Impedance gradient structure-based wave-absorbing and heat-proof composite material, preparation method and application thereof

Abstract

The present application relates to a kind of wave-absorbing-heat insulation composite material based on impedance gradient structure and its preparation method and application, it is related to electromagnetic wave absorbing material technical field, the composite material includes fiber reinforcement and resin matrix, fiber reinforcement is sequentially arranged heat insulation zone and wave-absorbing zone along electromagnetic wave incident direction, wave-absorbing zone includes by the mixed fiber layer that electrically conductive fiber and wave-transparent fiber are mixed and woven.The present application constructs impedance gradient structure, and preferably nano-pore organic silicon resin is used as matrix, solve the existing wave-absorbing material absorption band narrow, single function, poor high-temperature environment adaptability and the process complexity caused by dependence on additional wave-absorbing agent, long-term stability is insufficient and other technical problems.The composite material realizes wave-absorbing-heat insulation multifunctional integration, with wideband high-efficiency wave-absorbing characteristics in 2-18GHz frequency band, and can still maintain excellent wave-absorbing performance after high-temperature ablation and thermal aging, and application scene is widely.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing materials technology, and in particular to a wave-absorbing and heat-insulating composite material based on an impedance gradient structure, its preparation method and application. Background Technology

[0002] Currently, the density and coverage of electromagnetic waves in space have significantly increased, leading to increasingly prominent potential hazards from electromagnetic interference and radiation. Against this backdrop, developing composite materials that combine broadband absorption and multifunctional integration has become a key research direction for enhancing electromagnetic protection capabilities and adapting to complex application scenarios.

[0003] Currently, single-layer absorbing materials suffer from narrow absorption bands, insufficient functional synergy, and poor adaptability to extreme environments, making them unsuitable for complex applications. In contrast, multi-layer structures, by combining functional layers with differentiated electromagnetic parameters and coordinating multiple loss mechanisms, can achieve efficient absorption of electromagnetic waves across different bands, effectively broadening the absorption bandwidth. Impedance gradient design, by adjusting parameters such as dielectric constant and permeability of each layer along the thickness direction, enables a smooth impedance transition from free space to the material's interior, significantly reducing electromagnetic wave reflectivity and enhancing energy dissipation efficiency through various attenuation mechanisms, thereby greatly improving absorption performance.

[0004] However, existing microwave absorbing materials with impedance gradients still have obvious limitations: First, the preparation process is complex, and it mostly relies on methods such as layer-by-layer coating, stepwise sintering or chemical vapor deposition, resulting in long production cycles and poor batch consistency; Second, the functionality is limited, with most materials only having microwave absorbing properties and lacking supporting functions such as heat insulation and load-bearing, making it difficult to meet the multi-functional integrated application needs of complex scenarios. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a microwave absorbing-heat insulation composite material and its preparation method and application, in order to solve one of the following technical problems: (1) Single-layer structure microwave absorbing materials have narrow absorption frequency bands, insufficient functional synergy, and poor adaptability to high temperature environment; (2) The preparation process of microwave absorbing materials with impedance gradient in the prior art is complicated, and they mostly rely on layer-by-layer coating, step-by-step sintering or chemical vapor deposition, which leads to long production cycle and high cost; (3) The existing microwave absorbing materials with impedance gradient have single functionality. Most materials only have microwave absorbing properties and lack supporting functions such as heat insulation and load bearing, which makes it difficult to meet the multi-functional integrated application needs of complex scenarios.

[0006] The microwave absorbing-heat insulation composite material of the present invention does not require the addition of additional microwave absorbing agents. By simply adjusting the composition of the microwave absorbing composite, the microwave absorption performance can be significantly improved while ensuring a certain mechanical strength. That is, the effective absorption bandwidth can be broadened with low reflection loss.

[0007] To achieve the above objectives, the first aspect of the present invention provides a microwave absorbing and heat-insulating composite material based on an impedance gradient structure, the composite material comprising a fiber reinforcement and a resin matrix filling the gaps between the fiber reinforcements;

[0008] The fiber reinforcement includes a heat insulation zone and a wave absorption zone arranged sequentially along the electromagnetic wave incident direction. The wave absorption zone includes a blended fiber layer, and the heat insulation zone includes a fiber cloth and / or fiber web made of wave-transparent fibers.

[0009] The hybrid fiber layer comprises a hybrid fiber mesh made of conductive fibers and wave-transparent fibers.

[0010] Furthermore, the absorbing region includes a transition layer and a hybrid fiber layer spaced apart along the electromagnetic wave incident direction, wherein the transition layer is a wave-transparent fiber layer.

[0011] Furthermore, the conductive fiber is made by carbonizing organic fibers.

[0012] Furthermore, the organic fiber is selected from at least one of phenolic fiber, polyimide fiber, biomass fiber, and viscose fiber.

[0013] Furthermore, the wave-transparent fiber is selected from at least one of glass fiber, quartz fiber and aramid fiber.

[0014] Furthermore, in the absorbing region, the mass percentage of conductive fibers in the hybrid fiber layer along the electromagnetic wave incident direction increases.

[0015] Furthermore, in the hybrid fiber layer, the mass percentage of adjacent conductive fibers increases by 5-10% along the electromagnetic wave incident direction.

[0016] Furthermore, in the hybrid fiber layer, the areal density of the hybrid fiber web is 40-90 g / m². 2 .

[0017] Furthermore, the number of layers of the hybrid fiber layer in the absorbing region is ≥3.

[0018] Furthermore, in the hybrid fiber layer, the mass percentage of conductive fibers is 10-40%.

[0019] Furthermore, the thickness of the heat insulation zone is 10-15 mm.

[0020] Furthermore, in the absorbing region, the thickness of the hybrid fiber layer is 2-5 mm, and the thickness of the transition layer is 1-5 mm.

[0021] Furthermore, in the composite material, the resin matrix accounts for 50-70 wt% of the composite material.

[0022] Furthermore, the resin matrix is ​​a nanoporous silicone resin, and the average pore size of the resin matrix is ​​20-70 nm.

[0023] A second aspect of the present invention provides a method for preparing the microwave absorbing and heat-insulating composite material based on the impedance gradient structure described in the first aspect, comprising:

[0024] S1. Under a protective atmosphere, organic fibers are carbonized at high temperature to obtain conductive fibers;

[0025] S2. The conductive fiber and the wave-transparent fiber are mixed evenly to obtain a hybrid fiber layer;

[0026] S3. The heat insulation zone and the wave absorption zone are sequentially stacked along the electromagnetic wave incident direction. The wave absorption zone includes a mixed fiber layer and a transition layer that are spaced apart to obtain a composite fiber layer.

[0027] S4. The composite fiber layer is made into a fiber preform by needle punching, vacuum impregnated with a resin matrix, and then cured and molded.

[0028] The conditions for high-temperature carbonization include: carbonization temperature of 600-750℃, heating rate of 1-10℃ / min, and holding time of 1-3h.

[0029] The transition layer is a wave-transparent fiber layer, the mixed-woven fiber layer includes a mixed-woven fiber mesh made of conductive fibers and wave-transparent fibers, and the heat insulation zone includes fiber cloth and / or fiber mesh made of wave-transparent fibers.

[0030] Furthermore, the vacuum degree during vacuum impregnation is -0.08 to -0.1 MPa.

[0031] Furthermore, the curing conditions include: a curing temperature of 120-180℃ and a curing time of 12-24h.

[0032] The third aspect of this invention provides an application of the composite material described in the first aspect in an integrated electromagnetic protection and thermal insulation system.

[0033] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0034] 1. This invention, by setting up a heat insulation zone and a wave-absorbing zone, can simultaneously achieve the functions of heat insulation and electromagnetic wave absorption, and the two complement each other. When the composite material faces a high-temperature environment, the heat is blocked and dissipated by the heat insulation zone, allowing the wave-absorbing zone to maintain a relatively low operating temperature, thereby reducing the difficulty of wave absorption. At the same time, the heat insulation zone and the gradient-designed wave-absorbing zone together form a continuous path from matching to loss, which together improves the wave absorption performance under the condition of low room temperature thermal conductivity. It can maintain a wide effective absorption bandwidth even after ablation at at least 1000℃, achieving a minimum reflection loss of -22.2dB, while the effective absorption bandwidth reaches 13.6GHz, and can meet the multi-functional integrated application requirements of complex scenarios.

[0035] 2. The composite material prepared by this invention has strong designability. By changing the carbonization temperature of organic fibers, the intrinsic conductivity of conductive fibers can be controlled, thereby improving the absorption capacity of electromagnetic waves in different frequency bands. By adjusting the content of conductive fibers in the blended fiber layers, electromagnetic waves can be easily transmitted, achieving better impedance matching with free space. By controlling the gradient relationship between the content of conductive fibers in different blended fiber layers, the optimal impedance gradient and attenuation gradient can be constructed, enabling a smooth transition of wave impedance, reducing surface reflection, thereby improving wave absorption performance and broadening the effective absorption bandwidth, specifically 2-18 GHz.

[0036] 3. This invention utilizes carbonized organic fibers (such as phenolic fibers) as a built-in conductive network to replace easily detachable external microwave absorbers. Combined with a layer of blended fibers that gradually increases in mass percentage along the electromagnetic wave incident direction (conductive fiber mass percentage increases by 5-10%) and an interlayer transparent fiber transition layer, a synergistic mechanism for smooth impedance transition and multi-frequency resonance attenuation is constructed. Simultaneously, nanoporous silicone resin is selected as the matrix (average pore size 20-70 nm), whose high-temperature ceramicization properties prevent total electromagnetic wave reflection caused by carbonization. The 10-15 mm thick transparent fiber insulation zone effectively blocks heat transfer to the absorption zone. The combined effect of these technologies achieves broadband absorption (effective absorption bandwidth of 2-18 GHz) while significantly improving the material's performance stability after thermo-oxidative aging, with an absorption retention rate as high as 83-91%, meeting the requirements for high-temperature, long-term electromagnetic protection.

[0037] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from the description and drawings, which are particularly pointed out. Attached Figure Description

[0038] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0039] Figure 1 This is a schematic diagram of the composite material structure obtained in Example 1;

[0040] Figure 2 The images show the front, bottom, and side views of the composite material prepared in Example 1.

[0041] Figure 3 The curve showing the change in reflection loss of the composite material prepared in Example 1 as a function of frequency;

[0042] Figure 4 The reflection loss curves of the composite material obtained in Example 2 before and after ablation are shown.

[0043] Figure 5 The reflection loss curves of the composite material obtained in Example 3 before and after ablation are shown.

[0044] Figure 6 The composite material obtained in Example 4 has reflection loss curves before and after ablation.

[0045] Figure 7 The reflection loss curve of the composite material obtained in Example 5;

[0046] Figure 8 The image shows the reflection loss curve of the composite material obtained in Example 6.

[0047] Figure Labels

[0048] 1. Heat insulation zone; 2. Wave absorption zone; 201. Blended fiber layer; 202. Transition layer. Detailed Implementation

[0049] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0050] Currently, microwave absorbing materials with impedance gradients still have significant limitations: First, the preparation process is complex, often relying on methods such as adding additional microwave absorbing agents, layer-by-layer coating, stepwise sintering, or chemical vapor deposition, resulting in long production cycles, poor batch consistency, and poor long-term stability; Second, the functionality is limited, with most materials only possessing microwave absorbing properties and lacking supporting functions such as heat insulation and load-bearing, making it difficult to meet the multi-functional integrated application needs of complex scenarios.

[0051] Based on this, the first aspect of the present invention provides a wave-absorbing and heat-insulating composite material based on an impedance gradient structure, the composite material comprising a fiber reinforcement and a resin matrix filling the gaps between the fiber reinforcements;

[0052] The fiber reinforcement includes a heat insulation zone 1 and a wave absorption zone 2 arranged sequentially along the electromagnetic wave incident direction. The wave absorption zone 2 includes a mixed fiber layer 201. The heat insulation zone 1 includes a fiber cloth and / or fiber web made of wave-transparent fibers.

[0053] The mixed-fiber layer 201 comprises a mixed-fiber mesh made of conductive fibers and wave-transparent fibers.

[0054] In this invention, Figure 1 This is a cross-section of the layered structure of the composite material of the present invention. Along the incident direction of the electromagnetic wave, it first passes through the heat insulation zone 1 and then enters the wave absorption zone 2. The heat insulation zone 1 is composed of a fiber cloth or mesh made of wave-transparent fibers, while the wave absorption zone 2 is composed of alternating layers of mixed-woven fiber layers 201 and wave-transparent fiber transition layers 202. By setting up the heat insulation zone 1 and the wave absorption zone 2, the functions of heat insulation and electromagnetic wave absorption can be achieved simultaneously, and the two complement each other. When the composite material faces a high-temperature environment, the heat is blocked and dissipated by the heat insulation zone 1, allowing the wave absorption zone 2 to maintain a relatively low operating temperature, reducing the difficulty of wave absorption. Simultaneously, the heat insulation zone 1 and the wave absorption zone 2 with its impedance gradient design together form a continuous path from matching to loss, jointly achieving improved wave absorption performance and broadening the effective absorption bandwidth under conditions of low room temperature thermal conductivity. Figure 2 The images show the physical appearance of the composite material, including its front (a), bottom (b), and side (c), demonstrating that the composite material of the present invention has a complete and uniform macroscopic structure. The overall thickness of the material and the density of its layered structure can be observed from the side view.

[0055] According to some embodiments of the present invention, the absorbing region 2 includes a transition layer 202 and a mixed fiber layer 201 arranged at intervals along the electromagnetic wave incident direction, wherein the transition layer 202 is a wave-transparent fiber layer.

[0056] It should be noted that by inserting a low dielectric constant transition layer 202 between the hybrid fiber layers 201, dual optimizations can be achieved: First, in terms of propagation constant, a smoother wave impedance gradient is formed, which significantly reduces the distributed reflection of electromagnetic waves at the multilayer interface and ensures that energy effectively penetrates into the interior of the composite material; Second, in terms of energy distribution, the ohmic loss efficiency of the hybrid fiber layer 201 is greatly improved. Through the synergistic mechanism of "matching-resonance-attenuation", simple unidirectional absorption is transformed into multi-band resonant absorption, which effectively broadens the absorption bandwidth.

[0057] According to some embodiments of the present invention, the conductive fiber is obtained by carbonizing organic fibers.

[0058] In this invention, extensive experiments have revealed that carbonization conditions (especially carbonization temperature) significantly influence the wave absorption effect of the final wave-absorbing and heat-insulating composite material. A suitable carbonization temperature allows the resulting conductive fibers to possess appropriate electrical conductivity, fully utilizing their dielectric loss to dissipate electromagnetic waves. According to some embodiments of the invention, considering the advantages of conductive fibers obtained by carbonizing different organic fibers, the preparation of the composite material becomes more flexible. Specifically, the organic fibers are selected from at least one of phenolic fibers, polyimide fibers, biomass fibers, and viscose fibers.

[0059] According to some embodiments of the present invention, considering the low dielectric constant and extremely small loss factor, the wave-transparent fiber is specifically selected from at least one of glass fiber, quartz fiber, and aramid fiber. According to some embodiments of the present invention, in the wave-absorbing region 2, the mass percentage of conductive fibers in the hybrid fiber layer 201 along the electromagnetic wave incident direction increases progressively.

[0060] It should be noted that the increasing percentage of conductive fiber mass is intended to create an impedance gradient structure and attenuation gradient field in absorbing region 2. This structure causes the complex permittivity and characteristic impedance of the composite material to gradually change from the surface to the interior. First, the lower conductive fiber content on the surface reduces the initial reflection of incident electromagnetic waves and allows them to penetrate efficiently into the composite material. Then, along the direction of electromagnetic wave incidence, the gradually increasing conductive fiber content means a simultaneous enhancement of conductivity loss, achieving layer-by-layer attenuation of electromagnetic waves. This smooth transition structure enables broadband impedance matching and efficient energy absorption, thereby further improving the absorption effect.

[0061] According to some embodiments of the present invention, considering that the mass percentage increase of conductive fibers is less than 5%, the gradient is too gentle, and the material needs to be made thicker to achieve effective absorption, while the mass percentage increase of conductive fibers is greater than 10%, the interlayer impedance changes abruptly, resulting in severe reflection and destroying the broadband absorption effect, specifically, in the hybrid fiber layer 201, the mass percentage increase of conductive fibers is 5-10%, for example 5%, 6%, 7%, 8%, 9%, 10%.

[0062] According to some embodiments of the present invention, taking into account structural integrity and electromagnetic uniformity, specifically, in the hybrid fiber layer 201, the areal density of the hybrid fiber mesh is 40-90 g / m². 2 .

[0063] According to some embodiments of the present invention, specifically, the bulk density of the transition layer 202 is 0.2-0.6 g / cm³. 3 .

[0064] According to some embodiments of the present invention, specifically, the bulk density of the heat insulation zone 1 is 0.2-0.4 g / cm³. 3 .

[0065] According to some embodiments of the present invention, in order to avoid the absorption peak being narrow due to the fact that single-layer or double-layer structures can only rely on their intrinsic loss mechanisms and cannot cover a wide frequency band, the number of layers of the mixed-woven fiber layer 201 in the absorbing region 2 is ≥3, for example 3, 4, 5, 6, 7, 8, 9, or 10 layers, preferably 3-5 layers.

[0066] According to some embodiments of the present invention, in the hybrid fiber layer 201, the mass percentage of conductive fibers is 10-40%, for example, it can be 10%, 12%, 15%, 16%, 18%, 20%, 22%, 25%, 28%, 30%, 35%, or 40%. When the conductive fiber content is less than 10%, the fiber spacing is too large, making it difficult to form an effective conductive path or polarization center, resulting in a low dielectric constant and loss factor of the composite material and insufficient electromagnetic loss capability. If the conductive fiber content is greater than 40%, the conductive fibers easily form a dense continuous conductive network, causing the complex dielectric constant of the material to increase sharply, thereby causing the composite material to induce strong electromagnetic wave surface reflection, thus reducing loss and resulting in insufficient wave absorption effect.

[0067] According to some embodiments of the present invention, considering the significant delay of heat transfer from the high-temperature environment to the microwave absorbing region 2 in the composite material, and to provide thermal stability assurance for the microwave absorbing functional layer, the thickness of the heat insulation region 1 is 10-15mm, for example 10mm, 11mm, 12mm, 13mm, 14mm, or 15mm. If it is less than 10mm, the thermal resistance will be insufficient, while if it exceeds 15mm, it will unnecessarily increase the material weight and volume, thus increasing the cost.

[0068] According to some embodiments of the present invention, considering that the absorbing material needs to accommodate multiple reflections and efficient energy conversion, the thickness of the hybrid fiber layer 201 in the absorbing region 2 is 2-5 mm, and the thickness of the transition layer 202 is 1-5 mm. By optimizing the thickness of the hybrid fiber layer 201, the transition layer 202, and the heat insulation region 1, efficient electromagnetic wave absorption, loss, and control can be achieved while ensuring the overall thickness and weight of the material.

[0069] According to some embodiments of the present invention, in the composite material, the resin matrix accounts for 50-70 wt% of the composite material.

[0070] In this invention, if the resin matrix content is too high, it will lead to insufficient microwave absorption capacity and strength. If the resin matrix content is too low, the resin will be difficult to completely impregnate, resulting in excessive brittleness of the composite material and a decrease in microwave absorption performance.

[0071] According to some embodiments of the present invention, considering that resin matrices such as phenolic resin and epoxy resin with C-C or CO bonds in their main chain structure have a high degree of carbonization after high temperature and ablation, they will form a continuous residual carbon distribution, causing total reflection of electromagnetic waves and thus losing their wave absorption performance, nanoporous organosilicon resin has an abundant Si-O structure, and organosilicon resin will undergo ceramization, allowing electromagnetic waves to penetrate rather than be totally reflected, thus having a good wave absorption effect. Therefore, the resin matrix of the present invention is a nanoporous organosilicon resin.

[0072] Furthermore, the average pore size of the resin matrix is ​​20-70 nm, for example, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 50 nm, 60 nm, 65 nm, and 70 nm. It should be noted that the average pore size of the nanopore structure within the above range can reduce the overall dielectric constant of the composite material, making it easier for electromagnetic waves to enter the material rather than be reflected. When electromagnetic waves enter the composite material, they undergo repeated reflection and scattering between the pore walls of the nanopores, thereby further dissipating the energy of the electromagnetic waves and exhibiting excellent wave absorption effects.

[0073] A second aspect of the present invention provides a method for preparing the microwave absorbing and heat-insulating composite material based on the impedance gradient structure described in the first aspect, comprising:

[0074] S1. Under a protective atmosphere, organic fibers are carbonized at high temperature to obtain conductive fibers;

[0075] S2. The conductive fiber and the wave-transparent fiber are mixed evenly to obtain a mixed fiber layer 201.

[0076] S3. The heat insulation zone 1 and the wave absorption zone 2 are sequentially stacked along the electromagnetic wave incident direction, wherein the wave absorption zone 2 includes a mixed fiber layer 201 and a transition layer 202 arranged at intervals to obtain a composite fiber layer.

[0077] S4. The composite fiber layer is made into a fiber preform by needle punching, vacuum impregnated with a resin matrix, and then cured and molded.

[0078] The conditions for high-temperature carbonization include: carbonization temperature of 600-750℃, heating rate of 1-10℃ / min, and holding time of 1-3h.

[0079] The transition layer 202 is a wave-transparent fiber layer, the mixed fiber layer 201 includes a mixed fiber mesh made of conductive fibers and wave-transparent fibers, and the heat insulation zone 1 includes a fiber cloth and / or fiber mesh made of wave-transparent fibers.

[0080] In this invention, the carbonization temperature has a significant impact on the microwave absorption effect of the composite material. A suitable carbonization temperature allows the resulting conductive fibers to have appropriate conductivity, fully utilizing their dielectric loss to dissipate electromagnetic waves. If the carbonization temperature is below 600℃, there will be more non-carbon elements remaining and the carbon skeleton will have a low degree of ordering, resulting in low conductivity, which is not conducive to the dissipation of electromagnetic waves and thus affects the microwave absorption effect. On the other hand, a carbonization temperature above 750℃ will increase the graphitization tendency, resulting in high conductivity and total internal reflection of electromagnetic waves, which will also reduce the microwave absorption effect.

[0081] It is understood that the protective gas may be nitrogen or an inert gas.

[0082] It is understood that the mixed-weave fiber layer 201 exists in the form of a mixed-weave fiber web, and the wave-transparent fiber layer exists in the form of fiber cloth and / or fiber web.

[0083] It is understood that the organic fibers undergo pretreatment such as degreasing, washing, and drying before carbonization. The drying temperature is 80-120℃, for example, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, or 120℃, and the drying time is 2-4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours.

[0084] In this invention, the organic fiber is selected from at least one of phenolic fiber, polyimide fiber, biomass fiber, and viscose fiber.

[0085] Understandably, considering the need to ensure good processability of the conductive fibers and the structural uniformity of the subsequent fiber preforms, the diameter of the conductive fibers is set at 5-15μm, such as 5μm, 6μm, 8μm, 10μm, 12μm, 15μm, and the length is set at 5-50mm, such as 5mm, 6mm, 8mm, 10mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm.

[0086] Understandably, considering the need to ensure good processability of the transparent fibers and the structural uniformity of the subsequent fiber preforms, the diameter of the transparent fibers is set at 8-20μm, such as 8μm, 10μm, 12μm, 15μm, 16μm, 20μm, and the length is set at 10-80mm, such as 10mm, 12mm, 15mm, 20mm, 25mm, 28mm, 30mm, 35mm, 40mm, 45mm, 50mm, 55mm, 60mm, 70mm, 75mm, 80mm.

[0087] In this invention, the wave-transparent fiber is selected from at least one of glass fiber, quartz fiber and aramid fiber.

[0088] According to some embodiments of the present invention, in step S4, the vacuum degree during vacuum impregnation is -0.08 to -0.1 MPa, for example -0.08 MPa, -0.085 MPa, -0.09 MPa, -0.095 MPa, or -0.1 MPa. Satisfying the above range enables the resin matrix to quickly and fully fill all the pores of the preform, avoiding defects such as bubbles and insufficient adhesive, thereby forming a dense and uniform microwave-absorbing and heat-insulating composite material.

[0089] According to some embodiments of the present invention, the curing conditions include: a curing temperature of 120-180℃, such as 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 160℃, 170℃, 180℃, and a curing time of 12-24h, such as 12h, 13h, 14h, 15h, 16h, 18h, 20h, 22h, 24h.

[0090] In this invention, the curing conditions meet the above-mentioned range, which enables the cross-linking reaction of the resin matrix to be more thorough, firmly bonding the microwave absorbing zone 2 and the heat insulation zone 1 into a solid whole, so that the final composite material has excellent mechanical properties while improving microwave absorption performance.

[0091] The third aspect of this invention provides an application of the composite material described in the first aspect in an integrated electromagnetic protection and thermal insulation system.

[0092] The composite material that meets the requirements of the present invention can maintain a wide effective absorption bandwidth, specifically 2-18 GHz, even after ablation at a maximum temperature of 1000°C, and has a wide range of applications.

[0093] To more clearly describe the present invention, the following embodiments and comparative examples are provided for further illustration.

[0094] In the following examples and comparative examples, the room temperature thermal conductivity of the composite material was measured by the flat plate heat flow meter method;

[0095] The density of the composite material is calculated by measuring its mass and volume;

[0096] The composite materials prepared in the examples and comparative examples were cut into 300mm × 300mm flat plates, and their reflection loss in the 2-18GHz range was tested using the bow method according to GJB2038A-2011. Unless otherwise specified, the phenolic fibers described below were pretreated by degreasing, washing, and drying (100℃, 2h).

[0097] The long-term performance of the composite material was characterized by thermo-oxidative aging test: According to GB / T7141-2021, the sample was placed in a 200℃ oven and compressed air (50mL / min) was introduced for 200h. Then, according to GJB2038A-2011, the reflection loss in the range of 2-18GHz was tested using the bow method to obtain the reflection loss after aging. The absorption performance retention rate was calculated using the formula, where the absorption performance retention rate = (reflection loss after aging / reflection loss before aging) × 100%.

[0098] In the following examples, conductive fibers (25 mm in length, 12 μm in diameter) and quartz fibers (12 μm in diameter, 28 mm in length) were mixed, and then combed, web-formed, and fixed to obtain a density of 0.22 g / cm³. 3 The mixed-weave fiber layer 201; wherein, seven kinds of mixed-weave fiber layers (first mixed-weave fiber layer to seventh mixed-weave fiber layer) are prepared by the above method, wherein, the first mixed-weave fiber layer has a conductive fiber mass percentage of 10%; the second mixed-weave fiber layer has a conductive fiber mass percentage of 15%; the third mixed-weave fiber layer has a conductive fiber mass percentage of 20%; the fourth mixed-weave fiber layer has a conductive fiber mass percentage of 25%; the fifth mixed-weave fiber layer has a conductive fiber mass percentage of 30%; the sixth mixed-weave fiber layer has a conductive fiber mass percentage of 35%; and the seventh mixed-weave fiber layer has a conductive fiber mass percentage of 13%.

[0099] The nanoporous silicone resin was prepared according to the method in Example 1 of CN118931205A, and the average pore size of the resin matrix was 50 nm.

[0100] Example 1

[0101] S1: In a nitrogen atmosphere, phenolic fibers are placed in a carbonization furnace and heated from room temperature to 300°C at a rate of 5°C / min, held for 30 min, then heated to 730°C at a rate of 2°C / min, held for 2 h, and then naturally cooled to room temperature to obtain conductive fibers.

[0102] S2, Stack 8mm thick, 0.22g / cm³ layers sequentially along the direction of electromagnetic wave incidence. 3 The fiber preform consists of a quartz fiber layer (insulation zone 1), a 4mm thick first mixed fiber layer, a 4mm thick third mixed fiber layer, and a 4mm thick fifth mixed fiber layer, which are connected by a needle-punching process to form a fiber preform with a needle-punching density of 25 needles / cm. 2 .

[0103] S3: The above fiber preform is laid in a 330mm×330mm mold, and nanoporous silicone resin is injected under a vacuum of -0.1MPa. Then, the mold after injection is placed in an oven at 140℃ for curing and molding for 24 hours, and then dried at 100℃ for 18 hours to obtain the composite material.

[0104] In this composite material, the number of layers of the braided fiber layer 201 in the microwave absorbing region 2 is 3, and the content of conductive fiber in the braided fiber layer 201 along the electromagnetic wave incident direction increases by 10%; the resin matrix accounts for 60 wt% of the composite material.

[0105] The density of the composite material was tested to be 0.45 g / cm³. 3 The thermal conductivity at room temperature is 0.042 W / m·K. Figure 3 As can be seen, the composite material has a minimum reflection loss of -25.7dB and an effective absorption bandwidth of 6.2GHz when it is 25mm thick, and the absorption performance retention rate after the thermo-oxidative aging test is 86%.

[0106] Example 2

[0107] The method is the same as in Example 1, except that in step S2, 12mm thick, 0.22g / cm³ layers are stacked sequentially along the electromagnetic wave incident direction. 3 Quartz fiber layer (insulation zone 1), 4mm thick second mixed fiber layer, 5mm thick fourth mixed fiber layer, 4mm thick sixth mixed fiber layer.

[0108] In this composite material, the number of layers of the braided fiber layer 201 in the microwave absorbing region 2 is 3, and the content of conductive fiber in the braided fiber layer 201 along the electromagnetic wave incident direction increases by 10%; the resin matrix accounts for 60 wt% of the composite material.

[0109] The density of the composite material was tested to be 0.49 g / cm³. 3 The thermal conductivity at room temperature is 0.044 W / m·K. Figure 4 As can be seen from the reflection loss curve, the composite material has a minimum reflection loss of -24.4dB and an effective absorption bandwidth of 11GHz when it is 25mm thick, and the absorption performance retention rate after the thermo-oxidative aging test is 90%.

[0110] Example 3

[0111] The method is the same as in Example 1, except that in step S2, 6mm thick sheets with a density of 0.22g / cm³ are sequentially stacked along the incident direction of the electromagnetic wave. 3 Quartz fiber layer (insulation zone 1), 4mm thick first mixed-woven fiber layer, 1mm thick layer with a density of 0.4g / cm³ 3Quartz fiber cloth (transition layer 202), a 4mm thick third blended fiber layer, and a 1mm thick layer with a density of 0.4g / cm³. 3 Quartz fiber cloth (transition layer 202), 4mm thick fifth blended fiber layer.

[0112] In this composite material, the number of layers of the braided fiber layer 201 in the microwave absorbing region 2 is 3, and the content of conductive fiber in the braided fiber layer 201 along the electromagnetic wave incident direction increases by 10%; the resin matrix accounts for 60 wt% of the composite material.

[0113] The density of the composite material was tested to be 0.47 g / cm³. 3 The thermal conductivity at room temperature is 0.044 W / m·K. Figure 5 As can be seen from the reflection loss curve, the composite material has a minimum reflection loss of -25.9dB and an effective absorption bandwidth of 10.6GHz when it is 25mm thick, and the absorption performance retention rate after the thermo-oxidative aging test is 90%.

[0114] Example 4

[0115] The method is the same as in Example 1, except that in step S2, 8mm thick sheets with a density of 0.22g / cm³ are sequentially stacked along the incident direction of the electromagnetic wave. 3 Quartz fiber layer (insulation zone 1), 4mm thick second mixed-woven fiber layer, 2mm thick layer with a density of 0.4g / cm³ 3 Quartz fiber cloth (transition layer 202), a 5mm thick fourth blended fiber layer, and a 2mm thick layer with a density of 0.4g / cm³. 3 Quartz fiber cloth (transition layer 202), 4mm thick sixth mixed fiber layer.

[0116] In this composite material, the number of layers of the braided fiber layer 201 in the microwave absorbing region 2 is 3, and the content of conductive fiber in the braided fiber layer 201 along the electromagnetic wave incident direction increases by 10%; the resin matrix accounts for 60 wt% of the composite material.

[0117] The density of the composite material was tested to be 0.51 g / cm³. 3 The thermal conductivity at room temperature is 0.053 W / m·K. Figure 6 As can be seen from the reflection loss curve, the composite material has a minimum reflection loss of -22.2dB and an effective absorption bandwidth of 13.6GHz when it is 25mm thick, and the absorption performance retention rate after the thermo-oxidative aging test is 88%.

[0118] Example 5

[0119] The method is the same as in Example 1, except that in step S1, the phenolic fiber is carbonized at a rate of 5°C / min from room temperature to 300°C, and then at a rate of 2°C / min to 630°C, and held at that temperature for 2 hours. After naturally cooling to room temperature, conductive fiber is obtained.

[0120] In this composite material, the number of layers of the braided fiber layer 201 in the microwave absorbing region 2 is 3, and the content of conductive fiber in the braided fiber layer 201 along the electromagnetic wave incident direction increases by 10%; the resin matrix accounts for 60 wt% of the composite material.

[0121] The density of the composite material was tested to be 0.47 g / cm³. 3 The thermal conductivity at room temperature is 0.042 W / m·K. Figure 7 As can be seen from the reflection loss curve, the composite material has a minimum reflection loss of -23.7dB and an effective absorption bandwidth of 3.3GHz when it is 25mm thick, and the absorption performance retention rate after the thermo-oxidative aging test is 91%.

[0122] Example 6

[0123] The method is the same as in Example 1, except that the density of the blended fiber layer 201 in S2 is 0.20 g / cm³. 3 .

[0124] In this composite material, the number of layers of the braided fiber layer 201 in the microwave absorbing region 2 is 3, and the content of conductive fiber in the braided fiber layer 201 along the electromagnetic wave incident direction increases by 10%; the resin matrix accounts for 60 wt% of the composite material.

[0125] The density of the composite material was tested to be 0.52 g / cm³. 3 The thermal conductivity at room temperature is 0.05 W / m·K. Figure 8 As can be seen from the reflection loss curve, the composite material has a minimum reflection loss of -19.4dB and an effective absorption bandwidth of 5.6GHz when it is 25mm thick. The absorption performance retention rate after the thermo-oxidative aging test is 88%.

[0126] Example 7

[0127] The method is the same as in Example 1, except that in step S2, 8mm thick sheets with a density of 0.22g / cm³ are sequentially stacked along the incident direction of the electromagnetic wave. 3 Quartz fiber layer (insulation zone 1), 4mm thick first mixed-woven fiber layer, 2mm thick layer with a density of 0.4g / cm³ 3 Quartz fiber cloth (transition layer 202), a 5mm thick second blended fiber layer, and a 2mm thick layer with a density of 0.4g / cm³. 3Quartz fiber cloth (transition layer 202), 4mm thick third blended fiber layer.

[0128] In this composite material, the number of layers of the braided fiber layer 201 in the microwave absorbing region 2 is 3, and the content of conductive fiber in the braided fiber layer 201 along the electromagnetic wave incident direction increases by 5%; the resin matrix accounts for 60 wt% of the composite material.

[0129] The density of the composite material was tested to be 0.53 g / cm³. 3 The thermal conductivity at room temperature is 0.048 W / m·K. The composite material has a minimum reflection loss of -25.7 dB and an effective absorption bandwidth of 7.5 GHz when it is 25 mm thick. The absorption performance retention rate after the thermo-oxidative aging test is 87%.

[0130] Example 8

[0131] The method is the same as in Example 1, except that in step S2, 8mm thick sheets with a density of 0.22g / cm³ are sequentially stacked along the incident direction of the electromagnetic wave. 3 Quartz fiber layer (insulation zone 1), 4mm thick first mixed-woven fiber layer, 2mm thick layer with a density of 0.4g / cm³ 3 Quartz fiber cloth (transition layer 202), a 5mm thick third blended fiber layer, and a 2mm thick layer with a density of 0.4g / cm³. 3 Quartz fiber cloth (transition layer 202), 4mm thick fourth blended fiber layer;

[0132] In this composite material, the number of layers of the braided fiber layer 201 in the microwave absorbing region 2 is 3. In the braided fiber layer 201 along the electromagnetic wave incident direction, the content of conductive fiber increases by 10% and 5% respectively; the resin matrix accounts for 60 wt% of the composite material.

[0133] The density of the composite material was tested to be 0.50 g / cm³. 3 The thermal conductivity at room temperature is 0.044 W / m·K. The composite material has a minimum reflection loss of -23.6 dB and an effective absorption bandwidth of 8.8 GHz when it is 25 mm thick. The absorption performance retention rate after the thermo-oxidative aging test is 85%.

[0134] Example 9

[0135] The method is the same as in Example 3, except that in step S2, 8mm thick sheets with a density of 0.22g / cm³ are stacked sequentially along the incident direction of the electromagnetic wave. 3 Quartz fiber layer (insulation zone 1), 4mm thick second mixed-woven fiber layer, 2mm thick layer with a density of 0.4g / cm³ 3 Quartz fiber cloth (transition layer 202), a 5mm thick second blended fiber layer, and a 2mm thick layer with a density of 0.4g / cm³.3 Quartz fiber cloth (transition layer 202), 4mm thick second mixed fiber layer;

[0136] In this composite material, the number of layers of the braided fiber layer 201 in the microwave absorbing region 2 is 3, and the content of conductive fiber in the braided fiber layer 201 along the electromagnetic wave incident direction is 0% each time; the resin matrix accounts for 60 wt% of the composite material.

[0137] The density of the composite material was tested to be 0.54 g / cm³. 3 The thermal conductivity at room temperature is 0.049 W / m·K. The composite material has a minimum reflection loss of -15.6 dB and an effective absorption bandwidth of 4.7 GHz when it is 25 mm thick. The absorption performance retention rate after the thermo-oxidative aging test is 87%.

[0138] Example 10

[0139] In step S2, 8mm thick sheets of material with a density of 0.22g / cm³ are sequentially stacked along the incident direction of the electromagnetic wave. 3 Quartz fiber layer (insulation zone 1), 4mm thick second mixed-woven fiber layer, 2mm thick layer with a density of 0.4g / cm³ 3 Quartz fiber cloth (transition layer 202), a 5mm thick seventh blended fiber layer (conductive fiber mass percentage is 13%), and a 2mm thick layer with a density of 0.4g / cm³. 3 Quartz fiber cloth (transition layer 202), 4mm thick second mixed fiber layer;

[0140] In this composite material, the number of layers of the braided fiber layer 201 in the microwave absorbing region 2 is 3. In the braided fiber layer 201 along the electromagnetic wave incident direction, the content of conductive fiber increases by 3% and -2% respectively; the resin matrix accounts for 60 wt% of the composite material.

[0141] The density of the composite material was tested to be 0.49 g / cm³. 3 The thermal conductivity at room temperature is 0.051 W / m·K. The composite material has a minimum reflection loss of -18.2 dB and an effective absorption bandwidth of 8.6 GHz when it is 25 mm thick. The absorption performance retention rate after the thermo-oxidative aging test is 83%.

[0142] Comparative Example 1

[0143] The method is the same as in Example 3, except that the absorbing region 2 does not use an impedance gradient structure, but only has a single layer of hybrid fiber 201, that is, in step S2, 8mm thick and 0.22g / cm² fibers are stacked sequentially along the electromagnetic wave incident direction. 3 The quartz fiber layer (insulation zone 1) is 12 mm thick and has a density of 0.22 g / cm³. 3The third layer of blended fibers is connected by a needle-punching process to form a fiber preform with a needle-punching density of 25 needles / cm. 2 .

[0144] The density of the composite material was tested to be 0.43 g / cm³. 3 The thermal conductivity at room temperature is 0.048 W / m·K. The composite material has a minimum reflection loss of -17.8 dB and an effective absorption bandwidth of 2.9 GHz when it is 25 mm thick. The absorption performance retention rate after the thermo-oxidative aging test is 92%.

[0145] Comparative Example 2

[0146] The method is the same as in Example 1, except that in step S2, 8mm thick, 0.22g / cm³ layers are stacked sequentially along the electromagnetic wave incident direction. 3 The quartz fiber layer (insulation zone 1), 12 mm thick, has a density of 0.22 g / cm³. 3 The fifth blended fiber layer.

[0147] The density of the composite material was tested to be 0.45 g / cm³. 3 The thermal conductivity at room temperature is 0.052 W / m·K. The composite material has a minimum reflection loss of -23.2 dB and an effective absorption bandwidth of 4.2 GHz when it is 25 mm thick. The absorption performance retention rate after the thermo-oxidative aging test is 81%.

[0148] Comparative Example 3

[0149] S1: Weigh 1g of methyl methacrylate and add it to 400ml of N,N-dimethylformamide. Stir thoroughly at room temperature until dissolved. Weigh 2.5g of a mixture of multi-walled carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) in a 1:1 mass ratio and add it to the above solution in portions. Sonicate for 15min to disperse evenly, and stir thoroughly until a suspension is formed to obtain the electrically modified microwave absorbing slurry; the average particle size of the electrically modified microwave absorbing agent is 100nm.

[0150] S2: Each time, 25g of the above slurry is weighed and uniformly dispersed onto a single-sheet quartz fiber mesh using a spraying process. The amount of multi-walled carbon nanotubes and reduced graphene oxide (RGO) in a 1:1 mass ratio is varied to prepare a series of electromodified fiber monosheets, including a first, second, and third electromodified fiber monosheet. The mass percentages of the electromodified microwave absorber in the electromodified fiber monosheets are 1%, 2%, and 3%, respectively, and the fiber mass percentage is 20%, with the remainder being methyl methacrylate and silicone resin as binders. The electromodified fiber monosheets are then dried in an 80℃ oven for 10 hours to obtain electromodified quartz fibers. The average diameter of the original fibers in the modified fibers is 10μm, and the density of the quartz fiber monosheet is 0.27g / cm³. 3The thickness of the electromodified fiber monolayer is 0.2 mm, and the coating slurry amount of the modified fiber monolayer is 500 g / m². 2 .

[0151] S3: Take the above-mentioned electromodified quartz fiber monosheets and layer them sequentially to a thickness of 8mm and a density of 0.27g / cm. 3 A quartz fiber layer, a 6mm thick quartz fiber needle-punched mesh layer, a first electromodified fiber monolayer, a second electromodified fiber monolayer, and a third electromodified fiber monolayer are stacked sequentially, with each electromodified fiber monolayer being 2mm thick. These layers are then connected using a stitching process to form a fiber preform with a needle-punching density of 20 needles / cm². 2 The fiber preform was laid in a 330mm×330mm mold, and silicone resin was injected under pressure until the fiber preform was completely impregnated with the silicone resin solution. The mold was then sealed. The mold was placed in a 100℃ oven for curing for 24 hours, and then dried at 80℃ for 12 hours. The silicone resin was a nanoporous silicone resin. The nanoporous silicone resin was prepared by mixing polysiloxane with a degree of polymerization of 1000 and silane monomers at a molar ratio of 1:100 with an appropriate amount of alkaline catalyst, under the conditions of curing temperature of 100℃ and curing time.

[0152] The density of the composite material was tested to be 0.54 kg / m³. 3 The room temperature thermal conductivity is 0.048 W / m·K. Further testing of its reflection loss in the 2-18 GHz range was conducted using the bow-shaped method according to GJB2038A-2011. At a thickness of 25 mm, the composite material exhibited a minimum reflection loss of -29.0 dB and an effective absorption bandwidth of 8.5 GHz. The absorption performance retention rate after the thermo-oxidative aging test was 69%.

[0153] To further illustrate the excellent ablation resistance of the composite material prepared in this embodiment, the composite materials prepared in Examples 2-4 were selected and experiments were conducted under the following conditions: the composite material was heated for 1200 s at 10 kPa and 1000 °C using a quartz lamp heating device. The composite material prepared in Example 2 had a back temperature of 130 °C, a room temperature thermal conductivity of 0.056 W / m·K, a minimum reflection loss of -19.3 dB, and an effective absorption bandwidth of 7.1 GHz.

[0154] The composite material prepared in Example 3 has a back temperature of 130°C, a room temperature thermal conductivity of 0.056 W / m·K, a minimum reflection loss of -22.3 dB, and an effective absorption bandwidth of 8.6 GHz.

[0155] The composite material prepared in Example 4 has a back temperature of 130°C, a room temperature thermal conductivity of 0.056 W / m·K, a minimum reflection loss of -20.6 dB, and an effective absorption bandwidth of 12.9 GHz.

[0156] As can be seen, the composite materials represented by Examples 2-4 have excellent ablation resistance. When heated for 1200s at 10kPa and 1000℃, the minimum reflection loss and effective absorption bandwidth only decrease slightly under the premise that the room temperature thermal conductivity remains unchanged, but they still have good wave absorption effect.

[0157] Furthermore, the average reflection loss results of the composite materials prepared in the examples and comparative examples in different frequency bands are shown in Table 1.

[0158] Table 1

[0159]

[0160] The results above show that, compared with embodiments 1-6, the main changes lie in the carbonization temperature of the organic fibers, the content of conductive fibers in the blended absorbing fibers, and the density of the blended absorbing fiber mesh. By adjusting these preparation process parameters, the impedance matching and electromagnetic wave attenuation capabilities of the materials can be optimized, thereby enhancing electromagnetic wave absorption. Simultaneously, the composite materials prepared by each method exhibit low thermal conductivity and good heat insulation performance.

[0161] Comparing Examples 1 and 3 with Examples 2 and 4, it can be seen that by setting a transition layer 202 between the mixed fiber layers 201, the minimum reflection loss can be further reduced. This change is more obvious in the low frequency band, and at the same time, the effective absorption bandwidth can be further broadened.

[0162] Comparing Examples 1-6 with Comparative Examples 1-2, it can be found that the impedance gradient structure has a superior electromagnetic wave absorption effect compared to the single-layer absorbing structure. This is because the gradient change in impedance allows electromagnetic waves to fully penetrate the material, effectively improving electromagnetic absorption efficiency.

[0163] Comparing Example 1 and Comparative Example 3, it can be seen that by forming a conductive network through the carbonized organic fiber itself, rather than by adding an external absorbing agent, the performance degradation caused by the poor bonding between the absorbing agent and the matrix interface can be effectively avoided.

[0164] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A wave-absorbing and heat-insulating composite material based on an impedance gradient structure, characterized in that, The composite material includes a fiber reinforcement and a resin matrix filling the gaps between the fiber reinforcements; the resin matrix is ​​a nanoporous silicone resin. The fiber reinforcement includes a heat insulation zone and a wave absorption zone arranged sequentially along the electromagnetic wave incident direction. The wave absorption zone is a mixed-woven fiber layer and a transition layer arranged at intervals along the electromagnetic wave incident direction. The transition layer is a wave-transparent fiber layer. The heat insulation zone is a fiber cloth and / or fiber web made of wave-transparent fibers. The hybrid fiber layer is a hybrid fiber mesh made of conductive fibers and wave-transparent fibers. The conductive fiber is made by carbonizing organic fiber at a temperature of 600-750℃, a heating rate of 1-10℃ / min, and a holding time of 1-3h. In the microwave absorbing region, the mass percentage of conductive fibers in the hybrid fiber layer along the electromagnetic wave incident direction increases by 5-10%. The organic fiber is selected from phenolic fiber, and the wave-transparent fiber is selected from quartz fiber; In the hybrid fiber layer, the areal density of the hybrid fiber web is 40-90 g / m². 2 ; The number of layers of the hybrid fiber layer in the absorbing region is ≥3; In the hybrid fiber layer, the mass percentage of conductive fibers is 10-40%. The thickness of the insulation zone is 10-15mm; In the microwave absorbing region, the thickness of the hybrid fiber layer is 2-5 mm, and the thickness of the transition layer is 1-5 mm; the bulk density of the transition layer is 0.2-0.6 g / cm³. 3 The bulk density of the heat insulation zone is 0.2-0.4 g / cm³. 3 ; In the composite material, the resin matrix accounts for 50-70 wt% of the composite material. The average pore size of the resin matrix is ​​20-70 nm.

2. A method for preparing the wave-absorbing and heat-insulating composite material based on impedance gradient structure as described in claim 1, characterized in that, include: S1. Under a protective atmosphere, organic fibers are carbonized at high temperature to obtain conductive fibers; S2. The conductive fiber and the wave-transparent fiber are mixed evenly to obtain a hybrid fiber layer; S3. The heat insulation zone and the wave absorption zone are sequentially stacked along the electromagnetic wave incident direction. The wave absorption zone includes a mixed fiber layer and a transition layer that are spaced apart to obtain a composite fiber layer. S4. The composite fiber layer is made into a fiber preform by needle punching, vacuum impregnated with a resin matrix, and then cured and molded. The conditions for high-temperature carbonization include: carbonization temperature of 600-750℃, heating rate of 1-10℃ / min, and holding time of 1-3h. The transition layer is a wave-transparent fiber layer, the mixed-woven fiber layer is a mixed-woven fiber mesh made of conductive fibers and wave-transparent fibers, and the heat insulation zone is a fiber cloth and / or fiber mesh made of wave-transparent fibers.

3. The method according to claim 2, characterized in that, In step S4, the vacuum degree during vacuum impregnation is -0.08 to -0.1 MPa; And / or, the curing conditions include: a curing temperature of 120-180℃ and a curing time of 12-24h.

4. The application of the composite material described in claim 1 in integrated electromagnetic protection and thermal insulation.

Images