Wave-absorbing metamaterial with nested hexagonal resonant structure as well as preparation method and application of wave-absorbing metamaterial

Abstract

The invention relates to the technical field of electromagnetic functional materials, in particular to a nested hexagonal resonant structure wave-absorbing metamaterial and a preparation method and application thereof. The wave-absorbing metamaterial with the nested hexagonal resonant structure sequentially comprises a metal resonant layer, a homogeneous wave-absorbing coating and a metal matrix layer, the metal resonance layer is formed by periodically arranging a plurality of metal resonance units on the surface of the homogeneous wave-absorbing coating in an array manner; each metal resonance unit is of a nested hexagonal structure formed by arranging a plurality of structural units, and each structural unit is a hollow hexagonal metal patch. Through the combination of the homogeneous wave-absorbing coating and the metal resonance layer, the wave-absorbing metamaterial with the nested hexagonal resonance structure not only can realize effective absorption of an S wave band under the sub-wavelength scale, but also is beneficial to widening the effective absorption bandwidth and improving the absorption efficiency, simplifies the complex layered stacking framework of a traditional broadband wave absorber from the structural design, and has the advantages of simple structure and low cost. The method has the engineering application advantages of high process adaptability, high preparation feasibility and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic functional materials, and particularly relates to a nested hexagonal resonant structure absorbing metamaterial, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of wireless communication technology, whether in the civilian or military fields, the communication frequency bands are gradually expanding towards the S band, and the resulting electromagnetic pollution has posed a serious threat to the operation of precision electronic equipment, the protection of biological health, and the stealth performance of military equipment. Therefore, the development of high-performance low-frequency absorbing materials is of great significance in both the national defense and civilian industrial fields.

[0003] Currently, the development of low-frequency absorbing materials below 6 GHz mainly faces the inherent contradiction between the material thickness and the absorption bandwidth. The strategy of improving the low-frequency absorption performance by increasing the material thickness is difficult to break through due to the limitation of the Rozanov limit theory. To achieve the target frequency band coverage, the existing broadband designs generally need to adopt the design of increasing the overall thickness, but such designs often cause problems such as excessive weight and deterioration of mechanical flexibility, seriously weakening their applicability in lightweight scenarios.

[0004] Although metamaterials can break through the limitations of the electromagnetic parameters of natural materials through artificial subwavelength structure design, and can expand the effective absorption bandwidth under the condition of equivalent thickness and weight to traditional absorbing composite materials. However, the currently designed metamaterial materials generally adopt complex metal patterns, such as multi-level fractal structures and nested ring structures, etc., which rely on high-precision lithography processes and have industrialization obstacles such as high manufacturing costs and poor environmental tolerance. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a nested hexagonal resonant structure absorbing metamaterial, a preparation method thereof, and an application thereof.

[0006] The nested hexagonal resonant structure absorbing metamaterial of the present invention can not only achieve effective absorption in the S band at the subwavelength scale, but also has the characteristics of simple structure and process compatibility, providing a research direction for breaking through the technical bottleneck in the field of electromagnetic protection. The frequency range of the S band is 2 GHz to 4 GHz.

[0007] To achieve the above object, the technical solution of the present invention is as follows.

[0008] The first aspect of the present invention provides a nested hexagonal resonant structure absorbing metamaterial, which sequentially includes a metal resonant layer, a homogeneous absorbing coating, and a metal matrix layer; the metal resonant layer is formed by periodically arranging a plurality of metal resonant units on the surface of the homogeneous absorbing coating; each metal resonant unit is formed by arranging a plurality of structural units to form a nested hexagonal structure, and each structural unit is a hollow hexagonal metal patch.

[0009] The present invention mainly adopts the superstructure design of a metal resonant layer. By constructing an array structure of metal resonant units on the surface of a homogeneous absorbing coating to form a metal resonant layer, through the combination of the homogeneous absorbing coating and the metal resonant layer, not only can the input impedance Z of the overall absorbing metamaterial in be closer to the air impedance Z air , which helps to broaden the effective absorption bandwidth, but also can utilize the metal resonant layer. Through its structural loss and the intrinsic loss of the absorbing coating, the loss effect of the absorbing metamaterial on the electromagnetic waves in the S band can be increased, and the absorption efficiency can be improved. Thus, the nested hexagonal resonant structure absorbing metamaterial of the present invention can achieve high-efficiency absorption at a deep sub-wavelength thickness, solving the problems in the prior art when developing absorbing materials in the <6 GHz low-frequency band, such as the inherent contradiction between the material thickness and the absorption bandwidth, the high manufacturing cost and poor environmental tolerance of the metamaterial design, and the resulting excessive weight and deteriorated mechanical flexibility, which limits its application in lightweight scenarios.

[0010] In the present invention, the combination of the metal resonant layer and the homogeneous absorbing coating can improve the impedance matching characteristics of the absorbing metamaterial in the S-band range, reduce the reflection of electromagnetic waves, and then enable the electromagnetic waves to better enter the interior of the absorbing metamaterial and be converted into other forms of energy, thereby improving the electromagnetic wave absorption efficiency.

[0011] Preferably, the homogeneous absorbing coating is formed by coating a magnetic-dielectric composite absorbing coating on the surface of a metal matrix layer and then curing it; the magnetic-dielectric composite absorbing coating is prepared by mixing carbonyl iron powder, biomass carbon powder and epoxy resin in a solvent system.

[0012] The present invention uses carbonyl iron powder, biomass carbon powder and epoxy resin as raw materials to prepare a magnetic-dielectric composite absorbing coating by mixing. This is an absorbing coating with intrinsic electromagnetic wave loss, which can achieve the loss absorption of electromagnetic waves with a relatively low thickness, helping to reduce the overall thickness of the absorbing metamaterial. The obtained homogeneous absorbing coating has both magnetic loss and dielectric loss.

[0013] The present invention constructs a metal resonant layer superstructure with a periodic nested hexagonal topological configuration on the homogeneous absorbing coating with intrinsic electromagnetic wave loss. Through the electromagnetic resonance effect, surface current regulation mechanism and multi-scale electromagnetic coupling effect between units generated by the nested hexagonal structure metal resonant units at a specific frequency band, the synergistic optimization of the impedance matching characteristics and energy conversion efficiency of the absorber is realized, combined with the magnetic / dielectric loss synergy of the homogeneous absorbing coating, which is beneficial to achieving effective absorption in the S band at the sub-wavelength scale, and the effective absorption bandwidth is 1.6 GHz.

[0014] Preferably, the mass ratio of carbonyl iron powder, biomass carbon powder and epoxy resin is 5:0.1-0.3:1.

[0015] Preferably, the biomass carbon powder is charcoal powder; the solvent is at least one of ethanol, toluene, acetone and ethyl acetate.

[0016] Preferably, the periodic size of each metal resonant unit is 160 mm to 220 mm.

[0017] The metal resonant layer of the present invention is obtained by arranging metal resonant units in a periodic array. By adjusting the periodic size of the metal resonant units, its electromagnetic parameters are changed, so that the nested hexagonal resonant structure absorbing metamaterial of the present invention has the ability to achieve effective absorption in the low frequency band at sub-wavelength thickness.

[0018] Preferably, the total thickness of the metal resonant layer and the homogeneous absorbing coating ≤ 3 mm; the outer diameter of the circumscribed circle of the hollow hexagonal metal patch is 5 mm to 8 mm, and the thickness is 0.1 mm to 0.5 mm.

[0019] The sub-wavelength size in the frequency range of 2 GHz to 18 GHz is ≤ 16.7 mm. The present invention mainly designs a nested hexagonal resonant structure absorbing metamaterial with a thickness ≤ 3 mm. The nested hexagonal resonant structure absorbing metamaterial of the present invention has the ability to achieve effective absorption in the low frequency band at a thickness ≤ 3 mm.

[0020] Preferably, the thickness of the homogeneous absorbing coating is 1 mm to 2 mm; the thickness of the metal matrix layer is 1 mm to 2 mm.

[0021] Preferably, the material of the hollow hexagonal metal patch is copper, and the dielectric constant of the hollow hexagonal metal patch is 0.99; the material of the metal matrix layer is aluminum. The material of the metal matrix layer of the present invention is mainly selected from conductive metals, such as aluminum.

[0022] The second aspect of the present invention provides a preparation method of the nested hexagonal resonant structure absorbing metamaterial described in the first aspect, including the following steps:

[0023] Mix carbonyl iron powder, biomass carbon powder and epoxy resin evenly in a solvent system to prepare a magnetic-dielectric composite absorbing coating; after coating the magnetic-dielectric composite absorbing coating on the surface of the metal matrix layer, let it stand until it becomes a semi-cured gel state, and periodically arrange metal resonant units on the surface of the homogeneous absorbing coating in the semi-cured gel state. After standing until the homogeneous absorbing coating is cured, a nested hexagonal resonant structure absorbing metamaterial is obtained.

[0024] The present invention uses a coated magnetic-dielectric composite absorbing coating to form a homogeneous absorbing coating, and prepares a metal resonant layer on the homogeneous absorbing coating through a patch process to form a nested hexagonal resonant structure absorbing metamaterial. Among them, the metal resonant layer covers the surface of the homogeneous absorbing coating through a prefabricated hollow hexagonal metal patch array, which simplifies the manufacturing process of the absorbing metamaterial and reduces the industrialization cost.

[0025] The third aspect of the present invention provides an application of the nested hexagonal resonant structure absorbing metamaterial described in the first aspect in the preparation of electromagnetic wave absorbing metamaterials, characterized in that the electromagnetic wave absorbing metamaterial is an electromagnetic wave absorbing metamaterial for wireless communication, electromagnetic compatibility, electromagnetic shielding or radar stealth.

[0026] The electromagnetic wave absorbing metamaterial described in the present invention can achieve effective absorption in the S band, with a reflection loss RL < -10 dB, a microwave absorption rate greater than 90%, and an effective bandwidth of 1.6 GHz, covering most of the S band.

[0027] Advantages of the present invention:

[0028] 1. The present invention mainly adopts the superstructure design of the metal resonant layer. By constructing an array structure of metal resonant units on the surface of the homogeneous absorbing coating to form a metal resonant layer, through the combination of the homogeneous absorbing coating and the metal resonant layer, not only can the input impedance Z of the whole absorbing metamaterial in be closer to the air impedance Z air , which helps to broaden the effective absorption bandwidth, but also can utilize the metal resonant layer. Through its structural loss and the intrinsic loss of the absorbing coating, the loss effect of the absorbing metamaterial on the electromagnetic waves in the S band can be increased, and the absorption efficiency can be improved, so that the nested hexagonal resonant structure absorbing metamaterial of the present invention can achieve high-efficiency absorption under the deep sub-wavelength thickness.

[0029] 2. The nested hexagonal resonant structure absorbing metamaterial of the present invention can not only achieve effective absorption in the S band at the sub-wavelength scale, but also simplify the complex layered stacking structure of the traditional broadband absorber from the structural design, and has engineering application advantages such as strong process adaptability and high preparation feasibility.

[0030] 3. The present invention constructs a metal resonant layer superstructure with a periodic nested hexagonal topological configuration on the homogeneous absorbing coating with intrinsic electromagnetic wave loss. Through the electromagnetic resonance effect, surface current regulation mechanism and multi-scale electromagnetic coupling effect between units generated by the metal resonant units of the nested hexagonal structure, the synergistic optimization of the impedance matching characteristics and energy conversion efficiency of the absorber is realized, combined with the magnetic / dielectric loss synergy of the homogeneous absorbing coating, which is beneficial to achieving effective absorption in the S band at the sub-wavelength scale, and the effective absorption bandwidth is 1.6 GHz. Description of the Drawings

[0031] Figure 1 This is a schematic structural diagram of the wave - absorbing unit of the nested - hexagon resonance - structure wave - absorbing metamaterial according to an embodiment of the present invention.

[0032] Figure 2 This is a schematic structural diagram of the nested - hexagon resonance - structure wave - absorbing metamaterial according to an embodiment of the present invention.

[0033] Among them, (a) is a top - view schematic diagram of the nested - hexagon resonance - structure wave - absorbing metamaterial; (b) is a side - view schematic diagram of the nested - hexagon resonance - structure wave - absorbing metamaterial.

[0034] Figure 3 This is a micro - morphology diagram of the material for preparing the homogeneous wave - absorbing coating according to an embodiment of the present invention. Among them, (a) and (b) are micro - morphology diagrams of carbonyl iron particles at different magnification factors; (c) and (d) are micro - morphology diagrams of charcoal particles at different magnification factors.

[0035] Figure 4 This is an electromagnetic - parameter curve graph of the magnetic - dielectric composite wave - absorbing coating prepared in Example 1 of the present invention. Among them, (a) is a curve of the real - part dielectric constant varying with frequency; (b) is a curve of the imaginary - part dielectric constant varying with frequency; (c) is a curve of the real - part magnetic permeability varying with frequency; (d) is a curve of the imaginary - part magnetic permeability varying with frequency.

[0036] Figure 5 This is a simulated reflection - loss graph of the homogeneous wave - absorbing coating and the nested - hexagon resonance - structure wave - absorbing metamaterial prepared in Example 1 of the present invention. Among them, (a) is the simulated reflection - loss graph of the homogeneous wave - absorbing coating prepared in Example 1 of the present invention; (b) is the simulated reflection - loss graph of the nested - hexagon resonance - structure wave - absorbing metamaterial prepared in Example 1 of the present invention.

[0037] Explanation of reference numerals:

[0038] 1. Metal resonance layer; 11. Structural unit; 2. Homogeneous wave - absorbing coating; 3. Metal matrix layer. Detailed implementation manners

[0039] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further elaborates on the present invention in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0041] The communication frequency band in the civilian field is generally from 2.4 GHz to 5 GHz, and the radar communication frequency band in the military field is generally from 2 GHz to 4 GHz. The S band is from 2 GHz to 4 GHz.

[0042] The present invention mainly aims at the broadband wave absorption requirement of thin-layer structures in the low-frequency band. By adopting a metal resonant layer superstructure design, an array structure of metal resonant units is constructed on the surface of a homogeneous wave-absorbing coating to form a metal resonant layer, thereby realizing the cooperative action mechanism of intrinsic dielectric loss and structural electromagnetic loss. By optimizing the morphological parameters of the metal resonant units, while maintaining the intrinsic absorption characteristics of the conventional coating, the present invention effectively excites the multiple resonance effects generated by structural modulation, and significantly broadens the low-frequency absorption bandwidth. The wave-absorbing metamaterial with a nested hexagonal resonant structure of the present invention can not only achieve effective absorption in the S band at the sub-wavelength scale, but also simplifies the complex layered stacking structure of the traditional broadband wave absorber from the structural design, and has engineering application advantages such as strong process adaptability and high preparation feasibility.

[0043] It should be noted that, through the combination of a homogeneous wave-absorbing coating and a metal resonant layer in the present invention, wherein the metal resonant layer is composed of an array arrangement of a nested hexagonal structure formed by a plurality of hollow hexagonal metal patches, so that the induced current generated under the irradiation of incident electromagnetic waves can rapidly attenuate the energy of the electromagnetic waves. According to the equivalent circuit theory, the gap between the hollow hexagonal metal patches is regarded as a capacitor C; the flowing charges of the hollow hexagonal metal patches form an inductor L, storing charges or the polarization accumulation between discontinuous units, forming an LC oscillation circuit, so that its resonance frequency matches the electromagnetic wave frequency in the S band to achieve electromagnetic wave absorption.

[0044] Through the combined design of the metal resonant layer and the homogeneous wave-absorbing coating in the present invention, the input impedance Zin of the overall wave-absorbing metamaterial can be made closer to the air impedance Zair, which helps to broaden the effective absorption bandwidth. Through the structural loss of the metal resonant layer and the intrinsic loss of the wave-absorbing coating, the present invention increases the loss effect of the wave-absorbing metamaterial on the electromagnetic waves in the S band and improves the absorption efficiency, so that the wave-absorbing metamaterial with a nested hexagonal resonant structure of the present invention can achieve high-efficiency wave absorption at a deep sub-wavelength thickness.

[0045] The wave-absorbing metamaterial with a nested hexagonal resonant structure of the present invention will be further described below with reference to the accompanying drawings.

[0046] As Figures 1 to 2 , a wave-absorbing metamaterial with a nested hexagonal resonant structure successively includes a metal resonant layer 1, a homogeneous wave-absorbing coating 2, and a metal matrix layer 3; the metal resonant layer 1 is formed by periodically arranging a plurality of metal resonant units on the surface of the homogeneous wave-absorbing coating 2; each metal resonant unit is formed by arranging a plurality of structural units 11 to form a nested hexagonal structure, and each structural unit 11 is a hollow hexagonal metal patch.

[0047] Specifically, in the embodiments of the present invention, a superstructure design of the metal resonance layer 1 is mainly adopted. By constructing an array structure of metal resonance units on the surface of the homogeneous absorbing coating 2 to form the metal resonance layer 1, through the combination of the homogeneous absorbing coating 2 and the metal resonance layer 1, not only can the input impedance Z of the whole absorbing metamaterial in be closer to the air impedance Z air , which helps to broaden the effective absorption bandwidth, but also the metal resonance layer 1 can be utilized. Through its structural loss and the intrinsic loss of the absorbing coating, the loss effect of the absorbing metamaterial on the electromagnetic waves in the S band is increased, and the absorption efficiency is improved. As a result, the nested hexagonal resonance structure absorbing metamaterial of the embodiments of the present invention can achieve efficient absorption at a deep sub-wavelength thickness.

[0048] Specifically, in the embodiments of the present invention, the combination of the metal resonance layer 1 and the homogeneous absorbing coating 2 can improve the impedance matching characteristics of the absorbing metamaterial in the S band range, reduce the reflection of electromagnetic waves, and then enable the electromagnetic waves to better enter the interior of the absorbing metamaterial and be converted into other forms of energy, thereby improving the electromagnetic wave absorption efficiency.

[0049] On the basis of the above embodiments, the homogeneous absorbing coating 2 is formed by coating a magnetic-dielectric composite absorbing coating on the surface of the metal matrix layer 3 and then curing it; the magnetic-dielectric composite absorbing coating is prepared by mixing carbonyl iron powder, biomass carbon powder and epoxy resin in a solvent system.

[0050] Specifically, the embodiments of the present invention use carbonyl iron powder, biomass carbon powder and epoxy resin as raw materials to prepare a magnetic-dielectric composite absorbing coating by mixing. This is an absorbing coating with intrinsic electromagnetic wave loss, which can achieve the loss absorption of electromagnetic waves with a relatively low thickness, helps to reduce the overall thickness of the absorbing metamaterial, and the obtained homogeneous absorbing coating 2 has both magnetic loss and dielectric loss.

[0051] Among them, the mass ratio of carbonyl iron powder, biomass carbon powder and epoxy resin is 5: 0.1-0.3: 1. The biomass carbon powder is charcoal powder; the solvent is at least one of ethanol, toluene, acetone and ethyl acetate.

[0052] Specifically, in the embodiments of the present invention, by constructing a superstructure of the metal resonance layer 1 with a periodic nested hexagonal topological configuration on the homogeneous absorbing coating 2 with intrinsic electromagnetic wave loss, through the electromagnetic resonance effect, surface current regulation mechanism and multi-scale electromagnetic coupling effect between units generated by the nested hexagonal structure metal resonance units at a specific frequency band, the collaborative optimization of the impedance matching characteristics and energy conversion efficiency of the absorber is realized, combined with the magnetic / dielectric loss coordination of the homogeneous absorbing coating 2, so as to be beneficial to achieve effective absorption in the S band at the sub-wavelength scale, and the effective absorption bandwidth is 1.6 GHz.

[0053] Based on the above embodiments, the periodic dimension of each of the metal resonant units is 160 mm to 220 mm.

[0054] Specifically, the metal resonant layer 1 of the present invention is obtained by arranging metal resonant units in a periodic array. By adjusting the periodic dimension of the metal resonant units, its electromagnetic parameters are changed, so that the nested hexagonal resonant structure absorbing metamaterial of the present invention has the ability to achieve effective absorption in the low-frequency band at a sub-wavelength thickness.

[0055] Based on the above embodiments, the total thickness of the metal resonant layer and the homogeneous absorbing coating ≤ 3 mm; the outer diameter of the hollow hexagonal metal patch is 5 mm to 8 mm, and the thickness is 0.1 mm to 0.5 mm. The nested hexagonal resonant structure absorbing metamaterial of the embodiment of the present invention has the ability to achieve effective absorption in the low-frequency band at a thickness ≤ 3 mm. Among them, the thickness of the homogeneous absorbing coating 2 is 1 mm to 2 mm; the thickness of the metal matrix layer 3 is 1 mm to 2 mm.

[0056] Based on the above embodiments, the material of the hollow hexagonal metal patch is copper, and the dielectric constant of the hollow hexagonal metal patch is 0.99; the material of the metal matrix layer 3 is aluminum. The material of the metal matrix layer 3 of the present invention is mainly selected from conductive metals, such as aluminum.

[0057] The inhomogeneous absorbing system of the embodiment of the present invention breaks through the performance bottleneck of traditional homogeneous coatings. A metal resonant layer 1 is constructed on the basis of a 2-mm-thick uniform absorbing coating 2. The metal resonant layer 1 is composed of a plurality of hexagonal hollow copper sheet units, and these units are arranged and combined in an array form of a nested hexagonal structure. This hexagonal array structure can effectively regulate the propagation of electromagnetic waves. Through the periodicity and symmetry of the structure, effective absorption of electromagnetic waves in a specific frequency band is achieved, successfully breaking through the limit constraint of the Rozanov theory on the performance of absorbing materials, realizing wide-band high-efficiency absorption at a deep sub-wavelength scale with a total thickness of only 2.25 mm, with an effective bandwidth of 1.6 GHz, covering most of the S band, and the reflection loss RL < -10 dB, and the microwave absorption rate exceeding 90%.

[0058] The embodiment of the present invention solves the "thickness-bandwidth" performance mutual exclusion problem existing in traditional homogeneous absorbing materials. This technology adopts a multi-layer structure design including a metal resonant layer 1, a homogeneous absorbing coating 2, and a metal matrix layer 3. While achieving effective absorption in the S band, it has engineering advantages such as ultra-thin, lightweight, and strong environmental adaptability, providing solutions for national defense and civilian fields such as electromagnetic protection of 5G communication base stations and stealth skins of new-generation aircraft.

[0059] The nested hexagonal resonant structure absorbing metamaterial is composed of a metal resonant layer 1, a homogeneous absorbing coating 2, and a metal matrix layer 3. Among them, the metal resonant layer 1 adheres to the surface of the homogeneous absorbing coating 2, and the homogeneous absorbing coating 2 adheres to the surface of the metal matrix layer 3; the metal resonant layer 1 consists of an array of nested hexagonal structures composed of several copper sheets. Each structure array is composed of seven copper sheets. One copper sheet is placed at the center of the structure array, and the remaining six copper sheets are arranged circumferentially around the central hexagon at an equal angular spacing of 60°, forming an array with six-fold rotational symmetry; the homogeneous absorbing coating 2 is prepared by mixing carbonyl iron, charcoal, and epoxy resin through multiple stirring - oscillation processes.

[0060] The technical solution of the present invention will be further described below through specific embodiments.

[0061] In the following embodiments, unless otherwise specified, the methods are all conventional methods; the reagents and materials, unless otherwise specified, can be purchased on the market.

[0062] Example 1

[0063] A preparation method of a nested hexagonal resonant structure absorbing metamaterial includes the following steps:

[0064] S1. Pretreatment of the metal matrix layer: Select an aluminum plate with a size of 200mm×200mm×1.0mm as the metal matrix layer. Ultrasonically clean it with anhydrous ethanol to remove surface oil stains, and finally rinse it with deionized water for 10 minutes to ensure that the absorbing coating can cover it evenly, obtaining the metal matrix layer.

[0065] S2. Preparation of the magnetic-dielectric composite absorbing coating: Weigh carbonyl iron powder, charcoal powder, and epoxy resin according to a certain mass ratio. The mass ratios of carbonyl iron powder, charcoal powder, and epoxy resin are shown in Table 1. Among them, carbonyl iron powder is denoted as CIP; charcoal powder is denoted as CH. After mixing carbonyl iron powder, charcoal powder, and epoxy resin, add ethanol as a solvent, and through the synergistic effect of mechanical stirring and ultrasonic oscillation, the dispersion of carbonyl iron powder and activated carbon material in the epoxy resin matrix is realized, and the magnetic-dielectric composite absorbing coating is prepared.

[0066] S3. Preparation of the homogeneous absorbing coating: Use a scraper to evenly attach the magnetic-dielectric composite absorbing coating to the surface of the metal matrix layer, and the homogeneous absorbing coating is prepared. The thickness of the homogeneous absorbing coating is controlled at 2mm, and it is left standing at room temperature until a semi-cured coating is formed.

[0067] S4. Preparation of the metal resonant layer: The copper hollowed - out hexagonal patch with a thickness of 0.25 mm is prepared by laser cutting method, and the copper hollowed - out hexagonal patches are arranged in a nested hexagonal array on the surface of the semi - cured coating to prepare the metal resonant layer on the surface of the uniform wave - absorbing coating. The composite structure is continuously left to cure at room temperature for 6 h - 12 h. After the coating is completely cured, the nested hexagonal resonant structure wave - absorbing metamaterial is obtained.

[0068] Table 1 Feeding conditions of different mass ratios of carbonyl iron powder, charcoal powder, and epoxy resin

[0069] Number Mass ratio of carbonyl iron powder, charcoal powder and epoxy resin 1 5：0.1：1 2 5：0.15：1 3 5：0.2：1 4 5：0.25：1 5 5：0.3：1

[0070] Comparative Example 1

[0071] A preparation method of a homogeneous wave - absorbing material is the same as the preparation steps of Example 1, except that the preparation of the metal resonant layer is not carried out, and it includes the following steps:

[0072] S1. Pretreatment of the metal matrix layer: Select an aluminum plate with a size of 200 mm×200 mm×1.0 mm as the metal matrix layer. The surface oil stain is removed by ultrasonic cleaning with absolute ethanol, and finally it is rinsed with plasma water for 10 min to ensure that the wave - absorbing coating can be evenly covered, and the metal matrix layer is obtained.

[0073] S2. Preparation of the magnetic - dielectric composite wave - absorbing coating: Weigh carbonyl iron powder, charcoal powder, and epoxy resin according to the mass ratio of 5:0.3:1. After mixing carbonyl iron powder, charcoal powder, and epoxy resin, add ethanol as the solvent. Through the synergistic effect of mechanical stirring and ultrasonic oscillation, the dispersion of carbonyl iron powder and activated carbon material in the epoxy resin matrix is realized, and the magnetic - dielectric composite wave - absorbing coating is prepared.

[0074] S3. Preparation of the uniform wave - absorbing coating: The magnetic - dielectric composite wave - absorbing coating is uniformly attached to the surface of the metal matrix layer by using a scraper to prepare the uniform wave - absorbing coating. The thickness of the uniform wave - absorbing coating is controlled at 2 mm. After standing at room temperature until it is completely cured, a homogeneous wave - absorbing coating is formed on the surface of the metal matrix layer, and the homogeneous wave - absorbing material is obtained.

[0075] The nested hexagonal resonant structure wave - absorbing metamaterial with excellent wave - absorbing performance in the S - band is prepared in Example 1 of the present invention. Taking the nested hexagonal resonant structure wave - absorbing metamaterial of Example 1 as an example, research is carried out and compared with the homogeneous wave - absorbing material of Comparative Example 1. The specific research methods and results are as follows:

[0076] In the embodiment of the present invention, the carbonyl iron / charcoal composite material is used as the magnetic / dielectric double - loss electromagnetic absorber. A homogeneous wave - absorbing coating is formed through the coating process, and a resonant layer is constructed by arranging metal copper sheets in a specific array based on the patch process, and then the nested hexagonal resonant structure wave - absorbing metamaterial is prepared.

[0077] The nested hexagonal resonant structure absorbing metamaterial prepared in the embodiment of the present invention matches the S-band through the LC resonance of the copper sheet gap capacitance and the mobile charge inductance, combined with the intrinsic loss of the uniform absorbing coating with a mass ratio of carbonyl iron powder and charcoal powder of 5:0.1-0.3, to increase the material's ability to resist electromagnetic wave loss. At the same time, the design scheme combining the metal resonant layer with the homogeneous absorbing coating improves the material's impedance characteristics, achieves electromagnetic wave reflection suppression, and ultimately achieves 1.5GHz broadband and efficient absorbing at a sub-wavelength thickness, breaking through the bottleneck of the contradiction between the low-frequency absorption performance and thickness of traditional absorbing materials.

[0078] The nested hexagonal resonant structure absorbing metamaterial prepared in the embodiment of the present invention adopts a three-layer composite structure: the upper layer is a metal resonant layer, the middle layer is a homogeneous absorbing coating layer, and the lower layer is a metal matrix layer. The metal resonant layer is composed of a nested hexagonal structure array of metal sheets.

[0079] like Figure 1 As shown in the figure, each array unit is composed of seven hexagonal hollow copper patches, with one copper patch placed in the center of the array and six identical copper patches arranged around the periphery at 60° equal angular intervals, forming a spatial configuration with strict six-fold rotational symmetry. The radius of the circumscribed circle of all copper patches is D1 = 6mm, the radius of the circumscribed circle of the hollowed-out part in the middle is D2 = 3mm, and the period size of the absorbing unit of the nested hexagonal resonant structure absorbing metamaterial is L = 200mm.

[0080] like Figure 2 As shown, the nested hexagonal resonant structure absorbing metamaterial is composed of a number of absorbing units arranged periodically in a two-dimensional plane, and the arrangement of each absorbing unit is consistent. The height of the metal resonance layer is 0.25 mm, the height of the homogeneous absorbing coating is 2.0 mm, and the height of the metal matrix layer is 1.0 mm.

[0081] Figure 3 The scanning electron microscopy images of carbonyl iron and charcoal particles are shown respectively. Figure 3 In Figures (a) and (b), the carbonyl iron particles are onion-like layered morphology with a diameter of 3.0 μm to 5.0 μm, which is conducive to multi-scale magnetic coupling. Figure 3 (c) and (d) , the charcoal particles adopt an irregular polygonal geometry, which enhances the dielectric polarization through defect-mediated charge accumulation.

[0082] Figure 4Shows the electromagnetic parameter variation curves of magnetic-dielectric composite absorbing coatings with different mass ratios in the frequency band of 2 GHz to 18 GHz. The electromagnetic response of the magnetic-dielectric composite absorbing coating is controlled by the real and imaginary parts of its permittivity and permeability. Among them, ε' represents the real part of the permittivity, μ' represents the real part of the permeability, and the energy storage capacity is quantified by ε' and μ'; ε" represents the imaginary part of the permittivity, μ" represents the imaginary part of the permeability, and the energy dissipation is reflected by ε" and μ".

[0083] As Figure 4 Shown in the (a) figure of Figure 4 , the real part of the permittivity ε' of the magnetic-dielectric composite absorbing coating shows a monotonic decrease in the range of 2 GHz to 18 GHz, which is a characteristic of the dispersion behavior caused by the retarded polarization response relative to the alternating field. At the same time, the imaginary part of the permittivity ε" shows obvious fluctuation peaks in three regions: 2 GHz to 4 GHz, 8 GHz to 10 GHz, and 12 GHz to 16 GHz, as shown in the (b) figure of

[0084] These non-monotonic trends indicate the activation of the multi-polarization relaxation process. The real part of the permeability μ' shows a monotonic decrease in the range of 2 GHz to 18 GHz, as shown in the (c) figure of Figure 4 , reflecting the reduction of magnetic energy storage at higher frequencies. At the same time, the imaginary part of the permeability μ" shows obvious resonance peaks at 6 GHz and 11 GHz, as shown in the (d) figure of Figure 4 , indicating the frequency-selective magnetic loss mechanism.

[0085] The nested hexagonal resonant structure absorbing metamaterial of the embodiment of the present invention adopts a combined design of a metal resonant layer and a homogeneous absorbing coating, introducing a new electromagnetic resonance and coupling mechanism, effectively improving the absorbing ability of the absorbing metamaterial in the S band. Specifically, this combination organically combines the intrinsic loss of the traditional homogeneous absorbing coating and the structural loss of the metal resonant layer, achieving high-efficiency absorption under the condition of sub-wavelength thickness. Experiments show that the absorbing metamaterial designed in the embodiment of the present invention successfully achieves broadband and high-efficiency absorption in the frequency band of 2 GHz to 4 GHz, breaking through the contradiction bottleneck between the absorption performance and thickness of traditional absorbing materials in the low-frequency band.

[0086] Figure 5 Shows the comparison of the reflection loss performance of the homogeneous absorbing coating and the nested hexagonal resonant structure absorbing metamaterial in the frequency band of 2 GHz to 18 GHz.

[0087] As Figure 5As shown in Figure (a), the effective absorption range of homogeneous absorbing coatings with different mass ratios, where RL < -10 dB, is mainly distributed in the C and Ku bands, that is, 4 GHz to 10 GHz. Among them, the homogeneous absorbing coating sample with a mass ratio of carbonyl iron powder, charcoal powder, and epoxy resin of 5:0.3:1 exhibits the optimal performance. Its effective bandwidth is 3.8 GHz, covering the frequency range from 4.7 GHz to 8.5 GHz, and the peak reflection loss reaches -24 dB. This means that within the frequency band of 4.7 GHz to 8.5 GHz, the homogeneous absorbing coating sample with a mass ratio of carbonyl iron powder, charcoal powder, and epoxy resin of 5:0.3:1 can provide effective electromagnetic wave absorption performance, and the entire broadband span is 3.8 GHz.

[0088] It is worth noting that the nested hexagonal resonant structure absorbing metamaterial achieves a significant optimization of the absorbing characteristics through structural design, such as Figure 5 In Figure (b), when the homogeneous absorbing coating of the nested hexagonal resonant structure absorbing metamaterial uses a mass ratio of carbonyl iron powder, charcoal powder, and epoxy resin of 5:0.3:1, the effective absorption frequency band extends to the low-frequency S band, that is, 2 GHz to 4 GHz, and the effective bandwidth reaches 1.6 GHz, specifically covering the frequency range from 2.3 GHz to 3.9 GHz. Compared with Figure 5 the homogeneous coating shown in Figure (a), the low-frequency extension ability is increased by 42%. This means that the nested hexagonal resonant structure absorbing metamaterial exhibits excellent absorbing performance within the frequency range of 2.3 GHz to 3.9 GHz and can effectively absorb electromagnetic waves within this frequency band. At the same time, when the mass ratio of carbonyl iron powder, charcoal powder, and epoxy resin is 5:0.3:1, the nested hexagonal resonant structure absorbing metamaterial obtains a minimum reflection loss peak of -27 dB at 3 GHz, which is a 12.5% improvement compared to the peak absorbing performance of the homogeneous coating.

[0089] The experimental results show that the nested hexagonal resonant structure absorbing metamaterial prepared with a mass ratio of carbonyl iron powder, charcoal powder, and epoxy resin of 5:0.3:1 exhibits excellent electromagnetic attenuation characteristics in the S band. Its effective absorption bandwidth covers 80% of the S band. This targeted optimization characteristic for the S band gives it significant advantages in electromagnetic shielding applications in specific frequency bands.

[0090] In summary, the embodiment of the present invention adopts the design of constructing a metal resonant layer structure on the surface of a homogeneous absorbing coating, innovatively integrating the dual mechanisms of intrinsic loss and resonant loss, and realizing the efficient absorption of S-band electromagnetic waves at the sub-wavelength scale. The carbonyl iron / charcoal / epoxy resin composite system is used as the absorbing matrix, and the intrinsic electromagnetic attenuation ability of the coating is significantly enhanced through the synergistic effect of magnetic loss and dielectric loss. The metal resonant layer forms an LC resonant network through a periodically arranged nested hexagonal copper sheet array, enabling the resonant frequency to accurately cover the target frequency band of 2 GHz to 4 GHz. Secondly, the strong local electric field and eddy current effect induced by resonance cooperate with the dielectric / magnetic loss of the absorbing coating. This significantly improves the attenuation loss characteristics of the absorbing metamaterial and successfully constructs an optimized triangular performance relationship of "wide frequency band - thin coating - strong loss".

[0091] The absorbing metamaterial with a nested hexagonal resonant structure proposed in the embodiment of the present invention innovatively breaks through the physical limit of "thickness - bandwidth" of traditional absorbing materials in the S band through cross-scale collaborative design of structure - material. The embodiment of the present invention designs and uses a carbonyl iron / charcoal composite material to construct a homogeneous absorbing coating, and the total thickness of the metal resonant layer and the homogeneous absorbing coating is ≤ 3 mm. Combining with the metal resonant layer composed of a hexagonal hollow copper patch array, a unique coating - patch composite structure is formed. Through the electromagnetic synergistic effect between the metal resonant unit and the dielectric matrix, not only excellent impedance matching characteristics are achieved, but also a multi-mechanism electromagnetic attenuation system of "intrinsic loss - structural dissipation" is innovatively constructed. Experimental results show that the absorbing metamaterial with a nested hexagonal resonant structure prepared in the embodiment of the present invention exhibits a wide-frequency absorption characteristic of 1.6 GHz in the S band, and its effective absorption bandwidth covers 80% of the S band. Its breakthrough lies in simultaneously achieving the dual optimization goals of expanding the absorption bandwidth and thinning the material. This composite structure design based on conventional coating processes provides a solution with both high performance and low cost advantages for lightweight electromagnetic protection equipment in the engineering field, and is particularly suitable for S-band application scenarios with strict requirements for material thickness and absorption bandwidth.

[0092] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A nested hexagonal resonant structure absorbing metamaterial, characterized in that, It comprises a metal resonance layer, a homogeneous absorbing coating layer and a metal matrix layer in sequence; the metal resonance layer is composed of a plurality of metal resonance units arranged in a periodic array on the surface of the homogeneous absorbing coating layer; each of the metal resonance units is a nested hexagonal structure formed by arranging a plurality of structural units, and each of the structural units is a hollow hexagonal metal patch.

2. The nested hexagonal resonant structure absorbing metamaterial according to claim 1, wherein The homogeneous absorbing coating is formed by coating a magnetic-dielectric composite absorbing coating on the surface of a metal matrix layer and then curing the coating; the magnetic-dielectric composite absorbing coating is prepared by mixing carbonyl iron powder, biomass carbon powder and epoxy resin in a solvent system.

3. The nested hexagonal resonant structure absorbing metamaterial according to claim 2, characterized in that, The mass ratio of carbonyl iron powder, biomass carbon powder and epoxy resin is 5:0.1-0.3:

1.

4. The nested hexagonal resonant structure absorbing metamaterial according to claim 2, wherein The biomass charcoal powder is charcoal powder; the solvent is at least one of ethanol, toluene, acetone and ethyl acetate.

5. The nested hexagonal resonant structure absorbing metamaterial according to claim 1, wherein The periodic size of each of the metal resonance units is 160 mm to 220 mm.

6. The nested hexagonal resonant structure absorbing metamaterial according to claim 1, characterized in that, The total thickness of the metal resonant layer and the homogeneous absorbing coating is ≤3mm; The diameter of the circumscribed circle of the hollow hexagonal metal patch is 5 mm to 8 mm, and the thickness is 0.1 mm to 0.5 mm.

7. The nested hexagonal resonant structure absorbing metamaterial according to claim 1, characterized in that, The thickness of the homogeneous wave-absorbing coating is 1 mm to 2 mm; the thickness of the metal matrix layer is 1 mm to 2 mm.

8. The nested hexagonal resonant structure absorbing metamaterial according to claim 1, wherein The hollow hexagonal metal patch is made of copper, and the dielectric constant of the hollow hexagonal metal patch is 0.99; the material of the metal matrix layer is aluminum.

9. A method for preparing the nested hexagonal resonant structure absorbing metamaterial according to any one of claims 2 to 8, characterized in that, The following steps are involved: The carbonyl iron powder, biomass carbon powder and epoxy resin are uniformly mixed in a solvent system to prepare a magnetic-dielectric composite absorbing coating; The magnetic-dielectric composite absorbing coating is coated on the surface of the metal matrix layer and allowed to stand until it reaches a semi-cured gel state. Metal resonant units are periodically arrayed on the surface of the homogeneous absorbing coating in the semi-cured gel state and allowed to stand until the homogeneous absorbing coating is cured to obtain a nested hexagonal resonant structure absorbing metamaterial.

10. Use of the nested hexagonal resonant structure absorbing metamaterial according to any one of claims 1 to 8 in preparing an electromagnetic wave absorbing metamaterial, characterized in that The electromagnetic wave absorbing metamaterial is an electromagnetic wave absorbing metamaterial used in wireless communication, electromagnetic compatibility, electromagnetic shielding or radar stealth.

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