Preparation method of multilayer structure broadband wave absorbing material

Abstract

The application belongs to the technical field of electromagnetic wave absorbing materials, and discloses a preparation method of a multilayer structure broadband wave absorbing material. First, the relative dielectric constant and the relative magnetic permeability of a single-layer material are tested; then, an impedance recursive formula is established based on the transmission line theory, two-layer combinations are taken as optimization units, and the optimal impedance matching surface layer is determined by global search; finally, the layer-by-layer optimization of the thickness of each layer is realized by using the layer-by-layer recursive method. The application breaks through the limitation of the Kramers-Kronig relationship on homogeneous materials, establishes a full-process designable method from electromagnetic parameter testing to structure optimization, overcomes the blindness of the existing layer structure experience trial and error, and is suitable for different wave absorbing agents and matrix systems, and has universality.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing materials technology, specifically relating to a method for preparing a multilayer broadband absorbing material. Background Technology

[0002] With the rapid development of technologies such as radar detection and 5G communication, the demand for high-performance electromagnetic wave (EMW) absorbing materials in military stealth and civilian electromagnetic compatibility fields is becoming increasingly urgent. Traditional techniques mainly involve blending powdered absorbing agents with a polymer matrix to prepare homogeneous composite materials. However, these materials suffer from a fundamental technical bottleneck: according to the Kramers-Kronig relation, the high imaginary part of the electromagnetic parameters required for strong absorption inevitably leads to a drastic change in the real part with frequency, making the ideal impedance matching condition only valid within an extremely narrow frequency band, making it difficult to simultaneously achieve effective absorption bandwidth (EAB) and absorption intensity. To overcome these limitations, researchers have recently turned to multilayer structure engineering, attempting to optimize impedance matching and energy dissipation through gradient electromagnetic parameter control between functional layers. However, existing layered structure designs generally lack theoretical guidance and often employ empirical trial-and-error strategies, such as simply increasing or decreasing the filler content layer by layer or constructing electromagnetic parameter gradients based on subjectively set fixed proportions. This blind and aimless design approach makes it difficult to accurately calculate the equivalent electromagnetic parameters of each layer and the optimal thickness matching relationship, resulting in uncontrollable interlayer interface reflections, limited improvement in absorption bandwidth, and the inability to pre-design for specific frequency bands. In addition, existing methods have failed to establish a quantitative calculation model from electromagnetic parameter testing to multilayer structure optimization, and cannot achieve full-process designability of "material-structure-performance", which seriously restricts the engineering application of broadband strong absorbing materials.

[0003] Therefore, there is an urgent need to develop a multi-layer structure pre-design method based on impedance matching theory and establish a quantifiable layer-by-layer recursive optimization method to systematically solve the blindness of traditional empirical trial-and-error design and achieve accurate design and performance prediction of broadband absorbing material structures. Summary of the Invention

[0004] To address the technical bottlenecks of traditional homogeneous absorbing materials, which are constrained by the Kramers-Kronig relationship and cannot simultaneously achieve ultra-wideband and strong absorption, and the lack of theoretical guidance in the design of existing layered structures, which relies on empirical trial and error, the present invention aims to provide a method for preparing multilayered broadband absorbing materials that is universally applicable.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a multilayer broadband absorbing material, wherein the total number of layers in the multilayer broadband absorbing material is n, n≥2, and the layers are sequentially arranged from the surface layer downwards as layer 1, layer 2, ..., layer n; the preparation steps are as follows: S1. According to different electromagnetic component ratios, m homogeneous single-layer absorbing materials are prepared using conventional techniques, where m ≥ n; the electromagnetic components mainly consist of a matrix and an absorbing agent. S2. Electromagnetic parameters of homogeneous monolayer absorbing materials: The ε'-f curve, ε''-f curve, μ'-f curve, and μ''-f curve of each homogeneous monolayer absorbing material in the 2~18GHz frequency band were tested using a vector network analyzer. The relative permittivity corresponding to each frequency was obtained based on the ε'-f curve and ε''-f curve. ε r The relative permeability at each frequency is obtained from the μ'-f curve and the μ''-f curve. μ r Where ε' is the real part of the permittivity; ε'' is the imaginary part of the permittivity; μ' is the real part of the permeability; μ'' is the imaginary part of the permeability; and f is the frequency. ε r It is the relative permittivity; μ r Relative permeability; Then, the intrinsic impedance and complex transmission constant corresponding to each frequency are calculated according to formulas (1) and (2), respectively; where, ε n The relative permittivity of the nth layer; μ n The relative permeability of the nth layer; η 0 represents the intrinsic impedance of free space; η n The intrinsic impedance of the nth layer; γ n Let n be the complex transmission constant of the nth layer; j The imaginary unit; f For frequency; c The speed of light; ; ; S3. Determination of the impedance matching surface layer: Based on the impedance recursion formula (3) of transmission line theory, the process is recursively applied layer by layer. The objective function is to maximize the effective absorption bandwidth EAB when the reflection loss RL1 ≤ -10dB. The homogeneous single-layer absorbing materials prepared in step S1 are combined in pairs. Using the two-layer combination as the optimization unit, a global search is employed to determine the surface material corresponding to the maximized EAB as the impedance matching surface layer of the multilayer broadband absorbing material, i.e., the first layer. Z n Let n be the wave impedance of the nth layer. Z n-1 The wave impedance of the (n-1)th layer, η n-1 The intrinsic impedance of the (n-1)th layer, tn-1 The thickness of the (n-1)th layer is... r n-1 The complex transmission constant of the (n-1)th layer; ; S4. Gradient structure optimizes the thickness of each layer layer by layer: S4.1 After determining the first layer material of the multilayer broadband absorbing material in step S3, the remaining homogeneous single-layer absorbing materials prepared in step S1, except for the first layer material, are sequentially determined as the second, ..., nth layers of the multilayer broadband absorbing material in order (arranged according to gradually increasing dielectric constant, gradually decreasing dielectric constant, or wave-like arrangement). S4.2 According to formula (3), a layer-by-layer recursive approach is adopted to reduce reflection loss. RL Maximizing the effective absorption bandwidth (EAB) when 1 ≤ -10 dB is the objective function. Using a two-layer combination as the optimization unit, a global search is employed to determine the design thickness of the first n-1 layers layer by layer. t 1. t 2, ... t n-1 Meanwhile, the fitted thickness of the nth layer is retained. t n ; S5. Fabrication of multilayer broadband absorbing materials: According to the design thickness of the first n-1 layers determined in step S4 t 1. t 2, ... t n-1 and the fitted thickness of the nth layer t n The homogeneous single-layer absorbing materials of corresponding thickness are stacked sequentially to prepare multi-layer broadband absorbing materials using conventional techniques.

[0006] Preferably, the specific process of step S3 is as follows: S3.1, Using the metal substrate as the third layer, perform impedance recursion to obtain the wave impedance of the third layer. Z 3=0, and the wave impedance of the second layer of absorbing material is obtained according to formula (3). Z 2, as shown in formula (4); ; S3.2, Based on the wave impedance of the second layer of absorbing material Z 2. Continuing to recursively derive formula (3), the wave impedance of the first layer of absorbing material is obtained. Z 1. As shown in formula (5); ; S3.3 Calculate the overall reflection loss of the absorbing material according to formula (6); where,Z 0 represents free space impedance; ; S3.4. Combine the homogeneous monolayer absorbing materials prepared in step S1 in pairs, using the two-layer combination as the optimization unit, and taking the reflection loss as the optimization factor. RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the first layer design thickness as the basis. t The thickness of the fitted layer 1 and layer 2 t 2 is the optimization variable. A global search is performed in the range of 0.1~5mm. Through successive calculations, the homogeneous single-layer absorbing material corresponding to the maximum EAB is determined as the impedance matching surface layer of the multi-layer broadband absorbing material, i.e., the first layer.

[0007] Preferably, the specific process of step S4.2 is as follows: S4.2.1 For an n-layer broadband absorbing material, the (n+1)th layer is a metal substrate, and the wave impedance of the (n+1)th layer is... Z n+1 =0, and the wave impedance of the nth layer of absorbing material is obtained according to formula (3). Z n As shown in formula (7); ; According to wave impedance Z n According to formula (3), the wave impedance of the (n-1)th layer is calculated. Z n-1 As shown in formula (8); ; According to wave impedance Z n-1 According to formula (3), the wave impedance of the (n-2)th layer is calculated. Z n-2 Then, based on the wave impedance Z n-2 According to formula (3), the wave impedance of the (n-3)th layer is calculated. Z n-3 And so on, until the wave impedance of the first layer is calculated. Z 1. As shown in formula (9); ; Calculate the overall reflection loss of the absorbing material according to formula (10); ; Based on the actual requirement of the number of layers n of the multilayer broadband absorbing material to be prepared, operate according to the following steps S4.2.2~S4.2.6; however, for an n-layer broadband absorbing material, the design thickness of the first n-1 layers should be fixed. t1. t 2, ... t n-2 , t n-1 At the same time, retain the fitting thickness of the nth layer. t n ; S4.2.2, For two-layer broadband absorbing materials: According to Z 3=0, obtained by recursively applying formulas (7) to (9). Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the first layer design thickness as the basis. t The thickness of the fitted layer 1 and layer 2 t 2. As an optimization variable, a global search is performed within the range of 0.1~5mm, while the design thickness of the first layer is fixed. t 1; S4.2.3 For a 3-layer broadband absorbing material: fix the design thickness of the first layer. t 1; According to Z 4 = 0, obtained by recursively applying formulas (7) to (9). Z 3. Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the second layer design thickness as the basis. t 2 and 3rd layer fitting thickness t 3 is the optimization variable; a global search is performed within the range of 0.1~5mm, while the design thickness of the second layer is fixed. t 2; S4.2.4 For a 4-layer broadband absorbing material: fix the design thickness of the first layer. t 1. Design thickness of the second layer t 2; According to Z 5 = 0, obtained by recursively applying formulas (7) to (9). Z 4. Z 3. Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the design thickness of the 3rd layer as the basis. t Fitted thickness of layers 3 and 4 t 4. As an optimization variable, a global search is performed within the range of 0.1~5mm, while the design thickness of the third layer is fixed. t 3; S4.2.5 For a 5-layer broadband absorbing material: fix the design thickness of the first layer. t 1. Design thickness of the second layer t 2. Thickness of the third layer t 3; According to Z 6 = 0, obtained by recursively applying formulas (7) to (9). Z 5. Z 4. Z 3. Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the design thickness of the 4th layer as the basis. t Fitted thickness of layers 4 and 5 t 5 is the optimization variable, and a global search is performed within the range of 0.1~5mm, while the design thickness of the 4th layer is fixed. t 4; S4.2.6 Following the method in steps S4.2.2~S4.2.5, for an n-layer broadband absorbing material: fix the design thickness of the first n-2 layers. t 1. t 2, ... t n-2 ;according to Z n+1 =0, obtained by recursively applying formulas (7) to (9). Z n , Z n-1 , Z n-2 ... Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the design thickness of the (n-1)th layer as the criterion. t n-1 and the thickness of the nth layer t n To optimize variables, a global search was performed within the range of 0.1~5mm, while the design thickness of the (n-1)th layer was fixed. t n-1 .

[0008] Fortunately, all global searches involved were performed using Python software.

[0009] Ideally, the step size for all global searches involved is 0.1 mm.

[0010] Preferably, the absorbing agent is one or more materials with electromagnetic loss characteristics.

[0011] Preferably, the microwave absorbing agent is one or more of MXene, graphene nanosheets (GNP), carbon nanotubes (CNT), carbonyl iron powder (CIP), and nickel particles (Ni).

[0012] Preferably, the matrix is ​​a thermoplastic polymer matrix.

[0013] Preferably, the matrix is ​​one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), thermoplastic polyurethane (TPU), polyether ether ketone (PEEK), epoxy resin or polyimide.

[0014] In this invention, the wave impedance calculation of the multilayer broadband absorbing material follows the exact reverse order of thickness design, with the wave impedance calculated from the bottom layer (…). Z n+1 Starting from =0), the wave impedance is recursively calculated up to the first layer. Z 1; Thickness design starts from the surface layer (layer 1), first with... t 2. The fitted thickness ranges from 0.1 to 5 mm to obtain the optimal design thickness for the surface layer. t 1; then fix the design thickness of the surface layer. t 1. With t The fitted thickness ranges from 0.1 to 5 mm, thus obtaining the optimal design thickness for the second layer. t 2; then fix the design thickness of the surface layer and the second layer. t 1. t 2, with t 4. The fitted thickness ranges from 0.1 to 5 mm, thus obtaining the optimal design thickness for the third layer. t 3; and so on, successively obtaining the design thickness of the first n-1 layers. t 1, t 2, t 3, ... t n-1 For multi-layered broadband absorbing materials, the wave impedance is always changing, so layer-by-layer recursive calculations must be performed each time.

[0015] Beneficial effects: (1) Overcoming the Kramers-Kronig relation constraint to achieve collaborative optimization of ultra-wideband strong absorption: This invention guides the design of multilayer structures using an impedance recursion method, effectively overcoming the inherent contradiction that traditional homogeneous materials, constrained by the Kramers-Kronig relationship, cannot simultaneously achieve wide bandwidth and strong absorption. The designed multilayer absorbing material, with a total thickness of 2-12 mm, achieves an effective absorption bandwidth (EAB) exceeding 10 GHz, and a low reflection loss. RL minThe absorption rate is below -60dB, which significantly improves the microwave absorption performance compared to traditional homogeneous materials. (2) Overcome the blindness of trial and error, and significantly reduce R&D costs and cycle: Unlike existing technologies that rely on trial and error based on experience and blindly adjust the filler content in random layered designs, this invention innovatively constructs a collaborative optimization system based on impedance recursion and global search algorithms. This method achieves full-process pre-design from electromagnetic parameter testing to structural optimization through a three-step strategy of "testing-screening-recursive optimization". While ensuring optimization accuracy, it significantly reduces experimental costs and shortens the R&D cycle, effectively avoiding the defects of poor experimental repeatability, uncontrollable interlayer reflection and high resource consumption in traditional methods. (3) Good engineering applicability and scalability: The method of this invention is compatible with existing microwave absorbing material preparation processes, requiring no complex chemical modification or expensive equipment. Through examples, it has been verified that the method achieves excellent broadband microwave absorption performance in both Ni@MXene / PVDF-HFP and Ni@MXene / PEEK systems, fully demonstrating its universality and scalability. It has important application value for next-generation electromagnetic stealth equipment, electromagnetic compatibility of 5G communication equipment, and anti-interference protection of precision instruments. Attached Figure Description

[0016] Figure 1 Scanning electron microscope images of different absorbing agents, a1~a5 correspond to Ni to MXene mass ratios of 4∶0, 3∶1, 2∶2, 1∶3, and 0∶4, respectively.

[0017] Figure 2 : ε'-f curves, ε''-f curves, μ'-f curves and μ''-f curves of different homogeneous monolayer absorbing materials. a1~a4 correspond to homogeneous monolayer Ni@MXene / PVDF-HFP absorbing materials, and b1~b4 correspond to homogeneous monolayer Ni@MXene / PEEK absorbing materials.

[0018] Figure 3 In Example 1, the reflection loss of Zxy varies with frequency and the thickness of the fitted substrate in a two-dimensional contour plot. a1~a4 correspond to Z43, Z42, Z41, and Z40 respectively; b1~b4 correspond to Z34, Z32, Z31, and Z30 respectively; c1~c4 correspond to Z24, Z23, Z21, and Z20 respectively; d1~d4 correspond to Z14, Z13, Z12, and Z10 respectively; and e1~e4 correspond to Z04, Z03, Z02, and Z01 respectively.

[0019] Figure 4Example 3: Two-dimensional contour plot of the reflection loss of Zpxy as a function of frequency and substrate thickness. a1~a3 correspond to Zp12, Zp13, Zp14, respectively; b1~b3 correspond to Zp21, Zp23, Zp24, respectively; c1~c3 correspond to Zp31, Zp32, Zp34, respectively; d1~d3 correspond to Zp41, Zp42, Zp43, respectively.

[0020] Figure 5 Two-dimensional contour plots showing the variation of reflection loss of different layers of absorbing materials in Examples 1-3 and Comparative Examples 1-2 with frequency and bottom layer thickness. a1-a4 correspond to the 2-layer, 3-layer, 4-layer and 5-layer structures of Example 1, b1-b4 correspond to the 2-layer, 3-layer, 4-layer and 5-layer structures of Example 2, c1-c4 correspond to the 2-layer, 3-layer, 4-layer and 5-layer structures of Comparative Example 1, d1-d4 correspond to the 2-layer, 3-layer, 4-layer and 5-layer structures of Comparative Example 2, and e1-e3 correspond to the 2-layer, 3-layer and 4-layer structures of Example 3.

[0021] Figure 6 Example 1 of the bow-shaped method test: The reflection loss of the 3-layer broadband Ni@MXene / PVDF-HFP absorbing material prepared in step S5 varies with frequency.

[0022] Figure 7 Comparative Example 3: Two-dimensional contour plots of reflection loss of different homogeneous single-layer absorbing materials as a function of frequency and thickness. (a) corresponds to L(4∶0), (b) corresponds to L(3∶1), (c) corresponds to L(2∶2), (d) corresponds to L(1∶3), and (e) corresponds to L(0∶4). Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0024] In Example 1, the Ni@MXene microwave absorbing agent can be prepared according to references 1-3, but the present invention prefers to prepare it according to the method of reference 3; the homogeneous monolayer Ni@MXene / PVDF-HFP microwave absorbing material can be prepared according to references 4-6, but the present invention prefers to prepare it according to the method of reference 6; the references are as follows: [1] L. Liang, R. Yang, G. Han, Y. Feng, B. Zhao, R. Zhang, Y. Wang, C. Liu, Enhanced Electromagnetic Wave-Absorbing Performance of MagneticNanoparticles-Anchored 2D Ti3C2Tx MXene. ACS Appl. Mater. Interfaces 2020, 12(2), 2644-2654. 10.1021 / acsami.9b18504. [2] A. Liu, H. Qiu, X. Lu, H. Guo, J. Hu, C. Liang, M. He, Z. Yu, Y.Zhang, J. Kong, J. Gu, Asymmetric Structural MXene / PBO Aerogels for High-Performance Electromagnetic Interference Shielding with Ultra-Low Reflection. Adv. Mater. 2025, 37 (5), 2414085. https: / / doi.org / 10.1002 / adma.202414085. [3] Feng Yuezhan, Liang Luyang, Han Gaojie, Li Liang, Zhou Bing, Wang Yaming, Liu Chuntai. An MXene-magnetic metal composite material and its preparation method. CN109712769B, 2020-11-03. [4] L. Liang, P. Xu, Y. Wang, Y. Shang, J. Ma, F. Su, Y. Feng, C. He,Y. Wang, C. Liu, Flexible polyvinylidene fluoride film with alternating oriented graphene / Ni nanochains for electromagnetic interference shielding and thermal management. Chem. Eng. J. 2020, 395, 125209. https: / / doi.org / 10.1016 / j.cej.2020.125209. [5] Y. Zhou, J. Sun, Z. Li, B. Zhou, C. Liu, Y. Feng, Regulatingintegral alignment of magnetic MXene nanosheets in layered composites to achieve high-effective electromagnetic wave absorption. Compos. Sci. Technol.2024, 256, 110746. https: / / doi.org / 10.1016 / j.compscitech.2024.110746. [6] Y. Zhou, W. Zhang, D. Pan, Z. Li, B. Zhou, M. Huang, L. Mi, C. Liu, Y. Feng, C. Shen, Absorption–Reflection–Transmission Power CoefficientGuiding Gradient Distribution of Magnetic MXene in Layered Composites for Electromagnetic Wave Absorption. Nano-Micro Lett. 2025, 17 (1), 147. 10.1007 / s40820-025-01675-7.

[0025] Example 1 A method for preparing a multilayer broadband Ni@MXene / PVDF-HFP microwave absorbing material (optimal surface layer + gradient-following layer) includes the following steps: S1. Preparation of homogeneous single-layer absorbing material: S1.1 Five Ni@MXene microwave absorbing agents were prepared by adjusting the mass ratio of Ni to MXene to 4:0, 3:1, 2:2, 1:3, and 0:4, respectively, using the method disclosed in Reference 3. Scanning electron micrographs of the different absorbing agents are shown below. Figure 1 As shown, a1 to a5 correspond to the microwave absorbing agents obtained by mass ratios of 4∶0, 3∶1, 2∶2, 1∶3, and 0∶4, respectively. Figure 1 a1 and Figure 1 a5 exhibits uniformly sized monodisperse Ni particles and pure MXene nanosheets with a size of 6µm. Other microwave absorbers (3:1, 2:2, 1:3) show a gradual decrease in the number of Ni particles. Figure 1 a2~1a4); S1.2. Weigh out the five Ni@MXene absorbing agents obtained in step S1.1 according to the addition amount of 10wt% (the total mass percentage of absorbing agent + matrix). Using PVDF-HFP as the matrix, obtain five homogeneous monolayer Ni@MXene / PVDF-HFP absorbing materials according to the method disclosed in Reference 6. The Ni@MXene / PVDF-HFP absorbing materials prepared by Ni to MXene mass ratios of 4∶0, 3∶1, 2∶2, 1∶3, and 0∶4 are labeled as L(4∶0), L(3∶1), L(2∶2), L(1∶3), and L(0∶4), respectively. S2. Acquisition of electromagnetic parameter data for homogeneous single-layer absorbing materials: The five homogeneous monolayer Ni@MXene / PVDF-HFP absorbing materials obtained in step S1.2 were hot-pressed into concentric ring samples with a thickness of 2 mm (inner diameter 3.04 mm, outer diameter 7.0 mm) at a hot-pressing temperature of 200℃ and a pressure of 2.6 MPa. The ε'-f curve, ε''-f curve, μ'-f curve, and μ''-f curve (ε' is the real part of the dielectric constant, ε'' is the imaginary part of the dielectric constant, μ' is the real part of the permeability, μ'' is the imaginary part of the permeability, and f is the frequency) of each sample were measured using a vector network analyzer in the 2~18 GHz frequency band. The results are as follows: Figure 2 As shown in Figure a, the results indicate that as the MXene content increases, the real and imaginary parts of the dielectric constant gradually increase, while as the Ni content decreases, the real and imaginary parts of the permeability gradually decrease. Based on the ε'-f curve and the ε''-f curve, and ε r =ε'-jε'', calculate the relative permittivity for each frequency. ε r Based on the μ'-f curve and the μ''-f curve and μ r =μ'-jμ'', calculate the relative permeability for each frequency. μ r Then, calculate the intrinsic impedance and complex transmission constant corresponding to each frequency according to formulas (1) and (2); where, ε n The relative permittivity of the nth layer; μ n The relative permeability of the nth layer; η 0 represents the intrinsic impedance in free space, with a value of approximately 377Ω; η n The intrinsic impedance of the nth layer; γ n Let n be the complex transmission constant of the nth layer; j The imaginary unit; f For frequency;c The speed of light has a value of 299,792,458 m / s; ; ; S3. Determination of the impedance matching surface layer: Based on the impedance recursion formula (3) of transmission line theory, the formula is recursively applied layer by layer to reduce reflection loss. RL The objective function is to maximize the effective absorption bandwidth EAB when 1≤-10dB. The homogeneous single-layer absorbing materials prepared in step S1 are combined in pairs. The two-layer combination is used as the optimization unit. A global search is adopted to determine the surface material corresponding to the maximum EAB as the impedance matching surface of the multi-layer broadband absorbing material, i.e., the first layer. Z n Let n be the wave impedance of the nth layer. Z n-1 The wave impedance of the (n-1)th layer, η n-1 The intrinsic impedance of the (n-1)th layer, t n-1 The thickness of the (n-1)th layer is... r n-1 The complex transmission constant of the (n-1)th layer; ; The specific process is as follows: S3.1, Using the metal substrate as the third layer, perform impedance recursion to obtain the wave impedance of the third layer. Z 3=0, and the wave impedance of the second layer of absorbing material is obtained according to formula (3). Z 2, as shown in formula (4); ; S3.2, Based on the wave impedance of the second layer of absorbing material Z 2. Continuing to recursively derive formula (3), the wave impedance of the first layer of absorbing material is obtained. Z 1. As shown in formula (5); ; S3.3 Calculate the overall reflection loss of the absorbing material according to formula (6); where, Z 0 represents the free space impedance, which is approximately 377 Ω. ; S3.4. Combine the five Ni@MXene / PVDF-HFP microwave absorbing materials prepared in step S1 in pairs, and label the combined materials as follows: Z xy, where x = 0, 1, 2, 3, or 4, and y = 0, 1, 2, 3, or 4. Zxy represents the combination of L(x∶4-x) as the first layer and L(y∶4-y) as the second layer, with the results being respectively Z 43. Z 42. Z 41. Z 40. Z 34. Z 32. Z 31. Z 30. Z twenty four, Z twenty three, Z twenty one, Z 20. Z 14. Z 13. Z 12. Z 10. Z 04、 Z 03、 Z 02、 Z 01, a total of five categories and 20 groups; using two-layer combinations as the optimization unit, with the first layer designed for thickness. t The thickness of the fitted layer 1 and layer 2 t 2 is the optimization variable (range 0.1~5mm, step size 0.1mm). The objective function is to maximize the effective absorption bandwidth EAB when the reflection loss RL1 ≤ -10dB. This is achieved through a global search using Python and successive calculations. Z A two-dimensional contour plot of the reflection loss of xy as a function of frequency and the thickness of the underlying layer (second layer), as shown below. Figure 3 As shown, a1~a4 correspond to Z43, Z42, Z41, Z40 respectively; b1~b4 correspond to Z34, Z32, Z31, Z30 respectively; c1~c4 correspond to Z24, Z23, Z21, Z20 respectively; d1~d4 correspond to Z14, Z13, Z12, Z10 respectively; and e1~e4 correspond to Z04, Z03, Z02, Z01 respectively. According to... Figure 3 The corresponding data are shown in Table 1. The results in Table 1 show that L(4∶0) has the best microwave absorption effect (EAB 7.44GHz) when it is used as the impedance matching surface layer (the first layer). ; S4. Gradient structure optimizes the thickness of each layer layer by layer: S4.1 After determining L(4∶0) as the impedance matching surface layer, i.e. the first layer, in step S3, the remaining homogeneous single-layer absorbing materials prepared in step S1, except for L(4∶0), are arranged in order of gradually increasing dielectric constant: L(3∶1), L(2∶2), L(1∶3), L(0∶4), which are successively determined as the second, third, fourth, and fifth layers of the multilayer broadband Ni@MXene / PVDF-HFP absorbing material; S4.2, Layer-by-layer optimization: For an n-layer broadband absorbing material, the (n+1)th layer is a metal substrate, and the wave impedance of the (n+1)th layer is... Z n+1 =0, and the wave impedance of the nth layer of absorbing material is obtained according to formula (3). Z n As shown in formula (7); ; According to wave impedance Z n According to formula (3), the wave impedance of the (n-1)th layer is calculated. Z n-1 As shown in formula (8); ; According to wave impedance Z n-1 According to formula (3), the wave impedance of the (n-2)th layer is calculated. Z n-2 Then, based on the wave impedance Z n-2 According to formula (3), the wave impedance of the (n-3)th layer is calculated. Z n-3 And so on, until the wave impedance of the first layer is calculated. Z 1. As shown in formula (9); ; Calculate the overall reflection loss of the absorbing material according to formula (10); ; The optimization is as follows: Optimize the 2-layer structure (labeled G2): According to Z 3=0, obtained by recursively applying formulas (7) to (9). Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the first layer design thickness as the basis. t The thickness of the fitted layer 1 and layer 2 t 2 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G2 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in a1, by Figure 5 a1 determines the design thickness of the first layer. t 1 = 3.2 mm, the optimal fitting thickness of the second layer t2=3.1mm, at which point the EAB of G2 reaches 5.92GHz; Optimize the 3-layer structure (marked as G3): fix the design thickness of the first layer. t 1 = 3.2 mm; according to Z 4 = 0, obtained by recursively applying formulas (7) to (9). Z 3. Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the second layer design thickness as the basis. t 2 and 3rd layer fitting thickness t 3 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G3 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in a2, by Figure 5 a2 determines the design thickness of the second layer. t 2 = 0.6 mm, the optimal fitting thickness of the third layer t 3=4.2mm, at which point the EAB of G3 reaches 10.4GHz; Optimize the 4-layer structure (marked as G4): fix the design thickness of the first layer. t 1=3.2mm, design thickness of the second layer t 2 = 0.6 mm; according to Z 5 = 0, obtained by recursively applying formulas (7) to (9). Z 4. Z 3. Z 2. Z 1 and RL 1. Based on the design thickness of the 3rd layer t Fitted thickness of layers 3 and 4 t 4 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G4 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in a3, by Figure 5 a3 determines the design thickness of the third layer. t 3 = 3.1 mm, the optimal fitting thickness for the 4th layer t 3 = 3.8mm, at which point the EAB of G4 reaches 10.32GHz; Optimize the 5-layer structure (marked as G5): fix the design thickness of the first layer. t 1=3.2mm, design thickness of the second layer t 2 = 0.6mm, the design thickness of the third layer t3 = 3.1 mm; according to Z 6 = 0, obtained by recursively applying formulas (7) to (9). Z 5. Z 4. Z 3. Z 2. Z 1 and RL 1. Design thickness based on the 4th layer t Fitted thickness of layers 4 and 5 t 5 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G5 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in a4, by Figure 5 a4 determines the design thickness of the 4th layer. t 4 = 1.6 mm, the optimal fitting thickness for the 5th layer t 5 = 3.4mm, at which point the EAB of G5 reaches 10.24GHz; The optimization results are summarized in Table 3, Example 1; S5. Taking the fabrication of a 3-layer broadband Ni@MXene / PVDF-HFP microwave absorbing material as an example, the fabrication process is as follows: According to the thickness parameters determined in step S4: t 1 = 3.2mm, t 2 = 0.6 mm t = 4.2mm, and single-layer materials of corresponding thickness L(4∶0), L(3∶1), and L(2∶2) are stacked in sequence and placed in a vacuum hot press at 200℃ and 2.6MPa to form a 3-layer structure broadband Ni@MXene / PVDF-HFP microwave absorbing material.

[0026] The microwave absorption performance (reflection loss-frequency curve) of this three-layer broadband Ni@MXene / PVDF-HFP absorbing material in the 2~18GHz frequency band was tested using the bow-shaped method. The results are as follows: Figure 6 As shown, the measured maximum reflection loss is less than -60dB and the effective absorption bandwidth is as high as 10.6GHz, which is highly consistent with the calculation result (10.4GHz) of the impedance recursion formula, verifying the accuracy and reliability of the method of the present invention.

[0027] Example 2 A method for preparing a multilayer broadband Ni@MXene / PVDF-HFP absorbing material (optimal surface layer + wave-like gradient) differs from Example 1 in that, in step S4.1: the homogeneous single-layer absorbing materials prepared in step S1, except for L(4∶0), are arranged in a wave-like pattern according to their dielectric constants: L(1∶3), L(3∶1), L(0∶4), L(2∶2), which are sequentially determined as the 2nd, 3rd, 4th, and 5th layers of the multilayer broadband Ni@MXene / PVDF-HFP absorbing material; Correspondingly, step S4.2 is optimized layer by layer as follows: Optimize the 2-layer structure (labeled G2): According to Z 3=0, obtained by recursively applying formulas (7) to (9). Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the first layer design thickness as the basis. t The thickness of the fitted layer 1 and layer 2 t 2 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G2 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in b1, by Figure 5 b1 determines the design thickness of the first layer. t 1 = 3.4 mm, the optimal fitting thickness of the second layer t 2 = 2.8mm, at which point the EAB of G2 reaches 7.44GHz; Optimize the 3-layer structure (marked as G3): fix the design thickness of the first layer. t 1 = 3.4 mm; according to Z 4 = 0, obtained by recursively applying formulas (7) to (9). Z 3. Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the second layer design thickness as the basis. t 2 and 3rd layer fitting thickness t 3 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G3 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in b2, by Figure 5 b2 determines the design thickness of the second layer. t 2 = 1.3 mm, the optimal fitting thickness of the third layert 3=3.9mm, at which point the EAB of G3 reaches 9.68GHz; Optimize the 4-layer structure (marked as G4): fix the design thickness of the first layer. t 1=3.4mm, design thickness of the second layer t 2 = 1.3 mm; according to Z 5 = 0, obtained by recursively applying formulas (7) to (9). Z 4. Z 3. Z 2. Z 1 and RL 1. Based on the design thickness of the 3rd layer t Fitted thickness of layers 3 and 4 t 4 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G4 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 4 As shown in b3, by Figure 4 b3 determines the design thickness of the third layer. t 3 = 3.2mm, the optimal fitting thickness for the 4th layer t 4 = 2.5mm, at which point the EAB of G4 reaches 11.44GHz; Optimize the 5-layer structure (marked as G5): fix the design thickness of the first layer. t 1=3.4mm, design thickness of the second layer t 2 = 1.3mm, the design thickness of the third layer t 3 = 3.2 mm; according to Z 6 = 0, obtained by recursively applying formulas (7) to (9). Z 5. Z 4. Z 3. Z 2. Z 1 and RL 1. Design thickness based on the 4th layer t Fitted thickness of layers 4 and 5 t 5 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G5 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in b4, by Figure 5 b4 determines the design thickness of the 4th layer. t 4 = 0.4 mm, the optimal fitting thickness for the 5th layer t 5 = 3.5mm, at which point the EAB of G5 reaches 11.60GHz; The optimization results are summarized in Table 3, Example 2; comprehensive comparison shows that the optimal EAB for 2- to 5-layer structures can reach 7.44-11.60 GHz. Figure 5 b and Table 3 Example 2), in which the EAB of the 5-layer structure G5 reaches 11.60 GHz. This result shows that, based on the preferred impedance matching surface layer, a reasonable gradient arrangement can further improve the microwave absorption performance. It also proves that surface layer screening is the core prerequisite for gradient structure design. Correspondingly, in step S5, taking the fabrication of a 5-layer broadband Ni@MXene / PVDF-HFP microwave absorbing material as an example, the fabrication process is as follows: According to the thickness parameters determined in step S4: t 1 = 3.4 mm t 2 = 1.3 mm, t 3=3.2mm, t4=0.4mm, t = 3.5mm. Single-layer materials of corresponding thickness L(4∶0), L(1∶3), L(3∶1), L(0∶4), L(2∶2) are stacked sequentially and placed in a vacuum hot press at 200℃ and 2.6MPa. The pressure is held for 10 minutes to fully fuse the interlayer interfaces. After cooling, a 5-layer broadband Ni@MXene / PVDF-HFP microwave absorbing material is obtained.

[0028] Comparative Example 1 A method for preparing a multilayer Ni@MXene / PVDF-HFP absorbing material (non-optimal surface layer + wavy gradient) differs from Example 1 in that: in step S4.1, the homogeneous single-layer absorbing material prepared in step S1 is arranged in a wavy pattern with a non-optimal surface layer and a wavy dielectric constant: L(0∶4), L(4∶0), L(3∶1), L(1∶3), L(2∶2), which are sequentially determined as the impedance matching surface layer of the multilayer broadband Ni@MXene / PVDF-HFP absorbing material, namely the 1st layer, the 2nd layer, the 3rd layer, the 4th layer, and the 5th layer; Correspondingly, step S4.2 is optimized layer by layer as follows: Optimize the 2-layer structure (labeled G2): According to Z 3=0, obtained by recursively applying formulas (7) to (9). Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the first layer design thickness as the basis. t The thickness of the fitted layer 1 and layer 2 t2 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G2 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in c1, by Figure 5 c1 determines the design thickness of the first layer. t 1 = 3.2 mm, the optimal fitting thickness of the second layer t 2 = 2.9mm, at which point the EAB of G2 reaches 3.92GHz; Optimize the 3-layer structure (marked as G3): fix the design thickness of the first layer. t 1 = 3.2 mm; according to Z 4 = 0, obtained by recursively applying formulas (7) to (9). Z 3. Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the second layer design thickness as the basis. t 2 and 3rd layer fitting thickness t 3 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G3 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in c2, by Figure 5 c2 determines the design thickness of the second layer. t 2 = 0.6 mm, the optimal fitting thickness of the third layer t 3=0.9mm, at which point the EAB of G3 reaches 3.06GHz; Optimize the 4-layer structure (marked as G4): fix the design thickness of the first layer. t 1=3.2mm, design thickness of the second layer t 2 = 0.6 mm; according to Z 5 = 0, obtained by recursively applying formulas (7) to (9). Z 4. Z 3. Z 2. Z 1 and RL 1. Based on the design thickness of the 3rd layer t Fitted thickness of layers 3 and 4 t 4 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G4 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in b3, by Figure 5 c3 determines the design thickness of the third layer. t3 = 3.1 mm, the optimal fitting thickness for the 4th layer t 4 = 1.1mm, at which point the EAB of G4 reaches 4.07GHz; Optimize the 5-layer structure (marked as G5): fix the design thickness of the first layer. t 1=3.2mm, design thickness of the second layer t 2 = 0.6mm, the design thickness of the third layer t 3 = 3.1 mm; according to Z 6 = 0, obtained by recursively applying formulas (7) to (9). Z 5. Z 4. Z 3. Z 2. Z 1 and RL 1. Design thickness based on the 4th layer t Fitted thickness of layers 4 and 5 t 5 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G5 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in c4, by Figure 5 c4 determines the design thickness of the 4th layer. t 4 = 1.6 mm, the optimal fitting thickness for the 5th layer t 5 = 1.9mm, at which point the EAB of G5 reaches 2.24GHz; The optimization results are summarized in Table 3, Comparative Example 1; the optimization results show that the optimal EAB for 2- to 5-layer structures is only 2.24-4.07 GHz. Figure 5 c) and Comparative Example 1 in Table 3, this result further verifies the key influence of gradient direction on microwave absorption performance: disordered wave-like arrangement disrupts the continuity gradient of impedance, leading to increased reflection at interlayer interfaces and limited absorption bandwidth.

[0029] Given that the optimal EAB in Comparative Example 1 was not good, no further multilayer structure absorbing material was prepared.

[0030] Comparative Example 2 A method for preparing a multilayer Ni@MXene / PVDF-HFP absorbing material (non-preferred surface layer + inverse gradient) differs from Example 1 in that: in step S4.1, the homogeneous single-layer absorbing material prepared in step S1 is arranged in the order of non-preferred surface layer and decreasing dielectric constant: L(0∶4), L(1∶3), L(2∶2), L(3∶1), L(4∶0), which are sequentially determined as the impedance matching surface layer of the multilayer broadband Ni@MXene / PVDF-HFP absorbing material, namely the 1st layer, the 2nd layer, the 3rd layer, the 4th layer, and the 5th layer; Correspondingly, step S4.2 is optimized layer by layer as follows: Optimize the 2-layer structure (labeled G2): According to Z 3=0, obtained by recursively applying formulas (7) to (9). Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the first layer design thickness as the basis. t The thickness of the fitted layer 1 and layer 2 t 2 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G2 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in d1, by Figure 5 d1 determines the design thickness of the first layer. t 1 = 1.2 mm, the optimal fitting thickness of the second layer t 2 = 1.1 mm, at which point the EAB of G2 reaches 1.1 GHz; Optimize the 3-layer structure (marked as G3): fix the design thickness of the first layer. t 1 = 1.2 mm; according to Z 4 = 0, obtained by recursively applying formulas (7) to (9). Z 3. Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the second layer design thickness as the basis. t 2 and 3rd layer fitting thickness t 3 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G3 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in d2, by Figure 5 d2 determines the design thickness of the second layer. t 2 = 0.8 mm, the optimal fitting thickness of the third layer t 3 = 3.3mm, at which point the EAB of G3 reaches 0.96GHz; Optimize the 4-layer structure (marked as G4): fix the design thickness of the first layer. t 1 = 1.2mm, design thickness of the second layer t 2 = 0.8 mm; according to Z 5 = 0, obtained by recursively applying formulas (7) to (9). Z 4. Z 3. Z2. Z 1 and RL 1. Based on the design thickness of the 3rd layer t Fitted thickness of layers 3 and 4 t 4 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G4 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in d3, by Figure 5 d3 determines the design thickness of the third layer. t 3 = 3.4 mm, the optimal fitting thickness for the 4th layer t 4 = 3.3mm, at which point the EAB of G4 reaches 1.48GHz; Optimize the 5-layer structure (marked as G5): fix the design thickness of the first layer. t 1 = 1.2mm, design thickness of the second layer t 2 = 0.8mm, the design thickness of the third layer t 3 = 3.4 mm; according to Z 6 = 0, obtained by recursively applying formulas (7) to (9). Z 5. Z 4. Z 3. Z 2. Z 1 and RL 1. Design thickness based on the 4th layer t Fitted thickness of layers 4 and 5 t 5 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G5 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in d4, by Figure 5 d4 determines the design thickness of the 4th layer. t 4 = 2.2mm, the optimal fitting thickness for the 5th layer t 5 = 3.9mm, at which point the EAB of G5 reaches 2.98GHz; The optimization results are summarized in Table 3, Comparative Example 2; the optimization results show that the optimal EAB for 2- to 5-layer structures is only 0.96-2.98 GHz. Figure 5 d and Table 3 Comparative Example 2) are much lower than the gradient arrangement in Example 1. This result further verifies the necessity of impedance matching surface layer selection: when a high dielectric constant material is located on the surface layer, impedance mismatch causes a large amount of electromagnetic waves to be reflected and cannot enter the interior of the material to be absorbed.

[0031] Given that the optimal EAB in Comparative Example 2 was not good, no further multilayer structure absorbing material was prepared.

[0032] Comparative Example 3 A method for preparing a multilayer Ni@MXene / PVDF-HFP microwave absorbing material differs from Example 1 in that: the layer-by-layer recursive step is omitted, and five homogeneous single-layer Ni@MXene / PVDF-HFP microwave absorbing materials L(4∶0), L(3∶1), L(2∶2), L(1∶3), and L(0∶4) are directly hot-pressed (200℃, 2.6MPa, 10min). Two-dimensional contour plots of the reflection loss of each sample as a function of frequency and fitted thickness are then tested, as shown below. Figure 7 As shown, (a) corresponds to L(4∶0), (b) corresponds to L(3∶1), (c) corresponds to L(2∶2), (d) corresponds to L(1∶3), and (e) corresponds to L(0∶4); from Figure 7 The EAB and corresponding fitted thickness data for each material are shown in Table 2.

[0033]

[0034] The results show that for the best composite material L(4∶0), with a fitted thickness of 8 mm, its EAB is 4.96 GHz, which is much lower than the 10.4 GHz of G3 in Example 1. This comparison fully verifies the significant advantages of gradient structure design over homogeneous materials, as well as the effectiveness of the layer-by-layer recursive preparation method of this invention.

[0035] Example 3 A method for preparing a multilayer broadband Ni@MXene / PEEK absorbing material differs from Example 1 in that: in step S1, PEEK is used instead of PVDF-HFP as the matrix, and Ni@MXene (mass ratio 1:1) is used as the absorbing agent. The amount of absorbing agent added is adjusted to 1%, 3%, 5% and 10% in sequence to prepare four homogeneous single-layer Ni@MXene / PEEK absorbing materials. The Ni@MXene / PEEK absorbing materials prepared with absorbing agent added at 1%, 3%, 5% and 10% are labeled as P1, P2, P3 and P4, respectively. Correspondingly, in step S2, the ε'-f curves, ε''-f curves, μ'-f curves, and μ''-f curves of the four samples P1 to P4 are as follows: Figure 2 As shown in b. Figure 2 b shows that the Ni@MXene / PEEK composite material also exhibits a trend of increasing dielectric constant with increasing absorber content, verifying the tunability of electromagnetic parameters in different matrix systems. The dielectric constants are ordered from low to high as P1, P2, P3, and P4. Correspondingly, the four Ni@MXene / PEEK absorbing materials prepared in step S1 were combined in pairs, and the resulting combinations were labeled as follows: Z pxy, x = 1, 2, 3 or 4, y = 1, 2, 3 or 4 Zpxy represents the combination of Px as the first layer and Py as the second layer, resulting in the following values: Z p12 Z p13 Z p14 Z p21 Z p23 Z p24 Z p31 Z p32 Z p34 Z p41 Z p42 Z p43, a total of four categories and 12 groups; using two-layer combinations as the optimization unit, with the first layer designed for thickness. t The thickness of the fitted layer 1 and layer 2 t 2 is the optimization variable (range 0.1~5mm, step size 0.1mm). The objective function is to maximize the effective absorption bandwidth EAB when the reflection loss RL1 ≤ -10dB. This is achieved through a global search using Python and successive calculations. Z A two-dimensional contour plot of the reflection loss of pxy as a function of frequency and the thickness of the underlying (second layer) fitted layer, as shown below. Figure 4 As shown, a1~a3 correspond to respectively Z p12 Z p13 Z p14, b1~b3 correspond to respectively Z p21 Z p23 Z p24, c1~c3 correspond to respectively Z p31 Z p32 Z p34, d1~d3 correspond to respectively Z p41 Z p42 Z p43; According to Figure 4 The corresponding data are shown in Table 1. The results in Table 1 show that P1 has the best microwave absorption effect when it is used as the impedance matching surface layer (layer 1) (EAB=9.12GHz). Correspondingly, in step S4.1, after determining P1 as the impedance matching surface layer, i.e. the first layer, in step S3, the other three homogeneous single-layer absorbing materials prepared in step S1 are arranged in descending order of dielectric constant: P4, P3, P2, which are successively determined as the second, third, and fourth layers of the multilayer broadband Ni@MXene / PEEK absorbing material. Correspondingly, step S4.2 is optimized layer by layer as follows: Optimize the 2-layer structure (labeled G2): According to Z 3=0, obtained by recursively applying formulas (7) to (9). Z2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the first layer design thickness as the basis. t The thickness of the fitted layer 1 and layer 2 t 2 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G2 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in e1, by Figure 5 e1 determines the design thickness of the first layer. t 1 = 4.0 mm, the optimal fitting thickness of the second layer t 2 = 2.3mm, at which point the EAB of G2 reaches 9.12GHz; Optimize the 3-layer structure (marked as G3): fix the design thickness of the first layer. t 1 = 4.0 mm; according to Z 4 = 0, obtained by recursively applying formulas (7) to (9). Z 3. Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the second layer design thickness as the basis. t 2 and 3rd layer fitting thickness t 3 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G3 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in e2, by Figure 5 e2 determines the design thickness of the second layer. t 2 = 0.1 mm, the optimal fitting thickness of the third layer t 3 = 3.3mm, at which point the EAB of G3 reaches 10.48GHz; Optimize the 4-layer structure (marked as G4): fix the design thickness of the first layer. t 1=4.0mm, design thickness of the second layer t 2 = 0.1 mm; according to Z 5 = 0, obtained by recursively applying formulas (7) to (9). Z 4. Z 3. Z 2. Z 1 and RL 1. Based on the design thickness of the 3rd layer t Fitted thickness of layers 3 and 4 t4 is the optimization variable (value range 0.1~5mm, step size 0.1mm). Through a global search using Python and successive calculations, a two-dimensional contour plot of the reflection loss of G4 as a function of frequency and the underlying fitted thickness is obtained, as shown below. Figure 5 As shown in b3, by Figure 5 e3 determines the design thickness of the third layer. t 3 = 3.2mm, the optimal fitting thickness for the 4th layer t 4 = 0.4mm, at which point the EAB of G4 reaches 10.65GHz; The optimization results are summarized in Table 3, Example 3; the optimization results show that the optimal EAB for 2- to 4-layer structures can reach 9.12-10.65 GHz. Figure 5 e and Table 3 (Example 3), in which the EAB of the 4-layer structure G4 reaches 10.65 GHz, which demonstrates the universality and effectiveness of the method of the present invention in different matrix systems; Correspondingly, in step S5, taking the fabrication of a 4-layer broadband Ni@MXene / PEEK absorbing material as an example, the fabrication process is as follows: According to the thickness parameters determined in step S4: t 1 = 4.0 mm t 2 = 0.1 mm, t With t3=3.2mm and t4=0.4mm, single-layer materials P1, P4, P3, and P2 of corresponding thicknesses are stacked sequentially and placed in a vacuum hot press at 350℃ and 2.6MPa for hot pressing. The pressure is held for 10 minutes to fully fuse the interlayer interfaces. After cooling, a 4-layer broadband Ni@MXene / PEEK microwave absorbing material is obtained.

[0036]

Claims

1. A method for preparing a multilayer broadband absorbing material, characterized in that, The multilayer broadband absorbing material has a total of n layers, n≥2, and the layers are arranged sequentially from the surface down as layer 1, layer 2, ..., layer n; the preparation steps are as follows: S1. According to different electromagnetic component ratios, m homogeneous single-layer absorbing materials are prepared using conventional techniques, where m ≥ n; the electromagnetic components mainly consist of a matrix and an absorbing agent. S2. Electromagnetic parameters of homogeneous monolayer absorbing materials: The ε'-f curve, ε''-f curve, μ'-f curve, and μ''-f curve of each homogeneous monolayer absorbing material in the 2~18GHz frequency band were tested using a vector network analyzer. The relative permittivity corresponding to each frequency was obtained based on the ε'-f curve and ε''-f curve. ε r The relative permeability at each frequency is obtained from the μ'-f curve and the μ''-f curve. μ r Where ε' is the real part of the permittivity; ε'' is the imaginary part of the permittivity; μ' is the real part of the permeability; μ'' is the imaginary part of the permeability; and f is the frequency. ε r It is the relative permittivity; μ r Relative permeability; Then, the intrinsic impedance and complex transmission constant corresponding to each frequency are calculated according to formulas (1) and (2), respectively; where, ε n The relative permittivity of the nth layer; μ n The relative permeability of the nth layer; η 0 represents the intrinsic impedance of free space; η n The intrinsic impedance of the nth layer; γ n Let n be the complex transmission constant of the nth layer; j The imaginary unit; f For frequency; c The speed of light; ； ； S3. Determination of the impedance matching surface layer: Based on the impedance recursion formula (3) of transmission line theory, the process is recursively applied layer by layer. The objective function is to maximize the effective absorption bandwidth EAB when the reflection loss RL1 ≤ -10dB. The homogeneous single-layer absorbing materials prepared in step S1 are combined in pairs. Using the two-layer combination as the optimization unit, a global search is employed to determine the surface material corresponding to the maximized EAB as the impedance matching surface layer of the multilayer broadband absorbing material, i.e., the first layer. Z n Let n be the wave impedance of the nth layer. Z n-1 The wave impedance of the (n-1)th layer, η n-1 The intrinsic impedance of the (n-1)th layer, t n-1 The thickness of the (n-1)th layer is... r n-1 The complex transmission constant of the (n-1)th layer; ； S4. Gradient structure optimizes the thickness of each layer layer by layer: S4.1 After determining the first layer material of the multilayer broadband absorbing material in step S3, the remaining homogeneous single-layer absorbing materials prepared in step S1, excluding the first layer material, are sequentially determined as the second, ..., nth layers of the multilayer broadband absorbing material. S4.2 According to formula (3), a layer-by-layer recursive approach is adopted to reduce reflection loss. RL Maximizing the effective absorption bandwidth (EAB) when 1 ≤ -10 dB is the objective function. Using a two-layer combination as the optimization unit, a global search is employed to determine the design thickness of the first n-1 layers layer by layer. t 1. t 2, ... t n-1 Meanwhile, the fitted thickness of the nth layer is retained. t n ; S5. Fabrication of multilayer broadband absorbing materials: According to the design thickness of the first n-1 layers determined in step S4 t 1. t 2, ... t n-1 and the fitted thickness of the nth layer t n The homogeneous single-layer absorbing materials of corresponding thickness are stacked sequentially to prepare multi-layer broadband absorbing materials using conventional techniques.

2. The method for preparing the multilayer broadband absorbing material as described in claim 1, characterized in that, The specific process of step S3 is as follows: S3.1, Using the metal substrate as the third layer, perform impedance recursion to obtain the wave impedance of the third layer. Z 3=0, and the wave impedance of the second layer of absorbing material is obtained according to formula (3). Z 2, as shown in formula (4); ； S3.2, Based on the wave impedance of the second layer of absorbing material Z 2. Continuing to recursively derive formula (3), the wave impedance of the first layer of absorbing material is obtained. Z 1. As shown in formula (5); ； S3.3 Calculate the overall reflection loss of the absorbing material according to formula (6); where, Z 0 represents free space impedance; ； S3.

4. Combine the homogeneous monolayer absorbing materials prepared in step S1 in pairs, using the two-layer combination as the optimization unit, and taking the reflection loss as the optimization factor. RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the first layer design thickness as the basis. t The thickness of the fitted layer 1 and layer 2 t 2 is the optimization variable. A global search is performed in the range of 0.1~5mm. Through successive calculations, the homogeneous single-layer absorbing material corresponding to the maximum EAB is determined as the impedance matching surface layer of the multi-layer broadband absorbing material, i.e., the first layer.

3. The method for preparing the multilayer broadband absorbing material as described in claim 1, characterized in that, The specific process of step S4.2 is as follows: S4.2.1 For an n-layer broadband absorbing material, the (n+1)th layer is a metal substrate, and the wave impedance of the (n+1)th layer is... Z n+1 =0, and the wave impedance of the nth layer of absorbing material is obtained according to formula (3). Z n As shown in formula (7); ； According to wave impedance Z n According to formula (3), the wave impedance of the (n-1)th layer is calculated. Z n-1 As shown in formula (8); ； According to wave impedance Z n-1 According to formula (3), the wave impedance of the (n-2)th layer is calculated. Z n-2 Then, based on the wave impedance Z n-2 According to formula (3), the wave impedance of the (n-3)th layer is calculated. Z n-3 And so on, until the wave impedance of the first layer is calculated. Z 1. As shown in formula (9); ； Calculate the overall reflection loss of the absorbing material according to formula (10); ； Based on the actual requirement of the number of layers n of the multilayer broadband absorbing material to be prepared, operate according to the following steps S4.2.2~S4.2.6; however, for an n-layer broadband absorbing material, the design thickness of the first n-1 layers should be fixed. t 1. t 2, ... t n-2 , t n-1 At the same time, retain the fitting thickness of the nth layer. t n ; S4.2.2, For two-layer broadband absorbing materials: According to Z 3=0, obtained by recursively applying formulas (7) to (9). Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the first layer design thickness as the basis. t The thickness of the fitted layer 1 and layer 2 t 2. As an optimization variable, a global search is performed within the range of 0.1~5mm, while the design thickness of the first layer is fixed. t 1; S4.2.3 For a 3-layer broadband absorbing material: fix the design thickness of the first layer. t 1; According to Z 4 = 0, obtained by recursively applying formulas (7) to (9). Z 3. Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the second layer design thickness as the basis. t 2 and 3rd layer fitting thickness t 3 is the optimization variable; a global search is performed within the range of 0.1~5mm, while the design thickness of the second layer is fixed. t 2; S4.2.4 For a 4-layer broadband absorbing material: fix the design thickness of the first layer. t 1. Design thickness of the second layer t 2; According to Z 5 = 0, obtained by recursively applying formulas (7) to (9). Z 4. Z 3. Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the design thickness of the 3rd layer as the basis. t Fitted thickness of layers 3 and 4 t 4. As an optimization variable, a global search is performed within the range of 0.1~5mm, while the design thickness of the third layer is fixed. t 3; S4.2.5 For a 5-layer broadband absorbing material: fix the design thickness of the first layer. t 1. Design thickness of the second layer t 2. Thickness of the third layer t 3; According to Z 6 = 0, obtained by recursively applying formulas (7) to (9). Z 5. Z 4. Z 3. Z 2. Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the design thickness of the 4th layer as the basis. t Fitted thickness of layers 4 and 5 t 5 is the optimization variable, and a global search is performed within the range of 0.1~5mm, while the design thickness of the 4th layer is fixed. t 4; S4.2.6 Following the method in steps S4.2.2~S4.2.5, for an n-layer broadband absorbing material: fix the design thickness of the first n-2 layers. t 1. t 2, ... t n-2 ;according to Z n+1 =0, obtained by recursively applying formulas (7) to (9). Z n , Z n-1 , Z n-2 ... Z 1 and RL 1. With reflection loss RL Maximizing the effective absorption bandwidth EAB when 1≤-10dB is the objective function, with the design thickness of the (n-1)th layer as the criterion. t n-1 and the thickness of the nth layer t n To optimize variables, a global search was performed within the range of 0.1~5mm, while the design thickness of the (n-1)th layer was fixed. t n-1 .

4. The method for preparing the multilayer broadband absorbing material as described in any one of claims 1 to 3, characterized in that: All global searches involved were performed using Python software.

5. The method for preparing the multilayer broadband absorbing material as described in claim 2 or 3, characterized in that: The step size for all global searches involved is 0.1 mm.

6. The method for preparing the multilayer broadband absorbing material as described in claim 1, characterized in that: The microwave absorbing agent is one or more of the materials with electromagnetic loss characteristics.

7. The method for preparing the multilayer broadband absorbing material as described in claim 6, characterized in that: The microwave absorbing agent is one or more of MXene, graphene nanosheets, carbon nanotubes, carbonyl iron powder, and Ni particles.

8. The method for preparing the multilayer broadband absorbing material as described in claim 1, characterized in that: The matrix is ​​a thermoplastic polymer matrix.

9. The method for preparing the multilayer broadband absorbing material as described in claim 8, characterized in that: The matrix is ​​one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, thermoplastic polyurethane, polyether ether ketone, epoxy resin or polyimide.

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