Sharkskin structure radar wave absorbing metamaterial and preparation method thereof

Abstract

This invention belongs to the field of flexible radar-absorbing metamaterials, specifically relating to a shark-skin-inspired radar-absorbing metamaterial and its fabrication method. The material structure comprises an upper resistive film pattern layer, a middle dielectric layer, and a bottom metal layer. The resistive film pattern layer is deposited on the dielectric layer using magnetron sputtering technology. The dielectric layer is tightly bonded to the metal layer using OCA optically transparent adhesive. The pattern of the resistive film pattern layer is a shark-skin-inspired structure, specifically comprising several shark-skin-inspired structural units. Each structural unit combines four cuboid shark-skin-inspired scutes covered by the resistive film with several groove structures without resistive film coverage. This invention, through optimized structural parameter design, achieves broadband radar absorption and stealth capabilities, overcoming the problems of narrow bandwidth and high density inherent in traditional radar-absorbing materials. It also possesses advantages such as small thickness, low cost, easy control, simple manufacturing process, and high temperature resistance, representing a significant breakthrough in terms of thinness, lightness, wide bandwidth, and strength.

Description

Technical Field

[0001] This invention belongs to the field of flexible absorbing metamaterials, specifically relating to a sharkskin-inspired radar absorbing metamaterial and its preparation method. Background Technology

[0002] With the development of modern science and technology, the impact of electromagnetic radiation on people's lives is increasing. Flights are delayed due to electromagnetic interference, mobile phones often interfere with the normal operation of various electronic diagnostic instruments, and indoor household appliances, as well as outdoor power plants, transmission towers, and large transformers, all radiate electromagnetic pollution into our living environment. Electromagnetic radiation causes direct and indirect harm to the human body through thermal effects, non-thermal effects, and cumulative effects. Absorbing materials can mitigate electromagnetic pollution and resist and weaken electromagnetic radiation. Surrounding electromagnetic wave sources with absorbing materials or placing them around the human body can effectively absorb harmful electromagnetic radiation and protect personal safety.

[0003] Radar stealth technology achieves stealth by reducing the radar cross-section (RCS) of a target, and is considered a necessary countermeasure to reduce radar cross-section. Radar absorbing materials can be applied to the surfaces of targets with complex shapes, possessing characteristics such as high load-bearing capacity and lightweight design, making them the most common and effective stealth method currently available. Traditional radar absorbing materials typically consist of a matrix material and an absorber, and have significant application value in electromagnetic wave absorption, shielding, and radar stealth. However, due to limitations in electromagnetic parameters and dispersion characteristics, traditional radar absorbing materials generally suffer from bottleneck problems such as high density, narrow absorption bandwidth, poor impedance matching, thick coating, and poor high-temperature resistance. Simply relying on traditional material doping or compositing methods cannot overcome these bottleneck problems.

[0004] Existing microwave absorbing materials currently suffer from problems such as narrow absorption bandwidth, poor heat resistance, large thickness, or poor impedance matching. For example, a publicly disclosed electromagnetic metamaterial, although thin at only 3 mm and capable of narrowband absorption at 6 frequency points, can only achieve a 64% absorption rate at 2.5 GHz, failing to meet the requirements of "wide" and "strong" absorption of metamaterials. Summary of the Invention

[0005] To address the problems of existing technologies, this invention provides a sharkskin-like radar absorbing metamaterial and its preparation method. This material is a flexible radar absorbing metamaterial that can be applied to military aircraft, enabling radar stealth capabilities. It also possesses advantages such as small thickness, wide absorption bandwidth, low cost, easy control, simple manufacturing process, and high temperature resistance, achieving a "thin," "light," "wide," and "strong" radar stealth material.

[0006] The technical solution of this invention is:

[0007] A sharkskin-inspired radar-absorbing metamaterial comprises three layers: an upper resistive film pattern layer, a middle dielectric layer, and a bottom metal layer. The resistive film pattern layer is deposited on the dielectric layer using magnetron sputtering technology. The dielectric layer is tightly bonded to the metal layer using OCA optically transparent adhesive. The pattern of the resistive film pattern layer is a sharkskin-inspired structure, specifically including several sharkskin-inspired structural units. Each structural unit comprises four cuboid sharkskin-inspired scutes covered by resistive film combined with several groove structures without resistive film coverage.

[0008] Furthermore, in the aforementioned sharkskin-inspired radar absorbing metamaterial, the period of the sharkskin-inspired structural unit in the resistive film pattern layer is denoted as p, with a size range of 4.5mm to 36mm; the width of the four cuboid sharkskin-inspired scutes within the structural unit is denoted as a, with a size range of 0.5mm to 4mm; the lengths are denoted as c1, with a size range of 1.4mm to 11.2mm; c2, with a size range of 2mm to 16mm; c3, with a size range of 2.5mm to 20mm; and c4, with a size range of 3mm to 24mm; the width of the groove structure is denoted as b, with a size range of 0.25mm to 2mm.

[0009] Furthermore, in the aforementioned sharkskin-inspired radar absorbing metamaterial, the resistive film pattern layer is formed by magnetron sputtering technology, and the material is a metal-nonmetal nanoparticle composite film, including but not limited to Al-SiO2, Al-Al2O3, Ag-SiO2, Ag-Al2O3, Au-SiO2, Au-Al2O3, W-SiO2, W-Al2O3, Mo-SiO2, Mo-Al2O3, Ti-SiO2, or Ti-Al2O3.

[0010] Furthermore, in the aforementioned sharkskin-like radar absorbing metamaterial, the dielectric layer is composed of a non-metallic medium, including but not limited to polyimide, SrTiO3, polyester, ZrO2, TiO2, SiO2, or Al2O3. The thickness of the dielectric layer is denoted as h, and its size ranges from 2.4 mm to 6.4 mm.

[0011] Furthermore, in the aforementioned sharkskin-like radar absorbing metamaterial, the metal layer is composed of metals, including but not limited to gold, silver, aluminum, tungsten, molybdenum, aluminum-nickel alloy, or stainless steel, with a thickness denoted as l and ranging from 0.02 mm to 0.05 mm.

[0012] Furthermore, in the aforementioned sharkskin-like radar absorbing metamaterial, the thickness range of the sharkskin-like radar absorbing metamaterial is 2.42 mm to 6.45 mm.

[0013] A method for preparing the above-mentioned sharkskin-inspired radar absorbing metamaterial, the method comprising the following steps:

[0014] Step 1: Prepare a photomask using laser lithography.

[0015] Step 2: The upper resistive film pattern layer is deposited on the intermediate dielectric layer using magnetron sputtering technology. After the deposition is completed, the mask is removed, and the shape of the upper resistive film pattern layer is obtained on the intermediate dielectric layer, achieving a tight bond between the two.

[0016] Step 3: Apply copper-clad film and bond it tightly to the underlying metal layer using OCA optically transparent adhesive.

[0017] Furthermore, in the above-mentioned method for preparing the sharkskin-like radar absorbing metamaterial, before preparing the pattern of the upper resistive film pattern layer, big data and artificial intelligence technologies are used to optimize the structural parameters p, h, a, b, l, c1, c2, c3, and c4 to achieve radar absorption functions in different bands.

[0018] Furthermore, the above-mentioned method for preparing the sharkskin-like radar absorbing metamaterial, step 2, employs a magnetron sputtering technique that consists of four stages: preparation, vacuuming, coating, and completion. The steps are as follows:

[0019] (1) Preparation stage: First, clean the cavity to avoid the influence of substances left in the cavity from the previous experiment on this experiment. Then load the sample and place the pre-treated substrate on the sample stage.

[0020] (2) Vacuuming stage: First, start the mechanical pump to pump the vacuum in the cavity to below 10Pa, and then start the molecular pump to pump the vacuum to a high vacuum of 3.0*10Pa.

[0021] (3) Coating stage: High-purity fluorine gas is introduced into the magnetron sputtering chamber. The flow control valve is adjusted to adjust the working gas pressure to 0.3 Pa. The sputtering power supply is turned on, and the target is sputtered and cleaned for 5 minutes under the condition of pure fluorine gas. The power supply is adjusted to the predetermined parameters, the sample stage is rotated, the baffle between the target and the sample stage is opened, and the timing of coating is started.

[0022] (4) End stage: Turn off the sample stage baffle, power supply and molecular pump. After the molecular pump stops, vent to the atmosphere and open the chamber cover to take out the sample.

[0023] Advantages and beneficial effects of the present invention:

[0024] This invention, a sharkskin-inspired radar-absorbing metamaterial, achieves broadband radar absorption and stealth capabilities through optimized structural parameter design. It overcomes the problems of narrow bandwidth and high density of traditional radar-absorbing materials, while also possessing advantages such as small thickness, low cost, easy control, simple manufacturing process, and high temperature resistance. It represents a significant breakthrough in terms of being thin, light, wide, and strong, and has important prospects for both military and civilian applications.

[0025] Existing microwave absorbing materials suffer from problems such as narrow absorption bandwidth, poor heat resistance, large thickness, or poor impedance matching. For example, a publicly disclosed electromagnetic metamaterial, although thin at only 3 mm and capable of narrowband absorption at 6 frequency points, only achieves a 64% absorption rate at 2.5 GHz, failing to meet the requirements of "wide" and "strong" absorption for metamaterials. Compared to this, the present invention enhances the absorption bandwidth and thickness, achieving an absorption bandwidth exceeding 9 GHz and a thickness of less than 3 mm.

[0026] A novel broadband radar absorbing material composed of carbonyl iron powder and conductive polyaniline (PAn) has an absorption of 5 dB in the 6–18 GHz range. Compared with this material, the present invention has superior performance in terms of absorption bandwidth, high temperature resistance, and thickness.

[0027] Compared to CN113285234A, a high-efficiency radar-absorbing metasurface material in the 8-14 GHz band, this invention, while achieving broadband absorption, maintains unchanged absorption performance before and after heat treatment at 1000K for 2 hours, making it well-suited for radar stealth applications in military weapons. Another multi-layered, high-temperature radar-absorbing material, compared to this invention, is thinner, has a wider bandwidth, is simpler to prepare, and has lower cost. It also maintains unchanged performance at high temperatures, showing better application prospects and meeting the requirements of "thin," "light," "wide bandwidth," and "strong" for radar-absorbing metamaterials.

[0028] Compared to CN110183230A, a multi-layered high-temperature radar absorbing material is currently produced by mixing fine carbon cluster powder prepared under different temperature conditions with epoxy resin in a certain proportion and then curing it in a mold. This material has a thickness of 1.85 mm and a minimum reflectivity of -30 dB in the 8–12.4 GHz frequency range, with an absorption bandwidth of nearly 60% where the reflectivity is less than -10 dB. This invention exhibits superior radar absorption performance, achieving an absorption rate greater than 80% in the 9.76–19.56 GHz frequency band and strong absorption with an absorption rate greater than 90% in a wide frequency range of 11.36–17.92 GHz. The radar absorption performance of this metamaterial remains unchanged after heat treatment at 1000 K for 2 hours, making it suitable for radar stealth applications in military weapons and enabling its better application in military applications. The magnetic multilayer microwave absorbing agent Fe / SiO2 prepared by magnetron sputtering has a reflectivity of less than -10dB, a bandwidth of 6.64GHz, and a thickness of 1.47mm. Compared with this, the present invention has excellent properties such as wide bandwidth and high temperature resistance, and can be better applied to military weapons.

[0029] The microwave absorption performance of cement-based porous composite materials prepared by filling ordinary silicate cement with foamed polystyrene was studied. The results showed that when the volume fraction of polystyrene was 60% and the thickness was 20 mm, the reflectivity was the lowest in the range of 8 to 18 GHz with a bandwidth of less than -10 dB and up to 6 GHz. Compared with this, the present invention has a thinner thickness and a wider microwave absorption bandwidth, realizing broadband absorption and ultra-thin thickness.

[0030] Meanwhile, as an artificial material with adjustable absorption performance, absorbing metamaterials can achieve perfect absorption of electromagnetic waves in the mid-to-high frequency band, but they face challenges in achieving wide incident angles and broadband absorption. This invention, however, utilizes big data and artificial intelligence technologies to continuously optimize the broadband absorption characteristics of a sharkskin-inspired periodic structure. This expands the absorption bandwidth of the radar absorbing metamaterial in the microwave band. Compared to previous absorbing materials, the sharkskin-inspired structure absorbing metamaterial exhibits superior absorption performance, a simpler fabrication process, is thinner and lighter, and possesses high-temperature resistance. Attached Figure Description

[0031] Figure 1 This is a scan of the shark's skin.

[0032] Figure 2 This is a schematic diagram of the sharkskin-like structure of the resistive film pattern layer of the present invention;

[0033] Figure 3 This is a three-dimensional image of the sharkskin-inspired radar-absorbing metamaterial of this invention.

[0034] Figure 4 This is a partial top view of the sharkskin-like radar absorbing metamaterial of the present invention;

[0035] Figure 5 This is a physical image of the sharkskin-inspired radar-absorbing metamaterial of this invention.

[0036] Figure 6 The absorption rate curve of the sharkskin-inspired radar absorbing metamaterial of this invention is shown.

[0037] Figure 7 The absorption rate curves of the metamaterial absorbing models with different resistive film resistance values ​​in the embodiments are shown.

[0038] Figure 8 The absorption rate curves are shown for metamaterial absorbing models with different dielectric layer thicknesses in the embodiments. Detailed Implementation

[0039] The following detailed description of specific embodiments of the present invention, in conjunction with the accompanying drawings and specific examples, is intended to illustrate the present invention but should not be construed as limiting its scope.

[0040] Example

[0041] like Figure 1 As shown, shark skin is composed of numerous uneven, tiny dentate scales and grooves. These scales and grooves on the shark skin surface form cavities of a certain volume, connected to the outside through small pores between the scales. This structure has a significant sound-absorbing effect: when external sound waves enter the cavity through the pores, they are reflected multiple times within the cavity, converting sound energy into heat energy to achieve sound absorption. Inspired by this, this invention designs a shark skin-like structure based on the dentate scale and groove structure of shark skin. Figure 2 As shown, this sharkskin-like structure achieves radar stealth. The 3D and top views of the designed sharkskin-like radar-absorbing metamaterial are shown below. Figure 3 and Figure 4 As shown, the metamaterial structure consists of an upper resistive film pattern layer, an intermediate dielectric layer, and a bottom metal layer.

[0042] Radar absorbing materials for military weapon stealth applications need to possess functions such as broadband absorption, high temperature resistance, lightweight, and flexibility. Based on comprehensive stealth requirements, a sharkskin-like radar absorbing metamaterial has been designed and fabricated. Its physical form is as follows... Figure 5 As shown. Figure 3 As shown, the metamaterial structure consists of an upper resistive film pattern layer, an intermediate dielectric layer, and a bottom metal layer. The upper resistive film pattern layer has a sharkskin-like structure, specifically comprising several sharkskin-like structural units. Each structural unit contains four cuboid sharkskin-like scutes covered by resistive film combined with several groove structures without resistive film coverage.

[0043] The upper resistive film pattern layer is composed of a metal-nonmetal nanoparticle composite film Al-SiO2, with a resistive film thickness of 200Ω; the middle dielectric layer is composed of a nonmetallic flexible SiO2 dielectric; and the bottom metal layer is composed of metallic Al.

[0044] The method for preparing this metamaterial is as follows:

[0045] Step 1: Prepare a photomask using laser lithography.

[0046] Step 2: The upper resistive film pattern layer is deposited on the intermediate dielectric layer using magnetron sputtering technology. After the deposition is completed, the mask is removed, and the shape of the upper resistive film pattern layer is obtained on the intermediate dielectric layer, achieving a tight bond between the two.

[0047] The magnetron sputtering technology used consists of four stages: preparation, vacuuming, coating, and finishing. The steps are as follows:

[0048] (1) Preparation stage: First, clean the cavity to avoid the influence of substances left in the cavity from the previous experiment on this experiment. Then load the sample and place the pre-treated substrate on the sample stage.

[0049] (2) Vacuuming stage: First, start the mechanical pump to pump the vacuum in the cavity to below 10Pa, and then start the molecular pump to pump the vacuum to a high vacuum of 3.0*10Pa.

[0050] (3) Coating stage: High-purity fluorine gas is introduced into the magnetron sputtering chamber. The flow control valve is adjusted to adjust the working gas pressure to 0.3 Pa. The sputtering power supply is turned on, and the target is sputtered and cleaned for 5 minutes under the condition of pure fluorine gas. The power supply is adjusted to the predetermined parameters, the sample stage is rotated, the baffle between the target and the sample stage is opened, and the timing of coating is started.

[0051] (4) End stage: Turn off the sample stage baffle, power supply and molecular pump. After the molecular pump stops, vent to the atmosphere and open the chamber cover to take out the sample.

[0052] Step 3: Apply copper-clad film and bond it tightly to the underlying metal layer using OCA optically transparent adhesive.

[0053] Before fabricating the pattern of the upper resistive film pattern layer, the structural parameters p, h, a, b, l, c1, c2, c3, and c4 are optimized using big data and artificial intelligence technologies to achieve radar absorption functions in different bands.

[0054] The metamaterial structure has a unit period of p = 4.5 mm. Each unit contains four cuboid-shaped, shield-like structures with a width of a = 0.5 mm and lengths of c1 = 1.4 mm, c2 = 2 mm, c3 = 2.5 mm, and c4 = 3 mm. The trench structure has a width of b = 0.25 mm. The dielectric layer has a thickness of h = 2.4 mm, and the metal substrate has a thickness of l = 0.5 mm. The absorptivity curve of this microwave-absorbing metamaterial is shown below. Figure 6 As shown, its absorption rate is greater than 80% in the 9.76-19.56GHz frequency band and can achieve strong absorption with an absorption rate of greater than 90% in the wide frequency range of 11.36-17.92GHz. The absorption performance of this absorbing metamaterial remains unchanged before and after heat treatment at 1000K for 2 hours, making it suitable for radar stealth in military weapons.

[0055] The upper resistive film pattern layer is designed based on the shark skin structure of the scales and grooves. The structural parameters p, h, a, b, l, c1, c2, c3, and c4 of the shark skin radar absorbing metamaterial are optimized using big data and artificial intelligence technology to achieve radar absorption function in different bands.

[0056] The optimization process is as follows:

[0057] Through a series of data analyses and optimizations, it was found that performance is better when the cell period size is at the millimeter level.

[0058] 1. Analysis of the influence of sheet resistance on absorption performance

[0059] Research has revealed that the resistance of the resistive film also has a certain influence on the wave absorption of the metamaterial absorption model, as shown in the following results. Figure 7 As shown:

[0060] When the periodic size of the resistive film pattern layer is 36 mm, analysis using CST Microwave Studio 2021 electromagnetic simulation software revealed the following:

[0061] When the resistance of the resistive film is less than 200Ω, the bandwidth becomes wider and the performance becomes better as the resistance of the resistive film increases.

[0062] When the resistance of the resistive film is greater than 200Ω, the bandwidth becomes narrower and the performance becomes worse as the resistance of the resistive film increases.

[0063] The selected resistive film is 200Ω.

[0064] 2. Analysis of the Influence of Dielectric Layer Thickness on Wave Absorption Performance

[0065] Using the controlled variable method, the sheet resistance was selected as R = 200Ω, the period as P = 36mm, and the dielectric layer thickness as h was adjusted. The optimization results are as follows: Figure 8 As shown:

[0066] Extensive simulation data revealed that a thicker dielectric layer enables ultra-wideband absorption in the mid-to-high frequency range, while a thinner dielectric layer enables broadband absorption in the mid-to-low frequency range. Considering practical application requirements, a dielectric layer thickness of 2.4 mm was selected, which enables broadband absorption in the mid-to-low frequency band.

Claims

1. A sharkskin-inspired radar-absorbing metamaterial, characterized in that, The material structure comprises three layers: an upper resistive film pattern layer, a middle dielectric layer, and a bottom metal layer. The resistive film pattern layer is deposited on the dielectric layer using magnetron sputtering technology. The dielectric layer is tightly bonded to the metal layer using OCA optically transparent adhesive. The resistive film pattern layer features a sharkskin-like structure, specifically including several sharkskin-like structural units. Each structural unit comprises four cuboid sharkskin-like scutes covered by resistive film and several groove structures without resistive film coverage. The period of the sharkskin-like structural unit of the resistive film pattern layer is denoted as p, with a size range of 4.5 mm to 36 mm; the width of the four cuboid sharkskin-like scutes within the structural unit is denoted as a, with a size range of 0.5 mm to 4 mm; the lengths are denoted as c1, with a size range of 1.4 mm to 11.2 mm, c2, with a size range of 2 mm to 16 mm, c3, with a size range of 2.5 mm to 20 mm, and c4, with a size range of 3 mm to 24 mm; the width of the groove structure is denoted as b, with a size range of 0.25 mm to 2 mm. The resistive film pattern layer material is a metal-nonmetal nanoparticle composite film, including but not limited to Al-SiO2, Al-Al2O3, Ag-SiO2, Ag-Al2O3, Au-SiO2, Au-Al2O3, W-SiO2, W-Al2O3, Mo-SiO2, Mo-Al2O3, Ti-SiO2, or Ti-Al2O3; The absorption metamaterial exhibits an absorption rate greater than 80% in the frequency range of 9.76–19.56 GHz and achieves strong absorption with an absorption rate greater than 90% in a wide frequency range of 11.36–17.92 GHz. The absorption performance of the metamaterial remains unchanged after heat treatment at 1000 K for 2 h.

2. The sharkskin-like radar absorbing metamaterial according to claim 1, characterized in that, The dielectric layer is composed of a non-metallic dielectric, including but not limited to polyimide, SrTiO3, polyester, ZrO2, TiO2, SiO2 or Al2O3. The thickness of the dielectric layer is denoted as h, and the size range is 2.4 mm to 6.4 mm.

3. The sharkskin-like radar absorbing metamaterial according to claim 1, characterized in that, The metal layer is made of metal, including but not limited to gold, silver, aluminum, tungsten, molybdenum, aluminum-nickel alloy or stainless steel, and its thickness is denoted as l, with a size range of 0.02 mm to 0.05 mm.

4. The sharkskin-like radar absorbing metamaterial according to claim 1, characterized in that, The thickness range of the sharkskin-like radar absorbing metamaterial is 2.42 mm to 6.45 mm.

5. A method for preparing the sharkskin-like radar absorbing metamaterial according to claim 1, characterized in that, The method includes the following steps: Step 1: Prepare a photomask using laser lithography. Step 2: The upper resistive film pattern layer is deposited on the intermediate dielectric layer using magnetron sputtering technology. After the deposition is completed, the mask is removed, and the shape of the upper resistive film pattern layer is obtained on the intermediate dielectric layer, achieving a tight bond between the two. Step 3: Apply copper-clad film and bond it tightly to the underlying metal layer using OCA optically transparent adhesive.

6. The method for preparing the sharkskin-like radar absorbing metamaterial according to claim 5, characterized in that, Before fabricating the pattern of the upper resistive film pattern layer, the structural parameters p, h, a, b, l, c1, c2, c3, and c4 are optimized using big data and artificial intelligence technologies to achieve radar absorption functions in different bands.

7. The method for preparing the sharkskin-like radar absorbing metamaterial according to claim 5, characterized in that, Step 2 utilizes magnetron sputtering technology, which consists of four stages: preparation, vacuuming, coating, and completion. The steps are as follows: (1) Preparation stage: First, clean the cavity to avoid the influence of substances left in the cavity from the previous experiment on this experiment. Then load the sample and place the pre-treated substrate on the sample stage. (2) Vacuuming stage: First, start the mechanical pump to pump the vacuum in the cavity to below 10Pa, and then start the molecular pump to pump the vacuum to a high vacuum of 3.0*10Pa; (3) Coating stage: High-purity fluorine gas is introduced into the magnetron sputtering cavity. The flow control valve is adjusted to adjust the working gas pressure to 0.3 Pa. The sputtering power supply is turned on and the target is sputtered and cleaned for 5 min under the condition of pure fluorine gas. The power supply is adjusted to the predetermined parameters, the sample stage is rotated, the baffle between the target and the sample stage is opened, and the timing of coating is started. (4) End stage: Turn off the sample stage baffle, power supply and molecular pump. After the molecular pump stops, vent to the atmosphere and open the chamber cover to take out the sample.

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