Low-emissivity high-wave-transmissivity metasurface structure and preparation method thereof

Abstract

The invention discloses a metasurface structure with low emissivity and high wave transmission and a preparation method of the metasurface structure. The structure comprises a substrate dielectric layer and a periodic composite metal layer arranged on the substrate dielectric layer. The composite metal layer is composed of a plurality of working units which are periodically arranged, each working unit comprises four metal square blocks which are distributed in a cross-shaped gap mode and a peripheral metal frame, and adjacent inner corners of the four metal square blocks are cut off so as to cooperatively form a rectangular channel in the center. The composite metal layer is of a copper-nickel-gold laminated structure. The preparation method mainly comprises the steps of substrate treatment, copper layer deposition and periodic array patterning, composite metal layer subsequent deposition and finished product post-treatment. According to the metasurface, in the wide frequency bands of 18-27 GHz and 30-40 GHz, the wave transmission rate is higher than 95%, meanwhile, the average emissivity is not higher than 0.35, the technical problem that high wave transmission and low detectability are difficult to consider at the same time is effectively solved, and the metasurface is simple in structure and suitable for batch production.

Description

Technical Field

[0001] This invention relates to the fields of electromagnetic functional materials and stealth technology, specifically to a low emissivity, high transmittance metasurface structure and its preparation method. Background Technology

[0002] Metasurfaces, through their artificially designed periodic unit structures, can flexibly control the reflection, transmission, and radiation characteristics of electromagnetic waves, making them one of the core technologies for achieving a synergistic "wave transmission-stealth" capability. Currently, the performance requirements for metasurfaces in related fields are becoming increasingly stringent, but existing technologies face the following two challenges: 1. It is difficult to achieve both high transmittance and low emissivity: Most low emissivity metasurfaces rely on a highly conductive metal layer to achieve low radiation characteristics, but the metal layer easily reflects electromagnetic waves, resulting in a significant decrease in transmittance (usually ≤70%); while high transmittance designs often simplify the metal structure, which will increase the emissivity (usually ≥0.5), making it impossible to meet both core requirements at the same time.

[0003] 2. Complex structure and high processing cost: Some solutions balance performance through multi-layer heterogeneous structures (such as more than 5 layers of dielectric-metal composite layers), but the interlayer bonding is difficult, interface defects are prone to occur, and special precision processing equipment is required, resulting in low mass production efficiency.

[0004] To address these challenges, existing technologies have explored different paths. For example, Chinese invention patent CN118664997A provides a multi-band compatible stealth solution, the core of which is to achieve multifunctional stealth by integrating a visible-infrared camouflage-compatible layer with a graphene metamaterial absorption layer. This solution focuses on multi-band (visible light, infrared, radar) compatibility and lightweight design, but its multi-layered composite structure is still inherently complex. Chinese invention patent CN109336048B discloses a method for preparing a superhydrophobic surface with a specific microstructure through two ultraviolet lithography processes. This technology demonstrates the idea of ​​controlling the surface structure through precision lithography, but its design goal and core function (droplet directional transport) are fundamentally different from those of metasurfaces controlled by electromagnetic waves. Chinese invention patent CN113745845B discloses a low-scattering metasurface array designed to suppress temporal sputtering effects, whose unit structure includes a resistive thin film, a dielectric layer, and a metal backplate. This scheme focuses on dual stealth performance in both the frequency and time domains, but its typical three-layer structure (especially with a metal backplate) emphasizes absorption and low scattering, often at the expense of wave transmission performance. Furthermore, the structure of the patented invention differs from that of this invention, and the functions implemented are also different.

[0005] In summary, existing technologies either struggle to simultaneously achieve high transmittance and low emissivity across a wide frequency range, or employ complex structures and difficult-to-fabricate designs in pursuit of a particular performance aspect. Therefore, developing a metasurface structure that can simultaneously achieve low emissivity and high transmittance across a wide frequency range while maintaining a relatively simple structure and ease of fabrication is crucial for overcoming current technological bottlenecks and promoting its practical application. Summary of the Invention

[0006] The purpose of this invention is to address the problems of difficulty in achieving synergy between "transparency and low emissivity" and poor performance over wide frequency bands in existing two-layer metasurfaces, and to provide a two-layer structure with low emissivity and high transmittance. Based on the optimized design of polytetrafluoroethylene vinyl plate and metallic copper pattern, it achieves a transmittance of ≥95% in the 18-27GHz and 30-40GHz wide frequency bands, and an emissivity of ≤0.35 in the 3μm~5μm and 8μm~14μm bands.

[0007] The technical solution of the present invention: a low emissivity and high transmittance metasurface structure, comprising a periodic composite metal layer and a substrate dielectric layer arranged from top to bottom; The composite metal layer is composed of multiple periodically arranged working units. Each working unit includes: four unit structures symmetrically distributed in a cross shape, with cross gaps between the unit structures; and a metal outer frame surrounding the four unit structures. In the central region of the cross gap, a square area is cut off from the adjacent corners of each unit structure, thus forming a rectangular channel in the center. The composite metal layer comprises, from top to bottom, a gold layer, a nickel layer, and a copper layer, wherein the copper layer has a thickness of 18 μm, the nickel layer has a thickness of 3 μm-6 μm, and the gold layer has a thickness of 0.1 μm-0.15 μm. The total area of ​​the composite metal layer and the metal frame accounts for 86% of the surface area of ​​the substrate dielectric layer.

[0008] Preferably, the substrate dielectric layer is F4BM or Rogers5880, the substrate flatness deviation is ≤0.02mm, its dielectric constant εr is 2.1~2.3, and the loss tangent tanδ is ≤0.004.

[0009] Preferably, the bulk conductivity of the multilayer metal material constituting the composite metal layer is ≥5.8×10⁻⁶. 7 S / m.

[0010] Preferably, the four unit structures are geometrically symmetrical about the center point of the cross gap and about mutually perpendicular coordinate axes passing through the center point; The four unit structures are independent metal blocks, which are located inside the area enclosed by the metal frame and are respectively arranged in the four quadrants of the cross coordinate system with the center point as the origin.

[0011] Preferably, the cross-shaped gap area is formed by the inner edge of the outer metal frame and the outer edges of the four metal blocks, and the outer edges of the metal blocks are enclosed by the outer edges of the metal blocks. This configuration isolates the four metal blocks from each other and does not have a direct connection with the outer metal frame.

[0012] Preferably, the working unit is a square with a side length of 3mm, the width of the cross-shaped slit is 0.1mm, and the rectangular channel is a square with a side length of 0.5mm.

[0013] Preferably, the metasurface structure has a transmittance of ≥95% in the 18GHz~27GHz and 30GHz~40GHz frequency bands, and an emissivity of ≤0.35 in the 3μm~5μm and 8μm~14μm frequency bands.

[0014] A method for fabricating a low-emissivity, high-transmittance metasurface structure includes the following steps: Step 1, Substrate Preparation: Provide a low-loss dielectric substrate, made of F4BM or Rogers5880 material. After precision cutting, plasma cleaning and drying, obtain a substrate dielectric layer with a clean surface and a flatness deviation of ≤0.02mm. Step 2, Copper Layer Deposition and Periodic Array Patterning: A copper layer with a thickness of 18 μm is deposited on the surface of the substrate dielectric layer using a vacuum sputtering process, ensuring a bulk conductivity ≥ 5.8 × 10⁻⁶. 7 S / m; Subsequently, the copper layer is patterned by photolithography-etching process to directly form the above-mentioned periodic working unit array on a single substrate, without the need for independent fabrication of individual working units. The array consists of multiple periodically arranged working units with a spatial period of 3mm. The array size is preset according to actual application requirements. Step 3, Subsequent Deposition of Composite Metal Layer: On the surface of the patterned copper layer array, a nickel layer with a thickness of 3μm-6μm and a gold layer with a thickness of 0.1μm-0.15μm are deposited sequentially using a vacuum sputtering process to form a composite metal layer of "structured copper layer + nickel layer + gold layer". The nickel and gold layers cover synchronously with the periodic pattern of the copper layer to ensure the overall configuration of the composite metal layer and the metal duty cycle of 86%. Step 4: Post-processing of finished product: The deposited metasurface structure is cleaned, flatness is tested and performance is sampled to remove residual contaminants on the surface, ensuring that the structure is free from deformation and plating defects, and finally obtains a low emissivity and high transmittance metasurface product with a predetermined area.

[0015] Preferably, in step one, the plasma cleaning process is used to thoroughly remove organic contaminants and micro-dust from the substrate surface, enhancing the adhesion between the copper layer and the substrate; the substrate cutting size is designed to match the preset array size, ensuring that a single substrate can accommodate a complete array of periodic working units. In step two, the photolithography-etching process requires precise control of the key dimensions of the working cells: the side length of the working cell is 3mm, the width of the cross-shaped slit is 0.1mm, and the side length of the central rectangular channel is 0.5mm. At the same time, it is necessary to ensure the alignment accuracy of each working cell in the array during periodic arrangement to ensure the consistency of the electromagnetic response of the array. In step three, the sputtering deposition of the nickel and gold layers must maintain a stable vacuum environment with a vacuum degree of ≥5×10⁻³Pa. During the deposition process, the substrate temperature must be controlled below 80℃ to avoid substrate deformation or damage to the copper layer pattern caused by high temperature. This ensures that the two thin films are uniformly covered on the surface of the copper layer array without any missing plating or peeling. In step four, surface cleaning is performed using anhydrous ethanol ultrasonic cleaning for ≤5 minutes. Flatness is tested using a laser interferometer to ensure that the surface flatness deviation of the finished product is ≤0.02mm. Performance sampling checks verify that the transmittance and emissivity of the 18-27GHz and 30-40GHz frequency bands meet the design requirements.

[0016] The beneficial effects of this invention are: 1. This invention achieves synergistic optimization of high transmittance and low emissivity, resulting in significant performance breakthroughs. Through a unique cross-shaped slit and central rectangular channel composite unit design, the electromagnetic response is precisely controlled across multiple wide frequency bands, including 18-27 GHz and 30-40 GHz, maintaining a transmittance consistently above 95%, while simultaneously achieving an average emissivity of no more than 0.35 in the 3μm-5μm and 8μm-14μm bands. This fundamentally resolves the core contradiction in traditional solutions where high transmittance and low emissivity (low detectability) are difficult to achieve simultaneously.

[0017] 2. This invention features a simple and reliable structure, reducing processing difficulty and cost. It employs a dual-layer structure of a single-layer patterned composite metal layer and a single dielectric substrate, significantly simplifying the structure compared to the complex stacked structures of five or more layers commonly used to achieve similar functions. This simplified structure means fewer high-risk process steps such as interlayer alignment and bonding, reducing the risk of performance inconsistencies or failures caused by interface defects. The underlying photolithography-etching process is a mature microfabrication technology, facilitating mass production and cost control. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the working unit structure of the present invention. Figure 1 ; Figure 2 This is a schematic diagram of the working unit structure of the present invention. Figure 2 ; Figure 3 This is a physical image of the low emissivity, high transmittance metasurface structure of the present invention; Figure 4 This is a schematic diagram of the wave transmission curve in Example 1. Figure 1 ; Figure 5 This is a schematic diagram of the wave transmission curve in Example 1. Figure 2 ; Figure 6 This is a schematic diagram of the metasurface structure in Example 2; Figure 7 This is a schematic diagram of the wave transmission curve in Example 2. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, it should not be construed that the scope of the subject matter of the present invention is limited to the following embodiments. All modifications, substitutions and alterations made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention are included within the scope of the present invention.

[0021] The low-emissivity, high-transmittance metasurface of this invention has a two-layer periodic structure, as shown in the reference. Figure 1 and Figure 2 From top to bottom, the layers are: top gold layer, middle nickel layer, bottom copper layer, and substrate dielectric layer (F4BM or Rogers5880). The specific design is as follows: Composite metal layer (gold layer + nickel layer + copper layer). Figure 1 The middle is yellow. Material and thickness: Copper layer thickness 18μm (conductivity ≥ 5.8 × 10⁻⁶) 7 (S / m), nickel layer thickness 3~6μm, gold layer thickness 0.1~0.15μm; the composite metal layer has both high conductivity and corrosion resistance, effectively reducing electromagnetic emission rate.

[0022] Pattern Design: This yellow metal structure can be disassembled into four core parts: an outer metal frame, four independent metal cubes, a cross-shaped gap, and a square channel in the center of the cross. The design function of each structure is to coordinate and regulate the electromagnetic response, as detailed below: 1. The outer yellow metal frame has the following functions: Function 1): Defining the unit period and resonance boundary. The metasurface is composed of "periodically arranged units". The outer frame is the "boundary structure" of a single unit. It not only defines the period size of the unit (determines the overall period parameters of the metasurface), but also serves as the "outer current path" for electromagnetic resonance, forming a complete resonant circuit with the internal structure.

[0023] Function 2): Provides a common coupling node. The frame is the "common connection point" of four independent metal blocks. It forms capacitive / inductive coupling with the internal blocks through the cross gap, ensuring that the electromagnetic response of the entire metal structure is "unit-level coordinated resonance" rather than the independent response of a single block.

[0024] 2. The four independent yellow metal cubes serve the following functions: Function 1): Excite electrical resonance (bright mode). Each cube is an independent electrical resonant unit. The electric field of the incident electromagnetic wave drives the free electrons within the cube, causing opposite charges to accumulate on the metal surfaces of the cube and adjacent gaps, forming an "electric dipole," equivalent to an LC resonant circuit (the metal wires of the cube are inductors, and the gaps are capacitors). Electrical resonance (bright mode, easily excited directly) occurs at the target frequency. Function 2): Ensure polarization symmetry. The four cubes are symmetrically distributed about the center and coordinate axes, allowing the structure to produce an approximately uniform electrical resonant response to incident waves of arbitrary polarization directions (such as TM and TE polarization), achieving a "polarization-insensitive" wave transmission effect.

[0025] 3. The cross-shaped gap has the following functions: Function 1): Constructing the "capacitor core" of electric resonance. The cross-shaped gap is the key "capacitor structure" of electric resonance: The metal on both sides of the gap (block and frame, block and block) is equivalent to the two plates of the capacitor. The width of the gap directly determines the capacitance value, thereby regulating the frequency of electric resonance (the narrower the gap, the larger the capacitance and the lower the resonance frequency).

[0026] Function 2): To realize the coupling channel of multiple resonant modes, the cross gap is the electromagnetic energy coupling path between the "four squares" and the "outer frame", allowing the energy of the electric resonance (bright mode) to be transferred to the subsequently excited magnetic resonance (dark mode), providing coupling conditions for the "EIT-like effect" (the core mechanism of wave transmission).

[0027] 4. The square channel in the center of the cross has the following functions: Function 1): Introducing additional resonant modes and enhancing coupling control. This channel is equivalent to adding a "micro-resonant unit" to the coupling path of the cross gap, which can excite higher-order magnetic resonant modes (a type of dark mode), expanding the resonant modes of the metal structure from "single electrical resonance + single magnetic resonance" to "multiple resonance superposition", improving the precision of electromagnetic response control. Function 2): Optimizing the bandwidth and sharpness of the transmission window. The size (side length) of the channel will change the coupling strength between the bright mode and the dark mode: a suitable cavity size can make the coupling stronger, making the "electromagnetic transparent window" (high transmission frequency band) narrower and the transmission peak sharper, while fine-tuning the resonant frequency, so that the transmission window accurately matches the target operating frequency band.

[0028] The working unit of the low emissivity, high transmittance metasurface structure of this invention has an overall size of 3mm×3mm and a metal duty cycle of 86%. It balances transmittance and low emissivity performance through precise size control. Its thickness is 0.01-0.02mm, and the electromagnetic wave emission loss is reduced by thinning the metal layer.

[0029] Material selection for the substrate dielectric layer: F4BM or Rogers 5880 (RT5880) are selected, with a thickness of 0.127mm; stable dielectric properties, low loss characteristics reduce electromagnetic wave absorption, suitable for wide-band applications, dielectric constant εr=2.1-2.3, loss tangent tanδ≤0.004 (low loss characteristics reduce electromagnetic wave absorption); substrate flatness deviation ≤0.02mm, ensuring the adhesion consistency and structural stability of the composite metal layer, and temperature resistance range suitable for complex application environments.

[0030] The metasurface cell period is matched to the individual cell size and set to 3mm. The array size is adjusted according to actual needs (e.g., 100×100 array, 200×200 array) to ensure stable performance over a wide frequency band. (Refer to...) Figure 3 .

[0031] Example 1: Wideband Low Emissivity High Transmittance Metasurface 1. Structural parameter setting Composite metal layer: Employs a copper-nickel-gold three-layer stacked structure. Specifically, the copper layer is 18 micrometers thick, the nickel layer is 4 micrometers thick, and the gold layer is 0.12 micrometers thick. This composite layer constitutes a periodic working unit structure.

[0032] Unit configuration: The period size of each working unit is 3 mm by 3 mm. Its configuration consists of four independent metal blocks arranged symmetrically in a cross shape, which are separated by a cross-shaped gap with a width of 0.1 mm. The corners of each metal block facing the center are cut off, and together they form a square groove with a side length of 0.5 mm at the center of the unit.

[0033] Substrate dielectric layer: Rogers RT / duroid 5880 high-frequency board with stable dielectric properties was selected as the substrate, with a thickness of 0.127 mm.

[0034] Array size: The above working unit structures are arranged in a repeating pattern of 74 x 74 on a two-dimensional plane with a period of 3 mm, forming a large-area metasurface array with a total size of 220 mm x 220 mm.

[0035] 2. Preparation method Step 1: Substrate Preparation: The Rogers 5880 substrate is machined to the predetermined dimensions using precision cutting technology, ensuring that the thickness uniformity deviation does not exceed 0.02 mm. Subsequently, the substrate surface is plasma-cleaned to thoroughly remove organic contaminants and micro-dust, enhancing the adhesion of the copper layer. Step 2, Copper Layer Deposition and Array Patterning: On a clean substrate surface, an 18μm thick copper layer is deposited using a high-precision magnetron sputtering device; a periodic array of working cells is directly formed on the copper layer surface using a photolithography-etching process, precisely controlling the dimensions of each working cell, such as the width of the cross gap and the side length of the central square groove, resulting in a neat and burr-free pattern edge.

[0036] Step 3, Composite Metal Layer Deposition: On the surface of the patterned copper layer array, a 4μm thick nickel layer and a 0.12μm thick gold layer are deposited sequentially by magnetron sputtering. During the deposition process, the vacuum environment is kept stable to ensure that the nickel and gold layers completely replicate the array pattern of the copper layer.

[0037] Step 4, Post-processing of finished product: The surface of the finished product is ultrasonically cleaned with anhydrous ethanol for 5 minutes to remove sputtering residue and contaminants; the surface flatness is checked by laser interferometer to ensure that the deviation is ≤0.02mm; samples are randomly selected for HFSS performance characterization to verify that the transmittance and emissivity meet the design requirements, and finally the metasurface finished product is obtained.

[0038] 3. Performance Testing and Results The metasurface samples were characterized using the simulation software HFSS. The following properties were obtained for the product: High wave transmission performance: Reference Figure 4 and Figure 5 Test results show that the metasurface maintains a transmittance of over 95% across a wide frequency band from 18.35 GHz to 26.7 GHz. Furthermore, its transmittance is nearly greater than 95% across a wide frequency band from 30 GHz to 40 GHz.

[0039] Low emissivity performance: In the 3μm~5μm and 8μm~14μm bands, the average emissivity of this metasurface is no higher than 0.35, effectively reducing its radar signal characteristics. The test results are shown in Table 1 below:

[0040] The metasurface successfully fabricated in this embodiment achieves synergistic optimization of electromagnetic response through a unique "cross-shaped slit + central square groove" composite metal unit design. It achieves an excellent combination of transmittance >95% and emissivity ≤0.35 in both wavebands (18.35-26.7GHz and 30-40GHz). This demonstrates that, with a relatively simple structure (single-layer metal patterning), this invention effectively solves the core contradiction of balancing high transmittance and low emissivity in traditional designs, meeting the stringent requirements of modern stealth platforms for integrated "transmittance-stealth" capabilities.

[0041] Example 2 (Comparative Example): Metasurface without a central square groove structure, reference Figure 6 The fabrication process, substrate material, metal layer material and thickness, unit cell period size (3mm×3mm), and overall array size of the metasurface in this comparative example are exactly the same as those in Example 1.

[0042] The only difference lies in the unit structure: the unit structure of this comparative example contains only four metal blocks separated by cross-shaped gaps (0.1 mm wide), without any cutting off of the corners of the four metal blocks, i.e., there is no central square groove as in Embodiment 1. Its structure can be regarded as a simplified version of the structure described in claim 1 of this invention.

[0043] 2. Performance Comparison Test Under the same test conditions, the wave transmission performance of this comparative sample was tested.

[0044] Test results: (Refer to) Figure 7 In the frequency range of 18 GHz to 27 GHz, the transmissivity of this centerless square groove metasurface is 90%.

[0045] Comparing this result with Example 1, it can be seen that, based on the exact same materials and processes, the transmission performance in the key frequency band (18-27GHz) was significantly reduced simply because the "central square groove" design feature was missing. The transmission rate dropped from over 95% to about 90%.

[0046] This comparative example powerfully demonstrates that the low-emissivity, high-transmittance metasurface structure of this invention, which defines a central rectangular channel formed by four cut-off corners, is not a redundant or decorative design, but rather a key and non-obvious structural feature for achieving ultra-wideband high transmittance. This design, without significantly increasing process complexity or cost, achieves a transmittance improvement of over 5% through precise control of the local current distribution and electromagnetic coupling of the unit cells. This significantly enhances the metasurface's ability to synergistically achieve high transmittance and low emissivity across a wide frequency range, showcasing the inventiveness and technical advantages of this invention.

[0047] The low emissivity, high transmittance metasurface structure and its preparation method provided by this invention have been described in detail above. Specific examples have been used to illustrate the structure and working principle of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make several improvements and modifications to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the scope of protection of the claims of this invention.

Claims

1. A low-emissivity, high-transmittance metasurface structure, characterized in that: It includes a periodic composite metal layer and a substrate dielectric layer arranged from top to bottom; The composite metal layer is composed of multiple periodically arranged working units. Each working unit includes: four unit structures symmetrically distributed in a cross shape, with cross gaps between the unit structures; and a metal outer frame surrounding the four unit structures. In the central region of the cross gap, a square area is cut off from the adjacent corners of each unit structure, thus forming a rectangular channel in the center. The composite metal layer comprises, from top to bottom, a gold layer, a nickel layer, and a copper layer, wherein the copper layer has a thickness of 18 μm, the nickel layer has a thickness of 3 μm-6 μm, and the gold layer has a thickness of 0.1 μm-0.15 μm. The total area of ​​the composite metal layer and the metal frame accounts for 86% of the surface area of ​​the substrate dielectric layer.

2. The low emissivity, high transmittance metasurface structure according to claim 1, characterized in that: The substrate dielectric layer is F4BM or Rogers5880, the substrate flatness deviation is ≤0.02mm, its dielectric constant εr is 2.1~2.3, and the loss tangent tanδ is ≤0.

004.

3. The low emissivity, high transmittance metasurface structure according to claim 1, characterized in that: The bulk conductivity of the multilayer metal material constituting the composite metal layer is ≥5.8×10⁻⁶. 7 S / m.

4. The low emissivity, high transmittance metasurface structure according to claim 1, characterized in that: The four unit structures are geometrically symmetrical about the center point of the cross gap and about the mutually perpendicular coordinate axes passing through the center point. The four unit structures are independent metal blocks, which are located inside the area enclosed by the metal frame and are respectively arranged in the four quadrants of the cross coordinate system with the center point as the origin.

5. The low emissivity, high transmittance metasurface structure according to claim 1, characterized in that: The cross-shaped gap area is formed by the inner edge of the outer metal frame and the outer edges of the four metal blocks, and the outer edges of the metal blocks are connected to each other. Its configuration isolates the four metal blocks from each other and has no direct connection with the outer metal frame.

6. The low emissivity, high transmittance metasurface structure according to claim 1 or 5, characterized in that: The working unit is a square with a side length of 3mm, the width of the cross-shaped slit is 0.1mm, and the rectangular channel is a square with a side length of 0.5mm.

7. The low emissivity, high transmittance metasurface structure according to claim 1, characterized in that: The metasurface structure has a transmittance of ≥95% in the 18GHz~27GHz and 30GHz~40GHz frequency bands, and an emissivity of ≤0.35 in the 3μm~5μm and 8μm~14μm frequency bands.

8. A method for preparing a low-emissivity, high-transmittance metasurface structure as described in any one of claims 1-7, characterized in that: Includes the following steps: Step 1, Substrate Preparation: A low-loss dielectric substrate is provided. After precision cutting, plasma cleaning and drying, a substrate dielectric layer with a clean surface and a flatness deviation of ≤0.02mm is obtained. Step 2, Copper Layer Deposition and Periodic Array Patterning: A copper layer is deposited on the surface of the substrate dielectric layer using a vacuum sputtering process, ensuring its conductivity is ≥5.8×10⁻⁶. 7 S / m; Subsequently, the copper layer is patterned by photolithography-etching process to directly form the periodic working unit array as described in claim 1 on a single substrate, the array size of which is preset according to actual application requirements; Step 3: Subsequent deposition of the composite metal layer: On the surface of the patterned copper layer array, a nickel layer and a gold layer are deposited sequentially using a vacuum sputtering process to form a structured copper-nickel-gold composite metal layer; Step 4: Post-processing of finished product: The deposited metasurface structure is cleaned, flatness is tested and performance is sampled to remove residual contaminants on the surface, ensuring that the structure is free from deformation and plating defects, and finally obtains a low emissivity and high transmittance metasurface product with a predetermined area.

9. The preparation method according to claim 8, characterized in that: In step one, the plasma cleaning process is used to thoroughly remove organic contaminants and dust from the substrate surface, enhance the adhesion between the copper layer and the substrate, and the substrate cutting size is designed to match the preset array size to ensure that a single substrate can accommodate a complete array of periodic working units. In step two, the photolithography-etching process requires precise control of the key dimensions of the working cells: ensuring that the side length of the working cell is 3mm, the width of the cross-shaped slit is 0.1mm, and the side length of the central rectangular channel is 0.5mm, while ensuring the alignment accuracy of each working cell in the array periodically, and ensuring the consistency of the electromagnetic response of the array. In step three, the sputtering deposition of the nickel and gold layers must maintain a stable vacuum environment with a vacuum degree of ≥5×10⁻³Pa. During the deposition process, the substrate temperature must be controlled below 80℃ to avoid substrate deformation or damage to the copper layer pattern caused by high temperature. This ensures that the two thin films are uniformly covered on the surface of the copper layer array without any missing plating or peeling. In step four, surface cleaning is performed using anhydrous ethanol ultrasonic cleaning for ≤5 minutes. Flatness is tested using a laser interferometer to ensure that the surface flatness deviation of the finished product is ≤0.02mm. Performance sampling inspection needs to verify that the transmittance of the 18-27GHz and 30-40GHz bands and the emissivity of the 3μm~5μm and 8μm~14μm bands meet the design requirements.

10. The preparation method according to claim 8, characterized in that: The periodic working cell array in step two is fabricated in one go, without the need for individual working cells to be fabricated independently; in step three, the nickel and gold layers are synchronously covered with the periodic pattern of the copper layer to ensure the overall configuration of the composite metal layer.

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