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Average apparent temperature variation and infrared thermal image (steady-state) of different emitters in the a,b) 3-5 µm and c,d) 8-14 µm ranges during thermal measurements in a practical environment. Roughly same emissivities are observed for selective emitter A# and the reference samples (B# or C#) in the 3-5 or 8-14 µm ranges, corresponding to the respective thermal images. The lower apparent temperature in both atmospheric windows indicates the better infrared stealth performance of the selective emitter.

Average apparent temperature variation and infrared thermal image (steady-state) of different emitters in the a,b) 3-5 µm and c,d) 8-14 µm ranges during thermal measurements in a practical environment. Roughly same emissivities are observed for selective emitter A# and the reference samples (B# or C#) in the 3-5 or 8-14 µm ranges, corresponding to the respective thermal images. The lower apparent temperature in both atmospheric windows indicates the better infrared stealth performance of the selective emitter.

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Engineering the radiation characteristics for the design of selective thermal emitters has been a hot topic for decades and is of great value in the fields of thermophotovoltaic systems, radiative cooling, and infrared stealth. In this paper, a Ag/Ge multilayer film based selective emitter for infrared stealth is demonstrated using an ultrathin met...

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Context 1
... if the impedance of a structure (Z = Z re + Z im i) in a certain spectral range is matched to that of air (Z air = 1 + 0i), with the real part Z re close to one and the imaginary part Z im close to zero, the incident waves in the corresponding waveband could penetrate into the structure rather than reflect at the surface. According to the impedance calculation [49] result of the selective emitter in Figure S5 in the Supporting Information, the incident waves in the 5-8 µm region could reach the ultrathin Ag layer (the thermal radiation part in the emitter) inside the emitter and result in high emissivity in this region, while the waves in the atmospheric windows are mainly reflected at the surface of the emitter and lead to relatively low emissivity. Therefore, we can tune the thermal radiation of the emitter concentrating on a desired infrared waveband by varying the thicknesses of the dielectric spacers based on the impedance matching principle. ...
Context 2
... infrared images were taken over a range of temperatures during the thermal measurement in a practical environment by 3-5 and 8-14 µm infrared cameras (see Experimental Section). For the selective emitter and its reference sample, under the 3-5 µm infrared camera, as shown in Figure 5a, despite the same band emissivity in this waveband, the selective emitter presents lower average apparent temperatures than the reference sample due to the reduction in real temperature caused by radiative cooling. The maximum difference in the average apparent temperature at steady-state between the two emitters reached 19 °C (Figure 5b, average apparent temperatures in black boxed areas). ...
Context 3
... the selective emitter and its reference sample, under the 3-5 µm infrared camera, as shown in Figure 5a, despite the same band emissivity in this waveband, the selective emitter presents lower average apparent temperatures than the reference sample due to the reduction in real temperature caused by radiative cooling. The maximum difference in the average apparent temperature at steady-state between the two emitters reached 19 °C (Figure 5b, average apparent temperatures in black boxed areas). Similar results were also observed for the emitters under the 8-14 µm infrared camera, as shown in Figure 5c,d. ...
Context 4
... maximum difference in the average apparent temperature at steady-state between the two emitters reached 19 °C (Figure 5b, average apparent temperatures in black boxed areas). Similar results were also observed for the emitters under the 8-14 µm infrared camera, as shown in Figure 5c,d. We can reduce the apparent temperatures and tune the thermal radiation characteristics in the atmospheric windows by coating the object with selective emissive materials to achieve infrared stealth. ...

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Citations

... [25][26][27][28][29][30][31][32] The latter has the advantage of being passive and that does not require an additional energy source. Currently, infrared stealth has been mainly realized by controlling the surface emissivity using metamaterials or metasurfaces [33][34][35][36][37][38][39] , phase-changing materials [40][41][42] and stimuli-responsive structures [43][44][45][46] , resulting in adaptive thermal camouflage [47][48][49][50][51][52] and multispectral camouflage [53][54][55][56] . The thermal metamaterial approach is the main paradigm for infrared camouflage. ...
... Researchers introduced multilayer medium micro-structures to modulate thermal radiation, which proves easy and flexible for fabrication. 25,35,51,56 However, the reported works have focused on camouflaging a given object with uniform temperature. [33][34][35]37,39,57 To perfectly camouflage a continuously changing thermal field, which widely exists in practical applications, the required emissivity profile is position-dependent and varies continuously. ...
... 25,35,51,56 However, the reported works have focused on camouflaging a given object with uniform temperature. [33][34][35]37,39,57 To perfectly camouflage a continuously changing thermal field, which widely exists in practical applications, the required emissivity profile is position-dependent and varies continuously. This problem was tackled by employing a form of discretization, in which a step-wise approximation of ideal emissivity parameters was made at the sacrifice of camouflage performance. ...
Article
Infrared camouflage based on artificial thermal metasurfaces has recently attracted significant attention. By eliminating thermal radiation differences between the object and the background, it is possible to hide a given object from infrared detection. Infrared camouflage is an important element that increases the survivability of aircraft and missiles, by reducing target susceptibility to infrared guided threats. Herein, a simple and practicable design is theoretically presented based on a multilayer film for infrared stealth, with distinctive advantages of scalability, flexible fabrication, and structural simplicity. The multilayer medium consists of silicon substrate, carbon layer and zinc sulfide film, the optical properties of which are determined by transfer matrix method. By locally changing the thickness of the coating film, the spatial tunability and continuity in thermal emission are demonstrated. A continuous change of emissive power is further obtained and consequently implemented to achieve thermal camouflage functionality. In addition, other functionalities, like thermal illusion and thermal coding, are demonstrated by thickness-engineered multilayer films.
... In addition to the high absorption between 300 and 2500 nm, low thermal emittance is required in this range for an ideal solar energy absorber because of blackbody radiation, and these enhancements can improve the efficiency of the absorber [25][26][27]. According to Kirchhoff's law, at thermal equilibrium, the spectral emissivity and absorption are equal at any specified temperature and wavelength [37]. Thus, absorption is equal to emission. ...
Article
The recognition of broadband and high-absorption solar energy has increased interest in the application of solar energy. In the present study, we use the particle swarm optimization and the finite-difference time-domain (PSO/FDTD) algorithm to design an optimal patternless solar absorber. This absorber contains a multilayer common metal‒dielectric flat film that enables perfect absorption within the broadband solar energy spectrum. The average absorption rate of the solar energy absorber associates with the proposed inverse design method for the wavelength range of 300–2500 nm is 98.2%. The performance of the absorber is stable within the incidence angle range of 0–40°, irrespective of whether the polarization mode is transverse electric or transverse magnetic, and the absorption performance remains high at a high incidence angle of 60°. The proposed 2-inch diameter solar energy absorber can be heated to 86 °C within 100 s, indicating a heating power of 950 W m⁻². The proposed absorber has a simple structure, low manufacturing cost, perfect ultra-wideband absorption that is independent of polarization, high thermal conversion performance, and substantial potential for solar energy applications.
... There are emerging efforts to design smart clothes with particular thermal-regulating structures to realize promising self-cooling or heat preservation. [14][15][16][17][18] Currently, many passive cooling materials with various microstructures, including multilayer photonic membranes, [19,20] hybrid nanofibrous films, [1,17,21] metamaterials, [1] porous polymers [22,23] have been applied to the cooling textiles. These unique structures covering human skins could efficiently reflect the solar heat to outer atmosphere, to achieve passive cooling without any extra energy consumption. ...
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Given health threat by global warming and increased energy consumption in regulating body temperature, it is an urgent need to construct smart temperature‐regulating materials. Herein, a novel fiber‐spinning asymmetric chemical assembly (FACA) method is proposed to construct nanofiber materials with asymmetric photothermal properties. The silver nanowires (AgNWs) and poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) with opposite thermal radiation are assembled on reduced graphene oxide (rGO) film, imparting AgNW/rGO/PVDF‐HFP film with Janus structure that can realize the AgNWs side consistently keeps temperature of ca. 11 o C lower than the side of PVDF‐HFP nanofiber regardless of the irradiation directions under 1 sun, suggesting the adjustable photothermal regulation. Such photothermally selective hybrid nanofiber film provides great potential as fabrics to achieve all‐weather smart clothes, promoting controllable and comprehensive utilization of solar energy.
... There are emerging efforts to design smart clothes with particular thermal-regulating structures to realize promising self-cooling or heat preservation. [14][15][16][17][18] Currently, many passive cooling materials with various microstructures, including multilayer photonic membranes, [19,20] hybrid nanofibrous films, [1,17,21] metamaterials, [1] porous polymers [22,23] have been applied to the cooling textiles. These unique structures covering human skins could efficiently reflect the solar heat to outer atmosphere, to achieve passive cooling without any extra energy consumption. ...
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Given health threat by global warming and increased energy consumption in regulating body temperature, it is an urgent need to construct smart temperature‐regulating materials. Herein, a novel fiber‐spinning asymmetric chemical assembly (FACA) method is proposed to construct nanofiber materials with asymmetric photothermal properties. The silver nanowires (AgNWs) and poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) with opposite thermal radiation are assembled on reduced graphene oxide (rGO) film, imparting AgNW/rGO/PVDF‐HFP film with Janus structure that can realize the AgNWs side consistently keeps temperature of ca. 11 o C lower than the side of PVDF‐HFP nanofiber regardless of the irradiation directions under 1 sun, suggesting the adjustable photothermal regulation. Such photothermally selective hybrid nanofiber film provides great potential as fabrics to achieve all‐weather smart clothes, promoting controllable and comprehensive utilization of solar energy.
... Additional applications of the presented MIR emitters/ absorbers worth mentioning here are beyond analytical scenarios and go beyond the scope of the present review, e.g., among others in military for stealth technology and thermovoltaics [3,104,105], and for power generation scenarios [44,56,106,107]. ...
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In the mid-infrared (MIR) spectral range, a series of applications have successfully been shown in the fields of sensing, security and defense, energy conservation, and communications. In particular, rapid and recent developments in MIR light sources have significantly increased the interest in developing MIR optical systems, sensors, and diagnostics especially for chem/bio detection schemes and molecular analytical application scenarios. In addition to the advancements in optoelectronic light sources, and especially quantum and interband cascade lasers (QCLs, ICLs) largely driving the increasing interest in the MIR regime, also thermal emitters and light emitting diodes (LEDs) offer opportunities to alternatively fill current gaps in spectral coverage specifically with analytical applications and chem/bio sensing/diagnostics in the focus. As MIR laser technology has been broadly covered in a variety of articles, the present review aims at summarizing recent developments in MIR non-laser light sources highlighting their analytical utility in the MIR wavelength range. Graphical abstract
... In particular, lightweight, low volume, and large-area treatments that are able to control the spectral emissivity profile of surfaces, have been shown to be of interest for thermal management through radiative cooling, [23][24][25] spectrally selective detectors and emitters, [8,[26][27][28][29][30][31][32] infrared imaging, [28,33,34] polarization control, [35][36][37] sensing, [38][39][40][41][42] and defense. [43][44][45][46][47][48][49][50][51][52] Engineering of the electromagnetic properties of materials over the different bands in mid-IR is therefore of considerable interest for controlling the reflectivity, absorption, and emissivity spectral response. ...
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... Another promising alternative configuration refers to the composite with fillers of polar oxides [13], metamaterials [14], carbon [15], conjugate polymers [16], photonic crystal [17], and phase-change materials [18]. As a matter of fact, they are normally macroscopically discontinuous and necessitate external binders or film shapes to achieve structural shaping, whereas the high emissivity additives tend to offset their intrinsic superiority [19]. Due to the lack of flexibility, their application may be not fit for some next-generation application scenarios, such as wearable smart textiles and flexible energy storage devices [20,21]. ...
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Advanced scenario-adaptable infrared (IR) stealth materials are crucial for creating localized closed thermal environments. Low emissivity over the broadest possible band is expected, as is superior mechanical deformability. Herein, we report a series of Ti-based MXenes with naturally low emissivity as ideal IR shielding materials. Over a wavelength ranging from 2.5 to 25 μ m, Ti 3 C 2 T X film delivers an average emissivity of 0.057 with the lowest point of 0.042. Such a low emissivity coupled with outstanding structural shaping capability is beyond the current grasp. The reflection-dominated mechanism is dissected. Also, some intriguing scenarios of IR stealth for wearable electronic devices and skin thermal control are demonstrated. This finding lights an encouraging path toward next-generation IR shielding by the expanding MXene family.
... Unfortunately, materials with low emissivity covering on the objects will hinder its heat radiating to the periphery, thus enhancing the surface temperature and weakening the camouflage performance. For ideal IR camouflage, the material should possess low emissivity in the atmospheric window and high emissivity in the non-atmospheric window, which can not only reduce IR signature, but also decrease the surface temperature of the object by radiating part of the energy [9][10][11][12]. Infrared selective emitter is an artificial engineering structure that can tailor emissivity in a specific IR band has been widely studied in the past [13]. ...
... Infrared selective emitter is an artificial engineering structure that can tailor emissivity in a specific IR band has been widely studied in the past [13]. The ISE with high emissivity in non-atmospheric has been realized by metamaterials [10,11,[14][15][16][17][18][19][20][21][22][23][24][25], photonic crystals [26][27][28], and multilayer structures [9,12,[29][30][31]. Generally, the ISE is composed of metal film, dielectric film and (or) patterned structure, which can realize high emissivity in the non-atmospheric window and keep low emissivity in the atmospheric window. ...
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Visible-infrared compatible camouflage is significant to enhance the equipment survivability through counteracting the modern detecting and surveillance systems. However, there are still great challenges in simultaneously achieving multispectral camouflage with high transmittance in visible, low emissivity in the atmospheric windows and high emissivity in the non-atmospheric window, which can be attributed to the mutual influence and restriction within these characteristics. Here, we proposed an optically transparent infrared selective emitter (OTISE) composed of three Ag-ZnO-Ag disk sub-cells with anti-reflection layers, which can synchronously improve the visible transmittance and widen absorption bandwidth in the non-atmospheric window by enhancing and merging resonance response of multi-resonators. Test results reveal that low emissivity in infrared atmospheric windows, high emissivity in the 5-8 µm non-atmospheric window and high optical transparency have been obtained. In addition, the radiative flux of OTISE in 3-5 µm and 8-14 µm are respectively 34.2% and 9.3% of that of blackbody and the energy dissipation of OTISE is 117% of that of chromium film. Meanwhile, it keeps good optical transparency due to the ultrathin Ag film. This work provides a novel strategy to design the optically transparent selective emissive materials, implying a promising application potential in visible and infrared camouflage technology.
... Infrared, thermal-emitter-based, layered metamaterials (LMMs) have many advantages over traditional emitters [1][2][3], such as adjustable wavelengths, low visible-light emission, and high efficiency. This type of emitter has broad applications in infrared monitoring [4], gas sensing [5], and radiation cooling [6], and is the research hot-spot in the energy [7][8][9] and sensing fields [10][11][12]. ...
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In this study, a multifunctional high-vacuum system was established to measure the electro-optical conversion efficiency of metamaterial-based thermal emitters with built-in heaters. The system is composed of an environmental control module, an electro-optical conversion measurement module, and a system control module. The system can provide air, argon, high vacuum, and other conventional testing environments, combined with humidity control. The test chamber and sample holder are carefully designed to minimize heat transfer through thermal conduction and convection. The optical power measurements are realized using the combination of a water-cooled KBr flange, an integrating sphere, and thermopile detectors. This structure is very stable and can detect light emission at the μW level. The system can synchronously detect the heating voltage, heating current, optical power, sample temperatures (both top and bottom), ambient pressure, humidity, and other environmental parameters. The comprehensive parameter detection capability enables the system to monitor subtle sample changes and perform failure mechanism analysis with the aid of offline material analysis using scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Furthermore, the system can be used for fatigue and high-low temperature impact tests.
... Dynamic control technology can also be employed to tune thermal emissivity through the introduction of electrochromic or thermochromic dyes, quantum wells, plasmonic resonators, ferroelectric materials onto the surface of the target [6]. Although a dynamic control of thermal emissivity was achieved for the resultant target, there were some problems emerging in the practical use, including low tenability, narrow spectral window, slow response speed, sustained electric consumption, and rigid substrates [7]. ...
Article
Infrared stealth technology plays a vital role in development of defense industry and new military equipment. The current study focused on a novel type of flexible and foldable composite films based on polyimide (PI)/phosphorene (PR) hybrid aerogel and phase change material (PCM) for infrared stealth and thermal camouflage applications. The composite films were successfully obtained by fabricating a PI/PR hybrid aerogel through prepolymerizaton, film casting, freeze-drying, and thermal imidization, followed by vacuum impregnation of polyethylene glycol (PEG) as a PCM into the aerogel framework. The combination of PI and PR nanoflakes endows the hybrid aerogel with an effective enhancement in mechanical properties, near infrared absorption, and infrared photothermal conversion. The resultant composite films not only present prominent tensile and fatigue-resistant performance but also exhibit a good thermal regulation capability with a high latent-heat capacity of over 150 J/g. More importantly, the composite films demonstrate good infrared stealth and thermal camouflage performance on the high-temperature targets through effective thermal buffer and insulation. With ultralight, flexible, foldable, shape-tunable, and thermal self-regulatory characteristics, the PI/PR aerogel/PEG composite films developed by this work exhibit great application potential in infrared stealth and thermal camouflage for new military equipment.