Electromagnetically transparent window based on double-layer metal microstructure

Abstract

The present invention discloses an electromagnetic transparent window based on a double-layer metal microstructure layer, wherein the electromagnetic transparent window is composed of the same artificial atomic periodic arrangement, the artificial atomic structure is composed of a metal microstructure layer / a dielectric layer / a metal microstructure layer and an anti-reflection film, the dielectric layer is a uniform and isotropic simple medium, the metal microstructure layer is located on the front and back sides of the dielectric layer, and a layer of anti-reflection film is respectively covered on the metal grid microstructures on both sides. The present invention adopts the above-mentioned electromagnetic transparent window based on a double-layer metal microstructure layer, and the transparent window exhibits significant high shielding performance in the microwave frequency band through the metal grid, and the anti-reflection film makes it have high wave transmittance in the visible light range, ensuring the wave transmittance performance in the visible light band, no longer at the expense of microwave shielding performance, and has a wide range of practical application value and development prospects.

Description

Technical Field

[0001] The invention relates to the technical field of optical windows, in particular to an electromagnetically transparent window based on a double-layer metal microstructure layer. Background Art

[0002] With the rapid development and evolution of electronic information technology, the application of electromagnetic waves is increasingly showing a dual trend of high energy and broadband. This development trend has led to the complexity of the electromagnetic environment, generated electromagnetic interference, and seriously affected the normal operation of electronic equipment. Optical windows play a vital role in the observation and detection applications of optoelectronic devices. As a key medium for information transmission, on the one hand, optical windows must exhibit excellent wave transmission performance in the visible light band to achieve efficient information transmission; on the other hand, due to the electromagnetic interference generated by wireless communication equipment, in order to prevent its electromagnetic interference from affecting the performance of the equipment, the optical window should also have outstanding electromagnetic shielding capabilities. Therefore, the development of an optical window that can effectively shield electromagnetic interference while ensuring efficient transmission of optical communications is of great significance to modern communication systems.

[0003] At present, the existing transparent electromagnetic shielding materials still have many deficiencies in the balance optimization of microwave shielding performance and optical wave transmission performance. For example: carbon-based materials have good environmental stability, but at the same time they also absorb a lot of visible light, making it difficult to achieve high transparency and high conductivity while shielding electromagnetic interference; although metal nanowire transparent conductive films have attracted much attention for their excellent optoelectronic properties, their film surface has large fluctuations, which limits their application in some application scenarios with high requirements for surface roughness; transparent conductive polymer films are seen as a solution in some cases, but their conductivity is also relatively limited, making it difficult to meet some current application scenarios with high requirements for conductivity; transparent conductive oxides such as ITO can efficiently transmit visible light, but their microwave shielding efficiency is low, which limits their use in application scenarios that require efficient microwave shielding. Summary of the invention

[0004] The purpose of the present invention is to provide an electromagnetic transparent window based on a double-layer metal microstructure layer. The transparent window exhibits significantly high shielding performance in the microwave frequency band through the metal grid microstructure, and at the same time, the anti-reflection film makes it have high transmittance in the visible light range, breaking through the limitations of traditional narrow-band visible light transmission technology and realizing ultra-wideband optical transparency. At the same time, while ensuring the transmission performance in the visible light band, it no longer sacrifices the microwave shielding performance, and has broad practical application value and development prospects.

[0005] To achieve the above-mentioned purpose, the present invention provides an electromagnetic transparent window based on a double-layer metal microstructure layer, wherein the electromagnetic transparent window is composed of the same periodic arrangement of artificial atoms, and the artificial atomic structure is composed of a metal microstructure layer / a dielectric layer / a metal microstructure layer and an anti-reflection film. The dielectric layer is a uniform and isotropic simple medium, and the metal microstructure layer is located on the front and back sides of the dielectric layer, and a layer of anti-reflection film is respectively covered on the metal grids on both sides. The anti-reflection film enables the electromagnetic transparent window to have high wave transmittance to electromagnetic waves in the infrared / visible light frequency band, and the metal grids on both sides of the dielectric layer enable the electromagnetic transparent window to have high shielding properties in the microwave frequency band.

[0006] Preferably, the material of the metal microstructure layer is any one of copper, aluminum, silver and gold.

[0007] Preferably, the dielectric layer side material is quartz glass, and the thickness of the dielectric layer is 1 mm.

[0008] Preferably, the material of the metal microstructure layer is gold.

[0009] Preferably, the metal microstructure layer has a thickness of 100 nm and a line width of 5 μm.

[0010] Preferably, the period of the metal microstructure layer is 200 μm or 400 μm.

[0011] The advantages and positive effects of the electromagnetically transparent window based on the double-layer metal microstructure layer described in the present invention are:

[0012] The transparent window of the present invention exhibits significantly high shielding performance in the microwave frequency band through the metal grid microstructure, and the anti-reflection film makes it have high transmittance in the visible light range, breaking through the limitations of traditional narrow-band visible light transmission technology and achieving ultra-wideband optical transparency. At the same time, while ensuring the transmission performance in the visible light band, it no longer sacrifices the microwave shielding performance, and has broad practical application value and development prospects.

[0013] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the transparent window and unit structure of the present invention, wherein A is the transparent window and B is the unit structure;

[0015] Figure 2 Schematic diagram of the unit structure of the transparent window metasurface of the present invention;

[0016] Figure 3 This is a graph showing the effect of the thickness of the metal microstructure layer on the electromagnetic shielding effectiveness of the present invention;

[0017] Figure 4 This is a result diagram showing the effect of the metal microstructure layer period on the electromagnetic shielding effectiveness of the present invention;

[0018] Figure 5 This is a result diagram showing the effect of the line width of the metal microstructure layer on the electromagnetic shielding effectiveness of the present invention;

[0019] Figure 6 This is a graph showing the electromagnetic shielding effectiveness results of the present invention with different line widths and periods but maintaining the same ratio of 1 / 40;

[0020] Figure 7 is a relationship diagram between the electromagnetic shielding effectiveness of the present invention and the theoretically calculated optical transmittance;

[0021] Figure 8 Graph showing the relationship between the electromagnetic shielding effectiveness of the present invention and the incident angle, wherein (a) is a TE polarized wave and (b) is a TM polarized wave;

[0022] Fig. 9 The whole picture and partial pictures under a microscope of the sample 1 of the verification example of the present invention, wherein (a) is the whole picture, and (b) and (c) are partial pictures;

[0023] Fig.10 The whole picture and partial pictures under a microscope of the second sample of the verification example of the present invention, wherein (a) is the whole picture, and (b) and (c) are partial pictures;

[0024] Fig.11 A comparison chart of the electromagnetic shielding effectiveness experimental test results and simulation results of a microwave frequency band sample of the present invention;

[0025] Fig.12 A comparison chart of experimental test results and simulation results of a sample of the present invention in the visible light band;

[0026] Fig.13 The electromagnetic shielding effectiveness test results of the second microwave frequency band of the verification example of the present invention are shown in Figure 1, wherein (a) is the electromagnetic shielding effectiveness test result of the 2.4-4.0 GHz frequency band, and (b) is the electromagnetic shielding effectiveness test result of the 4.0 GHz-6.0 GHz frequency band;

[0027] Fig.14 This is a diagram of the experimental test results of the visible light band of the second sample of the verification example of the present invention, where (a) is the intuitive effect of the sample, and (b) is the test result of the transmittance. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0029] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0030] Example

[0031] An electromagnetically transparent window based on a double-layer metal microstructure layer, the electromagnetically transparent window is composed of the same periodic arrangement of artificial atoms, the artificial atomic structure is composed of a metal microstructure layer / a dielectric layer / a metal microstructure layer and an anti-reflection film, the dielectric layer is a uniform and isotropic simple medium, the metal microstructure layer is located on the front and back sides of the dielectric layer, and a layer of anti-reflection film is respectively covered on the metal grid microstructure on both sides, the anti-reflection film makes the electromagnetic transparent window have high wave transmittance in the infrared / visible light frequency band electromagnetic waves, and the metal microstructures on both sides of the dielectric layer make the electromagnetic transparent window have high shielding properties in the microwave frequency band.

[0032] The present invention constructs an electromagnetic transparent window metasurface based on a double-layer metal microstructure, designs an efficient unit structure that can realize an electromagnetic transparent window through simulation, and processes the array composed of the unit structure and then verifies it experimentally. The results show that the transparent window exhibits significant high shielding performance in the microwave frequency band and has high wave transmittance in the visible light range. In the process of simulation design, electromagnetic simulation software (CST MicrowaveStudio) is mainly used. Among them, the frequency domain solver converts Maxwell's equations into frequency domain problems, and solves them for each frequency point respectively, which has certain advantages in terms of calculation accuracy and problem scale. Therefore, the simulation of the unit structure in the present invention is mainly based on the frequency domain solver.

[0033] like Figure 2 As shown, the unit structure of the transparent window is shown, ɡ represents the period of the unit structure, ɑ represents the half width of the metal microstructure line, that is, 2ɑ represents the line width of the metal microstructure. sub represents the thickness of the dielectric layer in the middle of the unit, h metal Represents the thickness of the metal microstructure. When simulating the unit structure of the transparent window, in order to truly and accurately reflect the electromagnetic response characteristics in the actual environment, ensure that the distance between the unit structure and the incident source is greater than one working wavelength.

[0034] like Figure 1 As shown in A, the unit structure of the designed transparent window is made of glass in the middle, with metal grid structures etched on both sides, and anti-reflection film coated on the grid. The glass is a quartz structure with a thickness of 0.5mm, and the metal grid is a 100nm thick gold material. The anti-reflection film is made of tantalum oxide and silicon dioxide superimposed on each other, and its thickness is: 15nm, 52.67nm, 38.24nm, 25nm, 75.31nm, 19.81nm, 39.58nm, 106nm.

[0035] Through theoretical analysis of the electromagnetic transparent window, the structure is equivalent to a theoretical model of "CAC", such as Figure 1 As shown in B, the metal grid is equivalent to the C layer in "CAC", and its thickness is d C , the relative dielectric constant is ε C ; The glass medium is equivalent to the A layer in "CAC", and its thickness is d A , the relative dielectric constant is constant ε A .

[0036] The material of the metal microstructure layer is any one of copper, aluminum, silver and gold. The preferred material of the metal microstructure layer is gold. When designing the metal microstructure layer of the transparent window, it is necessary to fully consider the influence of the conductivity and magnetic permeability of the conductive layer on the electromagnetic shielding effectiveness of the metal microstructure layer. Compared with the general materials copper (Cu) and aluminum (Al), gold (Au) and silver (Ag) show better conductivity. In addition, gold also has excellent chemical stability and oxidation resistance. Selecting gold with better conductivity as the metal microstructure layer of the transparent window can improve its electromagnetic shielding effectiveness and reliability.

[0037] The dielectric layer side material is quartz glass, and the thickness of the dielectric layer is 1 mm. Quartz glass (SiO2) is selected as the middle dielectric layer, its relative dielectric constant is 3.9, and its thickness is set to 1.0 mm. The simulated working frequency band is set in the range of 1-18 GHz.

[0038] The thickness of the metal microstructure layer is 100 nm, the line width is 5 μm, and the period of the metal microstructure layer is 200 μm or 400 μm.

[0039] (1) Simulate the thickness of the metal microstructure in the transparent window unit.

[0040] In this process, the period of the fixed metal microstructure was 100 μm and the line width was 5 μm. Figure 3 The effect of the thickness of the metal microstructure layer on the electromagnetic shielding effectiveness was simulated. The results show that in the range of 1-18 GHz, as h metal The increase in thickness will slightly improve the electromagnetic shielding effectiveness, but the overall impact is relatively limited. Although the increase in thickness will improve the shielding effectiveness, it will also increase the weight and cost of the material accordingly. Therefore, in practical applications, it is necessary to comprehensively weigh factors such as shielding effectiveness, weight and cost according to specific needs to determine the most appropriate thickness of the metal microstructure. Therefore, 100nm is selected as the thickness of the metal microstructure in the transparent window, that is, h metal Set to 100nm.

[0041] (2) The influence of unit structure period ɡ on electromagnetic shielding effectiveness.

[0042] The line width of the transparent window unit structure is fixed at 5μm and the simulation is performed. Figure 4 As shown in the figure, as the period continues to increase, the electromagnetic shielding effectiveness of the transparent window shows a sharp downward trend. When the period is expanded to 500μm, the electromagnetic shielding effectiveness of the transparent window is poor (<30dB) when the frequency is greater than 15GHz. The emergence of this phenomenon is mainly attributed to the fact that when the metal grid period is too large, the conductive path of the metal microstructure layer will become discontinuous, resulting in the inability to effectively shield the electromagnetic waves. When the period is too large, the gap between the metal microstructures becomes wider, making it easier for electromagnetic waves to penetrate the metal microstructure during propagation, resulting in a decrease in shielding effectiveness.

[0043] At the same time, while considering excellent electromagnetic shielding effectiveness, too small a period may lead to reduced optical transparency. Therefore, it is necessary to find a balance between electromagnetic shielding effectiveness and optical transparency to achieve the optimization of the transparent window in terms of both optical transparency and electromagnetic shielding effectiveness.

[0044] (3) The influence of line width 2ɑ in the transparent window unit structure on the electromagnetic shielding effectiveness.

[0045] The period parameter is fixed at 200 μm and a simulation is performed. Figure 5 As shown in the figure, as the line width increases, the electromagnetic shielding effectiveness of the transparent window increases. A larger line width means a higher conductivity on the metal grid, and a metal with high conductivity can more effectively dissipate the electromagnetic wave energy passing through the grid, thereby improving the shielding effectiveness.

[0046] The period and line width of the metal microstructure play a decisive role in the electromagnetic shielding effectiveness, and the above simulation further verifies the correctness of this view. The smaller the period and the larger the line width of the metal microstructure, the better the electromagnetic shielding effectiveness in the microwave frequency band, but this will also lead to a decrease in visible light transmittance. In order to alleviate the decrease in visible light transmittance caused by the improvement of microwave shielding effectiveness, an anti-reflection film structure is used to improve the transmittance.

[0047] (4) The ratio of line width to period is fixed at 1 / 40, the overall size of the metal microstructure is changed, and simulation is performed.

[0048] like Figure 6As shown in the figure, the smaller the size of the metal microstructure, the higher the electromagnetic shielding effectiveness of the transparent window while maintaining the transmittance of the visible light band. This phenomenon is mainly due to the fact that smaller microstructures will cause more interface scattering and interface reflection, thereby enhancing their scattering and absorption capabilities of electromagnetic waves. In addition, smaller microstructures can also provide a larger surface area, thereby increasing the contact area between the incident electromagnetic wave and the metal, and further improving the electromagnetic shielding effectiveness. Too small a size will affect the manufacturability and stability of the microstructure. The narrowest line width limit of the photolithography technology used in actual processing in the manufacturing process is 2μm, but this line width is difficult to prepare and is not conducive to large-scale preparation. Moreover, when processing multi-layer structures, too narrow a line width may cause difficulties in upper and lower alignment. Therefore, a line width of 5μm is selected as the design parameter of the transparent window metasurface.

[0049] (5) The influence of the unit period of metal microstructure layer on the electromagnetic shielding effectiveness.

[0050] like Figure 7 As shown, the circle curve is the theoretically calculated transmittance in the visible light band, and the triangle curve is the electromagnetic shielding effectiveness at the middle frequency of the microwave band, 9 GHz. By analyzing the results of these two curves, it is observed that with the increase of the period, the transmittance in the visible light band shows a steady upward trend, but the electromagnetic shielding effectiveness shows the opposite trend, that is, it gradually decreases. Here, considering the need to take into account the requirements of electromagnetic shielding effectiveness greater than 50dB and at the same time the transmittance in the visible light band greater than 90%, when the period of the metal microstructure layer is set to 200μm, the above two requirements can basically be met at the same time. Therefore, the period ɡ of the microstructure of the transparent window is set to 200μm, and the line width of the metal microstructure is determined to be 5μm.

[0051] (6) Changes in the electromagnetic shielding effectiveness of the transparent window metasurface when the incident angle changes.

[0052] Changes in the incident angle of electromagnetic waves will have a certain degree of negative impact on the performance of the transparent window metasurface, and it is necessary to simulate and analyze the angle robustness of the transparent window metasurface.

[0053] like Figure 8As shown in the figure, in the process of gradually increasing the incident angle of the electromagnetic wave, under transverse electric wave polarization, the electromagnetic shielding effectiveness of the transparent window metasurface shows an upward trend. However, in contrast, the electromagnetic shielding effectiveness of the transparent window metasurface under transverse magnetic wave polarization shows a downward trend. When the incident angle of the electromagnetic wave changes, the admittance of transverse electric wave polarization and transverse magnetic wave polarization has opposite changing trends. Specifically, this is because the electric field of transverse electric wave polarization is perpendicular to the incident surface, while the magnetic field of transverse magnetic wave polarization is perpendicular to the incident surface. When the incident angle changes, in the transverse electric wave polarization mode, as the incident angle increases, the admittance of the transparent metal metasurface unit increases, which leads to an improvement in the electromagnetic shielding effectiveness. In the transverse magnetic wave polarization mode, as the incident angle increases, the admittance of the transparent window metasurface unit decreases, which leads to a decrease in the electromagnetic shielding effectiveness. Although a larger incident angle in the transverse magnetic wave polarization mode will lead to a significant decrease in the electromagnetic shielding effectiveness, the electromagnetic shielding effectiveness is still higher than 40dB even at an incident angle of 60°. In addition, compared with the normal incidence case, the electromagnetic shielding effectiveness under two different polarization forms fluctuates less than ±10% in the range of 0° to 60°. This result shows that the designed transparent window metasurface unit has good robustness when dealing with oblique incidence.

[0054] Verification Example

[0055] Based on the parameters that the electromagnetic shielding effectiveness can basically reach a level of 40dB while maintaining a visible light transmittance of more than 90%, two samples were prepared and experimentally verified.

[0056] Preparation of sample 1: BF33 glass with a thickness of 1 mm and a relative dielectric constant of 4.5 was selected as the dielectric layer. The transmittance of this dielectric layer in the visible light band is about 91%. Then, metal microstructures with a thickness of 100 nm, a unit period of 200 μm, and a line width of 5 μm were etched on the front and back sides of the dielectric layer. The material used for the metal microstructure layer is Au.

[0057] Preparation of sample 2: HPFS 7978 wafer glass with a thickness of 1 mm and a relative dielectric constant of 4.5 is used as the dielectric layer, and an anti-reflection film made of magnesium fluoride (MgF2) is coated on the surface of the dielectric layer. Similar to sample 1, metal microstructures with a thickness of 100 nm, a unit period of 400 μm, and a line width of 5 μm are etched on both sides of the dielectric layer. The material used for the metal microstructure layer is Au.

[0058] The designed transparent window samples 1 and 2 were prepared using a more precise photolithography technique. Fig. 9 As shown in (a), it can be seen intuitively that the sample has good light transmittance. In addition, by observing the processed sample under a microscope, it can be found that its structure is very clear, the lines are clear, and the size error is not large. Fig. 9As shown in (b) and (c), Sample 1 is a small-sized sample, and its size is: 30mm×18mm.

[0059] like Fig.10 As shown in (a), it can be observed that sample 2 also exhibits excellent light transmittance. In addition, by carefully observing the processed sample under a microscope, it can be found that its microstructure is also clearly visible, with clear lines and minimal dimensional errors, as shown in Figure 1. Fig.10 As shown in (b) and (c), Sample 2 is a large-size sample, with a size of 60 mm × 60 mm.

[0060] (1) Sample-Experimental Verification

[0061] First, the microwave frequency band test is carried out, and the electromagnetic shielding effectiveness parameters in microwave and radio frequency circuits are measured using a vector network analyzer and a rectangular waveguide to evaluate the electromagnetic shielding effectiveness S of the sample and generate the frequency response curve of the sample. Fig.11 As shown, the electromagnetic shielding effectiveness results (circled line) of the transparent window sample 1 measured using a vector network analyzer and a rectangular waveguide are shown. The waveguide port size of the rectangular waveguide used is 22.5×10.1mm, and its operating frequency band is 8.2-12.4GHz, so the experimental test was carried out in the 8-13GHz frequency band. It can be seen that the results of the experimental test (circled line) fluctuate slightly compared with the results of the FDTD simulation (solid line), but the overall trend is basically consistent, and the average value of the electromagnetic shielding effectiveness in its test frequency band is 40dB. The experimental test of the vector network analyzer verifies that the transparent metal metasurface of the present invention has a strong electromagnetic shielding effectiveness.

[0062] Furthermore, the sample 1 was tested with near infrared / visible light, and the equipment used for the test was a spectrophotometer to calculate the light transmittance of the sample. Fig.12 As shown in the figure, the transmittance of transparent window sample 1 in the visible light / near infrared band was measured using a spectrophotometer (circled line). When compared with the theoretically calculated result (dashed line), it can be seen that the experimental test result is slightly lower than the theoretically calculated result. After careful analysis, it was found that this was because the metal microstructures on the front and back sides were not completely aligned during the processing, with an error of about 1-2μm, which caused the electromagnetic wave to be lost twice by the metal microstructure when passing through the transparent metal sample. In order to analyze this problem more accurately, the two losses were theoretically calculated:

[0063]

[0064] According to the results of the above calculation formula, it can be seen that the metal microstructure loss is considered twice, and the theoretical calculation results are basically consistent with the results measured by the spectrophotometer.

[0065] (2) Experimental verification of sample 2

[0066] For the microwave characteristic test of sample 2, the same equipment and method as sample 1 were used, that is, the experimental test was carried out through a vector network analyzer and a rectangular waveguide. In view of the fact that sample 2 is a large-scale sample, the frequency band range of 2.4 to 6 GHz was specifically selected for testing, which included the use of two rectangular waveguides with different operating frequency ranges of 2.4 to 4.0 GHz and 4.0 to 6 GHz for multi-band coverage. Fig.13 As shown in Figure 2, (a) and (b) show the electromagnetic shielding effectiveness of sample 2 in the frequency range of 2.4 to 6 GHz, and the values ​​are both over 40 dB. This test result is highly consistent with the preset design goal, providing strong empirical support for the simulation model, and also verifying the practicality and effectiveness of the preparation technology.

[0067] For the near-infrared / visible light band test of sample 2, a spectrophotometer was also used. Fig.14 (a) shows the intuitive effect of sample 2. It can be clearly observed that sample 2 is almost completely transparent, and there is almost no perceptible visual difference compared to the area without sample coverage. Fig.14 As shown in (b), the experimental test results of transmittance are further provided, and its value is stable near 0.9, showing extremely high light transmittance. This result is completely consistent with the preset design goal, further verifying the correctness of the theoretical analysis, and also confirming the role and necessity of the anti-reflection film.

[0068] Therefore, the present invention adopts the above-mentioned electromagnetic transparent window based on the double-layer metal microstructure layer. The transparent window exhibits significantly high shielding performance in the microwave frequency band and has high transmittance in the visible light range. It breaks through the limitations of traditional narrow-band visible light transmission technology and realizes ultra-wideband optical transparency. At the same time, while ensuring the transmission performance in the visible light band, it no longer sacrifices the microwave shielding performance. It has broad practical application value and development prospects.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. Electromagnetic transparent window based on double-layer metal microstructure layer, Features: The electromagnetic transparent window is composed of the same artificial atomic periodic arrangement, and the artificial atomic structure is composed of a metal microstructure layer / a dielectric layer / a metal microstructure layer and an anti-reflection film, so as to achieve ultra-wideband optical transparency and break through the limitations of traditional narrow-band visible light transmission technology. The dielectric layer is a simple medium that is uniform and isotropic, the metal microstructure layer is located on the front and back sides of the dielectric layer, and a layer of anti-reflection film is respectively covered on the metal grid microstructures on both sides, the anti-reflection film makes the electromagnetic transparent window have high wave transmittance in the infrared / visible light frequency band, and the metal grids on both sides of the dielectric layer make the electromagnetic transparent window have high shielding in the microwave frequency band; The dielectric layer is made of quartz glass and has a thickness of 1 mm. The electromagnetic shielding effectiveness of the transparent window metasurface unit is higher than 40dB at an incident angle of 60°; The thickness of the metal microstructure layer is 100 nm, the line width is 5 μm, and the period of the metal microstructure layer is 200 μm or 400 μm.

2. The electromagnetic transparent window based on the double-layer metal microstructure layer according to claim 1, Features: The material of the metal microstructure layer is any one of copper, aluminum, silver and gold.

3. The electromagnetic transparent window based on the double-layer metal microstructure layer according to claim 2, Features: The material of the metal microstructure layer is gold.

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