Tunable narrow-band terahertz metamaterial wave absorber based on graphene H-shaped structure

Abstract

The invention relates to the technical field of terahertz metamaterials, and provides a tunable narrow-band terahertz metamaterial wave absorber based on a graphene H-shaped structure. The terahertz wave absorber is of a three-layer composite structure, the bottom layer is a gold film supporting layer, the middle layer is a polyimide medium layer, and the top layer is graphene microstructure units which are periodically arranged and provided with H-shaped slits. The absorption characteristics of the three working frequency bands can be passively regulated and controlled by regulating and controlling geometric structure parameters of the wave absorber; by dynamically adjusting the Fermi level of the graphene, the absorption performance of the three frequency bands can be actively regulated and controlled, and the maximum modulation depth of the absorption rate can reach nearly 90%. The wave absorber with the passive structure regulation and control capability and the active electrical regulation and control capability shows remarkable application potential in the fields of terahertz wave stealth, target detection, imaging and the like.

Description

Technical Field

[0001] This invention relates to the field of terahertz wave technology, specifically to a tunable narrowband terahertz metamaterial absorber with a graphene H-type structure. Background Technology

[0002] Terahertz is a frequency band of electromagnetic radiation with wavelengths between microwaves and infrared radiation, ranging from approximately 0.03 millimeters to 3 millimeters, and energy levels between electrons and photons. Terahertz technology, also known as submillimeter-wave technology, refers to radio frequency technology operating within the terahertz frequency range. Terahertz wavelengths lie between infrared and microwaves, in a blank region of the electromagnetic spectrum, and have broad application potential in materials analysis, imaging, communication, and security inspection.

[0003] Terahertz waves can penetrate many non-conductive materials, such as paper and plastics, without causing damage to samples. Therefore, terahertz technology is an ideal tool in fields such as materials property research and biomedical imaging. Terahertz waves have very low energy and pose no significant harm to the human body, thus offering advantages in terms of human safety. Furthermore, terahertz waves do not produce harmful radiation. Terahertz waves can penetrate obstacles such as clouds and smoke and maintain stable transmission quality even at high speeds. Therefore, terahertz communication technology is widely used in high-speed data transmission, indoor communication, and radar communication.

[0004] Metamaterials are artificial materials possessing properties not found in natural materials, such as negative refractive index, negative permittivity, or negative permeability. They are materials with superior electromagnetic properties, capable of controlling the propagation and reflection of electromagnetic waves through specific structures and shapes, thereby achieving the manipulation and control of electromagnetic waves. The emergence of metamaterials is based on in-depth research into the electromagnetic properties of natural materials, revealing that natural materials cannot achieve complete control over electromagnetic waves. Metamaterials combine multiple different materials through specially designed structures and shapes, resulting in electromagnetic properties that are significantly different from those of individual materials. The electromagnetic properties of metamaterials are typically controlled through parameters of their microstructure and shape. Furthermore, metamaterials possess many unique and superior properties, such as negative refractive index, extraordinary dispersion, and negative impedance, thus finding wide application in electromagnetic wave manipulation, imaging, sensing, and energy conversion. Among these, metamaterials are widely used in optics, microwave, and radio frequency bands.

[0005] Graphene is a two-dimensional material composed of a single layer of carbon atoms arranged in a honeycomb-like pattern. It is one of the thinnest, strongest, and most conductive materials known, possessing many unique physical, chemical, and electronic properties that make it highly promising for applications in science, technology, and industry. Graphene's unique properties stem from its special structure. It is composed of carbon atoms, each forming an equilateral triangle with its three neighboring carbon atoms, creating a hexagonal grid structure. This structure gives graphene extremely high surface area and thermal stability, as well as outstanding performance in chemical, electronic, mechanical, and optical fields.

[0006] The tunability of terahertz devices is crucial, and tunable terahertz metamaterial devices have become the mainstream research in the terahertz field. Currently, terahertz technology has gained a good reputation in fields such as sensing, security detection, communication, and medical imaging, occupying an indispensable position. However, tunable metamaterials are not perfect and still have areas for improvement. For example, most metamaterial devices have limited adjustment ranges, stability issues, and accuracy problems. Therefore, developing low-loss, easily controllable, and high-performance terahertz metamaterial devices has become a key technical problem that urgently needs to be solved in the current terahertz device field, which is of great significance for promoting the application of terahertz technology in dynamic sensing, intelligent filtering, adaptive imaging, and other fields.

[0007] Research on graphene-based terahertz absorbers has made some progress. For example, Mahdi Rahmanshahi et al. proposed a tunable multi-band terahertz absorber based on graphene, which can achieve relatively high absorption in both broadband and narrowband applications. LiMei QI et al. proposed a graphene metamaterial absorber that is independent of broadband and polarization. This absorber has an azimuth-symmetric composite four-ring structure, with the composite ring structure absorbing more than 90% of the bandwidth at 7.1 THz. However, most existing devices can only achieve single-dimensional control (such as temperature control or electrical control only), making it difficult to simultaneously meet core requirements such as wide tunability, high efficiency, wide incident angle, and structural simplicity.

[0008] To address the shortcomings of existing technologies, this invention designs two graphene-based metamaterial terahertz control devices based on different design approaches. The first is a tunable narrowband terahertz metamaterial absorber based on a graphene H-type structure, consisting of a classic three-layer structure: metal-electrolyte-graphene. This graphene structure features internal perforations, enhancing the edge effect within the graphene. The active tunability of this device is investigated by altering the Fermi level of the graphene. The second is a narrowband terahertz filter composed of two layers of parallel graphene strips, located on the upper and lower sides of a thin, uniform dielectric layer. Summary of the Invention

[0009] To address the common technical shortcomings of existing tunable terahertz absorbers, such as limited control dimensions, narrow absorption bandwidth, significant performance degradation at large incident angles, and complex structures, this invention proposes a tunable narrowband terahertz metamaterial absorber based on a graphite H-type structure. This absorber uses graphene as the core functional layer, combined with a metamaterial resonant unit design. By precisely optimizing the composite thin film stacking structure, resonant unit geometric parameters, and electromagnetic coupling mechanism, it fully leverages the continuously tunable conductivity of graphene to achieve wide-range dynamic control of the absorption frequency band and absorption efficiency. This effectively overcomes the performance bottlenecks of traditional tunable absorbers in terms of control flexibility, bandwidth coverage, and angle compatibility.

[0010] To achieve the above and other related objectives, the present invention provides a tunable narrowband terahertz metamaterial absorber based on a graphene H-type structure. The structure is characterized in that: the converter is stacked with three functional layers in sequence along the thickness direction, from top to bottom: a graphene patch layer, a polyimide dielectric layer, and a gold substrate layer. The absorber is composed of a periodic array of metamaterial square structural units with no gaps between adjacent units and a unit periodic side length P = 32 μm.

[0011] The graphene patch layer is a square thin film structure with an H-shaped opening groove in the center of the square. The side length of the square is L=28μm, and the thickness of the graphene patch layer is 0μm.

[0012] The H-shaped opening groove consists of a pair of parallel transverse rectangular grooves and a longitudinal connecting groove connecting the centers of the pair of transverse rectangular grooves. The H-shaped opening groove is mirror-symmetrically distributed with respect to both the horizontal and vertical center lines of the graphene film layer. The transverse rectangular grooves have a length L1 = 20 μm and a width w = 4 μm; the longitudinal connecting groove has a length L2 = 10 μm and a width m = 4 μm.

[0013] The polyimide dielectric layer has a thickness h2 = 50 μm and a loss tangent tanδ of 0.0027.

[0014] The thickness of the metal base plate is h1=0.2μm, and the material of the metal base layer is gold.

[0015] Full-wave electromagnetic simulation was performed using the finite element method with CST Microwave Studio 2022 electromagnetic simulation software. A frequency domain solver was used during the simulation, and a tetrahedral adaptive mesh was employed. Unit cell boundary conditions were applied in the x and y directions, and open boundary conditions were applied in the z direction. The S-parameters obtained from the simulation can be used to calculate the absorber's absorption rate and bandwidth.

[0016] As described above, a tunable narrowband terahertz metamaterial absorber based on a graphene H-type structure is proposed. Its key feature is the active tunability achieved through independent electronic control of the graphene Fermi level. When the graphene Fermi level changes from 0.1 eV to 0.8 eV, the first absorption band exhibits a maximum absorption of 91.08% at a Fermi level of 0.4 eV. At a Fermi level of 0.8 eV, the maximum absorption rate reaches 97.53%. The corresponding maximum absorption rate increases from 10.77% to 83.65%, and the 3dB bandwidth also increases from 0.46 THz to 0.61 THz, with a blue shift in the absorption peak position. This is mainly due to the increased carrier concentration in graphene caused by the increase in the Fermi level, leading to an increase in the absorption rate of terahertz waves and a corresponding increase in the absorption bandwidth. It can be widely used in terahertz imaging, intelligent stealth and adjustable filtering, providing a high-efficiency and stable integrated absorbing solution for terahertz systems. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0018] Figure 1 This is a three-dimensional diagram and a side view of a tunable narrowband terahertz metamaterial absorber structural unit based on a graphene H-type structure according to the present invention.

[0019] Figure 2 This is a top view of a tunable narrowband terahertz metamaterial absorber structural unit based on a graphene H-type structure according to the present invention.

[0020] Figure 3 This invention relates to a tunable narrowband terahertz metamaterial absorber based on a graphene H-type structure, showing the absorption rate curve when graphene is in a metallic state at 0 eV. Detailed Implementation

[0021] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0022] Please see Figure 1 and Figure 2As shown, this invention provides a tunable narrowband terahertz metamaterial absorber based on a graphene H-type structure. The absorber is composed of several metamaterial square structural units arranged periodically, with no gaps between adjacent metamaterial square periodic structural units. Each metamaterial square structural unit consists of three layers from top to bottom: a graphene patch layer, a polyimide dielectric layer, and a gold substrate layer, with a unit periodic side length P = 32 μm.

[0023] The graphene patch layer is a square thin film structure with an H-shaped opening groove in the center of the square. The side length of the square is L=28μm, and the thickness of the graphene patch layer is 0μm.

[0024] The H-shaped opening groove consists of a pair of parallel horizontal rectangular grooves and a vertical connecting groove connecting the centers of the pair of horizontal rectangular grooves. The H-shaped opening groove is mirror-symmetrically distributed with respect to both the horizontal and vertical center lines of the graphene film layer. The horizontal rectangular grooves have a length L1 = 20 μm and a width w = 4 μm; the vertical connecting groove has a length L2 = 10 μm and a width m = 4 μm.

[0025] The polyimide dielectric layer has a thickness h2 = 50 μm and a loss tangent tanδ of 0.0027.

[0026] The thickness of the metal base plate is h1=0.2μm, and the material of the metal base layer is gold.

[0027] Graphene is composed of a single layer of carbon atoms arranged in a specific manner, and its surface conductivity is... It can be described by the Kubo model, including the in-band portion. and inter-band portion ,Right now

[0028]

[0029]

[0030]

[0031] The expression for the function H(x) is:

[0032]

[0033] w is the angular frequency of the incident terahertz wave, e is the charge of the electron, and K B Here, is Boltzmann's constant, h is the reduced Planck constant, T is temperature, τ is relaxation time, and E is... f This refers to the Fermi level of graphene. In the simulation model, the graphene thickness is set to 1 nm, the relative temperature T = 300 K, and the relaxation time τ = 0.1 ps. By changing the value of the Fermi level of graphene, the conductivity of graphene is adjusted, thereby simulating its tuning function.

[0034] Absorption rate is an important parameter reflecting the absorption performance of a device. The formula for calculating the absorption rate is:

[0035]

[0036] Among them, S 11 and S 21 These are the reflection and transmission coefficients, respectively, generated by the incident terahertz wave on the device surface. Because the thickness of the metal substrate is much greater than the skin depth of the incident terahertz wave propagating in the medium, the transmission coefficient S of this device... 21 The absorption rate is almost zero; the formula for absorption rate can be simplified as follows:

[0037] Please refer to Figure 3 As shown, after a terahertz wave is incident perpendicularly on the surface, three discrete perfect absorption peaks are excited in the 0.1-5 THz frequency band. An absorption peak with an absorptivity of A1 = 96.89% is obtained at the resonant point f1 = 0.755 THz; an absorption peak with an absorptivity of A2 = 94.78% is obtained at the resonant point f2 = 2.405 THz; and an absorption peak with an absorptivity of A3 = 98.05% is obtained at the resonant point f3 = 4.06 THz. Electromagnetic simulation results show that three high absorption peaks are excited across the entire 0.1-5 THz frequency band.

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Those skilled in the art will recognize that the present invention can be modified and varied in many ways. Several improvements and modifications can be made without departing from the original inventive technology, and all such modifications should be included within the scope of protection of the present invention.

Claims

1. A tunable narrowband terahertz metamaterial absorber based on a graphene H-type structure, comprising several metamaterial square structural units arranged in a periodic array with no gaps between the units. Each metamaterial square structural unit consists of three layers from top to bottom: a graphene patch layer, a polyimide dielectric layer, and a gold substrate layer. The periodic side length of the structural unit is P = 32 μm.

2. The tunable narrowband terahertz metamaterial absorber based on a graphene H-type structure as described in claim 1, characterized in that: The graphene patch layer is a square thin film structure, with its geometric center coinciding with the center of the underlying dielectric substrate. The periodic side length of the graphene patch is L = 28 μm. An H-shaped opening is formed in the center of the graphene patch layer. This cavity consists of a pair of parallel transverse rectangular slots and a longitudinal connecting slot connecting the centers of the pair of transverse rectangular slots. The H-shaped opening is mirror-symmetrically distributed with respect to both the horizontal and vertical center lines of the graphene film layer. The transverse rectangular slots have a length L1 = 20 μm and a width w = 4 μm; the longitudinal connecting slot has a length L2 = 10 μm and a width m = 4 μm.

3. The tunable narrowband terahertz metamaterial absorber based on a graphene H-type structure as described in claim 2, characterized in that: The polyimide dielectric layer has a thickness h2 = 50 μm and a loss tangent tanδ of 0.0027.

4. The tunable narrowband terahertz metamaterial absorber based on a graphene H-type structure as described in claim 3, characterized in that: The thickness of the metal base plate is h1=0.2μm, and the material of the metal base layer is gold.

5. The tunable narrowband terahertz metamaterial absorber with a graphene H-type structure as described in any of the preceding claims, characterized in that: By dynamically controlling the Fermi level of the graphene patch layer, continuous active tuning of the absorber's absorptivity at its resonant frequency can be achieved. When the graphene Fermi level changes from 0.1 eV to 0.9 eV, the absorptivity modulation depth at at least one resonant frequency can reach over 90%. This absorber, which combines passive structural control with active electrical control capabilities, shows significant application potential in terahertz stealth, target detection, and imaging.

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