A polarization conversion metasurface

Abstract

The present application relates to the field of electromagnetic stealth technology, and in particular to a polarization conversion metasurface. The polarization conversion metasurface includes: a first lattice and a second lattice; the first lattice is composed of N×N polarization conversion units, and the polarization conversion unit includes a pattern layer, a dielectric layer and a continuous bottom plate layer stacked in sequence in the vertical direction; wherein N≥2, the side where the pattern layer is located is the side where the electromagnetic wave is incident, and the pattern in the pattern layer is a pattern with gaps symmetrical along a 45° diagonal line, and the dielectric layer is used to assist the electromagnetic coupling between the pattern layer and the bottom plate layer; the second lattice is formed by mirroring the first lattice; the polarization conversion metasurface is formed by splicing the first lattice and the second lattice according to a preset arrangement rule. The metasurface provided in the present application can evenly disperse the electromagnetic waves reflected by the target and significantly reduce the RCS value in each direction.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic stealth technology, and in particular to a polarization conversion metasurface. Background Art

[0002] With the development of modern electronic warfare and wireless communication, electromagnetic stealth technology has become one of the hot topics in electromagnetic exploration. For targets in certain special application scenarios, the quality of their stealth performance directly affects people's safety, so how to reduce the probability of the target being detected by the other party's radar and other high-tech equipment is an issue that researchers must consider.

[0003] In the prior art, a polarization conversion metasurface is generally provided on the target surface to reduce the RCS value of the target, thereby reducing the risk of the target being detected. However, when the existing polarization conversion metasurface reduces the RCS value of a specific angular range of the target, it increases the risk of detection in other angular ranges.

[0004] Therefore, there is an urgent need for a polarization conversion metasurface that can evenly disperse the electromagnetic waves reflected by the target to reduce the target's RCS value in all directions. Summary of the invention

[0005] The present application provides a polarization conversion metasurface that can reduce the isotropic RCS value of a target within a wider bandwidth.

[0006] The embodiment of the present application provides a polarization conversion metasurface, including: a first lattice and a second lattice;

[0007] The first lattice is composed of N×N polarization conversion units, and the polarization conversion unit includes a pattern layer, a dielectric layer and a continuous bottom plate layer stacked in sequence along the vertical direction; wherein N≥2, the side where the pattern layer is located is the side where the electromagnetic wave is incident, the pattern in the pattern layer is a pattern with gaps that is symmetrical along a 45° diagonal line, and the dielectric layer is used to assist the electromagnetic coupling between the pattern layer and the bottom plate layer;

[0008] The second lattice is formed by mirroring the first lattice;

[0009] The polarization conversion metasurface is formed by splicing the first lattice and the second lattice according to a preset arrangement rule.

[0010] In a possible design, the unit period P of the polarization conversion unit is 5 mm;

[0011] The first lattice is composed of 3×3 polarization conversion units.

[0012] In a possible design, the pattern layer and the base layer are made of conductive metal.

[0013] In one possible design, the metal is copper, and the electrical conductivity of copper is 5.8×10 7 S / m, thickness is 0.035mm.

[0014] In a possible design, the dielectric layer has a thickness of 3 mm, a material of F4B-220, and a dielectric constant of 2.2C. 2 / (N·M 2 ), the dielectric loss tangent value is 0.0015.

[0015] In a possible design, the pattern in the pattern layer consists of a 45° inclined strip structure and a double ring structure, wherein the double ring structure consists of two concentric elliptical slit rings, each of which intersects with the strip structure and is symmetrical along the strip structure.

[0016] In a possible design, the strip structure has a length L=6 mm and a width W=0.25 mm.

[0017] In a possible design, the slotted elliptical ring consists of a first slotted elliptical ring with a major axis inner radius R1=2.4mm, a line width W1=0.2mm, an axial ratio AR1=0.9, and an opening angle α=90°, and a second slotted elliptical ring with a major axis inner radius R2=0.3mm, a line width W2=0.3mm, an axial ratio AR2=0.9, and an opening angle β=108°.

[0018] In a possible design, the preset arrangement rule is to arrange the first lattice and the second lattice evenly and equidistantly.

[0019] In a possible design, the preset arrangement rule is an arrangement of the first lattice and the second lattice determined by a genetic algorithm with the maximum value of the far-field scattering amplitude as the objective function.

[0020] An embodiment of the present application provides a polarization conversion metasurface, including a first lattice and a second lattice, the first lattice consisting of N×N polarization conversion units, and the second lattice being formed by mirroring the first lattice, so as to form a periodic structure and suppress the mutual coupling between the polarization conversion units; the polarization conversion unit comprises a pattern layer, a dielectric layer and a continuous base layer stacked in sequence along a vertical direction; on the one hand, since the pattern in the pattern layer is a pattern with gaps symmetrical along a 45° diagonal line, the electromagnetic wave can resonate along the 45° diagonal line direction, thereby changing the polarization direction of the electromagnetic wave and widening the bandwidth; on the other hand, since the first lattice and the second lattice are spliced ​​according to a preset arrangement rule, the electromagnetic waves reflected by the target can be evenly dispersed, significantly reducing the RCS values ​​in all directions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 is a side cross-sectional view of a polarization conversion unit provided by one embodiment of the present invention;

[0023] Figure 2 It is a schematic diagram of a layer scheme provided by an embodiment of the present invention;

[0024] Figure 3 is a first lattice broadband polarization conversion rate curve provided by an embodiment of the present invention;

[0025] Figure 4 A polarization conversion metasurface with an optimized coding structure determined by a genetic algorithm provided by an embodiment of the present invention;

[0026] Figure 5 : is a comparison diagram of single-station RCS reduction of an optimized coding structure and a uniform coding structure provided by an embodiment of the present invention;

[0027] Figure 6 This is a 3D far-field scattering pattern of an optimized coding structure at 13 GHz provided by an embodiment of the present invention.

[0028] Reference numerals:

[0029] 1- pattern layer;

[0030] 11- Strip structure;

[0031] 12-first slotted elliptical ring;

[0032] 13- second slotted elliptical ring;

[0033] 2- dielectric layer;

[0034] 3- Bottom layer. DETAILED DESCRIPTION

[0035] The present application is described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0036] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance; unless otherwise specified or explained, the term "multiple" refers to two or more; the terms "connected" and "fixed" should be understood in a broad sense, for example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0037] In the description of this specification, it should be understood that the directional words such as "upper" and "lower" described in the embodiments of the present application are described at the angles shown in the accompanying drawings and should not be understood as limiting the embodiments of the present application. In addition, in the context, it should also be understood that when it is mentioned that an element is connected to another element "upper" or "lower", it can not only be directly connected to another element "upper" or "lower", but also indirectly connected to another element "upper" or "lower" through an intermediate element.

[0038] The inventors found in their work that most of the current polarization conversion metasurfaces use a checkerboard structure to make the reflection phase difference between the incident electromagnetic wave and the reflected (transmitted) electromagnetic wave 180°. This structure can reduce the RCS value of planar targets by using the method of phase cancellation, but at the same time it will increase the risk of being detected in other angular domains.

[0039] To address this problem, the inventors proposed that a special pattern and a special arrangement of polarization conversion units can be set on the side of the polarization conversion unit where the electromagnetic wave is incident, so as to evenly disperse the electromagnetic waves reflected by the target, thereby reducing the RCS values ​​in all directions.

[0040] The embodiment of the present application provides a polarization conversion metasurface, including: a first lattice and a second lattice;

[0041] The first lattice consists of N × N polarization conversion units, such as Figure 1 As shown, the polarization conversion unit includes a pattern layer 1, a dielectric layer 2 and a continuous bottom plate layer 3 stacked in sequence along the vertical direction; wherein N≥2, the side where the pattern layer 1 is located is the side where the electromagnetic wave is incident, the pattern in the pattern layer is a pattern with gaps symmetrical along a 45° diagonal line, and the dielectric layer 2 is used to assist the electromagnetic coupling between the pattern layer 1 and the bottom plate layer 3;

[0042] The second lattice is formed by mirroring the first lattice;

[0043] The polarization conversion metasurface is composed of a first lattice and a second lattice spliced ​​together according to a preset arrangement rule.

[0044] In this embodiment, the first lattice is composed of N×N polarization conversion units, and the second lattice is formed by mirroring the first lattice, so that a periodic structure can be formed to suppress the mutual coupling between the polarization conversion units; further, since the pattern in the pattern layer is a pattern with gaps that is symmetrical along a 45° diagonal line, the electromagnetic wave can resonate along the 45° diagonal line direction, thereby changing the polarization direction of the electromagnetic wave and widening the bandwidth; in addition, since the first lattice and the second lattice are spliced ​​according to a preset arrangement rule, the electromagnetic waves reflected by the target can be evenly dispersed, significantly reducing the RCS values ​​in all directions.

[0045] It is understandable that the smaller the unit period of the polarization conversion unit, the better the effect of changing the polarization direction of the electromagnetic wave and widening the bandwidth, but the processing accuracy is required to be high. Therefore, in some embodiments, after comprehensively considering the cost of processing and manufacturing, the unit period P of the polarization conversion unit can be taken as 5mm. However, due to the small unit period, mutual coupling is likely to occur between the polarization conversion units. Therefore, in some embodiments, 3×3 polarization conversion units can be used to form a first lattice, and the first lattice is mirrored to form a second lattice. In this way, while ensuring the polarization conversion effect, the mutual coupling between the polarization conversion units can be effectively suppressed.

[0046] It should be noted that the unit period P=5 mm and 3×3 polarization conversion units forming the first lattice are only a preferred method, and the user can also make adjustments according to the expected reduction value of the RCS value in each direction, and the present application is not limited to this.

[0047] In some embodiments, the pattern layer 1 and the base layer 3 are made of conductive metals, such as gold, silver, copper, etc. The conductive metal can cause electromagnetic coupling between the pattern layer 1 and the base layer 3, forming a circular current, causing the electromagnetic wave to resonate, thereby effectively widening the bandwidth and generating polarization conversion.

[0048] In some embodiments, after comprehensive consideration of production costs, the conductive metal is preferably copper, and the electrical conductivity of copper is 5.8×10 7 S / m, thickness is 0.035mm. Of course, users can also choose other conductive metals, and this application does not make specific restrictions.

[0049] In some embodiments, in order to promote electromagnetic coupling between the pattern layer 1 and the bottom plate layer 3 and form a circular current, a dielectric layer needs to be provided between the pattern layer 1 and the bottom plate layer 3. The material of the dielectric layer 2 is preferably F4B-220 with a dielectric constant of 2.2C. 2 / (N·M 2 ), the dielectric loss tangent value is 0.0015, and the thickness of the dielectric layer 2 is preferably 3 mm, which can ensure the flexibility of the polarization conversion metasurface and increase the application range of the metasurface.

[0050] like Figure 2 As shown, in some embodiments, the pattern in the pattern layer 1 is composed of a 45° oblique strip structure 11 and a double ring structure, and the double ring structure is composed of two concentric elliptical slotted elliptical rings, each of which intersects with the strip structure 11 and is symmetrical along the strip structure 11. That is, a symmetrical structure design is performed along the main diagonal (v-axis) direction and the secondary diagonal (u-axis) direction of the polarization conversion unit. The setting of this pattern can increase the resonance of the electromagnetic wave along the 45° oblique diagonal direction, maximize the widening of the bandwidth and increase the polarization conversion.

[0051] After the pattern is determined, the physical parameters of the pattern need to be optimized to achieve specific amplitude-frequency response characteristics in the u-axis direction and the v-axis direction of the polarization conversion unit. In a preferred embodiment, the length L of the strip structure 11 is 6 mm and the width W is 0.25 mm. The slotted elliptical ring is composed of a first slotted elliptical ring 12 with a major axis inner radius R1=2.4 mm, a line width W1=0.2 mm, an axial ratio AR1=0.9, and an opening angle α=90°, and a second slotted elliptical ring 13 with a major axis inner radius R2=0.3 mm, a line width W2=0.3 mm, an axial ratio AR2=0.9, and an opening angle β=108°. In order to verify the polarization conversion rate (PCR) of the first lattice and the second lattice composed of the polarization conversion unit, the inventor processed the polarization conversion rate test board of the metasurface composed of the first lattice through the printed circuit board preparation technology, and tested the far-field co-polarization reflectivity and cross-polarization reflectivity of the polarization conversion rate test board through the "arch frame + broadband double horn antenna" test system, and calculated the measured broadband PCR curve through the formula, as shown in FIG. Figure 3 As shown in the figure, it can be seen that after adopting the above physical parameters, the metasurface composed of the first lattice can achieve a linear-cross polarization conversion efficiency of more than 90% in the 8.03-22.16 GHz frequency band, that is, the first lattice can achieve a linear-cross polarization conversion efficiency of more than 90% in the 8.03-22.16 GHz frequency band. Since the second lattice is formed by the mirror image of the first lattice, the second lattice has the same effect as the first lattice. Of course, the above size is only a preferred way, and the present application is not limited to this.

[0052] After the pattern and size of the polarization conversion unit are determined, the response frequency and action bandwidth of each resonant frequency point can be fine-tuned according to project requirements, and the polarization conversion unit is composed of a 3×3 first lattice and a second lattice formed by the mirror image of the first lattice. Finally, in order to better evenly disperse the electromagnetic waves reflected by the target, it is necessary to select a suitable arrangement of the first lattice and the second lattice.

[0053] According to the concept of information entropy, when the number of the first lattice and the second lattice constituting the polarization conversion metasurface is half, the single-station RCS reduction value is the largest. Therefore, in some embodiments, the first lattice and the second lattice can be arranged evenly and evenly, for example, according to the arrangement of the first lattice, the second lattice, the first lattice, the second lattice, etc., recorded as uniform coding, the uniform coding method can reduce the RCS value in most directions of the target, but there are still very few directions where the RCS value reduction effect is slightly poor.

[0054] like Figure 4 As shown, in other embodiments, the maximum value of the far-field scattering amplitude can be used as the objective function, and the arrangement of the first lattice and the second lattice can be determined by a genetic algorithm, which is recorded as an optimization code. Specifically, the maximum value of the far-field scattering amplitude is used as the objective function, and a genetic algorithm program is written by Matlab software to output the layout matrix of the optimized first lattice and the second lattice, and finally determine the specific structure of the polarization conversion metasurface. The polarization conversion metasurface determined by this optimization coding method can effectively reduce the RCS value of the target in all directions.

[0055] To verify Figure 4 The single-station RCS reduction effect of the optimized coded polarization conversion metasurface shown in the figure is shown in the figure. The inventor used a uniformly coded polarization conversion metasurface finished board with a size of 180mm×180mm×3mm as the experimental group and an optimized coded polarization conversion metasurface finished board with a size of 180mm×180mm×3mm as the experimental group, and tested the single-station RCS curves of the two polarization conversion metasurface finished boards by the free space method. The test results are shown in the figure. Figure 5 As shown in the figure, it can be seen that the metasurface determined by the optimized coding determined by the genetic algorithm can achieve a single-station RCS reduction of -10dB in the 9.82~23.15GHz frequency band, and its reduction performance is far better than the uniform coding structure.

[0056] In addition, in order to analyze the single-station RCS reduction mechanism of the above-mentioned optimized coding structure, the inventor selected the far-field scattering pattern of the 13 GHz frequency point, such as Figure 6 As shown in the figure, it can be seen that after the incident wave passes through the electromagnetic action of the present invention, the reflected electromagnetic wave is evenly dispersed into a form similar to diffuse reflection, and the RCS values ​​in all directions are maintained between -5.81 and -15.8, which greatly reduces the probability of being detected by the opponent's radar in the threat angle area.

[0057] It should also be noted that in order to ensure the accuracy of the test results, the inventors first measured the RCS of the empty room when measuring the RCS of the uniformly coded metasurface and the optimized coded metasurface, and then placed a metal calibration plate of the same size on the test bench to obtain a reference broadband RCS curve of the calibration plate. Finally, the finished board to be tested was placed on the test bench to obtain the actual single-station RCS curve of the finished board to be tested, and the actual data obtained from the calibration plate was subtracted to obtain the broadband single-station RCS reduction curve of the finished board to be tested. This can eliminate system errors and ensure the accuracy of the test results.

[0058] It should be noted that, in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprise a ..." do not exclude the presence of other identical factors in the process, method, article or device including the elements.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. 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 polarization conversion metasurface, characterized in that: including a first lattice and a second lattice; The first lattice is composed of N×N polarization conversion units, and the polarization conversion units include a pattern layer (1), a dielectric layer (2) and a continuous bottom plate layer (3) stacked in sequence along a vertical direction; wherein N≥2, the side where the pattern layer (1) is located is the side where the electromagnetic wave is incident, the pattern in the pattern layer (1) is a pattern with gaps that is symmetrical along a 45° diagonal line, and the dielectric layer (2) is used to assist the electromagnetic coupling between the pattern layer (1) and the bottom plate layer (3); The second lattice is formed by mirroring the first lattice; The polarization conversion metasurface is formed by splicing the first lattice and the second lattice according to a preset arrangement rule; The unit period P of the polarization conversion unit is 5 mm; The first lattice is composed of 3×3 polarization conversion units; The pattern in the pattern layer (1) is composed of a 45° inclined strip structure (11) and a double ring structure, wherein the double ring structure is composed of two concentric elliptical slotted elliptical rings, each of which intersects with the strip structure (11) and is symmetrical along the strip structure (11); The strip structure (11) has a length L=6 mm and a width W=0.25 mm; The slotted elliptical ring is composed of a first slotted elliptical ring (12) with a major axis inner radius R1=2.4 mm, a line width W1=0.2 mm, an axial ratio AR1=0.9, and an opening angle α=90°, and a second slotted elliptical ring (13) with a major axis inner radius R2=0.3 mm, a line width W2=0.3 mm, an axial ratio AR2=0.9, and an opening angle β=108°; The preset arrangement rule is to arrange the first lattice and the second lattice evenly and at equal intervals; The preset arrangement rule is an arrangement mode of the first lattice and the second lattice determined by a genetic algorithm with the maximum value of the far-field scattering amplitude as the objective function.

2. The polarization conversion metasurface according to claim 1, characterized in that: The material of the pattern layer (1) and the base layer (3) is a conductive metal.

3. The polarization conversion metasurface according to claim 2, characterized in that: The metal is copper, and the electrical conductivity of copper is 5.8×10 7 S / m, thickness is 0.035mm.

4. The polarization conversion metasurface according to claim 1, characterized in that: The dielectric layer (2) has a thickness of 3 mm, a material of F4B-220, a dielectric constant of 2.2C2 / (N·M2), and a dielectric loss tangent of 0.0015.

Images