A heat-insulating wave-absorbing shielding metasurface coating composite material for a drone and a preparation method thereof

Abstract

This invention discloses a heat-insulating and electromagnetic shielding metasurface coating composite material for unmanned aerial vehicles (UAVs). By constructing an activated carbon fiber / alumina composite structure and combining it with metasurface micro / nano pattern design, hydroxypropyl methylcellulose is introduced into the composite system to achieve uniform dispersion of the activated carbon fibers and enhance interfacial bonding. A three-dimensional composite network is constructed using the high specific surface area of ​​the activated carbon fibers and the heat-insulating properties of alumina sol. Simultaneously, broadband electromagnetic absorption and shielding are controlled through the metasurface periodic microstructure. This invention addresses the problems of insufficient heat insulation performance under high-temperature environments, easy fiber agglomeration, poor mechanical stability, and limited electromagnetic shielding effectiveness in existing UAV composite materials. It meets the application requirements of UAVs for multifunctional integrated coating materials in complex electromagnetic environments and extreme high and low temperature conditions. The material prepared by this invention possesses high temperature resistance, high strength and toughness, and broadband electromagnetic absorption properties, making it suitable for complex aerospace environments.

Description

Technical Field

[0001] This invention relates to the field of aerospace materials technology, and in particular to a heat-insulating and wave-absorbing shielding metasurface coating composite material for unmanned aerial vehicles and its preparation method. Background Technology

[0002] As drones evolve towards higher altitudes, higher speeds, and greater stealth capabilities, their applications in specialized civilian scenarios and aerospace fields are becoming increasingly widespread. The extreme environmental challenges faced by their fuselages and core components are becoming more prominent, making the integrated requirements for heat insulation, radar absorption, and electromagnetic shielding crucial for performance improvements. This type of coating composite material is vital for the operational safety and stealth performance of drones, serving as a core support for their stable operation. It constructs an efficient thermal barrier, blocking the effects of extreme high and low temperatures, solar radiation, and aerodynamic friction heat, keeping the temperature of core components such as avionics and batteries within a safe range and preventing malfunctions. Simultaneously, the heat-insulating and radar-absorbing shielding coating composite material for drones efficiently absorbs radar electromagnetic waves and blocks electromagnetic interference, while also providing infrared stealth. This enhances the survivability of drones and ensures flight safety and confidentiality in specialized civilian scenarios, making it a key material for drones to adapt to complex operating conditions and achieve functional upgrades.

[0003] Metasurface materials are a class of artificial electromagnetic materials composed of periodic structural units on a subwavelength scale. By controlling the geometry, size, and arrangement of these structural units, the reflection, transmission, absorption, and phase distribution of electromagnetic waves can be flexibly manipulated. Embedded metasurface structures, by embedding functional patches into the surface of a substrate material, create a stable interface between the patches and the substrate, effectively improving the structure's integration and environmental adaptability. Compared to traditional surface-mount structures, embedded designs maintain the continuity of the overall structure while achieving effective control over electromagnetic response; simultaneously, they induce multiple reflections and scattering effects of electromagnetic waves at the interface, significantly enhancing the material's absorption and electromagnetic shielding performance. These structures have broad application prospects in aerospace, electromagnetic protection, and stealth materials. Patent CN202211616280.X provides a method for preparing micron-sized heat-resistant fiber-reinforced alumina aerogel, comprising: step 1, preparing an alumina sol pre-sol; step 2, preparing an alumina sol; step 3, modifying heat-resistant fibers; step 4, preparing a fiber composite gel; step 5, aging the fiber composite gel; step 6, solvent replacement; and step 7, freeze-drying. After replacing the original solvent in the composite gel with a preferred ratio of tert-butanol and water, the micron-sized heat-resistant fiber-reinforced alumina composite gel after solvent replacement is pre-frozen and then freeze-dried under vacuum using a freezer and a freeze dryer, respectively, ultimately producing a micron-sized heat-resistant fiber-reinforced alumina aerogel composite material with good integrity, high specific surface area, good thermal insulation, and low shrinkage.

[0004] Patent CN202211167126.9 relates to a subcrystalline alumina nanofiber flexible aerogel and its preparation method. The preparation method includes: mixing aluminum sol and a binder to obtain a spinning solution; electrospinning the spinning solution to obtain an alumina nanofiber precursor, and drying it; repeatedly folding the alumina nanofiber precursor into fiber bundles, pressing them into shape, to obtain an alumina nanofiber aerogel precursor; holding the alumina nanofiber aerogel precursor at 400℃~600℃ for 0.8h~1.2h, cooling it to room temperature for desizing; heating it to 700℃~1000℃ and holding it for 10~60min, cooling it to room temperature, to obtain the subcrystalline alumina nanofiber flexible aerogel material. The technical problem solved is how to prepare a subcrystalline alumina nanofiber flexible aerogel that possesses good comprehensive properties, including a low density (≤0.03g / cm³). 3 It has a high thermal conductivity (≤0.02W / m·K), good heat insulation effect, and good mechanical properties (rebound rate ≥96.5% after 100 compressions).

[0005] Patent CN202410245675.6 relates to a high-temperature resistant alumina aerogel and its preparation method. The method includes adding a high-solids-content alumina hydrosol to an alcohol solvent and stirring until homogeneous to prepare an alumina sol with the alcohol solvent as the main solvent component; adding silica sol to the obtained alumina sol and mixing until homogeneous to obtain an alumina-silica sol; adding an initiator to the obtained alumina-silica sol and stirring until homogeneous, then adding a catalyst to promote gelation and polymerization; subjecting the obtained alumina-silica sol to high-temperature gelation and aging to obtain an alumina gel; and subjecting the alumina gel to supercritical drying to obtain a high-temperature resistant alumina aerogel. This invention uses high-solids-content alumina sol as raw material, eliminates the need for solvent replacement, and features a simple and easy-to-operate process. The prepared high-temperature resistant alumina aerogel still possesses a high specific surface area and pore volume at high temperatures of 1300~1500℃.

[0006] Patent CN202110679896.0 discloses a flexible sheet based on a carbon-based broadband absorbing metamaterial. This sheet includes a reflective layer and a dielectric layer embedded with periodically arranged structural units. The dielectric layer is positioned above the reflective layer. Its fabrication includes the following steps: A double-layered concentric cylindrical hole is mechanically punched in the dielectric layer according to the size of the periodic resonant structural unit, with every other unit cell P being the size; the side of the dielectric sheet with the smaller hole is cleaned with anhydrous ethanol and then the reflective layer is applied; graphene or carbon nanotubes are mixed evenly with an adhesive to form a carbon-based composite; this composite is then filled into the periodically arranged holes from step one using a scraper; and the composite is allowed to air dry until fully dry. This patented flexible sheet achieves a wide-bandwidth absorption effect in the 2-18 GHz range. It is simple to manufacture, easy to use, and can be applied to the object being tested, effectively reducing the radar wave characteristic signal of the target object.

[0007] Patent CN202011145497.8 relates to a reusable microfluidic absorbing metamaterial and its preparation method. The method involves: constructing metamaterial structural units on a silicon substrate surface; modifying the silicon substrate surface with fluorosilane; uniformly mixing epoxy resin, toughening agent, and curing agent to obtain an SMP epoxy resin prepolymer; casting the epoxy resin prepolymer onto the fluorosilane-modified silicon substrate surface and curing it at two different temperature stages; then demolding to obtain an SMP epoxy resin with a metamaterial structure; placing a pre-cured, flat SMP epoxy resin on the SMP epoxy resin surface, followed by curing and encapsulation; injecting liquid metal into the microcavities of the SMP epoxy resin, sealing the openings with SMP epoxy resin, and curing to obtain the microfluidic absorbing metamaterial. The material obtained by this invention has shape memory function, allowing it to change shape according to specific requirements during use, and after use, it can trigger shape memory to restore its original shape for repeated use.

[0008] Patent CN201910849844.6 belongs to the field of electromagnetic wave absorption and electromagnetic shielding materials technology. It discloses a high-efficiency microwave-absorbing ultrathin carbon fiber reinforced composite material and its design optimization method, consisting of two layers of carbon fiber reinforced planar structures. In each layer, a periodically arranged array of fibers with mutually parallel fiber axes is embedded in a ceramic matrix. The ceramic matrix serves to bind the fibers together and provide necessary mechanical or chemical properties. The two planar structures are stacked, with the fiber axes of different layers oriented in different directions, forming a thin-sheet composite structure. This composite structure can be further stacked in parallel to provide the entire laminated material. This invention can provide a continuously conductive network, effectively absorbing electromagnetic waves; achieving optimized electromagnetic properties; improving microwave absorption efficiency; and the periodic embedding of fibers in the ceramic matrix helps improve the mechanical properties of the laminated material and increase microwave absorption.

[0009] Patent CN202010472084.4 relates to an integrated microwave absorption / transmission material and its preparation method. The material sequentially comprises a metamaterial layer containing a metamaterial; the metamaterial is a periodic structure etched onto a carbon nanotube coating, with a sheet resistance of 5-20 Ω on the surface of the carbon nanotube coating; a foam layer composed of foam material; and a magnetic dielectric material layer containing a magnetic dielectric material. This invention forms a metamaterial with a certain impedance by etching a periodic pattern onto a nano-silver coating with a certain impedance. The metamaterial is then integrated as a surface layer with the foam layer and the magnetic dielectric material layer to form a broadband integrated microwave absorption / transmission material. The composite material has a reflectivity ≤-5dB in the 3-10GHz range, a transmittance ≥-2dB in the 18-20GHz range, and exhibits polarization insensitivity.

[0010] Patent CN202110028269.0 relates to a metasurface embedded load-bearing absorbing laminate and its preparation method, belonging to the field of multifunctional composite materials. This invention's metasurface embedded load-bearing absorbing laminate is composed of electromagnetic double-loss nanocomposite materials in different proportions and a conductive coating with a specific pattern periodically arranged covering the metasurface. The preparation method is an integrated molding process combining liquid polymer casting and vacuum bag hot pressing. The electromagnetic double-loss nanocomposite material is composed of epoxy resin, carbonyl iron particles, and multi-walled carbon nanotubes. This invention enables the laminate to have strong load-bearing capacity through carbon fiber cloth composite, and enhances the -10dB absorption bandwidth and reduces the structural thickness through the fusion design of gradient loss absorption mechanism and interface loss absorption mechanism. This invention can maintain absorption performance without degradation at large incident angles. The preparation method of this invention is simple, allows for mass production, is low-cost, and can integrate mechanical load-bearing function and broadband absorption function into a single composite structure.

[0011] While existing technologies have made some progress in the fields of thermal insulation, wave absorption, and electromagnetic shielding for unmanned aerial vehicles (UAVs), such as improving thermal insulation performance through alumina aerogel systems or achieving wave absorption modulation using carbon-based materials and metamaterial structures, significant shortcomings remain overall. Most technologies focus on optimizing a single performance aspect or simply achieve multifunctional combinations through simple stacking, lacking integrated solutions based on the synergistic design of material systems and structures. This makes it difficult to meet the comprehensive service requirements of UAVs in high-altitude, high-speed, and complex electromagnetic environments. In existing composite systems, reinforcing phases such as carbon fibers are prone to agglomeration, resulting in insufficient interfacial bonding and affecting structural stability and mechanical properties. Metasurface structures often employ surface attachment methods, leading to problems such as weak bonding and poor environmental adaptability. Furthermore, related fabrication processes generally suffer from complex procedures, poor controllability, and difficulty in achieving conformal coating. Therefore, this invention proposes an integrated coating material based on an activated carbon fiber / alumina composite system combined with an embedded metasurface structure. Hydroxypropyl methylcellulose is introduced to achieve stable fiber dispersion and interfacial reinforcement, while an embedded periodic structure is used to achieve electromagnetic performance modulation, achieving a synergistic unity of wave absorption and electromagnetic shielding while ensuring thermal insulation performance. The aim is to address the shortcomings of existing technologies and meet the application requirements of multifunctional integrated coating materials for drones in complex electromagnetic environments and extreme high and low temperature conditions. Summary of the Invention

[0012] This invention aims to provide a heat-insulating and electromagnetic shielding metasurface coating composite material for unmanned aerial vehicles (UAVs). By constructing an activated carbon fiber / alumina composite structure and combining it with metasurface micro-nano pattern design, hydroxypropyl methylcellulose is introduced into the composite system to achieve uniform dispersion of activated carbon fibers and enhance interfacial bonding. A three-dimensional composite network is constructed using the high specific surface area of ​​activated carbon fibers and the heat-insulating properties of alumina sol. At the same time, broadband electromagnetic absorption and electromagnetic shielding are controlled through the metasurface periodic microstructure. This invention solves the problems of insufficient heat insulation performance, easy fiber agglomeration, poor mechanical stability, and limited electromagnetic shielding effect of existing UAV composite materials under high-temperature conditions, thus meeting the application requirements of UAVs for multifunctional integrated coating materials in complex electromagnetic environments and extreme high and low temperature conditions.

[0013] The technical solution adopted to achieve the purpose of this invention patent is: a heat-insulating and wave-absorbing shielding metasurface coating composite material for UAVs, using activated carbon fiber (ACF) with a diameter of 11.95-13.66 μm as the reinforcing phase and alumina sol as the heat-insulating matrix, supplemented with an aqueous solution of hydroxypropyl methylcellulose (HPMC) to achieve dispersion and interface modification, and constructing a metasurface microstructure on the surface. The ACF is characterized by being a cylindrical reinforcing phase, which is dispersed in deionized water and pretreated by drying at 40-60℃ to remove surface impurities, and is uniformly dispersed within the coating, serving as the mechanical support and wave-absorbing loss skeleton of the entire coating; the alumina sol is the heat-insulating matrix, which synergistically forms a composite system with ACF, endowing the coating with superior performance. The composite coating exhibits superior heat insulation properties. The HPMC is added in the form of a 1.0-1.5 wt.% aqueous solution, prepared by mixing 2-3 g of HPMC powder with 197-198 g of deionized water at a constant temperature of 20-30°C. This stabilizes the ACF dispersion through hydrogen bonding, prevents ACF agglomeration through steric hindrance, and enhances the interfacial bonding between ACF and aluminum sol. The composite coating is prepared by adding pretreated ACF and aluminum sol to the HPMC aqueous solution at a specific mass ratio, followed by high-speed mechanical stirring to form a uniform precursor solution. This solution is then dried at 80°C for 6-8 hours to form a self-supporting block or directly sprayed into a film. The density of the composite coating is 1.2-1.5 g / cm³. 3 It has a thermal conductivity of 0.025-0.030 W / (m·K), a wave absorption frequency band covering 2-18 GHz, and an electromagnetic shielding effectiveness of 30-40 dB. It can adapt to the conformal requirements of different parts such as the fuselage and wings of drones, and has excellent mechanical stability and process feasibility. In addition, the surface of the composite coating is designed with metamaterial structure, and an embedded periodic metasurface structure is constructed on the coating surface through a prefabricated template embedding-in-situ curing integrated molding process. The embedded periodic metasurface structure adopts a square or circular unit cubic lattice arrangement, with a unit period of 3-10 mm. The metasurface patch is selected from graphene, with a patch thickness of 5-20 μm and an embedding depth of 5-20 μm into the coating surface.

[0014] Furthermore, the preparation method of the aforementioned heat-insulating and wave-absorbing shielding metasurface coating composite material for UAVs is characterized by comprising the following steps: 1) Add ACF with a diameter of 11.95-13.66μm to excess deionized water and disperse it at a low speed of 200-300r / min for 30-60min at room temperature to fully wet the fiber and preliminarily deflocculate it, removing dust and impurities adsorbed on the surface. After dispersion, filter and drain the water, and place it in a 60℃ constant temperature forced air drying oven to dry for 4-6h to completely remove residual moisture inside the fiber and obtain a clean surface and well dispersed ACF reinforcing phase, laying the foundation for subsequent composite dispersion. 2) Weigh 2-3g of HPMC powder and 197-198g of deionized water by mass ratio. Slowly sprinkle the HPMC powder into the deionized water to prevent clumping. Stir continuously at 300-400r / min for 60-90min under a constant temperature water bath at 20-30℃ until the HPMC is completely dissolved and the solution is homogeneous and transparent, to obtain an HPMC aqueous solution with a mass fraction of 1.0-1.5wt.%. After cooling to room temperature, let stand for 18-24h to defoam, utilizing the hydrogen bonding of HPMC molecules to provide a stable dispersion environment for ACF. 3) Add the pretreated ACF and aluminum sol to the above HPMC aqueous solution at the set mass ratio. First, stir at a low speed of 300-500 r / min for 5-10 min to achieve preliminary mixing, and then increase the speed to 8000-12000 r / min for 30-50 min to fully mix the ACF, aluminum sol and HPMC solution to form a homogeneous, stable precursor solution without obvious agglomeration. The steric hindrance effect of HPMC effectively inhibits the sedimentation and entanglement of ACF, ensuring the long-term stability of the system. 4) The obtained uniform precursor solution is directly sprayed onto the surface of the UAV substrate or injected into a custom mold for molding; after spraying or casting, the whole is placed in an 80℃ constant temperature forced air drying oven for 8-12 hours to allow the moisture in the system to evaporate slowly and uniformly, avoiding cracking and warping; finally, a self-supporting block material or a continuous and uniform composite coating with a dense structure and good interface bonding is obtained, providing a stable substrate for subsequent metasurface processing; 5) A square or circular hollow array with a period of 3-10 mm is prepared on a polyimide template by laser etching as a metasurface forming template; graphene patches are precisely embedded into the hollow area of ​​the template with a thickness of 5-20 μm to form a regular periodic array. 6) Gently press the metasurface array template onto the surface of the wet composite coating, controlling the applied pressure to 0.1-0.3MPa, so that the patch is embedded into the coating surface to a depth of 5-20μm, ensuring that the unit array is uniform, the position is stable, and the underlying dispersion structure is not damaged. 7) Place the coating of the template in a constant temperature oven at 60-70℃ for 2-4 hours to pre-dry. After the coating has initially set and the patch is completely fixed, slowly peel off the template, retaining the embedded metasurface microstructure, to avoid unit deformation or coating cracking. 8) The coating with embedded metasurface is placed in an 80℃ constant temperature forced air oven for a second curing for 4-6 hours to achieve complete drying of the substrate and interface strengthening, and finally obtain a metasurface composite coating for UAVs that combines heat insulation, wave absorption and electromagnetic shielding.

[0015] The beneficial effects achieved by this invention are: 1. Functional integrated design innovation with cross-scale multi-field coupling This invention achieves cross-scale, multi-functional synergy at the scientific theoretical level, successfully resolving the functional conflict between thermal protection and stealth shielding for unmanned aerial vehicles (UAVs) during high-altitude, high-speed flight. Traditional materials often struggle to achieve both ultra-low thermal conductivity and high-efficiency electromagnetic wave absorption because enhancing electromagnetic loss typically requires the introduction of conductive or magnetic components, which often increase the material's thermal conductivity. This research constructs a three-dimensional thermal barrier network at the microscopic level using activated carbon fiber (ACF) and alumina sol, while simultaneously achieving precise electromagnetic wave control at the macroscopic level through embedded metasurface periodic structures. This design approach organically combines the thermal phonon scattering mechanism with the electromagnetic resonant absorption mechanism, enabling the composite material to cover a wideband absorption band of 2-18 GHz even with a thermal conductivity as low as 0.03 W / m·K. This multi-field coupled integrated solution provides a novel physical model and material paradigm for solving the challenges of service in complex environments in the aerospace field.

[0016] 2. Scientific Regulation of Micronetwork Stability Based on Interface Engineering In the field of materials science, the uniform dispersion of high aspect ratio activated carbon fibers (ACFs) in sol systems has always been a bottleneck restricting performance consistency. This invention introduces hydroxypropyl methylcellulose (HPMC) and utilizes the hydrogen bonding between the hydroxyl groups on its molecular chain and the oxygen-containing functional groups on the ACF surface to construct a molecular-level coating layer on the fiber surface. This interface modification not only effectively suppresses the aggregation and sedimentation of ACF in the alumina sol matrix through steric hindrance but also establishes a stable chemical bonding interface at the microscopic level. From a rheological perspective, the addition of HPMC optimizes the viscoelastic properties of the precursor solution, ensuring the random and uniform distribution of functional phases during spraying. This sophisticated interface engineering design significantly improves the internal stress transfer efficiency of the coating, enhancing its mechanical load-bearing capacity and ensuring the continuity of the electromagnetic wave loss path within the material, thus avoiding electromagnetic shielding failure or hotspot effects caused by component segregation.

[0017] 3. Deep optimization of the electromagnetic wave interface response mechanism of embedded metasurfaces This invention represents a significant breakthrough in metamaterial structure design. By precisely embedding graphene patches 5-20 μm deep into the coating surface, a unique gradient impedance matching system is constructed. Compared to traditional surface-attached structures, this embedded design fundamentally alters the reflection characteristics of electromagnetic waves at the air-coating interface. When electromagnetic waves are incident, the embedded square or circular units act as subwavelength resonators, inducing strong conductivity and polarization losses, efficiently converting radar wave energy into heat. Simultaneously, the scientific ratio of embedding depth to unit period enables flexible modulation of the incident wave phase, further reducing the radar cross section (RCS) through destructive interference. This design not only achieves electromagnetic shielding effectiveness exceeding 30 dB but also significantly improves the material's performance stability under large-angle incident conditions, providing solid theoretical support and technical assurance for electromagnetic stealth of UAVs in complex maneuvers.

[0018] 4. Structural-functional evolution stability under extreme service environments The activated carbon fiber reinforced aluminate sol composite system constructed in this invention exhibits significant advantages in terms of material thermodynamic stability. ACF possesses excellent high-temperature creep resistance, while the inorganic network formed after aluminate sol curing exhibits extremely high chemical inertness and weather resistance. Through an in-situ curing integrated molding process, the metasurface structure and the substrate achieve deep atomic-scale fusion, fundamentally eliminating the risk of delamination and peeling of heterogeneous materials under extreme high and low temperature cycling or aerodynamic friction environments. This coating material can effectively block solar radiation heat and fuselage aerodynamic heat, controlling temperature fluctuations of internal avionics core components within safe thresholds. Its conformal characteristics allow the coating to seamlessly conform to the complex curved structure of the UAV, ensuring the continuity of stealth and thermal insulation performance at points of drastic geometric changes. This innovation not only improves the survivability of UAVs but also lays a crucial material foundation for the future development of high-performance unmanned aerial vehicles towards high altitude, long endurance, and high stealth. Specific implementation methods The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Example The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0020] Implementation Case 1 S1. Add 12.8 μm diameter ACF to excess deionized water and disperse at a low speed of 250 r / min for 45 min at room temperature to fully wet the fiber and preliminarily deflocculate it, removing dust and impurities adsorbed on the surface. After dispersion, filter and drain the fiber, and place it in a 60℃ constant temperature forced air oven to dry for 5 h to completely remove residual moisture inside the fiber, obtaining a clean surface and well dispersed ACF reinforcing phase, laying the foundation for subsequent composite dispersion.

[0021] S2. Weigh 3g of HPMC powder and 197g of deionized water by mass ratio. Slowly sprinkle the HPMC powder into the deionized water to prevent clumping. Stir continuously at 350r / min for 75min under a constant temperature water bath at 25℃ until the HPMC is completely dissolved and the solution is homogeneous and transparent to obtain an HPMC aqueous solution with a mass fraction of 1.5wt.%. After cooling to room temperature, let stand for 24h to defoam, utilizing the hydrogen bonding of HPMC molecules to provide a stable dispersion environment for ACF.

[0022] S3. Add the pretreated ACF and aluminum sol to the above HPMC aqueous solution at the set mass ratio. First, stir at a low speed of 400 r / min for 8 min to achieve preliminary mixing, and then increase the speed to 10000 r / min for 40 min to fully mix the ACF, aluminum sol and HPMC solution to form a homogeneous, stable precursor solution without obvious agglomeration. The steric hindrance effect of HPMC effectively inhibits the sedimentation and entanglement of ACF, ensuring the long-term stability of the system.

[0023] S4. The obtained uniform precursor solution is directly sprayed onto the surface of the UAV substrate or injected into a custom mold for molding. After spraying or casting, the whole is placed in an 80℃ constant temperature forced-air drying oven for 10 hours to allow the moisture in the system to evaporate slowly and uniformly, avoiding cracking and warping. Finally, a self-supporting block material or a continuous and uniform composite coating with a dense structure and good interface bonding is obtained, providing a stable substrate for subsequent metasurface processing.

[0024] S5. Using laser etching, a square or circular hollow array with a period of 6 mm is prepared on a polyimide template as a metasurface forming template; graphene patches are precisely embedded into the hollow area of ​​the template with a thickness of 12 μm to form a regular periodic array.

[0025] S6 gently presses the metasurface array template onto the surface of the wet composite coating, controlling the applied pressure to 0.2 MPa, so that the patch is embedded 12 μm deep into the coating surface, ensuring that the unit array is uniform, the position is stable, and the underlying dispersion structure is not damaged.

[0026] S7 places the coating of the template in a 65℃ constant temperature forced-air oven for 3 hours to pre-dry. After the coating has initially set and the patch is completely fixed, the template is slowly peeled off to retain the embedded metasurface microstructure and avoid unit deformation or coating cracking.

[0027] S8 further cures the coating with embedded metasurface in an 80℃ constant temperature forced-air oven for 5 hours to achieve complete drying of the substrate and interface strengthening, ultimately obtaining a metasurface composite coating for UAVs that combines heat insulation, wave absorption and electromagnetic shielding.

[0028] Implementation Case 2 S1. Add 11.95μm diameter ACF to excess deionized water and disperse at a low speed of 200r / min for 30min at room temperature to fully wet the fiber and preliminarily deflocculate it, removing dust and impurities adsorbed on the surface. After dispersion, filter and drain the fiber, and place it in a 60℃ constant temperature forced air oven to dry for 4h to completely remove residual moisture inside the fiber, obtaining a clean surface and well dispersed ACF reinforcing phase, laying the foundation for subsequent composite dispersion.

[0029] S2. Weigh 3g of HPMC powder and 197g of deionized water by mass ratio. Slowly sprinkle the HPMC powder into the deionized water to prevent clumping. Stir continuously at 300r / min for 60min under a constant temperature water bath at 20℃ until the HPMC is completely dissolved and the solution is homogeneous and transparent to obtain an HPMC aqueous solution with a mass fraction of 1.5wt.%. After cooling to room temperature, let stand for 24h to defoam, utilizing the hydrogen bonding of HPMC molecules to provide a stable dispersion environment for ACF.

[0030] S3. Add the pretreated ACF and aluminum sol to the above HPMC aqueous solution at the set mass ratio. First, stir at a low speed of 300 r / min for 5 min to achieve preliminary mixing, and then increase the speed to 8000 r / min for 30 min to fully mix the ACF, aluminum sol and HPMC solution to form a homogeneous, stable precursor solution without obvious agglomeration. The steric hindrance effect of HPMC effectively inhibits the sedimentation and entanglement of ACF, ensuring the long-term stability of the system.

[0031] S4. The obtained uniform precursor solution is directly sprayed onto the surface of the UAV substrate or injected into a custom mold for molding. After spraying or casting, the whole is placed in an 80℃ constant temperature forced-air drying oven for 8 hours to allow the moisture in the system to evaporate slowly and uniformly, avoiding cracking and warping. Finally, a self-supporting block material or a continuous and uniform composite coating with a dense structure and good interface bonding is obtained, providing a stable substrate for subsequent metasurface processing.

[0032] S5. Using laser etching, a square or circular hollow array with a period of 4 mm is prepared on a polyimide template as a metasurface forming template; graphene patches are precisely embedded into the hollow area of ​​the template with a patch thickness of 8 μm to form a regular periodic array.

[0033] S6 gently presses the metasurface array template onto the surface of the wet composite coating, controlling the applied pressure to 0.1 MPa, so that the patch is embedded 8 μm deep into the coating surface, ensuring that the unit array is uniform, the position is stable, and the underlying dispersion structure is not damaged.

[0034] S7 places the coating of the template in a 60℃ constant temperature forced-air oven for 2 hours to pre-dry. After the coating has initially set and the patch is completely fixed, the template is slowly peeled off to retain the embedded metasurface microstructure and avoid unit deformation or coating cracking.

[0035] S8 further cured the coating with embedded metasurface in an 80℃ constant temperature forced-air oven for 4 hours to achieve complete drying of the substrate and interface strengthening, ultimately obtaining a metasurface composite coating for UAVs that combines heat insulation, wave absorption and electromagnetic shielding.

[0036] The above are merely two specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the scope of protection of the present invention. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A heat-insulating and wave-absorbing shielding metasurface coating composite material for unmanned aerial vehicles (UAVs), comprising activated carbon fiber (ACF) with a diameter of 11.95-13.66 μm as the reinforcing phase, alumina sol as the heat-insulating matrix, and hydroxypropyl methylcellulose (HPMC) aqueous solution for dispersion and interface modification, thereby constructing a metasurface microstructure, characterized in that: The ACF is a reinforcing phase, cylindrical in shape. It is dispersed in deionized water and pretreated by drying at 40-60℃ to remove surface impurities. It is arranged in a uniformly dispersed state inside the coating, serving as the mechanical support and wave absorption loss skeleton of the entire coating. The aluminum sol serves as the thermal insulation matrix, synergistically forming a composite system with ACF to impart excellent thermal insulation properties to the coating. HPMC is added in the form of a 1.0-1.5 wt.% aqueous solution, prepared by mixing 2-3 g of HPMC powder with 197-198 g of deionized water at a constant temperature of 20-30°C. This stabilizes the ACF dispersion through hydrogen bonding, prevents ACF agglomeration through steric hindrance, and enhances the interfacial bonding between ACF and the aluminum sol. The composite coating is prepared by adding pretreated ACF and aluminum sol to the HPMC aqueous solution at a specific mass ratio, followed by high-speed mechanical stirring to form a uniform precursor solution. This solution is then dried at 80°C for 6-8 hours to form a self-supporting block or directly sprayed onto the surface to form a film. The density of the composite coating is 1.2-1.5 g / cm³. 3 It has a thermal conductivity of 0.025-0.030 W / (m·K), a wave absorption frequency band covering 2-18 GHz, and an electromagnetic shielding effectiveness of 30-40 dB. It can adapt to the conformal requirements of different parts such as the fuselage and wings of drones, and has excellent mechanical stability and process feasibility. In addition, the surface of the composite coating is designed with metamaterial structure, and an embedded periodic metasurface structure is constructed on the coating surface through a prefabricated template embedding-in-situ curing integrated molding process. The embedded periodic metasurface structure adopts a square or circular unit cubic lattice arrangement, with a unit period of 3-10 mm. The metasurface patch is selected from graphene, with a patch thickness of 5-20 μm and an embedding depth of 5-20 μm into the coating surface.

2. A method for preparing a heat-insulating and wave-absorbing shielding metasurface coating composite material for unmanned aerial vehicles, characterized in that, Includes the following steps: 1) Add ACF with a diameter of 11.95-13.66μm to excess deionized water and disperse it at a low speed of 200-300r / min for 30-60min at room temperature to fully wet the fiber and initially deflocculate it, removing dust and impurities adsorbed on the surface. After dispersion, filter and drain, then place in a 60℃ constant temperature forced-air drying oven for 4-6 hours to completely remove residual moisture inside the fiber and obtain an ACF reinforcing phase with a clean surface and good dispersion, laying the foundation for subsequent composite dispersion. 2) Weigh 2-3g of HPMC powder and 197-198g of deionized water by mass ratio. Slowly sprinkle the HPMC powder into the deionized water to prevent clumping. Stir continuously at 300-400r / min for 60-90min under a constant temperature water bath at 20-30℃ until the HPMC is completely dissolved and the solution is homogeneous and transparent, to obtain an HPMC aqueous solution with a mass fraction of 1.0-1.5wt.%. After cooling to room temperature, let stand for 18-24h to defoam, utilizing the hydrogen bonding of HPMC molecules to provide a stable dispersion environment for ACF. 3) Add the pretreated ACF and aluminum sol to the above HPMC aqueous solution at the set mass ratio. First, stir at a low speed of 300-500 r / min for 5-10 min to achieve preliminary mixing, and then increase the speed to 8000-12000 r / min for 30-50 min to fully mix the ACF, aluminum sol and HPMC solution to form a homogeneous, stable precursor solution without obvious agglomeration. The steric hindrance effect of HPMC effectively inhibits the sedimentation and entanglement of ACF, ensuring the long-term stability of the system. 4) The obtained uniform precursor solution is directly sprayed onto the surface of the UAV substrate or injected into a custom mold for molding; After spraying or pouring, the whole thing is placed in an 80℃ constant temperature forced-air drying oven for 8-12 hours to allow the moisture in the system to evaporate slowly and evenly, avoiding cracking and warping; finally, a self-supporting block material or a continuous and uniform composite coating with a dense structure and good interface bonding is obtained, providing a stable substrate for subsequent metasurface processing. 5) A square or circular hollow array with a period of 3-10 mm is prepared on a polyimide template by laser etching, which serves as a metasurface forming template; Graphene patches are precisely embedded into the hollowed-out areas of the template, with a patch thickness of 5-20μm, to form a regular periodic array; 6) Gently press the metasurface array template onto the surface of the wet composite coating, controlling the applied pressure to 0.1-0.3MPa, so that the patch is embedded into the coating surface to a depth of 5-20μm, ensuring that the unit array is uniform, the position is stable, and the underlying dispersion structure is not damaged. 7) Place the coating of the template in a constant temperature oven at 60-70℃ for 2-4 hours to pre-dry. After the coating has initially set and the patch is completely fixed, slowly peel off the template, retaining the embedded metasurface microstructure, to avoid unit deformation or coating cracking. 8) The coating with embedded metasurface is placed in an 80℃ constant temperature forced air oven for a second curing for 4-6 hours to achieve complete drying of the substrate and interface strengthening, and finally obtain a metasurface composite coating for UAVs that combines heat insulation, wave absorption and electromagnetic shielding.