Sensitive Temperature Measurements Research Articles

Boosting the sensitivity of Er3+-based luminescent ratiometric thermometry

Non-contact optical thermometry, based on the luminescence intensity ratio (LIR) of two thermally-coupled levels (TCLs), has received increasing attentions nowadays. Designing novel TCLs-based temperature sensor becomes one of the most significant things in the field of optical thermometry. In this work, a novel strategy for temperature measurement is proposed. It is based on the 4F7/2 and 4S3/2 TCLs, rather than the widely studied 2H11/2 and 4S3/2 TCLs of Er3+. Both the two pairs of TCLs have been confirmed to be under the control of the Boltzmann distribution and thus can be used for luminescence ratiometric thermometry. The former TCLs have a larger energy gap (1808 cm−1) than the latter ones (711 cm−1). Based on this fact, it is shown here that using the 4F7/2-4I15/2 and 4S3/2-4I15/2 transitions can achieve a more sensitive temperature measurement than that depending on the 2H11/2-4I15/2 and 4S3/2-4I15/2 transitions at the operating temperatures from 333 to 773 K. At 333 K, the relative sensitivity (SR) of the former two transitions is calculated to be ~2.3% K−1. By comparison, using the latter two transitions only has a SR of 0.9% K−1 at the same temperature.

Online Diagnostic System to Monitor Temperature of In-Flight Particles in Suspension Plasma Spray

Suspension plasma spray (SPS) is going through a transition phase from research and development to daily use on production lines. Improving repeatability and reproducibility of coating elements and parameters makes SPS a replacement of former well-developed processes. This transition can be achieved by using in-flight particles diagnostic systems to monitor and control key parameters that influence the coating microstructure. Temperature and velocity of the in-flight particles are among the most critical parameters that should be monitored. However, accurately characterizing the in-flight particles in SPS is particularly challenging due to the small particle size of coating materials, harsh spray conditions, considerably shorter spray distances compared to APS, possible interference from the solvent, and limitations of previous measurement systems. In this study, different strategies were investigated to improve the accuracy of temperature measurements of in-flight particles in SPS. For this purpose, two light collection configurations (double-point and single-point measurement) were investigated along with the influence of plasma radiation. The results were evaluated by collecting and studying splats. The size and shape of splats were correlated with the temperature of in-flight particles in order to confirm the accuracy of the sensor’s temperature measurements. In addition, the sensitivity of temperature measurements to the optical filter used for two-color pyrometry, reflection of plasma radiation from surrounding objects, and direct radiation from plasma were investigated. The results showed that the single-point measurement configuration was well adapted for SPS.

Sensitive and fast measurement of surface temperature with a thermogalvanic cell

Thermogalvanic cells may be viewed as electrochemical thermocouples. Here, we demonstrate their potential for sensitive and fast sensing of the surface temperature of a thin Au sheet, in contact with a 0.08 M equimolar ferri-/ferrocyanide solution in 26% KOH. We obtained a sensitivity of about 10 μK, because of the large Peltier coefficient of the electrochemical reaction at the electrode-electrolyte junction. The resolution is limited by the thermal noise of the electrochemical system and could be quantitatively explained by the thermal noise of a Randles equivalent circuit of the cell. Since no thermal contact resistances to bulky temperature sensors are involved, we achieved a response time smaller than 300 μs, which may be potentially lowered to a few microseconds. By using the thermogalvanic cell as a sensor for electrochemical microcalorimetry, we calibrated the system, in full agreement with a simulation of its thermal behavior.

High-sensitive Mach-Zehnder interferometer for humidity measurements based on concatenating single-mode concave cone and core-offset

A simultaneous relative humidity (RH) and temperature sensor based on a single mode fiber (SMF) Mach-Zehnder interferometer (MZI) with polyimide (PI) coating is proposed and experimentally demonstrated. The sensor with controlled length is fabricated by splicing a concave cone and core-offset on a segment of SMF. Experimental results show that the RH response sensitivity of the sensor is -0.12458 dB/%RH, -0.20216 dB/%RH and -0.15201 dB/%RH when the length of the sensing fiber is 2.5 cm, 3 cm and 3.5 cm, respectively. The temperature sensitivity is 0.0577 nm/ oC at the length of the sensing fiber is 3 cm. Consequently, the advantages of simple fabrication, low cost, high RH sensitivity and simultaneous RH and temperature measurement ability mean the sensor has great potential applications in the field of RH measurement.

Reflective SPR Sensor for Simultaneous Measurement of Nitrate Concentration and Temperature

In this paper, a reflective fiber optic sensor based on surface plasmon resonance (SPR) was proposed to measure nitrate concentration and temperature simultaneously. The sensor adopted reflective structure, and used gold film as metal film for exciting SPR. Then, Cu-nanoparticles/carbon nanotubes composite film was used as sensitive material to measure nitrate concentration, and it was coated on the surface of the gold film by the dip coating method. Finally, polydimethylsiloxane was coated on part of the sensing probe to produce two independent resonance dips in the output spectrum. When the nitrate concentration and temperature changed, the two resonance dips would all move, but with different sensitivities. By monitoring the wavelength shifts of the two dips, the nitrate concentration and temperature could be measured simultaneously with using the dual-wavelength matrix method. Experimental results demonstrated that the measurement sensitivity of the nitrate concentration could reach 3.25 nm/lg[M], and the temperature measurement sensitivity was −2.02 nm/°C. Moreover, the sensor had high-mechanical strength and was easy to package, which could be applied to remote measurement field.

Cascaded polarizer-PMF-Fabry–Pérot structure with a tunable initial state for ultra-highly sensitive temperature measurement

A reflective cascaded structure with a fiber Lyot filter and a Fabry–Pérot interferometer has been proposed and experimentally demonstrated for ultra-highly temperature measurement. The sensitivity of the sensor can be magnified to −31.4 nm °C−1 based on the Vernier effect, to our knowledge, which is the highest among all-fiber structures without other assisted coating or filling materials. The sensor possesses the remote sensing capability. Furthermore, the initial state can be tuned by loading strains on the Fabry–Perot cavity, so that the maximum sensing range is available at different initial temperatures, and then allowing the sensor to fulfill more practical application needs.

Simple fiber-optic sensor for simultaneous and sensitive measurement of high pressure and high temperature based on the silica capillary tube.

A simple fiber-optic sensor for simultaneous measurement of high pressure and high temperature was proposed. The sensor was simply fabricated by splicing two sections of silica capillary tubes (SCTs) with different inner diameters to the single-mode fiber. The thick core SCT functions as a Fabry-Perot (FP) micro-cavity and an anti-resonant reflecting waveguide at the same time. The two different sensing mechanisms lead to the high contrast sensitivity values of pressure and temperature (‒3.76 nm/MPa, 27.7 pm/°C and 4.24 nm/MPa, 0.82 pm/°C). We also proposed a simple and effective method to evaluate the actual sensitivities of two-parameter sensors by using linear programming, which shows that our sensor is more sensitive than others in high pressure and high temperature simultaneous detection. Besides, low cost, good mechanical property and convenient reflective probe make the sensor more competitive in actual application.

An intensity modulation based fiber-optic loop sensor for high sensitivity temperature measurement

The possibility of conducting high resolution temperature measurements using a power modulation based fiber-optic loop sensor (FOLS) is studied in this work. FOLS is an intensity modulation based sensor that is relatively inexpensive and easier to operate than frequency modulation based sensors. A sensing element is designed for temperature sensing while protecting FOLS from direct heat and possible thermal degradation over time. The resonance peaks present in the transmitted intensity signal are used to conduct high resolution temperature measurements. The measured temperature is found to closely match with the thermocouple measurements with an average difference of 2.53%. Also, the measurements are found to be repeatable. Theoretical and finite element results closely match with the experimental results by using FOLS along with designed actuator and present the possibility of developing the sensing elements for measuring temperature in the desired range and for use in a diverse range of environments.

Improved green upconversion emissions from CaWO4: Er3+-Yb3+ by Cr3+ codoping for optical thermometry

Optical temperature sensors based on rare earth ions activated luminescent materials have presented their capabilities in thermal reading with good stability and high spatial resolution. The ongoing challenge is to improve the luminescence for further enhancing temperature measurement sensitivity and accuracy. Here, several Er3+-Yb3+ codoped CaWO4 phosphors are prepared and Cr3+ ions are introduced, trying to modify the upconverion (UC) emissions from Er3+ ions. Under the excitation of 980 nm laser, green UC luminescence from 2H11/2 and 4S3/2 states of Er3+ is successfully strengthened with Cr3+ codoping. Through the analysis of characterization by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and time-resolved spectroscopy, it is found that the dopant of Cr3+ ions could affect the crystallinity and distort the crystal structure of the as-prepared samples. The thermometry behavior based on green emissions of Er3+ is studied via fluorescence intensity ratio method. It is interesting to observe that the temperature sensing performance has also been influenced by the incorporation of Cr3+. When introducing 9 mol% Cr3+ ions into Er3+-Yb3+ codoped CaWO4 phosphors, a maximum sensitivity of about 1.91% K−1 has been achieved. Combined with the intense green luminescence, CaWO4: Er3+-Yb3+-Cr3+ would be a promising candidate for optical thermometry with excellent measurement sensitivity and accuracy.

Multi-isotopologue laser absorption spectroscopy of carbon monoxide for high-temperature chemical kinetic studies of fuel mixtures

A laser absorption diagnostic technique, probing the mid-infrared vibrational bands of 12C16O and 13C16O near 4.9 µm, was developed for sensitive multi-isotopologue temperature and concentration measurements in high-temperature gaseous systems. Transitions in each of the P-branches of the fundamental bands of 12C16O and 13C16O were chosen based on absorption linestrength, relative spectral isolation, and temperature sensitivity. Five total rovibrational transitions are spectrally-resolved over a ∼ 1.2 cm−1 domain using a 50 kHz triangle scan function with a distributed-feedback quantum cascade laser, yielding a 100 kHz effective measurement rate of both isotopologues and respective temperatures, independent of mixture composition. In addition, relevant broadening parameters for the P(0,22) transition of 13C16O near 2007.8767 cm−1 were measured to enable higher time resolution ( > 1 MHz) measurements using fixed-wavelength methods. Time-resolved multi-isotopologue thermometry performance was validated in a shock tube over a range of temperatures (1100–2400 K) relevant to combustion kinetics investigations. The technique is utilized in shock-heated oxidation experiments with isotopically labeled fuel mixtures, simultaneously measuring both carbon monoxide isotopologues throughout the reactions. To the authors’ knowledge, these results demonstrate the first use of carbon isotope labeling with laser absorption spectroscopy to observe distinct competitive oxidation among different fuel components.

Frequency-modulated continuous-wave laser interferometric optical fiber temperature sensor

This paper presents an extrinsic Fabry-Perot (F-P) cavity optical fiber temperature sensor, which is based on the frequency-modulated continuous-wave laser interference. The temperature sensing probe is fabricated by a stainless-steel tube with high coefficient of thermal expansion to encapsulate the F-P cavity. Stainless steel tube is used as the F-P cavity and also the temperature sensitive component. The variation of cavity length caused by thermal expansion of F-P cavity is measured by frequency-modulated continuous-wave interferometric measurement technique. The experimental results show that the temperature measurement resolution of the fiber temperature sensor reached 0.0002 ℃ and the temperature measurement sensitivity reached 3022 nm/℃. The temperature sensor not only has high sensitivity and resolution, but also has a simple and stable structure and a good application prospect.

Scattering referenced aerosol phosphor thermometry

This work presents a new thermographic phosphor particle-based gas thermometry technique that utilizes the ratio of temperature-dependent luminescence intensity and the temperature-insensitive elastic Mie scattering from phosphor particles seeded into the gas. This method has the potential for high temperature sensitivity. However, the large range of particle sizes typical of thermographic phosphors results in additional uncertainty in the measured ratio and temperature. The uncertainty in the intensity ratio is measured as a function of phosphor seeding density for the phosphor Ce:LuAG. The added uncertainty in the single-shot ratio measurements, assumed to be due to the non-uniform particle size distribution (PSD), was estimated to range from 20% for a seeding density of 40 mm−3 to 10% at 210 mm−3. Measurements at heated jet exit temperatures of 750 K and 820 K revealed that, even with the added ratio uncertainty, single-shot temperature precisions better than 2% (<15 K) were achieved with seeding densities less than 150 mm−3. By combining ratio precision and temperature sensitivity measurements, it was estimated that the technique is capable of single-shot temperature precision better than 4% from 670 K to 1000 K, and better than 1.5% from 800 K to 900 K, for a seeding density of 300 mm−3. Measurements are limited to temperatures greater than approximately 600 K for Ce:LuAG due to low temperature sensitivity and a double-valued ratio below this temperature. These results demonstrate the potential of this new strategy to advance the state-of-the-art for APT measurements.

A Palm-Sized Cryoprobe System With a Built-In Thermocouple and Its Application in an Animal Model of Epilepsy.

The purpose of this study is to propose a palm-sized cryoprobe system with a built-in thermocouple (TC) for highly accurate and sensitive temperature measurements, and to verify the effectiveness of the system. Conventional cryoprobe systems based on the boiling effect of a refrigerant have triple coaxial tubes. In the proposed system, the outer and middle coaxial tubes are made of two different metals that are welded only at the probe tip, thereby forming a TC. The thermoelectric properties of the built-in TC and measurement accuracy were investigated in agar in a constant-temperature chamber. The system was also applied in a penicillin G-induced rat brain epilepsy model. We verified that the built-in TC has appropriate thermoelectric properties and that the system more accurately and sensitively measured transient temperature changes at the probe tip wall compared to conventional systems, showing the cooling performance of the system. In the rat model, epileptiform activities disappeared on freezing, and reliable cell necrosis was achieved at an end temperature of -45.2 ± 1.6 °C. The proposed system is suitable for reliable cryosurgery. The system is probably to be valuable for clarifying the relationship between freezing temperature and cell necrosis in vivo.

Experimental characterization and model validation of liquid jet impingement cooling using a high spatial resolution and programmable thermal test chip

High efficiency direct liquid jet impingement cooling with locally distributed outlets is very promising in high power electronic devices. In order to elucidate the flow-thermal interaction for micro-scale jet impingement cooling, sensitive temperature measurements with high spatial and temporal resolution are required. In this work, a programmable thermal test chip with 832 heater cells with 75% heater uniformity and 32 × 32 array of temperature sensors is introduced. The detailed measured temperature maps for different power dissipation patterns allow the in-depth study of the thermal performance of liquid jet impingement coolers and the detailed experimental validation of complex CFD models. The modeling and measurement study is applied to two jet impingement cooling implementations: (1) a single jet cooler with a 2 mm diameter nozzle, and (2) a multi-jet cooler with a 4 × 4 array of 500 µm inlet nozzles and distributed outlet nozzles. For both cooler configurations, the temperature measurements and CFD modeling results are investigated and compared for uniform and hot spot power dissipation patterns.

Optical measurement by a dual-frequency comb based on Rayleigh scattered Stokes light

The backward stimulated Brillouin scattering in the optical fiber leads to a forward peaked Rayleigh scattering light with the same frequency shift. A dual-frequency comb is proposed and experimentally demonstrated, in which the frequency difference is equal to the Brillouin frequency shift. Further, a temperature measurement scheme is design based on the novel dual-frequency comb, where the radio-frequency (RF) signal is directly detected; neither high frequency photo detector or extra Mach–Zehnder interferometer (MZI) structure is required. The beaten RF signal is of narrower linewidth because the related phases are reduced, which enhances the measurement with a higher resolution. The measurement structured is demonstrated, in which the sensitivity of temperature measurement is 1.08 MHz∕∘C, same as the MZI structure, while the resolution is improved to 4.5 times compared to the traditional structure in the experiment.

Detection of spindle thermal state accuracy of vertical CNC machine tool

In order to test the thermal accuracy of spindle system of mining vertical CNC machine tools, to enhance the error compensation ability of the system accuracy detection model and improve the machine tool processing accuracy, a test platform for thermal accuracy of spindle system was constructed. Five-point method was used to test the thermal accuracy of spindle system, and thermocouple and infrared thermal imager were used to measure the spindle system. Temperature change data at key points of temperature rise are used to identify temperature sensitive measurement points by grey comprehensive correlation analysis method. A thermal accuracy prediction model based on cooperative quantum particle algorithm is constructed. The prediction effect of the model is evaluated. The experimental results show that the thermal accuracy detection model has high detection accuracy.

A Dual-Parameter Sensor Based on the Asymmetry of Alcohol Filling the Photonic Crystal Fiber in Sagnac Loop

This paper proposes a novel temperature and stress sensor based on the asymmetric filling of alcohol into the photonic crystal fiber in a Sagnac loop. First, we etched the photonic crystal fiber and collapsed the air. Then, we filled alcohol into the asymmetric photonic crystal fiber. Next, we connected this structure into a Sagnac interference ring. When the ambient temperature changed, the thermal expansion effect of filled alcohol would lead to the change of birefringence of photonic crystal fiber, which made the interference spectrum of the sensor drift with the change of temperature. Furthermore, after adding transverse stress to the photonic crystal fiber, the fiber’s strain changed. With its strain changed, the birefringence of photonic crystal fiber also changed, which made the interference spectrum drift. The experimental results showed that when the temperature or the lateral stress is added, a red shift would occur in the interference spectrum. The temperature sensitivity was found to be 0.1864 nm/°C, and the lateral stress sensitivity was 0.6201 nm/N. The sensor achieved the highly sensitive measurement of temperature and stress. Concurrently, the structure has the advantages of high stability, anti-electromagnetic interference, and easy construction, and it provides a new method for obtaining birefringence of ordinary photonic crystal fiber. In addition, an application system of the sensor has been built. Monochromatic light source with 1554-nm wavelength was used in the experiment. The drift of interference spectrum is transformed into the change of light intensity. The relative error is less than 3%, which indicates a good application prospect.

Pr3+ Luminescence to Improve the Range, Accuracy and Sensitivity of Temperature Measurement

For years, various contact techniques were used to measure temperature. Development of novel and evolving technologies raised the interest in elaboration of non-contact thermometry. Nowadays, this is radiation pyrometry which is the method of choice for such purposes. Yet, it has important limitations – sensitivity to stray light or reflected radiation as well as sensitivity to flame interferences. Also accuracy of temperature measurement, which is not better than ~2 K, is not always satisfactory. Today technologies do not fulfill the needs of temperature sensing in microelectronics, microoptics, photonics, microfluidics, nanomedicine and they require alternative solutions. Among promising approaches, overcoming the limitations of other techniques, luminescent methods are of great interest. While the idea is not new [1], a real breakthrough using this technique was not yet achieved. Combining a high sensitivity and accuracy as well as broad range of temperature usability within one temperature sensor appeared challenging [2,3]. In this presentation we shall prove that Pr3+ luminescence characteristics may offer a lot in this field. While in some compositions this ion generates only 4f®4f luminescence due to relaxation of the higher 3P0 and lower 1D2 levels, in some others also 5d®4f luminescence may take place. We explored the possibility to use all these three luminescent components to sense the temperature accurately and in a broad range. The main argument for that is that all the three emissions are characterized by different mechanisms of their thermal quenching. Furthermore, temperature strongly affects the non-radiative relaxation between the three levels. Our presentation will show first results of the approach presented above using data for Sr2GeO4:Pr and will prove a validity and potential of this new attitude. Figure 1 presents profound changes in emission spectra of Sr2GeO4:Pr in the range of 17-600 K. [1] P. Neubert, US2085508 A, 1937. [2] L. D. Carlos, F. Palacio, Thermometry at the Nanoscale: Techniques and Selected Applications, Royal Society of Chemistry, Oxfordshire 2016. [3] C. D. S. Brites, P. P. Lima, N. J. O. Silva, A. Millán, V. S. Amaral, F. Palacio, L. D. Carlos, Nanoscale 2012, 4, 4799. Figure 1

Polymer optical fiber Bragg grating inscription with a single Nd:YAG laser pulse.

We experimentally demonstrate the first polymer optical fiber Bragg gratings inscribed with only one Nd:YAG laser (266 nm) pulse. The gratings have been inscribed in a single-mode poly (methyl methacrylate) optical fiber, with a core doped with benzyl dimethyl ketal for photosensitivity enhancement. One laser pulse with a duration of 8 ns and energy of 72 µJ is adequate to introduce a refractive index change of 0.5 × 10-4 in the fiber core. The stability of the gratings has been confirmed and the strain and temperature sensitivity measurements demonstrate their tunable properties.

Hybrid photonic crystal fiber for highly sensitive temperature measurement

A hybrid photonic crystal fiber (PCF) is proposed and demonstrated for highly sensitive temperature measurement. The hybrid PCF is formed by selectively infiltrating liquid crystal 5CB into the first ring of air holes around one silica core of a twin-core PCF (TCPCF). In the modified TCPCF, one silica core guides light with a total internal reflection (TIR) mechanism, while the other silica core guides light through a photonic bandgap (PBG) mechanism, due to the infiltration of high refractive index 5CB. The co-existing of TIR and PBG waveguiding mechanisms in the TCPCF leads to a hybrid light guiding mechanism PCF, i.e. hybrid PCF. Theoretical analysis reveals that the TIR-guided core mode, PBG-guided core modes and 5CB channel modes in the hybrid PCF can concurrently propagate and interfere with each other, which is further verified by experimental results. Besides, experimental investigation on the temperature response of the hybrid PCF shows that the temperature sensitivities can be up to 4.91 nm °C−1 for nematic phase of 5CB, and −3.68 nm °C−1 for isotropic phase of 5CB, respectively. The proposed hybrid PCF is promising for applications of temperature-tunable optical filtering in optical fiber communication, sensing and laser systems.