Angle-insensitive broadband polarization rotary wave-absorbing metasurface

Abstract

The invention discloses an angle-insensitive broadband polarization rotary wave-absorbing metasurface (1), and the reflection coefficient of the metasurface is lower than-10dB in the whole working frequency band of 12.5-31.8 GHz. The upper layer and the lower layer of the first dielectric plate are patterns (21) etched by an ITO (Indium Tin Oxide) film and a flexible substrate PET (Polyethylene Terephthalate) (22) of the ITO film respectively; the upper layer of the second dielectric plate is not provided with metal and is a flexible dielectric supporting layer (3) made of PVC; and the third layer is a metal bottom plate formed by an ITO (Indium Tin Oxide) film (41) and a flexible substrate PET (Polyethylene Terephthalate) (42) of the ITO film. According to the first layer, an ITO film is plated on a PET film and etched, a corresponding ITO film patch shape (21) is obtained, the polarization rotation function is achieved through the shape, the polarization rotation rate is larger than 75% at the frequency of 14.5-25 GHz, and RCS is reduced; the first layer, the second layer and the third layer jointly form a resonance circuit, most of incident wave energy is absorbed and converted into ohmic loss, the wave absorbing function is achieved, specifically, the wave absorbing rate is larger than 50% at 12.5-14.5 GHz and 25-31.8 GHz, the wave absorbing rate can reach 85% at 30.8 GHz, and RCS reduction is achieved.

Description

Technical Field

[0001] The present invention relates to a metasurface with reduced RCS, and specifically designs an angle-insensitive broadband polarization rotation absorbing metasurface. Background Art

[0002] RCS is a physical quantity that evaluates a target's ability to reflect radar. Its size is closely related to the difficulty of detecting and tracking the target. The lower the target's RCS, the lower the probability of being discovered and detected by enemy radar. Therefore, in modern electronic warfare systems, reducing the target's RCS is an important indicator in stealth technology.

[0003] The existing structure used to reduce the target RCS by polarization rotation is generally a conversion layer, a dielectric layer, and a metal floor layer. The conversion layer is made of metal material and has only polarization conversion function. Patent CN202411016142.7 discloses a broadband reflective polarization rotation metasurface with reduced radar cross section, which achieves RCS reduction by polarization rotation. However, this design only achieves RCS reduction by polarization rotation, and the material used in the polarization conversion layer is metal. The design is a rigid material and is not easy to conform to curved targets, which limits its application scope. Patent CN202111028041.8 discloses a RCS reduction metasurface design method and metasurface based on absorption-cancellation. The purpose of RCS reduction is achieved by constructing two metasurface absorbing units and regulating the two units to produce a phase difference within a preset range, setting the quantity ratio of the two absorbing units in the entire metasurface. However, the design requires designing two units, which has a high design complexity. In addition, when performing periodic arrangement, the ratio of the two units must be calculated based on the performance of the units, which limits the application scenarios of the metasurface units and has certain limitations. Summary of the invention

[0004] The purpose of the present invention is to design an angle-insensitive broadband polarization rotation absorbing metasurface in view of the shortcomings of the prior art: through the design of the metasurface, the metasurface has both electromagnetic wave absorption and polarization rotation functions, thereby reducing the RCS of the target. In addition, the metasurface unit design can achieve two functions using only one structure, and all the materials used are flexible materials, which are easy to conform to the curved surface, and have a wide range of application scenarios, simple structure, and easy preparation.

[0005] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions:

[0006] An angle-insensitive broadband polarization rotation absorbing metasurface unit (1) comprises, from top to bottom, an ITO thin film pattern layer (2), a flexible dielectric support layer (3), and a metal floor layer (4). The ITO thin film pattern layer (2) has a polarization rotation function, and because the pattern is symmetrical about a diagonal line, it has a polarization insensitive characteristic. When the structure forms an array with a mirror unit, the phases between the two units are canceled, and RCS reduction can be achieved; and the resonant structure of the ITO thin film pattern layer (2) is composed of two fan-shaped resistance films, which generates high ohmic loss.

[0007] The ITO thin film pattern layer (2) uses only one material and one pattern, and combines polarization conversion and wave absorption together, so that the ITO thin film pattern layer (2) can not only achieve wave absorption by using the polarization rotation function through the pattern (21) symmetrical about the diagonal line, but also achieve wave absorption by using the resistance resonance of the ITO resistor film (21) as a unit wave absorption layer, so that the unit has a better wave absorption effect.

[0008] Furthermore, each basic unit of an angle-insensitive broadband polarization rotation absorbing metasurface comprises, from top to bottom, a first layer (2) of polarization conversion-absorbing layer, a second layer (3) of flexible dielectric support layer, and a third layer (4) of metal floor layer, wherein:

[0009] The first layer (2) is an ITO thin film pattern layer (2), which is a polarization conversion-wave absorbing structure. Since the ITO thin film needs to be attached to a PET thin layer, PET (22) is used as a substrate for the ITO thin film (21). The ITO thin film is plated on the PET film and etched to obtain a corresponding ITO thin film patch shape (21) that is symmetrical about a diagonal line.

[0010] The second layer (3) is PVC as a flexible medium support layer (3), which can meet the application requirements of special scenarios.

[0011] The third layer (4) is a metal floor layer composed of an ITO film (41) and a flexible substrate PET (42) of the ITO film.

[0012] Furthermore, the RCS reduction metasurface of ITO thin film polarization rotation absorption includes:

[0013] An ITO thin film pattern layer (2), a flexible dielectric support layer (3) and a metal floor (4); the flexible dielectric support layer (3) is arranged on the metal floor, and the flexible dielectric support layer is used to separate the ITO thin film pattern layer from the metal floor and support the ITO thin film pattern layer at the same time;

[0014] The ITO thin film pattern layer (2), the flexible dielectric support layer (3) and the metal floor (4) are all made of flexible materials, can be bent, and have both polarization conversion and wave absorption functions, thereby achieving RCS reduction.

[0015] Furthermore, the structure of an ITO film pattern layer (2) of an angle-insensitive broadband polarization rotation absorbing metasurface realizes a polarization rotation function, and because the pattern is symmetrical about a diagonal line, it has a polarization-insensitive characteristic. When the structure forms an array with a mirror unit, the two units cancel each other in phase, and a polarization conversion function is realized at 13-21 GHz, with a polarization conversion rate greater than 66%. The resonant structure of the first layer (2) is composed of two fan-shaped resistor films, which produces high ohmic loss and can effectively reduce the reflected waves on the surface, so that the incident waves can more effectively enter the dielectric layer (3) made of PVC. The continuous and complete ITO film (41) and its PET substrate (42) at the bottom act as a metal floor, which can completely reflect electromagnetic waves and block the transmission of electromagnetic waves, so that it has better absorption characteristics. The absorption rate at 11-13 GHz and 21-27 GHz is greater than 50%, realizing the absorption function, and the absorption rate at 25.5 GHz can reach up to 85%.

[0016] Furthermore, each basic unit (1) of an angle-insensitive broadband polarization rotation absorbing metasurface has a length of 7.5 mm, a width of 7.5 mm, a thickness of 2.3 mm, and an electrical size of 0.46λ×0.46λ×0.14λ.

[0017] Furthermore, in an angle-insensitive broadband polarization rotation absorbing metasurface, each basic unit of the thin film pattern layer (2) has an upper ITO thin film pattern layer (2) with two fan-shaped patterns (21). The two fan-shaped patterns are located at the center of the metasurface, each fan-shaped pattern is symmetrical about a diagonal line, and the two fan-shaped patterns are symmetrical about a diagonal line, each fan-shaped pattern has a rotation angle of 130°, a rotation radius of 3 mm, and a fan-shaped width of 0.7 mm. The fan-shaped pattern is made of a thin film resistor (21) with a resistance value of 5Ω and a thickness of 260 nm, and a 0.175 mm PET (22) material is used as a substrate, the dielectric constant of PET is 3, and the loss tangent is 0.06.

[0018] Furthermore, a flexible dielectric support plate (3) of each basic unit of an angle-insensitive broadband polarization rotation absorbing metasurface has a thickness of 2 mm, a dielectric constant of 3.0, and a loss tangent of 0.014.

[0019] Furthermore, in an angle-insensitive broadband polarization rotation absorbing metasurface, the metal floor layer (4) of each basic unit has an ITO resistor film resistance (41) of 12 ohms and a thickness of 135 nm, and the flexible substrate PET (42) of the ITO film has a thickness of 0.125 mm, a dielectric constant of 3, and a loss tangent of 0.06.

[0020] Compared with the prior art, the present invention has the following characteristics:

[0021] 1. The present invention uses both polarization conversion and wave absorption in one structure to achieve RCS reduction;

[0022] 2. The present invention achieves an RCS attenuation of more than 10dB in the 11-27GHz frequency band;

[0023] 3. The basic unit of the present invention has a small electrical size and is easy to integrate on a small-sized target;

[0024] 4. The present invention is angle-insensitive and still has relatively good RCS reduction performance at large angles of incidence. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of the basic unit structure of the angle-insensitive broadband polarization rotation absorbing metasurface in an embodiment of the present invention;

[0026] Figure 2 Schematic diagram of the angle-insensitive broadband polarization rotation absorbing metasurface pattern layer of the present invention;

[0027] Figure 3 Schematic diagram of the broadband polarization rotation absorbing metasurface flexible dielectric layer of the present invention;

[0028] Figure 4 Schematic diagram of the broadband polarization rotation absorbing metasurface metal floor layer of the present invention;

[0029] Figure 5 yes Figure 2 Schematic diagram of polarization rotation of ITO thin film pattern layer

[0030] Figure 6 yes Figure 1 Schematic diagram of reflectivity curve of the metasurface unit shown;

[0031] Figure 7 yes Figure 1 Schematic diagram of polarization conversion rate curve of the metasurface unit shown;

[0032] Figure 8 yes Figure 1 Schematic diagram of the wave absorption performance curve of the metasurface unit shown;

[0033] Fig. 9 yes Figure 1 Schematic diagram of the planar array formed by the metasurface units shown.

[0034] Fig.10 yes Fig. 9 Schematic diagram of RCS and RCS reduction of the metasurface unit array and metal backplane.

[0035] Fig.11 yes Fig. 9Schematic diagram of RCS reduction corresponding to the metasurface unit array at different incident angles.

[0036] Fig.12 yes Fig. 9 The RCS far-field diagram of the metasurface unit array and metal backplane corresponding to 0° and 60° incidence when the incident frequency is 23 GHz. DETAILED DESCRIPTION

[0037] The following is an angle-insensitive broadband polarization rotation absorbing metasurface proposed by the present invention in conjunction with the accompanying drawings and specific embodiments.

[0038] Figure 1 The schematic diagram (1) of the unit structure of an angle-insensitive broadband polarization rotation absorbing metasurface of the present invention is shown. The metasurface adopts a layered laminated planar structure and has a three-layer dielectric substrate, wherein the upper and lower layers of the first dielectric plate (2) are respectively an ITO film (21) with an etched pattern and a flexible substrate PET (22) of the ITO film; the second dielectric plate is not provided with metal, and the second layer is a flexible dielectric layer (3); the upper ITO film (41) of the third dielectric layer is connected to the flexible dielectric layer PVC (3), and the lower layer is a flexible substrate PET (42) of the ITO film.

[0039] like Figure 1 As shown in FIG. 1 , when ITO film is selected as the pattern layer and the ground layer, it needs to be combined with a transparent flexible dielectric material to meet the application needs of special scenarios. Figure 3 As shown, PVC is used as the transparent flexible medium layer (3) between the pattern layer (2) and the floor layer (4).

[0040] like Figure 2 and Figure 4 As shown, when ITO film is used as the resistor film material, the ITO film needs to be attached to the PET thin layer, so the first pattern layer (2) and the third ground layer (4) both have two layers, the upper layer is the ITO film, and the lower layer is the flexible substrate PET of the ITO film.

[0041] like Figure 5 As shown, the ITO film pattern layer (2) is formed by etching a diagonal pattern on the resistor film, and a sector (21) symmetrical about the diagonal line is etched on the ITO film, such as Figure 5 As shown in (a), when the y-polarized wave is irradiated vertically on the ITO film pattern along the z-axis, the incident electric field can be decomposed into two mutually orthogonal electric field components along the u direction and the v direction. Decompose into and The reflected electric field is and The reflected electric field is and Therefore, the two reflected electric field components are orthogonal to each other. and The sum vector The polarization will be along the x-polarization, that is, the polarization conversion of the y-polarized wave to the x-polarized wave is realized.

[0042] Similarly, if the pattern is rotated 90°, the rotated unit can realize the principle of the ITO thin film pattern layer with polarization rotation function as shown below. Figure 5 As shown in (b), the polarization conversion of the y-polarized wave to the x-polarized wave can be achieved. And the polarization waves after the polarization conversion of the two patterns are equal in magnitude and opposite in direction.

[0043] Depend on Figure 6 It can be seen that the metasurface unit has three resonance points at 18 GHz and 24.5 GHz, and its reflection coefficient is lower than -10 dB in the entire working frequency band of 11-27 GHz. Figure 7 It can be seen that the polarization rotation rate of the metasurface unit in the frequency band of 14.5-25GHz is greater than 75%, so it has good polarization conversion ability in this frequency band. The resonance points of 14.9GHz and 21.6GHz are caused by polarization conversion. Figure 8 It can be seen that at 12.5-14.5GHz and 25-31.8GHz, most of the incident wave energy of the metasurface unit is absorbed and converted into ohmic loss. In this frequency band, wave absorption plays a major role, and the wave absorption rate is greater than 50%. At 30.8GHz, the wave absorption rate can reach up to 85%, so a resonance point appears at 30.8GHz.

[0044] In order to verify the feasibility of the angle-insensitive broadband polarization rotation absorbing metasurface unit designed in the present invention, Fig. 9 The schematic diagram of the chessboard array composed of the units proposed in the present invention is shown in FIG. The chessboard structure is composed of four 8×8 units that are symmetrical in pairs, i.e., four units with a size of 60×60 mm. 2 The total size of the chessboard is 120×120mm. 2 The size of each unit in the array (9) is 7.5 mm, the spacing between units in the array is also 7.5 mm, and the overall thickness is 2.3 mm. Fig.10 for Fig. 9 The RCS of the chessboard array composed of the metasurface units and the metal plate of the same size and the RCS reduction diagram of the two are compared through simulation comparison Fig.12 It can be seen that in the entire frequency band of 12-32 GHz, the RCS reduction is greater than 10 dB. At 19 GHz, the RCS reduction can reach up to 35 dB. This structure has good RCS reduction capability.

[0045] Fig.11 for Fig. 9 The RCS reduction diagram of the metasurface unit array and the metal backplane at different incident angles is shown. As can be seen from the figure, at vertical incidence and an incident angle of 20°, the RCS reduction of the metasurface array is greater than 10dB. At an incident angle of 40°, the RCS reduction of the 11-14GHz and 17-27GHz metasurface arrays is also greater than 10dB. At an incident angle of 60°, the RCS reduction of the metasurface array is greater than 5dB. Although it is lower than the RCS reduction at vertical incidence, it still has a good RCS reduction effect. This shows that the angle-insensitive broadband polarization rotation absorbing metasurface based on ITO film has less dependence on the incident angle at large angles, which is conducive to the effect when the metasurface is further conformal.

[0046] Fig.12 for Fig. 9 The RCS far-field diagram of the metasurface unit array and metal backplane corresponding to 0° and 60° incidence when the incident frequency is 23 GHz. Fig.12 (a) and (b) are 3D schematic diagrams of the RCS far field of the metasurface unit and the metal backplane at normal incidence, respectively; Fig.12 (c) and (d) are 3D schematic diagrams of the RCS far field of the metasurface unit and the metal backplane at 60° incidence. It can be seen that the metal backplane produces a main lobe reflection in the mirror direction, while the main lobe of the metasurface is dispersed into four. Compared with the metal backplane, the RCS of the metasurface is significantly reduced.

[0047] The above examples mainly illustrate the feasibility of an angle-insensitive broadband polarization rotation absorbing metasurface. Although only some of the implementation methods of this patent are described, this patent is not limited to the above implementation examples, and embodiments that do not deviate from the main purpose and scope should be protected by this patent.

Claims

1. An angle-insensitive broadband polarization rotation absorbing metasurface, characterized in that: The metasurface simultaneously utilizes polarization rotation and resistance resonance absorption to reduce RCS, wherein each basic unit (1) of the metasurface comprises, from top to bottom, a first layer (2), a second layer (3), and a third layer (4), wherein: the first layer (2) is a pattern (21) etched by an ITO film and a flexible substrate PET (22) of the ITO film; the second layer (3) is a flexible dielectric support layer (3) formed by PVC; and the third layer (1) is a metal floor formed by an ITO film and a flexible substrate PET (42) of an ITO film (41).

2. The angle-insensitive broadband polarization rotation absorbing metasurface according to claim 1, characterized in that: The first layer (2) of the metasurface is a polarization conversion-wave absorbing structure, PET (22) is used as a substrate for an ITO film (21), the ITO film is plated on the PET film and etched to obtain a corresponding ITO film patch shape (2); the second layer (3) is a transparent flexible dielectric layer made of PVC material; the third layer (4) is a metal floor composed of an ITO film (41) and a flexible substrate PET (42) of the ITO film.

3. The angle-insensitive broadband polarization rotation absorbing metasurface according to claim 1, characterized in that: The first ITO thin film pattern layer (2) is two sectors (21). The two sectors of the pattern are located at the center of the metasurface, and each sector is symmetrical about the diagonal line, and the two sectors are symmetrical about the diagonal line, so the formed pattern is polarization insensitive, and the pattern is simple and easy to form. The implementation structure of this case is a sector to achieve polarization rotation function and wave absorption function, but the design realizes both polarization rotation and wave absorption functions at the same time. The structure is not limited to the sector, and the material of the sector structure implemented in this case is a 5Ω resistor film as a resistor resonance to achieve the wave absorption function, but the design is not limited to the resistance value of 5Ω.

4. The angle-insensitive broadband polarization rotation absorbing metasurface according to claim 1, characterized in that: The structure of the ITO thin film pattern layer of the first layer (2) realizes the polarization rotation function, and because the pattern is symmetrical about the diagonal line, it has a polarization insensitive characteristic. When the structure forms an array with the mirror unit, the phases between the two units are cancelled, and the RCS can be reduced. The resonant structure of the first layer (2) is composed of two fan-shaped resistor films, which produces high ohmic loss and can effectively reduce the reflected waves on the surface, so that the incident waves can more effectively enter the dielectric layer (3) made of PVC. The continuous and complete ITO film and its PET substrate at the bottom serve as a metal floor, which can completely reflect the electromagnetic waves and block the transmission of the electromagnetic waves, so that it has better absorption characteristics and achieves the reduction of RCS.

5. The angle-insensitive broadband polarization rotation absorbing metasurface according to claim 1, characterized in that: Each basic unit (1) of the metasurface is 7.5 mm long, 7.5 mm wide, and 2.3 mm thick, and the electrical dimensions of the unit are 0.46×0.46×0.

14. The metasurface array is a periodically arranged checkerboard structure (9), which is composed of four n-shaped symmetrical x ×n y The unit composition is n x =n y = 8. The array structure (9) in this case is 8×8, but the array in this design is n x =n y =8 forms, all of which can realize the wave absorbing function by forming an array structure, so the implementation of this design is not limited to the array structure of this case.

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