Embedded low-frequency broadband metamaterial wave absorber with double magnetic dielectric layers and application of embedded low-frequency broadband metamaterial wave absorber

Abstract

The invention belongs to the technical field of metamaterials, and particularly relates to an embedded low-frequency broadband metamaterial wave absorber with double magnetic dielectric layers and application of the embedded low-frequency broadband metamaterial wave absorber. The embedded low-frequency broadband metamaterial wave absorber provided by the invention comprises a composite magnetic wave-absorbing coating and a sheet-shaped carbonyl iron magnetic wave-absorbing coating, wherein a square resistive film unit pattern layer is embedded in the sheet-shaped carbonyl iron magnetic wave-absorbing coating. The embedded low-frequency broadband metamaterial wave absorber can achieve low-frequency and broadband absorption performance under the condition of relatively low thickness, is simple in structure and easy to prepare, and has extremely high application value in practical application.

Description

Technical Field

[0001] The present invention belongs to the technical field of metamaterials, and in particular relates to an embedded low-frequency broadband metamaterial absorber with double magnetic dielectric layers and applications thereof. Background Art

[0002] Low-frequency absorbing materials (1-8 GHz) are key to achieving long-range stealth for weapons and equipment, protecting human health, and reducing electromagnetic interference in electronic communications equipment. Metamaterial absorbers, a novel periodic artificial structure based on artificial microstructure design, achieve efficient electromagnetic wave absorption through the periodic arrangement of subwavelength resonant units. The core principle is to achieve the synergistic effect of impedance matching and multiple loss mechanisms in a thin layer by manipulating the equivalent dielectric constant and magnetic permeability. Common metamaterial absorbers typically have a three-layer structure: from top to bottom, a patterned layer, a dielectric layer, and a metal reflective layer. By designing and periodically arranging the patterned unit layers of the metamaterial and leveraging the electromagnetic response of the unit structures, a series of unique electromagnetic properties not found in natural materials can be achieved, such as negative refraction, "perfect" imaging, and "invisibility cloaking."

[0003] However, the absorption bandwidth expansion of traditional low-frequency absorbing materials has reached its limit. Therefore, it is necessary to seek new technologies to improve the low-frequency and broadband absorption performance of low-frequency absorbing materials to meet the higher requirements of such materials in practical applications. Summary of the Invention

[0004] To address the above technical issues, the present invention provides an embedded low-frequency, broadband metamaterial absorber with dual magnetic dielectric layers and its applications. The embedded low-frequency, broadband metamaterial absorber provided by the present invention achieves both low-frequency and broadband absorption performance at a relatively low thickness, features a simple structure, is easy to manufacture, and possesses high practical value.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: In a first aspect, the present invention provides an embedded low-frequency, broadband metamaterial absorber having two magnetic dielectric layers, comprising a metal reflective layer, and a composite magnetic absorbing coating and a flaky carbonyl iron magnetic absorbing coating sequentially formed on the metal reflective layer. The composite magnetic absorbing coating has a resistive film unit pattern layer embedded therein. The composite magnetic absorbing coating is obtained by applying and drying a composite magnetic absorbing coating containing a flaky carbonyl iron / CoFe2O4 composite, wherein the composite magnetic absorbing coating has a mass percentage of not less than 65%. The flaky carbonyl iron magnetic absorbing coating is obtained by applying and drying a flaky carbonyl iron magnetic absorbing coating containing flaky carbonyl iron, wherein the mass percentage of the flaky carbonyl iron in the flaky carbonyl iron magnetic absorbing coating is not less than 65%. The total thickness of the composite magnetic absorbing coating and the flaky carbonyl iron magnetic absorbing coating is 2.3 to 2.5 mm. The resistive film unit pattern layer is composed of evenly distributed resistive film units.

[0006] This invention overcomes the low-frequency bottleneck of low-frequency absorbing materials by employing two layers of magnetic absorbing coatings made of different materials and inventively adopting an embedded structure (i.e., a resistive film unit pattern layer is embedded in the composite magnetic absorbing coating). This metamaterial absorber achieves broadband absorption performance with an absorption band below -8dB (2-8 GHz) and a bandwidth of up to 6 GHz at a thickness of 2.3-2.5mm, significantly improving the absorption bandwidth. Furthermore, the metamaterial absorber's relatively simple structure makes it easy to process and manufacture, effectively improving both low-frequency and broadband absorption performance.

[0007] Preferably, the mass percentage of the flaky carbonyl iron / CoFe2O4 complex in the composite magnetic absorbing coating is not less than 70%.

[0008] Preferably, the mass percentage of the flaky carbonyl iron in the flaky carbonyl iron magnetic microwave-absorbing coating is not less than 70%.

[0009] Preferably, the preparation method of the flaky carbonyl iron / CoFe2O4 complex is as follows: dispersing the flaky carbonyl iron into a PVP aqueous solution, ultrasonically treating it at 35~45°C for 2.5~3.5 hours, magnetically separating and drying to obtain flaky carbonyl iron treated with PVP surface; dissolving ferric chloride and cobalt chloride in distilled water that has been treated with oxygen removal, reacting at 28~32°C for 25~35 minutes, adding the flaky carbonyl iron treated with PVP surface, heating to 65~75°C, adjusting the pH to 9~11, stirring at 65~75°C until the solution changes color, stopping stirring, settling for 1~1.5 hours, washing the obtained precipitate and drying to obtain the flaky carbonyl iron / CoFe2O4 complex; wherein the molar ratio of ferric chloride to cobalt chloride is (3.5~4.5):2.5.

[0010] Further preferably, the preparation method of the flaky carbonyl iron / CoFe2O4 complex is as follows: dispersing the flaky carbonyl iron into a PVP aqueous solution, ultrasonically treating it at 40°C for 3 hours, magnetically separating and drying to obtain flaky carbonyl iron treated with PVP surface; dissolving ferric chloride and cobalt chloride in oxygen-removed distilled water, reacting at 30°C for 30 minutes, adding the flaky carbonyl iron treated with PVP surface, heating to 70°C, adjusting the pH to 9~11, stirring at 70°C until the solution changes color, stopping stirring, settling for 1 hour, washing the obtained precipitate and drying it to obtain the flaky carbonyl iron / CoFe2O4 complex; wherein the molar ratio of ferric chloride to cobalt chloride is 4:2.5.

[0011] Further preferably, the PVP mass percentage concentration of the PVP aqueous solution is 0.45% to 0.55%.

[0012] Further preferably, the raw materials of the composite magnetic absorbing coating further include modified epoxy resin, curing agent and diluent.

[0013] The mass ratio of the modified epoxy resin, curing agent, diluent and flaky carbonyl iron / CoFe2O4 composite can be conventionally adjusted according to the specific types and properties of the modified epoxy resin, curing agent and diluent, as long as a coating can be formed, and the present invention is not limited to this.

[0014] Preferably, the composite magnetic absorbing coating has a thickness of 1.3 to 1.5 mm, more preferably 1.5 mm.

[0015] Preferably, the preparation method of the flaky carbonyl iron is as follows: using a mixture of anhydrous ethanol, a titanate coupling agent and a silane coupling agent as a ball milling medium, and ball milling zirconium dioxide grinding balls and carbonyl iron powder to obtain the flaky carbonyl iron.

[0016] Further preferably, the mass ratio of the anhydrous ethanol, the titanate coupling agent and the silane coupling agent is 1:(0.4-0.6):(0.4-0.6).

[0017] More preferably, the diameter of the zirconium dioxide grinding balls is 7 to 9 mm, and more preferably 8 mm.

[0018] Further preferably, the mass ratio of the zirconium dioxide grinding balls to the carbonyl iron powder is (70-90):1, and further preferably is 80:1.

[0019] More preferably, the ratio of the sum of the mass of the zirconium dioxide grinding balls and the carbonyl iron powder to the volume of the mixed solution is (8-10):1, g:mL, and more preferably 9:1, g:mL.

[0020] Further preferably, the ball milling is carried out in a ball mill with a motor frequency of 15 Hz and a rotation speed of 450 rpm; and the ball milling time is 6 to 8 hours.

[0021] More preferably, the flaky carbonyl iron prepared by ball milling for 8 hours is used to prepare the flaky carbonyl iron / CoFe2O4 composite; and the flaky carbonyl iron prepared by ball milling for 6 hours is used to prepare the flaky carbonyl iron magnetic absorbing coating.

[0022] Further preferably, the raw materials of the flaky carbonyl iron magnetic radar absorbing coating further include modified epoxy resin, curing agent and diluent.

[0023] The mass ratio of the modified epoxy resin, curing agent, diluent and flaky carbonyl iron can be conventionally adjusted according to the specific types and properties of the modified epoxy resin, curing agent and diluent, as long as a coating can be formed, and the present invention is not limited to this.

[0024] The resistive film unit pattern in the resistive film unit pattern layer can be selected from a variety of shapes, such as a cross, square ring, square, or circular ring. For embedded metamaterials, a larger planar unit pattern, preferably a square, is more suitable. Therefore, the resistive film units in the resistive film unit pattern layer are preferably square resistive film units.

[0025] More preferably, the side length of the square resistive film unit is 3-3.8 mm. As the side length of the square pattern increases, the absorption peak gradually separates from a single absorption peak to a double absorption peak, and the distance between the two absorption peaks gradually increases. The frequency of the low-frequency absorption peak gradually decreases, and the absorption intensity gradually weakens, while the frequency of the high-frequency absorption peak remains constant and the absorption intensity gradually increases. Even more preferably, the side length is 3.8 mm. When L = 3.8 mm, a maximum absorption bandwidth of -10 dB is achieved.

[0026] Further preferably, the resistor film material of the square resistor film unit is conductive silver paste, and the sheet resistance is 0.008-0.015 Ω / m.

[0027] Preferably, the distance between the resistive film unit pattern layer and the metal reflective layer is 0.5-0.75 mm. This distance allows for a wide absorption bandwidth; distances that are too close or too far do not yield the desired bandwidth. Furthermore, a distance of 0.75 mm maximizes the bandwidth, reaching 6 GHz.

[0028] Preferably, the preparation method of the embedded low-frequency broadband metamaterial absorber is: applying the composite magnetic absorbing coating on the metal reflective layer, and when the thickness after curing reaches 0.5~0.75 mm, printing the resistive film unit pattern layer, and then applying the composite magnetic absorbing coating again on the resistive film unit pattern layer, and curing to obtain the composite magnetic absorbing coating; applying the flaky carbonyl iron magnetic absorbing coating on the composite magnetic absorbing coating, and curing to obtain the flaky carbonyl iron magnetic absorbing coating.

[0029] Further preferably, the composite magnetic absorbing paint is applied in small amounts and multiple times, and dried at 55-65° C. until solidified after each application.

[0030] Further preferably, before applying the composite magnetic absorbing coating to the metal reflective layer, the metal reflective layer is cleaned, degreased, and sanded. Optionally, the metal reflective layer is polished with sandpaper and then cleaned and dried with anhydrous ethanol to remove surface stains and increase surface roughness.

[0031] Preferably, the metal reflective layer is made of stainless steel or aluminum.

[0032] A second aspect of the present invention provides applications of the above-mentioned embedded low-frequency broadband metamaterial absorber in military stealth equipment and electromagnetic protection devices.

[0033] The beneficial effects of the present invention are: (1) The present invention combines a flaky carbonyl iron magnetic absorbing coating with a composite magnetic absorbing coating containing a flaky carbonyl iron / CoFe2O4 composite, and embeds a resistive film unit pattern layer in the composite magnetic absorbing coating to obtain a novel dual-magnetic dielectric layer embedded low-frequency broadband metamaterial absorber. This metamaterial absorber, with a thickness of 2.3 to 2.5 mm, can achieve a broadband absorption effect with an absorption frequency band of 2 to 8 GHz and a bandwidth of 6 GHz, below -8 dB. This breaks through the low-frequency bottleneck of low-frequency absorbing materials and can meet the higher requirements of such materials in practical applications.

[0034] (2) The embedded low-frequency broadband metamaterial absorber provided by the present invention has a simple structure, is easy to industrialize and manufacture, and has high market and large-scale application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the structure of the embedded low-frequency broadband metamaterial absorber in Example 1 of the present invention; Figure 2 SEM images of the carbonyl iron powder after ball milling for 6 h (a) and 8 h (b) in Example 1 of the present invention; Figure 3The embedded low-frequency broadband metamaterial absorber sample and the square resistor film unit pattern therein prepared in Example 1 of the present invention; Figure 4 Schematic diagram of the structure of the embedded low-frequency broadband metamaterial absorber in Example 2 of the present invention; Figure 5 is the reflectivity of the embedded low-frequency broadband metamaterial absorber prepared in Example 1 of the present invention; Figure 6 is the reflectivity of the embedded low-frequency broadband metamaterial absorber prepared in Examples 2 to 5 of the present invention; Figure 7 is the reflectivity of the embedded low-frequency broadband metamaterial absorber prepared in Examples 5 and 6 of the present invention and Comparative Examples 1 and 2; Figure 8 is the reflectivity of the embedded low-frequency broadband metamaterial absorber prepared in Examples 5, 7, and 8 of the present invention and Comparative Examples 3 and 4; Figure 9 Reflectivity of the embedded low-frequency broadband metamaterial absorber prepared in Example 1 of the present invention at different incident angles: (a) TE wave, (b) TM wave. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0037] The low-frequency absorbing materials in the existing technology have low absorption intensity and the absorption bandwidth expansion tends to be limited, which limits their application effects and application fields to a certain extent.

[0038] To address the above issues, an embodiment of the present invention provides an embedded low-frequency, broadband metamaterial absorber with dual magnetic dielectric layers, comprising a metal reflective layer, and a composite magnetic absorbing coating and a flaky carbonyl iron magnetic absorbing coating sequentially formed on the metal reflective layer, wherein the composite magnetic absorbing coating is embedded with a block resistor film unit pattern layer; the composite magnetic absorbing coating is obtained by applying and drying a composite magnetic absorbing coating containing a flaky carbonyl iron / CoFe2O4 composite, wherein the mass percentage of the flaky carbonyl iron / CoFe2O4 composite in the composite magnetic absorbing coating is not less than 70%; the flaky carbonyl iron magnetic absorbing coating is obtained by applying and drying a flaky carbonyl iron magnetic absorbing coating containing the flaky carbonyl iron, wherein the mass percentage of the flaky carbonyl iron in the flaky carbonyl iron magnetic absorbing coating is not less than 70%.

[0039] The solutions of the present invention are described below through specific embodiments.

[0040] The stirring ball mill used in the following examples is manufactured by Changsha Zhongjing Chemical Machinery Co., Ltd., model SJM-2; the titanate coupling agent is manufactured by Nanjing Pinning Coupling Agent Co., Ltd., model DN-101; the silane coupling agent is manufactured by Shanghai MacLean Biochemical Technology Co., Ltd., model KH-550; the modified epoxy resin is manufactured by Yaoshan Industrial (Shanghai) Co., Ltd., model NPEL-127; the curing agent is a modified epoxy resin curing agent manufactured by Yaoshan Industrial (Shanghai) Co., Ltd., model YS-5618; and the diluent is manufactured by Shanghai Resin Factory Co., Ltd., model 5748.

[0041] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0042] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0043] Example 1 This embodiment provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers, which consists of a three-layer structure (such as Figure 1 As shown in the figure, the layers from top to bottom are: the first layer is a sheet-like carbonyl iron magnetic absorbing coating, the second layer is a composite magnetic absorbing coating with an embedded square resistor film unit pattern layer, and the third layer (bottom layer) is a stainless steel metal reflective layer. The first layer has a thickness of h1 = 1 mm, and the second layer has a thickness of h2 = 1.5 mm. The square resistor film unit has a side length L = 3.8 mm, a period P (the linear distance between the squares) = 6 mm, and a height h = 0.75 mm from the bottom layer. The resistor film unit is made of conductive silver paste with a sheet resistance of 0.01 Ω / m.

[0044] The preparation method of the embedded low-frequency broadband metamaterial absorber is as follows: 1. Flake carbonyl iron magnetic absorbing coating A stirred ball mill was used with 8 mm diameter ZrO2 grinding balls. The ball-to-material ratio and liquid-to-material ratio were 80:1 and 9:1, respectively. A combined milling medium consisting of a mixture of anhydrous ethanol, an auxiliary agent (titanate coupling agent), and a silane coupling agent in a mass ratio of 1:0.5:0.5 was added to the mill. 1600 g of grinding balls and 20 g of carbonyl iron powder were added. The mill motor was set to 15 Hz and 450 rpm. The materials were ball-milled for 6 and 8 hours. The carbonyl iron powder was then collected by magnetic separation after each milling time and dried in a drying oven at 60°C for 1 hour. Figure 2These are SEM images of carbonyl iron powder after ball milling for 6 h and 8 h. It can be seen from the figure that carbonyl iron is in flaky or granular form. As the ball milling time increases, the diameter of the flaky particles increases and the flake thickness decreases.

[0045] Weigh the modified epoxy resin, curing agent, diluent, and flaky carbonyl iron ball-milled for 6 hours in a mass ratio of 5:1:2:20. First, mix the modified epoxy resin, diluent, and flaky carbonyl iron ball-milled for 6 hours and quickly stir until evenly combined. Add the curing agent and stir until evenly combined before painting.

[0046] 2. Composite magnetic absorbing coating 1 g of PVP was added to 200 mL of distilled water and mechanically stirred until completely dissolved to obtain a PVP aqueous solution. 2 g of flaky carbonyl iron powder, ball-milled for 8 h, was added to the PVP aqueous solution and ultrasonically dispersed in a 40°C waterbath for 3 h. The solution was then magnetically separated and dried to obtain PVP-surface-treated flaky carbonyl iron. 200 mL of distilled water was stirred under nitrogen to remove oxygen. 0.67 g of ferric chloride and 0.30 g of cobalt chloride were weighed in a stoichiometric ratio and dissolved in the distilled water. The solution was stirred in a 30°C waterbath for 30 min. The ultrasonically dispersed PVP-surface-treated flaky carbonyl iron was added to the solution. The solution was heated to 70°C in a waterbath. Ammonia was added dropwise to a pH between 9 and 11. The solution was mechanically stirred in a 70°C waterbath until it changed color. Stirring was stopped and the solution was allowed to settle for 1 h. The solution was then rinsed three times with anhydrous ethanol and magnetically separated and dried to obtain a flaky carbonyl iron / CoFe2O4 complex.

[0047] Weigh the modified epoxy resin, curing agent, diluent, and flaky carbonyl iron / CoFe2O4 composite material in a mass ratio of 5:1:2:20. First, mix the modified epoxy resin, diluent, and flaky carbonyl iron / CoFe2O4 composite and stir quickly until evenly combined. Add the curing agent and stir until evenly combined before painting.

[0048] 3. Embedded absorber coating process Step 1: Pretreatment of the metal reflective layer. Use sandpaper to polish the steel plate and then clean and dry it with anhydrous ethanol to remove surface stains and increase surface roughness.

[0049] The second step is to apply a flaky carbonyl iron / CoFe2O4 composite magnetic absorbing coating to the treated steel plate using multiple, small-scale coatings. The coating thickness is carefully controlled to minimize sedimentation of the absorber. After each application, the coating is placed in a 60°C drying oven for 2 hours to cure. The coating thickness is then measured. When the thickness reaches 0.75 mm, the surface is polished to a smooth, even finish. The coating is then placed on a work surface and a screen printer is used to print a block resistor film pattern on the coating, forming a block resistor film pattern layer. The flaky carbonyl iron / CoFe2O4 composite magnetic absorbing coating is then applied again over the block resistor film pattern layer using multiple, small-scale coatings. Drying and curing are performed after each application until a thickness of 1.5 mm is achieved, resulting in the composite magnetic absorbing coating. The method for printing the block resistor film unit pattern on the coating involves customizing a polyurethane screen according to the size and shape of the block resistor film unit (L = 3.8 mm). The screen is secured to a screen clamp, and the relative position of the screen and coating is adjusted to ensure a close fit. Conductive silver paste is poured onto the screen, and the screen printer is turned on. A scraper is used to repeatedly apply the paste from right to left onto the coating surface. The number of application cycles is adjusted based on the desired pattern to ensure a clear and complete pattern. After screen printing, the sample is placed in a drying oven and cured at 80°C for 15 minutes to obtain the block resistor film unit pattern layer.

[0050] Step 3: Polish the surface of the composite magnetic absorbing coating to make it smooth and flat. Then, apply a flaky carbonyl ferromagnetic absorbing coating to the composite magnetic absorbing coating using a small, repeated application process. After each application, place the coating in a 60°C drying oven for 2 hours to cure. The coating thickness is then measured until it reaches 1.0 mm, resulting in a flaky carbonyl ferromagnetic absorbing coating. This results in an embedded low-frequency, broadband metamaterial absorber with dual magnetic dielectric layers.

[0051] The embedded low-frequency broadband metamaterial absorber sample and the square resistor film unit pattern layer are as follows Figure 3 shown.

[0052] Example 2 This embodiment provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers, which consists of a three-layer structure (such as Figure 4(As shown in the figure), the layers from top to bottom are: the first layer is a sheet-like carbonyl iron magnetic absorbing coating, the second layer is a composite magnetic absorbing coating with an embedded cross-shaped resistive film unit pattern layer, and the third layer (bottom layer) is a stainless steel metal reflective layer. The first layer has a thickness of h1 = 1 mm, and the second layer has a thickness of h2 = 1.5 mm. The cross-shaped resistive film unit has a side length of L = 3.8 mm, L1 = 1.4 mm, a period of P = 6 mm, and a height of h = 0.75 mm from the bottom layer. The resistive film unit is made of conductive silver paste with a sheet resistance of 0.01 Ω / m.

[0053] The preparation method of the embedded low-frequency broadband metamaterial absorber is as follows: 1. Flaky carbonyl iron magnetic microwave-absorbing coating: basically the same as Example 1, except that the ball milling time is only 6 h.

[0054] 2. Composite magnetic absorbing coating: basically the same as Example 1, except that the flaky carbonyl iron powder is ball-milled for 6 hours.

[0055] 3. Embedded absorber coating process: basically the same as Example 1, except that a cross-shaped resistive film unit pattern layer is printed on the coating layer. The resistive film unit pattern is cross-shaped with a side length of L=3.8 mm and L1=1.4 mm.

[0056] Example 3 This embodiment provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers. The structure and preparation method thereof are basically the same as those of Embodiment 2, with the only difference being that L1 = 2.2 mm.

[0057] Example 4 This embodiment provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers. The structure and preparation method thereof are basically the same as those of Embodiment 2, with the only difference being that L1 = 3 mm.

[0058] Example 5 This embodiment provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers, which consists of a three-layer structure, the structure of which is the same as that of embodiment 1.

[0059] The preparation method of the embedded low-frequency broadband metamaterial absorber is as follows: 1. Flaky carbonyl iron magnetic microwave-absorbing coating: basically the same as Example 1, except that the ball milling time is only 6 h.

[0060] 2. Composite magnetic absorbing coating: basically the same as Example 1, except that the flaky carbonyl iron powder is ball-milled for 6 hours.

[0061] 3. Embedded absorber coating process: same as in Example 1.

[0062] Example 6 This embodiment provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers, which consists of a three-layer structure. The structure is basically the same as that of Example 1, except that the height h of the block resistor film unit from the bottom layer is 0.5 mm.

[0063] The preparation method of the embedded low-frequency broadband metamaterial absorber is as follows: 1. Flake carbonyl ferromagnetic microwave-absorbing coating: same as Example 5.

[0064] 2. Composite magnetic wave-absorbing coating: same as in Example 5.

[0065] 3. Embedded absorber coating process: basically the same as Example 5, except that in the second step, when the thickness is 0.5 mm, the coating surface is polished to make the coating surface smooth and flat, and then placed on a work surface, and a square resistor film unit pattern is printed on the coating using a screen printer.

[0066] Example 7 This embodiment provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers. The structure and preparation method thereof are basically the same as those of Embodiment 5, with the only difference being that L=3 mm.

[0067] Example 8 This embodiment provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers. The structure and preparation method thereof are basically the same as those of Example 5, with the only difference being that L=3.4 mm.

[0068] Example 9 This embodiment provides an embedded low-frequency, broadband metamaterial absorber with two magnetic dielectric layers, having the same structure as in Example 1. The first layer has a thickness of h1 = 0.9 mm, the second layer has a thickness of h2 = 1.4 mm, the square resistor film unit has a side length L = 3.8 mm, a period P (the linear distance between the squares) = 6 mm, and a height h = 0.75 mm from the bottom layer. The resistor film unit is made of conductive silver paste, with a sheet resistance of 0.008 Ω / m.

[0069] The preparation method of the embedded low-frequency broadband metamaterial absorber is as follows: 1. Flake carbonyl iron magnetic absorbing coating A stirred ball mill was used with 7 mm diameter ZrO2 grinding balls. 142 ml of a combined ball milling medium consisting of a mixture of anhydrous ethanol, an auxiliary agent (titanate coupling agent), and a silane coupling agent in a mass ratio of 1:0.4:0.6 was added to the ball mill. 1400 g of grinding balls and 20 g of carbonyl iron powder were added. The ball mill motor frequency was set to 15 Hz and the speed was 450 r / min. The above materials were ball milled for 6 h and 8 h, and then the carbonyl iron powder after ball milling at different times was collected by magnetic separation and dried in a drying oven at 60°C for 1 h.

[0070] Weigh the modified epoxy resin, curing agent, diluent, and flaky carbonyl iron ball-milled for 6 hours in a mass ratio of 6:1.5:2.5:19. First, mix the modified epoxy resin, diluent, and flaky carbonyl iron ball-milled for 6 hours and quickly stir until evenly combined. Add the curing agent and stir until evenly combined before painting.

[0071] 2. Composite magnetic absorbing coating 0.9 g of PVP was added to 200 mL of distilled water and mechanically stirred until completely dissolved to obtain a PVP aqueous solution. 2 g of flaky carbonyl iron powder, ball-milled for 8 h, was added to the PVP aqueous solution and ultrasonically dispersed in a 45°C waterbath for 2.5 h. The solution was then magnetically separated and dried to obtain PVP-surface-treated flaky carbonyl iron. 0.68 g of ferric chloride and 0.30 g of cobalt chloride were weighed and dissolved in 200 mL of distilled water under nitrogen and stirred to remove oxygen. The solution was stirred in a 32°C waterbath for 25 min. The ultrasonically dispersed PVP-surface-treated flaky carbonyl iron was added to the solution. The solution was heated to 65°C in a waterbath and ammonia was added dropwise to a pH between 9 and 11. The solution was mechanically stirred in a 65°C waterbath until it changed color. Stirring was stopped and the solution was allowed to settle for 1 h. The solution was then rinsed three times with anhydrous ethanol and magnetically separated and dried to obtain a flaky carbonyl iron / CoFe2O4 complex.

[0072] Weigh the modified epoxy resin, curing agent, diluent, and flaky carbonyl iron / CoFe2O4 composite material in a mass ratio of 6:1.5:2.5:19. First, mix the modified epoxy resin, diluent, and flaky carbonyl iron / CoFe2O4 composite and quickly stir until evenly combined. Add the curing agent and stir until evenly combined before painting.

[0073] 3. Embedded absorber coating process Step 1: Pretreatment of the metal reflective layer. Use sandpaper to polish the steel plate and then clean and dry it with anhydrous ethanol to remove surface stains and increase surface roughness.

[0074] The second step is to apply a flaky carbonyl iron / CoFe2O4 composite magnetic absorbing coating to the treated steel plate using multiple, small-scale coatings. The coating thickness is carefully controlled to minimize sedimentation of the absorber. After each application, the coating is placed in a 55°C drying oven for 2.5 hours to cure. The coating thickness is then measured. When the thickness reaches 0.7 mm, the surface is polished to a smooth, even surface. The coating is then placed on a work surface and a screen printer is used to print a block resistor film pattern on the coating, forming a block resistor film pattern layer. The flaky carbonyl iron / CoFe2O4 composite magnetic absorbing coating is then applied again over the block resistor film pattern layer using multiple, small-scale coatings. Drying and curing are performed after each application until the coating reaches a thickness of 1.4 mm. This results in a composite magnetic absorbing coating. The method for printing the block resistor film unit pattern on the coating involves customizing a polyurethane screen according to the size and shape of the block resistor film unit (L = 3.8 mm). The screen is secured to a screen clamp, and the relative position of the screen and coating is adjusted to ensure a close fit. Conductive silver paste is poured onto the screen, and the screen printer is turned on. A scraper is used to repeatedly apply the paste from right to left onto the coating surface. The number of application cycles is adjusted based on the desired pattern to ensure a clear and complete pattern. After screen printing, the sample is placed in a drying oven and cured at 80°C for 15 minutes to obtain the block resistor film unit pattern layer.

[0075] Step 3: Polish the surface of the composite magnetic absorbing coating to make it smooth and flat. Then, apply a flaky carbonyl ferromagnetic absorbing coating to the composite magnetic absorbing coating using a small, repeated application process. After each application, place the coating in a 55°C drying oven for 2.5 hours to cure. The coating thickness is then measured until it reaches 0.9 mm, resulting in a flaky carbonyl ferromagnetic absorbing coating. This results in an embedded low-frequency, broadband metamaterial absorber with dual magnetic dielectric layers.

[0076] Example 10 This embodiment provides an embedded low-frequency, broadband metamaterial absorber with dual magnetic dielectric layers. Its structure is the same as in Example 1, with the metal reflective layer made of aluminum. The first layer has a thickness of h1 = 1.1 mm, and the second layer has a thickness of h2 = 1.3 mm. The square resistor film unit has a side length of L = 3.8 mm, a period P (the linear distance between the squares) of 6 mm, and a height of h = 0.75 mm from the bottom layer. The resistor film unit is made of conductive silver paste, with a sheet resistance of 0.015 Ω / m.

[0077] The preparation method of the embedded low-frequency broadband metamaterial absorber is as follows: 1. Flake carbonyl iron magnetic absorbing coating A stirred ball mill was used with 9 mm diameter ZrO2 grinding balls. 227.5 ml of a combined milling medium consisting of a mixture of anhydrous ethanol, an auxiliary agent (titanate coupling agent), and a silane coupling agent in a mass ratio of 1:0.6:0.4 was added to the ball mill. 1800 g of grinding balls and 20 g of carbonyl iron powder were added. The ball mill motor frequency was set to 15 Hz and the speed was 450 r / min. The above materials were ball-milled for 6 h and 8 h, and then the carbonyl iron powder after ball-milling at different times was collected by magnetic separation and dried in a drying oven at 60°C for 1 h.

[0078] Weigh the modified epoxy resin, curing agent, diluent, and flaky carbonyl iron ball-milled for 6 hours in a mass ratio of 5.5:1.5:1.5:19. First, mix the modified epoxy resin, diluent, and flaky carbonyl iron ball-milled for 6 hours and quickly stir until evenly combined. Add the curing agent and stir until evenly combined before painting.

[0079] 2. Composite magnetic absorbing coating 1.1 g of PVP was added to 200 mL of distilled water and mechanically stirred until completely dissolved to obtain a PVP aqueous solution. 2 g of flaky carbonyl iron powder, ball-milled for 8 h, was added to the PVP aqueous solution and ultrasonically dispersed in a 35°C waterbath for 3.5 h. The solution was then magnetically separated and dried to obtain PVP-surface-treated flaky carbonyl iron. 0.53 g of ferric chloride and 0.30 g of cobalt chloride were weighed and dissolved in 200 mL of distilled water under nitrogen and stirred to remove oxygen. The solution was stirred in a 28°C waterbath for 35 min. The ultrasonically dispersed PVP-surface-treated flaky carbonyl iron was added to the solution. The solution was heated to 75°C in a waterbath and ammonia was added dropwise to a pH between 9 and 11. The solution was mechanically stirred in a 75°C waterbath until it changed color. Stirring was stopped and the solution was allowed to settle for 1.5 h. The solution was then rinsed three times with anhydrous ethanol and magnetically separated and dried to obtain a flaky carbonyl iron / CoFe2O4 complex.

[0080] Weigh the modified epoxy resin, curing agent, diluent, and flaky carbonyl iron / CoFe2O4 composite material in a mass ratio of 5.5:1.5:1.5:19. First, mix the modified epoxy resin, diluent, and flaky carbonyl iron / CoFe2O4 composite and quickly stir until evenly combined. Add the curing agent and stir until evenly combined before painting.

[0081] 3. Embedded absorber coating process Step 1: Pretreatment of the metal reflective layer. Use sandpaper to polish the steel plate and then clean and dry it with anhydrous ethanol to remove surface stains and increase surface roughness.

[0082] The second step is to apply a flaky carbonyl iron / CoFe2O4 composite magnetic absorbing coating to the treated steel plate using multiple, small-scale coatings. The coating thickness is carefully controlled to minimize sedimentation of the absorber. After each application, the coating is placed in a 65°C drying oven for 2 hours to cure. The coating thickness is then measured. When the thickness reaches 0.65 mm, the surface is polished to a smooth, even finish. The coating is then placed on a work surface and a screen printer is used to print a block resistor film pattern on the coating, forming a block resistor film pattern layer. The flaky carbonyl iron / CoFe2O4 composite magnetic absorbing coating is then applied again over the block resistor film pattern layer using multiple, small-scale coatings. Drying and curing are performed after each application until a thickness of 1.3 mm is achieved, resulting in the composite magnetic absorbing coating. The method for printing the block resistor film unit pattern on the coating involves customizing a polyurethane screen according to the size and shape of the block resistor film unit (L = 3.8 mm). The screen is secured to a screen clamp, and the relative position of the screen and coating is adjusted to ensure a close fit. Conductive silver paste is poured onto the screen, and the screen printer is turned on. A scraper is used to repeatedly apply the paste from right to left onto the coating surface. The number of application cycles is adjusted based on the desired pattern to ensure a clear and complete pattern. After screen printing, the sample is placed in a drying oven and cured at 80°C for 15 minutes to obtain the block resistor film unit pattern layer.

[0083] Step 3: Polish the surface of the composite magnetic absorbing coating to make it smooth and flat. Then, apply a flaky carbonyl ferromagnetic absorbing coating to the composite magnetic absorbing coating using a small, repeated application process. After each application, place the coating in a 65°C drying oven for 2 hours to cure. The coating thickness is then measured until it reaches 1.1 mm, resulting in a flaky carbonyl ferromagnetic absorbing coating. This results in a dual-magnetic dielectric layer embedded low-frequency, broadband metamaterial absorber.

[0084] Comparative Example 1 This comparative example provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers, which consists of a three-layer structure. The structure is basically the same as that of Example 1, except that the height h of the block resistor film unit from the bottom layer is 1.25 mm.

[0085] The preparation method of the embedded low-frequency broadband metamaterial absorber is as follows: 1. Flake carbonyl ferromagnetic microwave-absorbing coating: same as Example 5.

[0086] 2. Composite magnetic wave-absorbing coating: same as in Example 5.

[0087] 3. Embedded absorber coating process: basically the same as Example 5, except that in the second step, when the thickness is 1.25 mm, the coating surface is polished to make the coating surface smooth and flat, and then placed on a work surface, and a square resistor film unit pattern is printed on the coating using a screen printer.

[0088] Comparative Example 2 This comparative example provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers, which consists of a three-layer structure. The structure is basically the same as that of Example 1, except that the height h of the block resistor film unit from the bottom layer is 1.5 mm.

[0089] The preparation method of the embedded low-frequency broadband metamaterial absorber is as follows: 1. Flake carbonyl ferromagnetic microwave-absorbing coating: same as Example 5.

[0090] 2. Composite magnetic wave-absorbing coating: same as in Example 5.

[0091] 3. Embedded absorber coating process: basically the same as Example 5, except that in the second step, when the thickness is 1.5 mm, the coating surface is polished to make the coating surface smooth and flat, and then placed on a work surface, and a square resistor film unit pattern is printed on the coating using a screen printer.

[0092] Comparative Example 3 This embodiment provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers. The structure and preparation method thereof are basically the same as those of Example 5, with the only difference being that L=4.2 mm.

[0093] Comparative Example 4 This embodiment provides an embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers. The structure and preparation method thereof are basically the same as those of Example 5, with the only difference being that L=4.6 mm.

[0094] Test Example 1 The reflectivity was tested using a dual-antenna bow reflection method: 0.5-18 GHz transmitting and receiving antennas were placed side by side and connected to a vector network analyzer, and the reflectivity of the embedded low-frequency broadband metamaterial absorber samples prepared in Examples 1-8 and Comparative Examples 1-4 was tested.

[0095] The test results of Example 1 are as follows Figure 5 As shown in the figure, the embedded low-frequency broadband metamaterial absorber sample has a broadband absorption in the absorbing frequency band below -8dB of 2-8 GHz and a bandwidth of 6 GHz.

[0096] The test results of Examples 2 to 5 are as follows: Figure 6As shown in the figure, the cross width significantly affects the reflectivity of the metamaterial absorber. As the width increases, the high-frequency absorption peak gradually strengthens, the low-frequency absorption peak gradually weakens, the distance between the two absorption peaks increases, and the corresponding bandwidth gradually increases. When the cross width is equal to the length, the maximum absorption bandwidth is -10 dB, and at this point, the resistive film pattern also changes from a centrally connected cross to a square.

[0097] The test results of Examples 5, 6 and Comparative Examples 1 and 2 are as follows: Figure 7 As shown in the figure, the position of the block resistor film directly affects the absorption properties of the embedded metamaterial. As h increases, the two absorption peaks gradually separate, the absorption bandwidth increases, the low-frequency absorption peak intensity remains essentially unchanged, and the high-frequency absorption peak intensity gradually weakens. The maximum absorption bandwidth is achieved when the resistor film is located at a distance of h = 0.75 mm from the metal backplane. The higher the position of the resistor film within the dielectric layer, the greater the thickness of the carbonyl iron@CoFe2O4 flaky dielectric layer affected by electromagnetic resonance, promoting enhanced low-frequency absorption. Simultaneously, the electromagnetic field modulation effect of the resistor film on the carbonyl iron flaky dielectric layer is enhanced, thereby improving high-frequency absorption performance.

[0098] The test results of Examples 5, 7, 8 and Comparative Examples 3 and 4 are as follows: Figure 8 As shown in the figure, as the side length of the square pattern increases, the single absorption peak gradually separates into a double absorption peak, and the distance between the two absorption peaks gradually increases. The frequency of the low-frequency absorption peak gradually decreases, and the absorption intensity gradually weakens, while the frequency of the high-frequency absorption peak remains constant and the absorption intensity gradually increases. When L = 3.8 mm, the maximum absorption bandwidth is -10dB.

[0099] Figure 9 The following are reflectivity curves of the embedded low-frequency, broadband metamaterial absorber produced in Example 1 at different incident angles. In the TE polarization mode, overall absorption performance decreases with increasing incident angle. At angles of incidence no greater than 30°, the reflectivity reaches -8 dB in the 2.1-7 GHz range. In the TM polarization mode, increasing the incident angle enhances the metamaterial's absorption of electromagnetic waves. Therefore, the embedded low-frequency, broadband metamaterial absorber provided by the present invention exhibits excellent wide-angle absorption characteristics.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An embedded low-frequency broadband metamaterial absorber with dual magnetic dielectric layers, characterized in that: The invention comprises a metal reflective layer, and a composite magnetic absorbing coating and a flaky carbonyl iron magnetic absorbing coating sequentially formed on the metal reflective layer. The composite magnetic absorbing coating has a resistive film unit pattern layer embedded therein. The composite magnetic absorbing coating is obtained by applying and drying a composite magnetic absorbing coating containing a flaky carbonyl iron / CoFe2O4 composite, wherein the composite magnetic absorbing coating contains no less than 65% by mass of the flaky carbonyl iron / CoFe2O4 composite. The flaky carbonyl iron magnetic absorbing coating is obtained by applying and drying a flaky carbonyl iron magnetic absorbing coating containing flaky carbonyl iron, wherein the flaky carbonyl iron content in the flaky carbonyl iron magnetic absorbing coating is no less than 65% by mass. The total thickness of the composite magnetic absorbing coating and the flaky carbonyl iron magnetic absorbing coating is 2.3-2.5 mm. The resistive film unit pattern layer is composed of evenly distributed resistive film units.

2. The embedded low-frequency broadband metamaterial absorber according to claim 1, characterized in that: The mass percentage of the flaky carbonyl iron / CoFe2O4 composite in the composite magnetic absorbing coating is not less than 70%; and / or The mass percentage of the flaky carbonyl iron in the flaky carbonyl iron magnetic wave-absorbing coating is not less than 70%; and / or The preparation method of the flaky carbonyl iron / CoFe2O4 complex comprises: dispersing the flaky carbonyl iron into a PVP aqueous solution, ultrasonically treating the solution at 35-45° C. for 2.5-3.5 hours, magnetically separating and drying the solution to obtain the PVP surface-treated flaky carbonyl iron; dissolving ferric chloride and cobalt chloride in oxygen-removed distilled water, reacting the solution at 28-32° C. for 25-35 minutes, adding the PVP surface-treated flaky carbonyl iron, heating the solution to 65-75° C., adjusting the pH to 9-11, stirring the solution at 65-75° C. until the solution changes color, stopping stirring, settling the solution for 1-1.5 hours, washing the resulting precipitate, and drying the resulting precipitate to obtain the flaky carbonyl iron / CoFe2O4 complex; wherein the molar ratio of ferric chloride to cobalt chloride is (3.5-4.5):2.5; and / or The thickness of the composite magnetic wave-absorbing coating is 1.3 to 1.5 mm.

3. The embedded low-frequency broadband metamaterial absorber according to claim 2, characterized in that: The preparation method of the flaky carbonyl iron / CoFe2O4 complex comprises: dispersing the flaky carbonyl iron into a PVP aqueous solution, ultrasonically treating the solution at 40°C for 3 hours, magnetically separating and drying the solution to obtain the PVP surface-treated flaky carbonyl iron; dissolving ferric chloride and cobalt chloride in oxygen-removed distilled water, reacting the solution at 30°C for 30 minutes, adding the PVP surface-treated flaky carbonyl iron, heating the solution to 70°C, adjusting the pH to 9-11, stirring the solution at 70°C until the solution changes color, stopping stirring, settling the solution for 1 hour, washing the resulting precipitate, and drying the resulting precipitate to obtain the flaky carbonyl iron / CoFe2O4 complex; wherein the molar ratio of ferric chloride to cobalt chloride is 4:2.5; and / or The PVP mass percentage concentration of the PVP aqueous solution is 0.45% to 0.55%; and / or The raw materials of the composite magnetic absorbing coating further include modified epoxy resin, curing agent and diluent; and / or The thickness of the composite magnetic wave-absorbing coating is 1.5 mm.

4. The embedded low-frequency broadband metamaterial absorber according to claim 1, characterized in that: The preparation method of the flaky carbonyl iron comprises the following steps: using a mixed solution of anhydrous ethanol, a titanate coupling agent and a silane coupling agent as a ball milling medium, and ball milling zirconium dioxide grinding balls and carbonyl iron powder to obtain the flaky carbonyl iron.

5. The embedded low-frequency broadband metamaterial absorber according to claim 4, characterized in that: The mass ratio of the anhydrous ethanol, titanate coupling agent and silane coupling agent is 1: (0.4-0.6): (0.4-0.6); and / or The diameter of the zirconium dioxide grinding balls is 7 to 9 mm; and / or The mass ratio of the zirconium dioxide grinding balls to the carbonyl iron powder is (70-90):1; and / or The ratio of the sum of the mass of the zirconium dioxide grinding balls and the carbonyl iron powder to the volume of the mixed solution is (8-10):1, g:mL; and / or The ball milling is carried out in a ball mill with a motor frequency of 15 Hz and a rotation speed of 450 rpm; the ball milling time is 6 to 8 hours; and / or The raw materials of the flaky carbonyl iron magnetic wave-absorbing coating further include modified epoxy resin, curing agent and diluent.

6. The embedded low-frequency broadband metamaterial absorber according to claim 1, characterized in that: The resistance film units in the resistance film unit pattern layer are block resistance film units; and / or The distance between the resistive film unit pattern layer and the metal reflective layer is 0.5-0.75 mm.

7. The embedded low-frequency broadband metamaterial absorber according to claim 6, characterized in that: The side length of the square resistor film unit is 3 to 3.8 mm; and / or The resistor film material of the square resistor film unit is conductive silver paste, and the sheet resistance is 0.008-0.015 Ω / m.

8. The embedded low-frequency broadband metamaterial absorber according to any one of claims 1 to 7, characterized in that: The method for preparing the embedded low-frequency broadband metamaterial absorber comprises: applying the composite magnetic absorbing coating on the metal reflective layer, and when the thickness after curing reaches 0.5 to 0.75 mm, printing the resistive film unit pattern layer, and then applying the composite magnetic absorbing coating again on the resistive film unit pattern layer, and curing to obtain the composite magnetic absorbing coating layer; applying the flaky carbonyl iron magnetic absorbing coating on the composite magnetic absorbing coating layer, and curing to obtain the flaky carbonyl iron magnetic absorbing coating layer; and / or The material of the metal reflective layer is stainless steel or aluminum.

9. The embedded low-frequency broadband metamaterial absorber according to claim 8, characterized in that: The composite magnetic absorbing paint is applied in small amounts and multiple times, and dried at 55-65° C. until solidified after each application; and / or Before applying the composite magnetic wave-absorbing paint on the metal reflective layer, the metal reflective layer is cleaned, degreased and sanded.

10. Use of the embedded low-frequency broadband metamaterial absorber according to any one of claims 1 to 9 in military stealth equipment and electromagnetic protection devices.

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