides and noble metal particles. Techniques for doping metal ions, metal oxides and nanosized metal particles into porous sol-gel material have also been developed. Optical properties of sol-gel derived materials in ambient and high temperature gases have been studied by using fiber optic spectroscopic techniques, such as fiber optic ultraviolet/visible absorption spectrometry, fiber optic near infrared absorption spectrometry and fiber optic fluorescence spectrometry. Fiber optic spectrometric techniques have been developed for investigating the optical properties of these sol-gel derived materials prepared as porous optical fibers or as coatings on the surface of silica optical fibers. Optical and electron microscopic techniques have been used to observe the microstructure, such as pore size, pore shape, sensing agent distribution, of sol-gel derived material, as well as the size and morphology of nanometer metal particle doped in sol-gel derived porous silica, the nature of coating of sol-gel derived materials on silica optical fiber surface. In addition, the chemical reactions of metal ion, nanostructured semiconductor metal oxides and nanometer sized metal particles with gas components at room temperature and high temperatures have also been investigated with fiber optic spectrometric methods. Three classes of fiber optic sensors have been developed based on the thorough investigation of sol-gel chemistry and sol-gel derived materials. The first group of fiber optic sensors uses porous silica optical fibers doped with metal ions or metal oxide as transducers for sensing trace NH{sub 3} and H{sub 2}S in high temperature gas samples. The second group of fiber optic sensors uses sol-gel derived porous silica materials doped with nanometer particles of noble metals in the form of fiber or coating for sensing trace H{sub 2}, NH{sub 3} and HCl in gas samples at for applications ambient temperature. The third classes of fiber optic sensors use sol-gel derived semiconductor metal oxide coating on the surface of silica optical fiber as transducers for selectively sensing H{sub 2}, CH{sub 4} and CO at high temperature. In addition, optical fiber temperature sensors use the fluorescence signal of rare-earth metal ions doped porous silica optical fiber or the optical absorption signal of thermochromic metal oxide materials coated on the surface of silica optical fibers have also been developed for monitoring gas temperature of corrosive gas. Based on the results obtained from this project, the principle of fiber optic sensor techniques for monitoring matrix gas components as well as trace components of coal gasification derived syngas has been established. Prototype sensors for sensing trace ammonia and hydrogen sulfide in gasification derived syngas have been built up in our laboratory and have been tested using gas samples with matrix gas composition similar to that of gasification derived fuel gas. Test results illustrated the feasibility of these sensors for applications in IGCC processes.

This paper presents the findings of a project sponsored by the BP Technology Innovation Board with the objective of developing a technology for continuously monitoring casing and completion mechanical deformation in intelligent wells. The innovation idea: " a permanent strain-sensing system in intelligent wells to continuously monitor the axial, lateral and cross-sectional deformation of casing and completion, with the desire to have the combined features of gyroscope, multifinger caliper, radioactive logs, and conventional mechanical deformation monitoring systems" was proposed to and funded for research by the BP Technology Innovation Board in 2000. The preliminary development evaluation was completed in late 2002. Production from soft reservoirs can suffer significant compaction resulting in casing and completion damage. This often leads to well failures with the consequent production loss and costs of replacement or repair. Current reservoir compaction and wellbore deformation monitoring technologies suffer from several drawbacks. A new technology is needed that combines characteristics of long distance profile sensing, 2 to 3 feet spatial resolution, the ability to measure large deformation (at least 2% strain), and multiple deformation modes. Based on a review of available sensing technologies, Sensornet's DTSS (simultaneous Distributed Temperature and Strain Sensing) technology18,19,20 was selected for the evaluation as it appeared to meet some special sensing requirements of this application. A large scale mechanical test (15 feet long, 7 inch OD, P110 casing deployed with both fiber optic sensors and conventional strain gauge rosettes) was designed and executed with the aim of evaluating:the capability and technical limit of the DTSS technology for large and sophisticated strain profile sensing;the effectiveness of load transfer; andthe reliability of the designed downhole sensing system. The experiments produced some very interesting results:It was for the first time, to our knowledge, that pure mechanical compressional strain was directly measured (without the need for pre-tensioning the fiber) by a fiber sensor using Brillouin scattering;For the first time temperature and sophisticated deformation modes were simultaneously and independently measured in a single fiber;The DTSS system measured strain up to the breaking point of the casing testing system (2.83% stretch), which is the largest strain ever published in the literature measured by fiber sensor. The experiments also helped to outline further work needed for adopting this technology for downhole applications. Introduction Production from soft reservoirs, especially those that are over pressured and thick, can cause significant amounts of reservoir compaction, leading to surface subsidence, overburden deformation, casing damage (offset, bending, crushing/ovalization, and restricted entry, see Figure 1), and well failures (lost access to the well due to severe casing damage such as severing of casing in the overburden, casing and completion buckling/collapse in the producing intervals resulting in completion failure such as loss of sand control integrity, and intolerable annular pressure build up due to loss of seal integrity, see Figure 2)1–6.

A wide range of applications such as healthcare, human comfort, agriculture, food processing and storage, and electronics manufacturing also require fast and accurate measurement of humidity and temperature. Optical fiber-based sensors have several advantages over electronic sensors, and much research has been conducted in this area in recent years. This paper describes the current trends in fiber optic temperature and humidity sensors. The evolution of optical structures aimed at humidity detection is presented, as well as a new design of an optical sensor used for this purpose. The main methods of humidity determination using fiber-optic laser reflection based on Optical fiber humidity sensor (FPI) were analyzed and experimental results were obtained. Based on temperature-sensitive strain variation, a method for temperature determination based on the specific spectral back-reflection effect of fiber Bragg gratings (FBGs) is considered. Experimental analyses were conducted on the light reflection of humidity-sensitive agarose using optical fibers based on the Fabry-Perot Interferometer (FPI). It exhibits a good linear response to relative humidity, ranging from 25 % to 95 %. During temperature measurement, the deformation changes of the Fiber Bragg Grating fibers showed excellent performance, ranging from –5 °C to 70 °C. New structures, such as resonators, are being explored to improve the resolution of fiber optic temperature and humidity sensors. In addition, recent studies on polymer optical fibers show that the sensitivity of this type of sensor has not yet been achieved. Thus, materials sensitive to humidity and temperature still need to be investigated to improve sensitivity and resolution

Optical fiber temperature sensors can provide accurate temperature information and adapt to different temperature environments well, so they have been widely used. Traditional optical fiber temperature sensors depend upon optical fiber grating or nonlinear back scatting, both of which need complex measurement systems and high cost. So, a simple and chip temperature sensing method was put forward based on fiber delay technology, and the temperature information was obtained by measuring additional delay of optical signal in fiber. Establishing an experiment system by using the frequency domain phase method, we obtained the delay coefficient which describes the relationship between delay and temperature, so that the feasibility of the method was proved.

This paper introduces the use of a Rayleigh backscatter-based distributed fiber optic sensor to map the temperature field in air flow for a thermal fatigue application. The experiment involves a pair of air jets at 22 and 70 °C discharging from 136 mm hexagonal channels into a 1 × 1 × 1.7 m tank at atmospheric pressure. A 40 m-long, ϕ155 µm fiber optic sensor was wound back and forth across the tank midplane to form 16 horizontal measurement sections with a vertical spacing of 51 mm. This configuration generated a 2D temperature map with 2800 data points over a 0.76 × 1.7 m plane. Fiber optic sensor readings were combined with PIV and infrared measurements to relate flow field characteristics to the thermal signature of the tank lid. The paper includes sensor stability data and notes issues encountered using the distributed temperature sensor in a flow field. Sensors are sensitive to strain and humidity, and so accuracy relies upon strict control of both.

Sensor technology has been applied widely. Optical fiber sensor has lots of advantages: high sensitivity, long measurement length, high geometric plasticity, has become a hot research topic in sensor technology. Since modern industrial depends on temperature measurement at a large extent, it is significant for the research of optical fiber temperature sensor system. In this paper, the implementation of algorithm used in distributed optical fiber sensor system was discussed.

The objective of the work presented was to develop a high-frequency total temperature sensor based on Luna Innovations’ optical fiber temperature sensor. The intended application is the characterization of inlet pressure and temperature distortions utilized to test hot gas ingestion performance of air-breathing propulsion. The sensors described here measured total temperature changes of nearly 200 °R (111°C) with transients exceeding 20,000 °R per second (11,111°C/s) in wind tunnel experiments at M0.65. The optical fiber sensors are better than 6 times faster than fine-wire thermocouple total temperature probes. Finally, initial algorithm work towards minimizing the total temperature time response is presented. The data obtained from these sensors will improve the design of emerging gas turbines providing key data for analysis of off-specification performance and CFD model verification. The probes represent the state-of–the-art in total temperature measurement and will have a significant impact on the aerospace propulsion instrumentation industry.

In a distributed fiber optic temperature sensing system, the intensity of Raman Stokes backscattering light serving as reference light increases with the increase of temperature, leading to measurement errors in the system. A novel method of dynamically calibrating Raman Stokes backscattering light intensity is proposed to improve temperature accuracy for distributed fiber optic temperature sensors. According to the real-time Stokes intensity distribution in the reference fiber, Stokes intensity curve of the whole fiber at a reference temperature is simulated, and the temperature response of Stokes light is corrected. The ratio of Raman anti-Stokes light intensity to the calculated Stokes light intensity is used to demodulate temperature along the fiber. The experimental results indicate that the temperature accuracy of the distributed optical fiber temperature sensor system after making the Stokes optical dynamic calibration is increased up to 4.3 ℃ compared with that from the conventional method. And the accuracy of temperature measurement is improved by 8.9 ℃ when combined with Rayleigh noise suppression method. This study provides a new solution for a distributed fiber optic temperature sensor system to monitor high temperature environment temperature.

This paper demonstrates the development of optical temperature sensor based on the etched silica-based planar waveguide Bragg grating. Topics include design and fabrication of the etched planar waveguide Bragg grating optical temperature sensor. The typical bandwidth and reflectivity of the surface etched grating has been ∼0.2 nm and ∼9 %, respectively, at a wavelength of ∼1552 nm. The temperature-induced wavelength change is found to be slightly non-linear over ∼200 °C temperature range. Typically, the temperature-induced fractional Bragg wavelength shift measured in this experiment is 0.0132 nm/°C with linear curve fit. Theoretical models with nonlinear temperature effect for the grating response based on waveguide and plate deformation theories agree with experiments to within acceptable tolerance.