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Abstract
Infrared (IR) thermal camouflage and management are deeply desirable in the field of military and astronomy. While IR compatible with laser camouflage technology is extensively studied to counter modern detection systems, most existing strategies for visible light camouflage focus on color matching, which is not suitable for scenarios requiring transparency. In this work, we propose an optically transparent metamaterial with multi-band compatible camouflage capability based on the inverse design. The metamaterial consists of Ag grating, Si3N4 dielectric spacer layer, Ag reflection layer, and Si3N4 anti-reflective layer. An ideal multi-band compatible spectrum is involved in the inverse design algorithm. Calculated results demonstrate high transmittance (T0.38-0.78µm = 0.70) in the visible region, low reflectance (R1.55µm = 0.01) in laser working wavelength, high reflectance (R3-5µm = 0.86 and R8-14µm = 0.92) in the dual-band atmospheric window, and high emissivity (ɛ5-8µm = 0.61) for the non-atmospheric window. The radiative heat flux in the detected band is 31W/m2 and 201W/m2 respectively. Furthermore, the incident and polarized insensitivity of the proposed metamaterial supports applicability for practical situations. This work, emphasizes an effective strategy for conducting optically transparent design with compatible IR-laser camouflage as well as radiative cooling properties by an automated design approach.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
For a long time, researchers have been working to study the interaction between matter on a sub-wavelength scale and light allowing metamaterials to make great strides in the fields of angular momentum devices, tunable lenses, perfect absorption, infrared camouflage, and more [1]. In both modern military applications and civilian fields, IR camouflage technology is designed to hide an object's infrared signature from IR detectors. According to Planck's blackbody law, anything above absolute 0 K emit electromagnetic energy outward. Infrared detection technology, which utilizes the infrared signal emitted by objects to search and track, has reached a level of maturity and widespread use in military equipment or soldiers’ reconnaissance [2–4]. Steffen-boltzmann law points out that the intensity of the infrared signal emitted by an object is proportional to the fourth power of the absolute temperature (T) and the object’s surface emissivity (ɛ). Therefore, there are two intuitive methods to achieve infrared camouflage: temperature control or adjustment of surface emissivity. However, the temperature regulation for realizing infrared camouflage needs additional heating or cooling devices which are complex and tough [5–10]. Researchers have focused more on emissivity tuning, designing low of emissivity coatings to blur the infrared signature of objects [11–19]. Covering the full band of low-emissivity materials prevents heat dissipation to the outside, leading to an increase in temperature that is detrimental to camouflage [20,21]. Therefore, according to the atmospheric transmission properties [22], it is necessary to maintain high emissivity in non-atmospheric windows to promote effective radiative heat dissipation [11,23,24].
In addition to infrared detection technology, the active lidar detection technology based on the cats’ eyes effect [25,26] plays an important role in anti-sniper reconnaissance and military equipment deployment information acquisition. Similar to the phenomenon observed in the reflective properties of a cats’ eyes, when the laser beam illuminates the optical window of the target photoelectric device and enters the field of view of the optical system, a portion of the laser beam is reflected. This reflected beam is then captured and filtered by the laser detector [27]. After analyzing the echo power, the position of the detected target can be accurately determined [28]. Most of the ways to achieve laser camouflage are to reduce the laser echo energy to minimize the detection probability. With the development of technology, advanced multi-band detection means have emerged, and corresponding multi-band including laser, infrared and microwave compatible camouflage solutions have also emerged [12,29–31].
Turning to visible light camouflage, it mainly relies on manipulating the color of the display [18], utilizing techniques such as electrothermochromic materials [32], conductive polymers [33], or mechanical drives [34]. The selective emitter, multispectral camouflage and color matching are not optically transparent and render light impenetrable. Consequently, their advanced applications with broad spectrum requirements or multispectral compatibility are limited, such as scenarios for anti-counter-sniper detection systems and cockpit windows for information acquisition. The camouflage scheme that uses phase change material to selectively regulate spectrum or metal/insulator/metal (MIM) structure to achieve low IR emissivity fails to meet the requirement of high visible light transmittance [12,23,35]. While visible light transparency and infrared radiation regulation have been achieved by using ITO [36], a transparent conductive thin film, or by adjusting carrier concentration [37] or employing a nanogrid [38] pattern, these approaches have not taken into consideration laser camouflage or radiation heat dissipation [39]. Therefore, high transmission of visible light, low reflection and high absorption of laser, low emissivity of IR with thermal management, the strategic combination of the three, a transparent muti-band compatible scheme, is imperative to investigate.
In order to address the demands of such applications, several objectives must be achieved: (1) high transmittance of visible band (0.38-0.78µm); (2) low emissivity of IR detection bands; (3) high emissivity of 5-8µm band for heat dissipation; (4) low reflectance and high absorptance of laser wavelength (1.55µm). Considering eye safety, low reflectance of laser must correspond to high absorptance and low transmittance. Since Near-infrared (NIR) laser at 1.55µm falls within proximity to the visible wavelength, it is imperative to minimize interference between these wavelengths during the design process, while also addressing the mutual constraints imposed by distinct spectral requirements, such as high transmittance for visible light and low emissivity for IR radiation.
In our work, we have designed a metamaterial for optically transparent compatible camouflage via an optimization algorithm that can simultaneously satisfy wide-spectrum camouflage requirements in visible, laser, and IR. It consists of ultra-thin metal Ag and dielectric material Si3N4. Using the abnormal transmission characteristics of nanoscale ultra-thin Ag film, we can effectively enhance visible transmission (T0.38-0.78µm = 0.70) and minimize reflection by selecting dielectric material Si3N4 which can match the impedance of Ag film. Additional laser camouflage of 1.55µm (R1.55µm = 0.01) and IR camouflage with radiation heat loss (R3-5µm = 0.86, R8-14µm = 0.92 and ɛ5-8µm = 0.61) are realized by further adding the cross grating and disk array structure. Thanks to the remarkable properties of nanostructure to regulate the light field, the optical field energy of electromagnetic waves is absorbed because of ohmic loss. It effectively reduces the intense laser reflection and increases the emissivity of non-atmospheric windows, which is beneficial to the compatibility between different spectral requirements. In contrast to previous work, our design enables both laser and infrared camouflage with thermal management while being transparent in the visible. It opens up the possibility of multispectral camouflage scenarios that require transparency and can maintain the initiative on the battlefield.
2. Structure and method
2.1 Structure design
The structure diagram of the multispectral compatible camouflage optical transparent metamaterial (MCTM) designed in this paper is shown in Fig. 1(a), which consists of cross micro-nano structure array (Ag), dielectric spacer layer (Si3N4), disk array (Ag), dielectric spacer layer (Si3N4), infrared reflector layer (Ag), and anti-reflective layer (Si3N4) from top to bottom. The dielectric/metal/dielectric (DMD) three-layer film composed of Si3N4 and Ag can enable visible light to pass through and inhibit the infrared characteristic radiation of the target object, which greatly reduces the probability of being captured by the infrared camera. We further introduce the cross and disk laminated metal array, which can absorb the electromagnetic wave energy of laser while selectively radiating energy. Due to the plasmon resonance and the inherent characteristics of the material, the designed MCTM achieves the compatibility of high transmittance in the visible band and laser-infrared camouflage. There are dual detection bands in the IR range because the other bands of light are blocked, scattered and reflected by molecules and impurities in the atmosphere. That is to say, the dual atmospheric windows (3-5µm and 8-14µm) are detected bands, and the non-atmospheric window (5-8µm) is an undetected band. As shown in Fig. 1(b), the shaded blue is atmospheric transmittance, and the solid blue and orange lines are ideal spectral curves.
Fig. 1. Multispectral camouflage compatible optical transparency scheme. (a) Application scenarios for the thermal camouflage in the dual-band infrared transparent window, thermal management in non-window band, and laser camouflage in NIR band (1.55 µm) based on the MCTM of inverse design. (b) Atmospheric transmittance (blue shade) and ideal spectrum for this design (solid blue and orange line).
In this paper, the Finite Difference Time Domain (FDTD) method is used to analyze the model. The plane wave is set to incident from the positive direction of the z axis to MCTM. Periodic boundary conditions are set in the x and y directions, and the perfect matching layer is set in the z direction. The transmission and reflection spectrum of MCTM can be obtained from the monitor of simulation software.
2.2 GA design
Thanks to the development of computer technology, optimization algorithms have been widely used in the fields of metamaterials, photonic circuits, and sensing, striving for lower-cost, more compact, and superior-performance design solutions [40–44]. Genetic algorithm (GA) is a random search algorithm that simulates Darwinian genetic selection and survival of the fittest. When solving complex combinatorial optimization problems, it can provide an optimal solution for the objective function. Specific design ideas of GA have been reported in previous works [45,46]. In this paper, GA is used to inverse design MCTM. As shown in Fig. 2, the fitness function of design GA is defined as FOM:
When the thickness of Ag is greater than the critical thickness, the visible transmission performance decreases, so the thickness of Ag is fixed at 10 nm in our design to save optimization time, which scale can be manufactured. The structural parameters of the model are taken as individual genes in the GA population, which are composed of 46 binary numbers, including thickness (t3, t5) and grating structure parameters (r, l and w). The GA [46,47] randomly generates the initial population, and the FDTD solves for each individual. The range of the initial population is described in Table 1. Depending on the solution results, FOM is calculated and sorted. In the selection process, the 30 elite with the highest FOM value in the current population are retained by us as part of the next-generation population, which helps the population evolve towards high-quality individuals. Next, hybridization and mutation are carried out to generate a new population. The above steps are repeated until the optimal design parameters are output. In this paper, the population size was set as 200, the mutation probability as 10%, the hybridization probability as 70%, and the maximum number of iterations as 25 generations.
Table 1. The range of the initial population.
3. Result and discussion
3.1 Simulated result
The structural parameters of MCTM are shown in Fig. 1(a). The thickness of lower anti-reflective layer Si3N4 is set as t1 = 0.04µm, the thickness of metal reflective layer as t2 = 0.01µm, and the thickness of medium spacer layer Si3N4 as t3 = 0.221µm. The thickness of metal disk t4 = 0.01µm, the thickness of medium disk t5 = 0.035µm, and their radius r = 0.586µm. The wire-length (l) and wire-width (w) of the Ag cross array are set at 0.174µm and 0.734µm, respectively, and the period of the lattice (p) is about 1.2µm. Our design can be obtained by the conventional magnetron sputtering method for film layer stacking, and using an electron beam etching system to complete the determination of patterning, and finally, the transfer of patterning is further completed by deposition or etching [48–52]. The transmission, reflection and absorption spectra of the design structure are numerically simulated, as shown in Fig. 3, the average visible light transmittance is 70% and the maximum is 81.4%, which indicates the structure possesses high optical transparency in the full-visible band. The introduced grating structure increases the laser energy loss, and the ultra-low reflectance 1% at 1.55µm is obtained to match the laser detection. The average reflectance of the IR detected bands is 86% and 92% respectively, corresponding to the low absorptivity of 15% and 8%, because the transmittance in this band is almost zero. In the undetected band (5-8µm), the average absorptivity is 61% and the maximum is 91.7%.
Fig. 3. The calculated result of MCTM: (a) transmittance of visible band; (b) reflectance and absorptance of NIR; (c) reflectance and absorptance of IR.
According to Kirchhoff's law, the emissivity of an object at a certain temperature and wavelength is equal to the absorptivity under thermal equilibrium conditions [53]. Our designs have low emissivity in the detected bands and high emissivity in the undetected band, which fully meet the spectral requirements of IR camouflage with thermal management.
In the inverse design, we use the function FOM mentioned above to evaluate the model performance. The closer FOM is to 1, the better the performance will be. It can be imagined that if the traditional nested scanning optimization method is used for the 5 model parameters waiting to be decided, a considerable number of samples need to be completed to identify favorable models (FOM > 0.6). For example, set parameters in a small range, t1 (20-50 nm), t3 (50-200 nm), r (500-600 nm), l (100-200 nm) and w (100-200 nm). To simplify the model, certain parameters are fixed, and a scanning step of 2 nm. Even with this setup, approximately 150 million model samples would be required, and there is a risk of obtaining numerous subpar models (FOM < 0.5) or even none that meet the desired criteria. The traditional parameter scanning method necessitates constant adjustment of scopes and the development of rules governing parameter changes, which is not only time-consuming but also arduous. In contrast, the inverse design process facilitated by GA eliminates the need for human intervention. Figure 4(a) illustrates the evolutionary process, where the parameter accuracy is set at 1 nm. Figure 4(b) presents the performance statistical distribution of 5000 models designed using GA. This outcome exemplifies the superiority of GA-based design. It can be seen that the majority of these models meet the criteria for high-quality models due to the guiding optimization idea of GA. Compared with the traditional forward design method, the inverse design approach employing GA demonstrates significantly higher design efficiency.
Fig. 4. (a) The inverse design evolution process of the MCTM. (b) Statistics of the FOM value distribution of 25 iterations (blue bars) and normal distribution fitting (orang line).
3.2 Theoretical analysis
3.2.1 Material analysis
In almost all metal materials, the highest electrical conductivity and the lowest visible light absorption characteristics coexist in Ag, and the ultra-thin Ag film has a higher visible light transmittance than the commonly used transparent conductive film ITO [52]. Ag is one of the ideal selections for the design of DMD, an anti-reflective film system, which has been widely applied in the field of transparent conductive material [54]. The refractive index and extinction coefficient of Ag used in the simulations are obtained by fitting the Lorent-Drude model [55] as shown in Fig. 5(a). The counterpart of Si3N4 is shown in Fig. 5(b) [56,57]. Si3N4 has a high refractive index, and the absorption of Si3N4 in visible and even NIR band is close to 0, with almost no loss, which contributes to the realization of high visible light transmittance as well as protects the intermediate Ag reflector. It is one of the best dielectric layer materials to be selected.
3.2.2 Optical characteristics of visible and infrared
We analyze the electric field distribution at the xz section of an ultra-thin Ag film with a thickness of 10 nm at 0.48µm wavelength as shown in Fig. 6(a). It is observed that the energy is attenuated in the Ag film. The transmittance properties of thin films are not only related to their optical properties and thickness but also to the adjacent medium [58]. The use of Si3N4 film as anti-reflective layers matches the film to the free-space impedance and reduces the reflectance of visible light. The electric field of the xz section of Si3N4/Ag/Si3N4 three-layer film is shown in Fig. 6(b), which implies the formation of a standing wave pattern. The reflection waves interact with each other to destructively interfere with the standing waves, thus reducing the reflectivity. In the visible range, in addition to the intrinsic absorption inherent in the material, there is a higher level of electromagnetic wave energy propagating through the film. However, the lower-frequency wave like NIR and IR encounter considerable reflection and are unable to penetrate the film. Consequently, this part of the electromagnetic wave is neither absorbed nor able to pass through. As can be seen from Fig. 6(c), some visible transmittance performances are sacrificed by adding the top layer disk and cross grating array to meet the multispectral requirements. It is acceptable without worry because it still adheres to the high transmittance criterion of visible light. The diameter of the disk exceeds the maximum wavelength of visible light, thus the disk can be seen almost as a thin layer for most visible light passing through normally. The width of the cross grating array is far less than the minimum wavelength of visible light, and the occlusion area ratio is quite small, ensuring visible transmission.
Fig. 6. The electric field diagram of xz section of: (a) a single ultra-thin Ag film of 10 nm at 0.48 µm; (b) Si3N4 /Ag/ Si3N4 three-layer film at 0.48 µm; (c) MCTM at 0.48 µm; (d) MCTM at 0.7 µm.
It can be seen from Fig. 3(a) that the transmission effect of the MCTM decreases after 700 nm. Considering the behavior of the plasma [59,60], it can be divided into local type plasma and propagating type plasma. As shown in Fig. 6(d), we believe that local plasmon resonances occur around both the cross and disk metals, while there are interactions between them, and propagating plasmas appear between adjacent periods. The multiple weak electric fields generated here are the main reason for the decrease in transmittance, but the transmittance can still reach 50% in this case.
The electromagnetic field distribution of MCTM at the absorption peak is shown in Fig. 6. The disk metal as the middle metal layer with the top cross-shaped metal and the bottom layered metal can be regarded as two Fabry-Perot (F-P) cavity structures superimposed on each other. The two F-P cavities induce opposite charge distributions between their top metal and bottom metal dipoles at resonant wavelengths by the incident electric field, thus generating electric fields in opposite directions. These opposite parallel induced currents generate a concentrated magnetic field in the dielectric layer located between the top and bottom metal layers [61]. Specifically, at a resonance wavelength of 1.55 µm as shown in Fig. 7(a)-(c), a localized magnetic field distribution is generated in the first F-P cavity, resulting in higher-order magnetic resonance. The charge distribution in the metal at the bottom of the second F-P cavity shows an opposite pattern to that in the metal in the middle layer, which excites the third-order magnetic resonance in the second dielectric layer. At the 6.65um resonant wavelength as shown in Fig. 7(d)-(f), the incident electromagnetic wave induces an increase in charge aggregation, resulting in a stronger electric field. The magnetic field is confined within the two dielectric layers and produces low-order magnetic resonance. In addition, localized surface plasmon resonance is excited at the edges of both cross and disk metals, and this localized plasma behavior originates from electromagnetic confinement resulting from internal interactions. The superposition of magnetic fields generated by localized plasma and F-P leads to the synergistic action of multiple modes. The coupled electromagnetic waves are converted to thermal energy through ohmic losses, which in turn gives rise to high absorption phenomena [62,63].
Fig. 7. The electromagnetic field distribution of MCTM at 1.55 µm: (a) electric field diagram in xz section; (b) magnetic field diagram in xz section; (c) electric field diagram in xy section. The electromagnetic field distribution of MCTM at 6.65 µm: (d) electric field diagram in xz section; (e) magnetic field diagram in xz section; (f) electric field diagram in xy section.
3.2.3 Infrared camouflage with thermal management
Most natural objects have a blackbody-like radiation spectrum. At a certain temperature T, the average emissivity of an object in a particular band can be expressed by spectral emissivity and blackbody irradiance [61].
In which ${I_{bb}}$ is the spectral irradiance of the blackbody, ${\lambda _1}$ and ${\lambda _2}$ represent the starting and ending wavelengths, $\varepsilon (\lambda )$ is the emitter emissivity. According to the Eq. (2), the average emissivity $\mathrm{\bar{\varepsilon }}$ below 27°C in the 3-5µm, 5-8µm, and 8-14µm bands are calculated to be 0.15, 0.61, and 0.08, respectively. The radiation temperature Tr detected by the infrared camera is determined by the inverse function of the detected power P(ɛ, T) [11]:
where ${\varepsilon _{IR}}$ is the default emissivity (working in 7.5-14µm), which is usually ${\varepsilon _{IR}} = 1$ for the IR camera. P is the radiation power detected by the infrared detector, corresponding to the radiation power of the blackbody at the temperature T. The radiation intensity received by the infrared thermal imager is the sum of the object's own radiation and the reflection of environmental radiation on the object.In order to quantitatively analyze the attenuation and energy dissipation of infrared signal for infrared camouflage, we calculate the radiative flux of infrared camouflage considering temperature T = 473 K and unit area, as shown in Fig. 8(a). In the detected band, the blackbody radiative flux is 193 W/m2 and 756 W/m2. The counterparts of MCTM are 31 W/m2 and 201 W/m2, accounting for 16% and 26% of the blackbody radiative flux, respectively. Comparing MCTM and low emissivity metal Ag, the radiative heat flux of MCTM and Ag is 378 W/m2 and 57 W/m2 in the undetected band, corresponding to the former is about 6.6 times that of the latter. In summary, our proposed MCTM coexists with IR camouflage in the detected band and a high heat dissipation performance in the undetected band, using ideal blackbody radiation as a reference, which denotes obvious wavelength-selective emission to reduce IR features and dissipate accumulated energy.
Fig. 8. (a) The spectral radiation intensity of the blackbody (blue line), MCTM (orange line) and Ag (mulberry line) at 473 K. (b) The integrated power of MCTM (solid orange line), self -radiation Prad (dotted yellow line), environmental reflection Pref (dotted green line) and blackbody (blue line). (c) The relation between radiant and real temperature of the MCTM.
The detected power comes from the sum of radiation and reflection. According to the emissivity spectrum, the radiation and reflection power of the MCTM at the operating band of the IR camera are calculated by integration. As shown in Fig. 8(b), the radiation temperature of MCTM increases with temperature, but the radiation power of the structure is always lower than that of the blackbody at the same temperature. For example, when our structure temperature is 200 °C, the power captured by the infrared camera is 239 W/m2 about 21% of the blackbody, which corresponds to the power radiated by the blackbody at 44 °C. Under the condition of ambient temperature, the infrared power of the structure is equal to the blackbody radiation power due to the compensation of the ambient reflected power. The relationship between actual and radiant temperature is clearly shown in Fig. 8(c).
3.3 Overall performance evaluation
To comprehensively evaluate the overall performance of our designed metamaterial, we define a function as a multiband compatible efficiency of visible light, laser, infrared thermal camouflage and thermal management, which is inspired by previous studies [64], as shown in Eq. (5).
Here, ${\lambda _1},{\lambda _2},{\lambda _{min}},{\lambda _3},{\lambda _4}$ and ${\lambda _{max}}$ are 0.38, 0.78, 3, 5, 8 and 14 µm. $T(\lambda )$ and $R(\lambda )$ represent the transmittance and reflectance of $\lambda $. The reflectance of atmospheric windows represents the IR thermal camouflage performance, the emissivity of non-atmospheric windows represents the radiation refrigeration function, and the average transmittance represents the visibility performance. The higher the eff value is, the better the overall performance is. We compare the design of this article with others, as shown in Table 2. Transparent camouflage necessitates high transmittance within the visible range. Infrared thermal camouflage requires high reflectivity in atmospheric window bands to ensure that hot objects can be hidden in the environment. To improve the camouflage performance, the radiant heat dissipation of non-atmospheric windows is taken into account, which relies on high emissivity. Laser camouflage mandates a high absorptivity at working wavelengths. It becomes apparent that the structure we designed possesses certain advantages to achieve camouflage compatibility of multiband. Compared with previous research works, our work achieves infrared camouflage with effective thermal management based on visible light transparency. It significantly improves the radiative cooling performance in the non-atmospheric window region, further enhancing its camouflage capability. Notably, it also features NIR laser camouflage, which meets the need for a multi-band compatible camouflage scheme. In summary, our work has not only made significant progress in IR camouflage but also excelled in laser camouflage and visible light transparency. These advantages improve the concealment, survivability, and maneuverability of military equipment on the battlefield, providing greater advantages for military operations.
Table 2. Optically transparent multiband compatible camouflage performance comparison
3.4 Discussion of polarization and angle sensitivity
Considering applications for practical environments, we conducted an investigation into the sensitivity of polarization and incidence angle. Figure 9(a) and (b) illustrates the reflection spectra of TM to TE polarization of the designed structure from the NIR to IR spectrum range. It can be seen from the results that it is not sensitive to any angle of polarization incident light waves. Then, we discussed its sensitivity to the incident angle, as depicted in Fig. 9(c)-(f). At a large incident angle (45°), it continues to exhibit exceptional absorption and radiation characteristics at the NIR and non-atmospheric and maintains an impressively low emissivity within the atmospheric window. The reflectivity at the laser operating wavelength undergoes some changes. When the incident angle is increased to 45°, the reflectivity at 1.55 µm is 37% for TM waves and 50% for TE waves. The reflectivity increases for TE waves, but it remains below 40% at incidence angles below 35°. These results highlight the insensitivity of the design to the incident angle. In general, our design exhibits an advantageous attribute of being highly tolerant to both polarization and incidence angles, aligning precisely with our intended objectives.
Fig. 9. The dependence of reflectance on the polarization angle: (a) at NIR; (b) at IR. The dependence of reflectance on the incident angle: (c) TM incident at NIR; (d) TM incident at IR; (e) TE incident at NIR; (f) TE incident at IR.
4. Conclusion
In conclusion, we demonstrate a robust and versatile structure termed MCTM which offers compatibility across visible, IR, and laser bands incorporating thermal management. The MCTM based on the principle of DMD, consists of anti-reflective layers and a metal layer, and achieves phase matching by adjusting the thickness of the film to reduce the reflection of visible light. The suppression effect of the IR object comes from the reflectance of the metal layer in the IR band. And then, the cross and disk gratings are introduced to realize laser camouflage and radiation heat dissipation. Our calculated results highlight the high visible transmittance (70%), the low reflectance (1%) of the laser working wavelength, the low emissivity (15% and 8%) of the IR detection dual-band atmospheric window and the high emissivity (61%) of the non-atmospheric window 5-8µm. Notably, the inverse design is utilized for realizing compatible camouflage performance of MCTM from the visible to the IR range. In comparison to traditional IR camouflage or transparent metamaterials with thermal management, our design providing additional camouflage functionalities and delivering superior performance. These advancements provide potential avenues for multispectral compatibility from visible to IR spectrum, paving the way for enhancing camouflage capabilities in a variety of applications.
Funding
Key Research and Development Program of Guangxi (AB22080048); Science and Technology Major Project of Guangxi (2020AA21077007, 2020AA24002AA); Postgraduate Scientific Research lnnovation Project of HunanProvince (CX20230009); Program for New Century Excellent Talents in University (NCET-12-0142); Natural Science Foundation of Hunan Province (13JJ3001); Foundation of NUDT (JC13-02-13, ZK17-03-01); China Postdoctoral Science Foundation (2018M633704); National Key Research and Development Program of China (2022YFF0706005); National Natural Science Foundation of China (12272407, 60907003, 61805278, 62275269, 62275271).
Disclosures
The authors declare no conflicts of interest.
Data availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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