Infrared / radar compatible stealth material with fractal structure and preparation method thereof

Abstract

The invention discloses an infrared / radar compatible stealth material with a fractal structure and a preparation method thereof, belonging to the field of infrared / radar compatible stealth materials, and used to solve the problem of compatible stealth of low-frequency band radar and infrared waves. The technical key points are a radar absorbing coating with a Sierpinski square blanket fractal structure, the radar absorbing coating comprising a substrate and an absorbing coating covered on the substrate, the absorbing coating forming the fractal structure; an infrared stealth layer with a Sierpinski square blanket fractal structure, the infrared stealth layer comprising an aluminum foil supersurface, the aluminum foil supersurface forming the fractal structure; the infrared stealth layer is arranged on the radar absorbing coating, the effect is to broaden the effective absorbing bandwidth of the material in the S-C band below -10dB, and reduce reflection loss and infrared emissivity.

Description

Technical Field

[0001] The invention belongs to the field of infrared / radar compatible stealth materials, and in particular relates to a method for preparing a low-frequency infrared / radar compatible stealth metamaterial with a fractal structure. Background Art

[0002] Infrared stealth materials can reduce the detectability of military targets in the infrared band, thereby improving the concealment of the target. The materials control the infrared radiation characteristics of the target to match the infrared characteristics of the surrounding environment, reducing the possibility of being discovered by infrared detectors.

[0003] Radar absorbing materials (RAM) or radar stealth materials are mainly used to reduce the reflection of radar waves from objects, thereby reducing their visibility on radar. These materials achieve the absorption effect by converting the energy of incident radar waves into other forms of energy (usually heat).

[0004] In modern warfare, information control greatly influences the direction of the war, so it is particularly important to strengthen detection and stealth technology. With the rapid development of multi-band detection technology, infrared detection and radar detection have become the two most important detection methods. Infrared / radar compatible stealth has become a research hotspot in stealth material technology. However, existing stealth compatible materials generally have disadvantages such as heavy weight, large thickness, narrow stealth band, and poor low-frequency band absorption performance, which greatly restricts the rapid development of detection technology.

[0005] Generally, a compatible material is considered to be compatible in terms of infrared reflection and radar absorption only when its radar absorption reflection loss is lower than -10dB and its infrared emissivity is lower than 0.3. However, since the stealth mechanisms of infrared and radar are completely opposite, achieving coordinated compatibility of completely conflicting mechanisms is the key and difficulty in the research of infrared / radar compatible stealth materials. Existing materials are difficult to meet the above requirements. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides an infrared / radar compatible stealth material with a fractal structure and a preparation method thereof, which are used to solve the problem of compatible stealth of low-frequency radar and infrared waves in a thin thickness. It can broaden the effective absorbing bandwidth of the material with reflection loss below -10dB in the SC low-frequency band, reduce reflection loss, make the infrared emissivity lower than 0.3, and achieve stealth compatibility effect.

[0007] In a first aspect, the infrared / radar compatible stealth material with a fractal structure according to some embodiments of the present application includes:

[0008] A radar absorbing coating having a Sierpinski square blanket fractal structure, the radar absorbing coating comprising a substrate and an absorbing coating covering the substrate, the absorbing coating forming the fractal structure;

[0009] An infrared stealth layer having a Sierpinski square blanket fractal structure, wherein the infrared stealth layer comprises an aluminum foil super surface, and the aluminum foil super surface forms the fractal structure;

[0010] The infrared stealth layer is arranged on the radar absorbing coating layer.

[0011] According to the infrared / radar compatible stealth material with a fractal structure recorded in some embodiments of the present application, the radar absorbing coating of the radar absorbing coating is formed into any one of the first to third levels of fractal structures, and the aluminum foil supersurface of the infrared stealth layer is formed into any one of the first to third levels of fractal structures.

[0012] According to the infrared / radar compatible stealth material with a fractal structure recorded in some embodiments of the present application, the radar absorbing coating has three levels of fractal structures, and the aluminum foil super surface of the infrared stealth layer has three levels of fractal structures.

[0013] According to the infrared / radar compatible stealth material with a fractal structure recorded in some embodiments of the present application, the fractal structure is obtained by arranging graphic units with a certain gap, wherein:

[0014] The primary fractal structure is formed into a solid first square;

[0015] The graphic unit of the secondary fractal structure is formed by dividing the solid first square of the graphic unit of the primary fractal structure into nine solid second squares of equal length and hollowing out the second square located at the center of the first square;

[0016] The graphic unit of the three-level fractal structure is formed by dividing each solid second square of the graphic unit of the two-level fractal structure into nine solid third squares of equal length, and hollowing out the third square located at the center of each second square.

[0017] According to the infrared / radar compatible stealth material with a fractal structure recorded in some embodiments of the present application, the infrared stealth layer is applied on the radar absorbing coating layer.

[0018] According to some embodiments of the present application, the infrared / radar compatible stealth material with a fractal structure has an effective absorption bandwidth of 1.42 to 2.29 GHz in the SC low-frequency band, a reflection loss of -16.9 to -11.0 dB, and an infrared emissivity of <0.3.

[0019] According to the infrared / radar compatible stealth material with a fractal structure recorded in some embodiments of the present application, the infrared emissivity is ≥ 0.272.

[0020] According to the infrared / radar compatible stealth material with a fractal structure recorded in some embodiments of the present application, the effective absorption bandwidth is 2.29 GHz, the reflection loss is -16.9, and the infrared emissivity is 0.272.

[0021] In a second aspect, according to some embodiments of the present application, a method for preparing an infrared / radar compatible stealth material having a fractal structure comprises:

[0022] S100. Preparation of radar absorbing coating with Sierpinski square blanket fractal structure;

[0023] S200. Preparation of an infrared stealth layer having a Sierpinski square blanket fractal structure;

[0024] S300. Arrange the infrared stealth layer on the radar absorbing coating.

[0025] According to the method for preparing an infrared / radar compatible stealth material having a fractal structure described in some embodiments of the present application, the step S100 of preparing a radar absorbing coating having a Sierpinski square blanket fractal structure comprises the following steps:

[0026] S110. Coating an absorbing coating on the aluminum plate, wherein the absorbing coating is prepared by mixing carbonyl iron powder and polyurethane in a mass ratio of (1 to 5): 1;

[0027] S120. Use a mold having a graphic unit structure to emboss the absorbing coating layer, so that the graphic units of the fractal structure are formed and gaps between the graphic units are formed, and the fractal structure is formed on the absorbing coating layer.

[0028] According to the method for preparing an infrared / radar compatible stealth material having a fractal structure described in some embodiments of the present application, the step S200 of preparing an infrared stealth layer having a Sierpinski square blanket fractal structure comprises the following steps:

[0029] S210. The aluminum foil is applied to the PC sheet to form an aluminum foil super surface;

[0030] S220. Etching is performed on the aluminum foil super surface to shape the graphic units of the fractal structure and form gaps between the graphic units, thereby shaping the fractal structure on the aluminum foil super surface.

[0031] According to the method for preparing an infrared / radar compatible stealth material with a fractal structure recorded in some embodiments of the present application, the thickness of the absorbing coating is 1.5-2.5 mm, the thickness of the aluminum foil is 0.04-0.08 mm, the thickness of the PC sheet is 0.2 mm, the first square is a 9 mm×9 mm square, the second square is a 3 mm×3 mm square, and the third square is a 1 mm×1 mm square.

[0032] Beneficial effects of the present invention:

[0033] In the first aspect, the infrared / radar compatible stealth material with a fractal structure of the present invention significantly improves the absorbing performance of the compatible stealth material in the SC low-frequency band by setting the radar absorbing coating and the infrared stealth layer to a Sierpinski square blanket fractal structure with non-integer dimensionality and adaptability, while reducing the density of the radar absorbing coating, so that the radar absorbing coating has the properties of stretchability, impact resistance, friction resistance, etc. while becoming light and thin.

[0034] In the second aspect, the infrared / radar compatible stealth material with a fractal structure of the present invention increases the fractal order of the bottom radar absorbing coating and the top infrared stealth layer, and finds that when the mass, size, thickness, etc. are constant, as the fractal order increases, the infrared / radar compatibility becomes more stable, the effective bandwidth in the SC low-frequency band becomes wider, the reflection loss becomes smaller, and the infrared emissivity becomes lower. When the fractal order of the radar absorbing coating and the infrared stealth layer is both level 3, the resulting stealth material has a maximum effective absorbing bandwidth of 2.29 GHz, a minimum reflection loss of -16.9 dB, and a minimum infrared emissivity of 0.272. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of a 3D printing mold. a is the primary fractal structure, b is the secondary fractal structure, and c is the tertiary fractal structure.

[0036] Figure 2 These are sample images of infrared stealth layers of 1-3 levels of fractals, a is the first-level fractal structure, b is the second-level fractal structure, and c is the third-level fractal structure.

[0037] Figure 3 These are sample images of radar absorbing coatings with 1-3 fractal levels, a is the first-level fractal structure, b is the second-level fractal structure, and c is the third-level fractal structure.

[0038] Figure 4 It is a comparison chart of reflection loss measured by increasing the fractal order of each layer of the obtained compatible material, a is a comparison chart of embodiments X1 to X3 and comparative example D1, b is a comparison chart of embodiments X4 to X6 and comparative example D2, and c is a comparison chart of embodiments X7 to X9 and comparative example D3.

[0039] Figure 5 This is the SEM image of the radar absorbing coating.

[0040] Figure 6 This is a comparison chart of reflection losses measured for a material that is a combination of an infrared stealth layer with a fractal structure and a radar absorbing layer without a fractal structure. a is a comparison chart for Example D4, b is a comparison chart for Example D5, and c is a comparison chart for Example D6.

[0041] Figure 7 yes Figure 1 Partial graph of c.

[0042] Figure 8 yes Figure 2 The enlarged view of Figure 2 The enlarged view of a and b is Figure 2 The enlarged view of b, c is Figure 2 Enlarged view of c.

[0043] Fig. 9 yes Figure 3 The enlarged view of Figure 3 The enlarged view of a and b is Figure 3 The enlarged view of b, c is Figure 3 Enlarged view of c. DETAILED DESCRIPTION

[0044] The specific implementation methods of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific implementation methods. Starting from the structure of the metamaterial, the present invention uses an internal extension fractal structure with high space utilization to improve the defects of the above-mentioned stealth compatible materials, and can make the material lighter and thinner without changing the material properties. Due to its non-integer dimension and self-similarity characteristics, the fractal structure can effectively reduce wave reflection while increasing wave loss, thereby achieving infrared / radar compatible stealth performance of the material. Among them, the Sierpinski square blanket is a typical fractal structure with a certain filling degree. Therefore, the layered metamaterial with the Sierpinski square blanket fractal structure can solve the problem of compatible stealth of low-frequency band radar and infrared waves in thin thickness. While broadening the effective absorption bandwidth of the material with reflection loss below -10dB in the SC low-frequency band, the infrared emissivity is made lower than 0.3, achieving a good stealth compatibility effect.

[0045] In the first embodiment, the infrared / radar compatible stealth material with a fractal structure of this embodiment includes, from bottom to top, a radar absorbing coating with a fractal structure and an infrared stealth layer with a fractal structure, wherein the absorbing coating is a uniform mixture of carbonyl iron powder and polyurethane, the infrared stealth layer is an aluminum foil metasurface, and the fractal structure is an array graphic unit of a Sierpinski square blanket fractal structure whose structural units are at a fractal level of 1-3; the fractal method of the graphic unit is: dividing a solid square into 9 small squares of equal length, then removing the small square in the middle, and then repeating this operation for each remaining small square, and obtaining the final Sierpinski square blanket fractal structure through three cycles of iteration.

[0046] In one embodiment, the absorbing coating has a thickness of 1.5 to 2.5 mm, and is composed of a uniform mixture of carbonyl iron powder and polyurethane in a mass ratio of (1 to 5): 1; the infrared stealth layer is an aluminum foil super surface composed of an aluminum foil and a polycarbonate (PC) sheet pasted together, the aluminum foil has a thickness of 0.04 to 0.08 mm, the PC sheet has a thickness of 0.2 mm, and the aluminum foil is pasted on the PC sheet; the fractal structure is an array graphic unit of a Sierpinski square blanket fractal structure with a fractal level of 1 to 3, the fractal structure unit size obtained by the first-level fractal is a small square of 9 mm × 9 mm, the minimum square size of the structural unit obtained by the second-level fractal is 3 mm × 3 mm, and the minimum regular shape size of the structural unit obtained by the third-level fractal is 1 mm × 1 mm.

[0047] The method for preparing an infrared / radar compatible stealth material with a fractal structure in this embodiment includes the following steps: S100: preparing a radar absorbing coating with a fractal structure.

[0048] S200: preparing an infrared stealth layer having a fractal structure.

[0049] S300: Disposing the infrared stealth layer on the radar absorbing coating layer.

[0050] Wherein, in step S100, preparing a radar absorbing coating having a fractal structure specifically includes:

[0051] S110. Prepare an absorbing coating on an aluminum plate. First, mix carbonyl iron powder and polyurethane in a certain mass ratio, then spread the mixture on a flat plate and let it stand at room temperature for 2 hours until the surface solidifies to form an absorbing coating whose interior is not completely solidified. In this step, preferably, carbonyl iron powder and polyurethane are uniformly mixed in a preferred mass ratio of 4:1, and the thickness of the obtained absorbing coating is 2 mm. In an embodiment, step S110 specifically includes:

[0052] S111. Add 240g of carbonyl iron powder and 60g of polyurethane into a disposable plastic cup, and add various additives such as dispersant, defoamer, diluent, curing agent, etc., mix them preliminarily with a stirring rod, put them in a blender, and then evenly mix them mechanically for 8 minutes and stir them mechanically.

[0053] S112. After the stirring is completed, the mixture is cooled slightly and placed in an ultrasonic oscillator for ultrasonic treatment at room temperature for 8 minutes. The purpose of ultrasonic treatment at room temperature is to prevent the mixture from being too viscous and not conducive to subsequent preparation.

[0054] S113. After the ultrasonic treatment is completed, take out the disposable plastic cup containing the mixture, repeat the above stirring and ultrasonic steps for three cycles, so that the spherical carbonyl iron powder is evenly mixed in the polyurethane to finally form a uniform mixture.

[0055] S114. The uniform mixture is evenly coated on an aluminum plate with a thickness of 2 mm, and placed on a level gauge at room temperature for 2 hours to form a semi-cured absorbing coating, and the thickness H0 of the cured absorbing coating is 2 mm. The absorbing coating is gently squeezed, and slight deformation of the cured absorbing coating can be felt.

[0056] S120: Use a mold with a graphic unit structure to stamp an absorbing coating that is not completely solidified inside, and form an image unit on the absorbing coating. The graphic unit is a fractal structure of level 1 to 3 of the Sierpinski square blanket. The mold can be manufactured by 3D printing technology. The graphic unit structure is a hollow or raised structure formed inside the mold, such as Figure 1 As shown, a mold with a hollow interior is used to stamp an unsolidified radar absorbing coating, and the graphic units of the mold are a Sierpinski square blanket fractal structure that is fractalized at levels 1-3 and arranged in a periodic manner. During the stamping process, it is ensured that the mold walls of each graphic unit of the mold have been embedded in the absorbing coating and the bottom surface of the absorbing coating is completely separated until the absorbing coating is completely solidified; and the wall height of the mold graphic unit should be higher than the radar absorbing coating.

[0057] In an embodiment, Figure 1 and Figure 7As shown, the thickness H1 of the prepared mold is 5mm, the thickness H1-H0 of the graphic unit wall (member) is 3mm, and the width L2 of the graphic unit wall (member) is 0.48mm. The primary fractal size of the first graphic unit of the Sierpinski square carpet is 9mm×9mm, where 9mm is the side length L1 of the square Square1 of the primary fractal of the first graphic unit. The secondary fractal size of the second graphic unit of the Sierpinski square carpet is 3mm×3mm, where 3mm is the side length L2 of the square Square2 of the secondary fractal of the second graphic unit. The tertiary fractal size of the third graphic unit of the Sierpinski square carpet is 1mm×1mm, where 1mm is the side length L3 of the square Square3 of the tertiary fractal of the third graphic unit.

[0058] like Figure 1 As shown, it can be understood that the first graphic unit is a slot of a square Square 1 formed on a mold with a thickness H1 of 5 mm, the thickness H1-H0 of the wall (member) of the square Square 1 is 3 mm, and the width L2 is 0.48 mm. Figure 2-3 As shown, the first image unit is a 9mm×9mm square Square1 separated by equal gaps. The second image unit is to divide the square Square1 of the first image unit into nine equal parts, each of which is a 3mm×3mm square Square2, and the 3mm×3mm square Square2 in the center is formed into a square Square2 hollowed out. The third image unit is to divide the non-hollowed squares Square2 of the second image unit into nine equal parts, each of which is a 1mm×1mm square Square3, and the central 1mm×1mm square Square3 is formed into a square Square3 hollowed out. It can be understood that the above-mentioned nine-equal division expression only expresses the division on the image, not the segmentation. Therefore, based on the setting of the above-mentioned image unit, the hollowed-out part of the image unit corresponds to the protrusion on the graphic unit structure of the mold, and the non-hollowed-out part of the image unit corresponds to the hollowing out on the graphic unit structure of the mold.

[0059] In an embodiment, step S120 specifically includes:

[0060] S121. Use a mold to embed the graphic unit wall of the mold graphic unit structure into the absorbing coating coated on the aluminum plate, so that each graphic unit formed by the absorbing coating is divided by the 0.48mm graphic unit wall to form a gap between each graphic unit, until the absorbing coating is completely solidified to form a radar absorbing coating with the first fractal structure of the Sierpinski square blanket.

[0061] S122. Spray a release agent on the contact surface between the absorbing coating and the graphic unit structure of the mold in small amounts and multiple times to separate the mold from the absorbing coating. The absorbing coating forms a structural gap due to the separation from the graphic unit wall of the mold. The gap separates the inside and surface of the absorbing coating into a combination of periodically arranged Sierpinski square blanket fractal structural units. In this embodiment, a release agent is used to reduce the surface tension of the mold and the lubrication principle to perform a demolding process between the mold and the absorbing coating. Since the absorbing coating has adhesiveness, it is easy to adhere to the mold during the pressing process, and the two are not easy to separate. A release agent is required as an intermediate isolation layer to form a thin film between the coating and the mold, and then heating is used to make the release agent eliminate the adhesion between the mold and the absorbing coating, so that the mold and the absorbing coating are separated to achieve a good demolding effect.

[0062] S123. After the radar absorbing coating is completely solidified, the radar absorbing coating embedded in the mold is placed in a drying oven and heated to allow the release agent to eliminate the adhesion between the mold and the radar absorbing coating. Finally, the radar absorbing coating separated from the mold is left to cool at room temperature to form a radar absorbing coating with a fractal structure.

[0063] In step S120, Sierpinski square blanket graphic unit structure molds with fractal levels 1, 2, and 3 are used to form Sierpinski square blanket primary fractal structure, secondary fractal structure, and tertiary fractal structure on three radar absorbing coatings, and each formed radar absorbing coating is named L1 (such as Figure 3 a), L2 (such as Figure 3 b), L3 (such as Figure 3 c).

[0064] Wherein, in step S200, preparing an infrared stealth layer having a fractal structure specifically includes:

[0065] S210: Evenly and evenly attach an aluminum foil with a thickness of 0.04 to 0.08 mm to a PC sheet with a thickness of 0.2 mm to form an aluminum foil super surface. Subsequently, a Sierpinski square blanket fractal structure is prepared on the aluminum foil super surface. The method for preparing the fractal structure is: using a laser marking machine to perform laser etching on the aluminum foil super surface to form a Sierpinski square blanket fractal structure.

[0066] Among them, a laser marking machine is used to laser-etch the Sierpinski square blanket patterns of fractal levels 1, 2, and 3 on three aluminum foil super surfaces, respectively, to form the Sierpinski square blanket primary fractal structure, secondary fractal structure, and tertiary fractal structure, and each formed infrared stealth layer is named Y1 (such as Figure 2 a), Y2 (such as Figure 2 b), Y3 (such as Figure 2 c).

[0067] Among them, in step S300, the infrared stealth layer is arranged on the radar absorbing coating layer, and the prepared infrared stealth layer can be applied to the absorbing coating layer. In this embodiment, the designed variable is the fractal level, which is level 1, level 2, and level 3 respectively. In this embodiment, the prepared infrared stealth layer is applied to the absorbing coating layer, and the finally prepared infrared / radar compatible stealth material is named according to the fractal level of the absorbing coating layer and the infrared stealth layer structural unit.

[0068] In a second embodiment, an infrared / radar compatible stealth material with a fractal structure includes, from bottom to top, an absorbing coating with a fractal structure and an infrared stealth layer with a fractal structure in order to achieve effective infrared / radar compatibility. The absorbing coating material is composed of a uniform mixture of carbonyl iron powder and polyurethane in a certain mass ratio, and the infrared stealth layer is an aluminum foil super surface.

[0069] The fractal structure is a Sierpinski square carpet fractal structure. The Sierpinski square carpet fractal structure is a typical structure with anti-reflection characteristics and self-similarity. In the field of stealth technology, it can effectively reduce wave reflection while increasing wave loss. Its construction is based on square fractal. The fractal iteration rule is: first, take a small square, then divide it into nine parts evenly, remove the small square in the center, and complete the iteration. Thereafter, as the fractal level increases, the remaining small squares are repeatedly cut and removed in sequence, and the iterative upgrade is continuously completed. Finally, molds whose structural units are Sierpinski square carpet structures with 1st, 2nd, and 3rd fractal levels are prepared respectively.

[0070] The first-level fractal size of the Sierpinski square blanket is 9 mm×9 mm, the second-level fractal size is 3 mm×3 mm, and the third-level fractal size is 1 mm×1 mm. The present invention improves the wave absorbing performance of the obtained compatible stealth metamaterial in the SC low-frequency band by continuously optimizing the mass ratio of the spherical carbonyl iron powder and the polyurethane of the radar coating and increasing the fractal order of the infrared layer and the radar layer.

[0071] As a preferred technical solution of the present invention, the mass ratio of carbonyl iron powder to polyurethane in the absorbing coating is in the range of (1-5):1, and the thickness of the absorbing coating is in the range of 1.5-2.5 mm.

[0072] As a preferred technical solution of the present invention, the infrared stealth layer has a size of 0.24-0.28 mm, including a PC sheet with a thickness of 0.2 mm and an aluminum foil with a thickness of 0.04-0.08 mm.

[0073] Furthermore, the radar absorbing coating with a fractal structure of the present invention comprises the following steps:

[0074] (1) Preparation of semi-cured radar absorbing coating.

[0075] (2) Using a mold imprinting process, a fractal structure is prepared on the semi-cured radar absorbing coating prepared in step (1).

[0076] The present invention also provides a method for preparing a radar absorbing coating having a fractal structure, comprising the following steps:

[0077] Carbonyl iron powder and polyurethane are uniformly mixed in a mass ratio of (1-5):1, and the mixture is evenly spread on an aluminum plate with a thickness of 2 mm, and left to stand horizontally at room temperature for 2 hours to form a semi-cured absorbing coating.

[0078] Furthermore, a mold having a Sierpinski square blanket 1 to 3 level fractal structure is used to emboss the prepared semi-cured absorbing coating, wherein the mold is a graphic structure with a hollow interior. The mold is completely embedded in the absorbing coating, ensuring that the mold graphic unit divides the bottom surface of the absorbing coating, and then the mold and the absorbing coating are separated, and a structural gap is formed in the process of separating the absorbing coating from the wall of the mold, and then the absorbing coating is left to stand at room temperature to solidify naturally, thereby obtaining a radar absorbing coating with a fractal structure.

[0079] Furthermore, the mold is prepared from resin by 3D printing technology, the mold unit graphic wall height is 3 mm, the mold wall thickness is 0.48 mm, and the total mold height is 5 mm, to ensure that it can completely imprint the absorbing coating and divide the underlying surface.

[0080] Furthermore, the method for separating the mold from the surface of the absorbing coating is: spraying a release agent composed of mineral oil, silicone oil, polymer, surfactant, etc. along the contact surface of the mold and the absorbing coating, after spraying a small amount multiple times, placing the absorbing coating embedded with the mold in a drying oven at 40-60°C, heating to allow the release agent to take effect, eliminating the adhesion between the absorbing coating and the mold, and facilitating the separation of the absorbing coating from the mold, and finally, cooling the absorbing coating separated from the mold at room temperature to obtain a radar absorbing coating with a fractal structure.

[0081] Furthermore, the method for preparing the infrared stealth layer with a fractal structure described in the present invention is:

[0082] Aluminum foil with a thickness of 0.04 to 0.08 mm was laminated on a PC sheet with a thickness of 0.2 mm to form an aluminum foil supersurface, and the above-mentioned Sierpinski square blanket fractal structure was prepared on the aluminum foil supersurface. Finally, an infrared stealth layer with structural units of Sierpinski square blanket 1st level fractal, 2nd level fractal, and 3rd level fractal was prepared.

[0083] The present invention also provides a specific preparation method for preparing the Sierpinski square blanket fractal structure on an aluminum foil supersurface: placing the aluminum foil supersurface on a worktable of a laser marking machine, performing laser etching on the aluminum foil supersurface, and finally preparing an infrared stealth layer with a fractal structure having fractal levels of 1, 2, and 3.

[0084] As a preferred technical solution of the present invention, considering that the unit area of ​​the infrared aluminum foil needs to be ≥70% to ensure its infrared stealth performance, each fractal unit on the absorbing coating and the aluminum foil metasurface should be separated by a gap with a width of 0.48 mm.

[0085] Example X1: Material name Y1L1, composition: Sierpinski square blanket primary fractal structure infrared stealth layer and Sierpinski square blanket primary fractal structure radar absorbing coating.

[0086] Example X2: Material name Y2L1, composition: Sierpinski square blanket secondary fractal structure infrared stealth layer and Sierpinski square blanket primary fractal structure radar absorbing coating.

[0087] Example X3: Material name Y3L1, composition: Sierpinski square blanket three-level fractal structure infrared stealth layer and Sierpinski square blanket one-level fractal structure radar absorbing coating.

[0088] Example X4: Material name Y1L2, composition: Sierpinski square blanket primary fractal structure infrared stealth layer and Sierpinski square blanket secondary fractal structure radar absorbing coating.

[0089] Example X5: Material name Y2L2, composition: Sierpinski square blanket secondary fractal structure infrared stealth layer and Sierpinski square blanket secondary fractal structure radar absorbing coating.

[0090] Example X6: Material name Y3L2, composition: Sierpinski square blanket three-level fractal structure infrared stealth layer and Sierpinski square blanket two-level fractal structure radar absorbing coating.

[0091] Example X7: Material name Y1L3, composition: Sierpinski square blanket first-level fractal structure infrared stealth layer and Sierpinski square blanket third-level fractal structure radar absorbing coating.

[0092] Example X8: Material name Y2L3, composition: Sierpinski square blanket secondary fractal structure infrared stealth layer and Sierpinski square blanket tertiary fractal structure radar absorbing coating.

[0093] Example X9: Material name Y3L3, composition: Sierpinski square blanket three-level fractal structure infrared stealth layer and Sierpinski square blanket three-level fractal structure radar absorbing coating.

[0094] The compatible materials of the above-mentioned embodiments 1 to 9 all have infrared emissivity lower than 0.3, and the lowest infrared emissivity is 0.272 (X9).

[0095] Comparative Example D1: L1, composition: a single radar absorbing coating having a Sierpinski square blanket first-order fractal structure.

[0096] Comparative Example D2: L2, composition: a single radar absorbing coating having a Sierpinski square blanket secondary fractal structure.

[0097] Comparative Example D3: L3, composition: a single radar absorbing coating having a three-level fractal structure of a Sierpinski square blanket.

[0098] Comparative Example D4: Y1L0, composition: a Sierpinski square blanket primary fractal structure infrared stealth layer and a radar absorbing coating without a fractal structure.

[0099] Comparative Example D5: Y2L0, composition: a Sierpinski square blanket secondary fractal structure infrared stealth layer and a radar absorbing coating without a fractal structure.

[0100] Comparative Example D6: Y3L0, composition: a Sierpinski square blanket three-level fractal structure infrared stealth layer and a radar absorbing coating without a fractal structure.

[0101] The effective absorption bandwidth and minimum reflection loss of Examples X1 to X9 in the SC low-frequency band are as follows:

[0102]

[0103]

[0104] It can be seen from the table that with the increase of the fractal order of the radar absorbing coating and the infrared stealth layer, the effective absorbing bandwidth of the infrared / radar compatible stealth material with a fractal structure prepared in the embodiment is significantly broadened, and the minimum reflection loss is also significantly reduced.

[0105] The mold used for imprinting the bottom radar absorbing coating in this embodiment is shown in FIG. Figure 1 and Figure 7 , infrared stealth layer with fractal structure Figure 2 , radar absorbing coating with fractal structure Figure 3 The infrared / radar compatible stealth material with fractal structure prepared in the embodiment is tested for reflection loss in the SC low frequency band. The test results are shown in Figure 4 , characterization of radar absorbing coating (SEM) see Figure 5 .

[0106] Depend on Figure 4As can be seen from the table: a single radar absorbing coating with a fractal structure can be regarded as having no absorbing performance in the SC low-frequency band. After the introduction of the infrared stealth layer with a fractal structure, when other parameters of the radar absorbing coating and the infrared stealth layer remain unchanged, as the fractal levels of the radar absorbing coating and the infrared stealth layer increase, the infrared / radar compatibility effect becomes more stable, the effective bandwidth in the SC low-frequency band becomes wider, the reflection loss becomes smaller, and the infrared emissivity becomes lower. Finally, when the fractal levels of the radar absorbing coating and the infrared stealth layer are increased to level 3, the reflection loss and infrared emissivity are tested, and it is found that the infrared / radar compatible stealth material with a three-level fractal structure prepared in Example X9 has the largest effective absorption bandwidth of 2.29 GHz, the smallest reflection loss of -16.9 dB, and the lowest infrared emissivity of 0.272 in the SC low-frequency band.

[0107] Depend on Figure 6 : D4's Y1L0: The effective absorbing bandwidth with reflection loss lower than -10dB is 0.8GHz (2.3GHz-3.1GHz). D5's Y2L0: The effective absorbing bandwidth with reflection loss lower than -10dB is 0.9GHz (2.3GHz-3.2GHz). D6's Y3L0: The effective absorbing bandwidth with reflection loss lower than -10dB is 0.9GHz (2.4GHz-3.3GHz). It can be seen that the material composed of the infrared stealth layer with fractal structure and the radar absorbing coating without fractal structure has almost no absorbing performance.

[0108] As described above, a single radar absorbing coating with a fractal structure or a material composed of an infrared stealth layer with a fractal structure and a radar absorbing coating without a fractal structure has no or almost no absorbing performance in the SC low-frequency band. The present invention combines the infrared stealth layer and the radar absorbing coating into a compatible material, and sets a Sierpinski square blanket fractal structure for any layer, so that the compatible material has good absorbing performance in the SC low-frequency band, and further, as the number of fractal structures increases, the wider the effective bandwidth in the SC low-frequency band, the smaller the reflection loss, and the lower the infrared emissivity. The infrared / radar compatible stealth material with a three-level fractal structure prepared in Example X9 has the largest effective absorption bandwidth of 2.29 GHz, the smallest reflection loss of -16.9 dB, and the lowest infrared emissivity of 0.272 in the SC low-frequency band.

[0109] The present invention belongs to the field of infrared and radar compatible stealth materials, and specifically relates to an infrared / radar compatible stealth material with a fractal structure and a preparation method thereof, which has good wave absorption performance in the low-frequency band. The infrared / radar compatible stealth material with a fractal structure of the present invention comprises a radar wave absorbing coating with a fractal structure arranged from bottom to top, and an infrared stealth layer with a fractal structure. By introducing a Sierpinski square blanket fractal structure with non-integer dimensionality and adaptability, and increasing the fractal order of the fractal structure on the bottom wave absorbing coating and the top infrared stealth layer, the wave absorption performance of the obtained compatible stealth material in the SC low-frequency band is significantly improved, and the defects of the traditional wave absorbing coating being heavy and thick, and the traditional double-layer metamaterial having poor wave absorption performance in the low-frequency band are improved. The preparation process of each functional layer is simple and efficient, and the raw material price is low, the production cost is low, and it has good development prospects.

[0110] The above embodiments are only for illustrating the technical concept and features of the present invention, so that people familiar with the technology can fully understand the content of the present invention and implement it accordingly, but the disclosed protection scope is not limited to this. Any equivalent changes or improvements made according to the spirit of the present invention will be deemed to be included in the protection scope of the present invention.

Claims

1. An infrared / radar compatible stealth material with a fractal structure, characterized in that: include: A radar absorbing coating having a Sierpinski square blanket fractal structure, the radar absorbing coating comprising a substrate and an absorbing coating covering the substrate, the absorbing coating forming the fractal structure; An infrared stealth layer having a Sierpinski square blanket fractal structure, wherein the infrared stealth layer comprises an aluminum foil super surface, and the aluminum foil super surface forms the fractal structure; The infrared stealth layer is arranged on the radar absorbing coating; The radar absorbing coating of the radar absorbing coating is formed into any one of the first to third levels of fractal structures, and the aluminum foil super surface of the infrared stealth layer is formed into any one of the first to third levels of fractal structures; The material has an effective wave absorption bandwidth of 1.42 to 2.29 GHz in the SC low-frequency band, a reflection loss of -16.9 to -11.0 dB, an infrared emissivity of <0.3 and an infrared emissivity of ≥0.

272.

2. The material according to claim 1, characterized in that The radar absorbing coating has a three-level fractal structure, and the aluminum foil super surface of the infrared stealth layer has a three-level fractal structure. The effective absorbing bandwidth of the material is 2.29 GHz, the reflection loss is -16.9, and the infrared emissivity is 0.

272.

3. The material according to claim 1 or 2, characterized in that: The fractal structure is obtained by arranging graphic units with a certain gap, wherein: The primary fractal structure is formed into a solid first square; The graphic unit of the secondary fractal structure is formed by dividing the solid first square of the graphic unit of the primary fractal structure into nine solid second squares of equal length and hollowing out the second square located at the center of the first square; The graphic unit of the three-level fractal structure is formed by dividing each solid second square of the graphic unit of the two-level fractal structure into nine solid third squares of equal length, and hollowing out the third square located at the center of each second square.

4. The material according to claim 1, characterized in that The infrared stealth layer is applied on the radar absorbing coating layer.

5. The material according to claim 3, characterized in that: in, The thickness of the radar absorbing coating is 1.5-2.5 mm, the first square is a 9 mm×9 mm square, the second square is a 3 mm×3 mm square, and the third square is a 1 mm×1 mm square.

6. A method for preparing the material according to claim 1, characterized in that: include S100. Preparation of radar absorbing coating with Sierpinski square blanket fractal structure; S200. Preparation of an infrared stealth layer having a Sierpinski square blanket fractal structure; S300. Arrange the infrared stealth layer on the radar absorbing coating.

7. The method for preparing a material according to claim 6, characterized in that: in, The step S100 of preparing a radar absorbing coating having a Sierpinski square blanket fractal structure comprises the following steps: S110. Coating an absorbing coating on the aluminum plate, wherein the absorbing coating is prepared by mixing carbonyl iron powder and polyurethane in a mass ratio of (1-5):1; S120. Use a mold having a graphic unit structure to emboss the absorbing coating layer, so that the graphic units of the fractal structure are formed and gaps between the graphic units are formed, and the fractal structure is formed on the absorbing coating layer.

8. The method for preparing a material according to claim 7, characterized in that: The step S200 of preparing an infrared stealth layer having a Sierpinski square blanket fractal structure comprises the following steps: S210. The aluminum foil is applied to the PC sheet to form an aluminum foil super surface; S220. Etching is performed on the aluminum foil super surface to shape the graphic units of the fractal structure and form gaps between the graphic units, thereby shaping the fractal structure on the aluminum foil super surface.

9. The method for preparing a material according to claim 8, characterized in that: in, The thickness of the absorbing coating is 1.5-2.5 mm, the thickness of the aluminum foil is 0.04-0.08 mm, the thickness of the PC sheet is 0.2 mm, the first square is a 9 mm×9 mm square, the second square is a 3 mm×3 mm square, and the third square is a 1 mm×1 mm square.

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