Electromagnetic wave absorption structure and ventilation equipment

Abstract

The invention discloses an electromagnetic wave absorption structure and ventilation equipment. The electromagnetic wave absorption structure comprises a reflecting layer, a dielectric layer and a metasurface layer which are sequentially stacked, the metasurface layer comprises first metamaterial units which are periodically arranged; the first metamaterial unit comprises a plurality of resonant structures which are arranged in an array, and in the resonant structure rows of the first metamaterial unit, the sizes of vertical projections of the plurality of resonant structures on the reflecting layer are sequentially reduced along the first direction; the resonant structure comprises two open rectangular rings which are arranged at an interval and a rectangular strip; the open rectangular ring comprises an opening; openings of the two open rectangular rings are arranged oppositely. The rectangular strip penetrates through the openings of the two open rectangular rings, the first end of the rectangular strip is connected with the long strip without the opening in one open rectangular ring, and the second end of the rectangular strip is connected with the long strip without the opening in the other open rectangular ring. The electromagnetic wave absorption structure and the ventilation equipment provided by the invention are simple in structure and can realize an electromagnetic wave conversion and absorption function.

Description

Technical Field

[0001] The present invention relates to the technical field of metamaterials, and in particular to an electromagnetic wave absorbing structure and ventilation equipment. Background Art

[0002] The application of electromagnetic waves is closely related to information technology. With the rapid development of science and technology, the problem of electromagnetic leakage has also emerged. Especially in military equipment, the radiation generated by electromagnetic waves to the outside world will cause information leakage. Therefore, people's demand for electromagnetic shielding in different application scenarios is becoming increasingly urgent, and the materials and methods for achieving electromagnetic wave absorption have become a hot topic in current research. At present, metamaterials have become a key technology that has attracted much attention due to their unique and excellent electromagnetic wave regulation capabilities. The electromagnetic metamaterial absorber was proposed by Landy et al. of Boston University in the United States in 2008. The structure consists of a double open resonant ring, an FR-4 dielectric substrate and a copper metal strip from top to bottom, which can achieve nearly 100% efficient electromagnetic wave absorption at 11.65GHz. Its working principle is to absorb electromagnetic waves by using the resonant loss of the structure, so that the electromagnetic waves incident on the surface of the structure are neither reflected nor transmitted, and are lost inside the structure. However, with the continuous expansion of the frequency band used by electromagnetic waves, higher requirements are also put forward for the working bandwidth of the shielding structure. In practical applications, electromagnetic wave absorption at a single frequency point can no longer meet this demand.

[0003] The existing research method combines structures with different absorption frequencies and superimposes multiple absorption peaks on adjacent spectra to expand the working bandwidth. After arranging the metal resonant structures with separate absorption peaks, the original multiple absorption peaks are superimposed on each other to achieve broadband absorption. However, this method cannot guarantee continuous and efficient absorption performance within the working frequency band, and the average absorption performance within the wide band is significantly reduced. Another method is to use multi-layer absorption structure superposition to achieve broadband absorption. In this way, continuous and efficient absorption performance within the wide band can be obtained, but at the same time, a multi-layer structure is introduced, which increases the overall thickness of the absorber, increases the material cost, and increases the difficulty of manufacturing. In 2020, scholars from the Indian Institute of Technology designed a multi-layer absorber that works at 1.26-4.38GHz. Its structure includes three layers of metal super surface layer, three layers of FR-4 substrate, three air layers and a metal bottom plate, with a thickness of more than 20mm. In 2021, scholars from China University of Mining and Technology designed an ultra-wideband absorber consisting of three layers of square resistive film, with an absorption rate of more than 90% in the range of 4.73-39.04GHz. Its metamaterial unit consists of three layers of metal resonant rings loaded on the substrate, three layers of spacers and a metal bottom plate. It has a complex structure and a thickness of more than 9mm. In 2024, scholars from Sichuan University designed an electromagnetic shielding absorber for closed cabins. This resistive frequency selective surface metamaterial absorber has an absorption rate of 90% in the frequency range of 3.9-25.8GHz, and when the incident angle increases to 50°, the absorption rate is still higher than 80%, with excellent electromagnetic absorption performance. However, its structure is a six-layer structure, such as Figure 1As shown, it includes two metal layers 101 and two different dielectric substrates 102 and two air layers 103, with an overall thickness of more than 7 mm. During processing, the chip resistors need to be welded on the structural metal layer. The processing process is complicated and prone to errors. In 2011, Professor Capasso's team at Harvard University proposed the generalized Snell's theorem, and based on this principle, designed a phase gradient metasurface composed of V-shaped resonant units, realizing the abnormal reflection and transmission of electromagnetic waves. Based on this principle, the design of the metasurface phase gradient can realize beam deflection at any angle for electromagnetic waves in different frequency bands. In 2012, Sun Shulin of Fudan University proposed and verified that the conversion of space electromagnetic waves to surface waves can be realized through phase gradient metasurfaces. With the development of phase gradient metasurface technology, in recent years, reflective phase gradient metasurfaces are often used to reduce the radar cross section (RCS) by reflecting electromagnetic waves at abnormal angles to achieve electromagnetic stealth. Most of its structures are composed of only three layers: metal resonant structure, intermediate dielectric substrate and bottom metal plate. The structure is simple and easy to process, and the cost is lower than that of absorbing materials. However, in most designs, the phase is only adjusted so that the electromagnetic waves are incident on the metasurface and then abnormally reflected to other areas in the free space at a certain angle, without achieving complete electromagnetic wave absorption. In 2024, researchers from the China Aerospace Research Institute designed a reflective electromagnetic metasurface for RCS reduction based on the phase gradient principle. It can achieve a 16.5° deflection of the scattering direction of electromagnetic waves in the frequency range of 8-12 GHz, achieving a good electromagnetic stealth effect. The design meets the scattering direction control requirements for the RCS reduction function, but the electromagnetic waves emitted by the radar still exist in the free space at this time, and the electromagnetic waves cannot be absorbed by the structure.

[0004] Traditional absorbers can only achieve electromagnetic absorption at a single or multiple scattered frequency points. In order to meet the needs of broadband electromagnetic shielding, the structure and materials of metamaterial absorbers are also constantly changing. Existing broadband metamaterial absorbers have more excellent absorbing performance, but also have problems such as complex structure, large thickness, high cost, and difficult manufacturing process. This makes it difficult for some design schemes to be put into actual engineering applications, especially in electromagnetic shielding scenarios with large coverage area requirements. And absorbers composed of multi-layer structures with air layers or inflexible rigid materials can only be loaded and attached to the surface of flat structures. When faced with application scenarios that need to be attached to surfaces with irregular shapes or curved structures, this type of absorber cannot conformally fit with the surface of the structure, resulting in the electromagnetic wave absorption structure failing to achieve the expected absorbing effect, and even affecting the original function of the attached structure.

[0005] Phase gradient metasurfaces can be used to reduce RCS and achieve electromagnetic stealth. By controlling the phase of electromagnetic waves, the electromagnetic waves incident on the metasurface are reflected to the free space at an abnormal angle to avoid radar detection. Phase gradient metasurfaces have the advantages of simple structure and easy deployment. However, in this application field, the electromagnetic waves reflected by the metasurface still propagate in the free space, and the incident electromagnetic waves are not completely absorbed in the structure, and the electromagnetic shielding effect cannot be achieved. In addition, most of the existing multi-layer absorbing structures are made of hard substrates, which results in a thick overall thickness when achieving broadband absorption of electromagnetic waves, which is not conducive to the installation of special-shaped inner wall surfaces, and occupies a large space on the inner wall, which has a great impact on the size of the internal waveguide structure, thereby affecting the electromagnetic parameters of the original waveguide. Summary of the invention

[0006] The invention provides an electromagnetic wave absorption structure and ventilation equipment, which have a simple structure and can realize the electromagnetic wave conversion and absorption function.

[0007] According to one aspect of the present invention, an electromagnetic wave absorbing structure is provided, the electromagnetic wave absorbing structure comprising: a reflective layer, a dielectric layer and a super surface layer stacked in sequence;

[0008] The metasurface layer includes periodically arranged first metamaterial units;

[0009] The first metamaterial unit comprises a plurality of resonant structures arranged in an array, and in a row of resonant structures of the first metamaterial unit, along a first direction, sizes of vertical projections of the plurality of resonant structures on the reflective layer decrease in sequence;

[0010] The resonant structure includes two open rectangular rings arranged at intervals and a rectangular strip; the open rectangular ring includes an opening; the openings of the two open rectangular rings are arranged opposite to each other; the rectangular strip passes through the openings of the two open rectangular rings, and the first end of the rectangular strip is connected to a long strip without an opening in one of the open rectangular rings, and the second end of the rectangular strip is connected to a long strip without an opening in the other open rectangular ring.

[0011] Optionally, the metasurface layer further includes periodically arranged second metamaterial units;

[0012] The second metamaterial unit comprises a plurality of the resonant structures arranged in an array, and in a row of the resonant structures of the second metamaterial unit, along the first direction, the sizes of vertical projections of the plurality of the resonant structures on the reflective layer decrease in sequence;

[0013] The first metamaterial unit and the second metamaterial unit are arranged along a second direction; wherein the second direction is perpendicular to the first direction.

[0014] Optionally, in the resonant structure column of the first metamaterial unit, the sizes of the resonant structures are equal;

[0015] In the resonant structure column of the second metamaterial unit, the sizes of the resonant structures are equal.

[0016] Optionally, in the resonant structure row of the first metamaterial unit, a difference in reflection phase distribution between any two adjacent resonant structures is 2π / n1, where n1 is the number of the resonant structures in the resonant structure row of the first metamaterial unit;

[0017] In the resonant structure row of the second metamaterial unit, the difference in reflection phase distribution between any two adjacent resonant structures is 2π / n2, where n2 is the number of the resonant structures in the resonant structure row of the second metamaterial unit.

[0018] Optionally, the material of the dielectric layer is a flexible material.

[0019] Optionally, the reflective layer is made of metal material;

[0020] The material of the super surface layer is a metal material.

[0021] Optionally, the thickness of the dielectric layer is 1 mm.

[0022] Optionally, the thickness of the reflective layer is 0.035 mm;

[0023] The thickness of the metamaterial unit is 0.035 mm.

[0024] Optionally, the spacing between the two open rectangular rings is 0.1 mm;

[0025] The column width of the metamaterial unit column of the first metamaterial unit is 2.5 mm;

[0026] The column width of the metamaterial unit column of the second metamaterial unit is 2 mm.

[0027] According to another aspect of the present invention, a ventilation device is provided. The ventilation device includes a ventilation structure and the electromagnetic wave absorption structure provided by any embodiment of the present invention.

[0028] The embodiment of the present invention provides an electromagnetic wave absorption structure, which includes a reflective layer, a dielectric layer and a metasurface layer stacked in sequence. It can be seen that the electromagnetic wave absorption structure provided by this embodiment has a small number of layers and a simple structure. The metasurface layer includes a first metamaterial unit arranged periodically, and the first metamaterial unit includes a plurality of resonant structures arranged in an array. In the resonant structure row of the first metamaterial unit, along the first direction, the size of the vertical projection of the plurality of resonant structures on the reflective layer is reduced in sequence, thereby forming a phase gradient metasurface layer. The resonant structure includes two open rectangular rings and a rectangular strip arranged at intervals, the open rectangular ring includes an opening, the openings of the two open rectangular rings are arranged oppositely, the rectangular strip passes through the openings of the two open rectangular rings, and the first end of the rectangular strip is connected to a long strip in an open rectangular ring without an opening, and the second end of the rectangular strip is connected to a long strip in another open rectangular ring without an opening. The phase gradient metasurface layer formed by the resonant structure can convert electromagnetic waves into surface waves, and the surface waves continue to pass through the phase gradient metasurface layer along the first direction, so that the surface waves are rapidly attenuated and lost on the phase gradient metasurface layer, thereby realizing the electromagnetic wave conversion and absorption function. In summary, the electromagnetic wave absorption structure provided in this embodiment has a simple structure and can realize the electromagnetic wave conversion and absorption function.

[0029] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 It is a structural schematic diagram of an electromagnetic wave absorption structure in the related art;

[0032] Figure 2 is a schematic diagram of a three-dimensional structure of an electromagnetic wave absorption structure provided according to an embodiment of the present invention;

[0033] Figure 3 is a schematic diagram of a three-dimensional structure of an electromagnetic wave absorption structure including a resonance structure provided according to an embodiment of the present invention;

[0034] Figure 4 yes Figure 3 A schematic diagram of a top view of the electromagnetic wave absorption structure shown;

[0035] Figure 5 yes Figure 3 The left-side structural schematic diagram of the electromagnetic wave absorption structure shown;

[0036] Figure 6 is a schematic diagram of a decomposed structure of a resonant structure provided according to an embodiment of the present invention;

[0037] Figure 7 is a schematic diagram of a structure for converting an electromagnetic wave into a surface wave according to an embodiment of the present invention;

[0038] Figure 8 is a structural schematic diagram of another electromagnetic wave absorption structure provided according to an embodiment of the present invention;

[0039] Fig. 9 is a structural schematic diagram of an electromagnetic wave absorption structure including a second metamaterial unit provided according to an embodiment of the present invention;

[0040] Fig.10 is a schematic diagram of phase distribution of a metasurface 1 provided according to an embodiment of the present invention;

[0041] Fig.11 is a schematic diagram of the phase distribution of the metasurface 2 provided according to an embodiment of the present invention;

[0042] Fig.12 is a structural schematic diagram of a simulation structure provided according to an embodiment of the present invention;

[0043] Fig.13 is a schematic diagram of the reflection coefficient of a metasurface 1 and a metasurface 2 provided according to an embodiment of the present invention when an electromagnetic wave is vertically incident;

[0044] Fig.14 is a schematic diagram of electric field distribution when an electromagnetic wave is vertically incident on a metasurface 1 provided according to an embodiment of the present invention;

[0045] Fig.15 is a schematic diagram of electric field distribution when an electromagnetic wave is vertically incident on a metasurface 2 provided according to an embodiment of the present invention;

[0046] Fig.16 is a schematic diagram of the transmission coefficient of a metasurface 1 and a metasurface 2 provided according to an embodiment of the present invention when an electromagnetic wave is vertically incident;

[0047] Fig.17 is a schematic diagram of electric field distribution of an electromagnetic wave obliquely incident on a metasurface 1 provided according to an embodiment of the present invention;

[0048] Fig.18 is a schematic diagram of electric field distribution when an electromagnetic wave is obliquely incident on a metasurface 2 provided according to an embodiment of the present invention;

[0049] Fig.19is a schematic diagram of transmission coefficients of a transmission structure and an attenuation structure provided according to an embodiment of the present invention when an electromagnetic wave is incident obliquely;

[0050] Fig. 20 is a schematic diagram of transmission coefficients of another transmission structure and attenuation structure provided according to an embodiment of the present invention when electromagnetic waves are incident obliquely;

[0051] Fig.21 is the electric field distribution diagram when the attenuation structure is metasurface 1;

[0052] Fig. 22 is the electric field distribution diagram when the attenuation structure is metasurface 2;

[0053] Fig.23 is a schematic diagram of an S-parameter curve of a metasurface 1 provided according to an embodiment of the present invention;

[0054] Fig.24 is a schematic diagram of an S parameter curve of a metasurface 2 provided according to an embodiment of the present invention;

[0055] Fig.25 It is a schematic diagram of an absorption rate curve of a supersurface 1 and a supersurface 2 provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0056] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0057] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention 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 interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0058] Figure 2 is a schematic diagram of a three-dimensional structure of an electromagnetic wave absorption structure provided according to an embodiment of the present invention. Figure 3is a schematic diagram of a three-dimensional structure of an electromagnetic wave absorption structure including a resonance structure provided according to an embodiment of the present invention, Figure 4 yes Figure 3 The schematic diagram of the top view of the electromagnetic wave absorption structure shown in FIG. Figure 5 yes Figure 3 The left-view structure diagram of the electromagnetic wave absorption structure shown in FIG. Figure 2-Figure 5 The electromagnetic wave absorption structure provided in this embodiment includes: a reflective layer 100, a dielectric layer 200 and a metasurface layer 300 which are stacked in sequence; the metasurface layer 300 includes a first metamaterial unit 310 which is periodically arranged; the first metamaterial unit 310 includes a plurality of array-arranged resonant structures 311, and in the resonant structure row of the first metamaterial unit 310, along the first direction X, the sizes of the vertical projections of the plurality of resonant structures 311 on the reflective layer 100 decrease in sequence. Figure 6 is a schematic diagram of a decomposed structure of a resonant structure provided according to an embodiment of the present invention, with reference to Figure 6 The resonant structure 311 includes two open rectangular rings 301 and a rectangular strip 302 arranged at intervals; the open rectangular ring 301 includes an opening 3011; the openings 3011 of the two open rectangular rings 301 are arranged opposite to each other; the rectangular strip 302 passes through the openings 3011 of the two open rectangular rings 301, and the first end of the rectangular strip 302 is connected to a long strip without an opening in one of the open rectangular rings 301, and the second end of the rectangular strip 302 is connected to a long strip without an opening in the other open rectangular ring 301.

[0059] Specifically, the opening 3011 is located on one of the long strips of the open rectangular ring 301, the first end of the rectangular strip 302 can be connected to the midpoint of the long strip without an opening in one open rectangular ring 301, and the second end of the rectangular strip 302 can be connected to the midpoint of the long strip without an opening in another open rectangular ring 301.

[0060] The first metamaterial unit 310 can be regarded as including multiple rows of resonant structure rows, or as including multiple columns of resonant structure columns. In the resonant structure row of the first metamaterial unit 310, the shapes of the vertical projections of two adjacent resonant structures 311 on the reflective layer 100 are similar. The thickness of each resonant structure 311 is the same. In the resonant structure row, n resonant structures can be included. Exemplarily, n can be 6 or 5. When n is different, the absorption bandwidth of the electromagnetic wave absorption structure is different. Exemplarily, when n is 5, the absorption bandwidth range of the electromagnetic wave absorption structure can be 26.5GHz-50GHz, and when n is 6, the absorption bandwidth range of the electromagnetic wave absorption structure can be 15GHz-26.5GHz.

[0061] The first direction X may be a propagation direction of the surface wave. Figure 7is a schematic diagram of a structure for converting electromagnetic waves into surface waves according to an embodiment of the present invention, with reference to Figure 7 After the electromagnetic wave 401 in the free space is incident on the electromagnetic wave absorbing structure 400, it is first converted into a surface wave 402. The surface wave gradually decays along the first direction X, and then decays and loses inside the electromagnetic wave absorbing structure 400, thereby realizing the absorption of the electromagnetic wave by the electromagnetic wave absorbing structure 400.

[0062] Next, the principle of electromagnetic wave absorption structure of this embodiment absorbing electromagnetic waves is introduced:

[0063] This embodiment uses a phase gradient metasurface layer 300 to achieve the conversion of space waves to surface waves and the attenuation of surface waves. The phase gradient metasurface layer 300 achieves abnormal reflection of electromagnetic waves based on the generalized Snell's theorem. After the phase gradient metasurface layer 300 is regulated, the abnormal reflection angle θ of the electromagnetic wave is t for:

[0064]

[0065] Where ξ=dφ / dx is the metasurface phase gradient, k0=2π / λ, is the wave vector in vacuum, λ is the wavelength of the electromagnetic wave, θ i is the incident angle of the electromagnetic wave. t ≥90° means that the reflected wave is coupled as a surface wave along the metasurface plane.

[0066] The wave vectors of the incident and reflected electromagnetic waves in the horizontal direction satisfy the equation:

[0067] k r =k0sinθ i +ξ

[0068] When the incident electromagnetic wave is regulated by the metasurface layer 300 with a phase gradient of ξ, the horizontal wave vector k of the reflected wave is generated. r When it is greater than the free space wave vector k0, the conversion from space wave to surface wave can be realized. Wherein the phase gradient ξ of the metasurface layer 300 is 2π / np. n is the number of resonant structures 311 in the resonant structure row in the first metamaterial unit 310 along the first direction X, for example, Figure 2 The n in the equation is 6. p is the unit length, that is, the column width of the resonant structure column in the first metamaterial unit 310. Therefore, the design of the phase gradient metasurface layer 300 for surface wave conversion is related to the periodic length np, the wavelength λ of the electromagnetic wave, and the incident angle θ. i Related, satisfying λ / np+sinθ i When >1, the conversion from space wave to surface wave can be realized.

[0069] For the transformed wave vector k swWhen the surface wave passes through the phase gradient metasurface layer 300, the horizontal wave vector of the surface wave will continue to increase. sw +ξ=k s ′ w The surface wave vector k obtained by converting the space wave sw is already greater than the free space wave vector k0, so the new surface wave vector k s ′ w It is already much larger than the free space wave vector k0. When the generated surface wave is transmitted along the first direction X, the horizontal wave vector will continue to increase according to the value of the phase gradient after each resonant structure row cycle. Since k=2π / λ, the increase in the wave vector leads to a shorter wavelength, which enhances the spatial localization of the surface wave, and the electromagnetic field energy is more strongly concentrated at the interface between the dielectric layer 200 and the super surface layer 300. This will lead to enhanced ohmic loss and dielectric absorption, and the surface wave will have greater energy loss and faster attenuation within the propagation distance. With the regulation of the surface wave front by the phase gradient structure along the first direction X, the surface wave will eventually attenuate within the structure without scattering. The attenuation loss of the surface wave and the conversion from space wave to surface wave in the previous step jointly realize the electromagnetic wave absorption function.

[0070] The present embodiment provides an electromagnetic wave absorption structure, which includes a reflective layer, a dielectric layer and a metasurface layer stacked in sequence. It can be seen that the electromagnetic wave absorption structure provided by the present embodiment has a small number of layers and a simple structure. The metasurface layer includes a first metamaterial unit arranged periodically, and the first metamaterial unit includes a plurality of array-arranged resonant structures. In the resonant structure row of the first metamaterial unit, along the first direction, the size of the vertical projection of the plurality of resonant structures on the reflective layer decreases in sequence, thereby forming a phase gradient metasurface layer. The resonant structure includes two open rectangular rings and a rectangular strip arranged at intervals, the open rectangular ring includes an opening, the openings of the two open rectangular rings are arranged oppositely, the rectangular strip passes through the openings of the two open rectangular rings, and the first end of the rectangular strip is connected to a long strip in an open rectangular ring without an opening, and the second end of the rectangular strip is connected to a long strip in another open rectangular ring without an opening. The phase gradient metasurface layer formed by the resonant structure can convert electromagnetic waves into surface waves, and the surface waves continue to pass through the phase gradient metasurface layer along the first direction, so that the surface waves are rapidly attenuated and lost on the phase gradient metasurface layer, thereby realizing the electromagnetic wave conversion and absorption function. In summary, the electromagnetic wave absorption structure provided in this embodiment has a simple structure and can realize the electromagnetic wave conversion and absorption function.

[0071] Optional, Figure 8 is a schematic structural diagram of another electromagnetic wave absorption structure provided according to an embodiment of the present invention. Fig. 9 is a schematic structural diagram of an electromagnetic wave absorption structure including a second metamaterial unit provided according to an embodiment of the present invention, Figure 8 The structure shown can be considered as Figure 2 The structure shown is Fig. 9 The combination of structures shown, refer to Figure 2 , Figure 8 and Fig. 9 The metasurface layer 300 also includes a periodically arranged second metamaterial unit 320; the second metamaterial unit 320 includes a plurality of array-arranged resonant structures 311, and in the resonant structure row of the second metamaterial unit 320, along the first direction X, the sizes of the vertical projections of the plurality of resonant structures 311 on the reflective layer 100 decrease successively; the first metamaterial unit 310 and the second metamaterial unit 320 are arranged along the second direction Y; the second direction Y is perpendicular to the first direction X.

[0072] Specifically, the number of resonant structures 311 in the resonant structure row in the first metamaterial unit 310 and the number of resonant structures 311 in the resonant structure row in the second metamaterial unit 320 may be different. Exemplarily, the number of resonant structures 311 in the resonant structure row in the first metamaterial unit 310 is 6, and the number of resonant structures 311 in the resonant structure row in the second metamaterial unit 320 is 5.

[0073] In the electromagnetic wave absorption structure provided in this embodiment, the number of the resonant structures 311 in the resonant structure row in the first metamaterial unit 310 is different from the number of the resonant structures 311 in the resonant structure row in the second metamaterial unit 320, and / or the size of the vertical projection of the resonant structure 311 in the first set row and the first set column in the second metamaterial unit 320 on the reflective layer 100 is different from the size of the vertical projection of the resonant structure 311 in the first set row and the first set column in the first metamaterial unit 310 on the reflective layer 100.

[0074] The electromagnetic wave absorption structure provided in this embodiment, including the first metamaterial unit 310 and the second metamaterial unit 320, can achieve good electromagnetic wave absorption effect in a wide frequency band, and solve the problems of complex structure, high cost, large thickness, and difficult manufacturing of the current broadband absorber.

[0075] Next, the working principle of the electromagnetic wave absorption structure including the first metamaterial unit 310 and the second metamaterial unit 320 will be described in detail:

[0076] In this embodiment, the frequency range of electromagnetic waves is regulated to be 15GHz-50GHz, and its wavelength is 6mm-20mm. Based on the above principle, the period length of the phase gradient metamaterial unit (the metamaterial unit is the first metamaterial unit 310 or the second metamaterial unit 320) should conform to the subwavelength length. Due to the wide frequency band and large wavelength span, only one periodic structure cannot achieve uniform phase coverage at all frequency points, which will cause a significant decrease in the electromagnetic wave conversion effect, and directly affect the wave absorption effect. Therefore, the operating frequency band is divided into two sections: 15GHz-26.5GHz and 26.5GHz-50GHz, and the units of the same shape resonant structure 311 are arranged in different ways to phase-regulate electromagnetic waves in different frequency bands. The structure including multiple periodically arranged first metamaterial units 310, dielectric layer 200 and reflective layer 100 is called a metasurface 1, exemplarily, Figure 2 The structure shown may be a metasurface 1, and the structure including a plurality of periodically arranged second metamaterial units 320, a dielectric layer 200, and a reflective layer 100 is referred to as a metasurface 2. For example, Fig. 9 The structure shown may be a metasurface 2 .

[0077] Referring to Table 1, the properties of metasurface 1 and metasurface 2 are listed in Table 1. represents the phase difference between adjacent resonant structures 311, θ i It is the incident angle at which the metasurface satisfies the conversion of space waves to surface waves within the frequency band.

[0078] Table 1

[0079]

[0080] Resonant structures 311 with uniform phase distribution and different sizes are selected for periodic arrangement to form metasurface 1 and metasurface 2. The sizes of the resonant structures 311 in metasurface 1 and metasurface 2 are shown in Table 2. Fig.10 is a schematic diagram of phase distribution of a metasurface 1 provided according to an embodiment of the present invention, Fig.11 is a schematic diagram of the phase distribution of the metasurface 2 provided according to an embodiment of the present invention, with reference to Fig.10 and Fig.11 , with the change of size a, the reflection phase changes more evenly, indicating that both metasurface 1 and metasurface 2 can work in a wide bandwidth. Figure 3 , a can represent the distance between the long strips without openings in the two open rectangular rings.

[0081] Table 2 (Unit: mm)

[0082]

[0083]

[0084] Next, the simulation results of metasurface 1 and metasurface 2 are introduced in detail:

[0085] The designed metasurface 1 and metasurface 2 are simulated and analyzed in the same way. In order to verify the phase control capabilities of the designed metasurface 1 and metasurface 2, Fig.12 is a schematic diagram of a simulation structure provided according to an embodiment of the present invention, with reference to Fig.12 , a transmitting port 520 is placed above a portion of the metasurface 510 so that the electromagnetic wave is incident vertically onto the metasurface 510. A receiving port 530 is placed at the end of the simulation structure in the first direction X to verify the generation of the surface wave. The metasurface 510 is metasurface 1 or metasurface 2.

[0086] Fig.13 is a schematic diagram of the reflection coefficient of a metasurface 1 and a metasurface 2 when an electromagnetic wave is vertically incident according to an embodiment of the present invention, with reference to Fig.13 , under vertical incidence, the S11 curve values ​​of metasurface 1 and metasurface 2 in the working frequency band are both below -10dB, indicating that both metasurface 1 and metasurface 2 have good abnormal reflection effects. However, for this phase gradient metasurface, the horizontal wave vector does not meet the conditions for converting the space wave into a surface wave when the space wave is vertically incident. Fig.14 is a schematic diagram of electric field distribution when an electromagnetic wave is vertically incident on a metasurface 1 according to an embodiment of the present invention, Fig.15 is a schematic diagram of the electric field distribution of an electromagnetic wave vertically incident on a metasurface 2 according to an embodiment of the present invention, with reference to Fig.14 and Fig.15 , Fig.14 The xoz surface electric field distribution diagram of metasurface 1 at 25 GHz is shown. Fig.15 The xoz electric field distribution diagram of metasurface 2 at 40 GHz is shown. The electromagnetic wave is reflected obliquely back to the free space at a certain angle as shown by the arrow, because the wavelength and angle of the incident wave do not meet the conditions for the designed metasurface to convert space waves to surface waves. The metasurface cannot form effective surface wave conversion and electromagnetic wave absorption in all frequency bands.

[0087] Next, the angle of the transmitting port 520 is rotated counterclockwise so that the electromagnetic waves are emitted to the metasurface 1 and metasurface 2 at incident angles of 20° and 30°, respectively, providing an initial horizontal wave vector for the incident wave. Fig.16 is a schematic diagram of the transmission coefficient of a metasurface 1 and a metasurface 2 provided according to an embodiment of the present invention when an electromagnetic wave is vertically incident, with reference to Fig.16The value of S21 curve close to -10dB indicates that obvious surface waves are generated and transmitted along the first direction X on the structure to reach the receiving port 530. The mutation at some frequency points is caused by the mutation of the reflection phase of the metasurface layer 300 when the electromagnetic wave is incident at an oblique angle, which will not have a significant impact on the final electromagnetic wave absorption result. Fig.17 is a schematic diagram of electric field distribution of an electromagnetic wave obliquely incident on a metasurface 1 provided in an embodiment of the present invention, Fig.18 is a schematic diagram of electric field distribution of an electromagnetic wave obliquely incident on a metasurface 2 according to an embodiment of the present invention, with reference to Fig.17 and Fig.18 ,and Fig.14 and Fig.15 Compared with the case of vertical incidence, there are no more abnormal angle reflection waves, but obvious surface waves generated by conversion. Fig.17 The xoz electric field distribution of metasurface 1 at 25 GHz when the incident angle is 20°. Fig.18 The xoz electric field distribution of metasurface 2 at 40 GHz when the incident angle is 30°.

[0088] Fig.16 The S21 value of metasurface 1 is much lower than that of metasurface 2 in the low frequency band, indicating that the surface wave conversion and transmission effect is poor in the low frequency range of 15GHz-20GHz. Because for low-frequency incident waves, after being regulated by phase gradient metasurface 1, the horizontal wave vector of the reflected wave is much larger than k0. This will increase the loss of the surface wave in the structure during transmission, and at this time the surface wave no longer satisfies the wave vector matching with the transmission structure. After being generated, it cannot be stably transmitted along the structure, but attenuates the loss in the structure.

[0089] The simulation verifies that metasurface 1 and metasurface 2 can realize the conversion between space waves and surface waves without generating a large number of reflected waves propagating in free space. In order to attenuate the generated surface waves, they can continue to pass through the phase gradient metamaterial unit. At this time, the horizontal wave vector of the surface wave will continue to increase, resulting in a shorter wavelength and more concentrated wave energy at the interface. The localization effect of the surface wave is enhanced, resulting in enhanced Ohmic loss and dielectric absorption, and ultimately achieving the attenuation of the surface wave in the structure and realizing the electromagnetic wave absorption function.

[0090] Fig.19 is a schematic diagram of the transmission coefficient of a transmission structure and an attenuation structure provided according to an embodiment of the present invention when an electromagnetic wave is obliquely incident, with reference to Fig.19 The transmission structure includes a reflective layer and a dielectric layer that are stacked, and the attenuation structure can be a metasurface 1. Fig. 20 is a schematic diagram of the transmission coefficient of another transmission structure and attenuation structure provided according to an embodiment of the present invention when the electromagnetic wave is obliquely incident, with reference to Fig. 20 The transmission structure includes a reflective layer and a dielectric layer stacked in layers, and the attenuation structure may be a metasurface 2. Fig.19 and Fig. 20 , using the same transmitting port 520 to obliquely incident the electromagnetic wave to Fig.19 and Fig. 20 Transmission structure and attenuation structure, comparison of simulation result curves of transmission structure and attenuation structure Fig.19 and Fig. 20 As shown, the S21 values ​​of the two attenuation structures are decreased by more than 10 dB compared with the transmission structure, indicating that the surface wave energy has been lost before reaching the receiving port 530, verifying the attenuation effect of the phase structure on the surface wave. Fig.21 is the electric field distribution diagram when the attenuation structure is metasurface 1, Fig. 22 This is the electric field distribution diagram when the attenuation structure is metasurface 2, refer to Fig.21 and Fig. 22 , Fig.21 and Fig. 22 The surface wave transmission phenomenon can no longer be observed in the electric field distribution in the structure. The surface wave generated after the space wave is incident on the metasurface is directly lost and attenuated in the structure, and the incident wave will not be reflected in large quantities to propagate in the free space.

[0091] Fig.23 is a schematic diagram of an S parameter curve of a metasurface 1 provided according to an embodiment of the present invention, Fig.24 is a schematic diagram of an S parameter curve of a metasurface 2 provided according to an embodiment of the present invention, with reference to Fig.23 and Fig.24 , the coverage height of the receiving port 530 is increased to the same as that of the transmitting port 520, that is, covering the entire YOZ surface. At this time, the S parameter curves of metasurface 1 and metasurface 2 are as follows: Fig.23 and Fig.24 As shown, the S11 values ​​of the two metasurfaces under oblique incidence are less than -10dB at most frequency points in the wide frequency band range of 15GHz-50GHz, and the S21 values ​​are all less than -20dB, indicating that the electromagnetic wave absorption structure provided in this embodiment can greatly improve the electromagnetic wave absorption performance.

[0092] The electromagnetic wave absorption rate can be calculated by S parameters. When electromagnetic waves are incident on the surface of electromagnetic wave absorption structures, reflection or transmission will occur. The expressions of reflectivity and transmittance are R(ω) and T(ω), respectively. Where R(ω)=|S 11 | 2 , T(ω)=|S 21 | 2 The absorption rate A(ω) is expressed by the following formula:

[0093] A(ω)=1-|S 11 | 2 -|S 21 | 2

[0094] Where ω represents the frequency of the incident electromagnetic wave; R(ω) is the reflectivity of the absorber, which represents the energy intensity of the incident electromagnetic wave reflected by the metasurface; T(ω) is the transmittance of the absorber, which represents the energy intensity of the incident electromagnetic wave passing through the absorber; S 11 represents the reflection coefficient of the metasurface; S 21 represents the transmission coefficient of the metasurface; A(ω) represents the absorptivity of the absorber. The reflective layer in this embodiment can be a full-plane metal copper, the thickness of which far exceeds the skin depth of electromagnetic waves in the working frequency band. There is no transmission of electromagnetic waves, and the transmittance T(ω) = 0. However, a small amount of scattering at other angles in space will be generated at oblique incidence, and only S 11 Numerical values ​​cannot be used to calculate the accurate electromagnetic wave absorption rate of the electromagnetic wave absorption structure. Therefore, S in the calculation formula is replaced by 21 Change to the transmission coefficient for scattering to free space.

[0095] Fig.25 is a schematic diagram of an absorption rate curve of a super surface 1 and a super surface 2 provided according to an embodiment of the present invention, with reference to Fig.25 The absorption rates of metasurface 1 and metasurface 2 are both greater than 87% in the frequency range of 15GHz-50GHz. Only metasurface 2 has an absorption rate slightly less than 90% in the frequency range of 33GHz-36GHz. This shows that the phase gradient metasurface structure has a good electromagnetic shielding effect on incident electromagnetic waves in a wide frequency band.

[0096] The present invention applies the phase gradient theory to the field of electromagnetic wave absorption. The designed electromagnetic wave absorption structure can realize the conversion and absorption of spatial electromagnetic waves in the frequency range of 15GHz-50GHz, and has an absorption rate higher than 87% in the full frequency band.

[0097] Optional, continue to refer to Figure 2 and Fig. 9 In the resonance structure column of the first metamaterial unit 310, the sizes of the resonance structures 311 are equal; in the resonance structure column of the second metamaterial unit 320, the sizes of the resonance structures 311 are equal. This arrangement can make the attenuation degree of the surface wave passing through each resonance structure row of the first metamaterial unit 310 the same, and the attenuation degree of the surface wave passing through each resonance structure row of the second metamaterial unit 320 the same, thereby improving the conversion and absorption rate of spatial electromagnetic waves.

[0098] Optionally, in the resonant structure row of the first metamaterial unit, the difference in reflection phase distribution between any two adjacent resonant structures is 2π / n1, where n1 is the number of resonant structures in the resonant structure row of the first metamaterial unit; in the resonant structure row of the second metamaterial unit, the difference in reflection phase distribution between any two adjacent resonant structures is 2π / n2, where n2 is the number of resonant structures in the resonant structure row of the second metamaterial unit.

[0099] Specifically, the phase mutation is realized by periodically arranging the first metamaterial unit 310 and the second metamaterial unit 320 with a phase gradient. The first metamaterial unit 310 and the second metamaterial unit 320 with a phase gradient realize the phase difference by changing the size of the resonant structure 311 with a similar shape. The adjacent resonant structures 311 have a constant phase difference. In the resonant structure row of the first metamaterial unit 310, the difference in the reflected phase distribution of any two adjacent resonant structures 311 is 2π / n1. In the resonant structure row of the second metamaterial unit 320, the difference in the reflected phase distribution of any two adjacent resonant structures 311 is 2π / n2. The 2π phase coverage is satisfied within one period, thereby realizing the conversion of electromagnetic waves to surface waves.

[0100] Optionally, the material of the dielectric layer is a flexible material.

[0101] Specifically, the material of the dielectric layer is set to be a flexible material, so that the electromagnetic wave absorption structure provided in this embodiment can be bent, and when it is applied to the inner wall surface of other structures, it does not affect the size of the electromagnetic wave absorption structure. The dielectric layer can be selected from a flexible material polyimide with a dielectric constant ε=3.5. Compared with other absorbing materials and design methods, the electromagnetic wave absorption structure improved in this embodiment significantly reduces the material and manufacturing costs while ensuring good broadband electromagnetic wave absorption performance, and also has the characteristics of simple structure and easy deployment.

[0102] Optionally, the material of the reflective layer is a metal material; the material of the super surface layer is a metal material.

[0103] Specifically, the materials of the reflective layer and the super surface layer are both metal materials, which can improve the electromagnetic wave absorption rate and achieve broadband wave absorption. The materials of the reflective layer and the super surface layer can be copper.

[0104] Optionally, the thickness of the dielectric layer is 1 mm.

[0105] Specifically, the electromagnetic wave absorption structure is simulated. The surface current of the electromagnetic wave absorption structure under the incidence of x-polarized waves covers the part that changes with the size modification, indicating that the top metasurface layer forms a good electrical resonance for phase regulation. The reflection phase coverage range and its uniformity with frequency are both related to the thickness h of the dielectric layer. Increasing the value of h, the phase distribution can be more uniform in a wide frequency band, the working bandwidth increases, but the phase coverage range will decrease. In order to achieve 2π phase coverage of the electromagnetic wave absorption structure in a wide frequency band and relatively uniform distribution at each frequency point, the thickness of the dielectric layer h = 1mm is selected as the optimization parameter.

[0106] Optionally, the thickness d of the reflective layer is 0.035 mm; the thickness of the super surface layer is 0.035 mm.

[0107] Specifically, the thickness of the bottom reflective layer and the top super surface layer is set to 0.035mm, and the thickness of the middle dielectric layer is only 1mm. In this way, the overall thickness of the electromagnetic wave absorption structure is approximately 1mm, which is lower than the existing multi-layer absorbing structure, whose thickness exceeds 3mm.

[0108] Optional, continue to refer to Figure 3 and Figure 6 , the spacing g between the two open rectangular rings 301 is 0.1 mm; the column width p of the resonant structure column of the first metamaterial unit is 2.5 mm; the column width p of the resonant structure column of the second metamaterial unit is 2 mm, it can be seen that the size of the resonant structure 311 provided in this embodiment is relatively small. The line width w of the resonant structure 311 is 0.1 mm.

[0109] This embodiment provides a ventilation device, which includes a ventilation structure and an electromagnetic wave absorption structure provided by any embodiment of the present invention.

[0110] Specifically, the electromagnetic wave absorbing structure is attached to the inner wall of the ventilation structure to ensure that the electromagnetic wave absorbing structure absorbs the electromagnetic waves in the ventilation structure while the ventilation device is ventilating, thereby avoiding leakage of electromagnetic waves.

[0111] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0112] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An electromagnetic wave absorbing structure, characterized in that: include: A reflective layer, a dielectric layer and a super surface layer are stacked in sequence; The metasurface layer includes periodically arranged first metamaterial units; The first metamaterial unit comprises a plurality of resonant structures arranged in an array, and in a row of resonant structures of the first metamaterial unit, along a first direction, sizes of vertical projections of the plurality of resonant structures on the reflective layer decrease in sequence; The resonant structure includes two open rectangular rings arranged at intervals and a rectangular strip; the open rectangular ring includes an opening; the openings of the two open rectangular rings are arranged opposite to each other; the rectangular strip passes through the openings of the two open rectangular rings, and the first end of the rectangular strip is connected to a long strip without an opening in one of the open rectangular rings, and the second end of the rectangular strip is connected to a long strip without an opening in the other open rectangular ring.

2. The electromagnetic wave absorbing structure according to claim 1, characterized in that: The metasurface layer also includes periodically arranged second metamaterial units; The second metamaterial unit comprises a plurality of the resonant structures arranged in an array, and in a row of the resonant structures of the second metamaterial unit, along the first direction, the sizes of vertical projections of the plurality of the resonant structures on the reflective layer decrease in sequence; The first metamaterial unit and the second metamaterial unit are arranged along a second direction; wherein the second direction is perpendicular to the first direction.

3. The electromagnetic wave absorbing structure according to claim 2, characterized in that: In the resonant structure column of the first metamaterial unit, the sizes of the resonant structures are equal; In the resonant structure column of the second metamaterial unit, the sizes of the resonant structures are equal.

4. The electromagnetic wave absorbing structure according to claim 2, characterized in that: In the resonant structure row of the first metamaterial unit, the difference in reflection phase distribution between any two adjacent resonant structures is 2π / n1, where n1 is the number of the resonant structures in the resonant structure row of the first metamaterial unit; In the resonant structure row of the second metamaterial unit, the difference in reflection phase distribution between any two adjacent resonant structures is 2π / n2, where n2 is the number of the resonant structures in the resonant structure row of the second metamaterial unit.

5. The electromagnetic wave absorbing structure according to claim 1, characterized in that: The material of the dielectric layer is a flexible material.

6. The electromagnetic wave absorbing structure according to claim 1, characterized in that: The material of the reflective layer is a metal material; The material of the super surface layer is a metal material.

7. The electromagnetic wave absorbing structure according to claim 1, characterized in that: The thickness of the dielectric layer is 1 mm.

8. The electromagnetic wave absorbing structure according to any one of claims 1 to 7, characterized in that: The thickness of the reflective layer is 0.035 mm; The thickness of the metamaterial unit is 0.035 mm.

9. The electromagnetic wave absorbing structure according to claim 2, characterized in that: The spacing between the two open rectangular rings is 0.1 mm; The column width of the metamaterial unit column of the first metamaterial unit is 2.5 mm; The column width of the metamaterial unit column of the second metamaterial unit is 2 mm.

10. A ventilation device, characterized in that: It comprises a ventilation structure and the electromagnetic wave absorbing structure according to any one of claims 1 to 9.

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