Multifunctional reflective polarization conversion and absorber based on nested square ring metasurfaces

Abstract

The application belongs to the technical fields of electromagnetic metamaterials and microwave devices, and discloses a multifunctional reflection-type polarization conversion and wave absorber based on a nested square loop super surface, which is composed of reflection units, each of which comprises a metal resonance layer, an intermediate dielectric layer and a metal ground layer, the metal resonance layer has a nested loop topology structure with a non-continuous conductive path, and comprises an outer loop resonator and an inner loop resonator which are geometrically coincident with each other, are nested with each other, are both square open loop structures and have diagonal cut-off gaps, and form four L-shaped metal branches which are centrally rotationally symmetrically distributed, and the inner loop resonator is provided with a blocking gap, so that the L-shaped metal branches of the inner loop resonator are disconnected into non-closed metal segments. The application realizes multi-band and multifunctional electromagnetic wave regulation and control in a single passive structure, has the characteristics of high integration, strong frequency domain multiplexing and low preparation cost, and has wide application value in radar stealth and wireless communication systems.

Description

Technical Field

[0001] This application belongs to the field of electromagnetic metamaterials and microwave devices, specifically relating to a multifunctional reflective polarization converter and absorber based on a nested square ring metasurface. Background Technology

[0002] The polarization characteristics of electromagnetic waves play a crucial role in engineering applications such as wireless communication, satellite links, radar detection, imaging, and remote sensing. Effectively controlling the polarization state of electromagnetic waves can significantly improve communication capacity, suppress multipath interference, and reduce polarization mismatch losses. In particular, the linear-to-circular polarization (LP-CP) conversion technology is widely used in various antenna and radar systems due to the excellent anti-interference capabilities and insensitivity to antenna orientation of circularly polarized waves. Therefore, the development of compact and efficient polarization control devices has significant practical value.

[0003] Metasurfaces, as two-dimensional artificial electromagnetic materials composed of periodically arranged subwavelength units, provide an efficient and flexible platform for the amplitude, phase, and polarization control of electromagnetic waves. Compared to traditional bulky polarization devices, metasurfaces offer significant advantages such as ultra-thin profiles, light weight, low manufacturing costs, and ease of integration. Currently, reflective metasurfaces have been successfully applied to radar cross-section (RCS) reduction and high-performance antenna systems.

[0004] However, most existing metasurface designs still have significant limitations. First, the vast majority of designs can only achieve a single function within a limited frequency band, such as polarization conversion or absorption, which is insufficient to meet the demands of modern systems for multifunctional integration. Second, to achieve multifunctional integration, existing solutions generally fall into two categories: one is reconstructed metasurfaces with active devices such as PIN diodes, which, while enabling dynamic function switching, introduces bias circuitry, significantly increasing system complexity and cost; the other is passive metasurfaces with multi-layer stacked structures, which, while achieving functional reuse, result in increased device profile thickness due to the multi-layer structure and complex interlayer alignment processes, limiting their practical application in compact systems.

[0005] In summary, existing technologies struggle to effectively integrate multi-band polarization conversion and electromagnetic absorption while maintaining structural simplicity, low profile, and low cost. Therefore, developing a multifunctional metasurface based on a single-layer structure that simultaneously achieves linear-circular polarization conversion, cross-polarization conversion, and electromagnetic absorption without active components is of great significance for promoting the integrated development of radar stealth and wireless communication systems. Summary of the Invention

[0006] To overcome the problems of complex structure, large cross-sectional thickness and high cost of multifunctional metasurfaces in the prior art, this application provides a multifunctional reflective polarization converter and absorber based on nested square ring metasurfaces. By using the structure design of double-layer nested slotted square rings, different resonant modes are excited in different frequency bands, and frequency domain multiplexing of the cross-polarization rotation, circular polarization conversion and absorption functions of linear polarized waves is realized under single-layer PCB process.

[0007] To achieve the above objectives, this application employs the following technical solution:

[0008] This application discloses a multifunctional reflective polarization converter and absorber based on a nested square ring metasurface. The multifunctional reflective polarization converter and absorber consists of reflective units arranged in a two-dimensional array with periodic horizontal and vertical orientations in a plane. Each independent reflective unit is a three-layer composite structure of metal-dielectric-metal, consisting of a metal resonant layer, an intermediate dielectric layer, and a metal ground layer from top to bottom. The metal resonant layer is attached to the upper surface of the intermediate dielectric layer, and the metal ground layer covers the lower surface of the intermediate dielectric layer. The metal resonant layer has a nested ring topology with discontinuous conductive paths. The nested ring topology of the discontinuous conductive path of the metal resonant layer includes an outer ring resonator and an inner ring resonator that are geometrically coincident and nested together. The metal resonant layer works together with the intermediate dielectric layer and the bottom metal layer. When a linearly polarized electromagnetic wave is incident perpendicularly, the nested ring topology of the discontinuous conductive path of the metal resonant layer decomposes the incident wave into two mutually orthogonal polarization components. Magnetic resonance is excited between the metal resonant layer and the bottom metal ground layer, so that the equivalent input impedance of the metal resonant layer matches the free space wave impedance, thereby dissipating the energy of the incident electromagnetic wave and realizing the electromagnetic wave absorption characteristic.

[0009] A further improvement of this application is that: both the outer ring resonator and the inner ring resonator are square open rings, and diagonal cut-off gaps are respectively provided at the two symmetrical apex corners of the outer ring resonator and the inner ring resonator, forming four L-shaped metal branches distributed in a central rotational symmetry. At the same time, the inner ring resonator is provided with blocking gaps at the central axis of symmetry on the upper, lower and left sides parallel to the transmitting unit, so that the L-shaped metal branches of the inner ring resonator are broken into unclosed metal segments.

[0010] A further improvement of this application is that: the outer side length L2 of the outer ring resonator is set to 11.4 mm, and the diagonal gap width W2 is set to 1.5 mm; the outer side length L1 of the inner ring resonator is set to 7.5 mm, and the blocking gap width is... W 3 is set to 0.75 mm, and the metal linewidth W1 of the outer ring resonator and the inner ring resonator is set to 0.75 mm.

[0011] A further improvement of this application is that the cell period P of the reflective unit is set to 13 mm.

[0012] A further improvement of this application is that the intermediate dielectric layer is made of FR4 dielectric material, and the relative permittivity of FR4 dielectric material is... =4.3, loss tangent The dimensions of the intermediate dielectric layer are length × width × height = 13mm × 13mm × 3.3mm.

[0013] A further improvement of this application is that: both the metal resonant layer and the metal ground layer are copper foil layers, and the conductivity of the copper foil layer is... The thickness of both the metal resonant layer and the metal ground layer is 0.035 mm.

[0014] The beneficial effects of this application are:

[0015] This application breaks through the functional limitations of traditional single-layer metasurfaces, integrating three independent electromagnetic response mechanisms on a single device without increasing the number of physical layers, thus achieving high integration of multiple modes.

[0016] (2) Within three discrete frequency bands—3.69 to 3.87 GHz, 6.90 to 8.20 GHz, and 13.40 to 13.98 GHz—this application can deflect the polarization direction of a vertically incident linearly polarized wave by 90 degrees, while maintaining a polarization conversion efficiency (PCR) of over 90%, demonstrating highly efficient cross-polarization conversion performance.

[0017] (3) In the dual-band range of 3.90 to 6.75 GHz and 11.0 to 13.1 GHz, linearly polarized waves can be converted into circularly polarized waves. The 3dB axial ratio (AR) performance is stable within the working frequency band, and it has excellent linear-to-circular polarization conversion capability.

[0018] (4): It exhibits excellent absorption performance in the 14.3GHz to 14.5GHz frequency band, with an electromagnetic wave absorption rate exceeding 90%, and an absorption peak of up to 94% at the 14.4GHz resonant frequency point, demonstrating precise narrowband strong absorption characteristics.

[0019] (5) The total thickness of the multifunctional reflective polarization converter and absorber of this application is only about one-tenth of the working wavelength. It is manufactured based on the mature single-layer FR4 printed circuit board process, eliminating the need for multi-layer lamination and precise alignment processes, and eliminating expensive active components, thus having a very high cost-effectiveness for industrialization.

[0020] Based on the subwavelength scale unit topology design, this application maintains high stability in various polarization conversion efficiency and absorption rate indicators under oblique incidence angles ranging from 0° to 30°, making it particularly suitable for radar cross section reduction tasks under complex operating conditions and exhibiting strong environmental adaptability. Attached Figure Description

[0021] Figure 1 This is a three-dimensional structural schematic diagram of the reflective unit of the multifunctional reflective polarization converter and absorber of this application.

[0022] Figure 2 This is a front view of the reflective unit of the multifunctional reflective polarization converter and absorber of this application.

[0023] Figure 3 This is the multifunctional reflective polarization converter and absorber of this application. A diagram showing the amplitude and phase difference of the reflection coefficient when an axially polarized wave is incident perpendicularly.

[0024] Figure 4 For this application along shaft and The reflection coefficient amplitude (a) and its phase difference (b) curves when incident along the axial polarization direction.

[0025] Figure 5 This is a graph showing the polarization conversion rate (a), axial ratio (b), and absorptivity (c) of the multifunctional reflective polarization converter and absorber of this application in the operating frequency band.

[0026] Figure 6 This application relates to a functional reflective polarization converter and absorber. Axial ratio diagrams of high and low frequency bands for axially polarized waves incident at angles of 0°, 15° and 30°.

[0027] Figure 7 This application relates to a functional reflective polarization converter and absorber. Polarization conversion rate diagrams for axially polarized waves incident at angles of 0°, 15°, and 30°.

[0028] Figure 8 This application relates to a functional reflective polarization converter and absorber. Absorption rate diagrams of axially polarized waves at incident angles of 0°, 15°, and 30°.

[0029] Figure 9 This is a side view of the reflective unit of the multifunctional reflective polarization converter and absorber of this application. Detailed Implementation

[0030] The embodiments of the present invention will be disclosed below with reference to the drawings. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the present invention. That is, in some embodiments of the present invention, these practical details are not essential. In addition, for the sake of simplicity, some conventional structures and components will be shown in the drawings in a simple schematic manner.

[0031] like Figure 1 , Figure 2 and Figure 9 As shown, this application discloses a multifunctional reflective polarization converter and absorber based on a nested square ring metasurface. The multifunctional reflective polarization converter and absorber is a macroscopic two-dimensional planar electromagnetic device, and its overall physical structure is as follows: Figure 1 As shown, the multifunctional reflective polarization converter and absorber consists of reflective units arranged in a two-dimensional array with periodic transverse and longitudinal directions in a plane. The unit period P of the reflective units is set to 13 mm. Figure 9 As shown in the longitudinal cross-section, each independent reflecting unit is a three-layer composite structure of metal-dielectric-metal, consisting of a metal resonant layer 1, an intermediate dielectric layer 2, and a metal grounding layer 3 from top to bottom. The metal resonant layer 1 is attached to the upper surface of the intermediate dielectric layer 2, and the metal grounding layer 3 covers the lower surface of the intermediate dielectric layer 2. Through the geometric pattern modulation of the metal resonant layer 1, the phase accumulation of the intermediate dielectric layer 2, and the physical shielding of the metal grounding layer 3 by total internal reflection, a strong electromagnetic coupling effect is generated, thereby realizing multi-band, wide-angle electromagnetic control functions.

[0032] The metal resonant layer 1 is formed on a copper foil with a thickness of 0.035 mm using a standard printed circuit board (PCB) etching process. Its pattern topology is constructed as a nested ring topology with discontinuous conductive paths. The nested ring topology of the discontinuous conductive paths of the metal resonant layer 1 includes an outer ring resonator and an inner ring resonator with coincident geometric centers and nested together. Both the outer ring resonator and the inner ring resonator are square open rings, and diagonal cut-off gaps are respectively provided at the two symmetrical vertices of the outer ring resonator and the inner ring resonator, forming four L-shaped metal branches distributed in a central rotational symmetry. The diagonal cut-off gaps are configured to destroy the isotropy of the structure, so as to decompose the incident linearly polarized wave into two mutually orthogonal eigenpolarization components. At the same time, the inner ring resonator has blocking gaps at the central axis of symmetry parallel to the upper, lower and left sides of the reflecting unit, so that the L-shaped metal branches of the inner ring resonator are broken into unclosed metal segments. The blocking gaps are configured to generate near-field electromagnetic coupling with the outer ring resonator, so as to independently control the reflection amplitude and phase difference of the two orthogonal polarization components in multiple frequency bands, and collaboratively trigger the equivalent impedance matching of specific high frequency bands. The outer ring resonator has an outer side length L2 of 11.4 mm and a diagonal gap width W2 of 1.5 mm; the inner ring resonator has an outer side length L1 of 7.5 mm and a blocking gap width of... WThe linewidth W1 of the outer ring resonator and the inner ring resonator is set to 0.75 mm. This non-closed double-ring asymmetric morphology is the core of disrupting electromagnetic isotropy and introducing a specific phase difference.

[0033] The intermediate dielectric layer 2, serving as the main support and dielectric control layer, utilizes an FR4 epoxy fiberglass cloth laminate that balances performance and low processing costs, with a relative permittivity of [missing information]. =4.3, loss tangent The intermediate dielectric layer 2 has dimensions of length × width × height = 13mm × 13mm × 3.3mm. The choice of thickness of 3.3mm and the pattern design of the metal resonant layer enable the metasurface to excite strong magnetic resonance near 14.4 GHz. At the same time, the equivalent relative permeability and equivalent relative permittivity in this frequency band are effectively controlled to be consistent, achieving excellent impedance matching with free space, thereby minimizing reflection and achieving efficient absorption of incident electromagnetic waves.

[0034] The metal resonant layer 1, the intermediate dielectric layer 2, and the bottom metal layer 3 work together to achieve the function. When a linearly polarized electromagnetic wave is incident perpendicularly, the nested ring topology of the discontinuous conductive path of the metal resonant layer 1 decomposes the incident wave into two mutually orthogonal polarization components, namely the u-axis component and the v-axis component along the diagonal direction. Combined with the total reflection characteristics of the bottom metal layer 3 and the transmission characteristics of the intermediate dielectric layer 2, the two mutually orthogonal polarization components naturally generate the required reflection amplitude and phase delay in the target frequency band, thereby satisfying the physical conditions for cross-polarization or linear-circular polarization conversion, respectively.

[0035] To explore the underlying physical mechanism of multifunctional polarization control achieved in this application, anisotropy theory is introduced for analysis. The conventional Cartesian coordinate system is used... Rotating counterclockwise by 45° around the central axis creates two mutually orthogonal polarization components. Coordinate system. When the electromagnetic wave travels along... When incident perpendicularly, along Taking an axially polarized linearly polarized incident wave as an example, its electric field vector It can be decomposed into along shaft and Two orthogonal eigencomponents along the axial direction:

[0036]

[0037] in, The incident wave vector, The incident wave amplitude, The phase factor for electromagnetic waves propagating along the -z axis. The imaginary unit, Let the wave number be in free space. For along The unit vector along the axial direction. For along The unit vector along the axis.

[0038] Due to the asymmetric slotted structure of this application, the unit... and The response is basically symmetrical on the axis, therefore the cross-reflection component , The polarization state of the reflected wave will be completely determined by the intrinsic isopolarization reflection coefficient. and The amplitude and phase difference determine this.

[0039] Cross-polarization conversion mechanism:

[0040] like Figure 4 As shown in (a), the amplitude of the reflection coefficient is [value missing] in the three operating frequency bands of 3.69 GHz - 3.93 GHz, 6.90 GHz - 8.20 GHz, and 13.40 GHz - 13.98 GHz. At the same time, such as Figure 4 As shown in (b), the phase difference between the two orthogonal components in this frequency band ,satisfy The physical conditions. Among them, The phase of the co-polarized reflection component polarized along the u-axis. The phase of the co-polarized reflection component polarized along the v-axis.

[0041] At this time, the combined reflected wave electric field Evolved into:

[0042] This means that the resultant vector of the reflected wave along the u-axis and v-axis points precisely to... The axis, i.e., the incident axis. The axially polarized wave was completely twisted into Polarized waves. Combined Figure 3 and Figure 5 In (a), the polarization conversion efficiency (PCR) exceeded 90% in all of the above frequency bands. The reflected electric field vector, The composite phase factor of the reflected wave.

[0043] Linear-circular polarization conversion mechanism:

[0044] During the gaps between the cross-polarization bands, namely 3.90 GHz–6.75 GHz and 11.0 GHz–13.1 GHz, the reflection amplitude... It still holds true, but the phase difference between the two components has shifted, satisfying the phase difference condition. At this point, the electric field of the reflected wave becomes:

[0045] This mathematical characteristic perfectly matches the definition of a circularly polarized wave. Combined with... Figure 5 As shown in (b), the axial ratio (AR) of the reflected wave is less than 3 dB at this time, realizing a wideband linear-circular polarization conversion.

[0046] In the frequency band near 14.4 GHz, the strong absorption characteristics of this application originate from the tunable electromagnetic equivalent response of the metasurface. Given the total internal reflection properties of the bottom metal layer, the transmittance of electromagnetic waves is zero, and the absorption rate can be simplified to... The equivalent input impedance of the device can be expressed as: The reflection coefficient in, For free space wave impedance, Let be the equivalent relative permittivity of the metasurface. The vacuum permittivity, The equivalent relative permeability of the metasurface is denoted as . The value represents the vacuum permeability. By precisely controlling the dielectric layer thickness T=3.3mm and the size of the blocking gap, the equivalent relative permeability in this frequency band is made to approach the equivalent relative permittivity. This will lead to , making .like Figure 5 As shown in (c), the incident energy is completely introduced into the structure and converted into heat energy due to perfect impedance matching, with a peak absorption rate of up to 94%.

[0047] Finally, stability under oblique incidence conditions is particularly critical in the complex electromagnetic environments of practical engineering applications. Figure 6 , Figure 7 and Figure 8 The details of this embodiment at the angle of incidence are recorded in detail. The electromagnetic response curves were displayed at angles of 0°, 15°, and 30°. Simulation results clearly show that even with the incident angle increased to 30°, the electromagnetic resonance characteristics within the device were not significantly disrupted. The high maintenance of its polarization conversion rate, the broad 3dB axial ratio bandwidth, and the high-frequency absorption efficiency only experienced slight frequency shifts or amplitude oscillations, and the overall performance parameters did not deteriorate. This fully demonstrates that the nested ring topology of this single-layer discontinuous conductive path possesses excellent spatial angular stability and extremely high engineering practical value.

[0048] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A multifunctional reflective polarization converter and absorber based on a nested square ring metasurface, wherein the multifunctional reflective polarization converter and absorber is composed of reflective units arranged in a two-dimensional array with periodic transverse and longitudinal directions in a plane, characterized in that: Each independent reflecting unit is a three-layer composite structure of metal-dielectric-metal, consisting of a metal resonant layer (1), an intermediate dielectric layer (2), and a metal grounding layer (3) from top to bottom. The metal resonant layer (1) is attached to the upper surface of the intermediate dielectric layer (2), and the metal grounding layer (3) covers the lower surface of the intermediate dielectric layer (2). The metal resonant layer (1) has a nested ring topology with discontinuous conductive paths. The nested ring topology with discontinuous conductive paths includes an outer ring resonator and an inner ring resonator with coincident geometric centers. The metal resonant layer (1), the intermediate dielectric layer (2), and the bottom metal grounding layer (3) cooperate to ensure that when a linearly polarized electromagnetic wave is incident perpendicularly, the discontinuous conductive path of the metal resonant layer (1) is... The nested ring topology of the path decomposes the incident wave into two mutually orthogonal polarization components. The metal resonant layer (1) and the bottom metal ground layer (3) are excited to generate magnetic resonance, so that the equivalent input impedance of the metal resonant layer (1) matches the free space wave impedance, thereby dissipating the incident electromagnetic wave energy and realizing the electromagnetic wave absorption characteristic. The outer ring resonator and the inner ring resonator are both square open rings, and diagonal cut-off gaps are respectively set at the two symmetrical apex corners of the outer ring resonator and the inner ring resonator, forming four L-shaped metal branches distributed in a central rotational symmetry. At the same time, the inner ring resonator is provided with blocking gaps at the top, bottom and left central symmetry axes parallel to the reflection unit, so that the L-shaped metal branches of the inner ring resonator are broken into unclosed metal segments.

2. The multifunctional reflective polarization converter and absorber based on nested square ring metasurfaces according to claim 1, characterized in that: The outer ring resonator has an outer side length L2 of 11.4 mm and a diagonal gap width W2 of 1.5 mm. The inner ring resonator has an outer side length L1 of 7.5 mm and a blocking gap width W3 of 0.75 mm. The metal line width W1 of the outer ring resonator and the inner ring resonator is 0.75 mm.

3. The multifunctional reflective polarization converter and absorber based on nested square ring metasurfaces according to claim 1, characterized in that: The intermediate dielectric layer (2) is made of FR4 dielectric material, and the relative permittivity of FR4 dielectric material is... =4.3, loss tangent The dimensions of the intermediate medium layer (2) are length × width × height = 13mm × 13mm × 3.3mm.

4. The multifunctional reflective polarization converter and absorber based on nested square ring metasurfaces according to claim 1, characterized in that: Both the metal resonant layer (1) and the metal ground layer (3) are copper foil layers, and the conductivity of the copper foil layer is... The thickness of both the metal resonant layer (1) and the metal ground layer (3) is 0.035 mm.

5. The multifunctional reflective polarization converter and absorber based on nested square ring metasurfaces according to claim 1, characterized in that: The unit period P of the reflective unit is set to 13 mm.

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