A multilayer composite structure flexible frequency selective surface material and a method of making the same

Abstract

The present application relates to the field of electromagnetic function composite material, and specifically discloses a kind of multilayer composite structure flexible frequency selective surface material and preparation method thereof, from top to bottom sequentially include: acrylic polyvinylidene fluoride organic polymer coating environment-resistant layer, metal oxide organic film isolation layer, ultra-high molecular weight polymer fiber reinforced polymer matrix composite film mechanics reinforcing layer, band-pass frequency selection layer, encapsulation protective layer, band-pass frequency selection layer is hexagonal / circular ring nested type band-pass frequency selection pattern array, printed by the conductive coating layer formed by conductive filler / polymer resin matrix, encapsulation protective layer is ink coating.The flexible frequency selective surface material of the present application has the characteristics of light weight, high strength, salt spray / rain / ultraviolet and other harsh environment resistance, frequency selection wave transmission multifunction, good gas barrier performance, is conducive to maintaining the shape of air hangar made of skin, ensures the normal operation of radar equipment, and has good practical engineering application value.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electromagnetic functional composite materials, and particularly relates to a multilayer composite structure flexible frequency selective surface material and a preparation method thereof. BACKGROUND

[0002] During outdoor use, equipment such as communication radar vehicles and communication antennas are faced with complex environmental conditions such as strong wind, salt spray, rain, corrosion and electromagnetic radiation, which brings great challenges to the normal work and service life of the equipment. A core difficulty of the protective device of such equipment is to realize the mechanical load resistance, environmental resistance and electromagnetic shielding protection functions while ensuring the normal wave transmission function of the radar and antenna working frequency band. The protective skin material is a reliable means to improve the environmental resistance of these equipment and prolong the service life, but the traditional skin material does not have electromagnetic shielding function. The band-pass frequency selective surface is the only feasible means to realize the electromagnetic shielding and wave transmission function of the radar / antenna. At the same time, in order to shield the radar while not affecting the normal movement, operation and maintenance of the radar vehicle, the frequency selective skin is often prepared into an inflatable structure, which forms an arch structure in the state of being filled with helium and other gases inside, and the inside of the arch is used as a parking space for the radar vehicle, which requires the skin to have a gas isolation layer to provide good pressure resistance and gas retention capacity, so as to ensure that the gas inside the inflatable state does not leak and the overall arch structure can be maintained for a long time.

[0003] However, the current frequency selective surface material has the following problems: (1) the substrate is mostly a flat plate medium, 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 and ultraviolet light, and has poor wear resistance and corrosion resistance; (3) the frequency selective preparation adopts a metal plating film photoetching (PCB) process, which is complex, high in preparation cost and low in efficiency; (4) the gas isolation capacity is poor, and the gas can escape through the skin material, causing the inflatable hangar structure made of the skin to be unable to maintain, etc. The above-mentioned problems seriously limit the practical application of the material, and it is difficult to meet the performance requirements of lightweight, high strength, environmental resistance, low cost and wave transmission / shielding integrated protective material for communication radar vehicles, communication antennas and other equipment. In order to solve the above-mentioned problems and realize the functional requirements of lightweight, high strength, environmental resistance, wave transmission / shielding integrated protective material for communication radar vehicles, communication antennas and other equipment, the present application discloses a multilayer composite structure flexible frequency selective surface material and a preparation method thereof. SUMMARY

[0004] The present application aims to provide a multilayer composite structure flexible frequency selective surface material and a preparation method thereof, which solves the defects of the existing frequency selective surface material, such as heavy weight, poor mechanical strength, poor environmental resistance and complex preparation process.

[0005] In order to achieve the above object, the present application provides a multilayer composite structure flexible frequency selective surface material, which comprises, from top to bottom, an organic polymer coating environment-resistant layer, an isolation layer, a mechanical reinforcement layer, a conductive coating band-pass frequency selection layer and a packaging protective layer.

[0006] Preferably, in the multilayer composite structure flexible frequency selective surface material, the organic polymer coating environment-resistant layer is an acrylic polyvinylidene fluoride or a silicone-modified acrylic organic polymer coating, with a thickness of 10-100 μm, for enhancing the anti-aging and ultraviolet resistance of the frequency selection.

[0007] Preferably, in the multilayer composite structure flexible frequency selective surface material, the isolation layer is a metal oxide organic film, and more preferably a double-sided dense aluminum oxide polyester film with strong gas barrier ability, with a thickness of 50-200 μm, for enhancing the anti-twist and pressure fold resistance, as well as the gas barrier and air-tightness.

[0008] Preferably, in the multilayer composite structure flexible frequency selective surface material, the mechanical reinforcement layer is an ultrahigh molecular weight polymer fiber reinforced polymer matrix composite film, with a thickness of 50-200 μm, and the ultrahigh molecular weight polymer fiber is a polyethylene fiber, a PI fiber or an aramid fiber 1414, for enhancing the tensile and other mechanical load bearing capacity of the frequency selection material as a base material.

[0009] Preferably, in the multilayer composite structure flexible frequency selective surface material, the band-pass frequency selection layer is a conductive coating composed of a conductive filler / polymer resin matrix with a hexagonal / circular ring nested type band-pass frequency selection pattern array, with a thickness of 20-100 μm, a period size of 10-20 mm and an outer unit size of 8-15 mm, and the conductive filler is one or more of silver powder, aluminum powder and carbon powder. The band-pass frequency selection layer has a high wave permeability in a specific electromagnetic frequency band (0.5-2 GHz) and a high reflectivity outside the band (other frequency bands except 0.5-2 GHz), and meets the working requirements of radar equipment.

[0010] Preferably, in the multilayer composite structure flexible frequency selective surface material, the packaging protective layer is an ink coating, which is sprayed on the surface of the frequency selection pattern layer, with a thickness of 10-100 μm, for protecting the frequency selection units and enhancing the wear resistance and weather resistance.

[0011] Based on the same inventive concept, the present application further provides a preparation method of a multilayer composite structure flexible frequency selective surface material, which comprises the following steps:

[0012] (1) The mechanical reinforcing layer and the isolation layer are bonded: a low-temperature resistant polyurethane adhesive is uniformly coated between the mechanical reinforcing layer of the ultra-high molecular weight polymer fiber reinforced polymer matrix composite film and the metal oxide organic film isolation layer, and is uniformly laminated, compacted, and cured at a low temperature (60°C) for a period of time to ensure good bonding;

[0013] (2) The environmental resistance layer is coated: the bonded mechanical reinforcing layer and the isolation layer are laid flat, with the isolation layer on one side, and an organic polymer coating environmental resistance layer is uniformly coated, dried, and cured to form a uniform and continuous weather-resistant coating;

[0014] (3) Frequency selective conductive coating preparation: the conductive filler is washed, dried, and mixed with a resin solution matrix, and is thoroughly ground and dispersed to uniformly distribute the conductive filler therein, obtaining a high-weather-resistant, high-conductive composite conductive coating;

[0015] (4) Band-pass frequency selective layer preparation: a corresponding silk screen mold is customized according to the hexagonal / circular ring nested band-pass frequency selective surface pattern design scheme, the prepared mechanical reinforcing layer / isolation layer / environmental resistance layer combination is laid flat on the silk screen printing mold operation table, the mechanical reinforcing layer is upward, the silk screen mold is tightly pressed on the surface of the mechanical reinforcing layer, and the conductive coating is uniformly brushed on the surface, repeated several times, dried at room temperature, and heated for a period of time, so that the frequency selection pattern is completely shaped and firmly attached to the surface of the mechanical reinforcing layer, obtaining a band-pass frequency selective layer;

[0016] (5) Coating and packaging protective layer: an ink layer is uniformly sprayed on the surface of the band-pass frequency selective layer to achieve packaging and protection of the frequency selection pattern, obtaining a multi-layer composite structure flexible frequency selective surface material.

[0017] Preferably, in the above preparation method, in step (1), the ultra-high molecular weight polymer fiber is a polyethylene fiber, a PI fiber, or an aramid 1414 fiber.

[0018] Preferably, in the above preparation method, in step (1), the heating and curing temperature is 40-80°C, and the curing time is 1-8 hours.

[0019] Preferably, in the above preparation method, in step (2), the organic polymer coating is an acrylic polyvinylidene fluoride.

[0020] Preferably, in the above preparation method, in step (2), the environmental resistance layer coating method is spraying or brushing.

[0021] Preferably, in the above preparation method, in step (2), the heating and curing temperature is 40-80°C, and the curing time is 1-8 hours.

[0022] Preferably, in the above preparation method, in step (3), the conductive filler is one or more of silver powder, aluminum powder, and carbon powder.

[0023] Preferably, in the preparation method, the conductive filler powder washing method in step (3) 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 and prevent slurry pollution.

[0024] Preferably, in the preparation method, the ratio of the conductive filler powder to the resin solution in step (3) is 1 g / L to 10 g / L.

[0025] Preferably, in the preparation method, the silk screen mold in step (4) is 100 to 400 meshes.

[0026] Preferably, in the preparation method, the number of times of the silk screen printing in step (4) is 1 to 9.

[0027] Preferably, in the preparation method, the heating temperature in step (4) is 40 to 80 DEG C, and the curing time is 0.5 to 8 hours.

[0028] Preferably, in the preparation method, the ink layer spraying thickness in step (5) is 10 to 100 mu m.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] (1) The multilayer composite structure flexible frequency selective surface material has good flexibility, can be folded and stored, can be quickly deployed on the surface of radar / antenna equipment, and can be covered according to the shape, overcoming the defects of the traditional protective skin, such as being unable to be bent, occupying a large area, and being unable to be shielded according to the shape of the equipment; the material has good gas barrier performance, is beneficial to maintaining the shape of the inflatable hangar made of the skin, and ensures the normal operation of the radar equipment.

[0031] (2) The multilayer composite structure flexible frequency selective surface material uses a high-molecular lightweight environmental-resistant layer, a mechanical reinforcing layer, an isolation layer, and an encapsulation protective layer, greatly reduces the areal density of the skin, and solves the problems of the traditional protective skin, such as high areal density and large weight.

[0032] (3) The multilayer composite structure flexible frequency selective surface material uses silver / aluminum / carbon powder conductive fillers and a high-molecular resin matrix conductive coating for the frequency selection layer, has high conductivity and excellent adhesion, solves the problems of the traditional frequency selection coating and substrate interface, such as weak combination and easy falling off. Through optimization of the frequency selection pattern and the coating of the band-pass frequency selection layer, the material has a band-pass wave transmission function of high wave transmission rate in a specific electromagnetic frequency band (0.5 to 2 GHz) and high reflectivity outside the band (other frequency bands except 0.5 to 2 GHz), and meets the working requirements of the radar equipment.

[0033] (4) The frequency selection layer of the multilayer composite structure flexible frequency selection surface material is prepared by using a conductor coating screen printing process, the brushing process is simple, the cost is low, and the efficiency is high, and the bottleneck problem of the complex preparation process, high cost and low efficiency of the traditional frequency selection material PCB is solved.

[0034] (5) The multilayer composite structure flexible frequency selection surface material adopts a multilayer structure scheme of an environmental resistance layer, an isolation layer, a mechanical reinforcement layer, a frequency selection layer and a packaging protection layer, especially introduces a lightweight, high-strength ultrahigh molecular weight polymer fiber reinforced polymer matrix composite mechanical reinforcement layer, an organic polymer environmental resistance layer and an ink packaging protection layer, which greatly enhances the mechanical strength, salt spray / rain / ultraviolet and other harsh environmental resistance of the frequency selection protective skin material, and the wear resistance and anti-falling ability of the frequency selection, and solves the defects of poor weather resistance and easy falling of the traditional frequency selection material. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a decomposition structure schematic diagram of the multilayer composite structure flexible frequency selection surface material of the application;

[0036] Figure 2 is a hexagon / circle ring nested type band-pass frequency selection pattern array design scheme in the multilayer composite structure flexible frequency selection surface material of embodiment 1 of the application;

[0037] Figure 3 is a size description of the hexagon / circle ring nested type band-pass frequency selection pattern unit in embodiment 1 of the application;

[0038] Figure 4 is a silver conductive filler / epoxy resin matrix conductive coating prepared in embodiment 1 of the application;

[0039] Figure 5 is a screen printing device photo of embodiment 1 of the application;

[0040] Figure 6 is a multilayer composite structure flexible frequency selection surface material prepared in embodiment 1 of the application;

[0041] Figure 7 is a multilayer composite structure flexible frequency selection surface material prepared in embodiment 1 of the application;

[0042] Figure 8 is a multilayer composite structure flexible frequency selection surface material prepared in embodiment 2 of the application.

[0043] Legend: 1-Environmental resistance layer, 2-Isolation layer, 3-Mechanical reinforcement layer, 4-Band-pass frequency selection layer, 5-Packaging protection layer. DETAILED DESCRIPTION

[0044] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0045] Example 1

[0046] A multilayer composite flexible frequency selective surface material structure is shown in the attached figure. Figure 1 As shown, from top to bottom, it includes a multi-layer structure consisting of an environmentally resistant layer, an isolation layer, a mechanical reinforcement layer, a bandpass selective layer, and an encapsulation protection layer. The environmentally resistant layer is an acrylic polyvinylidene fluoride organic polymer coating with a thickness of 10 μm; the isolation layer is a double-sided alumina-coated polyester film with a thickness of 100 μm; 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 100 μm; and the bandpass selective layer is a hexagonal / ring nested bandpass frequency selective pattern array (see...). Figure 2 The periodic structure dimensions are as follows: period size 10 mm, outer unit size 8 mm, line width 1 mm, inner unit size 4 mm, radius 1 is 2.6 mm, radius 2 is 0.5 mm (see definition of each dimension). Figure 3 The mechanical reinforcement layer is formed 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 protective layer is an ink coating, sprayed on the surface of the frequency selective layer, with a thickness of 20μm.

[0047] The preparation method of a multilayer composite flexible frequency-selective surface material according to this embodiment includes the following steps:

[0048] (1) Bonding of mechanical reinforcement layer and isolation layer: A low-temperature resistant polyurethane adhesive is uniformly coated between the 100μm thick ultra-high molecular weight polyethylene fiber reinforced polyethylene composite film mechanical reinforcement layer and the 100μm thick alumina polyester film isolation layer. The adhesive is uniformly laminated, compacted, heated to 80℃ and cured for 2 hours to ensure good bonding.

[0049] (2) Coating the environmentally resistant layer: The bonded combination of ultra-high molecular weight polyethylene fiber reinforced polyethylene composite film mechanical reinforcement layer and alumina polyester film isolation layer is laid flat with the isolation layer side facing up. A commercially available acrylic polyvinylidene fluoride (manufacturer: Aladdin, CAS number: 24937-79-9) coating with a thickness of 10μm is uniformly sprayed, fully dried, and heated to 80℃ for 1 hour to form a uniform and continuous environmentally resistant layer;

[0050] (3) Preparation of frequency-selective conductive coating: The silver powder filler is washed with ethanol, dilute hydrochloric acid, water, and dried. It is then mixed with an epoxy resin matrix at a ratio of 1 g / L and thoroughly ground and dispersed to ensure that the conductive filler is evenly distributed and in contact with each other, thus obtaining a lightweight, highly weather-resistant, and highly conductive silver conductive filler / epoxy resin matrix conductive coating (see Figure 4 );

[0051] (4) Preparation of the band-pass frequency selective layer: according to the hexagon / circle ring nested band-pass frequency selective surface pattern design scheme, a corresponding 300-mesh screen printing mold (see Figure 5 ) is customized. The prepared mechanical reinforcement layer / isolation layer / environment-resistant layer combination is laid on the screen printing mold operating table, the mechanical reinforcement layer is upward, the screen printing mold is tightly pressed on the surface of the mechanical reinforcement layer, and the conductive paint is uniformly brushed on the surface. The operation is repeated 9 times, and after drying at room temperature, it is heated to 80°C for 0.5 hours for curing, so that the frequency selection pattern is completely shaped and firmly attached to the surface of the mechanical reinforcement layer, and the band-pass frequency selection layer is obtained;

[0052] (5) Coating of the frequency selection packaging protective layer: the ink layer is uniformly sprayed on the surface of the band-pass frequency selection layer, and the spraying thickness is 20 μm, so as to obtain the multilayer composite structure flexible frequency selective surface material (see Figure 6 ).

[0053] The performance test of the multilayer composite structure flexible frequency selective surface material prepared in the example is carried out, the wave transmission rate test is completed by using the focusing lens method, and the results are shown in Figure 7 , the wave transmission rate is greater than 54% in the range of 0.5~2.0 GHz, and the wave transmission rate is greater than 90% in the range of 0.93~1.62 GHz. The wave transmission bandwidth and the wave transmission rate value are better than those of the traditional frequency selection material; the tearing strength obtained by the trouser-shaped tearing method test is 1200 N; the mold resistance performance obtained by the local method test is 1 level; and the helium permeability obtained by the pressure difference method test is less than 0.2%.

[0054] Example 2

[0055] A multilayer composite structure flexible frequency selective surface material structure is shown in Figure 1 , which includes, from top to bottom, an environment-resistant layer, an isolation layer, a mechanical reinforcement layer, a frequency selection layer, and a packaging protective layer multilayer structure. The environment-resistant 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 ultrahigh molecular weight aramid fiber reinforced polyethylene composite film with a thickness of 120 μm; the band-pass frequency selection layer is a hexagon / circle ring nested band-pass frequency selection pattern array (see Figure 2 ) with a period size of 20 mm, an outer cell size of 15 mm, a line width of 1.5 mm, an inner cell size of 9 mm, a radius 1 of 6 mm, and a radius 2 of 1 mm (see Figure 3 for the definition of each size), which is printed on the surface of the mechanical reinforcement layer by silver / aluminum / carbon powder conductive fillers and epoxy resin matrix conductive paint, with a thickness of 100 μm; and the packaging protective layer is an ink coating sprayed on the surface of the frequency selection layer with a thickness of 20 μm.

[0056] The preparation method of the multilayer composite structure flexible frequency selective surface material of the embodiment comprises the following steps:

[0057] (1) Bonding of the mechanical reinforcing layer and the isolation layer: uniformly apply low-temperature resistant polyurethane adhesive glue between the 120 μm thick ultra-high molecular weight aramid fiber reinforced polyethylene composite film mechanical reinforcing layer and the 80 μm thick aluminum oxide polyester film isolation layer, uniformly laminate and compact, and heat to 50°C for curing for 8 hours to ensure good bonding;

[0058] (2) Coating of the environmental resistance layer: lay the bonded ultra-high molecular weight polyethylene fiber reinforced polyethylene composite film mechanical reinforcing layer and the aluminum oxide polyester film isolation layer combination, with the isolation layer on the top, uniformly spray the 20 μm thick acrylic polyvinylidene fluoride coating, fully dry, and heat to 80°C for curing for 1 hour to form a uniform and continuous environmental resistance layer;

[0059] (3) Preparation of the frequency selective conductive coating: mix the silver / aluminum / carbon powder mixed conductive filler with a mass ratio of 7:2:1 through ethanol washing, dilute hydrochloric acid washing, water washing, and drying, mix with the 5 g / L epoxy resin solution base at a ratio, fully grind and disperse to make the conductive filler uniformly distributed and capable of contacting each other, to obtain the silver / aluminum / carbon powder mixed conductive filler and the epoxy resin base conductive coating which are light, high-weather-resistant and high-conductive;

[0060] (4) Preparation of the band-pass frequency selective layer: according to the hexagon / circle ring nested type band-pass frequency selective surface pattern design scheme, customize the corresponding 200-mesh silk screen printing mold, lay the prepared mechanical reinforcing layer / isolation layer / environmental resistance layer combination on the silk screen printing mold operation table with the mechanical reinforcing layer on the top, press the silk screen mold tightly on the surface of the mechanical reinforcing layer, uniformly brush the conductive coating on the surface, repeat 5 times, dry at room temperature, and then heat to 5°C for curing for 8 hours, so that the frequency selective pattern is completely shaped and firmly attached to the surface of the mechanical reinforcing layer;

[0061] (5) Coating of the frequency selective packaging protection layer: uniformly spray the ink layer on the surface of the band-pass frequency selective layer, with a spraying thickness of 20 μm, to obtain the multilayer composite structure flexible frequency selective surface material.

[0062] The multilayer composite structure flexible frequency selective surface material prepared in the example is subjected to performance testing, the wave transmission rate is tested by using the focusing lens method, and the result is shown in Table 1. Figure 8, the wave permeability at 0.5-2.0 GHz is greater than 65%, the wave permeability at 0.85-1.60 GHz is greater than 90%, the tear strength obtained by using the trouser tear method is 1150 N, the mold resistance obtained by using the local method is level 1, and the helium permeability obtained by using the pressure difference method is less than 0.2%. In the embodiment, the mixed conductive filler is selected as the frequency selective printing paste, the period size and the unit size of the frequency selective pattern array are changed, the minimum value of the wave permeability at 0.5-2.0 GHz is increased by 11%, and the bandwidth of the wave permeability greater than 90% is expanded by 0.12 GHz.

[0063] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms described. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the application. The exemplary embodiments were chosen and described in order to explain the principles of the application and its practical application and to allow others skilled in the art to understand the application for various exemplary embodiments with various modifications being applicable. The scope of the application is intended to be defined by the claims and their equivalents.

Claims

1. A multilayer composite flexible frequency-selective surface material, characterized in that, From top to bottom, the layers consist of: an acrylic polyvinylidene fluoride organic polymer coating environmentally resistant layer, a metal oxide organic film isolation layer, an ultra-high molecular weight polymer fiber reinforced polymer matrix composite film mechanical reinforcement layer, a bandpass selective layer, and an encapsulation protective layer. The bandpass selective layer is a hexagonal / ring nested bandpass frequency selective pattern array, printed from a conductive coating composed of conductive filler / polymer resin matrix. The encapsulation protective layer is an ink coating. The thickness of the bandpass selective layer is 20~100μm. The periodic unit of the hexagonal / ring nested bandpass frequency selective pattern array includes inner hexagonal hole units and outer hexagonal units with overlapping centers. Sixteen circular holes are uniformly nested between the inner and outer hexagonal units, with the centers of the sixteen circular holes located on the same ring. The periodic size is 10~20mm, and the outer unit size is 8~15mm.

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

3. The multilayer composite flexible frequency selective surface material according to claim 1, characterized in that, The conductive filler is one or more of silver powder, aluminum powder, and carbon powder.

4. A method for preparing a multilayer composite flexible frequency-selective surface material as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Bonding of mechanical reinforcement layer and isolation layer: Low-temperature resistant polyurethane adhesive is uniformly coated between the mechanical reinforcement layer of ultra-high molecular weight polymer fiber reinforced polymer matrix composite film and the metal oxide organic film isolation layer, and uniformly laminated, compacted and heated to cure, so as to obtain a well bonded mechanical reinforcement layer and isolation layer. (2) Coating the environmentally resistant layer: lay the bonded mechanical reinforcement layer and isolation layer flat, with the isolation layer side up, and uniformly coat with an organic polymer coating. Dry, heat and cure to form a uniform and continuous environmentally resistant layer. (3) Preparation of frequency-selective conductive coating: After washing and drying the conductive filler, mix it with the resin solution matrix, grind and disperse it thoroughly so that the conductive filler is evenly distributed and can contact each other to obtain the conductive coating; (4) Preparation of bandpass frequency selection layer: The prepared mechanical reinforcement layer / isolation layer / environmental resistance layer combination is laid flat on the screen printing mold operating table with the mechanical reinforcement layer facing upward. The conductive coating is screen printed on the surface of the mechanical reinforcement layer to prepare a hexagonal / ring nested bandpass frequency selection pattern. The mixture is then heated and cured to obtain the bandpass frequency selection layer. (5) Coating and encapsulating protective layer: uniformly spray ink layer on the surface of the bandpass frequency selective layer to obtain a multi-layer composite flexible frequency selective surface material.

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

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

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

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

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

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

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