A metasurface unit and array based on a logarithmic spiral structure

Abstract

The application provides a logarithmic spiral structure-based metasurface unit and array, mainly reduces the complexity of the metasurface unit, and improves the absorption rate of multi-polarized incident waves. The application adopts a single-layer metal patch with a logarithmic spiral structure as a top layer of an absorption unit; the top layer of metal with a logarithmic spiral structure realizes a multi-resonance absorption effect, and a large broadband absorption performance can be obtained without using a multi-layer stacking structure; the application simplifies the mechanism and improves the absorption rate of multi-polarized incident waves.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic functional materials and metamaterials technology, and mainly relates to a metasurface unit and array based on a logarithmic spiral structure. Background Technology

[0002] Currently, there are various electromagnetic wave absorbing materials and structures, such as: (1) Traditional absorbing materials (such as carbon-based and ferrite coatings) have stable absorption performance, but they are thick and heavy, which is not conducive to the integration of high-frequency devices. (2) Absorption structures based on frequency-selective surfaces achieve absorption by loading metal patches on a dielectric substrate, but most of them only work at a single frequency point or in a narrow band. (3) Multi-layer stacking or gradient structure to realize multi-resonant unit absorption metasurface can achieve a certain bandwidth extension, but it is usually complicated to process and has a high cost. For example, the spiral stacked structure absorber proposed in patent CN116207514A uses the size reduction and rotation angle change of multiple spiral absorbing layers to stack multi-mode resonance to broaden the absorption bandwidth, but the structure depends on multi-layer stacking, which is complicated to process and has a large thickness; another example is the literature Broadband reflectionless metamaterials with customizable absorption–transmission-integrated performance (Appl. Phys. A123, 530 (2017)) which uses up to twenty layers of metal-dielectric gradient stacking structure to generate multiple resonances through metal-dielectric layers of different sizes to achieve broadband absorption, but such three-dimensional multi-layer structures have a high burden in terms of processing, alignment and cost, and it is difficult to meet the requirements of lightweight and ultra-thin, so there is still room for further optimization; (4) In existing literature on absorbing metasurfaces with curvature variation structures, such as Broadband metasurface absorber based on involute structure and surface plasmon resonance (Opt. Express 33, 26857-26868 (2025)), involute units are the starting point for design. Multimode resonance is achieved and the absorption bandwidth is broadened by exciting multiple localized surface plasmon resonances (LSPR) within the unit. However, multiple involute units of different sizes need to be arranged and combined, and the response to different polarization waves is different. Furthermore, there is still room for improvement in terms of thickness and bandwidth. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, reduce the complexity of the metasurface unit, and improve the absorption rate of multipolar incident waves, this invention provides a metasurface unit and array based on a logarithmic spiral structure.

[0004] The technical solution adopted by the present invention to solve its technical problem is a metasurface unit based on a logarithmic spiral structure, which includes, from top to bottom, a metal patch layer, a dielectric layer and a metal reflective layer; the metal patch layer includes a first spiral arm and a second spiral arm; the first spiral arm is formed by the combination of a first logarithmic spiral curve and a second logarithmic spiral curve. The first logarithmic spiral curve starts at (0,0), and its coordinates are ( satisfy:

[0005] in, The scale factor for the logarithmic spiral; The growth rate of the logarithmic spiral, θ represents the angular parameter of the first logarithmic spiral curve; The second logarithmic spiral curve starts at (0,0), and its coordinates satisfy the following:

[0006] θ is the angular parameter of the second logarithmic spiral curve; e is the natural constant. Connect the starting points of the first logarithmic spiral curve and the second logarithmic spiral curve with a straight line, and connect the ending points of the first logarithmic spiral curve and the second logarithmic spiral curve with a straight line. The resulting closed figure is the first spiral arm. With (0, Using 180 degrees clockwise as the center, rotate the first rotating arm 180 degrees to obtain the second rotating arm.

[0007] Furthermore, .

[0008] Furthermore, the material of the metal patch layer is copper, and the thickness of the metal patch layer is D2; the value of D2 ranges from 0.017mm to 0.035mm.

[0009] Furthermore, the material of the dielectric layer is FR4; the dielectric layer is a square thin plate; the side length of the dielectric layer is P; and the value of P ranges from 26mm to 30mm.

[0010] Furthermore, the metal reflective layer is a complete metal film used to block transmission and ensure complete reflection or absorption; Furthermore, the thickness of the metal reflective layer is D1; ​​D1 ranges from 0.017mm to 0.035mm. A metasurface array based on a logarithmic spiral structure is used, comprising four metasurface units arranged in a 2x2 configuration. The metasurface units in the first row and second column have the same orientation as those in the second row and first column. The metasurface units in the first row and first column have the same orientation as those in the first row and second column after rotating 90 degrees around the center of the dielectric layer. The metasurface units in the second row and second column have the same orientation as those in the first row and first column.

[0011] The beneficial effects of this invention are: Simulation results from CST Studio Suite show that the present invention has an absorption rate greater than 0.8 in the 22.3-32.5GHz range; the maximum absorption peak reaches 0.996; the absorption effect for both polarization waves remains consistent; the overall thickness is very narrow, with the thickness in the example being only 1.47mm, resulting in a significant reduction in weight; and it still maintains an absorption effect of over 0.7 within a bandwidth of 0° to 45° incident angle. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the overall structure of the absorption metasurface of the present invention; Figure 2 A schematic diagram of a logarithmic spiral metal patch with a unit structure; Figure 3 This is a side view of the unit structure; Figure 4 This is a schematic diagram of a unit cell arranged in four directions. Figure 5 The simulation shows the absorption rate as a function of frequency. Figure 6 To simulate the absorptivity of 45-degree oblique incidence; Where H is the thickness of the dielectric layer, D1 is the thickness of the metal reflective layer, and D2 is the thickness of the metal patch layer. Detailed Implementation

[0013] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0014] A metasurface unit based on a logarithmic spiral structure comprises, from top to bottom, a metal patch layer, a dielectric layer, and a metal reflective layer; The metal patch layer includes a first spiral arm and a second spiral arm; The first spiral arm is formed by the combination of a first logarithmic spiral curve and a second logarithmic spiral curve; The first logarithmic spiral curve starts at (0,0), and its coordinates are ( satisfy:

[0015] in, The scale factor for the logarithmic spiral; The growth rate of the logarithmic spiral, θ represents the angular parameter of the first logarithmic spiral curve; in ; The second logarithmic spiral curve starts at (0,0), and its coordinates satisfy the following:

[0016] θ represents the angular parameter of the second logarithmic spiral curve; Connect the starting points of the first logarithmic spiral curve and the second logarithmic spiral curve with a straight line, and connect the ending points of the first logarithmic spiral curve and the second logarithmic spiral curve with a straight line. The resulting closed figure is the first spiral arm. With (0, Using 180 degrees clockwise as the center, rotate the first spiral arm 180 degrees to obtain the second spiral arm; The material of the metal patch layer is copper, and the thickness of the metal patch layer is D2; the value of D2 ranges from 0.017mm to 0.035mm. The dielectric layer is made of FR4; the dielectric layer is a square thin plate; the side length of the dielectric layer is P; the value of P ranges from 26mm to 30mm; The metal reflective layer is a complete metal film used to block transmission and ensure complete reflection or absorption; The thickness of the metal reflective layer is D1; ​​D1 ranges from 0.017mm to 0.035mm. A metasurface array based on a logarithmic spiral structure is provided, comprising four metasurface units arranged in a 2x2 configuration. The metasurface units in the first row and second column have the same orientation as those in the second row and first column. The orientation of the metasurface units in the first row and first column is the same as that of the metasurface units in the first row and second column after rotating 90 degrees around the center of the dielectric layer. The orientation of the metasurface units in the second row and second column is the same as that of the metasurface units in the first row and first column. The absorption mechanism of this invention is based on the multimode electromagnetic resonance effect caused by the logarithmic spiral geometry, achieving broadband absorption through coupling localized surface plasmon resonance (LSPR) and impedance matching. The logarithmic spiral unit can excite multiple current paths at different frequencies, thus forming multi-resonant absorption; simultaneously, the rotational symmetry design ensures the same absorption response to incident waves of arbitrary linear polarization. Unlike existing spiral stacked structures, this scheme relies on the curvature variation within a single-layer plane to generate multi-frequency resonance, rather than depending on the stacking effect between different layer thicknesses, thereby achieving similar or even better broadband absorption performance at thinner thicknesses.

[0017] FR4 dielectric was selected as the intermediate dielectric layer. The thickness H is 1.47 mm; A copper sheet with a thickness of D1 is used as the metal base plate; The top layer of the metal pattern is made of copper material with a thickness of D2. The upper part of the metal pattern is mainly formed by two logarithmic spiral curves, starting from (0,0). The logarithmic spiral curves satisfy the following:

[0018] in The other logarithmic spiral curve satisfies the above function. The curve originating at (0,0) is rotated 180 degrees clockwise around the origin. The rotated curve satisfies...

[0019] The lines are connected to form a "half-S" shaped structure. The resulting shape is then rotated 90 degrees clockwise and the two are combined to form the final "S" metal structure. Each unit cycle is 28mm. The period of a unit cell is 56 mm.

[0020] Appendix Figure 1 The diagram shows the overall structure of the unit in this design. The unit mainly consists of a surface metal patch, an intermediate dielectric layer, and a bottom metal backplate. Appendix Figure 2 The metal patch structure of this design is shown; it is a copper sheet with an "S"-shaped graphic pattern. Appendix Figure 3 A side view of the unit is shown, illustrating the thickness of each layer; Appendix Figure 4 This diagram shows the structure of a unit cell consisting of four units arranged in a row. Appendix Figure 5 The graph shows the absorption rate of this design in the 20GHz to 35GHz frequency band. The red line parallel to the horizontal axis represents the absorption rate of this design. The absorption curves intersect at 22.3 GHz and 32.53 GHz, respectively, which yields a bandwidth of 10.33 GHz with an absorptivity greater than 0.8. Appendix Figure 6 The diagram shows a comparison of the absorptivity of this design under oblique and normal incidence. Black and red represent the absorptivity curves under normal and oblique incidence at 45 degrees, respectively. As can be seen from the diagram, the absorption performance under oblique incidence is still excellent. Compared with the absorption frequency under normal incidence, the absorption frequency under oblique incidence undergoes a blue shift, but it still maintains a high bandwidth absorption.

Claims

1. A metasurface unit based on a logarithmic spiral structure, characterized in that: From top to bottom, it includes a metal patch layer, a dielectric layer, and a metal reflective layer; the metal patch layer includes a first spiral arm and a second spiral arm; the first spiral arm is formed by the combination of a first logarithmic spiral curve and a second logarithmic spiral curve; connecting the starting points of the first and second logarithmic spiral curves with a straight line, and connecting the ending points of the first and second logarithmic spiral curves with a straight line, the resulting closed shape is the first spiral arm; with (0, Using ) as the center, rotate the first spiral arm 180 degrees clockwise to obtain the second spiral arm; where The scale factor for the logarithmic spiral; The growth rate of the logarithmic spiral, θ represents the angular parameter of the first logarithmic spiral curve; θ represents the angular parameter of the second logarithmic spiral curve.

2. The metasurface unit based on a logarithmic spiral structure according to claim 1, characterized in that, The first logarithmic spiral curve starts at (0,0), and its coordinates are ( satisfy: ； in, The scale factor for the logarithmic spiral; The growth rate of the logarithmic spiral, θ represents the angular parameter of the first logarithmic spiral curve; The second logarithmic spiral curve starts at (0,0), and its coordinates satisfy the following: ； The scale factor for the logarithmic spiral; The growth rate of the logarithmic spiral; θ represents the angular parameter of the second logarithmic spiral curve.

3. The metasurface unit based on a logarithmic spiral structure according to claim 1, characterized in that, The material of the metal patch layer is copper, and the thickness of the metal patch layer is D2; the value of D2 ranges from 0.017mm to 0.035mm.

4. The metasurface unit based on a logarithmic spiral structure according to claim 1, characterized in that, The dielectric layer is made of FR4; the dielectric layer is a square thin plate; the side length of the dielectric layer is P; the value of P ranges from 26mm to 30mm.

5. A metasurface unit based on a logarithmic spiral structure according to claim 1, characterized in that, The metal reflective layer is a complete metal film used to block transmission and ensure complete reflection or absorption.

6. A metasurface unit based on a logarithmic spiral structure according to claim 1, characterized in that, The thickness of the metal reflective layer is D1; ​​the range of D1 is 0.017mm-0.035mm.

7. A metasurface unit based on a logarithmic spiral structure according to claim 1, characterized in that, 。 8. A metasurface array based on a logarithmic spiral structure, comprising four metasurface units; the four metasurface units are arranged in a 2x2 configuration; wherein the metasurface units in the first row and second column have the same orientation as the metasurface units in the second row and first column; the metasurface units in the first row and first column have the same orientation as the metasurface units in the first row and second column after rotating 90 degrees around the center of the dielectric layer; and the metasurface units in the second row and second column have the same orientation as the metasurface units in the first row and first column.

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