Vanadium dioxide-based dual-band dual-function switchable terahertz metasurface

Abstract

The invention belongs to the technical field of communication, and particularly relates to a dual-band dual-function switchable terahertz metasurface. The terahertz metasurface is a two-dimensional array formed by periodically extending metamaterial units; the metasurface unit is composed of three metal layers and two substrate layers. The top metal layer is of a double-ring structure; the center of the middle metal layer is designed to be disc-shaped, and the periphery is filled with VO2 with the same thickness; the bottom metal layer is a reflecting layer; the two ends of the VO2 layer of the metasurface are connected with control voltage, when different external voltages are applied to VO2, two states of a metal state and a medium state are presented, and finally real-time switching of the two functions is achieved. Particularly, the function switching has a quite large implementation span, no matter which function the target function I is, the setting of the target function II is not limited, and the specific function of the metasurface is displayed by taking OAM multimode multiplexing switching as an example in the actual function implementation. The metasurface has a wide application prospect and is expected to play a key role in terahertz communication.

Description

Technical Field

[0001] This invention belongs to the field of communication technology, and specifically relates to a terahertz metasurface. Background Technology

[0002] Metasurface technology is currently facing a key challenge in its transition from static to dynamic applications. Traditional metallic or dielectric metasurfaces, once fabricated, have fixed electromagnetic responses, making them unsuitable for applications requiring real-time control. Therefore, researchers are dedicated to developing dynamically reconfigurable metasurfaces to achieve advanced functions such as beam control, focusing, and holography.

[0003] In the terahertz band, the extremely short wavelengths result in tiny unit sizes, rendering traditional control elements (such as diodes) unsuitable. Integrating phase change materials such as VO2 and graphene has become an effective solution. VO2 undergoes an insulator-metal phase transition at approximately 341 K, resulting in a significant change in its conductivity. Furthermore, it can be rapidly triggered at the picosecond level through thermal, optical, and electrical excitation, making it highly suitable for terahertz dynamic metasurfaces. Existing research has utilized VO2 to achieve Airy beam generation and programmable wavefront manipulation.

[0004] However, terahertz reconfigurable metasurfaces still face two major challenges: first, the micro- and nanostructures corresponding to high frequencies require extremely high processing precision, which is difficult to achieve with existing technologies; second, thermally triggered VO2 metasurfaces require a stable heating environment, limiting practical applications. These bottlenecks urgently need to be overcome to promote the practical application of the technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and defects in the prior art and provide a voltage-controlled, VO2-based, dual-band, dual-function switchable terahertz metasurface.

[0006] The dual-band, dual-function switchable terahertz metasurface provided by this invention has the following structure: Figure 1 As shown, the metasurface is a two-dimensional array formed by periodically extending carefully designed metamaterial units; each metasurface unit consists of three metal layers and two substrate layers; specifically, the top metal layer has a double-ring structure; the center of the middle metal layer is designed as a disk, and its periphery is filled with VO2 of equal thickness; the bottom metal layer is a reflective layer; different bias voltages are configured on the metasurface (specifically, control voltages are connected to both ends of the VO2 layer of the metasurface) to achieve different functions; Furthermore, in the metamaterial unit: a control voltage is connected to both ends of the metasurface VO2 layer. In the double-ring structure of the top layer, the inner ring (patch) has an inner radius of 20 ~ 135 μm, the outer ring has an inner radius of 40 ~ 270 μm, and the width (i.e., ring width) of the inner and outer ring patches is 10 ~ 20 μm; the spacing between the inner and outer ring patches is 5 ~ 120 μm; the metal patch is made of copper foil with a thickness of 150 ~ 300 nm; The central disk of the intermediate metal layer has a radius of 80 ~ 359 μm and is made of copper foil; the outer layer is VO2, and the thickness of both copper and VO2 is 150 ~ 300 nm. The material of the bottom reflective layer is copper foil with a thickness of 150~300 nm.

[0007] Furthermore: The substrate of the top metal layer is a polyimide (PI) medium with a thickness of 135~145 μm; The substrate of the intermediate metal layer is silicon (Si) dielectric with a thickness of 115~125 μm.

[0008] Furthermore: The two-dimensional array formed by extending the metamaterial units has a size of M×N. The number of row units M and column units N of the two-dimensional array can be taken as between 12 and 48 according to actual needs. In this embodiment, M=N=24.

[0009] In this invention, the metamaterial units in the two-dimensional array have the same metal patch structure and size; In this invention, the metamaterial unit dielectric substrate can be made of PI material with a dielectric constant of 3.5 and a loss tangent of 0.004. To increase the space for drilling assembly and soldering pins, the actual size is a cylinder with a radius of 4 cm and a thickness of 135-145 μm; and Si material with a dielectric constant of 11.9 and a conductivity of 2.5e-04 S / m, the actual size is a cylinder with a radius of 4 cm and a thickness of 135-145 μm.

[0010] In this invention, different bias voltages are applied to the metasurface to achieve different functions. Specifically, when the bias voltage is 5 to 10 V, VO2 transforms into a metallic state (conductivity of 2.5e+05 S / m); when no bias voltage is applied (i.e., the voltage is 0 V), VO2 remains in a dielectric state (conductivity of 200 S / m), thus enabling the metasurface to achieve different functions. Specifically: When VO2 is in two phase states (dielectric state / metallic state), it can implement any two phase-coded functions in the frequency bands around 70 ~ 90 GHz and 180 ~ 230 GHz, respectively; where: When VO2 is in the metallic state, the metasurface operates in the 180 ~ 230 GHz frequency band, at which time the metasurface can realize OAM multiplexing of + / -2 modes; When VO2 is in the dielectric state, the metasurface operates in the 70 ~ 90 GHz frequency band, at which time the metasurface can realize OAM multiplexing of + / -1 modes.

[0011] Simulation results show that: When VO2 is in the dielectric state, in the 75-85 GHz frequency band, the two OAM beams of the +1 and -1 modes deflect along the X-axis at +35 degrees and -35 degrees respectively, exhibiting a circular amplitude distribution. Within the 75-85 GHz frequency band, depending on the mode, the phase distribution has a 2π phase shift clockwise or counterclockwise along the entire concentric circle; When VO2 is in the metallic state, in the 185 ~ 225 GHz frequency band, the two OAM beams of the +2 and -2 modes deflect along the X-axis at +15 degrees and -15 degrees respectively and exhibit a circular amplitude distribution. Depending on the mode, the phase distribution has a 4π phase shift along the entire concentric circle clockwise or counterclockwise.

[0012] The terahertz metasurface designed in this invention can achieve two different functions in different frequency bands through voltage control: when the applied bias voltage is 5 ~ 10 V, VO2 is in a metallic state, which can realize OAM multiplexing of + / -2 modes; when the applied voltage is 0 V, VO2 is in a dielectric state, which can realize OAM multiplexing of + / -1 modes. It has the advantages of multiple functions, multiple frequency bands, simple structure, and reconfigurability. Attached Figure Description

[0013] Figure 1 The diagram shows the overall structure top view and the unit structure decomposition diagram of the vanadium dioxide-based dual-band dual-function switchable terahertz metasurface of the present invention.

[0014] Figure 2 This paper presents the simulated transmission coefficients of each cell in the vanadium dioxide-based dual-band dual-function switchable terahertz metasurface near 220 GHz when VO2 is in a metallic state. (a) is the transmission amplitude of the basic cell; (b) is the transmission phase of the basic cell; (c) is the transmission amplitude of the supplementary cell; and (d) is the transmission phase of the supplementary cell.

[0015] Figure 3 This invention relates to the simulated transmission amplitude of each unit of the vanadium dioxide-based dual-band dual-function switchable terahertz metasurface near 83 GHz when VO2 is in the dielectric state.

[0016] Figure 4The simulated transmission phases of each unit near 83 GHz of the vanadium dioxide-based dual-band dual-function switchable terahertz metasurface of the present invention are shown in (a) ~ (h), which correspond to the simulation results of different unit groups.

[0017] Figure 5 The simulation results of the 3D far-field radiation pattern of the vanadium dioxide-based dual-band dual-function switchable terahertz metasurface in the +2 and -2 modes of OAM multiplexing at 185 ~ 225 GHz are shown.

[0018] Figure 6 The simulation results of the phase distribution of the vanadium dioxide-based dual-band dual-function switchable terahertz metasurface in the present invention at 185 ~ 225 GHz are shown. The observation planes are deflected by +15° and -15° along the X-axis.

[0019] Figure 7 The simulation results of the 3D far-field radiation pattern of the vanadium dioxide-based dual-band dual-function switchable terahertz metasurface at 75 ~ 86 GHz for +1 and -1 mode OAM multiplexing are presented.

[0020] Figure 8 The simulation results of the phase distribution of the vanadium dioxide-based dual-band dual-function switchable terahertz metasurface at 75-86 GHz are shown. The observation planes are deflected by +35° and -35° along the X-axis.

[0021] The labels in the diagram are as follows: 1 is the inner metal ring patch of the top layer, 2 is the outer metal ring patch of the top layer, 3 is the top polyimide substrate, 4 is the middle metal disk patch, 5 is the middle VO2 layer, 6 is the silicon substrate, and 7 is the reflective metal patch. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments; this embodiment provides detailed implementation methods and specific operation processes, but the scope of protection of the present invention is not limited to the following embodiments.

[0023] When VO2 is in two phase states (dielectric state / metallic state), it can realize any two phase-coded functions in the frequency bands around 70 ~ 90 GHz and 180 ~ 230 GHz, respectively; When VO2 is in a metallic state after being energized, the metasurface in the 185 ~ 225 GHz band can deflect the +2 and -2 modes of OAM along the X-axis to +15° and -15° respectively when a linearly polarized electromagnetic wave incident perpendicular to the metasurface is energized. When VO2 is in a dielectric state without being energized, the metasurface in the 75 ~ 85 GHz band can deflect the +1 and -1 modes of OAM along the X-axis to +35° and -35° respectively when a linearly polarized electromagnetic wave incident perpendicular to the metasurface is energized.

[0024] like Figure 1 As shown, the metamaterial unit described in this embodiment consists of three metal layers, two substrate layers, and a VO2 layer surrounding the middle metal layer. Specifically, the top metal layer has a double-ring structure; the middle metal layer is designed as a disk, with the outer perimeter filled with VO2 of equal thickness; and the bottom metal layer is a reflective layer.

[0025] The two-dimensional array of metamaterial units described in this embodiment is formed by extending metamaterial units. The top metal patch of the unit is made of copper foil with a thickness of 200 nm. The upper PI dielectric layer has a thickness of 140 μm, and the lower Si dielectric layer has a thickness of 120 μm. The upper surface of the lower Si dielectric layer is a copper disk layer, and the periphery is VO. 2， The thickness of both metallic copper and VO2 is 200 nm.

[0026] Table 1 shows the design dimensions of specific units, where, R 1 represents the inner radius of the top inner ring (the outer ring radius is...). R 2 = 2 R 1. The ring width is 15 μm. R 3 represents the radius of the intermediate layer metal disk. The first-level serial numbers A to H correspond to phase coding covering 360 degrees at 45-degree intervals under + / -2 mode OAM multiplexing; the second-level serial numbers 1 to 8 correspond to phase coding covering 360 degrees at 45-degree intervals under + / -1 mode OAM multiplexing. For example, A1 indicates that in the corresponding... R 1. R In the 3-dimensional configuration, the cell phase is 45 degrees when VO2 is in the metallic state in the 180 ~ 230 GHz band, and the cell phase is 45 degrees when VO2 is in the dielectric state in the 70 ~ 90 GHz band; A2 indicates that in the corresponding R 1. R At size 3, the cell phase is 45 degrees when VO2 is in the metallic state in the 180 ~ 230 GHz band, and 90 degrees when VO2 is in the dielectric state in the 70 ~ 90 GHz band; B1 indicates that in the corresponding R 1. R In the 3-dimensional configuration, the cell phase is 90 degrees when VO2 is in the metallic state in the 180 ~ 230 GHz band, and 45 degrees when VO2 is in the dielectric state in the 70 ~ 90 GHz band; B2 indicates that in the corresponding R 1. R In the 3-dimensional case, the cell phase is 90 degrees when VO2 is in the metallic state in the 180 ~ 230 GHz band, and the cell phase is 90 degrees when VO2 is in the dielectric state in the 70 ~ 90 GHz band.

[0027] In this invention, the material of the metamaterial unit dielectric substrate can be PI material with a dielectric constant of 3.5 and a loss tangent of 0.004. In order to increase the space for drilling assembly and soldering pins, the actual size is a cylinder with a radius of 4 cm and a thickness of 140 μm. The material is Si material with a dielectric constant of 11.9 and a conductivity of 2.5e-04 S / m, and the actual size is a cylinder with a radius of 4 cm and a thickness of 140 μm.

[0028] Figure 2 The simulation results show the transmission coefficients of VO2 in the metallic state at various sizes, with amplitudes greater than 0.9 and phases covering 360 degrees at 45-degree intervals. Figure 3 , 4 The simulation results show the transmission coefficients of VO2 at various dimensions when it is in a dielectric state. The amplitude is generally greater than 0.8, and the phase covers 360 degrees at 45-degree intervals.

[0029] like Figure 5 , 6 As shown in the figure, the multiplexing of the two OAM beams can be clearly seen. At 185 ~ 225 GHz, the two OAM beams deflect along the X-axis at +15 degrees and -15 degrees respectively and present a circular amplitude distribution. At the same time, depending on the mode, the phase distribution has a 4π phase shift along the entire concentric circle clockwise or counterclockwise.

[0030] like Figure 7 , 8 As shown in the figure, it can be clearly seen that the metasurface in the 75 ~ 86 GHz band will realize +1 and -1 mode OAM multiplexing with deflection of +35° and -35° along the X-axis direction, and the phase will have a phase shift of 2π clockwise or counterclockwise along the entire concentric circle.

[0031] The technical solution of the present invention is not limited to the specific embodiments described above. For example, the present invention connects a control voltage to both ends of the VO2 layer of the metasurface, so that VO2 presents two states, a metallic state and a dielectric state, when different external voltages are applied, and finally realizes the real-time switching of the two functions. This function switching has a considerable implementation range, and no matter what the target function one is, it will not limit the setting of the target function two. In the actual function implementation, the OAM multimode multiplexing switching is used as an example to demonstrate the specific function of the metasurface. All technical modifications made according to the technical solution of the present invention fall within the protection scope of the present invention.

[0032] Table 1 shows the dimensions of the dual-band, dual-function switchable terahertz metasurface structure based on vanadium dioxide in the embodiments.

[0033] .

Claims

1. A dual-band, dual-function switchable terahertz metasurface, characterized in that, It is a two-dimensional array formed by periodically extending metamaterial units; the metasurface unit consists of three metal layers and two substrate layers; specifically, the top metal layer is a double-ring structure; the center of the middle metal layer is designed as a disk, and its periphery is filled with VO2 of equal thickness; the bottom metal layer is a reflective layer; different bias voltages are configured on the metasurface to achieve different functions.

2. The dual-band, dual-function switchable terahertz metasurface according to claim 1, characterized in that, In the double-ring structure of the top layer, the inner radius of the inner ring is 20 ~ 135 μm, the inner radius of the outer ring is 40 ~ 270 μm, the width of the inner and outer rings is 10 ~ 20 μm, and the distance between the inner and outer rings is 5 ~ 120 μm. The metal patch uses copper foil with a thickness of 150 ~ 300 nm; The disk at the center of the intermediate metal layer has a radius of 80 ~ 359 μm and is made of copper foil; the thickness of both the copper foil and the surrounding VO2 is 150 ~ 300 nm. The material of the bottom reflective layer is copper foil with a thickness of 150~300 nm.

3. The dual-band, dual-function switchable terahertz metasurface according to claim 1, characterized in that: The substrate of the top metal layer is a polyimide (PI) medium with a thickness of 135~145 μm; The substrate of the intermediate metal layer is silicon (Si) dielectric with a thickness of 115~125 μm.

4. The dual-band, dual-function switchable terahertz metasurface according to any one of claims 1-3, characterized in that, The two-dimensional array formed by the extension of the metamaterial units has a size of M×N, and the number of row units M and column units N of the two-dimensional array are respectively between 12 and 48.

5. The dual-band, dual-function switchable terahertz metasurface according to any one of claims 1-3, characterized in that, Each metamaterial unit in the two-dimensional array has the same metal patch structure and size.

6. The dual-band, dual-function switchable terahertz metasurface according to claim 5, characterized in that, The different bias voltages configured are used to achieve different functions. Specifically, when the bias voltage is 5 ~ 10 V, VO2 transforms into a metallic state; when no bias voltage is applied, i.e., the voltage is 0 V, VO2 remains in a dielectric state, enabling the metasurface to achieve different functions.

7. The dual-band, dual-function switchable terahertz metasurface according to claim 6, characterized in that, Specifically: When VO2 is in two phase states: dielectric state / metallic state, it can implement any two phase-coded functions in the frequency bands near 70 ~ 90 GHz and 180 ~ 230 GHz, respectively; where: When VO2 is in the metallic state, the metasurface operates in the 180 ~ 230 GHz frequency band, at which time the metasurface can realize OAM multiplexing of + / -2 modes; When VO2 is in the dielectric state, the metasurface operates in the 70 ~ 90 GHz frequency band, at which time the metasurface can realize OAM multiplexing of + / -1 modes.

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