Adaptive Camouflage Research Articles

Advanced Design for Stimuli-Reversible Chromic Wearables With Customizable Functionalities.

Smart wearable devices with dynamically reversible color displays are crucial for the next generation of smart textiles, and promising for bio-robots, adaptive camouflage, and visual health monitoring. The rapid advancement of technology brings out different categories that feature fundamentally different color-reversing mechanisms, including thermochromic, mechanochromic, electrochromic, and photochromic smart wearables. Although some reviews have showcased relevant developments from unique perspectives, reviews focusing on the advanced design of flexible chromic wearable devices within each category have not been reported. In this review, the development history and recent progress in smart chromic wearables across each category are systematically examined. The design strategies for each chromic wearable device are outlined with a focus on functional materials, synthesis processes, and advanced applications. Furthermore, integrated devices based on dual-stimuli and multi-stimuli responsive chromics with customizable functionalities are summarized. Finally, challenges and perspectives on the future development of smart chromic wearables are proposed. Such a systematic summary will serve as a valuable insight for researchers in this field.

Design and Synthesis of Multi-compartment Microcapsules via Pickering Emulsion Polymerization for Infrared Stealth and Adaptive Camouflage Applications.

High-performance color-changing compounds, recognized as prominent smart materials, dynamically alter their color in response to external environmental stimuli. However, existing compounds exhibit limited responsiveness and color diversity, presenting challenges in the development of textiles responsive to multiple stimuli. This research introduces a novel design for dual-responsive color-changing microcapsules, employing a Pickering emulsion template method. The larger compartment encloses photosensitive dyes, whereas the smaller one contains thermochromic phase-change colorants. Adjusting the density of nanocapsules in the smaller compartment on the microcapsule surface enables a spectrum of colors, including red, yellow, blue, and green, triggered by light and heat. When incorporated into textiles, these microcapsules bestow adaptive color-changing attributes and infrared stealth capabilities onto the fabrics. Additionally, by modulating the color via surface micro/nanostructures, textile surfaces can exhibit hydrophobic and oleophobic properties. Such enhancements extend the textiles' potential applications in areas like anti-counterfeiting and military operations.

A Typical Infrared Background Radiation Prediction Model Based on RF-VMD and Optimized Hybrid Neural Network

ABSTRACT The short-term prediction and adjustment of a target’s infrared radiation hold significant value in military camouflage applications. Existing radiation prediction models generally require real-time environmental and meteorological data support, resulting in lag in active camouflage. To meet the demand for active camouflage of background infrared (IR) radiation, a short-term background IR radiation prediction method based on historical data is proposed. First, a random forest (RF) is used to filter the collected multidimensional meteorological parameters. Variational mode decomposition (VMD) is applied for time-frequency analysis on these parameters, optimizing them with Bayesian algorithms and decomposing them into multivariate intrinsic mode functions (IMFs) with similar frequencies to reduce the impact of nonlinearity in the data. Based on the superimposed IMFs as inputs, a hybrid deep neural network prediction model is established. The model optimizes the CNN-LSTM network with residual connections and introduces a multi-head self-attention mechanism to enhance spatiotemporal feature extraction of the multidimensional meteorological parameters, focusing on key temporal feature regions. According to the experimental results, the constructed model demonstrates high prediction accuracy and adaptability across different background environments, with a low parameter count and fast prediction capability, meeting the practical application needs for various complex backgrounds.

Advances in luminescent fibers for interactive smart textiles

AbstractRecent advancements in luminescent fibers are transforming textiles by integrating lighting and display functionalities into fabrics for applications such as health monitoring, dynamic displays, and adaptive camouflage. Active electroluminescent fibers, powered by electric fields, enable tunable light emission, while passive photoluminescent fibers rely on photoluminescence or triboluminescence to emit light. Although challenges remain in achieving uniform luminescence and ensuring durability, breakthroughs in materials science, structural engineering, and system integration are addressing these issues. Innovations such as chipless electroluminescent textiles and thermally drawn photoluminescent fibers highlight significant progress, pointing toward a future where clothing facilitates health monitoring and dynamic interaction, advancing natural human–machine interfaces.

Developing a method to generate an adaptive real-time camouflage pattern based on electro-chromic active devices

Traditional camouflage faces limitations in modern combat, especially with moving targets or rapidly changing backgrounds. Adaptive camouflage, which adjusts colors and patterns in real time, provides a more flexible and effective solution. This paper presents a comprehensive study of popular adaptive camouflage principles worldwide and proposes a camouflage model for the visible light spectrum based on active electro-chromic principles. Evaluation results indicate that adaptive patterns achieve the lowest Camouflage Similarity Index (CSI) and the highest Universal Image Quality Index (UIQI) across various backgrounds, demonstrating the clear effectiveness of the proposed model. With 3 to 5 dominant colors, pattern generation time is under 1 second, and adaptive patterns exhibit the highest similarity to the background compared to fixed patterns.

Intrinsically adaptive camouflage material

Intrinsically adaptive camouflage material

Isomeric chlorination of conjugated thiophene side chain based on quinoxaline to design high-performance electrochromic polymers

The isomeric chlorination of the conjugated side chain is an effective method to improve the photoelectronic properties of polymers, but has not been well investigated in electrochromic performance. Herein, two new D-A-D type isomeric monomers, EQx-α-Cl and EQx-β-Cl, based on 2,3-bis(5-chloro-4-(2-ethylhexyl)thioph-en-2-yl)-6,7-difluoro-5,8-di(thiophen-2-yl)quinoxaline (Qx-α-Cl) and 2,3-bis(4-chloro-5-(2-ethylhexyl)thiophen-2-yl)-6,7-difluoro-5,8-di(thiophen-2-yl)quinoxaline (Qx-β-Cl) as the acceptor units by the isomeric chlorination of the different position of the conjugated thiophene side chain were designed and synthesized. Then their D-A-D type polymers (PEQx-α-Cl and PEQx-β-Cl) were synthesized by electrochemical polymerization. EQx-α-Cl not only exhibits slight red-shifted absorption onset and much stronger absorption with molar extinction coefficient of 1.16 × 105 M−1 cm−1 but also shows lower onset oxidation potential (Eonset) of 0.65 V compared with those of EQx-β-Cl (7.26 × 104 M−1 cm−1 and 0.73 V). And PEQx-α-Cl displayed yellow green at neutral state and dark green at oxidation state, respectively, and showed much better electrochemical stability and electrochromic performance including the higher optical contrast 37.7 % and the CE value of 319 cm2 C−1 at 890 nm in comparison with PEQx-β-Cl, which was beneficial to design the electrochromic materials toward adaptive camouflage application. These results demonstrated that the isomeric chlorination strategy of conjugated side chain is a promising approach which may open up a new horizon for designing and synthesizing the high-performance electrochromic polymers.

Underwater communication and optical camouflage of marine animals

Underwater communication and optical camouflage of marine animals

Flexible Meta-Tape with Wide Gamut, Low Lightness and Low Infrared Emissivity for Visible-Infrared Camouflage.

Full-spectral optical camouflage is of broad interest and in urgent demand because of everlasting safety pursuit in modern society. However, the widely existing dim scenarios call for not only broadband low thermal detectivity but also wide-gamut camouflaging colors with both low lightness and minimal chromatism. Here, a tape-like metamaterial (meta-tape) with broad spectral manipulation bandwidth from visible to mid-infrared is demonstrated. The ultrathin meta-tapes can exhibit different colors with wide gamut and low lightness from 20 to 40, enabling low color difference under various backgrounds down to 1.2 L*a*b*. The infrared emissivity is simultaneously suppressed down to 3.8% across 3 - 14µm. The outstanding optical performances are well preserved under various mechanical and thermal stability tests. The pronounced multispectral camouflage, combined with flexible and robust tape-like nature, makes the meta-tape a promising solution for VIS-IR compatible camouflage in diverse scenarios.

Programmable Robotic Shape Shifting and Color Morphing Dynamics Through Magneto-Mechano-Chromic Coupling.

Recreating natural organisms' dynamic shape-morphing and adaptive color-changing capabilities in a compact structure poses significant challenges but unlocks unprecedented hybridized robotic-visual applications. Overcoming programmability and predictability obstacles is key to achieving real-time, responsive changes in appearance and functionality, enhancing robot-environment-user interactions in ways previously unattainable. Herein, a Soft Magneto-Mechano-Chromic (SoMMeC) structure comprising a magnetic actuating and a synthetic photonic film, mirroring the intricate color-tuning mechanism of chameleons is devised. A model combining numerical simulation and a strain-dependent color evolution map enables precise predictions and controllable shape-color alterations across various geometrical and magnetization profiles. The SoMMeC exhibits rapid (0.1s), broad (full-visible spectrum), tether-free (remote magnetic manipulation), and programmable (model-guided control) color transformations, surpassing traditional limitations with its real-time response, broad and omnidirectional coloration for enhanced visibility, and robustness against external disturbances. The SoMMeC translates into dynamic advertising iridescence, adaptive camouflage, self-sensing, and multi-level encryption, and transcends traditional robotics by seamlessly blending dynamic movement with nuanced visual changes. It opens up a spectrum of applications that redefine robotic functionality through dynamic appearance modulation, making robotic systems more versatile, adaptive, and suitable for unexplored integrative functions.

Self-adaptive photochromism.

Organisms with active camouflage ability exhibit changeable appearance with the switching of environments. However, manmade active camouflage systems heavily rely on integrating electronic devices, which encounters problems including a complex structure, poor usability, and high cost . In the current work, we report active camouflage as an intrinsic function of materials by proposing self-adaptive photochromism (SAP). The SAP materials were fabricated using donor-acceptor Stenhouse adducts (DASAs) as the negative photochromic phases and organic dyes as the fixed phases (nonphotochromic). Incident light with a specific wavelength induces linear-to-cyclic isomerization of DASAs, which generates an absorption gap at the wavelength and accordingly switches the color. The SAP materials are in the primary black state under dark and spontaneously switch to another color upon triggering by transmitted and reflected light in the background. SAP films and coatings were fabricated by incorporating polycaprolactone and are applicable to a wide variety of surfaces.

A Facile Electrochemical Strategy for Achieving a High-Conductivity Polypyrrole Derivative with Intrinsic Metallic Transport as a High-Performance Electrochromic Conducting Polymer Film.

Conjugated polymer electrochromic materials (PECMs) with tailored optical and electrical properties are applied in smart windows, electronic displays, and adaptive camouflage. The limitation in the electrical conductivity results in slow and monotonous color switching. We present a polypyrrole film incorporated with a toluene-p-sulfonic group (PPy-TSO-F), via a one-step electrodeposition technique. The PPy-TSO-F thin film (110 nm) achieves an impressive electrical conductivity of 1011 S cm-1, a high carrier mobility of 82 cm2 V-1 s-1, and intrinsic metallic electronic behavior. It demonstrates exceptionally reversible multicolor switching, transitioning from emerald green (-1.5 V), to bluish green (-1.4 V), bright yellow (-1.2 V), greenish yellow (-0.6 V), reddish brown (0.1 V), dark brown (0.3 V), and atrovirens (0.6 V). The fast charge transport and high carrier mobility render the film with an ultrafast electrochromic switching speed of 0.01 s/0.02 s. This research provides a new route to designing ultrafast multicolor switching PECMs with metallic charge transport.

Pearl‐Inspired Colored Carbon Fibers with Electromagnetic Interference and Optical Camouflage Properties

Carbon fibers (CFs) are widely used in cutting‐edge and civilian fields due to their excellent comprehensive properties such as high strength and high modulus, superior corrosion and friction resistances, excellent thermal stability, light weight, and high electrical conductivity. However, their natural ultra‐black appearance is difficult to meet the aesthetic needs of today's civilian sector and the need for optical stealth in the military field. In addition, conventional coloring methods are difficult to effectively adhere to CF surfaces due to high crystallinity and highly inert surface caused by their graphite‐like structure. In this work, inspired by the nacre structural color of pearls, colored CFs with 1D photonic crystal structure are prepared by cyclically depositing amorphous (Al2O3 + TiO2) layers on the surface of carbon CFs through atomic layer deposition (ALD). The obtained CFs exhibit brilliant colors and excellent environmental durability in extreme environments. Moreover, the colored CFs also exhibit high EMI shielding effectiveness (45 dB) and optical stealth properties, which can be used in emerging optical devices and electromagnetic and optical stealth equipment.

Metamaterial-inspired infrared electrochromic devices with wideband microwave absorption for multispectral camouflage

Infrared (IR) electrochromic devices, capable of dynamically controlling thermal radiation, hold promising applications in adaptive camouflage. However, the strong microwave reflective properties inherent in the device’s electrodes present a significant challenge, rendering them susceptible to radar detection and weakening their camouflage effect. Inspired by the remarkable electromagnetic control capabilities of metamaterials, the integration of frequency selective surfaces into IR electrochromic devices is proposed to address this multispectral compatibility challenge. The designed integrated metadevices simultaneously exhibit large and reversible IR emissivity tunability (Δε≥0.55 at 3–5 μm, Δε≥0.5 at 7.5–13 μm) and wideband microwave absorption (reflection loss ≤−10 dB at 8.5–18 GHz). Furthermore, the monolithic integrated design of the shared barium fluoride substrate offers a simple device architecture, while careful design considerations mitigate coupling between IR electrochromism and microwave wideband absorption. This work introduces opportunities for the development of multispectral adaptive camouflage systems, offering potential advancements in concealment technology.

Electrically tunable infrared optics enabled by flexible ion-permeable conducting polymer-cellulose paper

Materials that provide dynamically tunable infrared (IR) response are important for many applications, including active camouflage and thermal management. However, current IR-tunable systems often exhibit limitations in mechanical properties or practicality of their tuning modalities, or require complex and costly fabrication methods. An additional challenge relates to providing compatibility between different spectral channels, such as allowing an object to be reversibly concealed in the IR without making it appear in the visible range. Here, we demonstrate that conducting polymer-cellulose papers, fabricated through a simple and cheap approach, can overcome such challenges. The papers exhibit IR properties that can be electrochemically tuned with large modulation (absolute emissivity modulation of 0.4) while maintaining largely constant response in the visible range. Owing to high ionic and electrical conductivity, the tuning of the top surface can be performed electrochemically from the other side of the paper even at tens of micrometer thicknesses, removing the need for overlaying electrode and electrolyte in the optical beam path. These features enabled a series of electrically tunable IR devices, where we focus on demonstrating dynamic radiative coolers, thermal camouflage, anti-counterfeiting tags, and grayscale IR displays. The conducting polymer-cellulose papers are sustainable, cheap, flexible and mechanically robust, providing a versatile materials platform for active and adaptive IR optoelectronic devices.

Delaying an Electromagnetic Pulse with a Reflective High-Integration Meta-Platform.

Delaying an electromagnetic (EM) wave pulse on a thin screen for a significant time before releasing it is highly desired in many applications, such as optical camouflage, information storage, and wave-matter interaction boosting. However, available approaches to achieve this goal either require thick and complex systems or suffer from low efficiencies and a short delay time. This paper proposes an ultra-thin meta-platform that can significantly delay an EM-wave pulse after reflection. Specifically, our meta-platform consists of three meta-surfaces integrated together, of which two are responsible for efficiently coupling incident EM-wave pulse into surface waves (SWs) and vice versa, and the third one supports SWs exhibiting significantly reduced group velocity. We employ theoretical model analyses, full-wave simulations, and microwave experiments to validate the proposed concept. Our experiments demonstrate a 13 ns delay of an EM pulse centered at 12.975 GHz, enabled by a λ/8-thick and 38-λ-long meta-device with an efficiency of 32% (or 70%) with (or without) material loss taken into account. A larger delay time can be enabled by devices with larger sizes considering that the SWs group velocity of our device can be further reduced via dispersion engineering. These findings establish a new road for delaying an EM-wave pulse with ultra-thin screens, which may lead to many promising applications in integration optics.

Construction of diverse adaptive camouflage nets based on soluble yellow-to-green switching electrochromic materials

The potential application of electrochromic (EC) materials and devices as adaptive camouflage in diverse environments requires further investigation. In this study, we aimed to enhance the camouflage effect of electrochromic devices (ECDs) by developing innovative EC camouflage nets. Three soluble EC materials (FTP, FEP and FBP) were synthesized by incorporating phenothiazine and ProDOT with different donors through direct(hetero) arylation polymerization. Due to the fine-tuning of the energy gap, the three materials exhibit yellow, yellowish-brown and reddish-brown colors in their neutral states, respectively. Particularly, FTP and FEP can switch between different yellow-to-green with superior EC performance. Furthermore, FTP-PEDOT and FEP-PEDOT ECDs were constructed. Notably, the FEP-PEDOT ECD demonstrated enhanced EC performance, characterized by a more noticeable yellow-to-green switch, faster switching times and improved cycle stability. To meet the adaptability for multi-environmental camouflage and wearable applications, we created diverse camouflage patterns using the mask-spray technique and developed three types (“stripe”/ “cross stripe”/ “block”) camouflage net ECDs. This study offers a comprehensive approach for developing adaptive camouflage nets tailored to diverse real combat settings.

Wideband water-based switchable metasurface absorber/reflector

A water-based switchable absorber/reflector (WSAR) based on toner-coated honeycomb is proposed. The structure consists of a metasurface absorbing layer, a toner honeycomb layer, a water layer and a metal plate. The combination of metasurface and coated toner honeycomb can realize the function of broadband absorption, and the water layer is used as a control purpose to obtain a good reflection effect by filling the container with water. When the water container is in the state of without water, it behaves as an electromagnetic wave absorber with good absorption performance in the frequency band of 4.72–17.50 GHz. When the water container is in the state of full water，it behaves as a reflector with good reflection performance (reflection coefficient close to −1 dB in the 4.5–10 GHz band) in the operating frequency band. The characteristics and mechanism of the WSAR are analyzed by using the energy loss and equivalent impedance matching, and the correctness of the design is verified by experiments. The proposed structure has certain application value in radar target stealth, electromagnetic compatibility, adaptive camouflage.

Multispectral Hierarchical Metamaterials with Broadband Microwave Absorption, Gradient Infrared Emissivity, and High Visible Transparency

AbstractThe rapid progression of multispectral detectors poses a serious threat to weapon systems and personnel. The efficiency of stealth camouflage materials, however, has strong wavelength dependence, which limits their functionality to a specific spectral range. Here, a multispectral hierarchical metamaterial (MHM) with broadband microwave absorption, gradient infrared (IR) emissivity, and high visible transparency is proposed. The MHM design entails the integration of two distinct functional layers: the infrared camouflage layer (IRCL) and the radar absorbing layer (RAL). Specifically, leveraging the low‐pass and high‐impedance properties of capacitive frequency selective surfaces and adjustable filling ratio of low IR radiation materials, the IRCL achieves simultaneous high microwave transmission and gradient IR emissivity designs (emissivity gradients > 0.15 at 3–5 and 8–14 µm). The RAL achieves broadband microwave absorption across radar C, X, Ku, and Ka bands through a circuit‐analog absorber designed with lossy materials. Furthermore, prioritizing materials with high transparency enhances the average optical transmittance (>61.8%) of MHM in 380–760 nm. These distinctive features underscore the potential of the proposed MHM for advanced applications in camouflage and stealth technologies.

Antiswelling Photochromic Hydrogels for Underwater Optically Camouflageable Flexible Electronic Devices.

Optical camouflage offers an effective strategy for enhancing the survival chances of underwater flexible electronic devices akin to underwater organisms. Photochromism is one of the most effective methods to achieve optical camouflage. In this study, antiswelling hydrogels with photochromic properties were prepared using a two-step solvent replacement strategy and explored as underwater optically camouflaged flexible electronic devices. The hydrophobic network formed upon polymerization of hydroxyethyl methacrylate (HEMA) ensured that the hydrogels possessed outstanding antiswelling properties. Internetwork hydrogen bonding interactions allowed the hydrogels to exhibit tissue-adaptable mechanical properties and excellent self-bonding capabilities. The introduction of polyoxometalates further enhanced the hydrogels' mechanical and self-bonding properties while imparting photochromic capability. The hydrogels could be rapidly and reversibly colored under 365 nm UV irradiation. The bleaching rate of the colored hydrogels increased with temperature, bleaching within 12 h at 60 °C but maintaining the color for more than 5 days at room temperature. The self-bonding and photochromic properties enabled the hydrogels to be easily assembled into optically camouflaged underwater flexible electronic devices for underwater motion sensing and wireless information transmission. An optically camouflaged strain sensor was first assembled for underwater limb motion sensing. Additionally, an underwater optically camouflaged wireless information exchange device was assembled to enable wireless communication with a smartphone. This work provided an effective strategy for the optical camouflage of underwater flexible electronic devices, presenting opportunities for next-generation underwater hydrogel-based flexible devices.