A broadband radar absorbing metamaterial and preparation method thereof

Abstract

The present invention discloses a method for preparing a broadband radar absorbing metamaterial, comprising: preparing a 3D printed material with electromagnetic absorbing function; testing the basic complex dielectric constant and complex magnetic permeability of the 3D printed material; designing absorbing layers with different sizes based on the basic complex dielectric constant and complex magnetic permeability based on a quarter-wavelength interference model to form a hollow unit structure; establishing a structural model of the radar absorbing metamaterial based on the hollow unit structure, and printing it using 3D printing technology to obtain a broadband radar absorbing metamaterial. The present invention uses a quarter-wavelength interference theoretical model, combined with the basic complex dielectric constant and complex magnetic permeability characteristics of the 3D printed material with absorbing function, to design a hollow unit structure with absorbing layers of different external sizes, effectively broadening the absorbing frequency band, providing a new idea for the design and preparation of broadband structural absorbing materials, and maximizing the application value of radar absorbing metamaterials.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic wave absorbing materials, and specifically relates to a broadband radar absorbing metamaterial and a preparation method thereof. Background Art

[0002] Stealth technology is an important means to improve the battlefield survival and penetration attack capabilities of weapons and equipment. The development of stealth technology is of great significance to enhancing the combat effectiveness of weapons. Absorbing materials are an important way to achieve radar stealth technology. In practical applications, they can be mainly divided into coated absorbing materials and structural absorbing materials. Coated absorbing materials are mostly composed of resin and dielectric or magnetic absorbers, which makes it difficult to effectively absorb electromagnetic waves in a wide frequency band. However, broadband structural radar absorbing materials based on metamaterial design concepts are receiving more and more attention.

[0003] With the development of 3D printing technology, it has been gradually applied to the preparation of absorbing metamaterials as a new type of material processing technology. For example, the Chinese invention patent with the authorization announcement number CN108640673B discloses a method for preparing absorbing gradient materials based on 3D printing technology. The material with a reduced electromagnetic parameter gradient is selected through the impedance matching principle. The prepared gradient absorbing material not only increases the proportion of electromagnetic waves incident on the material, but also enhances the material's absorption effect on electromagnetic waves. However, this method focuses on the regulation of impedance matching performance of multi-layer structures based on 3D printing technology, and lacks the optimization design of absorbing structures based on metamaterials.

[0004] For another example, the Chinese invention patent with application publication number CN113163697A discloses a method for preparing broadband electromagnetic wave absorbing metamaterials based on 3D printing, which reasonably matches the impedance of the wave-transmitting material and the electromagnetic functional material containing the wave-absorbing filler, combines the single layers with the ability to absorb electromagnetic waves of different frequency bands into a three-dimensional multilayer structure template, and forms it by 3D printing to form a metamaterial with broadband wave-absorbing characteristics. However, this method mainly realizes impedance gradient through different dielectric materials, and the 3D printing process is relatively complicated.

[0005] In summary, the existing broadband radar absorbing metamaterials based on 3D printing technology still have the problem of unclear theoretical guidance in design, and fail to combine well with the electromagnetic properties of the material itself, thus limiting the application of radar absorbing metamaterials; at the same time, the use of a variety of 3D printing materials also makes the printing process more complicated. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a broadband radar absorbing metamaterial and a preparation method thereof. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a broadband radar absorbing metamaterial, comprising:

[0008] Preparation of 3D printing materials with electromagnetic wave absorption function;

[0009] Testing the basic complex permittivity and complex magnetic permeability of the 3D printing material;

[0010] According to the basic complex dielectric constant and complex magnetic permeability, wave absorbing layers with different sizes are designed based on a quarter-wavelength interference model to form a hollow unit structure;

[0011] A structural model of the radar absorbing metamaterial is established according to the hollow unit structure, and 3D printing technology is used for printing to obtain a broadband radar absorbing metamaterial.

[0012] In one embodiment of the present invention, preparing a 3D printing material having an electromagnetic wave absorbing function includes:

[0013] Weigh a certain proportion of the absorber and the powder of the base material, remove the water, and then mix the two evenly to obtain the absorber raw material powder; wherein the filling amount of the absorber is 5% to 60%;

[0014] The electromagnetic absorbing raw material powder is added into a single screw extruder for wire drawing to obtain a 3D printing material with electromagnetic absorbing function.

[0015] In one embodiment of the present invention, testing the basic complex permittivity and complex magnetic permeability of the 3D printing material includes:

[0016] Set a wave absorbing frequency range, and select n frequency points within the range; wherein the n frequency points at least include the highest frequency and the lowest frequency within the wave absorbing frequency range;

[0017] The coaxial line method or waveguide method is used to test the complex dielectric constant and complex magnetic permeability corresponding to the selected frequency point.

[0018] In one embodiment of the present invention, the absorbing frequency range is 2-18 GHz, and the intervals between the plurality of frequency points are 0.1-2 GHz.

[0019] In one embodiment of the present invention, according to the basic complex permittivity and complex magnetic permeability, a hollow unit structure including multiple absorbing layers is designed based on a quarter-wavelength interference model, including:

[0020] According to the basic complex dielectric constant and complex permeability corresponding to each frequency point, based on the quarter-wavelength interference model, the quarter-wavelength interference thickness at different frequencies is calculated. The calculation formula is:

[0021]

[0022] Where c is the speed of light, f i represents the i-th frequency point, 1≤i≤n, and f1 to f n The frequency of Re decreases successively; i (μ r ε r ) represents the real part of the complex permittivity and complex permeability corresponding to the i-th frequency point;

[0023] Construct a solid geometric body as the bottom absorbing layer, whose thickness is a quarter wavelength interference thickness d1 corresponding to the maximum frequency f1;

[0024] A plurality of hollow geometric bodies of different sizes are sequentially constructed on the bottom absorbing layer as an upper absorbing layer to form a hollow unit structure together with the bottom absorbing layer; wherein the thickness of the plurality of hollow geometric bodies is d2-d1, d3-d2, ..., d n -d n-1 .

[0025] In one embodiment of the present invention, the projection of the bottom absorbing layer on the two-dimensional plane is a square; the projection of each of the hollow geometric bodies on the two-dimensional plane has the same outer contour, and the diameter of the circumscribed circle of the outer contour is the same as the side length of the square.

[0026] In one embodiment of the present invention, the outer contour and inner contour of each hollow geometric body projected on a two-dimensional plane are the same, and the shape is circular, hexagonal, or square, and the outer contour is concentric with the circumscribed circle of the inner contour.

[0027] In one embodiment of the present invention, the diameters of the circumscribed circle of the inner contour are as follows from bottom to top: Wherein, D represents the side length of the projection square of the bottom absorbing layer on the two-dimensional plane.

[0028] In a second aspect, the present invention also provides a broadband radar absorbing metamaterial, comprising a plurality of hollow unit structures, each of which comprises a plurality of absorbing layers of different sizes; wherein the size of the absorbing layer is designed and formed based on a quarter-wavelength interference model according to the basic complex dielectric constant and complex magnetic permeability of the 3D printing material.

[0029] In one embodiment of the present invention, the bottom absorbing layer of the hollow unit structure is a solid geometric body with a thickness of d1;

[0030] The upper absorbing layer of the hollow unit structure is a plurality of hollow geometric bodies of different sizes, and the thicknesses thereof are d2-d1, d3-d2, ..., d n -d n-1 ;

[0031] Among them, d1...d n They represent the quarter-wavelength interference thickness at different frequencies, and the calculation formula is:

[0032]

[0033] Where c is the speed of light, f i represents the i-th frequency point, 1≤i≤n, and f1 to f n The frequency of Re decreases successively; i (μ r ε r ) represents the real part of the complex permittivity and complex permeability corresponding to the i-th frequency point.

[0034] Beneficial effects of the present invention:

[0035] 1. The present invention uses a quarter-wavelength interference theoretical model, combined with the basic complex dielectric constant and complex magnetic permeability characteristics of the 3D printing material with absorbing function, to design a hollow unit structure with absorbing layers of different dimensions, effectively broadening the absorbing frequency band, providing a new idea for the design and preparation of broadband structural absorbing materials, and maximizing the application value of radar absorbing metamaterials;

[0036] 2. The preparation method provided by the present invention has strong designability and can use only one 3D printing material with wave-absorbing function to quickly complete processing and manufacturing using 3D printing technology, thereby reducing process complexity, shortening the processing cycle, and reducing processing costs;

[0037] 3. The broadband radar absorbing metamaterial provided by the present invention has the advantages of high absorption intensity, wide effective absorption bandwidth and light weight.

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic flow chart of a method for preparing a broadband radar absorbing metamaterial provided by an embodiment of the present invention;

[0040] Figure 2 are the complex dielectric constant and complex magnetic permeability of the 3D printing material provided by an embodiment of the present invention;

[0041] Figure 3 is a reflectivity curve of the 3D printing material provided by an embodiment of the present invention at different thicknesses;

[0042] Figure 4 is a quarter-wavelength interference thickness curve of a 3D printing material provided by an embodiment of the present invention;

[0043] Figure 5is a three-dimensional diagram of a circular hollow unit structure provided by an embodiment of the present invention;

[0044] Figure 6 yes Figure 5 sectional view of

[0045] Figure 7 is a reflectivity curve of a circular hollow unit structure with an outer diameter of 18 mm and 30 mm provided in an embodiment of the present invention;

[0046] Figure 8 is a three-dimensional diagram of a regular hexagonal hollow unit structure provided by an embodiment of the present invention;

[0047] Fig. 9 yes Figure 8 sectional view of

[0048] Fig.10 is a reflectivity curve of a regular hexagonal hollow unit structure with an outer diameter of 18 mm and 30 mm provided in an embodiment of the present invention;

[0049] Fig.11 is a model diagram of a broadband radar absorbing metamaterial provided by an embodiment of the present invention;

[0050] Fig.12 This is a 3D printed physical image of a circular unit structure with an outer diameter of 30 mm provided in an embodiment of the present invention;

[0051] Fig.13 This is a measured reflectivity curve of a circular unit structure with an outer diameter of 30 mm provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0053] Embodiment 1

[0054] In view of the problems existing in the prior art, this embodiment provides a broadband radar absorbing metamaterial based on a quarter-wavelength interference model and a design and preparation method thereof. First, a hollow unit structure with different dimensions is designed using the quarter-wavelength interference thickness of a 3D printed material at different frequencies. Then, a three-dimensional model is constructed based on the optimized hollow unit structure dimension parameters. Finally, a radar absorbing metamaterial structure sample is manufactured using 3D printing technology.

[0055] For details, see Figure 1 , Figure 1 1 is a flow chart of a method for preparing a broadband radar absorbing metamaterial provided by an embodiment of the present invention, which includes:

[0056] S1: Preparation of 3D printing materials with electromagnetic wave absorption function.

[0057] S11: Weigh a certain proportion of the microwave absorbing agent and the powder of the matrix material, remove moisture, and then mix the two uniformly to obtain microwave absorbing raw material powder; wherein the filling amount of the microwave absorbing agent is 5% to 60%;

[0058] In this embodiment, the material of the absorber may include but is not limited to Fe, Co, Ni, FeSi, FeCo, Fe3O4, Co3O4, Fe fiber, Ni fiber, Co fiber, alloy fiber, carbon black, carbon fiber, SiC, graphene, carbon nanotube, carbon microtube, carbon nanowire, carbon nanosheet, polyaniline, polythiophene or polypyrrole, and any combination thereof.

[0059] The matrix material may be polylactic acid (PLA), polyamide (PA), polyetheretherketone (PEEK), polycarbonate (PC), polyurethane (TPU), acrylonitrile-butadiene-styrene plastic (ABS), etc.

[0060] Furthermore, the absorbent and the powder of the matrix material may be dried in an oven to remove moisture. For example, the absorbent and the powder may be dried in an oven at 60° C. for 24 hours to remove moisture.

[0061] Furthermore, a high-speed mixer can be used to uniformly mix the two dried materials.

[0062] S12: Add the absorbing raw material powder into a single screw extruder for wire drawing to obtain a 3D printing material with electromagnetic absorbing function.

[0063] The following example uses carbon nanotubes and ABS powder as raw materials to illustrate the specific process of making 3D printing materials.

[0064] 8 g of carbon nanotubes and 92 g of ABS powder were weighed respectively, dried in an oven at 60°C for 24 h, and the powders were placed in a high-speed mixer and mixed for 5 min to obtain the original microwave-absorbing functional blended raw material, which was added to a single-screw extruder for wire drawing. The melting zone temperature was set to 220°C, the extrusion zone temperature was set to 190°C, and the mixture was cooled in the air. The pulling speed was adjusted to obtain a microwave-absorbing functional 3D printing material with a diameter of 1.75 mm.

[0065] S2: Test the basic complex permittivity and complex magnetic permeability of 3D printing materials.

[0066] First, a wave absorbing frequency range is set, and n frequency points are selected within the range; wherein the n frequency points at least include the highest frequency and the lowest frequency within the wave absorbing frequency range.

[0067] In this embodiment, f1, f2, ..., f n The selected frequency points are represented in order from high to low.

[0068] For example, the wave absorbing frequency range may be set to 2-18 GHz, and frequency points may be selected at intervals of 0.1 to 2 GHz.

[0069] Preferably, the frequency interval adopted in this embodiment is 2 GHz, and 9 frequency points can be obtained, namely f1 = 18 GHz, f2 = 16 GHz, ..., f9 = 2 GHz.

[0070] Then, the coaxial line method or waveguide method is used to test the complex dielectric constant and complex magnetic permeability corresponding to the selected frequency point.

[0071] For example, this embodiment uses the coaxial line method to test the complex dielectric constant and complex magnetic permeability of the 3D printing material with electromagnetic function prepared by using carbon nanotubes and ABS powder as raw materials in step S1 at 2 to 18 GHz. The test results are as follows: Figure 2 In addition, this embodiment also uses a transmission line model to calculate the reflectivity of the 3D printing material at different thicknesses within a frequency range of 2-18 GHz. The results are shown in Figure 3 shown.

[0072] S3: According to the basic complex permittivity and complex permeability, absorbing layers with different sizes are designed based on the quarter-wavelength interference model to form a hollow unit structure.

[0073] S31: According to the basic complex dielectric constant and complex magnetic permeability corresponding to each frequency point, based on the quarter-wavelength interference model, calculate the quarter-wavelength interference thickness at different frequencies.

[0074] Specifically, the quarter-wavelength interference model is:

[0075]

[0076] Where d is the quarter-wavelength interference thickness, c is the speed of light, f is the frequency, and Re(μ r ε r ) represents the real part of the complex permittivity and the complex permeability.

[0077] Substitute each frequency point in step S2 and its corresponding basic complex permittivity and complex permeability into the above equation to calculate the quarter-wavelength interference thickness at different frequencies, namely:

[0078]

[0079] Where c is the speed of light, f i represents the i-th frequency point, 1≤i≤n, and f1 to f n The frequency of Re decreases successively; i (μ r ε r) represents the real part of the complex permittivity and complex permeability corresponding to the i-th frequency point.

[0080] S32: construct a solid geometric body as a bottom absorbing layer, the thickness of which is a quarter wavelength interference thickness d1 corresponding to the maximum frequency f1.

[0081] S33: sequentially constructing a plurality of hollow geometric bodies of different sizes on the bottom absorbing layer as the upper absorbing layer to form a "bowl-shaped" hollow unit structure together with the bottom absorbing layer; wherein the thickness of the plurality of hollow geometric bodies is d2-d1, d3-d2, ..., d n -d n-1 .

[0082] Specifically, the projection of the bottom absorbing layer on the two-dimensional plane is a square; the projection of each hollow geometric body on the two-dimensional plane has the same outer contour, and the diameter of the circumscribed circle of the outer contour is the same as the side length of the square.

[0083] Furthermore, the outer contour and inner contour of the projection of each hollow geometric body on the two-dimensional plane are the same, and the shape is circular, hexagonal, or square, and the outer contour is concentric with the circumscribed circle of the inner contour.

[0084] In this embodiment, the size of the circumscribed circle of the inner contour can be adjusted as needed to ensure that it forms a hollow geometric body with the circumscribed circle.

[0085] Optionally, as an implementation method, the diameter of the circumscribed circle of the inner contour can be set to Wherein, D represents the side length of the projection square of the bottom absorbing layer on the two-dimensional plane.

[0086] The following takes 2 GHz as an interval and selects 9 frequency points in the absorbing frequency range of 2-18 GHz to design a hollow unit structure in which the inner and outer contours of the hollow geometric body projected on a two-dimensional plane are circular as an example, and the designed hollow unit structure is introduced in detail.

[0087] First, based on the basic complex dielectric constant and complex magnetic permeability, the quarter-wavelength interference thickness at 2 to 18 GHz is calculated based on the quarter-wavelength interference model. The results are as follows: Figure 4 shown.

[0088] Then, the hollow cell structure is designed based on this parameter.

[0089] Please see the joint Figure 5-6 , Figure 5 is a three-dimensional diagram of a circular hollow unit structure provided by an embodiment of the present invention, Figure 6 yes Figure 5The hollow unit structure has a bottom absorbing layer and 8 upper hollow structure absorbing layers, which are used to absorb electromagnetic waves of different frequencies and convert energy into heat. Among them, the bottom absorbing layer is projected on a two-dimensional plane as a square with a side length of D, which can be 10-50mm. The circumscribed circle of the projection of the 8 hollow geometric bodies on the two-dimensional plane is the circular outer contour of the eight hollow geometric bodies, and its diameter is also D, also known as the outer diameter D. The diameter of the circumscribed circle of the inner contour is set from bottom to top

[0090] Furthermore, the thickness d1 of the bottom absorbing layer is a quarter-wavelength interference thickness corresponding to the highest frequency of 18 GHz, and the distance between the lower surface of each upper absorbing layer and the lower surface of the bottom absorbing layer is a quarter-wavelength interference thickness corresponding to 16 GHz, 14 GHz, ..., 2 GHz, respectively. Therefore, the thickness of the multiple hollow geometric bodies is d2-d1, d3-d2, ..., d9-d8 from bottom to top.

[0091] In this embodiment, the electromagnetic simulation software CST Studio Suite is used to calculate the reflectivity of the circular hollow unit structure with D values ​​of 18 mm and 30 mm in the range of 2 to 40 GHz. The results are as follows: Figure 7 shown.

[0092] In another embodiment of the present invention, the inner and outer contours of the projection of the hollow geometric body on the two-dimensional plane may also be a regular hexagon, such as Figure 8-9 As shown, Figure 8 is a three-dimensional diagram of a regular hexagonal hollow unit structure provided by an embodiment of the present invention, Fig. 9 yes Figure 8 The profile size and thickness of the circular hollow unit structure can be referred to above, and will not be described in detail here.

[0093] Accordingly, the electromagnetic simulation software CST Studio Suite was used to calculate the reflectivity of the regular hexagonal hollow unit structure with D values ​​of 18 mm and 30 mm in the range of 2 to 40 GHz. The results are as follows: Fig.10 shown.

[0094] S4: A structural model of the radar absorbing metamaterial is established based on the hollow unit structure, and 3D printing technology is used to print it to obtain a broadband radar absorbing metamaterial.

[0095] Specifically, the hollow unit structure obtained in step S3 is three-dimensionally modeled to form a structural model of the radar absorbing metamaterial, such as Fig.11Then, the three-dimensional model is processed by the slicing software and copied to the 3D printer; the fused deposition 3D printer is used to introduce the 3D printing material into the nozzle to complete the production of the absorbing metamaterial structure sample, which is the broadband radar absorbing metamaterial, as shown in FIG. Fig.12 shown.

[0096] At this point, the preparation of broadband radar absorbing metamaterial is completed.

[0097] This embodiment uses a quarter-wavelength interference theoretical model, combined with the basic complex dielectric constant and complex magnetic permeability characteristics of the 3D printed material with absorbing function, to design a hollow unit structure with absorbing layers of different dimensions, effectively broadening the absorbing frequency band, providing a new idea for the design and preparation of broadband structural absorbing materials, and maximizing the application value of radar absorbing metamaterials.

[0098] In addition, the preparation method provided in this embodiment has strong designability and can quickly complete processing and manufacturing using 3D printing technology using only one type of 3D printing material with wave absorbing function, thereby reducing process complexity, shortening the processing cycle, and reducing processing costs.

[0099] Finally, the reflectivity of the broadband radar absorbing metamaterial was tested at 2 to 40 GHz using the bow method using a vector network analyzer. The results are as follows: Fig.13 The results show that the radar absorbing metamaterial with a circular unit structure manufactured by the method of the embodiment of the present application has a strong broadband absorbing performance, which verifies the accuracy of the simulation structure.

[0100] Embodiment 2

[0101] The present embodiment also provides a broadband radar absorbing metamaterial, which includes a plurality of hollow unit structures, each of which includes a plurality of absorbing layers of different sizes; wherein the size of the absorbing layer is designed and formed based on a quarter-wavelength interference model according to the basic complex dielectric constant and complex magnetic permeability of the 3D printing material.

[0102] In this embodiment, the bottom absorbing layer of the hollow unit structure is a solid geometric body with a thickness of d1;

[0103] The upper absorbing layer of the hollow unit structure is a plurality of hollow geometric bodies of different sizes, and the thicknesses thereof are d2-d1, d3-d2, ..., d n -d n-1 ;

[0104] Among them, d1...d n They represent the quarter-wavelength interference thickness at different frequencies, and the calculation formula is:

[0105]

[0106] Where c is the speed of light, f i represents the i-th frequency point, 1≤i≤n, and f1 to f n The frequency of Re decreases successively; i (μ r ε r ) represents the real part of the complex permittivity and complex permeability corresponding to the i-th frequency point.

[0107] The specific design process and structural dimensions of the broadband radar absorbing metamaterial structure provided in this embodiment refer to the above-mentioned embodiment 1, and will not be repeated in this embodiment.

[0108] The broadband radar absorbing metamaterial provided in this embodiment has the advantages of high absorption intensity, wide effective absorption frequency band, and light weight.

[0109] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0110] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A method for preparing a broadband radar absorbing metamaterial, characterized in that: include: Preparation of 3D printing materials with electromagnetic wave absorption function; Testing the basic complex permittivity and complex magnetic permeability of the 3D printing material; According to the basic complex dielectric constant and complex magnetic permeability, wave absorbing layers with different sizes are designed based on a quarter-wavelength interference model to form a hollow unit structure; A structural model of the radar absorbing metamaterial is established according to the hollow unit structure, and a 3D printing technology is used to print the structure to obtain a broadband radar absorbing metamaterial; Among them, testing the basic complex dielectric constant and complex magnetic permeability of the 3D printing material includes: Setting a wave absorbing frequency range, and selecting n frequency points within the range; wherein the n frequency points at least include the highest frequency and the lowest frequency within the wave absorbing frequency range; the wave absorbing frequency range is 2-18 GHz, and the intervals between the several frequency points are 0.1-2 GHz; Use the coaxial line method or waveguide method to test the complex dielectric constant and complex magnetic permeability corresponding to the selected frequency point; The method of designing a hollow unit structure including multiple absorbing layers based on a quarter-wavelength interference model according to the basic complex dielectric constant and complex magnetic permeability includes: According to the basic complex dielectric constant and complex permeability corresponding to each frequency point, based on the quarter-wavelength interference model, the quarter-wavelength interference thickness at different frequencies is calculated. The calculation formula is: Where c is the speed of light, f i represents the i-th frequency point, 1≤i≤n, and f1 to f n The frequency of Re decreases successively; i (μ r ε r ) represents the real part of the complex permittivity and complex permeability corresponding to the i-th frequency point; Construct a solid geometric body as the bottom absorbing layer, whose thickness is a quarter wavelength interference thickness d1 corresponding to the maximum frequency f1; A plurality of hollow geometric bodies of different sizes are sequentially constructed on the bottom absorbing layer as an upper absorbing layer to form a hollow unit structure together with the bottom absorbing layer; wherein the thickness of the plurality of hollow geometric bodies is d2-d1, d3-d2, ..., d n -d n-1 ; The projection of the bottom absorbing layer on the two-dimensional plane is a square; the projection of each of the hollow geometric bodies on the two-dimensional plane has the same outer contour, and the diameter of the circumscribed circle of the outer contour is the same as the side length of the square.

2. The method for preparing the broadband radar absorbing metamaterial according to claim 1, characterized in that: The 3D printing materials with electromagnetic wave absorption function include: Weigh a certain proportion of the absorber and the powder of the base material, remove the water, and then mix the two evenly to obtain the absorber raw material powder; wherein the filling amount of the absorber is 5% to 60%; The electromagnetic absorbing raw material powder is added into a single screw extruder for wire drawing to obtain a 3D printing material with electromagnetic absorbing function.

3. The method for preparing the broadband radar absorbing metamaterial according to claim 1, characterized in that: The outer contour and inner contour of each hollow geometric body projected on a two-dimensional plane are the same, and the shape is circular, hexagonal, or square, and the outer contour is concentric with the circumscribed circle of the inner contour.

4. The method for preparing the broadband radar absorbing metamaterial according to claim 3, characterized in that: The diameters of the circumscribed circle of the inner contour are as follows from bottom to top: Wherein, D represents the side length of the projection square of the bottom absorbing layer on the two-dimensional plane.

5. A broadband radar absorbing metamaterial, characterized in that: The broadband radar absorbing metamaterial is prepared by the method for preparing the broadband radar absorbing metamaterial according to any one of claims 1 to 4, and the broadband radar absorbing metamaterial includes a plurality of hollow unit structures, each of which includes a plurality of absorbing layers of different sizes; wherein the size of the absorbing layer is designed and formed based on a quarter-wavelength interference model according to the basic complex dielectric constant and complex magnetic permeability of the 3D printing material.

6. The broadband radar absorbing metamaterial according to claim 5, characterized in that: The bottom absorbing layer of the hollow unit structure is a solid geometric body with a thickness of d1; The upper absorbing layer of the hollow unit structure is a plurality of hollow geometric bodies of different sizes, and the thicknesses thereof are d2-d1, d3-d2, ..., d n -d n-1 ; Among them, d1...d n They represent the quarter-wavelength interference thickness at different frequencies, and the calculation formula is: Where c is the speed of light, f i represents the i-th frequency point, 1≤i≤n, and f1 to f n The frequency of Re decreases successively; i (μ r ε r ) represents the real part of the complex permittivity and complex permeability corresponding to the i-th frequency point.

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