Intelligent design method and structure of broadband flexible stealth skin

Abstract

The invention discloses an intelligent design method and structure of a broadband flexible stealth skin, and relates to the technical field of metamaterials and metasurface wave absorbers.The intelligent design method comprises the steps that unit structures which are the same in size and different in internal structure are designed, and each unit structure comprises a first unit structure and a second unit structure; the first unit structure and the second unit structure respectively realize broadband wave absorption in different frequency band ranges; the reflectivity and the phase of the unit structure are obtained through simulation calculation, and the size of the unit structure is optimized according to the reflectivity and the phase; arraying the two optimized unit structures to obtain a metasurface; and the far-field RCS value of the metasurface is calculated through a far-field formula. Based on the defect that some existing flexible metasurface wave absorbers are too narrow in wave absorbing bandwidth or cannot work at low frequency, the flexible metasurface wave absorber can work at a wide frequency band, and meanwhile, the flexibility can be guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of metamaterials and metasurface absorbers, and more specifically to an intelligent design method and structure of a broadband flexible stealth skin. Background Art

[0002] Metasurfaces are composed of subwavelength metal structures arranged on a substrate in a periodic or regular non-periodic manner. Different arrangements will produce various effects on incident electromagnetic waves, such as absorption, polarization conversion, directional scattering, and transmission, etc. Metasurfaces that can effectively absorb incident electromagnetic waves are called metasurface absorbers. Metasurface absorbers have broad application prospects in the fields of electromagnetic collection, sensing, and detection.

[0003] In the past few decades, modern scholars have been studying metasurface absorbers more and more frequently. Foreign scholars Salisbury, Jaumann and Dallenbach have each proposed metasurface absorbers, which can achieve absorbing effects within a relatively small bandwidth, but they are all very large in size. Due to the high resonant dispersion of metals, it is difficult for a single-layer metasurface to achieve broadband absorption. Broadband absorption can be achieved by stacking multilayer structures and loading lumped resistors, but this will increase the thickness of the metasurface. How to balance the thickness of the metasurface and the absorbing bandwidth is the current research difficulty.

[0004] Generally speaking, the thickness of the metasurface is restricted by the wavelength of the working band. Since the smaller the frequency of the electromagnetic wave, the larger the wavelength, the thickness of the metasurface working in the low frequency band is relatively thick, and correspondingly, the flexibility will become worse.

[0005] Therefore, how to provide an intelligent design method and structure of a broadband flexible stealth skin that can simultaneously achieve the characteristics of the metasurface working in the low frequency band and flexibility is an urgent problem that technical personnel in this field need to solve. Summary of the invention

[0006] In view of this, the present invention provides an intelligent design method and structure of a broadband flexible stealth skin, based on the fact that some existing flexible metasurface absorbers either have the disadvantage of too narrow absorbing bandwidth or cannot work at low frequencies. The method enables the metasurface absorber to work in a wide frequency band while ensuring flexibility.

[0007] In order to achieve the above object, the present invention adopts the following technical solution: an intelligent design method for a broadband flexible stealth skin, comprising:

[0008] Designing unit structures with the same size and different internal structures, wherein the unit structures include a first unit structure and a second unit structure, wherein the first unit structure and the second unit structure respectively realize broadband wave absorption within different frequency bands;

[0009] Obtaining the reflectivity and phase of the unit structure through simulation calculation, and optimizing the size of the unit structure according to the reflectivity and phase;

[0010] The two optimized unit structures are arranged to obtain a metasurface;

[0011] The far-field RCS value of the metasurface is calculated using the far-field formula.

[0012] Preferably, the two optimized unit structures are arranged, including:

[0013] Arranging the unit structures according to a specific arrangement order;

[0014] The specific order of arrangement is determined by the expected requirements.

[0015] Preferably, the array is randomly generated by adjusting the ratio of the two unit structures, the far-field RCS value of the metasurface is calculated, a data set is obtained, and a convolutional neural network is used to train the data set;

[0016] The array matrix of the unit structure is deduced according to expected requirements to obtain the overall metasurface.

[0017] Preferably, when a plane wave is incident perpendicularly to the metasurface, its far-field pattern F(θ, φ) is expressed as:

[0018]

[0019] Where p is the period of the unit structure, and the positions in the row and column directions are marked as m and n, respectively. A(m,n) and Respectively represent the amplitude and phase of the unit structure at the (m, n) position, k is the wave number, M and N are the total number of unit structures in the row and column directions, respectively, and i is the imaginary unit.

[0020] Preferably, the phase difference between the first unit structure and the second unit structure is 180°.

[0021] Preferably, a broadband flexible stealth skin structure comprises: a unit structure arranged in a specific array sequence; the unit structure comprises a first unit structure and a second unit structure, the first unit structure and the second unit structure respectively realize broadband wave absorption in different frequency bands;

[0022] The first unit structure includes a first flexible sponge, a first titanium wing conductive film, a second flexible sponge and a first metal conductive cloth arranged in sequence from top to bottom;

[0023] The second unit structure includes a second titanium wing conductive film, a third flexible sponge, a third titanium wing conductive film, a fourth flexible sponge and a second metal conductive cloth which are arranged in sequence from top to bottom.

[0024] Preferably, the first titanium wing conductive film and the third titanium wing conductive film are both of U-shaped structure;

[0025] The second titanium wing conductive film has a square structure.

[0026] Preferably, the titanium wing conductive film comprises a titanium wing and Teflon cloth;

[0027] The titanium wing is attached to the Teflon cloth;

[0028] The titanium wing conductive film is a first titanium wing conductive film, a second titanium wing conductive film or a third titanium wing conductive film.

[0029] Through the above technical solutions, it can be known that compared with the prior art, the present invention discloses an intelligent design method and structure of a broadband flexible stealth skin, including: designing unit structures of the same size and different internal structures, the unit structures including a first unit structure and a second unit structure, the first unit structure and the second unit structure respectively realizing broadband absorption in different frequency bands; obtaining the reflectivity and phase of the unit structure by simulation calculation, and optimizing the size of the unit structure according to the reflectivity and phase; arranging the two optimized unit structures to obtain a metasurface; and calculating the far-field RCS value of the metasurface by the far-field formula. Based on the fact that some existing flexible metasurface absorbers either have the disadvantage of too narrow absorption bandwidth or the disadvantage of being unable to work at low frequencies, the present invention can realize that the metasurface absorber can work in a wide frequency band while ensuring flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0031] Figure 1 This is a schematic diagram of the broadband flexible stealth skin structure provided by the present invention.

[0032] FIG. 2( a ) is a three-dimensional schematic diagram of a first unit structure provided in an embodiment of the present invention.

[0033] FIG. 2( b ) is a front view of the first unit structure provided in an embodiment of the present invention.

[0034] FIG. 2( c ) is a top view of the first unit structure provided in an embodiment of the present invention.

[0035] FIG. 2( d ) is a three-dimensional schematic diagram of a second unit structure provided in an embodiment of the present invention.

[0036] FIG. 2( e ) is a front view of the second unit structure provided in an embodiment of the present invention.

[0037] FIG. 2( f ) is a top view of the second unit structure provided in an embodiment of the present invention.

[0038] FIG. 3( a ) is a schematic diagram of reflectivity of two unit structures provided in an embodiment of the present invention.

[0039] FIG3( b ) is a schematic diagram showing the phases of two unit structures and the phase difference therebetween provided in an embodiment of the present invention.

[0040] Figure 4 A schematic diagram comparing the far-field formula provided in an embodiment of the present invention and the RCS curve obtained by simulation.

[0041] Figure 5 A basic code flow chart for the design of a deep learning model based on a convolutional neural network provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] The embodiment of the present invention discloses an intelligent design method for a broadband flexible stealth skin, comprising:

[0044] Unit structure design: determine the materials and structures used for the two unit structures, and optimize the structure size through the reflectivity and phase obtained by simulation calculation;

[0045] Array design combines the two designed unit structures into a whole through a specific arrangement sequence, and calculates the far-field RCS through the far-field formula.

[0046] Specifically, a unit structure with the same size and different internal structures is designed, wherein the unit structure includes a first unit structure and a second unit structure, and the first unit structure and the second unit structure respectively realize broadband wave absorption in different frequency bands;

[0047] Obtaining the reflectivity and phase of the unit structure through simulation calculation, and optimizing the size of the unit structure according to the reflectivity and phase;

[0048] The two optimized unit structures are arranged to obtain a metasurface;

[0049] The far-field RCS value of the metasurface is calculated using the far-field formula.

[0050] The two designed unit structures are arranged in a specific order and combined into an overall metasurface, and the far-field RCS of the overall metasurface is calculated using the theoretical far-field formula.

[0051] Specifically, the two optimized unit structures are arranged, including:

[0052] Arranging the unit structures according to a specific arrangement order;

[0053] The specific order of arrangement is determined by the expected requirements.

[0054] Specifically, the array is randomly generated by adjusting the ratio of the two unit structures, the far-field RCS value of the metasurface is calculated, a data set is obtained, and a convolutional neural network is used to train the data set;

[0055] The array matrix of the unit structure is deduced according to expected requirements to obtain the overall metasurface.

[0056] Specifically, when a plane wave is incident vertically onto the metasurface, its far-field pattern F(θ,φ) is expressed as:

[0057]

[0058] Where p is the period of the unit structure, and the positions in the row and column directions are marked as m and n, respectively. A(m,n) and Respectively represent the amplitude and phase of the unit structure at the (m, n) position, k is the wave number, M and N are the total number of unit structures in the row and column directions, respectively, i is the imaginary unit, and the square of i is equal to -1.

[0059] Specifically, the phase difference between the first unit structure and the second unit structure is 180°.

[0060] The embodiment of the present invention also discloses a broadband flexible stealth skin structure, such as Figure 1 As shown, it includes: a unit structure arranged in a specific array sequence; the unit structure includes a first unit structure and a second unit structure, and the first unit structure and the second unit structure respectively realize broadband wave absorption in different frequency bands;

[0061] The first unit structure includes a first flexible sponge, a first titanium wing conductive film, a second flexible sponge and a first metal conductive cloth arranged in sequence from top to bottom;

[0062] The second unit structure includes a second titanium wing conductive film, a third flexible sponge, a third titanium wing conductive film, a fourth flexible sponge and a second metal conductive cloth which are arranged in sequence from top to bottom.

[0063] Specifically, the first titanium wing conductive film and the third titanium wing conductive film are both of U-shaped structure;

[0064] The second titanium wing conductive film has a square structure.

[0065] Specifically, the titanium wing conductive film includes a titanium wing and Teflon cloth;

[0066] The titanium wing is attached to the Teflon cloth;

[0067] The titanium wing conductive film is a first titanium wing conductive film, a second titanium wing conductive film or a third titanium wing conductive film.

[0068] Figure 2(a)-Figure 2(f) A three-dimensional diagram of unit structure 1 (first unit structure) and unit structure 2 (second unit structure) is shown. Both unit structure 1 and unit structure 2 increase the bandwidth by multi-layer stacking. The two structures are not exactly the same. This is to produce different reflectivities and a phase difference between the two structures, so that the bandwidth can be further expanded in subsequent array layout.

[0069] Among them, unit structure 1 adopts a four-layer structure, from top to bottom respectively, the first flexible sponge, the first titanium wing conductive film, the second flexible sponge and the first metal conductive cloth, and unit structure 2 adopts a five-layer structure, from top to bottom respectively, the second titanium wing conductive film, the third flexible sponge, the third titanium wing conductive film, the fourth flexible sponge and the second metal conductive cloth, among which the first titanium wing conductive film and the third titanium wing conductive film refer to the titanium wing structure with a certain square resistance. The titanium wing structure is composed of a large square minus a small square in the middle, shaped like a "U" shape; the second titanium wing conductive film is a square structure; the first flexible sponge, the second flexible sponge, the third flexible sponge, the fourth flexible sponge, the first metal conductive cloth and the second metal conductive cloth are square structures of the same size.

[0070] The titanium wing structure adopts a "U"-shaped structure because the "U"-shaped structure can produce more resonance points compared to the square structure, thereby increasing the absorption bandwidth and having a greater impact on the phase of the unit structure, further expanding the phase difference between unit structure 1 and unit structure 2.

[0071] The thickness of the titanium wing is very thin and can be ignored, but the titanium wing needs to be attached to a piece of Teflon cloth with a thickness of 0.13mm to form a titanium wing conductive film. The titanium wing conductive film has the characteristics of low square resistance, high light transmittance and excellent flexibility, which provides conditions for the production of flexible skin. In the simulation, the relative dielectric constant of the Teflon cloth is set to 3. The size of the "U"-shaped ITO structure of unit structure 1 and unit structure 2 is the same, h represents the height of the flexible sponge, p represents the period of the first unit structure or the second unit structure, a1 represents the side length of the "U"-shaped large-diameter in the first titanium wing conductive film or the third titanium wing conductive film, a2 represents the side length of the "U"-shaped small-diameter in the first titanium wing conductive film or the third titanium wing conductive film, and b represents the side length of the titanium wing in the second titanium wing conductive film; the specific size parameters are: p = 5mm, a1 = 4.7mm, a2 = 3.9mm, h = 6mm, b = 4.7mm.

[0072] The simulation results show that when the square resistance of the first titanium wing conductive film and the third titanium wing conductive film is in the range of 35 ohms to 45 ohms, a large phase difference will occur between unit structure 1 and unit structure 2. When the square resistance is 35 ohms, the phase difference between unit structure 1 and unit structure 2 reaches the maximum. Since the impedance of air is 377 ohms, in order to achieve impedance matching with air, the square resistance of the second titanium wing conductive film should be between 350 ohms and 400 ohms. Considering that the square resistance of the actual processing material cannot be changed continuously, the square resistance of the first titanium wing conductive film and the third titanium wing conductive film is set to 35 ohms, and the square resistance of the second titanium wing conductive film is set to 350 ohms. In addition, a flexible sponge is selected as the dielectric substrate. Therefore, the titanium wing conductive film with excellent flexibility is combined with the flexible sponge to produce a flexible metasurface.

[0073] Specifically, the flexible sponge in the embodiment of the present invention is a first flexible sponge, a second flexible sponge, a third flexible sponge or a fourth flexible sponge.

[0074] Figures 3(a) and 3(b) show the simulation results of unit structure 1 (first unit structure) and unit structure 2 (second unit structure). Figure 3(a) shows that both unit structures have a certain wave absorption effect, among which the reflectivity of unit structure 1 in the range of 6GHz-16GHz is less than -10dB, and the wave absorption effect at low frequency (4GHz-6GHz) and high frequency (16GHz-18 GHz) is relatively poor. The reflectivity of unit structure 2 at low frequency and high frequency is significantly lower than that of unit structure 1, but the wave absorption effect in the mid-frequency band is poor. Therefore, if unit structure 1 and unit structure 2 can be combined, broadband wave absorption in the range of 4GHz-18 GHz can be achieved. Figure 3(b) shows that the phase difference between unit structure 1 and unit structure 2 meets 180°±60° in the range of 4GHz-14GHz. When there is a phase difference of 180° between the two structures, the reflectivity can be further reduced by arranging the array to improve the wave absorption effect.

[0075] After designing the unit structure, the unit structure is arrayed, and the arrayed structure is used as a whole metasurface. The far-field RCS of this metasurface can be calculated using the far-field formula. When a plane wave is incident vertically on the metasurface, its far-field pattern F(θ,φ) can be expressed by formula (1):

[0076]

[0077] The period of the unit structure is p, and the positions in the row and column directions are marked as m and n, respectively. Represent the amplitude and phase of the unit structure at the position (m, n), k is the wave number, M and N are the total number of unit structures in the row direction and column direction respectively. Since the phase difference between unit structure 1 and unit structure 2 is 180°, unit structure 1 and unit structure 2 can be represented by numbers 0 and 1 respectively. Therefore, the array order can be replaced by a two-dimensional matrix of size M*N containing only numbers 0 and 1. Once this two-dimensional matrix of size M*N is determined, the far-field RCS value of the overall metasurface can be calculated by formula (1).

[0078] In the embodiment of the present invention, M and N are both equal to 36. If the traversal scanning method is used, it is necessary to calculate 2 36 This method has a huge amount of calculation and takes a long time to calculate. Convolutional neural networks are good at processing sequence data, so the embodiment of the present invention introduces convolutional neural networks (CNN) into the deep learning model. The basic code flow of the deep learning model design based on convolutional neural networks is as follows: Figure 5 shown.

[0079] The neural network is constructed by stacking an input layer, three convolutional layers, a batch normalization layer, an activation function layer, three fully connected layers, and a regression layer. The first convolutional layer has 16 convolutional kernels of size 7×1, the second convolutional layer has 32 convolutional kernels of size 5×1, and the third convolutional layer has 32 convolutional kernels of size 3×1.

[0080] The data set can be determined in the following way: the proportion of unit structure 1 changes from 0.1 to 0.9, with a step of 0.1, for a total of 9 proportions. Each proportion generates 300 sets of random sequences, and the RCS value is calculated using the far-field formula, for a total of 2700 sets of data. The data set is trained using the above deep learning model.

[0081] According to actual needs, the expected electromagnetic response is input into the convolutional neural network model, and the predicted overall metasurface is as follows: Figure 1 The far-field RCS value obtained by simulating the entire metasurface using CST simulation software and the RCS value calculated by the far-field formula are shown in the attached figure. Figure 4Whether it is the simulation results or the theoretical calculation results, the average reflectivity in the range of 4.2GHz-18GHz is less than -10dB, which meets the expected requirements.

[0082] The stealth skin of the embodiment of the present invention is mainly composed of two unit structures of the same size and different internal structures arranged in a specific order. It can achieve broadband absorption in the range of 4.2GHz-18GHz, with a reflectivity of less than -10dB, and can be processed into flexible samples for easy disassembly and assembly.

[0083] In addition, the stealth skin provided by the embodiment of the present invention can realize the stealth of objects to C, X, and Ku band radars, wherein the frequency range of the C band is: 4GHz-8GHz; the frequency range of the X band is: 8GHz-12GHz; the frequency range of the Ku band is: 12GHz-18GHz; and the metasurface described in the embodiment of the present invention can realize broadband wave absorption in the range of 4.2GHz-18 GHz, and the working bandwidth covers the above three frequency bands, so it can produce electromagnetic confrontation to the radars of the above three bands, thereby realizing stealth.

[0084] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0085] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An intelligent design method for a broadband flexible stealth skin, characterized in that: include: Designing unit structures with the same size and different internal structures, wherein the unit structures include a first unit structure and a second unit structure, wherein the first unit structure and the second unit structure respectively realize broadband wave absorption within different frequency bands; Obtaining the reflectivity and phase of the unit structure through simulation calculation, and optimizing the size of the unit structure according to the reflectivity and phase; The two optimized unit structures are arranged to obtain a metasurface; The far-field RCS value of the metasurface is calculated using the far-field formula.

2. The intelligent design method of a broadband flexible stealth skin according to claim 1 is characterized in that: Arrange the two optimized unit structures, including: Arranging the unit structures according to a specific arrangement order; The specific order of arrangement is determined by the expected requirements.

3. The intelligent design method of a broadband flexible stealth skin according to claim 2 is characterized in that: By adjusting the ratio of the two unit structures to randomly generate arrays, the far-field RCS value of the metasurface is calculated to obtain a data set, and a convolutional neural network is used to train the data set. The array matrix of the unit structure is deduced according to expected requirements to obtain the overall metasurface.

4. The intelligent design method of a broadband flexible stealth skin according to claim 1 is characterized in that: When a plane wave is incident perpendicularly to the metasurface, its far-field pattern F(θ,φ) is expressed as: Where p is the period of the unit structure, and the positions in the row and column directions are marked as m and n, respectively. A(m,n) and Respectively represent the amplitude and phase of the unit structure at the (m, n) position, k is the wave number, M and N are the total number of unit structures in the row and column directions, respectively, and i is the imaginary unit.

5. The intelligent design method of a broadband flexible stealth skin according to claim 1 is characterized in that: The phase difference between the first unit structure and the second unit structure is 180°.

6. A broadband flexible stealth skin structure, characterized in that: include: A unit structure arranged in a specific array sequence; the unit structure comprises a first unit structure and a second unit structure, wherein the first unit structure and the second unit structure respectively realize broadband wave absorption in different frequency bands; The first unit structure includes a first flexible sponge, a first titanium wing conductive film, a second flexible sponge and a first metal conductive cloth arranged in sequence from top to bottom; The second unit structure includes a second titanium wing conductive film, a third flexible sponge, a third titanium wing conductive film, a fourth flexible sponge and a second metal conductive cloth which are arranged in sequence from top to bottom.

7. The intelligent design method of a broadband flexible stealth skin according to claim 1 is characterized in that: The first titanium wing conductive film and the third titanium wing conductive film both have a U-shaped structure; The second titanium wing conductive film has a square structure.

8. The intelligent design method of a broadband flexible stealth skin according to claim 1 is characterized in that: The titanium wing conductive film includes a titanium wing and Teflon cloth; The titanium wing is attached to the Teflon cloth; The titanium wing conductive film is a first titanium wing conductive film, a second titanium wing conductive film or a third titanium wing conductive film.

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