Measurements Of Thermal Radiation Research Articles

Measurement of near-field thermal radiation between multilayered metamaterials

Measurement of near-field thermal radiation between multilayered metamaterials

Wearable Ultrasound System Using Low-Voltage Time Delay Spectrometry for Dynamic Tissue Imaging.

Wearable ultrasound is emerging as a new paradigm of real-time imaging in freely moving humans and has wide applications from cardiovascular health monitoring to human gesture recognition. However, current wearable ultrasound devices have typically employed pulse-echo imaging which requires high excitation voltages and sampling rates, posing safety risks, and requiring specialized hardware. Our objective was to develop and evaluate a wearable ultrasound system based on time delay spectrometry (TDS) that utilizes low-voltage excitation and significantly simplified instrumentation. We developed a TDS-based ultrasound system that utilizes continuous, frequency-modulated sweeps at low excitation voltages. By mixing the transmit and receive signals, the system digitizes the ultrasound signal at audio frequency (kHz) sampling rates. Wearable ultrasound transducers were developed, and the system was characterized in terms of imaging performance, acoustic output, thermal characteristics, and applications in musculoskeletal imaging. The prototype TDS system is capable of imaging up to 6cm of depth with signal-to-noise ratio of up to 42dB at a spatial resolution of 0.33mm. Acoustic and thermal radiation measurements were within clinically safe limits for continuous ultrasound imaging. We demonstrated the ability to use a 4-channel wearable system for dynamic imaging of muscle activity. We developed a wearable ultrasound imaging system using TDS to mitigate challenges with pulse echo-based wearable ultrasound imaging systems. Our device is capable of high-resolution, dynamic imaging of deep-seated tissue structures and is safe for long-term use. This work paves the way for low-voltage wearable ultrasound imaging devices with significantly reduced hardware complexity.

Transient measurement of near-field thermal radiation between macroscopic objects.

The involvement of evanescent waves in the near-field regime could greatly enhance spontaneous thermal radiation, offering a unique opportunity to study nanoscale photon-phonon interaction. However, accurately characterizing this subtle phenomenon is very challenging. This paper proposes a transient all-optical method for rapidly characterizing near-field radiative heat transfer (NFRHT) between macroscopic objects, using the first law of thermodynamics. Significantly, a full measurement at a fixed gap distance is completed within tens of seconds. By simplifying the configuration, the transient all-optical method achieves high measurement accuracy and reliable reproducibility. The proposed method can effectively analyze the NFRHT in various material systems, including SiO2, SiC, and Si, which involve different phonon or plasmon polaritons. Experimental observations demonstrate significant super-Planckian radiation, which arises from the near-field coupling of bounded surface modes. Furthermore, the method achieves excellent agreement with theory, with a minimal discrepancy of less than 2.7% across a wide temperature range. This wireless method could accurately characterize the NFRHT for objects with different sizes or optical properties, enabling the exploration of both fundamental interests and practical applications.

CLIM: Co-occurrence with Laplacian Intensity Modulation and Enhanced Color Space Transform for Infrared-Visible Image Fusion

Thermal infrared and multispectral visible remote sensing image fusion combines thermal image information with corresponding visible scene content to generate a better representative fused image. Thermal images can distinguish targets using difference in thermal radiation measurements, whereas visible images contain better texture detail in multispectral wavelength bands. The article presents a novel methodology named CLIM to sharpen coarser spatial resolution multispectral remote sensing images using relatively higher spatial resolution broadband thermal infrared image. The boundary-preserving information is extracted from high resolution thermal infrared image using co-occurrence image filter, and is combined with Laplacian of Gaussian based sharpened image to extract salient features for injection. In addition, visible image is transformed to IHS color space, and intensity component is enhanced using CLAHE and inverse transformation to generate enhanced visible image for fusion. The procedure developed is evaluated with Indian Nano Satellite (INS) broadband thermal infrared images available at a spatial resolution of 175 m with same day acquisition MODIS multispectral visible images available at a relatively coarser spatial resolution of 500 m. The nearest acquisition of Landsat-8 thermal infrared images with MODIS multispectral visible images is also used for infrared–visible multi-modal image fusion. The CLIM fused image confirms that distinct features such as dam, ship docking zones and refinery regions, are better demarked and semantically more meaningful in comparison with individual thermal infrared and multispectral visible image. The proposed CLIM approach is compared with, and found to perform better than state-of-the-art image fusion techniques, both visually and quantitatively.

Dynamic optical spectroscopy and pyrometry of static targets under optical and x-ray laser heating at the European XFEL

Experiments accessing extreme conditions at x-ray free electron lasers (XFELs) involve rapidly evolving conditions of temperature. Here, we report time-resolved, direct measurements of temperature using spectral streaked optical pyrometry of x-ray and optical laser-heated states at the High Energy Density instrument of the European XFEL. This collection of typical experiments, coupled with numerical models, outlines the reliability, precision, and meaning of time dependent temperature measurements using optical emission at XFEL sources. Dynamic temperatures above 1500 K are measured continuously from spectrally- and temporally-resolved thermal emission at 450–850 nm, with time resolution down to 10–100 ns for 1–200 μs streak camera windows, using single shot and integrated modes. Targets include zero-pressure foils free-standing in air and in vacuo, and high-pressure samples compressed in diamond anvil cell multi-layer targets. Radiation sources used are 20-fs hard x-ray laser pulses at 17.8 keV, in single pulses or 2.26 MHz pulse trains of up to 30 pulses, and 250-ns infrared laser single pulses. A range of further possibilities for optical measurements of visible light in x-ray laser experiments using streak optical spectroscopy are also explored, including for the study of x-ray induced optical fluorescence, which often appears as background in thermal radiation measurements. We establish several scenarios where combined emissions from multiple sources are observed and discuss their interpretation. Challenges posed by using x-ray lasers as non-invasive probes of the sample state are addressed.

Six Years of IKFS-2 Global Ozone Total Column Measurements

Atmospheric ozone plays an important role in the biosphere’s absorbing of dangerous solar UV radiation and its contributions to the Earth’s climate. Nowadays, ozone variations are widely monitored by different local and remote sensing methods. Satellite methods can provide data on the global distribution of ozone and its anomalies. In contrast to measurement techniques based on solar radiation measurements, Fourier-transform infrared (FTIR) satellite measurements of thermal radiation provide information, regardless of solar illumination. The global distribution of total ozone columns (TOCs) measured by the IKFS-2 spectrometer aboard the “Meteor M N2” satellite for the period of 2015 to 2020 is presented. The retrieval algorithm uses the artificial neural network (ANN) based on measurements of TOCs by the Aura OMI instrument and the method of principal components for representing IKFS-2 spectral measurements. Latitudinal and seasonal dependencies on the ANN training errors are analyzed and considered as a first approximation of the TOC measurement errors. The TOCs derived by the IKFS-2 instrument are compared to independent ground-based and satellite data. The average differences between the IKFS-2 data and the independent TOC measurements are up to 2% (IKFS-2 usually slightly underestimates the other data), and the standard deviations of differences (SDDs) vary from 2 to 4%. At the same time, both the analysis of the ANN approximation errors of the OMI data and the comparison of the IKFS-2 results with independent data demonstrate an increase in discrepancies towards the poles. In the spring–winter period, SDDs reach 8% in the Southern and 6% in the Northern Hemisphere. The technique presented can be used to process the IKFS-2 spectral data, and as a result, it can provide global information on the TOCs in the period of 2015–2020, regardless of the solar illumination and the presence of clouds.

Thermal radiation and direct photon production measurements with dielectrons in Pb–Pb and pp collisions

The latest ALICE results on dielectron measurements in Pb–Pb collisions at √SNN = 5.02 TeV, and in minimum-bias (MB) and high-multiplicity (HM) pp collisions at √S = 13 TeV with LHC Run 2 data are reported. The results are compared to the predictions of dielectron yields from known hadronic sources and thermal radiation from the medium. The contribution of virtual direct photons is extracted from the data by fitting the measured invariant mass distributions. We present the direct to inclusive photon ratio, as well as the direct photon yield in both pp and central Pb–Pb collisions.

Transition from Phononic to Geometrical Mie Modes Measured in Single Subwavelength Polar Dielectric Spheres

Spherical dielectric resonators are highly attractive for light manipulation, thanks to their intrinsic electric and magnetic resonances. Here, we present measurements of the mid-infrared far-field thermal radiation of single subwavelength dielectric spheres deposited on a gold substrate, of radii ranging from 1 to 2.5 μm, which agree quantitatively with simulated absorption cross sections. For SiO2 microspheres, we evidence the excitation of both surface phonon-polariton (SPhP) modes and geometrical electric and magnetic Mie modes. The transition from a phonon-mode-dominated to a Mie-mode-dominated emission spectrum is observed, with a threshold radius of ∼1.5 μm. We also show that the presence of the metallic substrate augments the computed spheres absorption cross-section due to increased local field enhancement, arising from the near-field interaction of the spheres oscillating charges with their image in the metallic mirror. In contrast, measurements of single subwavelength SPhP-inactive PTFE spheres reveal that the mid-infrared response of such lossy spheres is dominated by their bulk absorption. Our results demonstrate how engineering the geometrical and dielectric properties of subwavelength scatterers can enable the control of thermal emission near room temperature, with exciting perspectives for applications such as radiative cooling.

Upper limit on the axion-photon coupling from magnetic white dwarf polarization

Polarization measurements of thermal radiation from magnetic white dwarf (MWD) stars have been proposed as a probe of axion-photon mixing. The radiation leaving the surface of the MWD is unpolarized, but if low-mass axions exist then photons polarized parallel to the direction of the MWD's magnetic field may convert into axions, which induces a linear polarization dependent on the strength of the axion-photon coupling $g_{a\gamma\gamma}$. We model this process by using the formalism of axion-photon mixing in the presence of strong-field vacuum birefringence to show that of all stellar types MWDs are the most promising targets for axion-induced polarization searches. We then consider linear polarization data from multiple MWDs, including SDSS J135141 and Grw+70$^\circ$8247, to show that after rigorously accounting for astrophysical uncertainties the axion-photon coupling is constrained to $|g_{a\gamma\gamma}| \lesssim 5.4 \times 10^{-12}$ GeV$^{-1}$ at 95% confidence for axion masses $m_a \lesssim 3 \times 10^{-7}$ eV. This upper limit puts in tension the previously-suggested explanation of the anomalous transparency of the Universe to TeV gamma-rays in terms of axions. We identify MWD targets for which future data and modeling efforts could further improve the sensitivity to axions.

Towards moss-dominated biocrust effects on soil temperature across seasons in drylands: Insight from continuous measurements of soil thermal properties and solar radiation

Globally widespread, biocrusts form a “living skin” on most dryland soils, helping govern fundamental ecosystem functions, particularly water and heat balances in drylands. Nevertheless, the underlying mechanisms of biocrust effects on topsoil thermal properties and temperature (T) are still unclear. In this study, we continuously measured thermal properties of moss-dominated biocrusts and bare soil (aeolian sand) at 1 cm depth by utilizing heat pulse probes for one year on the Chinese Loess Plateau. The surface soil water content (θ), net all-wave radiation (Jn), surface albedo (α), heat flux (G), and other properties were further measured to analyze their connections with soil thermal properties. Our results indicated that biocrusts decreased (F ≥ 1.91, P ≤ 0.031) heat capacity (C), thermal conductivity (λ), and thermal diffusivity (κ) by 1.6% (1.36 vs. 1.38 MJ m−3 K−1), 11.6% (0.62 vs. 0.69 W m−1 K−1), and 8.7% (0.62 vs. 0.69 × 10−7 m2 s−1) on average, respectively, in contrast to bare soil. Moreover, biocrusts variously regulated soil thermal properties in dry and wet seasons owing to the influences of rainfall events and θ. As compared with bare soil, the C, λ, and κ of biocrusts in dry season (Nov.–Apr.) were decreased by 5.7%, 19.0%, and 12.2%, respectively; while only the C was increased by 2.2% by biocrusts in wet season, but the λ and κ of biocrusts were similar to that of bare soil. Furthermore, biocrusts increased θ both in dry (by 5.0 times) and wet (by 3.5 times) seasons as compared with bare soil. Especially, biocrusts decreased α by 32.1% (0.19 vs. 0.28) and G (at 8 cm depth) by 20.0% (0.8 vs. 1.0 W m−2 s−1), and increased Jn by 30.1% (73.0 vs. 56.1 W m−2) in comparison to bare soil. Lastly, combining with the higher θ and lower α as well as the lower soil thermal properties, biocrusts greatly increased T by 1.7 ℃ (up to 4.5 °C; P < 0.001) on average. In conclusion, moss-dominated biocrusts have great regulating effects on surface soil thermal properties and T, and these effects are mostly attributed to their lower bulk density and α but higher porosity and water-holding capacity, which further change surface θ and T regimes and play a vital role in soil water and heat balances as well as other critical processes in drylands.

Temperature characteristics of Ge/ZnS one-dimension photonic crystal for infrared camouflage

In this paper, we investigate the temperature characteristics of Ge/ZnS one-dimension photonic crystal film for infrared camouflage, which is demonstrated low infrared emissivity at room temperature. The prepared film exhibits infrared camouflage capability with variable temperatures up to 400 °C. The infrared emissivity is 0.091 for 3–5 μm and 0.128 for 8–14 μm respectively at 400 °C. The thermal images also indicate the reduction of thermal radiation with the radiation temperature of 112.3 °C, while the real object temperature is 400 °C. This work demonstrates the infrared camouflage performance of Ge/ZnS one-dimension photonic crystal at variable temperatures. • We proposed an infrared camouflage structure for both 3–5 μm and 8–14 μm based on Ge/ZnS one-dimension photonic crystal. • The structure exhibits ideal dual-band infrared low emissivity characteristic up to 400 °C with temperature insensitivity. • The thermal radiation measurements indicate that the structure can meet the requirements of high-temperature infrared camouflage.

Enhancing anti-oxidation and thermal-radiation performance of the repaired borosilicate glass coating on C/C composites by Sm-doping

To repair the damaged SiC coated C/C composites, a double-layer system including a Sm-doped borosilicate glass external layer and a SiSiC inner layer was prepared by a slurry-based laser cladding technique. Isothermal oxidation experiment and indirect/direct thermal-radiation measurements were performed. The results showed that the absorbance of borosilicate glass to the laser at 900–1200 nm was improved significantly by Sm-doping. Consequently, the repaired coating with a more compact structure and better oxidation resistance was obtained. After oxidation at 1773 K for 10 h, the mass loss of the damaged sample could be reduced by 74.98% with repairing. By increasing laser-absorption and reducing viscosity, the thermal-radiation property of the repaired coating was enhanced to decrease the surface temperature greatly. A repair system with excellent thermal protection performance was achieved.

Fly-Ash-Based Geopolymers Reinforced by Melamine Fibers.

This paper presents the results of research on geopolymer composites based on fly ash with the addition of melamine fibers in amounts of 0.5%, 1% and 2% by weight and, for comparison, without the addition of fibers. The melamine fibers used in the tests retain their melamine resin properties by 100% and are characterized by excellent acoustic and thermal insulation as well as excellent filtration. In addition, these fibers are nonflammable, resistant to chemicals, resistant to UV radiation, characterized by high temperature resistance and, most importantly, do not show thermal-related shrinking, melting and dripping. This paper presents the results of density measurements, compressive and flexural strength as well as the results of the measurement of thermal radiation changes in samples subjected to a temperature of 600 °C. The results indicate that melamine fibers can be used as geopolymer reinforcement. The best result was achieved for 0.5% by weight amount of reinforcement, approximately 53 MPa, compared to 41 MPa for a pure matrix. In the case of flexural strength, the best results were obtained for the samples made of unreinforced geopolymer and samples with the addition of 0.5% by weight of melamine fibers, which were characterized by bending strength values above 9 MPa, amounting to 10.7 MPa and 9.3 MPa, respectively. The thermal radiation measurements and fire-jet test did not confirm the increasing thermal and fire resistance of the composites reinforced by melamine fiber.

First Satellite Measurements of Carbon Dioxide in the Earth’s Atmosphere (From the SI-1 Spectrometer Aboard the Meteor Satellite in 1979)

Spectral measurements of the outgoing thermal IR radiation carried out in 1977 and 1979 (SI-1 instrument, Meteor satellite) are used for estimating the CO2 content in the Earth’s atmosphere. A special algorithm based on the technique of artificial neural networks has been developed for solving the inverse problem of determining the CO2 content. The algorithm uses experimental spectra, as well as data on temperature and humidity from the NCEP CFSR reanalysis archive. Despite the presence of a noticeable variation in individual values of CO2 content in 1977 and 1979 (330–350 ppm), the estimates clearly demonstrate the seasonal variations of the carbon dioxide content for Europe and low values for the Southern Hemisphere. The spatial and temporal averaging of the retrieved CO2 estimates gives mean winter and spring–summer values for the European region at 338.2 and 336.5 ± 3.1 ppmv, correspondingly, which is in a good agreement with the ground-based measurements at Mauna Loa station.

Effects of the Bluff-Body Diameter on the Flow-Field Characteristics of Non-Premixed Turbulent Highly-Sooting Flames

ABSTRACT This paper presents a joint experimental and computational study of the effect of the bluff-body diameter on the flow field and residence time distribution (RTD) in a set of turbulent non-premixed ethylene/nitrogen flames with a high soot load. A novel optical design has been developed to undertake the PIV measurements successfully in highly-sooting turbulent flames, using polarizing filters. The mean velocity components and turbulent intensity are reported for three bluff-body burners with different bluff-body diameters (38, 50, and 64 mm), but which are otherwise identical in all other dimensions. The central jet diameter of 4.6 mm was supplied with a mixture of ethylene and nitrogen (4:1, by volume) to achieve a bulk Reynolds number of 15,000 for the reacting cases. Isothermal cases were also investigated to isolate the effect of heat release on the flow fiel. Pure nitrogen was utilized in the isothermal cases where the Reynolds number was kept the same as the reacting cases. The annular bulk velocity of the co-flowing air was kept constant at 20 m/s for all experiments. Computationally, a 2-D RANS model was developed, validated against the experimental data and was mainly used to investigate the effect of the bluff body diameter on the residence time in the recirculation zone. The flow structure for both isothermal and reacting cases was found to be consistent with the literature, exhibiting similar vortical structures of the recirculating zone and mixture fraction distribution, for similar momentum flux ratios. The flame length and volume were found to decrease by 20% and 9%, respectively, as the bluff diameter was increased from 38mm to 64mm. The length of the recirculation zone for the isothermal cases was found to be ~1.2DBB, while for the reacting cases it was ~1.5–1.75DBB. A stochastic tracking model was employed to estimate the pseudo-particles’ residence time distribution in the recirculation region. The model revealed that an increase in the bluff body diameter from 38mm to 64 mm leads to tripling of the mean residence time within the recirculation zone. Thermal radiation measurements from the recirculation zone show a 35% increase as the bluff body diameter is increased from 38 mm to 64 mm, whilst the total radiation from the whole flame drops by 15%, which is deduced to be due mostly to the decrease in flame volume. The effect of these differences on soot propensity and transport are described briefly and will be the subject of future investigations.

Thermal radiation measurements of downward spreading flames

Radiative emission from a flame is an important component of the heat transfer balance between flame and surroundings. When the residence time of the oxidizer increases radiation plays an important role, and a practical example is given by microgravity flames where the lack of buoyancy creates larger time scales of the problem. With a strong opposed-flow, however, radiation could become a secondary effect. This study presents experimental measurements of thermal radiation from downward spreading flames over thin sheets of PMMA (polymethyl methacrylate) in a normal gravity environment and no forced flow. Radiation data from these downward spreading flames can serve as a baseline for future microgravity experiments. The presented experiments are performed in an apparatus called Flame Stabilizer where a spreading flame is turned stationary in laboratory coordinates by moving the sample upwards at the same velocity as the downward spreading flame. A radiometer, capable of line of sight measurement, is mounted on a x-y-z position controller and used to map the radiation emitted by the flame and the burning solid perpendicular to the fuel surface. After establishing repeatability and consistency of the results, a family of radiation profile curves is generated to map the radiation field. The experiments are then repeated by varying fuel thickness; larger fuel thicknesses are found to generate stronger radiation signals as the flame size becomes bigger. Furthermore, the radiative response to the presence of char in a flame is illustrated by comparing the PMMA results with a cellulosic fuel. With the unburnt solid in the flame region, radiative emissions significantly increase.

UWB Patch Antenna with Composite Dielectric Substrate for Subcutaneous Biomedical Sensing

An ultra-wideband patch antenna intended as the front end of microwave imaging sensor is presented in this paper. The proposed antenna is meant for subcutaneous biomedical applications as thermal radiation measurements. Sensors for health applications can always gain from improved matching techniques when placed in direct contact with human tissue. While sensors commonly utilize dielectric gel as the coupling material, the novelty of the proposed antenna consists of the fact that instead of an external matching medium, the antenna incorporates the matching capability in its structure. The proposed antenna has a complex porous substrate structure enriched with conductive-dielectric fluid and metallic rods yielding the proper characteristics in order to reduce the impedance mismatching when in direct contact to the human body. Moreover it has the low profile and the small volume needed for medical imaging applications. Measurements of the electrical characteristics are in good agreement with the simulated ones and they validate the proposed design.

DC Arc discharge synthesized zirconia nanoparticles: shed light on arc current effects on size, crystal structure, optical properties and formation mechanism

In this study zirconia nanoparticles (NPs) were successfully synthesized via the direct current (DC) arc discharge method in water. Formation mechanism of NPs and the effect of arc current on morphological, structural and optical properties of NPs have been studied. The NPs were synthesized at four different currents in the 40–160 A range. SEM observations showed NPs are spherical in shape and their average size decrease from 40 to 22 nm by increasing the current from 40 to 160 A. XRD analysis revealed phase composition of NPs is a mixture of tetragonal and monoclinic for all the samples, and the phase fraction of NPs are arc current dependent in such a way that an increase in the current leads to an increase in the weight percent of the tetragonal phase. UV–vis spectroscopy indicated that the NPs exhibit optical characteristics of the wide energy band gap semiconductors with a significant amount of oxygen deficiency. Also the effect of the arc current on the energy band gap of NPs were investigated. An increase in the arc current decreases energy band gap of the NPs from 3.8 to 3.0 eV. Optical emission spectroscopy (OES) studies demonstrate formation of zirconia NPs at temperatures as high as 4953 K, thereby zirconium exited species react with some of oxygen containing species. Finally, Thermal radiation measurement is proposed as a nondestructive method to evaluate the active mechanisms in an arc discharge zone beside other methods such as OES.

Measurement of the Core Human Body Temperature by Means of Passive Acoustic Thermometry

The purpose of the study. To determine whether it is possible to use passive acoustic thermometry to measure the core temperature of human body regions. Materials and methods. Thermal acoustic radiation was measured by a multichannel acoustic thermograph with a threshold sensitivity of 0.3°С at an integration time of 10 s. A portable computer infrared thermograph with a sensitivity of 0.1°С was used to measure the superficial temperature. Results. Measurements of thermal acoustic radiation of the right hypochondrium of the study subject were carried out to obtain an integral temperature of the liver after intake of sugar. At the same time, blood glucose concentrations were measured. The glucose level increased from 4 to 8 mmol/l within an hour and a half; then it began to decline. The acoustic radiation temperature increased by 2°С with a half an hour delay after the increase in the glucose level. Model calculation showed that the liver temperature increased from 37 to 38°С. Conclusion. It was shown that passive acoustic thermometry can be used to measure the core temperature of different regions of the human body. The proposed method may be useful in the emergency medicine.

Midwave FTIR-Based Remote Surface Temperature Estimation Using a Deep Convolutional Neural Network in a Dynamic Weather Environment.

Remote measurements of thermal radiation are very important for analyzing the solar effect in various environments. This paper presents a novel real-time remote temperature estimation method by applying a deep learning-based regression method to midwave infrared hyperspectral images. A conventional remote temperature estimation using only one channel or multiple channels cannot provide a reliable temperature in dynamic weather environments because of the unknown atmospheric transmissivities. This paper solves the issue (real-time remote temperature measurement with high accuracy) with the proposed surface temperature-deep convolutional neural network (ST-DCNN) and a hyperspectral thermal camera (TELOPS HYPER-CAM MWE). The 27-layer ST-DCNN regressor can learn and predict the underlying temperatures from 75 spectral channels. Midwave infrared hyperspectral image data of a remote object were acquired three times a day (10:00, 13:00, 15:00) for 7 months to consider the dynamic weather variations. The experimental results validate the feasibility of the novel remote temperature estimation method in real-world dynamic environments. In addition, the thermal stealth properties of two types of paint were demonstrated by the proposed ST-DCNN as a real-world application.