Metasurface structure for generating OAM wave beam and design method of metasurface structure

Abstract

The invention relates to a metasurface structure for generating OAM wave beams and a design method thereof, the metasurface structure comprises basic units arranged in a periodic array mode, and each basic unit is composed of a metal substrate, a dielectric layer and a top metal resonance layer. The top metal resonance layer comprises two metal split rings which are arranged at an angle of 45 degrees and are connected through a metal arrow, the metal material is copper, the dielectric layer is made of polyimide, and the structural design is used for terahertz frequency band work. The top metal resonance layer provides different geometric phases and propagation phases by rotating at different angles and adjusting the width of a gap, so that OAM orbital angular momentum beams are generated in a terahertz frequency band.

Description

Technical Field

[0001] The present invention relates to the field of antenna technology, and in particular to a metasurface structure for generating an OAM beam and a design method thereof. Background Art

[0002] OAM (Orbital Angular Momentum) is one of the important physical quantities in electromagnetic waves, light waves, and sound waves. In recent years, OAM has become a research hotspot due to its huge application potential in communications, imaging, and quantum information. Especially in the field of optics, OAM can be used to achieve ultra-high capacity multi-channel communications and enhance image resolution. The OAM characteristics of electromagnetic waves make it an efficient signal encoding method, allowing multiple independent information streams to be transmitted through different OAM modes.

[0003] Metasurface is essentially a two-dimensional material that can precisely manipulate the propagation characteristics of electromagnetic waves on its surface, including its amplitude, phase, polarization, and angular momentum. OAM metasurface is a technology that regulates and controls waves by designing a two-dimensional surface with a specific geometry and structure (usually composed of sub-wavelength-scale units). By carefully designing the resonant structure of the metasurface, different OAM states can be given to electromagnetic waves, thereby achieving spatial modulation of electromagnetic waves.

[0004] The core idea of ​​OAM metasurface is to use different microstructure units (such as metal or dielectric structures) to achieve propagation phase control by changing the size of the subwavelength structure, and to achieve geometric phase control by changing the rotation direction of the subwavelength structure, and then use the composite phase to achieve independent decoupling of electromagnetic waves. OAM metasurface has a wide range of application scenarios in high-capacity communications, stealth technology, optical imaging and sensing, quantum communications and antenna design.

[0005] However, there are still many pain points in designing OAM metasurfaces. For example, the choice of materials has a great impact on the performance of the metasurface, and the design of the structural size will also have an impact on the performance of the metasurface; although complex structural design can achieve good performance, it increases the difficulty of calculation and processing costs; modeling multiple different resonant units of periodic structures will consume a lot of time and computing power; large-scale meshing has extremely high requirements for computer hardware, etc. Therefore, this example mainly solves the above pain points by selecting cheap materials, designing simple structures, and reducing computer calculation pressure through joint simulation and manual meshing.

[0006] OAM metasurfaces are an important research direction in the field of optics and electromagnetics in recent years, especially in controlling the propagation of light, achieving efficient information transmission, and enhancing the interaction between light and matter. Researchers usually face the following problems when designing OAM metasurfaces. First, OAM metasurfaces require precisely designed nanostructures to regulate the orbital angular momentum of light in a specific direction. This involves very fine optimization of the geometric design, size, and periodic unit arrangement of the metasurface unit. Secondly, the performance of OAM metasurfaces is closely related to the physical properties of the material, and the optical loss of the material will also affect the efficiency of the metasurface. When designing, factors such as material loss, dispersion, and optical nonlinearity should be considered. High-loss materials may lead to low efficiency or even failure to achieve the expected OAM mode. Therefore, the choice of materials will not only affect the performance of the structure, but also increase the cost. Furthermore, OAM metasurfaces not only need to control the orbital angular momentum of light, but often also need to take into account other optical properties, such as polarization, frequency, and propagation direction. Therefore, how to achieve multifunctional integration on the same metasurface is still an important challenge in designing metasurfaces.

[0007] After searching, the application publication number CN114374096A, a dual-mode orbital angular momentum focusing basic unit array and a super surface preparation method, the basic unit array includes Anisotropic unit cell structure and The present invention constructs a polarization-controlled dual-mode orbital angular momentum focusing basic unit array by arranging a plurality of anisotropic unit structures and a small number of isotropic unit structures, and then the basic unit array can be used to construct a metasurface in the future. In addition, the use of a basic unit array to form a metasurface can converge the OAM beam.

[0008] The patent adopts an axisymmetric H-shaped structure at the top, and an OAM convergence metasurface carrying different topological charges can be constructed through the compensation phase of the basic unit array. However, the basic unit of this structure cannot take into account other optical properties, such as the basic unit realizing polarization conversion of electromagnetic waves. Moreover, from the size of the patent structure and the selected dielectric layer material, it can be known that the operating frequency band of the patent is in the microwave frequency band, while the structure proposed in this example works in the terahertz frequency band, which has more obvious practical significance for the research of the new generation of mobile communications. Furthermore, the patent did not propose how to overcome the time-consuming modeling problems of multi-unit structures and the computing power problems of computer hardware caused by the number of grids. This example starts from the practical problems of how to quickly realize modeling and reduce computing power pressure, and gives a practical solution, which can provide a new way for rapid simulation for the corresponding researchers. Summary of the invention

[0009] The present invention aims to solve the above problems of the prior art. A metasurface structure for generating OAM beams is proposed. The technical solution of the present invention is as follows:

[0010] A metasurface structure for generating OAM beams, wherein the structure comprises basic units arranged in a periodic array, each basic unit is composed of a metal substrate, a dielectric layer and a top metal resonance layer, wherein the top metal resonance layer comprises two metal split rings arranged at a 45° angle and connected by metal arrows, wherein the metal material is copper, and the dielectric layer material is polyimide, and the structure is designed to work in the terahertz frequency band, and the metal substrate is mainly used to prevent electromagnetic waves from being transmitted, so that all electromagnetic waves passing through the dielectric layer are reflected to the resonance layer. The dielectric layer is mainly used to support the top resonance layer and provide The phase shift is: k0 is the wave vector constant in free space, ε d is the dielectric constant of the middle layer, and h is the thickness of the dielectric layer, is the refraction angle of the incident electromagnetic wave. The top metal resonant layer mainly generates OAM orbital angular momentum beams in the terahertz band by rotating different angles and adjusting the slit width to provide different geometric phases and propagation phases.

[0011] Furthermore, the bottom metal layer and the middle dielectric layer of the periodic unit are rectangular structures with a side length of p=13.5 μm, the thickness of the bottom metal layer is t1=0.2 μm, and the thickness of the middle dielectric layer is h=6 μm.

[0012] Furthermore, the thickness of the top metal resonance layer is t2=0.2 μm, the outer diameter (r1) and inner diameter (r2) of the split ring are 1.9 μm and 1.6 μm respectively; the length and width of the rectangular pattern connecting the two split rings are 4 μm and 0.6 μm respectively; the side lengths of the isosceles triangle are 1 μm,

[0013] Furthermore, the metal material is copper, the electrical conductivity is 5.96e+7S / m, the intermediate dielectric layer material is polyimide Pi, the dielectric constant is ε=3.5, and the magnetic permeability is μ=1.

[0014] A method for designing a metasurface structure for generating an OAM beam comprises the following steps: (a) calculating the phase distribution of a unit structure; (b) using Python programming and CST commercial software for joint simulation to construct an OAM metasurface with an 18*18 periodic structure; and (c) manually adjusting the grid size to reduce the computing resource requirements and ensure simulation accuracy and computing efficiency.

[0015] Furthermore, the calculation of the phase distribution in step (a) is based on a given topological charge and surface array size, and the phase compensation between units is achieved in step (b) by automatically distributing the size of the split ring opening and the rotation angle of the top resonant pattern.

[0016] Furthermore, the phase distribution of the calculation unit structure (a) specifically includes: according to the characteristics of the vortex beam, the phase distribution It is spiral, where l is the topological charge carried by the vortex beam, is the azimuth angle. According to the given l and the size of the surface array, the corresponding metasurface phase distribution can be calculated. After calculating the corresponding phase distribution, the 18*18 structure that generates the OAM beam can be constructed through Python and CST.

[0017] The advantages and beneficial effects of the present invention are as follows:

[0018] Compared with other similar metasurface structures, the present invention has the following advantages: 1. The metal material of the structure is copper, which can reduce the cost of raw materials in practical engineering applications; 2. The working band of this structure is in the terahertz band, and the working frequency band of common devices is in the microwave band, which leads to the terahertz band being called the terahertz blank. Therefore, this structure can provide more references and ideas for designing terahertz devices; 3. This structure is a classic sandwich structure with mature processing and manufacturing technology, and the top resonance pattern is not complicated, which significantly reduces the processing cost; 4. This structure can also be used as a polarization converter, and the bandwidth with a polarization conversion efficiency higher than 90% reaches 4.8THz, which has advantages that narrow-band polarization converters do not have. The results are as follows Figure 2 As shown; 5. The periodic structure of the structure adopts Phyton and CST joint simulation, which greatly reduces the modeling time; 6. The structure also has the characteristics of low profile and easy conformality, which provides an effective means for designing multifunctional devices based on phase-type metasurfaces.

[0019] The structure proposed in the present invention uses metallic copper as the resonant material. The material is easily available and affordable, overcoming the disadvantage of the high cost of precious metals. The dielectric layer in the middle is made of low-loss material, which has little effect on the efficiency of the metasurface. In the design process, the parameter optimization uses Phyton and CST joint simulation to reduce the time of manual adjustment of structural parameters, and the designed structural parameters are fine enough and the effect of generating OAM beams is good. The structure proposed in the present invention can not only generate QAM beams, but also flexibly control the polarization direction of the incident wave, realizing multi-functional integration on the same metasurface.

[0020] The OAM metamaterial structure designed by the present invention can provide different geometric phases by rotating the top resonant structure, and can provide different propagation phases by adjusting the size of the slit. At the same time, the OAM beam can be realized by adjusting the rotation angle and the slit width and presenting the corresponding distribution. Since it takes a lot of time to manually construct an 18*18 periodic structure, we use Python combined with CST simulation to easily realize phase compensation between units through programming, which saves a lot of manual modeling time and also achieves good beamforming.

[0021] In the design process of metasurfaces, rectangular and circular split rings are favored by a large number of researchers because the split ring can be equivalent to an RLC circuit model, which can allow the incident electromagnetic wave to resonate at the split ring, thereby regulating the electromagnetic wave. However, the structure with only a single split ring will have the problem of narrow bandwidth. Therefore, the idea of ​​designing multiple split rings can be adopted to construct a metasurface structure, and then multiple split rings can be connected through a metal structure to form a parallel RLC resonant circuit. The final result is that the resonance points will increase, thereby widening the bandwidth of the structure. Similarly, in most structures with rectangular resonant patterns, it can be found that electromagnetic resonance usually occurs at the four corners of the rectangle. Therefore, adding a metal arrow structure in the center of the ring can further enhance the bandwidth of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of a metasurface structure for generating an OAM beam according to a preferred embodiment of the present invention;

[0023] Figure 2 is the co-polarization reflection coefficient r of the unit structure ll and the cross-polarization reflection coefficient r rl , and the phase P of the co-polarization reflection coefficient xx and P yy .

[0024] Figure 3 It is the phase distribution diagram after theoretical calculation and the 18*18 OAM metasurface sample diagram generated based on the phase distribution diagram.

[0025] Figure 4 It is the simulated near-field amplitude distribution diagram and far-field scattering direction diagram of the designed metasurface when l is selected as -2 and the number of arrays is selected as 18*18. DETAILED DESCRIPTION

[0026] The following will describe the technical solutions in the embodiments of the present invention in detail in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention.

[0027] The technical solution of the present invention to solve the above technical problems is:

[0028] like Figure 1 (a) shows the side view of the OAM metamaterial unit structure designed in this example, and (b) shows the top view of the unit structure; Figure 2 (a) Co-polarization reflection coefficient r of the unit structure ll and the cross-polarization reflection coefficient r rl , (b) Phase P of the co-polarization reflection coefficient xx and P yy ; Figure 3 (a) Calculated phase distribution diagram, (b) 18*18 OAM metasurface generated based on the phase distribution; Figure 4 (a) Near-field amplitude distribution diagram of metasurface-2 mode simulation, (b) far-field scattering pattern.

[0029] An embodiment of the present invention provides an OAM metamaterial structure, comprising basic units arranged in a periodic array, wherein the basic units include a metal substrate, a dielectric layer and a top metal resonant layer, such as Figure 1 (a) As shown; the metal resonance layer includes two metal split rings arranged at a 45° angle, and the two split rings are connected together by a metal arrow, as shown Figure 1 (b) is shown. The specific dimensions of the structure are as follows: the bottom metal layer and the middle dielectric layer of the periodic unit are rectangular structures with a side length of p = 13.5μm, the thickness of the bottom metal layer is t1 = 0.2μm, the thickness of the middle dielectric layer is h = 6μm, the thickness of the top resonant layer is t2 = 0.2μm, the outer diameter (r1) and inner diameter (r2) of the split ring are 1.9μm and 1.6μm respectively; the length and width of the rectangular pattern connecting the two split rings are 4μm and 0.6μm respectively; the side lengths of the isosceles triangles are 1μm, The metal materials at the bottom and top of the structure are copper, with a conductivity of 5.96e+7S / m. The material of the middle dielectric layer is polyimide (Polyimide, abbreviated as Pi), with a dielectric constant of ε=3.5 and a magnetic permeability of μ=1. Since this material is not included in the CST material library, the optical characteristic curve of this material in the terahertz frequency band is imported through the Drude model.

[0030] Next is the optimization of the settings before simulation. After the 18*18 periodic structure is meshed in CST, the number of meshes will exceed 1 billion. The computer configuration used for the simulation in this case is AMD Ryzen 9 5900X12-Core Processor3.70GHz, and the memory is 32G, which is not enough to support such a large mesh calculation. Therefore, it is necessary to manually divide the mesh before simulation to reduce the memory requirement. The steps to manually set the mesh size are as follows: first find the GlobalProperties window in the CST interface, and manually adjust the value in Cells per wavelength in the pop-up window. In order to calculate more accurately, the value should be as small as possible. After setting, it is found that the device can support the value of Cells per wavelength = 15. The final mesh is divided into 40 million, and the computer can calculate and the accuracy meets the requirements.

[0031] The specific steps of Python and CST to construct an 18*18 periodic structure are as follows. Since the structure that generates the OAM beam is composed of unit structures with different phases, the first step is to calculate the phase distribution of the unit. According to the characteristics of the vortex beam, its phase distribution It is spiral, where l is the topological charge carried by the vortex beam, is the azimuth angle. According to the given l and the size of the surface array, the corresponding metasurface phase distribution can be calculated. After calculating the corresponding phase distribution, the 18*18 structure that generates the OAM beam can be constructed by combining Python with CST, as shown in Figure 3 Shown are the calculated phase distribution and the 18*18 structure arranged according to the phase distribution.

[0032] Finally, start the simulation and wait for the results. The simulation output also clearly shows that our structure can generate OAM beams. The simulation results are as follows: Figure 4 shown.

[0033] When designing the unit structure, CST commercial electromagnetic simulation software is used for modeling. When designing the model, the operating frequency band and size of the structure should be roughly determined. After determining the operating frequency band and approximate size, import the corresponding material from the material library. The CST material library comes with a variety of commonly used materials. If there is no corresponding material in the built-in material library, you can build the material by importing the Drude model of the material. The dielectric layer material in this example is the material parameter set by the Drude model. After the material is set, you can build a specific structural model. The bottom and middle parts of this example are both rectangles. You only need to draw the rectangle through CST and then modify the corresponding structural parameters and material properties. The pattern of the top resonant layer can be cut, added or other operations can be performed through the Boolean operation of CST after the regular graphics are established.

[0034] After the structure is built, the boundary conditions are set. Since the structure is a reflective metasurface, the incident direction of the electromagnetic wave is set to the positive direction of the Z axis and the outgoing direction is -Z, so it is set to open (addspace) in the Z direction and unit cell in the X and Y directions. After setting the boundary conditions, the simulation can be started. In order to save computing time and memory, the frequency domain simulation is used. After the simulation is completed, the corresponding formula can be entered in the structure post-processing window to view the results. And the structure size is continuously adjusted through the built-in optimization parameters to obtain the best effect.

[0035] After the unit structure optimization is completed, an 18*18 periodic unit structure can be constructed through Python and CST. Through Python programming, the automatic distribution of the opening size of the gap ring and the rotation angle of the top resonance pattern can be achieved to realize phase compensation between units and finally realize the OAM beam.

[0036] The following are two specific embodiments:

[0037] Example 1: OAM beam generation and polarization conversion in the terahertz band

[0038] This embodiment designs an OAM metasurface structure working in the terahertz frequency band, which is used to simultaneously generate an OAM beam and convert the polarization direction of the incident wave. The detailed parameters of the structure are as follows:

[0039] Metal substrate: The bottom metal layer uses copper as the substrate, with a thickness of t1 = 0.2 μm and a conductivity of 5.96e + 7S / m, ensuring low loss, high conductivity and sufficient thickness to achieve total reflection of electromagnetic waves. Dielectric layer: A layer of polyimide (Pi) with a thickness of h = 6 μm is evenly covered on the copper metal substrate, with a dielectric constant of ε = 3.5 and a magnetic permeability of μ = 1 to reduce signal loss in the structure.

[0040] Top metal resonance layer: On the polyimide layer, two metal split rings arranged at a 45° angle are designed. The thickness of the top resonance layer is t2 = 0.2μm. The outer diameter (r1) and inner diameter (r2) of the split ring are 1.9μm and 1.6μm respectively. The length and width of the rectangular pattern connecting the two split rings are 4μm and 0.6μm respectively. The side lengths of the isosceles triangle are 1μm, Implementation steps:

[0041] 1. Model construction: Use CST software to create a 3D model of the metasurface, import the material parameters of copper and polyimide, manually draw the geometry of the basic unit, and set the structural parameters of the metal substrate, dielectric layer, and top resonant layer.

[0042] 2. Phase distribution calculation: The phase distribution is calculated by Python programming, and a spiral phase distribution is obtained under a given topological charge number l=-2 and a surface array size of 18*18.

[0043] 3. Periodic structure modeling: Combined with the calculated phase distribution, CST and Python co-simulation are used to build a periodic array. By adjusting the opening size of the split ring and the rotation angle of the top resonant pattern, phase compensation between the units is achieved to ensure that the overall structure can effectively generate OAM beams.

[0044] 4. Grid division and simulation: Manually adjust the grid division in CST and determine the number of grid cells at each wavelength as N to balance the calculation accuracy and resource requirements. Perform frequency domain simulation, and the simulation results show that the structure can generate a clear OAM beam in the terahertz frequency band and demonstrate a good polarization conversion effect.

[0045] 5. Result analysis: Through the post-processing function of CST, the reflection coefficient, phase and polarization conversion efficiency are analyzed. The results show that at the operating frequency, the co-polarization reflection coefficient and the cross-polarization reflection coefficient meet expectations, the phase distribution of the co-polarization reflection coefficient meets the requirements of OAM beam generation, and the polarization conversion efficiency is higher than 90% in the terahertz frequency band, and the bandwidth reaches 4.8THz.

[0046] Example 2: Application of OAM metasurface in stealth technology

[0047] This embodiment focuses on applying the OAM metasurface structure to stealth technology, and uses the characteristics of the OAM beam to achieve stealth effects in specific radar frequency bands. The structural parameters are the same as those in Embodiment 1, but the structure is optimized for stealth function:

[0048] Optimized design: To maximize the stealth performance, the rotation angle of the top resonant pattern and the size of the slit in this embodiment are further optimized to ensure that the metasurface can effectively scatter the incident terahertz radar waves, changing their phase and polarization, thereby forming an "invisibility cloak" under radar detection.

[0049] Simulation analysis: In CST software, the optimized structure is simulated to analyze its scattering pattern under the incident terahertz radar wave. The simulation results show that the structure can significantly change the propagation direction of the incident radar wave and reduce the radar scattering cross section.

[0050] Multi-angle testing: Further testing the stealth effect of the metasurface at different incident angles to ensure that it can stably change the phase and polarization of radar waves within a wide angle range, thus improving the practicality of stealth technology.

[0051] Environmental adaptability: Considering the use environment of stealth equipment, the water resistance and polarization sensitivity of the metasurface structure were tested and optimized. The results show that even in harsh environments, the structure can still maintain stable OAM beam generation and stealth functions.

[0052] The innovations and beneficial effects of the present invention are mainly reflected in the following aspects, which are not easily achieved by conventional technical means, and therefore they embody significant creativity and practicality:

[0053] 1. Material selection and cost control: Copper is selected as the metal resonance layer material, rather than the more expensive precious metals (such as gold or silver) commonly used in similar applications. The wide applicability and low cost of copper greatly reduce the manufacturing cost of OAM metasurface structures and facilitate industrial production. This is not an intuitive choice, because copper is not as conductive as precious metals and may have greater losses in the terahertz band, but after precise calculations and optimization, this invention proves that copper can also achieve high efficiency performance under certain conditions, which is a major innovation.

[0054] 2. Application in the terahertz band: Most OAM metasurface structure designs focus on microwave or near-infrared optical bands, while the present invention applies these principles to the terahertz band, which is a relatively blank field with great potential. The terahertz band is also known as the "terahertz blank". The successful implementation of the present invention provides new ideas for the design of devices in this blank band, and the structures working in this band are relatively rare, which reflects its innovation.

[0055] 3. Computational optimization of manual meshing: In CST simulation software, manual adjustment of the mesh size is used to reduce the demand for computing resources, ensuring simulation accuracy while avoiding excessive consumption of computing resources. This optimization method is non-intuitive and unconventional, and requires a deep understanding of the operating mechanism of the simulation software and computing resource management to be effectively implemented, which is especially important for the simulation of large-scale structures.

[0056] 4. Modeling method of Python combined with CST simulation: Through the joint use of Python programming and CST software, fast phase compensation and model construction of 18*18 periodic structure are realized. This cross-software collaborative technical method can greatly reduce modeling time, reduce design difficulty, and improve design efficiency. In traditional modeling, this step often requires a lot of manual adjustments, while the present invention uses automated means to significantly improve the design cycle and reliability.

[0057] 5. Multifunctional integration: The metasurface structure of the present invention can not only generate OAM beams, but also be used as a polarization converter, and achieve a polarization conversion efficiency of more than 90% in the terahertz band, with a bandwidth of 4.8THz. This multifunctional integrated design is very advantageous in practical applications because it can reduce the number of devices and simplify the complexity of the system. However, it is not easy to achieve this level of integration, and requires a deep understanding of material properties, structural design, and frequency response.

[0058] 6. Low profile and easy conformality: The structure of the present invention has a low profile and is easy to conform to various substrates, which facilitates the integration of OAM metasurfaces in different application scenarios. For example, it can be easily applied to curved or non-planar surfaces to enhance its stealth performance or signal transmission characteristics.

[0059] 7. Compactness and simplicity of design: Through the carefully designed sandwich structure and top resonant pattern, the dual functions of OAM beam generation and polarization regulation are realized, while the structure itself is not complicated and is easy to manufacture and integrate, which is in sharp contrast to the traditional OAM metasurface design which is complex and difficult to process, reflecting the creativity of the design.

[0060] These innovations and beneficial effects not only solve the problems existing in existing technologies, such as high cost, long design cycle, and single function, but also propose new solutions in the intersection of materials science, electromagnetics, and computer technology. They are of great significance for promoting the practical application of OAM metasurface technology in the terahertz frequency band.

[0061] The systems, devices, modules or units described in the above embodiments may be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0062] Computer readable media include permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. Information can be computer readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer readable media does not include temporary computer readable media (transitory media), such as modulated data signals and carrier waves.

[0063] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity 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, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0064] The above embodiments should be understood to be only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the contents of the present invention, technicians can make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A metasurface structure for generating an OAM beam, characterized in that: The structure includes basic units arranged in a periodic array, each basic unit is composed of a metal substrate, a dielectric layer and a top metal resonance layer, the top metal resonance layer includes two metal split rings arranged at a 45° angle and connected by metal arrows, wherein the metal material is copper, and the dielectric layer material is polyimide. The structure is designed to work in the terahertz frequency band, the metal substrate is mainly used to prevent electromagnetic waves from being transmitted, so that all electromagnetic waves passing through the dielectric layer are reflected to the resonance layer; the dielectric layer is mainly used to support the top resonance layer and provide The phase shift is: k0 is the wave vector constant in free space, ε d is the dielectric constant of the middle layer, and h is the thickness of the dielectric layer, According to the refraction angle of the incident electromagnetic wave, the top metal resonance layer mainly provides different geometric phases and propagation phases by rotating different angles and adjusting the slit width, thereby generating an OAM orbital angular momentum beam in the terahertz band.

2. The supersurface structure according to claim 1, characterized in that: The bottom metal layer and the middle dielectric layer of the periodic unit are rectangular structures with a side length of p=13.5 μm, the thickness of the bottom metal layer is t1=0.2 μm, and the thickness of the middle dielectric layer is h=6 μm.

3. The super surface structure according to claim 1, characterized in that: The thickness of the top metal resonance layer is t2=0.2 μm, the outer diameter (r1) and inner diameter (r2) of the split ring are 1.9 μm and 1.6 μm respectively; the length and width of the rectangular pattern connecting the two split rings are 4 μm and 0.6 μm respectively; the side lengths of the isosceles triangle are 1 μm, 4. The supersurface structure according to claim 1, characterized in that: The metal material is copper, with an electrical conductivity of 5.96e+7S / m. The material of the intermediate dielectric layer is polyimide Pi, with a dielectric constant of ε=3.5 and a magnetic permeability of μ=1.

5. A method for designing a metasurface structure for generating an OAM beam, characterized in that: The following steps are involved: (a) Calculate the phase distribution of the unit structure; (b) Use Python programming and CST commercial software for joint simulation to construct an OAM metasurface with an 18*18 periodic structure; (c) Manually adjust the grid size to reduce computing resource requirements and ensure simulation accuracy and computing efficiency.

6. The design method according to claim 5, characterized in that: The calculation of the phase distribution in step (a) is based on a given topological charge and surface array size, and the phase compensation between units is achieved by automatically distributing the size of the split ring opening and the rotation angle of the top resonant pattern in step (b).

7. The design method according to claim 5, characterized in that: The phase distribution of the calculation unit structure (a) specifically includes: according to the characteristics of the vortex beam, its phase distribution It is spiral, where l is the topological charge carried by the vortex beam, is the azimuth angle. According to the given l and the size of the surface array, the corresponding metasurface phase distribution can be calculated. After calculating the corresponding phase distribution, the 18*18 array structure can be constructed through Python and CST to generate the OAM beam structure.

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