A double-symmetry p-b phase high-transparency super surface structure sequence and unit pattern design method

Abstract

The application relates to a double-symmetry P-B phase high-transmittance super surface structure sequence and a unit pattern design method, and belongs to the field of artificial electromagnetic super materials. The designed double-symmetry P-B phase high-transmittance super surface is a coded super surface which is sequentially stacked by a pattern layer, a transparent dielectric layer and a metal mesh layer. The application proposes a method for realizing the design of the geometric parameters of the pattern layer meshed unit pattern patch based on a transmission matrix and an equivalent circuit method, greatly reduces the design time, simplifies the design process, and can be applied to the design of pattern patches in different target frequency bands. Meanwhile, the super surface structure sequence is obtained by optimizing the fitness function about the multi-point scattering characteristics in the target frequency band, so that the coded super surface has low scattering performance in the target frequency band. In addition, the designed super surface can realize wide-band high-transmittance, is widely applied to high-performance light windows of aerospace, medical treatment and precision instrument equipment, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electromagnetic metasurface design, and particularly relates to a high-transparency metasurface unit pattern design method based on an equivalent circuit and a transmission line model and a fitness function for coding metasurface structure sequence optimization design. BACKGROUND

[0002] Radar stealth technology is to dynamically control or reduce the radar signature of the target by artificial means, so that it is difficult to be found, identified and attacked. Radar stealth technology is a frontier issue that all countries attach great importance to, and is closely related to the national defense strength. In order to weaken the reconnaissance ability of the enemy's radar, it has become a hot and difficult technology to develop electromagnetic stealth technology for military targets and important civilian targets. Among them, the metasurface with RCS (Radar Cross Section) reduction function has a wide application prospect in radar stealth technology, such as stealth aircraft, missiles, etc. RCS is the most basic parameter in scattering characteristics, which is a measure of the return power of the target in a given direction under plane wave illumination. As a two-dimensional metamaterial composed of sub-wavelength units, metasurface can flexibly manipulate electromagnetic waves and is widely used in the design and preparation of low-scattering radar stealth devices. Compared with bulk metamaterials, metasurfaces can achieve the effect of controlling the phase, amplitude and other electromagnetic properties of electromagnetic waves by carefully designing the pattern layer unit pattern, and thus realize many electromagnetic behaviors that do not exist in nature. In 2014, Professor Cui Tiejun's research group of Southeast University first proposed coded metasurface, which introduced the binary coding idea in digital circuits into the design of metasurface unit arrangement, further improving the flexibility of metasurface phase control. Due to the flexibility of coded metasurface in controlling electromagnetic scattering waves, it is widely used in low-scattering radar stealth devices with RCS reduction function, such as patents 201810346302.2, 201811205798.8, 201910186499.2, 202010090009.1, 202010432807.8, 202010459009.4, 202010848147.1, 202010881824.X, 202110102410.7, 202110742160.3, 202111342357.4, 202111550541.8, etc. However, in the design method of the above low-scattering radar stealth metasurface unit pattern, a single metasurface unit pattern is designed, and the design method is not universal and requires a large number of simulations in the design process, limiting the design efficiency. In addition, in the intelligent algorithm for optimizing the structure sequence design of coded metasurface, only the backscattering energy value at a certain frequency point in the working frequency band is evaluated, and the overall backscattering energy uniformization performance of the coded metasurface in the target working frequency band cannot be considered. In addition, most of the low-scattering metasurfaces at present do not have optical transparency, which is not conducive to application occasions that require optical transparency, such as light windows of aircraft / satellites / ships / cars, optical instrument light windows and display panels, electromagnetic isolation room and security facility light windows, transparent elements of communication equipment, mobile phone touch screen, etc.

[0003] Currently, the design of low-scattering coding metasurface invisibility devices is achieved by designing the phase control of its sub-wavelength microstructure unit pattern, mainly divided into two methods: one is to change the size of the unit structure parameters to achieve 360° phase coverage, such as patents 201510073145.9, 201710039036.4, 201710603567.1, 201810221894.5, 201810346302.2, 201811205797.3, 201910675022.0, 202010086717.8, 202011608676.0, 202110045262.X, 202111028041.8, etc. However, this method leads to strong dependence on simulation and optimization in the unit design process, and also brings the designed metasurface with narrow bandwidth, large size, uneven phase distribution and other shortcomings that cannot be ignored.

[0004] The other is to apply P-B theory to design the metasurface unit pattern layer. The low-scattering metasurface with P-B phase characteristics refers to the characteristic that the reflection phase difference between the coding units is twice the geometric rotation angle of the pattern layer in the coding unit. Rotating the pattern layer by a certain angle can obtain multiple coding units with uniform distribution of reflection phase in the range of 360°, and the phase difference is only related to the pattern rotation angle, and is independent of the geometric shape and material. Therefore, the microstructure unit with P-B phase characteristics has the advantages of simple structure and stable phase difference in the radar invisibility band. Therefore, the design method of low-scattering metasurface unit pattern with P-B phase characteristics has been widely studied in the field of electromagnetic metasurface design:

[0005] 1. Patent 202111514049.5 "Design method of wideband low RCS array antenna based on interdigital arrangement metasurface", describes a design method of metasurface unit based on rectangular sheet. In this method, the size of the rectangular sheet and the bottom layer of the feed line applied to the pattern layer of the metasurface unit is set within a certain range and adjusted, and the pattern layer based on the rectangular sheet has P-B phase characteristics. The required phase difference between units is obtained by rotating the pattern layer, and coding is achieved to have obvious RCS reduction in the frequency range of 6-18 GHz under two polarizations.

[0006] 2. Patent 202111294875.3 discloses a broadband radar scattering cross-section reduction super surface with reflection and scattering characteristics, which is composed of square structure units including bottom metal plate, upper profiled metal strip and dielectric substrate. The upper profiled metal strip has P-B phase characteristics, and the encoding unit is obtained by rotating the square structure unit to form a coding super surface, which realizes good low scattering characteristics in the range of 12.05-16.18GHz and 20.2-28.85GHz, and good mirror reflection characteristics in the range of 17.76-19.44GHz.

[0007] 3. Patent 202020056168.5 discloses a transparent broadband low scattering super surface suitable for solar cell array, which is composed of single layer indium tin oxide (ITO) pattern film and double layer glass dielectric layer. The ITO film pattern is an asymmetric ring structure with P-B phase characteristics, and the "0" and "1" encoding units with 180° phase difference are obtained by rotating the ITO film pattern. Due to the existence of double layer glass dielectric, the coding super surface composed of "0" and "1" units reduces RCS by absorption, scattering cancellation and multi-directional scattering method, and realizes RCS reduction of more than 10dB compared with metal plate in the range of 8-16.2GHz.

[0008]

[0009] 4. Patent 201611166527.7 discloses an ultrathin ultrawideband random coding RCS reduction super surface scatterer, which is composed of metal plate, dielectric layer and pattern layer. The pattern layer is composed of metal structure line, including two V-shaped resonators, one cut line resonator and two V-shaped metal line structures. The pattern has P-B phase characteristics, and the coding unit is obtained by rotating the pattern layer. The unit arrangement combination method is optimized by genetic algorithm, which realizes RCS reduction of more than 10dB in the frequency range of 17.1-41.2GHz.

[0010]

[0011] The above low scattering coding super surface unit pattern design method with P-B phase characteristics commonly uses trial and error method, which is complicated and needs to find the optimal solution that meets the requirements through a large number of full-wave simulation. The simulation process requires a large number of parameters, consumes a lot of time and computing resources, and greatly reduces the efficiency of super surface unit pattern design. Moreover, the existing design method optimizes the parameters of a single super surface unit pattern to meet the low RCS requirement in the working frequency band, which makes the design method not universal. Therefore, the current super surface unit pattern design method with P-B phase characteristics lacks theoretical guidance.

[0012] ​​In addition, the super surface unit pattern layer and the back plate in the above-mentioned patents 201510073145.9, 201611166527.7, 201710039036.4, 201710603567.1, 201810221894.5, 201810346302.2, 201910675022.0, 202010086717.8, 202110045262.X, 202111028041.8, 202111294875.3, and 202111514049.5 adopt opaque metal patches such as copper, and the dielectric layer adopts opaque high polymer polymers such as F4B and polyimide, so that the super surface does not have optical transparency. In 201811205797.3 (ITO, quartz glass), 202020056168.5 (ITO, double-layer glass), and 202011608676.0 (ITO, PET, PMMA), the transparent ITO film is used as the pattern layer and the back plate of the super surface unit, and the dielectric layer adopts transparent media such as quartz glass and PMMA. However, the ITO film is difficult to achieve wide-band high transmittance, so that the super surface unit is difficult to achieve wide-band high optical transparency, and cannot meet the requirements of some high transparency occasions.

[0013] In summary, the existing P-B theory-based coding super surface unit pattern layer design technology lacks efficient theoretical guidance design methods, and in the coding super surface structure sequence design optimization method, only the backward scattering energy value at a certain frequency point in the working frequency band is evaluated, and the overall backward scattering energy uniformization performance of the coding super surface in the target working frequency band cannot be considered. In addition, the existing coding super surface unit pattern layer design technology cannot consider the high optical transparency of the super surface. The above transparent coding super surface devices all use ITO film as the pattern layer and the back plate of the coding super surface unit, and have the problems of poor transmittance and inability to achieve wide-band transparency. SUMMARY

[0014] The present application aims to overcome the deficiencies in the above-mentioned design technology of the P-B theory-based coding metasurface unit pattern layer, especially the trial-and-error process is complicated, and a large number of full-wave simulation is needed to find the optimal solution that meets the requirements, the parameter quantity is large in the simulation process, and a large amount of time and computing resources are consumed, which greatly reduces the design efficiency of the metasurface unit pattern patch, the design method has no universality, and the coding metasurface structure sequence optimization process cannot consider the overall backscattering energy equalization performance in the target working frequency band, and the metasurface cannot realize wide-band high transparency. A design method based on equivalent circuit and transmission matrix theory is proposed, which improves the design efficiency, and also designs the metasurface pattern layer unit grid pattern patch with the same non-cyclic, two-fold symmetry and P-B phase characteristic category. The grid pattern patch makes the coding metasurface realize wide-band high transparency. And a fitness function is proposed, which considers the overall backscattering energy equalization performance in the target working frequency band, and optimizes the design of the coding metasurface structure sequence.

[0015] The technical route adopted by the present application is: a two-fold symmetric P-B phase high-transmittance super surface unit pattern and structure sequence design method: a two-fold symmetric P-B phase high-transmittance super surface is composed of three layers of pattern layer, transparent dielectric layer and metal mesh layer in sequence; the super surface is a one-bit coding super surface, the pattern layer is composed of N*N (N>=5) groups of coding units with P-B phase characteristics arranged according to the structure sequence, the coding units are expressed as coding unit 0 and coding unit 1 according to a one-bit binary coding table; the P-B phase characteristic refers to the reflection phase difference between the coding unit 0 and the coding unit 1 is twice the geometric rotation angle of the coding unit 0 and the coding unit 1 when the pattern patch constitutes the coding unit 0 and the coding unit 1; the coding unit 0 is composed of M*M (M>=2) basic units 0 arranged in a two-dimensional array; the basic unit 0 contains a pattern patch with a rotation state of 0°; the coding unit 1 is composed of M*M (M>=2) basic units 1 arranged in a two-dimensional array, and the number of basic units is the same as that in the coding unit 0; the basic unit 1 contains a pattern patch with a rotation state of 90°; the basic unit 0 and the basic unit 1 are square in shape, each of which has and only one pattern patch, and the center of the pattern patch coincides with the center of the basic unit 0 and the basic unit 1; the square side length of the basic unit 0 and the basic unit 1 is equal; the pattern patch has the characteristics of non-cyclic, two-fold symmetry and anisotropy; the non-cyclic means that the pattern patch does not contain a hole part; the two-fold symmetry means that a right-angle coordinate system can be established with the center of the pattern patch as the origin in the plane of the pattern patch, and the pattern patch can be symmetrical along two mutually perpendicular symmetry axes, that is, the x and y axes; the distance from the center of the pattern patch to the farthest point in the x-axis direction is the geometric parameter d of the pattern patch in the x-axis direction; the distance from the center of the pattern patch to the farthest point in the y-axis direction is the geometric parameter l of the pattern patch in the y-axis direction; the anisotropy means that the geometric parameters d and l of the pattern patch in the two right-angle coordinate axes are different; the pattern patch is a meshed metal patch; the meshing means that the outline part of the pattern patch is retained, and the metal line width of the outline part is greater than or equal to the metal mesh line width, and the pattern patch is filled with the metal mesh except the outline part; the metal mesh is a mesh-like micro metal structure composed of mesh units arranged in a two-dimensional array; the structure sequence of the coding unit 0 and the coding unit 1 refers to the coding sequence optimized according to the genetic algorithm for the low-scattering super surface function, and the difference lies in that a plurality of frequency points are uniformly selected in the target frequency band, the fitness function in the genetic algorithm is the reciprocal of the product of the average value of the maximum value and the standard deviation of the coding super surface backscattering energy at these frequency points; the two-fold symmetric P-B phase high-transmittance super surface unit pattern design method, characterized in that the geometric parameters of the super surface unit pattern are obtained by the following steps:

[0016] I. Set the target working frequency band of the one-bit coding super surface;

[0017] II. According to the boundary conditions of Maxwell equations, the reflection field of the unit metasurface is obtained by the transmission process of the electromagnetic wave vertically incident on the unit metasurface, which is the minimum structure of the metasurface when the pattern layer only contains one basic unit, by applying the transmission matrix method combined with the transmission matrix of the electromagnetic wave in the pattern layer and the medium, wherein the reflection field of the unit metasurface is:

[0018]

[0019] wherein i=x, y represents the x and y directions of the rectangular coordinate axis; A i and B i respectively represent the electric field amplitudes of the forward and backward propagating electromagnetic waves on the pattern layer, A1 and B1 respectively represent the electric field amplitudes of the forward and backward propagating electromagnetic waves on the metal mesh layer, is the propagation coefficient, ω=2πf is the angular frequency, μ is the absolute magnetic permeability of the medium, μ=μ0μ r , μ0 is the vacuum magnetic permeability, μ r is the relative magnetic permeability of the medium; ε is the absolute dielectric constant of the medium, ε=ε0ε r , ε0 is the vacuum dielectric constant, ε r is the relative dielectric constant of the medium; h is the thickness of the medium layer; Y0=1 / Z0 is the free space admittance, Y1=1 / Z1 is the medium layer admittance, is the characteristic impedance of the medium layer; Y i =1 / Z eff-i is the characteristic admittance of the pattern layer of the unit metasurface, Z eff-i is the equivalent impedance of the pattern layer of the unit metasurface.

[0020] III. The relationship between the reflection coefficients of the field components in the x and y directions of the unit metasurface and the reflection field is obtained by the reflection field of the unit metasurface in step II, combined with the transmission matrix of the electromagnetic wave in the pattern layer and the transparent medium layer and the electric field amplitudes of the forward and backward propagating electromagnetic waves on the metal mesh, wherein the transmission matrixes of the electromagnetic wave in the pattern layer and the transparent medium layer are and Under ideal conditions, the electromagnetic wave is totally reflected on the metal mesh layer of the unit metasurface, and the normalized electric field amplitudes of the forward and backward propagating electromagnetic waves on the metal mesh layer are defined as:

[0021]

[0022] The relationship between the reflection coefficients r x and r y of the field components in the x and y directions of the unit metasurface and the corresponding reflection field is:

[0023] rx = B x / A x

[0024] r y = B y / A y

[0025] Set the target frequency band within a bit encoding metasurface needs to achieve the low scattering target, the unit metasurface in the target frequency band needs to have high reflectivity, that is, |r x | = |r y | = 1, the quantifiable target operating frequency band at the upper and lower frequency endpoints of the graphic patch in the x and y directions of the rectangular coordinate axis equivalent impedance Z eff-i ;

[0026] IV, the equivalent impedance equation is where L i is the equivalent inductance, C i is the equivalent capacitance, the equivalent inductive reactance the equivalent capacitive reactance According to the equation formed by the two equivalent impedance equations of the graphic patch in the x direction of the rectangular coordinate axis at the upper and lower frequency endpoints of the target operating frequency band, the solution space of the equivalent inductive reactance and the equivalent capacitive reactance of the graphic patch in the x direction of the rectangular coordinate axis is solved; Similarly, the solution space of the equivalent inductive reactance and the equivalent capacitive reactance of the graphic patch in the y direction of the rectangular coordinate axis is solved.

[0027] V, the relationship between the equivalent inductive reactance and the equivalent capacitive reactance in the x and y directions of the rectangular coordinate axis and the length of the graphic patch in the corresponding coordinate axis and the area of the graphic patch is:

[0028] where w x = S / 2l

[0029] where g ax = p-S / 2l

[0030] where w y = S / 2d

[0031] where g ay = p-S / 2d

[0032] where, p is the side length of the square corresponding to the basic unit 0 and the basic unit 1, S is the area of the graphic patch; F(p, η, λ) is:

[0033]

[0034]

[0035]

[0036]

[0037] wherein a is the electromagnetic wave incidence angle, and λ is the electromagnetic wave wavelength;

[0038] VI. Each set of equivalent inductive reactance and equivalent capacitive reactance values in the solution space in the x and y directions of the coordinate axis has a pair of geometric parameter values d and l corresponding thereto, and the values of the geometric parameters d and l of the patterned patch at this time can be quantified by applying the relationship in step V. A set of solutions in which the quantified values of the geometric parameters of the patterned patch in the x and y directions of the coordinate axis are the same is the final solution of the geometric parameters of the patterned patch of the two-fold symmetric P-B phase high-transmittance super surface unit pattern;

[0039] Preferably, in the above-mentioned two-fold symmetric P-B phase high-transmittance super surface structure sequence and unit pattern design method,

[0040] To encode the far-field scattering energy of the super surface, the expression is:

[0041]

[0042] wherein the reflection phase of the (m, n)th unit is A one-bit encoding super surface unit The value of the reflection phase is 0 or 180°; θ and are the pitch angle and azimuth angle in any direction; the wave vector k = 2π / λ; the encoding sequence optimized according to the genetic algorithm in accordance with the low scattering super surface function by using the fitness function, characterized in that: the fitness function is:

[0043]

[0044] Preferably, in the above-mentioned two-fold symmetric P-B phase high-transmittance super surface structure sequence and unit pattern design method, the non-cyclic, two-fold symmetric and anisotropic patterned patch includes a rectangular patch, a rhombic patch, an elliptical patch, a double-elliptical patch, a propeller-like patch, an H-shaped patch, a double-rhombic patch, a cross-like patch, and a leaf-like patch. The double-elliptical patch refers to two elliptical long axes of which one vertex is tangent to the origin of the symmetric axis coordinate system, and the long axes of the two elliptical patches fall on the coordinate axis y and are symmetric about the coordinate axis x.

[0045] Preferably, in the above-mentioned two-fold symmetric P-B phase high-transmittance super surface structure sequence and unit pattern design method, the transparent dielectric layer is any transparent material that can meet the light transmission requirements of the application scenario, and the transparent material can be used as a transparent light window material that meets the requirements of the use scenario.

[0046] Preferably, in the above-mentioned two-fold symmetric P-B phase high-transmittance super surface structure sequence and unit pattern design method, the metal mesh includes a square grid, a circular ring, a triangular distribution circular ring and a sub-circular ring array, a random distribution circular ring, a multi-period circular ring nesting, and an array mesh of a top-fan-shaped.

[0047] Preferably, in the above-mentioned two-fold symmetric P-B phase high-transmittance super surface structure sequence and unit pattern design method, the metal mesh line width is in the order of microns or sub-microns; the metal mesh and the grid pattern patch are composed of a metal with good electrical conductivity, and the thickness of the metal is greater than 100 nm.

[0048] The innovation and good effect of the present application are:

[0049] 1. The present application proposes a super surface unit pattern patch design method combining transmission matrix and equivalent circuit method, which is designed for non-cyclic, two-fold symmetric and anisotropic pattern patches. First, the target working frequency band of the coded super surface is set, the transmission matrix method is applied according to the boundary conditions of Maxwell's equation, the reflection field of the unit super surface is obtained from the transmission process of electromagnetic waves in the unit super surface, combined with the transmission matrix of electromagnetic waves in the pattern layer and the medium, then the relationship between the reflection coefficient and the reflection field of the unit super surface in the different coordinate axes in the rectangular coordinate system is obtained, and then according to the target that the one-bit coded super surface needs to achieve low scattering in the target frequency band, the unit super surface needs to have the characteristics of high reflectivity, the equivalent impedance of the pattern patch in the different coordinate axes in the rectangular coordinate system at the two endpoints of the target working frequency band is quantized, the origin of the coordinate system is the center of the pattern patch, and the symmetry axis is the two rectangular coordinate axes, then the relationship between the equivalent inductance and the equivalent capacitance in the different coordinate axes in the rectangular coordinate system and the length of the pattern patch in the corresponding coordinate axis and the area of the pattern patch is obtained according to the equivalent circuit method, finally, the equivalent inductance and the equivalent capacitance of the pattern patch in the different coordinate axes in the rectangular coordinate system are combined, the length of the pattern patch in the different coordinate axes in the rectangular coordinate system is quantized, and the same set of quantization results in the different coordinate axes in the rectangular coordinate system is used as the final length of the pattern patch in two directions, that is, the design of the super surface pattern layer pattern patch is completed. The present application realizes the efficient design of the super surface pattern layer pattern patch through theoretical guidance method, solves the problem that the traditional trial and error method is complicated, a large number of full-wave simulation is needed to find the optimal solution meeting the requirements, the parameter quantity is large in the simulation process, a large amount of time and computing resources are consumed, and the design efficiency of the super surface pattern layer pattern patch is greatly reduced. Moreover, the present application has a certain universality and can be designed for non-cyclic, two-fold symmetric and anisotropic pattern patches, rather than a single pattern patch optimization.

[0050] 2. On the basis of the innovation point 1, the unit composed of different rotating state pattern patches is arranged in a two-dimensional array to form two kinds of coding particles, a plurality of frequency points are uniformly selected in a target frequency band, the reciprocal of the product of the maximum value and the standard deviation of the backscattering energy of the coding metasurface at the frequency point is taken as the genetic algorithm fitness function, the coding sequence is optimized, and the two kinds of coding particles are arranged according to the coding sequence; the good effect of the setting is that: the one-bit coding metasurface has the RCS reduction of the backscattering energy less than-10dB in the target frequency band, so that the coding metasurface composed of the pattern patch designed by the application has excellent performance of low scattering in the target frequency band.

[0051] 3. The application proposes a two-fold symmetry P-B phase high-transparency metasurface, which is composed of three layers of pattern layer, transparent dielectric layer and metal mesh layer in sequence, wherein the pattern layer comprises coding units, the coding units are composed of basic units in a two-dimensional array, the basic units comprise designed meshed pattern patches, the outline part of the pattern patch is reserved, and the metal line width of the outline part is greater than or equal to the metal mesh line width, and the pattern patch is filled with the metal mesh except the outline part; the good effect of the setting is that: the problems of low transmittance caused by the large metal coverage area of the pattern layer in the traditional metasurface, the poor transmittance of the ITO film and the inability to realize wide-band transparency are solved, and the outline characteristics of the pattern patch are reserved to solve the problem of poor performance of the metasurface caused by the edge resonance of the pattern patch. The meshed pattern patch in the pattern layer and the metal mesh layer make the coding metasurface in the application have high optical transparency, in some embodiments, the meshed pattern patch and the metal mesh layer can select the same metal mesh, and the high-order diffraction energy distribution can be homogenized; the meshed pattern patch and the metal mesh layer can further improve the uniformity of the high-order diffraction energy distribution of the structure by using different types of meshes, such as triangular distribution circular ring and sub-circular ring array, mesh based on random distribution circular ring, etc.

[0052] In summary, the application can design the pattern patch of the coding metasurface pattern layer and the structure sequence by theoretical method, which is efficient, convenient and has certain universality, the coding metasurface composed of the designed super unit has excellent low scattering performance in the target frequency band and high optical transparency, and provides a high-performance light window for aerospace, medical treatment and precision instrument equipment. BRIEF DESCRIPTION OF DRAWINGS

[0053] In order to more clearly illustrate the technical solutions adopted by the application, the following briefly introduces the drawings needed to be used by the technical methods adopted or proposed by the application, and obviously, the drawings in the following description are only some embodiments described in the application, and those skilled in the art can also obtain other drawings according to these drawings without creating any creative labor.

[0054] Figure 1is a schematic diagram of a double-symmetric P-B phase high-transmission metasurface profile.

[0055] Figure 2 is a transmission process of electromagnetic wave in unit metasurface.

[0056] Figure 3 is a schematic diagram of the rectangular coordinate system established for the basic unit and the geometric parameters of the graphic patch.

[0057] Figure 4 is a schematic diagram of the basic unit and the graphic patch grating.

[0058] Figure 5 is a schematic diagram of different graphic patches.

[0059] Figure 6 is a schematic diagram of different types of metal mesh grating.

[0060] Figure 7 is a schematic diagram of the coded metasurface and the coded unit.

[0061] Figure 8 is a schematic diagram of the coded metasurface and the coded unit in Example 1.

[0062] Figure 9 is the reflectivity of the unit metasurface in Example 1.

[0063] Figure 10 is the reflection phase and phase difference of the coded unit in Example 1.

[0064] Figure 11 is the RCS reduction of the coded metasurface in Example 1 within the target frequency band.

[0065] Figure 12 is a schematic diagram of the coded metasurface and the coded unit in Example 1.

[0066] Figure 13 is the reflectivity of the unit metasurface in Example 1.

[0067] Figure 14 is the reflection phase and phase difference of the coded unit in Example 1.

[0068] Figure 15 is the RCS reduction of the coded metasurface in Example 1 within the target frequency band.

[0069] Figure part number explanation: 1. protective layer; 2. anti-reflection layer; 3. pattern layer; 4. adhesive layer; 5. transparent medium layer; 6. adhesive layer; 7. metal mesh layer; 8. anti-reflection layer; 9. protective layer; 31. coded unit 0; 32. coded unit 1; 33. basic unit 0; 34. basic unit 1; 35. graphic patch. DETAILED DESCRIPTION

[0070] The purpose of the present application is achieved in the following way: a two-fold symmetry P-B phase high-transmittance metasurface structure sequence and unit pattern design method, the two-fold symmetry P-B phase high-transmittance metasurface is composed of three layers of pattern layer 3, transparent dielectric layer 5 and metal mesh layer 7 in sequence; the metasurface is a one-bit coding metasurface, the pattern layer 3 is composed of N×N (N≥5) groups of coding units with P-B phase characteristics arranged in sequence, the coding units are expressed as coding unit 0 (31) and coding unit 1 (32) according to a one-bit binary coding table; the P-B phase characteristics refer to the reflection phase difference between the coding unit 0 (31) and the coding unit 1 (32) is twice the geometric rotation angle when the geometric patch (35) constitutes the coding unit 0 (31) and the coding unit 1 (32); the coding unit 0 (31) is composed of M×M (M≥2) basic units 0 (33) arranged in a two-dimensional array; the basic unit 0 (33) contains a geometric patch 35 with a rotation state of 0°; the coding unit 1 (32) is composed of M×M (M≥2) basic units 1 (34) arranged in a two-dimensional array, and the number of basic units is the same as that in the coding unit 0 (31); the basic unit 1 (34) contains a geometric patch (35) with a rotation state of 90°; the basic unit 0 (33) and the basic unit 1 (34) are square in shape, each of which has and only one geometric patch 35, and the center of the geometric patch 35 coincides with the center of the basic unit 0 (33) and the basic unit 1 (34); the square side length of the basic unit 0 (33) and the basic unit 1 (34) is equal; the geometric patch 35 has the characteristics of non-cyclic, two-fold symmetry and anisotropy; the non-cyclic means that the geometric patch 35 does not contain a hole part; the two-fold symmetry is that a rectangular coordinate system is established in the geometric patch plane with the center of the geometric patch 35 as the origin, and there is one rectangular coordinate system that makes the geometric patch 35 symmetrical along two mutually perpendicular symmetry axes, which are the x and y rectangular coordinate axes; the distance from the center of the geometric patch 35 to the farthest point of its projection in the coordinate x axis direction is the geometric parameter d of the geometric patch 35 in the coordinate x axis direction; the distance from the center of the geometric patch 35 to the farthest point of its projection in the coordinate y axis direction is the geometric parameter l of the geometric patch 35 in the coordinate y axis direction; the anisotropy is that the geometric parameter d of the geometric patch 35 in the two rectangular coordinate axis directions is not equal to l; the geometric patch 35 is a grid-shaped metal patch; the grid-shaped means that the outline part of the geometric patch 35 is retained, and the outline part metal line width is greater than or equal to the metal mesh line width, and the geometric patch 35 is filled with a metal mesh except for the outline part; the metal mesh is a grid-shaped micro metal structure composed of mesh units arranged in a two-dimensional array;The structural order of the coding unit 0 (31) and coding unit 1 (32) refers to the coding sequence optimized according to the low-scattering metasurface function by the genetic algorithm. The feature is that multiple frequency points are uniformly selected in the target frequency band, and the fitness function in the genetic algorithm is the reciprocal of the product of the average value and standard deviation of the backscattered energy of the coding metasurface at these frequency points; the double-symmetric PB phase high-transmittance metasurface unit pattern design method is characterized in that the geometric parameters of the metasurface unit pattern are obtained by the following steps:

[0071] I. Define the target operating frequency band of the one-bit coded metasurface;

[0072] II. Based on the boundary conditions of Maxwell's equations, and applying the transmission matrix method, combined with the transmission matrix of electromagnetic waves in the patterned layer and the medium, the reflection field of the unit metasurface is obtained from the transmission process of electromagnetic waves perpendicularly incident on the unit metasurface. The unit metasurface refers to the minimum structure of the metasurface when the patterned layer contains only one basic unit. The reflection field of the unit metasurface is:

[0073]

[0074] Where i = x, y, represents the x and y directions of the rectangular coordinate axes; A i and B i A1 and B1 represent the electric field amplitudes of the electromagnetic waves propagating in the forward and reverse directions on pattern layer 3, respectively, while A1 and B1 represent the electric field amplitudes of the electromagnetic waves propagating in the forward and reverse directions on metal mesh layer 7, respectively. ω is the propagation coefficient, ω = 2πf is the angular frequency, μ is the absolute permeability of the medium, and μ = μ0μ r μ0 is the free permeability, μ r ε is the relative permeability of the medium; ε is the absolute permittivity of the medium, ε = ε₀ε r ε₀ is the vacuum permittivity, ε r Where is the relative permittivity of the dielectric; h is the thickness of the dielectric layer; Y0 = 1 / Z0 is the free-space admittance. Y1 = 1 / Z1 is the dielectric layer admittance. Y is the characteristic impedance of the dielectric layer; i =1 / Z eff-i For the feature admittance of the unit metasurface patterned layer 3, Z eff-i The equivalent impedance of the unit metasurface pattern layer 3.

[0075] III. Based on the reflection field of the unit metasurface described in step II, combined with the transmission matrix of electromagnetic waves in pattern layer 3 and transparent dielectric layer 5, and the amplitudes of the electromagnetic wave electric fields propagating in the forward and reverse directions on the metal mesh 7, the relationship between the field component reflection coefficients and the reflection field of the unit metasurface in the Cartesian coordinate axes x and y is obtained; the transmission matrices of the electromagnetic waves in pattern layer 3 and transparent dielectric layer 5 are respectively... and Ideally, the electromagnetic wave is totally reflected on the unit metasurface metal mesh layer 7, and the normalized electromagnetic wave electric field amplitude of the forward and reverse propagation on the metal mesh layer 7 is defined as:

[0076]

[0077] The reflection coefficient r of the unit metasurface along the field component in the x and y directions of the rectangular coordinate axis x and r y The relationship between the corresponding reflected field and the relationship is:

[0078] r x = B x / A x

[0079] r y = B y / A y

[0080] Set the target frequency band within a bit encoding metasurface to achieve the target of low scattering, then the unit metasurface needs to have high reflectivity in the target frequency band, that is, |r x | = |r y | = 1, then the equivalent impedance Z of the graphic patch 35 in the x and y directions of the rectangular coordinate axis at the upper and lower frequency endpoints of the target working frequency band can be quantified eff-i ;

[0081] IV, the equivalent impedance equation is where L i is the equivalent inductance, C i is the equivalent capacitance, the equivalent inductive reactance the equivalent capacitive reactance According to the equation formed by the two equivalent impedance equations of the graphic patch 35 in the x direction of the coordinate axis at the upper and lower frequency endpoints of the target working frequency band, the solution space of the equivalent inductive reactance and the equivalent capacitive reactance of the graphic patch 35 in the x direction of the coordinate axis is solved; Similarly, the solution space of the equivalent inductive reactance and the equivalent capacitive reactance of the graphic patch 35 in the y direction of the coordinate axis is solved;

[0082] V, the relationship between the equivalent inductive reactance and the equivalent capacitive reactance in the x and y directions of the rectangular coordinate axis and the length of the graphic patch 35 on the corresponding coordinate axis and the area of the graphic patch 35 is:

[0083] where w x = S / 2l

[0084] where g ax = p-S / 2l

[0085] wherein w y = S / 2d

[0086] wherein g ay = p-S / 2d

[0087] wherein p is the side length of the square corresponding to the basic unit 0 (33) and the basic unit 1 (34), S is the area of the graphic patch 35; F(p, η, λ) is:

[0088]

[0089]

[0090]

[0091]

[0092] wherein α is the incident angle of the electromagnetic wave, and λ is the wavelength of the electromagnetic wave;

[0093] VI. Each set of equivalent inductive reactance and equivalent capacitive reactance values in the solution space in the x and y directions of the coordinate axis in step IV has a pair of geometric parameter values d and l corresponding thereto, and the values of the geometric parameters d and l of the graphic patch 35 at this time can be quantified by applying the relationship in step V; a set of solutions with the same quantified values of the geometric parameters of the graphic patch 35 in the x and y directions of the coordinate axis is the final solution of the geometric parameters of the two-fold symmetric P-B phase high-transmittance super surface unit pattern;

[0094] Figure 1 is a super surface profile schematic diagram of a two-fold symmetric P-B phase high-transmittance super surface unit pattern and structure sequence design method, the transparent dielectric layer 5 can be selected as any transparent material according to actual application requirements, including ordinary glass, quartz glass, infrared material and transparent resin material, the pattern layer 3 is processed on the surface of the transparent dielectric layer 5 according to a certain process flow, the metal mesh layer 7 is processed on the other side surface of the transparent dielectric layer 5 according to a certain process flow; the adhesion layers (4 and 6) help the pattern layer 3 and the metal mesh layer 7 to be fixed on both sides of the transparent dielectric layer 5; the single-layer or multi-layer anti-reflection films (2 and 8) enhance the light transmittance of the super surface unit; the single-layer or multi-layer protective layers (1 and 9) are used to protect the pattern layer 3 and the metal mesh layer 7, prevent the mesh part from being oxidized and corroded or scratched for a long time exposed in the air, and avoid affecting the electromagnetic properties of the pattern layer 3 and the metal mesh layer 7; in actual application, the pattern layer 3, the transparent dielectric layer 5 and the metal mesh layer 7 are necessary factors of the present application, and the adhesion layers (4 and 6), the anti-reflection films (2 and 8) and the protective layers (1 and 9) are selectively added according to the process and actual application requirements.

[0095] Figure 2is the transmission process of electromagnetic wave in unit metasurface, when electromagnetic wave is incident, it passes through pattern layer 3, transparent dielectric layer 5, metal mesh layer 7, then the metal mesh layer 7 reflects the electromagnetic wave again through transparent dielectric layer 5, pattern layer 3 to the free space, in the process, the reflection field of unit metasurface is:

[0096]

[0097] Wherein, i=x, y, represents the x and y direction of the rectangular coordinate axis; A i and B i respectively represent the electric field amplitude of the forward and backward propagating electromagnetic wave on the pattern layer, A1 and B1 respectively represent the electric field amplitude of the forward and backward propagating electromagnetic wave on the metal mesh layer, is the propagation coefficient, ω=2πf is the angular frequency, μ is the absolute magnetic permeability of the medium, μ=μ0μ r , μ0 is the vacuum magnetic permeability, μ r is the relative magnetic permeability of the medium; ε is the absolute dielectric constant of the medium, ε=ε0ε r , ε0 is the vacuum dielectric constant, ε r is the relative dielectric constant of the medium; h is the thickness of the dielectric layer; Y0=1 / Z0 is the free space admittance, Y1=1 / Z1 is the dielectric layer admittance, is the characteristic impedance of the dielectric layer; Y i =1 / Z eff-i is the characteristic admittance of the pattern layer 3 of unit metasurface, Z eff-i is the equivalent impedance of the pattern layer 3 of unit metasurface.

[0098] Figure 3 is the rectangular coordinate system established with the center of the graphic patch 35 as the origin, the symmetry axis of the graphic patch 35 is the two rectangular coordinate axes, the dashed box represents the non-cyclic, two-fold symmetric and anisotropic graphic patch 35, including rectangular, diamond, ellipse, double ellipse, propeller-like, H-shaped, double diamond, cross-like, leaf-like patch, the distance from the center of the graphic patch 35 to the boundary of the graphic patch 35 along the x direction of the rectangular coordinate axis is the length d of the graphic patch 35 in the x direction of the rectangular coordinate axis, the distance from the center of the graphic patch 35 to the boundary of the graphic patch 35 along the y direction of the rectangular coordinate axis is the length l of the graphic patch 35 in the y direction of the rectangular coordinate axis, the length of the graphic patch 35 in the x and y directions of the rectangular coordinate system is calculated by the relationship between the equivalent inductance and the equivalent capacitance in the x and y directions of the rectangular coordinate axis and the length of the graphic patch 35 in the corresponding coordinate axis and the area of the graphic patch 35:

[0099] Wherein w x =S / 2l

[0100] Wherein gax = p-S / 2l

[0101] where w y = S / 2d

[0102] where g ay = p-S / 2d

[0103] where p is the period of the basic unit (33 and 34), S is the area of the pattern patch 35. F(p, η, λ) is:

[0104]

[0105]

[0106]

[0107]

[0108] where η = w x , w ax , w y , w ay , α is the angle of incidence of electromagnetic waves, and λ is the wavelength of electromagnetic waves.

[0109] Figure 4 is a schematic diagram of the grid of the pattern patch 35, and the basic unit of the pattern layer is as shown in Figure 4 (a). The pattern patch 35 is partially large-area metal, which is not conducive to optical transmission performance. The present application uses a grid method to improve the transmittance of the super surface pattern layer 3. The outline part of the pattern patch 35 is retained, and the metal line width of the outline part is greater than or equal to the metal grid line width. The pattern patch 35 is filled with a metal grid except for the outline part, so that Figure 4 (a) shows a rectangular pattern patch unit and a square metal grid, and the pattern patch after grid is as shown in Figure 4 (b). The metal area is significantly reduced compared to Figure 4 (a), which helps to improve the optical transmittance of the super surface unit, while retaining the outline characteristics of the pattern patch to solve the problem of poor super surface performance caused by the edge resonance of the pattern patch.

[0110] Figure 5The schematic diagram of different pattern patches, (a) is a rectangle, (b) is a rhombus, (c) is an ellipse, (d) is a double ellipse, (e) is a propeller-like shape, (f) is an H shape, (g) is a double rhombus, (h) is a cross-like shape, and (i) is a leaf-like shape. The pattern patches in the basic unit of the pattern layer are all subjected to grating processing, the grating pattern patch in the basic unit 0 (33) is in a 0° rotation state, and the grating pattern patch in the basic unit 1 (34) is in a 90° rotation state. The coding unit 0 or 1 (31 or 32) is composed of MxM (M≥2) basic units 0 or 1 (33 or 34) arranged in a two-dimensional array.

[0111] Figure 6 The schematic diagram of different types of metal grating, (a) is a square grating, (b) is a circular ring grating, (c) is a triangular distributed circular ring and sub-circular ring array grating, (d) is a metal grating based on a random distributed circular ring, (e) is a metal grating based on a multi-period metal circular ring nested array, and (f) is a metal grating with a top-fan-shaped metal. In addition to the basic metal grating (a) and (b), the grating of type (c), (d), (e) and (f) can also be used to further homogenize the high-order diffraction energy of the metasurface unit. The sub-circular ring is introduced in (c), the random element is added in (d), the multi-period circular ring is used in (e), and the fan-shaped grating is used in (f). According to actual application, the above grating can be selected to meet the imaging requirements.

[0112] Figure 7 The schematic diagram of the coding unit and the coding metasurface, the pattern layer 3, the transparent medium layer 5 and the metal grating layer 7 are sequentially stacked and placed to form the coding metasurface, the pattern layer 3 is composed of NxN (N≥5) groups of coding units arranged randomly, the coding unit 0 (31) is composed of MxM (M≥2) basic units 0 (33) with a 0° rotation state of the pattern patch (35) arranged in a two-dimensional array, and the coding unit 1 (32) is composed of MxM (M≥2) basic units 1 (34) with a 90° rotation state of the pattern patch (35) arranged in a two-dimensional array. Taking the rectangular pattern patch, M=2 and N=10 as an example, the coding unit 0 (31) is shown in (a), the coding unit 1 (32) is shown in (b), the coding unit structure sequence is the coding sequence optimized according to the low scattering metasurface function by using the genetic algorithm, the structure sequence and the coding unit arrangement are shown in (c), the fitness function in the genetic algorithm is the reciprocal of the average value of the maximum value and the standard deviation of the backscattering energy of the coding metasurface at multiple frequency points selected uniformly in the target frequency band, and the fitness function is as follows. Figure 7 Figure 7 Figure 7

[0113]

[0114] ​​​​To encode the far-field scattering energy value of the metasurface:

[0115]

[0116] where the reflection phase of the (m, n)th unit is If the one-bit encoding metasurface unit has a value of 0 or 180°; and is the pitch angle and azimuth angle in any direction; and the wave vector k = 2π / λ;

[0117] Embodiment 1:

[0118] According to one embodiment of the present application, the length d and l of the rectangular pattern patch in the x and y directions of the rectangular coordinate system are designed as shown in Figure 5 (a). The area of the rectangle is expressed as S = 4*l*d. First, the target operating frequency band is set to 9-17 GHz, the basic unit period of the metasurface pattern layer is p = 9.2 mm, and the transparent dielectric layer thickness h = 2.8 mm. To achieve the low scattering goal of the metasurface in the target operating frequency band, the unit metasurface needs to achieve the ideal reflection coefficient |r x | = |r y | = 1 in the target operating frequency band, so the equivalent impedance of the rectangular pattern patch in the x and y directions of the rectangular coordinate system at the two endpoints of the target operating frequency band is quantified, then the equivalent inductance and equivalent capacitance of the pattern patch in the x and y directions of the rectangular coordinate system are quantified, and finally d = 0.9 mm and l = 3.5 mm of the rectangular pattern patch are quantified according to the relationship between the length of the pattern patch in the corresponding coordinate axis and the area of the pattern patch, completing the geometric parameter design of the rectangular pattern patch. For the design of the rectangular pattern patch, the design method proposed by the present application improves the single simulation efficiency of the unit metasurface based on the rectangular pattern patch by 25.71 times compared to CST, proving that the design method proposed by the present application greatly improves the design efficiency and is more convenient and fast. The designed rectangular pattern patch is shown as the pattern patch 35 in Figure 8 (a), wherein the grid rectangular patch uses a square grid with a period of 100 μm and a line width of 5 μm as shown in Figure 8 (d), the material is aluminum, the thickness is 200 nm, the transparent dielectric layer uses quartz glass with a dielectric constant of 3.75 and a loss tangent angle of 0.01.

[0119] The effect of the present application can be further illustrated by Figure 9 , 10 , 11:

[0120] The reflectivity of the unit metasurface based on the rectangular pattern patch in the present embodiment is simulated, and the obtained unit metasurface reflectivity characteristics are shown in Figure 9As shown in (a) and (b), the reflection phases and phase differences of the obtained coding units 0 and 1 are as shown in (c) and (d). Figure 8 (a) and (b) are basic units 33 and 34, respectively. Figure 8 (a) and (b) are basic units 33 and 34, respectively. Figure 8 (a) and (b) are basic units 33 and 34, respectively. Figure 10 As shown in (c) and (d), the phase difference is always stable at 180° in the effective working frequency band of 9.47-17.57 GHz. Figure 8 (c) shows the structure sequence, which is arranged in 10x10 groups of coding unit size, and the coding metasurface pattern layer has a size of 184x184mm 2 The metal mesh used in the metasurface metal mesh layer is the same as the pattern layer, which is a square mesh as shown in (d). Figure 8 (d) shows the square mesh, in order to evaluate the backscattering performance of the metasurface, the radar cross section (RCS) value is simulated, and compared with the RCS value of the same size of metal aluminum plate, the obtained RCS reduction result is as shown in (e). Figure 11 As shown in (e), the RCS reduction value of the coding metasurface is always less than -10dB in the effective working frequency band of 9.47-17.57GHz, and has excellent low scattering performance.

[0121] The light transmittance of the designed metasurface in this embodiment is analyzed, the light transmittance of the grid-etched rectangular pattern patch is 98.5%, and the light transmittance of the metal mesh is 90.0%, so the light transmittance of the metasurface is 88.7%. Since the transmittance of quartz glass does not attenuate in the visible-infrared wide band range, the designed metasurface in this embodiment can realize high light transmittance in the visible-infrared wide band range, and is suitable for various transparent demand occasions.

[0122] Embodiment 2:

[0123] According to one embodiment of the present application, a leaf-like pattern patch as shown in (i) is designed. Figure 5 The length d and l of the leaf-like pattern patch in the x and y directions of the rectangular coordinate system are set as shown in (i), and the area expression of the leaf-like pattern is First, the target working frequency band is set to 9-17GHz, the metasurface pattern layer basic unit period p=9.2mm, and the transparent dielectric layer thickness h=2.8mm. In order to achieve the target of low scattering of the metasurface in the target working frequency band, the unit metasurface needs to achieve the ideal reflection coefficient |r x |=|r y|=1, the equivalent impedance of the target working frequency band two end point leaf-shaped pattern patch in the x and y direction of the rectangular coordinate axis is quantified, then the equivalent inductive reactance and equivalent capacitive reactance of the pattern patch in the x and y direction of the rectangular coordinate axis are quantified, finally, the d=1.1 mm and l=4.1 mm of the leaf-shaped pattern patch are quantified according to the relationship between the length of the pattern patch on the corresponding coordinate axis and the area of the pattern patch, and the geometric parameter design of the leaf-shaped pattern patch is completed; for the design of the leaf-shaped pattern patch, the design method proposed in the application improves the single simulation efficiency of the unit metasurface based on the leaf-shaped pattern patch by 35.82 times compared with CST, which proves that the design method proposed in the application greatly improves the design efficiency and is more convenient and fast. Figure 12 (a) shows the pattern patch 35, wherein the grid-shaped rectangular patch adopts a square grid with a period of 100 μm and a line width of 5 μm as shown in Figure 12 (d), the material is aluminum, the thickness is 200 nm, the transparent dielectric layer adopts quartz glass with a dielectric constant of 3.75 and a loss tangent angle of 0.01.

[0124] The effect of the application can be further illustrated by Figure 13 , 14 , 15.

[0125] The reflectivity of the unit metasurface based on the leaf-shaped pattern patch in the embodiment is simulated, and the reflectivity characteristics of the unit metasurface are as shown in Figure 13 , the effective working frequency band with a reflectivity greater than 90% is 9.47-17.57 GHz, which meets the set working frequency band; the reflection phases of the encoding units 0 and 1 composed of the basic units 0 and 1 are simulated, the basic units 0 and 1 are as shown in Figure 12 (a) and Figure 12 (b), the basic units 0 and 1 are as shown in Figure 12 (a) and (b), and the reflection phases and phase differences of the encoding units 0 and 1 are as shown in Figure 13 , the phase difference is always stable at 180° in the effective working frequency band 9.47-17.57 GHz; the encoding units are arranged according to the encoding sequence as shown in Figure 12 (c), to form an encoding metasurface pattern layer with a size of 10×10 encoding units, and the size of the encoding metasurface is 184×184 mm 2 , the grid of the metasurface metal grid layer is the same as that of the pattern layer, which is a square grid as shown in Figure 12 (d), in order to evaluate the backscattering performance of the metasurface, the radar cross section (RCS) value of the metasurface is simulated, and compared with the RCS value of the same size of aluminum plate, and the RCS reduction result is as shown in Figure 15As shown, the coding metasurface has an RCS reduction value less than -10 dB in the effective working frequency band 9.47-17.57 GHz, and has excellent low scattering performance.

[0126] The light transmittance of the designed metasurface in this embodiment is analyzed. The light transmittance of the grid-structured leaf-shaped pattern patch is 98.3%, and the light transmittance of the metal mesh grid is 90.0%. Therefore, the light transmittance of the metasurface is 88.5%. Since the quartz glass does not attenuate in the visible-infrared wide band range, the designed metasurface in this embodiment can realize high light transmittance in the visible-infrared wide band range, and is suitable for various transparent demand occasions.

[0127] The above description is only two specific examples of the present application. Obviously, for those skilled in the art, after understanding the content and principles of the present application, various modifications and changes in form and details can be made without departing from the principles and structures of the present application. However, these modifications and changes based on the idea of the present application are still within the protection scope of the claims of the present application.

Claims

1. A method for designing a two-fold symmetric P-B phase high-transmission metasurface structure sequence and unit pattern, the two-fold symmetric P-B phase high-transmission metasurface being composed of three layers of a pattern layer (3), a transparent dielectric layer (5), and a metal mesh layer (7) stacked in sequence; the metasurface being a one-bit coding metasurface, the pattern layer (3) being composed of N×N groups of coding units with P-B phase characteristics arranged according to a structure sequence, N≥5, the coding units being expressed as coding unit 0 (31) and coding unit 1 (32) according to a one-bit binary coding table; the P-B phase characteristics referring to a characteristic that a reflection phase difference between the coding unit 0 (31) and the coding unit 1 (32) is twice a geometric rotation angle of a pattern patch (35) when the pattern patch (35) constitutes the coding unit 0 (31) and the coding unit 1 (32); the coding unit 0 (31) being composed of M×M basic units 0 (33) arranged in a two-dimensional array, M≥2; the basic unit 0 (33) containing the pattern patch (35) with a rotation state of 0°; the coding unit 1 (32) being composed of M×M basic units 1 (34) arranged in a two-dimensional array, M≥2, and the number of basic units being the same as that in the coding unit 0 (31); the basic unit 1 (34) containing the pattern patch (35) with a rotation state of 90°; the basic unit 0 (33) and the basic unit 1 (34) being square in shape, each having and only having one pattern patch (35), and the center of the pattern patch (35) coinciding with the center of the basic unit 0 (33) and the basic unit 1 (34); the square side length of the basic unit 0 (33) and the basic unit 1 (34) being equal; the pattern patch (35) having the characteristics of non-cyclic, two-fold symmetry, and anisotropy; the non-cyclic referring to that the pattern patch (35) does not contain a hole part; the two-fold symmetry referring to that a rectangular coordinate system can be established in the plane of the pattern patch (35) with the center of the pattern patch (35) as the origin, and the pattern patch (35) can be symmetrical about two mutually perpendicular symmetry axes, the symmetry axes being the two rectangular coordinate axes x and y; the distance from the center point of the pattern patch (35) to the farthest point of the projection of the pattern patch (35) in the coordinate x-axis direction being a geometric parameter d of the pattern patch (35) in the coordinate x-axis direction. The distance from the center point of the graphic patch (35) to the point farthest from the center point in the y direction is the geometric parameter l of the graphic patch (35) in the y direction; the anisotropy is the geometric parameter d ≠ l of the graphic patch (35) in the two orthogonal coordinate directions; the graphic patch (35) is a grid metal patch; the grid refers to the outline part of the graphic patch (35) being retained, and the outline part having a metal line width greater than or equal to the metal grid line width, and the graphic patch (35) being filled with a metal grid except for the outline part; the metal grid is a grid-shaped micro metal structure formed by grid units arranged in a two-dimensional array; the structure sequence of the coding unit 0 (31) and the coding unit 1 (32) refers to a coding sequence optimized according to a genetic algorithm and a low-scattering metasurface function, and the method is characterized in that, A plurality of frequency points are uniformly selected in a target frequency band, and the fitness function in the genetic algorithm is the reciprocal of the product of the average value of the maximum value and the standard deviation of the backscattering energy of the coded metasurface at the frequency points; a double-symmetry P-B phase high-transmittance metasurface unit pattern design method, characterized by that the geometric parameters of the metasurface unit pattern are obtained by the following steps: I. Set a target working frequency band of a one-bit coded metasurface; II. According to the boundary conditions of Maxwell's equations, the transmission matrix method is applied, the transmission matrix of electromagnetic waves in the pattern layer and the medium is combined, and the reflection field of the unit metasurface is obtained from the transmission process of the electromagnetic wave vertically incident on the unit metasurface, wherein the unit metasurface refers to the smallest structure of the metasurface when the pattern layer (3) only contains one basic unit; the reflection field of the unit metasurface is: where i=x, y represents the x and y direction of the orthogonal coordinate axis; A i and B i respectively represent the electric field amplitude of the electromagnetic wave propagating forward and backward on the pattern layer (3), A1 and B1 respectively represent the electric field amplitude of the electromagnetic wave propagating forward and backward on the metal mesh layer (7), is the propagation coefficient, ω=2πf is the angular frequency, μ is the absolute magnetic permeability of the medium, μ=μ0μ r , μ0 is the magnetic permeability of vacuum, μ r is the relative magnetic permeability of the medium; ε is the absolute dielectric constant of the medium, ε=ε0ε r , ε0 is the dielectric constant of vacuum, ε r is the relative dielectric constant of the medium; h is the thickness of the medium layer; Y0=1 / Z0 is the admittance of free space, Y1=1 / Z1 is the admittance of the medium layer, is the characteristic impedance of the medium layer; Y i =1 / Z eff-i is the characteristic admittance of the unit super surface pattern layer (3), Z eff-i is the equivalent impedance of the unit super surface pattern layer (3); III. The relationship between the reflection coefficient of the field component of the unit super surface in the x and y directions of the rectangular coordinate axis and the reflected field is obtained by combining the reflected field of the unit super surface described in step II, the transmission matrix of the electromagnetic wave in the pattern layer (3) and the transparent medium layer (5), and the normalized electromagnetic wave electric field amplitude of the forward and backward propagation electromagnetic wave on the metal mesh (7). The transmission matrix of the electromagnetic wave in the pattern layer (3) and the transparent medium layer (5) is respectively and Under ideal conditions, the electromagnetic wave is totally reflected on the metal mesh layer (7) of the unit super surface, and the normalized electromagnetic wave electric field amplitude of the forward and backward propagation electromagnetic wave on the metal mesh layer (7) is defined as: The unit metasurface along the straight coordinate axis x and y direction field component reflection coefficient r x and r y The relationship between the corresponding reflected field is: r x = B x / A x r y = B y / A y If a low scattering target is set for a one-bit coding metasurface in a target frequency band, the unit metasurface needs to have high reflectivity in the target frequency band, that is, |r x | = |r y | = 1, the equivalent impedance Z of the graphic patch (35) in the x and y directions of the rectangular coordinate axis at the upper and lower frequency endpoints of the target working frequency band can be quantified eff-i ; IV. The equivalent impedance equation is where L i is the equivalent inductance, C i is the equivalent capacitance, the equivalent inductive reactance X Li = ωL i , and the equivalent capacitive reactance B Ci = ωC i ; according to the equation set composed of the two equivalent impedance equations in the x direction of the coordinate axis of the graphic patch (35) at the upper and lower frequency endpoints of the target working frequency band, the solution space of the equivalent inductive reactance and the equivalent capacitive reactance of the graphic patch (35) in the x direction of the coordinate axis is solved; similarly, the solution space of the equivalent inductive reactance and the equivalent capacitive reactance of the graphic patch (35) in the y direction of the coordinate axis is solved; V. The relationship between the equivalent inductance and the equivalent capacitance in the x and y directions of the right-angle coordinate system, the length of the graphic patch (35) in the corresponding coordinate axis, and the area of the graphic patch (35) is: where w x = S / 2l where g ax = p - S / 2l where w y = S / 2d where g ay = p - S / 2d Wherein, p is the side length of the corresponding square of the basic unit 0 (33) and the basic unit 1 (34), S is the area of the graphic patch (35); F(p, η, λ) is: Wherein, α is the electromagnetic wave incidence angle, and λ is the electromagnetic wave wavelength; VI. Each set of equivalent inductance and equivalent capacitance values in the solution space in the x and y directions of the coordinate axis has a pair of geometric parameter values d and l corresponding thereto, and the values of the geometric parameters d and l of the graphic patch (35) at this time can be quantified by applying the relationship in step V; a set of solutions with the same quantified values of the geometric parameters of the graphic patch (35) in the x and y directions of the coordinate axis is the final solution of the geometric parameters of the double-symmetry P-B phase high-transmittance metasurface unit pattern.

2. A method for designing a two-fold symmetric P-B phase high-transmission metasurface structure sequence and unit pattern according to claim 1, The expression for encoding the metasurface far-field scattering energy is: wherein The reflection phase of the (m,n)th unit is A one-bit encoding metasurface unit The value of is 0 or 180°; θ and Is the pitch angle and azimuth angle in any direction; the wave vector k=2π / λ; the encoding sequence optimized according to the genetic algorithm according to the low scattering metasurface function by adopting a fitness function, characterized by: the fitness function is:

3. The design method of a two-fold symmetric P-B phase high-transmission metasurface structure sequence and unit pattern according to claim 1, characterized in that: The non-cyclic, double-symmetry and anisotropic graphic patch (35) includes a rectangle, a diamond, an ellipse, a double ellipse, a propeller-like shape, an H shape, a double diamond, a cross-like shape, and a double sine shape.

4. The design method of a two-fold symmetric P-B phase high-transmission metasurface structure sequence and unit pattern according to claim 1, characterized in that: The transparent dielectric layer (5) is any transparent material that can meet the light transmission requirements of the application, and the transparent material can be used as a transparent light window material that meets the requirements of the application.

5. The design method of a two-fold symmetric P-B phase high-transmission metasurface structure sequence and unit pattern according to claim 1, characterized in that: The metal grid (7) includes a square grid, a circular ring, a triangular distribution circular ring and a sub-circular ring array, a random distribution circular ring, a multi-period circular ring nesting, and a top-fan-shaped array grid.

6. The design method of a two-fold symmetric P-B phase high-transmission metasurface structure sequence and unit pattern according to claim 1, characterized in that: The metal mesh grid line width is in the order of microns or sub-microns; the metal mesh grid and the grid mesh pattern patch are both composed of metal with good conductivity, and the metal thickness is greater than 100 nm.

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