CN115000719A - Polarization conversion super surface - Google Patents

Abstract

The present application relates to the technical field of electromagnetic stealth, 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 units are stacked in sequence along a vertical direction The pattern layer, the medium layer and the continuous bottom layer; 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 symmetrical along a 45° diagonal line. a pattern with slits, the dielectric layer is used to assist electromagnetic coupling between the pattern layer and the base layer; the second lattice is formed by mirroring the first lattice; the polarization conversion The metasurface is formed by splicing the first lattice and the second lattice according to a preset arrangement rule. The metasurface provided by the present application can evenly disperse the electromagnetic waves reflected by the target, and significantly reduce the RCS value in all directions.

Description

A polarization switching metasurface

technical field

The invention relates to the technical field of electromagnetic stealth, in particular to a polarization conversion metasurface.

Background technique

With the development of modern electronic countermeasures and wireless communication, electromagnetic stealth technology has become one of the hot spots of electromagnetic exploration. For targets in some special application scenarios, the quality of their stealth performance directly affects people's safety. Therefore, how to reduce the probability of the target being detected by the opponent's radar and other high-tech equipment is a problem that researchers must consider.

In the prior art, the RCS value of the target is generally reduced by setting a polarization conversion metasurface on the target surface, so as to reduce the risk of the target being detected. However, when the existing polarization conversion metasurface reduces the RCS value in a specific angular domain of the target, it increases the risk of detection in other angular domains.

Therefore, there is an urgent need for a polarization conversion metasurface that can uniformly disperse the electromagnetic waves reflected by the target, so as to reduce the RCS value of the target in all directions.

SUMMARY OF THE INVENTION

The present application provides a polarization conversion metasurface capable of reducing the isotropic RCS value of a target in a wide bandwidth range.

Embodiments of the present application provide a polarization conversion metasurface, including: a first crystal lattice and a second crystal lattice;

The first lattice is composed of N×N polarization conversion units, and the polarization conversion units include a pattern layer, a dielectric layer and a continuous bottom layer stacked in sequence along the vertical direction; wherein, N≥2, so the 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 slits symmetrical along a 45° oblique diagonal, and the dielectric layer is used to assist the pattern layer and all Electromagnetic coupling occurs between the bottom layers;

the second lattice is formed by mirroring the first lattice;

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

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

The first lattice consists of 3×3 of the polarization conversion units.

In a possible design, the material of the pattern layer and the base layer is a metal with electrical conductivity.

In one possible design, the metal is copper, and the copper has a conductivity of 5.8×10 ⁷ S/m and a thickness of 0.035 mm.

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

In a possible design, the pattern in the pattern layer is composed of an oblique 45° strip structure and a double-ring structure, wherein the double-ring structure is composed of two concentric elliptical slit elliptical rings, each of which is The slotted elliptical rings respectively intersect with the strip-shaped structures and are symmetrical along the strip-shaped structures.

In a possible design, the length L=6mm and the width W=0.25mm of the strip structure.

In a possible design, the slotted elliptical ring consists of a first axis with inner radius R ₁ =2.4mm, line width W ₁ =0.2mm, axial ratio AR ₁ =0.9, and opening angle α=90° The slotted elliptical ring is composed of a second slotted elliptical ring with a major axis inner radius R ₂ =0.3mm, a line width W ₂ =0.3mm, an axial ratio AR ₂ =0.9, and an opening angle β=108°.

In a possible design, the preset arrangement rule is to evenly arrange the first crystal lattice and the second crystal lattice at equal intervals.

In a possible design, the preset arrangement rule is that the arrangement of the first lattice and the second lattice determined by a genetic algorithm takes the maximum value of the far-field scattering amplitude as an objective function. cloth method.

Embodiments of the present application provide a polarization conversion metasurface, including a first lattice and a second lattice, the first lattice is composed of N×N polarization conversion units, and the second lattice is composed of a first lattice In this way, a periodic structure can be formed and the mutual coupling between the polarization conversion units can be suppressed; the polarization conversion unit includes a pattern layer, a dielectric layer and a continuous bottom layer stacked in sequence along the vertical direction; on the one hand, due to the The pattern in the pattern layer is a symmetric pattern with a slit along a 45° diagonal line, so the electromagnetic wave can be resonated along the 45° diagonal direction, thereby changing the polarization direction of the electromagnetic wave and widening the bandwidth; On the one 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 uniformly dispersed, and the RCS value in each direction can be significantly reduced.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are For some embodiments of the present invention, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

1 is a side cross-sectional view of a polarization conversion unit according to an embodiment of the present invention;

2 is a schematic diagram of a layer pattern provided by an embodiment of the present invention;

3 is a first lattice broadband polarization conversion rate curve diagram provided by an embodiment of the present invention;

4 is an optimized coding structure polarization conversion metasurface determined according to a genetic algorithm provided by an embodiment of the present invention;

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

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

Reference number:

1- pattern layer;

11-stripe structure;

12- The first slotted oval ring;

13- The second slotted oval ring;

2-dielectric layer;

3- Bottom layer.

Detailed ways

The present application will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application.

In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the terms "first" and "second" are only used for the purpose of description, and cannot be understood as indicating or implying relative importance; unless otherwise specified Or to illustrate, the term "plurality" refers to two or more; the terms "connection" and "fixed" should be understood in a broad sense, for example, "connection" can be a fixed connection or a detachable connection, or Connected integrally, or connected electrically; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations.

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 from the perspective shown in the accompanying drawings, and should not be construed as referring to the embodiments of the present application. limited. Also, in this context, it should also be understood that when an element is referred to as being "on" or "under" another element, it can not only be directly connected "on" or "under" the other element, but also Indirectly connected "on" or "under" another element through intervening elements.

The inventors found in their work that most of the polarization conversion metasurfaces currently use a checkerboard structure to make the reflection phase difference between the incident electromagnetic wave and the reflected (transmitted) electromagnetic wave 180°. RCS value, but at the same time increases the risk of other angular domains being detected.

In response to this problem, the inventor proposes that a special pattern and a special arrangement of the polarization conversion units can be set on the side where the electromagnetic waves are incident in the polarization conversion unit, so as to evenly disperse the electromagnetic waves reflected by the target, thereby reducing the RCS in all directions value.

Embodiments of the present application provide a polarization conversion metasurface, including: a first crystal lattice and a second crystal lattice;

The first lattice is composed of N×N polarization conversion units. As shown in FIG. 1 , the polarization conversion unit includes a pattern layer 1 , a dielectric layer 2 and a continuous base 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 a slit symmetrical along a 45° diagonal line, and the dielectric layer 2 is used to assist the pattern layer 1 and the bottom plate Electromagnetic coupling occurs between layers 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.

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 and mutual coupling between the polarization conversion units can be suppressed Further, since the pattern in the pattern layer is a pattern with slits symmetrical along the 45° diagonal diagonal, the electromagnetic wave can be resonated along the 45° diagonal direction, thereby changing the polarization direction of the electromagnetic wave and Widen the bandwidth; in addition, since the first lattice and the second lattice are spliced according to the preset arrangement rule, the electromagnetic waves reflected by the target can be uniformly dispersed, and the RCS value in each direction can be significantly reduced.

It can be understood 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 broadening the bandwidth, but requires higher processing accuracy. Therefore, in some embodiments, after comprehensively considering the manufacturing cost, the unit period of the polarization conversion unit may be taken as P=5mm. However, due to the small period of the unit, 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 the first lattice, and the first lattice is formed by a mirror image. The second crystal lattice can effectively suppress the mutual coupling between the polarization conversion units while ensuring the polarization conversion effect.

It should be noted that the unit period P=5mm and 3×3 polarization conversion units to form the first lattice is only a preferred way, and the user can also adjust it according to the expected reduction of the RCS value in each direction. This is limited.

In some embodiments, the material of the pattern layer 1 and the base layer 3 is a conductive metal. For example, gold, silver, copper, etc., conductive metals can cause electromagnetic coupling between the pattern layer 1 and the backplane layer 3 to form a ring current and resonate electromagnetic waves, thereby effectively widening the bandwidth and generating polarization conversion.

In some embodiments, after comprehensively considering the production cost, the conductive metal is preferably copper, and the conductivity of copper is 5.8×10 ⁷ S/m and the thickness is 0.035 mm. Of course, the user can also select other conductive metals, which are not specifically limited in this application.

In some embodiments, in order to promote electromagnetic coupling between the pattern layer 1 and the base layer 3 and form a ring current, a dielectric layer needs to be arranged between the pattern layer 1 and the base layer 3, and the material of the dielectric layer 2 is preferably F4B. -220, the dielectric constant is 2.2C ² /(N·M ² ), the dielectric loss tangent is 0.0015, and the thickness of the dielectric layer 2 is preferably 3mm, which can ensure the flexibility of the polarization conversion metasurface and increase the Scope of application.

As shown in FIG. 2 , in some embodiments, the pattern in the pattern layer 1 is composed of an oblique 45° strip structure 11 and a double-ring structure, and the double-ring structure is composed of two concentric elliptical slit elliptical rings, Each slotted elliptical ring respectively intersects with the strip structure 11 and is symmetrical along the strip structure 11 . That is, the symmetric structure design is carried out along the main diagonal (v-axis) direction and the sub-diagonal (u-axis) direction of the polarization conversion unit. The setting of the pattern can increase the resonance of the electromagnetic wave along the diagonal direction of 45°, maximally widen the bandwidth and increase the polarization conversion.

After the pattern is determined, the physical parameters of the pattern also need to be optimized to achieve specific amplitude-frequency response characteristics in the u-axis and v-axis directions of the polarization conversion unit. In a preferred manner, the length L=6mm and the width W=0.25mm of the strip structure 11 . The slotted elliptical ring consists of a first slotted elliptical ring 12 with a major axis inner radius R ₁ =2.4mm, a line width W ₁ =0.2mm, an axial ratio AR ₁ =0.9, an opening angle α=90°, and a major axis inner The second slit elliptical ring 13 is composed of a radius R ₂ =0.3 mm, a line width W ₂ =0.3 mm, an axial ratio AR ₂ =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 inventors processed the polarization of the metasurface composed of the first lattice through a printed circuit board fabrication technique Conversion rate test board, and the far-field co-polarization reflectivity and cross-polarization reflectivity of the polarization conversion rate test board were tested by the "arch frame + broadband double horn antenna" test system, and the measured broadband was calculated by the formula. The PCR curve is shown in Figure 3. It can be seen from the figure that after using the above physical parameters, the metasurface composed of the first lattice can achieve a line-to-cross polarization conversion efficiency of more than 90% in the 8.03-22.16GHz frequency band , that is, the first lattice can achieve a line-to-cross polarization conversion efficiency of more than 90% in the frequency band of 8.03-22.16 GHz. Since the second lattice is mirrored from the first lattice, the second lattice has the same effect as the first lattice. Of course, the above dimensions are only a preferred way, and the present application is not limited thereto.

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

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-site RCS reduction value is the largest. Therefore, in some embodiments, the first crystal lattice and the second crystal lattice may be uniformly arranged at equal intervals, for example, according to the arrangement of the first crystal lattice, the second crystal lattice, the first crystal lattice, the second crystal lattice . . . The distribution method is denoted as uniform encoding. The uniform encoding method can reduce the RCS value in most directions of the target, but there are still very few directions in which the RCS value reduction effect is slightly worse.

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

In order to verify the single-station RCS reduction effect of the optimized coding polarization conversion metasurface shown in Fig. 4, the inventors used a uniform coding polarization conversion metasurface finished board with a size of 180mm×180mm×3mm as the experimental group, and the size of 180mm× The 180mm×3mm optimized coding polarization conversion metasurface finished board was used as the experimental group, and the single-station RCS curves of the two polarization conversion metasurface finished boards were tested by the free space method. The test results are shown in Figure 5. It can be seen that the metasurface determined by the optimal coding determined by the genetic algorithm can achieve a single-station RCS reduction of -10dB in the frequency band of 9.82-23.15GHz, and its reduction performance is far better than that of the uniform coding structure.

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, as shown in FIG. The reflected electromagnetic waves are 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 domain.

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 chamber when performing the RCS measurement of the uniformly encoded metasurface and the optimized encoded metasurface, and then placed the same size metal calibration on the test bench. board, obtain the reference broadband RCS curve of the calibration board, and finally place the finished board to be tested on the test bench to obtain the actual single-station RCS curve of the finished board to be tested, and subtract the actual data obtained from the calibration board. The broadband single-station RCS reduction curve of the finished board to be tested is obtained, which can remove systematic errors and ensure the accuracy of the test results.

It should be noted that, in this document, 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 a relationship between these entities or operations. There is no such actual relationship or sequence. Moreover, the terms "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that a process, method, article or device that includes a list of elements includes not only those elements, but also includes not explicitly listed or other elements inherent to such a process, method, article or apparatus. Without further limitation, an element qualified by the phrase "comprising a..." does not preclude the presence of additional identical elements in the process, method, article, or device that includes the element.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be The technical solutions described in the foregoing embodiments are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. A polarization converting super-surface comprising a first crystal lattice and a second crystal lattice;

the first crystal lattice consists of N multiplied by N polarization conversion units, and each polarization conversion unit comprises a pattern layer (1), a dielectric layer (2) and a continuous bottom plate layer (3) which are sequentially stacked along the vertical direction; the pattern layer (1) is positioned on one side where electromagnetic waves are incident, the pattern in the pattern layer (1) is a pattern with gaps and is symmetrical along a 45-degree diagonal line, and the dielectric layer (2) is used for assisting the pattern layer (1) and the bottom plate layer (3) to generate electromagnetic coupling;

the second lattice is formed by mirroring the first lattice;

the polarization conversion super surface is formed by splicing the first crystal lattice and the second crystal lattice according to a preset arrangement rule.

2. The polarization converting meta-surface of claim 1, wherein a unit period P of the polarization converting unit is 5 mm;

the first lattice is composed of 3 × 3 polarization conversion units.

3. The polarization converting super surface according to claim 1, wherein the material of the pattern layer (1) and the backplane layer (3) is a metal having electrical conductivity.

4. The polarization converting super surface of claim 3, wherein the metal is copper and the conductivity of the copper is 5.8 x 10 ⁷ S/m and a thickness of 0.035 mm.

5. The polarization converting super-surface according to claim 1, wherein the dielectric layer (2) has a thickness of 3mm, a material of F4B-220, and a dielectric constant of 2.2C ² /(N·M ² ) And a dielectric loss tangent of 0.0015.

6. The polarization converting meta-surface according to claim 1, wherein the pattern in the pattern layer (1) consists of one slanted 45 ° bar structure (11) and a double ring structure consisting of two slotted elliptical rings of concentric ellipses, each of which intersects the bar structure (11) and is symmetrical along the bar structure (11).

7. The polarization converting meta-surface according to claim 6, wherein the stripe structures (11) have a length L of 6mm and a width W of 0.25 mm.

8. The polarization converting metasurface of claim 6, wherein said slotted elliptical ring has a major axis inner radius R ₁ 2.4mm, line width W ₁ 0.2mm, axial ratio AR ₁ A first slotted elliptical ring (12) with an opening angle α of 0.9 and 90 ° and a major axis inner radius R ₂ 0.3mm, line width W ₂ 0.3mm, axial ratio AR ₂ A second slotted elliptical ring (13) with an opening angle beta of 108 degrees, which is equal to 0.9.

9. The polarization converting subsurface of any one of claims 1-8, wherein said predetermined arrangement is such that said first lattice and said second lattice are uniformly and equally spaced.

10. The polarization converting super-surface according to any one of claims 1 to 8, wherein the predetermined arrangement rule is an arrangement manner of the first lattice and the second lattice determined by a genetic algorithm with a maximum value of far-field scattering amplitude as an objective function.

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