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Our study is devoted to the thermophysical properties of solid and liquid nickel in the vicinity of the melting point. For this purpose, we use a first-principles calculation method based on quantum molecular dynamics and experimental measurements with a pulse heating technique. We provide experimental and calculated data on thermal expansion, molar enthalpy, sound velocity, resistivity, and normal spectral emissivity and analyze them together with available experimental and reference data on solid and liquid Ni. We confirm experimentally and computationally the strong temperature dependence of Ni density observed in several experiments. Our fusion enthalpy measurements are in good agreement with the recommended literature data, and the calculation predicts a slightly smaller change in enthalpy. The experimental measurements of nickel resistivity in the solid and liquid states agree with previous experimental data that take into account its correction for thermal expansion. At the same time, our calculation of the resistivity in the solid phase shows a systematic shift. For liquid nickel, we report a weak nonlinear temperature dependence of the normal spectral emissivity. Thus, taking advantage of experimental and ab initio computational approaches, we present consistent data on the thermophysical properties of solid and liquid Ni. [ABSTRACT FROM AUTHOR]

This work proposed a fast inverse design method for microwave and infrared (IR) bi-stealth metamaterials based on the equivalent circuit model (ECM). Using this method, we designed a microwave and IR bi-stealth metamaterial by deploying a multilayered structure of the indium tin oxide (ITO) film based metasurface. First, the IR emissivity of the ITO film was calculated in the framework of the ECM. Then, an ITO metasurface was proposed to implement low IR emission and high microwave transmission simultaneously. Based on the ECM of the square patch, the ECM of the whole metamaterial was established at the microwave band. An inverse design program was built by incorporating the ECM with genetic algorithm (GA). Structure parameters of the metamaterial were optimized by GA to achieve the broadest microwave stealth bandwidth for the given thickness. Finally, the sample of the optimized bi-stealth metamaterial was prepared and tested. The calculated, simulated, and measured results are in good agreement, showing that such a metamaterial has an IR emissivity of 0.18 in the band from 3 to 14 μm and an efficient microwave stealth band from 4.8 to 17 GHz with a thickness of 4.9 mm. The proposed method will benefit the design and application of microwave and IR bi-stealth metamaterials. [ABSTRACT FROM AUTHOR]

Efficient absorption of solar radiation holds the key to photothermal utilization; however, realizing solar absorber designs with high absorption efficiency remains challenging. Herein, a nickel-based metamaterial selective solar absorber with a nanopillar array structure was proposed to realize nearly perfect optical absorption over a broad spectrum. The average absorbance is up to 96% in the 300–2033 nm wavelength range. Notably, a reasonably detailed analysis of the physical mechanism of the proposed absorber was performed in this paper, attributing the exceptional broadband absorption to the concurrent interaction with surface plasmon resonance, quarter-wavelength resonance, and electric dipole resonance. The absorption efficiency declines significantly when λ > 2.5 μm, with only 20% absorptivity at λ = 6 μm in the radiation-absorbing transition region. This decline is desirable, as it contributes to reducing the emissivity in the mid-infrared range and, therefore, prevents self-radiation. The results demonstrate that the selective absorber possesses the potential to capture solar energy within a broadband, while avoiding undesirable self-radiation, thereby enhancing the integral efficiency of the solar energy conversion system. Moreover, the absorption spectrum shows insensitivity to polarization and angle of incidence. The selective solar absorber proposed here offers excellent performance with a simple structure, showing great promise in the field of photothermal conversion. [ABSTRACT FROM AUTHOR]

An improved photothermal technique for evaluating opaque coating thicknesses using a normalized DC component is proposed. The pump beam is modulated at a frequency that the generated thermal wave only exists in the coating layer and becomes invariant to the thickness changes. The DC component is normalized by the amplitude of the AC signal in order to eliminate the dependency on the pump intensity, surface absorptivity, and emissivity. Both theoretical analysis and experimental results demonstrate that the normalized DC component is linearly correlated to the coating thickness over a broad range. This method offers a significant advantage over existing photothermal methods by avoiding the tedious procedure of frequency trails for coatings of an unknown thickness. Also, the non-monotonic issue is successfully resolved. [ABSTRACT FROM AUTHOR]

Modulating the emissivity of yttria-stabilized zirconia (YSZ) ceramics in the 3–5 μm range through doping and structural adjustments is crucial for their application as high-temperature low-emissivity materials. This study examined YSZ composite ceramics with various levels of lanthanum fluoride (LaF 3) doping, sintered using a high-temperature solid-phase reaction method, to compare their infrared emissivity within the 3–5 μm range. A systematic investigation focused on the effects of the crystal structure and microporous structure evolution on the infrared emissivity of YSZ/LaF 3 composite ceramics. The results revealed that increasing the LaF 3 doping led to lattice expansion and an increase in oxygen vacancies within the YSZ. When the doping limit of La3+ ions is exceeded, La 2 Zr 2 O 7 is formed. At high doping levels, the formation of volatile ZrF 4 was identified as the primary cause of increased porosity of the composite ceramics. Consequently, the emissivity of the composite ceramics in the 3–5 μm range is minimized at a doping level of 3 mol%. For small amounts of doping, this represents the optimal balance between the lattice expansion and oxygen vacancies. However, at higher doping levels, the increased porosity becomes the dominant factor, reducing the emissivity of the composite ceramics. [ABSTRACT FROM AUTHOR]

Daytime radiative cooling material provides a low‐energy way of cooling because it can reflect sunlight and radiate heat without consuming any energy. However, there are still great difficulties in manufacturing low‐cost, high‐efficiency, sustainable, and biodegradable daytime radiative cooling materials. In this paper, poly (vinyl alcohol)/boron nitride (PVA/BN) composite aerogels were prepared by freeze‐drying technology. By adjusting the PVA concentration and BN content, the aerogel can achieve high sunlight reflectivity (96%), high mid‐infrared emissivity (96%) and good thermal insulation performance. Therefore, the temperature of the aerogel can be reduced to 12.5°C lower than the ambient temperature at night, and 5.5°C lower than the ambient temperature under the direct sunlight of 900 W/m2. This aerogel opens an environmentally sustainable pathway for radiative cooling applications. [ABSTRACT FROM AUTHOR]

Passive cooling is a cooling technology that does not require external energy input, with most passive cooling strategies having high manufacturing difficulty and cost. In this study, we prepared lightweight aerogels (0.093 g/cm3) with high porosity (91.3%), directional pores, enhanced elastic recovery performance, and lower thermal conductivity (0.046 W/mK) through simple mixing, directional freezing, and freeze‐drying. The prepared samples have a reflectance of 87% in the ultraviolet—visible—near‐infrared (UV‐Vis‐NIR) range (0.2–2.5 μm) and an emissivity of 93.6% in the atmospheric transparency window. After covering the box with axial and transverse aerogel samples, the temperature inside the box relative to the uncovered sample box decreased by 12.9 and 13.4°C, respectively. This work provides a feasible method for the research of simply prepared passive cooling materials. [ABSTRACT FROM AUTHOR]

In this study, cerium dioxide (CeO 2) materials doped with one (Gd3+, GDC), two (Gd3+ and Na+, GNDC), and three (Gd3+, Na+, and Eu3+, EGNDC) components were, respectively, prepared, and their high-temperature infrared emissivity was investigated through experimental measurements and theoretical calculations. The experimental results show that GDC exhibits the highest oxygen vacancy concentration, highest conductivity, and narrowest band gap; furthermore, it exhibits an ultralow infrared emissivity (0.202 at 600 °C). The band structure calculations reveal that the Fermi level of GDC shows the highest total density of states, and electrons are more likely to enter the conduction band, which increases the conductivity and thus reduces the infrared emissivity. Furthermore, the infrared reflectance decreases gradually with increasing number of doping components, and the highest infrared reflectance and lowest infrared emissivity for GDC are obtained at 3–5 μm. These findings are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, we consider a mathematical model, which has a unique mechanism of heat transfer in the stretching/shrinking straight fin with an exponential profile. The thermal conductivity, internal heat generation, and heat transfer coefficient are considered temperature‐dependent. Heat is exposed to the surroundings by convection and radiation. The governing differential equation and boundary conditions are presented in a dimensionless form. In our study, we considered variable surface emissivity, that is, a constant, and the linear function of a temperature. The convective heat transfer parameter is considered a power‐low type. The novelty of this work is the application of temperature‐dependent surface emissivity, and the problem is solved by the Legendre wavelet collocation method. A comparative analysis of the present results in the context of previous findings is presented in the form of a table for validation and found exactly the same. The impacts of distinct variables are presented in the form of figures and discussed in detail. The present analysis is focused on real‐world applications and offers valuable insights for improving the design of fins. [ABSTRACT FROM AUTHOR]

Microwave emissivity is an important parameter for over-land retrieval of atmospheric variables such as water vapour, rainfall, and snowfall. However, it remains unclear for the dynamic response of multi-frequency microwave emissivity to prior rainfall over heterogeneous land surfaces. This study combined multi-frequency Microwave Land Surface Emissivity (MLSE) under all-weather conditions with hourly in-situ rainfall to investigate the response of MLSE to rainfall over different vegetation types in Hainan Island in China. Specifically, we explored the change of MLSE at 6.925, 10.65, 18.7, 23.8 and 36.5 Ghz to rainfall intensity in four rainfall cases, followed with statistical characteristics of MLSE to rainfall and dry duration (DD) across different vegetation types during 2003–2010. We found that the magnitude of decline in MLSE (0.004–0.06) is dependent on the rainfall intensity and duration, and the reduction caused by short-lasting heavy rain (daily rainfall >100 mm) was 2–6 times higher than that by light long-lasting rain (daily rainfall <80 mm). Among different microwave frequencies, the MLSE at 23.8 Ghz was most reduced by rainfall, while less reduction was found at low microwave frequencies such as at 6.925 and 10.65 Ghz. More importantly, the change of MLSE after rainfall was significantly different among vegetation types. Over woody savannas and forested lands, MLSE slightly decreased (about 0.004) in the first two hours of DD, whereas a rapid increase was observed in the first hour of DD over areas dominated with woody savanna, grassland, and cropland. These findings improve our understanding of the multi-frequency MLSE in response to rainfall over complex land surfaces, and benefit the microwave retrieval of rainfall over land. [ABSTRACT FROM AUTHOR]

Temperature‐adaptive variable emissivity reflectors offer an electricity‐free and environmentally friendly cooling strategy, holding substantial potential to improve the global energy landscape. However, challenges associated with unoptimized solar absorptance can lead to overcooling or overheating when the modulation of infrared emittance is held constant, thereby increasing extra energy consumption. Herein, a temperature‐adaptive variable emissivity reflector based on W‐Mg co‐doped VO2 (W‐Mg‐VER) is proposed, engineered to optimize solar absorptance (αL = 0.40) while maintaining effective infrared emittance modulation (Δɛ = 0.69) near ambient temperature. To maximize year‐round energy savings in regions experiencing significant daily temperature fluctuations, W‐Mg co‐doped VO2 is employed to reduce solar absorptance by modifying electron occupancy in the V 3d orbital and expanding the optical bandgap. Outdoor experiments have validated the remarkable temperature management and energy‐saving capabilities of the W‐Mg‐VER, facilitated by its seamless transition between radiative cooling and heat‐retaining modes. Numerical simulation indicates that a W‐Mg‐VER roof covering 100 m2 would save 152.9 GJ of energy annually in locations with significant daily temperature variations. Moreover, W‐Mg‐VER demonstrates robust performance, exhibiting less than 1% degradation in emittance tunability and solar absorptance after 10 000 cycles. This approach provides valuable insights and practical guidance for significantly enhancing global energy savings. [ABSTRACT FROM AUTHOR]

Accurate measurement of the infrared spectral emissivity of nickel-based alloys is significant for applications in aerospace. The low thermal conductivity of these alloys limits the accuracy of direct emissivity measurement, especially during the oxidation process. To improve measurement accuracy, a surface temperature correction method based on two thermocouples was proposed to eliminate the effect of thermal conductivity changes on emissivity measurement. By using this method, the infrared spectral emissivity of Inconel 601, Inconel 625, and Inconel 718 alloys was accurately measured during the oxidation process, with a temperature range of 673–873 K, a wavelength range of 3–20 μm, and a zenith angle range of 0–80°. The results show that the emissivity of the three alloys is similar in value and variation law; the emissivity of Inconel 718 is slightly less than that of Inconel 601 and Inconel 625; and the spectral emissivity of the three alloys strongly increases in the first hour, whereafter it grows gradually with the increase in oxidation time. Finally, Inconel 601 has a lower emissivity growth rate, which illustrates that it possesses stronger oxidation resistance and thermal stability. The maximum relative uncertainty of the emissivity measurement of the three alloys does not exceed 2.6%, except for the atmospheric absorption wavebands. [ABSTRACT FROM AUTHOR]

For today's high‐quality steel production, good control of slag composition is essential in secondary steelmaking. However, the conventional slag analysis practice, involving sampling, sample preparation, and analysis, is very time‐consuming. This work is the first step toward an investigation of infrared (IR)‐based systems and can be used for online slag composition monitoring using the principle that different slag compositions have different emissivities in the IR wavelength range. Therefore, this work experimentally determines emissivity values of slags as a function of composition at steelmaking temperature, since available data for slags are very limited in the literature. The emissivities of three different slag compositions belonging to the Al2O3–CaO–SiO2–MgO system are investigated at 1773 K. The investigated emissivities are in the range of 0.75–0.87, with the best repeatability seen in the slag which is fully liquid at 1773 K. Variations in emissivities are observed within the other slags due to the presence of solid phases. Although the data clearly indicate a difference of emissivities as a function of slag composition, further experiments must be performed to evaluate the emissivities of other characteristic slags at different temperatures in order to further assess the applicability of IR‐based systems for slag composition control. [ABSTRACT FROM AUTHOR]

Electromagnetic performance regulation in mid‐infrared (MIR) and microwave (MW) spectrums is crucially significant, which can be achieved by heterophase introduction and structural manufacturing. In this work, Si‐O amorphous phase is introduced into Pt film by magnetron co‐sputtering technique, the film thickness is optimized by adjusting deposition time. After annealing treatment, a double‐layered structure is constructed with the migration and growth of Pt crystals, in which the lower layer is composed of Pt coarse grains while the upper layer is Si‐O amorphous phase with embedded Pt fine grains. Furthermore, due to the thickness difference, diverse kinds of structural patterns (arrays or mesh) can be obtained with the solid‐state dewetting of the lower layer. According to the increasing thickness, the infrared emissivity can decrease from 0.67 to 0.25 (8–14 μm), demonstrating a great decline of apparent temperature of 162.9 °C when the background is 300 °C. And the microwave transmissivity also exhibits tremendous variation over 90% (from 96% to 5%), realizing the transformation from transmitting to shielding. [ABSTRACT FROM AUTHOR]

Results of investigating the emissivity of metals of group II of the Periodic Table in the interval of temperatures "solid body–liquid" have been presented. Selection of the objects of investigation, i.e., metallic beryllium, magnesium, and calcium, has been argued by the absence, in practice, of data on the emissivity of these elements in a broad temperature range from periodic and reference literature. The measurement method was radiative, and the technique of heating of a metal specimen, resistive. A structure of a cylindrical model of an ideal black body with an emissivity factor no lower than 0.99 has been presented. The material of the equilibrium-radiation source was metallic tantalum. The estimate of experimental uncertainty amounted to 5–8%. Graphic illustrations of experimental results on each investigated element have been presented. The obtained complex experimental data on normal integral emissivity within the limits of each phase of state of the metals grew monotonically. In the region of phase transition of the first kind, the characteristic abrupt change in the emissivity of the metals was observed. Investigation results have been discussed and compared with the literature data of other authors. A theoretical calculation of the emissivity of these metals from the classical electromagnetic theory has been carried out with the Foot approximation. The conclusion has been drawn on the disagreement between the theoretical calculations on emissivity and the experimental data. [ABSTRACT FROM AUTHOR]

Upcoming submillimeter wave satellite missions require an improved understanding of sea ice emissivity to separate atmospheric and surface microwave signals under dry polar conditions. This work investigates hectometer-scale observations of airborne sea ice emissivity between 89 and 340 GHz , combined with high-resolution visual imagery from two Arctic airborne field campaigns that took place in summer 2017 and spring 2019 northwest of Svalbard, Norway. Using k -means clustering, we identify four distinct sea ice emissivity spectra that occur predominantly across multiyear ice, first-year ice, young ice, and nilas. Nilas features the highest emissivity, and multiyear ice features the lowest emissivity among the clusters. Each cluster exhibits similar nadir emissivity distributions from 183 to 340 GHz. To relate hectometer-scale airborne measurements to kilometer-scale satellite footprints, we quantify the reduction in the variability of airborne emissivity as footprint size increases. At 340 GHz , the emissivity interquartile range decreases by almost half when moving from the hectometer scale to a footprint of 16 km , typical of satellite instruments. Furthermore, we collocate the airborne observations with polar-orbiting satellite observations. After resampling, the absolute relative bias between airborne and satellite emissivities at similar channels lies below 3 %. Additionally, spectral variations in emissivity at nadir on the satellite scale are low, with slightly decreasing emissivity from 183 to 243 GHz , which occurs for all hectometer-scale clusters except those predominantly composed of multiyear ice. Our results will enable the development of microwave retrievals and assimilation over sea ice in current and future satellite missions, such as the Ice Cloud Imager (ICI) and EUMETSAT Polar System – Sterna (EPS–Sterna). [ABSTRACT FROM AUTHOR]

In this paper, a stacked cylinder solar absorber with a bimetallic dielectric layer ( F e and A l 2 O 3 ) is proposed. Simulations using the finite-difference time-domain method reveal the proposed absorber can achieve an average absorbance greater than 90% in the visible to near-infrared wavelength range (455–3527 nm). Beyond this, in the solar radiation range of 280 ~ 4000 nm, under AM 1.5, the weighted average absorption is 96.36%. By exploring the mechanism of this absorption, we analyze the electromagnetic field distribution maps of the three peaks. It can be seen that the reason for the bandwidth absorption is that the depth of the bimetallic dielectric cylinder generates surface plasma of different wavelengths. The incident angle insensitivity and polarization independence of the absorber are also studied in detail. The simulation results show that the thermal emissivity is increased when the temperature goes up, a high thermal emissivity of 94.3% is obtained when the temperature is 1700 K. Due to the high-temperature resistance of Fe and A l 2 O 3 , the proposed model can be widely used in photothermal conversion and thermal radiators. [ABSTRACT FROM AUTHOR]

For modern land surface models (LSMs) representing a singular bulk vegetation layer, the longwave optical properties (i.e., emissivity, reflectivity, and transmittivity) of vegetation layer are derived with a simplified constraint of assuming zero leaf reflectivity. This constraint is necessary, for instance, to the Beer–Lambert (B–L) law to establish a relationship between the optical properties and leaf area index. However, the simplified constraint leads to an overestimation of land surface emissivity in the vegetated regions. In this study, we introduce a new scheme considering realistic leaf reflectivity values rather than assuming zero. This new scheme is based on the relationship derived from the B–L law, but it is statistically augmented to consider the effects of leaf reflections. It is designed to emulate a multi‐vegetation‐layer numerical model known as the Norman model, which is capable of numerical calculations of multi‐reflections among leaves. This new method consists of only a couple of simple equations; despite its simplicity, it very closely mimics the Norman model; The discrepancy of the results between the new method and the Norman model is less than measurement uncertainties for any combination of input parameters. When the new scheme is implemented in the Community Land Model version 5 (CLM5), the land surface emissivity values are simulated much more consistently with global measurements, resulting in significant alterations of land surface energy budget. The enhanced realism through our new scheme is poised to contribute to more accurate numerical weather and climate simulations. Plain Language Summary: In many state‐of‐the‐art land surface models (LSMs), vegetation is represented as a single layer overlying the ground. In calculations for land surface processes, it is essential to determine the emissivity, reflectivity, and transmittivity of a vegetation layer; these properties for longwave radiation are, typically, either calculated using a simple function that relates them to the leaf area index or are prescribed to be constants. All these methods utilized a simplified constraint of zero leaf reflectivity, resulting in an apparent overestimation of the land surface emissivity over vegetated surface. In this study, a new method is developed to eliminate the simplified constraint and to consider leaf reflections. The new method is designed to be simple, having only a couple of simple equations, but involving the effect of multiple reflections of radiative beams among leaves. When the new method is applied to an LSM with realistic values of leaf reflectivity, the LSM yields much more accurate global patterns of land surface emissivity, accompanied by significant changes in land surface energy balance. Owing to its simplicity, this method is expected to be applied readily to various LSMs, potentially contributing to enhanced realism of weather and climate simulations. Key Points: A new scheme considers leaf reflection when deriving vegetation layer longwave optical properties for land surface modelDespite its simplicity, the new scheme demonstrates accuracy comparable to expensive numerical multi‐layer radiative transfer modelThe new scheme generates land surface emissivity values exhibiting greater agreements with satellite retrievals compared to previous schemes [ABSTRACT FROM AUTHOR]

Thermal camouflage is a highly coveted technology aimed at enhancing the survivability of military equipment against infrared (IR) detectors. Recently, two-dimensional (2D) nanomaterials have shown low IR emissivity, widely tunable opto-electronic properties, and compatibility with stealth applications. Among these, graphene and graphene-like materials are the most appealing 2D materials for thermal camouflage applications. In multilayer graphene (MLG), charge density can be effectively tuned through sufficiently intense electric fields or through electrolytic gating. Therefore, MLG's optical properties, like infrared emissivity and absorbance, can be controlled in a wide range by voltage bias. The large emissivity modulation achievable with this material makes it suitable in the design of thermal dynamic camouflage devices. Generally, the emissivity modulation in the multilayered graphene medium is governed by an intercalation process of non-volatile ionic liquids under a voltage bias. The electrically driven reduction of emissivity lowers the apparent temperature of a surface, aligning it with the background temperature to achieve thermal camouflage. This characteristic is shared by other graphene-based materials. In this review, we focus on recent advancements in the thermal camouflage properties of graphene in composite films and aerogel structures. We provide a summary of the current understanding of how thermal camouflage materials work, their present limitations, and future opportunities for development. [ABSTRACT FROM AUTHOR]

In this work, an approximate solution is given to compute the gas emissivities and absorptivities for H2O–CO2–CO mixtures. The proposed model is valid for temperatures from 300 to 2700 K and pressure path‐length (PxL) $({P}_{x}L)$ from 0.06 to 40 atm m. In the calculation of the analytical solution (AS), the nonlinear methods of Galerkin and Ritz were implemented based on the residual solution of the differential roots of the Finite Element Method. For each point value (PxL;T) $({P}_{x}L;T)$ using the AS, the spectral absorptivity aλ ${a}_{\lambda }$ and emissivity ελ ${\varepsilon }_{\lambda }$ were determined, while for the gas mixture the emissivity εm ${\varepsilon }_{m}$ and absorptivity am ${a}_{m}$ were computed using the Hottel Graphical Method (HGM) and the proposed method. In the emissivity calculations, the HGM shows less adjustment, with values of ±20% and ±15% for 79.1% and 56.2% of the available analytical data, while the proposed model correlates adequately with the available data, showing an average deviation of ±15% and ±10% for 91.4% and 76.2% of the available data. In the absorptivity estimations, the HGM shows a weaker fit, with values of ±20% and ±15% for 77.3% and 51.4% of the experimental data, respectively, while the proposed model shows good agreement with the available data, with a mean deviation of ±15% and ±10% for 89.8% and 74.1% of the test made. [ABSTRACT FROM AUTHOR]

Flame temperature and spectral emissivity were the important parameters characterizing the sufficient degree of fuel combustion and the particle radiative characteristics in the Rocket Based Combined Cycle (RBCC) combustor. To investigate the combustion characteristics of the complex supersonic flame in the RBCC combustor, a new radiation thermometry combined with Levenberg-Marquardt (LM) algorithm and the least squares method was proposed to measure the temperature, emissivity and spectral radiative properties based on the flame emission spectrum. In-situ measurements of the flame temperature, emissivity and spectral radiative properties were carried out in the RBCC direct-connected test bench with laser-induced plasma combustion enhancement (LIPCE) and without LIPCE. The flame average temperatures at fuel global equivalence ratio (α) of 1.0b and 0.6 with LIPCE were 4.51% and 2.08% higher than those without LIPCE. The flame combustion oscillation of kerosene tended to be stable in the recirculation zone of cavity with the thermal and chemical effects of laser induced plasma. The differences of flame temperature at α = 1.0b and 0.6 were 503 K and 523 K with LIPCE, which were 20.07% and 42.64% lower than those without LIPCE. The flame emissivity with methane assisted ignition was 80.46% lower than that without methane assisted ignition, due to the carbon-hydrogen ratio of kerosene was higher than that of methane. The spectral emissivities at 600 nm with LIPCE were 1.25%, 22.2%, and 4.22% lower than those without LIPCE at α = 1.0a (with methane assisted ignition), 1.0b (without methane assisted ignition) and 0.6. The effect of concentration in the emissivity was removed by normalization to analyze the flame radiative properties in the RBCC combustor chamber. The maximum differences of flame normalized emissivity were 50.91% without LIPCE and 27.53% with LIPCE. The flame radiative properties were stabilized under the thermal and chemical effects of laser induced plasma at α = 0.6. [ABSTRACT FROM AUTHOR]

Selective infrared radiation is crucial for achieving infrared stealth and heat dissipation. Artificially designed superstructure film (SF) provides several advantages for controlling and modulating infrared radiation, making them a promising solution for these applications. The research described in this work has successfully produced broadband selective infrared radiation by using a surface made up of circular patches that are combined. Numerical simulations show that this SF can achieve broadband selective radiation with 3–5 μm mid-wave infrared (MWIR) suppression and 8–14 μm long-wave infrared (LWIR) emission. The spectral selectivity can be easily switched to high emissivity in MWIR and low emissivity in LWIR by simply changing the basal layer. The resonance mechanism for achieving broadband spectral selectivity in the SF may be due to a combination of multimode plasmon resonances that are induced by the structural nonrotational symmetry of the circular patches. By applying the selective radiation SF on the tail nozzle or the vehicle, the effect of thermal management is very significant. Selective radiation SF can reduce radiant energy in the 3−5 μm band by a significant amount at 500 °C, resulting in a 46 °C cooler temperature than that at the body without the SF. At 80 °C, radiated energy in the 8–14 μm band is also considerably reduced and the temperature is 10 °C lower than that of the body without the SF. There will be obvious advantages in potential applications for infrared stealth and heat dissipation by the designed SF, a simple and convenient manufacturing process. [ABSTRACT FROM AUTHOR]

All-dielectric metamaterials consisting of high-index, sub-wavelength, and periodically decorated arrays allow for efficient manipulation of electromagnetic permittivity and permeability with lower losses at the optical frequencies. In this study, we propose a planar multilayer structure composed of dielectric interlayers (Al2O3/Ge/ITO/Soda Lime Glass) to achieve perfect and broadband absorption of mid- and long-infrared (IR) wavelengths. Analyzing the spectral properties of the designed structure proved that it possesses exquisite importance in thermal application when considering the IR signature reduction in the long wavelength range, as well as the reduced radiated energy dissipation along with the undetected band and the requirements for IR camouflage. This intrinsic merit of dielectric metamaterials stems from their inherent selective absorption/emission. In that respect, Kirchhoff's law states that the emissive and absorptive powers of all bodies are similar for radiation of the same wavelength at the same temperature. The temperature difference may occur not only from the properties of the surfaces but also from the optical properties of materials and environmental conditions. Studying the thermal camouflage at different background temperatures found that the camouflage material substantially reduces the contrast between the target and the background. Beyond that, extensive assessments validated that the contrast in the resulting short tips is due to the differences in the reflective properties of the material and the background. Our simulations and experiments lay the groundwork for structuring cost-effective all-dielectric thermal camouflage metaplatforms with high performance and the strong potential to be employed in practical military and defense applications. [ABSTRACT FROM AUTHOR]

The rapid progression of multispectral detectors poses a serious threat to weapon systems and personnel. The efficiency of stealth camouflage materials, however, has strong wavelength dependence, which limits their functionality to a specific spectral range. Here, a multispectral hierarchical metamaterial (MHM) with broadband microwave absorption, gradient infrared (IR) emissivity, and high visible transparency is proposed. The MHM design entails the integration of two distinct functional layers: the infrared camouflage layer (IRCL) and the radar absorbing layer (RAL). Specifically, leveraging the low‐pass and high‐impedance properties of capacitive frequency selective surfaces and adjustable filling ratio of low IR radiation materials, the IRCL achieves simultaneous high microwave transmission and gradient IR emissivity designs (emissivity gradients > 0.15 at 3–5 and 8–14 µm). The RAL achieves broadband microwave absorption across radar C, X, Ku, and Ka bands through a circuit‐analog absorber designed with lossy materials. Furthermore, prioritizing materials with high transparency enhances the average optical transmittance (>61.8%) of MHM in 380–760 nm. These distinctive features underscore the potential of the proposed MHM for advanced applications in camouflage and stealth technologies. [ABSTRACT FROM AUTHOR]

In this paper, we describe a method for retrieving the surface emissivity of specular surfaces across the wavenumber range of 400–1600 cm -1 using novel radiance measurements of the Far-INfrarEd Spectrometer for Surface Emissivity (FINESSE) instrument. FINESSE is described in detail in Part 1 of this paper. We apply the method to two sets of measurements of distilled water. The first set of emissivity retrievals is of distilled water heated above ambient temperature to enhance the signal-to-noise ratio. The second set of emissivity retrievals is of ambient temperate water at a range of viewing angles. In both cases, the observations agree well with calculations based on compiled refractive indices across the mid- and far-infrared. It is found that the reduced contrast between the up- and downwelling radiation in the ambient temperature case degrades the performance of the retrieval. Therefore, a filter is developed to target regions of high contrast, which improves the agreement between the ambient temperature emissivity retrieval and the predicted emissivity. These retrievals are, to the best of our knowledge, the first published simultaneous retrievals of the surface temperature and emissivity of water that extend into the far-infrared and demonstrate a method that can be used and further developed for the in situ retrieval of the emissivity of other surfaces in the field. [ABSTRACT FROM AUTHOR]

The Far-INfrarEd Spectrometer for Surface Emissivity (FINESSE) instrument combines a commercial Bruker EM27 spectrometer with a front-end viewing and calibration rig developed at Imperial College London. FINESSE is specifically designed to enable accurate measurements of surface emissivity, covering the range 400–1600 cm -1 , and, as part of this remit, can obtain views over the full 360° angular range. In this part, Part 1, we describe the system configuration, outlining the instrument spectral characteristics, our data acquisition methodology, and the calibration strategy. As part of the process, we evaluate the stability of the system, including the impact of knowledge of blackbody (BB) target emissivity and temperature. We also establish a numerical description of the instrument line shape (ILS), which shows strong frequency-dependent asymmetry. We demonstrate why it is important to account for these effects by assessing their impact on the overall uncertainty budget on the level 1 radiance products from FINESSE. Initial comparisons of observed spectra with simulations show encouraging performance given the uncertainty budget. [ABSTRACT FROM AUTHOR]

When undertaking optical sparse projection reconstruction, the reconstruction of the tested field often requires the utilization of a priori knowledge to compensate for the lack of information due to the sparse projection angle. In order to reconstruct the radiation field of unknown materials or in situations where a priori knowledge cannot be obtained, this paper proposes an extremely sparse tomography multispectral temperature field reconstruction algorithm that analyzes the similarity (the similarity here compares and calculates the Euclidean distance of the spectral emissivity values at various wavelengths between different spectral curves) of radiation characteristics of materials under the same pressure and concentration but different temperature, describes the similarity between the radiation information of the tested field using the dynamic time warping (DTW) algorithm, and uses the similarity sum of the radiation information among the subregions of the temperature field as the optimization objective. This is combined with the equation-constrained optimization algorithm and multispectral thermometry to establish the statistical law between the missing information and finally realize the reconstruction of the temperature field. Simulation experiments show that, without any a priori knowledge, the method in this paper can realize reconstruction of the temperature field with an accuracy of 1.53–12.05% under two projection angles and has fewer projection angles and stronger robustness than other methods. [ABSTRACT FROM AUTHOR]

In the extreme space environment, spacecraft endure dramatic temperature variations that can impair their functionality. A VO2-based smart radiator device (SRD) offers an effective solution by adaptively adjusting its radiative properties. However, current research on VO2-based thermochromic films mainly focuses on optimizing the emissivity tunability (Δε) of single-cycle sandwich structures. Although multi-cycle structures have shown increased Δε compared to single-cycle sandwich structures, there have been few systematic studies to find the optimal cycle structure. This paper theoretically discusses the influence of material properties and cyclic structure on SRD performance using Finite-Difference Time-Domain (FDTD) software, which is a rigorous and powerful tool for modeling nano-scale optical devices. An optimal structural model with maximum emissivity tunability is proposed. The BaF2 obtained through optimization is used as the dielectric material to further optimize the cyclic resonator. The results indicate that the tunability of emissivity can reach as high as 0.7917 when the BaF2/VO2 structure is arranged in three periods. Furthermore, to ensure a longer lifespan for SRD under harsh space conditions, the effects of HfO2 and TiO2 protective layers on the optical performance of composite films are investigated. The results show that when TiO2 is used as the protective layer with a thickness of 0.1 µm, the maximum emissivity tunability reaches 0.7932. Finally, electric field analysis is conducted to prove that the physical mechanism of the smart radiator device is the combination of stacked Fabry–Perot resonance and multiple solar reflections. This work not only validates the effectiveness of the proposed structure in enhancing spacecraft thermal control performance but also provides theoretical guidance for the design and optimization of SRDs for space applications. [ABSTRACT FROM AUTHOR]

This paper investigates the theoretical and experimental cooling performance of textile materials utilizing radiative cooling technology. By applying Kirchhoff's law, the emissivity of surfaces is determined, revealing that materials with high transmission values can achieve comparable cooling performance to those with high reflection values. Notably, materials exhibiting moderate reflectance and transmittance in the solar range tend to absorb minimal solar radiation, thus offering high theoretical cooling performance. However, practical applications like building envelopes or clothing present challenges due to the impact of background radiation on overall cooling capacity. Despite their intrinsic cooling properties, a significant portion of solar radiation is transmitted, complicating matters as the background can significantly affect overall cooling performance. This study provides a solution that accounts for the influence of background materials. Based on spectral data, various background materials and their impact on different semi-transparent comparison materials can be considered, and cooling performance can be simulated. This enables the simulation of cooling performance for various application scenarios and facilitates comparisons between transparent, semi-transparent, and opaque textile materials. [ABSTRACT FROM AUTHOR]

Thermal camouflage technology can effectively hide an object by lowering its infrared emissivity and reducing its surface temperature. So far, it has been a challenge to realize thermal camouflage at high-temperatures with a single material. Here, we report a Ti 3 AlC 2 MAX phase material that exhibits excellent thermal camouflage properties from room temperature to 500 °C, and maintains a low emissivity of 0.25 at 500 °C, which is difficult to achieve for most metals due to the rapid increase in emissivity caused by oxidation. The thermal camouflage mechanism of Ti 3 AlC 2 was analyzed on the basis of experimental results and first-principles calculations, providing a feasible approach to select other MAX phases (such as Ti 3 SiC 2 , Cr 2 AlC, and Ti 2 AlC) with attractive thermal camouflage performance. Ti 3 AlC 2 and other MAX phases are promising candidates for thermal camouflage applications due to their low emissivity, high-temperature stability, good oxidation resistance and ease of fabrication. [ABSTRACT FROM AUTHOR]

High emissivity coatings on hypersonic vehicle surfaces dissipate heat by emitting thermal radiation. While the difficulty of increasing emissivity limits the performance of coatings to improve heat-dissipation of the thermal insulation felt. Herein, a novel high-reflectivity and high-emissivity integrated double-layer coating was developed to enhance the thermal insulation performance of the alumina fiber fabric. The coating comprised of TiO 2 @SiO 2 (T@S) as reflective agent and ZrO 2 /SiC w (ZSC) as emittance agents, was applied on the surface of alumina fiber fabric (AFF). The reflecting effect of radiation heat from the high reflective agent enhanced the thermal insulation properties of the double-layer coating. In the wavelength range of 0.4–2.5 μm, the average emissivity of the ZSC coating was 0.83 and the average reflectivity of the T@S coating was 0.63. With continuous heating at 1400 °C for 10 min with a butane torch, the temperature on the backside of the T@S–ZSC-coated AFF remained relatively stable at 225 °C, which is notably decreased by 80 °C compared to that of the single-layer ZSC-coated AFF. The tensile strength of AFF with T@S–ZSC coating reached 35 MPa after being heat treated at 1200 °C. Moreover, the bonding strength between the coating and the AFF substrate was measured to be 0.15 MPa. The double-layer coating with high emissivity and reflectivity, along with a flexible AFF substrate, offers a promising solution for addressing the challenging of surface heat-dissipation in hypersonic vehicles. [ABSTRACT FROM AUTHOR]

All‐day passive daytime radiative coolers (PDRC) offer a promising solution for energy‐free cooling of buildings and devices. This study investigates the use of various cellulose‐derivative networks to achieve optimal and stable cooling performance. These results showed that the mixed cellulose ester network has a maximum solar reflectance of 97%. While cellulose acetate network has a maximum infrared emissivity of 96% in the atmospheric transparency window band, which is a near‐perfect infrared emitter, the nitrocellulose network shows the highest cooling temperature, with a significant reduction of 14 °C from the ambient temperature and a power of 124 W·m−2 during the daytime and at night of 7.7 °C and 72.8 W·m−2. This study also analyzes the dampness's effect on the cooling performance of cellulose‐derivative networks. The cooling performance of the nitrocellulose network drops ≈ 3 °C (from 14 to 11.3 °C) when the relative humidity of the day exceeds ≈ 30% is observed. These findings indicate that the capacity of a material to absorb water from the surrounding air significantly influences its performance as a passive cooler, primarily due to changes in its optical properties. This is an important insight, as it highlights the need to consider environmental factors like relative humidity and sample hydrophobicity for PDRC systems. [ABSTRACT FROM AUTHOR]

The regulation of infrared (IR) thermal radiation has received widespread attention; the proposals have been made for various devices that use electrochromic materials. However, the visible appearance of the mentioned devices also changes when the IR states are altered. Herein, the memristive mechanism is utilized to regulate IR emissivity and design a novel transparent memristor‐type modulator featuring an Indium tin oxide (ITO)/HfO2/ITO structure. The modulator exhibits a dynamic emissivity variation of 0.38 in the IR region of 2.5–25 μm, without compromising transparency in the visible region under the application of an electric voltage. The migration of oxygen vacancies results in the modification of interface barriers and the formation of oxygen vacancy‐enriched regions, thereby enabling the modulator to exhibit resistive switching behavior and regulate IR emissivity. An array of modulators is also assembled, demonstrating the ability to independently display visible and IR information. In this work, new possibilities are presented for various applications such as multispectral displays, energy‐efficient thermoregulation, encrypted information displays, and camouflage. [ABSTRACT FROM AUTHOR]

Although violation of Kirchhoff's Law of Thermal Radiation has been claimed in a magneto-optic structure, it is shown that Kirchhoff's Law of Thermal Radiation has not been violated, noting that violation of Kirchhoff's Law of Thermal Radiation would imply that the Second Law of Thermodynamics has also been violated. [ABSTRACT FROM AUTHOR]

Non-linearity (NL) correction is a critical procedure to guarantee that the calibration accuracy of a spaceborne sensor approaches a reasonable level (i.e., better than 0.5 K). Unfortunately, such an NL correction is still not used in spectrum calibration from the Geostationary Interferometric InfraRed Sounder (GIIRS) onboard the Fengyun-4A (FY-4A) satellite. Different from the classical NL correction method where the NL coefficient is estimated from out-band spectral artifacts in an empirical low-frequency region, originally with prelaunch results and updated under in-orbit conditions, a new NL correction method for a spaceborne Fourier transform spectrometer (including GIIRS) is proposed. In particular, the NL parameter μ , independent of different working conditions (namely the thermal fields from environmental components), can be determined from laboratory results before launch and directly utilized during in-orbit calibration. Moreover, to overcome the inaccurate linear coefficient from the two-point calibration that influences the NL correction, an iteration algorithm is established to make both the linear and the NL coefficients converge to their stable values, with relative errors less than 0.5 % and 1 %, respectively, which is universally suitable for NL correction of both infrared and microwave sensors. Using the onboard internal blackbody (BB), which is identical to the in-orbit calibration, the final calibration accuracy for all the detectors and all the channels with the proposed NL correction method is validated to be around 0.2–0.3 K at an ordinary reference temperature of 305 K. Significantly, the relative error in the classical method NL parameter immediately transmitting to that of the linear one in theory, which inevitably introduces some additional errors around 0.1–0.2 K for the interfering radiance no longer exists. Moreover, the adopted internal BB with higher emissivity produces better NL correction performance in practice. The proposed NL correction method is scheduled for GIIRS implementation on board the FY-4A satellite and its successor after modifying their possible spectral response function variations. [ABSTRACT FROM AUTHOR]

Regions near latitude 0° are characterized by warm-humid climate and also by high cloudiness. In these regions, metal roofs has been the most widely used typology. However, in the last decades, the use of heavy concrete roofs has increased significantly. Given its material characteristics, this roof typology offers a higher thermal resistance and thermal mass than a metal roof. Most strategies focus on the use of these characteristics, as well as the use of high reflectivity and emissivity. However, the impact of cloudiness on the effectiveness of these strategies has been little addressed. This research focuses on the impact of reflectivity and emissivity change on the thermal performance of these two roofs in a cloudy warm-humid climate. To achieve this objective, simulations validated with measurements were used. The results show that the efficiency of reflectivity and emissivity is lower in this region compared to other regions. The impact of these properties is further reduced with increasing thermal mass or decreasing thermal transmittance, so the effectiveness of reflectivity and emissivity is minimal on the concrete roof. Finally, this study supports that a metal roof with a reflectivity and emissivity above 0.70 can offer lower daily average temperatures than a concrete roof. [ABSTRACT FROM AUTHOR]

With the rapid development and wide application of visible (VIS) and infrared (IR) detections, it is necessary to explore visible-infrared (VIS-IR) compatible camouflage. Here, we report a VIS-IR compatible and independent camouflage device which is composed of the upper IR-transparent VIS-color-patterned layer and the lower electrochromic IR layer. The upper layer has amorphous photonic structure of polystyrene nanospheres (PSNSs). By customizing the PSNS size, various colors can be realized for VIS camouflage. The lower electrochromic IR layer takes advantage of multiwall carbon nanotubes (MWCNTs) as the electrode as well as the IR active material. Experimental results reveal that different colors (including blue, green, and purple) have been obtained, and the IR emissivity can be electrically regulated from 0.43 to 0.9. Moreover, the prototype also exhibits good electrical stability as well as hydrophobic characteristic (the water contact angle of the outmost surface exceeds 120°). These output performances demonstrate the success of our design strategy for promoting the finding applied in camouflage fields as well as energy conservation fields. [ABSTRACT FROM AUTHOR]

With the rapid improvement of equipment integration technology, multi-spectrum detectors are integrated into compact volumes and widely used for object detection. Confront with this challenge, it is essential to propose a strategy to design a single-layer metasurface with multi-spectrum responses in microwave and infrared ranges. In this work, we proposed a method of designing meta-atoms, which is capable of achieving functional electromagnetic response at microwave and infrared individually. As a demonstration, a metasurface with four different occupation ratios and coding permutation features is designed, fabricated, and tested. In the microwave band, the pixel meta-atom is designed to realize highly efficient cross-polarization conversion between 5.0 and 10.0 GHz, which shows the metasurface can behave as ultra-low Radar Cross Section (RCS) reflectors in the working band; In the infrared band, different occupation ratio of meta-atoms are designed to realize the infrared emissivity from 0.60 to 0.80 in 3–14 μm, which can be used to exhibit digital infrared camouflage pattern. This work promotes the ability to use single-layer design to achieve digital infrared camouflage and microwave RCS reduction simultaneously. The one-layer design is simple in geometry, simplified in process, low cost in economy, and large scale in fabrication, which can promote practical use in compatible microwave stealth and infrared camouflage. [ABSTRACT FROM AUTHOR]

The heat generation of the human body dramatically varies between resting and active status, so dynamic heat dissipation is required to ensure optimal thermal comfort. Herein, we propose a spectrally self-adaptive smart fabric (SSSF) by covering polyester fabric with silver nanowires, which autonomously adjusts its emissivity in response to the body's movement status from dry to wet states. During periods of inactivity, the SSSF maintains radiative heat insulation with a low emissivity state of 0.39. Conversely, during vigorous physical activity, its emissivity is improved to 0.83 when the sweat penetrates the SSSF, facilitating greater heat dissipation. Comparative experiments demonstrate the superior thermal management capabilities of the SSSF, with a 19.5 % reduction in heat dissipation power relative to traditional fabrics when in the low emissivity mode, and an impressive 67.6 % enhancement in heat dissipation power as it changes from low to high emissivity mode. This work provides an adaptive approach to emissivity modulation, offering an effective solution for dynamic heat dissipation of humans across various states of activity, thereby enhancing personal thermal comfort. [ABSTRACT FROM AUTHOR]

Context. The extragalactic background light (EBL) carries a huge astrophysical and cosmological content. Its frequency spectrum and redshift evolution are determined by the integrated emission of unresolved sources, with these being galaxies, active galactic nuclei, or more exotic components. The near-UV region of the EBL spectrum is currently not well constrained, yet a significant improvement can be expected thanks to the soon-to-be launched Ultraviolet Transient Astronomy Satellite (ULTRASAT). Intended to study transient events in the 2300–2900 Å observed band, this detector will provide wide field maps tracing the UV intensity fluctuations at the largest scales. Aims. In this paper, we suggest how to exploit the ULTRASAT full-sky map as well as its low-cadence survey in order to reconstruct the redshift evolution of the UV-EBL volume emissivity. We build upon the work of Chiang et al. (2019, ApJ, 870, 120), who used the clustering-based redshift (CBR) technique to study diffuse light maps from GALEX. Their results showed the capability of the cross correlation between GALEX and SDSS spectroscopic catalogs in constraining UV emissivity, highlighting how CBR is sensitive only to extragalactic emissions, avoiding foregrounds and Galactic contributions. Methods. In our analysis, we introduce a framework to forecast the CBR constraining power when applied to ULTRASAT and GALEX in cross correlation with the five-year DESI spectroscopic survey. Results. We show that these will yield a strong improvement in the measurement of the UV-EBL volume emissivity. For λ = 1500 Å non-ionizing continuum below z ∼ 2, we forecast a 1σ uncertainty ≲26% (9%) with conservative (optimistic) bias priors using the ULTRASAT full-sky map. Similar constraints can be obtained from its low-cadence survey, which will provide a smaller but deeper map. Finally, we discuss how these results will foster our understanding of UV-EBL models. [ABSTRACT FROM AUTHOR]

The paper proposes an ultra-wideband frequency selective rasorber (FSR) with low infrared emissivity for the composite detection threat of both radars and infrared sensors. Firstly, the equivalent circuit (EC) method based on transmission line (TL) theory is utilized to analyze the absorption/transmission conditions. Then, based on the analysis above, sinusoidal microstrip lines with non-frequency-varying characteristics are adopted in the design, which significantly enhances the transmission bandwidth of FSR. The FSR demonstrates an absorption band ranging from 2.65 GHz to 8.80 GHz and a transmission band ranging from 9.15 GHz to 17.71 GHz. Furthermore, an infrared shielding layer (IRSL) exhibiting low emissivity in the infrared band and high transmittance in the microwave band is applied to the FSR. The simulation and experiment results verify that the IRSL-FSR demonstrates an ultra-wide transmission band ranging from 9.16 GHz to 17.94 GHz and an ultra-wide absorption band ranging from 2.66 GHz to 8.01 GHz. Additionally, it exhibits a low emissivity value (0.23) in 8–14 μm, providing a viable solution to the formidable challenge of radar-infrared bistealth for satellites and other communication-enabled flying platforms. [ABSTRACT FROM AUTHOR]

We present a Bayesian inference method to characterize the dust emission properties using the well-known dust- |${\rm H\,{\small I}}$| correlation in the diffuse interstellar medium at Planck frequencies |$\nu \ge 217$|  GHz. We use the Galactic |${\rm H\,{\small I}}$| map from the Galactic All-Sky Survey (GASS) as a template to trace the Galactic dust emission. We jointly infer the pixel-dependent dust emissivity and the zero level present in the Planck intensity maps. We use the Hamiltonian Monte Carlo technique to sample the high-dimensional parameter space (⁠|$D \sim 10^3$|⁠). We demonstrate that the methodology leads to unbiased recovery of dust emissivity per pixel and the zero level when applied to realistic Planck sky simulations over a 6300  |$\rm {deg}^2$| area around the Southern Galactic pole. As an application on data, we analyse the Planck intensity map at 353 GHz to jointly infer the pixel-dependent dust emissivity at |$N_{\rm side}=32$| resolution (1.8° pixel size) and the global offset. We find that the spatially varying dust emissivity has a mean of 0.031 MJy sr |$^{-1}$| |$(10^{20} \, \mathrm{cm^{-2}})^{-1}$| and |$1\sigma$| standard deviation of 0.007 MJy sr |$^{-1}$| |$(10^{20} \, \mathrm{cm^{-2}})^{-1}$|⁠. The mean dust emissivity increases monotonically with increasing mean |${\rm H\,{\small I}}$| column density. We find that the inferred global offset is consistent with the expected level of cosmic infrared background (CIB) monopole added to the Planck data at 353 GHz. This method is useful in studying the line-of-sight variations of dust spectral energy distribution in the multiphase interstellar medium. [ABSTRACT FROM AUTHOR]

The ongoing advancements and growing adoption of infrared detection technology have spurred a tremendous amount of interest in thermal camouflage technology. Various approaches are employed to develop infrared camouflage materials capable of manipulating emissivity or surface temperature. However, the range of thermal radiation regulation implemented by these materials is still somewhat limited. In this paper, a combined emissivity and temperature regulation strategy that integrates a thermoelectric device (TED) and a thermochromic structure is proposed. By utilizing this strategy, it becomes possible to simultaneously control the surface temperature and the emissivity without needing additional complex excitation. As a concept demonstration, large tunabilities of 0.38 for long‐wave infrared (8–14 µm) emittance and 87 °C for surface temperature are observed, resulting in a prominent tunability of the thermal radiation temperature that is 15.4 °C greater than that of a conventional TED with constant emissivity. This work aims to introduce a new design paradigm for future thermal radiation management and camouflage techniques. [ABSTRACT FROM AUTHOR]

Water condensation on a surface strongly affects its effective emissivity, especially in the atmospheric window, a wavelength range essential for outdoor applications related to energetically passive cooling and heating. The evolution of emissivity of a silicon surface during dropwise and filmwise water deposition is studied. The evolution of the spectral radiative properties shows that the increase in effective emissivity due to the growth of a droplet pattern is steeper than for a growing water film of equivalent thickness. The change of surface emissivity takes place in the first moments of condensation where droplets as small as 10 µm drastically impact the reflectance of the pristine surface. The upper limit of effective emissivity is reached for a droplet radius or film thickness of 50 µm. During dropwise condensation, effective emissivity is weighted by the drop surface coverage and then remains within an asymptotic maximum value of 0.8, while in case of filmwise condensation, it is shown to reach 0.9 corresponding to water emissivity. Micrometer‐scale spatially‐resolved infrared spectral images enable to correlate the spatial variation of spectral properties to the droplet size and localization. Such findings are of interest to the implementation of moisture‐controlled emissivity tuning and radiative sky‐coolers for dew harvesting. [ABSTRACT FROM AUTHOR]

An emergent need exists for solid state tunable coherent light emitters in the mid-infrared range for spectroscopy, sensing, and communication applications where current light sources are dominated by spontaneous emitters. This paper demonstrates a distinct class of coherent thermal emitters operating in the mid-infrared wavelength regime. The structure of the light source consists of a dielectric metasurface fabricated on a phononic substrate. In this study, we present the first implementation of off-Γ Friedrich–Wintgen bound states in the continuum at mid-infrared wavelengths suitable for developing the next generation of coherent light emitters. Numerical analysis of the emissivity spectrum reveals the interference of resonances leading to avoided crossings and the formation of Friedrich–Wintgen bound states in the radiation spectrum. Additionally, significant localized field enhancements are observed within the metasurface at operating wavelengths. The emissivity spectra measured by reflectivity and emission experiments exhibit temporally coherent emission peaks in the vicinity of the bound state in the continuum, the first such demonstration in the mid-infrared region for wavelengths longer than 7 µm. These results represent a new approach for significant advancement in realizing mid-infrared coherent light emitters with promising implications for future technologies. [ABSTRACT FROM AUTHOR]

Silicon crystal for solar cells are mainly produced by the Czochralski (CZ) method, in which the quality and production cost of silicon crystal are mainly affected by the thermal field of the crystal growth furnace. While the thermal field is significantly influenced by the heat shield material, in this study, the effect of thermal conductivity and emissivity of the heat shield material on the global thermal field was investigated by numerical simulation in Ansys Fluent software. The heat shield surface is divided into two parts, the high-temperature side part (close to the crucible and melt) and the low-temperature side part (close to the crystal), which are named as Hot-Side-Material and Cold-Side-Material, respectively. The results show that the same material can be chosen for both parts and the smaller the thermal conductivity and the emissivity of the material, the better the thermal field. As the thermal conductivity and emissivity of the heat shield surface material decrease, the melt-crystal (m-c) interface deflection decreases; the maximum thermal stress of the crystal and the required heater power are also reduced, while the crystal axial temperature gradient increases. Therefore, it is recommended to select material with low emissivity and low thermal conductivity as heat shield surface material. [ABSTRACT FROM AUTHOR]

The development of multispectral detection emphasizes the significance of multispectra‐compatible camouflage technology, necessitating compatible camouflage for visible and infrared bands. Conventional painted camouflage is hindered by high infrared emissivity, and crafting patterns with existing low‐emissivity materials is hindered by the lack of adequate colors. Herein, this study introduces a method to reduce the emissivity while maintaining its original color. By covering a metafilm that reflects most infrared radiation on conventional patterned camouflage, low‐emissivity coatings are achieved. The thickness of the metafilm is optimized, effectively reducing color differences between uncoated and coated camouflage. Monochromatic substrates with the metafilm retain original colors with small color differences (e.g., 0.61) and demonstrate low infrared emissivity (0.03). Patterned camouflage yields an area‐weighted color difference of 9.09 with an infrared emissivity of 0.05. Experimental application on grassland backgrounds demonstrates visual integration with the background. Infrared thermography shows that coated camouflages, compared to uncoated ones, exhibits significantly reduced radiant temperature (29.5 °C vs. 43.0 °C) when heated to 50 °C against a 29.5 °C background, enhancing its blending capability. This metafilm effectively mitigates infrared emissivity while maintaining original colors and patterns, facilitating efficient camouflage across visible and infrared spectrums. [ABSTRACT FROM AUTHOR]