A graphene-v02-based terahertz ultra-wideband adjustable wave absorber

Abstract

The application discloses a graphene-VO2-based terahertz ultra-wideband adjustable wave absorber and belongs to the technical field of terahertz technology, comprising, from top to bottom, a phase change material layer, a first dielectric layer, a graphene layer, a second dielectric layer and a reflection layer; the phase change material layer comprises a plurality of periodically arrayed VO2 umbrella-shaped patches; each VO2 umbrella-shaped patch is a regular octagon structure composed of eight congruent isosceles triangles; there are gaps between adjacent isosceles triangles; and adjacent VO2 umbrella-shaped patches are not connected with each other. The umbrella-shaped VO2 patches arranged in an array are combined with the graphene layer to realize ultra-wideband wave absorption in a 3-10 THz wave band, and the absorption rate is kept above 90%; and by respectively controlling the conductivity of the phase change material layer and the Fermi level of the graphene layer, the wave absorber presents different working states and has the characteristics of functional diversity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of terahertz, and particularly relates to a graphene-VO2-based terahertz ultra-wideband adjustable wave absorber. BACKGROUND

[0002] The frequency range of terahertz is generally 0.1 THz-10 THz, and the wave band is between the microwave wave band and the infrared wave band. Because of its wideband, low energy, strong penetration and other unique properties, it has broad application in the fields of communication, sensing, imaging and the like. The traditional structure of the terahertz absorber cannot be adjusted once the structure is fixed, so the tunable terahertz absorber becomes a hot research problem.

[0003] Vanadium dioxide VO2 as a common phase change material, under the external excitation of direct current bias, ultraviolet irradiation and the like, will change from an insulating state to a metallic state, resulting in a rapid increase in electrical conductivity, and the value changes by about 3-6 orders of magnitude, and the process is reversible. By introducing VO2 into the structure of the terahertz absorber, the performance of the absorber can be adjusted, and the flexibility is high. Graphene as a special two-dimensional honeycomb-like adjustable material, when the structure is fixed, the Fermi level can be changed by adjusting the voltage at both ends, thereby manipulating the electrical conductivity of graphene. The introduction of the terahertz absorber structure can also achieve dynamic adjustable characteristics.

[0004] At present, most of the tunable terahertz absorbers have a narrow working bandwidth (within 5 THz), therefore, reasonable design of the structure and position of the VO2 layer and the graphene layer can effectively improve the performance of the terahertz absorber. SUMMARY

[0005] The application aims at the problems in the prior art, and provides a graphene-VO2-based terahertz ultra-wideband adjustable wave absorber, which has the advantages of extremely wide absorption bandwidth and good absorption performance.

[0006] The technical scheme adopted by the application is as follows:

[0007] A graphene-VO2-based terahertz ultra-wideband adjustable wave absorber, characterized by comprising, from top to bottom, a phase change material layer, a first dielectric layer, a graphene layer, a second dielectric layer and a reflection layer; the phase change material layer comprises a plurality of periodically arrayed VO2 umbrella-shaped patches, each VO2 umbrella-shaped patch is a regular octagon structure composed of eight congruent isosceles triangles, there is a gap between adjacent isosceles triangles, and adjacent VO2 umbrella-shaped patches are not connected to each other.

[0008] Further, the side length of the regular octagon structure is 8-12 μm, and the gap size between adjacent isosceles triangles is 0.1-0.8 μm.

[0009] Further, the thickness of the phase change material layer is 0.03-0.3 μm.

[0010] Further, the thickness of the graphene layer is 0.001 μm.

[0011] Further, the thickness of the first dielectric layer and the second dielectric layer is 3.5-7.5 μm and 2.5-5.5 μm respectively.

[0012] Further, the material of the reflection layer is metal such as copper or gold, and the thickness is 2-4 μm.

[0013] Further, the conductivity of the phase change material layer is adjusted by ultraviolet irradiation, and the Fermi energy level of the graphene layer is adjusted by adjusting the direct current bias voltage between the graphene layer and the reflection layer.

[0014] The working principle of the graphene-VO2-based terahertz ultra-wideband tunable wave absorber is as follows: on one hand, the phase change material layer is irradiated by ultraviolet light to cause insulator-metal phase transition, and the conductivity gradually increases; on the other hand, the Fermi energy level of the graphene layer is changed by adjusting the direct current bias voltage between the graphene layer and the reflection layer; by combining the above two adjustment methods, the terahertz ultra-wideband absorption of the wave absorber is realized, and the specific process is as follows:

[0015] When the phase change material layer is in an insulating state and the Fermi energy level of the graphene layer is 0 eV, the wave absorber exhibits full reflection characteristics in the entire terahertz wave band;

[0016] When the phase change material layer is in an insulating state, the Fermi energy level of the graphene layer is adjusted, and the wave absorber exhibits high reflection characteristics in the entire terahertz wave band, and the reflectivity is tunable;

[0017] When the Fermi energy level of the graphene layer is 0 eV, the conductivity of the phase change material layer is increased, and the wave absorber exhibits a wide absorption state in the 3-8.6 THz wave band;

[0018] When the Fermi energy level of the graphene layer is adjusted to 0.65-0.75 eV, the conductivity of the phase change material layer is increased, and the wave absorber exhibits an ultra-wideband absorption state in the 3-10 THz wave band;

[0019] When the conductivity of the phase change material layer and the Fermi energy level of the graphene layer are adjusted simultaneously, the wave absorber realizes a modulation depth of more than 97% at two perfect absorption points, and has good switching characteristics.

[0020] The beneficial effects of the present application are as follows:

[0021] The application provides a graphene-VO2-based terahertz ultra-wideband adjustable wave absorber, which adopts an array-arranged umbrella-shaped VO2 patch as a phase change material layer, so that the wave absorber shows a relatively wide wave absorption state in a 3-8.6 THz wave band, the graphene layer with adjustable Fermi energy is introduced into two dielectric layers, so that the wave absorber shows an ultra-wideband wave absorption in a 3-10 THz wave band, the absorption rate is kept above 90 %, and the wave absorber has the advantages of wide absorption bandwidth and good absorption performance; in addition, the conductivity of the phase change material layer and the Fermi energy of the graphene layer are controlled respectively, so that the wave absorber shows different working states and has the characteristics of functional diversity. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A structure schematic view of the graphene-VO2-based terahertz ultra-wideband adjustable wave absorber provided for the embodiment 1 is shown in the figure.

[0023] Figure 2 A local structure schematic view of the graphene-VO2-based terahertz ultra-wideband adjustable wave absorber provided for the embodiment 1 is shown in the figure.

[0024] Figure 3 A local top view of the graphene-VO2-based terahertz ultra-wideband adjustable wave absorber provided for the embodiment 1 is shown in the figure.

[0025] Figure 4 A structure schematic view of the VO2-based terahertz adjustable wave absorber provided for the comparative example is shown in the figure.

[0026] Figure 5 Absorption spectrum line graphs of the VO2-based terahertz adjustable wave absorber provided for the comparative example under different VO2 conductivities are shown in the figures.

[0027] Figure 6 Reflection rate curve graphs of the graphene-VO2-based terahertz ultra-wideband adjustable wave absorber provided for the embodiment 1 under different graphene layer Fermi energies when the VO2 conductivity is 10 S / m are shown in the figures.

[0028] Figure 7 Absorption spectrum line graphs of the graphene-VO2-based terahertz ultra-wideband adjustable wave absorber provided for the embodiment 1 under different graphene layer Fermi energies when the VO2 conductivity is 200000 S / m are shown in the figures.

[0029] Figure 8 Absorption spectrum line graphs of the graphene-VO2-based terahertz ultra-wideband adjustable wave absorber provided for the embodiment 1 under different VO2 conductivities when the graphene layer Fermi energy is 0.75 eV are shown in the figures.

[0030] Figure 9A schematic diagram of the graphene-VO2-based terahertz ultra-wideband tunable absorber provided in Embodiment 1 when realizing the switching function when simultaneously adjusting the VO2 conductivity and the Fermi level of the graphene layer;

[0031] Figure 10 An absorption spectrum line graph of the graphene-VO2-based terahertz ultra-wideband tunable absorber provided in Embodiment 1 when the phase change material layer is in the metal state and the Fermi level of the graphene layer is 0.75 eV, the absorption rate changes with the polarization angle;

[0032] Figure 11 An absorption spectrum line graph of the graphene-VO2-based terahertz ultra-wideband tunable absorber provided in Embodiment 1 when the phase change material layer is in the metal state and the Fermi level of the graphene layer is 0.75 eV, the absorption rate changes with the incident angle;

[0033] The explanation of each mark in the drawing is as follows:

[0034] 1: phase change material layer; 2: first dielectric layer; 3: graphene layer; 4: second dielectric layer; 5: reflective layer; 6: microstructure unit. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0036] Embodiment 1

[0037] The present embodiment provides a graphene-VO2-based terahertz ultra-wideband tunable absorber, the structure is as shown in Figure 1 from top to bottom, including a phase change material layer 1, a first dielectric layer 2, a graphene layer 3, a second dielectric layer 4 and a reflective layer 5.

[0038] The absorber can be regarded as being composed of a plurality of periodically arrayed microstructure units 6, the side length P of the microstructure unit 6 is 28 μm, the structure is as shown in Figure 2 and Figure 3 from top to bottom, including a phase change material layer 1, a first dielectric layer 2, a graphene layer 3, a second dielectric layer 4 and a reflective layer 5; wherein the phase change material layer 1 is a VO2 umbrella-shaped patch, the structure is a regular octagon composed of 8 congruent isosceles triangles, the side length R of the regular octagon is 0.98 μm, there is a gap with a width L of 0.4 μm between adjacent isosceles triangles.

[0039] The VO2 umbrella-shaped patches in adjacent microstructure units 6 are not connected to each other.

[0040] In this embodiment, the thickness of the phase change material layer 1 is 0.05 μm; the materials of the first dielectric layer 2 and the second dielectric layer 4 are quartz, and the thicknesses thereof are 4.5 μm and 3 μm, respectively; the thickness of the graphene layer 3 is 0.001 μm; and the material of the reflective layer 5 is gold, and the thickness thereof is 3 μm.

[0041] In this embodiment, the conductivity of the phase change material layer can be adjusted independently by irradiating the phase change material layer with ultraviolet light; and the Fermi energy level of the graphene layer can be adjusted independently by adjusting the direct current bias voltage between the graphene layer and the reflective layer.

[0042] Comparative Example

[0043] This comparative example provides a VO2-based terahertz adjustable wave absorber, which has the structure as shown in Figure 4 Compared with the graphene-VO2-based terahertz ultra-wideband adjustable wave absorber provided in Example 1, the difference is only that there is no graphene layer 3 between the first dielectric layer 2 and the second dielectric layer 4; and the other structures and sizes are unchanged.

[0044] In order to illustrate the performance of the graphene-VO2-based terahertz ultra-wideband adjustable wave absorber provided in Example 1, the wave absorbers obtained in Example 1 and the comparative example are respectively simulated and verified, and the results are as follows:

[0045] The simulation results of the VO2-based terahertz adjustable wave absorber provided in the comparative example are as shown in Figure 5 By irradiating the phase change material layer with ultraviolet light, the conductivity σ VO2 of the phase change material layer can be adjusted to be 10-200000 S / m, and it can be seen that the absorptivity of the wave absorber of the comparative example can be modulated between 3.6-8.5 THz, the relative bandwidth is 4.9 THz, and the function is single.

[0046] The simulation results of the graphene-VO2-based terahertz ultra-wideband adjustable wave absorber provided in Example 1 are as shown in Figures 6 to 11 , and are as follows:

[0047] When the phase change material layer 1 is in an insulating state and the Fermi energy level of the graphene layer 3 is 0 eV, the wave absorber exhibits a full reflection characteristic in the entire terahertz wave band 0-10 THz; when the conductivity of VO2 is 10 S / m, i.e., the phase change material layer 1 is in an insulating state, the Fermi energy level of the graphene layer 3 is adjusted to be 0-0.8 eV, as shown in Figure 6 , the absorber realizes a high reflection characteristic in the entire terahertz wave band 0-10 THz, and the reflectivity can be tuned.

[0048] When the conductivity of VO2 is 200000 S / m, i.e., the phase change material layer 1 is in a metallic state, the Fermi energy level of the graphene layer 3 is adjusted to be 0-0.8 eV, as shown in Figure 7As shown in the figure, the absorption of the absorber has a higher increase in the high frequency range of 3.57-10 THz, and is more than 90%, and basically does not affect the absorption in the low frequency range.

[0049] When the Fermi energy level of the graphene layer 3 is 0.75 eV, the conductivity of the VO2 is gradually increased, and when the conductivity of the VO2 is increased to 20000 S / m, as shown in the figure, Figure 8 As shown in the figure, the absorber realizes the super wideband adjustable absorption characteristics in the frequency range of 3.57-10 THz.

[0050] Meanwhile, the conductivity of the VO2 and the Fermi energy level of the graphene layer 3 are adjusted, and the Fermi energy level of the graphene layer 3 is adjusted to 0.75 eV, the conductivity of the VO2 is 20000 S / m, and the Fermi energy level of the graphene layer 3 is 0 eV, and the conductivity of the VO2 is 10 S / m, as shown in the figure, Figure 9 As shown in the figure, the modulation depth of 97.9% (4.3 THz) and 96.8% (8.25 THz) can be realized at two perfect absorption points, respectively, and the switch characteristics are good.

[0051] From the figure, Figure 10 It can be seen that when the phase change material layer 1 is in a metal state and the Fermi energy level of the graphene layer 3 is 0.75 eV, the absorber always has good absorption characteristics when the terahertz wave is incident at different polarization angles, that is, the absorption rate in the frequency range of 3.57-10 THz is more than 90%, indicating that the absorber has polarization angle insensitivity characteristics.

[0052] From the figure, Figure 11 It can be seen that when the phase change material layer 1 is in a metal state and the Fermi energy level of the graphene layer 3 is 0.75 eV, the absorber still has relatively good absorption characteristics when the terahertz wave is obliquely incident at a certain angle, and when the incidence angle of the terahertz wave is increased by 65°, the absorption rate of the absorber can still reach more than 90%, indicating that the absorber has certain incidence angle insensitivity characteristics.

[0053] In summary, the present application proposes a graphene-VO2 based terahertz super wideband adjustable absorber, which realizes super wideband absorption, high reflectivity and switching function without increasing the complexity of the structure, greatly expands the absorption bandwidth of the terahertz absorber, has the advantages of simple structure, large modulation depth, etc., and can be applied to electromagnetic stealth, terahertz switch and modulator fields.

[0054] The above is only a specific embodiment of the present application, any feature disclosed in the specification can be replaced by other equivalent or similar purpose alternative features unless specifically described; all features disclosed, or steps in all methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A graphene-VO2-based terahertz ultra-wideband tunable absorber, characterized in that, The metamaterial absorber comprises, from top to bottom, a phase change material layer, a first dielectric layer, a graphene layer, a second dielectric layer and a reflective layer; the phase change material layer comprises a plurality of periodically arrayed VO2 umbrella-shaped patches, each VO2 umbrella-shaped patch is a regular octagonal structure composed of eight congruent isosceles triangles, there is a gap between adjacent isosceles triangles, and adjacent VO2 umbrella-shaped patches are not connected with each other; the side length of the regular octagonal structure is 8-12 μm, and the gap size between adjacent isosceles triangles is 0.1-0.8 μm; When the Fermi energy level of the graphene layer is 0 eV, by increasing the conductivity of the phase change material layer, the wave absorber exhibits a relatively wide absorption state in the 3-8.6 THz wave band; when the Fermi energy level of the graphene layer is adjusted to 0.65-0.75 eV, by increasing the conductivity of the phase change material layer, the wave absorber exhibits a super-wideband absorption state in the 3-10 THz wave band; when the conductivity of the phase change material layer and the Fermi energy level of the graphene layer are adjusted simultaneously, the maximum modulation depth of the wave absorber at two perfect absorption points is 97.9% and 96.8%, respectively. 2.The graphene-VO2-based terahertz ultra-wideband tunable absorber according to claim 1, wherein, The thickness of the phase change material layer is 0.03-0.3 μm. 3.The graphene-VO2-based terahertz ultra-wideband tunable absorber according to claim 1, wherein, The thickness of the graphene layer is 0.001 μm. 4.The graphene-VO2-based terahertz ultra-wideband tunable absorber according to claim 1, wherein, The thicknesses of the first dielectric layer and the second dielectric layer are 3.5-7.5 μm and 2.5-5.5 μm, respectively. 5.The graphene-VO2-based terahertz ultra-wideband tunable absorber according to claim 1, wherein, The material of the reflective layer is copper or gold, and the thickness is 2-4 μm.

Images