Infrared Camouflage Research Articles

Multispectral pattern camouflage materials based on PU/Al-flake composite: A CNN-based evaluation

With the continuous progress in optical sensor technologies, the emergence of imagery detection systems operating in the infrared (IR) band has become a reality. In response, we present a novel approach designed to deceive imagery IR detectors targeting fighter jets. To implement this method, we developed a specialized coating technique using a Polyurethane (PU)/Aluminum (Al)-flake composite. This composite coating enables the precise application of IR camouflage patterns while preserving the existing visible camouflages on aircraft surfaces. We customized fighter jet IR image datasets by integrating flow and heat transfer numerical analysis results with real-world background measurements. We then employed the YOLOv3 algorithm, based on a convolutional neural network (CNN), which is known for its high performance in object detection. Through this approach, we analyzed the effects of various pattern shapes on camouflage performance. The proposed PU/Al-flake composite coating offers a versatile and effective solution for overlapping IR camouflage patterns onto existing visible camouflages, providing enhanced protection against advanced IR imagery detection systems. This study highlights the potential of a comprehensive approach to developing and evaluating multispectral camouflage materials and effective camouflage strategies, emphasizing practical applications and real-world performance against IR image detectors.

Detection and Anti-Detection with Microwave-Infrared Compatible Camouflage Using Asymmetric Composite Metasurface.

Detection and anti-detection with multispectral camouflage are of pivotal importance, while suffer from significant challenges due to the inherent contradiction between detection and anti-detection and conflict microwave and infrared (IR) stealth mechanisms. Here, a strategy is proposed to asymmetrically control transmitted microwave wavefront under radar-IR bi-stealth scheme using composite metasurface. It is engineered composed of infrared stealth layer (IRSL), microwave absorbing layer (MAL), and asymmetric microwave transmissive structure (AMTS) with polarization conversion from top to bottom. Therein, IR emissivity, microwave reflectivity, and transmissivity are simultaneously modulated by elaborately designing the filling ratio of ITO square patches on IRSL, which ensures both efficient microwave transmission and IR camouflage. Furthermore, full-polarized backward microwave stealth is achieved on MAL by transmitting and absorbing microwaves under x- and y- polarization, respectively, while forward wavefront is controlled by precise curvature phase compensation on AMTS according to ray-tracing technology. For verification, a proof-of-concept metadevice is numerically and experimentally characterized. Both results coincide well, demonstrating spiral detective wavefront manipulation under y-polarized forward wave excitation while effective reduction of radar cross section within 8-18GHz and low IR emissivity (<0.3) for backward detection. This strategy provides a new paradigm for integration of detection and anti-detection with multispectral camouflage.

Inverse design of metamaterial for dual-band infrared camouflage along with dual-band thermal management

The optical metamaterial for infrared camouflage with thermal management is an artificial structure available to not only evade the detection of various thermal imagers operating in distinct infrared wavebands but also ensure the thermal stability of the target. However, designing such an optical metamaterial is challenging due to the necessity to optimize numerous structural parameters simultaneously, especially metamaterials that are compatible with multiple functions. Herein, this paper proposes a novel inverse design method, combining African vultures optimization algorithm (AVOA) with rigorous coupled-wave analysis (RCWA), to design an optical metamaterial capable of achieving infrared camouflage and thermal management compatibly. The proposed metamaterial enables dual-band infrared camouflage for mid-wave infrared (MWIR, 3–5 μm) and long-wave infrared (LWIR, 8–14 μm), along with thermal management through dual-band non-atmospheric windows of 5–8 μm and 14–17 μm. Comparing to other intelligent optimization algorithms, the AVOA is exceptionally efficient, which only takes less time than others to get better results. This work not only provides theoretical guidance to design an optical metamaterial for infrared camouflage with thermal management, but also has the potential to solve the multi-objective optimization problems of multi-band or wide-band radiative modulation.

Foldable sandwich fabric-based composites with thermal insulation and low emissivity for highly efficient infrared stealth

Fabric-based infrared (IR) stealth composites with thermal insulation and low emissivity are desirable for improving IR camouflage of military targets and thermal management of special environments. Therefore, a flexible and foldable composite fabric with a sandwich structure is delicate designed in this work aiming to realize dual-modes IR effects. Polyester fabric chemically plated with copper-nickel (Cu/Ni@PF) and aluminum foil (AF) are on the top and bottom, respectively, acting as low emissivity layers. The medium layer is constructed by silica aerogel microspheres (SAM) with thickeners and waterborne polyurethanes (WPU) functioned as thermal insulation. The thermal conductivity of as-prepared composite fabric is only 0.05904 W/(m·K). When the AF is heated to 70 °C, the introduction of the SAM in the medium layer with the thickness of 300 μm makes Cu/Ni@PF as top surface exhibit a obvious temperature difference of 11.7 °C, demonstrating excellent thermal insulation. The AF maintains a low emissivity of less than 0.2, and the emissivity of Cu/Ni@PF was also as low as 0.296 at 8–14 μm, which can effectively shield the IR signal. Thanks to the Cu/Ni@PF as the top surface, the radiation temperature displays only 36.3 °C when heated at 70 °C, which meaning the dramatic IR signal strength reduce. Therefore, this dual-modes flexible and foldable composite can be a potential candidate in the IR stealth fields.

Study on Infrared (IR) Camouflage Using Mylar in the Defense Sector

Abstract: This project investigates the feasibility of utilizing Mylar, a highly reflective polyester film, for infrared (IR) camouflage in the defense sector. Through a comprehensive analysis of Mylar's optical properties, including its reflectivity and reflectance, this study aims to assess the material's potential for reducing thermal signatures and enhancing stealth capabilities of military assets. The research involves theoretical and numerical analysis to evaluate Mylar's performance under various environmental conditions, such as temperature extremes, humidity, and exposure to ultraviolet (UV) radiation. Furthermore, the project explores the integration of Mylar-based IR camouflage into existing defense systems, including vehicle coatings, personnel gear, and tactical equipment. Recommendations for the deployment and optimization of Mylar-based camouflage solutions are provided, addressing factors such as material selection, camouflage design, compatibility with sensor systems, and logistical support. The findings demonstrate Mylar's efficacy in decreasing IR detectability, providing a cost-effective and versatile solution in IR camouflage. This research contributes significantly to the field of defense technology, offering practical insights and paving the way for further advancements in stealth and counter-detection measures in military applications.

Carbonyl iron/glass fiber cloth composites: Achieving multi-spectrum stealth in a wide temperature range

Multispectral camouflage in a wide temperature range is still a challenging issue owing to the incompatibility of stealth mechanisms corresponding to different spectra. Herein, we develop a flexible flaky carbonyl iron (FCI)/glass fiber (GF) cloth, using all-in-one design of microwave absorption and infrared (IR) stealth to eliminate the above contradictions. Due to micron-scale gaps and height differences on the surface of GF cloth modified with Fe3O4, FCI gains a special vertical structure, which not only induces multiple eddy centers in FCI to enhance magnetic loss but also reduces the microwave reflection area, achieving a synergistic improvement in attenuation and impedance characteristics. Therefore, FCI/GF cloth with a thickness of 2.0 mm obtains a maximum effective absorbing bandwidth of 5.82 GHz in a range of 25–400 °C. On the other hand, combination of FCI and GF cloth decreases IR emissivity while maintaining wonderful heat insulation performance, allowing objects over 250 °C to obtain promising thermal IR camouflage. The all-in-one design successfully breaks barriers faced by traditional hierarchical radar-IR compatible stealth materials such as strong reflection, great thickness, loss and impedance mismatch.

Femtosecond laser-textured superhydrophilic coral-like structures spread AgNWs enable strong thermal camouflage and anti-counterfeiting

Modulating the thermal emission of a material in the infrared (IR) range can be essential for various practical applications such as smart textiles, camouflage, and anti-counterfeiting. Although many different materials or structures have been proposed, the complex manufacturing processes are still hindering their widespread use. Herein, a facile femtosecond laser processing technology and a drop-coating method are introduced to form a patternable low emissivity film. Laser-treated polyimide films resulted in superhydrophilic structured surfaces that are uniformly coated with silver-nanowires (AgNWs) in aqueous solutions for low emissivity surfaces. Furthermore, the emissivity of the samples is as low as ∼0.2 without deterioration over 800 bending-releasing cycles. The as-prepared films also display good thermal camouflage properties, namely, the films reduced the thermal radiation temperature of an object by 35.8 °C when the object temperature was ∼69.1 °C. Additionally, this IR camouflage effect of the AgNWs coated samples shows excellent stability even in harsh environments such as immersion in water, acid, alkali, and salt solution and applied voltage. We also show that information encryption was possible by adjusting the amount of AgNWs. The design of this programmable patterned low emissivity film indicates an idea for the thermal camouflage and anti-counterfeiting technology, which can carry more abundant application scenario and disguise them more complex and sophisticated.

Multiresonant Selective Emitter with Enhanced Thermal Management for Infrared Camouflage.

Tailoring the optical properties of metamaterials is crucial for improving the performance of infrared (IR) applications. Generally, IR camouflage materials are required to have low IR-emission properties for the detected bands (3-5 and 8-12 μm), in which IR detection is accomplished. However, the heat residue by suppressed thermal radiation degrades the thermal dissipation capacity and thermal stability of IR camouflage materials. Herein, a multilayer metal-dielectric-metal (MDM) selective emitter with high IR-emission performance in the undetected band for thermal management and low IR-emission performance in the detected band for IR camouflage is introduced. Compared to a conventional selective emitter and a low-emission material (Au film), the multiresonance selective emitter exhibited 125 and 2910% increases in heat dissipation within the undetected band, respectively. In addition, the proposed camouflage material exhibited a substantial reduction in emissive energy within the detected bands of 3-5 and 8-12 μm, with reductions of 72 and 83%, respectively, compared to that of a high-emission surface. The effectiveness of our IR camouflage was demonstrated by IR camera measurements. When the surface temperature was 360 K, the radiance temperatures of the multilayer multipeak selective emitter were 314 and 309 K for the 3-5 and 8-12 μm bands, respectively. Thermal management experiments demonstrated the enhanced thermal stability of the multiresonance selective emitter, especially in conditions of low pressure and high heat flux, when compared to that of the low-emissivity film. This work provides a practical strategy to enhance the thermal emission of a selective emitter, expanding its potential beyond IR camouflage to various energy applications.

Manipulating CNT Films with Atomic Precision for Absorption Effectiveness–Enhanced Electromagnetic Interference Shielding and Adaptive Infrared Camouflage

AbstractPromoting advanced functional films that integrate protective behaviors for synergetic radar, infrared (IR), and visible light is confronted with extreme challenges. The effective integration of shielding capacity and IR camouflage into single‐component carbon films remains an enormous challenge because of limited conductivity and high IR absorption. In this work, carbon nanotube (CNT) films with excellent electromagnetic interference (EMI) shielding, switchable IR camouflage, and energy conversion are obtained via a (FCCVD) method and subsequent defect engineering strategies induced by temperature (Strategy I) and N/S co‐doping (Strategy II). Wherein the effect on the electronic configuration as well as multi‐spectra performance is deeply explored. Ascribing to the synergistic effects of strategies, defective CNT films present superior EMI shielding effectiveness (SE) with a high absorption effectiveness ratio of 86.9%, and a large span of emissivity (0.479), which provides the necessary condition for various application scenarios. Under the applied electric field excitation, the IR radiation of CNT films can adapt to rapidly changing surroundings, such as low‐high/high‐low temperatures. Besides, the desirable energy conversion performance and de‐icing can be achieved. This work supplies a feasible strategy for designing EM absorption, adaptive IR camouflage, and energy conversion to confront multiband surveillance.

Laser Dynamic Control of the Thermal Emissivity of a Planar Cavity Structure Based on a Phase-Change Material.

Tailoring the thermal emission of a material in the long-wave infrared (IR) range of 8-13 μm is crucial for many IR-adaptive applications, including personal thermal management, IR camouflage, and radiative cooling. Although various materials and surface structures have been proposed for these purposes, space-selective and dynamic control of their emissivity is challenging. In this study, we present a planar surface cavity structure consisting of a Ge2Sb2Te5 (GST) film on top of a thin metal reflector to modulate its emissivity by using an ultraviolet laser beam. A laser-induced phase change in GST allowed for the local control of emissivity. The average emissivity in the long-wave IR range was tunable from 0.15 to 0.77 simply by changing the laser energy deposited on the GST film. This enabled the laser printing of high-contrast emissivity patterns, which were erasable by subsequent thermal annealing. Emissivity-modulated GST cavities could be fabricated on not only rigid substrates but also flexible plastic substrates such as polyimide. The GST surface cavity was highly flexible and remained stable upon repeated bending to a curvature radius of 0.5 cm. This study provides a promising route for realizing scalable and flexible thermal emitters with tunable surface emissivity.

A flexible electrochromic device with variable infrared emissivity based on W18O49 nanowire cathode and MXene infrared transparent conducting electrode

Electrochromism with tunable infrared (IR) responses has emerged as an intriguing technology for adaptive IR camouflage and radiative thermal management. Its current development is however hindered by low IR emissivity modulation and unsatisfactory cycle life. Herein, a flexible IR electrochromic device with large IR emissivity modulation and high stability is fabricated by combining an oxygen-deficient W18O49 nanowire cathode and a MXene-based IR transparent conducting electrode. The nanowire structure and abundant oxygen vacancies of W18O49 works in synergy with the high IR transparence of the MXene conducing electrode, to provide the IR emissivity to vary from 0.8 to 0.4 within 3–5 μm (△ε = 0.4), and from 0.77 to 0.3 within 8–14 μm (△ε = 0.47). A long cycle life of more than 2000 cycles was also verified, which could be attributed to the high stability of W18O49 and no material phase transition during cycling. This work demonstrates a viable pathway to design and build high performance flexible IR electrochromic devices for adaptive thermal management.

Stepless IR Chromism in Ti3 C2 Tx MXene Tuned by Interlayer Water Molecules.

Real-time control over infrared (IR) radiation of objects is highly desired in a variety of areas such as personal thermal regulation and IR camouflage. This requires the dynamic modulation of IR emissivity in a stepless manner over a wide range (>50%), which remains a daunting challenge. Here, an emissivity modulation phenomenon is reported in stacked 2D Ti3 C2 Tx MXene nanosheets, from 12% to 68% as the intercalation/discharging of water molecules within the interlayers. The intercalation of water molecules dynamically changes the electronic properties and the complex permittivity in IR frequencies of Ti3 C2 Tx . This emissivity modulation is a stepless and reversible process without the assistance of any external energy input. Further, intercalating cellulose nanofibers into the Ti3 C2 Tx interlayers makes this dynamic process highly repeatable. Last, a sweat-responsive adaptive textile that can improve thermal comfort of human body under changes in metabolic rates and environmental conditions is demonstrated, showing great potential of this mechanism in passive on-demand radiation modulation.

Visibly transparent multifunctional camouflage coating with efficient thermal management.

Camouflage technology has attracted growing interest in many thermal applications. In particular, high-temperature infrared (IR) camouflage is crucial to the effective concealment of high-temperature objects but remains a challenging issue, as the thermal radiation of an object is proportional to the fourth power of temperature. Here, we proposed a coating to demonstrate high-temperature IR camouflage with efficient thermal management. This coating is a combination of hyperbolic metamaterial (HMM), gradient epsilon near zero (G-ENZ) material, and polymer. HMM makes the coating transparent in the visible range (300-700 nm) and highly reflective in the IR region, so it can serve as a thermal camouflage in the IR. G-ENZ and polymer support BE mode (at higher angles ∼50° to 90° in the 11-14 µm atmospheric window) and vibrational absorption band (in 5-8 µm non-atmospheric for all angles), respectively. So it is possible to achieve efficient thermal management through radiative cooling. We calculate the temperature of the object's surface, considering the emissivity characteristics of the coating for different heating temperatures. A combination of silica aerogel and coating can significantly reduce the surface temperature from 2000 K to 750 K. The proposed coating can also be used in the visible transparent radiative cooling due to high transmission in the visible, high reflection in the near-IR (NIR), and highly directional emissivity in the atmospheric window at higher angles, and can therefore potentially be used as a smart window in buildings and vehicles. Finally, we discuss one more potential future application of such a multifunctional coating in water condensation and purification.

Tunable Mid-infrared Selective Emitter with Thermal Management for Infrared Camouflage

Tunable Mid-infrared Selective Emitter with Thermal Management for Infrared Camouflage

Easy-to-Manufacture In-Line 2D Nano Antenna for Enhanced Radiation-Cooled IR Camouflage

Deterministic control of infrared (IR) emitting is attractive for applications in sensors and camouflage. Functional materials and structures that can restrain the surface temperature rise via radiation cooling and inhibit the detectable emitting for camouflage have been developed, yet ideal coordination between the cooling and camouflage considering both design and manufacture purposes remains challenging. Here, we reported an in-line 2D nano antenna for IR camouflage. The in-line 2D configuration was intended for rapid and easy-to-manufacture via efficient direct-writing techniques, e.g., femtosecond laser. We innovatively adopted the detectable IR radiation power as the optimization fitness function, based on the particle swarm optimization (PSO) algorithm, to execute powerful cooling and simultaneously minimize the emitting within the atmospheric window for enhanced camouflage. The optimized structure was manufactured and was compared with the previous IR camouflage structures. The PSO structure reduced the detectable IR radiation power by 55.5–73.6% and suppressed the lock-on range by 33.3–48.6%. Moreover, the function of the in-line 2D nano antenna is insensitive to polarization and angle incidence, which is essential for industrial use. Our work proposed new examples of functional structure design-manufacture strategy for applications including but certainly not limited to cooling, sensors, and camouflage of high-power density advanced systems.

A novel infrared stealth coating material IR-PAN with excellent infrared radiation feature fusion performance of vegetation background

In this work, to explore the optimal coating process parameters of superior infrared (IR) camouflage performance in vegetation background, the effect of IR unit materials with different substrate surface (Al and Foam) on the surface temperature and IR image at different temperatures were studied. Wherein, the emissivity values of IR unit range from 0 to 0.933, and the scope of the substrate thickness is 0.2–1.2 cm. Besides, in order to further improve the IR camouflage performance of such IR unit materials, an IR/AlN/SiC composite coating (IR-PAN) was prepared and the IR fusion effect was also evaluated by the temperature difference, IR radiation energy difference and the fusion effect of the thermal image between IR-PAN and the traditional coatings. Finally, the experimental results showed that the target background temperature difference, radiation energy difference and the infrared fusion effect of IR-PAN were better than the traditional coatings because of the addition of the underlying coating, which buffered the heat and reduced the difference between the target and background thermal inertia. The temperature difference reduced from 2.58 °C to 1.13 °C, the energy difference of infrared radiation decreased from 1.6 e−3 J to 8.3 e−7 J and more fusion of thermal images was observed. IR-PAN exhibited better corrosion resistance, higher thermal conductivity of 0.463 (about 0.25 higher than traditional epoxy resin coating), hardness of 6H, impact resistance of 50/kg·cm−1, adhesion grade 1 (better mechanical properties) and the optimum AlN content of 20%.

Spectrally-switchable infrared selective emitters for adaptive camouflage

Infrared (IR) camouflage can conceal and disguise weapons, equipment, and installations in infrared regions to minimize the detection or identification. Current researches focus mainly on statical IR camouflage and cannot readily adapt complex application scenes. Herein, we proposed two adaptive IR camouflage emitters, for which the radiation can be changed to adapt various scenes through switching emissivity spectra. The first emitter based on multilayer film is fabricated and demonstrated of possessing two modes 0 and 1. At mode 0, the emitter can achieve IR camouflage and radiative cooling in 5–8 μm (non-atmosphere window). This mode is valuable for improving operation stability between individual and equipment in low-temperature (below 68 °C) environment. At mode 1, the emitter possesses low emissivity in 3–14 μm, which assures thermally-robust IR camouflage in broad temperature range above 68 °C. This emitter is free from ion etching and simple in fabrication, which is prominent for large scale manufacture. To further improve the radiative cooling effect of mode 0 in 5–8 μm, an enhancement emitter is proposed based on metamaterial design. The propagating surface plasmon resonance (PSPR) is utilized to improve maximum emissivity from 0.69 to 0.92 and average emissivity from 0.52 to 0.78 in 5–8 μm at mode 0. The proposed emitters can facilitate development in adaptive IR camouflage, smart skin, and intelligent compatible camouflage device.

Three‐Dimensional Electrochromic Soft Photonic Crystals Based on MXene‐Integrated Blue Phase Liquid Crystals for Bioinspired Visible and Infrared Camouflage

Developing bioinspired camouflage materials that can adaptively change color in the visible and infrared (IR) regions is an intriguing but challenging task. Herein, we report an emerging strategy for fabricating dynamic visible and IR camouflage materials by the controlled in situ growth of novel photopolymerizable blue phase liquid crystals with cubic nanoarchitectures onto highly aligned MXene nanostructured thin films. The resulting MXene-integrated 3D soft photonic crystals exhibit vivid structural colors and reversible switching between a bright colored state and a dark black state under a low DC electric field. As an illustration, proof-of-concept pixelated devices that allow for pixel-controllable electrochromism are demonstrated. Furthermore, a free-standing electrochromic flexible film of such 3D soft photonic crystals is fabricated, where visible electrochromism and thermal camouflage are enabled by leveraging the superior electrothermal conversion and low mid-IR emissivity of MXene nanomaterials.

Three‐Dimensional Electrochromic Soft Photonic Crystals Based on MXene‐Integrated Blue Phase Liquid Crystals for Bioinspired Visible and Infrared Camouflage

AbstractDeveloping bioinspired camouflage materials that can adaptively change color in the visible and infrared (IR) regions is an intriguing but challenging task. Herein, we report an emerging strategy for fabricating dynamic visible and IR camouflage materials by the controlled in situ growth of novel photopolymerizable blue phase liquid crystals with cubic nanoarchitectures onto highly aligned MXene nanostructured thin films. The resulting MXene‐integrated 3D soft photonic crystals exhibit vivid structural colors and reversible switching between a bright colored state and a dark black state under a low DC electric field. As an illustration, proof‐of‐concept pixelated devices that allow for pixel‐controllable electrochromism are demonstrated. Furthermore, a free‐standing electrochromic flexible film of such 3D soft photonic crystals is fabricated, where visible electrochromism and thermal camouflage are enabled by leveraging the superior electrothermal conversion and low mid‐IR emissivity of MXene nanomaterials.

Camouflage Assessment of Aluminium Coated Textiles for Woodland and Desertland Combat Background in Visible and Infrared Spectrum under UV Vis IR Background Illumination

Aluminium powder (AP) formulated polyamide 6, 6 (PA 6, 6), cotton fabric and hollow tubular polyester beg (HTPB) were experimented for spectral, chromatic and imaging principle of woodland and desertland camouflage textiles in visible (Vis) and infrared (IR) spectrum under three-dimensional background illumination of ultraviolet (UV)-Vis-IR for concealment and detection of target signature, AP formulated fabric practiced by defense professional. Cotton and polyamide 6, 6 fabric, HTPB were coated and padded with AP powder formulated polyurethane (PU) based binder. Reflection profile of woodland combat background (CB) and coated-padded textiles have been depicted in terms of multidimensional illumination properties of Vis imaging such as chromatic intensity, spectral reflection, Kubelka-Munk (K-M) reflectance, color rendering and photonic response. A symmetrical chromatic value (L*, a*, b*) of AP coated fabric has been portrayed for concealment of target signature against woodland CB. Spectral reflection, chromatic illumination, K-M reflectance and scanning electron microscopy have also been critically confirmed five-time durability of color fastness to wash, tested by AATCC method 61-2013. HTPB-phase change material (PCM) formulation has been found temperature controllable effect of target object (TOB) in terms of heat energy at limited temperature, 30°C. Heat energy versus target concealment of IR imaging principle can be implemented for high-performance camouflage textiles design. The reflection profile of AP coated fabric can be applied for multidimensional camouflage coloration/patterning/HTPB-PCM based IR camouflage technology and direct applications of defence pavilion/tents/clothing against woodland/desertland CB. Therefore, the key phenomenon of this article has been focused on remote sensing properties of eucalyptus tree, scientific name, Eucalyptus Mannifera, a common CB of woodland and AP formulated fabric for defence application against woodland and desertland CB in terms of concealment of defence surveillance under consideration of laboratory and field trialling of woodland and desertland camouflage textiles assessment in Vis-IR spectrum. Therefore, a standardised methodology of camouflage textiles assessment for CDRI has been established under a new technique with conformist machine and technology which may be a new contribution to carry out further research and development for the fighting protection in combat environment under maintaining a standardized sequence from laboratory trialling to field experimentation in a limited timeframe of research.