Terahertz multifunctional metasurface device based on graphene and vanadium dioxide

Abstract

The invention relates to a terahertz multifunctional metasurface device based on graphene and vanadium dioxide. Comprising a top VO2 structural layer, a first polyimide dielectric layer, a VO2 thin film layer, a first metal structural layer, a second polyimide dielectric layer, a graphene structural layer, a silicon dioxide layer, a third polyimide dielectric layer and a second metal structural layer which are sequentially arranged from top to bottom. According to the invention, dynamic switching of transmission type linear-circular polarization conversion, reflection type cross polarization conversion, broadband wave absorption and other functions can be realized on the same structure, and switching of transmission / reflection modes is realized. The bandwidths of the transmission type linear-circular polarization converter and the reflection type cross polarization converter can be dynamically adjusted by changing the Fermi level of graphene; the broadband wave absorber and the reflection type cross polarization converter can act on incident LP waves and CP waves, and the sensitivity of the metasurface to incident electromagnetic wave polarization is indicated.

Description

Technical Field

[0001] The invention belongs to the technical field of terahertz supersurface functional devices, and in particular relates to a terahertz multifunctional supersurface device based on graphene and vanadium dioxide. Background Art

[0002] Terahertz (THz) waves refer to electromagnetic waves with a frequency range of 0.1THz to 10THz. Compared with microwaves and light waves, terahertz waves have extraordinary characteristics such as ultra-wideband, ultra-high speed, easy material combination, high signal-to-noise ratio, strong penetration and low photon energy. These characteristics make terahertz waves have very important application prospects, and therefore people have conducted extensive scientific research on its related functional devices.

[0003] However, terahertz functional devices constructed with traditional materials have many problems such as limited magnetic response, severe high-frequency loss, difficulty in adapting to high-frequency characteristics, and lack of adjustability and reconfigurability. Therefore, metamaterials (metasurfaces) came into being. Metasurfaces are two-dimensional planar components composed of sub-wavelength periodic units of metals or dielectrics. They have electromagnetic properties such as negative refractive index and negative dielectric constant that some traditional natural materials do not have. They can be regarded as two-dimensional metamaterials. However, compared with three-dimensional metamaterials, it has thinner thickness and lower loss, so it is more flexible in adjusting electromagnetic waves, and metasurfaces also reduce processing costs and difficulties. Based on these good advantages, metasurfaces make it possible to propose, design and manufacture highly integrated, small-size and high-performance devices.

[0004] With the in-depth study of terahertz metasurface functional devices, researchers have found that metasurfaces based on traditional metal materials cannot adjust the dielectric constant, which has some limitations on the design of dynamically tunable terahertz multifunctional metasurfaces. Therefore, in order to achieve adjustability, tunable materials (such as photosensitive silicon, graphene, vanadium dioxide and Dirac semimetals, etc.) can be added when designing the metasurface structure to realize the integration of metasurface functions. By changing the external environmental conditions, the physical or chemical properties of the tunable material can be changed, thereby causing the functional transformation of the metasurface.

[0005] Among the related functional devices, absorbers and polarization converters are two important aspects of terahertz metasurface applications. Among them, the main function of the absorber is to absorb and dissipate the energy of electromagnetic waves, while the polarization converter can achieve the conversion of polarization state by manipulating the phase and amplitude of the incident electromagnetic wave. Among the polarization converters with various functions, the linear-circular polarization converter is particularly concerned. This is because circularly polarized (CP) waves have the characteristics of orthogonal polarization, strong anti-interference, high compatibility, and easy implementation, which makes CP waves widely used in many fields such as communication, radar, and biomedicine. However, the emission source of CP waves is very scarce, and most CP waves are converted from linearly polarized (LP) waves.

[0006] However, among some of the current terahertz multifunctional metasurfaces, few have the function of transmission-type linear-circular polarization conversion. For metasurfaces with linear-circular polarization conversion function, either their function is single, or they only have one mode of reflection or transmission. There are very few terahertz multifunctional metasurfaces that contain both modes. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a terahertz multifunctional metasurface device based on graphene and vanadium dioxide, which can realize dynamic switching of functions such as transmission-type linear-circular polarization conversion, reflection-type cross-polarization conversion and broadband absorption on the same structure.

[0008] The present invention solves the technical problem by the following technical solutions:

[0009] A terahertz multifunctional metasurface device based on graphene and vanadium dioxide, comprising a top layer of VO2 arranged in sequence from top to bottom 2 Structural layer, first polyimide dielectric layer, VO 2 A thin film layer, a first metal structure layer, a second polyimide dielectric layer, a graphene structure layer, a silicon dioxide layer, a third polyimide dielectric layer and a second metal structure layer.

[0010] Moreover, the top VO 2 Structural layer, VO 2 The thickness of the thin film layer, the first metal structure layer and the second metal structure layer are all 0.18-0.22 μm; the thickness of the graphene structure layer is 0.34-0.36 nm; the thickness of the first polyimide dielectric layer, the second polyimide dielectric layer and the third polyimide dielectric layer are 8-12 μm, 14-18 μm and 17-21 μm respectively, and the thickness of the silicon dioxide layer is 0.08-0.12 μm.

[0011] Moreover, the top VO 2The shape of the structural layer includes two sub-parts, one of which is composed of an open ring and a hexagon; the other is composed of an open hexagonal ring and a circle. Both sub-parts have 2, and the overall structure is obliquely symmetrical. The radius of the open ring r 1 =30μm, r 2 =25μm, crack w 3 = 8 μm, the radius of the circle r 3 =15 μm, the side lengths of the open hexagonal ring and the hexagon are l 3 =15μm, l 4 =30μm and l 5 =25μm.

[0012] Moreover, the top VO 2 The relative dielectric constant of the structural layer is calculated as follows:

[0013]

[0014] Where: ∞ =12 is the dielectric constant at infinite frequency; γ = 5.75×10 13 rad / s represents the collision frequency constant; ω p (σ 0 )=1.4×10 15 rad / s,σ 0 =3×10 5 s / m; σ is VO 2 The conductivity of VO is 20S / m. 2 Insulating state, σ is 2×10 5 S / m represents VO 2 of metallic state.

[0015] Moreover, the first metal structure and the second metal structure are both made of a conductivity of 4.56×10 7 The first polyimide dielectric layer, the second polyimide dielectric layer and the third polyimide dielectric layer are all made of a polyimide material with a dielectric constant of 3 and a loss tangent of 0.02.

[0016] Moreover, the shapes of the first metal structure and the second metal structure include two sub-parts, one of which is composed of a rectangle connecting two semicircles, and the other is composed of a pair of "bow"-shaped slit ellipses, and the structural parameters are: a = 96 μm, b = 47 μm, c = 26 μm, d = 33 μm, l = 12 μm, l 1 =5μm, l 2 =3μm, r=12μm, w=5μm, w 1 =4.5μm, w 2 =2μm.

[0017] Moreover, the graphene structure layer is composed of an isosceles right triangle with two adjacent rectangles and inclined graphene stripes, the length of the rectangle is n = 30 μm, the width is m = 2 μm, the right angle side of the isosceles right triangle is f = 17 μm, the side length of the inclined graphene stripes is e = 16 μm, and the surface conductivity σ(ω) of the graphene structure layer is obtained by converting the intra-band conductivity σ intra (ω) and interband conductivity σ inter (ω) is derived from the Kubo equation, and σ(ω) is expressed as:

[0018] σ(ω)=σ intra (ω)+σ inter (ω) (2)

[0019]

[0020] Where: ω represents the angular frequency of the incident wave, μ c represents the graphene chemical potential (or graphene's Fermi level, usually denoted as E f ), the relaxation time is τ (1ps), e is the charge of the electron, T is the temperature (300K), k B is the Boltzmann constant, is the reduced Planck constant;

[0021] In the terahertz band, σ intra The σ(ω) of graphene in the proposed metasurface is expressed by formula (3). In practical applications, the E of graphene f The relationship between the bias voltage and the

[0022]

[0023] Where: V f represents the Fermi velocity. When the temperature is 300K, the value is 1×10 6 m / s,V g represents bias voltage, t s is the dielectric layer thickness, ε r and ε 0 are the dielectric constant and the vacuum permittivity, respectively.

[0024] The advantages and beneficial effects of the present invention are:

[0025] 1. The terahertz multifunctional metasurface proposed in the present invention realizes the switching of transmission / reflection modes and has rich functions. It can be used as a transmission-type linear-circular polarization converter, a reflection-type cross-polarization converter and a broadband absorber.

[0026] 2. The bandwidth of the transmission-type linear-circular polarization converter and the reflection-type cross-polarization converter of the present invention can be dynamically adjusted by changing the Fermi level of graphene.

[0027] 3. The broadband absorber and reflective cross-polarization converter of the present invention can both act on incident LP waves and CP waves, indicating the sensitivity of the metasurface to the polarization of the incident electromagnetic wave. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 (a) is a unit structure diagram of the terahertz multifunctional metasurface proposed in the present invention. Figure 1 (b) is a side view of the structure;

[0029] Figure 2 (a) is VO 2 Schematic diagram of structural layers; Figure 2 (b) is a schematic diagram of the metal structure layer structure; Figure 2 (c) is a schematic diagram of the graphene structure layer;

[0030] Figure 3 (a) to (d) are respectively the transmission coefficient curve, phase difference curve, ellipticity χ curve and AR curve of the present invention for x-LP wave incidence;

[0031] Figure 4 Different graphene E of the present invention f The AR curve chart below;

[0032] Figure 5 (a) and (b) are respectively a reflection coefficient curve diagram and a polarization conversion rate curve diagram of the present invention under x-LP incidence; Figure 5 (c) and (d) are the reflection coefficient curve and polarization conversion rate curve under RHCP wave incidence, respectively;

[0033] Figure 6 Different graphene E of the present invention f Next PCR r x and PCR r + ;

[0034] Figure 7 (a) and (b) are respectively the reflection and transmission coefficient curves, the absorption rate curves and the relative impedance curves of the present invention under x-LP incidence;

[0035] Figure 8 (a) and (b) are respectively the reflection and transmission coefficient curves and the wave absorption rate curves under the RHCP wave incidence of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below through specific embodiments. The following embodiments are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0037] As Figure 1 shown, a terahertz multifunctional metasurface device based on graphene and vanadium dioxide is innovative in that it includes a top-layer VO 2 structural layer, a first polyimide dielectric layer, a VO 2 thin film layer, a first metal structural layer, a second polyimide dielectric layer, a graphene structural layer, a silica layer, a third polyimide dielectric layer, and a second metal structural layer.

[0038] Figure 1 (a) and 1(b) respectively represent the unit structure (period p = 130 μm) of the metasurface and its side view. From Figure 1 (b), it can be seen that the unit structure has a total of 6 layers, including a top-layer VO 2 structural layer with a thickness of h 2 = 0.2 μm ( Figure 2 (a)), a VO 2 thin film layer with a thickness of h 2 = 0.2 μm, 2 metal structural layers with a thickness of h 2 = 0.2 μm ( Figure 2 (b)), a graphene structural layer with a thickness of h 4 = 0.35 nm ( Figure 2 (c)), and a silica layer with a thickness of h 5 = 0.1 μm. The dielectric layer is polyimide (PI) with a dielectric constant of 3 and a loss tangent of 0.02, and its three-layer thicknesses from top to bottom are h 6 = 10 μm, h 1 = 16 μm, and h 3 = 19 μm. Among them, the function of the VO 2 thin film layer is to realize the switching between the transmission and reflection modes of the terahertz multifunctional metasurface, and the function of graphene is to dynamically adjust the bandwidth by modifying its Fermi level (E f ).

[0039] As Figure 2 (a) shown, the shape of the top-layer VO 2 structural layer includes two sub-parts. One sub-part is composed of an open ring and a hexagon; the other part is composed of an open hexagonal ring and a circle. There are 2 of each of the two sub-parts, and the overall structure is skew-symmetric. The radius of the open ring is r 1 = 30 μm, r 2 = 25 μm, the crack width w 3 = 8 μm, and the radius of the circle is r 3=15 μm, the side lengths of the open hexagonal ring and the hexagon are l 3 =15μm, l 4 =30μm and l 5 =25μm.

[0040] Moreover, the top VO 2 The relative dielectric constant of the structural layer is calculated as follows:

[0041]

[0042] Where: ∞ =12 is the dielectric constant at infinite frequency; γ = 5.75×10 13 rad / s represents the collision frequency constant; ω p (σ 0 )=1.4×10 15 rad / s,σ 0 =3×10 5 s / m; σ is VO 2 The conductivity of VO is 20S / m. 2 Insulating state, σ is 2×10 5 S / m represents VO 2 of metallic state.

[0043] like Figure 2 As shown in (b), the first metal structure and the second metal structure are both made of a conductivity of 4.56×10 7 The first polyimide dielectric layer, the second polyimide dielectric layer and the third polyimide dielectric layer are all made of a polyimide material with a dielectric constant of 3 and a loss tangent of 0.02.

[0044] The shapes of the first metal structure and the second metal structure include two sub-parts, one of which is composed of a rectangle connecting two semicircles, and the other is composed of a pair of "bow"-shaped slotted ellipses, and the structural parameters are: a = 96 μm, b = 47 μm, c = 26 μm, d = 33 μm, l = 12 μm, l 1 =5μm, l 2 =3μm, r=12μm, w=5μm, w 1 =4.5μm, w 2 =2μm.

[0045] like Figure 2As shown in (c), the graphene structure layer is composed of an isosceles right triangle with two adjacent rectangles and inclined graphene stripes, the length of the rectangle is n = 30 μm, the width is m = 2 μm, the right angle side of the isosceles right triangle is f = 17 μm, the side length of the inclined graphene stripes is e = 16 μm, and the surface conductivity σ(ω) of the graphene structure layer is obtained by dividing the intra-band conductivity σ intra (ω) and interband conductivity σ inter (ω) is derived from the Kubo equation, and σ(ω) is expressed as:

[0046] σ(ω)=σ intra (ω)+σ inter (ω) (2)

[0047]

[0048] Where: ω represents the angular frequency of the incident wave, μ c represents the graphene chemical potential (or graphene's Fermi level, usually denoted as E f ), the relaxation time is τ (1ps), e is the charge of the electron, T is the temperature (300K), k B is the Boltzmann constant, is the reduced Planck constant;

[0049] In the terahertz band, σ intra The σ(ω) of graphene in the proposed metasurface is expressed by formula (3). In practical applications, the E of graphene f The relationship between the bias voltage and the

[0050]

[0051] Where: V f represents the Fermi velocity. When the temperature is 300K, the value is 1×10 6 m / s,V g represents bias voltage, t s is the dielectric layer thickness, ε r and ε 0 are the dielectric constant and the vacuum permittivity, respectively.

[0052] The terahertz multifunctional supersurface device based on graphene and vanadium dioxide proposed in the present invention changes the Fermi level (E f ), VO 2 The conductivity of the metasurface and the direction of the electromagnetic wave incident on the metasurface can be used as a transmission-type linear-circular polarization converter, a reflection-type cross-polarization converter and a broadband absorber. The detailed working principle is as follows:

[0053] First, we introduce its related research as a transmission-type linear-circular polarization converter.2 In the insulating state (conductivity is 20S / m), VO 2 The thin film layer is equivalent to the dielectric layer, and the metasurface is transmissive in this case.

[0054] When an x-type linearly polarized (x-LP) wave (or a y-type linearly polarized (y-LP) wave) is incident vertically onto the proposed terahertz multifunctional metasurface along the forward direction, the transmission coefficient (given by t ij Indicates, meaning: ji polarization conversion) and phase difference ( Respectively represent t xx (t yy ) and t yx (t xy ) is the phase difference between Figure 3 (a) and 3(b) (only x-LP wave results are shown). yx =t xx (t xy =t yy )and (k is an integer) When both conditions are met, the incident LP wave is converted into a CP wave. Taking the x-LP wave as an example, we can use Figure 3 In (a) and 3(b), it is preliminarily concluded that the x-LP wave is converted into CP wave in the frequency domain range of 1.15-1.50 THz.

[0055] For further precision, the Stokes parameter is introduced:

[0056]

[0057] Where: S 0 represents the total electric field strength of the transmitted wave, S 3 represents the corresponding right-handed circularly polarized (RHCP) or left-handed circularly polarized (LHCP). Ellipticity is defined as χ = S 3 / S 0 , χ=1 or -1 represents LHCP wave and RHCP wave respectively. The related results are as follows Figure 3 (c) In the range of 1.16-1.52 THz, the ellipticity χ is between -1 and -0.95, indicating that the x-LP wave is converted into the RHCP wave in this range.

[0058] Axial ratio (AR, unit: dB) is an important parameter to characterize CP waves and is defined as the ratio of the major axis to the minor axis:

[0059]

[0060] According to relevant standards, AR = 0 indicates a perfect CP wave. However, in the context of engineering simulation, AR < 3 can be considered a perfect CP wave. Figure 3 It can be found in (d) (only the part with AR<12 is shown): AR<3 in the range of 1.16-1.52 THz, further confirming that the x-LP wave is converted into a relatively perfect CP wave in this frequency domain.

[0061] Figure 4 Demonstrated different graphene E f The impact on AR can be found as E f As the E increases, the AR<3 portion also increases, that is, the frequency domain range of the x-LP wave converted into the CP wave increases, indicating that the working bandwidth of the linear-circular polarization converter can be adjusted by adjusting E f To adjust dynamically.

[0062] When VO 2 From insulating state to metallic state (conductivity from 20 to 2×10 5 S / m), VO 2 The thin film layer is equivalent to the metal layer, and accordingly, the entire metasurface changes from a transmission type to a reflection type. At this time, depending on the direction of the electromagnetic wave incident on the metasurface, it can realize the functions of reflective cross-polarization conversion and broadband wave absorption respectively.

[0063] When the electromagnetic wave is incident in the reverse direction, the proposed terahertz multifunctional metasurface acts as a reflective cross-polarization converter. This polarization converter can not only realize the cross-polarization conversion between x-LP wave and y-LP wave, but also realize the cross-polarization conversion between RHCP wave and LHCP wave. For the former, taking the x-LP wave incident as an example, assuming that the graphene E f is 1.1eV. Figure 5 As shown in (a), in the frequency domain of 0.83-1.54 THz, the cross-polarization reflection coefficient r yx remains above 0.6, while the co-polarization reflection coefficient r xx If it is lower than 0.2 or even lower than 0.1, it means that the incident x-LP wave is reflected as y-LP wave. To further illustrate its conversion efficiency, the polarization conversion ratio (PCR) is introduced:

[0064]

[0065] The results are as follows Figure 5 As shown in (b), in the frequency range of 0.81-1.74 THz, PCR r x Value is greater than 90%.

[0066] When a CP wave is incident on the metasurface, it can also exhibit the function of cross-polarization conversion. Taking the RHCP wave as an example, its reflection coefficient (“+” represents RHCP wave, “-” represents LHCP wave) and PCR r + The results are as follows Figure 5 (c) and 5(d). In the 0.83-1.56THz frequency domain, the cross-polarization reflection coefficient r -+ remains above 0.6, while the co-polarization reflection coefficient r ++ It is lower than 0.2 or even lower than 0.1, which indicates that the incident RHCP wave is reflected as LHCP wave. By analogy with formula (8), we can get PCR in the range of 0.81-1.73 THz: r + Greater than 90%.

[0067] For both types of reflective cross-polarization converters, when the graphene E f When the PCR is 0.5eV, 0.8eV and 1.1eV respectively, r x and PCR r + The changes are as follows Figure 6 As shown in (a) and 6(b), it can be found that no matter whether the incident LP wave or CP wave, as E f Increase, PCR r x and PCR r + More than 90% of the parts increased, reflecting the adjustability of graphene Fermi level to the working bandwidth.

[0068] Finally, the description of its use as a broadband absorber is introduced. The switching between broadband absorber and reflective cross-polarization conversion function is achieved by changing the incident direction of the electromagnetic wave, while other conditions remain unchanged, that is, the incident direction of the electromagnetic wave changes from reverse to forward, and VO 2 It is still in the metallic state. As a broadband absorber, it can absorb incident LP waves and CP waves.

[0069] Taking the incident x-LP wave as an example, Figure 7 In (a), it can be clearly seen that r yx , t yx and t xx The amplitude of is about 0.1 in the whole frequency band, indicating that they are all 2 The structural layer and PI layer absorb;

[0070] About r xx, within 2.26-4.33THz, its amplitude is less than 0.3. The absorbing performance of the broadband absorber is explained by introducing the total absorbance: A = 1–R–T, A represents the total absorbance, R is the reflectivity (R = |r yx | 2 +|r xx | 2 ), T is the transmittance (T=|t yx | 2 +|t xx | 2 ). Due to the metallic VO 2 The presence of thin film, t yx and t xx The value of is very small, so their sum of squares can be ignored (T≈0), then the formula is simplified to A=1–R, R=|r yx | 2 +|r xx | 2 The results are as follows Figure 7 As shown in (b), it can be seen that the absorption rate exceeds 90% within 2.24-4.30 THz.

[0071] In addition, impedance matching theory can be used to elucidate the absorption characteristics and internal mechanisms of metasurfaces:

[0072]

[0073] Where Z r is defined as the relative impedance, S 11 and S 21 When the real and imaginary parts of the relative impedance are approximately equal to 1 and 0, respectively, the broadband absorber can achieve complete absorption (A = 1).

[0074] For CP wave incidence, take the incident RHCP wave as an example. Figure 8 The amplitude curve shown in (a) is no longer explained. Figure 8 (b) In the frequency range of 2.23-4.30 THz, the metasurface absorbs the incident RHCP wave with an absorptivity of over 90%. Figure 7 (b) and 8(b) show that the metasurface exhibits excellent characteristics in absorbing LP waves or CP waves.

[0075] In addition, considering the complex electromagnetic environment in the real environment, the effects of different angles of incidence and polarization on linear-circular polarization conversion, linear cross-polarization conversion and broadband absorber functions when the x-LP wave is incident on the metasurface are studied. For the linear-circular polarization converter, it can maintain functional stability at an incident angle of 0°-15° and a polarization angle of 0°-5°; for the linear cross-polarization converter, it can maintain functional stability at an incident angle of 0°-30° and a polarization angle of 0°-10°; for the broadband absorber, it can maintain functional stability at an incident angle of 0°-60° and a polarization angle of 0°-80°.

[0076] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A terahertz multifunctional metasurface device based on graphene and vanadium dioxide, characterized in that: It includes a top VO2 structure layer, a first polyimide dielectric layer, a VO2 film layer, a first metal structure layer, a second polyimide dielectric layer, a graphene structure layer, a silicon dioxide layer, a third polyimide dielectric layer and a second metal structure layer which are arranged in sequence from top to bottom.

2. The terahertz multifunctional supersurface device based on graphene and vanadium dioxide according to claim 1, characterized in that: The thickness of the top VO2 structural layer, the VO2 thin film layer, the first metal structural layer and the second metal structural layer are all 0.18-0.22 μm; the thickness of the graphene structural layer is 0.34-0.36 nm; the thickness of the first polyimide dielectric layer, the second polyimide dielectric layer and the third polyimide dielectric layer are 8-12 μm, 14-18 μm and 17-21 μm respectively, and the thickness of the silicon dioxide layer is 0.08-0.12 μm.

3. The terahertz multifunctional supersurface device based on graphene and vanadium dioxide according to claim 1, characterized in that: The shape of the top VO2 structural layer includes two sub-parts, one of which is composed of an open ring and a hexagon; the other is composed of an open hexagonal ring and a circle. Both sub-parts have 2, and the overall structure is obliquely symmetrical. The radius of the open ring is r1=30μm, r2=25μm, the crack w3=8μm, the radius of the circle is r3=15μm, and the side lengths of the open hexagonal ring and the hexagon are l3=15μm, l4=30μm and l5=25μm respectively.

4. The terahertz multifunctional supersurface device based on graphene and vanadium dioxide according to claim 1, characterized in that: The relative dielectric constant of the top VO2 structure layer is calculated as follows: Where: ∞ =12 is the dielectric constant at infinite frequency; γ = 5.75×10 13 rad / s represents the collision frequency constant; ω p (σ0)=1.4×10 15 rad / s,σ0=3×10 5 s / m; σ is the conductivity of VO2, σ is 20S / m to indicate the insulating state of VO2, σ is 2×10 5 S / m represents the metallic state of VO2.

5. The terahertz multifunctional supersurface device based on graphene and vanadium dioxide according to claim 1, characterized in that: The first metal structure and the second metal structure are both made of a conductivity of 4.56×10 7 The first polyimide dielectric layer, the second polyimide dielectric layer and the third polyimide dielectric layer are all made of a polyimide material with a dielectric constant of 3 and a loss tangent of 0.

02.

6. The terahertz multifunctional supersurface device based on graphene and vanadium dioxide according to claim 1, characterized in that: The shapes of the first metal structure and the second metal structure include two sub-parts, one of which is composed of a rectangle connecting two semicircles, and the other is composed of a pair of "bow"-shaped slit ellipses, and their structural parameters are: a=96μm, b=47μm, c=26μm, d=33μm, l=12μm, l1=5μm, l2=3μm, r=12μm, w=5μm, w1=4.5μm, w2=2μm.

7. The terahertz multifunctional supersurface device based on graphene and vanadium dioxide according to claim 1, characterized in that: The graphene structure layer is composed of an isosceles right triangle with two adjacent rectangles and inclined graphene stripes, wherein the length n of the rectangle is 30 μm, the width m is 2 μm, the right angle side f of the isosceles right triangle is 17 μm, the side length e of the inclined graphene stripes is 16 μm, and the surface conductivity σ(ω) of the graphene structure layer is obtained by converting the intra-band conductivity σ intra (ω) and interband conductivity σ inter (ω) is derived from the Kubo equation, and σ(ω) is expressed as: Where: ω represents the angular frequency of the incident wave, μ c represents the graphene chemical potential (or graphene's Fermi level, usually denoted as E f ), the relaxation time is τ (1ps), e is the charge of the electron, T is the temperature (300K), k B is the Boltzmann constant, is the reduced Planck constant; In the terahertz band, σ intra The σ(ω) of graphene in the proposed metasurface is expressed by formula (3). In practical applications, the E of graphene f The relationship between the bias voltage and the Where: V f represents the Fermi velocity. When the temperature is 300K, the value is 1×10 6 m / s,V g represents bias voltage, t s is the dielectric layer thickness, ε r and ε0 are the dielectric constant and the vacuum permittivity, respectively.

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