A terahertz multi-band dynamically adjustable sensor based on graphene metamaterials

Abstract

The present invention belongs to the field of terahertz metamaterial devices, and provides a terahertz multi-band dynamically adjustable sensor based on graphene metamaterials, which is used to solve the problems of complex device structure, few working frequency bands, poor absorption efficiency and low sensing sensitivity existing in existing terahertz metamaterial sensors. The present invention is composed of a plurality of sensing units spliced ​​together, and the sensing unit is composed of a metal reflection layer 1, a silicon dielectric layer 2 and a graphene metamaterial layer 3, and the graphene metamaterial layer and the metal reflection layer are respectively arranged on the upper surface and the lower surface of the silicon dielectric layer; the graphene metamaterial layer adopts a 90° rotationally symmetrical structure, and is composed of a tic-tac-toe structure and a circular ring, and the tic-tac-toe structure is arranged in the circular ring, and the tic-tac-toe structure is arranged along the center line, and a gap is correspondingly opened in the circular ring; based on this, the terahertz metamaterial sensor provided by the present invention has excellent sensing performance, and at the same time has the advantages of simple structure, multiple working frequency bands, high absorption efficiency and insensitivity to incident angles.

Description

Technical Field

[0001] The present invention belongs to the field of terahertz metamaterial devices, relates to a terahertz sensor, and specifically provides a terahertz multi-band dynamically adjustable sensor based on graphene metamaterial. Background Art

[0002] Metamaterials are artificially designed periodic structures using existing materials. They have many properties that natural materials do not have, such as negative refractive index, perfect absorption, and chiral metamaterial properties. In recent years, with the continuous development of terahertz technology, terahertz sensors based on metamaterials have also been continuously innovated and developed. For example, the patent document with publication number CN117451663A discloses a windmill-type terahertz metamaterial sensor, which has three resonant absorption peaks in the range of 1.5THz to 3THz, and the absorption rate is more than 90%, with the maximum sensitivity and FOM values ​​of 859GHz / RIU and 10RIU respectively. -1 For another example, the patent document with publication number CN117740718A discloses a high-sensitivity terahertz sensor based on asymmetric split ring (ASR) / symmetric split ring (SSR) dual-ring Fano resonance, whose maximum sensor sensitivity is as high as 10.78THz / RIU, but it is only a single Fano resonance absorption peak; it can be seen that through the metamaterial structure design, a metamaterial absorber sensor with multiple resonance peaks can be realized, and the sensor performance can also be improved.

[0003] At present, traditional single-band metamaterial sensors can only achieve single-point matching between the characteristic frequency of the material to be measured and the resonant frequency of the sensor. The small amount of information data will affect the detection accuracy and sensitivity of the sensor. In contrast, multi-band metamaterial sensors can achieve multi-point matching between the resonant frequency of the sensor and the characteristic frequency of the material to be measured, increase the amount of information reflecting the difference of the measured material, and thus improve the accuracy and sensitivity of material sensing. In order to achieve multi-band terahertz sensing, traditional metamaterial sensors mainly use a combination of multiple microstructures to form a coplanar single-layer structural unit or a multi-layer metal microstructure stack structure, resulting in a large device structure unit, which is not conducive to the miniaturization of the device; moreover, multiple microstructure combinations or multi-layer structure stacks increase the difficulty and accuracy of device preparation, which is not conducive to the practical application and commercialization of the device. It can be seen that the design of a miniaturized, multi-band, significantly absorbed, and simple structured dynamically adjustable terahertz metamaterial sensor has very important practical significance and application value. Summary of the invention

[0004] The purpose of the present invention is to provide a terahertz multi-band dynamically adjustable sensor based on graphene metamaterials, so as to solve the problems of existing terahertz metamaterial sensors, such as complex device structure, few operating frequency bands, poor absorption efficiency and low sensing sensitivity.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A terahertz multi-band dynamically adjustable sensor based on graphene metamaterial is composed of a plurality of spliced ​​sensing units, wherein the sensing unit is composed of a metal reflection layer 1, a silicon dielectric layer 2 and a graphene metamaterial layer 3; the graphene metamaterial layer is arranged on the upper surface of the silicon dielectric layer, and the graphene metamaterial layer is located at the center; the metal reflection layer is arranged on the lower surface of the silicon dielectric layer, and the metal reflection layer covers the lower surface of the silicon dielectric layer; the graphene metamaterial layer adopts a 90° rotationally symmetrical structure, and is composed of a tic-tac-toe structure and a circular ring, the tic-tac-toe structure is arranged in the circular ring and is located at the center, the tic-tac-toe structure is arranged along the center line of the upper surface of the silicon dielectric layer, the circular ring is provided with four notches at the center line of the upper surface of the silicon dielectric layer, and the cut end faces of the notches are parallel to the center line of the upper surface of the silicon dielectric layer.

[0007] Furthermore, the structural period of the sensing unit is 320 μm to 340 μm.

[0008] Furthermore, in the graphene metamaterial layer, the width of the tic-tac-toe structure is W = 37 μm, the length of the tic-tac-toe structure is L = 180 μm, the side length of the central square of the tic-tac-toe structure is a = 76 μm; the inner diameter of the ring is R1 = 112 μm, the outer diameter of the ring is R2 = 150 μm, and the spacing between the cut end faces of the notch is g = 65 μm.

[0009] Furthermore, the thickness of the graphene metamaterial layer is 0.34 nm.

[0010] Furthermore, the thickness of the metal reflective layer is 0.1 μm to 0.5 μm.

[0011] Furthermore, the thickness of the silicon dielectric layer is 200 μm to 240 μm.

[0012] Furthermore, the material used for the metal reflective layer is gold, silver or copper.

[0013] Based on the above technical solution, the beneficial effects of the present invention are:

[0014] 1) The present invention designs a terahertz multi-band dynamically adjustable sensor based on a single-layer patterned graphene metamaterial layer, which can achieve perfect absorption in four working frequency bands within the range of 0.2THz to 1.0THz, and the maximum quality factor Q reaches 140.2, and the minimum half-maximum full width FWHM is 17GHz;

[0015] 2) The Fermi level E of the graphene metamaterial in the present invention is based on FThe terahertz metamaterial sensor is regulated by the thickness H of the silicon dielectric layer. When the Fermi level of the graphene metamaterial increases from 0.2eV to 0.6eV, the four operating frequencies of the terahertz metamaterial sensor all move toward high frequencies, and the absorption performance can be dynamically controlled. At the same time, as the thickness H of the silicon dielectric layer increases, the four operating frequencies of the terahertz metamaterial sensor all move toward low frequencies, and the absorption performance can be controlled.

[0016] 3) The terahertz multi-band dynamically adjustable sensor provided by the present invention has excellent sensing performance. The maximum sensitivity S and quality factor FOM of its four working frequency bands reach 900GHz / RIU and 48.53RIU respectively. -1 ; Moreover, under different polarization modes and incident angles, it can achieve efficient absorption performance, and the working frequency band remains almost unchanged, which can meet the actual application needs;

[0017] In summary, the present invention provides a terahertz multi-band dynamically adjustable sensor based on graphene metamaterials, which has excellent sensing performance and has the advantages of simple structure, multiple operating frequency bands, high absorption efficiency and insensitivity to incident angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the unit structure of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterial in the present invention.

[0019] Figure 2 It is a schematic diagram of the structure of the graphene metamaterial layer in the present invention.

[0020] Figure 3 This is a diagram showing the absorption efficiency simulation results of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterials in the present invention.

[0021] Figure 4 This is a diagram of the relative impedance simulation results of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterials in the present invention.

[0022] Figure 5 is the absorption efficiency of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterial in the present invention with respect to the Fermi level E of the graphene metamaterial F 's change curve graph.

[0023] Figure 6 The graph is a variation curve of the absorption efficiency of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterial in the present invention with respect to the thickness H of the silicon dielectric layer.

[0024] Figure 7 This is a curve diagram showing the variation of the absorption efficiency of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterials in the present invention with respect to the ambient refractive index n.

[0025] Figure 8 Schematic diagram of the linear relationship between the operating frequency and the ambient refractive index of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterials in the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0027] This embodiment provides a terahertz multi-band dynamically adjustable sensor based on graphene metamaterials, which can realize dynamically adjustable multi-working frequency band sensing detection within the terahertz frequency band, and has the characteristics of simple structure, obvious absorption and high sensitivity.

[0028] The terahertz multi-band dynamically adjustable sensor based on graphene metamaterial is composed of a plurality of sensing units. Figure 1 As shown, a square structure is adopted, which is composed of a metal reflective layer 1, a silicon dielectric layer 2 and a graphene metamaterial layer 3; the graphene metamaterial layer 3 is arranged on the upper surface of the silicon dielectric layer 2, and the graphene metamaterial layer is located in the center; the metal reflective layer 1 is arranged on the lower surface of the silicon dielectric layer 2, and the metal reflective layer covers the lower surface of the silicon dielectric layer; the graphene metamaterial layer is as shown in FIG. Figure 2 As shown, a 90° rotationally symmetrical structure is adopted, which is composed of a tic-tac-toe structure and a circular ring. The tic-tac-toe structure is arranged in the circular ring and is located at the center. The tic-tac-toe structure is arranged along the midline of the upper surface of the silicon dielectric layer. The circular ring has four notches at the midline of the upper surface of the silicon dielectric layer, and the cutting end faces of the notches are parallel to the midline of the upper surface of the silicon dielectric layer.

[0029] In this embodiment, the structural period of the sensing unit is P=320μm-340μm, the side length of the silicon dielectric layer is also P, the thickness of the silicon dielectric layer is H=200μm-240μm, and the dielectric constant of the silicon dielectric layer is ε=11.9; the material of the metal reflective layer is gold, silver or copper, and its conductivity is 3.56×10 7 S / m~5.96×10 7 S / m, thickness h=0.1μm~0.5μm; the thickness of the graphene metamaterial layer is 0.34nm, wherein the width W of the tic-tac-toe structure is 37μm, the length L of the tic-tac-toe structure is 180μm, and the side length a of the central square of the tic-tac-toe structure is 76μm; the inner diameter R1 of the ring is 112μm, the outer diameter R2 of the ring is 150μm, and the spacing g between the cutting end faces of the notch is 65μm.

[0030] In terms of working principle, the graphene metamaterial in the present invention is a kind of carbon atom in the form of sp 2The two-dimensional carbon nanomaterial composed of a hexagonal honeycomb lattice of hybrid orbitals has excellent optoelectronic properties such as high carrier mobility, strong conductivity and strong biosorption; the surface conductivity σ(ω) of the graphene metamaterial is expressed as:

[0031] σ0=0mtra(@)+0nter0,

[0032]

[0033] Among them, σ intra (ω) and σ inter (ω) represents the intra-band conductance and inter-band conductance of graphene metamaterials respectively; j represents an imaginary number, j×j=-1; e represents the charge of the electron, e=1.6×10- 19 C; K B represents the Boltzmann constant, K B =1.38×10- 23 J / K; represents the reduced Planck constant, T represents the ambient temperature, ω represents the incident frequency of the electromagnetic wave, and in the present invention, T is set to 273K, and ω is 0.2-1.0THz; E F and τ refer to the Fermi level and relaxation time of graphene metamaterials, respectively;

[0034] Furthermore, the total conductivity σ(ω) of the graphene metamaterial is converted into the bulk conductivity σ v (ω) is calculated, σ v (ω) = σ(ω) / Δ, where Δ represents the thickness of the graphene metamaterial; accordingly, the dielectric constant ε(ω) of the graphene metamaterial can be obtained from the bulk conductivity σ v (ω) is calculated as follows:

[0035]

[0036] Among them, ε0 represents the dielectric constant of vacuum, ε0 = 8.85 × 10- 12 F / m;

[0037] From the above formula, it can be seen that the dielectric constant can be dynamically adjusted by controlling the Fermi level of the graphene metamaterial. A dielectric constant model of the graphene metamaterial can be established to simulate and analyze its dynamic modulation properties in terahertz sensors.

[0038] Based on this, this embodiment sets the Fermi level E of the graphene metamaterial layer to F=0.2eV~0.6eV, the thickness of the single-layer graphene metamaterial Δ=0.34nm, and the graphene materials with different Fermi levels are calculated by MATLAB software and imported into the three-dimensional electromagnetic field simulation software CST for structural modeling and simulation of terahertz metamaterial sensors; during the simulation process, the frequency range of the incident electromagnetic wave is set to 0.2THz~1.0THz, the transmission direction of the incident light wave is perpendicular to the XY direction and incident downward, the periodic unit boundary conditions are selected in the X and Y directions, and the free space boundary conditions are selected in the Z-axis direction, and the simulation accuracy is automatically generated by the software.

[0039] The beneficial effects of the present invention are explained below in combination with simulation results. The absorption performance of the terahertz metamaterial sensor in the present invention can be expressed by the absorption rate A(w), specifically:

[0040] A(w)=1-T(w)-R(w),

[0041] Wherein, T(w) and R(w) represent transmission efficiency and reflection efficiency respectively;

[0042] Obviously, when T(w) and R(w) are small enough, the absorption efficiency A(w) is the maximum; since the thickness of the metal reflective layer in the present invention is much greater than its skin depth in the terahertz frequency band (0.393 μm to 3.77 μm), it is sufficient to suppress the transmission of terahertz waves, so the transmission efficiency T(w) is almost zero; therefore, the absorption rate A(w) in the present invention can be obtained by the following formula:

[0043] A(w))=1-R(w),

[0044] When the reflection efficiency R(w) is close to zero, perfect absorption can be achieved. On this basis, the terahertz multi-band dynamically adjustable sensor based on graphene metamaterials in this embodiment achieves perfect absorption in four frequency bands in the range of 0.2THz to 1.0THz, and its working modes in the absorption peak frequency band are respectively represented as mode A, mode B, mode C and mode D, as shown in FIG. Figure 3 As shown, the centers of the four absorption peak frequency bands are located at 0.296THz, 0.499THz, 0.701THz and 0.891THz, and the absorption efficiencies correspond to 99.87%, 99.11%, 99.05% and 99.97%, respectively. According to the definition of the quality factor Q, the quality factors Q of the terahertz metamaterial sensor in the four working modes are calculated to be 29.6, 62.4, 140.2 and 89.1, respectively; in addition, it can be seen that the full width at half maximum FWHM of the terahertz metamaterial sensor in the present invention in the four working modes is 37GHz, 34GHz, 17GHz and 22GHz, respectively.

[0045] Impedance matching is an important factor to ensure perfect coupling between the device and the incident electromagnetic wave. According to the impedance matching theory of terahertz metamaterial sensors, in order to achieve perfect absorption, the electromagnetic wave input impedance Zi n Matches the free space impedance Z0 (Z0 = 377Ω), that is, the relative equivalent impedance Z (Z = Zi n / Z0) is 1; in the present invention, the relative equivalent impedance Z of the terahertz metamaterial sensor can be calculated by the following formula:

[0046]

[0047] Among them, S 11 With S 21 represent the scattering parameters related to reflection efficiency and transmission efficiency respectively;

[0048] According to the effective impedance matching theory, the relative impedance Z of the terahertz metamaterial sensor in the range of 0.2THz to 1.0THz is as follows: Figure 4 As shown in the figure, when the electromagnetic wave input impedance of the terahertz metamaterial sensor matches the impedance of free space, that is, the real part of the relative impedance Z is close to 1, and the imaginary part is close to 0, in this case, the reflection on the device surface can be significantly reduced and perfect absorption performance can be achieved; it can be seen that the real part of the relative impedance Z at 0.296THz, 0.499THz, 0.701THz and 0.891THz is 1, and the imaginary part is 0, that is, the sensor achieves perfect matching with the impedance of free space, and obtains perfect absorption of 99.87%, 99.11%, 99.05% and 99.97% respectively.

[0049] For terahertz metamaterial sensors with fixed structural parameters, dynamic tunability has more important application value. g Regulating the Fermi level E of graphene metamaterials F The process can be expressed as:

[0050]

[0051] Among them, V g is the value of the external gate voltage, ε0 represents the vacuum dielectric constant, ε r represents the relative dielectric constant of graphene metamaterial, e represents the electron charge, V F is the Fermi velocity, H represents the thickness of the silicon dielectric layer;

[0052] Based on the tunability of graphene materials, the absorption efficiency of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterials in this embodiment is about the Fermi level E of the graphene metamaterial. F The change curve of Figure 5As shown in the figure, as the Fermi level of graphene metamaterial increases from 0.2eV to 0.6eV, the four operating frequencies of the terahertz metamaterial sensor all move toward high frequencies, and the modulation ranges of the operating frequencies are 0.288THz~0.309THz, 0.488THz~0.527THz, 0.683THz~0.737THz and 0.867THz~0.936THz, respectively. This means that by adjusting the graphene Fermi level, multiple operating frequencies of the sensor can be dynamically controlled within the range of 0.2THz~1.0THz, increasing the practical application efficiency of the terahertz metamaterial sensor.

[0053] At the same time, the absorption performance and operating frequency of the terahertz metamaterial sensor proposed in the present invention can also be adjusted by the thickness of the silicon dielectric layer; the absorption efficiency of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterial in this embodiment varies with the thickness H of the silicon dielectric layer as shown in FIG. Figure 6 As shown in the figure, the thickness H of the silicon dielectric layer increases from 210μm to 230μm. With the increase of the thickness H, the absorption performance of the terahertz metamaterial sensor in each frequency band can be adjusted. At the same time, the operating frequency points at all four frequencies move toward low frequencies. This is because the terahertz metamaterial sensor proposed in the present invention realizes the loss absorption of the incident electromagnetic wave through Fabry–Perot interference, and the path phase of the terahertz wave when it is transmitted in the dielectric silicon layer It can be expressed as:

[0054]

[0055] Where H and ε are the thickness and dielectric constant of the dielectric layer, respectively, f is the frequency of the interfering electromagnetic wave, and c = 3×10 8 m / s is the speed of light in a vacuum, and θ is the angle of incidence of the electromagnetic wave;

[0056] When the electromagnetic wave is incident vertically, the path phase and the incident angle θ can be approximated as fixed values. Therefore, when the thickness H of the silicon dielectric layer increases, the frequency f of the interfering electromagnetic wave will decrease, causing the absorption operating frequency of the device to move toward a lower frequency.

[0057] In summary, the terahertz multi-band dynamically adjustable sensor based on graphene metamaterials proposed in the present invention has excellent modulation characteristics; and in practical applications, it is also very important that the terahertz metamaterial sensor is insensitive to oblique incidence. In this embodiment, the absorption efficiency of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterials is studied with respect to the change of the incident angle. When the incident angle is 0°, the absorption efficiency of TE polarization and TM polarization is the same, that is, the terahertz metamaterial sensor has the characteristic of being polarization-independent; at the same time, with the increase of the incident angle, the strength of the absorption performance of the terahertz metamaterial sensor hardly changes; it can be seen that the terahertz multi-band dynamically adjustable sensor based on graphene metamaterials proposed in the present invention has the characteristic of wide-angle insensitivity.

[0058] In addition, in order to expand the application scope of the sensor, this embodiment further simulates and tests the sensing characteristics of the terahertz metamaterial sensor. By covering different substances to be tested on the surface of the graphene metamaterial layer to produce changes in the environmental refractive index parameters, the absorption characteristics of the terahertz metamaterial sensor are changed. Therefore, by monitoring the offset of the operating frequency of the terahertz metamaterial sensor, the sensing detection of the substance to be tested can be achieved. The absorption efficiency of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterial in this embodiment is shown in the curve of the change of the environmental refractive index n. Figure 7 As shown in FIG. 1 , as the ambient refractive index n increases from 1.00 to 1.04, the operating frequency band of the terahertz metamaterial sensor gradually moves to a low frequency, and the absorption efficiency remains almost unchanged. At the same time, according to the calculation formula of the sensor sensitivity S: S = Δf / Δn, Δf and Δn are the changes in the operating frequency and the ambient refractive index, respectively. The linear relationship between the operating frequency and the ambient refractive index of the terahertz multi-band dynamically adjustable sensor based on graphene metamaterials in this embodiment is shown in FIG. Figure 8 As shown in the figure, when the ambient refractive index n increases from 1.00 to 1.04, the sensitivity of the terahertz metamaterial sensor at the four operating frequencies reaches 300GHz / RIU, 525GHz / RIU, 825GHz / RIU and 900GHz / RIU respectively. In addition, according to the calculation formula of the quality factor FOM: FOM = S / FWHM, FWHM represents the full width at half maximum at the resonance frequency, the calculated FOM of the four operating frequencies of the terahertz metamaterial sensor reaches 8.18RIU -1 , 15.41RIU -1 , 48.53RIU -1 and 40.91RIU -1 ; The results show that the terahertz metamaterial sensor provided by the present invention has excellent sensing performance and broad application prospects, and can be widely used in the field of terahertz sensing and detection.

[0059] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A terahertz multi-band dynamically adjustable sensor based on graphene metamaterials, composed of a plurality of sensing units, characterized in that: The sensing unit is composed of a metal reflection layer (1), a silicon dielectric layer (2) and a graphene metamaterial layer (3); the graphene metamaterial layer is arranged on the upper surface of the silicon dielectric layer, and the graphene metamaterial layer is located at the center of the upper surface of the silicon dielectric layer; the metal reflection layer is arranged on the lower surface of the silicon dielectric layer, and the metal reflection layer covers the lower surface of the silicon dielectric layer; the graphene metamaterial layer adopts a 90° rotationally symmetrical structure, consisting of a tic-tac-toe structure and a circular ring, the tic-tac-toe structure is arranged in the circular ring and is located at the center of the circular ring, the tic-tac-toe structure is arranged parallel to the central axis of the upper surface of the silicon dielectric layer, the circular ring has four notches at the central axis of the upper surface of the silicon dielectric layer, and the cut end faces of the notches are parallel to the central axis of the upper surface of the silicon dielectric layer; in the graphene metamaterial layer, the thickness of the graphene metamaterial layer is 0.34 nm, the width of the tic-tac-toe structure is 0.10 nm, and the width of the tic-tac-toe structure is 0.10 nm. W =37μm, length of the tic-tac-toe structure L =180μm, the side length of the central square of the tic-tac-toe structure a =76μm; inner diameter of the ring R 1 = 112 μm, the outer diameter of the ring R 2 = 150 μm, the distance between the cut ends of the notch g =65μm; the Fermi level of the graphene metamaterial is 0.2 eV~0.6 eV; the thickness of the silicon dielectric layer is 210μm~230μm.

2. The terahertz multi-band dynamically adjustable sensor based on graphene metamaterial according to claim 1, characterized in that: The structural period of the sensing unit is 320μm~340μm.

3. The terahertz multi-band dynamically adjustable sensor based on graphene metamaterial according to claim 1, characterized in that: The thickness of the metal reflective layer is 0.1 μm~0.5 μm.

4. The terahertz multi-band dynamically adjustable sensor based on graphene metamaterial according to claim 1, characterized in that: The material used for the metal reflective layer is gold, silver or copper.

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