CN117791172A - Electromagnetic transparent window based on double-layer metal microstructure layer - Google Patents
Electromagnetic transparent window based on double-layer metal microstructure layer Download PDFInfo
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Abstract
The invention discloses an electromagnetic transparent window based on a double-layer metal microstructure layer, which consists of the same artificial atomic periodic arrangement, wherein an artificial atomic structure consists of a metal microstructure layer/a medium layer/a metal microstructure layer and an antireflection film, the medium layer is a uniform and isotropic simple medium, the metal microstructure layer is positioned on the front side and the back side of the medium layer, and a layer of antireflection film is respectively covered on metal grid microstructures on the two sides. The electromagnetic transparent window based on the double-layer metal microstructure layer is adopted, the transparent window shows remarkable high shielding performance in a microwave frequency band through the metal grid, meanwhile, the antireflection film has high wave transmittance in a visible light range, and the wide practical application value and development prospect are realized on the basis of guaranteeing the wave transmittance performance of the visible light frequency band without sacrificing the microwave shielding performance.
Description
Technical Field
The invention relates to the technical field of optical windows, in particular to an electromagnetic transparent window based on a double-layer metal microstructure layer.
Background
With the rapid development and evolution of electronic information technology, the application of electromagnetic waves increasingly shows a dual trend of high energy and wide bandwidth. This trend has contributed to the complexity of the electromagnetic environment, and the electromagnetic interference has produced, has seriously affected the normal operation of electronic equipment. The optical window plays a critical role in the observation and detection applications of optoelectronic devices. As a key medium for information transmission, on the one hand, the optical window must exhibit excellent wave-transparent performance in the visible light band to achieve efficient information transmission; on the other hand, the optical window should also have excellent electromagnetic shielding capability in order to prevent electromagnetic interference generated by the wireless communication device from affecting the device performance. Therefore, the development of an optical window which can effectively shield electromagnetic interference and ensure efficient transmission of optical communication is of great significance to modern communication systems.
At present, the existing transparent electromagnetic shielding material still has a plurality of defects in the balance optimization of the microwave shielding performance and the optical wave-transmitting performance. Such as: the carbon-based material has good environmental stability, but has larger visible light absorption, and is difficult to realize high transparency and high conductivity while shielding electromagnetic interference; although the transparent conductive film of the metal nanowire is paid attention to by the excellent photoelectric performance, the surface fluctuation of the film is larger, so that the application of the transparent conductive film of the metal nanowire in application scenes with higher requirements on surface roughness is limited; transparent conductive polymer films are regarded as a solution in some cases, but the conductivity of the transparent conductive polymer films is relatively limited, so that the transparent conductive polymer films are difficult to meet the current application scenes with higher requirements on the conductivity; transparent conductive oxides such as ITO can efficiently transmit visible light, but have low microwave shielding efficiency, so that the transparent conductive oxides are limited in application scenes in which efficient microwave shielding is required.
Disclosure of Invention
The invention aims to provide an electromagnetic transparent window based on a double-layer metal microstructure layer, the transparent window shows remarkable high shielding performance in a microwave frequency band through a metal grid microstructure, meanwhile, the antireflection film enables the window to have high wave transmittance in a visible light range, the limitation of the traditional narrow-band visible light wave transmittance technology is broken through, the ultra-wide-band optical transparency is realized, meanwhile, the microwave shielding performance is not sacrificed on the basis of guaranteeing the wave transmittance performance of the visible light frequency band, and the electromagnetic transparent window has wide practical application value and development prospect.
In order to achieve the above purpose, the invention provides an electromagnetic transparent window based on a double-layer metal microstructure layer, wherein the electromagnetic transparent window is formed by the same artificial atomic periodic arrangement, the artificial atomic structure is formed by a metal microstructure layer/a medium layer/a metal microstructure layer and an antireflection film, the medium layer is a uniform and isotropic simple medium, the metal microstructure layer is positioned on the front side and the back side of the medium layer, the metal grids on the two sides are respectively covered with the antireflection film, the antireflection film enables the electromagnetic transparent window to have high wave permeability on electromagnetic waves in an infrared/visible light frequency band, and the metal grids on the two sides of the medium layer enable the electromagnetic transparent window to have high shielding property on a microwave frequency band.
Preferably, the material of the metal microstructure layer is any one of copper, aluminum, silver and gold.
Preferably, the dielectric layer side material is quartz glass, and the thickness of the dielectric layer is 1mm.
Preferably, the material of the metal microstructure layer is gold.
Preferably, the thickness of the metal microstructure layer is 100nm, and the line width is 5 μm.
Preferably, the period of the metal microstructure layer is 200 μm or 400 μm.
The electromagnetic transparent window based on the double-layer metal microstructure layer has the advantages and positive effects that:
the transparent window of the invention has obvious high shielding performance in a microwave frequency band through the metal grid microstructure, the antireflection film has high wave transmittance in a visible light range, the limitation of the traditional narrow-band visible light wave transmission technology is broken through, the ultra-wide band optical transparency is realized, and meanwhile, the cost of sacrificing the microwave shielding performance is not required on the basis of guaranteeing the wave transmission performance of the visible light frequency band, so that the transparent window has wide practical application value and development prospect.
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
Drawings
FIG. 1 is a schematic view of a transparent window and a cell structure of the present invention, wherein A is the transparent window and B is the cell structure;
FIG. 2 is a schematic diagram of the unit structure of the super-structured surface of the transparent window of the present invention;
FIG. 3 is a graph showing the effect of the thickness of the metal microstructure layer on electromagnetic shielding effectiveness;
FIG. 4 is a graph showing the effect of the period of the metal microstructure layer on the electromagnetic shielding effectiveness according to the present invention;
FIG. 5 is a graph showing the effect of the line width of the metal microstructure layer on the electromagnetic shielding effectiveness;
FIG. 6 is a graph showing electromagnetic shielding effectiveness results of the present invention with different line widths and periods but maintaining the same ratio of 1/40;
FIG. 7 is a graph showing the relationship between electromagnetic shielding effectiveness and theoretically calculated optical transmittance;
FIG. 8 is a graph showing the variation of electromagnetic shielding effectiveness with incidence angle according to the present invention, wherein (a) is TE polarized wave and (b) is TM polarized wave;
FIG. 9 is an overall photograph and a partial photograph under a microscope of a sample one of the verification example of the present invention, wherein (a) is an overall photograph, and (b) and (c) are partial photographs;
FIG. 10 is a photograph of a whole of sample II and a partial photograph under a microscope, wherein (a) is a whole photograph, and (b) and (c) are partial photographs;
FIG. 11 is a graph comparing electromagnetic shielding effectiveness test results and simulation results of a sample of the verification example of the present invention in a microwave band;
FIG. 12 is a graph comparing experimental test results and simulation results of a sample of the verification example of the present invention in the visible light band;
FIG. 13 is a graph showing experimental results of electromagnetic shielding effectiveness in microwave frequency bands of sample two according to the present invention, wherein (a) is the electromagnetic shielding effectiveness test result in the frequency band of 2.4-4.0 GHz, and (b) is the electromagnetic shielding effectiveness test result in the frequency band of 4.0-6.0 GHz;
fig. 14 is a graph of experimental results of two visible light bands of a sample according to a verification example of the present invention, where (a) is a visual effect of the sample and (b) is a result of the transmittance test.
Detailed Description
The technical scheme of the invention is further described below through the attached drawings and the embodiments.
Unless defined otherwise, technical or scientific terms used herein should be given the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs.
Examples
The electromagnetic transparent window based on the double-layer metal micro-structure layer is composed of the same artificial atomic periodic arrangement, the artificial atomic structure is composed of a metal micro-structure layer/a medium layer/a metal micro-structure layer and an antireflection film, the medium layer is a uniform and isotropic simple medium, the metal micro-structure layer is positioned on the front side and the back side of the medium layer, the metal grid micro-structures on the two sides are respectively covered with the antireflection film, the antireflection film enables the electromagnetic transparent window to have high wave permeability in an infrared/visible light frequency band, and the metal micro-structures on the two sides of the medium layer enable the electromagnetic transparent window to have high shielding property in a microwave frequency band.
The invention constructs an electromagnetic transparent window super-structure surface based on a double-layer metal microstructure, designs an efficient unit structure capable of realizing the electromagnetic transparent window through simulation, processes an array formed by the efficient unit structure, and then performs experimental verification, and the result shows that the transparent window shows remarkable high shielding performance in a microwave frequency band and has high wave transmittance in a visible light range. In the process of performing the simulation design, electromagnetic simulation software (CST Microwave Studio) is mainly adopted. The frequency domain solver converts Maxwell's equations into frequency domain problems, solves each frequency point respectively, and has certain advantages in terms of calculation accuracy and problem scale. Therefore, the simulation of the unit structure of the invention is mainly based on a frequency domain resolver.
As shown in fig. 2, the cell structure of the transparent window is shown, gra represents the period of the cell structure, a represents half width of the metal microstructure line, i.e. 2α representsThe linewidth of the metal microstructure is obtained. h is a sub Represents the thickness of the medium layer in the middle of the unit, h metal Representing the thickness of the metal microstructure. When the unit structure of the transparent window is simulated, in order to truly and accurately reflect the electromagnetic response characteristic in the actual environment, the distance between the unit structure and the incident source is ensured to be larger than one working wavelength.
As shown in A in FIG. 1, the designed transparent window unit structure is made of glass in the middle, the front and back sides are etched with metal grid structures, and the grid is plated with an antireflection film. The glass has a quartz structure, the thickness is 0.5mm, and the metal grid is a gold material with the thickness of 100nm. The anti-reflection film is formed by overlapping tantalum oxide and silicon dioxide, and the thickness of the anti-reflection film is as follows: 15nm,52.67nm,38.24nm,25nm,75.31nm,19.81nm,39.58nm,106nm.
By theoretical analysis of the electromagnetic transparent window, the structure is equivalent to a theoretical model of "CAC", as shown in FIG. 1B, the metal mesh corresponds to the C layer in "CAC", and the thickness is d C A relative dielectric constant of ε C The method comprises the steps of carrying out a first treatment on the surface of the The glass medium corresponds to layer A in "CAC" and has a thickness d A The relative dielectric constant is a constant epsilon A 。
The material of the metal microstructure layer is any one of copper, aluminum, silver and gold. Preferably, the material of the metal microstructured 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 permeability of the conductive layer on the electromagnetic shielding effectiveness of the metal microstructure layer, and gold (Au) and silver (Ag) exhibit superior conductivity compared to general materials copper (Cu) and aluminum (Al). In addition, gold has excellent chemical stability and oxidation resistance, and gold with better conductivity is selected as a metal microstructure layer of the transparent window, so that the electromagnetic shielding effectiveness and reliability of the transparent window can be improved.
The material of the dielectric layer side is quartz glass, and the thickness of the dielectric layer is 1mm. Quartz glass (SiO) 2 ) The dielectric constant of the intermediate dielectric layer was 3.9, and the thickness thereof was 1.0mm. The operating frequency band for the simulation is set in the range of 1-18 GHz.
The thickness of the metal microstructure layer was 100nm and the line width was 5. Mu.m. The period of the metal microstructure layer is 200 μm or 400 μm.
(1) And (5) performing simulation on the thickness of the metal microstructure in the transparent window unit.
In this process, the period of the fixed metal microstructure was 100 μm and the line width was 5. Mu.m. Fig. 3 simulates the effect of the thickness of the metal microstructured layer on electromagnetic shielding effectiveness. The results show that in the range of 1-18GHz, with h metal The electromagnetic shielding effectiveness is slightly improved but the overall effect is limited. Although an increase in thickness results in an increase in shielding effectiveness, this also increases the weight and cost of the material accordingly. Therefore, in practical applications, the shielding effectiveness, weight, cost, and other factors need to be comprehensively balanced according to specific requirements to determine the thickness of the most suitable metal microstructure. Thus, 100nm is chosen here as the thickness of the metal microstructure in the transparent window, i.e. h metal Set to 100nm.
(2) Influence of the cell structure period x on the electromagnetic shielding effectiveness.
The line width of the transparent window unit structure was fixed to 5 μm and simulation was performed. As shown in fig. 4, the electromagnetic shielding effectiveness of the transparent window shows a sharp decrease with increasing period. When the period is extended to 500 μm, the electromagnetic shielding performance of the transparent window at this time is poor (< 30 dB) at a frequency greater than 15 GHz. This phenomenon occurs mainly due to the fact that in the case where the period of the metal mesh is too large, the conductive path of the metal microstructure layer becomes discontinuous, thereby causing electromagnetic waves to be not effectively shielded. When the period is too large, gaps between the metal microstructures become wider, so that electromagnetic waves more easily penetrate the metal microstructures in the propagation process, thereby causing a decrease in shielding effectiveness.
Meanwhile, an excessively small period may cause a decrease in optical transparency while considering excellent electromagnetic shielding effectiveness. Therefore, a balance between electromagnetic shielding effectiveness and optical transparency needs to be found to achieve optimization of the transparent window in terms of both optical transparency and electromagnetic shielding effectiveness.
(3) The influence of the line width 2 alpha in the transparent window unit structure on the electromagnetic shielding effectiveness.
The cycle parameters were fixed at 200 μm and simulated. As shown in fig. 5, as the line width increases, the electromagnetic shielding performance of the transparent window increases. The larger line width means higher conductivity on the metal grid, while the high conductivity metal can more effectively dissipate electromagnetic wave energy through the grid, thereby improving shielding effectiveness.
The period and line width of the metal microstructures play a decisive role in electromagnetic shielding effectiveness, and the above simulation further verifies the correctness of this concept. The smaller the period of the metal microstructure is, the larger the line width is, the better the electromagnetic shielding efficiency of the metal microstructure in the microwave frequency band is, but the lower the visible light transmittance is caused, and in order to relieve the lower visible light transmittance caused by the improvement of the microwave shielding efficiency, the structure of an antireflection film is adopted to improve the transmittance.
(4) The ratio of the line width to the period is fixed to be 1/40, the whole size of the metal microstructure is changed, and the simulation is carried out.
As shown in fig. 6, the smaller the size of the metal microstructure, the higher the electromagnetic shielding effectiveness of the transparent window while maintaining the transmissivity in the visible light band. This phenomenon is mainly due to the fact that smaller-sized microstructures cause more interfacial scattering and interfacial reflection, thereby enhancing the scattering and absorption capabilities of electromagnetic waves. In addition, the microstructure with smaller size can provide larger surface area, so that the contact area between the incident electromagnetic wave and the metal is increased, and the electromagnetic shielding effectiveness is further improved. Too small a size may cause the manufacturability and stability of the microstructure to be affected, and the limit value of the narrowest line width of the photolithographic technique used in practical processing in the manufacturing engineering is 2 μm, but the manufacturing difficulty of the line width is high, which is unfavorable for mass production, and too narrow line width may cause difficulty in alignment up and down when the multilayer structure is processed. Therefore, a line width of 5 μm was chosen as a design parameter for the transparent window superstructural surface.
(5) Influence of the metal microstructure layer unit period on electromagnetic shielding effectiveness.
As shown in fig. 7, the circle curve is the theoretically calculated wave transmittance of the visible light band, and the triangle curve is the electromagnetic shielding effectiveness of 9GHz at the intermediate frequency point of the microwave band. Analysis of the two curve results shows that the wave transmission rate of the visible light frequency band steadily increases with the period, but the electromagnetic shielding effectiveness shows the opposite trend, namely gradually decreases. Here, in consideration of the requirement that the electromagnetic shielding efficiency is greater than 50dB and the transmittance in the visible light range is greater than 90%, the two requirements can be basically satisfied at the same time when the period of the metal microstructure layer is 200 μm. Therefore, the period of the microstructure of the transparent window was set to 200 μm while the line width of the metal microstructure was determined to be 5 μm.
(6) The electromagnetic shielding effectiveness of the transparent window superstructural surface changes as the angle of incidence changes.
The variation of the incident angle of the electromagnetic wave can have a certain negative effect on the performance of the super-structured surface of the transparent window, and the angle robustness of the super-structured surface of the transparent window needs to be simulated and analyzed.
As shown in fig. 8, in the process of increasing the incident angle of electromagnetic waves, the electromagnetic shielding effectiveness of the super-structured surface of the transparent window shows an increasing trend under the polarization of transverse electric waves. In contrast, however, the electromagnetic shielding effectiveness of the transparent window superstructural surface under transverse magnetic wave polarization shows a decreasing trend. The admittances of transverse wave polarization and transverse magnetic wave polarization have opposite changing tendencies when the incident angle of electromagnetic waves is changed. Specifically, this is because the electric field of transverse wave polarization is perpendicular to the incident plane, and the magnetic field of transverse wave polarization is perpendicular to the incident plane. When the incident angle is changed, as the incident angle increases in the transverse wave polarization mode, the admittance of the transparent metal super-structured surface unit increases, which results in an improvement in electromagnetic shielding effectiveness. In the transverse magnetic wave polarization mode, the admittance of the transparent window super-structured surface unit decreases with the increase of the incident angle, which results in the decrease of the electromagnetic shielding effectiveness. Although a larger incident angle in the transverse magnetic wave polarization mode results in a significant decrease in electromagnetic shielding effectiveness, the electromagnetic shielding effectiveness is still higher than 40dB even at an incident angle of 60 °. Furthermore, the electromagnetic shielding effectiveness in both different polarization forms fluctuates by less than ±10% in the range of 0 ° to 60 ° compared to the normal incidence case. This result shows that the designed transparent window super-structured surface unit has good robustness when dealing with oblique incidence.
Verification example
Two samples were prepared and tested on the basis of the electromagnetic shielding effectiveness reaching a level of substantially 40dB while maintaining a visible light transmittance of 90% or more as a parameter.
Preparation of sample one: BF33 glass with the thickness of 1mm and the relative dielectric constant of 4.5 is selected as a dielectric layer, the wave transmittance of the dielectric layer in the visible light frequency band is about 91 percent, then the front and back sides of the dielectric layer are respectively etched with the thickness of 100nm, the unit period is 200 mu m, the line width is 5 mu m, and the metal microstructure layer is made of Au.
Preparation of sample two: adopting HPFS 7978 wafer glass with the thickness of 1mm and the relative dielectric constant of 4.5 as a dielectric layer, and plating magnesium fluoride (MgF) on the surface of the dielectric layer 2 ) An antireflection film made of a material. Similar to the first sample, a metal microstructure with a thickness of 100nm, a unit period of 400 μm and a line width of 5 μm was etched on both sides of the dielectric layer, and the material used for the metal microstructure layer was Au.
And preparing the designed transparent window sample I and sample II by adopting a photoetching technology with higher precision. From the view of fig. 9 (a), it can be seen that the sample has a good light transmittance, and further, the structure of the sample is very clear, the lines are clear, and the dimensional errors are not large as those of fig. 9 (b) and (c) when the processed sample is observed by a microscope. Sample one is a small-sized sample, the size of which is: 30mm by 18mm.
As shown in fig. 10 (a), it was found that the second sample exhibited excellent light transmission properties as well, and further, by carefully observing the processed sample with a microscope, the microstructure was clearly visible as well, the lines were clear, and the dimensional errors were very small, as shown in fig. 10 (b) and (c). Sample two is a large-size sample, and its size is: 60mm by 60mm.
(1) Sample one experiment verification
Firstly, testing a microwave frequency band, measuring electromagnetic shielding effectiveness parameters in a microwave and radio frequency circuit by using a vector network analyzer and a rectangular waveguide to evaluate electromagnetic shielding effectiveness S of a sample and generate a frequency response curve of the sample. As shown in fig. 11, electromagnetic shielding effectiveness results (circle lines) of a transparent window sample one were shown by using a vector network analyzer and a rectangular waveguide, the size of the waveguide opening of the rectangular waveguide used was 22.5×10.1mm, and the operating frequency band thereof was 8.2-12.4GHz, so that experimental tests were performed in the 8-13GHz frequency band. It can be seen that the results of the experimental tests (circled lines) slightly float up and down compared to the results of the FDTD simulation (solid lines), but the overall trend is substantially identical and the electromagnetic shielding effectiveness in its test frequency band has an average value of 40dB. The experimental test of the vector network analyzer proves that the transparent metal super-structured surface has strong electromagnetic shielding effect.
Further, near infrared/visible light test was performed on the first sample, and the light transmittance of the sample was calculated using a spectrophotometer. As shown in fig. 12, the result of transmittance (circle line) of the transparent window sample in the visible/near infrared band was measured by using a spectrophotometer, and compared with the result of theoretical calculation (broken line), it was found that the result of experimental test was slightly lower than the result of theoretical calculation. Through careful analysis, it was found that the metal microstructures on both sides are not perfectly aligned during processing, with an error of about 1-2 μm, which results in electromagnetic waves being lost to the transparent metal sample by the two metal microstructures. To analyze this problem more accurately, theoretical calculations were made for its two losses:
from the results of the above calculations, it can be seen that the theoretical calculation results obtained by considering the metal microstructure loss twice are substantially identical to those measured by a spectrophotometer.
(2) Experiment verification of sample two
For the microwave characteristic test of the sample II, the same equipment and method as the sample I are adopted, namely, the experimental test is carried out through a vector network analyzer and a rectangular waveguide, and in view of the fact that the sample II is a prepared large-size sample, the frequency range of 2.4-6 GHz is selected for the test in a targeted manner, and the method comprises the step of using two rectangular waveguides with different working frequency ranges of 2.4-4.0 GHz and 4.0-6 GHz for multi-frequency coverage. As shown in fig. 13, (a) and (b) show electromagnetic shielding effectiveness of sample two in the frequency range of 2.4 to 6GHz, which exceeds 40dB. The test result is consistent with the preset design target, powerful demonstration support is provided for the simulation model, and meanwhile the practicability and effectiveness of the preparation technology are verified.
For the near infrared/visible band test of sample two, a spectrophotometer was also used. Fig. 14 (a) shows the visual effect of sample two, which can be clearly and intuitively observed, showing almost complete transparency with almost no perceptible visual difference compared to the area without sample coverage. As shown in fig. 14 (b), further provided is an experimental test result of transmittance, the value of which is stabilized around 0.9, showing extremely high transmittance, which also completely coincides with the preset design target, further verifying the correctness of theoretical analysis, and also verifying the effect and necessity of an antireflection film.
Therefore, the electromagnetic transparent window based on the double-layer metal microstructure layer is adopted, the transparent window shows remarkable high shielding performance in a microwave frequency band, has high wave transmittance in a visible light range, breaks through the limitation of the traditional narrow-band visible light wave transmittance technology, realizes the ultra-wide-band optical transparency, and has wide practical application value and development prospect without sacrificing the microwave shielding performance on the basis of guaranteeing the wave transmittance performance of the visible light frequency band.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention and not for limiting it, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that: the technical scheme of the invention can be modified or replaced by the same, and the modified technical scheme cannot deviate from the spirit and scope of the technical scheme of the invention.
Claims (6)
1. Electromagnetic transparent window based on double-deck metal micro-structure layer, its characterized in that: 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 medium layer/a metal microstructure layer and an antireflection film, the medium layer is a uniform and isotropic simple medium, the metal microstructure layer is positioned on the front side and the back side of the medium layer, the metal grid microstructures on the two sides are respectively covered with the antireflection film, the antireflection film enables the electromagnetic transparent window to have high wave permeability in an infrared/visible light frequency band, and the metal grids on the two sides of the medium layer enable the electromagnetic transparent window to have high shielding property in a microwave frequency band.
2. The electromagnetically transparent window based on a bilayer metal microstructured layer as claimed in claim 1, wherein: the material of the metal microstructure layer is any one of copper, aluminum, silver and gold.
3. The electromagnetically transparent window based on a bilayer metal microstructured layer as claimed in claim 1, wherein: the dielectric layer is made of quartz glass, and the thickness of the dielectric layer is 1mm.
4. The electromagnetically transparent window based on a bilayer metal microstructured layer according to claim 2, wherein: the metal microstructure layer is made of gold.
5. The electromagnetically transparent window based on a bilayer metal microstructured layer as claimed in claim 1, wherein: the thickness of the metal microstructure layer is 100nm, and the line width is 5 mu m.
6. The electromagnetically transparent window based on a bilayer metal microstructured layer as claimed in claim 1, wherein: the period of the metal microstructure layer is 200 μm or 400 μm.
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