Direct Temperature Measurements Research Articles

Measurement of brightness temperature of two-dimensional electron gas in channel of a high electron mobility transistor at ultralow dissipation power

A technically simple and physically clear method is suggested for direct measurement of the brightness temperature of two-dimensional electron gas (2DEG) in the channel of a high electron mobility transistor (HEMT). The usage of the method was demonstrated with the pseudomorphic HEMT as a specimen. The optimal HEMT dc regime, from the point of view of the “back action” problem, was found to belong to the unsaturated area of the static characteristics possibly corresponding to the ballistic electron transport mode. The proposed method is believed to be a convenient tool to explore the ballistic transport, electron diffusion, 2DEG properties and other electrophysical processes in heterostructures.

Thermodynamic temperature assignment to the point of inflection of the melting curve of high-temperature fixed points

The thermodynamic temperature of the point of inflection of the melting transition of Re-C, Pt-C and Co-C eutectics has been determined to be 2747.84 ± 0.35 K, 2011.43 ± 0.18 K and 1597.39 ± 0.13 K, respectively, and the thermodynamic temperature of the freezing transition of Cu has been determined to be 1357.80 ± 0.08 K, where the ± symbol represents 95% coverage. These results are the best consensus estimates obtained from measurements made using various spectroradiometric primary thermometry techniques by nine different national metrology institutes. The good agreement between the institutes suggests that spectroradiometric thermometry techniques are sufficiently mature (at least in those institutes) to allow the direct realization of thermodynamic temperature above 1234 K (rather than the use of a temperature scale) and that metal-carbon eutectics can be used as high-temperature fixed points for thermodynamic temperature dissemination. The results directly support the developing mise en pratique for the definition of the kelvin to include direct measurement of thermodynamic temperature.

Ground Thermal Diffusivity Calculation by Direct Soil Temperature Measurement. Application to very Low Enthalpy Geothermal Energy Systems.

This paper presents a methodology and instrumentation system for the indirect measurement of the thermal diffusivity of a soil at a given depth from measuring its temperature at that depth. The development has been carried out considering its application to the design and sizing of very low enthalpy geothermal energy (VLEGE) systems, but it can has many other applications, for example in construction, agriculture or biology. The methodology is simple and inexpensive because it can take advantage of the prescriptive geotechnical drilling prior to the construction of a house or building, to take at the same time temperature measurements that will allow get the actual temperature and ground thermal diffusivity to the depth of interest. The methodology and developed system have been tested and used in the design of a VLEGE facility for a chalet with basement at the outskirts of Huelva (a city in the southwest of Spain). Experimental results validate the proposed approach.

Large and robust resistive switching in co-sputtered Pt-(NiO-Al2O3)-Pt devices

We have systematically investigated the resistive switching and electroresistance behavior in Pt-[NiO-Al2O3]-Pt (PNAP) capacitor-like structures. The PNAP devices show a large ON-OFF ratio (∼107), which is strongly dependent on the rate of the voltage sweep. Interestingly, the devices exhibit a robust electroresistance behavior in the high resistance OFF state and show an intriguing change of sign of rectification with increasing end voltage. Our direct measurement of the surface temperature of the sample during resistive switching indicates that RESET process is assisted by Joule heating effects. The results are explained on the basis of plausible interplay between Schottky barrier modification due to the trapped charge carriers at the metal–oxide interface and percolation effects of conducting nanofilaments.

Laboratory scale geophysical measurements aimed at monitoring the thermal affected zone in Underground Thermal Energy Storage (UTES) applications

Underground Thermal Energy Storage systems have showed to be a useful and increasing technical solution for covering heating and cooling and domestic hot water buildings' demand. Thermal influence of these plants is however not still debated as it deserves and correct monitoring strategies appear to be of major importance both to better understand processes and to highlight their environmental effects into high populated areas. Litho-, hydro- and bio-sphere can indeed be adversely affected by temperature variations induced in the underground by heat storage applications. For this purpose, a geophysical monitoring approach using time-lapse electrical resistivity measurements contemporary to analogical simulations is here tested at laboratory scale. Results of the experiments are reported comparing measured apparent resistivity with direct temperature measurements and numerical simulations of heat propagation. Data presented confirmed that electrical resistivity has powerful relation with temperature variation in monitored media. In addition, they showed that also without performing data inversion valid temperature estimation can be carried out. Post-processing calibration of apparent resistivity data showed to be in acceptable agreement with both temperature measurements and numerical simulations. Simple apparent electrical resistivity variations appear therefore to be a promising, economic, quick and non-invasive tool for mapping thermal modifications induced in the underground by shallow geothermal applications.

A critical review of techniques to determine the magnet temperature of permanent magnet synchronous motors under real-time conditions

The permanent magnet synchronous motor (PMSM) is widely applied in highly utilised automotive traction drives and other industrial applications. With regards to the device life-time, thermal utilisation, safe operation and control performance, the permanent magnet temperature is of great interest. Since a direct magnet temperature measurement is not feasible due to constructional and cost issues in most applications, this contribution gives a review on state-of-the-art model-based magnet temperature determination techniques regarding PMSM. In this context, the existing publications can be classified into thermal models, flux observers and voltage signal injection approaches. Firstly, brief introductions of these methods are given, followed by a direct comparison regarding drawbacks and benefits. This evaluation exhibits the individual constraints of each approach motivating their fusion as an outlook of further investigations in this research field.

A reliable computing framework for dynamic line rating of overhead lines

Indirect methods for dynamic loadability analysis have been recognized as enabling methodologies for improving the overhead line exploitation, since they do not require the need of a direct measurement of the conductor temperature, implying simple and inexpensive installation, and maintenance procedures. Despite these benefits, indirect methods suffer for several limitations, which mainly derive from the strong uncertainties affecting the loadability estimation process. To overcome these limitations, a novel self-validated computing framework for indirect loadability analysis of overhead line is proposed in this article. Experimental results obtained on a real 150kV overhead line are presented and discussed in order to assess the effectiveness of the proposed methodology.

Thermal Characterization Using Optical Methods of AlGaN/GaN HEMTs on SiC Substrate in RF Operating Conditions

Performance and reliability of wide bandgap high-power amplifiers are correlated with their thermal behavior. Thermal model development and suitable temperature measurement systems are necessary to quantify the channel temperature of devices in real operating conditions. As a direct temperature measurement within a channel is most of the time not achievable, the common approach is to measure the device temperature at different locations close to the hotspot and then to use simulations to estimate the channel temperature. This paper describes a complete thermal characterization of AlGaN/gallium nitride (GaN) on silicon carbide high electron-mobility transistors (HEMTs) when devices are operating in dc bias, pulsed, and continuous wave. Infrared thermography, charge-coupled device-based thermoreflectance microscopy, and micro-Raman spectroscopy have been performed to extract the thermal resistance of the components. Results have been compared with simulations using a 3-D finite-element model to estimate the operating channel temperature. Measurements have shown that the RF-biased thermal resistance and the dc-biased thermal resistance of GaN HEMTs are similar.

Analytical review of some relevant methods and devices for the determination of the specific volume on thermoplastic polymers under processing conditions

This article reviews some of the most representative methods and devices to measure the specific volume in polymeric materials found in literature. Each method is described and a comparison between the experimental conditions and typical injection molding processing conditions is discussed. In general, the main difficulty with specific volume measurements is determination of the temperature distribution through sample thickness, particularly when achieving typical processing conditions is intended. Therefore, the necessity of developing a new device which allows direct measurements of pressure and temperature at various positions along the sample thickness in order to calculate the cooling condition was identified.

Empirical metallicity-dependent calibrations of effective temperature against colours for dwarfs and giants based on interferometric data

We present empirical metallicity-dependent calibrations of effective temperature against colours for dwarfs of luminosity classes IV and V and for giants of luminosity classes II and III, based on a collection from the literature of about two hundred nearby stars with direct effective temperature measurements of better than 2.5 per cent. The calibrations are valid for an effective temperature range 3,100 - 10,000 K for dwarfs of spectral types M5 to A0 and 3,100 - 5,700 K for giants of spectral types K5 to G5. A total of twenty-one colours for dwarfs and eighteen colours for giants of bands of four photometric systems, i.e. the Johnson ($UBVR_{\rm J}I_{\rm J}JHK$), the Cousins ($R_{\rm C}I_{\rm C}$), the Sloan Digital Sky Survey (SDSS, $gr$) and the Two Micron All Sky Survey (2MASS, $JHK_{\rm s}$), have been calibrated. Restricted by the metallicity range of the current sample, the calibrations are mainly applicable for disk stars ([Fe/H]$\,\gtrsim\,-1.0$). The normalized percentage residuals of the calibrations are typically 2.0 and 1.5 per cent for dwarfs and giants, respectively. Some systematic discrepancies at various levels are found between the current scales and those available in the literature (e.g. those based on the infrared flux method IRFM or spectroscopy). Based on the current calibrations, we have re-determined the colours of the Sun. We have also investigated the systematic errors in effective temperatures yielded by the current on-going large scale low- to intermediate-resolution stellar spectroscopic surveys. We show that the calibration of colour ($g-K_{\rm s}$) presented in the current work provides an invaluable tool for the estimation of stellar effective temperature for those on-going or upcoming surveys.

Temperature Calibration for In Situ Environmental Transmission Electron Microscopy Experiments.

In situ environmental transmission electron microscopy (ETEM) experiments require specimen heating holders to study material behavior in gaseous environments at elevated temperatures. In order to extract meaningful kinetic parameters, such as activation energies, it is essential to have a direct and accurate measurement of local sample temperature. This is particularly important if the sample temperature might fluctuate, for example when room temperature gases are introduced to the sample area. Using selected-area diffraction (SAD) in an ETEM, the lattice parameter of Ag nanoparticles was measured as a function of the temperature and pressure of hydrogen gas to provide a calibration of the local sample temperature. SAD permits measurement of temperature to an accuracy of ±30°C using Ag lattice expansion. Gas introduction can cause sample cooling of several hundred degrees celsius for gas pressures achievable in the ETEM.

Stream temperature estimated in situ from thermal-infrared images: best estimate and uncertainty

The paper aims to show a technique to estimate in situ the stream temperature from thermal-infrared images deepening its best estimate and uncertainty. Stream temperature is an important indicator of water quality and nowadays its assessment is important particularly for thermal pollution monitoring in water bodies. Stream temperature changes are especially due to the anthropogenic heat input from urban wastewater and from water used as a coolant by power plants and industrial manufacturers. The stream temperatures assessment using ordinary techniques (e.g. appropriate thermometers) is limited by sparse sampling in space due to a spatial discretization necessarily punctual. Latest and most advanced techniques assess the stream temperature using thermal-infrared remote sensing based on thermal imagers placed usually on aircrafts or using satellite images. These techniques assess only the surface water temperature and they are suitable to detect the temperature of vast water bodies but do not allow a detailed and precise surface water temperature assessment in limited areas of the water body. The technique shown in this research is based on the assessment of thermal-infrared images obtained in situ via portable thermal imager. As in all thermographic techniques, also in this technique, it is possible to estimate only the surface water temperature. A stream with the presence of a discharge of urban wastewater is proposed as case study to validate the technique and to show its application limits. Since the technique analyzes limited areas in extension of the water body, it allows a detailed and precise assessment of the water temperature. In general, the punctual and average stream temperatures are respectively uncorrected and corrected. An appropriate statistical method that minimizes the errors in the average stream temperature is proposed. The correct measurement of this temperature through the assessment of thermal- infrared images obtained in situ via portable thermal imager is confirmed by the direct measurement of stream temperature using an ordinary technique based on an appropriate thermometer.

Characterization of electrocaloric properties by indirect estimation and direct measurement of temperature–electric field hysteresis loops

The electrocaloric properties of Pb(Zr,Ti)O3(PZT)-based and Ba(Zr,Ti)O3 ceramics and Pb(Mg,Nb)O3–PbTiO3 (PMN–PT) crystals were investigated by the indirect estimation and direct measurement of temperature–electric field (T–E) hysteresis loops. The measured T–E loops showed a similar shape to strain–electric field (s–E) loops. The adiabatic temperature change ΔT due to electrocaloric effects was estimated from the polarization change of these samples. ΔTs of 0.48 and 0.66 K were estimated for the (Pb,La)(Zr,Ti)O3 (PLZT)(9.1/65/35) ceramics and PMN–PT crystals under a field of 30 kV/cm, respectively. The measured temperature changes ΔTs in these samples upon the release of the electric field from 30 kV/cm to zero were 0.39 and 0.36 K, respectively.

A real-time heat strain index using foot temperature and heart rate while wearing personal protective equipment in hot environments

Over the past century, a number of indices to assess heat stress and strain in hot environments have been developed, but there are few non-invasive indices to evaluate the heat strain of workers wearing personal protective equipment. ISO 7933 [1] presents an analytical method to determine heat stress using calculation of the predicted heat strain but the calculation is complicated to apply for real-time monitoring. Moran and colleagues [2,3] derived a simple and useful index based on rectal temperature (Tre) and heart rate (HR) (Physiological Strain Index, PSI) but the index is limited at work in fields because of the direct measurement of rectal temperature. The purpose of this study was to present a non-invasive method to monitor heat strain in real-time using foot temperature (Tfoot) and HR of workers wearing personal protective equipment with protective boots in hot environments.

Contribution of Electric Current into Densification Kinetics During Spark Plasma Sintering of Conductive Powder

The shrinkage kinetics of a conductive material (copper powder) under spark plasma sinter‐forging conditions in the presence and absence of the electric current passing directly through the specimen is investigated from both experimental and theoretical points of view. The experiments on the current‐assisted and current‐insulated spark plasma sinter‐forging are conducted using specially developed spark plasma sintering tooling which has a number of particular features. The tooling enables direct temperature measurement at the free lateral surface of a powder sample as well as the simultaneous in situ measurement of the radius and height of a porous cylindrical sample during spark plasma sinter‐forging, rendering conditions of bi‐axial dilatometry. The continuum theory of sintering‐based constitutive model of free upsetting (hot forging with free lateral surface) is refined taking into account the obtained experimental data on the current‐insulated mode of spark plasma sinter‐forging. It is shown that the model framework traditionally utilized for the description of hot deformation of powder materials is not suitable for the simulation of the considered current‐assisted spark plasma sintering modes. Thus, the necessity of the development of new, specific to spark plasma sintering, constitutive models taking into account the direct contributions of electric current into mass transfer, is demonstrated.

Silicon-photonic PTAT temperature sensor for micro-ring resonator thermal stabilization.

We present a scheme for thermal stabilization of micro-ring resonator modulators through direct measurement of ring temperature using a monolithic PTAT temperature sensor. The measured temperature is used in a feedback loop to adjust the thermal tuner of the ring. The closed-loop feedback system is demonstrated to operate in presence of thermal perturbations at 20Gb/s.

Measurements of the directional spectral emissivity based on a radiation heating source with alternating spectral distributions

A method was developed to simultaneously measure the directional spectral emissivity and the temperature of samples with diffuse surfaces at high temperatures using a radiation heating source with alternating spectral distributions and multiple wavelength measurements. The method avoids the need for direct measurements of the sample surface temperature to determine the spectral emissivity. The inverse problem for the spectral emissivity and the temperature of a sample irradiated by a simulated radiation source was analyzed numerically to illustrate the excellent solution accuracy of the measurement method for various noise levels and spectral emissivities in the near-infrared spectra. The solution uncertainties for the spectral emissivity and temperature were smaller for the sample with a larger spectral emissivity. Measurements with a 99.9% purity graphite sample irradiated by a quartz lamp array as the radiation heating source verified the applicability of the method. The spectral emissivities and temperatures of the graphite sample were calculated using the Levenberg–Marquardt algorithm for two heating conditions with alternating spectral distributions and 30 wavelengths in the spectral range of 1.15–1.60μm. The uncertainties in the spectral emissivity and temperature were very small. The method is useful for accurately measuring the sample spectral emissivity without direct temperature measurements at high temperatures.

A new procedure for estimating the cell temperature of a high concentrator photovoltaic grid connected system based on atmospheric parameters

The working cell temperature of high concentrator photovoltaic systems is a crucial parameter when analysing their performance and reliability. At the same time, due to the special features of this technology, the direct measurement of the cell temperature is very complex and is usually obtained by using different indirect methods. High concentrator photovoltaic modules in a system are operating at maximum power since they are connected to an inverter. So that, their cell temperature is lower than the cell temperature of a module at open-circuit voltage since an important part of the light power density is converted into electricity. In this paper, a procedure for indirectly estimating the cell temperature of a high concentrator photovoltaic system from atmospheric parameters is addressed. Therefore, this new procedure has the advantage that is valid for estimating the cell temperature of a system at any location of interest if the atmospheric parameters are available. To achieve this goal, two different methods are proposed: one based on simple mathematical relationships and another based on artificial intelligent techniques. Results show that both methods predicts the cell temperature of a module connected to an inverter with a low margin of error with a normalised root mean square error lower or equal than 3.3%, an absolute root mean square error lower or equal than 2°C, a mean absolute error lower or equal then 1.5°C, and a mean bias error and a mean relative error almost equal to 0%.

Estimations of heat transfer from Grotto’s North Tower: A NEPTUNE Observatory case study

The overall heat transfer through an active hydrothermal sulfide edifice, in particular the North Tower of Grotto, has been estimated at 80MW or greater based on the following in situ measurements and assumptions: (1) The heat transfer by diffuse flow is estimated at 33–380MW based on extrapolating the acoustically mapped area to all sides of the North Tower (“visible” area=30m2; extrapolated area=100m2) and using the range of available spot measurements of temperature (6–23°C) and vertical velocity (0.07–0.28m/s). The lower number (33MW) is more likely, but there is insufficient knowledge of the temporal and spatial variability of diffuse flow to be certain. (2) The heat transfer by focused flow is estimated at 30–70MW based on summing the estimated individual rates of heat transfer for 4 out of 7 documented black smokers and flanges. (3) Conductive heat transfer out of the mound is unknown, but is likely to be much less than the advective heat transfer. Additionally, the plume transport of heat is estimated at 20–40MW based on the direct measurement of temperature within the plume (at 5–25m above the top of the edifice). Despite uncertainties, the lower estimate of plume versus smoker heat transfer suggests that heat transfer is dominantly by diffuse flow. Furthermore, not all plumes from individual smokers may merge even for so small an area as the North Tower of Grotto.

Traceable Calibration of a Radiation Thermometer in the Range 100 °C to 300 °C by Model Fitting

The Norwegian Metrology Service (JV) offers calibration of blackbodies, thermal imagers, and radiation thermometers to the national clients. The temperature measurements are traceable to the ITS-90 with a set of reference blackbodies covering the range from 10 °C to 1700 °C. However, between 100 °C and 300 °C we do not have a direct measurement of the cavity temperature from a traceable sensor, and rely instead on a pyrometer to provide the reference temperature. The pyrometer is regularly calibrated externally at a handful of predefined temperatures. In this work we present a calibration scheme for the pyrometer which allows calibration at the JV premises: the pyrometer is set to record the measured radiation level at predefined temperatures below 100 °C and just above 300 °C. The calibration data are used to fit a Sakuma–Hattori model, and subsequent readings of the radiation level can be input to the model to extract the corresponding temperature. We present uncertainty budgets for the calibration data, which is subsequently used to estimate a combined uncertainty at arbitrary measured temperatures between 100 °C and 300 °C. Finally, temperatures obtained with the described scheme are compared with recent calibration values obtained externally, and we show that this is a reasonable way to achieve traceable calibration of the pyrometer with adequate precision and low uncertainty. The model fitting has the added benefit of a continuous calibration curve throughout the relevant temperature range rather than at a handful of arbitrary points.