A tunable terahertz metamaterial band-stop filter

Abstract

The present invention discloses a tunable terahertz metamaterial band-stop filter, belonging to the field of terahertz metamaterial technology. The tunable terahertz metamaterial band-stop filter comprises a plurality of periodically arranged unit structures; the unit structures comprise a top layer, a dielectric layer, and a bottom layer arranged sequentially from top to bottom; the centers of the top, dielectric, and bottom layers lie on the same straight line; the top and bottom layers are both metal-vanadium dioxide composite layers, and the top and bottom layers have the same resonant unit structure; the resonant unit structure comprises a metal structure and a vanadium dioxide structure. The present invention solves the problem that existing metamaterials, once the structural parameters are determined, can only achieve filtering functions at specific resonant frequencies.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz metamaterials, and in particular relates to an adjustable terahertz metamaterial band-stop filter. Background Art

[0002] Terahertz waves, lying between microwaves and far-infrared waves, typically refer to electromagnetic waves with frequencies between 100 GHz and 10 THz. They possess low energy and strong penetration, and hold great potential for application in imaging, communications, biology, medicine, and security. However, the lack of terahertz-enabled devices prevents them from fully meeting the demands of practical applications. Therefore, breakthroughs in terahertz-enabled devices, including modulators, filters, absorbers, and optical switches, are urgently needed. Metamaterials, as artificial structures, typically consist of periodically arranged array elements. They possess the ability to manipulate electromagnetic waves at subwavelength scales by adjusting the shape and size of the array elements to adjust their equivalent permittivity and permeability. This allows for the realization of physical phenomena not found in nature, such as negative refractive index, zero refractive index, and backward waves.

[0003] In recent years, with the continuous deepening and expansion of research, metamaterials have been widely used in various functional devices, such as biochemical sensors, resonators, waveguide modulators, absorbers and filters. Among them, metamaterial filters, as one of the key devices for realizing terahertz communication, detection, imaging and other technologies, have become one of the research hotspots of researchers. At present, terahertz filters with angle, single frequency, multi-frequency and broadband resistance have been realized. However, once the structural parameters of the metamaterial are determined, the filtering function can only be realized at a specific resonant frequency.

[0004] Once a passive metamaterial is designed, its optical properties are fixed, and its operating frequency and performance cannot be dynamically adjusted. Therefore, research on active metamaterials with adjustable optical parameters is extremely urgent. Vanadium dioxide (VO2), a controllable phase-change material, can be controlled to transition from an insulating state to a metallic state by modulating light, electricity, or heat. Therefore, this invention uses vanadium dioxide to achieve reconfigurable and tunable terahertz metamaterials. Summary of the Invention

[0005] The present invention provides an adjustable terahertz metamaterial band-stop filter, which solves the problem that once the structural parameters of existing metamaterials are determined, the filtering function can only be achieved at a specific resonant frequency.

[0006] In order to solve the above technical problems, the technical solution of the present invention is: an adjustable terahertz metamaterial band-stop filter, wherein the adjustable terahertz metamaterial band-stop filter includes a plurality of unit structures arranged periodically;

[0007] The unit structure includes a top layer, a dielectric layer, and a bottom layer arranged in sequence from top to bottom; the center points of the top layer, the dielectric layer, and the bottom layer are located on the same straight line;

[0008] The top layer and the bottom layer are both metal-vanadium dioxide composite layers, and the resonance unit structures of the top layer and the bottom layer are the same; the resonance unit structure includes a metal structure and a vanadium dioxide structure.

[0009] Furthermore, the metal structure is a square metal ring, and four inner walls of the square metal ring are connected to two connected vanadium dioxide strips.

[0010] Furthermore, the material of the metal structure is any one of aluminum, copper and gold.

[0011] Furthermore, the metal structure and the vanadium dioxide structure have the same thickness.

[0012] Furthermore, the side length of the square metal ring is smaller than the side length of the dielectric layer; and the four side edges of the square metal ring are respectively arranged in parallel with the four side edges of the dielectric layer.

[0013] Furthermore, the length of the square metal ring is 86-96 μm, and the width of the square metal ring is 6-8 μm.

[0014] Furthermore, the two connected vanadium dioxide strips are in any one of a T-shape, a square and a rectangle.

[0015] Furthermore, the material of the dielectric layer is any one of ToPaS material, Polyimide material, silicon dioxide material and polydimethylsiloxane material.

[0016] Furthermore, the periodic arrangement of the unit structure adopts a square wafer arrangement.

[0017] The beneficial effects of the present invention are: (1) the present invention adopts a composite layer-medium-composite layer structure, which greatly broadens the band-stop width and band-stop depth of the filter;

[0018] (2) The periodic unit structure of the present invention is symmetrical. Under the condition of vertical incidence of electromagnetic waves, changes in the polarization angle will not affect the performance of the terahertz metamaterial band-stop filter. That is, the filter has good stability in response to the polarization angle.

[0019] (3) The composite layer of the present invention is composed of a metal structure and a vanadium dioxide structure. Vanadium dioxide is used as part of the resonant structure. Vanadium dioxide is a phase-changing material with a low phase transition temperature. The vanadium dioxide unit can be controlled to transition from a metal to an insulating phase by modulating light, electricity, and heat, thereby realizing the bandwidth and center frequency adjustability of the terahertz metamaterial band-stop filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the unit structure of the adjustable terahertz metamaterial band-stop filter of the present invention.

[0021] Figure 2 This is a side view of the unit structure of the adjustable terahertz metamaterial band-stop filter of the present invention.

[0022] Figure 3 This is a result diagram of the reflection coefficient and transmission coefficient of the adjustable terahertz metamaterial band-stop filter of the present invention.

[0023] Figure 4 This is a transmission coefficient diagram of the adjustable terahertz metamaterial band-stop filter of the present invention.

[0024] Figure 5 This is a schematic diagram of the influence of different incident electromagnetic wave polarization angles on the filter transmission coefficient of the present invention.

[0025] Among them, 1 is the top layer, 2 is the dielectric layer, and 3 is the bottom layer. DETAILED DESCRIPTION

[0026] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific descriptions and embodiments. Those skilled in the art can make various other specific variations and combinations based on the technical teachings disclosed in the present invention without departing from the essence of the present invention, and such variations and combinations are still within the scope of protection of the present invention.

[0027] Example 1

[0028] like Figure 1 and Figure 2 As shown, the present invention provides an adjustable terahertz metamaterial band-stop filter, wherein the adjustable terahertz metamaterial band-stop filter includes a plurality of unit structures arranged periodically;

[0029] The unit structure includes a top layer 1, a dielectric layer 2, and a bottom layer 3 arranged in sequence from top to bottom; the center points of the top layer 1, the dielectric layer 2, and the bottom layer 3 are located on the same straight line;

[0030] The top layer 1 and the bottom layer 3 are both metal-vanadium dioxide composite layers, and the top layer 1 and the bottom layer 3 have the same resonance unit structure; the resonance unit structure includes a metal structure and a vanadium dioxide structure.

[0031] The metal structure is a square metal ring, and the four inner walls of the square metal ring are all connected to two connected vanadium dioxide strips.

[0032] The material of the metal structure is any one of aluminum, copper and gold.

[0033] In this embodiment 1, the top layer 1, dielectric layer 2 and bottom layer 3 are generally designed to be square. The metal structure can be made of high conductivity metal materials such as aluminum, copper, and gold, and the thickness of the structure is determined according to specific needs.

[0034] The metal structure and the vanadium dioxide structure have the same thickness.

[0035] The side length of the square metal ring is smaller than the side length of the dielectric layer 2 ; the four side edges of the square metal ring are respectively arranged parallel to the four side edges of the dielectric layer 2 .

[0036] The length of the square metal ring is 86-96 μm, and the width of the square metal ring is 6-8 μm.

[0037] The two connected vanadium dioxide strips are in any one of T-shaped, square and rectangular shapes.

[0038] In this embodiment 1, a T-shaped structure is used as an example. The length of the first vanadium dioxide strip can be 4-10 μm and the width can be 4-12 μm. The width of the second vanadium dioxide strip can be 4-10 μm and the length can be 28-36 μm.

[0039] The material of the dielectric layer 2 is any one of ToPaS material, Polyimide material, silicon dioxide material and polydimethylsiloxane material.

[0040] In this embodiment 1, the relative dielectric constant, tangent loss angle, thickness and other parameters of the dielectric layer will affect the operating frequency and performance of the device. Therefore, the material and specific structural parameters of the dielectric layer can be determined according to actual needs.

[0041] The periodic arrangement of the unit structure adopts a square wafer arrangement.

[0042] In this embodiment 1, the different shapes of the composite layer, the different equivalent inductances and capacitances, have a certain impact on parameters such as the center frequency and bandwidth. Different metal materials also have a certain impact on parameters such as the center frequency and bandwidth. At the same time, the thicker the dielectric thickness, the narrower the bandwidth and the deeper the band-stop depth; the wider the square metal width, the wider the bandwidth, and the band-stop depth remains basically unchanged; this has a certain impact on parameters such as the center frequency and bandwidth. In addition, different choices of dielectrics also have a certain impact on parameters such as the center frequency and bandwidth. Therefore, in practical applications, the corresponding composite layer shape, dielectric material, and dielectric thickness can be selected to achieve the desired effect.

[0043] In this embodiment 1, for the above-mentioned metamaterial band-stop filter, vanadium dioxide has many crystal structures. In the insulating state, vanadium dioxide presents a monoclinic crystal structure, and the electrons in the crystal are constrained between atoms and cannot move arbitrarily, so it exhibits insulating properties with very low electrical conductivity; in the metallic state, vanadium dioxide presents a square rutile structure, and the electrons in the crystal can move arbitrarily, so it exhibits metallic properties with very high electrical conductivity.

[0044] The temperature at which vanadium dioxide transforms from its monoclinic phase to its rutile phase is 68°C. When the temperature reaches its phase transition temperature of 68°C, the electrical conductivity of vanadium dioxide undergoes a dramatic change, up to five orders of magnitude, gradually transforming from an insulating state to a metallic state with good conductive properties.

[0045] In addition, the phase change process of vanadium dioxide is reversible. Therefore, when the ambient temperature gradually decreases, the structure gradually changes from a square rutile structure to a monoclinic structure, and the conductivity with metallic characteristics gradually decreases, and eventually returns to an insulator. Therefore, the conductivity of vanadium dioxide can be controlled by changing external conditions, thereby improving device performance.

[0046] In this embodiment 1, the dielectric constant of the vanadium dioxide structure is expressed as:

[0047]

[0048] Where ε(·) represents the dielectric constant, ω represents the angular frequency of the incident electromagnetic wave, and ε ∞ represents the high-frequency dielectric constant, γ represents the collision frequency, ω p (·) represents plasma frequency, σ represents conductivity, and j represents a complex number.

[0049] And the dielectric constant of the vanadium dioxide structure can be described by the Drude model, that is, the above formula, where ε ∞ =12,γ=5.75×10 13 rad / s, ω p (σ0)=1.4×10 15 rad / s,σ0=3×10 5 S / m.

[0050] Example 2

[0051] The resonant unit structures of the top layer 1 and the bottom layer 3 in this embodiment 2 are exactly the same, consisting of a square ring metal structure and a T-shaped vanadium dioxide structure connected to its four inner wall positions. The specific structural parameters include the length l1, width w1 and thickness t1 of the square ring, the length l2, width w2 and thickness t1 of the first vanadium dioxide structure, the length l3, width w3 and thickness t1 of the second vanadium dioxide structure, and the specific structural parameters of the dielectric layer are the dielectric layer thickness t2 and the period p.

[0052] The terahertz metamaterial band-stop filter is arranged in a periodic structure with square elements at a period of p. The dielectric layer of the terahertz metamaterial band-stop filter is made of silicon dioxide, with a dielectric constant of 3.75 and a thickness of 35 μm. Both the length and width are period p, where p = 100 μm.

[0053] In this embodiment 2, in the metal-vanadium dioxide composite layer of the terahertz metamaterial band-stop filter, the metal structural material is aluminum, and the electrical conductivity is 3.56×10 7 The first vanadium dioxide structure has a length of l2 = 6 μm, a width of w2 = 6 μm, and a thickness of t1 = 0.7 μm. The second vanadium dioxide structure has a length of l3 = 28 μm, a width of w3 = 6 μm, and a thickness of t1 = 0.7 μm.

[0054] In the metal-vanadium dioxide composite layer, the vanadium dioxide structure is T-shaped, and the electrical conductivity of vanadium dioxide can change with temperature. The critical temperature for vanadium dioxide to change from an insulating state to a metallic state is 68°C. When the temperature is low and vanadium dioxide is in the insulating phase, the electrical conductivity is about 10S / m, and the electromagnetic wave absorption capacity is relatively weak. When the temperature rises to 68°C, the electrical conductivity changes by 4 to 5 orders of magnitude. At this time, vanadium dioxide transforms into a metallic phase, and the electrical conductivity can reach 2×10 5 S / m, the ability to absorb electromagnetic waves is enhanced.

[0055] The terahertz band-stop filter was simulated and analyzed using CST Microwave Studio software. The wave vector k was parallel to the z-axis and perpendicular to the structural plane of the triple-band-stop filter. The magnetic field and electric field were parallel to the x-axis and y-axis, respectively. The boundary conditions along the z-axis were set to open, and the boundary conditions along the x- and y-axis were set to periodic.

[0056] Figure 3 The reflection coefficient and transmission coefficient result diagram of the terahertz metamaterial band-stop filter of this embodiment 2 is shown in FIG. The horizontal axis is the frequency and the vertical axis is the reflection coefficient S11 and the transmission coefficient S21. Figure 3As can be seen in the figure, the filter has two resonant frequencies, 0.54THz and 0.67THz, with band-stop depths of -39.824dB and -43.48dB at the resonant frequencies, respectively. Between the resonant frequencies, the shallowest band-stop depth is -29.35dB. The center frequency is 0.605THz, and the 3dB bandwidth is 0.458THz.

[0057] Figure 4 The transmission coefficient diagram of vanadium dioxide in the terahertz metamaterial band-stop filter of this embodiment when it is in the insulating state and the metallic state is shown in FIG. Figure 4 It can be seen that when the room temperature is 28 ° C, the carrier concentration of vanadium dioxide is very low. At this time, the conductivity of vanadium dioxide is about 10S / m, and vanadium dioxide is in an insulating state. At this time, the two central resonant frequencies of the filter are 0.616THz and 0.73THz, respectively, the band stop depths are -50.04dB and -55.65dB, respectively, and the center frequency is 0.673THz. When the temperature increases to 47 ° C, the conductivity of vanadium dioxide increases accordingly to 1000S / m. At this time, the two central resonant frequencies of the filter are 0.615THz and 0.72THz, respectively, the band stop depths are -43.147dB and -48.856dB, respectively, and the center frequency is 0.6675THz. When the temperature increases to 68 ° C, the conductivity of vanadium dioxide increases sharply to 2×10 5 S / m, vanadium dioxide transforms into a metallic state. At this time, the band-stop depths at the resonant frequencies of 0.54THz and 0.67THz are -39.824dB and -43.48dB respectively, and the center frequency is 0.605THz.

[0058] As can be seen from the above, as the external temperature increases, vanadium dioxide changes from an insulator to a metallic state, and the center frequency of the filter redshifts from 0.673THz to 0.605THz, and the band-stop depth becomes shallower, thus realizing the tunability of the center operating frequency and bandwidth depth of the filter.

[0059] Figure 5 For different polarization angles of incident electromagnetic waves The influence of the value on the transmission coefficient of the filter is shown. When the polarization angle of the incident electromagnetic wave changes from 0° to 90°, the transmission coefficient curves are almost completely overlapped. Therefore, the change of polarization angle has no effect on the performance of the three-band rejection filter. The filter has good stability in response to polarization angle, thereby improving its practical application value.

[0060] In addition, by changing the structural parameters of the terahertz metamaterial band-stop filter structural unit, such as the square ring length l1, width w1 and thickness t1, the first vanadium dioxide structure length l2, width w2 and thickness t1, the second vanadium dioxide structure length l3, width w3 and thickness t1, the dielectric layer thickness t2, the period p, etc., the band-stop range of the terahertz metamaterial band-stop filter can be controlled.

[0061] In summary, the present invention proposes to add the phase change material vanadium dioxide to the design of the metamaterial to realize a reconfigurable terahertz metamaterial, thereby realizing a terahertz filter with adjustable resonant frequency. At the same time, the metamaterial in this aspect has a simple structure, a compact size, and is easy to carry, making it adaptable to different application scenarios.

Claims

1. A tunable terahertz metamaterial band-stop filter, characterized in that: The tunable terahertz metamaterial band-stop filter includes a plurality of unit structures arranged periodically; The unit structure comprises a top layer (1), a dielectric layer (2) and a bottom layer (3) arranged in sequence from top to bottom; the center points of the top layer (1), the dielectric layer (2) and the bottom layer (3) are located on the same straight line; The top layer (1) and the bottom layer (3) are both metal-vanadium dioxide composite layers, and the top layer (1) and the bottom layer (3) have the same resonance unit structure; the resonance unit structure includes a metal structure and a vanadium dioxide structure; The metal structure is a square metal ring, and the four inner walls of the square metal ring are connected to two connected vanadium dioxide strips; The two connected vanadium dioxide strips are in a T-shape.

2. The tunable terahertz metamaterial band-stop filter according to claim 1, wherein: The material of the metal structure is any one of aluminum, copper and gold.

3. The tunable terahertz metamaterial band-stop filter according to claim 1, wherein: The metal structure and the vanadium dioxide structure have the same thickness.

4. The tunable terahertz metamaterial band-stop filter according to claim 1, wherein: The side length of the square metal ring is smaller than the side length of the dielectric layer (2); and the four side edges of the square metal ring are respectively arranged parallel to the four side edges of the dielectric layer (2).

5. The tunable terahertz metamaterial band-stop filter according to claim 1, wherein: The length of the square metal ring is 86-96 μm, and the width of the square metal ring is 6-8 μm.

6. The tunable terahertz metamaterial band-stop filter according to claim 1, characterized in that: The material of the dielectric layer (2) is any one of ToPaS material, Polyimide material, silicon dioxide material and polydimethylsiloxane material.

7. The tunable terahertz metamaterial band-stop filter according to claim 1, wherein: The periodic arrangement of the unit structure adopts a square wafer arrangement.

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