Flexible sheet of broadband wave-absorbing metamaterial based on carbon-based materials and preparation method thereof

Abstract

The present invention provides a flexible sheet of broadband wave-absorbing metamaterial based on carbon-based materials. The sheet comprises a reflective layer and a dielectric layer embedded with periodically arranged structural units. The dielectric layer is arranged above the reflective layer. The preparation of the sheet comprises the following steps: the dielectric layer is arranged according to the size of the periodic resonant structural unit, and every other unit cell is arranged. P The size of the double-layer concentric cylindrical hole is mechanically punched; the small hole side of the medium plate with the hole is cleaned with anhydrous ethanol, and the reflective layer is applied; the graphene or carbon nanotubes are mixed with the adhesive to form a carbon composite for use; the graphene or carbon nanotubes are filled into the periodically arranged holes in step 1 with a scraper; the carbon composite is dried naturally until it is completely dry. The flexible sheet of this patent achieves a wide-band wave absorption effect in the range of 2 to 18 GHz, has a simple manufacturing process, is easy to use, can be applied to the object to be measured, and effectively reduces the characteristic signal of the radar wave of the target object.

Description

Technical Field

[0001] The present invention relates to the field of special functional materials, and in particular to an artificial electromagnetic absorbing material, which has the characteristics of light weight, flexibility, thin layer, and wide-band absorbing. The material can be applied to the outer surface of equipment to achieve electromagnetic compatibility, or applied to the outer surface of weapons and equipment to achieve radar stealth effect. The present invention particularly relates to a flexible sheet of a wide-band absorbing metamaterial based on a carbon-based material and a preparation method thereof. Background Art

[0002] Metamaterials are a new type of artificial material that has been vigorously developed at home and abroad in recent years. Through artificial design, they can achieve extraordinary physical properties that are not available in nature, and also provide an unprecedented new idea for the development of absorbing materials. Electromagnetic absorbing metamaterials are artificial electromagnetic materials that can absorb electromagnetic waves at a sub-wavelength scale and are composed of periodically arranged structural units. Since NILandy studied and prepared perfect absorbing metamaterials in 2008, electromagnetic absorbing metamaterials have been widely studied and greatly developed.

[0003] In 2013, Dalian University of Technology disclosed a tunable artificial electromagnetic metamaterial, in which topological materials and graphene materials are introduced into the electromagnetic absorbing metamaterial to change the resonance frequency corresponding to the absorption peak, thereby making the frequency band of its absorption spectrum tunable. The absorbing artificial electromagnetic metamaterial is a multilayer structure, with a metal layer, a dielectric layer, and a metal layer grown on the substrate material, a periodic resonant unit array made on the top metal layer, and finally a topological material layer or a graphene material layer plated on the surface of the periodic resonant unit array.

[0004] In 2017, South Korea disclosed an ultra-wideband absorbing metamaterial. The metamaterial absorber of the invention includes: a first substrate layer, which includes a first conductor pattern, and on multiple upper surfaces of the first conductor pattern, hexagonal structural units symmetrical with respect to the incident direction of the radio wave are arranged. The electromagnetic wave first enters the first substrate; the second substrate layer is arranged below the first substrate layer, which includes a second conductor pattern, and the second conductor pattern has a plurality of hexagonal structural units symmetrically arranged in a shape corresponding to the first conductor pattern; an air layer is formed between the first substrate layer and the second substrate layer.

[0005] In 2017, the Air Force Engineering University disclosed an integrated wave-absorbing and wave-transmitting metamaterial. The metamaterial structural unit includes a first prism and a second prism. The first prism and the second prism are both composed of multiple first dielectric layers and multiple first metal layers alternately stacked in a direction perpendicular to the frequency selective surface unit; the frequency selective surface unit includes a second dielectric layer and a second metal layer on the second dielectric layer, and the middle metal area of ​​each edge of the second metal layer is etched away to form a groove.

[0006] Another patent published by South Korea in 2018 announced a metamaterial perfect absorber with a three-layer structure. The three-layer structure is as follows: the bottom layer is the substrate, which is a reflective layer; the middle layer is an insulating layer; and above the insulating layer are two periodically arranged nanostructures, one of which is electrically connected to each other, and the second is a nanostructure that is separated from each other and electrically insulated; the two nanostructures contain the same material.

[0007] A paper published in 2018 used a mixture of conductive carbon black and polyethylene as a coating. By adjusting the conductive carbon black hole content and coating thickness to control the sheet resistance, a multilayer periodic sheet structure was designed that can achieve broadband absorbing performance in the range of 2.35-18GHz.

[0008] In 2019, Shenzhen Guangqi announced an absorber material, which includes a three-layer structure. The bottom layer is a reflective layer, the middle layer is an absorbing layer, and the top layer is a plurality of metamaterial unit array layers. Each metamaterial unit array layer is divided into a plurality of identical metamaterial units. This material has excellent wide-band absorbing effect and also achieves good wide-angle absorption effect.

[0009] In general, there are few reports in the currently published patents and articles on broadband absorbing metamaterial flexible sheets made by embedding carbon-based materials as periodic structural units. Summary of the invention

[0010] To solve the above problems, the present invention provides a broadband absorbing metamaterial flexible sheet based on carbon-based materials and a preparation method thereof. The high dielectric loss characteristics and mid-frequency dispersion characteristics of graphene or carbon nanotubes are utilized as periodic structural units, and low-loss flexible films are used as dielectric materials to design a broadband absorbing metamaterial flexible sheet embedded with a carbon-based material composite. The material achieves a broadband absorbing effect in the range of 2 to 18 GHz through a variety of mixing mechanisms. The material has a simple manufacturing process and is easy to use. It can be applied to the object to be measured, effectively reducing the characteristic signal of the target object's radar wave.

[0011] The technical solution adopted by the present invention to solve the above technical problems is: a flexible sheet of broadband absorbing metamaterial based on carbon-based materials, the sheet comprising a reflective layer and a dielectric layer embedded with periodically arranged structural units, and the dielectric layer is arranged above the reflective layer.

[0012] Furthermore, the periodically arranged structural units are prepared from a mixture of graphene or carbon nanotubes and an adhesive.

[0013] Furthermore, the weight ratio of graphene or carbon nanotubes to the adhesive is 5-20%.

[0014] Furthermore, the adhesive is any one of an epoxy resin system, a polyurethane resin system or a fluorocarbon resin system having a low dielectric constant.

[0015] Furthermore, the periodic structural units are uniformly arranged and embedded in the dielectric layer. The periodic structural units are double-layer concentric cylindrical structures. The size of each part of the periodic resonator is marked: the periodic size of the unit cell is marked as P ; The diameter and height of the upper cylinder are marked as y and x , the diameter and height of the lower cylinder are marked as w and t .

[0016] Furthermore, the unit cell periodicity P The diameter of the upper cylinder is y The diameter of the lower cylinder w relation: P > y > w .

[0017] Furthermore, the dielectric layer is a flexible low-loss dielectric material, such as polyester film, polycarbonate, polyimide or any other flexible film material, and the thickness of the dielectric plate is h = x + t .

[0018] Furthermore, the reflective layer may be a metal material such as steel, iron, copper, silver, or aluminum, or may be a carbon fiber material having total reflective capability.

[0019] The method for preparing a flexible sheet of a broadband wave-absorbing metamaterial based on a carbon-based material comprises the following steps:

[0020] Step 1: Place the dielectric layer according to the unit size of the periodic resonance structure, every other unit cell P The size of the machine is to make a double-layer concentric cylindrical hole. The diameter and height of the lower cylindrical hole are w and t , the diameter and height of the upper cylindrical hole are y and x ;

[0021] Step 2: Clean the side of the medium plate with small holes with anhydrous ethanol and apply the reflective layer;

[0022] Step 3: Evenly stir the graphene or carbon nanotubes and the adhesive to form a carbon composite for later use;

[0023] Step 4: Use a scraper to fill it into the periodically arranged holes in step 1, and scrape off the excess carbon-based composite with the scraper;

[0024] Step 5: Place the sample horizontally and let it dry naturally until the carbon composite is completely dry.

[0025] The beneficial effects of the present invention are as follows: the broadband absorbing metamaterial flexible patch based on carbon-based materials of the present invention has thin layer, flexibility, broadband high absorbing performance, simple manufacturing process, easy use, can be applied to the outer surface of electronic equipment, effectively reduce the electromagnetic radiation of the equipment, and achieve electromagnetic compatibility between devices; it can also be applied to the outer surfaces of aircraft, ships, military vehicles and facilities, etc., effectively reduce their radar scattering cross-section, achieve radar stealth effect, and has good military significance and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the SEM image of the microscopic morphology of graphene;

[0027] Figure 2 This is the TEM image of the microscopic morphology of graphene;

[0028] Figure 3 Schematic diagram of the complex dielectric constant of graphene composites containing different proportions (weight ratio) of graphene;

[0029] Figure 4 The overall construction of a broadband absorbing metamaterial flexible patch based on a double-layer structure of graphene composite materials;

[0030] Figure 5 Single unit cell construction of broadband absorbing metamaterial flexible patch based on double-layer structure of graphene composite material;

[0031] Figure 6 It is a side view and dimension identification diagram of a single unit cell of the present invention;

[0032] FIG7 is a photo of a polyester board with double-layer concentric cylindrical holes dug out of the present invention;

[0033] FIG8 is a photograph of a sample of the flexible broadband absorbing metamaterial of the present invention;

[0034] FIG9 is a photograph of a sample of the flexible broadband absorbing metamaterial of the present invention;

[0035] Figure 10 Comparison of the measured and simulated flexible broadband absorbing metamaterial sample. DETAILED DESCRIPTION

[0036] The embodiments of the present invention are described in detail in conjunction with the accompanying drawings. This embodiment is based on the technical solution of the present invention and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0037] According to the attached drawings, a flexible sheet of broadband absorbing metamaterial based on carbon-based materials includes a reflective layer and a dielectric layer embedded with periodically arranged structural units, the dielectric layer is arranged above the reflective layer, and the periodically arranged structural units are prepared from a mixture of graphene or carbon nanotubes and an adhesive.

[0038] In order to broaden the absorbing band of the absorbing metamaterial, the upper embedded periodic structural unit is made of a mixture of graphene or carbon nanotubes with high dielectric loss and dispersion characteristics in the microwave band and an adhesive. Generally, graphene or carbon nanotubes with large dielectric loss are used, and the filling weight ratio is generally within 10~20%, and mixed with the adhesive to form a composite. The weight ratio of graphene or carbon nanotubes to the adhesive is 5~20%. Figure 1 and Figure 2 This is the microscopic morphology of graphene powder provided by Xiamen Kaina Company. Figure 1 This is a schematic diagram of the structure of graphene powder SEM. Figure 2 is a schematic diagram of the structure of graphene powder TEM. Graphene was mixed with adhesive at weight ratios of 5%, 10%, and 15%. The complex dielectric constant of the mixture was tested. Figure 3 ;

[0039] Furthermore, the adhesive is any one of high molecular polymers of epoxy resin system, polyurethane resin system or fluorocarbon resin system with low dielectric constant.

[0040] Furthermore, the periodic structural units are evenly arranged and embedded in the dielectric layer. The periodic structural units are double-layer concentric cylindrical structures. The size markings of the various parts of the periodic resonator are shown in Figure 4 (c) As shown in Figure 6: The unit cell periodic size is marked as P ; The diameter and height of the upper cylinder are marked as y and x , the diameter and height of the lower cylinder are marked as w and t .

[0041] Furthermore, the unit cell periodicity P The diameter of the upper cylinder is y The diameter of the lower cylinder w relation: P > y > w .

[0042] Furthermore, the dielectric layer is a flexible low-loss dielectric material, which can be any one of polyester film, polycarbonate, polyimide or other flexible film materials. The real part of the dielectric constant of the dielectric layer material is generally controlled within the range of 3 to 6, and the dielectric loss is generally controlled within 0.1; the thickness of the dielectric plateh = x + t .

[0043] Furthermore, the reflective layer may be a metal material such as steel, iron, copper, silver, or aluminum, or may be a carbon fiber material having total reflective capability.

[0044] The method for preparing a flexible sheet of a broadband wave-absorbing metamaterial based on a carbon-based material comprises the following steps:

[0045] Step 1: Place the dielectric layer according to the unit size of the periodic resonant structure, every other unit cell P The size of the machine is to make a double-layer concentric cylindrical hole. The diameter and height of the lower cylindrical hole are w and t , the diameter and height of the upper cylindrical hole are y and x , the photo of the dielectric plate with holes is shown in Figure 7;

[0046] Step 2: Clean the side of the medium plate with small holes with anhydrous ethanol, and apply metal materials such as copper film or aluminum film, or other materials with microwave total reflection ability as a reflective layer; this step of applying the reflective surface can also be completed in the last step;

[0047] Step 3, mixing the graphene or carbon nanotubes and the adhesive evenly to form a carbon composite for later use;

[0048] Step 4: Use a scraper to fill it into the periodically arranged holes in step 1, and scrape off the excess carbon-based composite with the scraper;

[0049] Step 5: Place the sample horizontally and let it dry naturally until the carbon composite is completely dry.

[0050] The prepared sample is visible Figure 6 (a) is Figure 8 and (b) is Figure 9; according to the test standard GJB2038A-2011 or GJB2038-94, the sample is tested using an anechoic chamber or an arch frame method. The main performance indicators are shown in Table 1, and the sample test results are shown in Figure 10:

[0051] Table 1 Main performance indicators of broadband absorbing metamaterial flexible sheet samples based on carbon materials

[0052]

[0053] Example 1

[0054] The broadband absorbing metamaterial flexible patch based on carbon materials consists of two layers: the bottom layer is a metal reflective layer, the upper layer is a 2.7 mm dielectric layer, and the dielectric layer is embedded with a periodically arranged double-layer cylindrical carbon composite unit array. The structural diagram is shown in the figure. Figure 4 As shown, the electromagnetic wave is incident from the top layer Z direction; the embedded double-layer cylindrical carbon composite unit array uses a mixture of graphene powder and epoxy resin with a weight ratio of 15%, and the electromagnetic parameters are as follows Figure 3 As shown. The dimensions of the resonant unit are as follows: P = 13mm, x = 1.5mm, y = 4mm, t = 1.2mm and w =2.2mm, the dielectric plate is polyester film (relative dielectric constant is 3.8, loss tangent is 0.03), the dielectric plate thickness h = 2.7 mm; the reflecting surface is a copper film (σ =5.8×107S / m) with a thickness of 0.036 mm.

[0055] Production process: ⑴ Use mechanical punching to make holes in the polyester board. P The size of a periodic structural unit hole is mechanically polished, such as Figure 5 As shown; ⑵ 15% by weight of graphene powder and epoxy resin are uniformly mixed to form a carbon composite for use, and the composite is filled into the periodically arranged holes of the polyester board with a scraper, and the excess carbon composite is scraped off with a scraper; ⑶ The sample is placed horizontally and dried naturally until the carbon composite is completely dry; ⑷ The side of the polyester board with small holes is cleaned with anhydrous ethanol and then a copper film with a thickness of 0.036 mm is applied. The prepared flexible patch sample is shown in Figure 6 (a) That is Figure 8.

[0056] The sample was tested for 2-18 GHz reflectivity using the arch frame method according to the test standard GJB2038A-2011. The test results are shown in Figure 10. The reflectivity (2-18 GHz) -10dB effective bandwidth is 8.8 GHz.

[0057] Example 2

[0058] The broadband absorbing metamaterial flexible patch based on carbon materials consists of two layers: the bottom layer is a copper film reflective layer, the upper layer is a 2.7mm polycarbonate film, and the dielectric layer is embedded with a periodically arranged double-layer cylindrical carbon composite unit array. The structural diagram is shown in the figure. Figure 4 As shown, the electromagnetic wave is incident from the top layer Z direction; the embedded double-layer cylindrical carbon composite unit array uses a mixture of graphene powder and polyurethane resin with a weight ratio of 15%. The resonant unit size is as follows: P = 13mm,x = 1.5mm, y = 4mm, t = 1.6mm and w =2.2mm, the dielectric plate is a polycarbonate film (relative dielectric constant is 2.9, loss tangent is 0.01), the dielectric plate thickness h = 3.1 mm; the reflecting surface is a copper film (σ =5.8×107S / m) with a thickness of 0.036 mm.

[0059] Production process: ⑴ The polycarbonate film is punched mechanically, and every other P ⑴ Mix 15% by weight of graphene powder and polyurethane resin evenly to form a carbon composite for later use, fill it into the periodically arranged holes of the polycarbonate film with a scraper, and scrape off the excess carbon composite with a scraper; ⑶ Place the sample horizontally and dry it naturally until the carbon composite is completely dry; ⑷ Clean the small hole side of the polycarbonate film with anhydrous ethanol and apply a copper film with a thickness of 0.036 mm.

[0060] The sample was tested for 2-18GHz reflectivity using the arch frame method according to the test standard GJB2038A-2011. The test results are as follows: reflectivity (2-18GHz) -10dB effective bandwidth 8GHz.

[0061] Example 3

[0062] The broadband absorbing metamaterial flexible patch based on carbon materials consists of two layers: the bottom layer is a metal reflective layer, the upper layer is a 2.7 mm dielectric layer, and the dielectric layer is embedded with a periodically arranged double-layer cylindrical carbon composite unit array. The structural diagram is shown in the figure. Figure 4 As shown, the electromagnetic wave is incident from the top layer Z direction; the embedded double-layer cylindrical carbon composite unit array uses a mixture of graphene powder and epoxy resin with a weight ratio of 15%, and the electromagnetic parameters are as follows Figure 3 As shown. The dimensions of the resonant unit are as follows: P = 13mm, x = 1.3mm, y = 4mm, t = 1.4mm and w =2.2mm, the dielectric plate is a polyimide film (relative dielectric constant is 3.5, loss tangent is 0.0027), the dielectric plate thickness h = 2.7 mm; the reflecting surface is a copper film (σ=5.8×107S / m) with a thickness of 0.036 mm.

[0063] Production process: ⑴ The polyimide film is punched mechanically, and every otherP The size of a periodic structural unit hole is mechanically polished, such as Figure 4 As shown; (2) 15% by weight of graphene powder and epoxy resin are uniformly mixed to form a carbon composite for use, and the composite is filled into the periodically arranged holes of the polyimide film with a scraper, and the excess graphene composite is scraped off with a scraper; (3) The sample is placed horizontally and dried naturally until the carbon composite is completely dry; (4) The side of the polyimide film with small holes is cleaned with anhydrous ethanol and then a copper film with a thickness of 0.036 mm is applied. The prepared flexible patch sample is shown in FIG. Figure 6 (a) That is Figure 8.

[0064] The sample was tested for 2-18 GHz reflectivity using the arch frame method according to the test standard GJB2038A-2011. The test results are shown in Figure 10. The reflectivity (2-18 GHz) -10dB effective bandwidth is 8.5 GHz.

[0065] The above embodiments are only used to illustrate the technical solution of the present invention and are not intended to limit the present invention. The present invention is described in detail with reference to the preferred embodiments. It should be understood by those skilled in the art that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, and should be included in the scope of the claims of the present invention.

Claims

1. A flexible sheet of broadband wave-absorbing metamaterial based on carbon-based materials, characterized by: The sheet material comprises a reflective layer and a dielectric layer embedded with periodically arranged structural units, wherein the dielectric layer is arranged above the reflective layer; the periodic structural units are uniformly arranged and embedded in the dielectric layer, and the periodic structural units are double-layer concentric cylindrical structures; the periodically arranged structural units are prepared from a mixture of graphene or carbon nanotubes and an adhesive; the weight ratio of graphene or carbon nanotubes to the adhesive is 5-20%; and the adhesive is any one of an epoxy resin system, a polyurethane resin system or a fluorocarbon resin system with a low dielectric constant.

2. The carbon-based broadband absorbing metamaterial flexible sheet according to claim 1 is characterized in that: The dimensions of each part of the periodic resonator are marked: the periodic dimension of the unit cell is marked as P; the diameter and height of the upper cylinder are marked as y and x respectively, and the diameter and height of the lower cylinder are marked as w and t respectively.

3. The carbon-based broadband absorbing metamaterial flexible sheet according to claim 2 is characterized in that: The relationship between the unit cell periodicity P, the upper cylinder diameter y and the lower cylinder diameter w is: P > y > w.

4. The carbon-based broadband absorbing metamaterial flexible sheet according to claim 3 is characterized in that: The dielectric layer is a flexible low-loss dielectric material, any one of polyester film, polycarbonate, polyimide or other flexible film materials, and the thickness of the dielectric plate is h = x + t.

5. The carbon-based broadband microwave absorbing metamaterial flexible sheet according to claim 1, characterized in that: The reflective layer is steel, iron, copper, silver, aluminum, or a carbon fiber material with full reflective capability.

6. The method for preparing a flexible sheet of broadband wave-absorbing metamaterial based on carbon-based materials according to any one of claims 1 to 5, characterized in that: The method comprises the following preparation steps: Step 1: According to the unit size of the periodic resonant structure, a double-layer concentric cylindrical hole is mechanically punched in the dielectric layer every other unit cell P, wherein the diameter and height of the lower cylindrical hole are w and t respectively, and the diameter and height of the upper cylindrical hole are y and x respectively; Step 2: Clean the side of the medium plate with small holes with anhydrous ethanol and apply the reflective layer; Step 3, mixing the graphene or carbon nanotubes and the adhesive evenly to form a carbon composite for later use; Step 4: Use a scraper to fill it into the periodically arranged holes in step 1, and scrape off the excess carbon-based composite with the scraper; Step 5: Place the sample horizontally and let it dry naturally until the carbon composite is completely dry.

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