Military Camouflage Research Articles

Carbon dots as multifunctional electrolyte additives toward multicolor and low self-discharge electrochromic energy storage devices

Electrochromic energy storage devices (EESDs), integrating energy storage and electrochromism into one cell that can change appearance based on their working states, are presently attracting considerable attention in a wide range of applications. EESDs with long-term stability, multicolor display and slow self-discharge rate are highly desired to broaden their practical applications. However, considering the complexity of integrating various components and multi-layer configurations, obtaining high-performance EESDs with exceptionally aesthetic versatility and excellent anti-self-discharge function via simple approaches is still a big challenge. Herein, a novel concept of EESD with multicolor electrochromic displays and low self-discharge rate was successfully designed and fabricated via employing carbon dots (CDs) as electrolyte additives. The prototype EESD could not only present vivid colors in 2D regional space but also exhibit remarkable electrochromic and electrochemical performances, such as fast switching responses (4.3/5.6 s for the coloration/bleaching processes), high coloration efficiency (∼134.8 cm2 C − 1), high volumetric power/energy density (364 mW cm−3/34.7 mWh cm−3 and 7420 mW cm−3/17.4 mWh cm−3), along with outstanding cycling stability. Furthermore, the as-fabricated EESD can also demonstrate a reversible and steady electrochromic and electrochemical behavior under harsh temperatures between -25 °C and 65 °C, presenting enormous potential for consumers to monitor the working status of electronics in full-temperature conditions. Encouragingly, the resultant EESD exhibits slow self-discharge rate (such as 10.2 mVh−1at -25 °C, 19.4 mVh−1at 20 °C and 26.5 mVh−1at 65 °C), which are comparable with some previous researches that based on electrolyte anti-self-discharge modification. It is envisioned that this work may provide a feasible strategy to develop multifunctional EESDs for broad applications in military camouflage and intelligent electronics.

Dynamic Performance of Hybrid Infrared Modulator Based on Single‐Walled Carbon Nanotubes and Ionic Liquid Enabling Fast Response

Herein, a new type of infrared film using single‐walled carbon nanotubes (SWNTs) is developed. The optimal sonication settings to produce SWNTs with the highest possible absorption of infrared light are discovered. A hybrid infrared modulator that combines SWNTs with ionic liquids, with a very fast response time is also developed. By carefully controlling the size of the SWNT bundles and the pore size of the filter membrane used to deposit the SWNTs, a response time of a few hundred microseconds (635 μs) at the half‐power point is achieved, which is the optical 3‐dB point. This technology has the potential to be used in a variety of innovative applications, such as smart windows and military camouflage, due to its excellent infrared optical properties.

Fabry-Perot cavity tunable multicolor flexible electrochromic device based on porous filter membrane

In recent years, Fabry-Perot (F-P) cavity-type electrochromic devices composed of more stable inorganic materials have been extensively investigated for achieving colorful reflective displays and military camouflage functions. However, the majority of reported substrates for colorful F-P cavity electrochromic devices are rigid conductive glasses, which hinders their practical application in flexible reflective displays and camouflage. Herein, we construct a WO3/W/Au bilayer F-P cavity multicolor tunable electrochromic device based on a flexible porous filter membrane, in which WO3, an inorganic electrochromic material, is used as the electrochromic layer, metallic W as the partial reflective layer, and metallic Au as the total reflective and conductive layer. Highly flexible bilayer F-P cavity multicolor electrochromic devices have been prepared by combining UV-curable electrolytes and thermoplastic sealing procedures. By adjusting the thickness of the WO3 layer, a wide spectrum of colors including yellow, purplish red, violet, blue, green, olivine, peach, etc. can be obtained. In addition, by adjusting the driving voltage of the electrochromic device, more precise color adjustment can be achieved. The electrochromic device has a fast coloring (2.06 s) and bleaching (2.70 s) response time, providing a new solution for future flexible colorful reflective display devices.

Development of camouflage fabric based on continuous thermochromic and electrothermal material

In order to solve the problem of single-color change when thermochromic materials are used at present, this study designs continuous thermochromic camouflage fabric based on the subtractive color matching of dyes, which provides the basis for realizing the integrated transformation of the three camouflage color systems of jungle color, desert color and ocean color. In this study, the electrothermal fabric with silver-coated fiber as the electrothermal element is combined to achieve the purpose of controllable heat source in the process of use, and the electrothermal color change double-layer fabric that can continuously change color through electrothermal control is prepared. Under the voltage of 4 ∼ 6 V, the color change layer fabric can reach the temperature of 34 ∼ 44 °C, and the first color change occurs when the voltage is greater than 4 V but less than 5 V, and the second color change occurs when the voltage is greater than 5 V, realizing continuous thermal color change. It has certain fabric flexibility and wearability, and can supply heat source by itself to meet the demand of product color change at any time. This has reference significance for the development of military camouflage textile products, and provides convenience for the reduction of military reserves in combat.

Surface Deposition of Ni(OH)2 and Lattice Distortion Induce the Electrochromic Performance Decay of NiO Films in Alkaline Electrolyte

NiO, an anodic electrochromic material, has applications in energy‐saving windows, intelligent displays, and military camouflage. However, its electrochromic mechanism and reasons for its performance degradation in alkaline aqueous electrolytes are complex and poorly understood, making it challenging to improve NiO thin films. We studied the phases and electrochemical characteristics of NiO films in different states (initial, colored, bleached and after 8000 cycles) and identified three main reasons for performance degradation. First, Ni(OH)2 is generated during electrochromic cycling and deposited on the NiO film surface, gradually yielding a NiO@Ni(OH)2 core–shell structure, isolating the internal NiO film from the electrolyte, and preventing ion transfer. Second, the core–shell structure causes the mode of electrical conduction to change from first‐ to second‐order conduction, reducing the efficiency of ion transfer to the surface Ni(OH)2 layer. Third, Ni(OH)2 and NiOOH, which have similar crystal structures but different b‐axis lattice parameters, are formed during electrochromic cycling, and large volume changes in the unit cell reduce the structural stability of the thin film. Finally, we clarified the mechanism of electrochromic performance degradation of NiO films in alkaline aqueous electrolytes and provide a route to activation of NiO films, which will promote the development of electrochromic technology.

Research progress in conductive polymer-based electrochromic fabrics

Conductive polymer-based electrochromic fabrics show promising applications in new intelligent displays, flexible smart wearables, and military camouflage, thanks to their flexibility, light weight, high degree of controllability, and wide range of color change. However, despite these advantages, electrochromic textiles that rely on conductive polymers face several limitations, such as discomfort during use, instability in structure, and issues with the continuous production technology of electrochromic fibers. These factors hinder their further development. To address these limitations and promote the industrialization of conductive polymer-based electrochromic fabrics, this paper provides a comprehensive analysis that covers various aspects of electrochromic devices, including device structure, color-change mechanisms, electrochromic materials, application of electrochromic textiles, and the advantages and disadvantages of commonly used conductive polymers in electrochromic fabrics. By exploring these aspects, a better understanding of the structure and performance of conductive polymer-based electrochromic fabrics can be achieved, leading to a more effective promotion of their industrialization. Moreover, progress in the research of conductive polymer-based electrochromic fabrics is systematically reviewed from the structural design perspective, both domestically and internationally. Finally, the challenges that conductive polymer-based electrochromic fabrics currently face are discussed, and their future development trends are presented.

Military camouflage classification with Mask R-CNN algorithm

Camouflage, which is used as an art of hiding by living things in nature, started to be used in the military field in the 19th century with the widespread use of long-range firearms. When factors such as different nations, environment and climate are considered, we come across camouflages in various colors and patterns. Over time, the camouflage patterns adopted and used by countries or unions have become national identity. This study is on the classification and segmentation of camouflaged soldiers of 5 countries with deep learning. While the similarity of the camouflaged area with the background makes segmentation difficult, it becomes difficult to classify each camouflage pattern due to the cut of the fabric and the different locations of the pattern pieces on each soldier. There are different studies in the literature that are referred to as camouflage or pattern classification. The mentioned studies are in the form of segmentation of camouflaged object or classification of camouflaged objects of different types. Since the segmented and classified objects in this study are camouflaged soldiers, what is expected from the deep learning algorithm is to classify the objects mainly according to the camouflage pattern, not their outlines. In the study, 861 camouflaged soldier images were collected for 5 countries (Türkiye-Azerbaijan, USA, Russia, China, France) and polygonal labeling was made. Türkiye and Azerbaijan are considered a class as they have similar camouflages. For the solution of the problem, military camouflage classification was discussed with the Mask R-CNN algorithm, which is widely used today for object detection, segmentation and classification, and the importance of deep learning algorithms has been proven with such a difficult problem. The training resulted in 0.005219 classification loss and 0.03985 masking loss. The classification and segmentation success rate of the study is 95%.

A Mo/Si multilayer film based selective thermal emitter for high-temperature infrared stealth application

Thermal radiation regulation technology plays a vital role in the fields of military camouflage and energy utilization. Here, a Mo/Si multilayer film based selective thermal emitter for high-temperature infrared stealth application is demonstrated by virtue of the tunneling effect of ultrathin metal layers as well as impedance matching to modulate the radiation properties. The fabricated selective emitter exhibits low emissivity of ε3-5μm≈0.26 and ε8-14μm≈0.36 at the atmospheric windows for infrared “invisibility” and high emissivity of ε5-8μm≈0.75 at the non-atmospheric window for radiative cooling. As observed from infrared thermal images, the prepared sample shows reduced surface temperature compared to the ambient temperature. The radiation temperature on sample surface is only 425.7 °C when the heating temperature increase to 600 °C, indicating the good dissipation ability of surface heat at high temperature. Moreover, the multilayer film device exhibits good infrared camouflage capability and thermal stability as the heating temperature reaches up to 650 °C. The fabricated selective thermal emitter has promising prospects in high-temperature infrared stealth technology.

The Blue Beret

The Blue Beret

Camouflaged Adversarial Patch Attack on Object Detector

Adversarial attacks have received great attentions for their capacity to distract state-of-the-art neural networks by modifying objects in physical domain. Patch-based attack especially have got much attention for its optimization effectiveness and feasible adaptation to any objects to attack neural network-based object detectors. However, despite their strong attack performance, generated patches are strongly perceptible for humans, violating the fundamental assumption of adversarial examples. In this paper, we propose a camouflaged adversarial patch optimization method using military camouflage assessment metrics for naturalistic patch attacks. We also investigate camouflaged attack loss functions, applications of various camouflaged patches on army tank images, and validate the proposed approach with extensive experiments attacking Yolov5 detection model. Our methods produce more natural and realistic looking camouflaged patches while achieving competitive performance.

Fabrication life prediction model for HDPE/Cr2O3 composites toward roof passive cooling

Passive cooling materials have been widely investigated to reduce building energy consumption. However, references about life prediction of the materials are insufficient. In this work, a novel life prediction model based on the passive cooling composites was established. The inorganic pigment chromium oxide (Cr2O3) was introduced into the high density polyethylene (HDPE) matrix to prepare HDPE/Cr2O3 composites with high long wave infrared (LWIR) emissivity and near infrared (NIR) reflectivity. The composites showed excellent cooling performance and color stability. The addition of ultraviolet absorber (UVA) and hindered amine light stabilizer (HALS) further improved the UV resistance of HDPE/Cr2O3 composites. HALS performs better and meets the needs of long-life outdoor use. Furthermore, a new failure point selection method is proposed and a model is established to predict the actual service life of HDPE/Cr2O3 composites, which provides theoretical guidance for the outdoor long-life use of the polymer composites. Based on the model, the fabricated HDPE/Cr2O3/HALS system can be used for more than 15 years. The long-term cooling composites can be used for building roof and wall to effectively reduce the indoor temperature and realize the sustainable use of energy. Besides, if used in military engineering, it has excellent cooling function and military camouflage effect. In addition, the composites can also be widely used in outdoor decoration, artificial lawn, floating materials and other fields.

Low infrared emissivity composite materials for multi-band camouflage

Infrared camouflage textile materials have the advantages of softness, portability, and wearability. They are the main raw materials of infrared camouflage clothing, backpacks, camouflage nets, and tents. In this paper, from the perspective of reducing infrared emissivity to achieve the purpose of camouflage, metal materials were selected as functional particles and combined with textile materials to prepare polyurethane infrared camouflage composite materials with low emissivity, whose lowest emissivity in the wavelength range of 2–22 μm can reach 0.58. On this basis, two kinds of low infrared emissivity composite materials that can be used for multi-band camouflage were developed. One is to add modified graphene into the coating to improve the conductivity of the coating and reduce the gloss of the coating, to prepare visible and infrared camouflage coated fabric. When the amount of graphene is 10% of the filler content, the coated fabric has low gloss and low emissivity at the same time. Compared with the fabric without graphene coating, the glossiness is reduced by 31%, while the infrared emissivity is only increased by 0.1. The second is to prepare composite materials with infrared camouflage and microwave absorption functions by compounding low infrared emissivity and microwave absorbing coating. The minimum infrared emissivity of the two composites was 0.76 and 0.58, respectively. In this study, a variety of materials was used to prepare low infrared emissivity fabrics with low glossiness or good microwave absorption capacity, which provided a reference for the preparation of multi-band camouflage fabrics and was expected to be applied in the field of military camouflage.

Theoretical investigation of electrochromic mechanism in D-A conjugated polymers in visible and infrared bands.

Electrochromic materials have been widely-applied in military camouflage and intelligent materials, in consideration of the multicolor display and infrared absorption. However, most of them have a narrow width of absorption spectra, and the electrochromic mechanism is still not well understood, especially in materials based on a copolymer structure in visible and infrared bands. Therefore, based on the polaron model, in order to enhance polarizability, we designed an "electronic donors-electronic acceptor" (D-A) type π-conjugated electrochromic polymer, which has an abundant color (wavelengths from 450 nm to 750 nm) with voltage range (from -0.2 V to 1.0 V). Employing first-principle calculations, we investigated the electrochromism of the polymer, which has a strong connection with the introduced new molecular orbital in the polaron (or cation), comparing with those in the neutral molecule. This study addressed the underlying mechanism for the electrochromic phenomenon and the behavior of the cation. It indicated the polaron molecular orbitals provide the photon absorption, whose energies are in the visible range and result in the electrochromic abundant color. In this work, we provide a molecular design for the adjustment of visible and infrared band absorption, which could have broad application in multicolor and infrared electrochromic materials.

Preparation and Electrochromic Properties of Benzodithiophene-Isoindigo Conjugated Polymers with Oligoethylene Glycol Side Chains.

Functional polymers featuring good processability in non-halogenated, benzene-free green solvents are highly desired due to health and environmental concerns. Herein, a series of novel D-A type conjugated polymers, PBDT-IIDs, are designed and successfully prepared by "green" functionalization of the polymers with highly hydrophilic, highly polar, highly flexible, and biocompatible oligoethylene glycol (OEG) side chains in order to improve the processability. These series polymers are named PBDT-IID2, PBDT-IID3, and PBDT-IID4, respectively, according to the number of oxygen atoms in the side chain. After confirmation by structural characterization, the basic properties of PBDT-IIDs are also investigated. With the increase in the OEG side chain length, the polymer PBDT-IID4 not only has good solubility in the halogen solvent chlorobenzene, but also exhibits excellent solubility in the green halogen-free solvent methyltetrahydrofuran (Me-THF). As a result, the green solvent Me-THF can also be applied to prepare PBDT-IIDs' electrochromic active layers, except for chlorobenzene and toluene. The electrochromism of PBDT IIDs under both positive and negative voltages has a practical application potential. The several controllable switches between dark green and khaki (0-0.6 V) are expected to show great potential in the field of military camouflage. Furthermore, according to the principle of red, green, and blue (RGB) mixing, light blue-green in the reduced state (-1.6 V) can be used in the preparation of complementary ECDs to provide one of the three primary colors (green).

Different ion-based electrolytes for electrochromic devices: A review

Initially, electrochromic (EC) technology was an attractive research topic aiming at the development of green buildings and smart displays. Nowadays, EC technology has been extended in various fields of energy storage systems, wearable devices, military camouflage, intelligent thermal control, etc. Electrochromic devices (ECDs) have been considered promising candidates for next-generation multi-functional devices due to their prominent advantages in integrated intelligence, low energy consumption, flexibility, displayable, and adjustable features. Electrochromism refers to the reversible change in color, transmittance, or reflectance of materials via a low voltage. Generally, the EC process lies in the dual adjustment of electrons and ions, so the transmission kinetics of electrolyte ions plays an extremely key role in EC performance. Although Li-ion-based ECDs are still mainstream, the emerging ion-based ECDs (such as Na + , K + , Ca 2+ , Mg 2+ , Zn 2+ , Al 3+ , etc) with improved performance have been reported one after another in recent years. This review summarized existing studies about advanced EC design by driving different electrolyte ions and analyzed their positive influence and side effect on EC performance. Meanwhile, the corresponding preparation method, structure design, and ions transport mechanism were discussed in detail. Finally, the facing challenges and development direction of related filed in the future were proposed. Hopefully, this review can provide useful help for the suitable selection of electrolyte cations for different EC systems and the promotion of diverse ion-based ECDs in practical application.

A light-weight, thin-thickness, flexible multifunctional electrochromic device integrated with variable optical, thermal management and energy storage

Multifunctional electrochromic devices with diversified functions are highly desirable for intelligent electronic systems compared to conventional electrochromic devices with sole applicability. Herein, a multifunctional electrochromic device integrated with variable optical, thermal management and energy storage is realized by preparing nanowire‐structured coral-like PANI films on a flexible gold-plated membrane through the combination of galvanostatic and cyclic voltammetric electrodeposition techniques. The multifunctional electrochromic devices achieve reversible color changes between brownish-yellow, green and dark-green. The maximum emissivity changes of the multifunctional electrochromic device in the ranges of 3–5 μm, 8–14 μm and 2.5–15 μm are 0.42, 0.49 and 0.47, respectively. Moreover, a specific capacitance of 355 F g−1 is obtained for the multifunctional electrochromic devices at a current density of 1 A g−1. The multifunctional electrochromic devices also have such advantages as light-weight, thin-thickness, flexible and can be fabricated in a multipixel and large area. With versatility characteristics, the multifunctional electrochromic devices are highly promising for intelligent electronic systems in electronic clothing, military camouflage and thermal control system of spacesuits.

Research on target recognition technology of GISC spectral imaging based on active laser lighting

Aiming at the application requirements of spectral imaging technology in satellite remote sensing, biomedical diagnosis, marine detection and rescue, agricultural and forestry monitoring and classification, military camouflage identification, etc., this paper uses 532 and 650 nm lasers as light sources, and uses multi-spectral intensity correlation imaging equipment—snapshot spectroscopic cameras based on ghost imaging via sparsity constraints (GISC) enable precise identification of targets. In this paper, the principle of snapshot GISC spectral imaging is expounded, and the experimental research work of GISC spectral imaging target recognition technology based on active laser illumination is carried out. The experimental results show that using a 532 nm laser as the light source to illuminate the target object can accurately identify the green target letter “I”; using a 650 nm laser as the light source to illuminate the target object can accurately identify the red target letter “Q”. And gives spectral imaging results of the color target “QIT” acquired by the GISC spectroscopic camera through a single exposure at the wavelength range from 446 to 698nm, with both pseudo-color map and color fusion map. In order to further illustrate the feasibility of the experiment, the spectral distribution of the reconstructed image is analyzed, which has important practical significance and engineering value.

ITO/Cu multilayer electrodes for high-brightness electrochromic displays

Fabry–Perot (F–P) nanocavity-type electrochromic devices with multicolor tunability have attracted significant interest in the past two years for their potential uses in a wide variety of applications, such as electronic display, military camouflage, and dynamic decoration. However, challenges such as insufficient brightness, lengthy switching times, and poor cycling stability have yet to be overcome. Herein, we demonstrate electrochromic electrodes based on ITO/Cu as both the current collector and the reflective layer, with WO3 as the electrochromic material, forming a unique three-layered structure. The constituted WO3/ITO/Cu films present a high brightness value of about 84% before coloration, and a decent brightness value of 48% after coloration at −0.8 ​V. Moreover, a fast switching time between different coloration states (tc ​= ​2.2 ​s; tb ​= ​1 ​s) is recorded, attributed to the extremely low sheet resistivity of the ITO/Cu current collector. The films also reveal excellent electrochemical cycling stability across 2000 cycles.

Vanadium-Substituted Dawson-Type Polyoxometalate-TiO2 Nanowire Composite Film as Advanced Cathode Material for Bifunctional Electrochromic Energy-Storage Devices.

Polyoxometalates (POMs) demonstrate potential for application in the development of integrated smart energy devices based on bifunctional electrochromic (EC) optical modulation and electrochemical energy storage. Herein, a nanocomposite thin film composed of a vanadium-substituted Dawson-type POM, i.e., K7[P2W17VO62]·18H2O, and TiO2 nanowires were constructed via the combination of hydrothermal and layer-by-layer self-assembly methods. Through scanning electron microscopy and energy-dispersive spectroscopy characterisations, it was found that the TiO2 nanowire substrate acts as a skeleton to adsorb POM nanoparticles, thereby avoiding the aggregation or stacking of POM particles. The unique three-dimensional core−shell structures of these nanocomposites with high specific surface areas increases the number of active sites during the reaction process and shortens the ion diffusion pathway, thereby improving the electrochemical activities and electrical conductivities. Compared with pure POM thin films, the composite films showed improved EC properties with a significant optical contrast (38.32% at 580 nm), a short response time (1.65 and 1.64 s for colouring and bleaching, respectively), an excellent colouration efficiency (116.5 cm2 C−1), and satisfactory energy-storage properties (volumetric capacitance = 297.1 F cm−3 at 0.2 mA cm−2). Finally, a solid-state electrochromic energy-storage (EES) device was fabricated using the composite film as the cathode. After charging, the constructed device was able to light up a single light-emitting diode for 20 s. These results highlight the promising features of POM-based EES devices and demonstrate their potential for use in a wide range of applications, such as smart windows, military camouflage, sensors, and intelligent systems.

Progress and challenges in flexible electrochromic devices

Electrochromic (EC) technology has made tremendous progresses and demonstrated potential applications in various fields such as green building, smart displays, military camouflage, etc. In recent years, flexible electrochromic devices (FECDs) have attracted growing interests due to their promising applications in flexible electronics and smart wearable. In spite of fascinating flexibility, the construction of FECDs faces more challenges compared with their rigid analogues because of more complex configures and assemblies. Thus, a comprehensive review is presented here to provide guidance for developing high-performance FECDs. In this review, the core components of FECD and their flexible features are firstly introduced. Then, recent advances and progress in the construction of FECDs are summarized in detail based on the different EC materials. Some critical performances are presented and compared between different devices to indicate the development direction of both EC materials and flexible transparent electrodes of FECDs. Finally, some challenges encountered in the fabrication and operation of FECDs are discussed and corresponding solutions are proposed. It is anticipated that this review will provide new insights into developing high-performance flexible ECDs toward applications in smart wearable and flexible electronics.