A spatial and polarization multiplexed programmable metasurface

Abstract

The application discloses a kind of space and polarization multiplexing programmable metasurface, by programmable metasurface and digital voltage control module two parts composition.Wherein, programmable metasurface is by programmable unit and is arranged periodically in space, and four varactor diodes are loaded in the top of unit structure, and are connected to the feed line of bottom layer through metallization hole and then are connected to digital voltage control module, provide independent bias voltage for the varactor diode arranged in horizontal and vertical direction, can be used to regulate and control the amplitude and phase of corresponding reflected wave respectively.Combining generalized Snell theory and particle swarm optimization algorithm, by designing the phase distribution in the orthogonal direction of metasurface, the metasurface not only can regulate and control the spatial deflection direction of reflected wave, but also can control its polarization state to cover any point on Poincare sphere, to realize the simultaneous regulation and control of electromagnetic wave in space domain and polarization domain, and is expected to be applied in radar detection and wireless communication and other fields.

Description

Technical Field

[0001] This invention relates to a spatially and polarized multiplexed programmable metasurface, belonging to the field of novel artificial electromagnetic materials technology. Background Technology

[0002] Metasurfaces, composed of two-dimensional arrays of subwavelength planar metals or dielectric atoms, have been widely used to control electromagnetic waves with multiple degrees of freedom, among which polarization modulation is an important research topic. Using phase control principles, many general methods based on passive polarization-modulated metasurfaces have been proposed, including propagation phase, geometric phase, and combinations thereof. However, the functionality of these passive metasurfaces cannot be changed after fabrication. Fortunately, by integrating metasurfaces with active components or phase-change materials, programmable metasurfaces can be formed, enabling dynamic control of electromagnetic waves.

[0003] Programmable metasurfaces have been widely used in dynamic holographic imaging, reconfigurable smart surfaces, and other applications. Furthermore, these reconfigurable metasurfaces are also used for the dynamic manipulation of the polarization states of electromagnetic waves or light, enabling multifunctional polarization control. However, most existing work based on pure phase control is limited to dynamic polarization transitions between co-polarized waves, cross-polarized waves, or linearly circularly polarized waves. Therefore, achieving real-time polarization manipulation with more degrees of freedom remains a challenge.

[0004] In recent years, time-domain metasurfaces have been proposed by applying time-varying periodic bias voltages to active elements loaded on metasurfaces. These metasurfaces have demonstrated remarkable capabilities in controlling the amplitude and phase distributions of different harmonics. Since the amplitude and phase of electromagnetic waves can be manipulated simultaneously, time-varying metasurfaces can achieve even more powerful functions, such as editing arbitrary linear polarizations, even generating arbitrary polarizations, and synthesizing linear and nonlinear polarizations. However, these time-varying metasurfaces must be derived by continuously applying time-varying periodic bias voltages, and the generation of harmonics inevitably consumes additional spectral resources, which still limits their practical application in polarization modulation. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a spatial and polarization multiplexed programmable metasurface, filling the gap in the existing metasurfaces that cannot simultaneously modulate electromagnetic waves in the spatial and polarization domains, and providing greater freedom for polarization modulation.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A spatial and polarization multiplexed programmable metasurface includes a programmable metasurface and a digital voltage control module. The programmable metasurface is a two-dimensional matrix formed by periodically arranging programmable units in space. Each programmable unit integrates two varactor diodes in the horizontal and vertical directions. The digital voltage control module provides bias voltages to the varactor diodes in the horizontal and vertical directions, enabling the varactor diodes in the horizontal and vertical directions to operate within different capacitance ranges, so that each programmable unit can adjust the reflection phase coverage to 320°.

[0008] By combining generalized Snell's theory and particle swarm optimization algorithm, the polarization matrix of the space and polarization multiplexed programmable metasurface is designed to control the deflection direction, amplitude and phase of the horizontal and vertical polarization components in the reflected wave, thereby realizing the control of the deflection direction and polarization state of the reflected wave, and the polarization state covers any point on the Poincaré sphere.

[0009] In a preferred embodiment of the present invention, in the programmable metasurface, varactor diodes in the same row are controlled by the same bias voltage, varactor diodes in the same column are controlled by the same bias voltage, and the voltage distribution output by the digital voltage control module independently controls the phase distribution in the horizontal and vertical directions of the programmable metasurface.

[0010] As a preferred embodiment of the present invention, the programmable unit includes a top layer, an intermediate layer, a bottom layer, and two dielectric layers. The top layer, intermediate layer, and bottom layer are all metal layers, and a dielectric layer is disposed between the top layer and the intermediate layer, and between the intermediate layer and the bottom layer. The top layer is composed of five metal patches, and four varactor diodes are loaded on the five metal patches. The four varactor diodes are connected to the feed line of the bottom layer through metallized holes. The digital voltage control module is physically connected to the programmable unit to provide bias voltage for real-time control of the varactor diodes in the horizontal and vertical directions.

[0011] In a preferred embodiment of the present invention, both dielectric layers are F4B dielectric layers, and the relative permittivity of the F4B dielectric layer is 2.2, the loss angle is 0.001, and the thickness is 1 mm.

[0012] As a preferred embodiment of the present invention, the polarization matrix of the spatial and polarization multiplexed programmable metasurface is designed by combining generalized Snell's theory and particle swarm optimization algorithm, as follows:

[0013] Using the amplitude value of a specified far-field radiation pattern as the optimization objective, the particle fitness value is evaluated using a particle swarm optimization algorithm. In each iteration, the particle velocity, particle extrema, and swarm extrema are updated. When the loop termination condition is met, the final far-field radiation pattern and the horizontal and vertical phase distributions φ of the current spatially and polarized multiplexed programmable metasurface are output. x and φ y .

[0014] In a preferred embodiment of the present invention, the deflection directions, amplitudes, and phases of the horizontal and vertical polarization components in the controlled reflected wave are the same, and the polarization state of the reflected beam is controlled by the amplitudes and phases of the horizontal and vertical polarization components.

[0015] As a preferred embodiment of the present invention, the polarization matrix is ​​composed of phase distributions corresponding in the horizontal and vertical directions.

[0016] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0017] 1. The spatial and polarization multiplexed programmable metasurface proposed in this invention, by introducing an optimized polarization matrix, can not only control the spatial domain characteristics of electromagnetic waves and customize the deflection direction of reflected beams, but also achieve coverage of any point on the Poincaré sphere in the polarization domain.

[0018] 2. The spatial and polarization multiplexing programmable metasurface proposed in this invention can further have the ability to multiplex spatial and polarization diversity, customize different polarization states in multiple radiation beams, and radiate different polarization waves to different locations in space simultaneously and independently.

[0019] 3. This invention is easy to process, operates in the microwave frequency band, adopts conventional printed circuit board technology, the varactor diodes of the unit are commercially mature varactor diodes, and the digital voltage control module is made of field programmable gate array (FPGA), digital-to-analog converter and voltage amplifier. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the programmable spatial and polarization multiplexed metasurface of the present invention;

[0021] Figure 2 These are diagrams of metasurface unit structures, where (a) is a layered structure diagram and (b) is a bottom layer feeder layout diagram.

[0022] Figure 3 These are the simulation results of the unit reflection amplitude and phase, where (a) is the reflection amplitude and (b) is the phase;

[0023] Figure 4 This is a flowchart of the phase distribution optimization process using the particle swarm optimization algorithm;

[0024] Figure 5 This is a diagram of a Poincaré ball;

[0025] Figure 6 These are schematic diagrams of eight different polarization states;

[0026] Figure 7The beam pointing to θ = -20° is the polarization matrix corresponding to different polarization codes and its simulated far-field radiation pattern. Among them, (a)-(d) correspond to polarization codes 000, 001, 010 and 011 respectively, and (e)-(h) correspond to the polarization matrix of (a)-(d) respectively.

[0027] Figure 8 The beam pointing at θ = 30° has polarization matrices corresponding to different polarization codes and their simulated far-field radiation patterns. Among them, (a)-(d) correspond to polarization codes 100, 101, 110 and 111 respectively, and (e)-(h) correspond to the polarization matrices of (a)-(d) respectively.

[0028] Figure 9 These are the polarization matrices and their simulated far-field radiation patterns corresponding to different beam directions and polarization codes. Among them, (a) is the polarization matrix when the polarization code for the beam pointing to θ = -20° is 100 and the polarization code for the beam pointing to θ = 30° is 101; (b) is the polarization matrix when the polarization code for the beam pointing to θ = -20° is 110 and the polarization code for the beam pointing to θ = 30° is 111; (c) corresponds to the polarization matrix of (a); and (d) corresponds to the polarization matrix of (b).

[0029] Figure 10 These are samples of metasurface processing, where (a) is a front view, (b) is a rear view, and (c) is an enlarged view of four local units;

[0030] Figure 11 These are the test results of the reflection amplitude and phase of the metasurface, where (a) is the reflection amplitude and (b) is the phase.

[0031] Figure 12 It is a far-field testing device in a standard microwave anechoic chamber;

[0032] Figure 13 These are the test results of the far-field radiation patterns corresponding to different polarization codes with a beam pointing at θ = -20°, where (a)-(d) correspond to polarization codes 000, 001, 010 and 011 respectively;

[0033] Figure 14 These are the test results of the far-field radiation patterns corresponding to different polarization codes with a beam pointing at θ = 30°, where (a)-(d) correspond to polarization codes 100, 101, 110 and 111, respectively;

[0034] Figure 15 These are the test results of simulated far-field radiation patterns corresponding to different beam directions and different polarization codes. Among them, (a) is when the beam direction is θ = -20° and the polarization code is 100, and the beam direction is θ = 30° and the polarization code is 101; (b) is when the beam direction is θ = -20° and the polarization code is 110, and the beam direction is θ = 30° and the polarization code is 111. Detailed Implementation

[0035] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0036] This invention provides a programmable spatial polarization multiplexing information metasurface, capable of deflecting spatial beams and customizing their polarization state in the radiation direction. It consists of two parts: a programmable metasurface and a digital voltage control module. The programmable metasurface is constructed from programmable units arranged periodically in space. Each unit integrates two varactor diodes in both the horizontal and vertical directions. The digital voltage control module provides accurate bias voltages to the varactor diodes in the horizontal and vertical directions, allowing them to operate within different capacitance ranges, thus enabling the unit to adjust the reflection phase coverage up to 320°. By combining generalized Snell's theory and particle swarm optimization algorithms, and by designing the polarization matrix of the metasurface, the deflection direction, amplitude, and phase of the horizontal and vertical polarization components in the reflected wave can be controlled, thereby achieving the regulation of the reflected wave's deflection direction and polarization state, which covers any point on the Poincaré sphere.

[0037] like Figure 1 As shown, the metasurface designed in this invention is a reflective programmable information metasurface. Each unit is loaded with four varactor diodes. By adjusting the varactor range in the horizontal and vertical directions, the reflected phase of electromagnetic waves in the vertical and horizontal directions can be independently controlled in real time. As an example, using a 45° polarized wave as the incident wave, when the incident wave irradiates the metasurface, the phase distribution in the horizontal and vertical directions can be further optimized by a particle swarm optimization algorithm. This allows for the simultaneous and independent control of the amplitude and phase of the beam in the same radiation direction, thereby achieving a preset polarization state on the specified beam.

[0038] Figure 2 (a) is a diagram of the metasurface unit structure. The unit structure consists of three metal (copper) layers and two dielectric (F4B) layers, where the dielectric has a relative permittivity of 2.2 and a loss angle of 0.001, and a dielectric thickness h of 1 mm. The two dielectric layers are bonded together by Rogers 4450F adhesive layers. Other unit structure parameters are a = 5.7 mm, b = 2 mm, c = 1.75 mm, d = 3.1 mm, and p = 15 mm. Four varactor diodes (MAVR-000120-14110P) are soldered at the gaps between the five metal patches on the upper layer of the unit, and their equivalent circuit is a series connection of a resistor, an inductor, and a variable capacitor. The bottom layer feed layout of the unit is as follows. Figure 2 As shown in (b).

[0039] Figure 3(a) and (b) are the simulation results of the unit reflection amplitude and phase. The results show that the reflection amplitude of the x-polarized and y-polarized waves is above 0.6 over the entire variable capacitance range, and the reflection phase covers up to 320°. The electromagnetic loss mainly comes from the internal resistance of the varactor diode.

[0040] Figure 4 This is a flowchart illustrating the phase distribution optimization process using the particle swarm optimization algorithm. Figure 2 A modular structure was designed, consisting of 16×16 units, forming a programmable spatial and polarization multiplexed information metasurface with a total size of 240×240mm. 2 This is to demonstrate its powerful ability to manipulate the polarization state of electromagnetic waves. The desired reflection beam deflection angle, as well as the amplitude and phase difference (θ, Δθ) of the x and y polarization components, are considered. x A y , ΔΦ), where The phase distribution (φ) on the programmable spatial and polarization multiplexing information metasurface is further optimized using the Particle Swarm Optimization (PSO) algorithm. x ,φ y The PSO algorithm obtains the corresponding far-field pattern by evaluating fitness and updating particle velocity and data values ​​in each iteration, and combines the ideal far-field pattern to obtain the final phase distribution φ of the spatially and polarized multiplexed metasurface. x and φ y .

[0041] Figure 5 This is a schematic diagram of a Poincaré sphere. The sphere is constructed in a Cartesian coordinate system with Stokes parameters (S1, S2, S3). An arbitrary polarization state |P> is determined by the coordinates (2ψ, 2χ), where ψ is the azimuth and χ is the ellipticity. The polarizations |R>, |L>, |A>, |D>, |H>, and |V> on the Poincaré sphere represent right-handed circular polarization, left-handed circular polarization, anti-angle, diagonal, horizontal, and vertical polarization, respectively.

[0042] Figure 6 This is a schematic diagram of eight different polarization states. For simplicity, we only verify eight different polarization states to illustrate the powerful spatial polarization modulation capability of the programmable spatial and polarization multiplexed metasurface, which is difficult to achieve with previous programmable polarization modulation metasurfaces. Figure 6 The diagram shows eight different polarization states represented by 3-bit numbers, which will be helpful for describing the corresponding polarization states later. Starting from the 45° line polarization, the numbers are encoded clockwise as 000, 001, 010, 011, 100, 101, 110, and 111.

[0043] Figures 7-8 These are specific examples of different polarization codes. Figure 7(a)-(d) show the polarization matrices (P1-P4) corresponding to the four sets of polarization codes 000, 001, 010 and 011, which represent the phase distribution required for a highly directional reflection beam along θ = -20°. Figure 7 (e)-(h) represent the simulation results of the far-field radiation patterns of the x-polarized wave and the y-polarized wave, with their reflection amplitudes and phase differences as follows: (A x / A y ,ΔФ)=(1,0),(A x / A y ,ΔФ)=(1,π),(A x / A y ,ΔФ)=(2,0) and (A x / A y ,ΔФ)=(2,π). Figure 8 Figures (a)-(d) show the polarization matrices (P5-P8) for four sets of polarization codes 100, 101, 110, and 111, representing the phase distribution required for a highly directional reflected beam along θ = 30°. The simulated far-field radiation patterns of their x-polarization and y-polarization components are shown in the figures. Figure 8 As shown in (e)-(h). Their reflection amplitude and phase difference are respectively: (A x / A y ,ΔФ)=(1,3π / 2,(A x / A y ,ΔФ)=(1,π / 2),(A x / A y ,ΔФ)=(1,5π / 4) and (A x / A y , ΔФ)=(2,7π / 4). Based on the above results, they all show good beam deflection and polarization control performance.

[0044] Figure 9 This is a simulated far-field pattern of the beam pointing at θ = -20° and θ = 30°, with polarization codes 100 and 101, and 110 and 111 respectively, corresponding to the polarization matrices. Case 1, Figure 9 (c) shows the relationship with Figure 9 The simulated far-field radiation pattern corresponding to the polarization matrix P9 shown in (a) indicates that the beam pointing to θ = -20° has (A x / A y , ΔФ)=(1,3π / 2), the beam pointing to θ=30° has (A x / A y , ΔФ)=(1,π / 2). In case 2, we consider the polarization code of the beam pointing to θ=-20° as 110, and the polarization code of the other beam pointing to θ=30° as 111. Figure 9 (d) shows the relationship with Figure 9 The polarization matrix P shown in (b) 10 Corresponding simulations show that a beam pointing at θ = -20° has (A x / A y , ΔФ)=(1,5π / 4), the beam pointing to θ=30° has (A x / A y , ΔФ)=(1,7π / 4). The above two cases show that the polarization state in the two beam deflection directions can be independently controlled.

[0045] Figure 10 This is a prototype of the metasurface. To verify the polarization control capability of the programmable spatial and polarization multiplexed information metasurface in actual operation, a prototype with an overall size of 240×240mm was fabricated using printed circuit board (PCB) technology. 2 The metasurface sample consists of 16×16 metasurface units. Figure 10 (a) is a front view of a programmable spatial and polarization multiplexed metasurface. Figure 10 (b) is a photograph of the metasurface rear view and the digital voltage control module. The magnified partial view of the metasurface shows four unit structures, and its front and back views are as follows. Figure 10 As shown in (c).

[0046] Figure 11 These are the test results for the amplitude and phase of the metasurface reflection. To verify the amplitude and phase characteristics of the proposed unit structure, we tested the amplitude and phase of the metasurface reflection. During the experiment, V x and V y A varactor diode that can be independently controlled in both horizontal and vertical directions. Figure 11 (a) and (b) present the measurement results of the reflection amplitude and phase as a function of bias voltage at different frequencies, showing that by changing the bias voltage from 0 to 15V, the reflection phase of the metasurface can be continuously controlled, and the reflected waves of x-polarized and y-polarized waves have almost the same electromagnetic response. The phase change range of x- and y-polarized waves at 10GHz is 315°, and the mapping relationship between the reflection phase of the metasurface unit and the bias voltage is established.

[0047] Figure 12 It is a far-field testing device in a standard microwave anechoic chamber. Figure 12The experimental setup for measuring the far-field pattern of a programmable spatially and polarized-multiplexed metasurface in a standard microwave anechoic chamber is shown. The metasurface is fixed on a test turntable, with a metamaterial lens antenna positioned 70 cm in front of it as the incident wave excitation source to generate a 45° linearly polarized plane wave. Another standard rectangular horn receiving antenna is fixed 10 m in front of the metasurface. Notably, the far-field patterns of the x-polarized and y-polarized component amplitudes and phases are obtained by testing the E-plane and H-plane of the standard rectangular horn receiving antenna separately.

[0048] Figures 13-15 This is an experimental verification of the aforementioned polarization coding. Figure 13 These are the test results for the far-field radiation patterns corresponding to beam pointing at θ = -20° and polar codes 000, 001, 010, and 011. Figure 13 (a)-(d) show the test crossover of the far-field radiation patterns corresponding to the four sets of polar codes 000, 001, 010 and 011, with the reflected wave being a highly directional beam with a deflection angle θ = -20°. Figure 14 Images (a)-(d) show the test results of the far-field radiation patterns corresponding to the four sets of polar codes 100, 101, 110, and 111, with the reflected wave being a highly directional beam with a deflection angle θ = 30°. Figure 15 (a) is the measurement result of the far-field radiation pattern corresponding to the polarization matrix P9. Figure 15 (b) corresponds to the polarization matrix P 10 The measured far-field radiation pattern results are very consistent with the simulation results.

[0049] The design and optimization algorithm of this invention have significant application prospects. The same concept can also be extended to transmissive or all-space metasurfaces, and the relevant operating frequency bands can be extended to acoustic, millimeter-wave, infrared, and optical bands. The optimization algorithm is not limited to particle swarm optimization; for example, genetic algorithms, immune algorithms, and simulated annealing algorithms can all be used as optimization algorithms in this invention. The above embodiments are merely illustrative of the technical concept of this invention and should not be construed as limiting the scope of protection of this invention. Any modifications made to the technical solution based on the technical concept proposed in this invention fall within the scope of protection of this invention.

Claims

1. A spatially and polarized multiplexed programmable metasurface, characterized in that, The spatial and polarization multiplexing programmable metasurface includes a programmable metasurface and a digital voltage control module. The programmable metasurface is a two-dimensional matrix formed by the periodic arrangement of programmable units in space. Each programmable unit integrates two varactor diodes in the horizontal and vertical directions. The digital voltage control module provides bias voltages to the varactor diodes in the horizontal and vertical directions, so that the varactor diodes in the horizontal and vertical directions operate in different capacitance ranges, and each programmable unit can adjust the reflection phase coverage to 320°. In the programmable metasurface, varactor diodes in the same row are controlled by the same bias voltage, varactor diodes in the same column are controlled by the same bias voltage, and the voltage distribution output by the digital voltage control module independently controls the phase distribution in the horizontal and vertical directions of the programmable metasurface. Combining generalized Snell theory and particle swarm optimization algorithm, the polarization matrix of the space and polarization multiplexed programmable metasurface is designed to control the deflection direction, amplitude and phase of the horizontal and vertical polarization components in the reflected wave, thereby realizing the control of the deflection direction and polarization state of the reflected wave, and the polarization state covers any point on the Poincaré sphere. The polarization matrix consists of corresponding phase distributions in the horizontal and vertical directions. Using the amplitude value of a specified far-field pattern as the optimization objective, particle fitness values ​​are evaluated using a particle swarm optimization algorithm. In each iteration, particle velocity, particle extrema, and swarm extrema are updated. When the loop termination condition is met, the final far-field pattern and the current horizontal and vertical phase distributions of the space-polarization multiplexed programmable metasurface are output. and .

2. The spatial and polarization multiplexing programmable metasurface according to claim 1, characterized in that, The programmable unit includes a top layer, a middle layer, a bottom layer, and two dielectric layers. The top layer, middle layer, and bottom layer are all metal layers, and a dielectric layer is set between the top layer and the middle layer, and between the middle layer and the bottom layer. The top layer consists of five metal patches, and four varactor diodes are loaded on the five metal patches. The four varactor diodes are connected to the feed line of the bottom layer through metallized holes. The digital voltage control module is physically connected to the programmable unit, providing bias voltage to control the varactor diodes in the horizontal and vertical directions in real time.

3. The spatial and polarization multiplexing programmable metasurface according to claim 2, characterized in that, Both dielectric layers are F4B dielectric layers, with a relative permittivity of 2.2, a loss angle of 0.001, and a thickness of 1 mm.

4. The spatial and polarization multiplexing programmable metasurface according to claim 1, characterized in that, In the regulation of the deflection direction, amplitude, and phase of the horizontal and vertical polarization components in the reflected wave, the deflection direction of the horizontal and vertical polarization components is the same, and the polarization state of the reflected beam is regulated by the amplitude and phase of the horizontal and vertical polarization components.

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