A gradient impedance multi-fiber hybrid broadband absorbing structure

Abstract

A gradient impedance-gradient multi-fiber hybrid broadband absorbing structure is provided, comprising a multi-fiber preform and a low-loss matrix. The low-loss matrix fills within the multi-fiber preform and covers it, with a covering thickness of <0.2 mm. The multi-fiber preform is formed by weaving together high-loss, medium-loss, and low-loss fibers. The multi-fiber preform includes an impedance matching layer formed by low-loss fiber weaving, an impedance transition layer formed by mixing low-loss and medium-loss fibers, and an absorption attenuation layer formed by mixing medium-loss and high-loss fibers. The impedance matching layer, impedance transition layer, and absorption attenuation layer are stacked sequentially to form a three-dimensional structure. This invention can effectively control its microwave electromagnetic characteristics, achieve a reasonable impedance gradient change, and significantly improve broadband absorption performance.

Description

Technical Field

[0001] This invention relates generally to the field of stealth technology for high-speed aircraft, and more particularly to a gradient impedance gradient multi-fiber hybrid broadband absorbing structure. Background Technology

[0002] The development of advanced aircraft has created an urgent need for integrated broadband radar stealth materials. Research on materials that combine mechanical load-bearing capacity with broadband radar absorption performance has become one of the key issues restricting the development of stealth technology for new high-speed aircraft. Currently, multi-layered composite adhesive radar-absorbing materials are gradually failing to meet the high strength and impact resistance requirements of stealth components in high-speed aircraft. Structural-functional integration is an inevitable trend in the development of radar-absorbing materials for high-speed aircraft.

[0003] Chinese patent CN106671514 A discloses a discontinuous impedance gradient structure microwave absorbing composite material. The structure consists of a wave-transparent layer, a low-concentration electrical loss layer, a wave-transparent layer, a high-concentration electrical loss layer, and a wave-transparent layer from top to bottom. The wave-transparent layer is composed of quartz glass fiber cloth and epoxy resin. The low-concentration electrical loss layer and the high-concentration electrical loss layer are composed of T700 short-cut carbon fiber mixed with epoxy resin in different proportions. Its shortcomings are that there are only two true impedance gradient layers, the gradient change range is limited, and only short-cut carbon fiber is used as the electromagnetic loss material, resulting in a single electromagnetic loss capability and poor mechanical properties.

[0004] Chinese patent CN112851359 B discloses a microwave-absorbing SiBCN nanofiber and its preparation method. This fiber has a strong absorption capacity at a certain frequency, but the effective absorption bandwidth is only 3.45 GHz, which cannot meet the requirements of broadband microwave absorption performance. Summary of the Invention

[0005] In view of the shortcomings and defects of the broadband absorbing structural materials mentioned above, this invention provides a gradient impedance gradient multi-fiber hybrid broadband absorbing structure. This absorbing structure forms a specific structure of braid by reasonably matching fibers with different loss capabilities. Combined with an appropriate type of matrix, it can effectively control its microwave electromagnetic characteristics, achieve reasonable impedance gradient changes, and significantly improve broadband absorbing performance.

[0006] The technical solution of this invention is a gradient impedance multi-fiber hybrid broadband absorbing structure, comprising a multi-fiber preform and a low-loss matrix; the low-loss matrix fills within the multi-fiber preform and covers it, with a covering thickness <0.2 mm; the multi-fiber preform is formed by a mixture of high-loss, medium-loss, and low-loss fibers, and includes a low-loss fiber woven to form an impedance matching layer, a mixture of low-loss and medium-loss fibers woven to form an impedance transition layer, and a mixture of medium-loss and high-loss fibers woven to form an absorption attenuation layer; the impedance matching layer, impedance transition layer, and absorption attenuation layer are stacked sequentially to form a three-dimensional structure; the selection and weaving method of the high-loss, medium-loss, and low-loss fibers in the multi-fiber preform are as follows: according to design requirements, the types of high-loss, medium-loss, and low-loss fibers and the type of low-loss matrix are selected, with a reflection coefficient S11 better than -10 across the entire frequency band. Using dB as the criterion, the specific type, content, weaving method, and detailed arrangement relationship between fibers are determined through simulation using the finite element full-wave analysis software HFSS. Finally, a braided model is established according to the determined fiber type, content, weaving method, and detailed arrangement relationship between fibers.

[0007] Furthermore, the aforementioned low-loss fibers are selected from at least one of silicon nitride fibers, SiBN ceramic fibers, quartz fibers, Al2O3 fibers, and mullite fibers; the medium-loss fibers are selected from one or two of near-stoichiometric silicon carbide fibers and polyborosilicate fibers heat-treated at 1600 ℃; the high-loss fibers are selected from one or two of carbon fibers, high-carbon high-oxygen silicon carbide fibers, and high-carbon low-oxygen silicon carbide fibers; and the low-loss matrix is ​​selected from one of silicon nitride ceramic matrices, epoxy resin matrices, and mullite ceramic matrices.

[0008] Furthermore, the dielectric constant of the aforementioned low-loss fibers is <10, and the loss tangent is <0.01; among the medium-loss fibers, the resistivity of near-stoichiometric silicon carbide fibers and polyborosilicate fibers heat-treated at 1600 °C is 10. -1 ~10 13 Ω·cm; In the high-loss fiber: the resistivity of carbon fiber is 10 -7 ~10 -5 Ω·cm, resistivity of high-carbon, high-oxygen silicon carbide fiber and high-carbon, low-oxygen silicon carbide fiber 10 -5 ~10 -1 Ω·cm;

[0009] The dielectric constant of the low-loss substrate is <10, and the loss tangent is <0.01.

[0010] Furthermore, the aforementioned low-loss fiber weaving, low-loss fiber and medium-loss fiber mixed weaving, and medium-loss fiber and high-loss fiber mixed weaving adopt one of plain weaving, twill weaving, and three-dimensional weaving, with a distribution density of 4 to 20 bundles / cm.

[0011] Furthermore, the aforementioned three-dimensional weaving method is a 0° orthogonal plain weave cross-layer deep cross-linking weave; specifically, the plain weave cross-layer deep cross-linking weave method is as follows: after the weft yarn and warp yarn are woven in a 0° orthogonal plain weave for a predetermined number of bundles in the same horizontal weave layer, the weft yarn crosses the layer upwards or downwards into the third layer relative to the first layer before crossing the layer and weaves a predetermined number of bundles in a 0° orthogonal plain weave with the warp yarn in the third layer, and then crosses the layer in the opposite direction again into the original weave layer and weaves a predetermined number of bundles in a 0° orthogonal plain weave with the warp yarn, and then repeats the first upward or downward crossing layer into the third layer to continue weaving, and so on; the weft yarn crosses the layer in the manner of adjacent weft yarn bundles going up and down respectively; the width of the weft yarn crossing the layer is the same as the width of the predetermined number of bundles woven in a 0° orthogonal plain weave, and no warp yarn is woven within the width of the crossing layer.

[0012] Furthermore, the predetermined number of bundles is at least 2 bundles of warp yarns; the cross-layer width is at least the width of 2 bundles of warp yarns.

[0013] Furthermore, the aforementioned multi-fiber preform is a three-dimensional woven preform formed based on plain weave single-span deep cross-linking weave, woven in the following steps:

[0014] Step 1: The first and second woven layers of the three-dimensional woven prefabricated component are woven with low-loss fibers. The low-loss fibers are arranged orthogonally and periodically in the warp and weft directions. There are 6 to 20 bundles of warp yarns and 4 to 14 bundles of weft yarns per 1 cm of the fabric.

[0015] Step 2: The third and fourth woven layers of the three-dimensional woven preform are constructed using medium-loss fibers and low-loss fibers that cross over from the first and second woven layers in a plain weave. Simultaneously, the medium-loss fibers and low-loss fibers are arranged orthogonally and periodically in both the warp and weft directions. In the third and fourth woven layers of the three-dimensional woven preform, the volume ratio of low-loss fibers to medium-loss fibers is 1:3, and the fabric has 6-20 warp bundles and 4-14 weft bundles per 1 cm.

[0016] Step 3: In the fifth and sixth woven layers of the three-dimensional woven preform, medium-loss fibers and high-loss fibers are selected and orthogonally plain-woven with the medium-loss fiber weft yarns that cross over from the third and fourth woven layers. At the same time, the medium-loss fibers and high-loss fibers are orthogonally periodically arranged in the warp and weft directions, respectively. In the fifth and sixth woven layers of the three-dimensional woven preform, the volume ratio of medium-loss fibers to high-loss fibers is 1:1, and there are 6 to 20 warp yarns and 4 to 14 weft yarns per 1 cm of fabric.

[0017] The bulk density of the three-dimensional woven prefabricated fabric is 1.6–2.4 g / cm³. 3 The areal density is 600–1400 g / m³ 2 The thickness is 3 to 3.5 mm.

[0018] Furthermore, the aforementioned multi-fiber preform is a three-dimensional woven preform based on plain or twill weave, woven into shape according to the following steps:

[0019] The first step is to select low-loss fibers and use plain or twill weave to establish the upper two layers of two-dimensional fabric for the woven body model; the low-loss fibers are arranged orthogonally and periodically in the warp and weft directions; there are 6 to 20 bundles of warp and weft yarns per 1 cm of the fabric.

[0020] The second step is to mix plain or twill weave of medium-loss and low-loss fibers: select low-loss and medium-loss fibers and use plain or twill weave to establish a two-layer two-dimensional fabric for the woven body model; the low-loss and medium-loss fibers are arranged orthogonally and periodically in the warp and weft directions, and the volume ratio of low-loss and medium-loss fibers is 1:1; there are 6 to 20 bundles of warp and weft yarns per 1 cm of fabric.

[0021] Step 3: Plain or twill mixed weaving of medium-loss and high-loss fibers: Select medium-loss and high-loss fibers and use plain or twill weaving to establish the bottom two layers of two-dimensional fabric for the woven body model; the medium-loss and high-loss fibers are arranged orthogonally and periodically in the warp and weft directions, and the volume ratio of medium-loss and high-loss fibers is 1:1; there are 6 to 20 bundles of warp and weft yarns per 1 cm of fabric.

[0022] Step 4: Stack the two-dimensional fabric created in the above steps from top to bottom to form a woven fabric model. The bulk density of the fabric is 2.2–3.5 g / cm³. 3 The areal density is 800–2000 g / m³ 2 The thickness is 3 to 3.5 mm.

[0023] The beneficial technical effects of this invention are as follows:

[0024] 1. Based on the wave absorption performance requirements of specific components in different application scenarios, this invention first adopts a mixed weaving of multi-fibers with different loss capabilities. Through the simulation design method of finite element software, with the reflection coefficient S11 being better than -10dB in the entire frequency band as the criterion, appropriate types of reinforcing fibers, content ratios, weaving methods and specific fiber arrangement relationships are selected, resulting in a structure with excellent impedance matching and broadband wave absorption performance.

[0025] 2. This invention utilizes finite element method (FEM) simulation design, combined with periodic boundary conditions and criterion optimization, to accurately obtain the types of fibers with various loss capabilities required for the structural model. Furthermore, it precisely calculates the fiber content, proportion, and weaving method to achieve optimal wave absorption performance. This FEM simulation optimization design method significantly reduces experimental trial-and-error costs, while simultaneously elevating the material structure design approach to a precise, controllable, and adjustable level.

[0026] 3. The three-dimensional structure proposed in this invention, constructed by a periodic and orderly mixed weaving method of high-loss fibers, medium-loss fibers and low-loss fibers, can effectively regulate the dielectric spectrum characteristics of microwave electromagnetic response by controlling the content, proportion and arrangement of fibers with different loss capabilities, thereby obtaining excellent and reasonable impedance matching characteristics and achieving excellent broadband absorption performance.

[0027] 4. The present invention employs fiber blending with different dielectric properties to significantly reduce the overall dielectric constant of the braid, bringing it close to the optimal dispersion curve of the dielectric constant of the absorbing material. At the same time, by reasonably matching fibers with different impedance characteristics, impedance gradient changes are achieved, thereby greatly improving the broadband absorption performance of the braid.

[0028] 5. The multi-fiber mixed plain weave cross-layer deep cross-linked three-dimensional structure established in this invention is a three-dimensional integrated structure, similar to a three-dimensional woven cross-linked structure. Compared with the three-dimensional structure of plain weave or twill weave, the plain weave cross-layer deep cross-linked three-dimensional structure has a certain strength in the Z-axis direction, which can meet the mechanical requirements of complex components in various directions. At the same time, the weft yarn part of the cross-layer section can be equivalent to a segment of short fibers in the Z-direction, which is equivalent to introducing short fiber wave-absorbing units into the structure, making the wave absorption mechanism more diversified and the wave absorption mechanism more varied.

[0029] 6. The braided body model designed in this invention has a simple weaving method and uses common multi-fiber materials, which has guiding significance for the design of broadband wave-absorbing structures. Attached Figure Description

[0030] These and / or other aspects and advantages of the present invention will become clearer and more readily understood from the following detailed description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0031] AppendixFigure 1 These are three views of the plain weave cross-layer deep cross-linked braid in this invention, where (a) is a top view; (b) is a front view; and (c) is a left view.

[0032] Appendix Figure 2 This is a three-dimensional model of an orthogonal 1×1 plain weave structure woven from carbon fiber, near-stoichiometric silicon carbide fiber, and silicon nitride fiber + quartz fiber used in Example 1 of this invention.

[0033] Appendix Figure 3 This is an electromagnetic parameter diagram of the composite material woven from carbon fiber, near-stoichiometric silicon carbide fiber, and silicon nitride fiber used in Example 1 of this invention.

[0034] Appendix Figure 4 This is an impedance matching diagram of the composite material woven from carbon fiber, near-stoichiometric silicon carbide fiber, and silicon nitride fiber used in Example 1 of this invention.

[0035] Appendix Figure 5 The reflection loss curve is shown for the composite material woven from carbon fiber, near-stoichiometric silicon carbide fiber, and silicon nitride fiber used in Example 1 of this invention.

[0036] Appendix Figure 6 This is a diagram showing the electromagnetic parameters of the near-stoichiometric silicon carbide fiber braid used in Comparative Example 1 of this invention.

[0037] Appendix Figure 7 This is the impedance matching diagram of the near-stoichiometric silicon carbide fiber braid used in Comparative Example 1 of this invention.

[0038] Appendix Figure 8 This is the reflection loss curve of the near-stoichiometric silicon carbide fiber braid used in Comparative Example 1 of this invention;

[0039] Appendix Figure 9 This is a three-dimensional structural model of an orthogonal 2×2 twill weave made of carbon fiber, near-stoichiometric silicon carbide fiber and silicon nitride fiber used in Example 2 of this invention;

[0040] Appendix Figure 10 This is an electromagnetic parameter diagram of the composite material woven from carbon fiber, near-stoichiometric silicon carbide fiber, and silicon nitride fiber used in Example 2 of this invention.

[0041] Appendix Figure 11 This is the impedance matching diagram of the composite material woven from carbon fiber, near-stoichiometric silicon carbide fiber, and silicon nitride fiber used in Example 2 of this invention.

[0042] Appendix Figure 12 The reflection loss curve is shown for the composite material made of carbon fiber, near-stoichiometric silicon carbide fiber and silicon nitride fiber used in Example 2 of this invention.

[0043] Appendix Figure 13 This is a three-dimensional structural model of an orthogonal, plain weave, multi-layered deep cross-linked structure woven from carbon fiber, near-stoichiometric silicon carbide fiber, and silicon nitride fiber used in Example 3 of this invention.

[0044] Appendix Figure 14 This is an electromagnetic parameter diagram of the composite material woven from carbon fiber, near-stoichiometric silicon carbide fiber, and silicon nitride fiber used in Example 3 of this invention.

[0045] Appendix Figure 15 This is the impedance matching diagram of the composite material woven from carbon fiber, near-stoichiometric silicon carbide fiber, and silicon nitride fiber used in Example 3 of this invention.

[0046] Appendix Figure 16 The reflection loss curve is shown for the composite material made of carbon fiber, near-stoichiometric silicon carbide fiber and silicon nitride fiber used in Example 3 of this invention. Detailed Implementation

[0047] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] Example 1

[0049] Service requirements are: reflectivity better than -10 dB in the X and Ku bands;

[0050] The finite element method (FEM) software HFSS was used for simulation calculations. Based on the actual situation, since the electromagnetic wave is projected from infinity onto the material surface, it can be considered a plane wave. Therefore, the incident electromagnetic wave at the port was set as a plane wave in the simulation. The fibers can be placed perpendicular or parallel to the electric field direction, and each fiber has a periodic arrangement structure in the X and Y directions. Therefore, two pairs of periodic boundary conditions were set around the model. Furthermore, to simulate a metallic reflective substrate, the lower surface of the model was set as a perfect electrical conductor boundary.

[0051] Using a reflection coefficient S11 better than -10 dB across the entire frequency band as a criterion, simulation calculations using the finite element full-wave analysis software HFSS determined that the high-loss fiber in the multi-fiber hybrid braid is carbon fiber; the medium-loss fiber is near-stoichiometric silicon carbide fiber; and the low-loss fiber is silicon nitride fiber and quartz fiber. The volume ratio of high-loss fiber to medium-loss fiber to low-loss fiber is 1:2:3. The weaving method is 0° orthogonal, 1×1 plain weave. The detailed arrangement of the fibers is as follows: the top two layers are plain orthogonal weaves of silicon nitride fiber and quartz fiber, with a volume ratio of 1:1; the middle two layers are plain orthogonal weaves of silicon nitride fiber and silicon carbide fiber, with a volume ratio of 1:1; the bottom two layers are plain orthogonal weaves of silicon carbide fiber and carbon fiber, with a volume ratio of 1:1. The six layers of plain weave two-dimensional fabric are stacked sequentially from top to bottom to form an orthogonal plain weave three-dimensional structure. The resulting orthogonal 1×1 plain weave three-dimensional structure model of the mixed high-loss, medium-loss, and low-loss fibers is shown in the figure below. Figure 2 As shown. The low-loss matrix was determined to be an epoxy resin matrix, filled within the braided structure and coated over it, with a coating thickness of <0.2 mm. The electromagnetic response spectrum parameters and reflection loss curve of the resulting structure are shown in the figure. Figures 3-5 As shown.

[0052] Comparative Example 1

[0053] All other conditions were the same as in Example 1, except that all high-loss carbon fibers and all low-loss silicon nitride fibers in the braided structure were replaced in equal amounts with medium-loss near-stoichiometric silicon carbide fibers. The impedance matching diagram of the resulting near-stoichiometric silicon carbide fiber braid is shown below. Figure 7 As shown, the electromagnetic response spectrum parameters and reflection loss curve of the obtained structure are as follows: Figures 6-8 As shown.

[0054] Example 2

[0055] Service requirements are: reflectivity better than -10 dB in the X and Ku bands;

[0056] The finite element method (FEM) software HFSS was used for simulation calculations. Based on the actual situation, since the electromagnetic wave is projected from infinity onto the material surface, it can be considered a plane wave. Therefore, the incident electromagnetic wave at the port was set as a plane wave in the simulation. The fibers can be placed perpendicular or parallel to the electric field direction, and each fiber has a periodic arrangement structure in the X and Y directions. Therefore, two pairs of periodic boundary conditions were set around the model. Furthermore, to simulate a metallic reflective substrate, the lower surface of the model was set as a perfect electrical conductor boundary.

[0057] Using a reflection coefficient S11 better than -10 dB across the entire frequency band as a criterion, simulation calculations using the finite element full-wave analysis software HFSS determined that the high-loss fiber in the multi-fiber hybrid braid is carbon fiber; the medium-loss fiber is near-stoichiometric silicon carbide fiber; and the low-loss fiber is silicon nitride fiber. The volume ratio of high-loss fiber to medium-loss fiber to low-loss fiber is 1:2:3. The weaving method is 0° orthogonal, 2×2 twill weave. The detailed arrangement of the fibers is as follows: the top two layers are silicon nitride fiber 2×2 twill orthogonal weave; the middle two layers are silicon nitride fiber and silicon carbide fiber 2×2 twill orthogonal weave, with a volume ratio of 1:1; the bottom two layers are silicon carbide fiber and carbon fiber 2×2 twill orthogonal weave, with a volume ratio of 1:1. The six layers of plain weave two-dimensional fabric are stacked sequentially from top to bottom to form a 2×2 orthogonal twill three-dimensional structure. The resulting orthogonal 2×2 twill three-dimensional structure model of the mixed high-loss, medium-loss, and low-loss fibers is shown in the figure below. Figure 9 As shown. The low-loss matrix was determined to be an epoxy resin matrix, filled within the braided structure and coated over it, with a coating thickness of <0.2 mm. The electromagnetic response spectrum parameters and reflection loss curve of the resulting structure are shown in the figure. Figures 10-12 As shown.

[0058] Example 3

[0059] Service requirements are: reflectivity better than -10 dB in the X and Ku bands;

[0060] The finite element method (FEM) software HFSS was used for simulation calculations. Based on the actual situation, since the electromagnetic wave is projected from infinity onto the material surface, it can be considered a plane wave. Therefore, the incident electromagnetic wave at the port was set as a plane wave in the simulation. The fibers can be placed perpendicular or parallel to the electric field direction, and each fiber has a periodic arrangement structure in the X and Y directions. Therefore, two pairs of periodic boundary conditions were set around the model. Furthermore, to simulate a metallic reflective substrate, the lower surface of the model was set as a perfect electrical conductor boundary.

[0061] Using a reflection coefficient S11 that is better than -10 dB across the entire frequency band as a criterion, simulation calculations using the finite element full-wave analysis software HFSS determined that the high-loss fiber in the multi-fiber hybrid braid is carbon fiber; the medium-loss fiber is near-stoichiometric silicon carbide fiber; and the low-loss fiber is silicon nitride fiber. The volume ratio of high-loss fiber to medium-loss fiber to low-loss fiber is 2:3:5. The weaving method is 0° orthogonal, plain weave, cross-layer deep cross-linking weave. The detailed arrangement of the fibers is as follows: the upper two layers at the high position are woven with silicon nitride fibers; the middle two layers at the high position have silicon carbide fibers in the warp direction and alternating silicon carbide fibers and silicon nitride fibers from the upper two layers in the weft direction, with the warp and weft fibers woven at 0° orthogonal, and the volume ratio of silicon nitride fibers to silicon carbide fibers is 1:3; the lower two layers at the high position have silicon carbide fibers and carbon fibers in the warp direction and alternating carbon fibers and silicon carbide fibers from the middle two layers in the weft direction, with the warp and weft fibers woven at 0° orthogonal, and the volume ratio of silicon carbide fibers to carbon fibers is 1:1. The resulting orthogonal, plain weave, deep cross-linked three-dimensional structural model of the mixed high-loss, medium-loss, and low-loss fibers is shown in the figure below. Figure 13 As shown. The six-layer woven body is woven in a three-dimensional integrated manner during the weaving process.

[0062] To more clearly illustrate the method and structure of plain weave single-span deep cross-linking weave, this embodiment provides... Figure 1 Supplementary Explanation:

[0063] The plain weave cross-layer deep cross-linking weave method specifically refers to: the weft yarn and warp yarn are woven in a 0° orthogonal plain weave within the same horizontal weave layer with a predetermined number of bundles ( Figure 1 After the second bundle is shown, the weft yarn crosses the layer upwards or downwards into the third layer relative to the first layer before crossing the layer, and weaves a predetermined number of bundles with the warp yarns in the third layer at 0° orthogonal plain weave. Then it crosses the layer in the opposite direction again into the original weaving layer and weaves a predetermined number of bundles with the warp yarns at 0° orthogonal plain weave. After that, the first upward or downward crossing into the third layer is repeated to continue weaving. This process is repeated.

[0064] The weft yarns are crossed in a manner where adjacent weft yarn bundles are moved up and down respectively (adjacent weft yarns in the same knitting layer alternately cross up and down).

[0065] The width of the weft yarn across the layers is the same as the width of the predetermined number of bundles in the 0° orthogonal plain weave, and no warp yarns are woven within the width of the weft yarn (e.g., ...). Figure 1 The middle position shown in (a) and (b) indicates that the weft yarn crossover width is 2 bundles of warp yarn width.

[0066] As is known to those skilled in the art, depending on design requirements, weft yarns and warp yarns can be woven in 0° orthogonal plain weave within the same horizontal weave layer for 3 bundles or more, and then cross over to the next layer. The width of the crossover is not limited to 2 bundles.

[0067] The low-loss matrix was determined to be an epoxy resin matrix, which was filled within the braided structure and coated over it, with a coating thickness of <0.2 mm. The electromagnetic response spectrum parameters and reflection loss curve of the resulting structure are shown below. Figures 14-16 As shown.

[0068] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A gradient impedance multi-fiber hybrid broadband absorbing structure, characterized in that: Including multi-fiber preforms and low-loss matrix; The low-loss matrix is ​​filled into the multi-fiber preform and covers the multi-fiber preform with a coating thickness of <0.2 mm. The multi-fiber preform is formed by weaving a mixture of high-loss fibers, medium-loss fibers, and low-loss fibers. The multi-fiber preform includes a low-loss fiber woven to form an impedance matching layer, a low-loss fiber and a medium-loss fiber mixed woven to form an impedance transition layer, and a medium-loss fiber and a high-loss fiber mixed woven to form an absorption attenuation layer. The impedance matching layer, impedance transition layer and absorption attenuation layer are stacked sequentially to form a three-dimensional structure; The selection and weaving methods for high-loss, medium-loss, and low-loss fibers in the multi-fiber preform are as follows: Based on the design requirements, the types of high-loss, medium-loss, and low-loss fibers and the type of low-loss matrix are selected. The reflection coefficient S11 is better than -10 dB across the entire frequency band as the criterion. The specific types, contents, weaving methods, and detailed arrangement relationships between fibers are determined by simulation using the finite element full-wave analysis software HFSS. Finally, a woven body model is established according to the determined types, contents, weaving methods, and detailed arrangement relationships between fibers. The low-loss fiber is selected from at least one of silicon nitride fiber, SiBN ceramic fiber, quartz fiber, Al2O3 fiber, and mullite fiber; the medium-loss fiber is selected from one or two of near-stoichiometric silicon carbide fiber and polyborosilicate fiber heat-treated at 1600 ℃; the high-loss fiber is selected from one or two of carbon fiber, high-carbon high-oxygen silicon carbide fiber, and high-carbon low-oxygen silicon carbide fiber; the low-loss matrix is ​​selected from one of silicon nitride ceramic matrix, epoxy resin matrix, and mullite ceramic matrix. The low-loss fibers have a dielectric constant <10 and a loss tangent <0.01; among the medium-loss fibers, the near-stoichiometric silicon carbide fibers and the polyborosilicate fibers heat-treated at 1600 °C have a resistivity of 10. -1 ~10 13 Ω·cm; In the high-loss fiber: the resistivity of carbon fiber is 10 -7 ~10 -5 Ω·cm, resistivity of high-carbon, high-oxygen silicon carbide fiber and high-carbon, low-oxygen silicon carbide fiber 10 -5 ~10 -1 Ω·cm; the dielectric constant of the low-loss substrate is <10, and the loss tangent is <0.01; The low-loss fiber weaving, the mixed weaving of low-loss and medium-loss fibers, and the mixed weaving of medium-loss and high-loss fibers adopt one of plain weaving, twill weaving, and three-dimensional weaving, with a distribution density of 4 to 20 bundles / cm.

2. The gradient impedance multi-fiber hybrid broadband absorbing structure as described in claim 1, characterized in that: The three-dimensional weaving method is a 0° orthogonal plain weave cross-layer deep cross-linking weave; The specific method of plain weave cross-layer deep cross-linking is as follows: after the weft yarn and warp yarn are woven in a 0° orthogonal plain weave for a predetermined number of bundles in the same horizontal weave layer, the weft yarn crosses the layer upwards or downwards into the third layer relative to the first layer before crossing the layer and woven in a 0° orthogonal plain weave with the warp yarn in the third layer for a predetermined number of bundles. Then, it crosses the layer in the opposite direction again into the original weave layer and woven in a 0° orthogonal plain weave with the warp yarn for a predetermined number of bundles. After that, the first upward or downward crossing into the third layer is repeated to continue weaving. This process is repeated. The weft yarns are laid across layers by adjacent weft yarn bundles being laid vertically and horizontally respectively; The width of the weft yarn across the layer is the same as the width of the predetermined number of bundles of the 0° orthogonal plain weave, and no warp yarns are woven within the width of the layer.

3. The gradient impedance multi-fiber hybrid broadband absorbing structure as described in claim 2, characterized in that: The predetermined number of bundles is at least 2 bundles of warp yarns; The span width is at least the width of two warp yarns.

4. The gradient impedance multi-fiber hybrid broadband absorbing structure as described in claim 2, characterized in that: The multi-fiber preform is a three-dimensional woven preform formed based on plain weave single-span deep cross-linking weave, and is woven into it according to the following steps: Step 1: The first and second woven layers of the three-dimensional woven prefabricated component are woven with low-loss fibers. The low-loss fibers are arranged orthogonally and periodically in the warp and weft directions. There are 6 to 20 bundles of warp yarns and 4 to 14 bundles of weft yarns per 1 cm of the fabric. Step 2: The third and fourth woven layers of the three-dimensional woven preform are constructed using medium-loss fibers and low-loss fibers that cross over from the first and second woven layers in a plain weave. Simultaneously, the medium-loss fibers and low-loss fibers are arranged orthogonally and periodically in both the warp and weft directions. In the third and fourth woven layers of the three-dimensional woven preform, the volume ratio of low-loss fibers to medium-loss fibers is 1:3, and the fabric has 6-20 warp bundles and 4-14 weft bundles per 1 cm. Step 3: In the fifth and sixth woven layers of the three-dimensional woven preform, medium-loss fibers and high-loss fibers are selected and orthogonally plain-woven with the medium-loss fiber weft yarns that cross over from the third and fourth woven layers. At the same time, the medium-loss fibers and high-loss fibers are orthogonally periodically arranged in the warp and weft directions, respectively. In the fifth and sixth woven layers of the three-dimensional woven preform, the volume ratio of medium-loss fibers to high-loss fibers is 1:1, and there are 6 to 20 warp yarns and 4 to 14 weft yarns per 1 cm of fabric. The bulk density of the three-dimensional woven prefabricated fabric is 1.6–2.4 g / cm³. 3 The areal density is 600–1400 g / m³ 2 The thickness is 3 to 3.5 mm.

5. The gradient impedance-gradient multi-fiber hybrid broadband absorbing structure as described in claim 1, characterized in that: The multi-fiber preform is a three-dimensional woven preform based on plain or twill weave, woven into shape according to the following steps: The first step is to select low-loss fibers and use plain or twill weave to establish the upper two layers of two-dimensional fabric for the woven body model; the low-loss fibers are arranged orthogonally and periodically in the warp and weft directions; there are 6 to 20 bundles of warp and weft yarns per 1 cm of the fabric. The second step is to mix plain or twill weave of medium-loss and low-loss fibers: select low-loss and medium-loss fibers and use plain or twill weave to establish a two-layer two-dimensional fabric for the woven body model; the low-loss and medium-loss fibers are arranged orthogonally and periodically in the warp and weft directions, and the volume ratio of low-loss and medium-loss fibers is 1:1; there are 6 to 20 bundles of warp and weft yarns per 1 cm of fabric. Step 3: Plain or twill mixed weaving of medium-loss and high-loss fibers: Select medium-loss and high-loss fibers and use plain or twill weaving to establish the bottom two layers of two-dimensional fabric for the woven body model; the medium-loss and high-loss fibers are arranged orthogonally and periodically in the warp and weft directions, and the volume ratio of medium-loss and high-loss fibers is 1:1; there are 6 to 20 bundles of warp and weft yarns per 1 cm of fabric. Step 4: Stack the two-dimensional fabric created in the above steps from top to bottom to form a woven fabric model. The bulk density of the fabric is 2.2–3.5 g / cm³. 3 The areal density is 800–2000 g / m³ 2 The thickness is 3 to 3.5 mm.

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