Control Of Thermal Radiation Research Articles

Inverse-design laser-infrared compatible stealth with thermal management enabled by wavelength-selective thermal emitter

With the fast development of multi-band detection technology, the demand for multi-band stealth technology with thermal management in military and civilian fields is increasing. Although the metasurfaces can achieve multi-band stealth and thermal management, their fabrication is complex and costly. In this paper, a simple multilayer structure is used to realize laser-infrared compatible stealth with thermal management. More importantly, the traditional method of optimizing metasurface structures by manually scanning parameters consumes a lot of computational time and resources. In order to speed up design of nanostructures, we propose a wavelength-selective thermal emitter (WSTE) composed of ZnS/Ge3Sb2Te6 (GST) multilayer films and a Ni reflector using inverse design method. The simulation results show that, in the crystalline phase, the WSTE has low spectral emissivity (ε3-5μm = 0.12, ε8-14μm = 0.22) in the mid-wave infrared (MWIR) and long-wave infrared (LWIR), high spectral emissivity (ε5-8μm = 0.72) in the non-atmospheric window and high absorptivity (A1.06μm = 0.90, A1.55μm = 0.97, A10.6μm = 0.91) in the laser wavelengths, which indicates that the WSTE can simultaneously achieve MWIR, LWIR and laser stealth with radiative heat dissipation. The method proposed in this paper overcomes the problems of single-band stealth and inefficient. Moreover, by varying the crystallization fraction of the GST, the WSTE can achieve dynamic control of thermal radiation in the wavelength range of 3–14 µm. The simulated infrared images verify that WSTE has good infrared stealth performance. Finally, the effects of incidence angle and polarization angle on the emission spectrum of WSTE are studied, which can demonstrate the infrared stealth is insensitive to both. In conclusion, the WSTE is attractive in advanced photonics applications, such as radiative cooling and infrared stealth.

Si/InAs/Ag metamaterial for strong nonreciprocal thermal emitter with dual polarization under a 0.9 T magnetic field

The current nonreciprocal thermal emitter has been proven to completely violate the previous Kirchhoff's law. And the majority of related nonreciprocal devices operate under single polarization with few dual-polarization nonreciprocal designs. Therefore, dual-polarization nonreciprocal thermal radiation has great research prospects. In addition, many previous designs of nonreciprocal devices required external magnetic field energy of 3 T even higher, which is difficult to meet in practical applications. Therefore, this article investigates the strong nonreciprocal dual-polarization thermal radiation of cuboid arrays under lower external magnetic field. It is constructed by silicon, silver layer, InAs layer, and cuboid arrays. Finally, dual-polarization nonreciprocal radiation was achieved in a magnetic field of only 0.9 T, and the nonreciprocal efficiency has been significantly improved. The physical phenomenon of dual-polarization strong nonreciprocal radiation exhibited by the proposed device was explained by utilizing the electromagnetic field distribution at the resonant wavelength. It can also maintain good nonreciprocal properties under different structural parameters. Therefore, our proposed solution provides new opportunities for energy harvesting and thermal radiation control.

Recent advances in vanadium dioxide for dynamic thermal radiation modulation: A review

Thermal radiation of materials can be manipulated for the necessary applications in thermal management and infrared camouflage. To our knowledge, controlling surface emissivity is crucial for modulating thermal radiative energy, therefore, dynamic modulation of emissivity has received more attention. Vanadium dioxide (VO2) stands out as a highly promising candidate due to its capacity for reversible transition from monoclinic VO2(M) to rutile VO2(R) near room temperature. This transition results in a rapid change from transparent to opaque within the mid-infrared spectrum accompanied by a reduction in emissivity. This review offers an overview of recent progresses in the dynamic control of thermal radiation of the surface by using VO2. It also summarizes the preparation, modulation mechanisms, and applications of positive and negative differential emissivity devices. Finally, the challenges and opportunities in advancing research on VO2-based smart devices are discussed.

A dual-mode infrared thermal stealth structure compatible with radar bands

Currently, multi-spectral stealth technology has become crucial in countering advanced military and civilian detection methods. Metamaterials, known for their adaptable designs and superior wavefront manipulation capabilities, effectively meet the complex requirements of infrared and radar bands for material properties, thus being widely used in developing multi-band thermal stealth materials. In this study, we propose a tunable metamaterial structure based on phase-change material vanadium oxide. This structure operates in two modes facilitated by the temperature-induced phase transition of vanadium oxide, which modifies the effective cavity thickness and influences the infrared resonance of the coupled cavity-plasma system. This modulation enables tunable control of thermal radiation within the 3 μm–14 μm wavelength range, achieving effective infrared thermal camouflage across varying environmental backgrounds. Additionally, the structure achieves high radar absorption across the ultra-wideband radar frequencies of 3.65 GHz–18 GHz and 26.5 GHz–34 GHz, with average absorption of 0.89 and 0.85, respectively. Hence, the proposed metamaterial structure effectively provides infrared thermal stealth compatibility with radar bands in both low-temperature (270 K–310 K) and high-temperature (380 K–420 K) environments.

Localized thermal emission from topological interfaces.

The control of thermal radiation by shaping its spatial and spectral emission characteristics plays a key role in many areas of science and engineering. Conventional approaches to tailoring thermal emission using metamaterials are hampered both by the limited spatial resolution of the required subwavelength material structures and by the materials' strong absorption in the infrared. In this work, we demonstrate an approach based on the concept of topology. By changing a single parameter of a multilayer coating, we were able to control the reflection topology of a surface, with the critical point of zero reflection being topologically protected. The boundaries between subcritical and supercritical spatial domains host topological interface states with near-unity thermal emissivity. These topological concepts enable unconventional manipulation of thermal light for applications in thermal management and thermal camouflage.

Directional thermal emission and display using pixelated non-imaging micro-optics

Thermal radiation is intrinsically broadband, incoherent and non-directional. The ability to beam thermal energy preferentially in one direction is not only of fundamental importance, but it will enable high radiative efficiency critical for many thermal sensing, imaging, and energy devices. Over the years, different photonic materials and structures have been designed utilizing resonant and propagating modes to generate directional thermal emission. However, such thermal emission is narrowband and polarised, leading to limited thermal transfer efficiency. Here we experimentally demonstrate ultrabroadband polarisation-independent directional control of thermal radiation with a pixelated directional micro-emitter. Our compact pixelated directional micro-emitter facilitates tunable angular control of thermal radiation through non-imaging optical principles, producing a large emissivity contrast at different view angles. Using this platform, we further create a pixelated infrared display, where information is only observable at certain directions. Our pixelated non-imaging micro-optics approach can enable efficient radiative cooling, infrared spectroscopy, thermophotovoltaics, and thermal camouflaging.

Elevating Low-Grade Heat Harvesting with Daytime Radiative Cooling and Solar Heating in Thermally Regenerative Electrochemical Cycles.

Thermal radiation control has garnered growing interest for its ability to provide localized cooling and heating without energy consumption. However, its direct application for energy harvesting remains largely underexplored. In this work, we demonstrate a novel system that leverages daytime radiative cooling and solar heating technologies to continuously power charging-free thermally regenerative electrochemical cycle (TREC) devices, turning ubiquitous low-grade ambient heat into electricity. Notably, by harnessing a substantial 35 °C temperature differential solely through passive cooling and heating effects, the integrated system exhibits a cell voltage of 50 mV and a specific capacity exceeding 20 mAh g-1 of PB. This work unlocks the potential of readily available low-grade ambient heat for sustainable electricity generation.

Thermally tunable nonreciprocal radiation in lithography-free vanadium dioxide-dielectric-Weyl semimetal stack

Nonreciprocal thermal radiation (NTR) holds great promise in revolutionizing energy harvesting and conversion process, has become a hot topic of various research fields ranging from renewable energy, molecular sensing, to thermal circuitry and camouflage. Despite intensive effort into enhance the nonreciprocal response, static manipulation of NTR has limited the potential application, dynamic control of thermal radiation is highly demanded. Here, by using a multilayered stack comprised of vanadium dioxide (VO2) thin film, germanium (Ge) spacer layer, Weyl semimetal (WSM) layer terminated by molybdenum (Mo) substrate, we propose a thermally tunable nonreciprocal emitter. The effects of the incident angle (θi), azimuthal angle (ϕi), and the thickness of each layer for the VO2/Ge/WSM stack on the characteristics of thermal radiation have been discussed thoroughly. Dominant peaks and dips of nonreciprocity have been obtained with an incident angle of θi=60° and azimuthal angle of ϕi=0°. A switching effect between the near-unity nonreciprocity (”ON”) and zero nonreciprocity (”OFF”) states are induced when the temperature increases from 20 °C to 68 °C. It is shown that the magnitude and sign of the nonreciprocity can be managed simultaneously for transverse electric (s-) and transverse magnetic (p-) polarizations. The proposed structure shows good near-unity nonreciprocity stability in a wide range of θi and ϕi. This structurally lithography-free nonreciprocal thermal emitter not only provides the ability to tune nonreciprocal radiative properties, but also leads to the possible development of power scavenging and conversion devices.

Ultrathin metasurface on a 100 nm-thick dielectric membrane absorbs infrared rays.

Flat optics based on metasurfaces produce unprecedented two-dimensional planar optical elements that cannot be developed with naturally occurring materials. However, it remains to be shown whether metasurfaces on ultrathin dielectric membranes can be adopted in a broad range of optical elements as flat optics. Here we demonstrate that a fabricated ultrathin metasurface composed of double-sided metal structures on a 100 nm-thick SiNx membrane absorbs infrared rays with a high absorptance of 97.1% at 50.1 THz. This ultrathin metasurface and its fabrication method would be a welcome contribution to a wide range of trailblazing applications, including ultrathin absorbers for imaging and light detection and ranging (LIDAR), directivity control of thermal radiation, and polarization control of vacuum ultraviolet light.

Research on Temperature Simulation of Underground Coal Gasification Wellbore

This study aims to integrate the theoretical distribution calculation of temperature and pressure during the gasification process through the derivation of heat conduction, thermal radiation and pressure control theory in the underground coal gasification process, and analyze the temperature of the underground coal gasification process through finite element modeling. Field influencing factors and pressure changes over time. It is of great significance to obtain the relevant parameters of the gasification chamber in the underground coal gasification process.

Ultra-efficient machine learning design of nonreciprocal thermal absorber for arbitrary directional and spectral radiation

Development of nanophotonics has made it possible to control the wavelength and direction of thermal radiation emission, but it is still limited by Kirchhoff's law. Magneto-optical materials or Weyl semimetals have been used in recent studies to break the time-reversal symmetry, resulting in a violation of Kirchhoff's law. Currently, most of the work relies on the traditional optical design basis and can only realize the nonreciprocal thermal radiation at a specific angle or wavelength. In this work, on the basis of material informatics, a design framework of a multilayer nonreciprocal thermal absorber with high absorptivity and low emissivity at any arbitrary wavelength and angle is proposed. Through a comprehensive investigation of the underlying mechanism, it has been discovered that the nonreciprocal thermal radiation effect is primarily attributed to excitation of the cavity mode at the interface between the metal and the multilayer structure. Moreover, the impact of factors, such as layer count, incidence angle, extinction coefficient, and applied magnetic field on nonreciprocal thermal radiation, is thoroughly explored, offering valuable insights to instruct the design process. Additionally, by expanding the optimization objective, it becomes feasible to design fixed dual-band or even multi-band nonreciprocal thermal absorbers. Consequently, this study offers essential guidelines for advancing the control of nonreciprocal thermal radiation.

Manipulation of Spatial Infrared Emission Based on W‐Doped Vanadium Oxide Films toward Thermal Coding

AbstractActive thermal radiation control of an object requires adaptive and flexible strategies to cope with emissivity engineering and its temperature dependence. On the other hand, the concept of digital coding allows a high degree of freedom in manipulating the interacting physical quantities based on local discretized features. Learning from this idea, this study put forward the manipulation of spatial infrared emission based on tungsten (W)‐doped VO2 films toward thermal coding. Here, 1‐bit coding worksheets created by low‐emissivity, that is, code ‘0′, and high‐emissivity, that is, code ‘1′, shift with materials metal‐insulator phase transition to encode emissive information in the temperature domain. It is shown experimentally that this concept has marked implications on thermal radiation control at Mid‐infrared, among which are as follows: digital anti‐counterfeiting by in‐plane spatial coding of a group of VO2 thin films with various W‐doping density and infrared camouflage by out‐of‐plane spatial coding of them. With a W‐doping gradient of 0%, 0.8%, and 1.7%, the three‐phase transition points in the temperature domain, that is, 72, 63, and 45 °C, give a remarkable modulation range of 27 °C. These phenomena pave the way for new classes of emissivity engineering for more accurate, flexible, and adaptive thermal radiation control.

Tunable smart mid infrared thermal control emitter based on phase change material VO2 thin film

Thermal radiation is one of the three ways of heat transfer, among which the mid-infrared thermal radiation has attracted much attention. At present, static control of thermal emissivity has been unable to meet the practical application, the device of dynamic control of thermal radiation is expected. In this paper, we study an intelligent thermal controlled radiation emitter based on a layered structure formed by phase change material Vanadium Dioxide. The transition denaturation of Vanadium Dioxide can realize the switching process from heat dissipation at high temperature to heat preservation at low temperature. In the mid-infrared wavelength range of 5–13 μm, significant differences in emission characteristics are observed due to variations in the imaginary part of the dielectric constant of Vanadium Dioxide. When it is in the high temperature metallic state, the optimal structural parameters, from top to bottom, are 10 nm, 350 nm, 320 nm, and 200 nm. With these parameters, the structure exhibits an emissivity of 0.78 and a full width at half maximum of 8.03 μm. This configuration achieves effective thermal radiation dissipation, as governed by the Stefan-Boltzmann’s law. On the other hand, when the structure is in the low temperature dielectric state, it exhibits a low absorption effect with an emissivity of 0.10, thus avoiding excessive heat loss. The radiative modulation capability and thermal stability were achieved through the use of thermochromic material Vanadium Dioxide which exhibits temperature switchable behavior. Additionally, the thermal control emitter, utilizing its resonant cavity, enables tunability of peak wavelength and demonstrates a certain degree of independence with respect to polarization and incident angle. The designed emitter structure is simple and easy to fabricate, holding significant prospects for applications in engineering insulation materials, infrared camouflage, and thermal management.

Deep learning-based inverse design of microstructured materials for optical optimization and thermal radiation control

Microstructures with engineered properties are critical to thermal management in aerospace and space applications. Due to the overwhelming number of microstructure design variables, traditional approaches to material optimization can have time-consuming processes and limited use cases. Here, we combine a surrogate optical neural network with an inverse neural network and dynamic post-processing to form an aggregated neural network inverse design process. Our surrogate network emulates finite-difference time-domain simulations (FDTD) by developing a relationship between the microstructure’s geometry, wavelength, discrete material properties, and the output optical properties. The surrogate optical solver works in tandem with an inverse neural network to predict a microstructure’s design properties that will match an input optical spectrum. As opposed to conventional approaches that are constrained by material selection, our network can identify new material properties that best optimize the input spectrum and match the output to an existing material. The output is evaluated using critical design constraints, simulated in FDTD, and used to retrain the surrogate—forming a self-learning loop. The presented framework is applicable to the inverse design of various optical microstructures, and the deep learning-derived approach will allow complex and user-constrained optimization for thermal radiation control in future aerospace and space systems.

Design of micro‐ and macro‐scale polymeric metamaterial solutions for passive and active thermal camouflaging applications

AbstractThis work utilizes predictive modeling techniques to guide and inform metamaterial design for heat management solutions and thermal radiation control. Specifically, micro‐ and macro‐scale polyethylene‐based solutions are proposed for passive and active thermal camouflage. A micro‐scale post design is proposed for highly‐tunable infrared emissivity based on varying unit cell geometrical configurations. Actively modulating these micro‐features through lateral straining of up to 3% allows for redshifting the emissivity spectrum by up to 0.5 µm. Macro‐scale lenticular lens designs allow for a more passive form of camouflage due to its emissive stability for a range of configurations (e.g., single and sandwiched structures, increasing lens radii and height). Overall, the proposed metamaterial designs allow the tailoring of optical properties to improve thermal radiating performance.

Broadband hyperbolic thermal metasurfaces based on the plasmonic phase-change material In3SbTe2.

Thermal radiation modulation facilitated by phase change materials (PCMs) needs a large thermal radiation contrast in broadband as well as in a non-volatile phase transition, which are only partially satisfied by conventional PCMs. In contrast, the emerging plasmonic PCM In3SbTe2 (IST) that undergoes a non-volatile dielectric-to-metal phase transition during crystallization offers a fitting solution. Here, we have prepared IST-based hyperbolic thermal metasurfaces and demonstrated their capabilities to modulate thermal radiation. By laser-printing crystalline IST gratings with different fill factors on amorphous IST films, we have achieved multilevel, large-range, and polarization-dependent control of the emissivity modulation (0.07 for the crystalline phase and 0.73 for the amorphous phase) over a broad bandwidth (8-14 μm). With the convenient direct laser writing technique that supports large-scale surface patterning, we have also demonstrated promising applications of thermal anti-counterfeiting with hyperbolic thermal metasurfaces.

Experimental Determination of Absolute Spectral Radiance and Emissivity of a Photonic Crystal Filament

A recent discovery of super-Planckian radiation in the far-field has attracted a great deal of interest in thermal radiation control using photonic crystals (PC) architecture. The finding is based on a careful comparison of radiation intensity emitted from a PC nano-filament and a blackbody at the same temperature and same wavelength at λ∼1.7 μm. Extending that finding, we determined the absolute spectral radiance of such a PC filament at λ∼1.7 μm at elevated temperature, T = 445–723 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> °</sup> K, and compared its value to that predicted by Planck's blackbody radiation law. Our data confirmed that the PC spectral radiance surpassed that of a blackbody by an order-of-magnitude. We also determined the spectral emissivity of our PC filament and showed that its value far exceeded unity at resonance and fell below unity away from resonance. The observation of non-equality between absorptivity and emissivity suggests that a strong optical non-reciprocity takes place in our PC nano-filament.

Nonreciprocal Thermal Photonics for Energy Conversion and Radiative Heat Transfer

Nonreciprocal thermal photonics is an emerging topic in thermal radiation control. Recent advances in using this approach for energy harvesting, thermal management, and even communication have stimulated substantial interest in the subject. The authors review recent developments, challenges, and opportunities in the unidirectional transfer of heat energy via light, to provide a snapshot of the current status of the field, and to advance future research in it.

Deep learning based analysis of microstructured materials for thermal radiation control

Microstructured materials that can selectively control the optical properties are crucial for the development of thermal management systems in aerospace and space applications. However, due to the vast design space available for microstructures with varying material, wavelength, and temperature conditions relevant to thermal radiation, the microstructure design optimization becomes a very time-intensive process and with results for specific and limited conditions. Here, we develop a deep neural network to emulate the outputs of finite-difference time-domain simulations (FDTD). The network we show is the foundation of a machine learning based approach to microstructure design optimization for thermal radiation control. Our neural network differentiates materials using discrete inputs derived from the materials’ complex refractive index, enabling the model to build relationships between the microtexture’s geometry, wavelength, and material. Thus, material selection does not constrain our network and it is capable of accurately extrapolating optical properties for microstructures of materials not included in the training process. Our surrogate deep neural network can synthetically simulate over 1,000,000 distinct combinations of geometry, wavelength, temperature, and material in less than a minute, representing a speed increase of over 8 orders of magnitude compared to typical FDTD simulations. This speed enables us to perform sweeping thermal-optical optimizations rapidly to design advanced passive cooling or heating systems. The deep learning-based approach enables complex thermal and optical studies that would be impossible with conventional simulations and our network design can be used to effectively replace optical simulations for other microstructures.

Tunable mid-infrared selective emitter based on inverse design metasurface for infrared stealth with thermal management.

Infrared (IR) stealth with thermal management is highly desirable in military applications and astronomy. However, developing selective IR emitters with properties suitable for IR stealth and thermal management is challenging. In this study, we present the theoretical framework for a selective emitter based on an inverse-designed metasurface for IR stealth with thermal management. The emitter comprises an inverse-designed gold grating, a Ge2Sb2Te5 (GST) dielectric layer, and a gold reflective layer. The hat-like function, which describes an ideal thermal selective emitter, is involved in the inverse design algorithm. The emitter exhibits high performance in IR stealth with thermal management, with the low emissivity (ɛ3-5 µm =0.17; ɛ8-14 µm =0.16) for dual-band atmospheric transmission windows and high emissivity (ɛ5-8 µm =0.85) for non-atmospheric windows. Moreover, the proposed selective emitter can realize tunable control of thermal radiation in the wavelength range of 3-14 µm by changing the crystallization fraction of GST. In addition, the polarization-insensitive structure supports strong selective emission at large angles (60°). Thus, the selective emitter has potential for IR stealth, thermal imaging, and mid-infrared multifunctional equipment.