Single-layer fully-polarized reflective double-sided image metasurface and design method thereof

Abstract

The invention discloses a single-layer fully-polarized reflective double-sided image metasurface and a design method. The reflective double-sided image metasurface is composed of a positive structure metasurface, a complementary structure metasurface and an intermediate dielectric substrate. The positive structure metasurface is formed by periodically extending and arranging m * m polarization conversion units in a plane, and arbitrary polarization conversion and phase regulation and control of electromagnetic waves of a specific frequency band are achieved. The polarization conversion unit is composed of an upper-layer chamfered rectangular patch or elliptical patch metal; the complementary structure metasurface is formed by periodically extending and arranging m * m complementary I-shaped units in a plane, and radar cross section reduction of back incident electromagnetic waves is achieved. Each complementary I-shaped unit is composed of a circular ring groove and I-shaped ring groove metal. The reflective double-sided image metasurface can realize polarization conversion under the excitation of forward arbitrary polarization electromagnetic waves and is used for near-field energy detection, can reduce the radar cross section under the excitation of backward orthogonal electromagnetic waves, and has the advantages of high working efficiency, small thickness and the like.

Description

Technical Field

[0001] The present invention belongs to the field of stealth technology and polarization detection design, and particularly relates to a single-layer fully polarized reflection double-sided image metasurface and a design method thereof. Background Art

[0002] In recent years, in order to achieve highly integrated electromagnetic devices, double-sided image metasurfaces have become a research hotspot. The double-sided image metasurface is realized by independently regulating electromagnetic waves with different incident directions, different frequencies or different polarization modes through designing different structural units based on the resonance principle. It introduces two or more layers of structural units, and each layer of structural units has different electromagnetic response characteristics. Since each layer of structural units can perform certain electromagnetic regulation on electromagnetic waves with different incident directions, signal transmission and reception can be achieved simultaneously, so it can reduce the volume and complexity of the device. In order to further improve the integration and radiation efficiency, diffraction technology and filtering technology are introduced into the metasurface, and it is possible to realize the propagation of electromagnetic waves on the front and back sides along asymmetric directions by introducing a grating structure, thereby realizing independent beam regulation in two directions on the double side. However, traditional double-sided image metasurfaces can only regulate single-linearly polarized or circularly polarized electromagnetic waves within two or more layers of structures, which limits engineering applications. Therefore, simultaneously realizing the regulation of electromagnetic waves of a double-sided image metasurface based on a single-layer dielectric structure is of great significance for improving the performance of communication systems, and also has important engineering application value for new electromagnetic devices integrating polarization detectors and invisibility cloaks. Summary of the Invention

[0003] The present invention applies a reflective double-sided image structure to a double-sided image metasurface, and discloses a single-layer fully polarized reflection double-sided image metasurface and a design method thereof that simultaneously satisfy the requirements of ultra-thin structure, polarization conversion and high-performance radiation.

[0004] The present invention provides a single-layer fully polarized reflection double-sided image metasurface, which includes a plurality of reflective double-sided image units. Each reflective double-sided image unit includes a positive structure metasurface unit, a dielectric plate, and a complementary structure metasurface unit;

[0005] The positive structure metasurface is disposed above the dielectric plate and includes at least one of a chamfered rectangular patch unit and an elliptical patch unit; both the chamfered rectangular patch unit and the elliptical patch unit include a square outer ring; a chamfered rectangular patch is provided inside the square outer ring of the chamfered rectangular patch unit, and the chamfered rectangular patch is a patch obtained by cutting off two corners of a rectangle symmetrically along the center at a predetermined truncation angle; an elliptical patch is provided inside the square outer ring of the elliptical patch unit, and the two foci of the ellipse in the elliptical patch are arranged along the diagonal;

[0006] The complementary structure metasurface includes complementary I-shaped units; the complementary I-shaped units include circular grooves etched on a complete metal and I-shaped ring grooves within the circular grooves; the I-shaped ring grooves include ring grooves with two openings and strip grooves connecting the two side ring grooves.

[0007] When the incident electromagnetic wave is reflected by the patch, by adjusting the structural dimensions of the two types of patches, the orthogonal cross-polarization channels of the reflected electromagnetic wave exhibit different phase responses, respectively satisfying the phase responses of 0 - 360°, thereby achieving phase coverage.

[0008] Furthermore, the unit period of the reflective double-sided image unit is P = 10 mm;

[0009] The width of the square outer ring of the chamfered rectangular patch unit is g = 0.4 mm, the length of the rectangular patch is l = 7.2 mm, the length of the chamfered side patch is w = 5.7 mm, the truncation angle of the chamfered rectangular patch is α1 = 45°, and the rotation angle is β1 = 0°;

[0010] The elliptical patch unit has the same square outer ring as the chamfered rectangular patch unit, the minor axis length of the elliptical patch is a = 2.7 mm, the major axis length is b = 5.4 mm, and the rotation angle of the elliptical patch is β2 = 45°;

[0011] In the complementary I-shaped unit, the outer diameter of the circular groove is r1 = 2.3 mm, the inner diameter is r2 = 2.1 mm, the outer diameter of the I-shaped ring groove is r0 = 1.5 mm, the width of the middle opening is d = 1.5 mm, and the difference between the inner and outer diameters of the I-shaped ring groove and the width of the strip groove are both dr = 0.6 mm.

[0012] A design method for a single-layer fully polarized reflective double-sided image metasurface is also provided. The design method for the single-layer fully polarized reflective double-sided image metasurface includes the following steps:

[0013] Step 1, design the reflective double-sided image unit, and arrange the spatial phase of the reflective double-sided image metasurface by using the transmission phase and the geometric phase;

[0014] Step 2, design the positive structure metasurface unit. The positive structure metasurface is a polarization conversion metasurface for realizing the polarization conversion function, and arrange the spatial phase of the polarization conversion metasurface by using the phase compensation method;

[0015] Step 3, design the complementary structure metasurface unit. The complementary structure metasurface is a stealth metasurface for realizing the stealth function, and arrange the spatial phase of the stealth metasurface by using the phase compensation method;

[0016] Step 4, design the single-layer fully polarized reflective double-sided image metasurface.

[0017] Furthermore, in step 1, the reflective double-sided image unit can efficiently reflect in two operating frequency bands of 9.0 - 10.5 GHz and 14.0 - 17.0 GHz, and can arbitrarily control electromagnetic waves in the entire space;

[0018] The reflective double-sided image unit includes a positive structure metasurface unit, a dielectric plate, and a complementary structure metasurface unit;

[0019] The positive structure metasurface is disposed above the dielectric plate and includes at least one of a chamfered rectangular patch unit and an elliptical patch unit; both the chamfered rectangular patch unit and the elliptical patch unit include a square outer ring; a chamfered rectangular patch is provided inside the square outer ring of the chamfered rectangular patch unit, and the chamfered rectangular patch is a patch obtained by cutting off two corners of a rectangle symmetrically along the center at a predetermined truncation angle; an elliptical patch is provided inside the square outer ring of the elliptical patch unit, and the two foci of the ellipse in the elliptical patch are arranged along the diagonal;

[0020] The complementary structure metasurface includes a complementary I-shaped unit; the complementary I-shaped unit includes an annular groove etched on a complete metal and an I-shaped annular groove inside the annular groove; the I-shaped annular groove includes an annular groove with two openings and a strip groove connecting the two side annular grooves;

[0021] When the LCP wave is incident along the -z direction, the positive structure metasurface can perform polarization conversion to generate independently controllable orthogonal circularly polarized waves and orthogonal linearly polarized waves; when the linearly polarized wave in the y direction is incident along the +z direction, the complementary structure metasurface can reduce the radar cross section to achieve stealth.

[0022] Furthermore, in step 2, the polarization conversion metasurface includes two polarization conversion units, namely a chamfered rectangular patch unit and an elliptical patch unit;

[0023] The polarization conversion unit can totally reflect the incident LCP wave into four independently controllable orthogonal circularly polarized waves and orthogonal linearly polarized waves, and by changing the rotation angles β1 and β2 of the chamfered rectangular unit or the elliptical unit, 0 - 360° phase control and polarization control can be achieved within 9.0 - 10.5 GHz.

[0024] Furthermore, in step 2, based on the phase difference Δφ required by the polarization conversion mode, the polarization conversion unit further scans the structural parameters of the polarization conversion unit on the basis of satisfying the phase difference Δφ to meet the phase coverage of the polarization conversion channel;

[0025] The structural parameters of the polarization conversion unit include the length l of the rectangular patch, the length w of the chamfered side patch, the truncation angle α1 of the chamfered rectangular patch, the rotation angle β1, the minor axis length a of the elliptical patch, the major axis length b of the elliptical patch, and the rotation angle β2 of the elliptical patch.

[0026] Furthermore, in step 2, the metal patch of the polarization conversion unit is irradiated by an arbitrarily polarized plane wave propagating in the -z direction, and the incident field can be written in the following form:

[0027]

[0028] where E x and E y are the electric field components polarized in the x and y directions and can be expressed as A x and A y are the electric field amplitudes of the polarization components in the x and y directions respectively, and φ x and φ y are the phases of the polarization components in the x and y directions respectively;

[0029] Δφ = φ y - φ x is the phase difference of the polarization component in the y direction relative to the polarization component in the x direction;

[0030] Express how an arbitrarily polarized wave is reflected into beams of different polarization states through Stokes parameters and electric field components; the relationships between the Stokes parameters S0, S1, S2, S3 and the electric field components are:

[0031] S0 = |E x | 2 + |E y | 2 = A x 2 + A y 2

[0032] S1 = |E x | 2 - |E y | 2 = A x 2 - A y 2

[0033]

[0034] where, Δφ = φ y - φ x is the phase difference of the polarization component in the y direction relative to the polarization component in the x direction, is the complex conjugate of E u ; according to the electric field components E x and E y , calculate the polarization angle χ and the azimuth angle ψ:

[0035]

[0036] According to the Stokes parameters, the point coordinates of each polarization state in the Poincaré sphere can be represented by the polarization angle χ and the azimuth angle ψ

[0037] S1 = cos(2χ)cos(2ψ)

[0038] S2 = cos(2χ)sin(2ψ)

[0039] S3 = sin(2ψ)

[0040] To determine the polarization state of the reflected electromagnetic wave, the ellipticity and the sense of rotation of the polarization state of the reflected beam are described by the polarization angle χ and the azimuth angle ψ; where χ = 0 is linear polarization, ψ = 0° is x polarization, ψ = 90° is y polarization, χ > 0 is right-handed elliptical polarization, and χ < 0 is left-handed elliptical polarization

[0041] Even further, in step 3, the stealth metasurface includes complementary I-shaped units; the complementary I-shaped units include circular grooves etched on a complete metal and I-shaped grooves within the circular grooves; the I-shaped grooves include circular grooves with two openings and strip grooves connecting the two side circular grooves

[0042] The central patch sizes of the polarization conversion units are all larger than the outer diameter of the circular grooves of the anisotropic stealth units, which are used to prevent electromagnetic waves from propagating along the +z direction, thereby achieving efficient reflection

[0043] Even further, in step 3, the stealth metasurface ensures that the electromagnetic waves incident in the -z direction can be efficiently reflected by optimizing the structural parameters of the complementary I-shaped units

[0044] The structural parameters of the complementary I-shaped units include the width d of the middle opening of the two circular grooves in the I-shaped grooves

[0045] The beneficial effects achieved by the present invention are as follows

[0046] Compared with the traditional multi-layer stacked double-sided image metasurface, the present invention can achieve high reflection, multi-functional integration, and multi-polarization channel phase regulation on a single-layer dielectric substrate. The present invention proposes an effective design method, and can design the independent phase regulation of electromagnetic waves in the whole space according to requirements and in accordance with the design process

[0047] The present invention has very objective polarization conversion and beamforming effects, forming beams for electromagnetic waves of different polarization modes in one half of the space, and achieving RCS reduction in the other half of the space. In simulation calculations, electromagnetic waves of four polarization modes can be measured and focused at four positions on the xoy-plane with F = 180 mm respectively; in the other half of the space, an overall -15 dBsm can be achieved within the operating frequency band of 14.0 - 17.0 GHz, achieving good RCS reduction and stealth effects. Description of the Drawings

[0048] Figure 1 It is a schematic diagram of a single-layer fully-polarized reflective double-sided image metasurface.

[0049] Figure 2 They are the topological structure, chamfered rectangular patch, elliptical patch, and complementary I-shaped unit of the reflective double-sided image unit. (a) Topological structure; (b) Chamfered rectangular patch; (c) Elliptical patch; (d) Complementary I-shaped unit.

[0050] Figure 3 They are the side views of the current distributions of the reflective double-sided image unit under the action of electromagnetic waves in different directions. (a) Incident along the +z direction; (b) Incident along the -z direction.

[0051] Figure 4 The surface current distributions of different units under the incidence of electromagnetic waves in different directions. At the f1 operating frequency band, (a) Elliptical patch; (b) Complementary I-shaped unit; at the f2 operating frequency band, (c) Elliptical patch; (d) Complementary I-shaped unit.

[0052] Figure 5 They are the electromagnetic characteristic curves of the polarization conversion unit simulation. (a) Reflection amplitude and phase when LCP - x; (b) Reflection amplitude, phase, and phase difference when LCP - y.

[0053] Figure 6 They are the numerical characteristics of the polarization conversion unit library simulation. (a) Reflection amplitude, phase, and phase difference when LCP - LCP; (b) Reflection amplitude, phase, and phase difference when LCP - y; (c) Reflection amplitude, phase, and phase difference when LCP - x; (d) Reflection amplitude, phase, and phase difference when LCP - RCP.

[0054] Figure 7 They are the reflection amplitude and phase of the anisotropic stealth unit simulation.

[0055] Figure 8 They are the theoretical phase distributions of the single-layer fully-polarized reflective double-sided image metasurface on different metasurfaces. (a) Theoretical phase distribution of the positive structure metasurface at the center frequency of 10 GHz; (b) Theoretical phase distribution of the complementary structure metasurface at the center frequency of 10 GHz.

[0056] Figure 9 It is the 1D electric field intensity diagram with the central frequency point of 10.0 GHz. (a) LCP-LCP; (b) LCP-y; (c) LCP-x; (d) LCP-RCP.

[0057] Figure 10 It is the electric field intensity distribution diagram of different polarization conversions for the simulation of the positive structure metasurface. (a) LCP-LCP; (b) LCP-y; (c) LCP-x; (d) LCP-RCP.

[0058] Figure 11 It is the 3D simulated radiation diagram excited by the LCP plane wave along the -z direction at different frequencies. (a) f = 9.5 GHz; (b) f = 10.0 GHz; (c) f = 10.5 GHz.

[0059] Figure 12 It is the 3D simulated radiation diagram under the excitation of the y-polarized wave with the central frequency of 15.6 GHz.

[0060] Figure 13 It is the result diagram of the monostatic RCS reduction of the complementary structure metasurface varying with frequency. Detailed implementation manners

[0061] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer with the description. However, these embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. Those skilled in the art should understand that the details and forms of the technical solutions of the present invention can be modified or replaced without departing from the spirit and scope of the present invention, but such modifications and replacements all fall within the protection scope of the present invention.

[0062] The single-layer full-polarization reflection double-sided image metasurface includes a plurality of reflection double-sided image units, and the reflection double-sided image unit includes a positive structure metasurface unit, a dielectric plate, and a complementary structure metasurface unit, as Figure 1 shown.

[0063] In order to achieve full-polarization conversion and invisibility functions in two half-spaces respectively, the designed reflection double-sided image unit should achieve high reflection and 360° phase coverage for electromagnetic waves in two working frequency bands, as Figure 2 shown.

[0064] The positive - structured metasurface unit consists of two layers of patch metals and one layer of dielectric substrate, with a period of P. The upper - layer structure is a polarization - conversion metasurface, which includes two types of polarization - conversion units: a chamfered - rectangle patch unit and an elliptical - patch unit. The chamfered - rectangle patch unit includes a square outer ring and a chamfered - rectangle patch. The chamfered - rectangle patch is a patch obtained by cutting off two corners of a rectangle symmetric about the center along a predetermined truncation angle. The width of the square outer ring is g, the length of the rectangular patch is l, the length of the chamfered - side patch is w, the truncation - angle of the chamfered - rectangle patch is α1, the rotation angle is β1, and the chamfered positions of the chamfered - rectangle patch at the initial rotation angle are located at the upper - right and lower - left corners of the rectangle. The elliptical - patch unit includes a square outer ring and an elliptical patch. The two foci of the ellipse in the elliptical patch are arranged along the diagonal. The length of the minor axis of the elliptical patch is a, the length of the major axis is b, the rotation angle of the elliptical patch is β2, and the major axis of the elliptical patch is arranged along the diagonal from the upper - left to the lower - right at the initial rotation angle. The middle layer is a dielectric substrate with a thickness of H. The bottom layer is a stealth metasurface, which includes complementary I - shaped units. The complementary I - shaped units include a circular ring groove etched on a complete metal and an I - shaped ring groove inside the ring groove. The outer diameter of the circular ring groove is r1, its inner diameter is r2, the outer diameter of the etched I - shaped ring groove is r0, the width of the middle opening is d, the difference between the inner and outer diameters of the I - shaped ring groove and the width of the strip groove are both dr, and the strip groove of the I - shaped ring groove is parallel to the x - axis at the initial rotation angle.

[0065] When the incident electromagnetic wave is reflected by the patch, by adjusting the structural dimensions of the two types of patches, the orthogonal cross - polarization channels of the reflected electromagnetic wave show different phase responses, respectively satisfying the phase responses of 0 - 360° (i.e., different polarization - conversion phase covers. For example, when LCP is incident, by changing the structural parameters of the chamfered - rectangle patch and the elliptical patch, it can be achieved that the phase of 0 - 360° is satisfied in the channel), so as to achieve phase coverage.

[0066] To meet the working requirements of broadband radiation and stealth, the CST software is used to simulate and optimize the unit structural parameters. The optimized structural parameters are: P = 10mm, H = 2mm, g = 0.4mm, l = 7.2mm, w = 5.7mm, α1 = 45°, β1 = 0°, β2 = 45°, a = 2.7mm, b = 5.4mm, r1 = 2.3mm, r2 = 2.1mm, r0 = 1.5mm, d = 1.5mm, dr = 0.6mm.

[0067] To study the electromagnetic characteristics of the reflective double - image unit, a series of simulations of the unit are carried out using the CST software. During the unit simulation, the x and y directions are set as periodic - boundary conditions, and the z direction is set as an open - boundary condition. The unit is excited by a wave port.

[0068] Furthermore, the present invention also provides a design method for the single-layer fully polarized reflection double-sided image metasurface, which includes the following steps:

[0069] Step 1, design of the reflection double-sided image unit

[0070] Compared with the traditional multi-layer stacked structure, the reflection double-sided image unit can broaden the working bandwidth, reduce the number of dielectric layers, lower the design difficulty, and shorten the R & D cycle. Based on this, this patent designs a reflection double-sided image unit, which can efficiently reflect at two working frequencies f1 and f2 and arbitrarily control the electromagnetic waves in the whole space. This unit consists of two layers of patch metals and one layer of dielectric board, with a period of P; the upper structure of this unit is a polarization conversion metasurface, and the polarization conversion metasurface includes two types of polarization conversion units: a chamfered rectangular patch unit and an elliptical patch unit. The chamfered rectangular patch unit includes a square outer ring and a chamfered rectangular patch. The chamfered rectangular patch is a patch obtained by cutting off two corners of a rectangle symmetric about the center along a predetermined truncation angle; the width of the square outer ring is g, the length of the rectangular patch is l, the length of the chamfered side patch is w, the truncation angle of the chamfered rectangular patch is α1, the rotation angle is β1, and the chamfered position of the chamfered rectangular patch is located at the upper right and lower left corners of the rectangle at the initial rotation angle. The elliptical patch unit includes a square outer ring and an elliptical patch; the two foci of the ellipse in the elliptical patch are arranged along the diagonal, the minor axis length of the elliptical patch is a, the major axis length is b, the rotation angle of the elliptical patch is β2, and the major axis of the elliptical patch is arranged along the diagonal from the upper left to the lower right at the initial rotation angle. The middle layer is a dielectric substrate with a thickness of H; the bottom layer is a stealth metasurface, and the stealth metasurface includes a complementary I-shaped unit. The complementary I-shaped unit includes an annular groove etched on a complete metal and an I-shaped annular groove in the annular groove; the outer diameter of the annular groove is r1, its inner diameter is r2, the outer diameter of the etched I-shaped annular groove is r0, the middle opening width is d, the difference between the inner and outer diameters of the I-shaped annular groove and the strip groove width are both dr, and the strip groove of the I-shaped annular groove is parallel to the x-axis at the initial rotation angle. Use the parameter sweeping function of CST software to simulate and optimize the unit structure parameters to determine the optimal structure parameters.

[0071] When the working frequencies of the two layers of patches of the single-layer fully polarized reflection double-sided image metasurface satisfy a certain difference, the positive structure and the complementary structure provide metal floors for each other, reducing the coupling effect between the two layers of patches and enabling arbitrary control of the electromagnetic waves in the whole space. Here, the phase of the positive structure metasurface unit is The phase of the complementary structure metasurface is

[0072] Based on this, by calculating the phase distribution corresponding to the preset function, the phases required for the upper and lower patches are obtained, and the units are arranged at the corresponding positions. Finally, a reflective double-sided image metasurface containing 30×30 units is designed. When the LCP wave is incident along the -z direction, the positive-structure metasurface can perform polarization conversion to generate four independently controllable orthogonal circularly polarized waves and orthogonal linearly polarized waves; when the linearly polarized wave in the y direction is incident along the +z direction, the complementary-structure metasurface can reduce the radar cross-section to achieve stealth.

[0073] Step 2: Design the upper patch and use the phase compensation method to design the spatial phase for arranging the polarization conversion metasurface.

[0074] In the previous step, a reflective double-sided image unit was designed, which can efficiently reflect electromagnetic waves at the operating frequency bands f1 (9.0 - 10.5 GHz) and f2 (14.0 - 17.0 GHz). To construct a positive-structure metasurface, this patent designs two types of patches, a chamfered rectangular patch and an elliptical patch. The width of the square outer ring of both patches is g. The length of the rectangular patch of the chamfered rectangular patch is l, the length of the chamfered side patch is w, the truncation angle of the chamfered rectangular patch is α1, the rotation angle is β1, the minor axis length of the elliptical patch is a, the major axis length is b, and the rotation angle of the elliptical patch is β2. Combining Figure 2 , the corresponding derivation of the polarization conversion theory is carried out.

[0075] Assume that a metal patch without rotation and size change is irradiated by an arbitrarily polarized plane wave propagating in the -z direction. The incident field can be written in the following form:

[0076]

[0077] where, E x and E y are the electric field components polarized in the x and y directions, which can be expressed as A x and A y are the electric field amplitudes of the polarization components in the x and y directions respectively, v x and φ y are the phases of the polarization components in the x and y directions respectively.

[0078] To more intuitively represent the process of polarization conversion, it is introduced into the Poincaré sphere, and the Stokes parameters and electric field components are used to represent how an arbitrarily polarized wave is reflected into beams of different polarization states. The relationship between the Stokes parameters S0, S1, S2, S3 and the electric field components is:

[0079] S0 = |E x | 2 + |E y | 2= A x 2 + A y 2 (2)

[0080] S1 = |E x | 2 - |E y | 2 = A x 2 - A y 2 (3)

[0081]

[0082] where Δφ = φ y - φ x is the phase difference between the polarization components in the y - direction and the x - direction, is the complex conjugate of E y . According to the electric field components E x and E y , the polarization angle χ and the azimuth angle ψ can be calculated:

[0083]

[0084] According to the Stokes parameters, the point coordinates of each polarization state in the Poincaré sphere can be represented by the polarization angle χ and the azimuth angle ψ

[0085] S1 = cos(2χ)cos(2ψ) (8)

[0086] S2 = cos(2χ)sin(2ψ) (9)

[0087] S3 = sin(2ψ) (10)

[0088] To determine the polarization state of the reflected electromagnetic wave, the ellipticity and the sense of rotation of the polarization state of the reflected beam are described by the polarization angle χ and the azimuth angle ψ. Among them, χ = 0 is linear polarization (ψ = 0° is x - polarization, ψ = 90° is y - polarization), χ > 0 is right - handed elliptical polarization, and χ < 0 and is left - handed elliptical polarization.

[0089] According to the required polarization state for reflection, the coordinates of this polarization state in the Poincaré sphere can be determined and further substitute these coordinates into the above formulas (8) to (10) to calculate the corresponding polarization angle X and azimuth angle ψ, and further calculate the required electric field parameters based on formulas (6) to (7) and finally according to the above - mentioned electric field components (phase difference Δφ, electric field amplitude A x and A y ).

[0090] Analyze the change of polarization state during the reflection process through the Fresnel formula and the Poincaré sphere. Use the simulation software CST to finely scan the chamfered rectangular patch and the elliptical patch to form a unit library, and select the chamfered rectangular patch or the elliptical patch with suitable structural parameters according to requirements such as the required phase difference and electric field amplitude.

[0091] On this basis, more modes of polarization conversion can be realized (such as circular to elliptical polarization, linear to elliptical polarization, etc.). On the premise of confirming a certain polarization conversion designed, according to the phase difference Δφ required by the polarization conversion mode, by adjusting the structural parameters of the two patches, on the basis of meeting the phase difference Δφ, further scan the structural parameters (l, w, α1, β1, β2, a, and b) to meet the phase coverage of the polarization conversion channel (where out and in represent the polarization states of the outgoing and incident electromagnetic waves respectively). Finally, different modes of polarization conversion and beamforming functions can be realized.

[0092] When the LCP wave is incident vertically, calculate the required compensation phase φ(x,y) at different positions of the positive structure metasurface according to formula (11):

[0093]

[0094] Here, φ(x,y) represents the compensation phase required to achieve electromagnetic wave focusing, and (x,y) represents the relative position of the patch on the positive structure metasurface. is the initial phase, k0 = 2π / λ0 is the free space wave vector, λ0 is the wavelength at the operating frequency f0, and F is the focal length. Among them, the compensation phase φ(x,y) to be compensated is closely related to the operating frequency f0.

[0095] Specific structural parameter design: To study the electromagnetic characteristics of the chamfered rectangular patch and the elliptical patch, use the full-wave simulation software CST MICROWAVE STUDIO (2020) to perform a series of simulations on the two patches. During the simulation process, the periodic boundary conditions are set in the x and y directions, and the open boundary conditions are set in the z direction. The patch is excited by the wave port. Figure 3 Give the side view of the current distribution of the patch when the LCP wave is incident along the -z direction. The reflection caused by the LCP wave incidence is mainly concentrated on the polarization conversion patch (chamfered rectangular patch or elliptical patch), and is directly reflected to the complementary I-shaped unit without any polarization conversion or phase regulation. This phenomenon indicates that most of the LCP waves are reflected by the "floor" provided by the polarization conversion patch and the complementary I-shaped unit, and the polarization conversion and phase regulation caused by the LCP wave incidence have little effect on the underlying complementary I-shaped unit, as Figure 4(a) and (b). On the other hand, when the y-polarized electromagnetic wave is incident along the +z direction, the metal patch (the chamfered rectangular or elliptical patch) at the center of the upper layer provides a ground plane for the lower layer patch, achieving high-efficiency co-polarization reflection, and the introduced complementary structure directly reflects the x-polarized electromagnetic wave, as Figure 4 (c) and (d). From Figure 4 it can be seen that when different polarized electromagnetic waves excite the designed reflective double-sided metasurface along the +z direction and -z direction, the unexcited side of the metasurface provides a reflection ground plane for the other side, and they work independently without affecting each other.

[0096] Based on the fact that the two patches can work independently, specific designs are carried out for four polarization conversion modes. Figure 5 The reflection coefficient and phase of the unit when the LCP electromagnetic wave is incident along the -z direction are given. Here, two methods are used for analysis. The first is to use the cross-circular polarization transmission coefficient t LR and the co-circular polarization transmission coefficient t LL to independently study the LCP and RCP components of the reflected field; the second is to decompose the electric field component of the reflected field along the x and y directions to facilitate the study of multiple polarization conversions. In this embodiment, 4 typical polarization conversions are designed, namely co-polarization reflection (LCP-LCP), left-handed circular polarization to y polarization (LCP-y), left-handed circular polarization to x polarization (LCP-x), and cross-polarization conversion (LCP-RCP). Here, a positive structure metasurface is built by non-interleaving the four polarization conversion units, and polarization detection is realized by near-field energy harvesting.

[0097] As Figure 6 (a) shows, when using chamfered rectangular patches and elliptical patches of different sizes, the reflection amplitude of co-polarization reflection (LCP-LCP) is greater than 0.95, and the phase can achieve 0 - 360° coverage in the range of 9.0 - 10.5 GHz. The optimized structural parameters using the full-wave simulation software CST 2020 are: l LL = 7.2 mm, w LL = 5.7 mm, α 1,LL = 45°, β 1,LL = 0°, β 2,LL = 45°, a LL = 3.2 mm, b LL = 3.4 mm. Here, a y-polarized plane wave excitation is used to prove that the unit can achieve the conversion of LCP wave to linearly polarized wave. As Figure 6 (b) shows, using the transmission phase principle, by adjusting the unit size, the phase difference of the reflected electromagnetic wave is kept at 90° or -90°, and the amplitude satisfies Based on this, by adjusting the unit structure size, while maintaining the phase difference required for polarization conversion, the phase can achieve 360° coverage in the range of 9.0 - 10.5 GHz. The optimized structural parameters are: l yL = 6.8 mm, w yL = 5.3 mm, α 1,yL = 45°, β 1,yL = 0°, β 2,yL = -45°, α yL = 2.7 mm, b yL = 5.4 mm. At this time, the polarization angle X = 0 and the azimuth angle ψ = 90°, indicating that the incident LCP wave is converted into a y-polarized wave and reflected. As Figure 6 (c) shows, by adjusting the unit size, the phase difference of the reflected electromagnetic wave is maintained at 180° or 0°, and the amplitude satisfies Based on this, by adjusting the unit structure size, while maintaining the phase difference required for polarization conversion, the phase can achieve 360° coverage in the range of 9.0 - 10.5 GHz. The optimized structural parameters are: l xL = 6.8 mm, w xL = 5.3 mm, α 1,xL = 45°, β 1,xL = -45°, β 2,xL = 45°, a xL = 2.7 mm, b xL = 5.4 mm. At this time, the polarization angle χ = 0 and the azimuth angle ψ = 0°, indicating that the incident LCP wave is converted into an x-polarized wave and reflected. As Figure 6 (d) shows, only using rectangular chamfered patches, and using geometric phase and transmission phase, the reflection amplitude of the patches remains above 0.93, and through the geometric phase introduced by rotation, the phase can achieve 360° coverage in the range of 9.0 - 10.5 GHz. The optimized structural parameters are: l RL = 6.8 mm, w RL = 4.4 mm, α 1,yL = 45°, β 1,RL = 0° and 180°. Except that the RCP to LCP polarization channel only requires rectangular chamfered patches, a single type of patch cannot fully meet the 0 - 360° phase coverage for other polarization conversion modes. Two types of patches need to be combined, and by using the transmission phase, that is, changing the structural parameters (l, w, α1, β1, β2, a, and b), the phase difference required in the second step of the invention content can be achieved as well as the 0 - 360° phase coverage required for different polarization conversions. At the same time, according to the attachment Figure 4It can be seen that the coupling effect between patches with different structures is relatively small, indicating that the two types of patches can be combined to design polarization conversions of different modes and complete the phase regulation and beamforming without element coupling.

[0098] Finally, according to the above content, the compensation phases required at different positions are calculated, and corresponding patches are arranged at the corresponding positions. Finally, a positive-structured metasurface containing 30×30 units is designed. The positive-structured metasurface can achieve arbitrary polarization conversion when LCP waves are incident, identify the polarization state of incident electromagnetic waves through near-field energy detection, and can perform phase compensation to achieve the beam focusing function.

[0099] Step 3: Design complementary I-shaped units and arrange the spatial phases of the anisotropic stealth structure using the phase compensation method

[0100] In the previous step, a positive-structured metasurface with polarization conversion and beamforming was designed, which can efficiently reflect electromagnetic waves at the operating frequency band f1 (9.0 - 10.5 GHz). To construct a complementary-structured metasurface, an anisotropic structure for realizing the stealth function, namely a complementary I-shaped unit, was designed. The complementary I-shaped unit includes a circular ring groove etched on a complete metal and an I-shaped ring groove inside the ring groove; the outer diameter of the circular ring groove is r1, the inner diameter is r2, the outer diameter of the etched I-shaped ring groove is r0, the middle opening width is d, and the difference between the inner and outer diameters of the I-shaped ring groove and the width of the strip groove are both dr. The optimized structural parameters using the full-wave simulation software CST 2020 are: r1 = 2.3 mm, r2 = 2.1 mm, r0 = 1.5 mm, d = 1.5 mm, dr = 0.6 mm. At this time, the center patch sizes of the above-designed polarization conversion units are all larger than the outer diameter of the circular ring groove of the anisotropic stealth unit, which can be used to prevent electromagnetic waves from propagating along the +z direction, thereby achieving efficient reflection. Finally, CST 2020 is used to simulate the unit characteristics. By optimizing the unit structural parameters, it is ensured that electromagnetic waves incident in the -z direction can be efficiently reflected. On this basis, only the opening width d needs to be changed to regulate the transmission phase in the reflection mode without changing the other structural parameters. Here, S yy and represent the co-polarization reflection amplitude and phase when a y-polarized wave is incident. When the structural parameter d varies from 0.1 mm to 1.9 mm and the incident angle remains unchanged, the reflection amplitude is greater than 0.8. At the same time, Figure 7 shows that at 15.6 GHz, while fixing other structural parameters and changing the middle opening width d of the etched I-shaped ring groove from 0.1 mm to 1.9 mm, using the characteristic of the transmission phase ( where k0 is the free-space wave vector, n is the refractive index, and d0 is the transmission distance), that is, by changing the structural parameters of the unit, the underlying anisotropic stealth unit can achieve 360° phase coverage.

[0101] When an electromagnetic wave is reflected by a complementary structure metasurface, the phase of the scattered wave after reflection can be expressed as:

[0102]

[0103] Δφ sc = π (13)

[0104] where E sc,i is the scattered electric field from different scattering sources, and Δφ sc is the phase difference between scattering sources. When a linearly polarized wave in the y - direction is incident perpendicularly, random phases are generated through a random function and 2 - bit phase, and the phase difference Δφ sc of each scattering source should satisfy formula (13) to achieve the effect of RCS reduction. The compensation phases required at different positions are calculated according to the random function, and anisotropic stealth units with broadband reflection functions are arranged at the corresponding positions. Finally, a complementary structure metasurface containing 30×30 units is designed. The complementary structure metasurface can scatter the reflected electromagnetic wave when a linearly polarized wave in the y - direction is incident, thereby realizing RCS reduction.

[0105] Step 4, Single - layer fully - polarized reflection dual - image metasurface and design

[0106] Place the positive - structure metasurface above the complementary - structure metasurface and align the centers. The distance between the two metasurfaces is set as H. Use CST simulation software to select an appropriate thickness H of the dielectric substrate, usually set H = 2mm. The LCP wave is efficiently reflected by the positive - structure metasurface and generates independently controllable orthogonal circularly polarized beams and orthogonal linearly polarized beams radiating along the +z direction through the transmission phase and geometric phase; the linearly polarized wave in the y - direction is incident along the +z direction, reflected by the complementary - structure metasurface, and generates a scattered beam radiating along the -z direction through the transmission phase.

[0107] Determine that the operating frequency bands of this reflection dual - image metasurface are f1(9.0 - 10.5GHz) and f2(14.0 - 17.0GHz), and the size is 300mm×300mm. First, use formula (1 - 4) to calculate the phases and amplitudes required for the positive - structure metasurface to achieve four polarization conversions. The phase calculations of the four polarization - conversion directional beams are as shown in formula (5), where k0 is the wave vector in free space, F is the focal length, the F / D ratio is set to 0.6, the aperture D is 300mm, and the focal length F is 180mm. According to the calculated phase distributions at different positions, Figure 8 (a) shows the phase distributions required for four individual LCP, y - polarized, x - polarized, and RCP beams. In addition, the phase distribution required for the complementary - structure metasurface can be obtained using the random function and formula (6), as shown in Figure 8 (b).

[0108] With the designed positive structure metasurface and complementary structure metasurface, the final single-layer fully polarized reflective double-sided image metasurface can be constructed as follows: Place the positive structure metasurface above the complementary structure metasurface and align the centers of the two metasurfaces. The distance between them is set as H, and the value of H is 2.0 mm. The positive structure metasurface excited by the LCP plane wave along the -z direction reflects LCP wave, y-polarized wave, x-polarized wave and RCP wave respectively after four polarization conversions, and the four polarized waves are focused at F = 180 mm. Then, the complementary structure metasurface excited by the y-polarized plane wave along the +z direction generates scattered waves radiating along the -z direction through random coding and transmission phase. On this basis, more modes of polarization conversion can be realized (such as circular to elliptical polarization, linear to elliptical polarization, etc.). On the premise of confirming a certain polarization conversion designed, according to the phase difference Δφ required by this polarization conversion mode, by adjusting the two patch structure parameters, on the basis of meeting the phase difference Δφ, further scan the structure parameters (l, w, α1, β1, β2, a and b) to meet the phase coverage of the polarization conversion channel (where out and in represent the polarization states of the outgoing and incoming electromagnetic waves) to achieve different modes of polarization conversion and beamforming functions.

[0109] Finally, this patent designs a single-layer fully polarized reflective double-sided image metasurface to verify the proposed design method and conducts full-wave simulation in CST 2020. Since the LCP and RCP waves contain x and y direction components, when extracting the reflected electric fields of the LCP and RCP waves, the x and y polarization conversions can be detected at the focal point F, that is, the "ghost image". Similarly, the "ghost images" of the LCP and RCP can also be seen when extracting the reflected electric fields of the x and y polarized waves. In addition, when extracting the distribution map of the reflected electric field of a certain linear polarization or circular polarization, due to the orthogonality of a pair of beams with a phase difference of 90°, the focal point of the other orthogonal polarized wave cannot be observed. As Figure 9 and 10 shown, LCP, y-polarized, x-polarized and RCP beams can be generated in the set directions. Figure 11 The far-field 3D radiation patterns at three frequency points within the working frequency band f1 are given. It can be seen that three different polarized focused beams (LCP, y-polarized and x-polarized beams) can be observed under LCP polarization. Figure 10 and Figure 11 It can be seen that the four generated polarization conversion beams are completely consistent with the positions and directions of the previous designs.

[0110] Figure 12The 3D simulated radiation pattern at the center frequency of 15.6 GHz under the excitation of y-polarized waves is given. It can be seen that when the y-polarized wave is incident along -z, the reflected beam is randomly scattered, and the overall profile is reduced, achieving RCS reduction. To further verify that the complementary structure metasurface can reduce RCS, the monostatic RCS in the entire operating frequency band of 14.0 - 17.0 GHz was calculated. From Figure 13 It can be seen that the RCS in the entire operating frequency band is less than -10 dBsm, and the RCS in the frequency band of 15.3 - 17.0 GHz is less than -15 dBsm, achieving good RCS reduction.

[0111] The above are only the specific steps of the present invention, which do not constitute any limitation to the protection scope of the present invention; all technical solutions formed by equivalent transformation or equivalent substitution fall within the scope of the protection of the present invention; the parts not detailed in the present invention belong to the well-known technologies of those skilled in the art.

Claims

1. A single-layer fully polarized reflective double-sided image metasurface, characterized in that, The single-layer fully polarized reflective double-sided image metasurface includes a plurality of reflective double-sided image units, and each reflective double-sided image unit includes a positive structure metasurface unit, a dielectric plate, and a complementary structure metasurface unit; The positive structure metasurface is disposed above the dielectric plate and includes at least one of a chamfered rectangular patch unit and an elliptical patch unit; both the chamfered rectangular patch unit and the elliptical patch unit include a square outer ring; a chamfered rectangular patch is provided inside the square outer ring of the chamfered rectangular patch unit, and the chamfered rectangular patch is a patch obtained by cutting off two corners of a rectangle symmetric about the center along a predetermined truncation angle; an elliptical patch is provided inside the square outer ring of the elliptical patch unit, and the two foci of the ellipse in the elliptical patch are arranged along the diagonal; The complementary structure metasurface includes a complementary I-shaped unit; the complementary I-shaped unit includes an annular groove etched on a complete metal and an I-shaped annular groove inside the annular groove; the I-shaped annular groove includes an annular groove with two openings and a strip groove connecting the two side annular grooves; When the incident electromagnetic wave is reflected by the patch, by adjusting the structural dimensions of the two patches, the orthogonal cross-polarization channels of the reflected electromagnetic wave exhibit different phase responses, respectively satisfying the phase responses of 0 - 360°, so as to achieve phase coverage.

2. The single-layer fully polarized reflection double-sided image metasurface according to claim 1, wherein The unit period of the reflective double-sided image unit is P = 10 mm; The width of the square outer ring of the chamfered rectangular patch unit is g = 0.4 mm, the length of the rectangular patch is l = 7.2 mm, the length of the chamfered side patch is w = 5.7 mm, the truncation angle of the chamfered rectangular patch is α1 = 45°, and the rotation angle is β1 = 0°; The elliptical patch unit has the same square outer ring as the chamfered rectangular patch unit, the minor axis length of the elliptical patch is a = 2.7 mm, the major axis length is b = 5.4 mm, and the rotation angle of the elliptical patch is β2 = 45°; In the complementary I-shaped unit, the outer diameter of the annular groove is r1 = 2.3 mm, the inner diameter is r2 = 2.1 mm, the outer diameter of the I-shaped annular groove is r0 = 1.5 mm, the width of the middle opening is d = 1.5 mm, and the difference between the inner and outer diameters of the I-shaped annular groove and the width of the strip groove are both dr = 0.6 mm.

3. A design method for a single-layer fully polarized reflective double-sided image metasurface, characterized in that, The design method of the single-layer fully polarized reflective double-sided image metasurface includes the following steps: Step 1, design the reflective double-sided image unit, and arrange the spatial phase of the reflective double-sided image metasurface by using the transmission phase and the geometric phase; Step 2, design the positive structure metasurface unit. The positive structure metasurface is a polarization conversion metasurface for realizing the polarization conversion function, and arrange the spatial phase of the polarization conversion metasurface by using the phase compensation method; Step 3, design the complementary structure metasurface unit. The complementary structure metasurface is a stealth metasurface for realizing the stealth function, and arrange the spatial phase of the stealth metasurface by using the phase compensation method; Step 4, design the single-layer fully polarized reflective double-sided image metasurface.

4. The design method of the single-layer fully polarized reflection double-sided image metasurface according to claim 3, wherein In Step 1, the reflective double-sided image unit can efficiently reflect in two working frequency bands of 9.0 - 10.5 GHz and 14.0 - 17.0 GHz, and can arbitrarily control the electromagnetic waves in the whole space at the same time; The reflective double-sided image unit includes a positive structure metasurface unit, a dielectric plate, and a complementary structure metasurface unit; The positive - structured metasurface is disposed above the dielectric substrate and includes at least one of a chamfered rectangular patch unit and an elliptical patch unit; both the chamfered rectangular patch unit and the elliptical patch unit include a square outer ring; inside the square outer ring of the chamfered rectangular patch unit, there is a chamfered rectangular patch, and the chamfered rectangular patch is a patch obtained by cutting off two corners of a rectangle with a central symmetry structure along a predetermined truncation angle; inside the square outer ring of the elliptical patch unit, there is an elliptical patch, and the two foci of the ellipse in the elliptical patch are arranged along the diagonal line. The complementary - structured metasurface includes a complementary I - shaped unit; the complementary I - shaped unit includes an annular groove etched on a complete metal and an I - shaped annular groove inside the annular groove; the I - shaped annular groove includes an annular groove with two openings and a strip groove connecting the two side annular grooves. When the LCP wave is incident along the - z direction, the positive - structured metasurface can perform polarization conversion to generate independently controllable orthogonal circularly polarized waves and orthogonal linearly polarized waves; when the linearly polarized wave in the y - direction is incident along the + z direction, the complementary - structured metasurface can reduce the radar cross - section to achieve stealth.

5. The design method of the single-layer fully polarized reflective double-sided image metasurface according to claim 3, characterized in that In step 2, the polarization - conversion metasurface includes two polarization - conversion units, namely a chamfered rectangular patch unit and an elliptical patch unit. The polarization - conversion unit can totally reflect the incident LCP wave into four independently controllable orthogonal circularly polarized waves and orthogonal linearly polarized waves, and by changing the rotation angles β1 and β2 of the chamfered rectangular unit or the elliptical unit, 0 - 360° phase control and polarization control can be achieved within 9.0 - 10.5 GHz.

6. The design method of the single-layer fully polarized reflection double-sided image metasurface according to claim 5, characterized in that, In step 2, based on the phase difference Δφ required by the polarization - conversion mode, the polarization - conversion unit further scans the structural parameters of the polarization - conversion unit to satisfy the phase coverage of the polarization - conversion channel on the premise of satisfying the phase difference Δφ. The structural parameters of the polarization - conversion unit include the length l of the rectangular patch, the length w of the chamfered - side patch, the truncation - angle α1 of the chamfered rectangular patch, the rotation angle β1, the minor - axis length a of the elliptical patch, the major - axis length b of the elliptical patch, and the rotation angle β2 of the elliptical patch.

7. The design method of the single-layer fully polarized reflection double-sided image metasurface according to claim 6, characterized in that, In step 2, the metal patch of the polarization - conversion unit is irradiated by an arbitrarily polarized plane wave propagating in the - z direction, and the incident field can be written in the following form: Among them, E x and E y are the electric field components polarized in the x and y directions, and can be expressed as A x and A y are the electric field amplitudes of the polarization components in the x and y directions respectively, φ x and φ y are the phases of the polarization components in the x and y directions respectively, and Δφ = φ y - φ x is the phase difference of the polarization component in the y direction relative to the polarization component in the x direction; The Stokes parameters and the electric - field components are used to represent how an arbitrarily polarized wave is reflected into beams of different polarization states; the relationships between the Stokes parameters S0, S1, S2, S3 and the electric - field components are: S0 = |E x | 2 +|E y | 2 = A x 2 +A y 2 S1 = |E x | 2 -|E y | 2 = A x 2 -A y 2 where Δφ = φ y - φ x is the phase difference between the y-direction polarization component and the x-direction polarization component, is the complex conjugate of E y ; according to the electric field components E x and E y , the polarization angle χ and the azimuth angle ψ are calculated: According to the Stokes parameters, the point coordinates of each polarization state in the Poincaré sphere can be represented by the polarization angle χ and the azimuth angle ψ S1 = cos(2χ)cos(2ψ) S2 = cos(2χ)sin(2ψ) S3 = sin(2ψ) To determine the polarization state of the reflected electromagnetic wave, the polarization angle χ and the azimuth angle ψ are used to describe the ellipticity and the sense of rotation of the polarization state of the reflected beam; where χ = 0 is linear polarization, ψ = 0° is x - polarization, ψ = 90° is y - polarization, χ>0 is right - hand elliptical polarization, and χ<0 is left - hand elliptical polarization.

8. The design method of the single-layer fully polarized reflection double-sided image metasurface according to claim 3, characterized in that In step 3, the stealth metasurface includes a complementary I - shaped unit; the complementary I - shaped unit includes an annular groove etched on a complete metal and an I - shaped annular groove inside the annular groove; the I - shaped annular groove includes an annular groove with two openings and a strip groove connecting the two side annular grooves. The central patch sizes of the polarization conversion units are all larger than the outer diameters of the circular grooves of the anisotropic stealth units, which are used to block the propagation of electromagnetic waves in the +z direction, thereby achieving efficient reflection.

9. The design method of the single-layer fully polarized reflection double-sided image metasurface according to claim 8, characterized in that, In step 3, the stealth metasurface ensures that the electromagnetic waves incident in the -z direction can be efficiently reflected by optimizing the structural parameters of the complementary I-shaped unit; The structural parameters of the anisotropic stealth unit include the width d of the middle opening of the two openings in the I-shaped ring groove.

Images