Double-sided wave-absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth and preparation method thereof

Abstract

The invention discloses a double-sided wave-absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth and a preparation method thereof, and belongs to the technical field of stealth materials. According to the double-sided wave-absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth, on the premise that the strength of the continuous fiber alumina fiber reinforced alumina composite material is guaranteed, the relative dielectric constant of a composite material body is reduced by controlling the porosity (the density of the composite material); and the frequency selective surface layer and the resistance type metamaterial layer are arranged, so that the thin double-sided wave-absorbing continuous fiber alumina fiber reinforced alumina composite material is obtained, and meanwhile, the material has relatively low infrared emissivity.

Description

Technical Field

[0001] This invention belongs to the field of stealth materials technology, and relates to a double-sided wave-absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth and its preparation method. Background Technology

[0002] For stealth aircraft, tail-end stealth is a design challenge. The engine nozzles at the tail of the aircraft are typical cavity structures, which strongly backscatter radar waves; they are also high-temperature components with strong infrared radiation. Stealth aircraft engines urgently require radar-absorbing materials that are compatible with infrared radiation.

[0003] Radar waves enter the engine cavity from the exhaust nozzle and are subjected to complex scattering by various components such as the cavity walls, turbine blades, exhaust nozzle trimmers, fairing cones, and mixers. These waves strike the front and back of certain components from multiple directions, necessitating double-sided absorbing materials used in the cavity. Furthermore, due to the high-temperature environment within the engine cavity, these double-sided absorbing materials also require high-temperature resistance and low infrared emissivity.

[0004] In addition, double-sided radar-absorbing stealth composite materials compatible with infrared stealth can also be used in the wings of high-speed aircraft. While withstanding the high temperatures caused by aerodynamic heating, they absorb radar waves on both sides and have low infrared emissivity and low infrared radiation intensity.

[0005] Chinese patent application CN120943643A discloses the design and preparation method of a high-temperature resistant microwave absorbing material based on alumina fibers. This material uses a high-temperature resistant ceramic precursor as the matrix, and the reinforcing phase consists of alternating layers of alumina fiber cloth and an alumina fiber mesh containing short-cut silicon carbide fibers, forming a three-dimensional reinforcing structure through a needle-punching process. The short-cut silicon carbide fibers are non-uniformly distributed within the mesh, constructing an array of reinforcing regions with locally geometrically regular patterns. The size and arrangement period vary gradient along the thickness direction, forming a vertically intermediate gradient structure within the material, improving the multipath propagation, reflection, and polarization loss of electromagnetic waves. However, the microwave absorbing material prepared by this patent cannot achieve double-sided absorption and is not compatible with infrared stealth. Furthermore, the short-cut silicon carbide fibers with microwave absorbing properties are generally carbon-rich, and their absorption performance will decrease after long-term use in a high-temperature, oxygen-rich environment. The microwave absorbing material prepared by this patent has a thickness of 4 mm.

[0006] Chinese patent application CN121688422A discloses a double-sided microwave-absorbing broadband stealth composite material and its preparation method. This double-sided microwave-absorbing broadband stealth composite material includes a non-metallic matrix composite body and five metamaterial layers spaced apart along the thickness direction of the non-metallic matrix composite body. An intermediate metamaterial layer is positioned at the middle of the thickness direction, and inner and outer metamaterial layers are symmetrically arranged sequentially from the intermediate metamaterial layer to both sides. However, this material uses a resin-based composite material as its body, resulting in a large thickness, making it difficult to withstand temperatures above 300°C, and it is incompatible with infrared stealth performance.

[0007] Chinese patent document CN106427115A discloses a high-temperature radar-infrared compatible stealth material based on a double-layer metamaterial. This material has a layered structure, comprising, from the inside out, a dielectric layer I, a resistive high-temperature metamaterial layer, a dielectric layer II, a modification layer, and a frequency-selective surface layer. Both dielectric layers I and II are oxide fiber-reinforced oxide-based composite materials. However, this material is not a double-sided absorbing design and is unsuitable for scenarios requiring double-sided absorption. The use of continuous aluminosilicate fibers as reinforcement results in low strength; typically, the room temperature tensile strength of continuous aluminosilicate fibers is approximately 1.0~1.7 GPa, and the tensile strength of mullite aluminosilicate fibers is around 2.0 GPa, with a strength retention rate of less than 60% at 1200℃. In contrast, high-purity alumina fibers have a tensile strength of 2.5~3.5 GPa and a strength retention rate greater than 90% at 1200℃. The use of high-purity alumina fibers requires overcoming the problem of their high dielectric constant affecting absorption performance, especially when using continuous alumina fiber-reinforced alumina as the matrix.

[0008] Chinese patent document CN106007799A discloses a radar and infrared compatible stealth material based on a dual-layer frequency selective surface. This material has a layered structure, consisting of a dielectric substrate layer, a resistive-capacitive frequency selective surface layer, an intermediate dielectric layer, and a metallic capacitive frequency selective surface layer, from the inside out. However, this material is not a double-sided absorbing design and is unsuitable for scenarios requiring double-sided absorbing capabilities. Using mullite fiber-reinforced mullite as the substrate results in low strength, with a tensile strength generally not exceeding 50 MPa. When using alumina fiber-reinforced alumina as the dielectric substrate layer, lithium aluminum silicon glass is selected as the intermediate dielectric layer. While lithium aluminum silicon glass has a relatively low dielectric constant, it is not resistant to high temperatures, with a heat distortion temperature not exceeding 500°C.

[0009] The existing literature (A polarization-insensitive and bifacially absorbing chiral metamaterial absorber, Acta Physica Sinica, 2011) introduces a polarization-insensitive and bifacially absorbing metamaterial absorber. The structural unit of this absorber consists of a chiral structure and a dielectric substrate. The absorber disclosed in this literature has a narrow absorption bandwidth (with two absorption peaks at 5.83 GHz and 8.19 GHz with absorption rates of 95.9% and 29.9%, respectively), is not compatible with infrared stealth, and the fabrication of the three-dimensional periodic structure is also difficult.

[0010] Therefore, developing a structural absorbing material that is resistant to high temperatures for a long time, is very thin, and has double-sided wave absorption can meet the material requirements of components such as aero engines and missile wings. Summary of the Invention

[0011] To address the lack of long-term high-temperature resistant, thin, and double-sided absorbing structural absorbing materials in existing technologies, this invention provides a double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth and its preparation method. It is also a continuous alumina fiber reinforced alumina structural stealth material with low infrared emissivity, thin thickness, and double-sided absorbing properties, mainly used in applications such as components inside cavities and projectile wings.

[0012] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: The objective of this invention is achieved through the following technical solution: A double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth includes a body, a first frequency selective surface layer, a second frequency selective surface layer, and an intermediate metamaterial layer. The matrix is ​​a continuous alumina fiber reinforced alumina ceramic matrix composite material with a density of 2.8 g / cm³. 3 ~3.0g / cm 3 The real part of the relative permittivity is 6.8~7.2; The first frequency selective surface layer and the second frequency selective surface layer are respectively disposed on the front and back sides of the body, and are discontinuous conductive layers composed of periodically arranged conductive units; wherein, the periodic pattern of the conductive units is a periodically arranged conductive square, the sheet resistance of the conductive squares of the first frequency selective surface layer and the second frequency selective surface layer is ≤1Ω / □, the period size is ≤3mm, and the ratio of the side length of the conductive square to the period size is 0.75~0.95; The intermediate metamaterial layer is located at the middle position in the thickness direction of the body, and the first outer metamaterial layer and the second outer metamaterial layer are symmetrically arranged from the intermediate metamaterial layer to both sides; all metamaterial layers are periodically arranged square conductive pattern units with different structural parameters and / or sheet resistance, the sheet resistance of the square conductive pattern units of the metamaterial layers is 5Ω / □~100Ω / □, and the side length of the square is 1mm~20mm; The infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material does not contain a continuously conductive metal reflective layer, and its total thickness is ≤3.1mm.

[0013] The continuous alumina fiber reinforced alumina ceramic matrix composite material (Al2O3f / Al2O3) of the present invention is an oxide ceramic matrix composite material with continuous alumina fiber as the reinforcing phase and alumina ceramic as the matrix. Its core advantages are high temperature resistance, oxidation resistance, high toughness, and low density. It is a key structural material in high temperature and oxygen environment and is very suitable for making the body of high temperature resistant and infrared stealth compatible double-sided microwave absorbing material, providing load-bearing and temperature resistance characteristics.

[0014] The first frequency selective surface layer and the second frequency selective surface layer of the present invention are discontinuous conductive layers composed of periodically arranged conductive units. By introducing the frequency selective surface layer, the infrared emissivity can be further reduced without affecting the absorption performance.

[0015] The present invention relates to a double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth. While ensuring the strength of the continuous alumina fiber reinforced alumina composite material, the relative permittivity of the composite material body is reduced by controlling the density of the composite material. Furthermore, by setting a frequency-selective surface layer and a resistive metamaterial layer, a very thin double-sided absorbing continuous fiber alumina fiber reinforced alumina composite material is obtained, while the material has a low infrared emissivity.

[0016] Furthermore, the first frequency selective surface layer and the second frequency selective surface layer are formed by printing and sintering a paste made of high-temperature resistant precious metal powder and glass powder, and the thickness of the first frequency selective surface layer and the second frequency selective surface layer is 5μm to 20μm.

[0017] Furthermore, the high-temperature resistant precious metal powder is at least one of silver, gold, platinum, and palladium, and the mass ratio of the high-temperature resistant precious metal powder to glass powder is 10~30:1; the infrared emissivity of the material surface with the first frequency selective surface layer and the second frequency selective surface layer is ≤0.3 in the 3μm~5μm band. The first and second frequency selective surface layers reduce radiation intensity to achieve infrared stealth, while simultaneously transmitting radar waves of 1 GHz~18 GHz, allowing radar waves to enter the material interior, where they are dissipated by the main body and all metamaterial layers in a coordinated manner, thus compatibility with radar absorption performance.

[0018] Furthermore, the thickness of the intermediate metamaterial layer is 5μm~20μm; the conductive pattern unit of the intermediate metamaterial layer is a periodically arranged discontinuous resistive blocks or a square ring structure with a central square hole; the sheet resistance of the resistive blocks is 20Ω / □~30Ω / □, the period size is 3mm~20mm, and the ratio of the side length of the resistive blocks to the period size is 0.5~0.95; the sheet resistance of the square ring structure is 5Ω / □~20Ω / □, the period size is 5mm~20mm, and the ratio of the side length of the central square hole in the square ring structure to the period size is 0.2~0.5; The thickness of the first and second metamaterial layers is 5μm to 20μm, the sheet resistance of their resistive blocks is 30Ω / □ to 60Ω / □, the period size is 3mm to 20mm, and each period contains 2 large resistive blocks and 2 small resistive blocks arranged interleaved with each other. The ratio of the side length of the large resistive blocks to the period size is 0.2 to 0.95, and the side length of the large resistive blocks is greater than the side length of the small resistive blocks.

[0019] Furthermore, a first inner metamaterial layer and a second inner metamaterial layer are respectively provided between the intermediate metamaterial layer and the first outer metamaterial layer and the second outer metamaterial layer. The intermediate metamaterial layer, the first inner metamaterial layer, the second inner metamaterial layer, the first outer metamaterial layer and the second outer metamaterial layer are distributed on different thicknesses within the body, and the vertical distance between adjacent metamaterial layers is ≥0.1mm. The thickness of the first inner metamaterial layer and the second inner metamaterial layer is 5μm~20μm, the sheet resistance of the resistor block is 30Ω / □~60Ω / □, the period size is 3mm~20mm, and the ratio of the side length of the resistor block to the period size is 0.2~0.95.

[0020] Furthermore, the intermediate metamaterial layer, the first inner metamaterial layer, the second inner metamaterial layer, the first outer metamaterial layer, and the second outer metamaterial layer are obtained by screen printing and sintering a slurry prepared from ruthenium dioxide and glass powder in a mass ratio of 0.5 to 5:1.

[0021] Furthermore, the infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material has a tensile strength >200 MPa, a radar wave absorption rate >50% in the 7.2 GHz to 18 GHz frequency band, and a radar wave absorption rate >75% in the 9.9 to 18 GHz frequency band.

[0022] Based on a general inventive concept, this invention also provides a method for preparing a double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth, comprising the following steps: S1. Prepare the resistive pastes for the intermediate metamaterial layer, the first inner metamaterial layer, the second inner metamaterial layer, the first outer metamaterial layer, and the second outer metamaterial layer; the conductive pastes for the first frequency selective surface layer and the second frequency selective surface layer; and the alumina paste. S2. Using screen printing technology, the resistive paste obtained in step S1 is used to print periodically arranged resistive blocks on a continuous alumina fiber fabric. After drying, the blocks are sintered to obtain a fabric containing an intermediate metamaterial layer, a first inner metamaterial layer, a second inner metamaterial layer, a first outer metamaterial layer, and a second outer metamaterial layer. S3. Continuous alumina fiber fabric is laid in the mold according to the designed thickness. The fabric containing the intermediate metamaterial layer, the first inner metamaterial layer, the second inner metamaterial layer, the first outer metamaterial layer and the second outer metamaterial layer obtained in step S2 is laid in the predetermined position. After the laying is completed, continuous alumina fiber is used for sewing to obtain the fiber preform. S4. The fiber preform obtained in step S3 is vacuum impregnated, pressurized, dried, and sintered using alumina slurry. This process of vacuum impregnation, pressurization, drying, and sintering is repeated until the density of the composite material reaches 2.8 g / cm³. 3 ~3.0 g / cm 3 After grinding and trimming, the composite material workpiece is obtained; S5. Using screen printing, conductive blocks arranged in a periodic pattern are printed on the front and back sides of the composite material workpiece obtained in step S4 using the conductive paste obtained in step S1. After drying, they are sintered to form a first frequency selective surface layer and a second frequency selective surface layer, thus obtaining the infrared stealth compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material.

[0023] Furthermore, the drying temperature is 140~160℃, and the drying time is 1~3h; the sintering temperature in step S2 is 800~1000℃, and the sintering time is 0.3~1h; the sintering temperature in step S4 is 1100~1200℃, and the sintering time is 0.5~2h; the sintering temperature in step S5 is 800~1000℃, and the sintering time is 0.3~1h.

[0024] Furthermore, during the vacuum impregnation process, the vacuum level is ≤-0.1MPa, the impregnation time is 2~12h, and the pressure is increased to a value of 0.1MPa or higher.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention provides a double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth. The continuous alumina fiber reinforced alumina composite material is used as the carrier body. A first frequency selective surface layer and a second frequency selective surface layer are printed on the front and back of the carrier body using a high-temperature resistant conductive / low emissivity paste. A multi-layer metamaterial layer is printed using a high-temperature resistant ruthenium oxide / glass powder resistive paste. The overall material can withstand a high temperature of 1000℃ for a long time, which meets the application requirements of high-temperature components such as aero engines and missile wings.

[0026] 2. This invention achieves low infrared emissivity (≤0.3) by setting a first frequency-selective surface layer and a second frequency-selective surface layer on both sides of the material, thus ensuring infrared stealth performance. At the same time, the surface layer has high transmittance to radar waves, allowing radar waves to enter the interior of the material. By precisely designing multiple symmetrically distributed resistive metamaterial layers inside the body, broadband and efficient absorption of incident radar waves is achieved in a coordinated manner, and a double-sided absorption effect is achieved. This structure achieves good compatibility between broadband radar wave absorption (absorption rate >50% for 7.2 GHz~18 GHz) and infrared stealth with a relatively thin thickness (≤3.1 mm). Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic cross-sectional view of the infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material prepared in Example 1 of the present invention. Figure 2 This is a schematic diagram of the first frequency-selective surface layer and the second frequency-selective surface layer in embodiments 1-2 of the present invention; Figure 3 This is a schematic diagram of the intermediate metamaterial layer in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the first inner metamaterial layer and the second inner metamaterial layer of the double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth prepared in Embodiment 1 of the present invention. Figure 5 This is a schematic diagram of the first and second metamaterial layers in Embodiment 1 of the present invention; Figure 6 This is a reflectance curve of the double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth prepared in Example 1 of the present invention. Figure 7 This is a transmittance curve of the infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material prepared in Example 1 of the present invention. Figure 8 This is an absorption rate curve of the double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth prepared in Example 1 of the present invention (absorption rate = 1 - transmittance - reflectance). Figure 9 The curve showing the tensile strength of the continuous alumina fiber reinforced alumina-based structure microwave absorbing material in Example 1 as a function of density is shown. Figure 10 This is a schematic diagram of the intermediate metamaterial layer in Embodiment 2 of the present invention; Figure 11 This is a schematic diagram of the first and second metamaterial layers in Embodiment 2 of the present invention; Figure 12 This is a reflectance curve of the double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth prepared in Example 2 of the present invention. Figure 13 This is a transmittance curve of the double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth prepared in Example 2 of the present invention. Figure 14 This is an absorption rate curve of the double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth prepared in Example 2 of the present invention. Legend: 1. Body; 21. First frequency-selective surface layer; 22. Second frequency-selective surface layer; 3. Intermediate metamaterial layer; 41. First inner metamaterial layer; 42. Second inner metamaterial layer; 51. First outer metamaterial layer; 52. Second outer metamaterial layer. Detailed Implementation

[0029] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0031] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0032] Example 1

[0033] A double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth, such as... Figure 1 As shown, the composite material does not include a continuously conductive metal reflective layer. Instead, it uses a continuous alumina fiber-reinforced alumina ceramic matrix composite as the substrate 1. The thickness of substrate 1 is 3 mm. By controlling the density of substrate 1, its dielectric constant can be reduced while ensuring the strength of the composite material. The density of substrate 1 is controlled at 2.9 g / cm³. 3 The relative permittivity real part is about 6.9, and the tensile strength of the composite material is >200MPa; A first frequency selection surface layer 21 and a second frequency selection surface layer 22 are provided on the front and back sides of the main body 1. These are discontinuous conductive / low emissivity layers composed of periodically arranged conductive units. An intermediate metamaterial layer 3 is disposed at the middle position in the thickness direction of the main body 1. A first inner metamaterial layer 41, a second inner metamaterial layer 42, a first outer metamaterial layer 51, and a second outer metamaterial layer 52 are symmetrically arranged from the intermediate metamaterial layer 3 to both sides. The intermediate metamaterial layer is 0.24 mm away from the first inner metamaterial layer 41 and the second inner metamaterial layer 42, and the first inner metamaterial layer 41 is 0.81 mm away from the first outer metamaterial layer 51 and the second inner metamaterial layer 42 is 0.81 mm away from the second outer metamaterial layer 52. The first frequency selective surface layer 21 and the second frequency selective surface layer 22 are made of conductive paste prepared from high-temperature resistant platinum powder and glass powder. The paste is obtained by screen printing, drying, and sintering, resulting in a film thickness of approximately 8 μm. The film consists of a periodic pattern of discontinuous conductive blocks, with a sheet resistance of 0.1 Ω / □. Figure 2 As shown, the period size P2 is 1.2 mm, the ratio of the side length L2 of the conductive block to the period size P2 is 0.85, and the emissivity in the 3 μm~5 μm band is 0.26. The intermediate metamaterial layer 3 is obtained by screen printing a resistive paste made of ruthenium dioxide and glass powder, followed by drying and sintering, resulting in a film thickness of 8 μm. The conductive pattern units of the intermediate metamaterial layer 3 are periodically arranged discontinuous resistive blocks, with a sheet resistance of 20Ω / □~30Ω / □. Figure 3 As shown, the period size P3 is 15.6 mm, and the ratio of the side length L3 of the resistor block to the period size P3 is 0.87. The first inner metamaterial layer 41, the second inner metamaterial layer 42, the first outer metamaterial layer 51, and the second outer metamaterial layer 52 are all made from a paste prepared with ruthenium dioxide and glass powder. The paste is obtained by screen printing patterns, drying, and then sintering, resulting in a film thickness of approximately 8 μm. The conductive pattern units of the first inner metamaterial layer 41, the second inner metamaterial layer 42, the first outer metamaterial layer 51, and the second outer metamaterial layer 52 are periodically arranged discontinuous resistive blocks, with a sheet resistance of 30 Ω / □ to 60 Ω / □. The patterns of the first inner metamaterial layer 41 and the second inner metamaterial layer 42 are as follows: Figure 4 As shown, the periodic dimension P4 is 15.6 mm, and the ratio of the side length L4 of the resistor block to the periodic dimension P4 is 0.72; the patterns of the first metamaterial layer 51 and the second metamaterial layer 52 are as follows. Figure 5 As shown, the period size P5 is 15.6mm, and each period contains 4 resistor blocks, of which 2 large resistor blocks and 2 small resistor blocks are arranged alternately. The ratio of the side length L51 of a single large resistor block to the period size P5 is 0.33, and the ratio of the side length L52 of a single small resistor block to the period size P5 is 0.26.

[0034] The preparation method of the continuous alumina fiber reinforced alumina-based structure microwave absorbing material in this embodiment includes the following steps: S1. Preparation of slurry: According to the formula, conductive particles such as ruthenium dioxide are mixed with glass powder at a mass ratio of 1.5:1 to obtain a mixed powder. 0.4 parts of single-component acrylic resin are added to each part of the mixed powder as a binder, and 1 part of ethyl acetate is added as a solvent to adjust the viscosity. The mixture is then mixed evenly using a three-roll mill to obtain a resistive slurry. According to the formula, high-temperature resistant platinum powder and glass powder are mixed at a mass ratio of 18:1, a small amount of wax powder and ethyl acetate are added, and the mixture is mixed evenly using a three-roll mill to obtain a conductive paste. Nano-alumina particles and solvent are mixed at a mass ratio of 8:3 and dispersed evenly using a three-roll mill to obtain alumina slurry. S2. Printing metamaterial layer: Using screen printing technology, periodic patterns are printed on continuous alumina fiber fabric with the above-mentioned resistive paste. After drying, the fabric is sintered at 900℃ for 30 minutes to obtain a fabric containing intermediate metamaterial layer 3, first inner metamaterial layer 41, second inner metamaterial layer 42, first outer metamaterial layer 51 and second outer metamaterial layer 52. S3, Laying and stitching: Continuous alumina fiber fabric is laid in the mold according to the designed thickness. The fabric containing the intermediate metamaterial layer 3, the first inner metamaterial layer 41, the second inner metamaterial layer 42, the first outer metamaterial layer 51 and the second outer metamaterial layer 52 is laid in the predetermined position. After the laying is completed, continuous alumina fibers are used for stitching to obtain the fiber preform. S4. Slurry Impregnation-Hot Pressing: Vacuum impregnate the above fiber preform with alumina slurry. Pressurize using a vacuum bag until the vacuum degree is less than -0.1MPa, impregnate for 6 hours, pressurize using a vacuum bag, place the preform in a vacuum bag, seal, and pressurize until the pressure is less than -0.1MPa. Dry the impregnated preform at 150℃ for 2 hours to obtain the impregnated and dried preform. S5. Sintering: The impregnated and dried preform is sintered at 1100℃ for 1 hour; S6. Post-densification: Repeat the slurry impregnation, hot pressing, and sintering process until the material density reaches 2.9 g / cm³. 3 about; S7. Grinding process: Grind the material to the required thickness using a grinding machine and trim the edges; S8. Preparation of reflective and frequency-selective layers: After the workpiece is polished, conductive paste is printed on the front and back sides by screen printing to obtain a first frequency-selective surface layer 21 and a second frequency-selective surface layer 22 with low emissivity. The paste contains a lot of platinum powder to ensure low reflectivity. After drying, it is sintered at 900℃ for 0.5h to finally obtain a continuous alumina fiber reinforced alumina matrix structure microwave absorbing material.

[0035] The reflectance curve of this embodiment is as follows: Figure 6 As shown, the transmittance curve is as follows: Figure 7 As shown, the absorptivity of the material is calculated according to the formula "absorptivity = 1 - reflectivity - transmittance". Figure 8 As shown.

[0036] It can be seen that the radar wave absorptivity of the continuous alumina fiber reinforced alumina matrix structure is >50% in the 7.2 GHz~18 GHz range and >75% in the 9.9 GHz~18 GHz range.

[0037] In contrast, dense alumina material has a density of 3.7 g / cm³. 3 ~3.95g / cm 3 The relative permittivity is 9.0~10.0.

[0038] For comparison, the tensile strength of the continuous alumina fiber reinforced alumina-based structure microwave absorbing material as a function of density was tested, as shown in the figure. Figure 9 As shown, the density exceeds 2.8 g / cm³. 3 The tensile strength increases slowly after flexural stress, and the flexural strength is at a density of 2.9 g / cm³. 3 The density of the composite material reaches its extreme value on both sides. Since the relative permittivity of air is approximately 1, which is very low, the lower the density, the greater the porosity and the smaller the permittivity. Taking into account factors such as process control precision and permittivity, this invention controls the composite material density to 2.8 g / cm³. 3 ~3.0g / cm 3 between.

[0039] Example 2

[0040] A double-sided absorbing continuous alumina fiber-reinforced alumina composite material compatible with infrared stealth is disclosed. It does not contain a continuously conductive metal reflective layer. The continuous alumina fiber-reinforced alumina ceramic matrix composite material is used as the substrate 1, with a thickness of 3 mm. Controlling the density of the substrate 1 reduces its dielectric constant while maintaining the composite material's strength. The density of the substrate 1 is controlled at 2.9 g / cm³.3 The relative permittivity real part is about 6.9, and the tensile strength of the composite material is >200MPa; A first frequency selection surface layer 21 and a second frequency selection surface layer 22 are provided on the front and back sides of the main body 1. These are discontinuous conductive / low emissivity layers composed of periodically arranged conductive units. An intermediate metamaterial layer 3 is provided at the middle position in the thickness direction of the body 1. A first outer metamaterial layer 51 and a second outer metamaterial layer 52 are symmetrically arranged from the intermediate metamaterial layer 3 to both sides. In this embodiment, the first inner metamaterial layer 41 and the second inner metamaterial layer 42 are not included. The intermediate metamaterial layer 3 and the first outer metamaterial layer 51 and the second outer metamaterial layer 52 are 0.42 mm apart. The first frequency selective surface layer 21 and the second frequency selective surface layer 22 are made of conductive paste prepared from high-temperature resistant platinum powder and glass powder. The paste is obtained by screen printing, drying, and sintering, resulting in a film thickness of approximately 8 μm. The film consists of a periodic pattern of discontinuous conductive blocks, with a sheet resistance of 0.1 Ω / □. Figure 2 As shown, the period size P2 is 1.2 mm, the ratio of the side length L2 of the conductive block to the period size P2 is 0.8, and the emissivity in the 3 μm~5 μm band is about 0.26. The intermediate metamaterial layer 3 is prepared using a resistive paste made of ruthenium dioxide and glass powder. The paste is obtained by screen printing patterns, drying, and sintering, resulting in a film thickness of approximately 8 μm. The conductive pattern units of the intermediate metamaterial layer 3 are periodically arranged square ring structures with a centrally cut square hole (discontinuous squares with a portion removed in the center). The sheet resistance of the pattern is 10 Ω / □~20 Ω / □. Figure 10 As shown, the period size P3 is 16 mm, and the ratio of the side length L3 of the central square hole in the square ring structure to the period size P3 is 0.46; unlike Example 1, the intermediate metamaterial layer 3 in this embodiment is a sensitive frequency selective surface. The first outer metamaterial layer 51 and the second outer metamaterial layer 52 are obtained by screen printing patterns using a paste made of ruthenium dioxide and glass powder, followed by drying and sintering. The resulting film thickness is approximately 8 μm. The conductive pattern units of the first outer metamaterial layer 51 and the second outer metamaterial layer 52 are periodically arranged square patterns, with a sheet resistance of 20 Ω / □ to 40 Ω / □. The patterns of the first outer metamaterial layer 51 and the second outer metamaterial layer 52 are as follows: Figure 11 As shown, the period size P5 is 8mm, and each period contains 4 resistor blocks, of which 2 large resistor blocks and 2 small resistor blocks are arranged alternately. The ratio of the side length L51 of a single small resistor block to P5 is 0.34, and the ratio of the side length L52 of a single large resistor block to P5 is 0.37.

[0041] The preparation method of the continuous alumina fiber reinforced alumina-based structure microwave absorbing material in this embodiment includes the following steps: S1. Preparation of slurry: According to the formula, conductive particles such as ruthenium dioxide are mixed with glass powder at a mass ratio of 1.5:1 to obtain a mixed powder. 0.4 parts of single-component acrylic resin are added to each part of the mixed powder as a binder, and 1 part of ethyl acetate is added as a solvent to adjust the viscosity. The mixture is then mixed evenly using a three-roll mill to obtain a resistive slurry. According to the formula, high-temperature resistant platinum powder and glass powder are mixed at a mass ratio of 18:1, a small amount of wax powder and ethyl acetate are added, and the mixture is mixed evenly using a three-roll mill to obtain a conductive paste. Nano-alumina particles and solvent are mixed at a mass ratio of 8:3 and dispersed evenly using a three-roll mill to obtain alumina slurry. S2. Printing metamaterial layer: Using screen printing technology, periodic patterns are printed on continuous alumina fiber fabric with the above-mentioned resistive paste. After drying, the fabric is sintered at 900℃ for 30 minutes to obtain a fabric containing intermediate metamaterial layer 3, first outer metamaterial layer 51, and second outer metamaterial layer 52. S3, Laying and stitching: Continuous alumina fiber fabric is laid in the mold according to the designed thickness. The fabric containing the intermediate metamaterial layer 3 and the first outer metamaterial layer 51 and the second outer metamaterial layer 52 is laid in the predetermined position. After the laying is completed, continuous alumina fiber is used for stitching to obtain the fiber preform. S4. Slurry Impregnation-Hot Pressing: Vacuum impregnate the above fiber preform with alumina slurry. Pressurize using a vacuum bag until the vacuum degree is less than -0.1MPa, impregnate for 6 hours, pressurize using a vacuum bag, place the preform in a vacuum bag, seal, and pressurize until the pressure is less than -0.1MPa. Dry the impregnated preform at 150℃ for 2 hours to obtain the impregnated and dried preform. S5. Sintering: The impregnated and dried preform is sintered at 1100℃ for 1 hour; S6. Post-densification: Repeat the slurry impregnation, hot pressing, and sintering processes until the material density reaches 2.9 g / cm³. 3 ; S7. Grinding process: Grind the material to the required thickness using a grinding machine and trim the edges; S8. Preparation of reflective and frequency-selective layers: After the workpiece is polished, conductive paste is printed on the front and back sides by screen printing to obtain a first frequency-selective surface layer 21 and a second frequency-selective surface layer 22 with low emissivity. The paste contains a lot of platinum powder to ensure low reflectivity. After drying, it is sintered at 900℃ for 0.5h to finally obtain a continuous alumina fiber reinforced alumina matrix structure microwave absorbing material.

[0042] The reflectance curve of this embodiment is as follows: Figure 12 As shown, the transmittance curve is as follows: Figure 13 As shown, the absorption rate curve is as follows: Figure 14As shown. In this embodiment, the total thickness of the continuous alumina fiber reinforced alumina-based structure radar-absorbing material is ≤3.1mm, and its radar wave absorptivity is >50% in the 6.8 GHz~18 GHz range and >70% in the 8.6 GHz~18 GHz range.

[0043] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that improvements and refinements made by those skilled in the art without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A double-sided, continuous alumina fiber-reinforced alumina composite material compatible with infrared stealth, characterized in that, It includes a body (1), a first frequency-selective surface layer (21), a second frequency-selective surface layer (22), and an intermediate metamaterial layer (3); The main body (1) is a continuous alumina fiber reinforced alumina ceramic matrix composite material with a density of 2.8 g / cm³. 3 ~3.0 g / cm 3 The real part of the relative permittivity is 6.8~7.2; The first frequency selective surface layer (21) and the second frequency selective surface layer (22) are respectively disposed on the front and back sides of the body (1), and are discontinuous conductive layers composed of periodically arranged conductive units; wherein, the periodic pattern of the conductive units is a periodically arranged conductive square, the sheet resistance of the conductive squares of the first frequency selective surface layer (21) and the second frequency selective surface layer (22) is ≤1Ω / □, the period size is ≤3mm, and the ratio of the side length of the conductive square to the period size is 0.75~0.95; The intermediate metamaterial layer (3) is located at the middle position in the thickness direction of the body (1), and the first outer metamaterial layer (51) and the second outer metamaterial layer (52) are symmetrically arranged from the intermediate metamaterial layer (3) to both sides; all metamaterial layers are periodically arranged square conductive pattern units with different structural parameters and / or sheet resistance, the sheet resistance of the square conductive pattern units of the metamaterial layer is 5Ω / □~100Ω / □, and the side length of the square is 1mm~20mm; The infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material does not contain a continuously conductive metal reflective layer, and its total thickness is ≤3.1mm.

2. The infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material according to claim 1, characterized in that, The first frequency selective surface layer (21) and the second frequency selective surface layer (22) are formed by printing and sintering a paste made of high-temperature resistant precious metal powder and glass powder. The thickness of the first frequency selective surface layer (21) and the second frequency selective surface layer (22) is 5μm to 20μm.

3. The infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material according to claim 2, characterized in that, The high-temperature resistant precious metal powder is at least one of silver, gold, platinum and palladium, and the mass ratio of the high-temperature resistant precious metal powder to the glass powder is 10~30:1; the infrared emissivity of the material surface with the first frequency selective surface layer (21) and the second frequency selective surface layer (22) in the 3μm~5μm band is ≤0.

3.

4. The infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material according to claim 1, characterized in that, The thickness of the intermediate metamaterial layer (3) is 5μm~20μm; the conductive pattern unit of the intermediate metamaterial layer (3) is a periodically arranged discontinuous resistive blocks or a square ring structure with a square hole in the center; the sheet resistance of the resistive blocks is 20Ω / □~30Ω / □, the period size is 3mm~20mm, and the ratio of the side length of the resistive blocks to the period size is 0.5~0.95; the sheet resistance of the square ring structure is 5Ω / □~20Ω / □, the period size is 5mm~20mm, and the ratio of the side length of the square hole in the center of the square ring structure to the period size is 0.2~0.5; The thickness of the first outer metamaterial layer (51) and the second outer metamaterial layer (52) is 5μm~20μm, the sheet resistance of their resistive blocks is 30Ω / □~60Ω / □, the period size is 3mm~20mm, each period contains 2 large resistive blocks and 2 small resistive blocks and they are arranged intersecting each other, wherein the ratio of the side length of the large resistive block and the small resistive block to the period size is 0.2~0.95, and the side length of the large resistive block is greater than the side length of the small resistive block.

5. The infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material according to claim 1, characterized in that, A first inner metamaterial layer (41) and a second inner metamaterial layer (42) are respectively provided between the intermediate metamaterial layer (3) and the first outer metamaterial layer (51) and the second outer metamaterial layer (52). The intermediate metamaterial layer (3), the first inner metamaterial layer (41), the second inner metamaterial layer (42), the first outer metamaterial layer (51) and the second outer metamaterial layer (52) are distributed on different thicknesses within the body (1), and the vertical distance between adjacent metamaterial layers is ≥0.1mm. The thickness of the first inner metamaterial layer (41) and the second inner metamaterial layer (42) is 5μm~20μm, the sheet resistance of the resistor block is 30Ω / □~60Ω / □, the period size is 3mm~20mm, and the ratio of the side length of the resistor block to the period size is 0.2~0.

95.

6. The infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material according to claim 5, characterized in that, The intermediate metamaterial layer (3), the first inner metamaterial layer (41), the second inner metamaterial layer (42), the first outer metamaterial layer (51), and the second outer metamaterial layer (52) are obtained by screen printing and sintering a slurry prepared from ruthenium dioxide and glass powder in a mass ratio of 0.5 to 5:

1.

7. The infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material according to any one of claims 1-6, characterized in that, The infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material has a tensile strength >200 MPa, a radar wave absorptivity >50% in the 7.2 GHz to 18 GHz frequency band, and a radar wave absorptivity >75% in the 9.9 to 18 GHz frequency band.

8. A method for preparing a double-sided absorbing continuous alumina fiber reinforced alumina composite material compatible with infrared stealth as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Prepare the resistive paste of the intermediate metamaterial layer (3), the first inner metamaterial layer (41), the second inner metamaterial layer (42), the first outer metamaterial layer (51) and the second outer metamaterial layer (52), the conductive paste of the first frequency selective surface layer (21) and the second frequency selective surface layer (22), and the alumina paste. S2. Using screen printing technology, the resistive paste obtained in step S1 is used to print periodically arranged resistive blocks on a continuous alumina fiber fabric. After drying, the blocks are sintered to obtain a fabric containing an intermediate metamaterial layer (3), a first inner metamaterial layer (41), a second inner metamaterial layer (42), a first outer metamaterial layer (51), and a second outer metamaterial layer (52). S3. Continuous alumina fiber fabric is laid in the mold according to the designed thickness. The fabric obtained in step S2, which includes the intermediate metamaterial layer (3), the first inner metamaterial layer (41), the second inner metamaterial layer (42), the first outer metamaterial layer (51), and the second outer metamaterial layer (52), is laid in the predetermined position. After the laying is completed, continuous alumina fiber is used for sewing to obtain the fiber preform. S4. The fiber preform obtained in S3 is vacuum impregnated, pressurized, dried, and sintered using alumina slurry. This process of vacuum impregnation, pressurization, drying, and sintering is repeated until the density of the composite material reaches 2.8 g / cm³. 3 ~3.0 g / cm 3 After grinding and trimming, the composite material workpiece is obtained; S5. Using screen printing, conductive blocks arranged in a periodic pattern are printed on the front and back sides of the composite material workpiece obtained in S4 using the conductive paste obtained in S1. After drying, they are sintered to form a first frequency selective surface layer (21) and a second frequency selective surface layer (22), thus obtaining the infrared stealth compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material.

9. The method for preparing the infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material according to claim 8, characterized in that, The drying temperature is 140~160℃ and the drying time is 1~3h; the sintering temperature in step S2 is 800~1000℃ and the sintering time is 0.3~1h; the sintering temperature in step S4 is 1100~1200℃ and the sintering time is 0.5~2h; the sintering temperature in step S5 is 800~1000℃ and the sintering time is 0.3~1h.

10. The method for preparing the infrared stealth-compatible double-sided absorbing continuous alumina fiber reinforced alumina composite material according to claim 8, characterized in that, During the vacuum impregnation process, the vacuum level is ≤-0.1MPa, the impregnation time is 2~12h, and the pressure is increased to a value of 0.1MPa or higher.

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