A flexible terahertz metamaterial sensor and a preparation method thereof

Abstract

The application discloses a flexible terahertz metamaterial sensor and a preparation method thereof, which comprises, from top to bottom, a reinforcing layer, a carbon nanotube film layer and a polymer substrate layer; the reinforcing layer is composed of a graphene and zinc oxide composite material; the reinforcing layer and the carbon nanotube film layer are consistent in shape and are both periodic strip structures. The super material sensor is based on the synergistic effect of a ternary system of zinc oxide / graphene / carbon nanotube, wherein zinc oxide nanoparticles grow directionally on a graphene sheet through a Zn-O-C bond, and a carbon nanotube film constructs a three-dimensional conductive network, thus solving the dielectric loss problem of a traditional noble metal-based sensor structure. The phonon resonance characteristics of zinc oxide are coupled with graphene plasmons, a high-efficiency charge transfer channel is formed at a heterojunction interface, and the conductivity and terahertz transmission efficiency are improved.

Description

Technical Field

[0001] This invention relates to the field of measurement technology, specifically to the field of metamaterials technology, and more particularly to a flexible terahertz metamaterial sensor and its fabrication method. Background Technology

[0002] Terahertz waves generally refer to electromagnetic radiation with frequencies ranging from 0.1 to 10 THz (corresponding to wavelengths of 3000 to 30 μm). This frequency band overlaps with millimeter waves in the long-wave direction and connects with infrared light in the short-wave direction. As a key frequency domain for the transition from macroscopic classical theory to microscopic quantum theory, and possessing dual characteristics of electronics and photonics, it is called the "terahertz gap" in the electromagnetic spectrum. This band shows significant application potential in imaging, matter detection, and qualitative identification.

[0003] Metamaterials, as artificially designed periodic structures, offer a new paradigm for electromagnetic wave manipulation. Unlike traditional materials, they can achieve unique electromagnetic responses such as negative permittivity, negative permeability, and negative refractive index through their subwavelength unit cell structure. This property is of great value—given that few materials in nature exhibit good electromagnetic responses in the terahertz frequency band, metamaterials, with their artificially designed structural parameters, can achieve precise electromagnetic manipulation of specific frequencies.

[0004] Currently, most flexible terahertz metamaterial sensors adopt a combination of noble metal matrix structure and polymer substrate. Such sensors are heavy, difficult to manufacture, and their terahertz wave transmission efficiency and sensitivity urgently need to be improved.

[0005] Therefore, it is necessary to provide a flexible terahertz metamaterial sensor and its fabrication method to solve the above-mentioned technical problems. Summary of the Invention

[0006] This invention overcomes the shortcomings of the prior art and provides a flexible terahertz metamaterial sensor and its preparation method.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a flexible terahertz metamaterial sensor, comprising a reinforcement layer, a carbon nanotube thin film layer and a polymer substrate layer sequentially bonded together from top to bottom;

[0008] The reinforcing layer is composed of a graphene and zinc oxide composite material;

[0009] The reinforcing layer and the carbon nanotube film layer have the same shape, both being periodically arranged strip structures.

[0010] In a preferred embodiment of the present invention, the thickness of the reinforcing layer is 8–15 μm, the thickness of the carbon nanotube film layer is 4–12 μm, and the thickness of the polymer substrate layer is 20–80 μm.

[0011] In a preferred embodiment of the present invention, the length of the strip structure is 5-9 μm and the width is 2-4 μm.

[0012] In a preferred embodiment of the present invention, the periodically arranged strip structure is divided into several units, each unit having a length and width of 10-14 μm, and each unit includes two parallel horizontal strip structures and two parallel vertical strip structures.

[0013] In a preferred embodiment of the present invention, the four strip structures within the unit are arranged in a square or cross shape.

[0014] A method for fabricating a flexible terahertz metamaterial sensor, comprising the following steps:

[0015] S1. Ethylene glycol and zinc acetate were added to the aqueous solution of graphene oxide in sequence, and after being mixed evenly, the mixture was reacted at 90℃~110℃ for 20~24h. After cooling to room temperature and washing, the zinc oxide / graphene composite material was obtained.

[0016] S2. The diluted carbon nanotube solution was used to prepare carbon nanotube films by vacuum filtration.

[0017] S3. Press the carbon nanotube film onto a glass plate, coat its surface with a zinc oxide / graphene composite material, and then dry it to form a composite film on the glass plate.

[0018] S4. Remove the composite film from the glass plate and divide it into several strip structures;

[0019] S5. The strip structure is attached to the polymer substrate according to the arrangement design and pressed together. After surface modification, the sensor is obtained.

[0020] In a preferred embodiment of the present invention, in step S1, ethylene glycol and graphene oxide aqueous solution are first mixed evenly, and then zinc acetate is added, and the mixture is stirred continuously at a constant temperature for 20-24 hours.

[0021] In a preferred embodiment of the present invention, the mass ratio of zinc oxide, graphene and carbon nanotubes in the composite film is 9:2:13-15.

[0022] In a preferred embodiment of the present invention, the drying temperature of S3 is 60℃~80℃, and the drying time is 2~3h.

[0023] In a preferred embodiment of the present invention, the polymer substrate is polyimide (PI) with a dielectric constant of 2 to 4.

[0024] In a preferred embodiment of the present invention, the preparation of the diluted carbon nanotube solution in S2 is specifically as follows: carbon nanotube powder is added to a dispersion, subjected to ultrasonic treatment to obtain a carbon nanotube solution, and the carbon nanotube solution is diluted in water.

[0025] In a preferred embodiment of the present invention, the dispersion is prepared by adding sodium dodecyl sulfate to deionized water and stirring at a constant speed until completely dissolved.

[0026] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0027] (1) This invention provides a flexible terahertz metamaterial sensor based on the synergistic effect of a zinc oxide / graphene / carbon nanotube ternary system. Zinc oxide nanoparticles are directionally grown on graphene sheets via Zn-OC bonds, and a three-dimensional conductive network is constructed using carbon nanotube films, solving the dielectric loss problem of traditional noble metal-based sensor structures. The phonon resonance characteristics of zinc oxide couple with the plasmon resonance of graphene, forming an efficient charge transfer channel at the heterojunction interface, improving conductivity and terahertz transmission efficiency. Compared to existing technologies, this reduces weight and dielectric loss, achieving high-sensitivity detection of polar molecules and providing a technological basis for in-situ monitoring of biomarkers.

[0028] (2) The strip-shaped units prepared by the focused ion beam etching process of this invention have sharp subwavelength edges, and their periodic square / cross-shaped arrangement excites multimodal electromagnetic resonance. The square-shaped closed cavity generates TE. 110 With TM 220 The standing wave structure ensures that the electric field intensity at the corners is much higher than the background field; the cross-shaped orthogonal nodes couple dipole-quadrupole resonances, achieving omnidirectional wave coverage. This structure significantly improves the sensitivity of the flexible terahertz metamaterial sensor and greatly expands its applicability to complex environments.

[0029] (3) The present invention uses wet composite film lamination technology to conformally bond the strip structure to the polyimide substrate, and eliminates the interfacial stress by low temperature gradient drying at 70-80℃. This process enables the zinc oxide / graphene layer and the carbon nanotube layer to form a permeable bond at the molecular level, which improves the interfacial bonding energy and reduces the resonant frequency shift during bending. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart of a preferred embodiment of the preparation method of a flexible terahertz metamaterial sensor of the present invention;

[0032] Figure 2 This is a three-dimensional structural diagram of the metamaterial sensor according to Embodiment 1 of the present invention;

[0033] Figure 3 This is a structural diagram of the U-shaped unit of the metamaterial sensor according to Embodiment 1 of the present invention;

[0034] Figure 4 This is a structural diagram of the cross-shaped unit of the metamaterial sensor according to Embodiment 2 of the present invention;

[0035] Figure 5 This is a summary table of the electrical conductivity of sample materials with different proportions according to the preferred embodiments of the present invention;

[0036] Figure 6 This is a graph showing the result of the shift in the resonant frequency of the sensor of this invention as a function of the sample's refractive index.

[0037] In the figure: 100, reinforcement layer; 200, carbon nanotube thin film layer; 300, polymer substrate layer. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0040] Figure 1A flowchart of a method for fabricating a flexible terahertz metamaterial sensor according to the present invention is shown. The method includes the following steps: Step S1: Ethylene glycol and zinc acetate are added sequentially to an aqueous solution of graphene oxide, mixed thoroughly, and reacted at 90℃~110℃ for 20~24h. After cooling to room temperature and washing, a zinc oxide / graphene composite material is obtained; Step S2: A carbon nanotube thin film is prepared from a diluted carbon nanotube solution by vacuum filtration; Step S3: The carbon nanotube thin film is pressed onto a glass plate, coated with the zinc oxide / graphene composite material, and dried to form a composite film on the glass plate; Step S4: The composite film is removed from the glass plate and divided into several strip structures; Step S5: The strip structures are arranged according to a design and bonded onto a polymer substrate, and after surface modification, the sensor is obtained.

[0041] This invention uses a non-metallic carbon-based composite material system (graphene + zinc oxide + carbon nanotubes) to replace the traditional noble metal-based (such as gold and silver) structure, combined with a unique periodic strip design, to realize a high-performance, lightweight, flexible, and cost-optimized terahertz metamaterial sensor.

[0042] The following is a detailed explanation of each step of the preparation method.

[0043] Step S1: Ethylene glycol and zinc acetate are added to the aqueous solution of graphene oxide in sequence. After mixing evenly, a mixed solution is obtained. The mixed solution is reacted at 90℃~110℃ for 20~24h. After cooling to room temperature and washing, the zinc oxide / graphene composite material is obtained.

[0044] In step S1, the graphene oxide aqueous solution is prepared by mixing graphene oxide powder with deionized water and ultrasonically treating it for 1.8 to 2 hours to obtain a graphene oxide aqueous solution. The graphene oxide powder is prepared by modifying commercial graphite powder using the Hμmmers method to obtain graphene oxide powder. Preferably, an ultrasonic instrument with an ultrasonic power of 20 to 100 W is used to ultrasonicate the graphene oxide aqueous solution for 1 to 2 hours to make the graphene oxide powder uniformly dispersed in the solution.

[0045] In step S1, ethylene glycol and graphene oxide aqueous solution are first mixed evenly, then zinc acetate is added, and the mixture is stirred at a constant temperature for 20–24 hours. The preferred mass ratio of ethylene glycol solution to graphene oxide aqueous solution is 4:1. The temperature is controlled at 20–30°C during stirring. Prolonged stirring helps the graphene oxide and zinc acetate molecules in the solution to fully contact and react. The stirred solution is then transferred to a reaction vessel and reacted at 90–110°C, maintaining the temperature constant. After the reaction is complete, the mixture is allowed to cool naturally to room temperature.

[0046] In step S1, deionized water is used for washing, and the deionized water is replaced 3 to 5 times during the washing process. The zinc oxide / graphene composite material prepared in this step is not dried and is in a non-cured state.

[0047] This step utilizes an ethylene glycol-assisted hydrothermal synthesis method to directionally grow zinc oxide nanoparticles on graphene sheets, forming a composite system with both high specific surface area and heterojunction charge transfer characteristics. Ethylene glycol acts as a reducing agent, partially reducing graphene oxide to highly conductive graphene, while simultaneously controlling the ZnO nucleation rate by complexing zinc ions, thus preventing particle aggregation. The low-temperature, long-duration reaction ensures that ZnO forms strong chemical bonds (Zn-OC bonds) along the (002) crystal plane of graphene. This structure not only enhances the terahertz response by utilizing the phonon resonance characteristics of ZnO but also accelerates carrier separation through the Schottky junction interface, improving dielectric sensitivity. This lays the material foundation for the ultrasensitive performance of subsequent sensors in the detection of trace polar molecules (such as H2O and ethanol).

[0048] Step S2: Add carbon nanotube powder to a dispersion, sonicate the dispersion to obtain a carbon nanotube solution, dilute the carbon nanotube solution in deionized water, and prepare a carbon nanotube film by vacuum filtration.

[0049] Preparation of dispersion in step S2: Add sodium dodecyl sulfate to deionized water and stir at a constant speed until completely dissolved; the mass fraction of sodium dodecyl sulfate is 1.0 to 1.5 wt%, and the temperature is controlled within 20 to 30°C during the stirring and dissolution process.

[0050] In step S2, the mass of carbon nanotube powder in the carbon nanotube solution is 0.3–0.8 mg / ml; carbon nanotube films are prepared by vacuum filtration, specifically by low vacuum and slow filtration, with the vacuum degree controlled at 0.1–0.2 atm. The thickness of the carbon nanotube film prepared by filtration is 8–12 μm, preferably 10 μm.

[0051] This step utilizes sodium dodecyl sulfate dispersion and low-pressure slow filtration technology to construct a self-supporting carbon nanotube film with a three-dimensional interpenetrating network structure. The hydrophobic chains of sodium dodecyl sulfate adsorb onto the carbon nanotube surface, forming an electrostatic shielding layer that ensures uniform dispersion of individual carbon nanotubes. Meanwhile, low-vacuum filtration promotes the directional alignment of the carbon nanotubes, forming a flexible conductive network with high porosity and high conductivity. The film thickness is precisely controlled within 8-12 μm (approximately 1 / 4 of the 0.3 THz wavelength λ), satisfying the quarter-wave impedance matching condition and achieving a terahertz transmission efficiency of over 85%. This design endows the film with both mechanical flexibility and electromagnetic resonance properties, making it an ideal carrier for lightweight metamaterial sensors.

[0052] Step S3: Press the carbon nanotube film onto a glass plate, then coat the carbon nanotube film with the zinc oxide / graphene composite material, and dry the film together with the glass plate at 60℃~80℃ for 2~3 hours to form a composite film on the glass plate.

[0053] In step S3, the carbon nanotube film prepared in step S2 is pressed tightly onto the surface of one glass plate using a double glass plate. The other glass plate has a frame structure and presses the four sides of the carbon nanotube film, exposing most of the carbon nanotube film in the middle.

[0054] Furthermore, a zinc oxide / graphene composite material with a thickness of 6–10 μm is uniformly coated onto the exposed carbon nanotube film surface, followed by isothermal drying for 2–3 hours. The wet zinc oxide / graphene composite material coated onto the wet carbon nanotube film surface provides a larger contact area between the two layers. The subsequent drying enhances the bonding force between the zinc oxide / graphene composite material and the carbon nanotube film, improving the sensor's performance and stability.

[0055] It is worth noting that in the composite film obtained in step S3, the mass ratio of zinc oxide, graphene and carbon nanotubes is 9:2:13 to 15.

[0056] The total mass of the zinc oxide / graphene composite material and the carbon nanotube film of the same size prepared by the above steps S1 to S3 is 10g. The proportions of zinc oxide, graphene and carbon nanotube materials are shown in Table 1.

[0057] Table 1. Material Proportions

[0058]

[0059] The prepared zinc oxide / graphene composite material and carbon nanotube film composite patch samples were placed on the worktable, and the conductivity of the sample materials was tested using the four-probe method. The results are as follows. Figure 4 The table summarizing the conductivity of samples with different ratios shows that when the graphene ratio in a 10g sample is between 0 and 0.8, the conductivity gradually increases as the graphene ratio increases. The conductivity reaches its peak when the graphene ratio is 0.8, and then the rate of increase in conductivity begins to slow down and gradually stabilizes as the graphene ratio continues to increase.

[0060] When a small amount of graphene is incorporated into a composite material, the graphene is relatively dispersed, and the contact between graphene particles is insufficient, so a conductive path cannot be formed within the composite material. When the graphene content is further increased, the composite material reaches its own percolation threshold, and the conductivity of the composite material increases rapidly. After reaching a peak, if the graphene content is further increased, the conductive path inside the composite material will tend to saturate, and the rate of increase in conductivity will slow down.

[0061] Adding an appropriate amount of graphene to the zinc oxide / graphene composite material can enhance the conductivity of the sensor by increasing its high conductivity. This improves the electron transmission efficiency between the reinforcing layer 100 and the carbon nanotube film layer 200, mitigating the conductivity mismatch between zinc oxide and carbon nanotubes that hinders electron transmission and affects terahertz wave transmission efficiency. Graphene can also form conductive pathways between the reinforcing layer 100 and the carbon nanotube film layer 200, promoting electron transmission and reducing electron scattering and transmission difficulties between them.

[0062] When the mass ratio of zinc oxide, graphene, and carbon nanotubes is 9:2:14, the presence of graphene connects zinc oxide and carbon nanotubes and retains more of the zinc oxide mass, allowing the high transmission and absorption capabilities of zinc oxide in the terahertz band to be utilized. This, combined with the interaction of graphene and carbon nanotubes, enhances the zinc oxide's sensitivity to terahertz radiation.

[0063] When the mass ratio of zinc oxide, graphene, and carbon nanotubes is 9:2:14, the inclusion of graphene tightly binds the zinc oxide and carbon nanotubes together. This not only preserves the abundant mass of zinc oxide but also fully utilizes its high transmission and absorption capabilities in the terahertz band. Through synergistic interaction with carbon nanotubes, the sensitivity to terahertz radiation is further enhanced.

[0064] Step S4: After the drying process is completed, the carbon nanotube / zinc oxide / graphene composite film is removed from the glass plate and divided into several strip structures.

[0065] The length of the strip-like structure is 5–9 μm and the width is 2–4 μm.

[0066] After the composite film is dried, it is precisely cut using focused ion beam etching technology: a low-current gallium ion beam (≤50pA) is used to precisely etch a strip structure along a preset path, and argon ion polishing (energy <100eV) is used to control the edge roughness to ≤50nm, completely eliminating burrs and structural damage caused by mechanical cutting; the prepared strip structure has sharp edges that generate a strong electric field aggregation effect under terahertz wave excitation—graphene plasmon resonance and carbon nanotube conductive network oscillate synergistically at the edge tip, increasing the local electric field strength to 20-30 times that of the background field. At the same time, the dielectric response of zinc oxide further enhances the charge density. The synergistic effect of the three improves the detection limit of trace molecules (such as chlorpyrifos pesticide or SARS-CoV-2 protein).

[0067] In this invention, both the reinforcing layer 100 and the carbon nanotube thin film layer 200 are configured as strip structures. The strip structure can effectively improve the diffraction efficiency and interference effect of terahertz waves, thereby enhancing the sensor's response to terahertz waves of specific frequencies. Simultaneously, due to the directionality of the strip structure, selective detection of terahertz waves incident from different directions can be achieved.

[0068] Step S5: The strip structure is attached to the polymer substrate according to the arrangement design. The surface of the strip structure is washed with deionized water and then dried at a constant temperature. After drying, a pressing operation is performed to make the strip structure completely attached to the polymer substrate. Then, the surface is smoothed and modified to obtain the sensor.

[0069] The preferred polymer substrate is polyimide (PI) with a dielectric constant of 2–4. Before use, both sides of the polymer substrate are cleaned. After cleaning, the polymer substrate is placed on a clean glass slide and transferred to a dust-free environment for drying.

[0070] Multiple strip structures are arranged periodically on a polymer substrate. The periodically arranged strip structures are divided into several units, each with a length and width of 10–14 μm. Each unit includes two parallel transverse strip structures and two parallel vertical strip structures. The transverse strip structures are all of equal size, and the vertical strip structures are all of equal size.

[0071] It is worth noting that each unit contains four strip structures arranged in a square or cross shape. This grid arrangement with different forms can achieve a wide range of responses to terahertz waves incident from different directions and improve the sensor's sensitivity and response speed.

[0072] Furthermore, deionized water is used for washing, and the deionized water is changed 3 to 5 times during the washing process; the surface of the strip structure is cleaned to remove impurities and other contaminants.

[0073] The drying temperature is controlled at 70-80℃ for 2-3 hours. The main purpose of this drying process is to remove moisture and ensure the dryness of the strip structure and the substrate.

[0074] Several reinforcing layers 100 and carbon nanotube thin film layers 200 were prepared according to a mass ratio of zinc oxide, graphene and carbon nanotubes of 9:2:14. They were then combined and divided into several strip structures of different sizes to fabricate terahertz sensor samples. The dimensions of the strip structures are shown in Table 2. Sample strip structure dimensions.

[0075] Table 2. Dimensions of the sample strip structure

[0076]

[0077] A standard refractive index calibration material, a silicone oil / titanium dioxide nanoparticle hybrid system, was used. By varying the titanium dioxide concentration (0-40 vol%), a continuous refractive index gradient (n=1.42–2.82) was achieved, covering the range from biological tissues (n≈1.38) to polymeric materials (n=1.65). The effect of the analyte's refractive index on the sensitivity of the terahertz sensor was analyzed using the resonant frequency shift method, as shown in Table 3.

[0078] Table 3. Summary of Terahertz Sensor Sample Sensitivity

[0079]

[0080] Table 3 shows that among samples 8-22, sample 15 performed best in the test, indicating that the optimal design for the strip structure is a length of 7 μm and a width of 3 μm. Under the same test conditions, the sensitivities of sample 15 at low-frequency and high-frequency resonances are 214 GHz / RIU and 311 GHz / RIU, respectively, demonstrating high sensitivity. The aspect ratio of sample 15 is approximately 2.33, satisfying the optimal excitation condition for localized surface plasmon resonance (LSPR). When the strip width is greater than 3 μm (samples 13-17), the penetration depth of the terahertz wave increases, but the edge electric field intensity decreases, and the high-frequency sensitivity decreases.

[0081] This invention replaces the noble metal base in existing technologies with carbon nanotube thin films and adds a zinc oxide and graphene composite material. Zinc oxide is a semiconductor material with a wide bandgap, exhibiting high electron mobility and optical activity, and possesses strong absorption and transmission capabilities for terahertz waves. Graphene, a two-dimensional material composed of a single layer of carbon atoms, possesses excellent electrical conductivity and carrier mobility, enabling efficient absorption and scattering of terahertz waves. The composite of zinc oxide with graphene and carbon nanotubes forms a heterojunction structure. This structure promotes carrier separation and transmission, improves the sensor's conductivity and absorption capacity for terahertz radiation, and enhances the sensor's photoelectric effect, thereby increasing its sensitivity to terahertz radiation.

[0082] Example 1:

[0083] Figure 2 A three-dimensional structural schematic diagram of a flexible terahertz metamaterial sensor according to an embodiment of the present invention is shown. The metamaterial sensor includes, from top to bottom, a reinforcing layer 100, a carbon nanotube thin film layer 200, and a polymer substrate layer 300; the reinforcing layer 100 is composed of a graphene and zinc oxide composite material; the reinforcing layer 100 and the carbon nanotube thin film layer 200 have the same shape, both being periodically arranged strip structures.

[0084] The reinforcing layer 100 has a thickness of 6–10 μm, the carbon nanotube film layer 200 has a thickness of 8–12 μm, and the polymer substrate layer 300 is polyimide (PI) with a thickness of 20–80 μm and a dielectric constant of 2–4.

[0085] In this embodiment, the strip structure has a length of 5–9 μm and a width of 2–4 μm. The edges of the strip structure can enhance the local electric field. The periodically arranged strip structure is divided into several units, each unit having a length and width of 10–14 μm. Each unit includes two parallel horizontal strip structures and two parallel vertical strip structures, arranged in a U-shape. Figure 3 As shown, the U-shaped unit structure forms a closed rectangular resonant cavity through four strip structures (two horizontal and two vertical). This design generates a strong electromagnetic field localization effect in the central region—when terahertz waves are incident perpendicularly, multimode standing waves (such as TE waves) are excited inside the cavity. 110 With TM 220 This closed-loop resonance pattern significantly enhances the sensitivity to vertically polarized terahertz waves. Simultaneously, the nanoscale cavity confines the target molecules within the electric field hotspot region, improving the detection sensitivity for biomolecules and significantly suppressing environmental electromagnetic noise interference.

[0086] Example 2:

[0087] Figure 4A schematic diagram of a cross-shaped unit structure of a flexible terahertz metamaterial sensor according to an embodiment of the present invention is shown. The metamaterial sensor includes, from top to bottom, a reinforcing layer 100, a carbon nanotube thin film layer 200, and a polymer substrate layer 300; the reinforcing layer 100 is composed of a graphene and zinc oxide composite material; the reinforcing layer 100 and the carbon nanotube thin film layer 200 have the same shape, both being periodically arranged strip structures.

[0088] The reinforcing layer 100 has a thickness of 6–10 μm, the carbon nanotube film layer 200 has a thickness of 8–12 μm, and the polymer substrate layer 300 is polyimide (PI) with a thickness of 20–80 μm and a dielectric constant of 2–4.

[0089] In this embodiment, the strip structure has a length of 5–9 μm and a width of 2–4 μm. The edges of the strip structure can enhance the local electric field. The periodically arranged strip structure is divided into several units, each with a length and width of 10–14 μm. Each unit includes two parallel transverse strip structures and two parallel vertical strip structures, arranged in a cross shape. The cross-shaped unit forms an intersection node at the center with orthogonal strip structures. Its open design simultaneously excites dipole and quadrupole resonance modes, generating an asymmetric electric field distribution at the intersection point. This structure breaks through the traditional single-direction response limitation: the transverse strip preferentially couples X-polarized waves (0.5–0.8 THz), and the longitudinal strip captures Y-polarized waves (1.1–1.4 THz), achieving omnidirectional incident wave coverage. When detecting complex systems with non-directional scattering (such as aerosol particles), the response speed is improved to the millisecond level, making it particularly suitable for in-situ monitoring of dynamic fluids.

[0090] Example 3:

[0091] This embodiment is based on a method for preparing a flexible terahertz metamaterial sensor according to the present invention, and prepares a metamaterial sensor sample.

[0092] The materials used in the preparation are sourced from the following sources:

[0093] Graphene oxide powder: XF020, purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd.;

[0094] Ethylene glycol: Superior grade, GC ≥ 99.8%, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0095] Zinc acetate dihydrate, ACS grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0096] Carbon nanotubes: XFN34, Nanointegris multi-walled carbon nanotube powder, purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd.

[0097] Sodium dodecyl sulfate: SDS, BioUltra, ≥99.5%, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0098] Polyimide substrate: PI film, dielectric constant: 3.4±0.2 (1kHz), purchased from Shenzhen Ruihuatai.

[0099] The specific preparation process includes the following steps:

[0100] Step 1: Mix 0.1 mg / ml of graphene oxide aqueous solution with ethylene glycol. The mass ratio of graphene oxide aqueous solution to ethylene glycol is 1:4. Then add zinc acetate to the mixture. At this time, the mass ratio of zinc to graphene in the solution is 9:2. React the mixed solution at 100℃ for 24 h. After cooling to room temperature and washing, the zinc oxide / graphene composite material is obtained.

[0101] Step 2: Add carbon nanotube powder to the dispersion and sonicate the dispersion to obtain a carbon nanotube solution. The mass of the carbon nanotube powder is 0.5 mg / ml. Dilute the carbon nanotube solution in deionized water and perform low-vacuum, slow filtration. The vacuum degree is controlled at 0.2 atm. The thickness of the carbon nanotube film prepared by filtration is 10 μm.

[0102] Step 3: Press the carbon nanotube film onto a glass plate, then coat the carbon nanotube film with a zinc oxide / graphene composite material. The coating thickness is 8 μm. Dry the film together with the glass plate at 70°C to obtain a composite film. The mass ratio of zinc oxide, graphene and carbon nanotubes is 9:2:14.

[0103] Step 4: After the drying process is completed, the composite film is removed from the glass plate and divided into several strip structures with a length of 7μm and a width of 3μm.

[0104] Step 5: The strip structure is attached to a 60μm thick polymer substrate. The strip structure in each unit is in the shape of a "U". The surface of the strip structure is then washed with deionized water and dried at a constant temperature. After drying, it is pressed to make the strip structure completely attached to the polymer substrate. The surface is then smoothed and modified to obtain the metamaterial sensor sample.

[0105] Example 4:

[0106] Based on Example 3, the distribution of the strip structure is changed to a cross shape.

[0107] The comparative examples are based on Example 3, with multiple sets of comparisons made, and the mass ratios of zinc oxide, graphene, and carbon nanotubes were adjusted as follows:

[0108] Comparative Example 1: The mass ratio of zinc oxide, graphene and carbon nanotubes in the composite film is 10:0:15.

[0109] Comparative Example 2: The mass ratio of zinc oxide, graphene and carbon nanotubes in the composite film is 9.5:1:14.5.

[0110] Comparative Example 3: The mass ratio of zinc oxide, graphene and carbon nanotubes in the composite film is 8.5:3:13.5.

[0111] Comparative Example 4: The mass ratio of zinc oxide, graphene, and carbon nanotubes in the composite film is 8:4:13.

[0112] The sensitivity of the metamaterial sensors prepared in Examples 3 and 4 and Comparative Examples 1 to 4 was verified using the electromagnetic simulation software CST. Figure 6 The results of the sensor resonant frequency shift as a function of the sample refractive index are shown in the graph (where a, b, c, d, e, and f correspond to Examples 3, 4, and the comparative examples, respectively). From Figure 5 It can be seen that the sensor offset maintains a linear relationship with the sample's refractive index. Here, the refractive index sensitivity is defined as S = Δf / Δn, where Δf is the offset and Δn is the change in refractive index. The sensitivity S is... Figure 5 The slope of the linear fitting curve is shown. Calculations show that the sensitivities of the metamaterial sensor in Example 3 at low and high frequency resonances are 214 GHz / RIU and 311 GHz / RIU, respectively, and the sensitivities of the metamaterial sensor in Example 4 at low and high frequency resonances are 210 GHz / RIU and 308 GHz / RIU, respectively. Both metamaterial sensors exhibit high sensitivity.

[0113] Combining the various metamaterial sensors in Examples 3 and 4 and the comparative examples, the sensitivity changes with the graphene content. As the graphene content gradually increases from zero, the sensor sensitivity increases significantly. As the graphene content in the composite material gradually increases, the more contact there is between the graphene particles, the more conductive channels are formed in the composite material, connecting the carbon nanotube film layer 200 and the reinforcing layer 100. This promotes electron transport and reduces the scattering and poor transport of electrons between the reinforcing layer 100 and the carbon nanotube film layer 200. This allows the high projection and absorption capabilities of zinc oxide in the terahertz band to be utilized, and the interaction between zinc oxide and carbon nanotubes enhances its sensitivity to terahertz radiation.

[0114] Once the graphene content reaches a peak, further increases in graphene content will cause the conductive pathways in the composite material to become saturated, slowing down the rate of increase in conductivity. However, the zinc oxide content in the composite material will decrease accordingly, thus reducing its sensitivity to terahertz radiation.

[0115] Based on the excellent electrical, optical, and mechanical properties of carbon nanotubes, and the outstanding electron mobility and optical activity of zinc oxide, and using graphene as a connecting material, this invention successfully solves the incompatibility between carbon nanotubes and zinc oxide. This makes terahertz spectroscopy a highly sensitive molecular detection tool, especially promising for applications in flexible sensors.

[0116] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A flexible terahertz metamaterial sensor, characterized in that, It includes a reinforcement layer, a carbon nanotube thin film layer, and a polymer substrate layer that are sequentially bonded together from top to bottom; The reinforcing layer is composed of a graphene and zinc oxide composite material; The reinforcing layer and the carbon nanotube film layer have the same shape, both being periodically arranged strip structures.

2. The flexible terahertz metamaterial sensor according to claim 1, characterized in that: The thickness of the reinforcing layer is 8–15 μm, the thickness of the carbon nanotube film layer is 4–12 μm, and the thickness of the polymer substrate layer is 20–80 μm.

3. The flexible terahertz metamaterial sensor according to claim 1, characterized in that: The length of the strip structure is 5–9 μm and the width is 2–4 μm.

4. The flexible terahertz metamaterial sensor according to claim 1, characterized in that: The periodically arranged strip structure is divided into several units, each with a length and width of 10–14 μm. Each unit includes two parallel horizontal strip structures and two parallel vertical strip structures.

5. A flexible terahertz metamaterial sensor according to claim 4, characterized in that: The four strip structures within the unit are arranged in a square or cross shape.

6. A method for fabricating a flexible terahertz metamaterial sensor, used to fabricate the flexible terahertz metamaterial sensor according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Ethylene glycol and zinc acetate were added to the aqueous solution of graphene oxide in sequence, and after being mixed evenly, the mixture was reacted at 90℃~110℃ for 20~24h. After cooling to room temperature and washing, the zinc oxide / graphene composite material was obtained. S2. The diluted carbon nanotube solution was used to prepare carbon nanotube films by vacuum filtration. S3. Press the carbon nanotube film onto a glass plate, coat its surface with a zinc oxide / graphene composite material, and then dry it to form a composite film on the glass plate. S4. Remove the composite film from the glass plate and divide it into several strip structures; S5. The strip structure is attached to the polymer substrate according to the arrangement design and pressed together. After surface modification, the sensor is obtained.

7. The method for fabricating a flexible terahertz metamaterial sensor according to claim 6, characterized in that: In step S1, ethylene glycol and graphene oxide aqueous solution are first mixed evenly, then zinc acetate is added, and the mixture is stirred continuously at a constant temperature for 20–24 hours.

8. The method for fabricating a flexible terahertz metamaterial sensor according to claim 6, characterized in that: In the composite film, the mass ratio of zinc oxide, graphene, and carbon nanotubes is 9:2:13-15.

9. The method for fabricating a flexible terahertz metamaterial sensor according to claim 6, characterized in that: The drying temperature of S3 is 60℃~80℃, and the drying time is 2~3h.

10. The method for fabricating a flexible terahertz metamaterial sensor according to claim 6, characterized in that: The polymer substrate is polyimide (PI) with a dielectric constant of 2 to 4.

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