A reflective broadband polarization conversion and phase accurate control unit structure metasurface

Abstract

The application discloses a kind of reflective broadband polarization conversion and phase accurate control unit structure metasurface, including several unit structures, each unit structure is square;Unit structure is from top to bottom respectively top metal pattern layer, dielectric layer and bottom metal reflection layer;Wherein, top metal pattern layer includes two metal resonance rings, wherein, internal metal resonance ring is a complete circular ring, and external metal resonance ring is that complete metal circular ring is handled with slot, and is set to two slots, two slots are mutually orthogonal.The application provides a kind of reflective broadband cross-polarization conversion and circular polarization phase adjustable metasurface with simple structure, can realize the greater frequency band coverage to incident electromagnetic wave, with higher bandwidth and precision, can effectively manage two degrees of freedom, and simplifies manufacturing complexity, and expands potential application field.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic metasurface technology, and in particular to a metasurface structure for a reflective broadband polarization conversion and phase precision control unit. Background Technology

[0002] Terahertz waves (THz) have attracted widespread attention due to their excellent maneuverability and penetrating power. As an artificially designed two-dimensional structure, metasurfaces offer significant advantages over traditional multilayer metal structures in electromagnetic wave manipulation, particularly in the terahertz band. Polarization and phase are fundamental properties of electromagnetic waves and play crucial roles in electromagnetic wave manipulation. Polarization describes the oscillation direction of the electromagnetic wave's electric field vector; precise control of polarization is essential for optimizing antenna design and improving imaging resolution. Phase describes the oscillation state of the electromagnetic wave at a specific point; phase control allows for wavefront adjustment, which is used in adaptive optics and holographic wavefront shaping to correct wavefront distortion and precisely guide the beam. Therefore, extending bandwidth in the terahertz band and flexibly controlling the polarization and phase of incident waves are currently among the hot topics in metasurface research.

[0003] Significant progress has been made in electromagnetic metasurfaces in the terahertz band. However, due to the complexity of the current working environment, many multifunctional devices rely on multilayer structures and phase change materials, which increases their complexity and manufacturing challenges. Summary of the Invention

[0004] In view of the aforementioned shortcomings of the prior art, the technical problem to be solved by the present invention is the narrow bandwidth, limited functionality, and complex structure of existing metasurfaces. The present invention provides a reflective broadband polarization conversion and phase precision control unit structure metasurface, offering a simple reflective broadband cross-polarization conversion and circular polarization phase-tunable metasurface. This enables wider frequency coverage of incident electromagnetic waves, higher bandwidth and precision, effective management of two degrees of freedom, simplifies manufacturing complexity, and expands potential application areas.

[0005] To achieve the above objectives, this invention provides a metasurface structure for a broadband polarization conversion and phase precision control unit, comprising several unit structures, each unit structure being square; the unit structures, from top to bottom, consist of a top metal pattern layer, a dielectric layer, and a bottom metal reflective layer; wherein,

[0006] The top metal pattern layer includes two metal resonant rings. The inner metal resonant ring is a complete circular ring, while the outer metal resonant ring is a complete circular ring with slots cut into it. The two slots are orthogonal to each other.

[0007] Furthermore, the two metal resonant rings in the top metal pattern layer and the bottom metal reflective layer are both covered by copper sheets.

[0008] Furthermore, the dielectric layer is made of polytetrafluoroethylene (PTFE) material with a dielectric constant of 2.33, a loss tangent of 0.0012, and a thickness of h = 28 μm.

[0009] Furthermore, the unit size of the unit structure is l = 100 μm.

[0010] Furthermore, the inner radius of the inner metal resonant ring of the top metal pattern layer is r4 = 5 μm, the outer radius is r3 = 10 μm, the inner radius of the outer metal resonant ring is r2 = 20 μm, and the outer radius is r1 = 45 μm; the opening angle of the two slots of the outer metal resonant ring is β = 60°, and the included angle between the center lines of the two slots is β1 = 90°.

[0011] Furthermore, the dielectric layer and the bottom metal reflective layer are set to be square in shape, and the side length of the dielectric layer and the bottom metal reflective layer is the same as the unit size of the unit structure.

[0012] Furthermore, by rotating the two metal resonant rings of the top metal pattern layer counterclockwise by α, a uniform phase change of the reflected wave is achieved, with a corresponding phase change of 2α.

[0013] Furthermore, the conductivity is 5.96*10 7 S / m, where the copper sheet thickness of the top metal pattern layer is d1 = 0.1 μm, and the copper sheet thickness of the bottom metal reflective layer is d2 = 1 μm.

[0014] Furthermore, the bandwidth of the metasurface was set to 0.7044 to 2.0859 Thz, with a relative bandwidth of 99%.

[0015] Furthermore, by controlling the incident polarization angle, the incident angle is made symmetrical about the y=x axis, and the modulation accuracy of the polarization angle can reach within 1°; when linearly polarized incident, the incident angle is symmetrical about the y=x axis.

[0016] Technical effect

[0017] This invention discloses a metasurface structure for broadband polarization conversion and precise phase control. It separates a top metal pattern layer and a bottom metal reflective layer through an intermediate dielectric layer. A resonant structure is formed by a slotted ring and an unslotted ring in the top metal pattern layer. The bottom metal reflective layer reflects the incident wave, ultimately creating a three-layered metasurface with high reflectivity and high bandwidth. This metasurface can effectively convert between incident x-polarized and y-polarized waves in the range of 0.7044 to 2.0859 Thz. Within this frequency band, the metasurface exhibits a reflectivity higher than 0.7 and a relative bandwidth of 99%. For linearly polarized incident waves, the metasurface can modulate different polarization angles about the y=x axis with a modulation accuracy of 1°. Simultaneously, it can convert between incident left-handed and right-handed circularly polarized waves within this bandwidth. Furthermore, by rotating the angle of the top pattern layer, full-phase control between 0 and 2π is achieved. Based on the reflection phase of the metasurface at 1.3 Thz, an array arrangement is implemented, successfully achieving both 2-bit and 4-bit encoding. Simultaneously, by arranging the focusing array using phases at the same frequency, focusing was achieved not only at 1.3 Thz, but also at 0.75 Thz and 1.8 Thz using the same array. This demonstrates that the metasurface not only exhibits uniform phase variation but also possesses broadband characteristics. The metasurface proposed in this invention integrates the above-mentioned functions into a single-unit structure metasurface.

[0018] Meanwhile, this invention has the advantages of simple structure, small size, high bandwidth, high polarization conversion rate, and easy fabrication. It also provides a new approach to polarization and phase manipulation in the terahertz band and can be applied to ultra-wideband anomalous refraction, focusing, orbital angular momentum, imaging, holography, communication and other fields, with broad application prospects.

[0019] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0020] Figure 1 These are top and right views of a metasurface structure for a reflective broadband polarization conversion and phase precision control unit according to a preferred embodiment of the present invention.

[0021] Figure 2 This is a reflection coefficient diagram of a metasurface of a reflective broadband polarization conversion and phase precision control unit structure according to a preferred embodiment of the present invention when the incident radiation is linearly polarized;

[0022] Figure 3 This is a reflection phase diagram of a metasurface of a reflection broadband polarization conversion and phase precision control unit structure according to a preferred embodiment of the present invention when the incident radiation is linearly polarized;

[0023] Figure 4 (a) is a schematic diagram of the operation of the x and y components of a metasurface of a reflective broadband polarization conversion and phase precision control unit structure metasurface of a preferred embodiment of the present invention when linearly polarized incident light passes through two orthogonal slots.

[0024] Figure 4 (b) is a schematic diagram of an arbitrary linearly polarized incident surface of a metasurface of a reflective broadband polarization conversion and phase precision control unit structure according to a preferred embodiment of the present invention, which is decomposed into x and y components and synthesized after orthogonal grooving.

[0025] Figure 5 The preferred embodiment of the present invention shows the transformation spectrum of a metasurface of a reflective broadband polarization conversion and phase precision control unit structure when the polarization angles are 15°, 30°, 60° and 75° respectively.

[0026] Figure 6 This is a diagram showing the relationship between the rotation angle α and the conversion angle θ of a metasurface in a preferred embodiment of the present invention, where the metasurface is maintained under x-polarized incident light.

[0027] Figure 7 This is a reflection coefficient diagram of a metasurface of a reflective broadband polarization conversion and phase precision control unit structure according to a preferred embodiment of the present invention when the incident radiation is circularly polarized and the top metal pattern layer is rotated.

[0028] Figure 8 This is a preferred embodiment of the present invention, showing the reflection phase diagram of a metasurface of a reflective broadband polarization conversion and phase precision control unit structure when the incident radiation is circularly polarized and the top metal pattern layer is rotated.

[0029] Figure 9 (a) is a diagram of a focusing array structure of a metasurface for a reflective broadband polarization conversion and phase precision control unit according to the circular polarization reflection phase arrangement at 1.3Thz, according to a preferred embodiment of the present invention.

[0030] Figure 9 (b) is a simulation diagram of a focusing array arranged according to the 1.3Thz phase when the incident wave of the metasurface of a reflective broadband polarization conversion and phase precision control unit structure is 1.3Thz, according to a preferred embodiment of the present invention.

[0031] Figure 9 (c) is a simulation diagram of a focusing array arranged according to a 1.3Thz phase when the incident wave of the metasurface of a reflective broadband polarization conversion and phase precision control unit structure is 0.75Thz.

[0032] Figure 9 (d) is a simulation diagram of a focusing array arranged according to a 1.3Thz phase when the incident wave of the metasurface of a reflective broadband polarization conversion and phase precision control unit structure is 1.8Thz, according to a preferred embodiment of the present invention.

[0033] Figure 10 This is a schematic diagram of the array structure and far-field effect of a metasurface for implementing 2-bit encoding in a preferred embodiment of the present invention, which is a structure for a reflective broadband polarization conversion and phase precision control unit.

[0034] Figure 11 This is a schematic diagram of the array structure and far-field effect of a metasurface implementing 4-bit encoding for a reflective broadband polarization conversion and phase precision control unit structure according to a preferred embodiment of the present invention. Detailed Implementation

[0035] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0036] In the following description, specific details, such as particular internal procedures and techniques, are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will appreciate that the invention may be practiced in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of the invention with unnecessary detail.

[0037] like Figure 1 As shown, this invention provides a metasurface structure for a broadband polarization conversion and phase precision control unit, which is a three-layer structure. The metasurface includes several unit structures, each of which is square; from top to bottom, the unit structures are a top metal pattern layer 1, a dielectric layer 2, and a bottom metal reflective layer 3; wherein,

[0038] The top metal pattern layer includes two metal resonant rings. The inner metal resonant ring 5 is a complete circular ring, while the outer metal resonant ring 4 is a complete circular ring with slots. The two slots are orthogonal to each other. The interaction of these two orthogonal slots gives the metasurface the ability to convert the polarization of any incident wave.

[0039] The inner radius of the inner metal resonant ring in the top metal pattern layer is r4 = 5 μm, and the outer radius is r3 = 10 μm. The inner radius of the outer metal resonant ring is r2 = 20 μm, and the outer radius is r1 = 45 μm. The opening angle of the two slots in the outer metal resonant ring is β = 60°, and the angle between the center lines of the two slots is β1 = 90°, meaning the two slots are orthogonal to each other. Both metal resonant rings in the top metal pattern layer and the bottom metal reflective layer are covered by copper sheets with a conductivity of 5.96 × 10⁻⁶. 7 S / m, where the copper sheet thickness of the top metal pattern layer is d1 = 0.1 μm, and the copper sheet thickness of the bottom metal reflective layer is d2 = 1 μm.

[0040] In this embodiment, the dielectric layer is made of polytetrafluoroethylene (Rogers RT5870) material, with a dielectric constant of 2.33, a loss tangent of 0.0012, and a thickness of h = 28 μm. Due to the transparency and low loss of polytetrafluoroethylene in the terahertz band, this dielectric is used to separate the top metal pattern layer and the bottom metal reflective layer.

[0041] In addition, the unit cell size of the unit cell structure is l = 100 μm. The dielectric layer and the bottom metal reflective layer are square in shape, and the side lengths of the dielectric layer and the bottom metal reflective layer are the same as the unit cell size of the unit cell structure.

[0042] Furthermore, by rotating the two metal resonant rings of the top metal pattern layer counterclockwise by α, a uniform phase change of the reflected wave is achieved, with a corresponding phase change of 2α. Under different rotation angles α, the reflection phase of the metasurface undergoes a uniform change, with a corresponding phase change of 2α. The array arrangement based on the characteristics of the reflection phase is used for focusing and 2-bit and 4-bit encoding applications.

[0043] To verify the performance of the reflective broadband polarization conversion and phase precision control unit structure metasurface of this embodiment, this embodiment employs the Finite-Domain Integral (FDTD) method to model and analyze the metasurface parameters in CST Microwave Studio software. During the simulation, to simulate an infinite element structure, the structure is arranged in a cell-like manner along the x and y axes to form a periodic arrangement. Simultaneously, a Floquet port excitation is set in the z direction to simulate electromagnetic wave propagation.

[0044] This invention discloses a simple reflective broadband polarization conversion and phase precision control unit structure metasurface. By slotting the outer metal resonant ring in the top metal pattern layer, and in this example, openings are made along the x-axis and y-axis respectively. Simulation experiments show that these two orthogonal openings can perform polarization conversion on the incident electromagnetic wave.

[0045] Simulation results were obtained using the CST Microwave Studio simulation software and the Finite-Domain Time-Domain Integration (FDTD) method. r yx and r xy For the cross-polarization components of x-polarized and y-polarized waves, r is used. xx r yy This represents the common polarization component of the x-polarized wave and the y-polarized wave. For example... Figure 2 and Figure 3 As shown, the results indicate that when x- and y-polarized waves are incident on the metasurface, the reflection coefficient r xy (r yx ) and r xx (r yy The amplitude and phase of r are equal, therefore r xy =r yx And r yy =r xx Within the frequency range of 0.7044–2.0859 THz, |r xy |(|r yx |) Exceeding 0.7, the relative bandwidth is 99.02%. In the frequency range of 0.7466–2.0571 THz, this value exceeds 0.9, with a relative bandwidth of 93.48%. Wherein, the relative bandwidth B... f The calculation formula is:

[0046]

[0047] Among them, f h and f l These refer to the upper and lower frequency limits of the bandwidth, respectively.

[0048] At 1.158 THz, |r xy |(|r yx |) is approximately 0.9869; while |r xx |(|r yy The value is only about 0.0018. These results indicate that the metasurface possesses broadband characteristics and high conversion efficiency.

[0049] Specifically, such as Figure 4 As shown in (a), when the electric field of the incident linearly polarized wave is decomposed into two orthogonal components along the x-axis and y-axis, the reflected wave is transformed by the orthogonal slots in the structure, causing the x-component to be rotated 90° clockwise and the y-component to be rotated 90° counterclockwise. Due to this orthogonal transformation, the x-component of the incident wave is transformed into the y-component of the reflected wave, and vice versa, thus creating a symmetrical relationship between the reflected and incident waves. More importantly, there is an inverse relationship between the polarization angles of the incident and reflected waves, i.e., as shown in (a). Figure 4 As shown in (b), the polarization axis of the reflected wave is symmetrical to the direction of the incident wave about the y = x axis. When the incident wave is linearly polarized, the polarization direction of the reflected wave also changes symmetrically along the y = x axis. Furthermore, in some cases, such as when the polarization angle is π / 4 or 3π / 4, the cross-polarization component of the reflected wave disappears, and only the common polarization component exists, which further strengthens the symmetry between the incident and reflected waves. Therefore, this design of the structure achieves the symmetry between the incident and reflected waves along the y = x axis.

[0050] To verify the output under different incident polarization angles, this embodiment used linearly polarized waves with polarization angles of γ = 15°, 30°, 60°, and 75°. According to the design principle, the polarization angles should be converted to 75°, 60°, 30°, and 15° respectively. The calculated spectrum is as follows: Figure 5 As shown. During online polarization, the rotation angle and polarization angle have the same numerical value. To more intuitively demonstrate the metasurface's ability to control polarization, this embodiment selects a frequency of 1.1580 THz, which has the highest conversion efficiency within the operating frequency band, to demonstrate the polarization state of the incident and reflected waves. During the verification process, this embodiment maintains the incident wave as x-polarized. As... Figure 6 As shown, the metasurface was rotated sequentially by angles α = 0°, 15°, 30°, 44.5°, 45°, 45.5°, 60° and 75°, and then the properties of the reflected waves were observed. Figure 6 The polarization states of the incident and reflected waves are shown, indicating that the transformation angle θ corresponds to -90°, -60°, -30°, -1°, 0°, 1°, 30°, and 60°, respectively. The calculation results are in high agreement with the theoretical analysis. When α = 44.5° and 45.5°, the reflected field can still undergo accurate polarization transformation, with the polarization angle accurately rotated by 1°.

[0051] Simultaneously, when a circularly polarized wave is incident, r is used. lr and r rl For the cross-polarization components of right-handed circular polarization and left-handed circular polarization waves, r is used. rr r ll It represents the common polarization component of the right-hand circularly polarized wave and the left-hand circularly polarized wave.

[0052] Figure 7 Let be the reflection amplitude of the metasurface under circularly polarized incident radiation at different rotation angles α. When the rotation degree α = 0, the amplitude of the circularly polarized incident wave of this invention is the same as that under linearly polarized incident radiation, and the reflection coefficient r rl (r lr ) and r rr (rll The amplitudes of each are equal. Within the frequency range of 0.7044–2.0859 THz, |r rl |(|r lr The relative bandwidth exceeds 0.7, reaching 99.02%. Within the frequency range of 0.7466–2.0571 THz, this value exceeds 0.9, with a relative bandwidth of 93.48%. Rotating the two metal resonant rings of the top metal pattern layer counterclockwise by α reveals that, assuming the amplitude of the circular polarization of the reflection does not change significantly with the rotation angle, the reflection phase undergoes a uniform change, with a change amplitude of approximately 2α. The specific reflection phase is as follows... Figure 8 As shown, Figure 8 (a) and (b) represent the phase spectra of the reflected phases under right-hand circularly polarized (RCP) and left-hand circularly polarized (LCP) incident conditions, respectively. Figure 8 (c) and (d) represent the phase spectrum diagrams showing the relationship between the rotation angle α and the frequency.

[0053] like Figure 9 As shown in (a), this is a schematic diagram of an array structure arranged using the reflection phase at 1.3Thz, based on the change in the circularly polarized phase of the reflection. A focusing array structure with 24*24 elements was arranged at 1.3Thz using CST software. The formula for calculating the phase of each element is as follows:

[0054]

[0055] This refers to the position within the arranged unit structure, λ represents the wavelength of the incident electromagnetic wave, (x, y) represents the relative position of the unit structure, and l represents the focal length.

[0056] The phase of the unit structures at each position is arranged using this formula. The boundaries of the array are all set to open boundaries to indicate that the array exists within an open space, such as... Figure 9 As shown in (b), this figure shows the focusing effect of the array when it is circularly polarized at 1.3Thz. It can be seen from the figure that the array successfully achieved the focusing function at the 1.3Thz frequency point, and its focal length is 2051μm.

[0057] To verify the broadband characteristics of this metasurface, since the amplitude of the metasurface does not vary much within its bandwidth, and the phase change is relatively uniform within the bandwidth, an array arranged according to the phase distribution at the 0.75Thz and 1.8Thz frequency points within its bandwidth (i.e., Figure 9 The focusing effect was observed for the array shown in (a), such as Figure 9As shown in (c), the metasurface achieves focusing functionality with a focal length of 1188 μm when circularly polarized incident at a frequency of 0.75 Thz. Figure 9 As shown in (d), the focusing function is also achieved when the circularly polarized incident light is at a frequency of 1.8Thz, with a focal length of 3094μm. This demonstrates the high bandwidth, high cross-polarization reflection efficiency, and uniform phase variation of the circular polarization characteristic of this invention. This embodiment proves the superior properties of this invention.

[0058] Simultaneously, based on the phase characteristics of circularly polarized incident radiation, a 24*24 unit structure 2-bit encoding array was designed at a frequency of 1.3ThZ. The selected phase consists of two units with an actual reflection phase difference of π. The actual reflection phase of encoding unit "0" is 0°, corresponding to an α angle of 70°; the actual reflection phase of encoding unit "1" is 180°, corresponding to an α angle of 159°. Each 3-column unit forms a sub-array and is designated as either "0" or "1". The array has an open boundary, with a total period of 2400μm. The core of this function is the ability to achieve highly controllable electromagnetic waves using a discrete digital encoding sequence, enabling more precise control, such as... Figure 10 As shown, the invented metasurface can achieve a 2-bit encoding far-field effect through the encoding operation of its reflection phase, verifying the controllability of the metasurface to incident electromagnetic waves.

[0059] Meanwhile, this invention also designs a 4-bit encoding array consisting of 24*24 units at a frequency of 1.3Thz. Similarly, two units with an actual reflection phase difference of π are selected, and the specific rotation angles of the encoding units "0" and "1" are the same as in the 2-bit encoding. Every 3*3 units form a sub-array, creating new unit structures for "0" and "1". The array has an open boundary, with a total period of 2400μm. Figure 11 As shown, the far field of the invented metasurface successfully achieved the effect of 4-bit encoding.

[0060] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A metasurface structure for a reflective broadband polarization conversion and phase precision control unit, characterized in that, It includes several unit structures, each unit structure is square, and the unit size of the unit structure is... l =100μm; the unit structure, from top to bottom, consists of a top metal pattern layer, a dielectric layer, and a bottom metal reflective layer; wherein... The top metal pattern layer includes two metal resonant rings. The inner metal resonant ring is a complete circular ring, while the outer metal resonant ring is a complete circular ring with two slots, which are orthogonal to each other. The inner radius of the inner metal resonant ring of the top metal pattern layer is... r 4 = 5μm, outer radius r 3 = 10μm, inner radius of the outer metal resonant ring r 2 = 20 μm, outer radius r 1 = 45 μm; the opening angle of the two slots in the external metal resonant ring is β =60°, the included angle between the center lines of the two slots is β 1 = 90°; The dielectric layer is made of polytetrafluoroethylene (PTFE) material with a dielectric constant of 2.33 and a loss tangent of 0.0012. The thickness of the dielectric layer is [missing information]. h =28μm; The two metal resonant rings in the top metal pattern layer and the bottom metal reflective layer are both covered by copper sheets; the conductivity is 5.96*10. 7 S / m, where the copper sheet thickness of the top metal pattern layer is... d 1 = 0.1 μm, the thickness of the copper sheet in the bottom metal reflective layer d 2 = 1 μm; By rotating the two metal resonant rings of the top metal pattern layer counterclockwise α This is to achieve a uniform phase change of the reflected wave, with a corresponding phase change of 2. α； The bandwidth of the metasurface is set to 0.7044 to 2.0859 THz, with a relative bandwidth of 99%. By controlling the incident polarization angle, the incident angle is emitted at an angle symmetrical about the y=x axis, and the modulation accuracy of the polarization angle reaches within 1°; when linearly polarized incident, the incident angle is symmetrical about the y=x axis.

2. The metasurface structure for a reflective broadband polarization conversion and phase precision control unit as described in claim 1, characterized in that, The dielectric layer and the bottom metal reflective layer are square in shape, and the side length of the dielectric layer and the bottom metal reflective layer is the same as the unit size of the unit structure.

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