Silicon Carbide-Based Extreme Environment Hybrid Design Temperature Sensor Using Optical Pyrometry and Laser Interferometry

To the best of the authors' knowledge, proposed and demonstrated is the first extreme environment temperature sensor using Blackbody (BB) radiation of a high-temperature material optical chip for coarse temperature measurement and classical Fabry-Perot (FP) laser interferometry via the same chip for fine temperature measurement. Such a hybrid design sensor can be used to accurately measure temperatures in excess of 750°C such as needed for gas turbines in power plants and aircraft engines. The proposed sensor is designed and demonstrated using an all-Silicon Carbide (SiC) probe for temperatures from 795°C to 1077°C with an estimated average measurement resolution of 0.1°C.     

Surface-mount sapphire interferometric temperature sensor

A fiber-optic high-temperature sensor is demonstrated by bonding a 45 degrees -polished single-crystal sapphire fiber on the surface of a sapphire wafer, whose optical thickness is temperature dependent and measured by white-light interferometry. A novel adhesive-free coupling between the silica and sapphire fibers is achieved by fusion splicing, and its performance is characterized. The sensor's interference signal is investigated for its dependence on angular alignment between the fiber and the wafer. A prototype sensor is tested to 1,170 degrees C with a resolution of 0.4 degrees C, demonstrating excellent potential for high-temperature measurement.     

High-temperature langatate elastic constants and experimental validation up to 900°C

This paper reports on a set of langatate (LGT) elastic constants extracted from room temperature to 1100°C using resonant ultrasound spectroscopy techniques and an accompanying assessment of these constants at high temperature. The evaluation of the constants employed SAW device measurements from room temperature to 900°C along 6 different LGT wafer orientations. Langatate parallelepipeds and wafers were aligned, cut, ground, and polished, and acoustic wave devices were fabricated at the University of Maine facilities along specific orientations for elastic constant extraction and validation. SAW delay lines were fabricated on LGT wafers prepared at the University of Maine using 100-nm platinum rhodium- zirconia electrodes capable of withstanding temperatures up to 1000°C. The numerical predictions based on the resonant ultrasound spectroscopy high-temperature constants were compared with SAW phase velocity, fractional frequency variation, and temperature coefficients of delay extracted from SAW delay line frequency response measurements. In particular, the difference between measured and predicted fractional frequency variation is less than 2% over the 25°C to 900°C temperature range and within the calculated and measured discrepancies. Multiple temperature-compensated orientations at high temperature were predicted and verified in this paper: 4 of the measured orientations had turnover temperatures (temperature coefficient of delay = 0) between 200 and 420°C, and 2 had turnover temperatures below 100°C. In summary, this work reports on extracted high-temperature elastic constants for LGT up to 1100°C, confirmed the validity of those constants by high-temperature SAW device measurements up to 900°C, and predicted and identified temperature-compensated LGT orientations at high temperature.     

Fiber-optic temperature sensor based on interaction of temperature-dependent refractive index and absorption of germanium film

The interaction of a large temperature-dependent refractive index and a temperature-dependent absorption of semiconductor materials at 1550 nm can be used to build a very sensitive, film coated fiber-optic temperature probe. We developed a sensor model for the optical fiber-germanium film sensor. A temperature sensitivity of reflectivity change of 0.0012/°C, corresponding to 0.1°C considering a moderate signal processing system, over 100°C within the temperature regime of -20°C to 120°C, has been demonstrated by experimental tests of the novel sensor. The potential sensitivity and further applications of the sensor are discussed.     

Carbon aerogel composites prepared by ambient drying and using oxidized polyacrylonitrile fibers as reinforcements

Carbon fiber-reinforced carbon aerogel composites (C/CAs) for thermal insulators were prepared by copyrolysis of resorcinol-formaldehyde (RF) aerogels reinforced by oxidized polyacrylonitrile (PAN) fiber felts. The RF aerogel composites were obtained by impregnating PAN fiber felts with RF sols, then aging, ethanol exchanging, and drying at ambient pressure. Upon carbonization, the PAN fibers shrink with the RF aerogels, thus reducing the difference of shrinkage rates between the fiber reinforcements and the aerogel matrices, and resulting in C/CAs without any obvious cracks. The three point bend strength of the C/CAs is 7.1 ± 1.7 MPa, and the thermal conductivity is 0.328 W m(-1) K(-1) at 300 °C in air. These composites can be used as high-temperature thermal insulators (in inert atmospheres or vacuum) or supports for phase change materials in thermal protection system.     

Signals of an intermodal fiber interferometer induced by laser frequency modulation

Signals of an intermodal fiber interferometer induced by laser optical frequency modulation are studied. Dependences of signal amplitudes and spectra on the laser frequency deviation are examined theoretically and experimentally for various optical fibers. It is established that the sensitivity of the intermodal fiber interferometer to the laser frequency variation essentially depends on the fiber refractive index profile. The minimal sensitivity corresponds to graded-index (α ≈ 2) multimode optical fibers. Step-index optical fibers (α = ∞) are more sensitive to the laser frequency variation by more than a factor of 100.     

Fiber optic pressure sensing with conforming elastomers

A novel pressure sensing scheme based on the effect of a conforming elastomer material on the transmission spectrum of tilted fiber Bragg gratings is presented. Lateral pressure on the elastomer increases its contact angle around the circumference of the fiber and strongly perturbs the optical transmission of the grating. Using an elastomer with a Young's modulus of 20 MPa, a Poisson ratio of 0.48, and a refractive index of 1.42, the sensor reacts monotonically to pressures from 0 to 50 kPa (and linearly from 0 to 15 kPa), with a standard deviation of 0.25 kPa and maximum error of 0.5 kPa. The data are extracted from the optical transmission spectrum using Fourier analysis and we show that this technique makes the response of the sensor independent of temperature, with a maximum error of 2% between 25°C and 75°C. Finally, other pressure ranges can be reached by using conforming materials with different modulii or applying the pressure at different orientations.     

Design principle for sensing coil of fiber-optic current sensor based on geometric rotation effect

The design principle exploiting the geometric rotation effect for the sensing coil of the fiber-optic current sensor (FOCS) on the basis of the polarization-rotated reflection interferometer is investigated. The sensing coil is formed by winding the low birefringence single-mode optical fiber in a toroidal spiral. The effects of the linear birefringence on the scale factor of the sensor can be suppressed with the reciprocal circular birefringence by appropriately designing the geometric parameters of the sensing coil. When the rated current is 1200 A(rms), the designed sensing coil can ensure the scale factor error of the sensor to satisfy the requirements of the 0.2 S class specified in IEC60044-8 over a temperature range from -40 °C to 60 °C.     

光纤结构参数对亚毫米沟槽装药爆速测试的影响研究

为了对亚毫米尺度SY共晶沟槽装药的爆速进行测试,采用光纤探针法设计了爆速测试系统,得到的信号稳定可靠,表明光纤探针法用于亚毫米沟槽装药的爆速测试是可行的。同时,为了研究光纤结构参数对爆速测试的影响,采用了3种不同结构参数的光纤进行试验。对爆速结果和信号参数进行数据分析可得:当光纤的数值孔径越大时,爆速测试的精度越高,信号的上升时间也越短,但对信号幅值基本没有影响;当光纤的芯径越大时,爆速测试的精度越高,信号的上升时间越短,信号的幅值也会增大。当光纤的数值孔径为0.22时,测试的精度最高,对应的爆速值为4.68 mm/μs,标准方差为0.12,平均相对误差为1.88%。     

Fiber-optic strain-displacement sensor employing nonlinear buckling

A new class of intrinsic fiber-optic strain-displacement sensors based on the precisely controlled nonlinear buckling of optical fibers and the resulting optical bend loss is introduced. A multimode fiber version of the sensor is described that exhibits a sensing range convenient for many structural monitoring applications (<100 nm to several millimeters), linear response over a wide range of displacements, and excellent repeatability. It is extremely simple to fabricate and employs inexpensive optoelectronics. A high-temperature version of the sensor is capable of operation at temperatures as high as 600 degrees C.     

Sensitivity-enhanced high-temperature sensing using all-solid photonic bandgap fiber modal interference

A wavelength-encoded interferometric high-temperature sensor based on an all-solid photonic bandgap fiber (AS-PBF) is reported. It consists of a small piece of AS-PBF spliced core offset with standard single-mode fibers. Two core modes LP(01) and LP(11) are conveniently utilized as optical arms to form Mach-Zehnder-type interference at both the first and the second photonic bandgaps, and the maximum extinction ratio exceeds 25?dB. Experimental and theoretical investigation of its response to temperature confirms that high temperatures up to 700?°C can be effectively sensed using such an AS-PBF interferometer, and benefiting from a large effective thermo-optic coefficient of fiber structure, the sensitivity can be significantly enhanced (71.5?pm/°C at 600?°C).     

Strength degradation of glass fibers at high temperatures

This article presents an experimental investigation into the effects of temperature and heating time on the tensile strength and failure mechanisms of glass fibers. The loss in strength of two glass fiber types (E-glass and Advantex^®, a boron-free version of E-glass) was investigated at temperatures up to 650 °C and heating times up to 2 h. The tensile properties were measured by fiber bundle testing, and the maximum strength was found to be temperature and time dependent. The higher softening point of the Advantex^® fibers is reflected in superior high-temperature performance. A phenomenological model is presented for calculating the residual strength of glass fiber bundles as functions of temperature and time. The strength reduction mechanism was determined by single-fiber testing. Fracture mirror sizes on the E-glass fibers were related to the fiber strength after high-temperature treatment. Based on fracture mirror measurements, it was established that (1) the mirror constant of the glass, which reflects the network structure, does not change during heat treatment and (2) the strength degradation is a result of larger surface flaws present after heat treatment.     

Fiber-optic temperature sensors based on differential spectral transmittance/reflectivity and multiplexed sensing systems

A concept for optical temperature sensing based on the differential spectral reflectivity/transmittance from a multilayer dielectric edge filter is described and demonstrated. Two wavelengths, λ(1) and λ(2), from the spectrum of a broadband light source are selected so that they are located on the sloped and flat regions of the reflection or transmission spectrum of the filter, respectively. As temperature variations shift the reflection or transmission spectrum of the filter, they change the output power of the light at λ(1), but the output power of the light at λ(2) is insensitive to the shift and therefore to the temperature variation. The temperature information can be extracted from the ratio of the light powers at λ(1) to the light at λ(2). This ratio is immune to changes in the output power of the light source, fiber losses induced by microbending, and hence modal-power distribution fluctuations. The best resolution of 0.2 °C has been obtained over a range of 30-120 °C. Based on such a basic temperature-sensing concept, a wavelength-division-multiplexed, temperature-sensing system is constructed by cascading three sensing-edge filters that have different cutoff wavelengths along a multimode fiber. The signals from the three sensors are resolved by detecting the correspondent outputs at different wavelengths.     

Dynamic thermal response of single-mode optical fiber for interferometric sensors

The dynamic temperature phase sensitivity of a three-layer optical fiber is calculated for unjacketed as well as Al- and Hytrel-coated fibers. The calculations include both the variation of the refractive index with temperature and the thermally induced axial and radial strains. The calculated phase sensitivity indicates that it is currently possible to measure a 1-microdegree C temperature change at frequencies exceeding 50 kHz with 1 cm of a metal coated optical fiber.     

Revisiting twin-core fiber sensors for high-temperature measurements

A twin-core fiber Michelson interferometer is evaluated as a high-temperature sensor. Although linear and reproducible operation up to 300°C is obtained, at higher temperatures (700°C) the refractive index shifts plastically and hysteresis is observed, rendering an untreated sensor head unusable. The shift is shown to be greatly reduced by an annealing process of the fiber for 10 h at 900°C, with which the linear response is preserved.     

ZrO2 thin-film-based sapphire fiber temperature sensor

A submicrometer-thick zirconium dioxide film was deposited on the tip of a polished C-plane sapphire fiber to fabricate a temperature sensor that can work to an extended temperature range. Zirconium dioxide was selected as the thin film material to fabricate the temperature sensor because it has relatively close thermal expansion to that of sapphire, but more importantly it does not react appreciably with sapphire up to 1800 °C. In order to study the properties of the deposited thin film, ZrO2 was also deposited on C-plane sapphire substrates and characterized by x-ray diffraction for phase analysis as well as by atomic force microscopy for analysis of surface morphology. Using low-coherence optical interferometry, the fabricated thin-film-based sapphire fiber sensor was tested in the lab up to 1200 °C and calibrated from 200° to 1000 °C. The temperature resolution is determined to be 5.8 °C when using an Ocean Optics USB4000 spectrometer to detect the reflection spectra from the ZrO2 thin-film temperature sensor.     

Radiation Thermometry Based on Photonic Crystal Fiber

Fiber-coupled radiometry allows for the radiometric measurement of high temperatures in environments where there is no line of sight to the target. However, transmission through conventional silica optical fibers degrades rapidly at elevated temperatures, and exotic fibers??such as sapphire fibers??typically cannot be bent. As part of a project to investigate the performance of solid oxide fuel cells, the feasibility of using an alternative fiber, solid-core silica photonic crystal fiber (PCF), was tested. The test system used an Inconel blackbody as a source, and a detection system based on an InGaAs array spectrometer with a wavelength range of 907 nm to 1681 nm. The temperature was determined from the spectrometer signal at particular wavelengths using the Planck relationship. Two tests were performed: (1) long-term high temperature soak tests to measure the drift and noise in thermal radiation levels, in which spectra are sequentially recorded over a long period of time with the blackbody cavity at a constant temperature and (2) temperature dependence tests, whereby thermal radiation spectra are recorded with the blackbody cavity at several temperatures. At 934 °C, the transmission of the PCF decreased at a rate of 0.078 % per hour corresponding to a temperature error of ?0.12 °C per hour. The transmission of conventional silica fiber decreased at a rate of 0.5 % per hour corresponding to a temperature error of ?0.8 °C per hour. While the PCF represents a significant improvement over conventional fiber, it is still not good enough for most practical purposes. At 600 °C there was no observable decline in transmission and there may be applications for PCF in that regime.     

High-Temperature Superconducting Fiber

In this study, we demonstrated superconductivity in a fiber with an yttrium barium copper oxide core and fused silica cladding. The fibers were fabricated via a modified melt-draw technique and post-process annealing treatment in excess oxygen. The fibers maintained overall diameters ranging from 100–900 microns and core diameters of 50–700 microns. Superconductivity of this fiber design was validated via the traditional four-point probe test method in a bath of liquid nitrogen at temperatures on the order of 93 K. The high-temperature superconducting fiber provides a glimpse of its cross cutting potential in fields of electromagnetism, healthcare, optics, and energy and lends credence to the promise for superconductivity.     

Erbium-doped silica fibers for intrinsic fiber-optic temperature sensors

The variation in the green intensity ratio ((2)H(11/2) and (4)S(3/2) energy levels to the ground state) of Er ions in silica fibers has been studied as a function of temperature. The different processes that are used to determine the population of these levels are investigated, in particular 800-nm excited-state absorption in Er-doped fibers and 980-nm energy transfer, in Yb-Er-codoped fibers. The invariance of the intensity ratio at a fixed temperature with respect to power, wavelength, and doped fiber length has been investigated and shown to permit the realization of a high-dynamic-range (greater than 600 °C), autocalibrated fiber-optic temperature sensor.     

Nitric oxide-releasing electrospun polymer microfibers

The preparation of electrospun polymer microfibers with nitric oxide (NO)-release capabilities is described. Polymer solutions containing disodium 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (PROLI/NO), a low-molecular-weight NO donor, were electrospun to generate fibers ranging from 100-3000 nm in diameter capable of releasing NO upon immersion in aqueous solutions under physiological conditions (pH 7.4, 37 °C), with kinetics depending on polymer composition and fiber diameter. The NO release half-life for PROLI/NO-doped electrospun fibers was 2-200 times longer than that of PROLI/NO alone. The influence of polymer concentration, applied voltage, capillary diameter, solution conductivity, flow rate, and additives on fiber properties are reported and discussed with respect to potential applications.