Multi-layer composite structure flexible frequency selective surface material and preparation method thereof

Abstract

The invention relates to the field of electromagnetic functional composite materials, and particularly discloses a multi-layer composite structure flexible frequency selective surface material and a preparation method thereof. The ultra-high molecular weight polymer fiber-reinforced polymer-based composite material thin-film mechanical enhanced band-pass frequency selection array sequentially comprises an acrylic acid polyvinylidene fluoride organic polymer coating environment-resistant layer, a metal oxide organic film isolation layer, an ultra-high molecular weight polymer fiber-reinforced polymer-based composite material thin-film mechanical enhanced layer, a band-pass frequency selection layer and a packaging protection layer from top to bottom, and the band-pass frequency selection layer is a hexagonal / circular ring nested band-pass frequency selection pattern array. The packaging protection layer is formed by printing a conductive coating composed of conductive filler / polymer resin matrix, and the packaging protection layer is an ink coating. The flexible frequency selective surface material has the characteristics of light weight, high strength, salt fog / rain / ultraviolet and other severe environments, frequency selective wave transmission and multiple functions, has good gas barrier property, is beneficial to maintaining the shape of an inflatable hangar made of a skin and ensuring normal operation of radar equipment, and has good practical engineering application value.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic functional composite materials, and in particular relates to a multi-layer composite structure flexible frequency selective surface material and a preparation method thereof. Background Art

[0002] During outdoor use, communication radar vehicles, antennas, and other equipment face complex environmental conditions such as strong winds, salt spray, rain, corrosion, and electromagnetic radiation, posing significant challenges to their proper operation and service life. A key challenge in the protective devices used for this type of equipment is achieving resistance to mechanical loads, environmental conditions, and electromagnetic shielding while also ensuring proper wave transmission within the radar and antenna operating frequency bands. Protective skin materials are a reliable way to enhance the environmental resistance and extend the service life of these equipment, but traditional skin materials lack electromagnetic shielding. Bandpass frequency selective surfaces (FSSs) are the only viable solution for achieving both electromagnetic shielding and wave transmission for radar / antenna systems. Furthermore, to shield the radar without impacting the normal movement, operation, and maintenance of the radar vehicle, the FSSs are often constructed as inflatable structures. When filled with a gas such as helium, they form an arched structure, which serves as the parking space for the radar vehicle. This requires the skins to have a gas barrier layer to provide excellent pressure resistance and gas retention, ensuring that the inflated state prevents gas leakage and maintains the overall arched structure for extended periods.

[0003] However, current frequency selective surface materials have the following problems: (1) The substrate is mostly made of flat dielectric, which is heavy and cannot be bent to fit the shape of the equipment; (2) The frequency selective surface pattern directly prepared on the surface of the equipment is directly exposed to harsh environments such as strong wind / salt spray / rain / UV, and has poor wear resistance and corrosion resistance; (3) The frequency selective preparation adopts metal coating photolithography (PCB) process, which is complex, has high preparation cost and low efficiency; (4) The gas isolation ability is poor, and gas can escape through the skin material, causing the inflatable hangar structure made of the skin to be unable to maintain. These bottleneck problems make it difficult to meet the performance requirements of lightweight, high strength, environmental resistance and low cost for protective materials of equipment such as communication radar vehicles and communication antennas, which seriously limits the practical application of such materials. In order to solve the above problems and realize the functional requirements of lightweight, high strength, environmental resistance and integrated wave transmission / shielding protective materials for equipment such as communication radar vehicles and communication antennas, the present invention discloses a multi-layer composite structure flexible frequency selective surface material and its preparation method. Summary of the Invention

[0004] The purpose of the present invention is to provide a multi-layer composite structure flexible frequency selective surface material and its preparation method, so as to solve the defects of existing frequency selective surface materials such as heavy weight, poor mechanical strength, poor environmental resistance, and complex preparation process.

[0005] To achieve the above objectives, the present invention proposes a multi-layer composite structure flexible frequency selective surface material, which includes, from top to bottom: an organic polymer coating environmental resistance layer, an isolation layer, a mechanical reinforcement layer, a conductive coating bandpass frequency selection layer and an encapsulation protection layer.

[0006] Preferably, in the above-mentioned multi-layer composite structure flexible frequency selective surface material, the organic polymer coating environmental resistant layer is acrylic polyvinylidene fluoride or silicone modified acrylic organic polymer coating with a thickness of 10~100μm, which is used to enhance the aging resistance and UV resistance of the frequency selection.

[0007] Preferably, in the above-mentioned multi-layer composite structure flexible frequency selective surface material, the isolation layer is a metal oxide organic film, and further preferably a double-sided dense aluminum oxide-coated polyester film with strong gas barrier ability, with a thickness of 50~200μm, which is used to enhance the anti-rubbing and compression resistance, as well as the gas barrier and inflatable hangar shape-forming capabilities.

[0008] Preferably, in the above-mentioned multi-layer composite structure flexible frequency selective surface material, the mechanical reinforcement layer is an ultra-high molecular weight polymer fiber reinforced polymer-based composite material film with a thickness of 50~200μm, and the ultra-high molecular weight polymer fiber is polyethylene fiber, PI fiber or aramid 1414 fiber, which is used as a base material to enhance the tensile and other mechanical load-bearing capacity of the frequency selective material.

[0009] Preferably, in the above-mentioned multi-layer composite structure flexible frequency selective surface material, the bandpass frequency selective layer is a conductive coating composed of a conductive filler / polymer resin matrix with a hexagonal / annular nested bandpass frequency selective pattern array, with a thickness of 20-100 μm. The hexagonal / annular nested bandpass frequency selective pattern array has a period size of 10-20 mm and an outer unit size of 8-15 mm. The conductive filler is one or more of silver powder, aluminum powder, and carbon powder. This material exhibits high transmittance within a specific electromagnetic frequency band (0.5-2 GHz) and high reflectivity outside the band (frequency bands other than 0.5-2 GHz), meeting the operational requirements of radar equipment.

[0010] Preferably, in the above-mentioned multi-layer composite structure flexible frequency selective surface material, the encapsulation protection layer is an ink coating sprayed on the surface of the frequency selective pattern layer with a thickness of 10~100μm, which is used to protect the frequency selective unit and enhance wear resistance and weather resistance.

[0011] Based on the same inventive concept, the present invention also provides a method for preparing a multi-layer composite structure flexible frequency selective surface material, comprising the following steps: (1) Bonding of mechanical reinforcement layer and isolation layer: evenly apply low-temperature resistant polyurethane glue between the mechanical reinforcement layer of ultra-high molecular weight polymer fiber reinforced polymer matrix composite film and the isolation layer of metal oxide organic film, evenly laminate and compact, and heat at low temperature (60°C) for a period of time to ensure good bonding; (2) Coating the environmental resistant layer: Lay the bonded mechanical reinforcement layer and the isolation layer flat, with the isolation layer on top, and evenly coat the organic polymer coating environmental resistant layer. Fully dry and heat-cure to form a uniform and continuous weather-resistant coating. (3) Preparation of frequency-selective conductive coating: Wash and dry the conductive filler and mix it with the resin solution matrix, grind and disperse it thoroughly to make the conductive filler evenly distributed in it, and obtain a composite conductive coating with high weather resistance and high conductivity; (4) Preparation of bandpass frequency selection layer: Customize the corresponding screen mold according to the hexagonal / circular nested bandpass frequency selection surface pattern design scheme, lay the prepared mechanical reinforcement layer / isolation layer / environmental resistance layer combination flat on the screen printing mold operation table, with the mechanical reinforcement layer facing up, press the screen mold tightly on the surface of the mechanical reinforcement layer, and evenly apply conductive paint on its surface. Repeat several times, dry at room temperature and heat for a period of time to make the frequency selection pattern completely fixed and firmly attached to the surface of the mechanical reinforcement layer to obtain the bandpass frequency selection layer; (5) Coating the encapsulation protection layer: spraying an ink layer evenly on the surface of the bandpass frequency selection layer to achieve encapsulation protection of the frequency selection pattern and obtain a multi-layer composite structure flexible frequency selection surface material.

[0012] Preferably, in the above preparation method, in step (1), the ultra-high molecular weight polymer fiber is polyethylene fiber, PI fiber or aramid 1414 fiber.

[0013] Preferably, in the above preparation method, in step (1), the heating curing temperature is 40-80° C., and the curing time is 1-8 hours.

[0014] Preferably, in the above preparation method, in step (2), the organic polymer coating is acrylic polyvinylidene fluoride.

[0015] Preferably, in the above preparation method, in step (2), the environmental resistant layer is coated by spraying or brushing.

[0016] Preferably, in the above preparation method, in step (2), the heating curing temperature is 40-80° C., and the curing time is 1-8 hours.

[0017] Preferably, in the above preparation method, in step (3), the conductive filler is one or more of silver powder, aluminum powder, and carbon powder.

[0018] Preferably, in the above preparation method, in step (3), the conductive filler powder washing method includes ethanol washing, dilute hydrochloric acid washing, and water washing, which are used to remove impurities and grease on the surface of the conductive filler to prevent slurry contamination.

[0019] Preferably, in the above preparation method, in step (3), the ratio of the conductive filler powder in the resin solution is 1 g / L to 10 g / L.

[0020] Preferably, in the above preparation method, in step (4), the screen mold has a mesh size of 100-400.

[0021] Preferably, in the above preparation method, in step (4), the screen printing step is repeated 1 to 9 times.

[0022] Preferably, in the above preparation method, in step (4), the heating temperature is 40-80° C., and the curing time is 0.5-8 hours.

[0023] Preferably, in the above preparation method, in step (5), the ink layer is sprayed to a thickness of 10 to 100 μm.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) The multi-layer composite structure flexible frequency selective surface material of the present invention has good flexibility, can be folded for storage, and can also be quickly deployed and covered on the surface of equipment such as radar / antenna, overcoming the defects of traditional protective skins that are not bendable, occupy a large area, and cannot cover the equipment in a form-fitting manner; it has good gas barrier properties, which is conducive to maintaining the shape of the inflatable hangar made of the skin and ensuring the normal operation of the radar equipment.

[0025] (2) The multi-layer composite structure flexible frequency selective surface material of the present invention adopts a polymer-based lightweight environmental resistant layer, a mechanical reinforcement layer, an isolation layer and an encapsulation protection layer, which greatly reduces the surface density of the skin and solves the problem of high surface density and heavy weight of traditional protective skin.

[0026] (3) The frequency-selective layer of the multi-layer composite structure flexible frequency-selective surface material of the present invention uses conductive fillers such as silver / aluminum / carbon powder and a polymer resin-based conductive coating. It has high conductivity and excellent adhesion, solving the problem of weak interface bonding and easy detachment between traditional frequency-selective coatings and substrates. By optimizing the frequency-selective pattern and coating of the bandpass frequency-selective layer, it has high transmittance within a specific electromagnetic frequency band (0.5-2 GHz) and high reflectivity outside the band (other frequency bands except 0.5-2 GHz), achieving the bandpass wave-transmitting function that meets the working requirements of radar equipment.

[0027] (4) The frequency selective layer of the multi-layer composite structure flexible frequency selective surface material of the present invention is prepared by the conductor coating screen printing process. The brush coating process is simple, low cost and high efficiency, which solves the bottleneck problem of the traditional frequency selective material PCB preparation process being complex, high cost and low efficiency.

[0028] (5) The multi-layer composite structure flexible frequency selective surface material of the present invention adopts a multi-layer structure scheme of environmental resistance layer, isolation layer, mechanical reinforcement layer, frequency selection layer and packaging protection layer, especially introducing a lightweight, high-strength ultra-high molecular weight polymer fiber reinforced polymer matrix composite material mechanical reinforcement layer, organic polymer environmental resistance layer and ink packaging protection layer, which greatly enhances the mechanical strength of the frequency selective protective skin material, its ability to withstand harsh environments such as salt spray / rain / UV, and its wear resistance and anti-shedding ability, thus solving the defects of traditional frequency selective materials such as poor weather resistance and easy shedding. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the decomposed structure of the multi-layer composite structure flexible frequency selective surface material of the present invention; Figure 2 This is the design scheme of the hexagonal / circular nested bandpass frequency selective pattern array in the multi-layer composite structure flexible frequency selective surface material in Example 1 of the present invention; Figure 3 1 is a dimension description of the hexagonal / circular nested bandpass frequency selection pattern unit in Example 1 of the present invention; Figure 4 The silver conductive filler / epoxy resin matrix conductive coating prepared in Example 1 of the present invention; Figure 5 This is a photo of the screen printing device of Example 1 of the present invention; Figure 6 This is a photo of the multi-layer composite structure flexible frequency selective surface material prepared in Example 1 of the present invention; Figure 7 This is a wave transmittance curve of a multi-layer composite structure flexible frequency selective surface material prepared in Example 1 of the present invention; Figure 8 This is the wave transmittance curve of the multi-layer composite structure flexible frequency selective surface material prepared in Example 2 of the present invention.

[0030] Legend: 1-environmental resistant layer, 2-isolation layer, 3-mechanical reinforcement layer, 4-bandpass frequency selection layer, 5-encapsulation protection layer. DETAILED DESCRIPTION

[0031] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0032] Example 1 A multi-layer composite structure flexible frequency selective surface material structure as shown in the attached Figure 1 As shown, from top to bottom, it includes: an environmental resistance layer, an isolation layer, a mechanical reinforcement layer, a bandpass frequency selection layer and a packaging protection layer multilayer structure, wherein the environmental resistance layer is an acrylic polyvinylidene fluoride organic polymer coating with a thickness of 10μm; the isolation layer is a double-sided aluminum oxide-coated polyester film with a thickness of 100μm; the mechanical reinforcement layer is an ultra-high molecular weight (greater than 20,000) polyethylene fiber reinforced polyethylene-based composite film with a thickness of 100μm; the bandpass frequency selection layer is a hexagonal / circular nested bandpass frequency selection pattern array (see Figure 2 ), the periodic structure dimensions are: period dimension 10 mm, outer unit dimension 8 mm, line width 1 mm, inner unit dimension 4 mm, radius 1 is 2.6 mm, radius 2 is 0.5 mm, (the definitions of each dimension are given in Figure 3 ), which is obtained by printing silver powder conductive filler and epoxy resin matrix conductive coating on the surface of the mechanical reinforcement layer, with a thickness of 50μm; the encapsulation protection layer is an ink coating, sprayed on the surface of the frequency selection layer, with a thickness of 20μm.

[0033] A method for preparing a multi-layer composite structure flexible frequency selective surface material of this embodiment includes the following steps: (1) Bonding of mechanical reinforcement layer and isolation layer: Apply low-temperature resistant polyurethane glue evenly between the 100 μm thick ultra-high molecular weight polyethylene fiber reinforced polyethylene composite material film mechanical reinforcement layer and the 100 μm thick alumina polyester film isolation layer, evenly laminate and compact, heat to 80 ° C and cure for 2 hours to ensure good bonding; (2) Coating the environmental resistant layer: Lay the bonded ultra-high molecular weight polyethylene fiber reinforced polyethylene-based composite film mechanical reinforcement layer and the alumina polyester film isolation layer assembly flat, with the isolation layer side on top, and evenly spray a 10 μm thick commercially available acrylic polyvinylidene fluoride (manufacturer: Aladdin, CAS number: 24937-79-9) coating, fully dry it, heat it to 80 ° C and cure it for 1 hour to form a uniform and continuous environmental resistant layer; (3) Preparation of frequency-selective conductive coating: wash the silver powder filler with ethanol, dilute hydrochloric acid, water, and dry it, then mix it with a 1g / L epoxy resin solution matrix, grind and disperse it thoroughly so that the conductive filler is evenly distributed and can contact each other, and obtain a lightweight, highly weather-resistant, and highly conductive silver conductive filler / epoxy resin matrix conductive coating (see Figure 4 ); (4) Bandpass frequency selection layer preparation: Customize the corresponding 300 mesh screen mold according to the hexagonal / circular nested bandpass frequency selection surface pattern design (see Figure 5), the prepared mechanical reinforcement layer / isolation layer / environmental resistance layer assembly is laid flat on the screen printing mold operating table with the mechanical reinforcement layer facing upward, the screen mold is pressed tightly on the surface of the mechanical reinforcement layer, and the conductive paint is evenly brushed on the surface. This is repeated 9 times, dried at room temperature, and then heated to 80°C for curing for 0.5 hours to completely shape the frequency selection pattern and firmly adhere to the surface of the mechanical reinforcement layer to obtain a bandpass frequency selection layer; (5) Coating the frequency selective packaging protective layer: spray the ink layer evenly on the surface of the bandpass frequency selective layer with a thickness of 20 μm to obtain a multi-layer composite structure flexible frequency selective surface material (see Figure 6 ).

[0034] The performance test of the multi-layer composite structure flexible frequency selective surface material prepared in this example was carried out, and the wave transmittance test was completed using the focusing lens method. The results are shown in Figure 7 The wave transmittance from 0.5 to 2.0 GHz is greater than 54%, of which the wave transmittance from 0.93 to 1.62 GHz is greater than 90%. The wave transmission bandwidth and wave transmittance values ​​are better than those of traditional frequency-selective materials. The tear strength obtained by the trouser-shaped tearing method is 1200N; the mildew resistance obtained by the local method test is level 1; the helium permeability obtained by the pressure difference method test is less than 0.2%.

[0035] Example 2 A multi-layer composite structure flexible frequency selective surface material structure such as Figure 1 As shown, from top to bottom, it includes: an environmental resistance layer, an isolation layer, a mechanical reinforcement layer, a frequency selection layer and a packaging protection layer multilayer structure, wherein the environmental resistance layer is an acrylic polyvinylidene fluoride organic polymer coating with a thickness of 10 μm; the isolation layer is a double-sided aluminum oxide-coated polyester film with a thickness of 80 μm; the mechanical reinforcement layer is an ultra-high molecular weight aramid 1414 fiber reinforced polyethylene-based composite film with a thickness of 120 μm; the bandpass frequency selection layer is a hexagonal / circular nested bandpass frequency selection pattern array (see Figure 2 ), period size 20 mm, outer unit size 15 mm, line width 1.5 mm, inner unit size 9 mm, radius 1 is 6 mm, radius 2 is 1 mm, (see the definition of each size for details) Figure 3 ), which is obtained by printing silver / aluminum / carbon powder conductive fillers and epoxy resin-based conductive coatings on the surface of the mechanical reinforcement layer, with a thickness of 100μm; the encapsulation protection layer is an ink coating, sprayed on the surface of the frequency selection layer, with a thickness of 20μm.

[0036] A method for preparing a multi-layer composite structure flexible frequency selective surface material according to this embodiment includes the following steps: (1) Bonding of mechanical reinforcement layer and isolation layer: Apply low-temperature resistant polyurethane glue evenly between the 120 μm thick ultra-high molecular weight aramid 1414 fiber reinforced polyethylene composite film mechanical reinforcement layer and the 80 μm thick alumina polyester film isolation layer, evenly laminate and compact, heat to 50 ° C and cure for 8 hours to ensure good bonding; (2) Coating the environmental resistant layer: lay the bonded ultra-high molecular weight polyethylene fiber reinforced polyethylene-based composite film mechanical reinforcement layer and the alumina polyester film isolation layer assembly flat, with the isolation layer side on top, and evenly spray an acrylic polyvinylidene fluoride coating with a thickness of 20 μm. Dry it thoroughly, heat it to 80 ° C and cure it for 1 hour to form a uniform and continuous environmental resistant layer; (3) Preparation of frequency-selective conductive coating: A silver / aluminum / carbon powder mixed conductive filler with a mass ratio of 7:2:1 is washed with ethanol, diluted hydrochloric acid, water, and dried, and then mixed with a 5g / L epoxy resin solution matrix. The conductive filler is fully ground and dispersed so that the conductive filler is evenly distributed and can contact each other, thereby obtaining a lightweight, highly weather-resistant, and highly conductive silver / aluminum / carbon powder mixed conductive filler and epoxy resin matrix conductive coating; (4) Preparation of bandpass frequency selection layer: Customize the corresponding 200-mesh screen mold according to the hexagonal / circular nested bandpass frequency selection surface pattern design scheme, lay the prepared mechanical reinforcement layer / isolation layer / environmental resistance layer assembly flat on the screen printing mold operation table, with the mechanical reinforcement layer side facing up, press the screen mold tightly on the surface of the mechanical reinforcement layer, and evenly apply conductive paint on its surface. Repeat 5 times, dry at room temperature, and then heat to 5℃ for curing for 8 hours to make the frequency selection pattern completely fixed and firmly attached to the surface of the mechanical reinforcement layer; (5) Coating the frequency-selective packaging protective layer: spray an ink layer evenly on the surface of the bandpass frequency-selective layer with a spraying thickness of 20 μm to obtain a multi-layer composite structure flexible frequency-selective surface material.

[0037] The performance test of the multi-layer composite structure flexible frequency selective surface material prepared in this example was carried out, and the wave transmittance test was completed using the focusing lens method. The results are shown in Figure 8 The transmittance from 0.5 to 2.0 GHz is greater than 65%, with a transmittance greater than 90% from 0.85 to 1.60 GHz. The tear strength measured using the trouser tear method is 1150N. The fungus resistance measured using the localized tear method is Class 1. The helium permeability measured using the differential pressure method is less than 0.2%. In this embodiment, a mixed conductive filler is used as the frequency-selective printing paste. By varying the periodicity and cell size of the frequency-selective pattern array, the minimum transmittance from 0.5 to 2.0 GHz is increased by 11%, and the bandwidth with a transmittance greater than 90% is extended by 0.12 GHz.

[0038] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A multi-layer composite structure flexible frequency selective surface material, characterized in that: From top to bottom, it includes: an acrylic polyvinylidene fluoride organic polymer coating environmental resistance layer, a metal oxide organic film isolation layer, an ultra-high molecular weight polymer fiber reinforced polymer-based composite film mechanical reinforcement layer, a bandpass frequency selection layer, and an encapsulation protection layer. The bandpass frequency selection layer is a hexagonal / circular nested bandpass frequency selection pattern array, which is obtained by printing a conductive coating composed of a conductive filler / polymer resin matrix, and the encapsulation protection layer is an ink coating.

2. The multi-layer composite structure flexible frequency selective surface material according to claim 1, characterized in that: The thickness of the environmental resistant layer is 10~100μm; the metal oxide organic film is a double-sided aluminum oxide-plated polyester film with a thickness of 50~200μm; the thickness of the mechanical reinforcement layer is 50~200μm, and the ultra-high molecular weight polymer fiber is polyethylene fiber, PI fiber or aramid 1414 fiber; the thickness of the encapsulation protective layer is 10~100μm.

3. The multi-layer composite structure flexible frequency selective surface material according to claim 1, characterized in that: The thickness of the bandpass frequency selection layer is 20~100μm, the period size of the hexagonal / circular nested bandpass frequency selection pattern array is 10~20mm, and the outer unit size is 8~15mm. The conductive filler is one or more of silver powder, aluminum powder, and carbon powder.

4. A method for preparing a multi-layer composite structure flexible frequency selective surface material according to any one of claims 1 to 3, characterized in that: The steps include: (1) Bonding of the mechanical reinforcement layer and the isolation layer: uniformly coating low-temperature resistant polyurethane glue between the ultra-high molecular weight polymer fiber reinforced polymer matrix composite film mechanical reinforcement layer and the metal oxide organic film isolation layer, uniformly laminating, compacting, heating and curing to obtain a well-bonded mechanical reinforcement layer and isolation layer; (2) Coating the environmental resistant layer: Lay the bonded mechanical reinforcement layer and the isolation layer flat, with the isolation layer on top, evenly coat the organic polymer coating, dry, heat and cure to form a uniform and continuous environmental resistant layer; (3) Preparation of frequency-selective conductive coating: Wash and dry the conductive filler and mix it with the resin solution matrix, grind and disperse it thoroughly so that the conductive filler is evenly distributed in it to obtain the conductive coating; (4) Preparation of bandpass frequency selection layer: The prepared mechanical reinforcement layer / isolation layer / environmental resistance layer assembly is laid flat on the screen printing mold operation table with the mechanical reinforcement layer facing upwards, and the conductive coating is screen-printed on the surface of the mechanical reinforcement layer to prepare a hexagonal / circular nested bandpass frequency selection pattern, which is then heated and cured to obtain a bandpass frequency selection layer; (5) Coating the encapsulation protective layer: spraying an ink layer evenly on the surface of the bandpass frequency selection layer to obtain a multi-layer composite structure flexible frequency selection surface material.

5. The preparation method according to claim 4, characterized in that In the step (1), the heating curing temperature is 40-80° C., and the curing time is 1-8 hours.

6. The preparation method according to claim 4, characterized in that In the step (2), the organic polymer coating is acrylic polyvinylidene fluoride, and the environmental resistant layer is coated by spraying or brushing.

7. The preparation method according to claim 4, characterized in that In the step (2), the heating curing temperature is 40-80° C., and the curing time is 1-8 hours.

8. The preparation method according to claim 4, characterized in that In the step (3), the conductive filler is one or more of silver powder, aluminum powder, and carbon powder, and the conductive filler powder washing method includes ethanol washing, dilute hydrochloric acid washing, and water washing.

9. The preparation method according to claim 4, characterized in that In the step (3), the ratio of the conductive filler powder in the resin solution is 1 g / L to 10 g / L.

10. The preparation method according to claim 4, characterized in that In the step (4), the screen mold is 100-400 mesh, the screen printing is repeated 1-9 times, the heating temperature is 40-80°C, and the heating time is 0.5-8 hours.

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