Military Camouflage Research Articles

Multiplexing Integration Meta‐Absorber in an Ultrathin Planar Board

A meta‐absorber is a type of metamaterial capable of absorbing incident electromagnetic waves, primarily used for isolating and attenuating these waves. Due to their unique properties, meta‐absorbers are widely used in areas of electronic shielding, radar cross‐section reduction, as well as military camouflage. To enhance the working bandwidth, conventional meta‐absorbers integrate multiresonance modes in different layers, resulting in increased thickness and limiting their applications. Herein, a multiplexing integration meta‐absorber is proposed in a one‐layer planar board, achieving an ultrathin thickness of 0.053 λ and an ultrawide absorption band covering the whole X and Ku bands (8.0–18.0 GHz) by harnessing the coupling of four resonant modes. Moreover, the designed meta‐absorber is insensitive to the polarization of incident waves and exhibits good angle stability within ±45°. The experimental results agree well with the simulations. These findings may inspire the development of ultrathin metadevices with multifunctionalities operating across different frequency domains.

Flexible All-Solid-State Zinc-Based Electrochromic Energy Storage Devices for Adaptive Military Camouflage

Flexible All-Solid-State Zinc-Based Electrochromic Energy Storage Devices for Adaptive Military Camouflage

Wartime experience of visual impressions: K. A. Korovin and the problem of camouflaging positions at the front during World War I

During World War I the development of new methods for camouflaging the troops demanded the involvement of not only military professionals but also of the artists. Thus, a famous artist and Academician of Painting, Konstantin Alekseevich Korovin (1861–1939), cooperated with the paint-disguise and camouflage service established on the South-West Front on the initiative of brothers A. N. and N. N. Suchkov. The documents deposited at the Russian State Military Historical Archives reflect Korovinʼs interest in the problems of military camouflage, his trips to the front and his inventions. In the documents published here (the letters to the Suchkov brothers; a memorandum and an explanatory report to the chief of engineers of the armies of the South-West Front; instructions for the so-called “color finder” for determining the color of paint after drying) the artist outlined the problems of camouflage at the front, gave advice on the best ways of concealing positions (camouflaging trenches by paint spraying, setting up observation points that merge with the terrain, the use of camouflage nets). Korovin was aware of the innovations in camouflage in the armies of Russiaʼs allies, and urged to adopt the best of what they had. According to Korovin, the leadership of camouflage teams should be entrusted to competent officers familiar with the rules and specifics of perception of color combinations. The documents suggest that Korovin was one of the pioneers in the military science of camouflage in Russia.

Search and recovery network for camouflaged object detection

Camouflaged object detection aims to accurately identify objects blending into the background. However, existing methods often struggle, especially with small object or multiple objects, due to their reliance on singular strategies. To address this, we introduce a novel Search and Recovery Network (SRNet) using a bionic approach and auxiliary features. SRNet comprises three key modules: the Region Search Module (RSM), Boundary Recovery Module (BRM), and Camouflaged Object Predictor (COP). The RSM mimics predator behavior to locate potential object regions, enhancing object location detection. The BRM refines texture features and recovers object boundaries. The COP fuse multilevel features to predict final segmentation maps. Experimental results on three benchmark datasets show SRNet's superiority over SOTA models, particularly with small and multiple objects. Notably, SRNet achieves performance improvements without significantly increasing model parameters. Moreover, the method exhibits promising performance in downstream tasks such as defect detection, polyp segmentation and military camouflage detection.

Multi‐stimuli‐responsive chromic switching self‐assembled with polyoxometalate and copper‐viologen frameworks

AbstractChromic materials with multi‐stimuli responses have received tremendous attention from industry and academia for their potential applications in smart windows, data storage, military camouflage, molecular switches, modulators, etc. To develop multi‐stimuli‐responsive color‐changing materials with high sensitivity and high stability, a polyoxometalate‐based copper‐viologen framework, formulated as Cu2(H2O)2(L)2[PW12O40][OH−]·2H2O (HNU‐97, H2L2+ = 1,1′‐(1,4‐phenylenebis(methylene))bis(4‐carboxypyridinium)), was prepared by a mild one‐step self‐assembly strategy. Structural analysis shows that HNU‐97 presents a supramolecular structure formed by a one‐dimensional copper‐viologen framework and polyoxometalates through rich hydrogen bonds, anion‐π interactions, etc. Discoloration studies show that HNU‐97 exhibits reversible and rapid response characteristics to various external stimuli, such as 10 s to UV radiation, 5 min to heating, and 5 min to ammonium/amine vapors. This mechanism reveals that different external excitation sources lead to different preferential transfer directions of electrons, resulting in different discoloration phenomena. To construct stimuli‐chromic materials with good mechanical properties, we successfully introduced HNU‐97 into the poly(vinyl alcohol) (PVA)/glycerol (Gly) hydrogel to obtain a composite HNU‐97@PVA/Gly. Remarkably, HNU‐97@PVA/Gly combines the merits of each component and can achieve significant response discoloration behavior under both UV irradiation and ammonia atmosphere. This work will provide an idea for the construction of multiple stimuli‐responsive materials.

Subdiffraction‐Limited Motheye‐Like Metastructures Fabrication by Dual‐Beam Overexposure Methodology Enhancing Broadband Infrared Antireflective Application

AbstractMaterials possessing broadband antireflective properties benefit applications of military camouflage, photovoltaic devices, and highly transparent windows. In this work, large area, high throughput subdiffraction‐limited motheye‐like metastructures featuring broadband infrared (3–12 µm) antireflectivity are realized through dual‐beam overexposure shrinking strategy and subsequent controllable anisotropic reactive‐ion‐etching process. Both overexposure and overdevelopment processes severely controlled in conventional lithography processes, attribute significantly to improving linewidth resolution to <150 nm when photoresist thickness exceeding 500 nm, even to one micron. For antireflective application, the motheye profiles with customized anisotropic ratio (>3.27) and tunable taper‐angle range (>12.2°) are also realized by regulating the competition of directional ion bombardment and isotropic chemical etching in sulfur hexafluoride (SF6) plasma. The corresponding reflectivity is theoretically well‐simulated and experimentally validated after accounting for the tunable profiles and fractional volume coverage of motheye‐like structures. A low reflectivity <2.0% with the uniformity of ±4.8% and averaged to 1.2% across the overall spectrum of 3–12 µm are achieved. Implementing such efficient shrinking approach can possess huge potential in applications of military camouflage, photovoltaic devices, and highly transparent windows.

A Flexible Long-Wave Infrared Radiation Modulator Integrated with Electrochromic Behavior for Dual-Band Camouflage.

Electrochromic devices (ECDs), which are capable of modulating optical properties in the visible and long-wave infrared (LWIR) spectra under applied voltage, are of great significance for military camouflage. However, there are a few materials that can modulate dual frequency bands. In addition, the complex and specialized structural design of dual-band ECDs poses significant challenges. Here, we propose a novel approach for a bendable ECD capable of modulating LWIR radiation and displaying multiple colors. Notably, it eliminates the need for a porous electrode or a grid electrode, thereby improving both the response speed and fabrication feasibility. The device employs multiwalled carbon nanotubes (MWCNTs) as both the transparent electrode and the LWIR modulator, polyaniline (PANI) as the electrochromic layer, and ionic liquids (HMIM[TFSI]) as the electrolyte. The ECD is able to reduce its infrared emissivity (Δε = 0.23) in a short time (resulting in a drop in infrared temperature from 50 to 44 °C) within a mere duration of 0.78 ± 0.07 s while changing its color from green to yellow within 3 s when a positive voltage of 4 V is applied. In addition, it exhibits excellent flexibility, even under bending conditions. This simplified structure provides opportunities for applications such as wearable adaptive camouflage and multispectral displays.

Design and Application of Bionic Camouflage Materials Simulating Spectral Reflection Characteristics of Plants: A Review

Hyperspectral remote sensing (RS) has rapidly developed in recent years and has been widely used in the military field. This technology not only brings huge opportunities for military reconnaissance but also poses unprecedented challenges to military camouflage, severely complicating the development of plant hyperspectral camouflage materials and technology. In this review, the spectral reflectance characteristics of plants and the application of hyperspectral RS in plant RS and military operations are reviewed. The development status of bionic camouflage materials that simulate the spectral reflection characteristics of plants is analyzed. With the existing hyperspectral camouflage materials and technology, bionic camouflage technology is limited by the inability of bionic materials to accurately imitate the characteristic absorption peaks of green vegetation, low stability and durability, and the large overall material thickness, which complicate actual large-scale application. On this basis, a future development direction and a trend of plant hyperspectral bionic camouflage materials and technology are proposed.

Electrofluorochromic Switching of Heat-Induced Cross-Linkable Multi-Styryl-Terminated Triphenylamine and Tetraphenylethylene Derivatives.

High-performance electrochromic (EC) and electrofluorochromic (EFC) materials have garnered considerable interest due to their diverse applications in smart windows, optoelectronics, optical displays, military camouflage, etc. While many different EC and EFC polymers have been reported, their preparation often requires multiple steps, and their polymer molecular weights are subjected to batch variation. In this work, we prepared two triphenylamine (TPA)-based and two tetraphenylethylene (TPE)-based derivatives functionalized with terminal styryl groups via direct Suzuki coupling with (4-vinylphenyl)boronic acid and vinylboronic acid pinacol ester. The two novel TPE derivatives exhibited green-yellow aggregation-induced emission (AIE). The EC and EFC properties of pre- and post-thermally treated derivatives spin-coated onto ITO-glass substrates were studied. While all four derivatives showed modest absorption changes with applied voltages up to +2.4 V, retaining a high degree of optical transparency, they exhibited obvious EFC properties with the quenching of blue to yellow fluorescence with IOFF/ON contrast ratios of up to 7.0. The findings therefore demonstrate an elegant approach to preparing optically transparent, heat-induced, cross-linkable styryl-functionalized EFC systems.

Visual Sensor with Host-Guest Specific Recognition and Light-Electrical Co-Controlled Switch.

Perception of UV radiation has important applications in medical health, industrial production, electronic communication, etc. In numerous application scenarios, there is an increasing demand for the intuitive and low-cost detection of UV radiation through colorimetric visual behavior, as well as the efficient and multi-functional utilization of UV radiation. However, photodetectors based on photoconductive modes or photosensitive colorimetric materials are not conducive to portable or multi-scene applications owing to their complex and expensive photosensitive components, potential photobleaching, and single-stimulus response behavior. Here, a multifunctional visual sensor based on the "host-guest photo-controlled permutation" strategy and the "lock and key" model is developed. The host-guest specific molecular recognition and electrochromic sensing platform is integrated at the micro-molecular scale, enabling multi-functional and multi-scene applications in the convenient and fast perception of UV radiation, military camouflage, and information erasure at the macro level of human-computer interaction through light-electrical co-controlled visual switching characteristics. This light-electrical co-controlled visual sensor based on an optoelectronic multi-mode sensing system is expected to provide new ideas and paradigms for healthcare, microelectronics manufacturing, and wearable electronic devices owing to its advantages of signal visualization, low energy consumption, low cost, and versatility.

The effect of an attractant toxic sugar bait (ATSB) incorporating <em>Bacillus thuringiensis israelensis </em>and methoprene on mosquito populations

Background: The threat posed by mosquito-borne diseases continues to increase globally. The increase of pesticide resistance is impacting vector control and public health globally. The development and testing of new pesticides faces several challenges, e.g., time for development, high cost, and regulatory hurdles. Adapting pesticides that are currently used within integrated vector management can help alleviate these challenges. Methoprene has demonstrated reduction of larval populations and fecundity in adult mosquitoes. The objective of the study was to demonstrate the efficacy of ProVector Entobac with methoprene (Entobac M) on mosquito populations in rural sites in Southeastern Georgia. Methods: ProVector® Military Camouflage Tubes with ProVector Entobac M pesticide were placed in a grid at test sites. A positive control test site and a negative control site were used to compare results statistically. Mosquito diversity and evenness among sites were measured using Shannon Diversity Index and Equitability. Results: Deployment of ProVector® Military Camouflage Tubes with ProVector Entobac M pesticide was effective in reducing total mosquito populations. The mosquito species shared among the test sites and positive control site were similar, and the negative control site was least similar in diversity and evenness. There was variation of control within Aedes, Anopheles, and Culex genera. Discussion: The aim of the study was to demonstrate the efficacy of the ProVector Military Camouflage Tube delivery of Entobac with methoprene (Entobac M) on mosquito populations. Mosquito-borne diseases are an increasing threat to communities around the world due to invasive species and global warming. In previous studies, ProVector® Entobac™ has been validated in laboratory and field studies to control both adult and larval mosquitoes in the United States and several other countries. Application of ecofriendly and target specific pesticides with no-resistance is critical in reducing mosquito populations and the risk of vector-borne diseases. Our study demonstrated a significant decrease in adult mosquito populations due to the utilization of a target specific mosquito larvicide that has been adapted to kill adult mosquitoes.

Chameleon-inspired supramolecular materials based on cucurbit[7]uril and viologens exhibiting full-color tunable photochromic behavior

Inspired by Chameleons' skin color tuning in response to environmental changes, we design and prepare three inclusion complexes based on the cucurbit[7]uril (Q[7]) host and three viologen guests. Upon light irradiation, the colors of these inclusion complexes in the solid state turn from light colors to vivid three primary colors, i.e., red, green, and blue, respectively. Ultraviolet–visible (UV–vis) diffuse reflectance and electron spin resonance (ESR) spectra reveal that the photochromism can be attributed to the generation of viologen radicals, originating from the photoinduced electron transfer. The results of quantum chemical calculation indicate that Q[7] in the inclusion complexes acts as the electron donor in the photoinduced electron transfer process. Using a color mixing approach and finely manipulating the proportions of the three inclusion complexes, a series of composite photochromic materials (CPMs) can be manufactured, covering a full-color gamut in visible light. On the other hand, due to the ignorable size and shape change of CPMs during the photochromatic processes, the CPMs-based reversible photochromic “printing” and photofading “erase” properties were also used for quick response (QR) code. Therefore, these prominent intelligent features of CPMs open new avenues to explore optical regulated nano-platforms for multiple anti-counterfeiting, biomimetics, and military camouflage applications.

Recent progress in transmissive and reflective electrochromic devices for multi-color modulation

Multi-color electrochromic devices (M-ECDs), which dynamically and reversibly regulate the visible optical properties of the objects, have received significant interest in various fields such as displays, flexible intelligent electronics, smart windows and military camouflage. This review provides comprehensive summaries of the latest advances in inorganic electrochromic materials and M-ECDs. We discuss the basic principles for achieving M-ECDs, from the intrinsic multicolor characteristics of materials to a combination with optical structures. The progress on the construction of multicolor electrochromic thin-films and associated devices are unfolded in detail based on their transmissive or reflective working scenarios. Moreover, the limitations and challenges are also outlined for consideration for the future development of M-ECDs.

Advanced inorganic nanomaterials for high-performance electrochromic applications.

Electrochromic materials and devices with the capability of dynamic optical regulation have attracted considerable attention recently and have shown a variety of potential applications including energy-efficient smart windows, multicolor displays, atuto-diming mirrors, military camouflage, and adaptive thermal management due to the advantages of active control, wide wavelength modulation, and low energy consumption. However, its development still experiences a number of issues such as long response time and inadequate durability. Nanostructuring has demonstrated that it is an effective strategy to improve the electrochromic performance of the materials due to the increased reaction active sites and the reduced ion diffusion distance. Various advanced inorganic nanomaterials with high electrochromic performance have been developed recently, significantly contributing to the development of electrochromic applications. In this review, we systematically introduce and discuss the recent advances in advanced inorganic nanomaterials including zero-, one-, and two-dimensional materials for high-performance electrochromic applications. Finally, we outline the current major challenges and our perspectives for the future development of nanostructured electrochromic materials and applications.

Infrared polarization model optimization and radiation characteristics of camouflage coatings

To investigate the polarization characteristics of the infrared radiation form camouflage a coating surface, an improved model for the two-component polarized bidirectional reflectance distribution function (pBRDF) is established. A new form of the geometric attenuation factor is used instead of the traditional Blinn shielding function, and diffuse scattering component caused by the rough surface is also taken into account in the micro mirro model. The expression of the degree of linear polarization (DOLP) of the infrared radiation is derived by using the optimized pBRDF, the valid of which is proved by experimental data. The numerical calculations results of DOLP of the three coatings are in good agreement with the experimental data. The expression is numerically evaluated and the influence of coating surface roughness, the effect of geometric attenuation diffuse scattering on the infrared DOLP is discussed. The greater the surface roughness of the coating is, the more obvious are the geometric attenuation effect and diffuse scattering effect caused by the roughness. These results provide theoretical and technical support for the realization of military camouflage, anti-camouflage, target recognition, and other fields.

Electrically Triggered Color‐Changing Materials: Mechanisms, Performances, and Applications

AbstractElectrically triggered color‐changing materials, termed as electrochromic materials, offer precise and programmable color transistions through the manipulation of electric field frequency and amplitude. They are used as displays, sensors, military camouflage, wearable devices, and anticounterfeiting materials. Their future advancements depend on clear understanding of the color change mechanisms and pros/cons between different electrochromic materials. To this end, we starts by categorizing electrochromism into two classes according to color production mechanism: chemical color‐based and physical color‐based. Within the former, color emerges from chemical molecules selectively absorbing specific wavelengths of light and color changes stem from electrochemical redox reactions. The latter, meanwhile, hinges upon electrically induced alterations in the geometries, dimensions, or arrangements of nano/micro structures, such as photonic crystals and plasmonic nanostructures. The principles of color changes in both categories are detailed, and compare their differences in terms of response time, operating voltage, degree of color change, and stability. At the end, their applications will be discussed spanning from smart windows to color display, dynamic camouflage, energy storage, and thermal management. This critical review is aimed to provide multidisciplinary insights that will benefit both novices and seasoned experts engaged in fundamental exploration or practical investigations of electrochromic materials.

Toward Camouflage Colors by Electrochemical Copolymerization

AbstractIn this paper, a new electrochromic copolymer containing 6,9‐bis(2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl)‐1,2,3,4‐tetrahydrophenazine (EBE) and 4‐(9‐benzyl‐9H‐carbazol‐3‐yl)‐7‐(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole (CBT) in the main chain was reported. The homopolymers, (Poly(EBE) and Poly(CBT)), were also prepared via electrochemical polymerization and their electrochemical, spectroelectrochemical and electrochromic properties were analyzed in order to compare their properties with those of copolymer (Poly(EBE‐co‐CBT)). The copolymer exhibited good switching property for military camouflage necessities with color change from hues of brown to green. Furthermore, it has been tried to analyze the effects of combination of two donor‐acceptor‐donor (DAD) type monomers with different symmetries on the copolymer properties.

Multispectral camouflage nanostructure design based on a particle swarm optimization algorithm for color camouflage, infrared camouflage, laser stealth, and heat dissipation.

With the development of camouflage technology, single camouflage technology can no longer adapt to existing environments, and multispectral camouflage has attracted much research focus. However, achieving camouflage compatibility across different bands remains challenging. This study proposes a multispectral camouflage metamaterial structure using a particle swarm optimization algorithm, which exhibits multifunctional compatibility in the visible and infrared bands. In the visible band, the light absorption rate of the metamaterial structure exceeds 90%. In addition, color camouflage can be achieved by modifying the top cylindrical nanostructure to display different colors. In the infrared band, the metamaterial structure can achieve three functions: dual-band infrared camouflage (3-5 µm and 8-14 µm), laser stealth (1.06, 1.55, and 10.6 µm), and heat dissipation (5-8 µm). This structure exhibits lower emissivity in both the 3-5-µm (ɛ=0.18) and 8-14-µm (ɛ=0.27) bands, effectively reducing the emissivity in the atmospheric window band. The structure has an absorption rate of 99.7%, 95.5%, and 95% for 1.06, 1.55, and 10.6 µm laser wavelengths, respectively. Owing to its high absorptivity, laser stealth is achieved. Simultaneously, considering the heat dissipation requirements of metamaterial structures, the structural emissivity is 0.7 in the non-atmospheric window (5-8 µm), and the heat can be dissipated through air convection. Therefore, the designed metamaterial structure can be used in military camouflage and industrial applications.

Mixed-valence system with near-infrared electrochromism of Fe(II)-based metal-organic coordination polymers

Near-infrared electrochromic materials have garnered great attention due to their potential applications in optical data storage and military camouflage. Herein, a networked metal-organic coordination polymer bearing multi-redox centra (Fe-MCP) was successfully prepared by coordination interaction of Fe ions with D-A-D-structure ligands through the liquid-liquid interface self-assembly strategy. The resultant uniform film exhibits improved NIR electrochromic attributed to the construction of mixed-valence system. Furthermore, a sandwich-structured electrochromic device was fabricated by combining Fe-MCP electrochromic layer, a gel composed of LiClO4, PMMA, and PC as the electrolyte layer, and anodically coloring PB as an ion storage layer. The resultant device illustrated an optical contrast of 31.4 % at 800 nm and 34.2 % at 1000 nm, a response speed of 4.0 s/8.3 s at 800 nm and 7.6 s/2.7 s at 1000 nm, and good cycling durability. The design principles proposed in this study provide a new insight for the preparation of high-performance NIR electrochromic materials.

Photochromic performance optimization of polyurethane microcapsules by interfacial polymerization method

AbstractSpiropyran photochromic materials have been widely studied in military camouflage, optical data storage, information encryption, and fashion ornaments. The non‐photochromism and low endurance of solid spiropyran make the challenges of their application. Photochromic microcapsules with a butyl acetate solution of spiropyran as core and polyurethane as shell are synthesized via interfacial polymerization. The optimized polyurethane photochromic microcapsules are prepared with a Tween 20 concentration of 4 wt%, core–shell ratio of 16:5, and spiropyran concentration of 0.40 wt%. Polyurethane photochromic microcapsules with a mean particle diameter of 0.33 μm are obtained. The morphology shows smooth spheres, and the core–shell structure is observed. Butyl acetate in the microcapsule core does not evaporate at a temperature lower than 218.01°C as the microcapsule shell insulates heat. The polyurethane photochromic microcapsules are mixed with adhesive, thickener, and water into a paste and screen‐printed on cotton fabric. The printed fabric shows the ΔE of 17.56, 11.93, and 6.96 after 80s irradiation with the xenon lamp intensity of 102, 68, and 34 mW cm−2. The light stability of the photochromic fabric is excellent as ΔE decreases about 8.28% after 20 cycles of UV‐Vis irradiation.