Lightweight broadband absorber based on metamaterial and magnetic foam material and preparation method

Abstract

The present invention relates to the field of electromagnetic wave absorption technology, specifically disclosing a lightweight broadband absorber based on metamaterials and magnetic foam materials and a preparation method. The lightweight broadband absorber includes a dielectric layer and a metamaterial layer, wherein the metamaterial layer is disposed on one surface of the dielectric layer and is composed of a plurality of periodically arranged absorbing units. The absorbing units are composed of a cross-shaped structure and an end-point symmetrical frame structure, wherein the cross-shaped structure is located at the center and the end-point symmetrical frame structure is disposed outside the cross-shaped structure; the cross-shaped structure and the end-point symmetrical frame structure are non-contacting. The dielectric layer is a magnetic foam, which is prepared by uniformly mixing and distributing magnetic metal additives in polyurethane foam. The lightweight broadband absorber of the present invention not only has a small size and low density, but also has an absorption rate of over 90% between 3GHz and 18GHz.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave absorption, and in particular to a lightweight broadband absorber based on metamaterials and magnetic foam materials and a preparation method thereof. Background Art

[0002] With the development of the electronics industry and the popularization of electronic equipment, the interference of electromagnetic pollution on instruments and equipment has become increasingly prominent. As an important supporting material for electromagnetic interference protection technology, absorbing materials have become a hot research topic at home and abroad.

[0003] Absorbing materials, as important absorbing media in the field of electromagnetic absorption, absorb incident electromagnetic waves and dissipate them into heat and other forms of energy. Typically, electromagnetic waves reflected and transmitted upon impacting a dielectric surface, and the material's absorption performance is primarily determined by two parameters: dielectric constant and magnetic permeability. Metamaterials, as new artificial composite materials of the 21st century, possess exceptional properties that allow them to absorb and dissipate incident electromagnetic waves to a significant degree, achieving near-zero transmission and reflection. Compared to traditional absorbers, metamaterial absorbers offer unique advantages, including unique electromagnetic parameters and electromagnetic controllability.

[0004] Due to these advantages, metamaterials have garnered widespread attention in the field of electromagnetic absorption. Metamaterial absorbers typically consist of three components, resembling a multilayer sandwich structure: a periodic unit array with a defined structure at the top, a high-loss dielectric interlayer in the middle, and a complete metal reflective baseplate at the bottom. Metamaterial absorbers typically utilize dielectric lossy materials (such as epoxy resins (FR-4) and PET), but these are less effective in increasing peak absorptivity and broadening the absorber's absorption bandwidth in the microwave band. Furthermore, conventional lossy materials such as these suffer from relatively large dielectric layers and high density.

[0005] Existing research has found that high absorption rates or both high absorption rates and low density can be achieved, but it is not possible to combine small size, low density, and high absorption rates. Therefore, it is necessary to design an absorber that is small in size, low in density, and high in absorption rates. Summary of the Invention

[0006] The object of the present invention is to provide a lightweight broadband absorber based on metamaterials and magnetic foam materials, which not only has a small volume and low density, but also has an absorption rate of more than 90% in the range of 3GHz-18GHz.

[0007] In addition, the present invention also provides a method for preparing the lightweight broadband absorber.

[0008] The present invention is achieved through the following technical solutions:

[0009] A lightweight broadband absorber based on metamaterials and magnetic foam materials includes a dielectric layer and a metamaterial layer. The metamaterial layer is disposed on one surface of the dielectric layer and is composed of a plurality of periodically arranged absorbing units. The absorbing units include a cross-shaped structure and an end-point symmetrical frame structure. The cross-shaped structure is located in the center, and the end-point symmetrical frame structure is disposed outside the cross-shaped structure. There is no contact between the cross-shaped structure and the end-point symmetrical frame structure.

[0010] The medium layer is magnetic foam, which is prepared by uniformly mixing and distributing magnetic metal additives in polyurethane foam.

[0011] The absorbing unit of the present invention is a sub-wavelength structure with a wavelength of millimeter wave, wherein the millimeter wavelength is the wavelength corresponding to the absorption frequency of the absorber, and the operating frequency range of the lightweight broadband absorber is 3GHz-18GHz.

[0012] If only polyurethane foam were used as the dielectric layer, while the overall density of the structure would be relatively low, the overall thickness of the absorber would still exceed 10 mm. The dielectric layer of the present invention is a magnetic foam, which broadens the microwave absorption band of the absorber, increasing the effective absorption bandwidth to greater than 10 GHz. Furthermore, by coating the dielectric layer with a metamaterial resonant structure, efficient absorption within the frequency band is achieved, resulting in practical absorption performance. This hierarchical structure, combining a periodic metamaterial surface structure with a magnetic polyurethane foam dielectric, easily achieves electromagnetic wave absorption within the test band. Without changing the structural pattern, experimental testing can determine a set of structural parameters that optimize the overall absorption performance, thus achieving excellent microwave absorption.

[0013] In summary, the magnetic polyurethane foam of the present invention is used as an absorbing medium and combined with a metamaterial to obtain a lightweight, efficient absorber. The lightweight broadband absorber of the present invention not only has a small volume and low density, with an overall design not exceeding 3mm, but also has an absorption rate of more than 90% in the 3GHz-18GHz range.

[0014] Furthermore, the cross-shaped structure is a centrally symmetrical structure; the internal spacing width of the end-point symmetrical frame structure is greater than the width of the cross-shaped structure.

[0015] If the internal spacing width of the symmetrical square structure is smaller than the width of the cross structure, simulation tests show that the peak absorption frequency point will shift to a low frequency, the peak absorption rate will drop by -10dB, and the absorption bandwidth will be affected.

[0016] Furthermore, the metamaterial layer is formed by sputtering metal onto one surface of the dielectric layer through a magnetron sputtering coating process.

[0017] Metamaterial absorbers have high requirements for the coating process and the uniformity and purity of the coating materials. The magnetron sputtering coating process can accurately control the thickness of the coating and obtain a thin film of uniform thickness on the sample substrate.

[0018] Furthermore, when the overall side length of the absorbing unit is 10 mm, the length of the endpoint-symmetrical square frame structure is 2.0-4.5 mm, and the length of the cross-shaped structure is twice the length of the endpoint-symmetrical square frame structure.

[0019] Furthermore, when the overall side length of the absorbing unit is 10 mm, the length of the end-point symmetrical square frame structure is 3 mm, the length and width of the end-point symmetrical square frame structure are 1 mm, and the width of the cross-shaped structure is 2 mm.

[0020] Furthermore, the thickness of the dielectric layer is 2-3 mm.

[0021] Furthermore, the magnetic metal additive includes iron nanofiber or carbonyl iron powder.

[0022] Furthermore, a metal thin film layer is provided on a surface of the dielectric layer opposite to the metamaterial layer.

[0023] Furthermore, the thickness of the metal film layer and the metamaterial layer are both 0.05 mm

[0024] A method for preparing a lightweight broadband absorber comprises the following steps:

[0025] S1. Preparing a dielectric layer: uniformly mixing a polyurethane foam material and a magnetic metal additive and allowing the mixture to foam to prepare an absorbing dielectric material, and then cutting the absorbing dielectric material into dielectric layers;

[0026] S2. Prepare a metamaterial layer on one surface of the dielectric layer using a magnetron sputtering coating process.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] The present invention uses magnetic polyurethane foam as an absorbing medium and combines it with a metamaterial to obtain a lightweight and efficient absorber. By designing a cross-shaped surface periodic metastructure, the absorption effect of the absorber in the frequency domain is effectively improved. By using polyurethane foam as the dielectric material base, the defect of high density of the absorber is solved. The overall structure is designed to be no more than 3mm, which solves the problem of large absorber thickness. Magnetic metal additives are added to the polyurethane foam to broaden the microwave absorption band of the absorber, making the effective absorption bandwidth greater than 10GHz and other beneficial effects, and having an absorption rate of more than 90% in the range of 3GHz-18GHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0030] Figure 1 Schematic diagram of the overall structure of the lightweight broadband absorber of the present invention;

[0031] Figure 2 is a schematic diagram of a metamaterial layer of the present invention;

[0032] Figure 3 is a side view of the lightweight broadband absorber of the present invention;

[0033] Figure 4 is a schematic diagram of the metal film layer of the present invention;

[0034] Figure 5 is a graph showing the real part of the dielectric constant from the first layer to the third layer in a direction perpendicular to the electric field in Example 1 of the present invention;

[0035] Figure 6 1 is a graph showing dielectric loss tangent data from the first layer to the third layer in a direction perpendicular to the electric field in Example 1 of the present invention;

[0036] Figure 7 is the S of the metamaterial and magnetic polyurethane foam composite absorber in Example 1 of the present invention at different sample thicknesses in the 2GHz-18GHz frequency band. 11 Reflection loss data graph;

[0037] Figure 8 The metamaterial and magnetic polyurethane foam composite absorber in Example 1 of the present invention has a fixed thickness of 3 mm and changes in the overall structure width and X i S under geometric change 11 Reflection loss diagram;

[0038] Figure 9 The S values ​​of different material thicknesses when no metamaterial resonant structure is added in Example 1 of the present invention are shown in FIG. 11 Reflection loss diagram.

[0039] Markings and corresponding parts names in the accompanying drawings:

[0040] 1-metamaterial layer; 2-dielectric layer; 3-metal film layer. DETAILED DESCRIPTION

[0041] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0042] Example 1:

[0043] like Figures 1-4 As shown, a lightweight broadband absorber based on metamaterials and magnetic foam materials includes a dielectric layer 2 and a metamaterial layer 1. The metamaterial layer 1 is arranged on one surface of the dielectric layer 2 and is composed of a plurality of absorbing units arranged periodically. Figure 1 、 Figure 2 The structure shown is an array unit in a periodic array, namely, an absorbing unit. The entire metamaterial layer 1 is arranged in accordance with Figure 1 、 Figure 2 The structure shown is arranged periodically, and the absorbing unit includes a cross-shaped structure and an endpoint-symmetrical square frame structure, the cross-shaped structure is located in the center, and the endpoint-symmetrical square frame structure is arranged outside the cross-shaped structure; there is no contact between the cross-shaped structure and the endpoint-symmetrical square frame structure; wherein the cross-shaped structure is formed by two rectangular strips intersecting vertically; the endpoint-symmetrical square frame structure is composed of four L-shaped frames, and the four L-shaped frames are respectively arranged at the four corners of the square plane where the cross-shaped structure is located, and the outer sides of the two right-angled sides of the L-shaped frame are aligned with the edges of the square plane where the cross structure is located; the length and width of the L-shaped frame are not equal, wherein the length of the L-shaped frame refers to the length of the outer sides of the two right-angled sides, such as Figure 2 X shown i .

[0044] The dielectric layer 2 is a magnetic foam, which is prepared by uniformly mixing and distributing magnetic metal additives in polyurethane foam. The magnetic metal additives include iron nanofibers or carbonyl iron powder.

[0045] This embodiment uses magnetic polyurethane foam as the absorbing medium and combines it with a metamaterial to produce a lightweight, efficient absorber. By designing a cross-shaped surface periodic metastructure, the absorber's absorption efficiency in the frequency domain is effectively improved. By using polyurethane foam as the dielectric material base, the absorber's high density is addressed. The overall structure is designed to be no thicker than 3 mm, solving the problem of large absorber thickness. The addition of magnetic metal additives to the polyurethane foam broadens the absorber's microwave absorption band, increasing the effective absorption bandwidth to greater than 10 GHz, achieving beneficial effects such as an absorption rate of over 90% in the 3 GHz to 18 GHz range.

[0046] The operating frequency of the lightweight broadband absorber of this embodiment is 3 GHz-18 GHz. The absorbing unit is a sub-wavelength structure with a wavelength of millimeter wave, where the millimeter wavelength is the absorption wavelength corresponding to the operating frequency of the absorber.

[0047] In a preferred embodiment, the metamaterial layer 1 is deposited onto one surface of the dielectric layer 2 using a magnetron sputtering coating process. Compared to conventional surface coating techniques and redox coating methods, magnetron sputtering offers fast deposition rates, low substrate temperature rise, and minimal damage to the film. Metamaterial absorbers place high demands on the coating process, including the uniformity and purity of the coating material. Magnetron sputtering allows for precise control of coating thickness, resulting in a uniform film on the sample substrate.

[0048] The method for preparing the lightweight broadband absorber described in this embodiment includes the following steps:

[0049] S1. Preparation of dielectric layer 2: uniformly mix polyurethane foam material and magnetic metal additives and allow to foam to form a wave-absorbing dielectric material, and cut the wave-absorbing dielectric material into dielectric layer 2; specifically:

[0050] The additive is prepared by mixing cross-structured ferromagnetic fibers as magnetic additives. The cross-structured ferromagnetic fibers can achieve excellent orientation effects in polyurethane foam. After static foaming, the polyurethane foam presents a soft and porous structure. The polyurethane foam is grouped and cut according to experimental requirements to obtain sample materials of different thicknesses.

[0051] S2. Prepare a metamaterial layer 1 on one surface of the dielectric layer 2 by using a magnetron sputtering coating process.

[0052] This embodiment achieves efficient microwave absorption across the frequency band by coating the dielectric absorbing layer with a metamaterial resonant structure, achieving practical absorption performance. This layered structure, combining a periodic metamaterial surface structure with a magnetic polyurethane foam dielectric, easily achieves electromagnetic wave absorption within the test band. Without changing the structural pattern, experimental testing can determine a set of structural parameters that optimize overall microwave absorption, ultimately achieving excellent microwave absorption.

[0053] Exemplary:

[0054] A metal film layer 3 is provided on the surface of the dielectric layer 2 opposite the metamaterial layer 1. The metal film layer 3 is a metal film made of a good metal conductor, which can be either copper or aluminum. The entire absorber consists of a three-layer structure, from top to bottom: the metamaterial layer 1, the dielectric layer 2, and the metal film layer 3. The cross-shaped structure is a centrally symmetrical structure; the internal spacing width of the end-symmetrical square frame structure is greater than the width of the cross-shaped structure. The internal spacing width refers to the distance between two adjacent L-shaped frames, such as Figure 2 X on both sides shown i The width of the middle is Y i -2X i; The width of the cross structure refers to the width of the rectangular bars that constitute the cross structure.

[0055] The magnetic foam is made of cross-structured ferromagnetic fibers uniformly mixed and distributed in polyurethane foam. The cross-section of the base part of the material is square, and the side length L is the same as the side length of the absorber. The dielectric constant ε∈(5.74,7.08) of the prepared material is made of polyurethane foam, cross-structured ferromagnetic fibers and other materials. When the mass fraction of the cross-structured ferromagnetic fibers is 20%, the volume content of the cross-structured ferromagnetic fibers after foaming reaches 2.48%. The density of the magnetic foam is measured to be 0.12g / cm 3 The cross section of the metamaterial layer 1 is a cross shape, and the length of the end symmetrical frame structure is X i =3mm, the overall side length of the periodic structure (wave absorbing structure) is Y i =10mm, the center of the cross-shaped structure coincides with the center of the base, which is a symmetrical structure. The structural parameters of each layer are independent of each other.

[0056] In order to determine a set of structural parameters with the best comprehensive wave absorbing effect, the following experiments were conducted:

[0057] The materials used for preparing the magnetic foam are polyurethane foam and cross-structured ferromagnetic fibers.

[0058] For the above-mentioned broadband and efficient absorber based on the composite structure of metamaterials and magnetic foam, the tested electromagnetic wave is a plane wave with vertical incidence, and the measured frequency range is selected as 2GHz-18GHz.

[0059] Depend on Figure 7 It can be seen that after testing multiple sets of thickness samples, the absorber has a single resonance peak in the 2GHz-18GHz frequency band, and the maximum resonance peak is near 6GHz. When the sample thickness changes from 1.5mm to 3.5mm, the metamaterial absorber reflection loss curve also changes accordingly, and the absorption peak frequency point shifts from high frequency to low frequency. When the thickness of the dielectric material sample increases successively, the reflection loss curve shows a trend of first rising and then falling, and the absorption efficiency shows a trend of first rising and then falling. Among the several groups of samples with different thickness parameters tested, the absorption effect is best when the material thickness reaches 2mm, and the absorption bandwidth reaches the maximum. Figure 7 As shown in the figure, when the sample thickness is between 2mm and 3mm, the sample absorption effect is also excellent, and the absorption bandwidth is close to 14GHz. According to the simulation diagram, when the material thickness reaches 2mm, the absorption effect is the best, and the absorption bandwidth reaches 15GHz. When the width of the surface structure changes, it affects the maximum resonance peak of the metamaterial. When the width of the surface metamaterial increases proportionally with the length, the reflection loss curve of the metamaterial absorber is as follows: Figure 8 As shown, Figure 8The figure shows that when the sample thickness is fixed at 3mm, the side length and surface structure length of the structure are adjusted proportionally to adapt to the changes in the periodic unit structure. The curve shown in the figure shows that when the side length changes, the absorption curve of the absorber shows a trend of first rising and then falling. When the side length of the sample is 10mm and the length of the end-point symmetrical metal square structure is 3mm, the absorption peak is the largest and the absorption bandwidth is the widest. When the dielectric absorber sample does not add surface metamaterials, S 11 Reflection loss diagram Figure 9 As shown in the figure, when the metamaterial resonant structure is not added, the thickness of the dielectric absorbing material becomes a structural parameter that affects the performance of the absorbing material, which is determined by Figure 9 It can be seen that the electromagnetic absorption performance of the material is similar when the thickness is similar. The difference in absorption performance between different thicknesses is due to multiple reflections and transmissions of electromagnetic waves within the dielectric absorber. When the test material thickness is 2mm, it is closer to 1 / 4 wavelength of the corresponding peak absorption frequency. Comparing the reflection loss graphs of samples without dielectric absorber and with surface metamaterial, it is found that the addition of metamaterial significantly increases the peak absorption frequency and broadens the absorption band of the absorber. After testing multiple sets of experimental samples with different structural parameters and comparing them, the structural parameters with the best overall absorption performance were determined. The optimal data are a metamaterial periodic unit with a side length of 10mm, a dielectric layer 2 thickness of 2mm, and a metal film layer 3 thickness of 0.05mm.

[0060] The metamaterial layer 1 is prepared using magnetron sputtering to form a periodic structure, and the surface structure is a cross-shaped and end-point symmetrical metal square structure. The length of the end-point symmetrical metal square junction is X i =3mm, the width is fixed at 1mm, the length of the cross structure in the center is fixed at 6mm, the width is fixed at 2mm, and the overall side length of the periodic structure unit is Y i =10mm, the metal film layer 3 (metal reflective layer) adopts a copper film with a thickness of 0.05mm, the thickness of the dielectric layer 2 is h=2mm, the electromagnetic properties of the magnetic foam are measured by experiment, and its dielectric constant and loss tangent change with frequency as shown in the following figure: Figure 5 、 Figure 6 shown.

[0061] The lightweight, broadband, and efficient absorber based on metamaterials and magnetic foam proposed in this embodiment can achieve over 90% efficient absorption of electromagnetic waves in the 3GHz-18GHz frequency band through a well-designed structure. At 6GHz, the metamaterial's reflectivity for electromagnetic waves reaches a minimum of -34dB. It also has the advantages of being lightweight, thin, and flexible, and excels in stretchability and foldability. It has good prospects in electromagnetic shielding, military stealth, and 5G fields.

[0062] The optimized structural design parameters result in a broadband and efficient absorber with a composite structure of metamaterial and magnetic polyurethane foam. The side length of the periodic structural unit (absorbing unit) of the metamaterial layer 1 is 10 mm, the thickness of the metamaterial layer 1 is 0.05 mm, that of the dielectric layer 2 is 2 mm, and the thickness of the metal film layer 3 is 0.05 mm.

[0063] The wave absorbing effect of the above-mentioned lightweight broadband absorber is shown in the figure below: Figure 7 As shown, in the complete 3GHz-18GHz frequency band, the obtained S 11 At 6 GHz, the reflectivity of the metamaterial for electromagnetic waves reaches a minimum of -34 dB. At this frequency, the reflected energy of the incident electromagnetic wave on the surface of the material is close to 0%, and the electromagnetic wave loss rate reaches its maximum in this band.

[0064] Result analysis: The lightweight broadband absorber based on metamaterials and magnetic polyurethane foam has an absorption rate of more than 90% in the 3GHz-18GHz microwave frequency band. The test shows good absorption effect, meets the requirements for broadband electromagnetic wave absorption, and verifies the rationality of the structural design in the test experiment.

[0065] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0066] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for understanding and reading by those familiar with this technology, and are not used to limit the conditions for implementation of the present invention. Therefore, they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose of the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", etc. quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of implementation of the present invention without substantially changing the technical content.

Claims

1. A lightweight broadband absorber based on metamaterials and magnetic foam materials, comprising a dielectric layer (2) and a metamaterial layer (1), wherein the metamaterial layer (1) is arranged on one surface of the dielectric layer (2), characterized in that: The metamaterial layer (1) is formed by a periodic arrangement of a plurality of absorbing units, wherein the absorbing units include a cross-shaped structure and an end-point symmetrical frame structure, wherein the cross-shaped structure is located in the center and the end-point symmetrical frame structure is arranged outside the cross-shaped structure; there is no contact between the cross-shaped structure and the end-point symmetrical frame structure; the dielectric layer (2) is a magnetic foam, which is prepared by uniformly mixing and distributing magnetic metal additives in polyurethane foam; The cross-shaped structure is a centrally symmetrical structure, and the internal spacing width of the endpoint-symmetrical square frame structure is greater than the width of the cross-shaped structure; wherein, the cross-shaped structure is formed by two rectangular strips intersecting vertically; the endpoint-symmetrical square frame structure is composed of four L-shaped frames, and the four L-shaped frames are respectively arranged at the four corners of the square plane where the cross-shaped structure is located, and the outer sides of the two right-angled sides of the L-shaped frame are aligned with the edges of the square plane where the cross-shaped structure is located.

2. The lightweight broadband absorber based on metamaterials and magnetic foam materials according to claim 1, characterized in that: The metamaterial layer (1) is formed by sputtering metal onto one surface of the dielectric layer (2) through a magnetron sputtering coating process.

3. The lightweight broadband absorber based on metamaterial and magnetic foam material according to claim 1, characterized in that: When the overall side length of the absorbing unit is 10 mm, the length of the end-point symmetrical square frame structure is 2.0-4.5 mm, and the length of the cross-shaped structure is twice the length of the end-point symmetrical square frame structure.

4. The lightweight broadband absorber based on metamaterial and magnetic foam material according to claim 3, characterized in that: When the overall side length of the absorbing unit is 10 mm, the length of the end-point symmetrical square frame structure is 3 mm, the length and width of the end-point symmetrical square frame structure are 1 mm, and the width of the cross structure is 2 mm.

5. The lightweight broadband absorber based on metamaterial and magnetic foam material according to claim 1, characterized in that: The thickness of the dielectric layer (2) is 2-3 mm.

6. The lightweight broadband absorber based on metamaterials and magnetic foam materials according to claim 1, characterized in that: The magnetic metal additive includes iron nanofiber or carbonyl iron powder.

7. The lightweight broadband absorber based on metamaterial and magnetic foam material according to any one of claims 1 to 6, characterized in that: A metal film layer (3) is provided on a surface of the dielectric layer (2) opposite to the metamaterial layer (1).

8. The lightweight broadband absorber based on metamaterial and magnetic foam material according to claim 7, characterized in that: The thickness of the metal film layer (3) and the metamaterial layer (1) are both 0.05 mm.

9. The method for preparing a lightweight broadband absorber according to any one of claims 1 to 8, wherein: The following steps are involved: S1. Preparing a dielectric layer (2): uniformly mixing a polyurethane foam material and a magnetic metal additive and allowing the mixture to foam to prepare a wave-absorbing dielectric material, and cutting the wave-absorbing dielectric material into dielectric layers (2); S2. Using a magnetron sputtering coating process, a metamaterial layer (1) is prepared on a surface of a dielectric layer (2).

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