Ka-band broadband absorption metasurface capable of reducing RCS (Radar Cross-Section)

Abstract

The invention discloses a Ka wave band broadband absorption metasurface capable of reducing RCS, which comprises a metal backboard layer, dielectric layers and metal patch pattern layers, the dielectric layers and the metal patch pattern layers are periodically, sequentially and alternately arranged on the metal backboard layer, and two kinds of metal patches of various sizes are laid on the surfaces of the metal patch pattern layers. The metal patches in the same metal patch pattern layer are rotationally and symmetrically distributed and arranged according to a space group by taking the center of the metal patch pattern layer as the center, and the thickness of the dielectric layer, the period sizes of the dielectric layer and the metal patch pattern layer and the size of the metal patch are changed, so that the broadband absorption metasurface absorbs electromagnetic waves of a specific frequency band; echoes are reduced; the metasurface has the advantages that the thickness of the metasurface is reduced while the bandwidth is guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of artificial electromagnetic materials, and in particular to a Ka-band broadband absorption metasurface capable of reducing RCS. Background Art

[0002] Commonly used absorbing materials such as split-point foam materials are mostly used in microwave darkrooms, but the material is thick and large in size, and cannot meet the needs of miniaturization of application products; carbon powder absorbing materials are relatively light and thin, but they are easy to age and require high maintenance costs; composite materials doped with metal particles or wire rods have good absorption effects for the entire band, but they are expensive and costly for large-scale applications; absorbing coatings usually use a multi-layer process involving spraying, electroplating, impregnation and other links. The process cost is high and relatively complex. It is difficult for impregnation and other processes to achieve uniform coverage of equipment with complex shapes, and the surface coating of equipment may also affect the material properties. Metamaterials, especially metasurfaces, have received much attention from researchers in recent years. It is an artificial composite medium at a subwavelength scale that can be artificially designed to have electromagnetic responses for specific frequency bands. It has been verified in the fields of absorption, phase control and polarization conversion. Thanks to its high absorption rate and good frequency selection characteristics, absorbing devices have become a hot research direction for metasurfaces.

[0003] Absorbing devices based on metasurfaces usually rely on surface impedance matching to allow electromagnetic waves in the working frequency band to enter the structure of the material and be lost in its dielectric layer. They have very good frequency selection characteristics and can design broadband, modulatable, and high-absorption absorbing devices in each frequency band. In the frequency bands where microwave metasurfaces are relatively more studied, metamaterial absorbing devices based on various resonant rings and multilayer structures have been widely studied. Transparent and flexible absorbing devices have also attracted the attention of researchers. For example, the literature "Liu Jingwen, Duan Junping, Zhang Binzhen. A flexible transparent metamaterial absorber based on ITO, Micro-Nano Electronics Technology [J], 2022, 59(10)." and the literature "Ma Yao, Wang Jianbao, Shi Lihua, Liu Jun, Liu Yicheng, Li Jie, Ran Yuzhou. A transparent and flexible metamaterial broadband microwave absorber, Journal of Composite Materials [J], 2022, 39(04)." both disclose transparent and flexible absorbing devices. However, the resonant structure of the metasurface is usually sub-wavelength in size and relatively small in size. Currently, it relies heavily on complex processes such as evaporation and photolithography, which makes it impossible to simplify the production process and form large-scale production, greatly hindering its practical application.

[0004] Radar stealth technology has received increasing attention. Shape design and radar absorbing materials can reduce the RCS (Radar Cross Section) of the target by dissipating the incident electromagnetic waves as heat or other forms of energy, thereby achieving stealth from radar detection. A key principle in the design of radar absorbing materials is to achieve good impedance matching. Most traditional radar absorbing materials use absorbing coatings, but they have the risk of falling off, and impedance matching depends on the combination of absorbers. As a solution, structural absorbing materials have received widespread attention, and a typical example is the absorbing metasurface.

[0005] Metasurface is an artificial composite structure formed by a certain arrangement and combination. Unlike traditional materials existing in nature, metasurface can adjust the electromagnetic parameters of the material itself by adjusting the parameters of the structure. The internal mechanism of the absorbing metasurface is the multiple resonances between different resistance modes. According to the transmission line theory, the frequency corresponding to the resonance peak can be adjusted to achieve a wide radar stealth band. Therefore, good impedance matching can be achieved through material selection and structural design. How to reduce the thickness of the metasurface while ensuring the bandwidth has become a hot research topic in the industry. Summary of the invention

[0006] The technical problem to be solved by the present invention is how to reduce the thickness of the metasurface while ensuring the bandwidth.

[0007] The present invention solves the above technical problems through the following technical means: a Ka-band broadband absorption metasurface for reducing RCS, comprising a metal backplane layer, a dielectric layer and a metal patch pattern layer, wherein the dielectric layer and the metal patch pattern layer are periodically and alternately arranged on the metal backplane layer, and the surface of the metal patch pattern layer is flattened with two types and multiple sizes of metal patches, and the metal patches in the same metal patch pattern layer are distributed and arranged according to the rotational symmetry of the space group with the center of the metal patch pattern layer being changed, and the broadband absorption metasurface absorbs electromagnetic waves in a specific frequency band and reduces echoes by changing the thickness of the dielectric layer, the periodicity of the dielectric layer and the metal patch pattern layer, and the size of the metal patches.

[0008] The present invention reduces the thickness of the metasurface by setting a tiled, periodically stacked structure, and utilizes the electromagnetic loss characteristics of the metasurface to absorb the energy of the incident electromagnetic wave and reduce the echo to achieve RCS reduction. Specifically, when the incident wave is vertically incident from one side of the metal patch structure of the metasurface, a large amount of reverse charge will be gathered at the upper and lower ends of the metal patch, and a pure electrical response will be generated on the metal patch stacking structure. The metal patch structure is strongly coupled with the reverse electrical response on the metal backplane layer, generating a magnetic response, resulting in an obvious trough on the reflectivity spectrum, corresponding to a perfect absorption peak. At the same time, the arrangement of the composite patch and the setting of the multi-layer stacking structure superimpose multiple such absorption peaks, widening the bandwidth, so that the overall structure reduces the thickness of the metasurface while ensuring the bandwidth.

[0009] Furthermore, when viewing the spatial layout from top to bottom, the size of the metal patch in the metal patch pattern layer of the current cycle is smaller than the size of the metal patch in the metal patch pattern layer of the next cycle.

[0010] Furthermore, the placement position of the metal patch in the metal patch pattern layer of the current cycle is exactly the same as the placement position of the metal patch in the metal patch pattern layer of the next cycle, and the center of the metal patch in the metal patch pattern layer of the current cycle and the center of the metal patch at the corresponding position in the metal patch pattern layer of the next cycle are on the same vertical line.

[0011] Furthermore, the metal patch pattern layer is provided with two square patches of different sizes, named S1 and S2, and nine rectangular patches of different sizes, named R1, R2, R3, R4, R5, R6, R7, R8, and R9.

[0012] Furthermore, the metal patch pattern layer is divided into four identical surface units, and the entire metal patch pattern layer is composed of a surface unit with a broadband absorption metasurface center and a The angle is rotated three times, so that the metal patches in the same metal patch pattern layer are distributed and arranged according to the rotational symmetry of the space group with the center of the metal patch pattern layer; in each surface unit, the first row is respectively arranged with S1, S2, S2, S1, and a 90° angle of each metal patch is facing upward and the diagonals are on a line, the second row is respectively arranged with S2, R7, R4, S2 and they are respectively aligned with S1, S2, S2, S1 in the vertical direction, the third row is respectively arranged with S2, R2, R7, S2 and they are respectively aligned with S1, S2, S2, S1 in the vertical direction, the fourth row is respectively arranged with S1, S2, S2, S1 and they are respectively aligned with S1, S2, S2, S1 in the first row in the vertical direction, and from left to right in the first row, between S1 and S2, between S2 and S2, and between S2 and S 1, there are first gaps below each of them, with a total of three first gaps, R9, R8 and R5 are set in these three first gaps respectively, and a 90° angle of each metal patch faces upward; in the second row, there are second gaps below each of them from left to right between S1 and R7, between R7 and R4, and between R4 and S2, with a total of three second gaps, R6, R3 and R8 are set in these three second gaps respectively, and a 90° angle of each metal patch faces upward; in the third row, there are third gaps below each of them from left to right between S1 and S2, between S2 and R7, and between R7 and S2, with a total of three third gaps, R1, R6 and R9 are set in these three third gaps respectively, and a 90° angle of each metal patch faces upward; each surface unit overlaps with the metal patch at the edge position of its adjacent surface unit.

[0013] Furthermore, the dielectric layer and the metal patch pattern layer are alternately arranged in a period of 2, and when the spatial layout is viewed from top to bottom, the metal patch pattern layer located below is defined as the lower pattern layer, and the metal patch pattern layer located above is defined as the upper pattern layer.

[0014] Furthermore, the side lengths of S1 and S2 in the upper pattern layer are 2.06mm and 1.86mm respectively; the lengths of R1, R2, R3, R4, R5, R6, R7, R8 and R9 in the upper pattern layer are 1.91mm, 1.96mm, 2.11mm, 1.98mm, 1.91mm, 1.89mm, 1.88mm, 1.76mm and 1.81mm respectively, and the corresponding widths are 2.02mm, 1.77mm, 1.82mm, 1.79mm, 2.04mm, 1.78mm, 2.02mm, 1.92mm and 1.81mm respectively. 9mm; the side lengths of S1 and S2 in the lower pattern layer are 2.16mm and 1.96mm respectively; the lengths of R1, R2, R3, R4, R5, R6, R7, R8 and R9 in the lower pattern layer are 2.06mm, 2.24mm, 2.32mm, 2.16mm, 2.08mm, 1.88mm, 2.14mm, 2.03mm and 1.9mm respectively, and the corresponding widths are 2.1mm, 1.89mm, 1.88mm, 1.97mm, 2.1mm, 2.08mm, 2.28mm, 2.28mm and 2.16mm respectively.

[0015] Furthermore, the material of the dielectric layer is selected from epoxy glass fiber board FR-4, and the material of the metal backplane layer and the metal patch pattern layer is copper, iron or aluminum.

[0016] Furthermore, at least one adhesive layer is disposed between the dielectric layer and the metal patch pattern layer of the current cycle and the dielectric layer and the metal patch pattern layer of the next cycle.

[0017] Furthermore, the thickness of the broadband absorption metasurface is 0.3 mm, the thickness of the dielectric layer is 0.1 mm, the thickness of the metal backplane layer and the metal patch pattern layer are both 0.018 mm, and the thickness of the adhesive layer is 0.04 mm.

[0018] The advantages of the present invention are:

[0019] (1) The present invention reduces the thickness of the metasurface by setting a flat, periodically stacked structure, and utilizes the electromagnetic loss characteristics of the metasurface to absorb the energy of the incident electromagnetic wave and reduce the echo to achieve RCS reduction. Specifically, when the incident wave is vertically incident from one side of the metal patch structure of the metasurface, a large amount of reverse charge will be gathered at the upper and lower ends of the metal patch, and a pure electrical response will be generated on the metal patch stacking structure. The metal patch structure is strongly coupled with the reverse electrical response on the metal backplane layer, generating a magnetic response, resulting in an obvious trough on the reflectivity spectrum, corresponding to a perfect absorption peak. At the same time, the arrangement of the composite patch and the setting of the multi-layer stacking structure superimpose multiple such absorption peaks, widening the bandwidth, so that the overall structure reduces the thickness of the metasurface while ensuring the bandwidth.

[0020] (2) The special arrangement of the metal patch pattern layer makes the structure polarization insensitive, which effectively meets the RCS reduction requirements within a wider frequency band of the Ka band.

[0021] (3) The thickness of the metasurface of the present invention is relatively thin, the dielectric thickness is 0.1 mm, and the overall metasurface thickness is 0.3 mm; the bandwidth is wide and the reduction effect is good, and the bandwidth above 10 dB can reach 9.5 GHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the reflection and transmission diagram of the incident wave in the absorbing material;

[0023] Figure 2 is a simulation diagram of the slow wave absorption theory, where Figure 2 (a) Schematic diagram of the slow-wave absorption process of the metasurface of a single-layer MIM structure; Figure 2 (b) is the dispersion curve of the waveguide mode (fundamental mode) of the metasurface with a single-layer MIM structure under different waveguide core layer widths W. Figure 2 (c) Correspondence between the metasurface cutoff wavelength λco and the waveguide core width W of the single-layer MIM structure

[0024] Figure 3 A schematic diagram of the structure of a Ka-band broadband absorption metasurface for reducing RCS disclosed in an embodiment of the present invention;

[0025] Figure 4 A schematic diagram of the layout of metal patches of a metal patch pattern layer in a Ka-band broadband absorption metasurface for reducing RCS disclosed in an embodiment of the present invention;

[0026] Figure 5 A schematic diagram of how to achieve the transition from single-frequency absorption to narrowband and then to broadband absorption through structural design in a Ka-band broadband absorption metasurface with reduced RCS disclosed in an embodiment of the present invention, wherein: Figure 5 (a) is a schematic diagram of a single-frequency absorption band. Figure 5 (b) is a schematic diagram of the absorption band after introducing several rectangular patches. Figure 5 (c) is a schematic diagram of the absorption band after introducing more square and rectangular patches of different sizes. Figure 5 (d) Figure 5 (c) is a schematic diagram of absorption bands after the structure is arranged into a stacked structure;

[0027] Figure 6 A simulated absorption spectrum of a TE wave at vertical incidence of a Ka-band broadband absorption metasurface with reduced RCS disclosed in an embodiment of the present invention;

[0028] Figure 7 The simulated absorption spectra of a Ka-band broadband absorption metasurface with reduced RCS for TM waves at different incident angles and different frequencies disclosed in an embodiment of the present invention;

[0029] Figure 8 The simulated absorption spectra of electromagnetic waves with different polarization angles of a Ka-band broadband absorption metasurface for reducing RCS disclosed in an embodiment of the present invention;

[0030] Fig. 9 The RCS performance of a Ka-band broadband absorption metasurface with reduced RCS disclosed in an embodiment of the present invention is compared with that of a metal plate of the same size. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are 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 are within the scope of protection of the present invention.

[0032] The Ka-band broadband absorption metasurface for reducing RCS provided by the present invention is set up based on the theoretical basis that a combination of multiple patches can absorb electromagnetic waves in a broadband manner. The theoretical basis is introduced in detail below. The so-called electromagnetic absorption refers to the use of high-loss materials or strong resonant structures to convert the energy of incident waves in a specific frequency band into ohmic heat or other forms of energy dissipation or absorption, thereby suppressing the reflection and transmission of the incident waves. For electromagnetic absorbing materials, their absorption performance is determined by the reflectivity R (ω) and transmittance T (ω) of the material. Therefore, the absorptivity A (ω) of the electromagnetic absorbing material can be expressed as:

[0033] A(ω)=1-R(ω)-T(ω)

[0034] like Figure 1As shown: The reflectivity R(ω) and transmittance T(ω) can be expressed as:

[0035]

[0036] For the absorber, by adjusting S 11 and S 21 The size of the device can achieve perfect electromagnetic absorption.

[0037] Generally, the complex dielectric constant ε of the material r =ε 1 -jε 2 and complex magnetic permeability μ r =μ 1 -jμ 2 To characterize the characteristics of electromagnetic waves in absorbing materials. The impedance Z of absorbing materials a The calculation formula is as follows:

[0038]

[0039] The reflection coefficient of the absorbing material for electromagnetic waves on its surface can be expressed as:

[0040]

[0041] Where Z 0 is the air impedance, Therefore, if impedance matching is to be achieved in theory, S 11 = 0, then ε is required r =μ r At this time, the real part and imaginary part of the complex dielectric constant and complex magnetic permeability of the material are required to be equal respectively. In this way, the reflectivity R(ω)=0, that is, all the incident electromagnetic waves enter the absorbing material.

[0042] Assume that the thickness of the absorbing material is d and the complex refractive index of the material is n r =n 1 +jn 2 The calculation formula is as follows:

[0043]

[0044] Normalized impedance of the material Z = Z a / Z 0 , then the transmission coefficient S 21 It can be expressed as:

[0045]

[0046] Where k is the propagation constant.

[0047] When Z = 1, we have

[0048]

[0049] In order to make the transmission coefficient as small as possible, the imaginary part of the refractive index n is required to be 2 As large as possible, the transmittance T(ω) can be expressed as:

[0050]

[0051] The dielectric layer of the material should have a large loss, that is, the imaginary parts of the complex dielectric constant and complex magnetic permeability of the material should be as large as possible.

[0052] The metasurface absorbing device based on the slow wave theory, such as the metasurface of a single-layer MIM structure, can be regarded as a waveguide structure. Assume that the width of the waveguide core layer is W and the period is P, as shown in Figure 2 As shown, Figure 2 (a) Schematic diagram of the slow-wave absorption process of the metasurface of a single-layer MIM structure; Figure 2 (b) is the dispersion curve of the waveguide mode (fundamental mode) of the metasurface with a single-layer MIM structure under different waveguide core layer widths W. Figure 2 (c) The correspondence between the metasurface cutoff wavelength λco and the waveguide core width W of the single-layer MIM structure.

[0053] Ideally, let the cladding medium of the waveguide be air, whose dielectric constant and magnetic permeability are ε0 and μ0 respectively. In anisotropic materials, the light of the TM mode propagates along the z direction, with a propagation constant of β. Its three vector fields are as follows:

[0054]

[0055] According to Maxwell's equations, we can simplify to get

[0056] H′ y (x)=-iωε z E z (x)

[0057]

[0058] Since the magnetic permeability of anisotropic materials has no dispersion, that is, μ y =μ 0 In anisotropic materials, for a three-layer planar waveguide of periodic medium-anisotropic material-medium, its light field distribution satisfies the wave equation.

[0059]

[0060] make

[0061] According to the symmetry, H y(x) field distribution function,

[0062]

[0063] According to the corresponding formula H' in the air medium y (x)=-iωε 0 E z (x), we can get the E of TM waveguide mode z (x) field distribution function,

[0064]

[0065] Using periodic boundary conditions, H y (x) and E z (x) At the border The conditions of continuity can be obtained, and the dispersion equation of periodic medium-anisotropic material-dielectric waveguide can be obtained.

[0066]

[0067] The propagation constant β and the incident photon frequency can be obtained To simplify the model, the loss is not considered. The dispersion curves of the waveguide mode (fundamental mode) under different waveguide core widths W are as follows: Figure 2 (b) is shown. Figure 2 (b) It can be seen that the dispersion curve of the waveguide mode is located to the right of the dispersion curve of light in air. The propagation constant β of the waveguide mode increases with the frequency of the incident photons. When the incident photons reach a certain frequency, namely the cutoff frequency, a degeneracy point appears. After the cutoff frequency, as the propagation constant β increases, the corresponding frequency of the incident photons decreases. At the degeneracy point, the group velocity of the corresponding mode is is 0, such as Figure 2 (b) is indicated by the circle marked on the curve. Therefore, for a waveguide of a certain width, the group velocity of the guided wave mode will reach 0 at a certain incident photon frequency.

[0068] The wavelength of the incident photon when the group velocity is 0 under different waveguide core widths is defined as the cut-off wavelength λco. Figure 2 (c) shows the corresponding relationship between the cut-off wavelength λco and the waveguide core width W. It can be seen that waveguides with different core widths can excite slow-wave modes at different incident wavelengths, and the cut-off wavelength and waveguide width change nearly linearly.

[0069] Based on the above theoretical principles, a MIM structure in the millimeter wave band can be designed. In a lossy medium, the frequency and intensity of its resonance are affected by the size of the resonance unit and the dielectric constant of the medium. Resonance units (i.e. metal patches) of multiple sizes can be designed in the horizontal or vertical direction to form a broadband absorption effect. Based on this, Figure 3As shown, the present invention proposes a Ka-band broadband absorption metasurface for reducing RCS, including a metal backplane layer 11, a dielectric layer and a metal patch pattern layer, wherein the dielectric layer and the metal patch pattern layer are periodically and alternately arranged on the metal backplane layer 11, and the surface of the metal patch pattern layer is flattened with two types and multiple sizes of metal patches, and the magnetic permeability and dielectric constant of the metasurface can be adjusted by changing the thickness of the dielectric layer, the periodic size of the dielectric layer and the metal patch pattern layer, and the size of the metal patch. The present invention continuously adjusts the above parameters so that the broadband absorption metasurface absorbs electromagnetic waves in a specific frequency band and reduces the echo to achieve RCS reduction. The specific structure obtained after the adjustment is described in detail below. In this embodiment, the dielectric layer and the metal patch pattern layer are alternately arranged in a period of 2, and the spatial layout is viewed from top to bottom, the metal patch pattern layer located below is defined as the lower pattern layer 13, the metal patch pattern layer located above is defined as the upper pattern layer 15, the dielectric layer located below is defined as the lower dielectric layer 12, and the dielectric layer located above is defined as the upper dielectric layer 14. At least one adhesive layer is provided between the dielectric layer and metal patch pattern layer of the current cycle and the dielectric layer and metal patch pattern layer of the next cycle. Therefore, the overall structure of the broadband absorption metasurface involved in this embodiment is, from top to bottom, an upper pattern layer 15, an upper dielectric layer 14, an adhesive layer, a lower pattern layer 13 and its corresponding lower dielectric layer 12, and a metal backplane layer 11.

[0070] Continue reading Figure 3 In this embodiment, the metal backplane layer 11, the upper pattern layer 15, and the lower pattern layer 13 are all made of copper, and the thickness is 0.018mm. The metal backplane layer 11 is used as an anti-transmission layer, which reflects the electromagnetic waves propagating to the metal backplane layer 11 to improve the absorption rate of the super surface for electromagnetic waves and reduce the echo. When the incident wave is vertically irradiated to the metal patch pattern layer of the super surface, a large number of opposite charges will be induced on the upper and lower surfaces of the patch, thereby stimulating a clear electrical response in the metal patch structure. This electrical response is strongly coupled with the reverse charge on the metal backplane layer 11, further inducing a magnetic response, causing the electromagnetic wave energy to be consumed in the dielectric layer, which appears as a significant trough in the reflection spectrum, corresponding to an ideal absorption peak. By carefully designing a variety of size structures and cleverly arranging them, the superposition of multiple such absorption peaks is achieved, thereby widening the bandwidth. Among them, the material of the upper dielectric layer 14 and the lower dielectric layer 12 is selected from epoxy resin-glass fiber compound with a thickness of 0.1mm. The lower pattern layer 13 and the upper dielectric layer 14 are connected by an adhesive layer. The thickness of the adhesive layer is related to the process. Different thicknesses will lead to changes in the size of the corresponding matching metal patch.

[0071] The metal patch pattern layer is provided with two square patches of different sizes, named S1 (the first group of square patches) and S2 (the second group of square patches), and is also provided with nine rectangular patches of different sizes, named R1 (the first group of rectangular patches), R2 (the second group of rectangular patches), R3 (the third group of rectangular patches), R4 (the fourth group of rectangular patches), R5 (the fifth group of rectangular patches), R6 (the sixth group of rectangular patches), R7 (the seventh group of rectangular patches), R8 (the eighth group of rectangular patches), and R9 (the ninth group of rectangular patches). The metal patch pattern layer of the broadband absorption metasurface can be divided into four parts along the center of the pattern, and each part can rotate arbitrarily around the center of the metal patch pattern layer. (n is an arbitrary integer) angles, and the metal patch pattern is also symmetrical along its diagonal. Figure 4 As shown, it is divided into 4 identical surface units, in each surface unit, the first row is respectively arranged with S1, S2, S2, S1, and a 90° angle of each metal patch is facing upwards while the diagonals are in a line, the second row is respectively arranged with S2, R7, R4, S2, and they are respectively aligned with S1, S2, S2, S1 in the vertical direction, the third row is respectively arranged with S2, R2, R7, S2, and they are respectively aligned with S1, S2, S2, S1 in the vertical direction, the fourth row is respectively arranged with S1, S2, S2, S1, and they are respectively aligned with S1, S2, S2, S1 in the first row in the vertical direction, and there are first gaps between S1 and S2, between S2 and S2, and below S2 and S1 in the first row from left to right, for a total of three first gaps. Gaps, R9, R8 and R5 are set in these three first gaps respectively, and a 90° angle of each metal patch faces upward; in the second row, there are second gaps between S1 and R7, between R7 and R4, and below R4 and S2 from left to right, with a total of three second gaps, R6, R3 and R8 are set in these three second gaps respectively, and a 90° angle of each metal patch faces upward; in the third row, there are third gaps between S1 and S2, between S2 and R7, and below R7 and S2 from left to right, with a total of three third gaps, R1, R6 and R9 are set in these three third gaps respectively, and a 90° angle of each metal patch faces upward; each surface unit overlaps with the metal patch at the edge position of its adjacent surface unit.

[0072] The placement of the metal patch in the metal patch pattern layer of the current cycle is exactly the same as the placement of the metal patch in the metal patch pattern layer of the next cycle, and the center of the metal patch in the metal patch pattern layer of the current cycle and the center of the metal patch at the corresponding position in the metal patch pattern layer of the next cycle are on the same vertical line. When the spatial layout is viewed from top to bottom, the size of the metal patch in the metal patch pattern layer of the current cycle is smaller than the size of the metal patch in the metal patch pattern layer of the next cycle. Specifically, the center of the square patch in the upper pattern layer 15 is on the same vertical line as the center of the square patch in the corresponding position in the lower pattern layer 13, and the size of the square patch on the same axis increases from the upper pattern layer 15 to the lower pattern layer 13; the center of the long patch in the upper pattern layer 15 is on the same vertical line as the center of the rectangular patch in the lower pattern layer 13, and the size of the rectangular patch on the same axis increases from the upper pattern layer 15 to the lower pattern layer 13; therefore, from a top view of the broadband absorbing metasurface, the lower pattern layer 13 and the upper pattern layer 15 present pyramid-like shapes. Through the nested design of the pyramid-like stacking structure and the metal patch tiling structure of different sizes, the superposition of multiple absorption peaks is achieved, thereby achieving broadband absorption of electromagnetic wave energy and reducing echoes.

[0073] The side lengths of S1 and S2 in the upper pattern layer 15 are 2.06mm and 1.86mm respectively; the lengths of R1, R2, R3, R4, R5, R6, R7, R8 and R9 in the upper pattern layer 15 are 1.91mm, 1.96mm, 2.11mm, 1.98mm, 1.91mm, 1.89mm, 1.88mm, 1.76mm and 1.81mm respectively, and the corresponding widths are 2.02mm, 1.77mm, 1.82mm, 1.79mm, 2.04mm, 1.78mm, 2.02mm, 1.92mm and 1.9mm respectively. ; The side lengths of S1 and S2 in the lower pattern layer 13 are 2.16mm and 1.96mm respectively; the lengths of R1, R2, R3, R4, R5, R6, R7, R8, and R9 in the lower pattern layer 13 are 2.06mm, 2.24mm, 2.32mm, 2.16mm, 2.08mm, 1.88mm, 2.14mm, 2.03mm, and 1.9mm respectively, and the corresponding widths are 2.1mm, 1.89mm, 1.88mm, 1.97mm, 2.1mm, 2.08mm, 2.28mm, 2.28mm, and 2.16mm respectively.

[0074] In terms of specific production, printed circuit board technology has the characteristics of low cost, simple processing, and easy batch production, which is particularly suitable for millimeter-level metamaterial processing and production. The size of the metasurface structure of the present invention is millimeter-level, and the printed circuit board technology is used to process and produce samples. The printed circuit board process attaches a metal film of a certain thickness to the dielectric substrate by electroplating or printing, so that the complete structure of the surface can show unique electromagnetic properties under the electromagnetic field of a specific frequency. The production process includes taking an FR-4 substrate of the required size, electroplating or printing a copper sheet of appropriate thickness, mechanically polishing and drying, and then covering the dry film and curing it by ultraviolet irradiation. The dry film after ultraviolet light exposure is insoluble in weak alkali, while the dry film of the unexposed part is generally soluble in weak alkali. The transfer of the metal patch pattern is completed through this layer of dry film. The non-transparent dry film part is washed away by the development technology, and the cured dry film is retained as a protective layer during the etching process. Acidic copper chloride is used as an etching solution to dissolve and corrode the copper surface exposed by the unexposed dry film after the action of sodium carbonate to obtain the required pattern. Finally, the exposed dry film of the resist layer is stripped off using strong alkali sodium hydroxide, and after surface and shape treatment, the sample is tested to complete the manufacturing of the sample.

[0075] Figure 5 It shows how to achieve the transition from single-frequency absorption to narrowband and then broadband absorption through structural design. Since the resonant frequency of the absorbing metasurface is directly affected by the geometry of the surface patch structure, several square patch structures of different sizes are combined onto the same metasurface unit to achieve a uniform absorption performance based on the absorption performance of the metasurface. Figure 5 (a) to broaden the absorption band. Figure 5 (b), it can be intuitively observed that the absorption bandwidth is effectively increased by more than 90% by introducing rectangular patches at specific locations in the structure. Figure 5 (c) It can be seen that by introducing more square and rectangular patches of different sizes, the absorption bandwidth of the absorption metasurface gradually increases, but the maximum value of its absorption peak keeps decreasing. Therefore, introducing multiple patches of different sizes into the absorption metasurface structure can increase the absorption bandwidth of the entire absorber, but it will also reduce the overall absorption effect, that is, there is a balance between the absorption bandwidth and the absorptivity. Figure 5 As shown in (d), a stacked structure is used to further expand the absorption bandwidth. However, it should be noted that the multi-layer design will not only increase the processing difficulty, but also weaken the conformal ability of the absorption metasurface, so the final structural design of the present invention is a compromise consideration.

[0076] like Figure 6 As shown, in the embodiment of the present invention, the metasurface in the embodiment of the present invention is simulated under the condition of vertical incident electromagnetic wave by using the finite difference time domain (FDTD) electromagnetic simulation method, and the corresponding S 11 Reflectance spectrum, calculated by formula The absorption spectrum of the metasurface at 26-40 GHz is obtained, as Figure 6 As shown, the calculated simulated average absorption rate of the material in the range of 27.5-37 GHz is about 90.1%, and the maximum absorption rate at certain frequencies exceeds 97%.

[0077] like Figure 7 As shown, the finite difference time domain (FDTD) electromagnetic simulation method is used to simulate the TM waves at different incident angles of the metasurface in the embodiment of the present invention. Figure 7 It can be seen that the metasurface in the embodiment of the present invention has a high absorption performance for TM waves in the range of 27.5-37 GHz, with an average absorption rate of more than 90%. Moreover, with the increase of the oblique incident angle of the electromagnetic wave, the absorption rate of the metasurface at 27.5-37 GHz TM waves does not decrease significantly.

[0078] like Figure 8 As shown, the finite-difference time-domain (FDTD) electromagnetic simulation method is used to simulate the metasurface in the embodiment of the present invention at different polarization angles, and the absorption performance of the metasurface at different polarization angles is observed. Figure 8 It can be seen that the absorption performance of the metasurface in the embodiment for millimeter waves in the range of 27.5-37 GHz remains almost unchanged when the polarization angles are 0°, 30°, 60° and 90°, respectively, and a relatively high absorption rate is maintained. Therefore, the metasurface in the embodiment has polarization-insensitive characteristics.

[0079] like Fig. 9 As shown, electromagnetic simulation software can be used to obtain Fig. 9 The single-station RCS results shown, compared with the metal plate of the same size, show that some frequency points between 27.5 and 37 GHz exceed the 10 dB reduction requirement, and on average reach the 10 dB reduction requirement.

[0080] In summary, the Ka-band broadband absorption metasurface of the present invention achieves an average RCS reduction of more than -10dB in the 27.5-37GHz frequency band. The simulation results show that the designed Ka-band broadband absorption metasurface has excellent broadband radar stealth performance. The special arrangement of the metal patch pattern layer makes the structure polarization insensitive. The thickness of the metasurface of the present invention is relatively thin, the dielectric thickness is 0.1mm, and the overall metasurface thickness is 0.3mm; the bandwidth is wide and the reduction effect is good. The bandwidth above 10dB can reach 9.5GHz, and the thickness of the metasurface is reduced while ensuring the bandwidth.

[0081] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Ka-band broadband absorption metasurface with reduced RCS, characterized in that: It includes a metal backplane layer, a dielectric layer and a metal patch pattern layer. The dielectric layer and the metal patch pattern layer are periodically and alternately arranged on the metal backplane layer, and the surface of the metal patch pattern layer is covered with two types and multiple sizes of metal patches. The metal patches in the same metal patch pattern layer are distributed and arranged according to the rotational symmetry of the space group with the center of the metal patch pattern layer. By changing the thickness of the dielectric layer, the period size of the dielectric layer and the metal patch pattern layer, and the size of the metal patch, the broadband absorption metasurface absorbs electromagnetic waves in a specific frequency band and reduces echoes.

2. The Ka-band broadband absorption metasurface with reduced RCS according to claim 1, characterized in that: When viewing the spatial layout from top to bottom, the size of the metal patch in the metal patch pattern layer of the current cycle is smaller than the size of the metal patch in the metal patch pattern layer of the next cycle.

3. The Ka-band broadband absorption metasurface with reduced RCS according to claim 1, characterized in that: The placement positions of the metal patches in the metal patch pattern layer of the current cycle are exactly the same as the placement positions of the metal patches in the metal patch pattern layer of the next cycle, and the centers of the metal patches in the metal patch pattern layer of the current cycle and the centers of the metal patches at the corresponding positions in the metal patch pattern layer of the next cycle are on the same vertical line.

4. The Ka-band broadband absorption metasurface with reduced RCS according to claim 1, characterized in that: The metal patch pattern layer is provided with two square patches of different sizes, named S1 and S2, and is also provided with nine rectangular patches of different sizes, named R1, R2, R3, R4, R5, R6, R7, R8, and R9.

5. The Ka-band broadband absorption metasurface with reduced RCS according to claim 4, characterized in that: The metal patch pattern layer is divided into four identical surface units. The entire metal patch pattern layer consists of a surface unit with a broadband absorption metasurface center with The angle is rotated three times, so that the metal patches in the same metal patch pattern layer are distributed and arranged according to the rotational symmetry of the space group with the center of the metal patch pattern layer; in each surface unit, the first row is respectively arranged with S1, S2, S2, S1, and a 90° angle of each metal patch is facing upward and the diagonals are on a line, the second row is respectively arranged with S2, R7, R4, S2 and they are respectively aligned with S1, S2, S2, S1 in the vertical direction, the third row is respectively arranged with S2, R2, R7, S2 and they are respectively aligned with S1, S2, S2, S1 in the vertical direction, the fourth row is respectively arranged with S1, S2, S2, S1 and they are respectively aligned with S1, S2, S2, S1 in the first row in the vertical direction, and from left to right in the first row, between S1 and S2, between S2 and S2, and between S2 and S 1, there are first gaps below each of them, with a total of three first gaps, R9, R8 and R5 are set in these three first gaps respectively, and a 90° angle of each metal patch faces upward; in the second row, there are second gaps below each of them from left to right between S1 and R7, between R7 and R4, and between R4 and S2, with a total of three second gaps, R6, R3 and R8 are set in these three second gaps respectively, and a 90° angle of each metal patch faces upward; in the third row, there are third gaps below each of them from left to right between S1 and S2, between S2 and R7, and between R7 and S2, with a total of three third gaps, R1, R6 and R9 are set in these three third gaps respectively, and a 90° angle of each metal patch faces upward; each surface unit overlaps with the metal patch at the edge position of its adjacent surface unit.

6. The Ka-band broadband absorption metasurface with reduced RCS according to claim 4, characterized in that: The dielectric layer and the metal patch pattern layer are alternately arranged in a cycle of 2, and when the spatial layout is viewed from top to bottom, the metal patch pattern layer located below is defined as the lower pattern layer, and the metal patch pattern layer located above is defined as the upper pattern layer.

7. The Ka-band broadband absorption metasurface with reduced RCS according to claim 6, characterized in that: The side lengths of S1 and S2 in the upper pattern layer are 2.06mm and 1.86mm respectively; the lengths of R1, R2, R3, R4, R5, R6, R7, R8 and R9 in the upper pattern layer are 1.91mm, 1.96mm, 2.11mm, 1.98mm, 1.91mm, 1.89mm, 1.88mm, 1.76mm and 1.81mm respectively, and the corresponding widths are 2.02mm, 1.77mm, 1.82mm, 1.79mm, 2.04mm, 1.78mm, 2.02mm, 1.92mm and 1.9mm respectively. ; The side lengths of S1 and S2 in the lower pattern layer are 2.16mm and 1.96mm respectively; the lengths of R1, R2, R3, R4, R5, R6, R7, R8, and R9 in the lower pattern layer are 2.06mm, 2.24mm, 2.32mm, 2.16mm, 2.08mm, 1.88mm, 2.14mm, 2.03mm, and 1.9mm respectively, and the corresponding widths are 2.1mm, 1.89mm, 1.88mm, 1.97mm, 2.1mm, 2.08mm, 2.28mm, 2.28mm, and 2.16mm respectively.

8. The Ka-band broadband absorption metasurface with reduced RCS according to claim 1, characterized in that: The material of the dielectric layer is selected from epoxy glass fiber board FR-4, and the material of the metal back plate layer and the metal patch pattern layer is copper, iron or aluminum.

9. The Ka-band broadband absorption metasurface with reduced RCS according to claim 1, characterized in that: At least one adhesive layer is disposed between the dielectric layer and the metal patch pattern layer of the current cycle and the dielectric layer and the metal patch pattern layer of the next cycle.

10. The Ka-band broadband absorption metasurface with reduced RCS according to claim 1, characterized in that: The thickness of the broadband absorption metasurface is 0.3 mm, the thickness of the dielectric layer is 0.1 mm, the thickness of the metal backplane layer and the metal patch pattern layer are both 0.018 mm, and the thickness of the adhesive layer is 0.04 mm.

Images