An ultra-wideband asymmetric transmission polarization converter based on chiral metasurface

Abstract

The present invention proposes an ultra-wideband asymmetric transmission polarization converter based on a chiral metasurface. The metasurface is composed of a series of periodically arranged unit structures, and the unit includes 5 metal layers and 4 dielectric substrates. The working process of the present invention is as follows: the incident electromagnetic wave with a polarization direction perpendicular to the direction of the metasurface slot line is converted into a cross-polarized electromagnetic wave with high efficiency through the metasurface, and the reverse incident electromagnetic wave of the same polarization will be reflected, thereby realizing asymmetric transmission. Compared with other polarization converters, the present invention has the advantages of wide bandwidth, high efficiency, and large angle, and can realize asymmetric transmission. It has great application prospects in radar and satellite communications, polarization conversion and other fields.

Description

Technical Field

[0001] The present invention belongs to the field of novel artificial electromagnetic materials, and in particular relates to an ultra-wideband asymmetric transmission polarization converter based on a chiral metasurface. Background Art

[0002] The polarization state is one of the most important characteristics of electromagnetic waves. For a long time, the regulation of polarization has been the focus of research in the field of electromagnetic waves. Electromagnetic metamaterials are a new type of material that is artificially designed and exhibits extraordinary electromagnetic properties. Once proposed, metamaterials have attracted much attention due to their powerful electromagnetic wave regulation capabilities and small space requirements. In particular, the emergence of metamaterials on a two-dimensional scale, namely metasurfaces, provides a more efficient technical means for the polarization regulation of electromagnetic waves. However, the performance of most polarization conversion metasurfaces is limited by narrow bandwidth and low efficiency, and they are often not applicable to scenarios requiring asymmetric transmission due to their symmetrical structure. Therefore, how to simultaneously achieve wide bandwidth, large angle and high-efficiency asymmetric transmission has become an important issue that needs to be solved in this field. Summary of the invention

[0003] Technical problem: In order to solve the common problems of current polarization converters such as narrow bandwidth, low efficiency, poor oblique incidence performance and inability to meet asymmetric transmission requirements, the present invention provides an ultra-wideband asymmetric transmission polarization converter based on a chiral metasurface, which can achieve high-efficiency and large-angle asymmetric transmission in a wider frequency band.

[0004] Technical solution: The present invention provides an ultra-wideband asymmetric transmission polarization converter based on a chiral metasurface, which is composed of metasurface units periodically arranged in two-dimensional space, wherein the metasurface units include three layers of metal structures, and a dielectric substrate is arranged between adjacent metal structures; the upper and lower metal structures are bandgap structures with the same width, but their directions are perpendicular to each other; the middle layer is a metal bandgap structure with a rotation angle between the upper and lower layers, serving as a transition structure.

[0005] Furthermore, the intermediate layer metal structure is a bandgap structure inclined at an angle of 45°, and has a circular cut in the middle.

[0006] Furthermore, the metasurface unit includes 5 layers of metal and 4 layers of dielectric substrate, that is, the 2nd layer of metal structure and the 4th layer of metal structure are respectively arranged between the upper layer and the middle layer of metal structure and between the middle layer and the lower layer of metal structure; the rotation angles of the 2nd layer and the 4th layer of metal structures differ by 45°.

[0007] Furthermore, the metal structures of the second and fourth layers are short strip lines that form an angle of 67.5° with the band gap directions of the upper and lower metal layers, respectively.

[0008] Furthermore, the metal structure is copper with a thickness of 0.035 mm.

[0009] Furthermore, the material of the dielectric substrate is a commercial dielectric material F4BM, with a relative dielectric constant of 2.65 and a loss tangent of 0.001.

[0010] The metasurface structure can convert incident electromagnetic waves with a polarization direction perpendicular to the surface metal band gap direction into transmitted cross-polarized electromagnetic waves within a certain frequency and angle range, while suppressing electromagnetic waves with the same polarization direction transmitted in the opposite direction, and has ultra-wideband asymmetric transmission characteristics.

[0011] The working process of the present invention is as follows: the incident electromagnetic wave with a polarization direction perpendicular to the direction of the metasurface slot line is converted into a cross-polarized electromagnetic wave with high efficiency through the metasurface, and the reverse incident electromagnetic wave of the same polarization will be reflected, thereby realizing asymmetric transmission.

[0012] Furthermore, the proposed ultra-wideband asymmetric transmission polarization converter based on chiral metasurface was experimentally verified, and the experimental verification includes:

[0013] 1. Various transmission and reflection properties of the metasurface under vertical incidence of electromagnetic waves;

[0014] 2. The metasurface has asymmetric transmission performance under oblique incidence of electromagnetic waves.

[0015] Beneficial effects: Compared with the prior art, the ultra-wideband asymmetric transmission polarization converter based on chiral metasurface of the present invention has the following advantages:

[0016] 1. The present invention can realize high-efficiency polarization conversion in an ultra-wide frequency band, and can expand the frequency band by adjusting parameters;

[0017] 2. The present invention has asymmetric transmission characteristics and is suitable for scenarios with special requirements;

[0018] 3. The present invention has good oblique incidence characteristics and can be used in complex working environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the appearance of an ultra-wideband asymmetric transmission polarization converter based on a chiral metasurface of the present invention;

[0020] Figure 2 A schematic diagram of the working principle of an ultra-wideband asymmetric transmission polarization converter based on a chiral metasurface of the present invention;

[0021] Figure 3 (a) is a top view of the supersurface structure unit of the present invention;

[0022] Figure 3(b) is a side view of the metasurface structure unit of the present invention, wherein the schematic diagram shows the 1st to 5th metal structures and the 1st to 4th dielectric substrates from top to bottom respectively;

[0023] Figure 4 (a) is a schematic diagram of the first metal structure of the supersurface unit of the present invention;

[0024] Figure 4 (b) is a schematic diagram of the second metal structure of the supersurface unit of the present invention;

[0025] Figure 4 (c) is a schematic diagram of the third metal structure of the supersurface unit of the present invention;

[0026] Figure 4 (d) is a schematic diagram of the metal structure of the fourth layer of the supersurface unit of the present invention;

[0027] Figure 4 (e) is a schematic diagram of the fifth metal structure of the metasurface unit of the present invention;

[0028] Figure 5 The simulation and experimental results of various transmission and reflection performances of the metasurface of the present invention under the condition of vertical incidence of electromagnetic waves;

[0029] Figure 6 This is a graph showing the experimental results of the asymmetric transmission performance of the metasurface of the present invention under oblique incidence of electromagnetic waves. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is now described in detail with reference to the accompanying drawings and embodiments.

[0031] The present invention discloses an ultra-wideband asymmetric transmission polarization converter based on a chiral metasurface, which is composed of periodically arranged (equally spaced two-dimensional square arrangement) metasurface units, each of which is a rectangular parallelepiped structure with a square cross-section. The structure includes five layers of metal and four layers of dielectric substrate from top to bottom. The first and fifth layers are bandgap structures with the same width, but their directions are perpendicular to each other to ensure the cross-polarization conversion capability of the metasurface; the third layer is a metal bandgap structure with a rotation angle between the first and fifth layers. As a transition structure, the third layer of metal enables the metasurface to have broadband characteristics on the basis of higher transmission efficiency, wherein a circular cut is made in the center of the third layer of metal to improve the performance of the metasurface under oblique incidence; the second and fourth layers of metal are the same metal strip lines with a rotation angle difference of 45°, which are mainly used to further improve the bandwidth of the metasurface. The material of the metal layer is copper and has a thickness of 0.035 mm. The dielectric substrate uses a commercial dielectric material F4B with a relative dielectric constant of 2.65 and a tangent loss of 0.001. The dimensions of each layer of structure are marked as follows: Figure 3 and Figure 4As shown, the parameters are as follows: a=6.2mm, h1=1.6mm, h2=1.4mm, h3=1.4mm, h4=1.6mm, w1=4.2mm, w2=2mm, w3=0.5mm, l=3.5mm, r=1.85mm, α=67.5°.

[0032] Figure 2 The work diagram of the metasurface is shown. The electromagnetic wave incident in the forward direction with the polarization direction perpendicular to the metal direction of the metasurface surface will be efficiently converted into a cross-polarized transmission wave, while the electromagnetic wave of the same polarization incident in the reverse direction will be reflected, thus realizing asymmetric transmission in the forward and reverse directions. This asymmetric characteristic comes from the chirality of the metasurface unit.

[0033] Figure 5 What is shown are the simulation and experimental results of the transmission performance of the metasurface under different incident conditions. In the case of forward transmission, the cross-polarization conversion efficiency of the metasurface reaches above 0.8 between 6 and 18 GHz, while the transmission coefficient is suppressed to below 0.3 during reverse transmission.

[0034] Figure 6 What is shown is the experimental results of the asymmetric characteristics of the metasurface under oblique incidence. In the incident angle range of 0-30°, the efficiency of forward transmission reaches above 0.8 between 6-18GHz, while the reverse transmission efficiency is less than 0.3.

[0035] The present invention proposes an ultra-wideband asymmetric transmission polarization converter based on a chiral metasurface, which can realize asymmetric transmission of electromagnetic waves in different directions with the same polarization state, has ultra-wideband, large angle, and high-efficiency polarization conversion capabilities, and has potential application prospects in satellite and radar communications, polarization control and other fields.

[0036] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. An ultra-wideband asymmetric transmission polarization converter based on a chiral metasurface, which is composed of metasurface units periodically arranged in two-dimensional space, characterized in that: The metasurface unit includes 5 layers of metal structures and 4 layers of dielectric substrates, and the dielectric substrates are arranged between adjacent metal structures; the upper and lower metal structures are bandgap structures with the same width, but the directions are perpendicular to each other; The middle layer is a metal bandgap structure between the upper layer and the lower layer, serving as a transition structure; the second metal structure and the fourth metal structure are respectively arranged between the upper and middle metal structures and between the middle and lower metal structures; the rotation angles of the second and fourth metal structures differ by 45°; The metal structure of the middle layer is a bandgap structure tilted at an angle of 45°, with a circular cut in the middle; The metal structures of the second and fourth layers are short strip lines that form an angle of 67.5° with the band gap direction of the uppermost and lowermost metal layers, respectively.

2. The ultra-wideband asymmetric transmission polarization converter based on a chiral metasurface according to claim 1, characterized in that: The metal structure is copper with a thickness of 0.035 mm.

3. The ultra-wideband asymmetric transmission polarization converter based on a chiral metasurface according to claim 1, characterized in that: The material of the dielectric substrate is a commercial dielectric material F4BM, with a relative dielectric constant of 2.65 and a loss tangent of 0.001.

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