Metamaterial frequency selective surface and preparation method thereof

Abstract

The invention discloses a metamaterial frequency selective surface and a preparation method thereof, and belongs to the technical field of electromagnetic wave frequency selective surfaces. The method comprises the following steps: designing a periodic array pattern with wave absorbing property, and carrying out selective laser cladding on a dielectric material paved with a metal powder layer according to the periodic array pattern. The metamaterial frequency selective surface is directly and efficiently prepared on the surface of the dielectric material, no extra coating or deposition step needs to be introduced in the process, and compared with photoetching, silk-screen printing, ink-jet printing and the like, the preparation process is simplified, the production cost is effectively reduced, and the stability and durability of the obtained structure are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave frequency selective surfaces, and in particular to a metamaterial frequency selective surface and a preparation method thereof. Background Art

[0002] A frequency selective surface (FSS) is a single-frequency or multi-frequency periodic array structure composed of a large number of passive resonant units, which is composed of periodically arranged metal patch units or aperture units periodically arranged on a metal screen. Such a surface can exhibit total reflection (patch type) or total transmission characteristics (aperture type) near the unit resonance frequency. It is often referred to as a "space filter" by those in the industry. A metamaterial frequency selective surface (Metamaterial Frequency Selective Surface, abbreviated as MFS) is a two-dimensional periodic structure or quasi-periodic structure based on metamaterial technology and having frequency selective characteristics.

[0003] Existing preparation methods for metamaterial frequency selective surfaces mainly include photolithography technology, electron beam lithography technology, nanoimprint technology, etc. Among them, photolithography technology relies on a mask and has a complex process and high cost, making it difficult to achieve large-area preparation; electron beam lithography technology has high resolution but low efficiency and slow processing speed, and is not suitable for large-scale production; although nanoimprint technology can batch replicate patterns, the template preparation is difficult, and pattern deformation or defects are likely to occur during the imprinting process. These limitations in terms of cost, efficiency, accuracy, and large-scale production restrict the wide application of metamaterial frequency selective surfaces in complex scenarios.

[0004] In addition, with the continuous development of technology and the increasing complexity of the application environment, higher performance requirements are put forward for materials, which not only need to meet frequency selection, but also need to have superhydrophobicity, such as the leading edge of the aircraft wing surface, fairing; ship mast; 5G / 6G communication base station antenna; leading edge protection of wind turbine blades, etc. A single frequency selection functional material can no longer meet the current application requirements. Summary of the Invention

[0005] In view of the above technical problems and requirements, the present invention provides a metamaterial frequency selective surface and a preparation method thereof, which solve the above problems and bring other technical effects due to the following technical features.

[0006] On the one hand, the present invention provides a preparation method for a metamaterial frequency selective surface, which is obtained by designing a periodic array pattern with wave absorption properties and performing laser selective area melting on a dielectric material paved with a metal powder layer according to the periodic array pattern.

[0007] The present invention uses a laser to perform selective area melting on a metal powder layer laid on the surface of a dielectric material according to a preset periodic array pattern. Under the action of the laser, on the one hand, the metal powder melts to form a preset periodic array pattern, thereby realizing the frequency selection function on the surface of the dielectric material. On the other hand, the metal powder is fully melted under the action of the laser, and the manufactured metamaterial structure is dense, effectively reducing the porosity, and significantly improving the mechanical strength and surface quality of the metamaterial structure compared with other methods such as coating and deposition.

[0008] According to a preferred embodiment of the present invention, the above-mentioned laser selective area melting includes: under the conditions that the laser wavelength is 1064 nm to 1550 nm, the laser power is 1000 W to 3000 W, the spot diameter is 10 μm to 100 μm, the scanning rate is 300 mm / s to 1000 mm / s, and the scanning pitch is 0.05 mm to 0.5 mm, a laser is used to perform selective area melting on the metal powder layer according to a periodic array pattern.

[0009] Through the precise control of the above laser parameters, the present invention can perform melting with a small size on the surface of the dielectric material, realizing high-precision forming of the frequency selective surface of the metamaterial and ensuring that the metal powder melts without burning the dielectric material as the substrate.

[0010] According to a preferred embodiment of the present invention, the above-mentioned metal powder layer is selected from the following materials: an alloy composed of one or more of copper, aluminum, iron, tungsten, nickel, silver, gold, cobalt, and titanium.

[0011] Preferably, the metal powder layer is a copper-nickel alloy powder. It has high electrical conductivity, higher than that of pure copper, is corrosion-resistant, and is easy to process and form.

[0012] Preferably, the metal powder layer is a silver-gold alloy powder. Its conductivity is better than that of pure silver, and the cost is low.

[0013] Preferably, the metal powder layer is a gold-nickel alloy powder. It has excellent electrical conductivity, extremely strong oxidation resistance, and good biocompatibility.

[0014] Preferably, the metal powder layer is an iron-nickel-cobalt alloy powder. It has a high magnetic permeability, a low coercive force, and the electromagnetic response can be tuned by an external magnetic field.

[0015] Preferably, the metal powder layer is a titanium-copper alloy powder. It has high strength and is corrosion-resistant.

[0016] According to a preferred embodiment of the present invention, the powder particle size of the above-mentioned metal powder layer is 15 μm to 45 μm, and the powder laying thickness is 50 μm to 100 μm.

[0017] In the embodiments of the present invention, the metal powder layer has a particle size in the range of 15 μm to 45 μm, and the laser can melt the powder well and make it clad. If the particle size is too large, the laser cannot melt the powder particles instantaneously, which will prolong the laser irradiation time, and the resulting high temperature will cause ablation of the dielectric material such as polymer composites. If the powder particle size is too small, it is not only easy to oxidize, but also the impact force generated during the laser processing is likely to blow away the powder. The laying thickness of the metal powder layer is in the range of 50 μm to 100 μm, and better electrical properties can be obtained. Too thick powder laying will lead to an increase in material weight, which is not conducive to low-cost manufacturing and the lightweight requirements during application on aircraft. If the thickness is too small, there is also a problem that it is easily blown away during the cladding process.

[0018] Preferably, the powder particle size of the metal powder layer is 20 μm to 40 μm. More preferably, the powder particle size of the metal powder layer is 25 μm to 35 μm.

[0019] Preferably, the powder laying thickness is 60 μm to 90 μm. More preferably, the powder laying thickness is 75 μm to 85 μm.

[0020] According to the preferred embodiment of the present invention, the above-mentioned dielectric material is an inorganic non-metallic ceramic material, an inorganic non-metallic composite material or a fiber-reinforced polymer composite material.

[0021] The present invention generates a metasurface frequency selective surface by laser selective cladding, which is applicable to inorganic non-metallic ceramic materials, inorganic non-metallic composite materials or fiber-reinforced polymer composite materials, and has a very wide application range.

[0022] Preferably, the inorganic non-metallic ceramic material is selected from the following materials: alumina ceramic, magnesia ceramic, silicon nitride ceramic, aluminum nitride ceramic, boron nitride ceramic, silicon carbide ceramic or boron carbide ceramic.

[0023] According to the preferred embodiment of the present invention, the above-mentioned inorganic non-metallic composite material is a quartz-reinforced composite material, a glass fiber-reinforced composite material, an alumina-based composite material, an alumina-reinforced composite material, a silicon carbide-based composite material or a silicon carbide-reinforced composite material.

[0024] The quartz-reinforced composite material includes quartz fiber-reinforced composite material and quartz powder-reinforced composite material.

[0025] Preferably, the quartz reinforced composite material is selected from the following materials: quartz fiber reinforced epoxy resin / carbon fiber (EP-CF-SiO2) composite material, quartz fiber reinforced polyimide / graphene (PI-Gr-SiO2) composite material, quartz fiber reinforced silicon-containing polyarylene resin / carbon nanotube (polysilarylene-CNT-SiO2) composite material, quartz fiber reinforced epoxy resin / ferrite (EP-ferrite-SiO2) composite material, quartz powder filled silicone rubber / ferrite (PDMS-ferrite-SiO2) composite material, quartz fiber reinforced boron nitride (BN-SiO2) composite material, quartz fiber reinforced silicon carbide (SiC-SiO2) composite material, quartz fiber reinforced silicon-containing polyarylene resin / graphene (polysilarylene-Gr-SiO2) composite material, quartz fiber reinforced polyimide / carbon nanotube (PI-CNT-SiO2) composite material, quartz fiber / carbon fiber / ferrite gradient composite material (SiO2-CF-ferrite), quartz powder filled silicone rubber / nano-ferrite (PDMS-nano-ferrite-SiO2) composite material.

[0026] Preferably, the glass fiber reinforced composite material is selected from the following materials: glass fiber reinforced epoxy resin composite material, glass fiber reinforced polyimide composite material, glass fiber reinforced cyanate ester resin composite material, glass fiber reinforced silicone resin composite material, glass fiber reinforced polystyrene (PS) / polypropylene (PP) composite material.

[0027] Preferably, the alumina-based composite material is a composite material with alumina ceramic as the matrix, and is selected from the following materials: alumina-carbon fiber (Al2O3-CF) composite material, alumina-graphene (Al2O3-Gr) composite material, alumina-silicon carbide (Al2O3-SiC) composite material, alumina-ferrite (Al2O3-ferrite) composite material, alumina-carbonyl iron (Al2O3-CIP) composite material, alumina-boron nitride (Al2O3-BN) composite material, alumina-silicon carbide (Al2O3-SiC) composite material, alumina-silicon nitride (Al2O3-Si3N4) composite material.

[0028] Preferably, the alumina reinforced composite material is a composite material with alumina particles or alumina fibers as the reinforcement, and is selected from the following materials: epoxy resin-alumina-carbon fiber (EP-Al2O3-CF) composite material, polyimide-alumina-graphene (PI-Al2O3-Gr) composite material.

[0029] Preferably, the silicon carbide-based composite material is a composite material with silicon carbide ceramics as the matrix, and is selected from the following materials: silicon carbide-ferrite (SiC-ferrite) composite material, silicon carbide-carbonyl iron (SiC-CIP) composite material, silicon carbide particle-reinforced silicon carbide (SiC-SiC) porous ceramics, silicon carbide / carbon fiber / ferrite gradient (SiC / CF / ferrite) composite material.

[0030] Preferably, the silicon carbide-reinforced composite material includes silicon carbide fiber-reinforced composite material, silicon carbide particle-reinforced composite material, and silicon carbide whisker-reinforced composite material, and is selected from the following materials: silicon carbide particle-filled epoxy resin (EP-SiC) composite material, silicon carbide fiber-reinforced boron nitride (BN-SiC) composite material, polyimide-silicon carbide (PI-SiC) composite material, epoxy resin-silicon carbide (EP-SiC) composite material, silicon carbide nanofiber-paraffin (SiC nanofiber-paraffin) composite material, silicon carbide nanoparticle-filled silicone rubber (PDMS-SiC) composite material.

[0031] According to a preferred embodiment of the present invention, the above fiber-reinforced polymer composite material is an aramid fiber-reinforced polymer composite material or a PBO fiber-reinforced polymer composite material.

[0032] Preferably, the aramid fiber-reinforced polymer composite material is selected from the following materials: aramid fiber / cyanate ester resin composite material, aramid fiber / polyimide resin composite material, aramid fiber / epoxy resin composite material, aramid fiber / polytetrafluoroethylene (PTFE) composite material, aramid fiber / polyphenylene sulfide (PPS) composite material.

[0033] Preferably, the PBO fiber-reinforced polymer composite material is selected from the following materials: PBO fiber-reinforced epoxy resin composite material, PBO fiber-reinforced cyanate ester resin composite material, PBO fiber-reinforced polyimide (PI) composite material, PBO fiber-reinforced polytetrafluoroethylene (PTFE) composite material, PBO fiber-reinforced polyphenylene sulfide (PPS) composite material, PBO fiber-reinforced polyether ether ketone (PEEK) composite material, PBO fiber-reinforced silicone rubber composite material, PBO fiber-reinforced liquid crystal polymer (LCP) composite material.

[0034] Preferably, the fiber-reinforced polymer composite material can also be selected from the following materials: carbon fiber / epoxy resin-carbon nanotube composite material, carbon fiber / polyimide-graphene composite material, glass fiber / polyethylene-ferrite composite material, aramid fiber / polyurethane-silicon carbide composite material, basalt fiber / epoxy resin-graphite composite material, carbon-modified sisal fiber / polylactic acid-polyaniline composite material, carbon fiber-carbon nanotube / epoxy resin-carbonyl iron composite material.

[0035] According to a preferred embodiment of the present invention, the above preparation method further includes laser modification: under the conditions that the laser power is 10W - 100W, the scanning speed is 300mm / s - 1000mm / s, and the scanning pitch is 0.05mm - 0.5mm, the metamaterial frequency selective surface is modified to obtain superhydrophobicity.

[0036] Based on laser selective melting, the present invention performs laser modification on the metamaterial frequency selective surface, changes its surface roughness through laser ablation, and forms microstructures such as micropores, microgrooves, and nanocolumns, thereby obtaining superhydrophobicity. The above-mentioned modified laser parameters provided by the present invention can better complete the laser modification process. The ablation depth obtained by this modification is generally less than 1μm, which is much smaller than the thickness of the laser-clad metal powder: 50μm - 100μm. Thus, ideal superhydrophobicity is obtained while not affecting the frequency selection function of the metamaterial structural layer, and the mechanical strength of the material surface is ensured, thereby improving the product quality.

[0037] It should be noted that during laser modification, the laser scans the entire metamaterial frequency selective surface, including the cladding area and the non-cladding area, so as to ensure that the entire metamaterial frequency selective surface has superhydrophobicity.

[0038] According to a preferred embodiment of the present invention, the unit pattern of the above periodic array pattern is in a regular hexagon nested structure, a maze ring structure, or a cross contour structure.

[0039] On the other hand, the present invention provides a metamaterial frequency selective surface prepared by the above preparation method. The metamaterial frequency selective surface includes a dielectric layer composed of a dielectric material and a metallurgical coating combined with the dielectric layer through laser selective melting. The metallurgical coating is a periodic array pattern.

[0040] According to a preferred embodiment of the present invention, the above metamaterial frequency selective surface further includes at least one of micropores, microgrooves, and nanocolumns.

[0041] The present invention has the following beneficial effects:

[0042] The present invention can directly and efficiently prepare a metamaterial frequency selective surface on the surface of a dielectric material. This process does not require the introduction of any additional coating or deposition steps. Compared with photolithography, screen printing, inkjet printing, etc., the preparation process is simplified, the production cost is effectively reduced, and the stability and durability of the obtained structure are significantly improved.

[0043] The present invention can achieve high-precision and high-quality control of the metamaterial frequency selective surface. By using an existing laser, it can achieve melting of micro-sized areas (for example, the spot diameter can be only 50 μm), ensuring high-precision forming of the metamaterial structure. The metal powder is fully melted under the action of the laser to form a dense metamaterial structure, effectively reducing the porosity and significantly improving the mechanical strength and surface quality of the material.

[0044] The present invention can complete the preparation of the metamaterial frequency selective surface on the surface of a dielectric material with a complex structure, and can manufacture metamaterials with complex geometric shapes and internal structures, such as tiny periodic patterns, porous structures, etc. These complex structures are difficult to achieve by traditional manufacturing methods, but can be easily completed in the present invention through precise laser control and pre-placement of the metal powder layer, providing greater freedom for the design and application of metamaterials.

[0045] The present invention has the processing ability for complex curved surfaces and can in-situ process the required complex metamaterial structure patterns on complex curved surfaces, making up for the deficiencies of traditional lay-up methods in processing complex curved surfaces. At the same time, the processing efficiency is higher, meeting the requirements for complex curved surface structures in practical applications.

[0046] The metamaterial structure patterns processed by the method provided by the present invention have new electromagnetic functions, such as wave absorption, frequency selection, electromagnetic deflection, etc. These functions can significantly improve the electromagnetic protection performance of weapons and equipment, expanding the application scope of metamaterials in the military field.

[0047] The present invention can obtain excellent physical properties. Through the dynamic focusing technology, the laser can penetrate deep into the material, enabling the integrated forming of multi-layer materials, enhancing the integrity and stability of the structure. At the same time, the optimization of the scanning path ensures uniform heat distribution inside the material, avoiding thermal stress concentration, thereby improving the fatigue resistance and durability of the metamaterial.

[0048] The present invention can realize the preparation of frequency selection patterns of various metals and alloy components, making up for the limitations of traditional screen printing and lithography, which can only prepare frequency selection structures of a few pure metals. Description of the Drawings

[0049] Figure 1 Schematic diagram of the periodic array pattern of the metamaterial frequency selective surface in Example 1;

[0050] Figure 2 S-parameter test results of the metamaterial frequency selective surface in Example 1;

[0051] Figure 3 Superhydrophobicity test results of the metamaterial frequency selective surface in Example 2;

[0052] Figure 4 Schematic diagram of the periodic array pattern of the metamaterial frequency selective surface in Example 3;

[0053] Figure 5 S-parameter test results of the metamaterial frequency selective surface in Example 3;

[0054] Figure 6 Superhydrophobicity test results of the metamaterial frequency selective surface in Example 4;

[0055] Figure 7 Schematic diagram of the periodic array pattern of the metamaterial frequency selective surface in Example 5;

[0056] Figure 8 S-parameter test results of the metamaterial frequency selective surface in Example 5;

[0057] Figure 9 Superhydrophobicity test results of the metamaterial frequency selective surface in Example 6;

[0058] Figure 10 Microscopic test diagram of the superhydrophobic microstructures on the surface of the present invention;

[0059] Figure 11 Schematic diagram of the periodic unit structure of the metamaterial frequency selective surface of the present invention. Detailed implementation manners

[0060] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. For those conditions not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0061] Some terms related to the present invention are explained and described below.

[0062] Metamaterial, same as the metamaterial structure, is a composite material that realizes special physical properties that natural materials do not possess through artificial design of microscopic structure units (usually sub-wavelength size). It can also be described or understood as a sub-wavelength structure or an absorbing impedance structure.

[0063] Selective laser melting is a process in which metal powder is melted by a laser beam according to a designed periodic array pattern and solidified on the surface of a dielectric material (or called a substrate) to form a metallurgical bonding coating, that is, a metamaterial structure layer.

[0064] Laser modification refers to an advanced manufacturing technology that uses the energy of a laser beam to precisely regulate the surface of a material to improve its physical, chemical or biological properties. In the present invention, it specifically refers to obtaining superhydrophobicity on the surface of the material.

[0065] In the embodiments of the present invention, the description of the particle size distribution of metal powder is described according to D10, D50, and D90 commonly used in the industry. They are characteristic particle size parameters defined based on the cumulative distribution curve and are often used to represent the distribution range and central tendency of the particle size of powder particles. Among them:

[0066] D10, the 10th percentile particle size, means that in the particle size distribution, 10% of the particle sizes are less than or equal to this value, and the remaining 90% of the particle sizes are greater than this value.

[0067] D50, the median particle size, or the median diameter, means that in the particle size distribution, 50% of the particle sizes are less than or equal to this value, and the remaining 50% of the particle sizes are greater than this value.

[0068] D90, the 90th percentile particle size, means that in the particle size distribution, 90% of the particle sizes are less than or equal to this value, and the remaining 10% of the particle sizes are greater than this value.

[0069] D100, also known as the "top particle size" or "maximum particle size", means that 100% of the particle sizes are less than or equal to this value, that is, the particle size of the largest particle in the sample.

[0070] The present invention will be further described in detail below with reference to the embodiments.

[0071] Embodiment 1

[0072] The embodiments of the present invention provide a method for preparing a metamaterial frequency selective surface with a regular hexagon nested structure on the surface of a glass fiber reinforced epoxy composite material. It is prepared by designing a periodic array pattern with an absorbent regular hexagon nested structure and performing laser selective area cladding on the glass fiber reinforced epoxy composite material paved with a copper metal powder layer according to the periodic array pattern. Specifically, it includes the following steps:

[0073] 1. Material preparation

[0074] Select a glass fiber reinforced epoxy composite material as the dielectric material, which has good mechanical properties and high temperature resistance and is suitable as the substrate of the frequency selective surface. Uniformly lay the copper metal powder on the surface of the composite material. The powder particle size is 15μm - 45μm (D10 = 15μm ± 2μm, D50 = 30μm ± 2μm, D90 = 45μm ± 2μm, D100 ≤ 50μm), and the powder laying thickness is 50μm to ensure that the powder can be fully melted during the laser cladding process and form a good bond with the substrate.

[0075] 2. Frequency selective surface pattern design

[0076] Design as Figure 1The periodic array pattern shown, which consists of a periodic regular hexagon nested structure with a clear symmetrical shape, arranged closely and regularly. Here, L represents the side length of the hexagonal unit, G represents the line width of the hexagonal metal mesh structure, H represents the height of the unit, and D represents the spacing between the hexagonal metal mesh and the hexagonal metal sheet. The geometric parameters of the pattern are: the side length of the unit L = 5 mm, the spacing D = 1 mm, the height H = 7 mm, and the line width G = 1 mm.

[0077] 3. Selective laser cladding

[0078] (1) Equipment selection: A fiber laser is used for laser cladding, which features high power stability, high beam quality, and high efficiency.

[0079] (2) Parameter settings: The laser wavelength is set to 1064 nm, the laser power is 1000 W, the spot diameter is 10 μm, the scanning speed is 300 mm / s, and the scanning pitch is 0.05 mm. Under these parameters, the laser can accurately perform selective laser cladding on the metal powder layer according to the preset pattern, ensuring good bonding between the cladding layer (also known as the metallurgical coating) and the substrate: glass fiber reinforced epoxy composite material, with high dimensional accuracy.

[0080] (3) Operating steps: First, fix the glass fiber reinforced epoxy composite material plate on the laser processing platform and evenly lay a layer of copper powder on its surface. Then turn on the laser and perform selective laser cladding on the metal powder layer according to the designed periodic regular hexagon nested structure pattern (as Figure 1 shown). During the interaction between the laser and the metal powder, the metal powder quickly melts and solidifies, forming a periodic structure of regular hexagon nests with metallurgical bonding to the substrate, thus obtaining a metamaterial frequency selective surface.

[0081] Frequency selection performance test: Use a vector network analyzer to test the prepared metamaterial frequency selective surface and measure its reflection coefficient (S11) and transmission coefficient (S21) at different frequencies. The test results are as Figure 2 shown. Near a frequency of 8.5 GHz, obvious resonance peaks appear in both S11 and S21. Among them, the value of S21 is infinitely close to 0 dB, meaning that electromagnetic waves can be transmitted through this frequency selective surface with almost no reflection at this frequency, while the corresponding S11 is about -18 dB, further proving the high transmission and low reflection characteristics of this laser cladding frequency selective surface. At frequency points far from the resonance frequency, such as in the frequency bands of 2 GHz - 4 GHz and 12 GHz - 13 GHz, S21 is less than -10 dB, while S11 is greater than -0.5 dB, indicating that within the above frequency bands, the transmittance of electromagnetic waves is only less than 10%, while the reflectance is greater than 90%, showing obvious frequency selection characteristics.

[0082] Example 2

[0083] In the embodiment of the present invention, a laser modification step is added on the basis of Embodiment 1 to obtain superhydrophobicity. The specific process is as follows:

[0084] 1. Equipment selection

[0085] Use a femtosecond laser to perform surface modification on the formed frequency selective surface to endow it with superhydrophobic properties.

[0086] 2. Parameter setting

[0087] Set the laser power to 10 W, the scanning speed to 300 mm / s, and the scanning pitch to 0.05 mm. The high energy and ultrashort pulse width of the femtosecond laser can generate micro-nano structures on the material surface, thereby changing its surface energy and roughness to achieve the superhydrophobic effect.

[0088] 3. Operation steps

[0089] Place the sample after laser selective area cladding on the femtosecond laser processing platform, adjust the focus position to make the laser focus on the frequency selective surface pattern. Then, scan the entire workpiece surface (including the cladding area and the substrate surface not clad with metal) according to the set parameters. The laser forms microscopic structures such as tiny concave-convex structures and nano-columns on the surface pattern. These structures can effectively reduce the surface energy of the material surface, increase the contact angle of water droplets on the surface, and thus achieve superhydrophobic properties. During the scanning process, the laser scans back and forth along the contour and internal details of the pattern multiple times to ensure that the entire surface is evenly treated by the laser.

[0090] Superhydrophobic performance test: Use a contact angle measuring instrument to test the contact angle of the surface after femtosecond laser modification treatment. The test results are as Figure 3 shown. The contact angle of water droplets on the surface reaches more than 147°, indicating that the surface has excellent superhydrophobic performance.

[0091] Embodiment 3

[0092] The embodiment of the present invention provides a metamaterial frequency selective surface with a maze ring unit structure prepared on the surface of an alumina ceramic material. It is prepared by designing a periodic array pattern of a maze ring unit structure with wave absorption properties and performing laser selective area cladding on the alumina ceramic material paved with a nickel metal powder layer according to the periodic array pattern. The specific steps include the following:

[0093] 1. Material preparation

[0094] A 3mm thick alumina ceramic substrate is selected as the dielectric material, which has high hardness, strength and wear resistance, and relatively low cost, making it suitable as the base material for the frequency selective surface. Nickel metal powder is evenly laid on the surface of the alumina ceramic substrate, with a powder particle size of 20μm to 40μm (D10 = 20μm ± 2μm, D50 = 30μm ± 2μm, D90 = 40μm ± 2μm, D100 ≤ 45μm), and the powder laying thickness is 70μm to ensure that the powder can be fully melted and form a good bond with the base material during the laser cladding process. Nickel powder has good electrical conductivity, thermal conductivity and magnetism, and plays an important role in alloy preparation, which can improve the forming performance and uniform distribution of the alloy.

[0095] 2. Frequency Selective Surface Pattern Design

[0096] Design as Figure 4 shown in the periodic array pattern. The center of the unit pattern is a larger rectangular block, and four smaller rectangular blocks extend from its four sides respectively, forming an overall structure of a maze ring. This structure has high geometric symmetry, which helps to achieve uniform electromagnetic response at specific frequencies. The geometric parameters of the pattern are: unit length L = 6mm, metal structure line width D = 1.5mm, height H = 15mm, and unit interval width G = 1.5mm.

[0097] 3. Selective Laser Melting

[0098] (1) Equipment selection: A fiber laser is used for laser cladding to ensure high power stability, high beam quality and high efficiency.

[0099] (2) Parameter setting: The laser wavelength is set to 1310nm, the laser power is 2500W, the spot diameter is 50μm, the scanning rate is 800mm / s, and the scanning pitch is 0.12mm. The setting of these parameters is aimed at ensuring that the laser can accurately perform selective laser melting on the nickel powder according to the preset frequency selective pattern, while ensuring good bonding between the cladding layer and the alumina substrate and high dimensional accuracy.

[0100] (3) Operation steps: Fix the alumina ceramic substrate on the laser processing platform, and evenly lay a layer of nickel powder on the surface of the base material. Then turn on the laser and perform selective laser melting on the nickel powder layer according to the designed periodic maze ring array pattern. During the interaction between the laser and the nickel powder, the nickel powder quickly melts and solidifies, forming a frequency selective periodic structure that is metallurgically bonded to the alumina ceramic substrate, and a metamaterial frequency selective surface is prepared.

[0101] Frequency Selective Performance Test: Use a vector network analyzer to test the prepared metamaterial frequency selective surface, and measure its reflection coefficient (S11) and transmission coefficient (S21) at different frequencies, as Figure 5As shown. Due to the differences in electromagnetic properties between nickel powder and aluminum powder, the predicted test results show that near a frequency of 5.2 GHz, obvious resonance peaks appear in both S11 and S21. Among them, the value of S21 is infinitely close to 0 dB, which means that electromagnetic waves can be transmitted through this frequency selective surface with almost no reflection at this frequency, and the transmission coefficient is greater than 98%; while the corresponding S11 is about -15 dB, and the corresponding reflection coefficient is less than 2%, further proving the high transmission and low reflection characteristics of this laser cladding frequency selective surface. At frequency points far from the resonance frequency, such as in the frequency bands of 2 - 3.3 GHz and 7.5 - 8 GHz (except for the resonance frequency, the frequency band range is slightly broadened), S21 is less than -10 dB, while S11 is greater than -0.5 dB, indicating that within the above frequency bands, the transmittance of electromagnetic waves is only less than 10%, while the reflectance is greater than 90%, showing obvious frequency selective characteristics, and the frequency selection range is broadened compared with the aluminum powder surface.

[0102] Example 4

[0103] In the embodiment of the present invention, a laser modification step is added on the basis of Example 3 to obtain superhydrophobicity. The specific process is as follows:

[0104] 1. Equipment selection

[0105] Use a femtosecond laser to perform surface modification on the formed frequency selective surface to endow it with superhydrophobic characteristics.

[0106] 2. Parameter setting

[0107] The laser power is set to 70 W, the scanning speed is 700 mm / s, and the scanning pitch is 0.12 mm. The high energy and ultrashort pulse width of the femtosecond laser can generate finer micro-nano structures on the nickel surface, thereby changing its surface energy and roughness to achieve the superhydrophobic effect.

[0108] 3. Operating steps

[0109] Place the sample after laser cladding on the femtosecond laser processing platform, adjust the focus position so that the laser is focused on the frequency selective surface pattern. Then, perform laser scanning on the entire workpiece surface according to the set parameters. The laser forms microscopic structures such as tiny concavo-convex structures and nano-columns on the surface pattern. These structures can effectively reduce the surface energy of the material surface, increase the contact angle of water droplets on the surface, and thus achieve superhydrophobic characteristics. During the scanning process, the laser scans back and forth along the contour and internal details of the pattern multiple times to ensure that the entire surface is evenly treated by the laser.

[0110] Superhydrophobic performance test: Use a contact angle measuring instrument to measure the contact angle of the surface after femtosecond laser treatment. The results are as Figure 6 shown. The contact angle of the water droplet on the surface reaches 160°, indicating that the surface has excellent superhydrophobic performance.

[0111] Example 5

[0112] This example provides a method for fabricating a metamaterial frequency selective surface with a cross-profile unit structure on the surface of a silicon carbide fiber composite material. It is fabricated by designing a periodic array pattern of cross-profile unit structures with wave-absorbing properties and performing selective laser cladding on the silicon carbide fiber composite material paved with an iron-cobalt alloy powder layer according to the periodic array pattern. The specific steps are as follows:

[0113] 1. Material preparation

[0114] Select a 2.5-mm-thick silicon carbide fiber composite material plate as the dielectric material, which has high-temperature performance, mechanical properties, corrosion resistance, and dimensional stability and is suitable as the substrate for the frequency selective surface. Uniformly lay an iron-cobalt alloy powder (mass fraction 1:1) on the surface of the silicon carbide fiber composite material plate. The powder particle size is 25 μm to 35 μm (D10 = 25 μm ± 2 μm, D50 = 30 μm ± 2 μm, D90 = 35 μm ± 2 μm, D100 ≤ 40 μm), and the powder laying thickness is 100 μm to ensure that the powder can be fully melted during the laser cladding process and form a good bond with the substrate. The iron-cobalt alloy powder has characteristics such as a concentrated particle size distribution, uniform element distribution, and low oxygen content, which helps to form a dense cladding layer.

[0115] 2. Frequency selective surface pattern design

[0116] Design a periodic array pattern as shown in Figure 7 which is composed of periodic arrangements of multiple identical cross-profile unit structures. Each unit structure is composed of multiple rectangles and lines and has geometric symmetry, which helps to achieve a uniform electromagnetic response at a specific frequency. The geometric parameters of the pattern are: unit length L = 6 mm, cross-edge height D = 1.2 mm, cross-edge width W = 3.6 mm, and metal pattern line width G = 0.5 mm.

[0117] 3. Selective laser cladding

[0118] (1) Equipment selection: Use a fiber laser for laser cladding to ensure high power stability, high beam quality, and high efficiency.

[0119] (2) Parameter setting: Set the laser wavelength to 1550 nm, the laser power to 3000 W, the spot diameter to 100 μm, the scanning rate to 1000 mm / s, and the scanning pitch to 0.5 mm. These parameter settings are designed to ensure that the laser can accurately perform selective cladding on the iron-cobalt alloy powder according to the preset cross-profile pattern, while ensuring good bonding between the cladding layer and the silicon carbide fiber composite material plate and high dimensional accuracy.

[0120] (4) Operating steps: Fix the silicon carbide fiber composite material plate on the laser processing platform, and evenly lay a layer of iron-cobalt alloy powder on the surface of the substrate. Then turn on the laser and perform selective laser cladding on the iron-cobalt alloy powder layer according to the designed periodic cross-profile array pattern. During the interaction between the laser and the iron-cobalt alloy powder, the powder quickly melts and solidifies, forming a periodic structure of cross-profile units metallurgically bonded to the silicon carbide fiber composite material plate, thus obtaining a metamaterial frequency selective surface.

[0121] Frequency selection performance test: Use a vector network analyzer to test the prepared metamaterial frequency selective surface, and measure its reflection coefficient (S11) and transmission coefficient (S21) at different frequencies. The results are as Figure 8 shown. Near the frequency of 7.5 GHz, obvious resonance peaks appear in both S11 and S21. Among them, the value of S21 is infinitely close to 0 dB, which means that electromagnetic waves can be transmitted through this frequency selective surface with almost no reflection at this frequency; while the corresponding S11 is about -17 dB, further proving the high transmission and low reflection characteristics of this laser cladding frequency selective surface. At frequency points far from the resonance frequency, such as in the frequency bands of 2 - 4 GHz and 1-2 - 14 GHz (except for the resonance frequency, the frequency band range is further broadened), S21 is less than -10 dB, while S11 is greater than -1 dB, indicating that within the above frequency bands, the transmittance of electromagnetic waves is only less than 10%, while the reflectance is greater than 90%, presenting obvious frequency selection characteristics, and the frequency selection range is further broadened compared with the surfaces of aluminum powder and nickel powder.

[0122] Example 6

[0123] In the embodiment of the present invention, a laser modification step is added on the basis of Example 5 to obtain superhydrophobicity. The specific process is as follows:

[0124] 1. Equipment selection

[0125] Use a femtosecond laser to perform surface modification on the formed frequency selective surface to endow it with superhydrophobic characteristics.

[0126] 2. Parameter setting

[0127] Set the laser power to 100 W, the scanning speed to 1000 mm / s, and the scanning pitch to 0.5 mm. The high energy and ultrashort pulse width of the femtosecond laser can generate finer micro-nano structures on the surface of the iron-cobalt alloy, thereby changing its surface energy and roughness to achieve the superhydrophobic effect.

[0128] 3. Operating steps

[0129] It should be noted that there seems to be a small error in the original text where "1-2 - 14 GHz" is written. It is assumed to be "12 - 14 GHz" in the translation. If this is not an error, please correct the translation according to the actual situation.Place the sample after laser cladding on the femtosecond laser processing platform, adjust the focus position to make the laser focus on the frequency selective surface pattern. Then, perform laser scanning on the entire workpiece surface according to the set parameters. The laser forms microscopic structures such as tiny concavo-convex structures and nanocolumns on the surface pattern. These structures can effectively reduce the surface energy of the material surface, increase the contact angle of water droplets on the surface, and thus achieve superhydrophobic properties. During the scanning process, the laser scans back and forth along the contour and internal details of the pattern to ensure that the entire surface is evenly treated by the laser.

[0130] Superhydrophobic performance test: Use a contact angle measuring instrument to measure the contact angle of the surface after femtosecond laser treatment. The results are as Figure 9 shown. The contact angle of the water droplet on the surface is 150°, indicating that the surface has excellent superhydrophobic performance.

[0131] See Figure 10 , which is the microscopic test diagram of the superhydrophobic microstructure of the surface of the present invention. By observing the microscopic morphology of the surface, it is found that a more refined microgroove, micropore, and nanocolumn micro-nano composite structure is formed on the metamaterial frequency selective surface after laser modification treatment. These structures are the key factors for achieving superhydrophobic performance.

[0132] See Figure 11 , which is the schematic diagram of the periodic unit structure of the metamaterial frequency selective surface of Embodiment 1 of the present invention. The metamaterial frequency selective surface includes a dielectric layer 2 (also referred to as the substrate in the embodiment of the present invention) composed of a dielectric material and a metallurgical coating 1 (also referred to as the metamaterial structure layer in the embodiment of the present invention) combined with the dielectric layer by laser selective area melting. The metallurgical coating 1 is a periodic array pattern. Only the unit structure is shown in the figure for the sake of brevity. The periodic array pattern can be referred to Figure 1 as shown.

[0133] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a metamaterial frequency selective surface, characterized in that, It is prepared by designing a periodic array pattern with wave absorption properties and performing selective laser melting on a dielectric material paved with a metal powder layer according to the periodic array pattern.

2. The preparation method of the metamaterial frequency selective surface according to claim 1, characterized in that The selective laser melting includes: under the conditions that the laser wavelength is 1064 nm to 1550 nm, the laser power is 1000 W to 3000 W, the spot diameter is 10 μm to 100 μm, the scanning rate is 300 mm / s to 1000 mm / s, and the scanning pitch is 0.05 mm to 0.5 mm, using a laser to perform selective melting on the metal powder layer according to the periodic array pattern.

3. The preparation method of the metamaterial frequency selective surface according to claim 1, characterized in that The metal powder layer is selected from the following materials: an alloy composed of one or more of copper, aluminum, iron, tungsten, nickel, silver, gold, cobalt, and titanium.

4. The preparation method of the metamaterial frequency selective surface according to claim 3, characterized in that The powder particle size of the metal powder layer is 15 μm to 45 μm, and the powder paving thickness is 50 μm to 100 μm.

5. The preparation method of the metamaterial frequency selective surface according to claim 1, characterized in that, The dielectric material is an inorganic non-metallic ceramic material, an inorganic non-metallic composite material, or a fiber-reinforced polymer composite material.

6. The preparation method of the metamaterial frequency selective surface according to claim 5, characterized in that, The inorganic non-metallic composite material is a quartz-reinforced composite material, a glass fiber-reinforced composite material, an alumina-based composite material, an alumina-reinforced composite material, a silicon carbide-based composite material, or a silicon carbide-reinforced composite material.

7. The manufacturing method of the metamaterial frequency selective surface according to claim 5, characterized in that, The fiber-reinforced polymer composite material is an aramid fiber-reinforced polymer composite material or a PBO fiber-reinforced polymer composite material.

8. The preparation method of the metamaterial frequency selective surface according to any one of claims 1 to 7, characterized in that, The preparation method further includes laser modification: under the conditions that the laser power is 10 W to 100 W, the scanning rate is 300 mm / s to 1000 mm / s, and the scanning pitch is 0.05 mm to 0.5 mm, performing modification treatment on the metamaterial frequency selective surface to obtain superhydrophobicity.

9. The preparation method of the metamaterial frequency selective surface according to any one of claims 1 to 7, characterized in that, The unit pattern of the periodic array pattern is a regular hexagon nested structure, a maze ring structure, or a cross contour structure.

10. A metamaterial frequency selective surface, characterized in that, Prepared by using the preparation method according to any one of claims 1 to 9, the metamaterial frequency selective surface includes a dielectric layer composed of a dielectric material and a metallurgical coating combined with the dielectric layer by selective laser melting, and the metallurgical coating is a periodic array pattern.

11. The metamaterial frequency selective surface according to claim 10, wherein The metamaterial frequency selective surface further includes at least one of micropores, microgrooves, and nanorods.

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