Microwave absorber and method for manufacturing the same

Abstract

This invention discloses a microwave absorber and its fabrication method. The microwave absorber includes multiple absorber units, each of which includes a dielectric layer and a patterned carbon-based conductive layer formed on the dielectric layer. The carbon-based conductive layer includes a central pattern and four peripheral patterns surrounding the central pattern. The central pattern includes a pair of parallel first vertical line segments and a first horizontal line segment connecting the middle of the first vertical line segments. Each first vertical line segment connects to two adjacent peripheral patterns. Each peripheral pattern includes a pair of parallel second vertical line segments and a second horizontal line segment connecting the middle of the second vertical line segments. The first vertical line segments connect to the second vertical line of one peripheral pattern and extend to the second horizontal line segment of another peripheral pattern. This microwave absorber facilitates bandwidth expansion and exhibits good broadband reflection suppression.

Description

Technical Field

[0001] This invention relates to a microwave absorber and its preparation method. Background Technology

[0002] Broadband microwave absorbers have important applications in electromagnetic compatibility, microwave absorption, and interference suppression in wireless systems. Engineering applications typically require microwave absorbers to be lightweight, adaptable, and capable of large-area fabrication, while maintaining stable absorption performance under different polarizations and incident angles. Grounded metamaterial / metasurface absorbers are easy to achieve in thinner designs and with adjustable impedance; however, while resistive metasurfaces can broaden the bandwidth to some extent through distributed losses, their broadband reflection suppression performance remains relatively low.

[0003] The information disclosed in the background section is only intended to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] This invention provides a microwave absorber and its preparation method. The microwave absorber is beneficial for bandwidth expansion and has a good broadband reflection suppression effect.

[0005] The present invention adopts the following technical solution: A microwave absorber includes multiple absorber units, each absorber unit comprising a dielectric layer and a patterned carbon-based conductive layer formed on the dielectric layer. The carbon-based conductive layer includes a central pattern and four peripheral patterns surrounding the central pattern. The central pattern includes a pair of parallel first vertical line segments and a first horizontal line segment connecting the middle portions of the first vertical line segments. Each of the first vertical line segments connects to two adjacent peripheral patterns. Each of the peripheral patterns includes a pair of parallel second vertical line segments and a second horizontal line segment connecting the middle portions of the second vertical line segments. The first vertical line segments connect to the second vertical line of one peripheral pattern and extend to the second horizontal line segment of the other peripheral pattern.

[0006] In some preferred embodiments, the gap formed between the first horizontal line segment and the two second vertical line segments of the outer pattern toward the side of the central pattern is filled by the end of the first vertical line segment.

[0007] In some preferred embodiments, there is a gap between the first transverse line segment and the outer pattern.

[0008] In some preferred embodiments, the central pattern is H-shaped as a whole, and the peripheral pattern is H-shaped as a whole.

[0009] In some preferred embodiments, the length of the first vertical line segment is greater than the length of the second vertical line segment, and the length of the first horizontal line segment is greater than the length of the second horizontal line segment.

[0010] In some more preferred embodiments, the widths of the two first vertical line segments are equal, and the widths of the two second vertical line segments of each of the outer patterns are equal; The width of the first horizontal line segment is equal to the width of the first vertical line segment, and the width of the second horizontal line segment is equal to the width of the second vertical line segment; The length of the second horizontal line segment is equal to the width of the first horizontal line segment; The ratio of the length of each outer pattern to the length of the center pattern is s, where 0.3 < s < 0.7; the length of the outer pattern is the sum of the length of the second horizontal line segment and half the width of each of the second vertical line segments, and the length of the center pattern is the sum of the length of the first horizontal line segment and half the width of each of the first vertical line segments. The length and width of the carbon-based conductive layer are equal; the carbon-based conductive layer is an axisymmetric shape. The outer pattern is spaced out.

[0011] In some preferred embodiments, the absorber unit includes a first dielectric layer, a first carbon-based conductive layer formed on the first dielectric layer, a second dielectric layer located on the first carbon-based conductive layer, and a second carbon-based conductive layer formed on the second dielectric layer. The first carbon-based conductive layer and the second carbon-based conductive layer are similar in shape, the area of ​​the first carbon-based conductive layer is larger than the area of ​​the second carbon-based conductive layer, and the first carbon-based conductive layer and the second carbon-based conductive layer are centered and aligned with each other.

[0012] In some preferred embodiments, the thickness of the first dielectric layer is greater than the thickness of the second dielectric layer; The sheet resistance of the first carbon-based conductive layer is less than the sheet resistance of the second carbon-based conductive layer; The first carbon-based conductive layer and / or the second carbon-based conductive layer are formed by printing carbon-based conductive adhesive. The first dielectric layer and / or the second dielectric layer include a silicone rubber foam layer, and the first carbon-based conductive layer and / or the second carbon-based conductive layer are printed on a polyimide film covering the surface of the silicone rubber foam layer. The first carbon-based conductive layer and the first dielectric layer have a gap at their edges, the second carbon-based conductive layer and the second dielectric layer have a gap at their edges, the length and / or width of the absorber unit is 10~500mm, the thickness of the first dielectric layer is 2~10mm, the thickness of the second dielectric layer is 1~8mm, the sheet resistance of the first carbon-based conductive layer is 10~100Ω / sq, and the sheet resistance of the second carbon-based conductive layer is 100~200Ω / sq.

[0013] The present invention also adopts the following technical solution: A method for preparing a microwave absorber, wherein the microwave absorber is as described above, the method comprising: A carbon-based conductive adhesive is applied to the surface of the dielectric layer and cured to form the carbon-based conductive layer.

[0014] In some preferred embodiments, the preparation method includes the following steps: A first dielectric layer having a surface coated with a first thin film is provided; A first carbon-based conductive layer is formed by screen printing on the first thin film; Provide a second dielectric layer with a second thin film coated on its surface; A second carbon-based conductive layer is formed by screen printing on the second thin film; The first dielectric layer and the second dielectric layer are aligned and stacked, with the second dielectric layer located above the first carbon-based conductive layer, to form the microwave absorber.

[0015] In some preferred embodiments, the preparation method further includes the following steps: The surface of the first dielectric layer without the second carbon-based conductive layer is attached to a metal plate to form a grounding structure.

[0016] The beneficial effects of this invention are as follows: The microwave absorber of this invention features a carbon-based conductive layer in each absorber unit comprising an H-shaped central pattern. Each of the four vertices of the central pattern is connected to an H-shaped peripheral pattern. This carbon-based conductive layer pattern facilitates bandwidth expansion, provides good width reflection suppression, and maintains acceptable stability even at oblique incidence angles. The parameters of the central and peripheral patterns can be set independently, simplifying design and debugging. The fabrication method of the microwave absorber of this invention involves forming a carbon-based conductive layer by patterned coating of a carbon-based conductive adhesive, which facilitates processing and assembly. Attached Figure Description

[0017] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is an exploded view of a microwave absorber unit according to an embodiment of the present invention.

[0019] Figure 2 This is a top view of a second dielectric layer and a second carbon-based conductive layer according to an embodiment of the present invention.

[0020] Figure 3 This is a top view of a first dielectric layer and a first carbon-based conductive layer according to an embodiment of the present invention.

[0021] Figure 4 This is a top view of a structure above a second dielectric layer according to an embodiment of the present invention.

[0022] Figure 5 This is a top view of a structure above a first dielectric layer according to an embodiment of the present invention.

[0023] Figure 6 This is a layout diagram of a microwave absorber according to an embodiment of the present invention.

[0024] Figure 7 Simulation and measured curves of the microwave absorber under normal incident TE polarization as an example.

[0025] Figure 8 Simulation and measured curves of the microwave absorber under normal incident TM polarization as an example.

[0026] Figure 9 Simulation and measured curves of TE / TM polarization of the microwave absorber under oblique incidence at 15°, 30°, and 45° for the example.

[0027] Figure label: 100. Absorber unit; 1. Second carbon-based conductive layer; 11. Central pattern; 111. First vertical line segment; 112. First horizontal line segment; 12. Outer pattern; 121. First vertical line segment; 122. First horizontal line segment; 2. Second dielectric layer; 21. Polyimide film; 3. First carbon-based conductive layer; 31. Central pattern; 311. First vertical line segment; 312. First horizontal line segment; 32. Outer pattern; 321. First vertical line segment; 322. First horizontal line segment; 33. Gap; 4. First dielectric layer; 41. Polyimide film. Detailed Implementation

[0028] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more readily understood by those skilled in the art. It should be noted that the description of these embodiments is for the purpose of aiding understanding the present invention, but does not constitute a limitation thereof.

[0029] The embodiment provides a microwave absorber, specifically a double-layer broadband microwave absorber based on a resistive metasurface structure, which can be fabricated on a high-temperature resistant flexible foam substrate through a printing process, taking into account broadband reflection suppression, manufacturing feasibility, and a certain degree of angular stability.

[0030] Reference Figures 1 to 6 As shown, the microwave absorber includes multiple absorber units 100. The multiple absorber units 100 are arranged in an array, with or without gaps between adjacent absorber units 100. In this embodiment, no gaps are configured between the absorber units 100. The multiple absorber units 100 are arranged in an n×m array, where n≥2, and / or m≥2. In a specific embodiment, both n and m are 20, that is, the microwave absorber includes a 20×20 array of absorber units 100, as shown. Figure 6 As shown.

[0031] The absorber unit 100 includes a dielectric layer and a patterned carbon-based conductive layer formed on the dielectric layer. The carbon-based conductive layer includes a central pattern and four peripheral patterns located around the central pattern. The central pattern is H-shaped in general, and the peripheral patterns are also H-shaped in general. One central pattern and four peripheral patterns are connected.

[0032] In this embodiment, the microwave absorber is a double-layer microwave absorber. For example... Figure 1 As shown, each absorber unit 100 includes a first dielectric layer 4, a first carbon-based conductive layer 3 formed on the first dielectric layer 4, a second dielectric layer 2 located on the first carbon-based conductive layer 3, and a second carbon-based conductive layer 1 formed on the second dielectric layer 2. (Combined) Figures 2 to 5 As shown, the first carbon-based conductive layer 3 and the second carbon-based conductive layer 1 are similar in shape. The area of ​​the first carbon-based conductive layer 3 is larger than the area of ​​the second carbon-based conductive layer 1. The first carbon-based conductive layer 3 and the second carbon-based conductive layer 1 are centered and aligned with each other.

[0033] The following is combined Figure 2 The pattern of the second carbon-based conductive layer 1 is described in detail.

[0034] The second carbon-based conductive layer 1 mainly consists of an H-shaped central pattern 11 and four H-shaped peripheral patterns 12. The size and area of ​​the peripheral patterns 12 are smaller than those of the central pattern 11. The length and width of the carbon-based conductive layer are equal, both being L1. The carbon-based conductive layer is an axisymmetric shape, in which the four peripheral patterns 12 are spaced apart from each other. The central pattern 11 includes a pair of parallel first vertical line segments 111 and a first horizontal line segment 112 connecting the middle of the first vertical line segments 111. Each first vertical line segment 111 connects between two adjacent peripheral patterns 12. Each peripheral pattern 12 includes a pair of parallel second vertical line segments 121 and a second horizontal line segment 122 connecting the middle of the second vertical line segments 121. The first vertical line segment 111 connects to the second vertical line of one of the peripheral patterns 12 and extends to the second horizontal line segment 122 of the other peripheral pattern 12.

[0035] In the second carbon-based conductive layer 1, the gap 33 formed between the first horizontal line segment 112 and the two second vertical line segments 121 of the outer pattern 12, facing the central pattern 11, is filled by the end of the first vertical line segment 111. That is, the end of the first vertical line segment 111 of the central pattern 11 and the two second vertical line segments 121 of the outer pattern 12 are connected and terminate at their second horizontal line segments 122. For ease of understanding, Figure 2 The boundary of the aforementioned gap is indicated by a dashed line, which is the boundary line between the central pattern 11 and the outer pattern 12; however, in the actual product, the central pattern 11 and the outer pattern 12 are formed as a single piece, and there is no boundary as indicated by the dashed line.

[0036] In the second carbon-based conductive layer 1, there is a gap between the first horizontal line segment 112 and the outer pattern 12, and the second horizontal line segment 122 and the four outer patterns 12 are not directly connected. The length of the first vertical line segment 111 is greater than the length of the second vertical line segment 121, and the length of the first horizontal line segment 112 is greater than the length of the second horizontal line segment 122. The widths of the two first vertical line segments 111 are equal, and the widths of the two second vertical line segments 121 of each outer pattern 12 are equal. The width of the first horizontal line segment 112 is equal to the width of the first vertical line segment 111, and the width of the second horizontal line segment 122 is equal to the width of the second vertical line segment 121. The length of the second horizontal line segment 122 is equal to the width of the first horizontal line segment 112. In this document, the term "line segment" refers to a strip-shaped pattern with a certain length and width, the term "width of line segment" refers to the dimension of the line segment perpendicular to its length direction, and the terms "horizontal" and "vertical" are two mutually perpendicular directions, for example, corresponding to respectively Figure 2 , 3 The left-right and up-down directions of the paper.

[0037] In the second carbon-based conductive layer 1, the ratio of the length s·L1 of each peripheral pattern 12 to the length L1 of the central pattern 11 is s, where 0.3 < s < 0.7. The length s·L1 of the peripheral pattern 12 is the sum of the length of the second horizontal line segment 122 and half the width of each second vertical line segment 121, and the length L1 of the central pattern 11 is the sum of the length of the first horizontal line segment 112 and half the width of each first vertical line segment 111. The widths of the first horizontal line segment 112, the second vertical line segment 121, and the first vertical line segment 121 are all equal, both being W1. Since the lengths of the first vertical line segment 111 and the first horizontal line segment 112 are equal, the length and width of the second carbon-based conductive layer 1 are also equal. The edges of the second carbon-based conductive layer 1 and the first dielectric layer 4 have gaps, i.e., the second carbon-based conductive layer 1 is offset from the edge of the first dielectric layer 4 by a certain distance.

[0038] The following is combined Figure 2 The pattern of the second carbon-based conductive layer 1 is described in detail. Compared with the second carbon-based conductive layer 1, the first carbon-based conductive layer 3 has a larger area, and the two have similar patterns. The first carbon-based conductive layer 3 is located directly above the second carbon-based conductive layer 1 and is centered.

[0039] In the first carbon-based conductive layer 3, the ratio of the length s·L2 of each peripheral pattern 32 to the length L2 of the central pattern 31 is s, where 0.3 < s < 0.7. The length s·L2 of the peripheral pattern 32 is the sum of the length of the second horizontal line segment 322 and half the width of each second vertical line segment 321. The length L2 of the central pattern 31 is the sum of the length of the first horizontal line segment 312 and half the width of each first vertical line segment 311. The widths of the first horizontal line segment 312, the second vertical line segment 321, and the first vertical line segment 321 are all equal, each being W2. Since the lengths of the first vertical line segment 311 and the first horizontal line segment 312 are equal, the length and width of the first carbon-based conductive layer 3 are also equal. The edges of the first carbon-based conductive layer 3 and the first dielectric layer 4 have gaps, i.e., the first carbon-based conductive layer 3 is offset from the edge of the first dielectric layer 4 by a certain distance. Wherein, L2 > L1, and W2 > W1.

[0040] The sheet resistance of the first carbon-based conductive layer 3 is less than that of the second carbon-based conductive layer 1. The sheet resistance of the first carbon-based conductive layer 3 is 10~100 Ω / sq, and the sheet resistance of the second carbon-based conductive layer 1 is 100~200 Ω / sq. The first carbon-based conductive layer 3 and / or the second carbon-based conductive layer 1 are formed by printing with carbon-based conductive adhesive.

[0041] The thickness t2 of the first dielectric layer 4 is greater than the thickness t1 of the second dielectric layer 2. High-temperature resistant silicone rubber foam is selected as the substrate for the first dielectric layer 4 and the second dielectric layer 2.

[0042] The first dielectric layer 4 includes a silicone rubber foam layer, and the first carbon-based conductive layer 3 is printed on a polyimide film 41 covering the surface of the silicone rubber foam layer, such as... Figure 5 As shown. The second dielectric layer 2 includes a silicone rubber foam layer, and the second carbon-based conductive layer 1 is printed on a polyimide thin film 21 covering the surface of the silicone rubber foam layer, as shown. Figure 4 As shown.

[0043] The length and / or width of the absorber unit 100 is 10~500mm, the thickness of the first dielectric layer 4 is 2~10mm, and the thickness of the second dielectric layer 2 is 1~8mm.

[0044] An embodiment provides a method for fabricating the above-described microwave absorber. The method for fabricating the microwave absorber includes the following steps: A first dielectric layer 4 with a first thin film coated on its surface is provided; A first carbon-based conductive layer 3 is formed by screen printing on the first thin film, such as... Figure 5 As shown; A second dielectric layer 2 with a second thin film coated on its surface is provided; A second carbon-based conductive layer 1 is formed by screen printing on the second thin film, such as... Figure 4 As shown; After aligning and stacking the first dielectric layer 4 and the second dielectric layer 2, with the second dielectric layer 2 positioned above the first carbon-based conductive layer 3, a microwave absorber is formed, such as... Figure 6 As shown.

[0045] The preparation method also includes the following steps: The surface of the first dielectric layer 4 without the second carbon-based conductive layer 1 is attached to a metal plate to form a grounding structure.

[0046] Specifically: High-temperature resistant silicone rubber foam is selected as the dielectric layer. Before printing, a polyimide (PI) film with a thickness of approximately 0.05 mm is coated on the foam surface to improve printability and dimensional stability. Carbon-based conductive paste is screen-printed into upper and lower layer resistance patterns (preferably with a mesh count greater than 200 mesh), and cured at room temperature for approximately 24 hours. After curing, the layers are assembled in the order of "upper printed part - first foam dielectric layer - lower printed part - second foam dielectric layer," and alignment marks are used to achieve interlayer alignment. During testing or use, the stack is attached to a metal plate to form a grounding structure. The upper and lower layers are printed using commercially available carbon-based conductive pastes with nominal sheet resistances of 166 Ω / sq and 52 Ω / sq, respectively. Sheet resistance can be measured at multiple locations using a four-probe method to confirm that the resistance uniformity of the printed layers meets the usage requirements.

[0047] Performance testing: The microwave absorber used for testing has a periodic structure in the x–y plane with a period of 16 mm; it includes 20×20 absorber units 100, and the overall size of the microwave absorber is 320 mm × 320 mm. From top to bottom, the microwave absorber comprises: a second carbon-based conductive layer 1, a second dielectric layer 2, a first carbon-based conductive layer 3, a first dielectric layer 4, and a metal backplate. The second dielectric layer 2 has a thickness of 2 mm (denoted as t1), and the first dielectric layer 4 has a thickness of 3 mm (denoted as t2). The sheet resistance of the second carbon-based conductive layer 1 is 166 Ω / sq, and the sheet resistance of the first carbon-based conductive layer 3 is 52 Ω / sq; in the patterns of the first carbon-based conductive layer 3 and the second carbon-based conductive layer 1, s is 0.5.

[0048] A free-space reflection testing system using a vector network analyzer and dual-horn antennas was employed, with a test frequency band of 2–18 GHz. During testing, the sample was placed on a metal plate, and the reflection coefficient S was measured under normal incidence (θ=0°) and oblique incidence (θ=15°, 30°, 45°) conditions. 11 The TE and TM polarization responses were obtained by rotating the antenna polarization direction, and then calibrated and normalized using a metal reference plate of the same size.

[0049] like Figure 7 and Figure 8 As shown, under normal incidence conditions, the polarizations of TE and TM both satisfy |S 11 The reflection suppression bandwidth of |<-10 dB is 6.85–18 GHz. For example... Figure 9 As shown, under oblique incidence conditions, according to |S 11 The -10 dB criterion is as follows: for TE polarization, the measured bandwidths are 5.88–18.00 GHz at 15°, 5.80–18.00 GHz at 30°, and 6.08–18.00 GHz at 45°; for TM polarization, the measured bandwidths are 5.04–18.00 GHz at 15°, 5.23–18.00 GHz at 30°, and 5.65–18.00 GHz at 45°.

[0050] The microwave absorber of this embodiment is lightweight, flexible, and suitable for large-area printing and surface mounting applications, while also offering broadband reflection suppression, manufacturing feasibility, and angular stability. The concentrically aligned and parameter-independent H-shaped fractal pattern of the upper and lower layers facilitates processing and assembly and promotes bandwidth expansion. The surface resistances of the upper and lower resistive patterns differ to achieve multimode dissipation and broadband impedance matching. The two carbon-based conductive layers are concentrically aligned, but their geometric parameters (L1, w1, L2, w2, s) can be set independently.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0052] As indicated in this specification and claims, the terms "comprising" and "including" only indicate the inclusion of expressly identified steps and elements, and these steps and elements do not constitute an exclusive list; the method or apparatus may also include other steps or elements. The term "and / or" as used herein includes any combination of one or more of the associated listed items.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0054] Any step in any method or process claim may be performed in any order, and is not limited to the order stated in the claims. The limitation of method + function or step + function is used only if all of the following conditions are met in a particular claim: a) it expressly states "method for..." or "step for..."; b) it expressly states the corresponding function. The structures, materials, or actions supporting the method + function are expressly described in the description herein. Therefore, the scope of the invention should be determined solely by the appended claims and their legal equivalents, and not by the description and examples given herein.

[0055] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are preferred embodiments. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and they should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made according to the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A microwave absorber, comprising a plurality of absorber units, characterized in that, The absorber unit includes a dielectric layer and a patterned carbon-based conductive layer formed on the dielectric layer. The carbon-based conductive layer includes a central pattern and four peripheral patterns surrounding the central pattern. The central pattern includes a pair of parallel first vertical line segments and a first horizontal line segment connecting the middle of the first vertical line segments. Each of the first vertical line segments connects to two adjacent peripheral patterns. Each of the peripheral patterns includes a pair of parallel second vertical line segments and a second horizontal line segment connecting the middle of the second vertical line segments. The first vertical line segments connect to the second vertical line of one of the peripheral patterns and extend to the second horizontal line segment of the other peripheral pattern.

2. The microwave absorber according to claim 1, characterized in that, The gap formed between the first horizontal line segment and the two second vertical line segments of the outer pattern, facing the center pattern, is filled by the end of the first vertical line segment.

3. The microwave absorber according to claim 1, characterized in that, There is a gap between the first horizontal line segment and the outer pattern.

4. The microwave absorber according to claim 1, characterized in that, The central pattern is H-shaped as a whole, and the outer pattern is H-shaped as a whole.

5. The microwave absorber according to claim 1, characterized in that, The length of the first vertical line segment is greater than the length of the second vertical line segment, and the length of the first horizontal line segment is greater than the length of the second horizontal line segment.

6. The microwave absorber according to claim 5, characterized in that, The widths of the two first vertical line segments are equal, and the widths of the two second vertical line segments of each of the outer patterns are equal; The width of the first horizontal line segment is equal to the width of the first vertical line segment, and the width of the second horizontal line segment is equal to the width of the second vertical line segment; The length of the second horizontal line segment is equal to the width of the first horizontal line segment; The ratio of the length of each outer pattern to the length of the center pattern is s, where 0.3 < s < 0.7; the length of the outer pattern is the sum of the length of the second horizontal line segment and half the width of each of the second vertical line segments, and the length of the center pattern is the sum of the length of the first horizontal line segment and half the width of each of the first vertical line segments. The length and width of the carbon-based conductive layer are equal; the carbon-based conductive layer is an axisymmetric shape. The outer pattern is spaced out.

7. The microwave absorber according to any one of claims 1 to 6, characterized in that, The absorber unit includes a first dielectric layer, a first carbon-based conductive layer formed on the first dielectric layer, a second dielectric layer located on the first carbon-based conductive layer, and a second carbon-based conductive layer formed on the second dielectric layer. The first carbon-based conductive layer and the second carbon-based conductive layer are similar in shape, the area of ​​the first carbon-based conductive layer is larger than the area of ​​the second carbon-based conductive layer, and the first carbon-based conductive layer and the second carbon-based conductive layer are centered and aligned with each other.

8. The microwave absorber according to claim 7, characterized in that, The thickness of the first dielectric layer is greater than the thickness of the second dielectric layer; The sheet resistance of the first carbon-based conductive layer is less than the sheet resistance of the second carbon-based conductive layer; The first carbon-based conductive layer and / or the second carbon-based conductive layer are formed by printing carbon-based conductive adhesive. The first dielectric layer and / or the second dielectric layer include a silicone rubber foam layer, and the first carbon-based conductive layer and / or the second carbon-based conductive layer are printed on a polyimide film covering the surface of the silicone rubber foam layer. The first carbon-based conductive layer and the first dielectric layer have a gap at their edges, the second carbon-based conductive layer and the second dielectric layer have a gap at their edges, the length and / or width of the absorber unit is 10~500mm, the thickness of the first dielectric layer is 2~10mm, the thickness of the second dielectric layer is 1~8mm, the sheet resistance of the first carbon-based conductive layer is 10~100Ω / sq, and the sheet resistance of the second carbon-based conductive layer is 100~200Ω / sq.

9. A method for preparing a microwave absorber, characterized in that, The microwave absorber is the microwave absorber as described in any one of claims 1 to 8, and the preparation method includes: A carbon-based conductive adhesive is applied to the surface of the dielectric layer and cured to form the carbon-based conductive layer.

10. The preparation method according to claim 9, characterized in that, The preparation method includes the following steps: A first dielectric layer having a surface coated with a first thin film is provided; A first carbon-based conductive layer is formed by screen printing on the first thin film; Provide a second dielectric layer with a second thin film coated on its surface; A second carbon-based conductive layer is formed by screen printing on the second thin film; The first dielectric layer and the second dielectric layer are aligned and stacked, with the second dielectric layer located on top of the first carbon-based conductive layer, to form the microwave absorber. The preparation method further includes the following steps: The surface of the first dielectric layer without the second carbon-based conductive layer is attached to a metal plate to form a grounding structure.

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