An intelligent design method and structure of a broadband flexible stealth skin

Abstract

The present invention discloses an intelligent design method and structure for a broadband flexible stealth skin, relating to the technical field of metamaterials and metasurface absorbers. The method includes: designing unit structures of identical size but 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 achieve broadband absorption within different frequency bands; obtaining the reflectivity and phase of the unit structures through simulation calculations, and optimizing the dimensions of the unit structures based on the reflectivity and phase; arranging the two optimized unit structures to obtain a metasurface; and calculating the far-field RCS value of the metasurface using a far-field formula. Based on the drawbacks of some existing flexible metasurface absorbers, which either have too narrow an absorption bandwidth or are unable to operate at low frequencies, the present invention enables metasurface absorbers to operate across a wide frequency band while maintaining flexibility.

Description

Technical Field

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

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

[0003] Over the past few decades, modern researchers have increasingly studied metasurface absorbers. Foreign researchers Salisbury, Jaumann, and Dallenbach have each proposed metasurface absorbers. These absorbers can achieve absorption within a relatively narrow bandwidth, but they are often quite large. Due to the high resonant dispersion of metals, broadband absorption is difficult to achieve with a single-layer metasurface. Broadband absorption can be achieved by stacking multiple layers and loading them with lumped resistors, but this increases the thickness of the metasurface. Balancing the thickness of the metasurface with the absorption bandwidth remains a current challenge.

[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 accordingly, the flexibility will become worse.

[0005] Therefore, how to provide an intelligent design method and structure for a broadband flexible stealth skin that can simultaneously achieve the characteristics of 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 for 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 present invention enables the metasurface absorber to work in a wide frequency band while ensuring flexibility.

[0007] To achieve the above objectives, 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 achieve broadband 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 in a specific order;

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

[0015] Preferably, an 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 represent the amplitude and phase of the unit structure at the (m, n) position, respectively, 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 realizing broadband wave absorption within 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 a 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 seen that compared with the existing technology, the present invention discloses an intelligent design method and structure for a broadband flexible stealth skin, including: designing unit structures of the same size but 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 achieving broadband 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 based on the reflectivity and phase; arranging the two optimized unit structures to obtain a metasurface; and calculating the far-field RCS value of the metasurface using a far-field formula. Based on the fact that some existing flexible metasurface absorbers either have the disadvantage of too narrow an absorption bandwidth or the disadvantage of being unable to operate at low frequencies, the present invention can achieve a metasurface absorber that can operate in a wide frequency band while maintaining 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 following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0031] Figure 1 Schematic diagram of the broadband flexible stealth skin structure provided by the present invention.

[0032] FIG2( a ) is a schematic three-dimensional diagram of a first unit structure provided in an embodiment of the present invention.

[0033] FIG2( b ) is a front view of the first unit structure provided by an embodiment of the present invention.

[0034] FIG2( c ) is a top view of the first unit structure provided by an embodiment of the present invention.

[0035] FIG2( d ) is a schematic three-dimensional diagram of a second unit structure provided by an embodiment of the present invention.

[0036] FIG2( e ) is a front view of the second unit structure provided by an embodiment of the present invention.

[0037] FIG2( f ) is a top view of the second unit structure provided by an embodiment of the present invention.

[0038] FIG3( a ) is a schematic diagram of the reflectivity of two unit structures provided in an embodiment of the present invention.

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

[0040] Figure 4 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 This is a flowchart of the basic code for the design of a deep learning model based on a convolutional neural network, provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts 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 and calculates the far-field RCS using the far-field formula.

[0046] Specifically, unit structures with the same size and different internal structures are designed, wherein the unit structures include a first unit structure and a second unit structure, and the first unit structure and the second unit structure respectively achieve broadband absorption within 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 in a specific order;

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

[0054] Specifically, the ratio of the two unit structures is adjusted to randomly generate an array, 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 on 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 Represent the amplitude and phase of the unit structure at the (m, n) position respectively, 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 within 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 a 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 including the first flexible sponge, the first titanium wing conductive film, the second flexible sponge and the first metal conductive cloth; unit structure 2 adopts a five-layer structure, from top to bottom respectively including 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 them, 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 with a small square subtracted from 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 titanium wings are very thin and negligible, but they need to be attached to a 0.13mm thick Teflon cloth to form a titanium wing conductive film. The titanium wing conductive film has low sheet resistance, high transmittance, and excellent flexibility, making it ideal for the fabrication of a flexible skin. During simulation, the relative dielectric constant of the Teflon cloth was set to 3. The dimensions of the U-shaped ITO structures in Unit Structures 1 and 2 are identical. h represents the height of the flexible sponge, p represents the period of the first or second unit structure, a1 represents the length of the larger aperture of the U-shaped structure in the first or third titanium wing conductive film, a2 represents the length of the smaller aperture of the U-shaped structure in the first or third titanium wing conductive film, and b represents the length of the titanium wing in the second titanium wing conductive film. The specific dimensional parameters are: p = 5mm, a1 = 4.7mm, a2 = 3.9mm, h = 6mm, and b = 4.7mm.

[0072] The simulation results show that when the square resistance of the first and third titanium wing conductive films 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 its 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 continuously changed, the square resistance of the first and third titanium wing conductive films 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 for unit structure 1 (the first unit structure) and unit structure 2 (the second unit structure). Figure 3(a) shows that both unit structures have a certain absorption effect. Unit structure 1 has a reflectivity of less than -10dB in the 6GHz-16GHz range, and its absorption effect is relatively poor at low frequencies (4GHz-6GHz) and high frequencies (16GHz-18GHz). Unit structure 2 has a significantly lower reflectivity than unit structure 1 at low and high frequencies, but its absorption effect is poor in the mid-frequency range. Therefore, if unit structures 1 and 2 can be combined, broadband absorption can be achieved in the 4GHz-18GHz range. Figure 3(b) shows that the phase difference between unit structures 1 and 2 satisfies 180°±60° in the 4GHz-14GHz range. When there is a 180° phase difference between the two structures, the reflectivity can be further reduced and the absorption effect improved by arranging them in an array.

[0075] After designing the unit structure, the unit structure is arrayed. 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. A(m,n) and Represent the amplitude and phase of the unit structure at position (m, n), k is the wave number, and M and N are the total number of unit structures in the row and column directions, respectively. Since the phase difference between unit structure 1 and unit structure 2 is 180°, the numbers 0 and 1 can be used to represent unit structure 1 and unit structure 2, respectively. Therefore, the array order can be replaced by a two-dimensional matrix of size M*N containing only the numbers 0 and 1. Once this M*N two-dimensional matrix is ​​determined, the far-field RCS value of the entire metasurface can be calculated using 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 convolution kernels of size 7×1, the second convolutional layer has 32 convolution kernels of size 5×1, and the third convolutional layer has 32 convolution kernels of size 3×1.

[0080] The dataset was generated as follows: the proportion of unit structure 1 was varied from 0.1 to 0.9, in increments of 0.1, for a total of nine ratios. For each ratio, 300 random sequences were generated, and the RCS values ​​were calculated using the far-field formula, resulting in a total of 2,700 data sets. The deep learning model described above was then used to train the dataset.

[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 4Both the simulation results and the theoretical calculation results show that the average reflectivity in the 4.2 GHz-18 GHz range is less than -10 dB, 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 achieve the stealth of objects against C-, X-, and Ku-band radars. Among them, 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 achieve broadband absorption in the range of 4.2GHz-18 GHz. The working bandwidth covers the above three frequency bands, so it can produce electromagnetic confrontation against radars in the above three bands, thereby achieving stealth.

[0084] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0085] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily 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 is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A broadband flexible stealth skin structure, characterized in that: include: A unit structure arranged in a specific array sequence; the unit structure includes a first unit structure and a second unit structure, wherein the first unit structure and the second unit structure respectively achieve broadband absorption within 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 arranged in sequence from top to bottom; The titanium wing conductive film includes a titanium wing and Teflon cloth; The titanium wing is attached to the Teflon cloth to form a titanium wing conductive film; 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; 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; The titanium wings in the first titanium wing conductive film and the third titanium wing conductive film have a certain square resistance, and the titanium wing structure is a U-shaped structure; The titanium wing in the second titanium wing conductive film has a certain square resistance, and the titanium wing structure is a square structure.

2. An intelligent design method for a broadband flexible stealth skin, applied to a broadband flexible stealth skin structure according to claim 1, 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 achieve broadband 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.

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

4. The intelligent design method of a broadband flexible stealth skin according to claim 3, characterized in that: By adjusting the ratio of the two unit structures to randomly generate an array, 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.

5. The intelligent design method of a broadband flexible stealth skin according to claim 2, characterized in that: When a plane wave is incident perpendicularly on 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 represent the amplitude and phase of the unit structure at the (m, n) position, respectively, 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.

6. The intelligent design method of a broadband flexible stealth skin according to claim 2, characterized in that: The phase difference between the first unit structure and the second unit structure is 180°.

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