Ultra-wideband absorber

Abstract

The invention discloses an ultra-wideband absorber which can be applied to the technical field of microwave metamaterial absorbers. A plurality of periodically arranged unit structures are arranged, an upper layer structure, a middle layer structure and a lower layer structure are arranged in each unit structure, then a PMMA dielectric layer, an I TO resistance film resonance layer and a PET dielectric layer are arranged in each of the upper layer structure, the middle layer structure and the lower layer structure, and the PET dielectric layer is arranged below the PMMA dielectric layer. The I TO resistive film resonance layer is etched on the PET dielectric layer, the I TO resistive film resonance layer in the upper layer structure is set to be a circular square ring gear type pattern, the I TO resistive film resonance layer in the middle layer structure is set to be a polygonal patch type pattern, and the I TO resistive film resonance layer in the lower layer structure is set to be a mesh grid type pattern. Therefore, the functions of ultra-wideband absorption, optical transparency, large-angle incidence, polarization angle polarization insensitivity, easy preparation and low manufacturing cost can be realized.

Description

Technical Field

[0001] The present application relates to the technical field of microwave metamaterial absorbers, and in particular to an ultra-wideband absorber. Background Art

[0002] In related technologies, with the leap forward of wireless communication technology, especially the accelerated deployment of 5G and even future 6G technologies, the complexity of the electromagnetic environment has increased dramatically, and the electromagnetic interference (EMI) and electromagnetic radiation problems generated during the operation of communication equipment have become increasingly prominent, thereby interfering with the stable operation of various electronic devices. Prior art Although traditional magnetic loss control materials such as ferrites and metal compounds have a deep application foundation in the field of microwave absorption, the increased weight and high density caused by the high filling ratio limit their application in lightweight equipment, and the lack of corrosion resistance further limits their scope of application. Traditional "perfect absorbers (MMA)" mostly rely on a combination of metal and rigid dielectric bases. This combination lacks optical transparency and color consistency in the visible light spectrum, thus limiting its application in modern high-tech fields such as stealth weapon windows and photovoltaic panels.

[0003] In summary, the technical problems existing in the relevant technologies need to be improved. Summary of the invention

[0004] The main purpose of the embodiments of the present application is to provide an ultra-wideband absorber that can effectively expand the scope of application.

[0005] To achieve the above-mentioned purpose, one aspect of an embodiment of the present application provides an ultra-wideband absorber, comprising a plurality of unit structures, all of which are periodically arranged;

[0006] Each of the unit structures comprises an upper structure, a middle structure and a lower structure;

[0007] The upper structure, the middle structure and the lower structure all include a PMMA dielectric layer, an ITO resistor thin film resonant layer and a PET dielectric layer; the PET dielectric layer is arranged below the PMMA dielectric layer; the ITO resistor thin film resonant layer is etched on the PET dielectric layer;

[0008] The ITO resistor thin film resonant layer in the upper structure includes a circular square ring gear-shaped pattern;

[0009] The ITO resistor thin film resonant layer in the middle layer structure includes a polygonal patch type pattern;

[0010] The ITO resistor thin film resonant layer in the lower structure includes a mesh grid pattern.

[0011] In some embodiments, the dielectric constant of the PMMA dielectric layer is 2.25; the dielectric constant of the PET dielectric layer is 3.

[0012] In some embodiments, the loss tangent of the PMMA dielectric layer is 0.001; and the loss tangent of the PET dielectric layer is 0.06.

[0013] In some embodiments, the thickness of the PMMA medium layer is 3 mm; the thickness of the PET medium layer is 0.125 mm.

[0014] In some embodiments, the resistance of the circular square ring gear pattern is 100Ω / sq; the resistance of the polygonal patch pattern is 60Ω / sq; and the resistance of the grid pattern is 3Ω / sq.

[0015] In some embodiments, the circular square ring gear-shaped pattern is obtained by combining two circular rings with different diameters and eight square patches of the same size and etched on the upper PET medium layer.

[0016] In some embodiments, the polygonal patch pattern is obtained by combining a plurality of square patches and etched on the middle PET medium layer.

[0017] In some embodiments, the square patch includes one first square patch and four second square patches; the size of the first square patch is larger than the size of the second square patch.

[0018] In some embodiments, the grid pattern includes a 4*4 square grid structure.

[0019] In some embodiments, the upper structure, the middle structure and the lower structure are tightly fitted.

[0020] The embodiments of the present application include at least the following beneficial effects: The present application provides an ultra-wideband absorber, which is configured by setting a plurality of periodically arranged unit structures, arranging an upper structure, a middle structure and a lower structure in each unit structure, and then arranging a PMMA dielectric layer, an ITO resistor thin film resonant layer and a PET dielectric layer in the upper structure, the middle structure and the lower structure, wherein the PET dielectric layer is arranged below the PMMA dielectric layer, and the ITO resistor thin film resonant layer is etched on the PET dielectric layer, and at the same time, the ITO resistor thin film resonant layer in the upper structure is arranged to be a circular square ring gear-type pattern, the ITO resistor thin film resonant layer in the middle structure is arranged to be a polygonal patch-type pattern, and the ITO resistor thin film resonant layer in the lower structure is arranged to be a grid-type pattern, thereby realizing ultra-wideband absorption, optical transparency, large-angle incident and polarization insensitivity to polarization angle, easy preparation and low manufacturing cost, thereby expanding the scope of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of the three-dimensional structure of the ultra-wideband absorber provided in an embodiment of the present application;

[0022] Figure 2 is a schematic diagram of the three-dimensional structure of the unit structure provided in the embodiment of the present application;

[0023] Figure 3 is a schematic diagram of a cross-sectional structure of a unit structure provided in an embodiment of the present application;

[0024] Figure 4 It is a structural schematic diagram of a circular square ring gear-type pattern provided in an embodiment of the present application;

[0025] Figure 5 is a schematic structural diagram of a polygonal patch-type pattern provided in an embodiment of the present application;

[0026] Figure 6 is a schematic structural diagram of a grid pattern provided in an embodiment of the present application;

[0027] Figure 7 This is a diagram showing the electromagnetic wave signal absorption effect of the ultra-wideband absorber provided in an embodiment of the present application under different polarizations when the electromagnetic wave is vertically incident;

[0028] Figure 8 This is a diagram showing the absorption effect of the ultra-wideband absorber provided in the embodiment of the present application on electromagnetic wave signals at different incident angles under TE polarization;

[0029] Fig. 9 This is a diagram showing the absorption effect of the ultra-wideband absorber provided in the embodiment of the present application on electromagnetic wave signals at different incident angles under TM polarization;

[0030] Fig.10 This is a diagram of the absorption effect of the ultra-wideband absorber provided in an embodiment of the present application when the polarization angle changes under different polarizations. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the embodiments of the present application, they are only examples of devices and methods consistent with some aspects of the embodiments of the present application.

[0032] It is understood that the terms "first", "second", etc. used in this application can be used to describe various concepts in this article, but unless otherwise specified, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another concept. For example, without departing from the scope of the embodiment of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the words "if" and "if" as used herein can be interpreted as "at the time of" or "when" or "in response to determination".

[0033] The terms "at least one", "multiple", "each", "any", etc. used in this application, at least one includes one, two or more, multiple includes two or more, each refers to each of the corresponding multiple, and any refers to any one of the multiple.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application.

[0035] Before describing the embodiments of the present application in detail, some nouns and terms involved in the embodiments of the present application are first described. The nouns and terms involved in the embodiments of the present application are subject to the following interpretations:

[0036] PMMA refers to acrylic or organic glass, and its chemical name is polymethyl methacrylate. It is an important plastic polymer material that was developed earlier. PMMA has good transparency, chemical stability and weather resistance, is easy to dye, easy to process, and has a beautiful appearance. It is widely used in the construction industry; its products can usually be divided into cast plates, extruded plates and molded materials.

[0037] ITO (indium tin oxides) is an N-type oxide semiconductor - indium tin oxide. ITO is obtained by doping indium oxide with tin (the doping ratio is usually In2O3: SnO2=9:1). The doped high-valent positive ions Sn replace the position of trivalent In in the In2O3 lattice, thereby providing excess electron carriers to the conduction band, forming an N-type degenerate semiconductor ITO (ITO film) with good transparent conductive properties. ITO film is an indium tin oxide semiconductor transparent conductive film, which usually has two performance indicators: resistivity and transmittance.

[0038] PET refers to polyethyleneterephthalate, with the chemical formula -OCH2-CH2OCOC6H4CO. It is a high polymer obtained by the dehydration condensation reaction of ethylene terephthalate. Ethylene terephthalate is obtained by the esterification reaction of terephthalic acid and ethylene glycol. PET is a milky white or light yellow, highly crystalline polymer with a smooth and shiny surface. It has excellent physical and mechanical properties in a wide temperature range, and the long-term use temperature can reach 120°C. It has excellent electrical insulation, and even at high temperature and high frequency, its electrical properties are still good, but its corona resistance is poor, and its creep resistance, fatigue resistance, friction resistance, and dimensional stability are all very good.

[0039] HFSS is the first commercial 3D structural electromagnetic field simulation software, which has been widely used in aviation, electronics, semiconductors, computers and other fields. HFSS has become the preferred tool and industry standard for high-frequency structure design with its unparalleled simulation accuracy and reliability, fast simulation speed, easy-to-use operation interface, and stable and mature adaptive mesh generation technology.

[0040] In related technologies, with the leap forward of wireless communication technology, especially the accelerated deployment of 5G and even future 6G technologies, the complexity of the electromagnetic environment has increased dramatically, and the electromagnetic interference (EMI) and electromagnetic radiation problems generated during the operation of communication equipment have become increasingly prominent, thereby interfering with the stable operation of various electronic devices. Prior art Although traditional magnetic loss control materials such as ferrites and metal compounds have a deep application foundation in the field of microwave absorption, the increased weight and high density caused by the high filling ratio limit their application in lightweight equipment, and the lack of corrosion resistance further limits their scope of application. Traditional "perfect absorbers (MMA)" mostly rely on a combination of metal and rigid dielectric bases. This combination lacks optical transparency and color consistency in the visible light spectrum, thus limiting its application in modern high-tech fields such as stealth weapon windows and photovoltaic panels.

[0041] In view of this, an ultra-wideband absorber is provided in an embodiment of the present application. The scheme arranges a plurality of periodically arranged unit structures, arranges an upper structure, a middle structure and a lower structure in each unit structure, and then arranges a PMMA dielectric layer, an ITO resistor thin film resonant layer and a PET dielectric layer in the upper structure, the middle structure and the lower structure, the PET dielectric layer is arranged below the PMMA dielectric layer, and the ITO resistor thin film resonant layer is etched on the PET dielectric layer. At the same time, the ITO resistor thin film resonant layer in the upper structure is arranged as a circular square ring gear pattern, the ITO resistor thin film resonant layer in the middle structure is arranged as a polygonal patch pattern, and the ITO resistor thin film resonant layer in the lower structure is arranged as a grid pattern, so that ultra-wideband absorption, optical transparency, large-angle incident and polarization insensitivity to polarization angle, easy preparation, and low production cost can be achieved, thereby expanding the scope of application.

[0042] The ultra-wideband absorber of the embodiment of the present application is described in detail below with reference to the accompanying drawings:

[0043] Reference Figure 1 , Figure 2 and Figure 3 The embodiment of the present application provides an ultra-wideband absorber, including a plurality of unit structures, all of which are arranged periodically; each unit structure includes an upper structure 110, a middle structure 120 and a lower structure 130; the upper structure 110, the middle structure 120 and the lower structure 130 all include a PMMA dielectric layer 210, an ITO resistor film resonant layer and a PET dielectric layer 220; the PET dielectric layer 220 is arranged below the PMMA dielectric layer 210; the ITO resistor film resonant layer is etched on the PET dielectric layer 220; the ITO resistor film resonant layer in the upper structure 110 includes a circular square ring gear-type pattern 231; the ITO resistor film resonant layer in the middle structure 120 includes a polygonal patch-type pattern 232; the ITO resistor film resonant layer in the lower structure 130 includes a grid-type pattern 233.

[0044] In the embodiment of the present application, the material and size of the PMMA dielectric layer in the upper structure, the middle structure and the lower structure are the same, and the material and size of the PET dielectric layer are also the same. The PMMA dielectric layer and the PET dielectric layer in the upper structure, the middle structure and the lower structure are stacked and tightly fitted. Specifically, the dielectric constant of the PMMA dielectric layer is 2.25; the dielectric constant of the PET dielectric layer is 3. The loss tangent of the PMMA dielectric layer is 0.001; the loss tangent of the PET dielectric layer is 0.06. The thickness of the PMMA dielectric layer is Hpmma=3mm; the thickness of the PET dielectric layer is Hpet=0.125mm. The resistance of the circular square ring gear type pattern is Rtop=100Ω / sq; the resistance of the polygonal patch type pattern is Rmid=60Ω / sq; the resistance of the grid type pattern is Rback=3Ω / sq.

[0045] In the embodiments of the present application, Figure 4 As shown in FIG. 1 , the circular square ring gear pattern is obtained by combining two circular rings with different diameters (the first circular ring has a diameter of R1 and the second circular ring has a diameter of R2) and eight square patches of the same size (the length and width are L3 and L2 respectively) and etched on the upper PET medium layer. Figure 5 As shown, the polygonal patch pattern is obtained by combining multiple square patches and etched on the middle PET medium layer; wherein the square patches include a first square patch and four second square patches, and the size L4 of the first square patch is larger than the size L5 or L6 of the second square patch. Figure 6 As shown, the grid pattern includes a 4*4 square grid structure, and the length of the square in the square grid structure is L B1 , width is L B2 .

[0046] In an embodiment of the present application, the finite element method in the HFSS software is used to perform full-wave numerical simulation of the ultra-wideband absorber, and a floquet port with a normal-incident plane transverse electric field wave and a transverse magnetic field wave is set in the z-axis direction of the transparent broadband metamaterial absorber (ultra-wideband absorber). The periodic boundaries of the transparent broadband metamaterial absorber in the x-axis direction and the periodic boundaries of the transparent broadband metamaterial absorber in the y-axis direction are used to simulate infinite periodic units.

[0047] Specifically, the specific structural parameters of the ultra-wideband absorber of the present application are shown in Table 1 (unit: mm):

[0048] Table 1

[0049] P 11.25 L1 11.05 L3 2.25 L4 8.25 L6 0.75 R1 7.25 <![CDATA[L B1 ]]> 2 <![CDATA[L B2 ]]> 1

[0050] Based on the above parameters, the finite element method in HFSS is used to perform full-wave numerical simulation analysis on the ultra-wideband absorber under different polarizations (TE, TM), and the results are as follows: Figure 7 The diagram shows the electromagnetic wave signal absorption effect when the electromagnetic wave is incident vertically.

[0051] The finite element method in HFSS is used to perform full-wave numerical simulation analysis on the ultra-wideband absorber under TE polarization, and the results are obtained. Figure 8 The figure shows the absorption effect of electromagnetic wave signals at different incident angles.

[0052] The finite element method in HFSS is used to perform full-wave numerical simulation analysis on the ultra-wideband absorber under TM polarization, and the results are as follows: Fig. 9 The figure shows the absorption effect of electromagnetic wave signals at different incident angles.

[0053] The finite element method in HFSS is used to perform full-wave numerical simulation analysis on the ultra-wideband absorber under different polarizations (TE, TM), and the results are as follows: Fig.10 The absorption effect diagram shown is when the polarization angle changes.

[0054] Specifically, this embodiment can achieve free space impedance matching and absorption in any frequency band while keeping the relative bandwidth unchanged by selecting the geometric parameters of each part as shown in Table 1. Among them, the fractional bandwidth (FBW) with an absorption rate greater than 90% is defined as the evaluation standard of the absorption performance, which is expressed as shown in the following formula:

[0055] FBW=2×(fH-fL) / (fH+fL);

[0056] In the formula, FBW represents fractional bandwidth, and fH and fL are the upper and lower limits of the frequency range where the absorption is above a reference value (usually 90%).

[0057] Specifically, after the relevant S parameters are obtained by HFSS electromagnetic simulation software in this embodiment, the absorption coefficient A(ω) of the ultra-wideband absorber can be calculated by the following formula:

[0058] A(ω)=1-R(ω)-T(ω);

[0059] In the formula, R(ω)=|S 11 (ω)| 2 , expressed as reflectivity; T(ω)=|S 21 (ω)| 2 , expressed as transmittance.

[0060] Understandably, reference Figure 7It can be clearly seen from the simulation result diagram that the ultra-wideband absorber of this embodiment operates in the 4-26GHz frequency band. When the electromagnetic wave is vertically incident, the absorption effect curves under TE and TM polarizations are consistent, indicating that the ultra-wideband absorber of this embodiment is polarization insensitive. In addition, the fractional bandwidth of the ultra-wideband absorber of this embodiment with an absorption rate greater than 90% reaches 145%, further indicating that the ultra-wideband absorber of this embodiment has the characteristics of ultra-wideband absorption.

[0061] refer to Figure 8 and Fig. 9 It can be clearly seen from the simulation result diagram that the ultra-wideband absorber of this embodiment has a good absorption effect on high-angle incident electromagnetic waves. Under TE polarization conditions, when the incident angle is limited to 45° or less, the ultra-wideband absorber of this embodiment exhibits excellent ultra-wideband absorption characteristics, and its fractional bandwidth is not less than 140%. Furthermore, even if the incident angle is increased to 60°, for the frequency band where the absorption rate is maintained above 80%, its fractional bandwidth can still be maintained at 130%; under TM polarization conditions, when the incident angle is limited to 60° or less, the ultra-wideband absorber of this embodiment also exhibits excellent ultra-wideband absorption characteristics, and its fractional bandwidth is not less than 120%. Furthermore, even if the incident angle is increased to 70°, for the frequency band where the absorption rate is maintained above 80%, its fractional bandwidth can still be maintained at 120%.

[0062] By reference Fig.10 It can be seen that the absorption effect curve of the ultra-wideband absorber of this embodiment remains stable and consistent when facing different polarization angles Ψ. This characteristic clearly reflects the excellent polarization angle insensitivity of the ultra-wideband absorber of this embodiment. This insensitivity enables the ultra-wideband absorber of this embodiment to maintain stable performance in a variety of complex electromagnetic environments, thereby greatly broadening its application range. Regardless of the electromagnetic conditions, the ultra-wideband absorber of this embodiment can effectively cope with it, showing a wide range of application prospects and strong practicality.

[0063] From the above content, it can be seen that the ultra-wideband absorber of the embodiment of the present application has the following beneficial effects:

[0064] First, the embodiments of the present application are prepared using common materials such as PET, PMMA, and ITO, and the preparation method is simple, the cost is low, and the optical transparency is good.

[0065] Second, the thickness of each unit structure in the embodiment of the present application is 9.375 mm, which is only 0.125 times the wavelength of the lowest operating frequency, and is thin and small in size.

[0066] Third, compared with the traditional ultra-wideband absorber in the embodiment of the present application, the ultra-wideband absorber in the embodiment of the present application has a simple structure, is easy to implement, has an ultra-wide absorption bandwidth, and has a good absorption effect for electromagnetic waves with high incident angles in TE and TM polarizations.

[0067] Fourth, a notable feature of the embodiment of the present application is that it exhibits a balanced absorption effect for different polarization angles, achieving polarization insensitivity. This feature indicates that it has an extremely broad application field and high applicability, and has good application prospects.

[0068] The embodiments described in the embodiments of the present application are intended to more clearly illustrate the technical solutions of the embodiments of the present application and do not constitute a limitation on the technical solutions provided in the embodiments of the present application. Those skilled in the art will appreciate that with the evolution of technology and the emergence of new application scenarios, the technical solutions provided in the embodiments of the present application are also applicable to similar technical problems.

[0069] Those skilled in the art will appreciate that the technical solutions shown in the figures do not constitute a limitation on the embodiments of the present application, and may include more or fewer steps than shown in the figures, or a combination of certain steps, or different steps.

[0070] The device embodiments described above are merely illustrative, and the units described as separate components may or may not be physically separated, that is, they may be located in one place or distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0071] Those skilled in the art will appreciate that all or some of the steps in the methods disclosed above, and the functional modules / units in the systems and devices may be implemented as software, firmware, hardware, or a suitable combination thereof.

[0072] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0073] It should be understood that in the present application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the objects associated before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0074] The units described above as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0075] The preferred embodiments of the present invention are described above with reference to the accompanying drawings, but the scope of the rights of the present invention is not limited thereto. Any modification, equivalent substitution and improvement made by a person skilled in the art without departing from the scope and essence of the present invention should be within the scope of the rights of the present invention.

Claims

1. An ultra-wideband absorber, characterized in that: It comprises a plurality of unit structures, and all the unit structures are arranged periodically; Each of the unit structures comprises an upper structure, a middle structure and a lower structure; The upper structure, the middle structure and the lower structure all include a PMMA dielectric layer, an ITO resistor thin film resonant layer and a PET dielectric layer; the PET dielectric layer is arranged below the PMMA dielectric layer; the ITO resistor thin film resonant layer is etched on the PET dielectric layer; The ITO resistor thin film resonant layer in the upper structure includes a circular square ring gear-shaped pattern; The ITO resistor thin film resonant layer in the middle layer structure includes a polygonal patch type pattern; The ITO resistor thin film resonant layer in the lower structure includes a mesh grid pattern.

2. The method according to claim 1, characterized in that: The dielectric constant of the PMMA dielectric layer is 2.25; the dielectric constant of the PET dielectric layer is 3.

3. The method according to claim 1, characterized in that The loss tangent of the PMMA dielectric layer is 0.001; the loss tangent of the PET dielectric layer is 0.

06.

4. The method according to claim 1, characterized in that: The thickness of the PMMA medium layer is 3 mm; the thickness of the PET medium layer is 0.125 mm.

5. The method according to claim 1, characterized in that The resistance of the circular square ring gear pattern is 100Ω / sq; the resistance of the polygonal patch pattern is 60Ω / sq; and the resistance of the grid pattern is 3Ω / sq.

6. The method according to claim 5, characterized in that The circular square ring gear-shaped pattern is obtained by combining two circular rings with different diameters and eight square patches of the same size and is etched on the upper PET medium layer.

7. The method according to claim 5, characterized in that The polygonal patch pattern is obtained by combining a plurality of square patches and is etched on the PET medium layer in the middle layer.

8. The method according to claim 7, characterized in that The square patch includes a first square patch and four second square patches; the size of the first square patch is larger than the size of the second square patch.

9. The method according to claim 5, characterized in that The grid pattern includes a square grid structure of 4*4 specifications.

10. The method according to claim 1, characterized in that The upper structure, the middle structure and the lower structure are tightly fitted.

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