A broadband absorbing structure and manufacturing method

Abstract

The present invention provides a broadband absorbing structure comprising: a hexagonal bottom interlayer and six absorbing walls with the same structure; the six absorbing walls are adjacent along the six sides of the bottom interlayer to form a hexagonal honeycomb cavity; wherein each of the absorbing walls comprises: a bottom honeycomb layer, which is vertically connected to the top surface of the bottom interlayer; an intermediate interlayer, which is arranged parallel to the bottom interlayer, and the bottom surface of the intermediate interlayer is connected to the top surface of the bottom honeycomb layer; an intermediate honeycomb layer, which is vertically connected to the top surface of the intermediate interlayer; and a surface interlayer, which is arranged parallel to the intermediate interlayer, and the bottom surface of the surface interlayer is connected to the top surface of the intermediate honeycomb layer. The broadband absorbing structure also comprises a bottom absorbing block, which is arranged inside the hexagonal honeycomb cavity and connected to the bottom interlayer. The present invention has the advantages of strong absorbing performance, wide absorbing range, stable structure, and simple manufacturing method.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic wave absorbing structures, and in particular relates to a broadband wave absorbing structure and a manufacturing method thereof. Background Art

[0002] With the advancement of microwave and communication technologies and the widespread application of electromagnetic materials, electromagnetic interference and electromagnetic compatibility (EMC) issues are attracting increasing attention from researchers. Absorbing structures, with their excellent electromagnetic wave absorption and shielding capabilities, are a common approach to addressing these issues. Electromagnetic materials are generally categorized into structural and coated types. Coated materials are typically thin films, which, due to thickness limitations, have limited absorption bandwidth. Structural electromagnetic materials not only address electromagnetic issues in equipment structures but also provide load-bearing capabilities, such as honeycomb structures and multi-layered graded impedance structures. They are typically fabricated through resin transfer molding, compression molding, and machining. Currently, the demand for "thin," "light," "wide," and "strong" electromagnetic materials is driven by competing demands for thickness, density, effective frequency band, and absorption and reflection efficiency, making it difficult to fully meet all four characteristics. For example, to achieve broadband absorption performance at a low structural thickness, absorber materials typically require a high absorbing particle ratio, resulting in high density and poor physical and chemical properties. Similarly, to achieve high shielding performance in all directions, conductive shielding materials require a high conductive particle ratio, resulting in high density and poor designability.

[0003] Current honeycomb absorbing structures primarily achieve good absorbing performance through methods such as immersion of the honeycomb walls, inclusion of absorbing agents in the honeycomb walls, and multi-layer stacking of absorbing honeycombs. However, these designs fail to prioritize the comprehensive selection of materials with superior absorbing properties, resulting in a poor cost-effectiveness in terms of thickness and broadband performance. Therefore, a new honeycomb absorbing structure is urgently needed that combines low-frequency and high-frequency absorbing layers to further broaden the absorbing bandwidth of the absorbing honeycomb. Summary of the Invention

[0004] The purpose of the present invention is to propose a broadband absorbing structure and manufacturing method, which combines the design and manufacturing of electromagnetic materials to realize the preparation of complex absorbing structures, improve the designability of the absorbing structure, and also improve other properties of the material, such as surface density and assembly, based on the characteristics of the absorbing structure.

[0005] To achieve the above objectives, the present invention provides a broadband absorbing structure, comprising: a hexagonal bottom interlayer and six absorbing walls with the same structure; the six absorbing walls are adjacent along the six sides of the bottom interlayer to form a hexagonal honeycomb cavity; wherein each of the absorbing walls comprises: a bottom honeycomb layer, which is vertically connected to the top surface of the bottom interlayer; an intermediate interlayer, which is arranged parallel to the bottom interlayer, and the bottom surface of the intermediate interlayer is connected to the top surface of the bottom honeycomb layer; an intermediate honeycomb layer, which is vertically connected to the top surface of the intermediate interlayer; and a surface interlayer, which is arranged parallel to the intermediate interlayer, and the bottom surface of the surface interlayer is connected to the top surface of the intermediate honeycomb layer.

[0006] Preferably, the broadband absorbing structure further comprises a bottom absorbing block, which is arranged inside the hexagonal honeycomb cavity and connected to the bottom interlayer.

[0007] Preferably, the bottom interlayer, the middle interlayer and the surface interlayer are made of glass fiber composite material or aramid fiber composite material; the bottom honeycomb layer and the middle honeycomb layer are made of Nomax honeycomb material with a surface coated with an absorbing coating.

[0008] Preferably, the thickness H1 of the surface interlayer, the thickness H3 of the middle interlayer and the thickness H3 of the bottom interlayer are in the range of 0.3 to 0.5 mm; the height H2 of the middle honeycomb layer and the height H4 of the bottom honeycomb layer are in the range of 4 to 10 mm, the side length d1 of the middle honeycomb layer and the side length d2 of the bottom honeycomb layer are in the range of 3 to 6 mm; the thickness of the honeycomb wall t1 of the middle honeycomb layer and the honeycomb wall t2 of the bottom honeycomb layer are 0.15 mm; the thickness of the surface absorbing coating T1 of the middle honeycomb layer and the thickness of the surface absorbing coating T2 of the bottom honeycomb layer are in the range of 0.1 to 0.3 mm; the bottom absorbing block is embedded in the interior of the hexagonal honeycomb cavity, the thickness H6 of the bottom absorbing block is in the range of 1 to 3 mm, and the cross section of the bottom absorbing block is a hexagon with a side length of

[0009] Preferably, the surface absorbing coatings of the middle honeycomb layer and the bottom honeycomb layer are both carbonyl iron or a mixture of ferrite and epoxy resin; the material of the absorbing block is a mixture of FeSi or FeSiAl and epoxy resin.

[0010] Preferably, the electromagnetic equivalent process of the broadband absorbing structure is calculated using a transmission-reflection method.

[0011] Preferably, the electromagnetic equivalent process calculated using the transmission-reflection method includes the following steps: step a, establishing a cross-sectional model of the absorbing wall, adjacently connecting six absorbing walls of the same structure to form a three-dimensional model of a hexagonal honeycomb volume unit, and forming a finite element model with multiple hexagonal honeycomb volume units; step b, performing simulation in CST software, using the finite element model established in step a and the finite difference time domain method to obtain a first transmission coefficient and a first reflection coefficient of the equivalent model; step c, obtaining electromagnetic parameters of the surface absorbing coating of the absorbing wall by an electromagnetic parameter testing method, and obtaining a second transmission coefficient and a second reflection coefficient of the surface absorbing coating by simulation calculation; step d, calculating the electromagnetic parameters by the Nicolson-Ross-Weil method based on the first transmission coefficient and the first reflection coefficient of the equivalent model obtained in step b and the first transmission coefficient and the first reflection coefficient of the surface absorbing coating obtained in step c.

[0012] Preferably, the broadband absorbing structure is composed of five absorbing layers, including a bottom interlayer, a bottom honeycomb layer, a middle interlayer, a middle honeycomb layer and a surface interlayer; the reflectivity RL of the material used in the broadband absorbing structure is optimized. If the thickness of each absorbing layer of the broadband absorbing structure is d k (k=1,2…,5), the relative complex permittivity and complex permeability are ε k and μ k , then the input impedance to vertically incident electromagnetic waves can be obtained by the following recursive formula: Among them, Z0 is the wave impedance of air; at the same time: Z in,1 =Z0Z1tanh(γ1d1), (k=2,…,n); where the propagation constant (k=1,…,n), j is the imaginary unit, f is the wave frequency, and C is the speed of light. The reflectivity of each absorbing layer material is calculated as follows:

[0013] Preferably, each absorbing layer in the broadband absorbing structure is optimized, and the thicknesses of the bottom interlayer, the middle interlayer, and the surface interlayer are equal; the thickness H2 of the middle honeycomb layer, the thickness H4 of the bottom honeycomb layer, and the thickness H6 of the bottom absorbing block are three independent thicknesses, and the optimization method of the independent thicknesses is completed using a genetic algorithm.

[0014] A method for manufacturing a broadband absorbing structure comprises the following steps:

[0015] Step S1, preparing a high-frequency absorbing slurry; the high-frequency absorbing slurry is prepared by mixing epoxy resin and carbonyl iron or ferrite, with the volume ratio of the two being 20% ​​to 45%, and adding a diluent, wherein the diluent is acetone, anhydrous ethanol, or nitro diluent, and the weight ratio of the diluent to the epoxy resin is 3:1 to 5:1;

[0016] Step S2, preparing a low-frequency absorbing slurry; mixing the low-frequency absorbing slurry epoxy resin with flake FeSi or flake FeSiAl in a volume ratio of 30% to 40%, and adding a diluent, wherein the diluent is acetone, anhydrous ethanol, or nitro diluent, and the weight ratio of the diluent to the epoxy resin is 3:1 to 5:1;

[0017] Step S3, dispersing the high-frequency absorbing slurry; adding a dispersant to the high-frequency absorbing slurry, and then stirring and dispersing it, the stirring speed is 650-750 rad / min, and the stirring time is 15-20 min;

[0018] Step S4, soaking the honeycomb layer with an absorbing slurry; soaking the surface of the middle honeycomb layer and the bottom honeycomb layer with the absorbing slurry, and performing multiple soaking treatments on the surface of the middle honeycomb layer and the bottom honeycomb layer to make the thickness of the absorbing coating 0.1 to 0.3 mm;

[0019] Step S5: The bottom absorbing block is prepared by spraying a low-frequency absorbing slurry. The bottom interlayer is used as a substrate, and the low-frequency absorbing slurry is sprayed on the top of the bottom interlayer to form the bottom absorbing block.

[0020] Step S6, assembling the interlayer and the honeycomb layer and forming them into an integrated whole; connecting the surface interlayer, the middle honeycomb layer, the middle interlayer, and the bottom honeycomb layer to form an assembled body of the absorbing wall, placing the assembled body of the absorbing wall on top of the bottom interlayer coated with the low-frequency absorbing slurry, and using vacuum hot pressing to achieve integrated manufacturing of the broadband absorbing structure.

[0021] In summary, compared with the prior art, the broadband absorbing structure and manufacturing method provided by the present invention have the following beneficial effects:

[0022] (1) The present invention uses a variety of absorbing materials for coating and filling, which not only takes into account the high-frequency and broadband absorbing characteristics, but also expands the low-frequency absorbing characteristics;

[0023] (2) The broadband absorbing structure designed in the present invention is formed by an integrated technology, which avoids the disadvantage of forming multiple layers of materials separately and then bonding them together. The absorbing structure has a large porosity and is lightweight. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart for the design and manufacturing of the broadband absorbing structure of the present invention;

[0025] Figure 2 A vertical cross-sectional view of a hexagonal honeycomb cavity of the broadband wave absorbing structure of the present invention;

[0026] Figure 3A finite element model of a honeycomb absorbing structure unit of the broadband absorbing structure of the present invention;

[0027] Figure 4 is the equivalent electromagnetic parameter of the broadband absorbing structure in this embodiment, where Figure 4 (a) is the dielectric constant, Figure 4 (b) is the magnetic permeability;

[0028] Figure 5 is the reflectivity performance curve of the broadband absorbing structure in this embodiment. DETAILED DESCRIPTION

[0029] The following will be combined with the appended Figure 1 ~Attached Figure 5 , the technical solutions, structural features, objectives achieved and effects in the embodiments of the present invention are described in detail.

[0030] It should be noted that the drawings are in a very simplified form and use non-precise proportions. They are only used to conveniently and clearly assist in explaining the embodiments of the present invention, and are not used to limit the conditions for the implementation of the present invention. Therefore, they have no substantive technical significance. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and purpose that can be achieved by the present invention.

[0031] It should be noted that, in the present invention, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only the elements explicitly listed, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0032] The design concept of the broadband absorbing structure of the present invention is as follows Figure 1 As shown, the method includes the following steps: step 1, designing a broadband absorbing structure, i.e., selecting the layers constituting the broadband absorbing structure; step 2, designing equivalent electromagnetic parameters of the broadband absorbing structure; step 3, optimizing the broadband absorbing structure; and step 4, preparing the broadband absorbing structure optimized in step 3.

[0033] 1. Broadband absorbing structure design

[0034] The broadband wave absorbing structure provided by the present invention comprises a hexagonal bottom interlayer 1 and six wave absorbing walls with the same structure; the six wave absorbing walls are adjacent to each other along the six sides of the bottom interlayer 1 to form a hexagonal honeycomb cavity; wherein, Figure 2 It is a vertical cross-sectional view of the hexagonal honeycomb cavity, and each of the absorbing walls includes: a bottom honeycomb layer 2, which is vertically connected to the top surface of the bottom interlayer 1; an intermediate interlayer 3, which is arranged parallel to the bottom interlayer 1, and the bottom surface of the intermediate interlayer 3 is connected to the top surface of the bottom honeycomb layer 2; an intermediate honeycomb layer 4, which is vertically connected to the top surface of the intermediate interlayer 3; a surface interlayer 5, which is arranged parallel to the intermediate interlayer 3, and the bottom surface of the surface interlayer 5 is connected to the top surface of the intermediate honeycomb layer 4; the broadband absorbing structure also includes a bottom absorbing block 6, which is arranged inside the hexagonal honeycomb cavity and connected to the bottom interlayer 1.

[0035] The bottom interlayer 1, the middle interlayer 3 and the surface interlayer 5 are made of glass fiber composite material or aramid fiber composite material; the bottom honeycomb layer 2 and the middle honeycomb layer 4 are made of Nomax honeycomb material coated with absorbing coating.

[0036] Among them, such as Figure 2 and Figure 3 As shown, the thickness H1 of the surface interlayer 5 ranges from 0.3 to 0.5 mm, the height H2 of the middle honeycomb layer 4 ranges from 4 mm to 10 mm, the side length d1 of the middle honeycomb layer 4 ranges from 3 mm to 6 mm (not shown in the figure), the thickness t1 of the honeycomb wall of the middle honeycomb layer 4 is 0.15 mm, and the thickness T1 of the surface absorbing coating of the middle honeycomb layer 4 ranges from 0.1 mm to 0.3 mm; the thickness H3 of the middle interlayer 3 ranges from 0.3 to 0.5 mm, the bottom honeycomb layer 2 has a similar structure to the middle honeycomb layer 4, and the bottom honeycomb layer 2 has a thickness of 0.1 mm to 0.3 mm. The height H4 ranges from 4 mm to 10 mm, the side length d2 of the bottom honeycomb layer 2 ranges from 3 mm to 6 mm (not shown in the figure), the thickness of the honeycomb wall t2 of the bottom honeycomb layer 2 is 0.15 mm, the thickness of the surface absorbing coating T2 of the bottom honeycomb layer 2 ranges from 0.1 mm to 0.3 mm, the thickness H5 of the bottom interlayer 1 ranges from 0.3 to 0.5 mm, the bottom absorbing block is embedded in the interior of the hexagonal honeycomb cavity, the thickness H6 of the bottom absorbing block 6 ranges from 1 mm to 3 mm, the cross section of the bottom absorbing block 6 is a hexagon with a side length of (not shown in the figure).

[0037] Furthermore, the surface absorbing coatings of the middle honeycomb layer 4 and the bottom honeycomb layer 2 are both carbonyl iron or a mixture of ferrite and epoxy resin; the material of the absorbing block 6 is a mixture of FeSi or FeSiAl and epoxy resin.

[0038] In this embodiment, the thickness H1 of the surface interlayer 5 is 0.5 mm, the height H2 of the middle honeycomb layer 4 is obtained through optimization design, the side length d1 of the middle honeycomb layer 4 is 6 mm, the thickness of the honeycomb wall t1 of the middle honeycomb layer 4 is 0.15 mm, the thickness of the surface absorbing coating T1 of the middle honeycomb layer 4 is 0.3 mm, and the surface absorbing coating is a mixture of carbonyl iron and epoxy resin; the thickness H3 of the middle interlayer 3 is 0.5 mm, the bottom honeycomb layer 2 has a similar structure to the middle honeycomb layer 4, and the height H4 of the bottom honeycomb layer 2 is 0.5 mm. Through optimization design, the side length d2 of the bottom honeycomb layer 2 is 6 mm, the thickness of the honeycomb wall t2 of the bottom honeycomb layer 2 is 0.15 mm, the surface absorbing coating T2 of the bottom honeycomb layer 2 is 0.2 mm thick, and the surface absorbing coating is a mixture of carbonyl iron and epoxy resin. The thickness of the bottom interlayer 1 and the thickness of the middle interlayer 3 are equal to 0.5 mm. The bottom absorbing block 6 is embedded in the interior of the first honeycomb cavity. The thickness H6 of the bottom absorbing block 6 is obtained through optimization design. The cross section of the bottom absorbing block 6 is a hexagon with a side length In this embodiment, the bottom absorbing block 6 is made of a mixture of FeSi and epoxy resin.

[0039] 2. Design of equivalent electromagnetic parameters of broadband absorbing structure

[0040] The electromagnetic parameter equivalent process of the broadband absorbing structure is calculated using the transmission-reflection method, which includes the following steps:

[0041] Step a: Establish the cross-section model of the absorbing wall, such as Figure 2 As shown, six absorbing walls with the same structure are adjacent to form a three-dimensional model of a hexagonal honeycomb volume unit, as shown Figure 3 As shown, in the finite element model composed of multiple hexagonal honeycomb volume units, two adjacent hexagonal honeycomb volume units share a honeycomb wall;

[0042] Step b, performing simulation in CST software (Computer Simulation Technology, a three-dimensional full-wave electromagnetic field simulation software), using the finite element model established in step a and the finite-difference time-domain method to obtain the first transmission coefficient and the first reflection coefficient of the equivalent model of step a;

[0043] Since the surface of the absorbing wall is also coated with a surface absorbing coating, it is also necessary to perform an equivalent simulation of the transmission reflection coefficient of the surface absorbing coating. In this embodiment, the surface absorbing coating of the absorbing wall is a mixture of carbonyl iron and epoxy resin with an added volume ratio of 45%.

[0044] Step c, obtaining electromagnetic parameters of the surface absorbing coating of the absorbing wall by an electromagnetic parameter testing method, and obtaining a second transmission coefficient and a second reflection coefficient of the surface absorbing coating by simulation calculation;

[0045] Step d, based on the first transmission coefficient and the first reflection coefficient of the equivalent model obtained in step b and the second transmission coefficient and the second reflection coefficient of the surface absorbing coating obtained in step c, the electromagnetic parameters are calculated by the Nicolson-Ross-Weil method; Figure 4 As shown, Figure 4 (a) is the simulated equivalent dielectric constant, Figure 4 (b) is the simulated equivalent magnetic permeability.

[0046] 3. Optimization design of broadband absorbing structure

[0047] In order to obtain an integrated structure for broadband wave absorption, the hexagonal honeycomb cavity structure of the broadband wave absorption structure is optimized. The hexagonal honeycomb cavity structure is composed of five wave absorption layers (including a bottom interlayer 1, a bottom honeycomb layer 2, a middle interlayer 3, a middle honeycomb layer 4, and a surface interlayer 5).

[0048] First, the reflectivity (RL) function of multiple absorbing layer materials is optimized. If the thickness of each absorbing layer of the broadband absorbing structure is d k (k=1,2…,5), the relative complex permittivity and complex permeability are ε k and μ k , then the input impedance of the five absorbing layers to vertically incident electromagnetic waves can be calculated using the following recursive formula:

[0049]

[0050] Where Z0 is the wave impedance of air;

[0051] Also available:

[0052] Z in,1 =Z0Z1tanh(γ1d1)

[0053]

[0054] Among them, the propagation constant (k=1,…,n), j is the imaginary unit, f is the wave frequency, C is the speed of light, and the reflectivity of each absorbing layer material is calculated as follows:

[0055]

[0056] The absorbing layers in the hexagonal honeycomb cavity structure were further optimized, where the thicknesses of the bottom interlayer 1, the middle interlayer 3, and the surface interlayer 5 were equal; the middle honeycomb layer H2, the bottom honeycomb layer H4, and the bottom absorbing block H6 had three independent thicknesses, and the optimization method of their independent thicknesses was completed using a genetic algorithm.

[0057] Specifically, according to the above optimization function, the reflectivity of the hexagonal honeycomb cavity material can be expressed as a function of three variables. The genetic algorithm selected a crossover factor of 0.9, a mutation factor of 0.05, an initial population of 800, and a maximum number of iterations of 10. The optimization objective function is the maximum number of frequencies at which the reflectivity (RL) falls below -8dB, with a total of 201 frequencies within the 1-18 GHz range. It should be noted that the above parameters are commonly used in genetic algorithms.

[0058] The optimization results obtained by genetic algorithm show that the height of the bottom honeycomb layer 2 of the hexagonal honeycomb cavity is 15mm, the thickness of the embedded bottom absorbing block 6 is 2mm, and the height of the middle honeycomb layer 4 is 8mm. The reflectivity curve of the hexagonal honeycomb cavity structure based on the above optimized structural parameters is as follows: Figure 5 As shown. Figure 5 The reflectivity performance curve shows that the absorbing material reaches -13dB at 1GHz, around -8dB at 2GHz, and can remain below -8dB above 6GHz. It reaches a minimum value near 10.5GHz, close to -18dB. The material's absorbing performance is weak in the 2-6GHz range, but can still be maintained below -6dB. This result shows that the high-frequency broadband and low-frequency absorbing properties of the optimized absorbing structure have been improved.

[0059] 4. Manufacturing method of broadband absorbing structure

[0060] The broadband wave absorbing structure provided by the present invention is manufactured by vacuum hot pressing technology, and the manufacturing method thereof is as follows:

[0061] Step S1, preparing high-frequency absorbing slurry;

[0062] The high-frequency absorbing slurry is a mixture of epoxy resin and carbonyl iron or ferrite (epoxy resin and carbonyl iron are mixed in this embodiment), with the volume ratio of the two being 20% ​​to 45% (the volume ratio in this embodiment is 45%), and a diluent is added, the diluent being acetone, anhydrous ethanol, nitro diluent, etc. (nitro diluent is used in this embodiment), and the weight ratio of the diluent to the epoxy resin is 3:1 to 5:1 (the weight ratio in this embodiment is 4:1);

[0063] Step S2, preparing low-frequency absorbing slurry;

[0064] Similar to the high-frequency absorbing slurry preparation method, the low-frequency absorbing slurry is prepared by mixing epoxy resin with FeSi flakes or FeSiAl flakes (in this embodiment, epoxy resin and FeSi flakes are mixed), with the volume ratio of the two being 30% to 40% (the volume ratio in this embodiment is 40%), and adding a diluent, such as acetone, anhydrous ethanol, or nitro diluent (in this embodiment, nitro diluent is used), with the weight ratio of the diluent to the epoxy resin being 3:1 to 5:1 (the weight ratio in this embodiment is 4:1);

[0065] Step S3, dispersing high-frequency absorbing slurry;

[0066] A dispersant is added to the high-frequency absorbing slurry, and then stirred and dispersed at a stirring speed of 650 to 750 rad / min (the dispersant used in this embodiment is white carbon black, weighing 1.5 g, and the stirring speed is 700 rad / min) for 15 to 20 minutes (the stirring time in this embodiment is 20 minutes);

[0067] Step S4, soaking the honeycomb layer with the microwave absorbing slurry;

[0068] The surface absorbing coating of the middle honeycomb layer 4 and the bottom honeycomb layer 2 is soaked in a high-frequency absorbing slurry. The surfaces of the middle honeycomb layer 4 and the bottom honeycomb layer 2 are soaked multiple times to ensure that the thickness of the absorbing coating is 0.1 to 0.3 mm (the thickness of the surface absorbing coating in this embodiment is 0.3 mm).

[0069] Step S5, spraying the bottom absorbing block;

[0070] The bottom absorbing block 6 is prepared by spraying a low-frequency absorbing slurry. The bottom interlayer 1 is used as a substrate, and the low-frequency absorbing slurry is sprayed on the top of the bottom interlayer 1 to form the bottom absorbing block 6. The coating thickness is 1 to 3 mm, that is, the thickness of the bottom absorbing block 6 is 1 to 3 mm (the thickness of the bottom absorbing block 6 in this embodiment is 2 mm);

[0071] Step S6: assembling the interlayer and the honeycomb layer and forming them into an integrated whole;

[0072] The surface interlayer 5, the middle honeycomb layer 4, the middle interlayer 3, and the bottom honeycomb layer 2 are connected to form an assembly of an absorbing wall, and the assembly of the absorbing wall is placed on the top of the bottom interlayer 1 coated with a low-frequency absorbing slurry (equivalent to assembling the bottom absorbing block 6 on the top of the bottom interlayer 1). Vacuum hot pressing is used to achieve integrated manufacturing of the broadband absorbing structure.

[0073] In summary, compared with the prior art, the broadband absorbing structure provided by the present invention has the advantages of strong absorbing performance, wide absorbing range, stable structure and simple manufacturing method.

[0074] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. After reading the above description, various modifications and substitutions of the present invention will become apparent to those skilled in the art. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A broadband absorbing structure, characterized in that: include: A hexagonal bottom interlayer (1) and six absorbing walls with the same structure; The six wave-absorbing walls are adjacent to each other along the six sides of the bottom interlayer (1) to form a hexagonal honeycomb cavity; Wherein, each of the wave-absorbing walls comprises: A bottom honeycomb layer (2) vertically connected to the top surface of the bottom sandwich layer (1); An intermediate interlayer (3) is arranged parallel to the bottom interlayer (1), and the bottom surface of the intermediate interlayer (3) is connected to the top surface of the bottom honeycomb layer (2); an intermediate honeycomb layer (4) vertically connected to the top surface of the intermediate interlayer (3); A surface interlayer (5) is arranged parallel to the middle interlayer (3), and the bottom surface of the surface interlayer (5) is connected to the top surface of the middle honeycomb layer (4); The broadband wave absorbing structure further comprises a bottom wave absorbing block (6), which is arranged inside the hexagonal honeycomb cavity and connected to the bottom interlayer (1); The thickness H1 of the surface interlayer (5), the thickness H3 of the middle interlayer (3), and the thickness H3 of the bottom interlayer (1) are in the range of 0.3 to 0.5 mm; The height H2 of the middle honeycomb layer (4) and the height H4 of the bottom honeycomb layer (2) are in the range of 4 mm to 10 mm, and the side length d1 of the middle honeycomb layer (4) and the side length d2 of the bottom honeycomb layer (2) are in the range of 3 mm to 6 mm; The thickness of the honeycomb wall t1 of the middle honeycomb layer (4) and the honeycomb wall t2 of the bottom honeycomb layer (2) is 0.15 mm; The thickness of the surface absorbing coating T1 of the middle honeycomb layer (4) and the thickness of the surface absorbing coating T2 of the bottom honeycomb layer (2) are in the range of 0.1 mm to 0.3 mm; The bottom absorbing block is embedded in the interior of the hexagonal honeycomb cavity. The thickness H6 of the bottom absorbing block (6) ranges from 1 mm to 3 mm, and the cross section of the bottom absorbing block (6) is a hexagon with a side length of 2. The broadband absorbing structure according to claim 1, wherein: The bottom interlayer (1), the middle interlayer (3) and the surface interlayer (5) are made of glass fiber composite material or aramid fiber composite material; The bottom honeycomb layer (2) and the middle honeycomb layer (4) are made of Nomax honeycomb material with a surface coated with a wave-absorbing coating.

3. The broadband absorbing structure according to claim 2, wherein: The surface absorbing coatings of the middle honeycomb layer (4) and the bottom honeycomb layer (2) are both carbonyl iron or a mixture of ferrite and epoxy resin; The material of the wave absorbing block (6) is a mixed material of FeSi or FeSiAl and epoxy resin.

4. The broadband absorbing structure according to claim 3, wherein: The electromagnetic equivalent process of the broadband absorbing structure is calculated using the transmission-reflection method.

5. The broadband absorbing structure according to claim 4, wherein: The electromagnetic equivalent process calculated using the transmission-reflection method includes the following steps: Step a, establishing a cross-sectional model of the absorbing wall, connecting six absorbing walls with the same structure to form a three-dimensional model of a hexagonal honeycomb volume unit, and forming a finite element model with multiple hexagonal honeycomb volume units; Step b: performing simulation in CST software, using the finite element model established in step a and the finite-difference time-domain method to obtain a first transmission coefficient and a first reflection coefficient of the equivalent model; Step c, obtaining electromagnetic parameters of the surface absorbing coating of the absorbing wall by an electromagnetic parameter testing method, and obtaining a second transmission coefficient and a second reflection coefficient of the surface absorbing coating by simulation calculation; Step d: Based on the first transmission coefficient and the first reflection coefficient of the equivalent model obtained in step b and the first transmission coefficient and the first reflection coefficient of the surface absorbing coating obtained in step c, the electromagnetic parameters are calculated using the Nicolson-Ross-Weil method.

6. The broadband absorbing structure according to claim 5, wherein: The broadband absorbing structure is composed of five absorbing layers, including a bottom interlayer (1), a bottom honeycomb layer (2), an intermediate interlayer (3), an intermediate honeycomb layer (4) and a surface interlayer (5); the reflectivity RL of the material used in the broadband absorbing structure is optimized. If the thickness of each absorbing layer of the broadband absorbing structure is d k (k=1,2…,5), the relative complex permittivity and complex permeability are ε k and μ k , then the input impedance to vertically incident electromagnetic waves can be obtained by the following recursive formula: Where Z0 is the wave impedance of air; Also available: Z in,1 =Z0Z1 tanh(γ1d1) Among them, the propagation constant (k=1,…,n), j is the imaginary unit, f is the wave frequency, and C is the speed of light. The reflectivity of each absorbing layer material is calculated as follows:

7. The broadband absorbing structure according to claim 6, wherein: Each absorbing layer in the broadband absorbing structure is optimized. The thicknesses of the bottom interlayer (1), the middle interlayer (3) and the surface interlayer (5) are equal. The thickness H2 of the middle honeycomb layer (4), the thickness H4 of the bottom honeycomb layer (2) and the thickness H6 of the bottom absorbing block (6) are three independent thicknesses. The optimization method of the independent thicknesses is completed using a genetic algorithm.

8. A method for manufacturing a broadband absorbing structure according to any one of claims 1 to 7, characterized in that: The steps include: Step S1, preparing a high-frequency absorbing slurry; the high-frequency absorbing slurry is prepared by mixing epoxy resin and carbonyl iron or ferrite, with the volume ratio of the two being 20% ​​to 45%, and adding a diluent, wherein the diluent is acetone, anhydrous ethanol, or nitro diluent, and the weight ratio of the diluent to the epoxy resin is 3:1 to 5:1; Step S2, preparing a low-frequency absorbing slurry; mixing the low-frequency absorbing slurry epoxy resin with flake FeSi or flake FeSiAl in a volume ratio of 30% to 40%, and adding a diluent, wherein the diluent is acetone, anhydrous ethanol, or nitro diluent, and the weight ratio of the diluent to the epoxy resin is 3:1 to 5:1; Step S3, dispersing the high-frequency absorbing slurry; adding a dispersant to the high-frequency absorbing slurry, and then stirring and dispersing it, the stirring speed is 650-750 rad / min, and the stirring time is 15-20 min; Step S4, soaking the honeycomb layer with the microwave absorbing slurry; The surface absorbing coating of the middle honeycomb layer (4) and the bottom honeycomb layer (2) is soaked in absorbing slurry, and the surfaces of the middle honeycomb layer (4) and the bottom honeycomb layer (2) are soaked multiple times to make the thickness of the absorbing coating 0.1 to 0.3 mm; Step S5, spraying the bottom absorbing block; the bottom absorbing block (6) is prepared by spraying a low-frequency absorbing slurry, with the bottom interlayer (1) as the substrate, and the low-frequency absorbing slurry is sprayed on the top of the bottom interlayer (1) to form the bottom absorbing block (6); Step S6, assembling the interlayer and the honeycomb layer and forming them into an integrated whole; connecting the surface interlayer (5), the middle honeycomb layer (4), the middle interlayer (3), and the bottom honeycomb layer (2) to form an assembled body of the absorbing wall, placing the assembled body of the absorbing wall on top of the bottom interlayer (1) coated with the low-frequency absorbing slurry, and adopting a vacuum hot pressing method to realize the integrated manufacturing of the broadband absorbing structure.

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