A broadband and multi-frequency switchable wave-absorbing and polarization-converting reconfigurable metasurface

Abstract

The present invention proposes a broadband and multi-frequency switchable absorbing and polarization conversion reconfigurable metasurface, which is used to solve the technical problems in the prior art that reconfigurable metasurfaces based on graphene and vanadium dioxide can only achieve limited functions and have a relatively single function bandwidth. The metasurface comprises four square dielectric substrates stacked in sequence from top to bottom, wherein the upper surface of the first dielectric substrate is printed with a square graphene patch, and the lower surface is printed with three square vanadium dioxide ring patches, the lower surface of the second dielectric substrate is printed with a square vanadium dioxide patch, the lower surface of the third dielectric substrate is printed with a group of square ring metal patches with notches in the diagonals, and the lower surface of the fourth dielectric substrate is printed with a square metal base plate. By adjusting the Fermi energy level of the square graphene patch and the temperature of the square vanadium dioxide ring patch and the square vanadium dioxide patch, broadband and multi-frequency switching of the working bandwidth and reconfigurable absorbing and polarization conversion can be achieved. The metasurface can be used in the fields of terahertz absorbing and terahertz communication.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz multifunctional devices, and relates to a reconfigurable metasurface based on graphene and vanadium dioxide, and specifically to a broadband and multi-frequency switchable wave-absorbing and polarization-converting reconfigurable metasurface, which can be used in the fields of terahertz wave absorption and terahertz communication. Technical Background

[0002] A reconfigurable metasurface is a metamaterial structure whose electromagnetic response can be adjusted through external stimuli. Traditional metasurfaces are typically static, with their electromagnetic response determined by their geometry and material parameters, making them incapable of flexible and dynamic regulation. Reconfigurable metasurfaces were initially studied to address performance limitations in wireless communications and radar systems. With the continuous advancement of technology, performance requirements for communications and radar systems are becoming increasingly demanding, and functional requirements are becoming increasingly diverse. Reconfigurable metasurfaces offer diverse functionality and flexibility, enabling precise control of multiple parameters such as the intensity, phase, and polarization of electromagnetic waves.

[0003] Currently, most common reconfigurable metasurfaces use materials with adjustable properties to achieve functional reconstruction. For example, the Chinese patent with authorization announcement number CN110441842 B, titled "A multifunctional device based on VO2 and graphene hybrid metamaterial", uses adjustable materials vanadium dioxide and graphene to design a multifunctional metasurface. A circular vanadium dioxide patch and a square graphene patch etched with a rectangular pattern are printed at the center of the upper surface of the dielectric substrate of the metasurface. The square graphene patch and the circular vanadium dioxide patch do not contact each other, and a square metal base is printed on the lower surface of the dielectric substrate. When the temperature of the circular vanadium dioxide patch is higher than 68°C, the vanadium dioxide has metallic properties and is in a metallic state. This invention can It can achieve perfect wave absorption in the range of 44 to 52 THz; when the temperature of vanadium dioxide is lower than 68°C, vanadium dioxide is regarded as a highly wave-transmitting dielectric material and is in an insulating state. When the Fermi level of the graphene patch is set to 0.95 eV, the invention can achieve line-to-line polarization conversion with a working bandwidth of less than 1 THz near a frequency of 14 THz. However, in the invention, the vanadium dioxide patch and the graphene patch are in the same plane, and can only achieve narrow-band wave absorption function and narrow-band line-to-line polarization function, and the relative bandwidth of the wave absorption and polarization conversion that can be achieved are relatively narrow. Summary of the Invention

[0004] The purpose of the present invention is to address the problems existing in the prior art and propose a broadband and multi-frequency switchable wave-absorbing and polarization-converting reconfigurable metasurface to solve the technical problems that the prior art can only achieve a limited number of functions and a single function relative to the bandwidth.

[0005] To achieve the above objectives, the technical solution adopted by the present invention includes N×N periodically arranged metasurface units, where N≥2; the metasurface unit includes four square dielectric substrates stacked in sequence from top to bottom, wherein a square graphene patch 11 is printed at the center of the upper surface of the first dielectric substrate 1, and a plurality of nested square vanadium dioxide annular patches 12 are printed at the center of the lower surface, wherein the lines connecting the midpoints of two groups of opposite sides of the square graphene patches 11 coincide with the two diagonals of the first dielectric substrate 1 respectively; a square vanadium dioxide patch 21 is printed on the lower surface of the second dielectric substrate 2; a group of square annular metal patches 31 with notches in the diagonals are printed on the lower surface of the third dielectric substrate 3; and a metal base plate 41 is printed on the lower surface of the fourth dielectric substrate 4.

[0006] When the square vanadium dioxide annular patch 12 and the square vanadium dioxide patch 21 are in an insulating state, the square graphene patch 11 and a group of square annular metal patches 31 with diagonal gaps resonate together to realize the polarization conversion function. Adjusting the Fermi level of the square graphene patch 11 can realize switching between the dual-frequency line-line polarization conversion function and the broadband line-line polarization conversion function; when the state of the square vanadium dioxide annular patch 12 and the square vanadium dioxide patch 21 changes from an insulating state to a metallic state, the polarization conversion metasurface will be reconstructed into an absorbing metasurface. The square graphene patch 11 and multiple square vanadium dioxide annular patches 12 resonate together to produce an absorbing effect. Adjusting the Fermi level of the square graphene patch 11 can realize switching between the broadband absorbing function and the dual-frequency absorbing function.

[0007] The above-mentioned broadband and multi-frequency switchable absorbing and polarization conversion reconfigurable metasurface, the multiple square vanadium dioxide annular patches 12 include a first square vanadium dioxide annular patch 121, a second square vanadium dioxide annular patch 122 and a third square vanadium dioxide annular patch 123 with equal width and increasing side lengths from the inside to the outside, and the two diagonals of the three square vanadium dioxide annular patches respectively coincide with the two diagonals of the first dielectric substrate 1.

[0008] In the above-mentioned broadband and multi-frequency switchable wave-absorbing and polarization-converting reconfigurable metasurface, the diagonal length of the square graphene patch 11 is smaller than the side length of the third vanadium dioxide annular patch 123 and a group of square annular metal patches 31 with notches at the diagonals.

[0009] In the above-mentioned broadband and multi-frequency switchable wave absorbing and polarization conversion reconfigurable metasurface, the diagonals of the group of square ring metal patches 31 with gaps respectively coincide with the two diagonals of the third dielectric substrate 3 .

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] 1. In the present invention, since the graphene patch and the vanadium dioxide patch are located in different planes, when the vanadium dioxide patch is in a metallic state, the square vanadium dioxide patch is equivalent to a metal base plate, and the square vanadium dioxide ring patch is equivalent to a metal resonant ring. At this time, the metasurface can realize wave absorption characteristics, and regulating the Fermi level of the square graphene patch can realize switching between broadband wave absorption function and dual-band wave absorption function; when the vanadium dioxide is in an insulating state, the square vanadium dioxide ring patch and the square vanadium dioxide patch can be regarded as lossless dielectric materials, and the square graphene patch and the square ring-shaped metal patch with a gap resonate together. Regulating the Fermi level of the square graphene patch can realize switching between broadband line-to-line polarization conversion function and dual-band line-to-line polarization conversion function. Compared with the existing technology, more functions can be realized, and each function can achieve broadband response and dual-band response. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0013] Figure 2 It is a top view of the first dielectric substrate of the present invention.

[0014] Figure 3 It is a top view of a square annular metal patch with notches at opposite corners according to the present invention.

[0015] Figure 4 It is a broadband wave absorption simulation model and a broadband wave absorption curve diagram of the present invention.

[0016] Figure 5 It is a dual-frequency wave absorption simulation model and a dual-frequency wave absorption curve diagram of the present invention.

[0017] Figure 6 It is a broadband line-to-line polarization conversion simulation model and a broadband polarization conversion curve diagram of the present invention.

[0018] Figure 7 It is a dual-frequency line-to-line polarization conversion simulation model and a dual-frequency polarization conversion curve diagram of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] Reference Figure 1The present invention includes a first dielectric substrate 1, a second dielectric substrate 2, a third dielectric substrate 3, and a fourth dielectric substrate 4, which are parallel to the xoy plane of the three-dimensional coordinate system and arranged in sequence from top to bottom. The side length of the four dielectric substrates is 110 μm. The first dielectric substrate 1 is made of polymethacrylimide with a thickness of 7 μm and a relative dielectric constant of 1.05, which has little effect on the propagation of electromagnetic waves. The thickness of the second dielectric substrate 2 is 32 μm. The lower surface of the second dielectric substrate 2 is printed with a square vanadium dioxide patch 21 with the same side length as the dielectric substrate. When the temperature of the vanadium dioxide patch is higher than 68°C, the second dielectric substrate 2 The vanadium oxide patch is in a metallic state, preventing electromagnetic waves from penetrating the square vanadium dioxide patch 21. The third dielectric substrate 3 has a thickness of 5 μm, and the fourth dielectric substrate 4 has a thickness of 17 μm. A square metal base plate 41 with a thickness of 0.3 μm and a side length of 110 μm is printed on the lower surface of the fourth dielectric substrate 4. When the vanadium dioxide patch temperature is below 68°C, the vanadium dioxide patch is in an insulating state, and the square metal base plate 41 can prevent electromagnetic waves from penetrating. The second dielectric substrate 2, the third dielectric substrate 3, and the fourth dielectric substrate 4 are made of a cyclic olefin copolymer with a dielectric constant of 2.35 + i 0.01.

[0021] Reference Figure 2 A square graphene patch 11 is printed on the upper surface of the first dielectric substrate 1. The lines connecting the midpoints of the two opposite sides of the square graphene patch 11 coincide with the two diagonals of the first dielectric substrate 1, so that the Fermi level of the graphene patch 11 can be regulated to achieve dual-band absorption. Three square vanadium dioxide ring patches are printed on the lower surface of the first dielectric substrate 1 on the xoy plane. The three square vanadium dioxide ring patches are printed on the lower surface of the first dielectric substrate 1 in the order of increasing side length from the center to the edge. The three square vanadium dioxide ring patches with increasing side length are used to broaden the absorption bandwidth. The first square vanadium dioxide ring patch 12 1 has a side length of 40 μm, the second square vanadium dioxide ring patch 122 has a side length of 60 μm, and the third square vanadium dioxide ring patch 123 has a side length of 80 μm. The width of the three vanadium dioxide ring patches is 2.5 μm and the thickness is 1 μm. The two diagonals of the three square vanadium dioxide ring patches coincide with the two diagonals of the first dielectric substrate 1 respectively to ensure that the metasurface has the same absorbing effect for incident waves of any polarization. In order to achieve better dual-frequency absorbing effect, the diagonal length of the square graphene patch 11 is less than the side length of the third vanadium dioxide ring patch 123, and the side length of the square graphene patch 11 is 50 μm.

[0022] Reference Figure 3The lower surface of the third dielectric substrate 3 is printed with a first square ring-shaped metal patch 311 with a gap and a second square ring-shaped metal patch 312 with a gap. The gap is square with a side length of 9 μm. When the Fermi level of the square graphene patch 11 is 0 eV and the vanadium dioxide patch is in an insulating state, a group of square ring-shaped metal patches 31 with a gap can perform line-to-line polarization conversion in multiple frequency bands close to each other, realizing broadband line-to-line polarization conversion. The length of the diagonal of the square graphene patch 11 is less than the side length of the group of square ring-shaped metal patches 31 with a gap. long, so as to achieve good dual-frequency line-to-line polarization conversion on the metasurface when the Fermi level of the square graphene patch 11 is 0.3 eV and the vanadium dioxide patch is in an insulating state; the diagonals of a group of notched square annular metal patches 31 respectively coincide with the two diagonals of the third dielectric substrate 3 to ensure that both the incident x-polarized wave and the y-polarized wave can achieve efficient line-to-line polarization conversion; this group of notched square annular metal patches has a side length of 65 μm, a width of 9 μm, a thickness of 2 μm, and a distance d of 20 μm from the edge of the third dielectric substrate 3.

[0023] The following is a description of the technical effects of the present invention in conjunction with simulation experiments:

[0024] 1. Simulation conditions and content:

[0025] The simulation software used is CST, and the Floquet mode is used to simulate infinite arrays and simulate the various functions of the metasurface. When the temperature of the vanadium dioxide patch is set to 70°C, the vanadium dioxide patch is in a metallic state. When the temperature of the vanadium dioxide patch is set to 50°C, the vanadium dioxide patch is in an insulating state. The electromagnetic properties of graphene, vanadium dioxide and gold in the terahertz frequency band are all given by the Drude model, and the electromagnetic wave is incident vertically on the metasurface unit along the -z direction.

[0026] Simulation 1: When the vanadium dioxide patch is in a metallic state and the Fermi level of the graphene patch is set to 0 eV, Figure 4 (a) shows the simulation of the absorbing function of the present invention, and the broadband absorption rate curve obtained is as follows: Figure 4 (b) shown.

[0027] Simulation 2, when the vanadium dioxide patch is in a metallic state and the Fermi level of the graphene patch is set to 1eV, as shown in Figure 5 (a) shows the simulation of the absorbing function of the present invention, and the broadband absorption rate curve obtained is as follows: Figure 5 (b) shown.

[0028] In simulation 3, when the vanadium dioxide patch is in an insulating state, the Fermi level of the graphene patch is set to 0 eV, as shown in Figure 6 (a) shows the simulation of the polarization conversion function of the present invention, and the broadband line-to-line polarization conversion rate curve is obtained, as shown in FIG. Figure 6 (b) shown.

[0029] In simulation 4, when the vanadium dioxide patch is in an insulating state and the Fermi level of the graphene patch is set to 0.3 eV, Figure 7 (a) shows the simulation of the polarization conversion function of the present invention, and the dual-frequency line-to-line polarization conversion rate curve is obtained, as shown in FIG. Figure 7 (b) shown.

[0030] 2. Analysis of simulation results:

[0031] Reference Figure 4 ,like Figure 4 As shown in (b), electromagnetic waves in the range of 0.75 to 1.88 THz will be absorbed by the metasurface, with an absorption rate greater than 90% and a relative bandwidth of 86%. Further analysis Figure 4 (b) The electric field distribution in the absorbing frequency band shows that the frequencies corresponding to the single absorbing resonance peaks are 0.9 THz, 1.33 THz and 1.82 THz, respectively. The absorption peak at 0.9 THz comes from the resonance generated by the interaction of the two square vanadium dioxide ring patches with larger side lengths, the absorption peak at 1.33 THz comes from the resonance generated by the interaction of the two square vanadium dioxide ring patches with smaller side lengths, and the absorption peak at 1.82 THz comes from the resonance generated by the square vanadium dioxide ring patch with the smallest side length itself. It can be seen that the broadband absorbing function comes from the widening of the bandwidth by the resonance peaks of multiple frequency points close to each other. The relative bandwidth of the absorbing device of the present invention is greater than 16.7%, which is wider than that of the prior art.

[0032] refer to Figure 5 The absorption rate curve is shown in Figure 5(b). The metasurface absorbs incident electromagnetic waves in the range of 0.81~1.15THz and 1.87~1.94THz, and the absorption efficiency reaches more than 90%. The absorption peaks in these two absorption bands correspond to frequency values ​​of 1.04THz and 1.90THz. It can be found that at these two frequencies, the induced electric field is mainly distributed on the square graphene patch and multiple square vanadium dioxide ring patches. The low-frequency resonance peak mainly comes from the joint action of the three square vanadium dioxide ring patches, while the high-frequency resonance peak mainly comes from the induced electric field on the two diagonals of the square graphene patch. The frequencies of the two absorption peaks are far apart, thus forming dual-frequency absorption.

[0033] refer to Figure 6 ,like Figure 6 As shown in (b), the metasurface can convert the main polarization wave into the cross-polarization wave in the frequency range of 0.72~1.40THz, with a relative bandwidth of 64.2%; the polarization conversion efficiency curve is shown in Figure 6 As shown in (b), Figure 6As shown in (b), the metasurface has two polarization conversion peaks, at 0.77 THz and 1.31 THz. Analysis of the electric field distribution at these two frequencies shows that at 0.77 THz, the induced electric field primarily originates from the joint resonance of the metal base plate and the diagonally notched square ring-shaped metal patch. The electric field is primarily distributed at the ends of the notched diagonal square ring-shaped metal patch and the projection of the notch on the metal base plate. At 1.31 THz, the induced electric field is primarily distributed at the ends of the notched diagonal square ring-shaped metal patch and at the right angles. The close frequency spacing between the two resonance peaks results in broadband line-to-line polarization conversion. The polarization conversion relative bandwidth of the present invention is greater than 7%, wider than that of the prior art.

[0034] refer to Figure 7 , the dual-frequency line-to-line polarization conversion rate curve is as follows Figure 7 As shown in (b), the polarization conversion peak in the 0.78THz to 0.85THz frequency range corresponds to a frequency of 0.82THz, while the polarization conversion peak in the 1.28THz to 1.47THz frequency range corresponds to a frequency of 1.37THz. Observing the electric field distribution at 0.82THz, it is found that the induced electric field is primarily distributed along the two opposite sides of the square graphene patch and at the ends of the two sides of a set of square ring-shaped metal patches with diagonal notches. Meanwhile, the electric field at 1.37THz is primarily distributed near the two opposite corners of the square graphene patch and at the ends of the two sides and right angles of the square ring-shaped metal patches with diagonal notches. The large frequency difference between the two resonant peaks results in dual-frequency line-to-line polarization conversion.

[0035] The above description is only a preferred embodiment of the present invention and does not limit the present invention. For ordinary technicians in this field, several modifications and improvements can be made without departing from the innovative concept of the present invention, but these changes all fall within the scope of protection of the present invention.

Claims

1. A broadband and multi-frequency switchable wave-absorbing and polarization-converting reconfigurable metasurface, comprising N×N periodically arranged metasurface units, where N ≥ 2; characterized by: The metasurface unit comprises four square dielectric substrates stacked in sequence from top to bottom, wherein a square graphene patch (11) is printed at the center of the upper surface of the first dielectric substrate (1), and a plurality of mutually nested square vanadium dioxide annular patches (12) are printed at the center of the lower surface, wherein the lines connecting the midpoints of two groups of opposite sides of the square graphene patch (11) coincide with the two diagonals of the first dielectric substrate (1); a square vanadium dioxide patch (21) is printed on the lower surface of the second dielectric substrate (2); a group of square annular metal patches (31) with notches in the diagonals are printed on the lower surface of the third dielectric substrate (3); and a metal base plate (41) is printed on the lower surface of the fourth dielectric substrate (4); When the square vanadium dioxide annular patch (12) and the square vanadium dioxide patch (21) are in an insulating state, the square graphene patch (11) and a group of square annular metal patches (31) with notches on the diagonals resonate together to realize a polarization conversion function, and adjusting the Fermi level of the square graphene patch (11) can realize switching between a dual-frequency line-line polarization conversion function and a broadband line-line polarization conversion function; when the state of the square vanadium dioxide annular patch (12) and the square vanadium dioxide patch (21) changes from an insulating state to a metallic state, the polarization conversion metasurface will be reconstructed into an absorbing metasurface, and the square graphene patch (11) and multiple square vanadium dioxide annular patches (12) resonate together to produce an absorbing effect, and adjusting the Fermi level of the square graphene patch (11) can realize switching between a broadband absorbing function and a dual-frequency absorbing function.

2. The broadband and multi-frequency switchable wave-absorbing and polarization-converting reconfigurable metasurface according to claim 1, characterized in that: The plurality of square vanadium dioxide annular patches (12) include a first square vanadium dioxide annular patch (121), a second square vanadium dioxide annular patch (122), and a third square vanadium dioxide annular patch (123) of equal width and increasing side length from the inside to the outside, and two diagonals of the three square vanadium dioxide annular patches respectively coincide with two diagonals of the first dielectric substrate (1).

3. The broadband and multi-frequency switchable wave-absorbing and polarization-converting reconfigurable metasurface according to claim 2, characterized in that: The diagonal length of the square graphene patch (11) is smaller than the side lengths of the third vanadium dioxide annular patch (123) and a group of square annular metal patches (31) with notches at the diagonals.

4. The broadband and multi-frequency switchable wave-absorbing and polarization-converting reconfigurable metasurface according to claim 1, characterized in that: The diagonals of the group of square ring metal patches (31) with gaps respectively coincide with the two diagonals of the third dielectric substrate (3).

Images