A broadband transparent metasurface and a method of manufacturing the same

Abstract

The application discloses a broadband transparent superstructure surface and a manufacturing method thereof. The superstructure surface is formed by arranging a "0" subarray and a "1" subarray, the "0" subarray is formed by "0" units arranged in a matrix form, the "0" unit is a super unit, the super unit is rotated 90 degrees around the z-axis to obtain a "1" unit, and the "1" subarray is formed by "1" units arranged in a matrix form. Compared with the "0" unit, the "1" unit has the same reflection coefficient amplitude but a phase difference of 180 degrees. The super unit is composed of a first dielectric layer, an upper resistive film pattern layer, a second dielectric layer, a lower resistive film pattern layer, a third dielectric layer and a ground layer which are stacked from top to bottom, the upper resistive film pattern layer is a square ring with a pair of diagonal oblique openings, and the lower resistive film pattern layer is a square ring. The superstructure surface of the application realizes an RCS reduction performance of -10 dB in a wide frequency band range, has low manufacturing cost and is suitable for promotion.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of polarized conversion, absorption and scattering integrated wide frequency band transparent superstructure and its manufacturing method, belong to superstructure design field. BACKGROUND

[0002] Metamaterial is a kind of artificial microstructure consisting of periodic subwavelength units, as an important development direction of advanced electromagnetic materials, break the limitation of natural material performance, realize the static and dynamic modulation of electromagnetic wave amplitude, frequency and polarization, and has been widely used in stealth materials and microwave devices. With the increasing demand of military practice on stealth level, the research of low radar cross section (RCS) metamaterial gradually becomes a hotspot. One of the main ways to achieve low radar cross section is to obtain low backscattering performance. At present, low backscattering performance can be mainly realized by two methods.

[0003] One method is to use lossy structures or super atoms to absorb incident wave energy, such as Jaumann absorber and Salisbury screen. In 2008, N.I.Landy et al. first proposed a perfect metamaterial absorber, which realized electric resonance and magnetic resonance by combining two kinds of metamaterial resonators, and can achieve nearly 100% high-efficiency electromagnetic absorption at a single frequency, opening up a new field of metamaterial absorbers. But according to Rozanov limit, due to the influence of thickness and structure, the absorption bandwidth of these absorbers is limited. After that, researchers realized multi-frequency or wideband absorption by combining multiple resonators on a single-layer structure or using multi-layer structure. With the further development of metamaterial absorbers, metamaterial absorbers are also proposed by loading lumped resistance or using resistive materials (such as resistive ink, indium tin oxide film, graphene, etc.) to realize impedance matching, further expanding the wideband absorption performance. However, the above researches all have the defect of high manufacturing and maintenance cost due to the material cost.

[0004] Another method is to reshape the scattered wave by introducing phase modulation, which will redirect the backscattered energy to other directions to diffuse. In 2007, Panquay et al. first proposed a chessboard structure composed of artificial magnetic conductor (AMC) and perfect electric conductor (PEC), which successfully divided the scattered wave into four beams, thus effectively reducing the RCS, and in order to broaden the working frequency band, two kinds of AMC structures working at different frequencies were combined into a chessboard, achieving a RCS reduction of-10 dB in a relative bandwidth of 40%, but the bandwidth is relatively limited. In recent years, metasurfaces have emerged, which are a kind of intelligent surfaces in the form of two-dimensional array composed of subwavelength metasurface units, which have the ability of arbitrary reflection phase control, providing a new solution for reducing RCS. In 2014, researchers proposed the concept of digitally encoded metasurface with random distribution of 1-bit phase metasurface units to achieve RCS reduction. With the in-depth research, researchers combined the far-field scattering mode analysis method with the optimization algorithm to obtain the optimal arrangement sequence of the metasurface units, which can uniformly scatter the incident wave to all directions, achieving the best diffusion performance. However, in the design process of digitally encoded metasurface, at least two different metasurface units are needed and the phase difference between them is kept at 180°, which undoubtedly increases the design and manufacturing difficulty.

[0005] From the above, it is urgent to design a technical solution that can solve the defects of the above two methods, improve the RCS reduction performance of the metasurface on the basis of widening the frequency band. SUMMARY

[0006] The purpose of the present application is to provide a kind of polarization conversion, absorption and scattering integrated wideband transparent metasurface and its manufacturing method, the metasurface achieves-10dB RCS reduction performance in wideband range, low manufacturing cost, suitable for promotion.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0008] A broadband transparent metasurface formed by a "0" sub-array and a "1" sub-array, the "0" sub-array is formed by "0" units arranged in a matrix form, the "0" unit is a metasurface unit, the metasurface unit is rotated 90° around the z-axis to obtain a "1" unit, the "1" sub-array is formed by the "1" units arranged in a matrix form, wherein: compared with the "0" unit, the "1" unit has the same reflection coefficient amplitude but the phase difference is 180°; the metasurface unit is composed of a first dielectric layer, an upper resistive film pattern layer, a second dielectric layer, a lower resistive film pattern layer, a third dielectric layer and a ground layer stacked from top to bottom, the upper resistive film pattern layer is a square ring with a pair of diagonal oblique openings, and the lower resistive film pattern layer is a square ring.

[0009] A manufacturing method of a broadband transparent metasurface, comprising the steps of:

[0010] 1) initially setting the structure parameters of the metasurface unit;

[0011] 2) calculating the equivalent impedance theoretical value of the metasurface unit by a genetic algorithm, so that the reflection coefficient amplitude is less than -10dB;

[0012] 3) performing numerical simulation according to the equivalent impedance theoretical value, and inversely obtaining the actual structure parameters of the metasurface unit, adjusting the structure of the metasurface unit according to the actual structure parameters, and completing the optimization of the metasurface unit, wherein: the difference between the actual value of the equivalent impedance of the metasurface unit obtained by inversion and the equivalent impedance theoretical value is less than 10%;

[0013] 4) obtaining the "0" unit based on the adjusted metasurface unit, and obtaining the "1" unit by rotating the metasurface unit 90° around the z-axis;

[0014] 5) constructing the "0" sub-array by the "0" unit, and constructing the "1" sub-array by the "1" unit;

[0015] 6) randomly arranging the "0" sub-array and the "1" sub-array to obtain the broadband transparent metasurface;

[0016] 7) optimizing the arrangement of the "0" sub-array and the "1" sub-array by a genetic algorithm, so that the proportion of low energy released by the scattered echo of the broadband transparent metasurface to the total energy exceeds 90% from the direction perpendicular to the upper surface of the broadband transparent metasurface, thereby obtaining the optimal broadband transparent metasurface;

[0017] 8) completing the manufacturing of the broadband transparent metasurface.

[0018] The present application has the advantages of:

[0019] 1、The super-structure surface of the present application can achieve a relative bandwidth of 150% (realizing wide-band coverage in the frequency band of 3.7GHz-25.9GHz) under the condition of single-station vertical incidence, and a relative bandwidth of 140% under the condition of double-station incidence angle not greater than 40°.

[0020] 2、The super-structure surface structure of the present application is transparent and has high transmittance, and maintains good optical transparent characteristics.

[0021] 3、The super-structure surface of the present application is manufactured by using common materials (ITO film and PMMA plate) with low cost, and has great reduced manufacturing cost, controllable manufacturing process, small manufacturing difficulty and low manufacturing cost. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is an example diagram of the super-structure surface of the present application.

[0023] Figure 2 is a structural schematic diagram of the super-structure unit.

[0024] Figure 3A is a structural schematic diagram of the lower resistance film pattern layer.

[0025] Figure 3B is a structural schematic diagram of the upper resistance film pattern layer.

[0026] Figure 4 is a process explanation diagram of the genetic algorithm for solving the optimal equivalent impedance.

[0027] Figure 5 is a curve comparison diagram of the optimized theoretical value and the inverted actual value of the reflection coefficient amplitude obtained based on the optimal equivalent impedance solved by the genetic algorithm.

[0028] Figure 6 is a reflection coefficient amplitude curve diagram of the same polarization and cross-polarization under linear polarization wave excitation of the "0" unit and the "1" unit.

[0029] Figure 7 is a reflection coefficient phase curve diagram of the same polarization and cross-polarization under linear polarization wave excitation of the "0" unit and the "1" unit.

[0030] Figure 8 is a three-dimensional scattering field diagram of the super-structure surface obtained after optimizing the arrangement of the "0" and "1" sub-arrays at the center frequency point of 11GHz.

[0031] Figure 9 is the echo release energy distribution diagram of the super-structured surface obtained after optimizing the arrangement of the "0" and "1" sub-arrays.

[0032] Figure 10 is a three-dimensional schematic diagram of the super-structured surface obtained after optimizing the arrangement of the "0" and "1" sub-arrays.

[0033] Figure 11 is a single station RCS simulation curve diagram of the super-structured surface and the all "1" sub-array surface.

[0034] Figure 12 is a simulation and test result curve diagram of the monopolar single station RCS reduction value of the super-structured surface under linear polarization wave excitation.

[0035] Figure 13 is a simulation and test result curve diagram of the cross-polar single station RCS reduction value of the super-structured surface under linear polarization wave excitation.

[0036] Figure 14 is a test result curve diagram of the monopolar double station RCS reduction value of the super-structured surface when the incident angle is 0°, 20° and 40°.

[0037] Figure 15 is a test result curve diagram of the cross-polar double station RCS reduction value of the super-structured surface when the incident angle is 0°, 20° and 40°. DETAILED DESCRIPTION

[0038] As Figure 1 , the present application proposes a wideband transparent super-structured surface 40 formed by arranging "0" sub-arrays 20 and "1" sub-arrays 30, the "0" sub-arrays 20 are formed by "0" units arranged in a matrix form, the "0" unit is a super-structured unit 10, the super-structured unit 10 is rotated 90° (clockwise or counterclockwise) around its z-axis to obtain a "1" unit, the "1" sub-arrays 30 are formed by "1" units arranged in a matrix form, wherein: compared with the "0" unit, the "1" unit has the same reflection coefficient amplitude but the phase difference is stable by 180°, that is, the phase difference between the cross-polar direction of the "1" unit and the cross-polar direction of the "0" unit is 180°; the super-structured unit 10 is composed of a first dielectric layer 11, an upper resistive film pattern layer 14, a second dielectric layer 12, a lower resistive film pattern layer 15, a third dielectric layer 13 and a ground layer 16 stacked from top to bottom, in other words, Figure 2, the super unit 10 comprises a first dielectric layer 11, a second dielectric layer 12 and a third dielectric layer 13 which are stacked in sequence, an upper resistive film pattern layer 14 is arranged between the first dielectric layer 11 and the second dielectric layer 12, a lower resistive film pattern layer 15 is arranged between the second dielectric layer 12 and the third dielectric layer 13, and a ground layer 16 is arranged below the third dielectric layer 13, the upper resistive film pattern layer 14 is a square ring with a pair of diagonal oblique openings 140 (as shown in Figure 3B ), which is used to transfer part of the energy of the incident wave to the cross-polarization direction to realize the scattering of the echo through the subsequent coding arrangement, the lower resistive film pattern layer 15 is a square ring without openings (as shown in Figure 3A ), which is used to absorb the incident wave, and the first dielectric layer 11, the second dielectric layer 12, the third dielectric layer 13 and the ground layer 16 are square and have no openings.

[0039] As shown in Figure 1 , an example of the broadband transparent superstructure surface 40 of the present application is shown in the figure, in which the shaded squares are the "0" sub-array 20 and the blank squares are the "1" sub-array 30.

[0040] In the present application, the direction in which the first dielectric layer 11, the second dielectric layer 12, the third dielectric layer 13, the upper resistive film pattern layer 14, the lower resistive film pattern layer 15 and the ground layer 16 are stacked in sequence is the height direction or the thickness direction, that is, the z direction, in other words, the z direction is the direction perpendicular to the first dielectric layer 11 or the direction perpendicular to the upper surface of the broadband transparent superstructure surface 40 of the present application, as shown in Figure 2 , the x direction and the y direction are defined in the plane perpendicular to the z direction, generally, the x direction is the width direction and the y direction is the length direction, and in the present application, the width and the length of each layer of the super unit 10 are equal, that is, each layer is square in shape.

[0041] In actual design, the matrix form of the arrangement of the "0" sub-array 20 and the "1" sub-array 30 is the same, that is, if the "0" sub-array is arranged in the form of a 2x3 matrix, the "1" sub-array is also arranged in the form of a 2x3 matrix, the only difference between the two is that the elements of the "0" sub-array are "0" units and the elements of the "1" sub-array are "1" units, thus, the "0" sub-array 20 and the "1" sub-array 30 are regularly arranged in the form of a matrix to form the broadband transparent superstructure surface 40 of the present application.

[0042] Of course, it is also possible that the matrix form of the arrangement of the "0" sub-array 20 and the "1" sub-array 30 is different, and similarly, the "0" sub-array 20 and the "1" sub-array 30 are arranged to form the rectangular broadband transparent superstructure surface 40 of the present application, and the specific arrangement manner is not limited.

[0043] In actual arrangement, the "0" units are closely adjacent to form a "0" sub-array 20, the "1" units are closely adjacent to form a "1" sub-array 30, and the "0" sub-array 20 and the "1" sub-array 30 are also closely adjacent to form the super-structured surface 40 of the application.

[0044] In the application, the thicknesses of the first, second and third dielectric layers 11, 12 and 13 are the same and much greater than the thicknesses of the upper resistive film pattern layer 14, the lower resistive film pattern layer 15 and the ground layer 16, and the thicknesses of the upper resistive film pattern layer 14, the lower resistive film pattern layer 15 and the ground layer 16 are usually negligible, wherein: the thicknesses of the first, second and third dielectric layers 11, 12 and 13 are 3 mm (i.e. d = 3 mm, as shown in Figure 2 ), the dielectric constant ε r is 2.8, the magnetic permeability μ r is 1, and the loss tangent tan δ is 0.001; the first, second and third dielectric layers 11, 12 and 13 and the ground layer 16 are square with a side length of 5 mm.

[0045] Further, it is understood with reference to Figure 3A and Figure 3B that the outer side length w3 of the upper resistive film pattern layer 14 and the outer side length w1 of the lower resistive film pattern layer 15 are initially set to 5 mm, and the inner side length w4 of the upper resistive film pattern layer 14 and the inner side length w2 of the lower resistive film pattern layer 15 are initially set to a value smaller than the outer side length at will, and the width of the oblique opening 140, the sheet resistance r1 of the upper resistive film pattern layer 14 and the sheet resistance r2 of the lower resistive film pattern layer 15 are initially set to a reasonable value at will, but the sheet resistance of the ground layer 16 does not need to be optimized and adjusted and can be directly set to 5 Ω / sq.

[0046] In the application, numerical simulation is performed according to the theoretical value of the equivalent impedance calculated by the genetic algorithm, the actual structural parameters of the super-structured unit 10 are obtained by inversion, the super-structured unit 10 is adjusted according to the actual structural parameters, and the optimization of the structural parameters of the super-structured unit 10 is completed, wherein: the theoretical value of the equivalent impedance obtained by the genetic algorithm makes the amplitude of the reflection coefficient (S11) of the "0" unit satisfy less than -10 dB; the actual value of the equivalent impedance of the super-structured unit 10 obtained by inversion should satisfy a difference of less than 10% from the theoretical value of the equivalent impedance; the outer side length w3 of the upper resistive film pattern layer 14 is adjusted from the initial value of 5 mm to 4.95 mm, and the inner side length w4 is adjusted from the initial value to 4.25 mm; the outer side length w1 of the lower resistive film pattern layer 15 is adjusted from the initial value of 5 mm to 4.95 mm, and the inner side length w2 is adjusted from the initial value to 3 mm; the width of the oblique opening 140 on the upper resistive film pattern layer 14 is adjusted from the initial value to 0.1 mm; and the sheet resistance r1 of the upper resistive film pattern layer 14 and the sheet resistance r2 of the lower resistive film pattern layer 15 are set to 50 Ω / sq.

[0047] In actual design, in order to realize high light transmittance, the first medium layer 11, the second medium layer 12 and the third medium layer 13 are made of transparent PMMA (polymethyl methacrylate) plates, and the upper resist film pattern layer 14, the lower resist film pattern layer 15 and the ground layer 16 are made of transparent ITO (indium tin oxide) thin films.

[0048] In the present application, based on antenna theory, the arrangement of the '0' subarray 20 and the '1' subarray 30 forming the wideband transparent metasurface 40 of the present application is optimized by genetic algorithm, so that the low energy released by the echo scattered after the wideband transparent metasurface 40 of the present application receives the incident wave from the direction perpendicular to the first medium layer 11 (or from the z direction) accounts for more than 90% of the total energy, at this time the wideband transparent metasurface formed is optimal.

[0049] Here, low energy refers to a lower energy state, and in the field, power below a certain threshold is defined as low energy, and the threshold can be reasonably set according to actual conditions and is not limited.

[0050] The present application also provides a manufacturing method of a wideband transparent metasurface, comprising the steps of:

[0051] 1) Initially set the structure parameters of the metasurface unit 10, wherein the thickness, side length, dielectric constant ε r , magnetic permeability μ r , loss tangent tan δ of the first medium layer 11, the second medium layer 12 and the third medium layer 13, the side length of the ground layer 16, the outer side length, the inner side length and the square resistance of the upper resist film pattern layer 14 and the lower resist film pattern layer 15, and the width of the oblique opening 140 of the upper resist film pattern layer 14 are all given an initial value;

[0052] 2) In order to achieve wideband wave absorption effect, the overall structure of the unit needs to satisfy the impedance matching condition with air, therefore, based on the equivalent circuit theory, the equivalent impedance theoretical value (main polarization direction) of the metasurface unit 10 is calculated by genetic algorithm, so that the reflection coefficient amplitude is less than -10dB, that is, the optimal equivalent impedance of the upper resist film pattern layer 14 and the lower resist film pattern layer 15 is obtained;

[0053] 3) Numerical simulation is performed according to the equivalent impedance theory value using electromagnetic simulation software, the actual structure parameters of the super unit 10 are obtained by inversion, the structure of the super unit 10 is adjusted according to the actual structure parameters, and the optimization of the super unit 10 is completed, wherein: the actual value of the equivalent impedance of the super unit 10 obtained by inversion and the theoretical value of the equivalent impedance should satisfy that the difference is less than 10%, and the adjustment of the super unit 10 mainly includes adjusting the outer edge length and the inner edge length of the upper resistive film pattern layer 14 and the lower resistive film pattern layer 15, the width of the oblique opening 140 of the upper resistive film pattern layer 14, and the square resistance of the upper resistive film pattern layer 14 and the lower resistive film pattern layer 15;

[0054] 4) Based on the adjusted super unit 10, a "0" unit is obtained, and a "1" unit is obtained by rotating the z-axis of the super unit 10 by 90° (clockwise or counterclockwise);

[0055] 5) A "0" subarray 20 is constructed by the "0" unit, and a "1" subarray 30 is constructed by the "1" unit;

[0056] 6) The "0" subarray 20 and the "1" subarray 30 are randomly arranged to obtain the wideband transparent super surface 40 of the application, wherein the "0" and "1" subarrays are randomly arranged to make the echo scattered as uniformly as possible in all directions;

[0057] 7) Based on the array antenna theory, the arrangement of the "0" subarray 20 and the "1" subarray 30 is optimized by genetic algorithm, so that the proportion of low energy released by the echo scattered after the wideband transparent super surface 40 of the application receives the incident wave from the direction perpendicular to the upper surface (i.e. the first dielectric layer 11) of the wideband transparent super surface 40 (or said from the z direction) exceeds 90% of the total energy, so as to obtain the optimal wideband transparent super surface;

[0058] 8) The manufacturing of the wideband transparent super surface 40 of the application is completed.

[0059] Here, the designed "0" subarray 20 and "1" subarray 30 have good wave absorbing performance, and after the "0" subarray 20 and "1" subarray 30 are combined and arranged to form the super surface 40 of the application, the super surface 40 of the application has good scattering performance, that is, the coding arrangement of the "0" subarray 20 and the "1" subarray 30 realizes the fusion of the absorption and scattering functions.

[0060] In step 1), the first dielectric layer 11, the second dielectric layer 12, the third dielectric layer 13 and the ground layer 16 are square with a side length of 5mm, the thickness of the first dielectric layer 11, the second dielectric layer 12 and the third dielectric layer 13 is 3mm (i.e. d=3mm), the dielectric constant ε r is 2.8, and the magnetic permeability μr Set to 1, the loss tangent tan delta is set to 0.001; the thickness of the upper resistive film pattern layer 14, the lower resistive film pattern layer 15 and the ground layer 16 is usually negligible; the outer edge length of the upper resistive film pattern layer 14 and the lower resistive film pattern layer 15 is initially set to 5mm.

[0061] In step 3): the outer edge length w3 of the upper resistive film pattern layer 14 is adjusted to 4.95mm, the inner edge length w4 is adjusted to 4.25mm, the outer edge length w1 of the lower resistive film pattern layer 15 is adjusted to 4.95mm, the inner edge length w2 is adjusted to 3mm, the width of the oblique opening 140 on the upper resistive film pattern layer 14 is adjusted to 0.1mm; the sheet resistance r1 of the upper resistive film pattern layer 14 and the sheet resistance r2 of the lower resistive film pattern layer 15 are set to 50Ω / sq, and the sheet resistance of the ground layer 16 does not need to be optimized and is directly set to 5Ω / sq.

[0062] For step 2), as Figure 4 and Figure 5 , the fitness function of the genetic algorithm is set to the average of the amplitude of the reflection coefficient (S11) (such as Figure 4 ), and through 180 generations of optimization, the fitness function finally reaches the minimum value (0.210683). At this time, the equivalent impedance of the super unit 10 is optimal, that is, the equivalent impedance theoretical value (main polarization direction), and accordingly the optimal equivalent impedance of the upper and lower resistive film pattern layers 14, 15 is obtained. Here, the equivalent impedance theoretical value should make the amplitude of the reflection coefficient of the super unit 10 less than -10dB, and from Figure 5 it can be seen that after optimization, the amplitude of the reflection coefficient reaches the minimum in the frequency range of 2GHz-26.5GHz, and the red curve in the figure shows the optimized theoretical value of the amplitude of the reflection coefficient, which is less than -10dB.

[0063] For step 3), according to the equivalent impedance theoretical value, the electromagnetic simulation software is used for numerical simulation, and the actual value of the equivalent impedance of the super unit 10 obtained by inversion should satisfy the requirement that the difference between the actual value and the theoretical value is less than 10%. As Figure 5 , the blue origin curve in the figure is the inversion actual value of the amplitude of the reflection coefficient corresponding to the super unit 10 obtained by inversion. From Figure 5 it can be seen that the difference between the actual value of the equivalent impedance and the theoretical value of the equivalent impedance is less than 10%. Accordingly, the structure parameters of the super unit 10 are adjusted to complete the optimization.

[0064] For the "0" unit and the "1" unit obtained through step 4), the reflection characteristics of the two are verified. When verifying, the "0" unit and the "1" unit are arranged in an infinite array (assuming that the row and column elements are infinite) respectively by using the periodic boundary for full-wave simulation. Figure 6 and Figure 7The graphs of the amplitude and phase of the reflection coefficient of the co-polarization and cross-polarization are shown for the "0" unit and the "1" unit under the excitation of the on-line polarized wave (perpendicular to the surface of the "0" unit and the "1" unit along the z direction) respectively. It can be seen from the graphs of the amplitude and phase of the reflection coefficient of the co-polarization and cross-polarization shown in Figs. 2 and 3 that the "0" unit and the "1" unit have the same amplitude of the reflection coefficient, the amplitude of the reflection coefficient of the co-polarization is less than -10 dB, and the amplitude of the reflection coefficient of the cross-polarization is less than -18 dB in the frequency range of 3.7 GHz to 25.9 GHz, which meets the target to be achieved by the present application. At the same time, the phase difference between the reflection coefficients of the cross-polarization of the "0" unit and the "1" unit is 180° and can be well maintained in the above frequency band (operating bandwidth), which ensures the effect of the RCS reduction in the wide frequency band. In summary, the "0" unit and the "1" unit obtained by step 4) have effectively achieved the excellent performance of the RCS reduction of -10 dB in the wide frequency band (in the frequency band of 3.7 GHz to 25.9 GHz). Figure 6 Figure 7 It can be seen from the graphs of the amplitude and phase of the reflection coefficient of the co-polarization and cross-polarization shown in Figs. 2 and 3 that the "0" unit and the "1" unit have the same amplitude of the reflection coefficient, the amplitude of the reflection coefficient of the co-polarization is less than -10 dB, and the amplitude of the reflection coefficient of the cross-polarization is less than -18 dB in the frequency range of 3.7 GHz to 25.9 GHz, which meets the target to be achieved by the present application. At the same time, the phase difference between the reflection coefficients of the cross-polarization of the "0" unit and the "1" unit is 180° and can be well maintained in the above frequency band (operating bandwidth), which ensures the effect of the RCS reduction in the wide frequency band. In summary, the "0" unit and the "1" unit obtained by step 4) have effectively achieved the excellent performance of the RCS reduction of -10 dB in the wide frequency band (in the frequency band of 3.7 GHz to 25.9 GHz).

[0065] For step 7), it is assumed that the "0" sub-array 20 is composed of 4x4 "0" units, the "1" sub-array 30 is composed of 4x4 "1" units, and the number ratio of the "0" sub-array 20 to the "1" sub-array 30 is set to 10:10. After the arrangement of the two is optimized by step 7), a meta-surface 40 with a size of 200 mm (length) x 200 mm (width) x 9 mm (thickness) is obtained, as shown in Fig. 5, in which the pink squares represent the "0" sub-array 20, and the green squares represent the "1" sub-array 30. Figure 10 Figure 8 The three-dimensional scattering field (Ex, Ey, and Ez represent the energy in the x, y, and z directions, respectively) of the meta-surface 40 at the center frequency point 11 GHz is shown in Fig. 6. Figure 9 Figure 10 The energy distribution diagram of the backscatter released by the meta-surface 40 is shown in Fig. 7 (the right side shows the energy contour diagram), which is viewed from the direction perpendicular to the upper surface of the meta-surface 40 (or said to be viewed from the z direction). Figure 9 It can be seen from Fig. 7 that the proportion of the low energy released by the backscatter scattered by the meta-surface 40 after receiving the incident wave to the total energy is more than 90%, which indicates that the energy is as evenly dispersed as possible. In other words, the energy released by the backscatter scattered by the wide-band transparent meta-surface 40 of the present application after receiving the incident wave is evenly scattered in multiple directions, achieving an effect similar to diffuse scattering, which further improves the scattering uniformity performance on the basis of achieving the performance of the RCS reduction of -10 dB in the wide frequency band (in the frequency band of 3.7 GHz to 25.9 GHz).

[0066] ​​​To verify the rationality and feasibility of the manufacturing method of the present application, full-wave simulation is performed on the manufactured metasurface 40 (hereinafter referred to as metasurface), and comparison is made with a metasurface of the same size and composed of all "1" sub-arrays (hereinafter referred to as "1" sub-array surface) to perform normalized quantitative analysis on the RCS reduction performance of the metasurface 40 of the present application. As shown in FIG. 8, the single station RCS simulation curves of the metasurface and the "1" sub-array surface are shown, wherein the co-polarization RCS values of the two are basically the same, and the cross-polarization RCS value of the metasurface is nearly 40 dB smaller than that of the "1" sub-array surface, which indicates that the metasurface 40 manufactured by the present application has excellent RCS reduction performance in the cross-polarization direction in addition to the co-polarization direction. Figure 11

[0067] The RCS reduction performance of the manufactured metasurface sample is simulated and tested as follows.

[0068] Figure 12 and Figure 13 respectively show the simulation and test results of the co-polarization and cross-polarization single station (single station radar detection) RCS reduction values when the linearly polarized wave is vertically incident on the metasurface 40 (or the first dielectric layer 11) of the present application along the z direction. From Figure 12 , Figure 13 It can be seen that the bandwidths corresponding to the -10 dB RCS reduction values obtained by simulation and test are 3.7 GHz-25.9 GHz (relative bandwidth of 150%) and 3.5 GHz-24.7 GHz (relative bandwidth of 150%) respectively, and the cross-polarization RCS reduction values obtained by simulation and test are both lower than -50 dB in the above respective frequency bands. It can be seen that the -10 dB RCS reduction performance in a wide frequency band has been well achieved.

[0069] In addition, the double station RCS reduction performance of the metasurface sample under the action of oblique incidence wave is tested. Figure 14 FIG. 9 shows the test results of the co-polarization double station (double station radar detection) RCS reduction values of the metasurface sample when the incident angle θ is 0°, 20° and 40°, Figure 15 FIG. 10 shows the test results of the cross-polarization double station RCS reduction values of the metasurface sample when the incident angle θ is 0°, 20° and 40°. From Figure 14 , Figure 15 It can be seen that when the incident angle increases to 40°, the bandwidth and amplitude corresponding to the -10 dB RCS reduction value of the metasurface are inevitably slightly decreased, but the metasurface still maintains effective RCS reduction performance in a relative bandwidth range of 140%, which indicates that the metasurface manufactured by the present application has good RCS reduction stability under the condition of an incident angle of 40° or less.

[0070] The present application has the advantages of:​

[0071] 1. Based on the -10dB RCS reduction performance achieved by the metasurface of the present invention, the relative bandwidth can reach 150% under single-station vertical incidence conditions (achieving wide-band coverage in the 3.7GHz-25.9GHz frequency band), and the relative bandwidth can also reach 140% under bi-station oblique incidence conditions with an incident angle of no more than 40°.

[0072] 2. The metasurface structure of the present invention is transparent and has high transmittance, maintaining good optical transparency. The metasurface manufactured by the present invention has good stealth performance in both single-station and dual-station radar detection under conditions of an incident angle of less than 40°, and is suitable for a variety of application scenarios.

[0073] 3. The metasurface of the present invention is manufactured using common materials with low cost (ITO film and PMMA plate), which greatly reduces the manufacturing cost. In addition, the manufacturing process is controllable, the manufacturing difficulty is small, and the manufacturing cost is low.

[0074] The above are preferred embodiments of the present invention and the technical principles used therein. For those skilled in the art, any obvious changes such as equivalent transformations, simple replacements, etc. based on the technical solution of the present invention, without departing from the spirit and scope of the present invention, are within the scope of protection of the present invention.

Claims

1. A broadband transparent metasurface, characterized in that: The broadband transparent metasurface is formed by an arrangement of a "0" subarray and a "1" subarray, wherein the "0" subarray is formed by "0" units regularly arranged in a matrix form, wherein the "0" unit is a metacell, and the metacell is rotated 90° about the z-axis to obtain a "1" unit, wherein the "1" subarray is formed by the "1" units regularly arranged in a matrix form, wherein: compared with the "0" unit, the "1" unit has the same reflection coefficient amplitude but a phase difference of 180°; the metacell is composed of a first dielectric layer, an upper resistive film pattern layer, a second dielectric layer, a lower resistive film pattern layer, a third dielectric layer, and a ground layer stacked from top to bottom, wherein the upper resistive film pattern layer is a square ring with a pair of oblique openings at its diagonal positions, and the lower resistive film pattern layer is a square ring.

2. The broadband transparent metasurface according to claim 1, wherein: The "0" subarray and the "1" subarray are arranged in the same matrix form, and the "0" subarray and the "1" subarray are regularly arranged in a matrix form to form the broadband transparent metasurface; Alternatively, the “0” sub-array and the “1” sub-array are arranged in a different matrix form.

3. The broadband transparent metasurface according to claim 2, wherein: The thickness of the first dielectric layer, the second dielectric layer and the third dielectric layer is the same and much greater than the thickness of the upper resistive film pattern layer, the lower resistive film pattern layer and the ground layer, wherein the thickness of the first dielectric layer, the second dielectric layer and the third dielectric layer is 3 mm, and the dielectric constant ε r is 2.8, magnetic permeability μ r is 1, and the loss tangent value tanδ is 0.001; the first dielectric layer, the second dielectric layer, the third dielectric layer and the ground layer are a square with a side length of 5 mm.

4. The broadband transparent metasurface according to claim 3, wherein: The outer side lengths of the upper resistive film pattern layer and the lower resistive film pattern layer are initially set to 5 mm, and the square resistance of the ground layer is set to 5Ω / sq; Numerical simulation is performed according to the theoretical equivalent impedance value calculated by the genetic algorithm, and actual structural parameters of the meta-unit are obtained by inversion. The meta-unit is then adjusted according to the actual structural parameters to optimize the structural parameters of the meta-unit, wherein: the theoretical equivalent impedance value obtained by the genetic algorithm ensures that the reflection coefficient amplitude of the "0" unit is less than -10 dB; the actual equivalent impedance value of the meta-unit obtained by inversion differs from the theoretical equivalent impedance value by less than 10%; the outer side length of the upper resistive film pattern layer is adjusted to 4.95 mm and the inner side length is adjusted to 4.25 mm; the outer side length of the lower resistive film pattern layer is adjusted to 4.95 mm and the inner side length is adjusted to 3 mm; the width of the oblique opening on the upper resistive film pattern layer is adjusted to 0.1 mm; and the sheet resistance of the upper and lower resistive film pattern layers is set to 50 Ω / sq.

5. The broadband transparent metasurface according to claim 4, wherein: The first dielectric layer, the second dielectric layer and the third dielectric layer are made of transparent PMMA plates; the upper resistive film pattern layer, the lower resistive film pattern layer and the ground layer are made of transparent ITO films.

6. The broadband transparent metasurface according to claim 4, wherein: The arrangement of the "0" subarray and the "1" subarray forming the broadband transparent metasurface is optimized by a genetic algorithm so that, viewed from a direction perpendicular to the first dielectric layer, low energy released by echoes scattered after the broadband transparent metasurface receives an incident wave accounts for more than 90% of the total energy.

7. A method for manufacturing a broadband transparent metasurface according to claim 1, characterized in that: Including steps: 1) Initially setting the structural parameters of the superstructure unit; 2) calculating, by genetic algorithm, a theoretical equivalent impedance value that makes the reflection coefficient amplitude of the meta-unit less than -10 dB; 3) performing numerical simulation according to the theoretical value of the equivalent impedance, inverting to obtain actual structural parameters of the meta-unit, adjusting the structure of the meta-unit according to the actual structural parameters, and completing the optimization of the meta-unit, wherein: the actual value of the equivalent impedance of the meta-unit obtained by inversion differs from the theoretical value of the equivalent impedance by less than 10%; 4) obtaining the "0" unit based on the adjusted meta-unit, and obtaining the "1" unit by rotating the meta-unit 90° with the z-axis as the rotation axis; 5) constructing the “0” subarray through the “0” unit, and constructing the “1” subarray through the “1” unit; 6) randomly arranging the “0” subarray and the “1” subarray to obtain the broadband transparent metasurface; 7) Optimizing the arrangement of the "0" subarray and the "1" subarray using a genetic algorithm so that, viewed from a direction perpendicular to the upper surface of the broadband transparent metasurface, the proportion of low energy released by the echo scattered by the broadband transparent metasurface after receiving the incident wave accounts for more than 90% of the total energy, thereby obtaining the optimal broadband transparent metasurface; 8) Complete the fabrication of the broadband transparent metasurface.

8. The manufacturing method according to claim 7, wherein: In step 1), the first dielectric layer, the second dielectric layer, the third dielectric layer and the ground layer are set to a square with a side length of 5 mm, the thickness of the first dielectric layer, the second dielectric layer and the third dielectric layer is set to 3 mm, and the dielectric constant ε r Set to 2.8, magnetic permeability μ r is set to 1, and the loss tangent value tanδ is set to 0.001; the outer side lengths of the upper resistive film pattern layer and the lower resistive film pattern layer are initially set to 5 mm.

9. The manufacturing method according to claim 8, wherein: In the step 3), the outer side length of the upper resistive film pattern layer is adjusted to 4.95 mm and the inner side length is adjusted to 4.25 mm; the outer side length of the lower resistive film pattern layer is adjusted to 4.95 mm and the inner side length is adjusted to 3 mm; the width of the oblique opening on the upper resistive film pattern layer is adjusted to 0.1 mm; the square resistance of the upper resistive film pattern layer and the square resistance of the lower resistive film pattern layer are set to 50 Ω / sq, and the square resistance of the ground layer is set to 5 Ω / sq.

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