Adjustable terahertz metamaterial band elimination filter

Abstract

The invention discloses an adjustable terahertz metamaterial band elimination filter, and belongs to the technical field of terahertz metamaterials, and the adjustable terahertz metamaterial band elimination filter comprises a plurality of unit structures which are periodically arranged; each unit structure comprises a top layer, a dielectric layer and a bottom layer which are sequentially arranged from top to bottom; the central points of the top layer, the dielectric layer and the bottom layer are positioned on the same straight line; the top layer and the bottom layer are both metal-vanadium dioxide composite layers, and the resonance units of the top layer and the bottom layer are the same in structure. The resonance unit structure comprises a metal structure and a vanadium dioxide structure. According to the invention, the problem that the filtering function can only be realized at a specific resonant frequency once the structural parameters of the existing metamaterial are determined is solved.

Description

Technical Field

[0001] The 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 are between microwaves and far-infrared waves, and usually refer to electromagnetic waves with a frequency range of 100GHz-10 THz. They have the characteristics of low energy and strong penetration, and have great application potential in imaging, communication, biology, medicine, and security applications. However, due to the lack of terahertz functional devices, they cannot fully meet the needs of practical applications. Therefore, terahertz functional devices including modulators, filters, absorbers, optical switches, etc. are in urgent need of breakthroughs. Metamaterials, as an artificial structure, are usually composed of periodically arranged array units. They have the ability to control the equivalent dielectric constant and equivalent magnetic permeability by changing the shape and size of the array units at the subwavelength scale to achieve the ability to manipulate electromagnetic waves, thereby realizing physical phenomena that do not exist in nature, such as negative refractive index, zero refractive index, backward waves, etc.

[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 wide-bandwidth 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] After the passive metamaterial is designed, its optical performance is fixed and its operating frequency and performance cannot be adjusted dynamically. Therefore, the research on active metamaterials with adjustable optical parameters is very urgent. Vanadium dioxide (VO2) is a controllable phase change material. The transition of vanadium dioxide from an insulating state to a metallic state can be controlled by modulating light, electricity or heat. Therefore, the present invention can realize the reconfiguration and tunability of terahertz metamaterials through vanadium dioxide. 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 the 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, the adjustable terahertz metamaterial band-stop filter comprising a plurality of unit structures arranged periodically;

[0007] The unit structure comprises 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 lines.

[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 as follows: (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 a 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 change from a metal phase 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 It 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-top layer, 2-medium layer and 3-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 should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope 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 comprises a plurality of unit structures arranged periodically;

[0029] 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;

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

[0031] 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.

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

[0033] In this embodiment 1, the top layer 1, the dielectric layer 2 and the bottom layer 3 are generally designed to be square. The material of the metal structure can be a high conductivity metal material such as aluminum, copper, gold, etc., and the thickness of the structure needs to be 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 in parallel with 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 a T-shape, a square and a rectangle.

[0038] In this embodiment 1, a T-shaped structure is used as an example. The length of the first vanadium dioxide strip may be 4 to 10 μm, and the width may be 4 to 12 μm. The width of the second vanadium dioxide strip may be 4 to 10 μm, and the length may be 28 to 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 shapes of the composite layers are different, and the equivalent inductance and capacitance are different, which have a certain influence on the center frequency, bandwidth and other parameters. The difference in metal materials has a certain influence on the center frequency, bandwidth and other parameters. At the same time, the thicker the dielectric thickness, the narrower the bandwidth and the deeper the band stop depth; the square metal width increases, the bandwidth becomes wider, and the band stop depth remains basically unchanged; it has a certain influence on the center frequency, bandwidth and other parameters. And the different choices of dielectrics also have a certain influence on the center frequency and bandwidth and other parameters. 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 insulation 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 the monoclinic phase to the rutile phase is 68°C. When the temperature reaches its phase transition temperature of 68°C, the conductivity of vanadium dioxide will undergo a huge change, up to five orders of magnitude, gradually changing 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 the square rutile structure to the monoclinic structure, and the conductivity with metallic characteristics gradually decreases, and finally returns to an insulator. Therefore, the conductivity of vanadium dioxide can be controlled by changing the external conditions, thereby improving the device performance.

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

[0047]

[0048] Among them, 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 resonance unit structures of the top layer 1 and the bottom layer 3 in this embodiment 2 are exactly the same, and are composed of a metal structure of a square ring and a T-shaped vanadium dioxide structure connected to the four inner wall positions thereof. 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 according to a square wafer with a period p. The dielectric layer of the terahertz metamaterial band-stop filter is made of silicon dioxide, with a dielectric constant of 3.75, a thickness of 35 μm, and a length and width of the period p, 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 S / m, with a length l1 = 88 μm, a width w1 = 8 μm, and a thickness t1 = 0.7 μm. The first vanadium dioxide structure has a length l2 = 6 μm, a width w2 = 6 μm, and a thickness t1 = 0.7 μm. The second vanadium dioxide structure has a length l3 = 28 μm, a width w3 = 6 μm, and a thickness t1 = 0.7 μm.

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

[0055] The terahertz band-stop filter is simulated and analyzed by CST microwave studio simulation software. The wave vector k is parallel to the z-axis and perpendicular to the structural plane of the three-band-stop filter. The magnetic field and electric field are parallel to the x-axis and y-axis respectively. The boundary conditions in the z-axis direction are set as open boundary conditions, and the boundary conditions in the x- and y-axis directions are set as periodic boundary conditions.

[0056] Figure 3 : is a result diagram of the reflection coefficient and transmission coefficient of the terahertz metamaterial band-stop filter of this embodiment 2, wherein the horizontal axis is the frequency and the vertical axis is the reflection coefficient S11 and the transmission coefficient S21. Figure 3It can be seen that the filter has two resonant frequencies, 0.54THz and 0.67THz, and the band stop depths at the resonant frequencies are -39.824dB and -43.48dB 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 Figure 2 is a transmission coefficient diagram of vanadium dioxide in the terahertz metamaterial band-stop filter of this embodiment when it is in an insulating state and a metallic state. 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, and 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 to 1000S / m accordingly. At this time, the two central resonant frequencies of the filter are 0.615THz and 0.72THz, respectively, and 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 turns 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 temperature of external conditions 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, realizing the tunability of the center operating frequency and bandwidth depth of the filter.

[0059] Figure 5 For different incident electromagnetic wave polarization angles The influence of the value on the transmission coefficient of the filter, when the polarization angle of the incident electromagnetic wave changes from 0° to 90°, the transmission coefficient curves are basically completely overlapped. Therefore, the change of polarization angle will not affect the performance of the three-band stop filter, and the filter has good stability in response to polarization angle, thereby improving the practical application value of the filter.

[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 into 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 small size, and is easy to carry, so that it can adapt to different application scenarios.

Claims

1. A tunable terahertz metamaterial band-stop filter, It is characterized in that The adjustable terahertz metamaterial band-stop filter comprises 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 comprises a metal structure and a vanadium dioxide structure.

2. The tunable terahertz metamaterial band-stop filter according to claim 1, It is characterized in that 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.

3. The tunable terahertz metamaterial band-stop filter according to claim 1, It is characterized in that The material of the metal structure is any one of aluminum, copper and gold.

4. The tunable terahertz metamaterial band-stop filter according to claim 1, It is characterized in that The metal structure and the vanadium dioxide structure have the same thickness.

5. The tunable terahertz metamaterial band-stop filter according to claim 1, It is characterized in that 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).

6. The tunable terahertz metamaterial band-stop filter according to claim 2, It is characterized in that The length of the square metal ring is 86-96 μm, and the width of the square metal ring is 6-8 μm.

7. The tunable terahertz metamaterial band-stop filter according to claim 2, It is characterized in that The two connected vanadium dioxide strips are in any one of a T-shape, a square and a rectangle.

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

9. The tunable terahertz metamaterial band-stop filter according to claim 1, It is characterized in that The periodic arrangement of the unit structure adopts a square wafer arrangement.

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