A terahertz multifunctional metasurface device based on graphene and vanadium dioxide

Abstract

The present 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, arranged sequentially from top to bottom. The present invention enables dynamic switching of transmission-type linear-circular polarization conversion, reflection-type cross-polarization conversion, and broadband absorber functions within the same structure, enabling transmission / reflection mode switching. The bandwidth of the transmission-type linear-circular polarization converter and the reflection-type cross-polarization converter can be dynamically adjusted by changing the graphene's Fermi level. Both the broadband absorber and the reflection-type cross-polarization converter can act on incident LP waves and CP waves, demonstrating the metasurface's sensitivity to the polarization of incident electromagnetic waves.

Description

Technical Field

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

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

[0003] However, terahertz devices constructed with traditional materials suffer from numerous issues, such as limited magnetic response, severe high-frequency losses, difficulty adapting to high-frequency characteristics, and a lack of adjustability and reconfigurability. This is why metamaterials (metasurfaces) have emerged. Metasurfaces are two-dimensional planar components constructed from subwavelength periodic units of metals or dielectrics. They possess electromagnetic properties such as negative refractive index and negative dielectric constant, which are not possessed by traditional natural materials. They can be considered two-dimensional metamaterials. However, compared with three-dimensional metamaterials, they are thinner and have lower losses, thus providing more flexible modulation of electromagnetic waves. Metasurfaces also reduce processing costs and complexity. Based on these advantages, metasurfaces make it possible to propose, design, and manufacture highly integrated, compact, and high-performance devices.

[0004] As research into terahertz metasurface functional devices deepens, researchers have discovered that metasurfaces based on traditional metal materials cannot adjust the dielectric constant, which poses some limitations for the design of dynamically tunable terahertz multifunctional metasurfaces. Therefore, to achieve tunability, tunable materials (such as photosensitive silicon, graphene, vanadium dioxide, and Dirac semimetals) can be incorporated into the metasurface structure to achieve integrated metasurface functionality. By altering external environmental conditions, the physical or chemical properties of the tunable material can be altered, thereby causing the metasurface's functionality to change.

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

[0006] However, among the current terahertz multifunctional metasurfaces, few possess the ability to convert linear polarization from transmission to circular polarization. For those that do, most have a single function, or only one mode: reflection or transmission. Very few terahertz multifunctional metasurfaces encompass both modes. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the existing technology 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 includes 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 arranged in sequence from top to bottom.

[0010] Moreover, the thicknesses 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 thicknesses 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 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. There are two sub-parts in each of them, and the overall structure is obliquely symmetrical. The radius of the open ring is r 1 = 30 μm, r 2 = 25 μm, 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 = 15 μm, l 4 = 30 μm and l 5= 25 μm.

[0012] Furthermore, the relative dielectric constant of the top VO2 structure layer is calculated as follows:

[0013] (1)

[0014] in: e ∞ = 12 is the dielectric constant at infinite frequency; c = 5.75 × 10 13 rad / s represents the collision frequency constant; oh p ( s 0) = 1.4 × 10 15 rad / s, s 0 = 3 × 10 5 s / m; σ is the electrical conductivity of VO2, σ is 20 S / m to indicate the insulating state of VO2, σ is 2 × 10 5 S / m represents the metallic state of VO2.

[0015] Moreover, the first metal structure and the second metal structure are both made of a material with 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 slotted ellipses, and their structural parameters are: a = 96 μm, b = 47 μm, c = 26 μm, d = 33 μm, l= 12 μm, l 1 = 5 μm, l 2 = 3 μm, r = 12 μm, w = 5 μm, w 1 = 4.5 μm, w 2= ​​2 μm.

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

[0018] (2)

[0019] (3)

[0020] (4)

[0021] in: oh represents the angular frequency of the incident wave, m c represents the graphene chemical potential (or graphene's Fermi level, usually expressed as E f ), the relaxation time is t (1 ps), e is the charge of the electron, T is the temperature (300 K), k B is the Boltzmann constant, h is the reduced Planck constant;

[0022] In the terahertz band, s intra Dominant, the graphene in the proposed metasurface s ( oh) is expressed by formula (3). In practical applications, the E f The relationship between and bias voltage is expressed as:

[0023] (5)

[0024] in: V f represents the Fermi velocity, which is 1 × 10 when the temperature is 300 K. 6 m / s, V g Indicates bias voltage, t s is the dielectric layer thickness, e r and e 0 are the dielectric constant and the vacuum permittivity, respectively.

[0025] The advantages and beneficial effects of the present invention are:

[0026] 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.

[0027] 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.

[0028] 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

[0029] 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;

[0030] Figure 2 (a) is a schematic diagram of the VO2 structure layer; 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;

[0031] Figure 3 (a) to (d) are the present invention's x - Transmission coefficient curve, phase difference curve, ellipticity χ curve and AR curve for LP wave incidence;

[0032] Figure 4 Different graphenes of the present invention Ef The AR curve chart below;

[0033] Figure 5 (a) and (b) are respectively x -Reflection coefficient curve and polarization conversion rate curve under LP incidence; Figure 5 (c) and (d) are the reflection coefficient curve and polarization conversion rate curve under RHCP wave incidence, respectively;

[0034] Figure 6 Different graphenes of the present invention E f Down PCR r x and PCR r + ;

[0035] Figure 7 (a) and (b) are respectively x -Reflection and transmission coefficient curves, absorptivity curves and relative impedance curves under LP incidence;

[0036] Figure 8 (a) and (b) are respectively the reflection and transmission coefficient curves and the wave absorption rate curves under the incidence of RHCP wave of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0038] like Figure 1 As shown, a terahertz multifunctional metasurface device based on graphene and vanadium dioxide has the following innovations: it includes a top VO2 structure layer, a first polyimide dielectric layer, a VO2 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 arranged in sequence from top to bottom.

[0039] Figure 1 (a) and Figure 1 (b) represent the unit structure of the metasurface (periodic p = 130 μm) and its side view. Figure 1 In (b), it can be seen that the unit structure has 6 layers, including h 2 = 0.2 μm thick top VO2 structural layer ( Figure 2 (a)), h 2 = 0.2 μm thick VO2 thin film layer, h2 = 2 metal structure layers with a thickness of 0.2 μm ( Figure 2 (b)), h 4 = 0.35nm thick graphene structure layer ( Figure 2 (c)) and h 5 = 0.1 μm thick silicon dioxide layer, the dielectric layer is polyimide (PI) with a dielectric constant of 3 and a loss tangent of 0.02, and the thickness of the three layers from top to bottom are h 6 = 10 μm, h 1 = 16 μm and h 3 = 19 μm. The role of the VO2 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 modify its Fermi level ( E f ) to dynamically adjust bandwidth.

[0040] like Figure 2 As shown in (a), the shape of the top VO2 structure 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. There are two sub-parts in each, and the overall structure is obliquely symmetrical. The radius of the open ring is r 1 = 30 μm, r 2 = 25 μm, 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 = 15 μm, l 4 = 30 μm and l 5= 25 μm.

[0041] Furthermore, the relative dielectric constant of the top VO2 structure layer is calculated as follows:

[0042] (1)

[0043] in: e ∞ = 12 is the dielectric constant at infinite frequency; c = 5.75 × 10 13 rad / s represents the collision frequency constant; oh p ( s 0) = 1.4 × 10 15 rad / s, s 0 = 3 × 10 5 s / m; σ is the electrical conductivity of VO2, σ is 20 S / m to indicate the insulating state of VO2, σ is 2 × 105 S / m represents the metallic state of VO2.

[0044] 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.

[0045] 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. The structural parameters are: a = 96 μm, b = 47 μm, c = 26 μm, d = 33 μm, l = 12 μm, l 1 = 5 μm, l 2 = 3 μm, r = 12 μm, w = 5 μm, w 1 = 4.5 μm, w 2= ​​2 μm.

[0046] like Figure 2 As shown in (c), the graphene structure layer is composed of an isosceles right triangle with two adjacent rectangles and inclined graphene stripes. n = 30 μm, width m = 2 μm, the right angle side of the isosceles right triangle f =17 μm, the side length of the inclined graphene stripes e = 16 μm, the surface conductivity of the graphene structure layer s ( oh ) is obtained by dividing the conductivity within the band s intra ( oh ) and interband conductivity s inter ( oh ) is derived from the Kubo equation, s ( oh ) is expressed as:

[0047] (2)

[0048] (3)

[0049] (4)

[0050] in: oh represents the angular frequency of the incident wave, m c represents the graphene chemical potential (or graphene's Fermi level, usually expressed as E f ), the relaxation time is t (1 ps), e is the charge of the electron, T is the temperature (300 K), k B is the Boltzmann constant, h is the reduced Planck constant;

[0051] In the terahertz band, s intra Dominant, the graphene in the proposed metasurface s ( oh ) is expressed by formula (3). In practical applications, the E f The relationship between and bias voltage is expressed as:

[0052] (5)

[0053] in: V f represents the Fermi velocity, which is 1 × 10 when the temperature is 300 K. 6 m / s, V g Indicates bias voltage, t s is the dielectric layer thickness, e r and e 0 are the dielectric constant and the vacuum permittivity, respectively.

[0054] The terahertz multifunctional metasurface device based on graphene and vanadium dioxide proposed in the present invention changes the Fermi level of graphene ( E f ), the conductivity of VO2 and the direction of the electromagnetic wave incident on the metasurface, it 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:

[0055] First, the related research on it as a transmission-type linear-circular polarization converter is introduced. When VO2 is in an insulating state (conductivity of 20 S / m), the VO2 thin film layer is equivalent to the dielectric layer, and the metasurface is transmission-type at this time.

[0056] when xLinear polarization ( x -LP) wave (or y Linear polarization ( y When the terahertz multifunctional metasurface is incident vertically along the forward direction, the transmission coefficient (given by t ij Indicates that: j - i polarization conversion) and phase difference ( f x ( f y ) respectively represent t xx ( t yy )and t yx ( t xy ) as the phase difference between Figure 3 (a) and Figure 3 (b) shows (only shows x -LP wave results). When t yx = t xx ( t xy = t yy )and f x = f xx – f yx = ±π / 2 + 2 k π( f y = f yy – f xy = ±π / 2 + 2 k π) ( k is an integer) When both conditions are met, the incident LP wave is converted into CP wave. x -LP wave as an example, according to Figure 3 (a) and Figure 3 (b) is initially obtained x -The conclusion that LP waves are converted into CP waves in the frequency range of 1.15-1.50 THz.

[0057] To further clarify the description, we introduce the stokes parameter:

[0058] (6)

[0059] in:S 0 represents the total electric field intensity of the transmitted wave, S 3 indicates 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 represent LHCP wave and RHCP wave respectively. The relevant results are as follows Figure 3 In the range of 1.16-1.52 THz, the ellipticity χ is between -1 and -0.95, indicating that within this range x -LP waves are converted to RHCP waves.

[0060] 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:

[0061] (7)

[0062] According to relevant standards, AR = 0 indicates a perfect CP wave. However, in the context of engineering simulations, AR <3 can be regarded as a perfect CP wave. Figure 3 (d) can be found (only displayed AR <12): 1.16-1.52 THz range AR <3, further confirmed x -LP waves are converted into relatively perfect CP waves in this frequency domain.

[0063] Figure 4 Showing different graphene E f The impact on AR can be found as follows: E f The increase of AR The part <3 also increases, that is, x -The frequency domain range of LP wave converted into CP wave increases, indicating that the working bandwidth of linear-circular polarization converter can be adjusted E f To dynamically adjust.

[0064] When VO2 changes from an insulating state to a metallic state (conductivity increases from 20 to 2 × 10 5 When the VO2 thin film layer is equivalent to the metal layer, the entire metasurface changes from a transmissive type to a reflective type. Depending on the direction of the electromagnetic wave incident on the metasurface, it can achieve reflective cross-polarization conversion and broadband absorption, respectively.

[0065] 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 x -LP wave and y -LP waves, and can also achieve cross-polarization conversion between RHCP waves and LHCP waves. x -LP wave incident as an example, assuming graphene E f is 1.1eV. Figure 5 As shown in (a), in the 0.83-1.54 THz frequency domain, the cross-polarization reflection coefficient r yx remains above 0.6, while the co-polarization reflection coefficient r xx Lower than 0.2 or even lower than 0.1, indicating that the incident x -LP waves are reflected as y -LP wave. To further illustrate its conversion efficiency, the polarization conversion ratio (PCR) is introduced:

[0066] (8)

[0067] The results are as follows Figure 5 As shown in (b), in the frequency range of 0.81-1.74 THz, PCR r x The value is greater than 90%.

[0068] When CP waves are incident on the metasurface, it can also exhibit the function of cross-polarization conversion. Taking RHCP waves as an example, the reflection coefficient (“+” represents RHCP waves, “-” represents LHCP waves) and PCR r + The results are as follows Figure 5 (c) and (d) of 5. In the 0.83-1.56 THz 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 r + Greater than 90%.

[0069] For both types of reflective cross-polarization converters, when graphene E f When the values ​​are 0.5 eV, 0.8 eV and 1.1 eV respectively, PCR r x and PCR r + The changes are as follows Figure 6 As shown in (a) and (b) of 6, it can be found that: no matter the incident LP wave or CP wave, as E f The increase, PCR r x and PCR r + More than 90% of the parts have increased, reflecting the adjustability of graphene Fermi level to the working bandwidth.

[0070] Finally, the device's function as a broadband absorber is explained. Switching between broadband absorption and reflective cross-polarization conversion is achieved by changing the incident direction of the electromagnetic wave, while other conditions remain unchanged: the incident direction of the electromagnetic wave changes from reverse to forward, and the VO2 remains in a metallic state. As a broadband absorber, it can absorb both incident LP and CP waves.

[0071] By incidence x -LP wave as an example, in Figure 7 In (a), it can be clearly found that r yx , t yx and t xx The amplitude of is about 0.1 in the whole frequency band, indicating that they are absorbed by the top VO2 structure layer and PI layer;

[0072] about r xx , within 2.26-4.33 THz, its amplitude is less than 0.3. The absorbing performance of the broadband absorber is explained by introducing the total absorption rate: A = 1 – R – T , A represents the total absorption rate, 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 presence of metallic VO2 film, t yx and t xx The value of is small, so their sum of squares can be ignored ( T ≈ 0), then the formula simplifies 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% in the range of 2.24-4.30 THz.

[0073] In addition, impedance matching theory can be used to elucidate the absorption characteristics and internal mechanisms of metasurfaces:

[0074] (9)

[0075] in Z r is defined as the relative impedance, S 11 and S 21 are the reflection coefficient and transmission coefficient respectively. 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).

[0076] For the CP wave incident, 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 (b) of 8 show that the metasurface exhibits excellent characteristics in absorbing LP waves or CP waves.

[0077] In addition, considering the complex electromagnetic environment in the real environment, the xWhen a -LP wave is incident on the metasurface, the impact of different incident angles and polarization angles on linear-circular polarization conversion, linear cross-polarization conversion, and broadband absorber functions is 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°.

[0078] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand 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 by: The method comprises a top VO2 structure layer, a first polyimide dielectric layer, a VO2 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, which are sequentially arranged from top to bottom; 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 two, and the overall structure is obliquely symmetrical. The shapes of the first metal structural layer and the second metal structural layer 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; The graphene structure layer consists of an isosceles right triangle with two adjacent rectangles and inclined graphene stripes.

2. The terahertz multifunctional metasurface 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 metasurface device based on graphene and vanadium dioxide according to claim 1, characterized in that: The radius of the split ring r 1 = 30 μm, r 2 = 25 μm, rip 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 = 15 μm, l 4 = 30 μm and l 5 = 25 μm.

4. The terahertz multifunctional metasurface 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: （1） in: ε ∞ = 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 the electrical conductivity of VO2, σ is 20 S / 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 metasurface 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 material with 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 metasurface device based on graphene and vanadium dioxide according to claim 1, characterized in that: The length of the rectangle n = 30 μm, width m = 2 μm, the right angle side of the isosceles right triangle f = 17 μm, the side length of the inclined graphene stripes e = 16 μm, the surface conductivity of the graphene structure layer σ ( ω ) is obtained by dividing the conductivity within the band σ intra ( ω ) and interband conductivity σ inter ( ω ) is derived from the Kubo equation, σ ( ω ) is expressed as: （2） （3） （4） in: ω represents the angular frequency of the incident wave, μ c represents the graphene chemical potential or the Fermi level of graphene, which is expressed as E f , the relaxation time is τ= 1 ps, e is the charge of the electron, T The temperature is 300 K, k B is the Boltzmann constant, H is the reduced Planck constant; In the terahertz band, σ intra Dominant, the graphene in the proposed metasurface σ ( ω ) is expressed by formula (3). In practical applications, the E f The relationship between and bias voltage is expressed as: （5） in: V f represents the Fermi velocity, which is 1 × 10 when the temperature is 300 K. 6 m / s, V g Indicates bias voltage, t s is the dielectric layer thickness, ε r and ε 0 are the dielectric constant and the vacuum permittivity, respectively.

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