A microwave absorbing coating based on a metasurface and its preparation method

Abstract

The application provides a wave-absorbing coating based on a super-structured surface and a preparation method thereof, and relates to the field of radar wave-absorbing functional coating. The wave-absorbing coating based on the super-structured surface comprises a bottom coating and a surface coating. The bottom coating is mainly composed of a base resin and a magnetic medium type wave-absorbing agent. The surface coating is mainly composed of a base resin and a carbon-based nanomaterial wave-absorbing agent. The surface of the surface coating is provided with a super-structure composed of periodically arranged convex polygonal resonant units. The wave-absorbing coating provided by the application has good full-band electromagnetic wave absorption performance, and the weight is reduced by more than 65% compared with the conventional wave-absorbing coating. The problems of the existing wave-absorbing coating, such as too large areal density and insufficient environmental resistance, can be solved, and the application range of the wave-absorbing coating is expanded.

Description

Technical Field

[0001] This invention belongs to the field of radar absorbing coating technology, specifically to a radar absorbing coating based on a metasurface and its preparation method. Background Technology

[0002] In informationized warfare, various advanced detection methods and precision strike systems pose a significant threat to the penetration and survivability of weapons and equipment. Among various military detection methods, radar detection accounts for over 60%, making it a major battlefield threat to weapons and equipment. As the requirements for lightweight, intelligent, and stealthy weapons and equipment gradually increase, the need for "thin, light, wide, and strong" radar stealth materials becomes more urgent. In the stealth systems of existing equipment, radar-absorbing coatings remain the most important radar stealth method, and their performance directly determines the battlefield survivability of currently deployed equipment.

[0003] Traditional radar-absorbing coatings primarily utilize magnetic metal particles and ferrites as absorbing agents. However, these materials suffer from significant drawbacks, including high areal density, susceptibility to oxidation, and poor high-temperature resistance, resulting in poor environmental adaptability and incompatibility with the stealth requirements of weaponry. In recent years, carbon-based multidimensional nanomaterials, such as carbon nanotubes and graphene, have emerged as a new generation of lightweight radar absorbing agents due to their superior mechanical, thermal, electromagnetic, and chemical properties. This provides an important and feasible approach to addressing the aforementioned problems associated with traditional magnetic radar-absorbing materials.

[0004] Chinese patent application No. 201210151472.8 discloses a carbon nanotube-doped polySchiff base / carbonyl iron powder composite stealth material, which is prepared by combining carbon nanotubes, polySchiff base, and carbonyl iron powder. The carbon nanotubes account for 6%–11% of the total composite material, the polySchiff base accounts for 27%–31%, and the remainder is nano-carbonyl iron powder. This material exhibits excellent microwave absorption performance, along with advantages such as wide absorption bandwidth, low cost, simple preparation, and low density, showing broad application prospects in microwave absorbing materials, antistatic materials, and electromagnetic shielding materials. Although this material achieves a reduction in coating density without affecting microwave absorption performance by adding carbon nanotubes, the proportion of carbon nanotubes added is small, thus limiting the improvement in coating density. Summary of the Invention

[0005] To address the issues of high density and poor environmental adaptability in existing microwave absorbing coatings composed of magnetic media-based microwave absorbing agents, this invention proposes a microwave absorbing coating based on metasurfaces and its preparation method, which significantly reduces the density of the microwave absorbing coating and enhances its environmental adaptability.

[0006] The aforementioned microwave absorbing coating based on a metasurface includes a base coating and a top coating. The base coating is mainly composed of a matrix resin and a magnetic medium-type microwave absorbing agent. The top coating is mainly composed of a matrix resin and a carbon-based nanomaterial microwave absorbing agent. The surface of the top coating is provided with a superstructure composed of periodically arranged protruding polygonal resonant units.

[0007] This invention introduces a novel, lightweight, multi-scale carbon-based nanomaterial absorbing agent with micro / nano hierarchical structures to significantly reduce the density of the absorbing coating and enhance its environmental adaptability. This is further enhanced by a surface superstructure resonant unit design in the top layer coating, which further reduces the coating density and broadens the absorption frequency domain. Furthermore, the absorbing coating based on the metasurface provided by this invention features a multi-layer structure. The top layer coating encapsulates the bottom layer containing the magnetic medium-type absorbing agent, isolating it from external contact and reducing negative performance changes caused by environmental influences. This addresses the current problem of performance degradation or functional failure of radar absorbing coatings in marine environments, while also reducing coating density and expanding application scenarios.

[0008] Preferably, the thickness ratio of the bottom coating to the top coating is 1 to 1:10.

[0009] Preferably, the thickness of the underlying coating is 0.1~1 mm.

[0010] Preferably, the thickness of the surface coating is 0.1~1 mm.

[0011] Preferably, the matrix resin includes epoxy resin or modified epoxy resin.

[0012] More preferably, the epoxy resin includes glycidyl ether epoxy resin, linear aliphatic epoxy resin, or glycidyl ester epoxy resin.

[0013] More preferably, the modified epoxy resin includes silicone-modified epoxy resin, acrylic-modified epoxy resin, or polyurethane-modified epoxy resin.

[0014] Preferably, the carbon-based nano-absorbing agent is a carbon nanotube absorbing agent.

[0015] Preferably, the magnetic medium type microwave absorber is a carbonyl iron microwave absorber.

[0016] Preferably, the surface of the underlying coating is provided with a superstructure composed of periodically arranged raised polygonal resonant units.

[0017] Preferably, the polygonal resonant unit has a side length of 1 to 4 mm, a protrusion height of 0.1 to 1 mm, and a gap width of 0.2 to 0.8 mm between adjacent polygonal resonant units.

[0018] Preferably, the shape of the polygonal resonant unit includes a square, a rectangle, a regular pentagon, a regular hexagon, and a regular octagon.

[0019] Preferably, the surface coating is mainly composed of the following raw materials: 2%~20% carbon-based nanomaterial microwave absorber, 75%~93% matrix resin, and the balance is dispersant, with the sum of the mass percentages of each component being 100%.

[0020] Preferably, the underlying coating is mainly composed of the following raw materials: 60%~80% magnetic medium type microwave absorbing agent, 15%~35% matrix resin, and the balance is dispersant, with the sum of the mass percentages of each component being 100%.

[0021] The method for preparing the microwave absorbing coating based on the metasurface includes the following steps:

[0022] Step 1: Roughen the surface of the substrate, clean it, and dry it in sequence.

[0023] Step 2: Apply the base coat coating to the substrate surface and cure it to form the base coat on the substrate surface;

[0024] Step 3: Apply the topcoat coating onto the base coat obtained in Step 2 and cure it to form the topcoat on the surface of the base coat.

[0025] Step 4: Use a high-precision engraving method to engrave the surface of the topcoat obtained in Step 3, so that the surface of the topcoat is a metasurface composed of periodically arranged polygonal resonant units with protrusions.

[0026] Preferably, the surface of the bottom coating prepared in step two is subjected to roughening treatment, cleaning treatment, and drying treatment in sequence.

[0027] Roughening the surface of the undercoat can increase the contact area between the topcoat and the undercoat, thereby increasing the interlayer adhesion.

[0028] Preferably, after the second step, a high-precision engraving method is used to engrave the surface of the bottom coating obtained in the second step, so that the surface of the bottom coating is a metasurface composed of periodically arranged polygonal resonant units with protrusions.

[0029] Metastructure design of the surface of the bottom coating can increase the bonding force between layers and form a metastructure interface of resonant units at the interface between the bottom coating and the top coating, thereby increasing the wave absorption effect.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) The absorbing coating based on metasurface provided by the present invention, through multi-layer design, enables each absorbing coating to compensate for each other's deficiencies. The top layer coating covers the bottom layer coating, which can effectively protect the bottom layer coating and prevent the external environment from causing adverse effects on the bottom layer coating, such as oxidation. At the same time, the bottom layer coating and the top layer coating cooperate with each other. Combined with the metasurface design of periodically arranged polygonal resonant units, the absorption frequency is broadened, so that the absorbing coating provided by the present invention has good full-band electromagnetic wave absorption performance.

[0032] (2) The microwave absorbing coating based on metasurface provided by the present invention, combined with the metasurface design, can not only broaden the microwave absorbing frequency, but also reduce the surface density of the coating, and reduce the weight by more than 65% compared with the traditional microwave absorbing coating.

[0033] (3) The microwave absorbing coating based on metasurface provided by the present invention enhances the environmental adaptability of the microwave absorbing coating through the protection of the underlying coating by the top layer coating and the metastructure design. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of the metasurface microwave absorbing coating formed by high-precision engraving according to the present invention. Detailed Implementation

[0035] The technical solution of the present invention will be further described and illustrated below through examples. All raw materials used in the examples are commercially available or prepared using conventional methods.

[0036] Example 1

[0037] A microwave absorbing coating based on a metasurface comprises a base coating and a top coating. The base coating has a thickness of 0.1 mm, and the top coating has a thickness of 1 mm. The base coating is composed of carbonyl iron microwave absorbing agent, polyurethane modified epoxy resin, and sodium methylene bis(naphthalene) sulfonate in a mass ratio of 80:15:5. The top coating is composed of carbon nanotube microwave absorbing agent, polyurethane modified epoxy resin, and sodium methylene bis(naphthalene) sulfonate in a mass ratio of 20:75:5. The surface of the top coating is engraved with a superstructure composed of periodically arranged raised rectangular resonant units. The elongated resonant units are rectangles with a length of 4 mm, a width of 1 mm, and a protrusion height of 1 mm. The gap width between adjacent polygonal resonant units is 0.8 mm.

[0038] The aforementioned metasurface-based microwave absorbing coating is prepared by the following method:

[0039] Step 1: Sand the substrate board with 120-grit sandpaper until there are obvious lines on the surface. Wipe the sanded substrate with gauze soaked in anhydrous ethanol until there are no impurities or stains on the surface of the cotton gauze. Let the substrate dry.

[0040] Step 2: Using a 1.0~2.0 mm nozzle spray gun, spray at a distance of 25~35 cm, ensuring the construction temperature is between 10~35℃ and the humidity is below 75%, spray the base coat consisting of 8 g carbonyl iron microwave absorber, 1.5 g polyurethane modified epoxy resin and 0.5 g sodium methylene bisnaphthalene sulfonate, transfer it into the curing equipment for complete curing, and form a base coat with a thickness of 0.1 mm on the substrate;

[0041] Step 3: Use 120-grit sandpaper to sand the base coating obtained in Step 2 until there are obvious textures on the surface. Wipe the sanded surface with gauze soaked in anhydrous ethanol until there are no impurities or stains on the cotton gauze surface. Let the substrate coated with the base coating dry.

[0042] Step 4: Using a 1.5~2.5 mm nozzle spray gun, spray at a distance of 25~35 cm, ensuring the construction temperature is between 10~35℃ and the humidity is below 75%. Spray a topcoat coating consisting of 20 g carbon nanotube absorbent, 75 g polyurethane modified epoxy resin, and 5 g sodium methylene bis(naphthalene) sulfonate onto the base coat obtained in Step 3. Transfer the coating to a curing device for complete curing, forming a topcoat with a thickness of 1 mm on the surface of the base coat obtained in Step 3.

[0043] Step 5: Use a CNC engraving machine to engrave the polygonal resonant unit into a rectangle. Set the length of the polygonal resonant unit to 4 mm, the width to 1 mm, the protrusion height to 1 mm, and the groove spacing to 0.8 mm. Engrave the surface of the topcoat obtained in Step 4 to make the surface of the topcoat a metasurface with periodically arranged rectangular resonant units with protrusions.

[0044] The reflectivity of the absorbing coating prepared in Example 1 was tested as follows: reflectivity R4GHz = -4.1 dB, R8GHz = -9.3 dB, R15GHz = -9.5 dB. The areal density of the absorbing coating prepared in Example 1 was 1.3 kg / m³. 2 .

[0045] Example 2

[0046] A microwave absorbing coating based on a metasurface comprises a base coating and a top coating. The thickness of the base coating is 0.5 mm, and the thickness of the top coating is 0.5 mm. The base coating is composed of carbonyl iron microwave absorbing agent, aliphatic flexible epoxy resin DER732, and sodium methylene bisnaphthalene sulfonate in a mass ratio of 60:35:5. The top coating is composed of carbon nanotube microwave absorbing agent, aliphatic flexible epoxy resin DER732, and sodium methylene bisnaphthalene sulfonate in a mass ratio of 2:93:5. The surface of the top coating is engraved with a superstructure composed of periodically arranged regular hexagonal resonant units. Each regular hexagonal resonant unit has a side length of 2 mm and a protrusion height of 0.5 mm. The gap width between adjacent polygonal resonant units is 0.2 mm.

[0047] The aforementioned metasurface-based microwave absorbing coating is prepared by the following method:

[0048] Step 1: Sand the substrate board with 120-grit sandpaper until there are obvious lines on the surface. Wipe the sanded substrate with gauze soaked in anhydrous ethanol until there are no impurities or stains on the surface of the cotton gauze. Let the substrate dry.

[0049] Step 2: Using a 1.0~2.0 mm nozzle spray gun, spray at a distance of 25~35 cm, ensuring the construction temperature is between 10~35℃ and the humidity is below 75%, spray a base coat consisting of 60 g carbonyl iron microwave absorber, 35 g aliphatic flexible epoxy resin DER732, and 5 g sodium methylene bisnaphthalene sulfonate. Transfer the coating to a curing device for complete curing, forming a base coat with a thickness of 0.5 mm on the substrate.

[0050] Step 3: Use a CNC engraving machine to engrave the polygonal resonant unit into a regular hexagon. Set the side length of the polygonal resonant unit to 2 mm, the protrusion height to 0.5 mm, and the groove spacing to 0.2 mm. Engrave the surface of the low-layer coating obtained in Step 2. After engraving, wipe the surface of the bottom layer coating with gauze soaked in anhydrous ethanol until there are no impurities or stains on the surface of the cotton gauze. Let the substrate coated with the bottom layer coating dry.

[0051] Step 4: Using a 1.5~2.5 mm nozzle spray gun, spray at a distance of 25~35 cm, ensuring the construction temperature is between 10~35℃ and the humidity is below 75%. Spray a topcoat consisting of 2 g carbon nanotube absorbent, 93 g aliphatic flexible epoxy resin DER732, and 5 g sodium methylene bisnaphthalene sulfonate onto the base coat obtained in Step 3. Transfer the coating to a curing device for complete curing, forming a topcoat with a thickness of 0.5 mm on the surface of the base coat obtained in Step 3.

[0052] Step 5: Use a CNC engraving machine to engrave the polygonal resonant unit into a regular hexagon. Set the side length of the polygonal resonant unit to 2 mm, the protrusion height to 0.5 mm, and the groove spacing to 0.2 mm. Engrave the surface of the topcoat obtained in Step 4 to make the surface of the topcoat a metasurface composed of periodically arranged regular hexagonal resonant units with protrusions.

[0053] The reflectivity of the absorbing coating prepared in Example 2 was tested as follows: R4GHz = -4.7 dB, R8GHz = -11.6 dB, R15GHz = -12.1 dB. The areal density of the absorbing coating prepared in Example 2 was 2.1 kg / m³. 2 .

[0054] Comparative Example 1

[0055] A microwave absorbing coating comprises a base layer and a top layer. The base layer has a thickness of 0.1 mm, and the top layer has a thickness of 1 mm. The base layer is composed of carbonyl iron microwave absorbing agent, polyurethane modified epoxy resin, and sodium methylene bisnaphthalene sulfonate in a mass ratio of 80:15:5. The top layer is composed of carbon nanotube absorber, polyurethane modified epoxy resin, and sodium methylene bisnaphthalene sulfonate in a mass ratio of 20:75:5.

[0056] The microwave absorbing coating described in this embodiment is prepared by the following method, with the steps as follows:

[0057] Step 1: Sand the substrate board with 120-grit sandpaper until there are obvious lines on the surface. Wipe the sanded substrate with gauze soaked in anhydrous ethanol until there are no impurities or stains on the surface of the cotton gauze. Let the substrate dry.

[0058] Step 2: Use a spray gun with a nozzle diameter of 1.0~2.0 mm, spray at a distance of 25~35 cm, ensure the construction temperature is between 10~35℃ and the humidity is below 75%, spray the base coat, and transfer it into the curing equipment for complete curing to obtain a base coating with a thickness of 0.1 mm on the substrate surface.

[0059] Step 3: Sand the cured base coating to a thickness of 0.1 mm. Wipe the sanded substrate with gauze soaked in anhydrous ethanol until the surface of the gauze is free of impurities and stains. Let the substrate dry.

[0060] Step 4: Use a spray gun with a nozzle diameter of 1.5~2.5 mm, spray at a distance of 25~35 cm, ensure the construction temperature is between 10~35℃ and the humidity is below 75%, spray the top coat on the base coat, and after spraying to the specified thickness, move it into the curing equipment for complete curing. After both the base coat and the top coat are cured, sand the top coat to 0.9 mm.

[0061] The reflectivity of the absorbing coating prepared in Comparative Example 1 was tested as follows: R4GHz = -2.8 dB, R8GHz = -6.7 dB, R15GHz = -5.4 dB. The areal density of the absorbing coating prepared in Comparative Example 1 was 1.8 kg / m³. 2 .

[0062] Comparative Example 2

[0063] A microwave absorbing coating is composed of carbonyl iron microwave absorbing agent, polyurethane modified epoxy resin and sodium methylene bisnaphthalene sulfonate in a mass ratio of 80:15:5, and the microwave absorbing coating has a thickness of 1.1 mm.

[0064] The microwave absorbing coating described in this embodiment is prepared by the following method, with the steps as follows:

[0065] Step 1: Sand the substrate board with 120-grit sandpaper until there are obvious lines on the surface. Wipe the sanded substrate with gauze soaked in anhydrous ethanol until there are no impurities or stains on the surface of the cotton gauze. Let the substrate dry.

[0066] Step 2: Use a spray gun with a nozzle diameter of 1.0~2.0 mm, spray at a distance of 25~35 cm, ensure the construction temperature is between 10~35℃ and the humidity is below 75%, spray the base coat, and transfer it into the curing equipment for complete curing to obtain a microwave absorbing coating with a thickness of 1.1 mm on the substrate surface.

[0067] The reflectivity of the absorbing coating prepared in Comparative Example 2 was tested as follows: R4GHz = -3.4 dB, R8GHz = -8.9 dB, R15GHz = -6.2 dB. The areal density of the absorbing coating prepared in Comparative Example 2 was 3.8 kg / m³. 2 .

[0068] For Examples 1 and 2, it can be seen that in Example 2, a superstructure composed of periodically arranged raised polygonal resonant units is also engraved on the surface of the bottom coating, which can also improve the absorption performance of the absorbing coating.

[0069] The only difference between Example 1 and Comparative Example 1 is that the surface of the absorbing coating prepared in Example 1 is engraved with a superstructure composed of periodically arranged raised rectangular resonant units, while the surface of the absorbing coating prepared in Comparative Example 1 is not engraved. A comparison between Example 1 and Comparative Example 2 shows that when the surface of the absorbing coating is not engraved into a superstructure, its absorption intensity of radar waves is significantly lower than that of the engraved absorbing coating. Furthermore, engraving a superstructure composed of periodically arranged raised rectangular resonant units on the surface of the absorbing coating not only improves its radar wave absorption capability across multiple frequency bands but also effectively reduces the areal density of the absorbing coating.

[0070] The only difference between the microwave absorbing coatings prepared in Example 1 and Comparative Example 2 is the composition of the coatings and the fact that the surface of the microwave absorbing coating prepared in Example 1 is engraved with a superstructure. It can be seen that the areal density of the microwave absorbing coating is 3.8 kg / m³. 2 It dropped to 1.3 kg / m 2 The areal density decreased by 65.8%. Without reducing the microwave absorption performance, the microwave absorbing coating provided by this invention for the metasurface can significantly reduce the areal density of traditional microwave absorbing coatings based on carbonyl iron absorbing agents.

[0071] It should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A metasurface-based wave-absorbing coating, characterized in that, It is composed of a bottom coating and a surface coating, the bottom coating is mainly composed of a base resin and a carbonyl iron wave-absorbing agent; the surface coating is mainly composed of a base resin and a carbon nanotube wave-absorbing agent; the surface of the surface coating is provided with a superstructure composed of periodically arranged convex polygonal resonant units; The length of the side of the polygonal resonant unit is 1-4 mm, the convex height is 0.1-1 mm, and the gap width between adjacent polygonal resonant units is 0.2-0.8 mm; The surface coating is mainly composed of the following raw materials: carbon nanotube wave-absorbing agent 2%-20%, base resin 75%-93%, and the balance is dispersant, and the sum of the mass percentages of the components is 100%. The bottom coating is mainly composed of the following raw materials: carbonyl iron wave-absorbing agent 60%-80%, base resin 15%-35%, and the balance is dispersant, and the sum of the mass percentages of the components is 100%. The thickness ratio of the bottom coating to the surface coating is 1-1:10; the thickness of the bottom coating is 0.1-1 mm; and the thickness of the surface coating is 0.1-1 mm.

2. The metasurface-based wave-absorbing coating of claim 1, wherein, The surface of the bottom coating is provided with a superstructure composed of periodically arranged convex polygonal resonant units.

3. The metasurface-based wave-absorbing coating of claim 1, wherein, The base resin includes an epoxy resin.

4. The metasurface-based wave-absorbing coating of claim 3, wherein, The epoxy resin includes a glycidyl ether type epoxy resin, a linear aliphatic type epoxy resin, a glycidyl ester type epoxy resin, a silicone modified epoxy resin, an acrylic modified epoxy resin, or a polyurethane modified epoxy resin.

5. The metasurface-based wave-absorbing coating of claim 1, wherein, It comprises the following steps: Step one, sequentially roughening, cleaning, and drying the surface of the substrate; Step two, coating the coating of the bottom coating on the surface of the substrate and curing to form the bottom coating on the surface of the substrate; Step three: coating the coating of the surface coating on the bottom coating prepared in step two and curing to form the surface coating on the surface of the bottom coating; Step four: using high-precision engraving method to engrave the surface of the surface coating prepared in step three, so that the surface of the surface coating is a superstructure surface composed of periodically arranged convex polygonal resonant units.

6. A method of preparing the metasurface-based wave-absorbing coating according to claim 5, characterized in that, Before step three, sequentially roughen, clean, and dry the surface of the bottom coating prepared in step two.

7. The metasurface-based wave-absorbing coating of claim 5, wherein, Before step three, use high-precision engraving method to engrave the surface of the bottom coating prepared in step two, so that the surface of the bottom coating is a superstructure surface composed of periodically arranged convex polygonal resonant units.

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