Wave-transparent stealth composite material frequency selection cover and forming method thereof

Abstract

The invention relates to the technical field of wave-transparent stealth composite materials, and discloses a wave-transparent stealth composite material frequency selection cover which is of a three-layer structure and comprises an outer layer, a middle layer and an inner layer, the outer layer is a wave-absorbing frequency selection layer and made of a carbon fiber wave-absorbing composite material, a frequency selection wave-transparent array structure is designed according to an equivalent circuit method, the middle layer is a wave-transparent medium layer, and the inner layer is made of a carbon fiber wave-absorbing composite material. The inner layer is a wave-transparent frequency selection layer, is a metal layer, and is provided with a frequency selection wave-transparent array structure consistent with the outer layer. The invention further discloses a forming method of the wave-transparent stealth composite material frequency selection cover. According to the wave-transparent stealth composite material frequency selection cover and the forming method thereof, the frequency selection cover not only has a selective wave-transparent function, but also has a broadband wave-absorbing function, and meanwhile has the characteristics of high temperature resistance and heat insulation.

Description

Technical Field

[0001] The present invention relates to the technical field of wave-transmitting stealth composite materials, and in particular to a wave-transmitting stealth composite material frequency-selective cover and a molding method thereof. Background Art

[0002] Frequency selective surface (FSS) is a functional surface that allows electromagnetic waves to selectively transmit according to frequency. It can effectively reduce the radar scattering surface (RCS) and improve the stealth performance of the aircraft.

[0003] The frequency selective cover achieves the purpose of stealth by realizing "in-band transmission and out-band reflection" through a frequency selective layer with a frequency selective surface. However, this frequency selective cover is only effective for a single radar station. If there are multiple radar stations, the stealth effect will be lost.

[0004] Therefore, it is necessary to add impedance technology to form a frequency selective radar absorber (FSR). Different from FSS, FSR can not only transmit in-band working signals, but also absorb out-of-band incident waves, thereby achieving multi-station RCS reduction. It has the functions of "in-band transmission and out-of-band absorption", achieving the purpose of frequency selective transmission and wave absorbing stealth. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies of the above-mentioned technology and provide a wave-transmitting stealth composite material frequency-selective cover and a molding method thereof. The frequency-selective cover not only has the function of selective wave transmission, but also has the function of broadband wave absorption, and at the same time has the characteristics of high temperature resistance and heat insulation.

[0006] To achieve the above-mentioned purpose, the wave-transmitting stealth composite material frequency-selective cover designed by the present invention has a three-layer structure, including an outer layer, a middle layer and an inner layer. The outer layer is a wave-absorbing frequency-selective layer, which is a carbon fiber wave-absorbing composite material, and is designed with a frequency-selective wave-transmitting array structure according to the equivalent circuit method. The middle layer is a wave-transmitting medium layer, which is a high-porosity fiber-reinforced aerogel material. The inner layer is a wave-transmitting frequency-selective layer, which is a metal layer, and is provided with a frequency-selective wave-transmitting array structure consistent with the outer layer.

[0007] Preferably, the wave-transmitting frequency band is 11 GHz to 12 GHz, and the wave-absorbing and stealth frequency band is 5 GHz to 11 GHz and 12 GHz to 18 GHz.

[0008] Preferably, the thickness of the outer layer is ≥2mm, the thickness of the middle layer is 5mm-10mm, which is determined by the wave transmission frequency, thermal insulation requirements, and material strength, and the thickness of the inner layer is 0.06mm-0.08mm, which is determined by the spray molding process and is determined based on the wave transmission frequency and the wave absorption band frequency.

[0009] Preferably, the thickness of the outer layer is 2.5 mm to 3.5 mm, which is determined according to the wave absorbing characteristics and wave absorbing frequency of the outer layer material to ensure that the wave absorbing loss reaches more than 10 dB.

[0010] Preferably, the surface of the outer layer is engraved with a frequency-selective wave-transmitting array structure, and the array unit structure is a regular hexagon. The structure is designed according to the wave-transmitting frequency band. The unit size of the frequency-selective wave-transmitting array structure on the inner layer is proportionally reduced relative to the frequency-selective wave-transmitting array structure on the surface of the outer layer, and is aligned with the frequency-selective wave-transmitting array structure of the outer layer. This structure can shift the wave-transmitting frequency up and down by adjusting the size of the frequency-selective wave-transmitting array structure.

[0011] Preferably, the bonding strength between the outer layer, the middle layer and the inner layer is not less than 0.5 MPa.

[0012] A method for forming a wave-transmitting stealth composite material frequency-selective cover, comprising the preparation of a wave-transmitting medium layer, a wave-absorbing frequency-selective layer and a wave-transmitting frequency-selective layer:

[0013] Preparation of the wave-transmitting medium layer: using quartz fiber reinforced aerogel composite material as the base material, laying a layer of 0.1 mm thick quartz fiber plain cloth sleeve on the inner and outer surfaces respectively, and placing it on the profiling core mold, placing it in a high-purity silica sol with a solid content of 25%, vacuum impregnating it for 2 to 3 hours, taking it out and drying it at 80 to 100°C for 6 to 10 hours, demolding it, placing it in a sintering furnace, sintering it at 600 to 700°C for 1.5 to 2 hours, polishing it with aluminum oxide sandpaper with a mesh size of 120 or more, and adsorbing or blowing off the dust on the inner and outer surfaces to obtain the wave-transmitting medium layer;

[0014] Preparation of the wave-absorbing frequency selection layer: using the wave-transmitting medium layer as the inner mold, first lay a layer of pre-treated contoured carbon fiber epoxy prepreg felt, then lay a layer of contoured carbon fiber epoxy prepreg cloth, alternately lay the layers to the required thickness, put in a vacuum bag, evacuate, and control the vacuum degree at -0.05MPa to -0.07MPa, then put it into a blast drying oven for curing, step-by-step heating at 2℃ / min to 4℃ / min to 150℃ to 160℃ for curing for 6h to 8h, take it out and demould it, and then use milling to process the wave-absorbing frequency selection layer according to the designed groove structure, and process the end face flush according to the size to obtain the wave-absorbing frequency selection layer;

[0015] Preparation of the wave-transmitting frequency-selective layer: a layer of silicone resin coating is made on the inner surface of the wave-transmitting medium layer, and then the surface of the silicone resin coating is subjected to plasma activation treatment to improve the surface energy and increase the adhesion with the metal layer, and then the frequency-selective wave-transmitting array structure metal layer is spray-formed on the surface according to the design structure, and then a layer of resin is coated on the surface of the metal layer to form a wave-transmitting frequency-selective layer.

[0016] Preferably, during the preparation of the wave-transmitting medium layer, the density of the quartz fiber reinforced aerogel composite material is 0.3 to 0.4 g / cm 3 , the dielectric constant is 1.3-1.4, and the density after impregnation is controlled at 0.5-0.6g / cm 3The dielectric constant is between 1.5 and 1.6, and the thermal conductivity is ≤0.07W / m·k. The hydrophobic treatment of the wave-transmitting medium layer adopts a liquid phase method, and the wave-transmitting medium layer is immersed in a 1:1 solution of trifluoropropylmethyldichlorosilane and n-hexane for 50 to 60 minutes. The container needs to be sealed during the immersion process to prevent moisture from entering. After taking it out, it is naturally left to evaporate for 1 to 2 hours. The hydrophobic treatment process needs to be carried out in an environment of 10°C to 35°C. The wave-transmitting medium layer adopts low dielectric materials to effectively improve the transmittance of the wave-transmitting frequency band, and at the same time has high thermal insulation and high temperature resistance.

[0017] Preferably, in the preparation process of the wave absorbing frequency selection layer, when the wave absorbing frequency selection layer is processed, the wave-transmitting medium layer needs to be leaked out of the bottom of the processing groove of the frequency-selective wave-transmitting array structure, and there is no residual carbon layer, and the outer surface of the processing groove needs to be processed around the R angle, the size of which is R0.8 to R1.2, which can effectively reduce the wave transmission interference. The carbon fiber epoxy prepreg cloth and the carbon fiber epoxy prepreg felt use 1.5% manganese dioxide, 4% carbon black, and 1.8% mesoporous carbon as a composite wave absorbing enhancer, and the mesoporous size of the mesoporous carbon is 34nm. The composite wave absorbing enhancer is first dispersed in an acetone solvent, and then ultrasonically dispersed evenly, and then two parts of type A epoxy resin are added, and then the carbon fiber cloth and carbon fiber felt are impregnated respectively to form a carbon fiber epoxy prepreg cloth and a carbon fiber epoxy prepreg felt, which are cut according to the cone size fan-shaped expansion diagram, and then can be laid on the cone product in a contoured manner. The carbon fiber epoxy prepreg cloth uses 1K carbon fiber cloth with a plain weave structure and a fiber cloth spacing of 2.2mm. The carbon fiber epoxy prepreg felt uses a surface density of 115g / m 2 .

[0018] Preferably, during the preparation of the wave-transmitting frequency-selective layer, a silicone resin coating is applied to the inner surface of the wave-transmitting medium layer with a thickness of 20 to 30 microns to improve the apparent quality and adhesion to the metal layer. The metal layer is an inert metal, including copper, silver or gold. A frequency-selective wave-transmitting array structure metal layer is spray-formed on the surface according to the design structure, and then a layer of resin is coated on the surface of the metal layer to form a wave-transmitting frequency-selective layer. The thickness of a single spray layer is 0.02 mm. After 3 to 4 layers are sprayed, the total thickness reaches 0.06 mm to 0.08 mm to ensure the continuity of the wave-transmitting frequency-selective layer. The spray-forming accuracy of the wave-transmitting frequency-selective layer is 50 microns. The silicone resin coated on the surface is methyl silicone resin with a silicon oxide content of 50 to 55%. KH550 is used as a curing agent. The curing temperature is room temperature for 48 hours and the coating thickness is 15 to 20 microns.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. It has the function of "in-band wave transmission and out-band absorption", effectively reducing the RCS of the aircraft and achieving the purpose of frequency-selective wave transmission and wave absorption stealth;

[0021] 2. It provides a 5GHz to 18GHz ultra-wideband wave-absorbing stealth frequency-selective structure and a frequency-selective cover forming method. The frequency-selective wave transmission can adjust the wave transmission frequency up and down by adjusting the size of the frequency-selective wave transmission array structure;

[0022] 3. The wave-transmitting medium layer adopts low-dielectric electric gel material, which effectively improves the wave transmittance of the wave-transmitting frequency band, and at the same time has high thermal insulation and high temperature resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic structural diagram of the wave-transmitting stealth composite material frequency-selective cover of the present invention;

[0024] Figure 2 It is a schematic diagram of the frequency selective wave-transmitting stealth structure in the frequency selective cover of the wave-transmitting stealth composite material of the present invention;

[0025] Figure 3 It is a schematic diagram of the frequency selective wave-transmitting array structure in the wave-transmitting stealth composite material frequency selective cover of the present invention. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0028] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] like Figure 1 and Figure 2As shown, a wave-transmitting stealth composite material frequency-selective cover has a three-layer structure, including an outer layer, a middle layer and an inner layer. The outer layer is a wave-absorbing frequency-selective layer, which is a carbon fiber wave-absorbing composite material and is designed with a frequency-selective wave-transmitting array structure according to an equivalent circuit method. The middle layer is a wave-transmitting medium layer, which is a high-porosity fiber-reinforced aerogel material. The inner layer is a wave-transmitting frequency-selective layer, which is a metal layer and is provided with a frequency-selective wave-transmitting array structure consistent with the outer layer.

[0030] Specifically, the wave transmission frequency band is 11GHz~12GHz, the wave absorbing stealth frequency band is 5GHz~11GHz and 12GHz~18GHz, the thickness of the outer layer is ≥2mm, preferably 2.5mm~3.5mm, which is determined according to the wave absorbing characteristics and wave absorbing frequency of the outer layer material to ensure that the wave absorbing loss reaches more than 10dB, the thickness of the middle layer is 5mm~10mm, which is determined by the wave transmission frequency, thermal insulation requirements and material strength, and the thickness of the inner layer is 0.06mm~0.08mm, which is determined by the spray molding process and is determined according to the wave transmission frequency and the wave absorbing band frequency.

[0031] At the same time, the surface of the outer layer is engraved with a frequency-selective wave-transmitting array structure, and the array unit structure is a regular hexagon. This structure is designed according to the wave transmission frequency band. The unit size of the frequency-selective wave-transmitting array structure on the inner layer is proportionally reduced relative to the frequency-selective wave-transmitting array structure on the outer layer surface, and is aligned with the frequency-selective wave-transmitting array structure of the outer layer. This structure can shift the wave transmission frequency up and down by adjusting the size of the frequency-selective wave-transmitting array structure, such as Figure 3 As shown, in the regular hexagonal structure, a is the frequency selective wave transmission array structure on the outer surface, and b is the frequency selective wave transmission array structure on the inner layer. In this embodiment, the side length a=2.86mm, b=2.71mm, and the line width c=0.1mm.

[0032] Finally, in this embodiment, the bonding strength between the outer layer, the middle layer and the inner layer is not less than 0.5 MPa.

[0033] A method for forming a wave-transmitting stealth composite material frequency-selective cover, comprising the preparation of a wave-transmitting medium layer, a wave-absorbing frequency-selective layer and a wave-transmitting frequency-selective layer:

[0034] Preparation of the wave-transmitting medium layer: using quartz fiber reinforced aerogel composite material as the base material, laying a layer of 0.1 mm thick quartz fiber plain cloth sleeve on the inner and outer surfaces respectively, and placing it on the profiling core mold, placing it in a high-purity silica sol with a solid content of 25%, vacuum impregnating it for 2 to 3 hours, taking it out and drying it at 80 to 100°C for 6 to 10 hours, demolding it, placing it in a sintering furnace, sintering it at 600 to 700°C for 1.5 to 2 hours, polishing it with aluminum oxide sandpaper with a mesh size of 120 or more, and adsorbing or blowing off the dust on the inner and outer surfaces to obtain the wave-transmitting medium layer;

[0035] Preparation of the wave-absorbing frequency selection layer: using the wave-transmitting medium layer as the inner mold, first lay a layer of pre-treated contoured carbon fiber epoxy prepreg felt, then lay a layer of contoured carbon fiber epoxy prepreg cloth, alternately lay the layers to the required thickness, put in a vacuum bag, evacuate, and control the vacuum degree at -0.05MPa to -0.07MPa, then put it into a blast drying oven for curing, put it into a blast drying oven, step-by-step increase of 2℃ / min to 4℃ / min to 150℃ to 160℃ for curing for 6h to 8h, take it out and demould it, use milling to process the wave-absorbing frequency selection layer according to the designed groove structure, and process the end face flush according to the size to obtain the wave-absorbing frequency selection layer;

[0036] Preparation of the wave-transmitting frequency-selective layer: a layer of silicone resin coating is made on the inner surface of the wave-transmitting medium layer, and then the surface of the silicone resin coating is subjected to plasma activation treatment to improve the surface energy and increase the adhesion with the metal layer, and then the frequency-selective wave-transmitting array structure metal layer is spray-formed on the surface according to the design structure, and then a layer of resin is coated on the surface of the metal layer to form a wave-transmitting frequency-selective layer.

[0037] In the process of preparing the wave-transmitting medium layer, the density of the quartz fiber reinforced aerogel composite material is 0.3-0.4 g / cm 3 , the dielectric constant is 1.3-1.4, and the density after impregnation is controlled at 0.5-0.6g / cm 3 The dielectric constant is between 1.5 and 1.6, and the thermal conductivity is ≤0.07W / m·k. The hydrophobic treatment of the wave-transmitting medium layer adopts a liquid phase method, and the wave-transmitting medium layer is immersed in a 1:1 solution of trifluoropropylmethyldichlorosilane and n-hexane for 50 to 60 minutes. The container needs to be sealed during the immersion process to prevent moisture from entering. After taking it out, it is naturally left to evaporate for 1 to 2 hours. The hydrophobic treatment process needs to be carried out in an environment of 10°C to 35°C. The wave-transmitting medium layer adopts low dielectric materials to effectively improve the transmittance of the wave-transmitting frequency band, and at the same time has high thermal insulation and high temperature resistance.

[0038] During the preparation of the wave-absorbing frequency-selective layer, when processing the wave-absorbing frequency-selective layer, the bottom of the processing groove of the frequency-selective wave-transmitting array structure needs to leak out the wave-transmitting medium layer, without any residual carbon layer, combined with Figure 2As shown, the outer surface of the processing groove needs to be processed around the R angle, the size of which is R0.8~R1.2. The carbon fiber epoxy prepreg cloth and carbon fiber epoxy prepreg felt use 1.5% manganese dioxide, 4% carbon black, and 1.8% mesoporous carbon as composite wave absorbing enhancers by mass fraction. The mesoporous carbon has a mesopore size of 34nm. The composite wave absorbing enhancer is first dispersed in acetone solvent and evenly dispersed by ultrasonic dispersion, and then double A-type epoxy resin is added. Then, the carbon fiber cloth and carbon fiber felt are impregnated respectively to form carbon fiber epoxy prepreg cloth and carbon fiber epoxy prepreg felt. They are cut according to the cone size fan-shaped expansion diagram, and then can be laid on the cone product in a contoured manner. The carbon fiber epoxy prepreg cloth uses 1K carbon fiber cloth with a plain weave structure and a fiber cloth spacing of 2.2mm. The carbon fiber epoxy prepreg felt uses a surface density of 115g / m 2 .

[0039] During the preparation of the wave-transmitting frequency-selective layer, a silicone resin coating with a thickness of 20 to 30 microns is applied to the inner surface of the wave-transmitting medium layer to improve the surface quality and adhesion to the metal layer. The metal layer is an inert metal, including copper, silver or gold. A frequency-selective wave-transmitting array structure metal layer is spray-formed on the surface according to the design structure, and then a layer of resin is coated on the surface of the metal layer to form a wave-transmitting frequency-selective layer. The thickness of a single spray layer is 0.02 mm. After 3 to 4 layers are sprayed, the total thickness reaches 0.06 mm to 0.08 mm to ensure the continuity of the wave-transmitting frequency-selective layer. The spray-forming accuracy of the wave-transmitting frequency-selective layer is 50 microns. The silicone resin coated on the surface is methyl silicone resin with a silicon oxide content of 50 to 55%. KH550 is used as a curing agent. The curing temperature is room temperature for 48 hours and the coating thickness is 15 to 20 microns.

[0040] The wave-transmitting stealth composite material frequency-selective cover and the molding method thereof of the present invention have the functions of "wave transmission in the band and absorption outside the band", effectively reduce the RCS of the aircraft, and achieve the purpose of frequency-selective wave transmission and wave-absorbing stealth; provide a 5GHz to 18GHz ultra-wideband wave-absorbing stealth frequency-selective structure and a frequency-selective cover molding method; the frequency-selective wave transmission can adjust the wave transmission frequency up and down by adjusting the structural size of the frequency-selective wave transmission array; the wave-transmitting medium layer adopts a low-dielectric electric gel material, which effectively improves the wave transmittance of the wave-transmitting frequency band, and at the same time has high thermal insulation performance and high temperature resistance.

[0041] It should be noted that the description of the above technical solutions is exemplary, and this specification can be embodied in different forms and should not be interpreted as being limited to the technical solutions set forth herein. On the contrary, providing these descriptions will make the disclosure of the present invention thorough and complete, and will fully convey the scope disclosed in this specification to those skilled in the art. In addition, the technical solutions of the present invention are limited only by the scope of the claims.

[0042] The various aspects disclosed for describing the present specification and claims are merely examples, and therefore, the present specification and claims are not limited to the details shown. In the above description, when the detailed description of the related known functions or configurations is determined to be unnecessary to obscure the focus of the present specification and claims, the detailed description will be omitted.

[0043] In the case of using “including”, “having” and “comprising” described in the present specification, unless otherwise used, there may also be another part or other parts, and the terms used may generally be in the singular but may also represent the plural form.

[0044] Finally, it should be pointed out that the above content is a further detailed description of the invention in combination with specific implementation methods. It cannot be considered that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, simple replacements made without departing from the concept of the present invention should be regarded as belonging to the protection scope of the present invention. The above embodiments are only more representative examples of the present invention. Obviously, the present invention is not limited to the above embodiments, and there can be many variations. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention should be considered to belong to the protection scope of the present invention.

[0045] At the same time, it should be noted that the description of the above technical solutions is exemplary, and this specification can be embodied in different forms and should not be construed as being limited to the technical solutions set forth herein. On the contrary, providing these descriptions will make the disclosure of the present invention thorough and complete, and will fully convey the scope disclosed in this specification to those skilled in the art. In addition, the technical solutions of the present invention are limited only by the scope of the claims. The features of the various embodiments of the present invention may be partially or completely combined or spliced ​​with each other, and may be performed in various different configurations as those skilled in the art may fully understand. The embodiments of the present invention may be performed independently of each other, or may be performed together in a mutually dependent relationship.

[0046] For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, and the above structures should be regarded as belonging to the protection scope of the present invention.

Claims

1. A wave-transmitting stealth composite material frequency-selective cover, characterized in that: It is a three-layer structure, including an outer layer, a middle layer and an inner layer. The outer layer is a wave-absorbing frequency-selective layer, which is a carbon fiber wave-absorbing composite material. A frequency-selective wave-transmitting array structure is designed according to the equivalent circuit method. The middle layer is a wave-transmitting medium layer, which is a high-porosity fiber-reinforced aerogel material. The inner layer is a wave-transmitting frequency-selective layer, which is a metal layer and is provided with a frequency-selective wave-transmitting array structure consistent with the outer layer.

2. The wave-transmitting stealth composite material frequency-selective cover according to claim 1, characterized in that: The wave-transmitting frequency band is 11GHz~12GHz, and the wave-absorbing and stealth frequency band is 5GHz~11GHz and 12GHz~18GHz.

3. The wave-transmitting stealth composite material frequency-selective cover according to claim 1, characterized in that: The thickness of the outer layer is ≥2 mm, the thickness of the middle layer is 5 mm to 10 mm, and the thickness of the inner layer is 0.06 mm to 0.08 mm.

4. The wave-transmitting stealth composite material frequency-selective cover according to claim 1, characterized in that: The thickness of the outer layer is 2.5 mm to 3.5 mm.

5. The wave-transmitting stealth composite material frequency-selective cover according to claim 1, characterized in that: The surface of the outer layer is engraved with a frequency-selective wave-transmitting array structure, and the array unit structure is a regular hexagon. The unit size of the frequency-selective wave-transmitting array structure on the inner layer is proportionally reduced relative to the frequency-selective wave-transmitting array structure on the surface of the outer layer, and is aligned with the frequency-selective wave-transmitting array structure of the outer layer.

6. The wave-transmitting stealth composite material frequency-selective cover according to claim 1, characterized in that: The bonding strength between the outer layer, the middle layer and the inner layer is not less than 0.5 MPa.

7. A method for forming a wave-transmitting stealth composite material frequency-selective cover according to any one of claims 1 to 6, characterized in that: Including the preparation of the wave-transmitting medium layer, the wave-absorbing frequency-selective layer and the wave-transmitting frequency-selective layer: Preparation of the wave-transmitting medium layer: using quartz fiber reinforced aerogel composite material as the base material, laying a layer of 0.1 mm thick quartz fiber plain cloth sleeve on the inner and outer surfaces respectively, and placing it on the profiling core mold, placing it in a high-purity silica sol with a solid content of 25%, vacuum impregnating it for 2 to 3 hours, taking it out and drying it at 80 to 100°C for 6 to 10 hours, demolding it, placing it in a sintering furnace, sintering it at 600 to 700°C for 1.5 to 2 hours, polishing it with aluminum oxide sandpaper with a mesh size of 120 or more, and adsorbing or blowing off the dust on the inner and outer surfaces to obtain the wave-transmitting medium layer; Preparation of the wave-absorbing frequency selection layer: using the wave-transmitting medium layer as the inner mold, first lay a layer of pre-treated contoured carbon fiber epoxy prepreg felt, then lay a layer of contoured carbon fiber epoxy prepreg cloth, alternately lay the layers to the required thickness, put in a vacuum bag, evacuate, and control the vacuum degree at -0.05MPa to -0.07MPa, then put it into a blast drying oven for curing, put it into a blast drying oven, step-by-step increase of 2℃ / min to 4℃ / min to 150℃ to 160℃ for curing for 6h to 8h, take it out and demould it, use milling to process the wave-absorbing frequency selection layer according to the designed groove structure, and process the end face flush according to the size to obtain the wave-absorbing frequency selection layer; Preparation of the wave-transmitting frequency-selective layer: a layer of silicone resin coating is made on the inner surface of the wave-transmitting medium layer, and then the surface of the silicone resin coating is subjected to plasma activation treatment, and then a frequency-selective wave-transmitting array structure metal layer is spray-formed on the surface according to the design structure, and then a layer of resin is coated on the surface of the metal layer to form a wave-transmitting frequency-selective layer.

8. The method for forming a wave-transmitting stealth composite material frequency-selective cover according to claim 7, characterized in that: During the preparation of the wave-transmitting medium layer, the density of the quartz fiber reinforced aerogel composite material is 0.3-0.4 g / cm 3 , the dielectric constant is 1.3-1.4, and the density after impregnation is controlled at 0.5-0.6g / cm 3 The dielectric constant is between 1.5 and 1.6, and the thermal conductivity is ≤0.07W / m·k. The hydrophobic treatment of the wave-transmitting medium layer adopts a liquid phase method. The wave-transmitting medium layer is immersed in a 1:1 solution of trifluoropropylmethyldichlorosilane and n-hexane for 50 to 60 minutes. The container needs to be sealed during the immersion process to prevent moisture from entering. After taking it out, it is naturally left to evaporate for 1 to 2 hours. The hydrophobic treatment process needs to be carried out in an environment of 10℃ to 35℃.

9. The method for forming a wave-transmitting stealth composite material frequency-selective cover according to claim 7, characterized in that: In the preparation process of the wave-absorbing frequency-selective layer, when the wave-absorbing frequency-selective layer is processed, the wave-transmitting medium layer needs to be leaked out of the bottom of the processing groove of the frequency-selective wave-transmitting array structure, and there is no residual carbon layer, and the outer surface of the processing groove needs to be processed around the R angle, with a size of R0.8 to R1.

2. The carbon fiber epoxy prepreg cloth and the carbon fiber epoxy prepreg felt use 1.5% manganese dioxide, 4% carbon black, and 1.8% mesoporous carbon as composite wave-absorbing enhancers by mass fraction. The mesoporous carbon has a mesopore size of 34nm. The composite wave-absorbing enhancer is first dispersed in an acetone solvent, and then ultrasonically dispersed evenly, and then double A-type epoxy resin is added. Then, the carbon fiber cloth and the carbon fiber felt are impregnated respectively to form a carbon fiber epoxy prepreg cloth and a carbon fiber epoxy prepreg felt. They are cut according to the cone size fan-shaped expansion diagram, and then can be laid on the cone product in a contoured manner. The carbon fiber epoxy prepreg cloth uses 1K carbon fiber cloth with a plain weave structure and a fiber cloth spacing of 2.2mm. The carbon fiber epoxy prepreg felt uses a surface density of 115g / m 2 .

10. The method for forming a wave-transmitting stealth composite material frequency-selective cover according to claim 7, characterized in that: During the preparation process of the wave-transmitting frequency-selective layer, a silicone resin coating with a thickness of 20 to 30 microns is applied to the inner surface of the wave-transmitting medium layer. The metal layer is an inert metal, including copper, silver or gold. The frequency-selective wave-transmitting array structure metal layer is spray-formed on the surface according to the design structure, and then a layer of resin is coated on the surface of the metal layer to form a wave-transmitting frequency-selective layer. The thickness of a single spray layer is 0.02 mm. After 3 to 4 layers are sprayed, the total thickness reaches 0.06 mm to 0.08 mm. The spray-forming accuracy of the wave-transmitting frequency-selective layer is 50 microns. The silicone resin coated on the surface is methyl silicone resin with a silicon oxide content of 50 to 55%. KH550 is used as a curing agent. The curing temperature is room temperature for 48 hours and the coating thickness is 15 to 20 microns.

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