Switchable metamaterial absorber based on vanadium dioxide and graphene and dynamic tuning method

Abstract

The invention discloses a switchable metamaterial absorber based on vanadium dioxide and graphene and a dynamic tuning method, and relates to the technical field of terahertz wave devices. The absorber is formed by continuously splicing periodic unit structures on a plane in an array form, and each periodic unit structure is sequentially provided with a vanadium dioxide-graphene composite metasurface, a dielectric layer and a metal reflecting layer from top to bottom; the vanadium dioxide-graphene composite metasurface is composed of a patterned graphene disc and three fan-shaped structure vanadium dioxide layers distributed around the graphene disc in the circumferential direction, the insulation-metal phase change state of vanadium dioxide and the Fermi level of graphene are regulated and controlled through external excitation, and flexible switching between broadband absorption and double-narrow-band absorption can be achieved. The absorber has the advantages of being compact in structure, easy and convenient to prepare, insensitive to polarization and the like, has excellent dynamic tuning performance and wide-angle stability, and has integration and multifunctional application prospects in the fields of terahertz communication, imaging, biosensing, environment monitoring and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of terahertz wave devices, in particular to a switchable metamaterial absorber based on vanadium dioxide and graphene and a dynamic tuning method. BACKGROUND

[0002] The frequency range of terahertz waves is generally defined in the 0.1-10 terahertz interval. In the past few decades, with the continuous emergence of new technologies, the field of terahertz science and technology has made rapid progress.

[0003] Due to the unique physical properties of terahertz waves, they have shown broad application prospects in the fields of medical diagnosis, imaging technology, communication transmission and sensor detection. These practical applications have put forward higher requirements for the response of the device, but there are few natural materials with high response characteristics in the terahertz frequency band. Since John Pendry first proposed the concept of metamaterials, the field has entered a stage of rapid development, especially in the terahertz frequency band, metamaterials have shown better electromagnetic response capabilities than natural materials.

[0004] In recent years, terahertz absorbers based on metamaterials have become a research hotspot. However, most of the current metamaterial absorbers have the limitation of single function, and after the device is prepared, its performance parameters are often fixed and cannot be adjusted. Therefore, the development of high-performance tunable metamaterial absorbers has become an important research direction in the field of terahertz technology.

[0005] As a functional metal oxide material, vanadium dioxide has attracted much attention in the field of terahertz absorbers. However, the current terahertz absorbers based on vanadium dioxide mainly reflect the regulation of multi-peak absorption intensity in terms of multi-band tuning function, and when the absorption peak position needs to be changed according to different application requirements, the structure size of the absorption device often needs to be adjusted, which makes it difficult to flexibly change the absorption characteristics of the terahertz absorber after it is prepared, becoming a bottleneck problem restricting the development of this technology. SUMMARY

[0006] The purpose of the present application is to provide a switchable metamaterial absorber based on vanadium dioxide and graphene and a dynamic tuning method to solve the problems existing in the prior art.

[0007] To achieve the above purpose, the present application provides the following solutions:

[0008] The present application provides a switchable metamaterial absorber based on vanadium dioxide and graphene, which is continuously spliced in an array form on a plane by a periodic unit structure, and the periodic unit structure is sequentially provided with a vanadium dioxide-graphene composite super surface, a dielectric layer and a metal reflection layer from top to bottom;

[0009] The vanadium dioxide-graphene composite super surface is composed of a patterned graphene disc and three fan-shaped structure vanadium dioxide layers distributed circumferentially around the graphene disc.

[0010] Further, the radius of the graphene disc is 3.8-4.2 μm, and the thickness is 1.8-2.2 nm.

[0011] The thickness of the fan-shaped structure vanadium dioxide layer is 0.05-0.07 μm, the outer radius is 13.8-14.2 μm, the inner radius is 3.8-4.2 μm, and the distance between the two radial sides of the fan shape is 1.4-1.6 μm.

[0012] The sum of the central angles of the three fan-shaped structure vanadium dioxide layers is 360°, and the included angles of adjacent fans are equal.

[0013] Further, the medium layer is a Topas medium layer, the thickness is 6.8-7.2 μm, and the relative dielectric constant is 2.35.

[0014] Further, the metal reflection layer is a silver layer, and the thickness is 4.8-5.2 μm.

[0015] Further, the period of the periodic unit structure is 29.8-30.2 μm.

[0016] Further, in the periodic unit structure, the total coverage range of the three fan-shaped structure vanadium dioxide layers matches the period.

[0017] The above structure of the switchable metamaterial absorber can maximize the absorption range while keeping the wideband absorption rate higher than 90%, and keep the narrowband absorption high while keeping it sharp.

[0018] The application also provides a dynamic tuning method for the above switchable metamaterial absorber, including the following two tuning modes:

[0019] Mode one: when the vanadium dioxide in the vanadium dioxide-graphene composite super surface is in a metallic state, and the Fermi energy level of graphene is 0 eV, the absorber has a wideband absorption performance of 3.2-10.0 THz, and the absorption rate is > 90%;

[0020] By changing the external excitation to increase the conductivity of vanadium dioxide, the continuous adjustment of the wideband absorption rate is realized.

[0021] Mode two: when the vanadium dioxide in the vanadium dioxide-graphene composite super surface is in an insulating state, and the Fermi energy level of graphene is 0.7 eV, the switchable metamaterial absorber has a double narrowband absorption performance.

[0022] By increasing the Fermi energy level of graphene from 0 eV to 0.7 eV, the continuous adjustment of the double narrowband absorption peak position is realized.

[0023] Further, in the first mode, the electrical conductivity of vanadium dioxide ranges from 200 S / m to 2*10 5 S / m.

[0024] When the electrical conductivity of vanadium dioxide ranges from 200 S / m to 2*10 5 S / m, the absorption rate of broadband absorption ranges from 0% to 100%.

[0025] Vanadium dioxide undergoes reversible transition between insulating state and metallic state near the critical temperature of 340K, and the present application uses this feature as a tunable absorber material and composites it with graphene, according to a specific structure design (periodic unit structure of vanadium dioxide-graphene composite super surface composed of patterned graphene discs and fan-shaped vanadium dioxide layers, Topas dielectric layer and silver metal layer arranged from top to bottom), the electrical conductivity of vanadium dioxide and the Fermi level of graphene can be adjusted by external excitation (such as temperature, electrical signal, etc.), so that the broadband absorption (3.2-10.0 THz frequency band, absorption rate > 90%) and double narrowband absorption characteristics can be flexibly switched, the broadband absorption rate can be continuously adjusted from 0% to 100%, and the double narrowband absorption peaks can be dynamically moved, effectively solving the technical bottleneck that the absorption characteristics of traditional terahertz absorbers are fixed and cannot be adjusted after being made, and meeting the actual needs of terahertz imaging, biological detection, sensing and other fields for diversified and flexible absorption characteristics.

[0026] The absorber proposed in the present application is continuously spliced in an array form on a plane by periodic unit structures, and the periodic unit structures are sequentially provided with a vanadium dioxide-graphene composite super surface, a dielectric layer and a metal reflection layer from top to bottom, and the absorber has excellent sensing performance, wherein the quality factors of the absorber in the double-band absorption mode are 10.3 and 506.25 respectively, and the sensitivities are 1.3 THz / RIU and 2.8 THz / RIU respectively, and the absorber can be further applied to the fields of environmental monitoring and biological sensing.

[0027] The present application changes the electrical conductivity of vanadium dioxide and the Fermi level of graphene by external excitation, realizes the switching of broadband and double narrowband absorption characteristics and the flexible adjustment of absorption rate and peak position, and through the prepared absorber and dynamic tuning method, a structure can meet the multiple needs of different terahertz absorption characteristics in practical applications, has greater advantages and application potential in flexible tuning, and solves the problem that the absorption characteristics of traditional terahertz absorbers are fixed once they are made.

[0028] The present application discloses the following technical effects:

[0029] The absorber designed in the application can realize the function switching of broadband and double-band absorption in a single structure, and is specifically realized by regulating the metal-insulator phase transition of vanadium dioxide and the Fermi energy level of graphene, and can meet the diversified needs of terahertz absorption characteristics in different application scenarios.

[0030] The absorber has good tunability: in the broadband absorption mode, the conductivity of vanadium dioxide can be adjusted to realize continuous adjustment of the absorption rate from 0% to 100%; in the double-narrow-band absorption mode, the Fermi energy level of graphene can be adjusted to realize dynamic regulation of the absorption peak position and absorption intensity.

[0031] The absorber has the advantages of simple and compact structure, convenient preparation and low cost, and has polarization-insensitive characteristics: when the incident angle is less than 45°, the absorber in the broadband mode can maintain an absorption rate of >80%; when the incident angle is less than 75°, the absorber in the double-band mode can maintain an absorption rate of >90%.

[0032] The absorber disclosed in the application is an integrated and ultra-thin planar device, without changing the structural characteristics of the absorber, only by applying external excitation such as electricity, magnetism, light and temperature, multifunctional switching can be realized in a single absorber. Therefore, the absorber can be widely applied to miniaturized and integrated systems, especially suitable for terahertz communication systems and detection systems, which can effectively reduce the volume and weight of the system, and provides a broad prospect for the application of future terahertz technology. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0034] Figure 1 The structure diagram of the periodic unit structure of the switchable metamaterial absorber based on vanadium dioxide and graphene according to the application; wherein, 1- fan-shaped structure vanadium dioxide layer; 2- graphene disc; 3- dielectric layer; 4- metal reflection layer.

[0035] Figure 2The following are wide-band dual-band absorption switching and tunable functional spectra of switchable metamaterial absorbers based on vanadium dioxide and graphene: (a) is a wide-band dual-band absorption switching spectrum based on vanadium dioxide phase transition; (b) is a wide-band absorption rate tunable spectrum under vanadium dioxide conductivity modulation; (c) is a spectrum with tunable dual narrowband absorption peak positions under graphene Fermi level modulation (wide-band absorption modulation); and (d) is a spectrum with tunable dual narrowband absorption peak positions under graphene Fermi level modulation (dual narrowband absorption modulation).

[0036] Figure 3 The diagram shows the electric field and current distribution of a switchable metamaterial absorber (broadband mode) based on vanadium dioxide and graphene at characteristic frequencies of 3.7 THz, 5.9 THz, and 9.9 THz. (a) shows the current distribution of the top vanadium dioxide-graphene composite metasurface at 3.7 THz, (b) shows the current distribution of the bottom metal reflective layer at 3.7 THz, (c) shows the current distribution of the top vanadium dioxide-graphene composite metasurface at 5.9 THz, (d) shows the current distribution of the bottom metal reflective layer at 5.9 THz, (e) shows the current distribution of the top vanadium dioxide-graphene composite metasurface at 9.9 THz, and (f) shows the current distribution of the bottom metal reflective layer at 9.9 THz.

[0037] Figure 4 The effects of analyte thickness hn and refractive index on narrowband and ultranarrowband absorption in a switchable metamaterial absorber (narrowband / ultranarrowband mode) based on vanadium dioxide and graphene are shown in Figure 1. (a) is a graph showing the effect of analyte thickness hn on the narrowband absorption peak, (b) is a graph showing the effect of analyte thickness hn on the ultranarrowband absorption peak, (c) is a graph showing the effect of analyte refractive index on the narrowband absorption peak, and (d) is a graph showing the effect of analyte refractive index on the narrowband absorption peak.

[0038] Figure 5 When using a switchable metamaterial absorber based on vanadium dioxide and graphene as a sensor, the analyte thickness h n Schematic diagrams of the dual-band electric and current distributions at 4.91 THz and 8.168 THz; (a) Schematic diagram of the switchable metamaterial absorber sensing application (hn is labeled as the analyte thickness), (b) Electric field distribution at 4.91 THz on the absorption side, (c) Electric field distribution at 8.168 THz on the absorption side, (d) Current distribution at 4.91 THz on the absorption bottom, and (e) Current distribution at 4.91 THz on the absorption top.

[0039] Figure 6Figures of the incident angle and polarization angle dependence of the wideband, narrowband and super-narrowband of the switchable metamaterial absorber based on vanadium dioxide and graphene; (a) the incident angle dependence of the absorber in the wideband mode, (b) the incident angle dependence of the absorber in the narrowband mode, (c) the incident angle dependence of the absorber in the super-narrowband mode, (d) the polarization angle dependence of the absorber in the wideband mode, (e) the polarization angle dependence of the absorber in the narrowband mode, (f) the polarization angle dependence of the absorber in the super-narrowband mode. DETAILED DESCRIPTION

[0040] Various exemplary embodiments of the present application will now be described in detail, without intent to limit the application, which is only limited by the claims. Understanding that these embodiments are given only as examples and are not to be used to limit the scope of the application, various aspects, features and embodiments of the present application are described in more detail.

[0041] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. In addition, any numerical range recited herein is intended to include all sub-ranges of the same numerical range. In other words, "between 1 and 10" is intended to include "between 1 and 2," "between 1 and 3," "between 1 and 4," and so on, as well as "between 3 and 10," "between 4 and 10," and so on. In addition, any reference to a number of an embodiment, such as "one" embodiment, is intended to mean that there are one or more of the described embodiments. Moreover, where a phrase similar to "at least one of A and B" is used, it is intended that the phrase be interpreted to mean that at least one of A or B is included, but not both. Similarly, where a phrase similar to "at least one of A, B, and C" is used, it is intended that the phrase be interpreted to mean that at least one of A or B or C is included, or two of the named phrases are included, or all three of the named phrases are included.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. All publications mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. In case of conflict, the content of the present specification will control.

[0043] Various modifications and changes can be made to the specific embodiments of the present application described herein without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those of ordinary skill in the art from consideration of the description and practice of the application disclosed herein. The description and examples are illustrative of the application and are not intended to limit the scope of the application.

[0044] With respect to the use of "comprising", "including", "containing", "having" and "ensing", as well as other similar forms, these terms are used to indicate the inclusion of one or more elements, features or steps, but do not preclude the presence or addition of one or more other elements, features or steps.

[0045] It should be noted that the present application does not describe in detail the conventional operation means in the art, and is not the focus of the present application.

[0046] The application provides a switchable metamaterial absorber based on vanadium dioxide and graphene, which is formed by continuously splicing periodic unit structures in an array form on a plane, wherein the periodic unit structure is sequentially provided with a vanadium dioxide-graphene composite super surface, a dielectric layer and a metal reflection layer from top to bottom.

[0047] The vanadium dioxide-graphene composite super surface is composed of a patterned graphene disc and three fan-shaped structure vanadium dioxide layers which are distributed in the circumferential direction of the graphene disc.

[0048] Further, the radius of the graphene disc is 3.8-4.2 μm, and the thickness is 1.8-2.2 nm.

[0049] The thickness of the fan-shaped structure vanadium dioxide layer is 0.05-0.07 μm, the outer radius is 13.8-14.2 μm, the inner radius is 3.8-4.2 μm, and the distance between the two radial sides of the fan-shaped structure is 1.4-1.6 μm.

[0050] The sum of the central angles of the three fan-shaped structure vanadium dioxide layers is 360°, and the included angles of adjacent fans are equal.

[0051] Further, the dielectric layer is a Topas dielectric layer, the thickness is 6.8-7.2 μm, and the relative dielectric constant is 2.35.

[0052] Further, the metal reflection layer is a silver layer, and the thickness is 4.8-5.2 μm.

[0053] Further, the period of the periodic unit structure is 29.8-30.2 μm.

[0054] Further, in the periodic unit structure, the total coverage area of the three fan-shaped structure vanadium dioxide layers matches the period.

[0055] Figure 1 It is a structural schematic view of the periodic unit structure of the switchable metamaterial absorber based on vanadium dioxide and graphene. The periodic unit structure is sequentially provided with a vanadium dioxide-graphene composite super surface, a dielectric layer and a metal reflection layer from top to bottom, wherein the vanadium dioxide-graphene composite super surface is composed of a patterned graphene disc and fan-shaped structure vanadium dioxide layers which are distributed in the circumferential direction of the graphene disc.

[0056] Figure 1 Center: 1-fan-shaped structure vanadium dioxide layer; 2-graphene disc; 3-dielectric layer; 4-metal reflection layer; the incident electromagnetic wave vector k is along the z-axis by default, the electric field component E is along the y-axis by default, and the magnetic field component H is along the x-axis by default.

[0057] The switchable metamaterial absorber can be prepared by a method known in the art, and the specific process does not affect the structure design and function implementation.

[0058] Based on the aforementioned switchable metamaterial absorber, the present invention also provides a dynamic tuning method, including the following two tuning modes:

[0059] Method 1: When the vanadium dioxide in the vanadium dioxide-graphene composite metasurface is in a metallic state and the Fermi level of graphene is 0 eV, the absorber has a broadband absorption performance of 3.2~10.0 THz and an absorption rate > 90%;

[0060] By changing the external excitation to increase the conductivity of vanadium dioxide, the broadband absorption rate can be continuously adjusted.

[0061] Method 2: When the vanadium dioxide in the carbon dioxide-graphene composite metasurface is in an insulating state and the Fermi level of graphene is 0.7 eV, the switchable metamaterial absorber has dual narrowband absorption performance.

[0062] The Fermi level of graphene was increased from 0 eV to 0.7 eV, enabling continuous adjustment of the position of the dual narrowband absorption peaks.

[0063] Furthermore, in Method 1, the electrical conductivity of vanadium dioxide ranges from 200 S / m to 2 × 10⁻⁶. 5 S / m.

[0064] When the conductivity of vanadium dioxide increases from 200 S / m to 2×10 5 At S / m, the absorptivity adjustment range for broadband absorption is 0%~100%.

[0065] By applying external stimuli (such as electrical, magnetic, optical, or temperature stimuli) to change the phase transition characteristics of vanadium dioxide material in the vanadium dioxide layer of the vanadium dioxide composite metasurface and the Fermi level of graphene in the graphene disk, it is possible to switch between broadband absorption and dual narrowband absorption functions, thereby achieving multifunctional tuning.

[0066] Example 1

[0067] This embodiment uses, as follows: Figure 1 The periodic unit cell structure shown is continuously assembled in an array to obtain an absorber. Specifically:

[0068] The graphene disk has a radius of 4μm and a thickness of 2nm;

[0069] The thickness of the vanadium dioxide layer with the fan-shaped structure is 0.06 μm; the outer radius is 14 μm, the inner radius is 4 μm, and the distance between the two radial sides of the fan is 1.5 μm.

[0070] The dielectric layer is a Topas dielectric layer with a thickness of 7 μm and a relative permittivity of 2.35;

[0071] The metal reflection layer is a silver layer with a thickness of 5 μm; and the period of the periodic unit structure is 30 μm.

[0072] The terahertz wave signal is input from the terahertz wave input end (vanadium dioxide-graphene composite super surface), but since the bottom is a metal layer, the terahertz wave signal cannot be transmitted and can only be output in the form of a reflected wave from the terahertz wave output end (vanadium dioxide-graphene composite super surface).

[0073] Figure 4 The influence of the thickness hn and the refractive index of the analyte of the vanadium dioxide and graphene-based switchable metamaterial absorber (narrowband / ultra-narrowband mode) on the narrowband and ultra-narrowband absorption; (a) is a curve graph showing the influence of the thickness hn of the analyte on the narrowband absorption peak, (b) is a curve graph showing the influence of the thickness hn of the analyte on the ultra-narrowband absorption peak, (c) is a curve graph showing the influence of the refractive index of the analyte on the narrowband absorption peak, and (d) is a curve graph showing the influence of the refractive index of the analyte on the narrowband absorption peak. The broadband absorption performance of the absorber constructed in this embodiment as a broadband absorber is shown in the graph, and the parameter conditions of the absorber at this time are: the conductivity of vanadium dioxide is 2×10 5 S / m (corresponding to the metallic state), and the Fermi energy level of graphene is 0 eV; when the vanadium dioxide is switched to the insulating state and the Fermi energy level of graphene is adjusted to 0.7 eV, the absorber can realize double narrowband absorption function.

[0074] In this embodiment, finite element theory is used for simulation, and in the simulation, periodic boundary conditions are set in the X and Y directions, and Floquet ports are set in the Z direction. Through simulation, the four-waveband and broadband absorption spectra of the proposed absorber are obtained when the vanadium dioxide is in the insulating state and the metallic state. In the simulation, the absorption is represented as:

[0075] A=1-R-T (1)

[0076] In the formula, A, R and T represent the absorption, reflectivity and transmittance, respectively; R=|S 11 | 2 ; T=|S 21 | 2 . |S 11 | and |S 21 | represent the reflection coefficient and the transmission coefficient, respectively.

[0077] Since the bottom metal can completely reflect electromagnetic waves, the transmittance T is 0, and formula (1) can be simplified as A=1-R.

[0078] Figure 2The wide-band dual-band absorption switching and tunable function spectrum of the switchable metamaterial absorber based on vanadium dioxide and graphene; (a) is the wide-band dual-band absorption switching spectrum based on vanadium dioxide phase transition, (b) is the wide-band absorption tunable spectrum under the regulation of vanadium dioxide conductivity, (c) is the dual-narrow-band absorption peak tunable spectrum under the regulation of graphene Fermi level (wide-band absorption regulation), (d) is the dual-narrow-band absorption peak tunable spectrum under the regulation of graphene Fermi level (dual-narrow-band absorption regulation). As shown in Figure 2 The absorption spectrum changes with the conductivity of vanadium dioxide (the Fermi level of graphene is 0 eV). When the temperature is greater than 340K, vanadium dioxide changes into a cubic rutile structure with metallic properties. The conductivity of vanadium dioxide increases with the increase of temperature, and the phase transition effect from the insulating state to the metallic state occurs when the temperature is close to 340K, at which time the conductivity of vanadium dioxide can increase by three to four orders of magnitude within a small temperature range. The phase transition of vanadium dioxide is reversible, and when the temperature decreases to below 340K again, the conductivity can completely recover to the initial state. From Figure 2 It can be seen that when vanadium dioxide is in a high conductivity state, the overall wide-band absorption effect is achieved, and when vanadium dioxide is in an insulating state and the Fermi level is 0.7 eV, the dual-narrow-band absorption effect is achieved in the terahertz waveband.

[0079] The optical properties of vanadium dioxide and silver in the terahertz range are characterized by the Drude model. The dielectric constant of silver is represented as:

[0080] (2)

[0081] In the formula, the plasma frequency ω p1 =1.16×10 16 rad / s; the collision frequency γ1 is 5.75×10 13 rad / s; ω is the frequency of the incident electromagnetic wave; is the imaginary unit.

[0082] The dielectric constant of vanadium dioxide is represented as:

[0083] (3)

[0084] In the formula, ε ∞ represents the high-frequency relative dielectric constant of vanadium dioxide, which is 12; γ2=5.75×10 13 rad / s is the collision frequency; ω p2 is the plasma frequency related to the conductivity of vanadium dioxide, which can be approximately represented as:

[0085] (4)

[0086] where σ0= 3 x 10 5 S / m; = ω p0 2 1.4 x 10 15 rad / s. σ is the conductivity of vanadium dioxide. Vanadium dioxide can realize the transition between insulating state and metallic state when the temperature changes. Vanadium dioxide presents insulating state at room temperature, and the conductivity is 200 S / m. When the temperature reaches the phase transition temperature, vanadium dioxide is in the metallic state, and the conductivity is 2 x 10 5 S / m.

[0087] Figure 3 Figures 1.4 are schematic diagrams of the electric field and current distribution of the switchable metamaterial absorber (wideband mode) based on vanadium dioxide and graphene at the characteristic frequencies of 3.7 THz, 5.9 THz and 9.9 THz; (a) is the current distribution diagram of the top vanadium dioxide-graphene composite super surface at 3.7 THz, (b) is the current distribution diagram of the bottom metal reflection layer at 3.7 THz, (c) is the current distribution diagram of the top vanadium dioxide-graphene composite super surface at 5.9 THz, (d) is the current distribution diagram of the bottom metal reflection layer at 5.9 THz, (e) is the current distribution diagram of the top vanadium dioxide-graphene composite super surface at 9.9 THz, and (f) is the current distribution diagram of the bottom metal reflection layer at 9.9 THz. As shown in the figures, in order to analyze the working mechanism of the absorber in depth, the electric field and surface current distribution characteristics of the wideband super surface are given. The incident wave adopts the y-axis polarization mode, and three characteristic frequency points of 3.7 THz, 5.9 THz and 9.9 THz are selected for analysis. Figure 3

[0088] As can be seen from the figures, when the frequency is 3.25 THz, the electric field energy is mainly concentrated in the dielectric channel region between the top two vanadium dioxide fan-shaped structures and the bottom fan-shaped structure, forming a local resonant cavity effect. As the frequency increases to 5.9 THz and 9.9 THz, the electric field intensity in the edge region of the channel is significantly enhanced. The surface current distribution analysis shows that at 3.7 THz and 9.9 THz, the reverse current between the vanadium dioxide fan-shaped patch and the bottom gold layer forms a closed loop, and at this time the middle vanadium dioxide layer is equivalent to a magnetic dipole, exciting strong magnetic resonance response.

[0089] It is particularly noteworthy that at the characteristic frequency of 5.9 THz, the surface current direction of the top two vanadium dioxide fan-shaped patches is opposite to that of the gold layer, forming magnetic resonance; while the current direction of the bottom fan-shaped patch is consistent with that of the gold layer, producing electric resonance. The synergistic effect of magnetic dipole resonance and electric dipole resonance makes the incident electromagnetic wave be effectively dissipated in the resonant cavity, thereby realizing absorption enhancement.

[0090] ​Figure 4 The effects of analyte thickness hn and refractive index on narrowband and ultranarrowband absorption in a switchable metamaterial absorber (narrowband / ultranarrowband mode) based on vanadium dioxide and graphene are shown in Figures (a), (b), (c), and (d). The graphs illustrate the influence of analyte thickness hn on the narrowband absorption peak, ultranarrowband absorption peak, refractive index, and refractive index on the narrowband absorption peak. Figure 4 As shown, when the device is used as a sensor, the thickness h of the analyte n The thickness of the analyte above the device can affect the sensing performance. As shown in the figure, the sensing characteristics of the dual narrowband sensor were analyzed, demonstrating the effect of the analyte thickness on the absorption peaks. The refractive indices of the medium above the device were set to 1.1 and 1.01, respectively. It can be seen that the absorption peak at 4.91 THz does not change significantly with increasing analyte thickness. The shapes of the four absorption peaks have unique advantages in different applications. Sharp and high absorption peaks (5.16 THz and 5.39 THz) have high selectivity and absorption efficiency, suitable for sensors and filters requiring high precision and high resolution, enabling accurate detection and filtering of signals at specific frequencies. Wide and relatively flat absorption peaks (4.00 THz and 4.41 THz), although with slightly lower absorption rates, have a wider bandwidth, giving them a significant advantage in stealth technology and energy harvesting. They can cover a wider frequency range, thereby reducing electromagnetic reflection or harvesting more energy over a larger spectrum. Therefore, sharp peaks perform well in high-precision detection and narrowband filtering, while wide peaks are more advantageous in broad-spectrum absorption and stealth applications.

[0091] Figure 5 When using a switchable metamaterial absorber based on vanadium dioxide and graphene as a sensor, the analyte thickness h n Schematic diagrams of the dual-band electric and current distributions at 4.91 THz and 8.168 THz; (a) Schematic diagram of the switchable metamaterial absorber sensing application (hn is labeled as the analyte thickness), (b) Electric field distribution at 4.91 THz (side-view), (c) Electric field distribution at 8.168 THz (side-view), (d) Current distribution at 4.91 THz (bottom-view), (e) Current distribution at 4.91 THz (top-view). Figure 5The diagram shows the cross-sectional electric field distribution of the absorber at 4.91 THz and 8.168 THz. It can be seen that the electric field at 4.91 THz is distributed near the metasurface, therefore the absorption peak is not affected by the analyte thickness. At 8.168 THz, surface plasmon resonance is excited, and the electric field is distributed above the metasurface. The more the analyte includes the electric field, the greater the sensing sensitivity. The diagram also shows the current distribution between the top graphene and the bottom metal layer under narrow-band absorption at 8.168 THz. At this frequency, vanadium dioxide is in an insulating state, equivalent to a lossless dielectric, and the parallel currents between the graphene patch and the bottom metal layer form an electrical resonance. Therefore, near-perfect absorption occurs at this frequency.

[0092] Figure 6 The following are the incident angle and polarization angle dependence plots for a switchable metamaterial absorber based on vanadium dioxide and graphene in broadband, narrowband, and ultranarrowband modes: (a) Incidence angle dependence plot for the absorber in broadband mode, (b) Incidence angle dependence plot for the absorber in narrowband mode, (c) Incidence angle dependence plot for the absorber in ultranarrowband mode, (d) Polarization angle dependence plot for the absorber in broadband mode, (e) Polarization angle dependence plot for the absorber in narrowband mode, and (f) Polarization angle dependence plot for the absorber in ultranarrowband mode. Figure 6 As shown, to investigate the performance of the absorber under non-perpendicular incident conditions, this study conducted oblique incident simulation analysis over a wide angle range (0°-85°) to systematically evaluate the broadband and dual-narrowband absorption characteristics of the device at different incident angles. In the simulation, the incident angle was defined as the angle between the electromagnetic wave incident direction and the zigzag axis, and a parametric study was performed using a scanning method with 2° increments. When the incident angle is less than 45°, the absorber still maintains a broadband absorption characteristic with an absorptivity greater than 80%. The narrowband absorptivity at 4.91 THz under TE wave decreases with increasing incident angle. When the incident angle is less than 75°, the absorber still maintains a broadband absorption characteristic with an absorptivity greater than 90%. The ultra-narrowband absorption peak at 8.168 THz under TE wave shifts to higher frequencies with increasing incident angle. When the incident angle is greater than 30°, the absorption peak shifts to lower frequencies with increasing incident angle. This characteristic allows the absorber to function as an angle-adjustable ultra-narrowband absorber. When the incident wave polarization angle changes from 0° to 90°, the absorption peak position and intensity of the device remain stable in both ultra-wideband and dual-narrowband absorption modes. Analysis results demonstrate that the absorber exhibits excellent polarization insensitivity across the entire polarization range, verifying its applicability in complex electromagnetic environments.

[0093] The application adopts the above-mentioned switchable metamaterial absorber based on vanadium dioxide and graphene and a dynamic tuning method, changes the conductivity of vanadium dioxide and the Fermi level of graphene through external excitation, switches between the insulating state and the metallic state, realizes flexible change of wideband absorption and double narrowband absorption peak positions, and solves the problem that the structure of the existing absorber needs to be changed when the absorber faces different requirements and changes the absorption peak position.

[0094] The above-described embodiments are only used to describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements of the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A switchable metamaterial absorber based on vanadium dioxide and graphene, characterized in that, It is formed by continuously splicing periodic unit structures in an array on a plane. The periodic unit structure is provided with a vanadium dioxide-graphene composite metasurface, a dielectric layer and a metal reflective layer from top to bottom. The vanadium dioxide-graphene composite metasurface consists of patterned graphene disks and three fan-shaped vanadium dioxide layers distributed around the graphene disks.

2. The switchable metamaterial absorber according to claim 1, characterized in that, The graphene disk has a radius of 3.8~4.2μm and a thickness of 1.8~2.2nm; The thickness of the vanadium dioxide layer in the fan-shaped structure is 0.05~0.07μm; the outer radius is 13.8~14.2μm, the inner radius is 3.8~4.2μm, and the distance between the two radial sides of the fan is 1.4~1.6μm. The sum of the central angles of the three sector-shaped vanadium dioxide layers is 360°, and the included angles of adjacent sectors are equal.

3. The switchable metamaterial absorber according to claim 1, characterized in that, The dielectric layer is a Topas dielectric layer with a thickness of 6.8~7.2μm and a relative permittivity of 2.

35.

4. The switchable metamaterial absorber according to claim 1, characterized in that, The metal reflective layer is a silver layer with a thickness of 4.8~5.2μm.

5. The switchable metamaterial absorber according to claim 1, characterized in that, The period of the periodic unit structure is 29.8~30.2μm.

6. The switchable metamaterial absorber according to claim 5, characterized in that, In the periodic unit structure, the total coverage of the three fan-shaped vanadium dioxide layers matches the period.

7. A dynamic tuning method based on the switchable metamaterial absorber according to any one of claims 1-6, characterized in that, The following two tuning methods are included: Method 1: When the vanadium dioxide in the vanadium dioxide-graphene composite metasurface is in a metallic state and the Fermi level of graphene is 0 eV, the absorber has a broadband absorption performance of 3.2~10.0 THz. By changing the external excitation to increase the conductivity of vanadium dioxide, the broadband absorption rate can be continuously adjusted. Method 2: When the vanadium dioxide in the vanadium dioxide-graphene composite metasurface is in an insulating state and the Fermi level of graphene is 0.7 eV, the switchable metamaterial absorber has dual narrowband absorption performance. The Fermi level of graphene was increased from 0 eV to 0.7 eV, enabling continuous adjustment of the position of the dual narrowband absorption peaks.

8. The dynamic tuning method according to claim 7, characterized in that, In Method 1, the electrical conductivity of vanadium dioxide ranges from 200 S / m to 2 × 10⁻⁶. 5 S / m.

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