Dual-spectrum unit structure, multi-dimensional multiplexing metasurface and design method

Abstract

The invention relates to the technical field of metasurface electromagnetic regulation and control, in particular to a double-spectrum unit structure, a multi-dimensional multiplexing metasurface and a design method. The structure comprises a bottom reflection layer, a dielectric layer and a top structure layer, wherein the top structure layer comprises an outer square ring, an outer ring structure, an inner ring structure and an isolation structure. The outer ring structure and the inner ring structure respond to incident electromagnetic waves under different target frequencies respectively, independent regulation and control of the circular polarization state are achieved, and the isolation structure restrains crosstalk. The metasurface is formed by periodically arranging a plurality of units, independent phase distribution can be applied to electromagnetic waves in different polarization states, and multi-target function regulation and control are achieved. The design method comprises the steps of constructing a unit structure library, performing electromagnetic simulation screening, calculating independent phase distribution, performing spin decoupling and generating a metasurface array arrangement scheme. The limitation of single regulation and control capability in the prior art is solved, and the spectrum utilization rate and the regulation and control capability of electromagnetic waves are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of metasurface electromagnetic control technology, and in particular to a dual-spectrum unit structure, a multi-dimensional multiplexed metasurface, and a design method. Background Art

[0002] With the rapid development of modern wireless communication technology, the scarcity of spectrum resources has become increasingly prominent. Limited spectrum resources are difficult to meet the growing demand for data transmission, which has prompted researchers to continuously explore new methods to improve spectrum utilization. Metasurface, a planar two-dimensional structure composed of periodic arrangements of sub-wavelength-sized units, has attracted widespread attention because of its ability to regulate the amplitude, phase, polarization and other dimensions of electromagnetic waves. However, most existing metasurface devices can only regulate a single degree of freedom of electromagnetic waves (such as frequency, polarization, etc.). This single regulation capability limits the application scope of metasurfaces in the realization of complex electromagnetic functions. For example, patent number CN114678693B discloses a metasurface unit structure for electromagnetic wave regulation. The structure realizes the regulation of electromagnetic wave amplitude and phase through the design of three conductor layers and two dielectric layers, but it is mainly aimed at the regulation of linearly polarized electromagnetic waves, and the operating frequency band is relatively narrow, which is difficult to meet the needs of independent regulation of multiple frequency bands and multiple polarization states. Therefore, developing a metasurface structure that can independently control the frequency and polarization degrees of freedom of electromagnetic waves is of great significance for improving spectrum utilization and realizing multi-target and multi-channel functional control. Summary of the Invention

[0003] The purpose of the present invention is to provide a dual-spectrum unit structure, a multi-dimensional multiplexed metasurface and a design method to solve the problem that existing metasurface devices can only regulate a single degree of freedom of electromagnetic waves (such as frequency or polarization), but cannot independently regulate the frequency and polarization degrees of freedom at the same time.

[0004] To achieve the above objectives, the following technical solutions are adopted.

[0005] A dual-spectrum unit structure, comprising:

[0006] A bottom reflective layer, made of a conductive material, for reflecting the regulated electromagnetic waves;

[0007] a dielectric layer, stacked on the bottom reflective layer, made of dielectric material and used to provide a medium for electromagnetic wave transmission;

[0008] The top structural layer is provided on the surface of the dielectric layer and includes:

[0009] The outer ring is made of conductive material and is arranged on the outermost side of the top structural layer to reduce the electromagnetic coupling between adjacent units. Its shape is a square frame with a circular opening embedded in it.

[0010] an outer ring structure, made of a conductive material, disposed in the circular opening, comprising at least one open ring unit, configured to respond to an incident electromagnetic wave at a first target frequency and independently control a first circular polarization state by superposition of a geometric phase and a transmission phase;

[0011] an inner ring structure, made of a conductive material, nested within the outer ring structure, and comprising at least one open ring unit for responding to an incident electromagnetic wave at a second target frequency and independently controlling a second circular polarization state by superposition of a geometric phase and a transmission phase;

[0012] an isolation structure, disposed between the outer ring structure and the inner ring structure, and consisting of a closed annular conductive structure, for suppressing frequency response crosstalk between the outer ring structure and the inner ring structure;

[0013] Among them, the opening direction and rotation angle of the outer ring structure and the inner ring structure are independently adjustable, and the operating frequencies of the outer ring structure and the inner ring structure are independently controlled by their geometric parameters, thereby realizing the decoupling control of left-handed and right-handed circularly polarized waves in dual bands.

[0014] Optionally, the outer ring structure includes a C-shaped open ring whose opening angle and rotation angle are adjustable, and is used to generate a geometric phase related to the incident circular polarization state by adjusting the rotation angle at the first target frequency, and control its resonant frequency by the ring size parameters, so that the reflection amplitude of the outer ring structure at the first target frequency is higher than a preset threshold, and the reflection amplitude at the second target frequency is lower than the first threshold.

[0015] Optionally, the inner ring structure includes a C-shaped open ring whose opening angle and rotation angle are adjustable, and is used to generate a geometric phase related to the incident circular polarization state by adjusting the rotation angle at the second target frequency, and control the resonant frequency by the ring size parameters, so that the reflection amplitude of the inner ring structure at the second target frequency is higher than a preset threshold, and the reflection amplitude at the first target frequency is lower than the second threshold.

[0016] Optionally, the isolation structure is an intermediate closed annular conductive layer, and the outer diameter and ring width of the isolation structure are fixed, and is used to block the near-field coupling between the outer ring structure and the inner ring structure through the electromagnetic shielding effect, so that the reflection amplitude of the outer ring structure at the second target frequency is lower than the first threshold, and the reflection amplitude of the inner ring structure at the first target frequency is lower than the second threshold.

[0017] A multi-dimensional multiplexed metasurface, wherein a plurality of the dual-spectrum unit structures are periodically arranged to form a metasurface array;

[0018] The metasurface array is configured to apply a first phase distribution and a second phase distribution to the left-handed circularly polarized wave and the right-handed circularly polarized wave, respectively, at the first target frequency, to achieve a first functional regulation; and to apply a third phase distribution and a fourth phase distribution to the left-handed circularly polarized wave and the right-handed circularly polarized wave, respectively, at the second target frequency, to achieve a second functional regulation;

[0019] Among them, the first phase distribution and the second phase distribution are generated by superimposing the geometric phase and the transmission phase of the outer ring structure, the third phase distribution and the fourth phase distribution are generated by superimposing the geometric phase and the transmission phase of the inner ring structure, and the first functional regulation and the second functional regulation are independently distributed in space.

[0020] Optionally, the first function is controlled to generate vortex beams, whose phase distribution includes an azimuthal phase component and a focusing phase component that vary with spatial coordinates; the second function is controlled to generate holographic imaging, whose phase distribution is iteratively generated by an improved Gerchberg-Saxton algorithm, which replaces the diffraction process between the imaging surface and the holographic surface with the Rayleigh-Sommerfeld diffraction formula, and iteratively optimizes the phase distribution through amplitude constraints.

[0021] Optionally, generating the first phase distribution and the second phase distribution includes the following steps:

[0022] Step S1: Based on target functional requirements, respectively calculating target phase distributions of left-handed circularly polarized waves and right-handed circularly polarized waves at the first target frequency;

[0023] Step S2: decomposing the target phase distribution into a transmission phase component and a rotation angle component by using a spin decoupling equation;

[0024] Step S3: adjusting the rotation angle of the outer ring structure according to the rotation angle component, and selecting a corresponding unit structure according to the transmission phase component.

[0025] A method for designing a multi-dimensional multiplexed metasurface comprises the following steps:

[0026] Constructing a dual-spectrum unit structure library, wherein the unit structure is a dual-spectrum unit structure described above, wherein the opening angle, rotation angle and size parameters of the outer ring structure and the inner ring structure are adjustable;

[0027] Screening out a candidate outer ring structure and a candidate inner ring structure having high reflection amplitudes at a first target frequency and a second target frequency, respectively, through electromagnetic simulation;

[0028] Calculating the independent phase distributions of left-handed and right-handed circularly polarized waves at the first target frequency and the second target frequency, respectively, according to target functional requirements;

[0029] Based on the spin decoupling method, the independent phase distribution is decomposed into a transmission phase distribution and a rotation angle distribution;

[0030] According to the decomposition results, units that meet the transmission phase and rotation angle requirements are selected from the unit structure library to generate a metasurface array arrangement scheme.

[0031] Optionally, the step of selecting, through electromagnetic simulation, a candidate outer ring structure and a candidate inner ring structure having high reflection amplitudes at the first target frequency and the second target frequency, respectively, specifically includes:

[0032] Performing parameter scanning on the outer loop structure to screen out candidate outer loop structures having a reflection amplitude higher than a preset threshold at the first target frequency and having no response to a second target frequency;

[0033] Performing parameter scanning on the inner loop structure to screen out candidate inner loop structures having a reflection amplitude higher than a preset threshold at the second target frequency and having no response to the first target frequency;

[0034] The crosstalk suppression effect of the isolation structure in the combination of the candidate outer ring structure and the candidate inner ring structure is verified, and the combination whose reflection amplitude exceeds the tolerance range is eliminated.

[0035] Optionally, the phase distribution is calculated using a modified Gerchberg-Saxton algorithm, including:

[0036] Initialize the amplitude distribution and random phase distribution of the target image to generate an initial complex amplitude field;

[0037] The complex amplitude distribution of the holographic surface is calculated using the Rayleigh-Sommerfeld diffraction formula, and its phase component is extracted;

[0038] Combining the phase component with the target amplitude distribution, diffracting it back to the imaging surface, and calculating the error index;

[0039] The phase distribution is iteratively updated until the error index is less than the convergence threshold or the maximum number of iterations is reached, and the final phase distribution is output.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] This application proposes a dual-spectrum unit structure that, through a unique three-layer structural design, achieves independent control of left-handed and right-handed circularly polarized waves at two different frequencies. The bottom reflective layer is made of conductive material, which can efficiently reflect the electromagnetic waves controlled by the top structure, ensuring the effective transmission of electromagnetic wave energy. The dielectric layer is made of dielectric material, providing a stable transmission medium for electromagnetic waves and reducing energy loss. The outer circular ring in the top structural layer effectively reduces the electromagnetic coupling between adjacent units and improves the independence of the units. The outer ring structure and the inner ring structure are designed for different target frequencies respectively. Through adjustable opening angles and rotation angles, independent control of the circular polarization state at their respective target frequencies is achieved. At the same time, the isolation structure effectively suppresses the frequency response crosstalk between the outer ring structure and the inner ring structure, ensuring decoupled control of left-handed and right-handed circularly polarized waves in dual frequency bands. It not only solves the limitations of the single control capability in the existing technology, but also significantly improves the spectrum utilization of electromagnetic waves, providing new possibilities for the realization of complex electromagnetic functions. The design of the outer ring structure and the inner ring structure was further optimized. By precisely controlling the opening angle, rotation angle, and ring size parameters, high reflection amplitude and low crosstalk characteristics were achieved at the target frequency, further improving the performance of the metasurface. Based on the dual-spectral unit structure, a multi-dimensional multiplexing metasurface was constructed, which can impose independent phase distributions on electromagnetic waves of different polarization states at different frequencies, realizing the control of complex functions such as vortex beam generation and holographic imaging. The multi-dimensional multiplexing metasurface not only improves spectrum utilization, but also expands the application field of the metasurface, providing modern wireless communication systems with more powerful electromagnetic control capabilities.

[0042] By designing a unique dual-spectral unit structure, independent control of both the frequency and polarization degrees of freedom of electromagnetic waves is achieved. The outer and inner ring structures respond to incident electromagnetic waves at different target frequencies, and the circular polarization state is independently controlled by superimposing the geometric phase and the transmission phase. This multi-dimensional control capability significantly enhances the electromagnetic control capabilities of the metasurface, providing new possibilities for the realization of complex electromagnetic functions.

[0043] This design method enables multi-target, multi-channel functional control on the same metasurface, improving the spectrum utilization of electromagnetic waves. By applying independent phase distributions to electromagnetic waves with different polarization states at different frequencies, it enables multiple functions such as vortex beam generation and holographic imaging, significantly increasing the channel capacity of single-frequency electromagnetic waves.

[0044] By setting up an isolation structure, the frequency response crosstalk between the outer and inner ring structures is effectively suppressed, ensuring the decoupling and regulation of left-handed and right-handed circularly polarized waves in dual frequency bands, and improving the performance and reliability of the metasurface.

[0045] Based on the spin decoupling method, the independent phase distribution is decomposed into the transmission phase distribution and the rotation angle distribution, enabling flexible control of the electromagnetic wave phase. By adjusting the opening angle and rotation angle of the outer and inner ring structures, the phase distribution of the electromagnetic wave can be precisely controlled to meet different application requirements.

[0046] By constructing a library of dual-spectral unit structures and using electromagnetic simulation to screen candidate structures with high reflection amplitudes at the target frequency, this design method provides an efficient and flexible design process. This not only improves design efficiency but also reduces manufacturing costs, making the design and application of metasurfaces more feasible.

[0047] This design method is applicable to a variety of application scenarios, including millimeter-wave wireless communications, information loading, and holographic image generation. By achieving multi-dimensional independent control of electromagnetic waves, this method provides more powerful electromagnetic control capabilities for modern wireless communication systems and has broad application prospects.

[0048] In summary, the multi-dimensional multiplexed metasurface design method of the present invention not only solves the limitations of the single control capability in the existing technology, but also significantly improves the spectrum utilization and electromagnetic control capability of electromagnetic waves, providing a new technical means for the realization of complex electromagnetic functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of the unit top structure and the geometric parameters of the middle closed loop.

[0050] Figure 2 Actual image of the metasurface that generates vortex light with topological charges of +1 and +2 under the incidence of right-handed and left-handed circularly polarized waves at 12.5 GHz, and with topological charges of +3 and +4 under the incidence of right-handed and left-handed circularly polarized waves at 22 GHz.

[0051] Figure 3 Actual image of the holographic metasurface that generates images of the holographic letters "H" and "B" under the incidence of 12.5GHz right-handed circularly polarized and left-handed circularly polarized waves, and that generates images of the holographic letters "K" and "D" under the incidence of 22GHz right-handed circularly polarized and left-handed circularly polarized waves.

[0052] Figure 4 The intensity and phase diagrams of the vortex optical metasurface simulation results under RCP and LCP incidence at a frequency of 12.5 GHZ.

[0053] Figure 5 The intensity and phase diagrams of the vortex optical metasurface simulation results under RCP and LCP incidence at a frequency of 22 GHZ.

[0054] Figure 6These are the simulation results of the holographic metasurface under RCP and LCP incident frequencies of 12.5 GHZ and 22 GHZ respectively.

[0055] Figure 7 Schematic diagram of the working principle of the metasurface.

[0056] Figure 8 (1) is the geometrical parameters of the outer C-type split ring, (2) is the amplitude-frequency response curve of the outer C-type split ring. (3) is the geometrical parameters of the inner C-type split ring, (4) is the amplitude-frequency response curve of the inner C-type split ring.

[0057] Figure 9 These are the cross-polarization phase response (POCSRR and PICSRR) and cross-polarization amplitude response (AOCSRR and AICSRR) curves of the OCSRR structure and ICSRR structure at frequencies of 12.5 GHz and 22 GHz.

[0058] Figure 10 Figure 2 shows the reflection amplitude and transmission phase responses of the dual-spectral unit at a frequency of 12.5 GHz when the ICSRR structure is rotated.

[0059] Figure 11 Figure 2 shows the reflection amplitude and transmission phase responses of the dual-spectral unit at a frequency of 22 GHz when the OCSRR structure is rotated.

[0060] Figure 12 This is the flow chart of the improved “GS” algorithm.

[0061] Among them: 1. bottom reflective layer; 2. dielectric layer; 3. top structural layer; 31. outer circular ring; 32. outer ring structure; 33. isolation structure; 34. inner ring structure. DETAILED DESCRIPTION

[0062] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application can be combined with each other.

[0063] The following detailed description is an exemplary description, which is intended to provide further detailed description of the present invention. Unless otherwise indicated, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art. The terms used in the present invention are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present invention.

[0064] Example 1

[0065] The dual-spectrum unit structure of the present invention is a novel structure for electromagnetic wave control, designed to achieve independent control of the electromagnetic wave frequency and polarization degrees of freedom. The structure includes a bottom reflective layer 1, a dielectric layer 2, and a top structural layer 3. The bottom reflective layer 1 is composed of a conductive material (such as copper) and has a thickness of 0.018mm. It is used to efficiently reflect the electromagnetic waves after being controlled by the top structural layer 3. The dielectric layer 2 is made of a dielectric material (such as F4B, with a dielectric constant of 2.65 and a loss tangent of 0.001) and has a thickness of 1.5mm. It is used to connect the bottom reflective layer 1 and the top structural layer 3, providing a stable electromagnetic wave transmission medium.

[0066] The top structural layer 3 is made of a conductive material (such as copper) with a thickness of 0.018 mm and includes an outer circular ring 31, an outer ring structure 32, an inner ring structure 34 and an isolation structure 33. The outer circular ring 31 is a square frame with an embedded circular opening, with a side length of 8 mm and a radius of 3.9 mm, which is used to reduce the electromagnetic coupling effect between adjacent units. The outer ring structure 32 includes at least one C-shaped open ring, whose opening angle and rotation angle are adjustable, and is used to respond to the incident electromagnetic wave at a first target frequency (such as 12.5 GHz) and achieve independent regulation of the first circular polarization state by superposition of geometric phase and transmission phase. The inner ring structure 34 is nested inside the outer ring structure 32 and also includes at least one C-shaped open ring, whose opening angle and rotation angle are adjustable, and is used to respond to the incident electromagnetic wave at a second target frequency (such as 22 GHz) and achieve independent regulation of the second circular polarization state by superposition of geometric phase and transmission phase.

[0067] The isolation structure 33 is a closed-loop conductive layer with a fixed outer diameter and width. It is used to block near-field coupling between the outer ring structure 32 and the inner ring structure 34 through electromagnetic shielding, thereby suppressing frequency response crosstalk. The operating frequencies of the outer ring structure 32 and the inner ring structure 34 are independently controlled by their geometric parameters, achieving decoupling and regulation of left-handed and right-handed circularly polarized waves in dual frequency bands. For example, the C-shaped split ring of the outer ring structure 32 has a high reflection amplitude at 12.5 GHz and a reflection amplitude of almost zero at 22 GHz; the C-shaped split ring of the inner ring structure 34 has a high reflection amplitude at 22 GHz and a reflection amplitude of almost zero at 12.5 GHz.

[0068] In a specific implementation, the geometric parameters of the C-shaped open rings of the outer ring structure 32 and the inner ring structure 34 can be optimized using electromagnetic simulation software (such as CST Studio Suite 2020). For example, the outer diameter of the C-shaped open ring of the outer ring structure 32 can be 3.5 mm, the ring width can be 0.6 mm, the opening angle can be 10°, and the rotation angle can be 0°; the outer diameter of the C-shaped open ring of the inner ring structure 34 can be 2.3 mm, the ring width can be 0.9 mm, the opening angle can be 8°, and the rotation angle can be 0°. These parameters can be adjusted according to specific application requirements to achieve the best electromagnetic wave control effect.

[0069] Specifically, such as Figure 7 As shown, the present invention is a frequency and polarization multiplexing metasurface, which is composed of 80*80 dual-spectrum units arranged periodically.

[0070] like Figure 1 As shown, the dual spectrum unit consists of a bottom reflective layer 1, a dielectric layer 2, and a top structure layer 3. The top structure layer 3 includes an outer circular ring 31, an outer C-shaped open ring, a middle closed ring, and an inner C-shaped open ring. The thickness of the top structure layer 3 is 0.018mm. The outer circular ring 31 is a rectangular parallelepiped with a side length of 8mm and a radius r minus 0.018mm from the middle. sc =3.9mm round cake, the outer diameter of the closed ring in the middle is r c =2.7mm, w c =0.2mm are fixed values. The outer diameter r1, ring width w1, opening angle β1, rotation angle θ1 of the external C-shaped open ring

[0071] The outer diameter r2, ring width w2, opening angle β2, and rotation angle θ2 of the internal C-shaped open ring are all variable parameters, so that the frequency domain solver in CST Studio Suite 2020 can be used to perform parameter sweeps to obtain units that meet the expected requirements. Figure 8 As shown, the outer C-shaped split ring has a high reflection amplitude at its operating frequency f1 = 12.5 GHz, while the reflection amplitude is almost zero at other frequencies, particularly at the inner C-shaped split ring's operating frequency f2. The inner C-shaped split ring has a high reflection amplitude at its operating frequency f2 = 22 GHz, while the reflection amplitude is almost zero at other frequencies, particularly at the outer C-shaped split ring's operating frequency f1. The inner and outer C-shaped split rings not only have high reflection amplitudes at their respective operating frequencies but also induce cross-polarization conversion responses in the incident electromagnetic wave, causing the reflected electromagnetic wave to carry a transmission phase and geometric phase that are independent of the polarization state. These two phases are key to achieving multi-target functions.

[0072]

[0073]

[0074] Table 1 shows the geometric parameter values ​​of eight carefully selected dual-spectrum units. Figure 9 It can be seen that at the frequency f1, the average polarization conversion amplitude of the outer C-type open ring of these 8 units is 0.9, and the average polarization conversion amplitude of the inner C-type open ring is less than 0.02. At the same time, the transmission phase of the 8 units covers 0-2π with a gradient of approximately π / 4. At the frequency f2, the average polarization conversion amplitude of the outer C-type open ring of the 8 selected units is less than 0.05, and the average polarization conversion amplitude of the inner C-type open ring is 0.86. At this time, the transmission phase of the 8 units still covers 0-2π with a gradient of approximately π / 4. It shows excellent single-frequency working characteristics. Figure 10 It can be seen that when the internal C-shaped split rings in all 8 units rotate, there is almost no effect on the amplitude response and transmission phase response of the unit at frequency f1. Figure 11 It can be seen that when the outer C-shaped split rings in all eight units rotate, there is almost no effect on the unit's amplitude response and transmission phase response at frequency f2. This fully demonstrates that the dual-spectrum unit proposed in this invention has excellent frequency selectivity and low crosstalk characteristics, and meets the phase control requirements for multi-objective functions.

[0075] Example 2

[0076] Based on the aforementioned dual-spectrum unit structure, the present invention further constructs a multi-dimensional multiplexed metasurface. This metasurface is formed by a periodic arrangement of multiple dual-spectrum unit structures to form a metasurface array, which is used to apply independent phase distributions to electromagnetic waves with different polarization states at different frequencies, thereby achieving multi-target functional control. Specifically, at a first target frequency, the metasurface array applies a first phase distribution and a second phase distribution to left-handed circularly polarized waves and right-handed circularly polarized waves, respectively, to achieve a first functional control; at a second target frequency, the metasurface array applies a third phase distribution and a fourth phase distribution to left-handed circularly polarized waves and right-handed circularly polarized waves, respectively, to achieve a second functional control.

[0077] like Figure 2 、 Figure 3 As shown, to verify the frequency selection and polarization multiplexing characteristics of the dual-spectral unit of the present invention, the first metasurface was designed with the target function of generating vortex light with topological charges of +1 and +2 under right-handed and left-handed circular polarization waves at 12.5 GHz, and with topological charges of +3 and +4 under right-handed and left-handed circular polarization waves at 22 GHz. Then, the second metasurface was designed with the second target function of generating holographic images of the letters "H" and "B" under right-handed and left-handed circular polarization waves at 12.5 GHz, and with generating holographic images of the letters "K" and "D" under right-handed and left-handed circular polarization waves at 22 GHz.

[0078] The first functional regulation may be vortex beam generation, the phase distribution of which includes an azimuthal phase component and a focusing phase component that vary with spatial coordinates.

[0079] Vortex light is an electromagnetic wave that carries orbital angular momentum (OAM). Theoretically, at a fixed frequency, an electromagnetic wave can have an infinite number of OAM modes, and different OAM modes do not interfere with each other during transmission, significantly improving spectrum efficiency. Its phase distribution can be calculated using the following formula.

[0080]

[0081] Where x and y correspond to the horizontal and vertical coordinates of the unit's geometric center, respectively. f is the focal length. The second term is the overall focused phase distribution, which can address the problem of vortex waves being difficult to receive due to their natural divergence during propagation. l is the topological charge of the OAM.

[0082] The second functional control can be holographic imaging, whose phase distribution is iteratively generated using a modified Gerchberg-Saxton algorithm. This algorithm replaces the diffraction process between the imaging surface and the holographic surface with the Rayleigh-Sommerfeld diffraction formula and iteratively optimizes the phase distribution with amplitude constraints.

[0083] The specific steps are as follows:

[0084] Initialize the amplitude distribution and random phase distribution of the target image: generate an initial complex amplitude field.

[0085] The complex amplitude distribution of the holographic surface is calculated using the Rayleigh-Sommerfeld diffraction formula, and its phase component is extracted. This phase component is combined with the target amplitude distribution, back-diffracted onto the imaging surface, and the error index is calculated. The error index can be evaluated by calculating the root mean square error (RMSE) between the target image and the generated image.

[0086] Iterate the phase distribution until the error index is less than the convergence threshold or the maximum number of iterations is reached, and then output the final phase distribution. For example, you can set the error threshold to 0.01 and the maximum number of iterations to 100.

[0087] Specifically, such as Figure 12As shown, the classical Gerchberg-Saxton (GS) algorithm was proposed by RWGerchberg and WOSaxton. It is a Fourier iteration algorithm that is often used to design phase-type holographic plates. Therefore, the classical GS algorithm projects the holographic image into the far-field Fraunhofer diffraction region. For microwave metasurfaces, the holographic image is usually projected into the near-field Rayleigh-Sommerfeld region. To this end, an improved GS algorithm is obtained by replacing the Fourier iteration formula in the classical GS algorithm with the Rayleigh-Sommerfeld diffraction formula. Assume that the plane where the metasurface is located (called the holographic surface) and the plane where the target image is located (called the imaging surface) are located on two xoy planes, and the distance along the z-axis is Δz. In the flowchart, the input |I| is the amplitude distribution of the target image. Combined with the phase distribution Ψ (the initial Ψ is a random phase distribution), the complex amplitude distribution of the imaging surface can be calculated as I=|I|e iT Then, the diffraction process from the imaging surface to the holographic surface is expressed as RS, and the calculation process is:

[0088]

[0089] Where M(x m ,y m ) represents the point (x m ,y m ) at the complex amplitude, I(x i ,y i ) represents the point (x i ,y i ). λ is the operating wavelength, k=2π / λ is the wave number, is the point (x i ,y i ) and point (x m ,y m By calculating any point on the holographic surface, we can get the complex amplitude distribution M=|M|e iΦ Then, the amplitude distribution |M| on the holographic surface is set to all 1, and the phase Φ is retained, and M′=e iΦ Next, the diffraction process from the holographic surface to the imaging surface can be expressed as RS-1, and the calculation process is:

[0090]

[0091] in By calculating any point on the imaging surface, the complex amplitude distribution I′=|I′|e iΨ Then, the calculated holographic image |I′| is compared with the target image |I|:

[0092]

[0093] If the difference Q between the calculated result and the target image satisfies a sufficiently small requirement, the algorithm stops iterating and outputs the pure phase distribution on the holographic surface. Otherwise, the target image amplitude distribution is combined with the calculated phase distribution Ψ to form a new complex amplitude distribution, and the iteration cycle continues. It is important to note that in addition to the stopping condition based on the difference Q, the upper limit of the number of iterations can also be set according to actual conditions. When the set number of iterations is reached, the algorithm terminates and outputs the result.

[0094] In practice, the metasurface array can be composed of 80×80 dual-spectrum units arranged in a periodic pattern. The size of each unit can be adjusted according to specific application requirements. For example, the unit period can be 10 mm to minimize electromagnetic coupling between adjacent units. The metasurface generated using this method can achieve vortex beam generation and holographic imaging at frequencies of 12.5 GHz and 22 GHz, respectively, significantly improving spectrum utilization and electromagnetic wave control capabilities.

[0095] like Figure 4 As shown, the simulation results of vortex optical metasurface under RCP and LCP incident frequency of 12.5GHZ are shown. Figure 5 The simulation results of the vortex light metasurface under RCP and LCP incidence at a frequency of 22 GHz are obtained by calculating the intensity and phase data of the electric field at 500 mm from the metasurface. Due to the inherent phase singularity of the vortex wave, a "donut"-shaped intensity distribution can be clearly observed, and the radius of the "donut" increases with the increase of the topological charge. In addition, it can be seen from the phase distribution results that the phase covers the range of 2π, 4π, 6π, and 8π in the counterclockwise direction, respectively. These results prove that focused vortex light with topological charges of +1, +2, +3, and +4, respectively, is generated under RCP and LCP incidence at 12.5 GHz and 22 GHz.

[0096] Figure 6 The following are simulation results of the holographic metasurface using RCP and LCP incident frequencies of 12.5 GHz and 22 GHz, respectively. The results are obtained by calculating the electric field intensity data at a distance of 300 mm from the metasurface.

[0097] Example 3

[0098] The present invention also provides a design method for a multi-dimensional multiplexed metasurface, which is based on the above-mentioned dual-spectrum unit structure and includes the following steps:

[0099] Constructing a dual-spectrum unit structure library: The unit structure is a dual-spectrum unit structure, in which the opening angle, rotation angle, and dimensional parameters of the outer ring structure 32 and the inner ring structure 34 are adjustable. For example, the outer diameter, ring width, opening angle, and rotation angle of the C-shaped open ring of the outer ring structure 32, as well as the outer diameter, ring width, opening angle, and rotation angle of the C-shaped open ring of the inner ring structure 34, are all variable parameters. These parameters can be optimized using electromagnetic simulation software to achieve the best electromagnetic wave control effect.

[0100] Electromagnetic simulation screening: Through electromagnetic simulation, a candidate outer ring structure 32 and a candidate inner ring structure 34 with high reflection amplitudes at the first target frequency and the second target frequency are screened. The specific steps include:

[0101] A parameter scan is performed on the outer ring structure 32 to screen out candidate outer ring structures 32 whose reflection amplitude at the first target frequency is higher than a preset threshold and which are unresponsive to the second target frequency. For example, the preset threshold may be 0.8, meaning that structures with reflection amplitudes higher than 0.8 are considered valid candidate structures.

[0102] A parameter scan is performed on the inner ring structure 34 to screen out candidate inner ring structures 34 having a reflection amplitude greater than a preset threshold at the second target frequency and no response to the first target frequency. For example, the preset threshold may be 0.8, meaning that structures with a reflection amplitude greater than 0.8 are considered valid candidate structures.

[0103] The crosstalk suppression effect of the isolation structure 33 in the combination of the candidate outer ring structure 32 and the candidate inner ring structure 34 is verified, and combinations with reflection amplitudes exceeding the tolerance range are eliminated. For example, the tolerance range can be set to 0.1, that is, combinations with reflection amplitudes exceeding 0.1 are considered invalid.

[0104] Computing Independent Phase Distributions: Calculate the independent phase distributions of left-handed and right-handed circularly polarized waves at the first and second target frequencies, respectively, based on the desired functional requirements. For example, for vortex beam generation, the phase distributions can include azimuthal and focusing phase components that vary with spatial coordinates. For holographic imaging, the phase distributions can be iteratively generated using a modified Gerchberg-Saxton algorithm.

[0105] Spin decoupling method: decompose the independent phase distribution into transmission phase distribution and rotation angle distribution. The specific steps include:

[0106] Based on the spin-independent geometric phase distribution and the spin-independent transmission phase distribution, the independent phase distribution is decomposed into a transmission phase component and a rotation angle component.

[0107] By improving the holographic "GS" algorithm or the vortex light phase distribution calculation method, two independent phase distributions are obtained and brought into the spin decoupling equation to solve the transmission phase and rotation angle.

[0108] Specifically, the spin decoupling method is a key technology for achieving independent phase control of incident right-handed circularly polarized waves (RCP) and left-handed circularly polarized waves (LCP) at a single frequency. Assume that there are two independent phase distributions ψ1(x, y) and ψ2(x, y), and the metasurface can realize these two phase distributions under RCP and LCP incidence. Then, based on the spin-independent geometric phase distribution 2σθ(x, y) and the spin-independent transmission phase distribution φ(x, y), ψ1(x, y) and ψ2(x, y) can be expressed as follows:

[0109] ψ1(x,y)=2θ(x,y)+φ(x,y)

[0110] ψ2(x,y)=-2θ(x,y)+φ(x,y)

[0111] In the design of this product, the direction of meta-atom rotation is clockwise, so σ = +1 corresponds to RCP incidence, and σ = -1 corresponds to LCP incidence. By improving the holographic "GS" algorithm or the vortex light phase distribution calculation method, two independent phase distributions ψ1(x, y) and ψ2(x, y) can be obtained. Substituting them into the above formula can solve the transmission phase φ(x, y) and rotation angle θ(x, y). Since a transmission phase and a rotation angle can uniquely determine a unit structure, the entire metasurface can be determined by the transmission phase distribution and the rotation angle distribution. Furthermore, the metasurface designed in this way can achieve independent phase control and spin decoupling under the irradiation of RCP and LCP.

[0112] Generate a metasurface array layout: Based on the decomposition results, select cells from the cell structure library that meet the transmission phase and rotation angle requirements to generate a metasurface array layout. For example, an 80×80 cell array can be selected. The size of each cell can be adjusted according to the specific application requirements to minimize electromagnetic coupling between adjacent cells.

[0113] In practice, metasurface arrays can be used in a variety of applications, such as millimeter-wave wireless communications, information loading, and holographic image generation. For example, in millimeter-wave wireless communications, metasurface arrays can achieve vortex beam generation and holographic imaging at frequencies of 12.5 GHz and 22 GHz, respectively, significantly improving spectrum utilization and electromagnetic wave control capabilities. The above design method enables independent multi-dimensional control of electromagnetic waves, providing modern wireless communication systems with more powerful electromagnetic control capabilities.

[0114] It is understood from common technical knowledge that the present invention may be implemented by other embodiments that do not depart from its spirit or essential features. Therefore, the embodiments disclosed above are, in all respects, merely illustrative and not exclusive. All modifications within the scope of the present invention or equivalent to the scope of the present invention are intended to be encompassed by the present invention.

Claims

1. A dual spectrum unit structure, characterized in that: include, A bottom reflective layer (1), made of a conductive material, for reflecting the regulated electromagnetic waves; a dielectric layer (2), stacked on the bottom reflective layer (1), made of a dielectric material, and used to provide an electromagnetic wave transmission medium; The top structural layer (3) is arranged on the surface of the dielectric layer (2) and comprises: An outer circular ring (31), made of a conductive material, is arranged on the outermost side of the top structural layer (3) and is used to reduce electromagnetic coupling between adjacent units. The outer circular ring (31) has a square frame with a circular opening embedded therein; An outer ring structure (32), made of a conductive material, is disposed in the circular opening and comprises at least one open ring unit, configured to respond to incident electromagnetic waves at a first target frequency and achieve independent regulation of a first circular polarization state by superposition of a geometric phase and a transmission phase; An inner ring structure (34), made of a conductive material, is nested inside the outer ring structure (32), and includes at least one open ring unit, which is used to respond to the incident electromagnetic wave at a second target frequency and achieve independent regulation of the second circular polarization state by superposition of the geometric phase and the transmission phase; an isolation structure (33), disposed between the outer ring structure (32) and the inner ring structure (34), and consisting of a closed annular conductive structure, for suppressing frequency response crosstalk between the outer ring structure (32) and the inner ring structure (34); The opening directions and rotation angles of the outer ring structure (32) and the inner ring structure (34) are independently adjustable, and the operating frequencies of the outer ring structure (32) and the inner ring structure (34) are independently controlled by their geometric parameters, so as to realize decoupling control of left-handed and right-handed circularly polarized waves in dual frequency bands.

2. A dual spectrum unit structure according to claim 1, characterized in that: The outer ring structure (32) comprises a C-shaped open ring, the opening angle and the rotation angle of which are adjustable, and is used to generate a geometric phase related to the incident circular polarization state by adjusting the rotation angle at the first target frequency, and to control its resonant frequency by means of a ring size parameter, so that the reflection amplitude of the outer ring structure (32) at the first target frequency is higher than a preset threshold, and the reflection amplitude at the second target frequency is lower than the first threshold.

3. A dual spectrum unit structure according to claim 1, characterized in that: The inner ring structure (34) comprises a C-shaped open ring, the opening angle and the rotation angle of which are adjustable, and is used to generate a geometric phase related to the incident circular polarization state by adjusting the rotation angle at the second target frequency, and to control the resonant frequency by the ring size parameter, so that the reflection amplitude of the inner ring structure (34) at the second target frequency is higher than a preset threshold, and the reflection amplitude at the first target frequency is lower than a second threshold.

4. A dual spectrum unit structure according to claim 1, characterized in that: The isolation structure (33) is a middle closed annular conductive layer. The outer diameter and ring width of the isolation structure (33) are fixed, and the isolation structure (33) is used to block the near-field coupling between the outer ring structure (32) and the inner ring structure (34) through an electromagnetic shielding effect, so that the reflection amplitude of the outer ring structure (32) at the second target frequency is lower than a first threshold, and the reflection amplitude of the inner ring structure (34) at the first target frequency is lower than a second threshold.

5. A multi-dimensional multiplexing metasurface, based on a dual-spectrum unit structure according to any one of claims 1 to 4, characterized in that: A plurality of the dual-spectrum unit structures are periodically arranged to form a metasurface array; A metasurface array is configured to apply a first phase distribution and a second phase distribution to a left-handed circularly polarized wave and a right-handed circularly polarized wave, respectively, at a first target frequency, to achieve a first functional control; and to apply a third phase distribution and a fourth phase distribution to a left-handed circularly polarized wave and a right-handed circularly polarized wave, respectively, at a second target frequency, to achieve a second functional control; The first phase distribution and the second phase distribution are generated by superimposing the geometric phase and the transmission phase of the outer ring structure (32), the third phase distribution and the fourth phase distribution are generated by superimposing the geometric phase and the transmission phase of the inner ring structure (34), and the first functional regulation and the second functional regulation are independently distributed in space.

6. The multi-dimensional multiplexed metasurface according to claim 5, characterized in that: The first function is controlled to generate a vortex beam, the phase distribution of which includes an azimuthal phase component and a focusing phase component that vary with spatial coordinates; The second function is holographic imaging, whose phase distribution is iteratively generated by the improved Gerchberg-Saxton algorithm. The algorithm replaces the diffraction process between the imaging surface and the holographic surface with the Rayleigh-Sommerfeld diffraction formula and iteratively optimizes the phase distribution through amplitude constraints.

7. The multi-dimensional multiplexed metasurface according to claim 5, characterized in that: Generating the first phase distribution and the second phase distribution includes the following steps: Step S1: Based on the target functional requirements, the target phase distributions of the left-handed circularly polarized wave and the right-handed circularly polarized wave at the first target frequency are calculated respectively; Step S2: Decompose the target phase distribution into a transmission phase component and a rotation angle component through the spin decoupling equation; Step S3: adjusting the rotation angle of the outer ring structure (32) according to the rotation angle component, and selecting a corresponding unit structure according to the transmission phase component.

8. A design method for a multi-dimensional multiplexed metasurface, based on a dual-spectrum unit structure according to any one of claims 1 to 4, characterized in that: The following steps are involved: Constructing a dual-spectrum unit structure library, wherein the unit structure is a dual-spectrum unit structure based on any one of claims 1 to 4, wherein the opening angle, rotation angle and size parameters of the outer ring structure (32) and the inner ring structure (34) are adjustable; Screening out a candidate outer ring structure (32) and a candidate inner ring structure (34) having high reflection amplitudes at a first target frequency and a second target frequency, respectively, through electromagnetic simulation; According to the target function requirements, the independent phase distributions of left-handed and right-handed circularly polarized waves at the first target frequency and the second target frequency are calculated respectively; Based on the spin decoupling method, the independent phase distribution is decomposed into the transmission phase distribution and the rotation angle distribution; According to the decomposition results, units that meet the transmission phase and rotation angle requirements are selected from the unit structure library to generate a metasurface array arrangement scheme.

9. The method for designing a multi-dimensional multiplexed metasurface according to claim 8, wherein: The steps of selecting a candidate outer ring structure (32) and a candidate inner ring structure (34) having high reflection amplitudes at a first target frequency and a second target frequency respectively through electromagnetic simulation specifically include: Performing parameter scanning on the outer ring structure (32) to screen out candidate outer ring structures (32) having a reflection amplitude higher than a preset threshold at a first target frequency and having no response to a second target frequency; Performing parameter scanning on the inner ring structure (34) to screen out candidate inner ring structures (34) having a reflection amplitude higher than a preset threshold at a second target frequency and having no response to the first target frequency; The crosstalk suppression effect of the isolation structure (33) in the combination of the candidate outer ring structure (32) and the candidate inner ring structure (34) is verified, and the combination whose reflection amplitude exceeds the tolerance range is eliminated.

10. The method for designing a multi-dimensional multiplexed metasurface according to claim 8, wherein: The phase distribution is calculated using the improved Gerchberg-Saxton algorithm, which includes: Initialize the amplitude distribution and random phase distribution of the target image to generate an initial complex amplitude field; The complex amplitude distribution of the holographic surface is calculated using the Rayleigh-Sommerfeld diffraction formula, and its phase component is extracted; Combine the phase component with the target amplitude distribution, diffract it back to the imaging surface, and calculate the error index; The phase distribution is iteratively updated until the error index is less than the convergence threshold or the maximum number of iterations is reached, and the final phase distribution is output.

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