An orbital angular momentum metasurface based on an ITO conductive layer and an implementation method thereof

Abstract

The application relates to the technical field of radio frequency antennas and electromagnetic super surface, and particularly discloses an orbital angular momentum super surface based on an ITO conductive layer and an implementation method, wherein the super surface is composed of a plurality of transmission type super surface units arranged in a two-dimensional array, each transmission type super surface unit comprises a horizontal parallel rectangular grating, four layers of transparent glass substrates and a vertical parallel rectangular grating which are sequentially and layerwisely arranged, the upper surfaces of the second and fourth layers of transparent glass substrates are provided with square frame structures, the upper surface of the third layer of transparent glass substrates is provided with a square frame and a modified I-shaped resonance unit; the rotation angle of the modified I-shaped resonance unit in each unit is adjusted according to the phase compensation value required by each transmission type super surface unit, so that a composite phase distribution is formed on the aperture surface of the two-dimensional array. The application has the advantages of optical transparency, wideband phase control capability, polarization conversion capability and multi-beam orbital angular momentum beam generation capability, and is suitable for intelligent glass, transparent window communication and multi-dimensional multiplexing wireless communication scenes.

Description

Technical Field

[0001] This invention relates to the field of radio frequency antennas and electromagnetic metasurfaces, and in particular to an orbital angular momentum metasurface based on an ITO conductive layer and its implementation method. Background Technology

[0002] As wireless communication technology develops towards higher speeds, larger capacities, lower latency, and multidimensional multiplexing, traditional communication resources, which rely on dimensions such as frequency, time, space, and polarization, are becoming increasingly scarce. Orbital angular momentum beams, due to their helical phase wavefront and mode orthogonality, can carry multiple independent information channels within the same frequency band, providing new degrees of freedom for increasing the capacity of wireless communication systems. Currently, orbital angular momentum beams are typically generated using helical phase plates, phased arrays, reflective arrays, or transmissive metasurface arrays. Among these, metasurfaces, with their advantages of low profile, easy integration, and flexible wavefront manipulation, have become an important technological approach for generating and controlling orbital angular momentum electromagnetic waves.

[0003] However, existing orbital angular momentum metasurface antennas still face several limitations. Firstly, traditional metallic metasurfaces are mostly made of opaque conductive materials such as copper and aluminum. While they possess good electromagnetic control capabilities, their optical opacity limits their application in smart glass, transparent windows, automotive windshields, transparent communication terminals, and integrated indoor-outdoor communication scenarios. For future transparent, covert, and environmentally integrated wireless systems, traditional opaque structures struggle to meet the demands of integrating visual transparency with electromagnetic functionality.

[0004] Secondly, while some existing transparent antennas or transparent metasurfaces can achieve certain electromagnetic control functions, they are mostly concentrated in single-beam, narrowband, or reflective operating modes, making it difficult to simultaneously achieve broadband operation, multi-beam orbital angular momentum generation, high transmission efficiency, and high optical transparency. Especially in the millimeter-wave band, the small unit size and high processing precision requirements mean that the sheet resistance, conductivity, film thickness, and substrate loss of the transparent conductive material significantly affect the transmission amplitude, phase control range, and polarization conversion efficiency, further increasing the design difficulty of transparent orbital angular momentum transmission arrays.

[0005] Furthermore, the generation of orbital angular momentum beams places high demands on the continuity of phase distribution and the phase coverage capability of the unit cells. If the metasurface unit cells cannot provide a stable 0° to 360° phase tuning range within the target frequency band, it can easily lead to problems such as helical phase distortion, beam splitting, reduced mode purity, and unclear far-field hollow intensity distribution. For multi-beam orbital angular momentum systems, the phase distributions corresponding to different beam directions and different topological charges need to be superimposed, which further increases the requirements for the broadband phase response, transmission amplitude consistency, and polarization conversion stability of the metasurface unit cells.

[0006] Furthermore, existing multi-beam orbital angular momentum structures often rely on complex feeding networks, multi-port excitation, or thick three-dimensional structures, which not only increases the system size and fabrication complexity but also hinders integration into transparent platforms. Especially in transparent communication scenarios, antennas not only need stable electromagnetic radiation performance but also require maintaining good optical transmittance and structural flatness as much as possible. How to realize broadband, high-efficiency, multi-beam, and engineerable orbital angular momentum transmissive metasurfaces on transparent substrates remains a pressing technical challenge. Summary of the Invention

[0007] The purpose of this invention is to provide a broadband multi-beam orbital angular momentum transmissive metasurface and its array design method based on a glass-ITO transparent conductive substrate. This metasurface employs a collaborative design of a transparent glass substrate and an indium tin oxide transparent conductive film, achieving transmission phase modulation, polarization conversion, and multi-beam orbital angular momentum beam generation for millimeter-wave electromagnetic waves while ensuring high optical transparency. By introducing orthogonal transparent gratings, square frame coupling structures, and modified I-shaped resonant units into the transmissive metasurface units, the units possess stable transmission amplitude response, continuous phase modulation capability, and good polarization conversion performance over a wide frequency range. Furthermore, based on the orbital angular momentum phase distribution and multi-beam phase superposition principle, multiple metasurface units are arranged in an array according to preset phase compensation values, thereby realizing broadband multi-beam orbital angular momentum electromagnetic wave radiation on a transparent platform.

[0008] To achieve the above objectives, the present invention provides an orbital angular momentum metasurface based on an ITO conductive layer, wherein the orbital angular momentum metasurface is composed of transmissive metasurface units arranged in a two-dimensional array; each transmissive metasurface unit includes a first transparent grating layer, a first transparent glass substrate, a second transparent glass substrate, a third transparent glass substrate, a fourth transparent glass substrate, and a second transparent grating layer, which are sequentially bonded together from top to bottom. The surfaces of the second, third, and fourth transparent glass substrates are all provided with transparent conductive patterns; the transparent conductive patterns, the first transparent grating layer, and the second transparent grating layer are composed of indium tin oxide transparent conductive films; the transparent conductive patterns include a square frame structure and a modified I-shaped resonant unit; The transmissive metasurface units are arranged according to different phase compensation values.

[0009] Preferably, the first transparent grating layer is composed of several parallel horizontal rectangular conductive strips; the second transparent grating layer is composed of several parallel vertical rectangular conductive strips; the vertical rectangular conductive strips in the second transparent grating layer are orthogonal to the horizontal rectangular conductive strips in the first transparent grating layer.

[0010] Preferably, the upper surfaces of the second and fourth transparent glass substrates are provided with square frame structures, and the upper surface of the third transparent glass substrate is provided with square frame structures and modified I-shaped resonant units. Preferably, the square frame structure includes a square outer frame and a square inner frame, with an annular conductive region formed between the square outer frame and the square inner frame; the central axis of the square frame structure is the same as the central axis of the transmissive metasurface unit.

[0011] Preferably, the improved I-shaped resonant unit includes a main resonant arm and end coupling arms respectively disposed at both ends of the main resonant arm; The main resonant arm has a rectangular structure, and the direction in which the main resonant arm extends is the first direction. The end coupling arm extends from the vertex of the main resonant arm in the second direction. The first direction and the second direction are perpendicular to each other. The path of the end coupling arm is an arc-shaped region. The arc-shaped region is the area formed between two circles with the same center and radii R1 and R2 respectively on the extension line of the first direction, where R1 < R2. The value of R2 is the distance from the center of the circle to the nearest vertex of the rectangular structure of the main resonant arm. The central axis of the improved I-shaped resonant unit is the same as the central axis of the transmissive metasurface unit; the improved I-shaped resonant unit is rotated around the central axis of the transmissive metasurface unit; the rotation angle of the improved I-shaped resonant unit is set according to the preset phase compensation value of the transmissive metasurface unit to which it is located.

[0012] Preferably, the preset phase compensation value includes a feed space phase compensation term and an orbital angular momentum spiral phase term; the feed space phase compensation term is used to compensate for the propagation path difference between the feed and each transmissive metasurface unit, and the orbital angular momentum spiral phase term is determined by the topological charge number and the azimuth angle, and is used to form an orbital angular momentum electromagnetic wave with a target topological charge number.

[0013] Preferably, when multiple orbital angular momentum beams need to be generated, the phase distributions corresponding to multiple different propagation directions or different topological charges are superimposed, and the rotation angle of the modified I-shaped resonant unit in each transmissive metasurface unit is determined according to the composite phase distribution after superposition. The plurality of orbital angular momentum beams include two or more off-axis beams deflected relative to the normal direction of the two-dimensional array, each off-axis beam carrying an orbital angular momentum topological charge of a different sign or order.

[0014] Preferably, the transparent glass substrate has a relative permittivity of 4.5 and a loss tangent of 0.0071; the indium tin oxide transparent conductive film has a thickness of 220±50nm and a sheet resistance of 6Ω. The periodic dimension of the transmissive metasurface unit is 5 mm, and the thickness of the first transparent glass substrate, the second transparent glass substrate, the third transparent glass substrate and the fourth transparent glass substrate is 1 mm.

[0015] Preferably, the two-dimensional array is a 40×40 element array with an array aperture of 200mm×200mm and a distance of 300mm between the feed source and the array aperture surface.

[0016] This invention also provides a method for realizing an orbital angular momentum metasurface based on an ITO conductive layer, characterized by comprising the following steps: S1. Determine the operating frequency band, unit cell period, array aperture, feed position, target beam direction, and target orbital angular momentum topological charge of the transmissive metasurface. S2. Design a transmissive metasurface unit consisting of a first transparent grating layer, a second transparent grating layer, a transparent glass substrate, a square frame structure, and a modified I-shaped resonant unit; S3. Change the rotation angle of the improved I-shaped resonant unit, establish the mapping relationship between the rotation angle and the transmission phase, and form a transmission phase control unit library; S4. Calculate the spatial phase compensation term from the feed source to each transmissive metasurface unit based on the spatial positional relationship between the feed source and the aperture surface of the two-dimensional array. S5. Calculate the orbital angular momentum spiral phase term based on the target orbital angular momentum topological charge and the location of each transmissive metasurface unit; S6. When it is necessary to generate multi-beam orbital angular momentum radiation, the phase distributions corresponding to multiple target beams are superimposed to obtain a composite phase distribution; the composite phase distribution includes at least the phase distributions corresponding to two target orbital angular momentum beams, and each target orbital angular momentum beam corresponds to a different propagation direction or a different sign of orbital angular momentum topological charge. S7. Determine the rotation angle of the modified I-shaped resonant unit in each transmissive metasurface unit based on the composite phase distribution. S8. Arrange the transmissive metasurface units according to the determined rotation angle to form a broadband multi-beam orbital angular momentum transmissive metasurface array.

[0017] The present invention employs the above-mentioned orbital angular momentum metasurface based on an ITO conductive layer and its implementation method, and has the following beneficial effects: (1) The present invention combines a transparent glass substrate with an ITO transparent conductive film to construct a transmissive metasurface that has both electromagnetic control function and optical transparency. Compared with traditional metal metasurfaces, it can maintain a good visual transparency effect while achieving millimeter wave front control, and is suitable for smart windows, transparent communication terminals and environmentally integrated wireless communication scenarios. (2) In this invention, a first transparent grating layer and a second transparent grating layer, which are orthogonal to each other, are set in the metasurface unit. The polarization state of electromagnetic waves is controlled by the synergistic effect of the upper and lower grating layers. This structure is beneficial to enhance the cross-polarization transmission component, improve the polarization conversion capability of the transmissive metasurface, and provide a basis for the stable formation of orbital angular momentum beams. (3) The present invention introduces an auxiliary coupling structure consisting of multiple square frame structures between transparent glass substrates and designs it in conjunction with the improved I-shaped resonant unit. The square frame structure can serve as a parasitic coupling resonant structure, enhancing the near-field coupling between layers, improving the transmission amplitude and phase response consistency of the unit in a wide frequency range, thereby improving the broadband working capability of the metasurface; (4) This invention achieves transmission phase modulation by rotating the modified I-shaped resonant unit, which can obtain continuous phase coverage over a wide frequency band. This method has a simple structure and clear modulation, which facilitates the establishment of a phase unit library and array design, and helps to reduce the design complexity of multi-beam orbital angular momentum transmission arrays; (5) Based on the principle of feed phase compensation and spiral phase superposition of orbital angular momentum, this invention assigns independent phase values ​​to each transmissive metasurface unit in the two-dimensional array, so that the metasurface forms an orbital angular momentum beam with a spiral phase wavefront on the transmission side. By further superimposing the phase distribution of multiple target beams, the simultaneous radiation of orbital angular momentum of multiple beams can be realized, thereby improving the space reuse capability and communication capacity; (6) The present invention adopts a planar, multi-layer transparent dielectric stacked structure, which is compact and easy to process, bond and array expand. Compared with orbital angular momentum antennas that rely on complex feeding networks or three-dimensional metal structures, the present invention is more suitable for large-aperture array integration in transparent scenarios and has good engineering implementation value; (7) The present invention can take into account broadband characteristics, multi-beam orbital angular momentum generation, polarization conversion and optical transparency in millimeter-wave transparent communication scenarios, and can provide a new low-profile and easy-to-integrate design scheme for future high-speed wireless communication, smart glass communication, vehicle-to-everything transparent window communication and multi-dimensional multiplexing systems. Attached Figure Description

[0018] Figure 1 This is an exploded view of a transmission metasurface unit in an orbital angular momentum metasurface based on an ITO conductive layer according to an embodiment of the present invention; wherein, 1-1 is a first transparent grating layer, 1-2 is a second transparent grating layer, 2-1 is a first transparent glass substrate, 2-2 is a second transparent glass substrate, 2-3 is a third transparent glass substrate, 2-4 is a fourth transparent glass substrate, 3-1 is a first ITO square frame structure, 3-2 is a second ITO square frame structure, 3-3 is a third ITO square frame structure, and 4 is a modified I-shaped resonant unit; Figure 2This is a schematic diagram of the structure of a transmissive metasurface unit in an orbital angular momentum metasurface based on an ITO conductive layer according to an embodiment of the present invention; wherein, (a) is a schematic diagram of the overall structure of the transmissive metasurface unit after assembly, (b) is a schematic diagram of the structure of the first transparent grating layer, (c) is a schematic diagram of the structure of the second transparent grating layer, (d) is a schematic diagram of the modified I-shaped resonant unit and its rotation angle definition, and (e) is a schematic diagram of the ITO square frame structure. Figure 3 This is a schematic diagram of a two-dimensional array structure of an orbital angular momentum metasurface based on an ITO conductive layer according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the multi-beam orbital angular momentum phase distribution and composite phase modulation of an orbital angular momentum metasurface based on an ITO conductive layer according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the spatial relationship between the feed and the transmission metasurface array of an orbital angular momentum metasurface based on an ITO conductive layer, and the multi-beam orbital angular momentum radiation according to an embodiment of the present invention. Figure 6 This is a schematic diagram of the transmission amplitude and transmission phase response of a transmission metasurface unit based on an ITO conductive layer orbital angular momentum metasurface at different rotation angles according to an embodiment of the present invention. Figure 7 This is a schematic diagram of the phase coverage capability and polarization conversion performance of a transmission metasurface unit based on an orbital angular momentum metasurface with an ITO conductive layer according to an embodiment of the present invention. Figure 8 This is a comparative schematic diagram of the influence of a square frame structure of an orbital angular momentum metasurface based on an ITO conductive layer on the broadband response of a transmissive metasurface unit according to an embodiment of the present invention; wherein, (a) is the surface current density distribution with and without the square frame structure at three typical frequency points of 17 GHz, 22 GHz and 27 GHz, (b) is the response curve of the transmission phase of the transmissive metasurface unit under different structural states as a function of frequency, and (c) is the response curve of the transmission amplitude of the transmissive metasurface unit under different structural states as a function of frequency. Figure 9 This is a schematic diagram of the far-field amplitude and phase distribution of a multi-beam orbital angular momentum beam generated by a transmissive metasurface array based on an ITO conductive layer according to an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0020] This invention discloses an orbital angular momentum metasurface based on an ITO conductive layer. This transmissive orbital angular momentum metasurface is constructed from a multilayer transparent glass substrate and an indium tin oxide (ITO) transparent conductive thin film. Through the synergistic effect of a first transparent grating layer, a second transparent grating layer, multiple ITO (indium tin oxide) square frame structures, and a modified I-shaped resonant unit, it achieves polarization conversion of incident electromagnetic waves, transmission phase modulation, and multi-beam orbital angular momentum beam generation. In this embodiment, the glass-ITO transparent transmissive array formed by the orbital angular momentum metasurface is used for multi-beam OAM wavefront modulation in the millimeter-wave band, while maintaining both optical transparency and electromagnetic modulation performance. The orbital angular momentum metasurface consists of transmissive metasurface units arranged in a two-dimensional array, with the transmissive metasurface units arranged according to different phase compensation values.

[0021] like Figure 1 As shown, the transmissive metasurface unit includes, from top to bottom, a first transparent grating layer 1-1, a first transparent glass substrate 2-1, a first ITO square frame structure 3-1, a second transparent glass substrate 2-2, a modified I-shaped resonant unit 4, a second ITO square frame structure 3-2, a third transparent glass substrate 2-3, a third ITO square frame structure 3-3, a fourth transparent glass substrate 2-4, and a second transparent grating layer 1-2, all vertically bonded together.

[0022] The first transparent grating layer 1-1, the second transparent grating layer 1-2, the first ITO square frame structure 3-1, the second ITO square frame structure 3-2, the third ITO square frame structure 3-3, and the modified I-shaped resonant unit 4 are all made of ITO transparent conductive film. The ITO transparent conductive film has conductivity and visible light transmittance, enabling the metasurface unit to maintain transparency while achieving millimeter-wave electromagnetic wave modulation. The first transparent glass substrate 2-1, the second transparent glass substrate 2-2, the third transparent glass substrate 2-3, and the fourth transparent glass substrate 2-4 serve as transparent dielectric support layers, supporting the ITO conductive patterns of each layer and providing a transmission propagation path for electromagnetic waves.

[0023] The transparent glass substrate can be made of low-loss glass material, with a relative permittivity of 4.5 and a loss tangent of 0.0071. The thickness of the ITO transparent conductive film can be set to 220±50 nm, with a sheet resistance of 6 Ω. The above parameters are only preferred embodiments. Those skilled in the art can adaptively adjust the glass substrate thickness, ITO film thickness, sheet resistance, and conductive pattern size according to the target operating frequency band, transparency requirements, processing technology, and transmission efficiency requirements.

[0024] like Figure 2 As shown in the figure, this embodiment further illustrates the structural composition of the transmissive metasurface unit. Figure 2 (a) is a schematic diagram of the overall structure after the transmission metasurface unit is assembled. w This is the side length of the transmissive metasurface unit. After assembly, the first transparent glass substrate 2-1, the second transparent glass substrate 2-2, the third transparent glass substrate 2-3, and the fourth transparent glass substrate 2-4 are sequentially bonded along the thickness direction, with ITO transparent conductive patterns located on the respective transparent glass substrate surfaces, thereby forming a multilayer transmissive electromagnetic control structure.

[0025] Figure 2 (b) is a schematic diagram of the structure of the first transparent grating layer 1-1. t 1 represents the width of the horizontal rectangular ITO conductive strip. t 2 represents the spacing between the horizontal rectangular ITO conductive strips; the first transparent grating layer 1-1 is composed of several parallel horizontal rectangular ITO conductive strips, used for polarization selection of incident electromagnetic waves. Figure 2 (c) is a schematic diagram of the structure of the second transparent grating layer 1-2; the second transparent grating layer 1-2 is composed of several parallel vertical rectangular ITO conductive strips, and the vertical rectangular ITO conductive strips in the second transparent grating layer 1-2 are orthogonally arranged with the horizontal rectangular ITO conductive strips in the first transparent grating layer 1-1. Through the combined effect of the upper and lower orthogonal transparent gratings, the cross-polarization transmission component can be enhanced, enabling the incident electromagnetic wave to complete polarization conversion during transmission.

[0026] Figure 2 (d) is a schematic diagram of the improved I-shaped resonant unit 4 and its rotation angle definition. R 1 is the inner radius of the arc region. R 2 represents the outer radius of the arc region. t3 represents the width of the main resonant arm. The improved I-shaped resonant unit 4 includes a main resonant arm, a first end coupling arm, and a second end coupling arm. The first and second end coupling arms are respectively located at both ends of the main resonant arm and intersect with it, enabling the improved I-shaped resonant unit 4 to form a transmission-type resonant structure with anisotropic electromagnetic response. The improved I-shaped resonant unit 4 can rotate angularly about the center of the transmission metasurface unit; let the rotation angle of the improved I-shaped resonant unit 4 be θ. By changing the rotation angle θ, the phase response of the transmitted electromagnetic wave can be changed. Multiple improved I-shaped resonant units 4 with different rotation angles θ can form a transmission phase modulation unit library for continuous phase modulation.

[0027] Figure 2 (e) is a schematic diagram of the ITO square frame structure. d The distance between the outer and inner borders is defined as the spacing between the outer and inner borders. The first ITO square border structure 3-1, the second ITO square border structure 3-2, and the third ITO square border structure 3-3 can all adopt this square border structure. The ITO square border structure includes an outer border and an inner border, forming an annular transparent conductive region between the outer and inner borders. The first ITO square border structure 3-1, the second ITO square border structure 3-2, and the third ITO square border structure 3-3 are correspondingly arranged along the central axis of the metasurface unit (the central axis is the same), and together with the modified I-shaped resonant unit 4, constitute the transmission phase modulation part. In this embodiment, the ITO square border structure is used as an auxiliary coupling structure, its function being to enhance the near-field coupling between the modified I-shaped resonant unit 4 and the adjacent transparent conductive layer, improve the transmission amplitude consistency and phase continuity of the unit over a wide frequency range, thereby improving the broadband phase modulation capability of the metasurface unit.

[0028] like Figure 3 As shown, the orbital angular momentum metasurface in this embodiment is composed of multiple transmissive metasurface units arranged in a two-dimensional array. Each transmissive metasurface unit has a different position on the array aperture surface, and the corresponding phase compensation value is also different. By adjusting the rotation angle θ of the modified I-shaped resonant unit 4 in each unit, a preset spatial phase distribution can be formed on the entire array aperture surface.

[0029] A two-dimensional array can be represented as consisting of M×N transmissive metasurface units, where M and N are both positive integers. In this embodiment, the two-dimensional array adopts a 40×40 unit arrangement; the array aperture, unit period, and feed distance can be designed according to the target operating frequency band and beam direction. In this embodiment, the period dimension of the transmissive metasurface unit is 5mm, and the thickness of the first, second, third, and fourth transparent glass substrates is 1mm. The above array size is only one embodiment, and the present invention is not limited to a specific number of arrays.

[0030] like Figure 4 The diagram illustrates the multi-beam orbital angular momentum phase distribution and composite phase control in this embodiment. The orbital angular momentum beam has a helical phase wavefront, and its phase distribution is related to the target topological charge and the azimuth angle on the array aperture surface. When a single orbital angular momentum beam needs to be generated, the phase compensation value required for each transmissive metasurface element is calculated based on the target topological charge, feed position, array element position, and operating frequency. The phase compensation value includes a feed space phase compensation term and an orbital angular momentum helical phase term. The feed space phase compensation term is used to compensate for the propagation path difference between the feed and different array elements, while the orbital angular momentum helical phase term is used to form a helical phase wavefront with the target topological charge on the transmission side. When multiple orbital angular momentum beams need to be generated simultaneously, the phase distributions corresponding to multiple target beams can be calculated separately, and then the phase distributions are superimposed to obtain the composite phase distribution on the array aperture surface. Subsequently, the rotation angle θ of the modified I-shaped resonant element 4 in each transmissive metasurface element is determined based on the composite phase distribution. Multiple orbital angular momentum beams include two or more off-axis beams deflected relative to the normal direction of the two-dimensional array, each off-axis beam carrying an orbital angular momentum topological charge of a different sign.

[0031] like Figure 5 The diagram illustrates the spatial relationship between the feed and the transmissive metasurface array, as well as a schematic of multi-beam orbital angular momentum radiation. The feed is positioned on one side of the transmissive metasurface array to radiate incident electromagnetic waves. After being modulated by the transmissive metasurface array, the incident electromagnetic waves form multiple off-axis orbital angular momentum beams on the other side of the array. In a preferred embodiment, the multiple orbital angular momentum beams include at least a first orbital angular momentum beam and a second orbital angular momentum beam. The first and second orbital angular momentum beams can be deflected in different directions relative to the array normal, and each carries orbital angular momentum topological charges of different signs or orders. Since orbital angular momentum modes with different topological charges have mutually distinguishable phase distribution characteristics, this structure can be used to improve the spatial multiplexing capability of wireless communication systems.

[0032] like Figure 6 The diagram shows the transmission amplitude and transmission phase response of the transmissive metasurface unit in this embodiment under different rotation angles. By changing the rotation angle θ of the modified I-shaped resonant unit 4, the transmissive metasurface unit can obtain different transmission phase responses; simultaneously, within the target frequency band, the transmission amplitude remains within a range suitable for array wavefront synthesis. This result demonstrates that the rotation angle θ of the modified I-shaped resonant unit 4 can be used as the main structural parameter for array phase assignment.

[0033] like Figure 7The diagram illustrates the phase coverage capability and polarization conversion performance of the transmissive metasurface unit in this embodiment. Multiple transmission phases corresponding to different rotation angles θ can cover a range from 0° to 360°, thus meeting the requirement of the orbital angular momentum beam for a complete helical phase distribution. Simultaneously, the transmissive metasurface unit can maintain high polarization conversion capability within the target frequency band, reducing the impact of co-polarization leakage on the mode purity of the orbital angular momentum beam.

[0034] like Figure 8 As shown in the figure, this embodiment illustrates the influence of the square frame structure on the broadband electromagnetic response of the transmissive metasurface unit. Figure 8 (a) Comparison of surface current density distribution at three typical frequency points of 17 GHz, 22 GHz and 27 GHz. Among them, the transmissive metasurface unit with square frame structure forms obvious coupling current distribution in both square frame region and modified I-shaped resonant unit region, indicating that the square frame structure can participate in the unit resonance process and enhance the near-field coupling between the modified I-shaped resonant unit and adjacent conductive patterns. Without square frame structure, the surface current is mainly concentrated in the modified I-shaped resonant unit body, the interlayer coupling path is relatively simple, and the broadband response control capability is weak.

[0035] Figure 8 (b) and Figure 8 (c) Further, comparative curves of the transmission phase response and transmission amplitude response of the transmission metasurface unit as a function of frequency are presented. The phase response shows that, within the target operating frequency band, the transmission phase can maintain continuous variation over a relatively wide frequency range after setting the square frame structure, which is beneficial for achieving the broadband phase compensation required for the orbital angular momentum array. The transmission amplitude response shows that, after setting the square frame structure, the unit can maintain a high and relatively stable transmission amplitude within the target frequency band, thus helping to reduce the impact of array aperture amplitude fluctuations on the quality of the multi-beam orbital angular momentum beam.

[0036] Therefore, the square frame structure is not simply a transparent conductive boundary, but rather works together with the improved I-shaped resonant unit as an auxiliary coupling resonant structure to enhance interlayer electromagnetic coupling, improve transmission amplitude consistency, and enhance the ability to continuously control the transmission phase over a wide frequency range.

[0037] like Figure 9The diagram illustrates the far-field amplitude and phase distribution of the multi-beam orbital angular momentum electromagnetic wave generated by the transmissive metasurface array in this embodiment. The far-field amplitude distribution shows that multiple off-axis radiation beams are formed on the transmission side of the array, and each beam exhibits a typical low-field-strength region near its local center. The far-field phase distribution shows that a continuously rotating spiral phase structure forms around each off-axis beam, with a phase singularity appearing near the center of the corresponding beam. This result demonstrates that the transmissive metasurface array can achieve multi-beam orbital angular momentum electromagnetic wave radiation through a composite phase distribution.

[0038] In this embodiment, when the transmissive metasurface unit is working, the incident electromagnetic wave first passes through the first transparent grating layer 1-1, which performs polarization selection on the incident electromagnetic wave; then the electromagnetic wave enters the phase modulation region composed of a multilayer transparent glass substrate and an ITO transparent conductive pattern. The first ITO square frame structure 3-1, the second ITO square frame structure 3-2, the third ITO square frame structure 3-3, and the modified I-shaped resonant unit 4 work together to modulate the amplitude and phase of the transmitted electromagnetic wave; finally, after the electromagnetic wave passes through the second transparent grating layer 1-2, it forms a cross-polarized transmission component, and under the combined phase modulation effect of the entire array aperture surface, it forms a target multi-beam orbital angular momentum beam.

[0039] An embodiment of a method for realizing an orbital angular momentum metasurface based on an ITO conductive layer includes the following steps: The first step is to determine the operating frequency band, unit cell period, array aperture, feed position, target beam direction, and target orbital angular momentum topological charge of the metasurface. The second step is to design a transmissive metasurface unit consisting of a first transparent grating layer 1-1, a second transparent grating layer 1-2, a transparent glass substrate, an ITO square frame structure, and a modified I-shaped resonant unit 4. The third step is to change the rotation angle θ of the improved I-shaped resonant unit 4, establish the mapping relationship between the rotation angle θ and the transmission phase, and form a transmission phase modulation unit library. The fourth step is to calculate the spatial phase compensation term from the feed to each transmissive metasurface unit based on the spatial positional relationship between the feed and the array aperture surface. The fifth step is to calculate the orbital angular momentum spiral phase term based on the target orbital angular momentum topological charge and the location of the array elements. The sixth step is to superimpose the phase distributions of multiple target beams to obtain a composite phase distribution when it is necessary to generate multi-beam orbital angular momentum radiation. Step 7: Determine the rotation angle θ of the modified I-shaped resonant unit 4 in each transmissive metasurface unit based on the composite phase distribution. The eighth step is to arrange the transmissive metasurface units according to the determined rotation angle θ to form a broadband multi-beam orbital angular momentum transmissive metasurface array.

[0040] In this embodiment, the orthogonal arrangement of the first transparent grating layer 1-1 and the second transparent grating layer 1-2 is beneficial to improving the polarization conversion capability of the transmitted electromagnetic wave; the multi-layer coupling arrangement of the first ITO square frame structure 3-1, the second ITO square frame structure 3-2, and the third ITO square frame structure 3-3 is beneficial to broadening the transmission phase modulation bandwidth; the rotational arrangement of the improved I-shaped resonant unit 4 is beneficial to achieving continuous phase adjustment; the combination of the transparent glass substrate and the ITO transparent conductive film is beneficial to maintaining optical transparency while achieving millimeter-wave electromagnetic wave modulation. Therefore, the present invention can realize broadband, multi-beam, orbital angular momentum beam generation and transparent integration.

[0041] Therefore, this invention employs the aforementioned orbital angular momentum metasurface based on an ITO conductive layer and its implementation method. It uses a multilayer transparent dielectric substrate and a transparent conductive thin film to form a transmissive metasurface unit, and further arranges multiple transmissive metasurface units in an array according to a preset composite phase distribution. This enables multi-beam orbital angular momentum electromagnetic wave radiation on a transparent platform. Compared to traditional opaque metallic metasurfaces or multi-beam antenna structures relying on complex feeding networks, this invention offers advantages such as planar structure, transparency, ease of integration, flexible phase modulation, and suitability for array expansion.

[0042] It is worth noting that all contents not described in detail in this invention are existing technologies and are well known to those skilled in the art.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An orbital angular momentum metasurface based on an ITO conductive layer, characterized in that, The orbital angular momentum metasurface is composed of transmissive metasurface units arranged in a two-dimensional array; each transmissive metasurface unit includes a first transparent grating layer, a first transparent glass substrate, a second transparent glass substrate, a third transparent glass substrate, a fourth transparent glass substrate, and a second transparent grating layer, which are sequentially bonded together from top to bottom. The upper surfaces of the second, third, and fourth transparent glass substrates are all provided with transparent conductive patterns; the transparent conductive patterns, the first transparent grating layer, and the second transparent grating layer are composed of indium tin oxide transparent conductive films; the transparent conductive patterns include a square frame structure and a modified I-shaped resonant unit; The transmissive metasurface units are arranged according to different phase compensation values; The upper surfaces of the second and fourth transparent glass substrates are provided with square frame structures, and the upper surface of the third transparent glass substrate is provided with square frame structures and a modified I-shaped resonant unit. The improved I-shaped resonant unit includes a main resonant arm and end coupling arms respectively disposed at both ends of the main resonant arm; The main resonant arm has a rectangular structure, and the direction in which the main resonant arm extends is the first direction. The end coupling arm extends from the vertex of the main resonant arm in the second direction. The first direction and the second direction are perpendicular to each other. The path of the end coupling arm is an arc-shaped region. The arc-shaped region is the area formed between two circles with the same center and radii R1 and R2 respectively on the extension line of the first direction, where R1 < R2. The value of R2 is the distance from the center of the circle to the nearest vertex of the rectangular structure of the main resonant arm. The central axis of the improved I-shaped resonant unit is the same as the central axis of the transmissive metasurface unit; the improved I-shaped resonant unit is rotated around the central axis of the transmissive metasurface unit; the rotation angle of the improved I-shaped resonant unit is set according to the preset phase compensation value of the transmissive metasurface unit to which it is located.

2. The orbital angular momentum metasurface based on an ITO conductive layer according to claim 1, characterized in that, The first transparent grating layer is composed of several parallel horizontal rectangular conductive strips; the second transparent grating layer is composed of several parallel vertical rectangular conductive strips; the vertical rectangular conductive strips in the second transparent grating layer are orthogonal to the horizontal rectangular conductive strips in the first transparent grating layer.

3. The orbital angular momentum metasurface based on an ITO conductive layer according to claim 1, characterized in that, The square frame structure includes a square outer frame and a square inner frame, with an annular conductive region formed between the square outer frame and the square inner frame; the central axis of the square frame structure is the same as the central axis of the transmissive metasurface unit.

4. The orbital angular momentum metasurface based on an ITO conductive layer according to claim 3, characterized in that, The preset phase compensation value includes a feed space phase compensation term and an orbital angular momentum spiral phase term. The feed space phase compensation term is used to compensate for the propagation path difference between the feed and each transmissive metasurface unit. The orbital angular momentum spiral phase term is determined by the topological charge number and the azimuth angle and is used to form an orbital angular momentum electromagnetic wave with a target topological charge number.

5. The orbital angular momentum metasurface based on an ITO conductive layer according to claim 4, characterized in that, When multiple orbital angular momentum beams are required, the phase distributions corresponding to multiple different propagation directions or different topological charges are superimposed, and the rotation angle of the modified I-shaped resonant unit in each transmissive metasurface unit is determined based on the composite phase distribution after superposition. The plurality of orbital angular momentum beams include two or more off-axis beams deflected relative to the normal direction of the two-dimensional array, each off-axis beam carrying an orbital angular momentum topological charge of a different sign or order.

6. The orbital angular momentum metasurface based on an ITO conductive layer according to claim 1, characterized in that, The transparent glass substrate has a relative permittivity of 4.5 and a loss tangent of 0.0071; the indium tin oxide transparent conductive film has a thickness of 220±50nm and a sheet resistance of 6Ω. The periodic dimension of the transmissive metasurface unit is 5 mm, and the thickness of the first transparent glass substrate, the second transparent glass substrate, the third transparent glass substrate and the fourth transparent glass substrate is 1 mm.

7. The orbital angular momentum metasurface based on an ITO conductive layer according to claim 1, characterized in that, The two-dimensional array is a 40×40 element array with an array aperture of 200mm×200mm and a distance of 300mm between the feed source and the array aperture surface.

8. A method for realizing an orbital angular momentum metasurface based on an ITO conductive layer as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Determine the operating frequency band, unit cell period, array aperture, feed position, target beam direction, and target orbital angular momentum topological charge of the transmissive metasurface. S2. Design a transmissive metasurface unit consisting of a first transparent grating layer, a second transparent grating layer, a transparent glass substrate, a square frame structure, and a modified I-shaped resonant unit; S3. Change the rotation angle of the improved I-shaped resonant unit, establish the mapping relationship between the rotation angle and the transmission phase, and form a transmission phase control unit library; S4. Calculate the spatial phase compensation term from the feed source to each transmissive metasurface unit based on the spatial positional relationship between the feed source and the aperture surface of the two-dimensional array. S5. Calculate the orbital angular momentum spiral phase term based on the target orbital angular momentum topological charge and the location of each transmissive metasurface unit; S6. When it is necessary to generate multi-beam orbital angular momentum radiation, the phase distributions corresponding to multiple target beams are superimposed to obtain a composite phase distribution; the composite phase distribution includes at least the phase distributions corresponding to two target orbital angular momentum beams, and each target orbital angular momentum beam corresponds to a different propagation direction or a different sign of orbital angular momentum topological charge. S7. Determine the rotation angle of the modified I-shaped resonant unit in each transmissive metasurface unit based on the composite phase distribution. S8. Arrange the transmissive metasurface units according to the determined rotation angle to form a broadband multi-beam orbital angular momentum transmissive metasurface array.

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