A cross-shaped broadband metamaterial absorber

Abstract

This invention discloses a broadband metamaterial absorber based on a swastika shape, comprising multiple absorbing units, each including a reflective layer; a dielectric substrate disposed on the reflective layer; and an ITO thin film resonant layer disposed on the dielectric substrate. The resonant layer has a cross-shaped structure. First extensions extend from the four ends of the resonant layer, making it swastika-shaped. Second extensions extend perpendicularly from the four first extensions, and the first and second extensions connect to form a corner structure. The circuit resonance in this invention is stable. When the surface impedance matches the free-space impedance within a wide bandwidth, electromagnetic waves of different frequencies can effectively enter the absorber and be absorbed, achieving broadband absorption. The addition of a corner structure to the resonant layer not only increases the length of the current path, thereby increasing the equivalent inductance, but also increases the propagation path length of electromagnetic waves within the metamaterial, thus broadening the absorption bandwidth.

Description

Technical Field

[0001] This utility model relates to a metamaterial absorber, and more particularly to a broadband metamaterial absorber based on a swastika shape. Background Technology

[0002] With the development of modern technology, electromagnetic interference and radiation problems are becoming increasingly serious. Absorbing materials can effectively reduce electromagnetic waves. Currently, common electromagnetic wave absorbing materials focus on the modification and design of absorbing agents, a process that is complex, time-consuming, and difficult to guarantee batch-to-batch stability. In practical applications, problems arise such as easy peeling of absorbing coatings, difficult and thick processing of absorbing honeycomb materials, and heavy absorbing prepregs. Absorbing metamaterials, however, not only avoid these defects but also achieve thin and lightweight characteristics, reducing weight and thickness while meeting absorption performance requirements.

[0003] The main way traditional microwave-absorbing metamaterials achieve their absorption function is by utilizing the electromagnetic resonance phenomenon generated by the metallic structure. Specifically, when an electromagnetic wave arrives, electrons within the metallic structure are driven by the electric field and begin to oscillate. The directional movement of these electrons creates an electric current. This current generates a magnetic field, which interacts with the originally incident electromagnetic wave. This interaction causes the metallic structure to absorb or scatter electromagnetic waves of certain frequencies, thus processing the electromagnetic waves. Absorbing electromagnetic waves is the key to the microwave absorber's function.

[0004] However, the electromagnetic resonance of this metallic structure is extremely sensitive to frequency changes and is highly unstable. This means that when the frequency of the electromagnetic wave changes slightly, the electromagnetic response of the metallic structure will change significantly. Its surface impedance can only match the free-space impedance within an extremely narrow frequency band near the resonant frequency. Due to the extremely narrow matching frequency band, the absorption bandwidth of traditional metamaterial absorbers is very narrow, limiting their practical applications. Utility Model Content

[0005] The purpose of this invention is to overcome the shortcomings of the prior art by providing a broadband metamaterial absorber based on a swastika shape, which has the advantages of thin thickness, wide absorption bandwidth, and easy control.

[0006] To achieve the above objectives, the technical solution adopted by this utility model is: a broadband metamaterial absorber based on a swastika shape, comprising multiple absorbing unit cells, wherein the absorbing unit cells include:

[0007] Reflective layer;

[0008] A dielectric substrate is disposed on the reflective layer;

[0009] A resonant layer is disposed on the dielectric substrate. The resonant layer is made of ITO thin film and has a cross-shaped structure.

[0010] The first extension extends from the four ends of the resonant layer, making the resonant layer swastika-shaped.

[0011] The second extension extends vertically from the four first extensions, and the four second extensions are arranged in an array with the center of the resonant layer as the center; wherein the first extension and the second extension are connected to form a corner structure.

[0012] Furthermore, the reflective layer is made of metal.

[0013] Furthermore, the dielectric substrate is made of polycarbonate (PC), polyimide (PA), polytetrafluoroethylene (PTFE), or epoxy resin (ER).

[0014] Furthermore, the thickness of this absorber is 2mm to 3mm.

[0015] Furthermore, the width of the first extension and the length of the second extension are the same, both being 2.99~3.04mm.

[0016] Furthermore, the width of the second extension is 2.3 to 2.55 mm.

[0017] Furthermore, the first extension and the second extension are rectangular in shape.

[0018] Due to the application of the above technical solution, this utility model has the following advantages compared with the prior art:

[0019] This invention relates to a swastika-shaped broadband metamaterial absorber. The circuit resonant composed of a resonant layer, a dielectric substrate, and a reflective layer has relatively fixed circuit parameters. The circuit resonance is relatively stable relative to frequency changes. This stability allows its surface impedance to match the free space impedance over a wide frequency band near the resonant frequency. In this way, electromagnetic waves of different frequencies can effectively enter the absorber and be absorbed, thus achieving broadband absorption and overcoming the narrow bandwidth of traditional metamaterial absorbers.

[0020] Secondly, the resonant layer has a corner structure composed of a first extension and a second extension. The corner structure increases the length of the current path, thereby increasing the equivalent inductance. The relative position change between the corner structures also affects the equivalent capacitance. The coordinated adjustment of the two helps to broaden the absorption bandwidth. Furthermore, the presence of the corner increases the propagation path length of electromagnetic waves inside the metamaterial, thereby broadening the absorption bandwidth. Attached Figure Description

[0021] The technical solution of this utility model will be further described below with reference to the accompanying drawings:

[0022] Figure 1This is a schematic diagram of the structure of an embodiment of the present utility model;

[0023] Figure 2 This is a schematic diagram of the structure of the absorbing unit in one embodiment of the present invention;

[0024] Figure 3 for Figure 2 Top view;

[0025] Figure 4 for Figure 3 A schematic diagram of the structure with length markers A, L1, and L2;

[0026] Figure 5 This is a comparison of simulation curves of the absorption rate of different patterned resonant layers in the embodiments of this utility model;

[0027] Figure 6 This is a comparison of the simulated absorption rate curves for varying geometric parameters A of the resonant layer in this embodiment of the invention.

[0028] Figure 7 This is a comparison of the simulated absorption rate curves for varying the geometric parameter L2 of the resonant layer in this embodiment of the invention.

[0029] Figure 8 This is a comparison of the absorption rate simulation curves for varying sheet resistance R of the resonant layer in this embodiment of the present invention.

[0030] Figure 9 This is a comparison chart of the simulation curves of the absorption rate of different dielectric layer materials selected in the embodiments of this utility model;

[0031] Wherein: 1. Absorbing unit; 10. Reflective layer; 11. Dielectric substrate; 12. Resonant layer; 13. First extension; 14. Second extension. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0033] This invention provides a broadband metamaterial absorber based on a swastika shape to solve the problem of narrow absorption bandwidth in existing metamaterial absorbers.

[0034] For ease of understanding, the specific processes in the embodiments of this application are described below. Please refer to [link / reference]. Figures 1 to 3This application discloses a broadband metamaterial absorber based on a swastika shape, comprising multiple absorbing units 1 arranged in a grid array. Each absorbing unit 1 includes a reflective layer 10, a dielectric substrate 11, a resonant layer 12, a first extension 13, and a second extension 14. The dielectric substrate 11 is disposed on the reflective layer 10. The resonant layer 12 is made of ITO thin film and is disposed on the dielectric substrate 11, and has a cross-shaped structure. The first extension 13 extends from the four ends of the resonant layer 12, making the resonant layer 12 swastika-shaped. The second extension 14 extends from the vertical direction of the four first extensions 13, and the four second extensions 14 are arranged in an array with the center of the resonant layer 12 as the center. The first extension 13 and the second extension 14 are connected to form a corner structure.

[0035] This invention relates to a broadband metamaterial absorber based on a swastika shape. Since the resonant layer 12 is an ITO thin film, which is a resistive film—a material with certain resistance characteristics—it can cause electromagnetic wave loss. When a resistive film structure is used, electromagnetic resonance is transformed into circuit resonance between the resonant layer 12, the dielectric substrate 11, and the reflective layer 10.

[0036] Circuit resonance is similar to the resonance phenomenon that occurs at a specific frequency in a circuit system composed of resistors, capacitors, and inductors. In this structure, the resonant layer 12 is equivalent to the resistor in the circuit, the dielectric substrate 11 can be considered as a dielectric with a certain dielectric constant, similar to the function of a capacitor, while the reflective layer 10 can act like an inductor because metals have certain response characteristics to magnetic fields.

[0037] The system consisting of resonant layer 12, dielectric substrate 11, and reflective layer 10 has relatively fixed circuit parameters, making the circuit resonance relatively stable with respect to frequency changes, unlike the electromagnetic resonance of metallic structures which is sensitive to frequency variations. This stability allows its surface impedance to match the free-space impedance over a wide frequency band near the resonant frequency. When the surface impedance matches the free-space impedance over a wide bandwidth, electromagnetic waves of different frequencies can effectively enter the absorber and be absorbed, thus achieving broadband absorption and overcoming the narrow bandwidth limitation of traditional metamaterial absorbers.

[0038] This absorber ultimately achieved an absorption performance with an absorptivity A(w) greater than 90% in the frequency range of 8.46~31.68 GHz.

[0039] Furthermore, both the first extension 13 and the second extension 14 are rectangular in shape, thus forming a vertical corner structure between the first extension 13 and the second extension 14.

[0040] Furthermore, the width of the first extension 13 and the length of the second extension 14 are the same, both being 2.99~3.04 mm.

[0041] Furthermore, the width of the second extension 14 is 2.3~2.55 mm.

[0042] Furthermore, in this embodiment, the resonant layer 12, after the first extension 13 is attached, forms a swastika pattern, which has the following advantages: ① The swastika pattern is composed of multiple regular geometric branches, and these branches have different sizes and relative positions, which can excite multiple electromagnetic resonance modes at different frequencies. Different resonance modes correspond to specific frequency ranges, and the superposition of multiple resonance modes enables the metamaterial to absorb electromagnetic waves in a wider frequency band.

[0043] ② The unique structure of the swastika pattern results in strong near-field coupling between the branches. This coupling allows previously isolated resonant modes to interact, generating new hybrid resonant modes. These hybrid modes can further broaden the absorption bandwidth of the metamaterial while enhancing the absorption intensity at specific frequencies.

[0044] ③ The swastika pattern possesses a certain degree of symmetry, which endows the metamaterial with relatively consistent response characteristics to electromagnetic waves with different polarization modes, i.e., polarization insensitivity. In actual electromagnetic environments, the polarization direction of electromagnetic waves is often complex and variable. The swastika metamaterial can maintain good absorption performance for both horizontally and vertically polarized electromagnetic waves, improving the applicability of the metamaterial in complex electromagnetic environments.

[0045] When the resonant layer 12 has a corner structure formed by the connection of the first extension 13 and the second extension 14, the following advantages can be achieved:

[0046] 1) Corner structures increase the length of the current path, thereby increasing the equivalent inductance; at the same time, the relative position changes between corner structures also affect the equivalent capacitance, and the coordinated adjustment of the two helps to broaden the absorption bandwidth.

[0047] 2) The presence of corners increases the propagation path length of electromagnetic waves inside metamaterials. When electromagnetic waves encounter corners, they undergo multiple reflections and scatterings, giving them more opportunities to interact with the lossy medium in the metamaterial, converting electromagnetic energy into heat or other forms of energy, thus achieving absorption at multiple frequency points and broadening the absorption bandwidth.

[0048] See Figure 5To demonstrate the effectiveness of this swastika-shaped absorber, several embodiments are described below. In the first embodiment, the resonant layer 12 is designed as a rectangular structure, with an absorption rate of only 66%, which is unsuitable for practical applications. In the second embodiment, the resonant layer is designed as the most common cross structure, which significantly improves the absorption rate, but the absorption bandwidth above 90% is relatively narrow, at 2.774 GHz (21.494~24.268 GHz). In the third embodiment, a first extension is added to each of the four ends of the cross structure in the second embodiment, making the resonant layer 12 a swastika structure. As can be seen from the figure, the absorption bandwidth is broadened due to the increase in resonant units, reaching an absorption bandwidth above 90% of 15.884 GHz (14.73~30.614 GHz). The absorption rate in the 8-14 GHz band was not improved. In the fourth implementation, based on the swastika structure, a second extension was added to each of its four ends. As a result, the absorption band with an absorption rate of over 90% was extended from 8.46 GHz to 31.678 GHz, achieving an ultra-wide absorption band of 23.218 GHz. The thickness was only 2.235 mm, which has excellent absorption characteristics.

[0049] See Figure 9 Furthermore, to verify the influence of the material selection of the dielectric plate 11 in the intermediate layer of the metamaterial absorber on the absorption rate, four common wave-transmitting materials, polycarbonate (PC), polyimide (PA), polytetrafluoroethylene (PTFE), and epoxy resin (ER), were selected for simulation and the results were compared.

[0050] When PC is selected as the dielectric substrate material, the absorption rate of this metamaterial absorber gradually increases within a certain frequency range (8.46~31.68GHz). Although it decreases in the high-frequency band, it can maintain a relatively high absorption rate in a wide frequency range.

[0051] When PA and ER with high dielectric constants are selected as dielectric substrate materials, the effective absorption bandwidth only starts from 12.716 GHz and 12.488 GHz. From the absorption rate curve, it can be found that the ER material with the highest dielectric constant has the worst absorption effect, with the absorption rate dropping to below 90% from 20.354 GHz, and the narrowest effective absorption bandwidth.

[0052] When using PTFE, which has the lowest dielectric constant, as the dielectric substrate material, the absorption rate at high frequencies (14.236~36.808GHz) is very good. However, considering practical applications, we prefer effective absorption in the 2~18GHz range.

[0053] As shown in Table 1 below, a comprehensive comparison shows that the material selection for the dielectric layer has a clear advantage when using PC. Of course, the selection of the dielectric layer is not limited to these four materials. As long as it is an effective wave-transmitting material of this absorber, it is within the protection scope of this absorber.

[0054] Table 1: Material Parameters of Dielectric Plate

[0055] Dielectric materials Dielectric constant Loss tangent Polycarbonate (PC) 2.9 0.01 Polyimide (PA) 3.5 0.0027 Polytetrafluoroethylene (PTFE) 2.1 0.0002 Epoxy resin (ER) 4 /

[0056] See Figure 4 Furthermore, to evaluate the impact of the values ​​of various parameters of the designed swastika-shaped structure on the absorption rate, a robustness analysis of the structural geometric parameters was performed. Based on the optimal design parameters, a variation of ±10% in geometric parameters such as A, L2, and R was introduced; where A is the width of the first extension 13 and the length of the second extension 14, L2 is the width of the second extension 14, and R is the sheet resistance value of each periodic unit resonant layer.

[0057] Figures 6 to 8 These are comparison graphs of simulated absorption rate curves with parameters A, L2, and R varying by ±10%. Figure 5 Figure 7 It can be seen that when the values ​​of the geometric parameters A and R of the resonant layer structure vary by ±10%, the absorption effect will be significantly reduced. Figure 6 The results show that increasing L2 by 10% yields little difference, but decreasing it by 10% narrows the effective absorption bandwidth. This indicates that due to size sensitivity, the fabrication of the resistive film requires high precision.

[0058] Since systematic geometric parameter errors are unavoidable in actual processing, it is necessary to determine the fluctuation range of each parameter to simulate potential errors in actual processing. After a series of parameter dimensional simulation calculations, the data shown in Table 2 are obtained. When parameter A is in the range of 2.99~3.04 mm, parameter L2 is in the range of 2.3~2.55 mm, and parameter R is in the range of 94~104 Ω / □, the absorption performance of the absorber is almost unaffected and almost coincides with the absorption rate curve of the optimal result, fluctuating within an acceptable range. This result proves the stability of the designed structure in practical engineering applications.

[0059] Table 2: Allowable range of variation for some physical parameters of metamaterial absorbers

[0060] parameter Range of values A 2.99-3.04 mm L2 2.3~2.55 mm R 94~104 Ω / □

[0061] To obtain a superior absorber, SolidWorks 2022 was used for modeling, and CST StudioSuite 2022 was used for simulation. The boundary conditions in the x and y directions were set to "unit cell," and the z-direction was set to open boundary, assuming that the electromagnetic wave was incident along the positive z-axis. To obtain the best absorption performance, simulation software was used to scan and optimize the relevant parameters. The optimal values ​​for each parameter of the metamaterial absorber were selected through a series of simulations, as shown in the table below.

[0062] The absorber is composed of periodically arranged unit structures with a side length of P. The thickness of the reflective layer 10 is set to H1, the thickness of the dielectric substrate 11 is set to H2, and the thickness of the resonant layer 12 is set to H3. The dielectric constant of the dielectric substrate 11 is 2.9, and the loss tangent is 0.01. The sheet resistance of each periodic unit resonant layer of the resonant layer 12 is R. A is the width of the first extension 13 and the length of the second extension 14. L1 is the vertical distance from the bottom of each second extension 14 to the bottom of the resonant layer 12. L2 is the width of the second extension 14.

[0063] Table 3: Physical parameters of metamaterial absorbers

[0064] parameter Value A 3 mm L1 13 mm L2 2.4 mm P 20 mm H1 0.2 mm H2 2 mm H3 0.035 mm R 100 Ω / □

[0065] At this time, when electromagnetic waves are incident on the surface of the absorber, the charge carriers in the conductive film will form plasma resonance, generating electromagnetic resonance at different frequencies, thereby achieving broadband absorption.

[0066] In summary, when the surface impedance matches the free space impedance over a wide frequency band, electromagnetic waves of different frequencies can effectively enter the absorber and be absorbed, thus achieving broadband absorption. At the same time, the presence of the resonant layer based on the swastika shape also broadens the absorption bandwidth, overcoming the shortcomings of traditional metamaterial absorbers with very narrow bandwidth and meeting practical application requirements.

[0067] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A broadband metamaterial microwave absorber based on a swastika shape, characterized in that, It is composed of multiple absorbing unit cells (1) distributed together, wherein the absorbing unit cell (1) includes: Reflective layer (10); A dielectric substrate (11) is disposed on the reflective layer (10); A resonant layer (12) is disposed on the dielectric substrate (11). The material of the resonant layer (12) is an ITO thin film, and the resonant layer (12) has a cross structure. The first extension (13) extends from the four ends of the resonant layer (12) respectively, making the resonant layer (12) swastika-shaped; The second extension (14) extends from the vertical direction of the four first extensions (13), and the four second extensions (14) are arranged in an array with the center of the resonant layer (12) as the center; wherein the first extension (13) and the second extension (14) are connected to form a corner structure.

2. The broadband metamaterial absorber based on the swastika shape as described in claim 1, characterized in that: The reflective layer (10) is made of metal.

3. The broadband metamaterial absorber based on the swastika shape as described in claim 1, characterized in that: The dielectric substrate (11) is made of polycarbonate, polyimide, polytetrafluoroethylene, or epoxy resin.

4. The broadband metamaterial absorber based on the swastika shape as described in claim 1, characterized in that: The thickness of this absorber is 2mm to 3mm.

5. The broadband metamaterial absorber based on the swastika shape as described in claim 1, characterized in that: The width of the first extension (13) and the length of the second extension (14) are the same, both being 2.99~3.04 mm.

6. The broadband metamaterial absorber based on the swastika shape as described in claim 1, characterized in that: The width of the second extension (14) is 2.3~2.55 mm.

7. The broadband metamaterial absorber based on the swastika shape as described in claim 1, characterized in that: The first extension (13) and the second extension (14) are both rectangular in shape.

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