Metal vortex metasurface for wireless communication encryption and preparation method

Abstract

The invention discloses a metal vortex metasurface for wireless communication encryption and a preparation method thereof. The metal vortex metasurface comprises a metal substrate; the dielectric layer is arranged on the surface of the metal substrate; the metal metasurface array layer is arranged on the surface of the dielectric layer; wherein the metal super-structure surface array layer comprises H-type microstructures, and the H-type microstructures are periodically arranged on the surface of the dielectric layer according to different rotation angles; the H-shaped microstructures are different in length and equal in interval, and are modulated through a geometric phase and a propagation phase in a composite mode. According to the invention, the H-shaped microstructures with different lengths are adopted to realize complete decoupling of the circularly polarized light beam in a microwave range, and meanwhile, in combination with a geometric phase modulation mode, the effect of respectively generating a synthetic vortex light beam and a common vortex light beam under the incidence of the left-handed circularly polarized light and the right-handed circularly polarized light can be realized; the method has huge potential in practical application in the fields of information encryption, wireless communication systems and microscopic imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of reflective electromagnetic metasurfaces, and in particular to a metal vortex metasurface for wireless communication encryption and a preparation method thereof. Background Art

[0002] Optical vortex electromagnetic waves, special beams that carry orbital angular momentum and possess a unique spiral phase wavefront, have unique physical properties that hold great potential in multimode fiber-optic communications, quantum information transmission, and micro-nano optical manipulation. In particular, in high-capacity optical communication systems, the orbital angular momentum of vortex beams can be used as a new degree of freedom to implement spatial multiplexing technology, significantly increasing the transmission capacity of communication systems. While traditional vortex beams exhibit an annular transverse intensity distribution and a spiral phase wavefront, synthetic vortices are a new type of vortex beam with a more complex intensity distribution. The emergence of synthetic vortices offers a new degree of freedom for optical manipulation applications.

[0003] Metasurfaces, a new type of photonic device composed of artificial subwavelength units, can not only achieve local manipulation of beam amplitude, phase, and polarization within the subwavelength range through the precise design of their tiny structural units, but also greatly improve the performance and functionality of optical components, opening up new prospects for micro-integrated photonic systems. Electromagnetic metasurfaces, a type of metasurface primarily used for controlling electromagnetic waves, can cover a wider range of electromagnetic bands, especially exhibiting excellent control capabilities in the microwave, millimeter wave, and radio frequency bands. Currently, the applications of electromagnetic metasurfaces cover multiple fields such as microwave communications, radar imaging, and radio frequency control.

[0004] Geometric phase modulation is a highly efficient way for metasurfaces to manipulate electromagnetic waves, adjusting their phase, amplitude, and polarization. However, the inherent conjugate symmetry of the geometric phase causes the metasurface to produce equal or opposite responses to right-handed and left-handed circularly polarized light, which greatly limits the flexibility and integration of the system. Therefore, there is an urgent need to design a metasurface that can independently manipulate incident right-handed and left-handed circularly polarized light. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a metal vortex metasurface and a preparation method for wireless communication encryption. The present invention adopts H-shaped microstructures of different lengths to achieve complete decoupling of circularly polarized light beams in the microwave range. At the same time, combined with the geometric phase modulation method, it can achieve the effect of generating a synthetic vortex beam and a normal vortex beam under the incidence of left-handed circularly polarized light and right-handed circularly polarized light, respectively.

[0006] In a first aspect, the present invention provides a metal vortex metasurface for wireless communication encryption, comprising:

[0007] metal substrate;

[0008] a dielectric layer, disposed on the surface of the metal substrate;

[0009] A metal metasurface array layer is disposed on the surface of the dielectric layer;

[0010] Among them, the metal metasurface array layer includes H-shaped microstructures, and several of the H-shaped microstructures are periodically arranged on the surface of the dielectric layer according to different rotation angles; the lengths of several of the H-shaped microstructures are different and the spacing is the same. Through the composite modulation of geometric phase and propagation phase, synthetic vortex electromagnetic waves are generated under the incidence of left-handed circularly polarized light, and ordinary vortex electromagnetic waves are generated under the incidence of right-handed circularly polarized light.

[0011] In one embodiment of the present invention, the H-type microstructure is a sub-wavelength microstructure, which is divided into 8 types. The lengths of the 8 H-type microstructures are 11.5mm, 8.8mm, 7.4mm, 6.4mm, 5.3mm, 3.7mm, 2.2mm, and 1mm respectively; the 8 H-type microstructures have the same thickness and width.

[0012] In one embodiment of the present invention, the width of the H-shaped microstructure is 9.2 mm, the pitch of the H-shaped microstructure is 16 mm, and the 2π phase distribution is covered with a 22.5° phase increment.

[0013] In one embodiment of the present invention, the thickness of the metal substrate and the H-shaped microstructure are both 0.2 mm.

[0014] In one embodiment of the present invention, the dielectric layer is made of polytetrafluoroethylene and has a thickness of 2 mm.

[0015] In one embodiment of the present invention, the metal substrate and the metal metasurface array layer are both made of copper.

[0016] In one embodiment of the present invention, the synthetic vortex electromagnetic wave is a vortex beam carrying a superimposed topological charge, and its near-field intensity is distributed in a petal shape; the ordinary vortex electromagnetic wave carries a single topological charge, and its near-field intensity is distributed in a ring shape, and the topological charge value is regulated by the rotation angle of the H-type microstructure.

[0017] In one embodiment of the present invention, the generated vortex electromagnetic wave mode purity is ≥81%, and the operating frequency band is 11.7 GHz.

[0018] In a second aspect, the present invention provides a method for preparing a metal vortex metasurface for wireless communication encryption, comprising the following steps:

[0019] S1. Design a metallic vortex metasurface by selecting H-shaped microstructures of varying lengths. By optimizing the rotation angle and arrangement period of the H-shaped microstructures, efficient reflection of incident circularly polarized light and complete spin decoupling in the microwave range are achieved.

[0020] S2. Selecting a metasurface array modulation method that combines geometric phase and propagation phase to achieve the effect of the metasurface generating synthetic vortex electromagnetic waves under left-handed circularly polarized light incidence and ordinary vortex electromagnetic waves under right-handed circularly polarized light incidence;

[0021] S3, constructing a multilayer structure, stacking a copper substrate, a polytetrafluoroethylene dielectric layer, and a copper H-shaped metasurface array layer in sequence;

[0022] S4. Parameter verification: confirm the topological charge and mode purity of the generated synthetic vortex electromagnetic wave and the ordinary vortex electromagnetic wave through near-field intensity distribution, phase distribution and far-field gain tests.

[0023] In one embodiment of the present invention, in step S1, the length and rotation angle combination of the H-type microstructure are optimized through electromagnetic simulation, so that when left-handed circularly polarized light is incident, a synthetic vortex with a topological charge of l1=-n, l2=+n is generated, and when right-handed circularly polarized light is incident, a normal vortex with a topological charge of l=-m is generated, where n=2, 3, 4, and m=1, 2, 3.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The metal vortex metasurface and preparation method for wireless communication encryption provided by the present invention use H-shaped microstructures of different lengths to achieve complete decoupling of circularly polarized light beams in the microwave range. At the same time, combined with the geometric phase modulation method, it can achieve the effect of generating a synthetic vortex beam and a normal vortex beam under the incidence of left-handed circularly polarized light and right-handed circularly polarized light, respectively. Microwave near-field and far-field experiments were used to experimentally verify the effect of the designed metal microwave metasurface. The high consistency between the experimental results and the simulation results proved the feasibility of the design. The purity of the orbital angular momentum mode of the generated vortex was calculated, and the results were all higher than 81%.

[0026] Furthermore, the metal vortex metasurface can produce a reflection effect of more than 0.82 in the 11.7 GHz frequency band and can achieve complete decoupling of circularly polarized waves, so as to achieve the effect of generating different types of vortex beams in independent polarization channels. By controlling the polarization state of the incident light, the type of vortex beam generated can be freely switched, and the mode purity of the generated vortex beam can reach more than 81%. The designed metal vortex metasurface can be applied to the field of wireless encrypted communication systems, demonstrating its multimodal encrypted transmission capability in millimeter wave channels, providing more opportunities and possibilities for controlling vortex fields in the microwave domain, and has great potential for practical applications in information encryption, wireless communication systems, and microscopic imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying any creative work.

[0028] Figure 1 (a) and (b) are schematic diagrams of the side and top layers of the metal vortex metasurface unit in an embodiment of the present invention.

[0029] Figure 2 (a) represents the geometric parameters of the 16 metasurface units described in the embodiment of the present invention; Figure 2 (b) is the simulation result of the reflection amplitude and phase of 16 metasurface units at 11.7 GHz according to an embodiment of the present invention; Figure 2 (c) is a schematic diagram of all metasurface units designed in an embodiment of the present invention.

[0030] Figure 3 (a)-(l) are simulation results of the near-field intensity and phase distribution of the metasurface described in the embodiment, when left-handed circularly polarized light and right-handed circularly polarized light are incident, respectively, to generate synthetic vortices with topological charges of l1=-2 and l2=2 (l1=-3 and l2=3 and l1=-4 and l2=4) and ordinary vortices with topological charges of l=-1 (l=-2 and l=-3); Figure 3 (m)-(x) in the figure are the corresponding experimental results.

[0031] Figure 4(a)-(f) are the simulation and experimental results of the mode purity of the metasurface described in the embodiment, which generates synthetic vortices with topological charges of l1=-2 and l2=2 (l1=-3 and l2=3 and l1=-4 and l2=4) and ordinary vortices with topological charges of l=-1 (l=-2 and l=-3) under the incidence of left-handed circularly polarized light and right-handed circularly polarized light, respectively.

[0032] Figure 5 (a)-(f) are comparisons of the experimental and simulation results of the far-field radiation gain of the metasurface generating vortices at a frequency of 11.7 GHz.

[0033] Figure 6 (a) is a schematic diagram of the application of the metasurface in the field of optical information encryption and multi-channel information transmission; Figure 6 (b) shows the encryption method of the metasurface in the field of optical information encryption and an encryption example diagram; Figure 6 (c) in the figure is the intensity distribution and mode purity diagram of the vortex beam generated by the metasurface in different channels. DETAILED DESCRIPTION

[0034] The following embodiments of the technical solution of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only examples and are not intended to limit the scope of protection of the present invention.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the present invention belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions.

[0036] In the description of the embodiments of the present invention, technical terms such as "first" and "second" are used solely to distinguish between different objects and should not be understood to indicate or imply relative importance, or to implicitly specify the quantity, specific order, or primary and secondary relationship of the technical features indicated. In the description of the embodiments of the present invention, "plurality" means more than two, unless otherwise specifically defined.

[0037] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least some embodiments of the present invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute a separate or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0038] Example 1

[0039] like Figure 1 (a) and Figure 1 As shown in (b) of FIG. , this embodiment provides a metal vortex metasurface for wireless communication encryption, comprising:

[0040] metal substrate;

[0041] a dielectric layer, disposed on the surface of the metal substrate;

[0042] A metal metasurface array layer is disposed on the surface of the dielectric layer;

[0043] Among them, the metal metasurface array layer includes H-shaped microstructures, and several of the H-shaped microstructures are periodically arranged on the surface of the dielectric layer according to different rotation angles; the lengths of several of the H-shaped microstructures are different and the spacing is the same. Through the composite modulation of geometric phase and propagation phase, synthetic vortex electromagnetic waves are generated under the incidence of left-handed circularly polarized light, and ordinary vortex electromagnetic waves are generated under the incidence of right-handed circularly polarized light.

[0044] Preferably, the H-shaped microstructure is a sub-wavelength microstructure, which is divided into 8 types. The lengths of the 8 H-shaped microstructures are 11.5 mm, 8.8 mm, 7.4 mm, 6.4 mm, 5.3 mm, 3.7 mm, 2.2 mm, and 1 mm, respectively; the 8 H-shaped microstructures have the same thickness and width.

[0045] Preferably, the width of the H-shaped microstructure is 9.2 mm, the pitch of the H-shaped microstructure is 16 mm, and the 2π phase distribution is covered with a phase increment of 22.5°.

[0046] Preferably, the thickness of the metal substrate and the H-shaped microstructure are both 0.2 mm.

[0047] Preferably, the dielectric layer is made of polytetrafluoroethylene and has a thickness of 2 mm.

[0048] Preferably, the metal substrate and the metal metasurface array layer are both made of copper. In this embodiment, a copper substrate is selected to achieve the light beam reflection function, improve the light beam reflection efficiency, and reduce production costs.

[0049] Preferably, the synthetic vortex electromagnetic wave is a vortex beam carrying a superimposed topological charge, and its near-field intensity is distributed in a petal shape; the ordinary vortex electromagnetic wave carries a single topological charge, and its near-field intensity is distributed in a ring shape, and the topological charge value is regulated by the rotation angle of the H-shaped microstructure.

[0050] Preferably, the mode purity of the generated vortex electromagnetic wave is ≥81%, and the operating frequency band is 11.7 GHz.

[0051] Example 2

[0052] This embodiment provides a method for preparing the metal vortex metasurface for wireless communication encryption described in Example 1, comprising the following steps:

[0053] S1. Design a metallic vortex metasurface by selecting H-shaped microstructures of varying lengths. By optimizing the rotation angle and arrangement period of the H-shaped microstructures, efficient reflection of incident circularly polarized light and complete spin decoupling in the microwave range are achieved.

[0054] S2. Selecting a metasurface array modulation method that combines geometric phase and propagation phase to achieve the effect of the metasurface generating synthetic vortex electromagnetic waves under left-handed circularly polarized light incidence and ordinary vortex electromagnetic waves under right-handed circularly polarized light incidence;

[0055] S3, constructing a multilayer structure, stacking a copper substrate, a polytetrafluoroethylene dielectric layer, and a copper H-shaped metasurface array layer in sequence;

[0056] S4. Parameter verification: confirm the topological charge and mode purity of the generated synthetic vortex electromagnetic wave and the ordinary vortex electromagnetic wave through near-field intensity distribution, phase distribution and far-field gain tests.

[0057] Preferably, in step S1, the length and rotation angle combination of the H-type microstructure are optimized by electromagnetic simulation, so that when left-handed circularly polarized light is incident, a synthetic vortex with a topological charge of l1=-n, l2=+n is generated, and when right-handed circularly polarized light is incident, a normal vortex with a topological charge of l=-m is generated, where n=2, 3, 4, and m=1, 2, 3.

[0058] Specifically, the design process of the present invention is as follows: First, H-shaped microstructures with different rotation angles and lengths are optimized to achieve complete decoupling of the incident light beam. Next, the H-shaped microstructures are periodically arranged according to the phase formula, and the generation of different types of vortices with different topological charges is discussed. The design effect is verified using near-field and far-field microwave experiments. The performance of the generated vortices is then analyzed, and the application of metal vortex metasurfaces is discussed.

[0059] The metal vortex metasurface array for wireless communication encryption provided by the present invention comprises a metal metasurface array layer, a dielectric layer and a metal substrate. Figure 1 In (a) and (b), the structural parameters are: p = 16 mm, d = 5.2 mm, w = 2 mm, t1 = 2 mm, t2 = 0.2 mm.

[0060] Figure 2Table (a) shows the parameters and schematic diagrams of 16 designed H-shaped microstructures with different lengths and rotation angles. The length m of the H-shaped microstructure varies from 1 mm to 11.5 mm. Figure 2 (b) is the simulation result of phase and amplitude of 16 optimized H-type microstructures at 11.7 GHz. Figure 2 From (b), we can see that the reflection amplitudes of the H-type microstructures are all higher than 0.82, and the 16 H-type microstructures can cover the 2π phase with a phase increment of 22.5°. Figure 2 (c) is a planar schematic diagram of all designed H-type microstructures.

[0061] Figure 3 Schematic diagram comparing the simulation and experimental results of the near-field intensity and phase distribution of synthetic vortices with topological charges of l1=-2 and l2=2 (l1=-3 and l2=3 and l1=-4 and l2=4) and ordinary vortices with topological charges of l=-1 (l=-2 and l=-3) generated by the metal vortex metasurface at 11.7GHz frequency when left-handed circularly polarized light and right-handed circularly polarized light are incident. Figure 3 It can be clearly seen that the synthetic vortices generated in both simulation and experiment exhibit petal-shaped near-field intensity distributions, while the ordinary vortices exhibit typical annular intensity distributions. The experimental results are generally highly consistent with the simulation results.

[0062] To further analyze the quality of the generated vortex, the output electromagnetic field was decomposed and the purity of each orbital angular momentum mode recorded in the focal plane was calculated. The electromagnetic field can be expanded and represented by a linear combination of fundamental modes.

[0063] Indicates: U(θ)=∑C pl e ilθ (1)

[0064] C pl =∫∫ R U(r)ψ pl *(r)d 2 r (2)

[0065] in |C pl | 2 It is used to express the purity of each orbital angular momentum mode in a vortex beam carrying a topological charge of l, ψ pl *(r) indicates basic mode. Figure 4The schematic diagram of the mode purity of the generated vortex beam is shown. Since the topological charges of the designed synthetic vortex are superimposed, when analyzing the mode purity effect, the mode weights of the synthetic vortex carrying topological charges of l1=-2 and l2=2 (l1=-3 and l2=3 and l1=-4 and l2=4) are superimposed and calculated respectively. Figure 4 As shown in the figure, the simulation result of the mode purity of the synthetic vortex with a topological charge of l = ±2 is 98.5% (85.5% when l = ±3, 81.4% when l = ±4); the measured result of the mode purity of the synthetic vortex with a topological charge of l = ±2 is 88.0% (96.0% when l = ±3, 89.8% when l = ±4). The simulation result of the mode purity of the ordinary vortex with a topological charge of l = -1 is 88.6% (87.4% when l = -2, 91.0% when l = -3); the measured result of the mode purity of the ordinary vortex with a topological charge of l = -1 is 90.0% (96.0% when l = -2, 92.0% when l = -3).

[0066] Figure 5 The simulation and measurement results of the far-field scattering of vortex electromagnetic waves generated by the metal vortex metasurface at a frequency of 11.7 GHz are shown in FIG. , where the solid line represents the simulation result and the dotted line represents the measurement result. Figure 5 It can be seen that the measurement results are highly consistent with the simulation results in general, and there is an obvious amplitude zero at the center of the beam, which is consistent with the typical far-field scattering characteristics of vortex beams.

[0067] Figure 6 (a) is a schematic diagram of the application of the metal metasurface in the field of information encryption and multi-channel information transmission in the microwave frequency band. Figure 6 As shown in (b), during the encryption process, the topological charge carried by the ordinary vortex electromagnetic wave generated by the incident right-handed circularly polarized light is numbered to correspond to the first hexadecimal digit from 0 to F, while the number of petals in the near-field intensity distribution of the synthetic vortex generated by the incident left-handed circularly polarized light is numbered to correspond to the second hexadecimal digit from 0 to F. During the encryption process, by combining the intensity distributions of the two vortex electromagnetic waves, a two-digit hexadecimal number can be represented. Figure 6 (b) in the figure also shows the encryption process of the letters "J", "N" and "U". Figure 6(c) in the figure shows the near-field intensity distribution of vortex electromagnetic waves carrying various topological charges and the purity of the corresponding orbital angular momentum mode in each channel. As an example, the light beam in each channel has high OAM mode purity and is transmitted independently in multiple channels without mutual interference. By combining the above two applications, a multi-channel independent encrypted transmission system for microwave frequency bands can be realized. While maintaining transmission stability and efficiency, this system can further encrypt the transmitted information, making the information more secure.

[0068] In this embodiment, the use of H-shaped microstructures of different lengths can achieve complete decoupling of circularly polarized light beams in the microwave range. At the same time, combined with the method of geometric phase modulation, it can achieve the effect of generating a synthetic vortex beam and an ordinary vortex beam under the incidence of left-handed circularly polarized light and right-handed circularly polarized light, respectively. Microwave near-field and far-field experiments were used to experimentally verify the effect of the designed metal microwave metasurface. The high consistency between the experimental results and the simulation results proved the feasibility of the design. The purity of the orbital angular momentum mode of the generated vortex was calculated, and the results were all higher than 81%. The designed metal vortex metasurface can be applied to the field of wireless encrypted communication systems, providing more opportunities and possibilities for controlling the vortex field in the microwave domain, and has great potential in practical applications in the fields of information encryption, wireless communication systems and microscopic imaging.

[0069] In summary, the present invention adopts compound phase modulation technology: for the first time, a metasurface modulation method combining geometric phase and propagation phase is proposed, breaking the traditional geometric phase conjugate symmetry limitation, and realizing complete spin decoupling and independent control of left / right circularly polarized light. The present invention adopts H-type multi-parameter collaborative design: through the periodic arrangement of 8 sub-wavelength H-type microstructure arrays of different lengths (1-11.5mm), combined with fixed width (9.2mm), spacing (16mm) and rotation angle, a reflection efficiency of >82% and 2π phase coverage are achieved in the 11.7GHz frequency band, generating high-purity (≥81%) vortex waves. The present invention adopts a dual-mode vortex generation mechanism: a single metasurface generates synthetic vortices (petal-shaped intensity distribution) and ordinary vortices (annular intensity distribution) under the incidence of left / right circularly polarized light, respectively, and supports dynamic switching of topological charges (l=±2 / ±3 / ±4). The present invention adopts a copper-based multi-layer composite structure: a reflective design of copper substrate (0.2mm) + polytetrafluoroethylene dielectric layer (2mm) + copper H-type array is adopted, which has both high reflection efficiency and low cost characteristics, and is adapted to the needs of wireless encrypted communications in the microwave frequency band. The multi-channel information encryption application of the present invention: the vortex type switching in independent channels is achieved through polarization state regulation, and the topological charge and petal number coding are combined to construct a hexadecimal multi-channel encryption system to improve the security of wireless communications. The metal vortex metasurface supports dynamic switching of topological charges and can construct a hexadecimal multi-channel encryption system, which significantly improves the security of wireless communications. The preparation method includes microstructure optimization, multi-layer assembly and performance verification, and has the advantages of high reflection efficiency, low cost and easy integration.

[0070] While the present invention has been described with reference to preferred embodiments, various modifications may be made and equivalent components may be substituted without departing from the scope of the present invention. In particular, the various technical features described in the various embodiments may be combined in any manner, provided no structural conflicts exist. The present invention is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A metal vortex metasurface for wireless communication encryption, characterized in that: include: metal substrate; a dielectric layer, disposed on the surface of the metal substrate; A metal metasurface array layer is disposed on the surface of the dielectric layer; Among them, the metal metasurface array layer includes H-shaped microstructures, and several of the H-shaped microstructures are periodically arranged on the surface of the dielectric layer according to different rotation angles; the lengths of several of the H-shaped microstructures are different and the spacing is the same. Through the composite modulation of geometric phase and propagation phase, synthetic vortex electromagnetic waves are generated under the incidence of left-handed circularly polarized light, and ordinary vortex electromagnetic waves are generated under the incidence of right-handed circularly polarized light.

2. The metal vortex metasurface for wireless communication encryption according to claim 1, characterized in that: The H-shaped microstructure is a sub-wavelength microstructure, which is divided into 8 types. The lengths of the 8 H-shaped microstructures are 11.5mm, 8.8mm, 7.4mm, 6.4mm, 5.3mm, 3.7mm, 2.2mm, and 1mm respectively; the 8 H-shaped microstructures have the same thickness and width.

3. The metal vortex metasurface for wireless communication encryption according to claim 1, characterized in that: The width of the H-shaped microstructure is 9.2 mm, the pitch of the H-shaped microstructure is 16 mm, and the H-shaped microstructure covers a 2π phase distribution with a phase increment of 22.5°.

4. The metal vortex metasurface for wireless communication encryption according to claim 1, characterized in that: The thickness of the metal substrate and the H-shaped microstructure are both 0.2 mm.

5. The metal vortex metasurface for wireless communication encryption according to claim 1, characterized in that: The dielectric layer is made of polytetrafluoroethylene and has a thickness of 2 mm.

6. The metal vortex metasurface for wireless communication encryption according to claim 1, characterized in that: The metal substrate and the metal metasurface array layer are both made of copper.

7. The metal vortex metasurface for wireless communication encryption according to claim 1, characterized in that: The synthetic vortex electromagnetic wave is a vortex beam carrying superimposed topological charges, and its near-field intensity is distributed in a petal shape; the ordinary vortex electromagnetic wave carries a single topological charge, and its near-field intensity is distributed in a ring shape, and the topological charge value is regulated by the rotation angle of the H-shaped microstructure.

8. The metal vortex metasurface for wireless communication encryption according to claim 1, characterized in that: The generated vortex electromagnetic wave mode purity is ≥81%, and the operating frequency band is 11.7 GHz.

9. A method for preparing a metal vortex metasurface for wireless communication encryption according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Design a metallic vortex metasurface by selecting H-shaped microstructures of varying lengths. By optimizing the rotation angle and arrangement period of the H-shaped microstructures, efficient reflection of incident circularly polarized light and complete spin decoupling in the microwave range are achieved. S2. Selecting a metasurface array modulation method that combines geometric phase and propagation phase to achieve the effect of the metasurface generating synthetic vortex electromagnetic waves under left-handed circularly polarized light incidence and ordinary vortex electromagnetic waves under right-handed circularly polarized light incidence; S3, constructing a multilayer structure, stacking a copper substrate, a polytetrafluoroethylene dielectric layer, and a copper H-shaped metasurface array layer in sequence; S4. Parameter verification: confirm the topological charge and mode purity of the generated synthetic vortex electromagnetic wave and the ordinary vortex electromagnetic wave through near-field intensity distribution, phase distribution and far-field gain tests.

10. The method for preparing a metal vortex metasurface for wireless communication encryption according to claim 9, characterized in that: In step S1, the length and rotation angle combination of the H-type microstructure are optimized through electromagnetic simulation, so that when left-handed circularly polarized light is incident, a synthetic vortex with a topological charge of l1 = -n, l2 = +n is generated, and when right-handed circularly polarized light is incident, a normal vortex with a topological charge of l = -m is generated, where n = 2, 3, 4, and m = 1, 2, 3.

Images