Vanadium dioxide-based dual-mode multi-peak tunable wave absorber

Abstract

The dual-mode multi-peak tunable wave absorber based on vanadium dioxide is a two-dimensional metasurface formed by basic structure units which are distributed in a periodic array mode, each basic structure unit comprises three layers of structures which are respectively a centrosymmetric nested VO2-metal composite superstructure layer, a VO2-metal composite superstructure layer, a VO2-metal composite superstructure layer, a VO2-metal composite superstructure layer and a VO2-metal composite superstructure layer from top to bottom, the vanadium dioxide outer ring and the vanadium dioxide connecting square blocks are distributed in a central symmetry mode, the metal frames are distributed in a nested mode, the metal frames are stacked layer by layer according to the size from large to small and are symmetrically distributed with the center of the vanadium dioxide outer ring as the center, and the vanadium dioxide outer ring is physically connected with the metal frame on the outermost ring. The vanadium dioxide connecting square blocks are distributed on the inner sides of the metal frames, connected with the metal frames and symmetrically distributed with the center of the vanadium dioxide outer ring as the center. An FR-4 dielectric layer and a metal reflecting layer. Vanadium dioxide is switched between a metal state and an insulation state by regulating and controlling the environment temperature, and dynamic reversible tuning of an absorption mode is achieved through temperature control.

Description

Technical Field

[0001] The present invention belongs to the field of metamaterial absorbers, and in particular relates to a dual-mode multi-peak tunable absorber based on vanadium dioxide. Background Art

[0002] Terahertz (THz) waves have important applications in high-speed communications, biomedical imaging, nondestructive testing, and stealth technology, but the development of efficient control devices such as absorbers and filters remains challenging. Traditional absorbers are mostly based on metal-dielectric periodic structures, achieving high absorption at specific frequencies through geometric resonance. However, their fixed operating frequency band and narrow bandwidth, such as single or double peaks, make them difficult to adapt to dynamic electromagnetic environments.

[0003] Metamaterials achieve extraordinary wave absorption properties by regulating equivalent electromagnetic parameters through artificial subwavelength periodic structures, breaking through the limitations of natural materials. While traditional metamaterial absorbers have excellent absorption performance, they still suffer from problems such as fixed structure, complex multi-peak design, and a single tuning scheme. Therefore, researchers have introduced functional materials such as graphene, liquid crystals, and phase change materials, coupled with metamaterial structures to achieve active control of the absorber. Vanadium dioxide has ultrafast insulating-to-metallic phase transition characteristics. When the temperature reaches around 340K, it achieves conductivity changes of multiple orders of magnitude, with a response time of picoseconds, making it an ideal candidate for dynamic metamaterials.

[0004] According to the reported literature, most vanadium dioxide-based metamaterial absorbers are tuned to a single frequency point, and high-quality metamaterials with tunable multi-peak absorption and multiple functions remain a challenge.

[0005] Therefore, how to solve the single-frequency limitation, single function and poor consistency of multi-peak absorption tuning in the dynamic tuning of vanadium dioxide-based metamaterial absorbers, and provide a vanadium dioxide-based dual-mode multi-peak tunable absorber that can achieve multi-peak and dynamically adjustable high-efficiency absorption in the terahertz band and has multi-functional integration is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] The purpose of the present invention is to provide a dual-mode multi-peak tunable absorber based on vanadium dioxide to address the problems in the prior art.

[0007] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0008] A dual-mode multi-peak tunable absorber based on vanadium dioxide, characterized by a two-dimensional metasurface composed of basic structural units distributed in a periodic array, each basic structural unit includes a three-layer structure, from top to bottom:

[0009] A centrosymmetric nested VO2-metal composite superstructure layer comprises a centrosymmetric outer ring of vanadium dioxide, a vanadium dioxide connecting block, and a plurality of nested metal frames, wherein the metal frames are stacked layer by layer from large to small in size and are all symmetrically distributed around the center of the vanadium dioxide outer ring. The vanadium dioxide outer ring is physically connected to the outermost metal frame, and the vanadium dioxide connecting blocks are distributed inside the metal frames and connect the metal frames, and are symmetrically distributed around the center of the vanadium dioxide outer ring.

[0010] The FR-4 dielectric layer isolates the centrosymmetrical nested VO2-metal composite superstructure layer and the metal reflective layer, assisting in energy dissipation through dielectric loss;

[0011] The metal reflective layer forms a Fabry-Perot resonant cavity with the centrally symmetrical nested VO2-metal composite superstructure layer to enhance the local field.

[0012] By regulating the ambient temperature, vanadium dioxide can be switched between the metallic state and the insulating state, and the absorption mode can be dynamically and reversibly tuned by temperature control:

[0013] When the vanadium dioxide is in an insulating state, the absorber forms a five-peak absorption mode with peak frequencies of 0.53 THz, 0.76 THz, 1.09 THz, 1.50 THz, and 2.17 THz;

[0014] When the vanadium dioxide is in a metallic state, the absorber switches to a two-peak absorption mode.

[0015] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0016] As a preferred technical solution of the present invention: in the centrally symmetrical nested VO2-metal composite superstructure layer, the metal frame is an aluminum frame, which is a square frame, with 5 nested frames, and each vanadium dioxide connecting block is set in the middle of the border of each metal frame to bridge the adjacent metal frames.

[0017] As a preferred technical solution of the present invention: the side lengths of the metal frames are l1=85μm, l2=65μm, l3=46μm, l4=32μm, l5=21μm, and the width of the metal frame is b=4.5μm;

[0018] The outer ring radius of the vanadium dioxide outer ring is 64 μm and the width is 3 μm.

[0019] As a preferred technical solution of the present invention: the width w of the vanadium dioxide connecting block is 11.5 μm, and the thickness h1 is 0.5 μm. The vanadium dioxide connecting blocks form a cross-shaped distribution in a nested metal frame.

[0020] As a preferred technical solution of the present invention: the dielectric constant ε of the FR-4 dielectric layer is 4.1, and the loss tangent angle tanδ is 0.03;

[0021] The thickness of the FR-4 dielectric layer h2 is 19.5 μm.

[0022] As a preferred technical solution of the present invention, the metal reflective layer is a continuous thin film structure, the selected material is aluminum, the thickness h3 = 1.2 ~ 1.5 μm, the conductivity is 3.56 × 10 7 S / m.

[0023] As a preferred technical solution of the present invention: the period length of the basic structural unit is 128 μm.

[0024] Compared with existing technologies, the dual-mode, multi-peak tunable absorber based on vanadium dioxide of the present invention has the following advantages: The present invention adopts a composite resonance design with a nested aluminum frame and vanadium dioxide (VO2) connection structure, combined with the insulating-metallic phase transition characteristics of VO2, successfully solving the three major technical problems existing in traditional metamaterial absorbers:

[0025] The present invention solves the problem of fixed frequency and low tuning freedom caused by the traditional absorber's reliance on a single resonant structure and unadjustable operating frequency band, by nesting aluminum frames stacked layer by layer from large to small, combined with dynamic conductivity control of VO2 connecting blocks. It realizes active switching between five-peak and two-peak absorption modes (0.4-2.4THz), significantly expanding the tunable range. By temperature-controlling the insulating state (<340K) to five-peak and the metallic state (≥340K) to two-peak, it adapts to different terahertz application scenarios such as communication frequency band selection and multimodal imaging, achieving dynamic multi-frequency compatibility:

[0026] The present invention uses the vanadium dioxide outer ring as a shared resonance unit and increases the absorption bandwidth to 1.64THz with five-peak coverage through multi-mode coupling. The absorption rate reaches more than 95%, of which the two-peak mode is 100%, solving the problem of single absorption peak and low absorption rate caused by a single resonance mode. The refractive index sensitivity corresponding to the five-peak mode reaches 0.1~0.576THz / RIU, realizing high-sensitivity sensing, which is used to detect changes in the refractive index before and after cell canceration.

[0027] The centrosymmetric design and subwavelength periodic arrangement of the present invention ensure stable performance at incident angles of 0° to 60° and arbitrary polarization (TE / TM), solving the problem that traditional structures are sensitive to polarization direction and incident angle and have poor environmental adaptability.

[0028] The vanadium dioxide-based dual-mode multi-peak tunable absorber of the present invention solves the problems of fixed frequency and low tuning freedom of traditional metamaterial absorbers. It has high absorption rate, multi-mode switching and sensing functions, and realizes the coordinated optimization of multi-peak dynamic tunability and multi-functional integration. It has great application prospects in the field of terahertz smart devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic structural diagram of a dual-mode multi-peak tunable absorber based on vanadium dioxide according to the present invention; Figure 2 is a side view of a single structural unit in the present invention; Figure 3 is a top view of a single structural unit in the present invention; Figure 4 This is an absorption curve of a dual-mode multi-peak tunable absorber based on vanadium dioxide when vanadium dioxide is in an insulating state. In the figure, TE represents the absorption spectrum under transverse electric waves, and the dotted line TM represents the absorption spectrum under transverse magnetic waves. The two lines overlap. Figure 5 This is an absorption curve of a dual-mode multi-peak tunable absorber based on vanadium dioxide when vanadium dioxide is in a metallic state. In the figure, the realized TE represents the absorption spectrum under transverse electric waves, and the dotted line TM represents the absorption spectrum under transverse magnetic waves. The two lines overlap. Figure 6 This is a graph of the absorption curves of vanadium dioxide in the dielectric state and metallic state when the metal frame and metal reflective layer of the centrosymmetrically nested VO2-metal composite superstructure are replaced with gold based on a dual-mode multi-peak tunable absorber of vanadium dioxide. Figure 7 This is a dual-mode multi-peak tunable absorber based on vanadium dioxide. When the FR-4 dielectric layer material is replaced with G-10, the absorption curves of vanadium dioxide in dielectric state and metallic state respectively; Figure 8 This is a schematic diagram of the equivalent impedance of a dual-mode multi-peak tunable absorber based on vanadium dioxide when the vanadium dioxide is in an insulating state; Figure 9 This is a schematic diagram of the equivalent impedance of a dual-mode multi-peak tunable absorber based on vanadium dioxide when vanadium dioxide is in a metallic state; Figure 10 This is an absorption spectrum of a vanadium dioxide dual-mode multi-peak tunable absorber at different polarization angles; Figure 11 This is an absorption spectrum of a vanadium dioxide dual-mode multi-peak tunable absorber at different incident angles; Figure 12 It is an absorption characteristic curve of the object under test with different refractive index based on the dual-mode multi-peak tunable absorber of vanadium dioxide; Figure 13 This is a sensitivity curve diagram of a vanadium dioxide dual-mode multi-peak tunable absorber used as a sensor; In the figure: basic structural unit 100; central symmetrical nested VO2-metal composite superstructure layer 10; vanadium dioxide outer ring 101; vanadium dioxide connecting block 102; metal frame 103; FR-4 dielectric layer 20; metal reflective layer 30. DETAILED DESCRIPTION

[0030] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] The present invention discloses a dual-mode multi-peak tunable absorber based on vanadium dioxide, which is a dual-mode multi-peak dynamically tunable metamaterial absorber of vanadium dioxide. It realizes five-peak and two-peak dynamic tuning through composite resonant structure and phase change regulation, solving the problems of poor multi-frequency compatibility and low tuning freedom in the prior art.

[0032] A vanadium dioxide dual-mode multi-peak tunable absorber is a two-dimensional metasurface composed of basic structural units distributed in a periodic array. Each basic structural unit includes three layers, from top to bottom:

[0033] A centrosymmetric nested VO2-metal composite superstructure layer, comprising a centrosymmetric outer ring of vanadium dioxide, a vanadium dioxide connecting block, and a plurality of nested metal frames, wherein the metal frames are stacked one on top of the other in descending order of size and are all symmetrically distributed around the center of the vanadium dioxide outer ring. The vanadium dioxide outer ring is physically connected to the four corners of the outermost metal frame. The vanadium dioxide connecting blocks are distributed inside the metal frames and connect the metal frames, and are symmetrically distributed around the center of the vanadium dioxide outer ring.

[0034] The FR-4 dielectric layer isolates the centrosymmetrical nested VO2-metal composite superstructure layer and the metal reflective layer, assisting in energy dissipation through dielectric loss;

[0035] The metal reflective layer forms a Fabry-Perot cavity with the centrally symmetrical nested VO2-metal composite superstructure layer to enhance the local field.

[0036] The phase transition temperature threshold of the vanadium dioxide film is 340K±5K. By regulating the ambient temperature, the vanadium dioxide can be switched between the metallic state and the insulating state, and dynamic reversible tuning of the absorption mode can be achieved through temperature control:

[0037] When the temperature is less than 340K, it is in the vanadium dioxide insulating state, forming a five-peak absorption mode with peak frequencies of 0.53THz, 0.76THz, 1.09THz, 1.50THz, and 2.17THz, and an absorption rate of ≥95%;

[0038] When the temperature is ≥340K, vanadium dioxide turns into a metallic state and switches to a two-peak absorption mode with an absorption rate of 100%.

[0039] The absorber comprises several basic structural units arranged in a periodic array along a horizontal plane. Each basic structural unit consists of three layers: a top, centrosymmetrically nested VO2-metal composite superstructure, an FR-4 dielectric layer, and a bottom, metal reflective aluminum layer. The centrosymmetrically nested VO2-metal composite superstructure consists of an outermost vanadium dioxide ring and small blocks, along with five aluminum frames. The metal reflective layer is a continuous metal film.

[0040] The metal frame of the centrosymmetrical nested VO2-metal composite superstructure is an aluminum frame. There are 5 aluminum frames, and the large and small metal frames are nested. The vanadium dioxide outer ring is on the outermost side. The vanadium dioxide blocks connect the 5 aluminum frames, and the connection point is the center of the aluminum frame edge. The overall pattern is symmetrically distributed. The outer ring radius of the vanadium dioxide outer ring is 64μm, the outer ring width is 3μm, the side length of the first aluminum frame is l1=85μm, the side length of the second aluminum frame is l2=65μm, the side length of the third aluminum frame is l3=46μm, the side length of the fourth aluminum frame is l4=32μm, and the side length of the fifth aluminum frame is l5=21μm. The width of all aluminum frames is b=4.5μm, and the width of the vanadium dioxide connecting block is w=11.5μm. The vanadium dioxide in the centrosymmetrical nested VO2-metal composite superstructure has an electrical conductivity of 5×10 5 The conductivity in the insulating state is 20 S / m. The thickness of the centrosymmetrical nested VO2-metal composite superstructure layer h1 is 0.5 μm.

[0041] The dielectric layer material is FR-4, with a dielectric constant ε=4.1 and a loss tangent , the thickness of the dielectric layer h2=19.5μm.

[0042] VO2 in the present invention is vanadium dioxide.

[0043] The FR-4 in the present invention specifically refers to a flame-retardant glass fiber reinforced epoxy resin laminate, which is an electronic grade composite material.

[0044] The metal reflective layer is made of aluminum, with an electrical conductivity of 3.56×10 7 S / m, and the thickness range h3 of the metal reflective layer is 1.2-1.5 μm.

[0045] In the present invention, the nested aluminum frame and vanadium dioxide connection structure, the top patterned layer is composed of 5 nested aluminum frames of different sizes, which are connected by vanadium dioxide blocks to form multiple coupled resonant units. The vanadium dioxide outer ring is combined and used as a shared resonant unit to broaden the absorption bandwidth and enhance mode coupling, thereby realizing a multi-resonance structure design.

[0046] The basic structural units are arranged periodically, and the length of each period is 128 μm.

[0047] In the vanadium dioxide and aluminum layers, the electrical conductivity of vanadium dioxide can be described by the Drude model:

[0048]

[0049] In the above formula, is the high frequency dielectric constant, which is , Refers to the collision frequency, which is , is the plasma frequency related to the electrical conductivity of vanadium dioxide and can be expressed in terms of the electrical conductivity of vanadium dioxide:

[0050]

[0051] In the above formula, For calculating the initial value of the plasma frequency, = is the initial value of the plasma frequency.

[0052] When vanadium dioxide is in an insulating state, ; When vanadium dioxide is in the metallic state, .

[0053] By changing the ambient temperature of the absorber and adjusting the conductivity of the vanadium dioxide material, vanadium dioxide can be reversibly controlled between the metallic state and the insulating state, thereby enabling the absorber to switch between the five-peak absorption mode and the two-peak absorption mode.

[0054] Beneficial effects of the present invention: The dual-mode multi-peak tunable absorber based on vanadium dioxide of the present invention has the advantages of multiple and adjustable absorption frequencies and high absorption rate compared to traditional absorbers. The phase state of vanadium dioxide is controlled by the ambient temperature. When vanadium dioxide is in an insulating state, the absorber is in a five-peak absorption mode with absorption peak frequencies of 0.53THz, 0.76THz, 1.09THz, 1.50THz, and 2.17THz, respectively, and absorption rates of 95.1%, 96.7%, 97%, 99.2%, and 99.7%, respectively, which are close to 100%; when vanadium dioxide is in a metallic state, the absorber is in a two-peak absorption mode with an absorption rate of 100%. When electromagnetic waves are incident as TE and TM waves, respectively, the absorption performance of the absorber remains unchanged.

[0055] The absorber provided by the present invention has the advantages of incident angle stability, polarization insensitivity and polarization insensitivity, and has potential application value in the fields of optical stealth, electromagnetic shielding, sensors, etc.

[0056] The absorber can also be used in sensors. Its five absorption peaks can correspond to five modes, with sensitivities reaching 0.1THz / RIU, 0.157THz / RIU, 0.226THz / RIU, 0.314THz / RIU and 0.576THz / RIU respectively, showing high sensitivity.

[0057] This invention uses a dual-mode, multi-peak tunable absorber based on vanadium dioxide to detect changes in the refractive index of cells before and after cancerous transformation. Dynamic switching between the insulating state (five peaks) and the metallic state (two peaks) is achieved through temperature control. Precise detection is achieved by exploiting the frequency shift of the absorber's terahertz resonance peak caused by changes in the refractive index (RI) of cancerous cells. In the insulating state, the five absorption peaks can rapidly and sensitively detect changes in the refractive index of cells before and after cancerous transformation, without the need for labeling.

[0058] Example 1

[0059] In order to achieve efficient multi-peak absorption and dynamic tuning in the terahertz band, the present invention provides a dual-mode multi-peak tunable absorber based on vanadium dioxide, which comprises a plurality of periodically arrayed structural units, such as Figure 1 In this embodiment, each structural unit is composed of a centrosymmetrical nested VO2-metal composite superstructure layer, an FR-4 dielectric layer and a metal reflective layer, as shown in FIG. Figure 2 and Figure 3 As shown. The number of metal frames - aluminum frames in the central symmetrical nested VO2-metal composite superstructure is 5, and the large and small frames are nested. The vanadium dioxide outer ring is on the outermost side. The vanadium dioxide blocks connect the 5 aluminum frames, and the connection point is the center of the aluminum frame edge. The overall pattern is symmetrically distributed, as shown. Figure 3 The material of the metal reflective layer is aluminum.

[0060] like Figure 2 , a single structural unit of a dual-mode multi-peak tunable absorber based on vanadium dioxide is a square, the side length of each structural unit is p, the dielectric layer material is FR-4, the dielectric constant ε=4.1, the loss tangent angle , with a thickness of h2. The schematic diagram of the centrosymmetric nested VO2-metal composite superstructure layer is shown in Figure 3 As shown, there are 5 aluminum frames, and the large and small frames are nested. The vanadium dioxide circle is on the outermost side, and the vanadium dioxide block connects the 5 aluminum frames. The connection point is the center of the aluminum frame edge, and the overall pattern is symmetrically distributed. The outer ring radius of the vanadium dioxide outer ring is 64μm, the outer ring width is 3μm, the side length of the first aluminum frame is l1=85μm, the side length of the second aluminum frame is l2=65μm, the side length of the third aluminum frame is l3=46μm, the side length of the fourth aluminum frame is l4=32μm, and the side length of the fifth aluminum frame is l5=21μm. The width of all aluminum frames is b=4.5μm, and the width of the vanadium dioxide connecting block is w2=11.5μm. The electrical conductivity of the vanadium dioxide and the vanadium dioxide in the aluminum layer in the metallic state is 2×10 5 S / m; the conductivity in the insulating state is 20S / m. The thickness of the centrosymmetrical nested VO2-metal composite superstructure layer is h1, and the thickness of the vanadium dioxide thin film layer is h2. The material of the metal reflective layer is aluminum, and the conductivity is 3.56×10 7 S / m, thickness is h3. Figure 4 As shown in FIG, the phase state of vanadium dioxide is controlled by ambient temperature. When vanadium dioxide is in an insulating state, the absorber is in a five-peak absorption mode, and its absorption peak frequencies are 0.53THz, 0.76THz, 1.09THz, 1.50THz, and 2.17THz, respectively. The absorption rates are 95.1%, 96.7%, 97%, 99.2%, and 100%, respectively. When electromagnetic waves are incident as TE and TM waves, respectively, the absorption performance of the absorber remains unchanged. When vanadium dioxide is in a metallic state, the absorber is in a two-peak absorption mode, and the absorption rate reaches 100%. When electromagnetic waves are incident as TE and TM waves, respectively, the absorption performance of the absorber remains unchanged. Figure 5 shown.

[0061] The metal layer and metal frame of the absorber can be replaced with other metal materials besides aluminum. Figure 6 As shown, the metal material in the absorber is replaced by gold, and the conductivity is 4.56×10 7 S / m, the absorption rate of the absorber is basically the same as the absorption rate when the metal material of the absorber is aluminum. At the same time, the dielectric layer of the absorber can also be replaced with a material with a dielectric constant similar to FR-4. Figure 7As shown in the figure, the dielectric layer of the absorber is replaced with G-10, whose dielectric constant ε=4.8 and loss tangent tanδ=0.025. The absorptivity of the absorber is basically the same as that when the dielectric layer material of the absorber is FR-4.

[0062] The mechanism of a dual-mode multi-peak tunable absorber based on vanadium dioxide in this embodiment mainly utilizes the theory of electromagnetic resonance and impedance matching. The main function of the centrally symmetrical nested VO2-metal composite superstructure layer is to make the vanadium dioxide and aluminum in the structural unit produce strong electromagnetic resonance with the incident electromagnetic wave of a specific frequency through patterned design, and the electromagnetic wave energy is concentrated in the local structure, thereby enhancing the interaction between the electromagnetic wave and the material. By regulating the electrical properties of vanadium dioxide to a specific state, the impedance matching of the incident electromagnetic wave in the target frequency band and the absorber interface can be achieved, reducing the reflection of the electromagnetic wave and enhancing the absorption. Among them, when the vanadium dioxide is in the dielectric state, the five aluminum frames each cause an absorption peak; when the vanadium dioxide is in the metallic state, the absorption peaks merge into two.

[0063] The principle of absorbers is further explained through impedance matching theory. When electromagnetic waves hit the surface of the absorber, minimizing the reflection of the electromagnetic waves and allowing them to enter the absorbing material can enhance the absorber's absorption rate. The relative impedance of the absorber can be calculated using the following formula: , where μ is the magnetic permeability and ε is the dielectric constant.

[0064] When the equivalent magnetic permeability and equivalent dielectric constant of the absorber match those of free space, the reflection coefficient of its structure will drop to 0. Figure 8 and Figure 9 The real and imaginary parts of the absorber's relative impedance, calculated from the S-parameters, are shown. The figure shows that when vanadium dioxide is in both the metallic and insulating phases, the real part of its relative impedance approaches 1, while the imaginary part approaches 0. This indicates that the designed absorber achieves impedance matching with free space, allowing incident electromagnetic waves to enter the structure to the greatest extent possible and be absorbed.

[0065] like Figure 10 , the absorption rate of the absorber remains unchanged when the polarization angle of the terahertz wave changes from 0° to 90°, indicating that the absorber in this example has polarization insensitivity. Figure 11 When the incident angle of the absorber changes, the first absorption peak remains unchanged, with the strongest stability and angle adaptability. The second and third absorption peaks remain unchanged before the incident angle is 30°, and decrease at 60°. The fourth and fifth absorption peaks will split to produce new resonance peaks as the angle increases. The generation of new resonance peaks may be due to the new local electromagnetic field generated by the field and absorber structure at different incident angles. In summary, we can conclude that the absorber has a certain absorption angle stability, among which the first absorption peak has the strongest adaptability, meets the wide-angle incidence requirements in different electromagnetic field environments, and has a wide range of applications.

[0066] Narrowband absorbers can be used as sensors in the field of sensing. The sensitivity of a sensor (S) is an important indicator for evaluating a sensor and is defined as: S = , Δf represents the change in frequency, and Δn represents the change in refractive index. Figure 12 When the refractive index of the object to be measured changes from 1.0 to 1.8, the absorption resonance peak of the absorber will red shift, as shown in Figure 13 The sensitivities of the five absorption peak modes of the absorber are 0.1THz / RIU, 0.157THz / RIU, 0.226THz / RIU, 0.314THz / RIU and 0.576THz / RIU respectively. The high refractive index sensitivity enables it to be used in many fields such as biomedicine and environmental monitoring.

[0067] By incorporating the unique electromagnetic properties of vanadium dioxide, this paper designs a novel dual-mode, multi-peak, dynamically adjustable absorber. This device achieves efficient absorption within both five and two peaks, and offers the ability to flexibly adjust absorption intensity. It is also insensitive to absorption angle and polarization, adapting to applications under complex incident conditions. Furthermore, this absorber can function as a highly sensitive sensor, potentially applicable in a variety of fields.

[0068] The present invention discloses a dual-mode multi-peak tunable absorber based on vanadium dioxide, which relates to the field of electromagnetic metamaterial technology. The absorber comprises a number of basic structural units arranged in a periodic array, and each structural unit has a multi-layer structure, which comprises, from top to bottom, a top centrally symmetrical nested VO2-metal composite metastructure layer, an FR-4 dielectric layer, and a metal reflective layer. Utilizing the thermo-induced phase change characteristics of vanadium dioxide, when vanadium dioxide is in a dielectric state, the absorber can achieve high-quality five-peak absorption; when vanadium dioxide is in a metallic state, the absorber can achieve two-peak absorption. The absorber has the characteristics of angular stability, polarization insensitivity, and polarization insensitivity, and has strong application flexibility. At the same time, the absorber can also be used in sensors. Compared with the same terahertz narrow-band sensor, the sensor of the present invention has great advantages in high refractive index sensitivity and can be applied to fields such as disease detection, drug analysis, and environmental monitoring.

[0069] The above-mentioned specific implementation methods are used to illustrate the present invention and are only preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit of the present invention and the scope of protection of the claims shall fall within the scope of protection of the present invention.

Claims

1. A dual-mode multi-peak tunable absorber based on vanadium dioxide, characterized in that: It is a two-dimensional metasurface composed of basic structural units distributed in a periodic array. Each basic structural unit consists of three layers, from top to bottom: A centrosymmetric nested VO2-metal composite superstructure layer comprises a centrosymmetric outer ring of vanadium dioxide, a vanadium dioxide connecting block, and a plurality of nested metal frames, wherein the metal frames are stacked layer by layer from large to small in size and are all symmetrically distributed around the center of the vanadium dioxide outer ring. The vanadium dioxide outer ring is physically connected to the outermost metal frame, and the vanadium dioxide connecting blocks are distributed inside the metal frames and connect the metal frames, and are symmetrically distributed around the center of the vanadium dioxide outer ring. The FR-4 dielectric layer isolates the centrosymmetrical nested VO2-metal composite superstructure layer and the metal reflective layer, assisting in energy dissipation through dielectric loss; The metal reflective layer forms a Fabry-Perot resonant cavity with the centrally symmetrical nested VO2-metal composite superstructure layer to enhance the local field. By regulating the ambient temperature, vanadium dioxide can be switched between the metallic state and the insulating state, and the absorption mode can be dynamically and reversibly tuned by temperature control: When the vanadium dioxide is in an insulating state, the absorber forms a five-peak absorption mode with peak frequencies of 0.53 THz, 0.76 THz, 1.09 THz, 1.50 THz, and 2.17 THz; When the vanadium dioxide is in a metallic state, the absorber switches to a two-peak absorption mode.

2. The vanadium dioxide-based dual-mode multi-peak tunable absorber according to claim 1, characterized in that: In the centrosymmetrical nested VO2-metal composite superstructure, the metal frame is an aluminum frame, which is a square frame with 5 nested frames. Each vanadium dioxide connecting block is set in the middle of the frame of each metal frame to bridge the adjacent metal frames.

3. The dual-mode multi-peak tunable absorber based on vanadium dioxide according to claim 2, characterized in that: The side lengths of the metal frames are l1=85 μm, l2=65 μm, l3=46 μm, l4=32 μm, and l5=21 μm, respectively, and the width of the metal frame is b=4.5 μm; The outer ring radius of the vanadium dioxide outer ring is 64 μm and the width is 3 μm.

4. The dual-mode multi-peak tunable absorber based on vanadium dioxide according to claim 3, characterized in that: The width of the vanadium dioxide connecting block is w = 11.5 μm, and the thickness is h1 = 0.5 μm. Each vanadium dioxide connecting block forms a cross-shaped distribution in a nested metal frame.

5. The dual-mode multi-peak tunable absorber based on vanadium dioxide according to claim 1, characterized in that: The dielectric constant of the FR-4 dielectric layer is ε=4.1, and the loss tangent angle tanδ is 0.03; The thickness of the FR-4 dielectric layer h2 is 19.5 μm.

6. The dual-mode multi-peak tunable absorber based on vanadium dioxide according to claim 1, characterized in that: The metal reflective layer is a continuous thin film structure, the material selected is aluminum, the thickness h3 = 1.2 ~ 1.5 μm, the conductivity is 3.56 × 10 7 S / m.

7. The vanadium dioxide-based dual-mode multi-peak tunable absorber according to claim 1, characterized in that: The period length of the basic structural unit is 128 μm.

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