Design method of electromagnetic stealth metasurface universal for any frequency band

Abstract

According to the electromagnetic stealth metasurface design method universal for any frequency band, the pattern area of the metasurface unit is divided into the grids, each grid can be pasted or not pasted, and therefore ever-changing paster patterns can be formed, the combinations are optimized through the particle swarm optimization, and the expected electromagnetic scattering characteristic is achieved. The design method comprises the two steps of metasurface unit optimization design, metasurface modeling and simulation verification. The metasurface unit optimization design is an automatic optimization design process following a particle swarm algorithm, m different metasurface units can be obtained, and the m different metasurface units present specific phase gradients on a center frequency and a neighborhood frequency band; the metasurface can be formed by selecting the metasurface units from the m different metasurface units. The invention aims to provide an electromagnetic stealth metasurface design method universal for any frequency band. According to the method, the metasurface unit combination meeting the requirement can be fully automatically generated only by giving the target frequency band and setting a small number of parameters according to the rule, and the requirement for human intervention is reduced to the maximum extent.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic stealth technology, and in particular to the design of an electromagnetic stealth metasurface. The present invention particularly proposes a metasurface morphology of a micro-grid unit structure and provides a design method for an electromagnetic stealth metasurface that is universal for any frequency band. Background Art

[0002] Metasurfaces are a type of subwavelength artificial periodic structure that can control electromagnetic waves by designing the structure of the constituent units and the arrangement of the unit arrays. They have received great attention in many fields, and their development in the field of electromagnetic stealth is particularly prominent. Currently, there are three implementation mechanisms for electromagnetic stealth metasurfaces: diffuse reflection, echo control, and wave absorption. Regardless of which mechanism is used, a key technical problem is encountered, namely, designing metasurface units with specific reflection phase-frequency characteristics in the target stealth frequency band. However, under the premise of a fixed medium size, it is very difficult to achieve such precise design by simply adjusting the patch pattern for the following reasons:

[0003] (1) The patch pattern itself represents complex distributed parameters, and the additional coupling with the dielectric, bottom metal, and other patch units makes the design of the electromagnetic scattering characteristics of the metasurface very difficult;

[0004] (2) Even if the expected reflection phase is achieved through fine-tuning the size parameters of the patch pattern and a large number of attempts, it is difficult to achieve the stability of the phase gradient of several patch units over a wider frequency band ("phase gradient" specifically refers to the reflection phase difference between a group of units that constitute the metasurface, which usually changes with frequency shift). This stability is an important prerequisite for achieving wide-band electromagnetic stealth.

[0005] Regarding point (1) above, current commercial electromagnetic simulation software (CST, Feko, HFSS, etc.) already has some simple parameter optimization functions, but can only optimize the size of the patch pattern given by the user so that the center frequency reflection phase of the unit moves to the required target value, but cannot automatically generate a metasurface unit with the expected electromagnetic scattering characteristics. For example, Chinese patent CN113721210A discloses a deep RCS reduction metasurface design method based on absorption-cancellation. The method for designing the two required metasurface units is to first preset a double-ring unit pattern and then use commercial simulation software to optimize its size parameters. This makes its optimization space constrained by the preset pattern, and the preset pattern cannot be applied to different frequency bands. This is exactly the "blind spot" of this type of design method. Chinese patents CN116259978A and CN107465000B are similar situations and will not be listed one by one. As for point (2) above, no targeted method has been proposed yet.

[0006] The above discussion demonstrates that designing the specific phase characteristics required for electromagnetic stealth metasurfaces using a "forward" or "a priori" approach is extremely difficult. Furthermore, designing using a "reverse" or "empirical" approach is highly unreliable and difficult to develop a broadly applicable approach. Current technological achievements in this field primarily offer solutions tailored to specific needs, lacking general guidance. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for designing electromagnetic stealth metasurfaces that is universal for any frequency band. By only giving a target frequency band and setting a small number of parameters according to the method, a metasurface unit combination that meets the requirements can be fully automatically generated, minimizing the need for human intervention.

[0008] To achieve the above objectives, the present invention provides a method for designing an electromagnetic stealth metasurface that is universal for any frequency band. The method divides the pattern area of ​​the metasurface unit into an N×N grid, and each grid is patched or not patched. The patch includes a top surface, a middle layer, and a bottom surface stacked in sequence. The design method includes:

[0009] 1) Optimal design of metasurface units;

[0010] 11) Setting parameters, including operation parameters and modeling parameters;

[0011] The operation parameters include f0, [f low , f high ], P0, ω j , α1, α2, α3, F f , I and m, f0 is the target stealth frequency band [f low , f high ] is the center frequency, P0 is the reflection phase that the metasurface unit is expected to obtain at f0;

[0012] The modeling parameters include H s 、H p 、W c 、W b , N and the types of materials of each layer of the patch, H p is the thickness of the top and bottom surfaces, H s is the thickness of the middle layer, W c is the side length of the unit, W b is the distance between the edge of the pattern area and the edge of the cell;

[0013] The objective function vector is:

[0014]

[0015] Where i is the number of iterations, l∈(1, 2, …, m), m represents the number of particles in the particle swarm in the particle swarm algorithm; the weight coefficient ω is j is the influence weight of each incident angle in the objective function in the i-th iteration; j represents different incident angles, j = 1, 2, ..., J; f ijl is the “sub-target value” of the metasurface unit represented by the lth particle in the particle swarm under the incident wave of the jth incident angle in the i-th iteration;

[0016]

[0017] α1, α2 and α3 are weight coefficients; F f is the termination value of the objective function; I is the maximum number of iterations;

[0018] 12) Calculate the number of free grids n in the unit pattern area grid number;

[0019] 13) Set the m n-dimensional position vectors X in the i-th iteration of the particle swarm algorithm i =(x i1 , x i2 ,...,x im ) and m n-dimensional velocity vectors V i =(v i1 , v i2 ,...,v im ), representing the distribution and dynamics of the particle swarm in the domain;

[0020] 14) X i Each vector in is converted into a 1-bit digital vector, that is, converted into X id =(x id1 , x id2 ,...,x idm ), each vector corresponds to a metasurface unit patch pattern;

[0021] 15) X id =(x id1 , x id2 ,...,x idm ) is converted one by one into an N×N digital matrix M i =(M i1 , M i2 ,...,M im ), corresponding to m types of metasurface unit patch patterns;

[0022] 16) According to M i =(M i1 , M i2 ,...,M im) and the modeling parameters set in step 1), establish a corresponding infinite periodic structure electromagnetic model for each metasurface unit;

[0023] 17) Simulate the m electromagnetic models one by one and obtain [f low , f high ] 2m×J reflection phase-frequency curve: C i =(C i1 , C i2 ,...,C il ,...,C im ), C il Contains 2J reflection phase-frequency curves obtained by the lth electromagnetic model;

[0024] 18) Analyze the curve cluster C i , we get the value of f0 and in [f low , f high ] in g i，j , where for the metasurface unit corresponding to the lth particle in the i-th iteration at the j-th incident angle, the two reflection phase-frequency curves generated by the TE and TM polarizations are: is the average value of their target phase deviation at f0, is the absolute value of their average reflection phase difference, g i，j，l For two curves in [f low , f high ], and further calculate other values ​​according to formula (4) to formula (6):

[0025]

[0026]

[0027]

[0028] 19) Store the value calculated in step 18) g i，j，l and g Ml ;

[0029] 110) According to g i，j，l and g Ml And formula (1) and formula (2) are used to calculate the objective function F of each electromagnetic model i ;

[0030] 111) Update the position vector X of the particle swarm i and velocity vector V i ;

[0031] 112) Determine the number of iterations i and the objective function value F i Whether the termination condition is met, if so, output the electromagnetic model obtained in step 16), if not, return to step 13);

[0032] 2) Metasurface modeling and simulation verification;

[0033] Select a hypersurface unit from the m different hypersurface units obtained in step 1) to form a hypersurface.

[0034] Compared with the prior art, the beneficial technical effects of the present invention are:

[0035] 1) The metasurface designed by the present invention does not require manual setting of the initial pattern of the unit patches;

[0036] 2) The microgrid metasurface unit optimization design proposed in this invention can ensure the accuracy and automation of microscopic unit design, ensuring that the design of the metasurface unit can meet the phase gradient at the micro level and has a high tolerance to incident angles and polarizations;

[0037] 3) The design method proposed in the present invention is a reverse design method starting from the required frequency band, which is goal-oriented and minimizes the need for manual intervention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The electromagnetic stealth metasurface design method universal for any frequency band of the present invention is given by the following embodiments and drawings.

[0039] Figure 1 The figure is a flow chart of the electromagnetic stealth metasurface design method applicable to any frequency band of the present invention.

[0040] Figure 2 This is a pre-processing flow chart of the present invention.

[0041] Figure 3 A top view of the micro-mesh metasurface unit and a case diagram with the patch pattern encoded as “1011010001”.

[0042] Figure 4 Schematic diagram of the infinite periodic structure of two types of metasurface units obtained by optimization in Example 1 of the present invention (only 3×3 are shown).

[0043] Figure 5 Graphs showing the reflection phase curves and phase difference curves of the two metasurface units in the 14 GHz to 22 GHz frequency band in Example 1 of the present invention.

[0044] Figure 6 This is a simulation diagram of the super surface in Example 1 of the present invention.

[0045] Figure 7 This is a physical picture of the super surface in Example 1 of the present invention.

[0046] Figure 8 This is a comparison diagram of the normal single-station RCS of the metasurface of Example 1 of the present invention and a metal plate of the same shape and size.

[0047] Figure 9 This is the bistatic RCS diagram for all elevation angles at 18 GHz normal incidence and 0° azimuth in Example 1 of the present invention (comparison between the metasurface and a metal plate of the same shape and size).

[0048] Figure 10 This is a normal single-station RCS reduction diagram (simulation and actual measurement) of the metasurface of Example 1 of the present invention relative to a metal surface of the same shape and size.

[0049] Figure 11 Schematic diagram of the metasurface unit in Example 2 of the present invention, wherein (a) is a unit with a target reflection phase of 170°, (b) is a unit with a target reflection phase of 80°, (c) is a unit with a target reflection phase of -10°, and (d) is a unit with a target reflection phase of -100°.

[0050] Figure 12 This is a top view of the metasurface of Example 2 of the present invention, where (a) is a global structure diagram and (b) is a microstructure diagram.

[0051] Figure 13 This is a graph showing the RCS-frequency relationship of the metasurface according to the second embodiment of the present invention.

[0052] Figure 14 Schematic diagram of the metasurface unit in Example 3 of the present invention, where (a) is a unit with a target reflection phase of 135°, and (b) is a unit with a target reflection phase of -45°.

[0053] Figure 15 This is a top view of the metasurface of Example 3 of the present invention, where (a) is a global structure diagram and (b) is a microstructure diagram.

[0054] Figure 16 This is a graph showing the RCS-frequency relationship of the metasurface according to the third embodiment of the present invention. DETAILED DESCRIPTION

[0055] The following will be combined Figures 1 to 16 The design method of electromagnetic stealth metasurface universal to any frequency band of the present invention is further described in detail.

[0056] To overcome the limitations of existing technologies, this paper proposes a metasurface with a microgrid unit structure. This involves dividing the patterned area of ​​the metasurface unit into a grid similar to "pixels." Depending on whether these grids are coated with metal micro-sheets, a variety of patch patterns can be formed. A machine learning algorithm is then used to optimize these combinations to achieve the desired electromagnetic scattering characteristics. Considering that the particle swarm algorithm is an unsupervised optimization algorithm and can still achieve good optimization results even without prior knowledge, a particle swarm algorithm-based method for optimizing microgrid metasurface structures is proposed, which is universally applicable to metasurface designs for any target stealth frequency band.

[0057] like Figure 1 The present invention provides a method for designing an electromagnetic stealth metasurface that is universal in any frequency band, including:

[0058] 1) Optimal design of metasurface units;

[0059] 11) Initialization: Set parameters, including operation parameters and modeling parameters. The operation parameters include f0, [f low , f hight ], P0, ω j , α1, α2, α3, F f , I and m, the modeling parameters include H s 、H p 、W c 、W b , N and the types of materials of each layer of the patch;

[0060] (1) Operation parameters

[0061] f0 is the target stealth frequency band [f low , f hight ] is the center frequency of the metasurface, P0 is the reflection phase that the metasurface unit is expected to obtain at f0, and m is the total number of individuals in the particle swarm algorithm. The larger m is, the stronger the global optimization ability is.

[0062] The objective function vector is:

[0063]

[0064] Where i is the number of iterations, l∈(1, 2, …, m), m represents the number of particles in the particle swarm; the weight coefficient ω is j is the influence weight of each incident angle in the objective function in the i-th iteration; j represents different incident angles, j = 1, 2, ..., J; f ijl is the “sub-target value” of the metasurface unit represented by the lth particle in the particle swarm under the incident wave of the jth incident angle in the i-th iteration;

[0065] fijl It includes three parts, namely phase accuracy, incident wave polarization sensitivity and phase curve flatness. The weight coefficients α1, α2 and α3 are set to f ijl The weight coefficients of the three parts of represent the preference for phase accuracy, incident wave polarization sensitivity, and phase curve flatness, which are:

[0066]

[0067] In addition, the termination value F of the objective function needs to be set f , the maximum number of iterations I and the number of free particles m; F f The larger it is, the longer the iterative convergence time is; the larger I is, the closer the optimized parameters are to the optimal value;

[0068] (2) Modeling parameters

[0069] Including the size parameters of the metasurface unit, the grid parameters of the pattern area, and the types of materials of each layer of the patch;

[0070] The present invention proposes a super surface with a micro-grid unit structure, such as Figure 3 , the pattern area of ​​the metasurface unit is divided into grids similar to "pixels". Each grid can be patched or not. Depending on whether these grids are patched or not, a variety of patch patterns can be formed. The patch includes a top surface, a middle layer and a bottom surface stacked in sequence, wherein the top surface and the bottom surface are both metal layers, and the middle layer is a dielectric layer;

[0071] Select the top metal material, bottom metal material and middle layer dielectric material according to the usage scenario, and set the thickness H of the top and bottom surfaces. p , the thickness of the middle layer H s , the side length W of the unit c , the distance W between the edge of the pattern area and the edge of the unit b , and the number of grids N×N for pattern area segmentation;

[0072] ①H s :The selection range is generally λ g / 8~λ g / 4,λ g is the waveguide wavelength of the dielectric (approximately equal to the operating wavelength in large-size dielectric slabs);

[0073] ②H p :The selection range is generally H s / 500~H s / 100;

[0074] ③W c :The selection range is generally λ g / 2~λ g ;

[0075] ④N: determines the size of the entire set of optimization objects, is proportional to the optimization accuracy and inversely proportional to the amount of calculation, and can be set according to actual conditions;

[0076] ⑤W b :The selection range is generally λ g / 20~λ g / 10, which can reduce the coupling effect between individuals in the patch array;

[0077] 12) Preprocessing: Calculate the number of free grids n in the grid number of the unit pattern area;

[0078] After testing, for the design of chessboard-type (i.e. micro-grid-type) electromagnetic stealth metasurface, the patch pattern is usually set to be fully symmetrical, such as Figure 3 In (b), there are 10 free grids in an 8×8 grid, coded as "1011010001". Once the patching scheme for a free grid is determined, the patch pattern for the entire unit is also determined. For a 10×10 grid, there are 15 free grids, corresponding to 32,768 possible patch patterns, which can achieve a good balance between design efficiency and accuracy.

[0079] See the pre-processing process for Figure 2 , the input is N, the output is n;

[0080] 13) Setting: Set the m n-dimensional position vectors X in the i-th iteration of the particle swarm algorithm i =(x i1 , x i2 ,…,x im ) and m n-dimensional velocity vectors V i =(v i1 , v i2 ,…,v im ), representing the distribution and dynamics of the particle swarm in the domain;

[0081] The initial setting can use a random number generator, and then the position vector X obtained by step 111) is updated i and velocity vector V i ;

[0082] 14) Process I: X i Each vector in is converted into a 1-bit digital vector, that is, converted into X id =(x id1 , x id2 ,…,x idm ), each (digital) vector corresponds to a metasurface unit patch pattern (i.e., corresponds to a free grid code), and formula (3) can be used as a conversion tool:

[0083]

[0084] Among them, x il(·) For X i The lth n-dimensional position vector x in il A single element in x id / (·) For X id The lth vector x in id / A single element in v id / (·) V id The lth vector v in id / A single element in

[0085] 15) Process II: X id =(x id1 , x id2 ,…,x idm ) is converted one by one into an N×N digital matrix M i =(M i1 , M i2 ,…,M im ), corresponding to m kinds of micro-grid patch patterns (i.e., corresponding to m kinds of metasurface unit patch patterns);

[0086] Conversion rule: X di Each vector in (corresponding to a free grid encoding, such as Figure 3 (b) is copied to the entire unit according to the rule of full symmetry, thus becoming an N×N digital matrix;

[0087] 16) Modeling: Based on M i =(M i1 , M i2 ,…,M im ) and the modeling parameters set in step 1), establish the electromagnetic model of m metasurface units (Floquet boundary, infinite periodic structure, such as Figure 4 );

[0088] 17) Simulation: Automatically simulate m electromagnetic models one by one (including incident waves in J directions and TE and TM polarization conditions), and obtain [f low , f hight ] 2m×J reflection phase-frequency curve: C i =(C i1 , C j2 ,…,C il ,…,C im ), C il Contains 2J reflection phase-frequency curves obtained by the lth electromagnetic model;

[0089] 18) Calculation I: Analyzing the Curve Cluster C i , we get the value of f0 and in [f low , f hight ] in g i，j , where for the metasurface unit corresponding to the lth particle in the i-th iteration at the j-th incident angle, the two reflection phase-frequency curves generated by the TE and TM polarizations are: is the average value of their target phase deviation at f0 (defined as the absolute value of the deviation between the average value of the reflected phase and the target reflected phase P0), is the absolute value of their average reflection phase difference (polarization phase deviation), g i，j，l For two curves in [f low , f hight ], and further calculate other values ​​according to formula (4) to formula (6):

[0090]

[0091]

[0092]

[0093] As the iteration continues, the and g Ml As θ increases, the "pressure" on the optimization of Equation (1) also increases, which accelerates the optimization process and also produces a certain degree of normalization (since the slope can reach infinity, the general normalization method cannot be used). In addition, each iteration takes into account the various incident angles of interest and the TE and TM polarization conditions. The optimization process aims to minimize the impact of the incident wave polarization.

[0094] 19) Historical value storage: store the value calculated in step 18) g i，j，l and g Ml ;

[0095] 110) Calculation II: Based on g i，j，l and g Ml And formula (1) and formula (2) calculate the objective function F of each electromagnetic model (particle) i , the individual historical extreme value of the lth particle ( F l =min i (F il ))The corresponding position vector The total historical extreme value of the entire particle swarm ( F =min l ( Fl ))The corresponding position vector

[0096] 111) Update: Update the position vector X of the particle swarm i and velocity vector V i , the update algorithm is:

[0097]

[0098] Where i is the number of iterations, l∈(1, 2, ..., m) is the particle number, v il 、x il They represent the speed and position of the lth particle at the i-th iteration, respectively, and are matrices V i 、X i The first row of (n elements per row, corresponding to n free grids), ω∈(0,1) is the weight coefficient, which indicates the preference between the current speed and the current extreme value, r 1i , r 2j ∈(0, 0.5) is the random fine-tuning coefficient (randomly generated in each iteration);

[0099] 112) Determine the number of iterations i and the objective function value F i Whether the termination condition is met, if so, output the electromagnetic model obtained in step 16), if not, return to step 13).

[0100] The above optimization process can call any electromagnetic simulation software to perform unit modeling at each step of iteration and electromagnetic characteristic simulation of its infinite periodic structure.

[0101] 2) Metasurface modeling and simulation verification;

[0102] Through step 1), electromagnetic models of m metasurface units (i.e., m different metasurface units) can be obtained, and the m different metasurface units present specific phase gradients at the center frequency and its neighboring frequency bands;

[0103] The metasurface is composed of a plurality of metasurface units; the m different metasurface units can form a plurality of different metasurfaces, and a metasurface unit is selected from the m different metasurface units obtained in step 1) to form a metasurface, wherein 1-bit and 2-bit metasurfaces are the most common, a 1-bit metasurface is composed of two units with a center frequency difference of 180°, and a 2-bit metasurface is composed of four units with a center frequency difference of 90°;

[0104] For the metasurface, the RCS reduction effect is verified through full-wave electromagnetic simulation.

[0105] Example 1:

[0106] In order to achieve effective RCS reduction in the frequency band centered at 18 GHz, this embodiment requires the design of an electromagnetic stealth metasurface. A double-sided copper-clad dielectric plate is available. The material of the dielectric plate is FR-4 epoxy resin with a thickness of H. s =1.7mm, its dielectric constant ε ｒ =4.3, electrical tangent loss tanσ=0.001, metal copper foil thickness H p =0.01mm. The electromagnetic stealth metasurface designed in this embodiment uses a 1-bit metasurface. It is only necessary to find two metasurface units whose reflection phase difference at the center frequency of 18 GHz is 180°. In the design method proposed in this invention, the reflection phases of these metasurface units can be arbitrarily set and automatically obtained. In this embodiment, two reflection phases of 40° and -140° are used as examples.

[0107] Set W c =6.8mm, W b =1.36mm, N=10;

[0108] According to the design method proposed in the present invention, the optimization results "101011101100101" and "111100000100001" are used as the free grid coding of the metasurface unit, and the patch pattern is fully symmetrical, and two metasurface units are obtained, whose infinite periodic structure (such as Figure 4 In (a) and (b)), the phases at 18 GHz are 41.86° and -153.55° respectively, which means there is a certain error. However, the "phase difference-frequency" curves of the two units in the 14 GHz to 22 GHz frequency band show that the absolute value of the reflection phase difference between the two in the frequency band of about 15.99 GHz to 19.97 GHz falls within the range of 143° to 217° (as shown in Figure 2). Figure 5 This range is generally considered to be the "effective phase-reversal range" of the two units of the 1-bit metasurface. It is expected that the best RCS reduction can be achieved in this frequency band (i.e., 15.99 GHz to 19.97 GHz).

[0109] The classic "chessboard" metasurface is composed of the above two units. Each tuple contains 5×5 units, and the entire metasurface contains 6×9 tuples, such as Figure 6 In order to verify whether the designed metasurface can play a practical role, a physical metasurface is made as shown in Figure 7 shown.

[0110] The metasurface is simulated to obtain the RCS of the metasurface, and the RCS of the metal surface with the same shape and size is obtained through simulation. Figure 8 This is the normal single-station RCS case from 14GHz to 22GHz. Figure 9The bistatic RCS at all elevation angles is shown for 18 GHz normal incidence and 0° azimuth. The simulation results show that the metasurface achieves a wide normal monostatic RCS reduction band (16.84 GHz to 22 GHz) near 18 GHz. At 18 GHz, the normally incident energy is effectively dispersed and reflected in multiple directions, exhibiting a good diffuse reflection effect.

[0111] Test the physical metasurface produced. Figure 10 The normal single-station RCS reduction of the metasurface relative to a metal surface of the same shape and size (simulation and measurement) is shown. The simulation shows that a minimum RCS reduction can be obtained near 18 GHz (18.18 GHz, -13.06 dBsm), which is consistent with the preset value. The measured results deviate due to material parameter errors and manufacturing precision limitations, but still achieve an RCS reduction of more than -10 dB in a fairly wide frequency band near 18 GHz (about 15 GHz to 19 GHz), showing good stealth effect and meeting the design requirements.

[0112] The above examples are based on an 18 GHz target frequency. In practice, the design method proposed in this invention can be applied to any target frequency band. The generation and optimization of patch patterns are fully automated, significantly reducing the need for manual intervention and improving design efficiency.

[0113] In addition, the simulation and actual measurement results of this embodiment also verify that the micro-grid metasurface designed by the design method proposed in the present invention has an ultra-wide RCS reduction frequency band and the ability to evenly disperse electromagnetic waves.

[0114] In order to verify the effectiveness of the design method provided by the present invention for any frequency band, Example 2 and Example 3 are briefly provided.

[0115] Example 2

[0116] X-band 2-bit electromagnetic stealth metasurface, target center frequency is 8 GHz, select dielectric material FR-4 epoxy resin. Set dielectric layer thickness H s =4.57mm, top and bottom thickness H p = 0.01 mm, the side length W of the square metasurface unit c =14mm, the pattern area is 10×10 grid (ie N=10), W b =1mm.

[0117] Four metasurface units are selected from the metasurface unit optimization results. The reflection phase difference of the four metasurface units at the center frequency of 8 GHz is 90° (assuming that four reflection phases of 170°, 80°, -10° and -100° are selected). The four metasurface unit patch patterns are as follows: Figure 11As shown in the figure, the actual reflected phases are 172.06°, 72.52°, -12.66°, and -98.50°, respectively, with deviations from the target phases of 1.1%, 4.15%, 1.5%, and 0.8% (with 1800° as the maximum deviation). Figure 12 As shown, the RCS reduction of the metal surface with the same size and shape is as follows Figure 13 shown.

[0118] Example 3:

[0119] Terahertz 1-bit electromagnetic stealth metasurface, target center frequency 1.2THz, select dielectric material FR-4 epoxy resin. Set the dielectric layer thickness H s =30.14um, top and bottom thickness H p =0.01um, the side length W of the square metasurface unit c =120um, the pattern area is 10×10 grid (ie N=10), W b =10um.

[0120] Two metasurface units are selected from the metasurface unit optimization results. The reflection phase difference of the two metasurface units at the center frequency of 1.2 THz is 180° (assuming that 135° and -45° reflection phases are selected). The patch patterns of the two metasurface units are as follows: Figure 14 As shown in Figure 1, the actual reflected phases are 132.13° and -41.36°, respectively, with deviations from the target phases of 1.59% and 2.0% (with 1800° as the maximum deviation). Figure 15 As shown, the RCS reduction of the metal surface with the same size and shape is as follows Figure 16 shown.

[0121] Matters not covered by the present invention are known technologies.

[0122] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A design method for electromagnetic stealth metasurfaces that is universal in any frequency band, characterized by: The pattern area of ​​the metasurface unit is divided into N×N grids, and each grid is patched or not patched. The patch includes a top surface, a middle layer, and a bottom surface stacked in sequence. The design method includes: 1) Optimal design of metasurface units; 11) Setting parameters, including operation parameters and modeling parameters; The operation parameters include f0, [f low , f high ], P0, ω j , α1, α2, α3, F f , I and m, f0 is the target stealth frequency band [f low , f high ] is the center frequency, P0 is the reflection phase that the metasurface unit is expected to obtain at f0; The modeling parameters include H s 、H p 、W c 、W b , N and the types of materials of each layer of the patch, H p is the thickness of the top and bottom surfaces, H s is the thickness of the middle layer, W c is the side length of the unit, W b is the distance between the edge of the pattern area and the edge of the cell; The objective function vector is: Where i is the number of iterations, l∈(1, 2, …, m), m represents the number of particles in the particle swarm in the particle swarm algorithm; the weight coefficient ω is j is the influence weight of each incident angle in the objective function in the i-th iteration; j represents different incident angles, j = 1, 2, ..., J; f ijl is the "sub-target value" of the metasurface unit represented by the lth particle in the particle swarm under the incident wave of the jth incident angle in the i-th iteration; α1, α2 and α3 are weight coefficients; F f is the termination value of the objective function; I is the maximum number of iterations; 12) Calculate the number of free grids n in the unit pattern area grid number; 13) Set the m n-dimensional position vectors X in the i-th iteration of the particle swarm algorithm i =(x i1 , x i2 ,...,x im ) and m n-dimensional velocity vectors V i =(v i1 , v i2 ,...,v im ), representing the distribution and dynamics of the particle swarm in the universe; 14) X i Each vector in is converted into a 1-bit digital vector, that is, converted into X id =(x id1 , x id2 ,...,x idm ), each vector corresponds to a metasurface unit patch pattern; 15) X id =(x id1 , x id2 ,...,x idm ) is converted one by one into an N×N digital matrix M i =(M i1 , M i2 ,...,M im ), corresponding to m types of metasurface unit patch patterns; 16) According to M i =(M i1 , M i2 ,...,M im ) and the modeling parameters set in step 1), establish a corresponding infinite periodic structure electromagnetic model for each metasurface unit; 17) Simulate the m electromagnetic models one by one and obtain [f low , f high ] 2m×J reflection phase-frequency curve: C i =(C i1 , C i2 ,...,C il ,...,C im ), C il Contains 2J reflection phase-frequency curves obtained by the lth electromagnetic model; 18) Analyze the curve cluster C i , we get the value of f0 and in [f low , f high ] in g i，j , where for the metasurface unit corresponding to the lth particle in the i-th iteration at the j-th incident angle, the two reflection phase-frequency curves generated by the TE and TM polarizations are: is the average value of their target phase deviation at f0, is the absolute value of their average reflection phase difference, g i，j，l For two curves in [f low , f high ], and further calculate other values ​​according to formula (4) to formula (6): 19) Store the value calculated in step 18) gi ，j，l and g Ml ; 110) According to g i，j，l and g Ml And formula (1) and formula (2) are used to calculate the objective function F of each electromagnetic model i ; 111) Update the position vector X of the particle swarm i and velocity vector V i ; 112) Determine the number of iterations i and the objective function value F i Whether the termination condition is met, if so, output the electromagnetic model obtained in step 16), if not, return to step 13); 2) Metasurface modeling and simulation verification; Select a hypersurface unit from the m different hypersurface units obtained in step 1) to form a hypersurface.

2. The method for designing an electromagnetic stealth metasurface universal for any frequency band as claimed in claim 1, wherein: In the step 11), H s Select the range to be λ g / 8~λ g / 4,λ g is the waveguide wavelength of the dielectric; H p Select the range H s / 500~H s / 100;W c Select the range to be λ g / 2~λ g ;W b Select the range to be λ g / 20~λ g / 10.

3. The method for designing an electromagnetic stealth metasurface universal for any frequency band as claimed in claim 1, wherein: The calculation methods of the free grid number n include: 121) Initialize, set n = 0, k = 0; 122) 123)Judgment Is it true? If so, output n. If not, return to step 122).

4. The method for designing an electromagnetic stealth metasurface universal for any frequency band as claimed in claim 1, wherein: Position vector X i and velocity vector V i The random number generator is used for the initial setting and is subsequently updated using step 111).

5. The method for designing an electromagnetic stealth metasurface universal for any frequency band as claimed in claim 1, wherein: In step 14), formula (3) is used as a conversion tool: Among them, x il(·) For X i The lth n-dimensional position vector x in il A single element in x idl(·) For X id The lth vector x in idl A single element in v idl(·) V id The lth vector v in idl A single element in .

6. The method for designing an electromagnetic stealth metasurface applicable to any frequency band as claimed in claim 1, wherein: The conversion rule in step 15) is: di Each vector in is copied to the entire unit according to the rule of full symmetry, that is, it becomes an N×N digital matrix.

7. The method for designing an electromagnetic stealth metasurface applicable to any frequency band as claimed in claim 1, wherein: The electromagnetic model established in step 16) is a Floquet boundary and an infinite periodic structure.

8. The method for designing an electromagnetic stealth metasurface applicable to any frequency band as claimed in claim 1, wherein: The updating algorithm in step 111) is: Where, v il 、x il They represent the speed and position of the lth particle at the i-th iteration, respectively, and are matrices V i , the first row of Xi, ω∈(0,1) is the weight coefficient, which indicates the preference between the current speed and the current extreme value, r 1i , r 2i ∈(0, 0.5) is the random fine-tuning coefficient; according to g i，j，l and g Ml And formula (1) and formula (2) calculate the position vector corresponding to the individual historical extreme value of the lth particle The position vector corresponding to the historical extreme value of the entire particle swarm 9. The method for designing an electromagnetic stealth metasurface universal for any frequency band as claimed in claim 1, wherein: The m different metasurface units obtained in step 1) exhibit specific phase gradients at the center frequency and its neighboring frequency bands.

10. The method for designing an electromagnetic stealth metasurface applicable to any frequency band as claimed in claim 1, wherein: In step 2), two metasurface units with a center frequency difference of 180° are selected from the m different metasurface units obtained in step 1) to form a metasurface, or four metasurface units with a center frequency difference of 90° are selected to form a metasurface.

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