Vanadium dioxide-assisted switchable multifunctional metamaterial devices

Abstract

The present invention discloses a vanadium dioxide-assisted switchable multifunctional metamaterial device. The multifunctional metamaterial device is composed of square periodic unit structures continuously spliced ​​in an array form on a plane; each square periodic unit structure is composed of different functional layers stacked, from top to bottom, the top vanadium dioxide patch array, the upper dielectric layer, the metal grating layer, the vanadium dioxide film, the lower dielectric layer and the bottom metal layer; the top vanadium dioxide patch array is composed of four hexagonal vanadium dioxide patches arranged in a 2×2 form on the surface of the upper dielectric layer; the metamaterial device can achieve the switching of three functions of broadband absorber, polarization converter and total reflection by changing the phase change characteristics of vanadium dioxide. The present invention provides a broad prospect for future terahertz applications.

Description

Technical Field

[0001] The invention belongs to the field of terahertz wave devices, and in particular relates to a vanadium dioxide-assisted switchable multifunctional metamaterial device. Background Art

[0002] Terahertz waves are between infrared light and microwaves in the electromagnetic spectrum, with frequencies between 0.1 and 10 THz. In recent years, terahertz science and related technologies have developed rapidly, showing broad application prospects in the fields of communications, sensing, imaging and non-destructive testing. These applications require not only efficient terahertz light sources, but also high-performance terahertz devices. At present, materials that can manipulate terahertz waves in nature are relatively scarce. In order to make more use of terahertz technology, researchers have developed materials that do not exist in nature - metamaterials. Metamaterials are artificially designed composite materials with a periodic arrangement of artificial microstructure units, breaking the boundaries of traditional materials and being able to manufacture electromagnetic functional structures with novel functions and easier preparation through existing technologies. It has broad application and development prospects in the fields of infrared imaging, filters, energy harvesting, electromagnetic stealth, sensors, etc., and has aroused great interest in the scientific community.

[0003] So far, it is a huge challenge to achieve high absorption, high polarization conversion, and tuning of total reflection performance and switching of functions in the terahertz range through a simple unit structure. Most metamaterial devices designed at present are not easy to change size after manufacturing and have single functions, which seriously limits their application in the terahertz field. In order to achieve adjustability or reconfigurability, researchers have introduced graphene, phase change materials, etc. in combination with metamaterial devices, and achieved the modulation or functional transformation of metamaterial devices by adjusting external conditions such as voltage, temperature or light, providing a new way for the development of switching and modulatable devices. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems existing in the prior art and provide a switchable multifunctional metamaterial device based on vanadium dioxide, which realizes multifunctional switching of broadband absorption, polarization conversion and total reflection by using a single metamaterial structure, and can be used to construct terahertz communication systems, electromagnetic stealth, modulation, electromagnetic energy collection and other fields.

[0005] The specific technical solutions adopted by the present invention are as follows:

[0006] A vanadium dioxide-assisted switchable multifunctional metamaterial device, which is formed by continuously splicing square periodic unit structures in an array form on a plane; each square periodic unit structure is composed of different functional layers stacked together, which are, from top to bottom, a top vanadium dioxide patch array, an upper dielectric layer, a metal grating layer, a vanadium dioxide film, a lower dielectric layer and a bottom metal layer; the top vanadium dioxide patch array is formed by four hexagonal vanadium dioxide patches arranged in a 2×2 form on the surface of the upper dielectric layer; the metamaterial device can realize switching of three functions of broadband absorber, polarization converter and total reflection by changing the phase change characteristics of vanadium dioxide.

[0007] Preferably, in the hexagonal vanadium dioxide patch, the lengths of the upper and lower sides of the hexagon are the same, both of which are 14 to 18 μm; the lengths of the other four sides of the hexagon except the upper and lower sides are the same; and the spacing between the upper and lower sides and the spacing between the left and right vertices are the same, both of which are 24 to 28 μm; the material of the hexagonal vanadium dioxide patch is vanadium dioxide, and the thickness is 0.1 to 0.2 μm.

[0008] Preferably, the material of the upper dielectric layer is polyimide, with a thickness of 8.5-12.5 μm, a relative dielectric constant of 3.1, and a loss angle of 0.05.

[0009] Preferably, the metal grating layer has two rectangular grating strips, the length of the rectangular grating strips is 80-120 μm, the width is 25-27 μm, and the gap width between the rectangular grating strips is 23-25 ​​μm; the material of the metal grating layer is gold, the thickness is 0.5-0.7 μm, and the relative dielectric constant is 4.561×10 7 S / m.

[0010] Preferably, the vanadium dioxide film is square with a side length of 80 to 120 μm, is made of vanadium dioxide, and has a thickness of 0.1 to 0.2 μm.

[0011] Preferably, the material of the lower dielectric layer is polyimide, with a thickness of 8.5-12.5 μm, a relative dielectric constant of 3.1, and a loss angle of 0.05.

[0012] Preferably, the material of the bottom metal layer is a metal that is not transparent to terahertz waves, preferably copper.

[0013] Preferably, the plane profile of the square periodic unit structure is a square with a side length of 80 to 120 μm.

[0014] Preferably, the metamaterial device is composed of square periodic unit structures continuously spliced ​​into a rectangle or a square.

[0015] Preferably, when vanadium dioxide is in a metallic state, the metamaterial device acts as a broadband absorber; when vanadium dioxide is in an insulating state and the polarization angle is 45°, the metamaterial device acts as a polarization converter to realize the conversion of linear polarization in different frequency bands into linear polarization and the conversion of linear polarization into circular polarization; when vanadium dioxide is in an insulating state and the polarization angle is 0°, the metamaterial device can realize total reflection.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The multifunctional metamaterial device designed by the present invention can realize completely different functions in a single structure, and can realize the conversion of different functions by changing the phase change characteristics of vanadium dioxide. In the present invention, the device has a high polarization conversion ability as a polarization converter, and can realize linear polarization and linear circular polarization; the device can realize total reflection when the polarization angle is 0°; when the device is used as an absorber, it can realize broadband absorption and the amplitude of the absorption band is more than 90%. The multifunctional metamaterial of the present invention has the advantages of simple and compact structure, convenient manufacturing, functional tunability, low cost, easy implementation, etc., and can also make the electromagnetic wave have polarization insensitivity when it is vertically incident. The multifunctional device proposed by the present invention can still maintain good performance as an absorber when the incident angle increases.

[0018] The metamaterial device disclosed in the present invention is an integrated, ultra-thin planar device. It does not need to change the structural characteristics of the device. It can realize multiple functions in a single metamaterial structure by applying electrical, magnetic, optical and temperature excitations. Therefore, the high-efficiency multifunctional device based on metamaterial combined with phase change material disclosed in the present invention can be widely used in miniaturized and integrated systems, especially in terahertz communication systems and detection systems, and can effectively reduce the volume and weight of the system. The present invention provides a broad prospect for future terahertz applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a three-dimensional schematic diagram of an array structure of a switchable multifunctional metamaterial device based on vanadium dioxide in an embodiment;

[0020] Figure 2 is a top plan view of a unit structure of a switchable multifunctional metamaterial device based on vanadium dioxide in an embodiment;

[0021] Figure 3 is the absorptivity, reflection of cross-polarized waves, and real and imaginary parts of relative impedance when the switchable multifunctional metamaterial based on vanadium dioxide in the embodiment is used as an absorber when the electromagnetic wave is vertically incident in the embodiment;

[0022] Figure 4is the absorption performance of the switchable multifunctional metamaterial based on vanadium dioxide in the embodiment at different incident angles when the electromagnetic wave is incident vertically in the embodiment;

[0023] Figure 5 is the ellipticity of the switchable multifunctional metamaterial based on vanadium dioxide in the embodiment when the electromagnetic wave is incident vertically in the embodiment as a polarization converter;

[0024] Figure 6 is the axial ratio and efficiency of the switchable multifunctional metamaterial based on vanadium dioxide in the embodiment when the electromagnetic wave is incident vertically in the embodiment as a polarization converter;

[0025] Figure 7 is the polarization conversion rate when the electromagnetic wave is vertically incident and the switchable multifunctional metamaterial based on vanadium dioxide in the embodiment is used as a polarization converter;

[0026] Figure 8 When the electromagnetic wave is incident vertically in the embodiment, the switchable multifunctional metamaterial based on vanadium dioxide in the embodiment acts as a reflection of co-polarization and cross-polarization during total reflection.

[0027] The reference numerals in the figure are: terahertz wave input end 1, terahertz wave output end 2, top vanadium dioxide patch array 3, upper dielectric layer 4, metal grating layer 5, vanadium dioxide film 6, lower dielectric layer 7 and bottom metal layer 8. DETAILED DESCRIPTION

[0028] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0029] In a preferred embodiment of the present invention, a switchable multifunctional metamaterial device based on vanadium dioxide is provided. The multifunctional metamaterial device is composed of a series of identical square periodic unit structures continuously spliced ​​in an array form on a plane. The shape of the spliced ​​device can be rectangular or square, depending on the requirements of the device.

[0030] like Figure 1 As shown, each square periodic unit structure is composed of different functional layers stacked together, which are, from top to bottom, a top vanadium dioxide patch array 3, an upper dielectric layer 4, a metal grating layer 5, a vanadium dioxide film 6, a lower dielectric layer 7 and a bottom metal layer 8. The top vanadium dioxide patch array 3 is composed of four hexagonal vanadium dioxide patches arranged in a 2×2 form on the surface of the upper dielectric layer 4.

[0031] In the present invention, the cross-sectional areas at any position of the upper dielectric layer 4, the vanadium dioxide film 6, the lower dielectric layer 7 and the bottom metal layer 8 are all squares of the same size, the top hexagonal vanadium dioxide patch is attached to the four corners of the upper surface of the upper dielectric layer, and the vanadium dioxide film 6 is attached to the upper surface of the lower dielectric layer 7. The structure of each layer is combined to form a square periodic unit, and its plane profile in a top view is square. The metamaterial device changes the phase change characteristics of the vanadium dioxide material in the top vanadium dioxide patch array 3 and the vanadium dioxide film 6 by applying external excitation, and can realize the switching of the three functions of broadband absorber, polarization converter and total reflection, thereby realizing multifunctional tuning.

[0032] In the multifunctional metamaterial device, the materials and parameters of each component can be adopted as follows:

[0033] like Figure 2 As shown, in the hexagonal vanadium dioxide patch, the lengths of the upper and lower sides of the hexagon are the same, both b = 14 ~ 18μm; the lengths of the other four sides of the hexagon except the upper and lower sides are the same; and the spacing between the upper and lower sides and the spacing between the left and right vertices are the same, both a = 24 ~ 28μm; the material of the hexagonal vanadium dioxide patch is vanadium dioxide, with a thickness of 0.1 ~ 0.2μm. The material of the upper dielectric layer 4 is polyimide, with a thickness of 8.5 ~ 12.5μm, a relative dielectric constant of 3.1, and a loss angle of 0.05. The metal grating layer 5 has two rectangular grating strips, the length of the rectangular grating strips is 80 ~ 120μm, the width is 25 ~ 27μm, and the gap width between the rectangular grating strips is 23 ~ 25μm; the material of the metal grating layer 5 is gold, with a thickness of 0.5 ~ 0.7μm, and a relative dielectric constant of 4.561×10 7 S / m. The vanadium dioxide film 6 is square, with a side length of 80 to 120 μm, made of vanadium dioxide, and with a thickness of 0.1 to 0.2 μm. The material of the lower dielectric layer 7 is polyimide, with a thickness of 8.5 to 12.5 μm, a relative dielectric constant of 3.1, and a loss angle of 0.05. The material of the bottom metal layer 8 is a metal that cannot transmit terahertz waves, such as copper. The plane profile of the square periodic unit structure is square, with a side length P of 80 to 120 μm.

[0034] It should be noted that in the above description of the hexagonal size of the hexagonal vanadium dioxide patch, the up, down, left, and right are based on Figure 2 It is defined by the plane shown in , the upper and lower sides are the two opposite sides of the hexagon, and the left and right vertices are the two vertices in the hexagon that are not in contact with the upper and lower sides.

[0035] The vanadium dioxide material used in the multifunctional metamaterial device has a conductivity of 200,000 S / m and 20 S / m in the metallic state and insulating state before and after the phase change, respectively. The metamaterial device disclosed in the present invention is an integrated, ultra-thin planar device. It does not need to change the structural characteristics of the device. It only needs to apply electrical, magnetic, optical and temperature excitations to make the vanadium dioxide undergo phase change, thereby realizing multiple functions in a single metamaterial structure, including:

[0036] When vanadium dioxide is in a metallic state, the metamaterial device acts as a broadband absorber, and the absorption peaks near the three absorption peaks all exceed 90%; when vanadium dioxide is in an insulating state and the polarization angle is 45°, the metamaterial device acts as a polarization converter, realizing the conversion of linear polarization in different frequency bands into linear polarization and the conversion of linear polarization into circular polarization; when vanadium dioxide is in an insulating state and the polarization angle is 0°, the metamaterial device can achieve total reflection.

[0037] Based on the above-mentioned vanadium dioxide switchable multifunctional metamaterial device, its specific technical effects are explained through examples.

[0038] Example 1

[0039] In this embodiment, the structure and shapes of each component of the switchable multifunctional metamaterial device based on vanadium dioxide are as described above, so they will not be repeated here. However, the specific parameters of each component are as follows:

[0040] like Figure 1 and Figure 2 As shown, the size parameters of the four hexagonal vanadium dioxide patches are the same. The lengths of the upper and lower sides b of the hexagon are the same, both b = 16μm; the lengths of the other four sides of the hexagon except the upper and lower sides are the same; and the spacing a between the upper and lower sides and the spacing a between the left and right vertices are the same, both a = 26μm; the material of the hexagonal vanadium dioxide patch is vanadium dioxide with a thickness of 0.1μm. The material of the upper dielectric layer 4 is lossy polyimide with a thickness of 10.5μm, a relative dielectric constant of 3.1, and a loss angle of 0.05. There are two rectangular grating strips in the metal grating layer 5. The length of the rectangular grating strips is 100μm, the width is 26μm, and the gap width between the rectangular grating strips is 24μm; the material of the metal grating layer 5 is gold, with a thickness of 0.6μm and a relative dielectric constant of 4.561×10 7S / m. The vanadium dioxide film 6 is square with a side length of 100μm. The material is vanadium dioxide and the thickness is 0.1μm, which is greater than the skin depth of the electromagnetic wave. The material of the lower dielectric layer 7 is lossy polyimide with a thickness of 10.5μm, a relative dielectric constant of 3.1, and a loss angle of 0.05. The material of the bottom metal layer 8 is metallic copper. The planar profile of the square periodic unit structure is square with a side length of P=100μm. In the top vanadium dioxide patch array 3 and the vanadium dioxide film 6, the conductivity of the metallic state and the insulating state of vanadium dioxide before and after the phase change are 200000S / m and 20S / m respectively. The phase change of vanadium dioxide can be achieved by applying electrical, magnetic, optical or temperature excitations.

[0041] The terahertz wave signal is input from the terahertz wave input terminal 1, but because the bottom is a metal layer, the terahertz wave signal cannot penetrate and can only be output from the terahertz wave output terminal 2 in the form of a reflected wave. Figure 3 As shown, the broadband absorption performance of the invention as a broadband absorber (the conductivity of vanadium dioxide is 200000S / m) is demonstrated. At this time, the absorber is composed of a top vanadium dioxide patch array, an upper dielectric layer, a metal grating and a vanadium dioxide film. When vanadium dioxide is in an insulating state, linear polarization can be converted to circular polarization in the range of 0 to 3.5 THz; in the range of 3.5 to 6 THz, when the polarization angle is 45°, linear polarization can be converted to linear polarization. When the polarization angle is 0°, total reflection can be achieved in the frequency range of 0.1-6 THz.

[0042] In this embodiment, based on the switchable multifunctional metamaterial of vanadium dioxide, when vanadium dioxide is in a metallic state, the structure can be used as a broadband absorber. Its absorption rate is defined as A = 1-RTR ⊥ , where R is the reflectivity, T is the transmittance, and R ⊥ is the parameter of cross-polarized wave reflection. In order to maximize the absorptivity, the reflectivity and transmittance are required to be as small as possible in the entire frequency range, electromagnetic waves cannot be transmitted, and the transmittance T approaches zero. The structure can be tuned according to the change of the conductivity of vanadium dioxide, and the change of the dielectric constant from the insulating state to the metallic state can achieve the wave absorption effect. At this time, the vanadium dioxide layer has a reflective property. Electromagnetic waves cannot be transmitted, and the transmittance T approaches zero.

[0043] like Figure 3 As shown, in order to evaluate the characteristics of the absorber designed in the embodiment, when the conductivity of vanadium dioxide is 200000 S / m, the following is obtained: Figure 3 Cross-polarization reflectance curve R of absorber ⊥ , the real part (Real), imaginary part (Imaginary) of the relative impedance and the absorption curve A(ω). Figure 3 It can be seen that the absorption rate is greater than 90% at 2.17-4.94 THz.

[0044] like Figure 4 As shown in the figure, when the TE polarized electromagnetic wave is incident on the absorber designed in the embodiment at different angles, the absorption performance obtained. It can be seen from the figure that the absorber proposed in this embodiment can maintain a high absorption rate in a wider frequency range when the incident electromagnetic wave in the TE mode is in the range of 0° to 50°.

[0045] like Figure 5 and Figure 6 As shown, in order to evaluate the characteristics of the polarization converter designed in the embodiment, when the conductivity of vanadium dioxide is 20S / m, Figure 5 and 6 Ellipticity, axial ratio, and efficiency of polarization converters. Figure 5 It can be seen that in the two ranges of 1.14~1.335THz and 3.566~3.663THz, the ellipticity is less than -0.9, which can realize the transition from linear polarization to left circular polarization; in the range of 1.784~3.344THz, the ellipticity is greater than 0.9, which can realize the transition from linear polarization to right circular polarization. Figure 6 In the ranges of 1.14-1.335THz, 3.566-3.663THz and 1.784-3.344THz, the axial ratio is less than the 3dB bandwidth, which can realize the transition from linear polarization to circular polarization. At the same time, in these frequency bands, the efficiency is greater than 90%.

[0046] like Figure 7 As shown, in order to evaluate the characteristics of the polarization converter designed in the embodiment, when the conductivity of vanadium dioxide is 20S / m and the polarization angle is 45°, the following is obtained: Figure 7 The polarization conversion rate of the polarization converter shown in FIG. 1 is as follows: From the figure, it can be seen that within 3.755 to 4.856 THz, the polarization conversion rate is greater than 0.9 and the relative bandwidth is 25.8%.

[0047] like Figure 8 As shown, in order to evaluate the total reflection characteristics designed in the embodiment, when the conductivity of vanadium dioxide is 20S / m and the polarization angle is 0°, the following is obtained: Figure 8 The co-polarization and cross-polarization curves of total reflection are shown. In the range of 0 to 6 THz, the cross-polarization curve approaches 0, while the co-polarization curve is almost greater than 90%.

[0048] The above results indicate that the vanadium dioxide-based switchable multifunctional metamaterial provided by the present invention has the advantages of simple structure, flexible adjustability, wide incident angle, multifunctional switchability, etc. At the same time, the device is small in size, thin in thickness, easy to integrate and manufacture, showing broad application prospects for the miniaturization and integration of future terahertz systems.

[0049] Although the present invention has been described with reference to specific features and embodiments thereof, it is apparent that various modifications and combinations thereof are possible. For example, the conductivity of the vanadium dioxide layer may be in the range of 20 to 2×10 5 S / m, the thickness is 0.1-0.2μm, and the thickness should be greater than the skin depth of the electromagnetic wave. The thickness of the intermediate dielectric layer can also be adjusted between 8.5 and 12.5μm. Accordingly, this specification and the drawings are merely exemplary illustrations of the invention as defined by the appended claims, and are deemed to have covered any and all modifications, variations, combinations or equivalents within the scope of the invention. Obviously, those skilled in the art can make various changes and modifications to the invention without departing from the scope of the invention. Thus, if these modifications and variations of the invention fall within the scope of the claims of the invention and equivalent technologies, the invention is also intended to include these modifications and variations.

Claims

1. A vanadium dioxide-assisted switchable multifunctional metamaterial device, characterized in that: The multifunctional metamaterial device is formed by continuously splicing square periodic unit structures in an array form on a plane; each square periodic unit structure is composed of different functional layers stacked together, which are, from top to bottom, a top vanadium dioxide patch array (3), an upper dielectric layer (4), a metal grating layer (5), a vanadium dioxide film (6), a lower dielectric layer (7) and a bottom metal layer (8); the top vanadium dioxide patch array (3) is formed by four hexagonal vanadium dioxide patches arranged in a 2×2 form on the surface of the upper dielectric layer (4); the metamaterial device can realize switching between three functions of broadband absorber, polarization converter and total reflection by changing the phase change characteristics of vanadium dioxide; The metal grating layer (5) has two rectangular grating strips, the length of the rectangular grating strips is 80-120 μm, the width is 25-27 μm, and the width of the gap between the rectangular grating strips is 23-25 ​​μm; When vanadium dioxide is in a metallic state, the metamaterial device acts as a broadband absorber; when vanadium dioxide is in an insulating state and the polarization angle is 45°, the metamaterial device acts as a polarization converter to realize the conversion of linear polarization in different frequency bands into linear polarization and the conversion of linear polarization into circular polarization; when vanadium dioxide is in an insulating state and the polarization angle is 0°, the metamaterial device can realize total reflection.

2. The vanadium dioxide-assisted switchable multifunctional metamaterial device according to claim 1, characterized in that: In the hexagonal vanadium dioxide patch, the lengths of the upper and lower sides of the hexagon are the same, both of which are 14-18 μm; the lengths of the other four sides of the hexagon except the upper and lower sides are the same; and the spacing between the upper and lower sides and the spacing between the left and right vertices are the same, both of which are 24-28 μm; The material of the hexagonal vanadium dioxide patch is vanadium dioxide, and the thickness is 0.1~0.2μm.

3. The vanadium dioxide-assisted switchable multifunctional metamaterial device according to claim 1, characterized in that: The material of the upper dielectric layer (4) is polyimide, with a thickness of 8.5-12.5 μm, a relative dielectric constant of 3.1, and a loss angle of 0.

05.

4. The vanadium dioxide-assisted switchable multifunctional metamaterial device according to claim 1, characterized in that: The material of the metal grating layer (5) is gold, with a thickness of 0.5-0.7 μm and a relative dielectric constant of 4.561× 10 7 S / m.

5. The vanadium dioxide-assisted switchable multifunctional metamaterial device according to claim 1, characterized in that: The vanadium dioxide film (6) is square in shape, has a side length of 80-120 μm, is made of vanadium dioxide, and has a thickness of 0.1-0.2 μm.

6. The vanadium dioxide-assisted switchable multifunctional metamaterial device according to claim 1, characterized in that: The material of the lower dielectric layer (7) is polyimide, with a thickness of 8.5-12.5 μm, a relative dielectric constant of 3.1, and a loss angle of 0.

05.

7. The vanadium dioxide-assisted switchable multifunctional metamaterial device according to claim 1, characterized in that: The material of the bottom metal layer (8) is a metal that is not permeable to terahertz waves.

8. The vanadium dioxide-assisted switchable multifunctional metamaterial device according to claim 1, characterized in that: The plane profile of the square periodic unit structure is a square, and the side length is 80-120 μm.

9. The vanadium dioxide-assisted switchable multifunctional metamaterial device according to claim 1, characterized in that: The metamaterial device is composed of square periodic unit structures continuously spliced ​​into a rectangle or a square.

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