CN114447619A - Dual-polarization tunable-direction terahertz metamaterial sensor and preparation method thereof - Google Patents
Dual-polarization tunable-direction terahertz metamaterial sensor and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a terahertz metamaterial sensor with tunable dual polarization directions and a preparation method thereof. The dual-polarization direction tunable terahertz metamaterial sensor comprises NxN structural units which are periodically arranged on a plane, wherein each structural unit is in a cuboid shape and comprises a dielectric layer and a graphene layer arranged on the dielectric layer, the graphene layer is in a two-graphene ring structure which is concentrically nested, an inner ring is a complete graphene ring, and an outer ring is a split graphene ring; the overlooking shape of the outer ring consists of a left split ring and a right split ring which are opposite, wherein the upper gap and the lower gap of the left split ring are on the same vertical longitudinal line, and the upper gap and the lower gap of the right split ring are also on the same vertical longitudinal line, but the upper gap and the lower gap of the right split ring are not overlapped with the upper gap and the lower gap of the left split ring. The terahertz metamaterial sensor provided by the invention is provided with two transparent windows in the dual-polarization direction, and is wide in regulation and control range and high in sensitivity.
Description
Technical Field
The invention relates to the technical field of terahertz metamaterial sensors, in particular to a terahertz metamaterial sensor with tunable dual polarization directions and a preparation method thereof.
Background
Terahertz (THz) waves refer to electromagnetic waves with the frequency within the range of 0.1-10 THz, are in a wave band for transition from macroscopic electronics to microscopic photonics, have unique physical characteristics such as fingerprint spectrum, safety, penetrability and the like in biomolecules, cells and tissues, and have good nondestructive detection characteristics. Therefore, the terahertz spectrum technology is particularly suitable for nondestructive detection of biological molecules, cells and the like.
Metamaterial (metamaterials) is a novel artificial material with special properties and composed of sub-wavelength units, the unique physical properties of the Metamaterial are deeply concerned by researchers, and graphene composed of a carbon atom single-layer structure is a hot spot in Metamaterial research. Graphene has nearly perfect photoelectric characteristics such as ultralow transmission loss and extremely high carrier mobility, and in recent years, various metamaterial devices based on graphene are gradually proposed and researched. Compared with the traditional metal elements in the nature, the Fermi level of the graphene can be adjusted by changing the grid voltage, so that the internal conductivity of the graphene is changed, and the graphene has more advantages and potentials in the aspect of tunability.
Electromagnetic Induced Transparency (EIT) is a quantum interference phenomenon, and the dispersion characteristic in the transparent window has good application prospect in the aspects of sensing and slow light. The Plasma Induced Transparency (PIT) phenomenon is an EIT-like effect, which can generate a clear transparency peak in a transmission spectrum, and thus has attracted extensive attention. In general, the phenomenon of initiating PIT mainly focuses on two ways: the bright and dark modes are coupled to each other and the bright and bright modes are coupled to each other.
With the continuous research on the structural characteristics of the terahertz metamaterial sensor, in recent years, terahertz metamaterial sensors in shapes of a metal split ring, an h-shaped sensor, a disc-shaped sensor, a cross-shaped sensor and the like are successively discovered. However, most sensors can only form a transparent window in a single polarization direction, and the modulation range and modulation depth can only be in a small range. The terahertz metamaterial sensor based on graphene can adjust the Fermi level of the sensor by changing the grid voltage, so that the internal conductivity of the graphene is changed, for example, the invention patent with the publication number of CN108390156A discloses a terahertz adjustable polarized wave insensitive electromagnetic induction transparent device based on a metamaterial, which comprises a plurality of basic units which are periodically arranged in the same direction; each basic unit comprises an upper graphene layer and a lower dielectric layer, and the dielectric layers are fixed on the substrate device; forming graphene square rings with openings on adjacent sides by carving graphene; and after the graphene layer is etched once, hollowing the middle of the substrate device, and finally plating a layer of conductive adhesive. The invention has the same electromagnetic induction transparency phenomenon for linearly polarized light in the x direction and the y direction, does not need to replace a device when the polarization mode of incident waves is changed, and can realize the adjustable electromagnetic induction transparency phenomenon by adjusting the external voltage under the condition of not changing the structure of the device. The modulation described in this invention is still unipolar.
Therefore, the existing terahertz metamaterial sensor capable of realizing the PIT phenomenon can only form a transparent window in one polarization direction, and is small in regulation range and generally low in sensing performance. How to design a terahertz metamaterial sensor which is wide in regulation and control range, high in sensitivity and convenient to process is a problem worthy of thinking and research.
Disclosure of Invention
The invention aims to provide a terahertz metamaterial sensor which is provided with two transparent windows in the dual-polarization direction, is wide in regulation and control range and high in sensitivity and is tunable in the dual-polarization direction and a preparation method thereof.
In order to solve the technical problems, the invention adopts the following technical scheme:
a dual-polarization direction tunable terahertz metamaterial sensor comprises N multiplied by N structural units which are periodically arranged on a plane, wherein N is a natural number larger than 0, each structural unit is in a cuboid shape, and the N multiplied by N structural units are continuously spliced on the plane; each structural unit comprises a medium layer and a graphene layer arranged on the medium layer, the graphene layer is of two concentrically nested graphene circular ring structures, the inner ring is a complete graphene circular ring, and the outer ring is a split graphene circular ring; the overlooking shape of the outer ring consists of a left split ring and a right split ring which are opposite, wherein the upper gap and the lower gap of the left split ring are on the same vertical longitudinal line, and the upper gap and the lower gap of the right split ring are also on the same vertical longitudinal line, but the upper gap and the lower gap of the right split ring are not overlapped with the upper gap and the lower gap of the left split ring.
In the technical scheme, the preferred x component of the left split ring from the center of the circle is 1-3 μm, and the preferred x component of the right split ring from the center of the circle is 3-5 μm. Correspondingly, the diameter of the outer ring of the inner ring in each structural unit is preferably 10-20 micrometers, the diameter of the outer ring is preferably 15-30 micrometers, and the widths of the inner ring and the outer ring are both 1-3 micrometers; and preferably, the period of the structural unit in the x-axis direction is 15-45 mu m, and the period in the y-axis direction is 15-45 mu m. Further preferably, the diameter of the outer ring of the inner ring in each structural unit is 10-15 micrometers, the diameter of the outer ring is 18-22 micrometers, and the widths of the inner ring and the outer ring are both 1-3 micrometers; and the period of the structural unit in the x-axis direction is 25-35 μm, and the period in the y-axis direction is 25-35 μm.
In the technical scheme, each structural unit is preferably in a cube shape, and the value of N is preferably more than or equal to 3.
As a preferred embodiment of the present application, it is preferable that the structural unit has a period of 30 μm in the x-axis direction and a period of 30 μm in the y-axis direction; the diameter of the outer ring of the inner ring is 12 micrometers, the diameter of the outer ring is 20 micrometers, and the widths of the inner ring and the outer ring are both 2 micrometers; the x component of the left split ring from the center of the circle is 2 μm, and the x component of the right split ring from the center of the circle is 4 μm.
In the technical scheme, the thickness of the graphene layer is preferably 1-5 nm, and further preferably 1-2 nm. The material and the thickness of the dielectric layer are selected to be the same as those of the prior art, specifically, the material of the dielectric layer can be any one of silicon dioxide, polyimide, quartz crystal, cyclic olefin polymer, Polytetrafluoroethylene (PTFE) and the like, and the silicon dioxide is preferred in the application. The thickness of the dielectric layer is preferably 0.1 to 0.5 μm, and more preferably 0.1 to 0.2 μm.
The invention relates to a preparation method of a terahertz metamaterial sensor with tunable dual polarization directions, which comprises the following steps:
1) selecting a dielectric material as a dielectric layer, and carrying out pretreatment to obtain the dielectric layer;
2) preparing graphene on a metal substrate;
3) spin-coating a polymethyl methacrylate solution on the surface of graphene on a metal substrate to obtain a substrate with a polymethyl methacrylate film on the surface of the graphene;
4) etching the substrate with the polymethyl methacrylate film on the surface of the graphene to remove the substrate, and then transferring the graphene and the polymethyl methacrylate film on the surface of the graphene to a dielectric layer;
5) and 4) carrying out gluing, exposure, development and fixation on the basis of the medium layer obtained in the step 4) to obtain a photoresist mask of the graphene layer, and then carrying out etching and stripping processes to obtain the graphene layer.
The operations in the above preparation methods, which are not described in detail, are the same as those in the prior art. The preparation method is adopted to obtain the medium layer and the imaging graphene layer positioned on the medium layer, and when the preparation method is specifically applied, a metal gate electrode and a conducting layer are required to be prepared on the graphene layer, and the specific operation is the same as that in the prior art.
Compared with the prior art, the invention is characterized in that:
1. according to the invention, a metamaterial basic model is used, in the x polarization direction, through the excitation of terahertz waves, an inner ring is equivalent to a bright film in a three-resonance submodel, and two split rings forming an outer ring are used as two quasi-dark films; in the y polarization direction, the right split ring in the outer ring serves as a bright film in the three-resonance submodel, the left split ring and the inner ring in the outer ring are equivalent to two quasi-dark films, and because the bright films and the two quasi-dark films in the two polarization directions are not of the same structure, the mutual destructive interference (coupling) of one bright film and the two quasi-dark films in different polarization directions enables the sensor to form two different transparent windows in the dual polarization direction, and meanwhile, the obtained sensor can be regulated and controlled within the frequency range of 0.5-4.5 THz, and the regulation and control range is wide.
2. The sensor disclosed by the invention realizes the characteristic of insensitivity to incident light angle, and the characteristic is favorable for reducing detection errors and realizing rapid and high-sensitivity detection on an object to be detected.
3. The sensor can realize dual regulation and control of changing the polarization direction of incident light and the Fermi level of graphene.
4. The sensor provided by the invention has the highest sensing sensitivity of 1.1THz/RIU, effectively solves the problem of low sensitivity of the existing terahertz metamaterial sensor, and can reduce the detection cost, simplify the experimental operation and reduce the experimental difficulty compared with the existing terahertz metamaterial sensor.
5. The sensor provided by the invention has the advantages of simple structure, excellent performance and easy realization of manufacturing process, and meets the requirement on cost performance in the sensor design process.
Drawings
Fig. 1 is a top view of a structural unit of the dual-polarization direction tunable terahertz metamaterial sensor provided by the invention.
Fig. 2 is a graph of the transmission spectrum of a sensor sample wafer in the dual polarization direction, which is obtained by arranging sensor structure units in the structure shown in fig. 1 in a plane periodically by 13 × 13.
FIG. 3 is a view showing F in the x-polarization direction of a sensor pattern in which sensor structural units having the structure shown in FIG. 1 are arranged periodically at 13X 13 positions on a plane1～F5The electric field distribution pattern of (c).
FIG. 4 is a view showing a sensor pattern f in the y-polarization direction, in which sensor elements having the structure shown in FIG. 1 are arranged in a plane at a period of 13X 131～f5The electric field profile at (a).
Fig. 5 is a graph of the transmission spectra of sensor samples obtained by periodically arranging 13 × 13 sensor structure units in a plane in the structure shown in fig. 1 at different incident angles in the x-polarization direction.
Fig. 6 is a graph of the transmission spectra of sensor samples obtained by periodically arranging 13 × 13 sensor structure units in a plane in the structure shown in fig. 1 at different incident angles in the y-polarization direction.
Fig. 7 is a graph of transmission spectra of fermi levels in the x-polarization direction of sensor samples obtained by periodically arranging 13 × 13 sensor structural units in a plane in the structure shown in fig. 1.
Fig. 8 is a graph of transmission spectrum of fermi levels in the y-polarization direction of a sensor sample obtained by periodically arranging 13 × 13 sensor structural units in a plane in the structure shown in fig. 1.
Fig. 9 is a graph showing the frequency change when the fermi level changes in each valley in the x-polarization direction of a sensor sample obtained by periodically arranging 13 × 13 on a plane in the sensor structure unit having the structure shown in fig. 1.
Fig. 10 is a graph showing the frequency change when the fermi level changes in the respective valleys in the y-polarization direction of a sensor sample obtained by periodically arranging 13 × 13 on a plane in the sensor structure unit having the structure shown in fig. 1.
Fig. 11 is a graph of transmission spectra corresponding to objects to be measured with different refractive indexes in the x-polarization direction of sensor samples obtained by periodically arranging 13 × 13 sensor structure units in a plane according to the structure shown in fig. 1.
Fig. 12 is a graph of transmission spectra corresponding to the objects to be measured with different refractive indexes in the y polarization direction of sensor samples obtained by periodically arranging 13 × 13 sensor structure units in a plane according to the structure shown in fig. 1.
Fig. 13 is a frequency shift curve of a sensor sample wafer obtained by periodically arranging 13 × 13 sensor structure units in a plane according to the structure shown in fig. 1, when a transmission window changes with the refractive index of an object to be measured in a dual polarization direction.
Fig. 14 is a three-dimensional structure diagram of a structural unit of the dual-polarization direction tunable terahertz metamaterial sensor.
Fig. 15 is a structural diagram of a terahertz graphene metamaterial device.
The reference numbers in the figures are:
1 dielectric layer, 2 inner ring, 3 outer ring, 3-1 left split ring, 3-2 right split ring, 4 metal gate electrode, 5 ion gel layer, W ring width, x1Left branchComponent x of split ring, x2The x component, phi, of the right split ring1Outer ring diameter of inner ring, [ phi ]2The outer ring diameter of the outer ring.
Detailed Description
The dual-polarization direction tunable terahertz metamaterial sensor is of a periodic structure and comprises NxN structural units which are periodically arranged on an xy plane, N is a natural number larger than 0, the value of N is preferably not less than 3, each structural unit is in a cuboid shape, more preferably a cube shape, and the NxN structural units are continuously spliced on the plane; each structural unit comprises a medium layer 1 and a graphene layer arranged on the medium layer 1.
The material of the dielectric layer 1 can be any one of silicon dioxide, polyimide, quartz crystal, cyclic olefin polymer, Polytetrafluoroethylene (PTFE) and the like, and the thickness of the dielectric layer 1 is usually 0.1 to 0.5 μm, and more preferably 0.1 to 0.2 μm.
The graphene layer is of two concentrically nested graphene circular ring structures, specifically an inner ring 2 and an outer ring 3 which are concentrically nested, the inner ring 2 is a complete graphene circular ring, and the outer ring 3 is a split graphene circular ring; the overlooking shape of the outer ring 3 consists of a left split ring 3-1 and a right split ring 3-2 which are opposite, wherein the upper gap and the lower gap of the left split ring 3-1 are on the same vertical line, the upper gap and the lower gap of the right split ring 3-2 are also on the same vertical line, but the upper gap and the lower gap of the right split ring 3-2 are not overlapped with the upper gap and the lower gap of the left split ring 3-1. The thickness of the graphene layer is preferably 1-5 nm, and more preferably 1-2 nm.
In each structural unit, the left split ring 3-1 constituting the outer ring 3 has an x component x from the center of the circle1And the x component x of the right split ring 3-2 from the center of the circle2Whether the sensor can be provided with two transparent windows in the dual-polarization direction or not is greatly influenced, in the application, the x component x of the left split ring 3-1 to the circle center11-3 μm, and the x component x of the right split ring 3-2 from the center of the circle2Is 3 to 5 μm. Correspondingly, the period in the x-axis direction is 15-45 mu m, the period in the y-axis direction is 15-45 mu m, and the outer ring of the inner ring 2 in each structural unit is straightRadial phi 110 to 15 mu m, and the diameter phi of the outer ring 3218-22 μm, and the ring widths W of the inner ring 2 and the outer ring 3 are both 1-3 μm. It is further preferable that the outer ring diameter Φ of the inner ring 2 in each structural unit 110 to 15 mu m, and the diameter phi of the outer ring 3218-22 μm, and the ring widths W of the inner ring 2 and the outer ring 3 are both 1-3 μm; and the period of the structural unit in the x-axis direction is 25-35 μm, and the period in the y-axis direction is 25-35 μm.
The preparation method of the terahertz metamaterial sensor with the tunable dual-polarization direction comprises the following steps:
1) selecting a dielectric material as a dielectric layer 1, and carrying out pretreatment to obtain the dielectric layer 1;
2) preparing graphene on a metal substrate (which can be any one of gold, silver, copper, aluminum and the like);
3) spin-coating a polymethyl methacrylate solution on the surface of graphene on a metal substrate to obtain a substrate with a polymethyl methacrylate film on the surface of the graphene;
4) etching the substrate with the polymethyl methacrylate film on the surface of the graphene to remove the substrate, and then transferring the graphene and the polymethyl methacrylate film on the surface of the graphene to the dielectric layer 1;
5) and (4) carrying out gluing, exposure, development and fixation on the basis of the medium layer 1 obtained in the step 4) to obtain a photoresist mask of the graphene layer, and then carrying out etching and stripping processes to obtain the graphene layer.
The operations in the above preparation methods, which are not described in detail, are the same as those in the prior art. The preparation method is adopted to obtain the dielectric layer 1 and the imaging graphene layer positioned on the dielectric layer 1, and when the method is applied specifically, the metal gate electrode 4 and the conducting layer (namely the ionic gel layer 5) are required to be prepared on the graphene layer, and the specific operation is the same as that in the prior art.
The present invention will be better understood from the following detailed description of preferred embodiments thereof, taken in conjunction with the accompanying drawings.
Example 1
The structure and preparation of the sensor according to the invention are illustrated by the block diagrams of fig. 1 and 14.
Referring to fig. 1 and 14, each structural unit of the sensor of the present invention includes a dielectric layer 1 and a graphene layer disposed on the dielectric layer 1, and both the period of the structural unit in the x-axis direction and the period of the structural unit in the y-axis direction are 30 μm; outer ring diameter Φ of inner ring 2 constituting graphene layer112 μm, outer ring diameter of the outer ring 3220 μm, and the ring widths W of the inner ring 2 and the outer ring 3 are both 2 μm; the x component x of the left split ring 3-1 from the center of the circle constituting the outer ring 312 μm, and the x component x of the right split ring 3-2 from the center of the circle2And was 4 μm. The dielectric layer 1 is made of silicon dioxide, the dielectric constant of the silicon dioxide is 3.9, and the thickness of the silicon dioxide is 0.1 mu m; the thickness of the graphene layer was 1 nm. The surface conductivity of the graphene is simply obtained by using a Drude model:
wherein the carrier relaxation time is:
wherein the carrier mobility μ is about 4m2Vs Fermi velocity VFIs 106m/s，
Is Planck constant, E is electron charge, τ is relaxation time(s), ω (rad/s) is angular frequency, EF(eV) is the Fermi level.
The structure adsorbed on graphene is a non-dispersive ionic gel layer (dielectric constant is 1.82), while the ultra-thin ionic gel layer as an electrode medium has little influence on the terahertz spectrum, so it can be ignored in the simulation.
The sensor designed by the application needs to be tested in a THz time-domain spectroscopy system, and the diameter of a THz light beam on a focusing plane in the THz time-domain spectroscopy system is about 5mm, so that the effective size of the sensor is larger than 5mm x 5mm, specifically, 15mm x 15mm in the embodiment.
The preparation method of the sensor comprises the following steps:
1) putting a silicon dioxide sheet with the thickness of 100nm into an acetone solution for ultrasonic treatment for 15 minutes, then putting the silicon dioxide sheet into absolute ethyl alcohol for ultrasonic treatment for 20 minutes, finally putting the silicon dioxide sheet on a heating plate, and heating the silicon dioxide sheet at 110 ℃ for 10 minutes to obtain a pretreated silicon dioxide sheet (hereinafter referred to as a silicon wafer).
2) The method comprises the steps of pretreating a copper foil substrate by using ferric nitrate, then using methane as a carbon source, using argon and hydrogen as a protective gas and a reducing gas respectively, heating the pretreated copper foil substrate to 1080 ℃, then reducing the temperature to 1020 ℃, then continuously reducing the temperature to normal temperature, and obtaining a graphene layer on a copper foil for later use.
3) And spin-coating the polymethyl methacrylate solution on the surface of the graphene on the copper foil by using a mechanical spin-coating method, pre-rotating at a rotating speed of 600r/min for 20 seconds, then rotating at a rotating speed of 3000 r/min for 100 seconds, then rotating at a rotating speed of 600r/min for 20 seconds, placing on a drying table after the spin-coating is finished, and drying at 120 ℃ for 20 minutes to obtain the copper foil with the polymethyl methacrylate film on the surface of the graphene.
4) Placing the copper foil obtained in the step 3) into an oxygen plasma etching machine for etching, wherein the power is 90%, the pressure is 0.2Pa, and the time is 30 seconds; and then placing the treated copper foil into a saturated ferric chloride solution for soaking for 4 hours, completely etching away copper, repeatedly replacing 5 times with deionized water when only graphene and polymethyl methacrylate float in the solution, completely replacing ferric chloride, finally fishing out the graphene with polymethyl methacrylate from the solution by using a pretreated silicon wafer, drying, placing into an acetone solution for soaking for 9 hours to remove the polymethyl methacrylate, washing for 3 times with deionized water, and completing the transfer of the graphene to the pretreated silicon wafer.
5) Coating a photoresist with the thickness of 1 micrometer on the surface of graphene by using a mechanical spin coating method (firstly spin-coating at the rotating speed of 600 rpm for 20 seconds, then spin-coating at the rotating speed of 4000 rpm for 60 seconds, and then spin-coating at the rotating speed of 600 rpm for 20 seconds), baking at 100 ℃ for 60 seconds, cooling, and then carrying out exposure, development and fixing processes to obtain a photoresist mask of the graphene layer; and then, performing oxygen plasma etching to etch away graphene which is not covered by the photoresist mask, then, placing the silicon wafer in an acetone solution to soak for 24 hours to remove the photoresist mask on the silicon wafer, cleaning the silicon wafer for 3 times by using deionized water, and then, drying the silicon wafer by blowing to obtain an imaged graphene structure, namely, an imaged graphene layer on the dielectric layer 1 is obtained, as shown in fig. 14.
6) And (2) spin-coating photoresist on the graphene layer by using a mechanical spin-coating method, wherein the spin-coating thickness is 1 mu m, baking the graphene layer for 60 seconds at 100 ℃, cooling the graphene layer, exposing, developing and fixing the graphene layer to obtain a photoresist mask for preparing the metal gate electrode 4, depositing metal on the photoresist mask for preparing the metal gate electrode 4 by using a material growth process, soaking the photoresist mask in an acetone solution for 24 hours to strip the metal and remove the photoresist, washing the photoresist mask for 3 times by using deionized water, and drying the photoresist mask to obtain the metal gate electrode 4 with the thickness of 1 mu m.
7) And (3) spin-coating the ion gel layer 5 with the thickness of 1 micrometer on the graphene layer by using a mechanical spin-coating method, and baking at 100 ℃ for 60 seconds to complete the preparation of the terahertz graphene metamaterial device, as shown in fig. 15.
Example 2: the sensor sample pieces obtained by periodically arranging the sensor structure units having the structure shown in fig. 1 on a plane by 13 × 13 were analyzed for the transmission characteristics, resonance mechanism, incident angle insensitivity, and the like of the obtained sensor sample pieces.
1. Transmission characteristic
In order to research the transmission characteristic of the sensor, the invention carries out numerical calculation of a finite element method based on CST Microwave studio software.
Fig. 2 is a transmission spectrum of the terahertz metamaterial sensor, and it can be seen from the figure that the sensor forms double transparent windows in dual polarization directions (i.e., x polarization direction and y polarization direction). The frequency range of the low-frequency double transparent window is 1-3.5 THz, and the frequency range of the high-frequency double transparent window is 2.5-4.5 THz. The transmission spectrum shows that the dual-polarization-direction dual-transparent window can achieve the effect of dual transparent windows in the dual polarization direction.
2. Analysis of resonance mechanism
In order to research the resonance mechanism of the terahertz metamaterial sensor, two methods are shown by CST softwareThe electric field pattern in the direction of the seed polarization. FIGS. 3 and 4 respectively show the terahertz metamaterial sensor in a dual polarization direction f1(F1) To f5(F5) The electric field distribution at (a). As can be seen from FIG. 3, F is in the x-polarization direction1＝2.804THz，F3＝3.276THz，F53.744THz, (fig. 4 shows f in the y polarization direction1＝1.672THz，f3＝1.968THz，f52.956 THz), the electric field is mainly distributed on the edges or structures of the inner graphene ring, the outer left graphene ring and the outer right graphene ring, since these three parts are directly coupled with the incident light at the corresponding frequencies, so that the corresponding tilt angles are formed in the corresponding transmission spectra. And F in the x-polarization direction22.996THz and F43.578THz (corresponding to a frequency f in the y polarization direction)21.810THz and f42.296THz) shows that instead of resonance of a single local structure, resonance coupling occurs overall, i.e. as a result of coupling interference between two quasi-dark films and a bright film.
3. Incident angle insensitive characterization
In order to test the sensitivity of the sensor to the change of the incident angle, the invention researches the transmission characteristics under the action of terahertz waves at different incident angles (0 degree, 20 degrees, 40 degrees, 60 degrees and 80 degrees). As shown in fig. 5 and 6, the resonant frequency in the transmission spectrum in the dual polarization direction is affected to a very small extent with the change of the incident angle. And when the incident angle exceeds 60 degrees, the transmissivity of the double transparent window still exceeds 80 percent. Therefore, the terahertz metamaterial sensor is insensitive to incident angle change.
4. Tunability
Based on the above researches, the graphene has a special advantage of tunability (the resonance frequency of plasma is changed by changing the fermi level of the graphene), and from fig. 7 and 8, it can be observed that a very obvious blue shift occurs in the transmission spectrum in the dual polarization direction when the fermi level is adjusted and controlled at 0.7-1.0 eV. Fig. 9 and 10 show three troughs, F, in the dual polarization direction1(f1)，F3(f3)，F5(f5) Plot of frequency change as a function of fermi level. It can be seen that the resonant frequency of the sensor in either the x-or y-polarization direction increases linearly with increasing fermi level, since the resonant frequency of the various components of the sensor also increases linearly with the fermi level, resulting in a blue shift of the final coupled resonant frequency. As can be seen from fig. 7 and 8, the change in the fermi level does not have a particularly large influence on the shape of the transmission spectrum, and therefore the change in the fermi level mainly affects the change in the resonance frequency. By utilizing the tunability of the graphene, the metamaterial sensor can be finely modulated within a controllable range.
5. Sensing performance
When the traditional terahertz metamaterial sensor detects an object to be detected, the object to be detected is attached to the surface of the periodic structure layer, so that the sensitivity of the sensor can be obtained by researching the response degree of the sensor to the change of the physical parameters of the surrounding medium.
The sensing sensitivity is an important index for measuring the sensing performance of the sensor and represents the spectrum deviation degree of the object to be measured under the unit refractive index change. The calculation formula of the sensing sensitivity is as follows:
in the formula, Δ f is a spectrum offset, and Δ n is a refractive index variation of the object.
Fig. 11 and 12 are transmission spectrum diagrams corresponding to the objects to be measured with different refractive indexes of the sensor in the x-polarization direction and the y-polarization direction, respectively. As can be seen from fig. 11 and 12, as the refractive index of the object to be measured increases, the transmission spectrum of the sensor undergoes a red shift, and the dual transparent windows f in the y polarization direction are calculated2And f4Has a sensitivity of S1＝0.5THz/RIU，S20.7THz/RIU, double transparent window F in x polarization direction2And F4Has a sensitivity of S3＝0.9THz/RIU，S4＝1.1THz/RIU。
Fig. 13 shows the variation of the frequency of the dual transparent windows in the dual polarization direction of the sensor by changing the refractive index of the object to be measured, and it can be known from fig. 13 that the frequency shift of both transparent windows relative to the refractive index of the object to be measured is linearly increased in both the x polarization direction and the y polarization direction, which indirectly proves that the sensing performance of the sensor is very good.
Claims (7)
1. A dual-polarization direction tunable terahertz metamaterial sensor comprises N multiplied by N structural units which are periodically arranged on a plane, wherein N is a natural number larger than 0, each structural unit is in a cuboid shape, and the N multiplied by N structural units are continuously spliced on the plane; it is characterized in that the utility model is characterized in that,
each structural unit comprises a dielectric layer (1) and a graphene layer arranged on the dielectric layer (1), the graphene layer is of two concentrically nested graphene circular ring structures, the inner ring (2) is a complete graphene circular ring, and the outer ring (3) is a split graphene circular ring; the overlooking shape of the outer ring (3) consists of a left split ring (3-1) and a right split ring (3-2) which are opposite, wherein the upper gap and the lower gap of the left split ring (3-1) are on the same vertical longitudinal line, the upper gap and the lower gap of the right split ring (3-2) are also on the same vertical longitudinal line, but the upper gap and the lower gap of the right split ring (3-2) are not overlapped with the upper gap and the lower gap of the left split ring (3-1).
2. The dual-polarization direction tunable terahertz metamaterial sensor according to claim 1, wherein the left split ring (3-1) has an x-component (x) from the center of the circle1) 1-3 μm, and the x component (x) of the right split ring (3-2) from the center of the circle2) Is 3 to 5 μm.
3. The dual polarized directionally tunable terahertz metamaterial sensor according to claim 1, wherein the outer ring diameter (Φ) of the inner ring (2)1) 10 to 20 μm, and the outer ring diameter (phi) of the outer ring (3)2) 15-30 μm, and the ring widths (W) of the inner ring 2 and the outer ring 3 are both 1-3 μm.
4. The dual-polarization direction tunable terahertz metamaterial sensor according to claim 1, wherein the period of the structural unit in the x-axis direction is 15-45 μm, and the period in the y-axis direction is 15-45 μm.
5. The dual-polarized directionally tunable terahertz metamaterial sensor of claim 1, wherein each structural unit is in the shape of a cube.
6. The dual-polarization direction tunable terahertz metamaterial sensor of claim 1, wherein the structural unit has a period of 30 μm in an x-axis direction and a period of 30 μm in a y-axis direction; the outer ring diameter (phi) of the inner ring (2)1) 12 μm, the outer ring diameter (phi) of the outer ring (3)2) 20 μm, the ring widths (W) of the inner ring (2) and the outer ring (3) are both 2 μm; the x component (x) of the left split ring (3-1) from the center of the circle1) 2 μm, the x component (x) of the right split ring (3-2) from the center of the circle2) And was 4 μm.
7. The method for preparing the dual-polarization direction tunable terahertz metamaterial sensor in claim 1, comprising the following steps:
1) selecting a dielectric material as the dielectric layer (1), and carrying out pretreatment to obtain the dielectric layer (1);
2) preparing graphene on a metal substrate;
3) spin-coating a polymethyl methacrylate solution on the surface of graphene on a metal substrate to obtain a substrate with a polymethyl methacrylate film on the surface of the graphene;
4) etching the substrate with the polymethyl methacrylate film on the surface of the graphene to remove the substrate, and then transferring the graphene and the polymethyl methacrylate film on the surface of the graphene to the dielectric layer (1);
5) and (4) carrying out gluing, exposure, development and fixation on the basis of the medium layer (1) obtained in the step 4) to obtain a photoresist mask of the graphene layer, and then carrying out etching and stripping processes to obtain the graphene layer.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115437040A (en) * | 2022-08-30 | 2022-12-06 | 湖南工商大学 | Dielectric super-surface structure with local field enhancement effect and application thereof |
| CN116106263A (en) * | 2023-04-07 | 2023-05-12 | 成都甄识科技有限公司 | Super-surface local plasmon sensor with high sensitivity and high quality factor |
| CN117148241A (en) * | 2023-10-30 | 2023-12-01 | 天津天达图治科技有限公司 | Intelligent metamaterial structure |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115437040A (en) * | 2022-08-30 | 2022-12-06 | 湖南工商大学 | Dielectric super-surface structure with local field enhancement effect and application thereof |
| CN116106263A (en) * | 2023-04-07 | 2023-05-12 | 成都甄识科技有限公司 | Super-surface local plasmon sensor with high sensitivity and high quality factor |
| CN117148241A (en) * | 2023-10-30 | 2023-12-01 | 天津天达图治科技有限公司 | Intelligent metamaterial structure |
| CN117148241B (en) * | 2023-10-30 | 2024-02-06 | 天津天达图治科技有限公司 | Intelligent metamaterial structure |
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