Electron density distribution method for optimally reducing RCS (Radar Cross Section) of metal plate by using non-uniform plasma

Abstract

The invention relates to an electron density distribution method for optimally reducing the RCS of a metal plate by a non-uniform plasma. The method comprises the following steps of: enabling electromagnetic waves to vertically enter the metal plate coated by the non-uniform plasma; selecting the optimization range of the electron density of the non-uniform plasma according to the frequency of the incident electromagnetic wave; according to the selected electron density range, the optimization range of the thickness of the non-uniform plasma is selected; determining the optimization range of the non-uniform plasma collision frequency; designing an electron density distribution function according to the selected electron density range; according to the selected electron density range, the non-uniform plasma thickness, the non-uniform plasma collision frequency and the electron density distribution function, performing optimal RCS reduction based on a genetic algorithm; the RCS reduction under the condition that the metal plate is coated by the non-uniform plasma is analyzed in detail, the RCS reduction is influenced by parameters such as the electron density range, the distribution, the plasma thickness and the collision frequency, and after the electron density range, the collision frequency and the non-uniform plasma thickness are determined, the RCS reduction is determined. The optimal electron density distribution can be obtained through optimization of the genetic algorithm, the optimal RCS reduction is obtained, and the method has the advantages of being fast, efficient and accurate.

Description

Technical Field

[0001] The present invention belongs to the technical field of plasma applications and radar RCS reduction, and particularly relates to a method for the electron density distribution of the optimal reduction of the RCS of a metal plate by non-uniform plasma. Background Technique

[0002] Stealth technology is the guarantee for the survival of weapons and equipment such as aircraft in modern battlefields. With the continuous change of battlefield requirements, stealth technology is developing in the direction of "wideband, low profile, multi-polarization, and large angle". According to the characteristics of different targets such as aircraft, common stealth technologies include shape stealth, absorbing material stealth, electromagnetic metasurface stealth, and plasma stealth, etc., among which the stealth technologies of shape and absorbing materials are relatively mature. Shape stealth technology is a technology that reduces the echo in a specific direction by designing the aerodynamic shape of an aircraft. The disadvantage of shape stealth technology is that it may conflict with aerodynamics and increase the difficulty of aerodynamic design. The stealth technology of absorbing materials is to lay or spray special absorbing materials on the surface of an aircraft, which can significantly reduce the intensity of the reflected wave. However, the disadvantage of absorbing material stealth is that when the thickness of the absorbing material is relatively thick, it will cause the weight of the aircraft to exceed the standard, making it unsuitable for stealth in the low-frequency range. Electromagnetic metasurface stealth technology uses the structure of electromagnetic metasurfaces to flexibly control the amplitude and phase, resulting in deviations in the reflection direction and polarization of electromagnetic waves, thereby reducing the radar cross-section (RCS) of the covered target. Metasurface stealth has the advantages of small size, light weight, and easy conformability. However, there are also disadvantages because its stealth frequency band is relatively narrow and it is difficult to achieve wideband stealth.

[0003] Plasma stealth technology is a new stealth technology concept and principle. Plasma is regarded as the fourth form of matter in addition to solids, liquids, and gases. Plasma contains free electrons, which will have absorption, reflection, refraction, and other effects on the propagation of electromagnetic waves. The presence of plasma on the surface of an aircraft will change its target scattering characteristics. Therefore, the interaction between plasma and electromagnetic waves can be used to reduce the radar cross-section (RCS) of the target. Plasma has the characteristics of a wide absorption frequency, high absorption rate, and easy maintenance of electromagnetic wave generating equipment. Therefore, plasma stealth technology has received extensive attention at home and abroad in recent years.

[0004] The invention patent "A method and device for configuring stealth parameters of plasma materials" with the application number CN202010761646.7 only analyzes the influence of plasma materials on the reflection coefficient of the target, and does not analyze in detail the influence of different plasma parameters on reflection; and the analysis of the reflection coefficient of the target in this invention does not analyze the far-field RCS result of the target.

[0005] "Research on the Influence of Plasma on the Scattering Characteristics of Millimeter Waves" (Master's thesis, author: Li Zhao, University of Electronic Science and Technology of China, 2023), analyzed the influence of different plasma parameters (electron density, collision frequency) on the RCS of sphere / cone targets, but the analyzed parameter range was small and the effect was not obvious; at the same time, the optimal analysis of plasma parameters on RCS reduction was not discussed, lacking practicality. Summary of the Invention

[0006] In order to overcome the defects existing in the above-mentioned prior art, the purpose of the present invention is to propose a method for obtaining the optimal electron density distribution for reducing the RCS of a metal plate by non-uniform plasma. For a metal plate target, after a given electromagnetic wave frequency, according to plasma parameters, including the electron density range, collision frequency, and plasma thickness, the best RCS reduction can be obtained, and for a metal plate target, after determining the electron density range, according to the electron density distribution, the plasma parameters for obtaining the best RCS reduction can be obtained, which has the advantages of being fast, efficient, and accurate.

[0007] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0008] A method for obtaining the optimal electron density distribution for reducing the RCS of a metal plate by non-uniform plasma, specifically including the following steps:

[0009] Step S1, making an electromagnetic wave perpendicularly incident on a metal plate 1 coated with non-uniform plasma;

[0010] Step S2, selecting the optimization range of the electron density n of the non-uniform plasma according to the incident electromagnetic wave frequency; e of the non-uniform plasma;

[0011] Step S3, according to the electron density n of the non-uniform plasma selected in Step S2; e select the optimization range of the thickness of the non-uniform plasma;

[0012] Step S4, determining the optimization range of the collision frequency of the non-uniform plasma;

[0013] Step S5, according to the electron density n of the non-uniform plasma selected in Step S2; e design an electron density distribution function;

[0014] Step S6, based on the genetic algorithm, perform optimal RCS reduction according to the electron density n of the non-uniform plasma, the thickness of the non-uniform plasma, the collision frequency of the non-uniform plasma, and the electron density distribution function selected in Steps S2 to S5. e The electron density n of the non-uniform plasma selected in Step S2;

[0015] The electron density n of the non-uniform plasma selected in Step S2; e and the characteristic frequency f of the non-uniform plasma; pThere is the following relationship:

[0016]

[0017] where e is the charge carried by an electron, and ε 0 is the vacuum permittivity, and m e is the electron mass; when the frequency of the electromagnetic wave is f L ~f H , the corresponding characteristic frequency range of the inhomogeneous plasma is f pL ~f pH , and the preset f pL <0.5f L , f pL >2f H .

[0018] In step S3, the thickness of the inhomogeneous plasma is selected to be greater than 1 wavelength of the low frequency, and the greater the plasma thickness, the more obvious the RCS reduction is.

[0019] In step S4, the collision frequency of the inhomogeneous plasma is close to the frequency of the incident electromagnetic wave. The greater the collision frequency, the more obvious the RCS reduction effect is.

[0020] The collision frequency of the inhomogeneous plasma in step S4 being close to the frequency of the incident electromagnetic wave is: collision frequency: electromagnetic wave frequency = 0.8~1.2:1.

[0021] The electron density distribution function in step S5 adopts:

[0022]

[0023] where n emax is the highest electron density, n emin is the lowest electron density, y L is the thickness of the inhomogeneous plasma, m is an adjustable variable, and 0.01≤m≤3.

[0024] The specific method of step S6 is: setting the electron density n e of the inhomogeneous plasma, the electron density distribution function, the collision frequency of the inhomogeneous plasma, and the thickness of the inhomogeneous plasma as optimization parameters, and performing optimization of the genetic algorithm through the Optimization module in the mathematical software. By adjusting the magnitude of the electron density distribution function, the electron density distribution is changed until the RCS is optimized to the optimal.

[0025] The frequency of the vertically incident electromagnetic wave in step S1 and step 2 is selected as 10 - 18 GHz;

[0026] The optimization range of the electron density n e of the inhomogeneous plasma in step S2 is selected as 1.24×1016 m -3 ~1.99×10 19 m -3 ;

[0027] The optimization range of the non-uniform plasma thickness described in step S3 is selected as 15 mm - 100 mm;

[0028] The optimization range of the non-uniform plasma collision frequency described in step S4 is selected as 5 GHz - 20 GHz.

[0029] The method for the optimal reduction of the RCS of a metal plate by a non-uniform plasma, which is used in the field of RCS reduction of aircraft targets.

[0030] Compared with the prior art, the present invention has the following innovative points:

[0031] 1. For a metal flat plate target, after a given electromagnetic wave frequency is given, the present invention selects appropriate plasma parameters, including the non-uniform plasma electron density range, the non-uniform plasma collision frequency, the non-uniform plasma thickness, etc., to obtain the best RCS reduction. This method is also applicable to spherical or other shaped targets; based on the ADE-FDTD algorithm, the present invention gives the reduction law of the RCS of a non-uniform plasma covering a flat plate target by different non-uniform plasma parameters, such as Figures 2 to 5 shown, to provide non-uniform plasma parameter settings for the actual RCS reduction; with good accuracy and high efficiency.

[0032] 2. For a metal flat plate target, after determining an appropriate non-uniform plasma electron density range, the present invention selects an appropriate non-uniform plasma electron density distribution to obtain the non-uniform plasma parameters for the best RCS reduction. This method is also applicable to spherical or other shaped targets; after determining the non-uniform plasma electron density range, the present invention can provide an appropriate electron density distribution to obtain the best RCS reduction, providing theoretical support for the optimal RCS reduction of the target and the non-uniform plasma simulation parameters.

[0033] In summary, while the present invention gives the reduction law of the radar RCS by different non-uniform plasma parameters, it provides the excitation power and parameter settings of the plasma for the actual RCS reduction; it also provides an appropriate electron density distribution after determining the non-uniform plasma electron density range to obtain the best RCS reduction, providing theoretical support for the optimal RCS reduction of the target and the non-uniform plasma simulation parameters, and has the advantages of fast, efficient and accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of electromagnetic wave incident on a metal plate coated with non-uniform plasma and electromagnetic wave reflection.

[0035] Figure 2 are RCS reduction diagrams at a frequency of 10-18 GHz under different electron density ranges.

[0036] Figure 3 are RCS reduction diagrams at a frequency of 10-18 GHz under different electron distributions.

[0037] Figure 4 are RCS reduction diagrams at a frequency of 10-18 GHz under different collision frequencies.

[0038] Figure 5 are RCS reduction diagrams at a frequency of 10-18 GHz under different non-uniform plasma thicknesses.

[0039] Figure 6 is a flowchart of a genetic-based optimization algorithm;

[0040] Figure 7 is the optimal RCS reduction result obtained by optimization.

[0041] Figure 8 is the optimal electron density distribution obtained by optimization.

[0042] Among them, 1. Metal plate target; 2. Non-uniform plasma; 3. Vertically incident electromagnetic wave; 4. Reflected wave.

[0043] Specific method

[0044] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Refer to Figure 1 As shown, a study on the electron density distribution for the optimal reduction of the RCS of a metal plate by a non-uniform plasma includes a simulation model in which an electromagnetic wave vertically enters a metal plate target coated with a non-uniform plasma. The model includes a metal plate target 1, a non-uniform plasma 2, a vertically incident electromagnetic wave 3, and a reflected wave 4.

[0046] A study on the electron density distribution for the optimal reduction of the RCS of a metal plate by a non-uniform plasma includes the following steps:

[0047] Step S1, making an electromagnetic wave vertically enter the metal plate 1 coated with a non-uniform plasma;

[0048] Step S2. Selecting an appropriate optimization range of the electron density n of the non-uniform plasma according to the frequency of the incident electromagnetic wave. There is the following relationship between the electron density n and the characteristic frequency f of the non-uniform plasma: e of e and the characteristic frequency f of the non-uniform plasma p exists the following relationship:

[0049]

[0050] Among them, e is the charge carried by an electron, and ε 0 is the permittivity of vacuum, and m e is the electron mass. Since when the frequency of the electromagnetic wave is close to the characteristic frequency of the corresponding inhomogeneous plasma, the plasma has resonant absorption of the electromagnetic wave, that is, RCS reduction. Therefore, to achieve the maximum attenuation of the electromagnetic wave by the inhomogeneous plasma, the characteristic frequency is usually selected to be close to the frequency of the electromagnetic wave. Assume that the frequency of the electromagnetic wave is f L ~f H , and the characteristic frequency range of the inhomogeneous plasma is f pL ~f pH , then the characteristic frequency and the electromagnetic wave frequency can be preset as follows: f pL <0.5f L , f pL >2f H .

[0051] Step S3: According to the optimized range of the electron density n e of the inhomogeneous plasma selected in step S2, the selection of the thickness of the inhomogeneous plasma can be carried out. The thickness of the inhomogeneous plasma is selected to be greater than 1 wavelength of the low frequency. The greater the thickness of the plasma, the more obvious the RCS reduction, so as to achieve better absorption of the electromagnetic wave by the inhomogeneous plasma. Reference can be made to Figure 5 as shown; generally, the thickness selection can be based on the actually allowed thickness, or the thickness can be set to 1 wavelength of the low frequency for design;

[0052] Step S4: Optimized selection of the collision frequency of the inhomogeneous plasma. Referring to Figure 4 , it can be seen that the greater the collision frequency, the more obvious the RCS reduction effect, but generally the collision frequency can be selected near the center frequency of the incident electromagnetic wave frequency;

[0053] Step S5: According to the range of the electron density n e of the inhomogeneous plasma selected in step S2, the design of the electron density distribution can be carried out. The electron density distribution function can be selected as the following formula:

[0054]

[0055] where n emax is the highest electron density, n emin is the lowest electron density, y L is the plasma thickness, m is an adjustable variable, and the adjustment range is 0.01~3. By adjusting the size of m, the electron density distribution can be changed; three other distributions can be obtained.

[0056] Step S6: The electron density n eBased on the electron density range, non-uniform plasma thickness, non-uniform plasma collision frequency, and electron density distribution function, an analysis of optimal RCS reduction using a genetic algorithm was carried out: The electron density range, electron density distribution function, collision frequency, and thickness were set as optimization parameters, and the genetic algorithm was optimized through the Optimization module in mathematical software, such as Figure 6 , by adjusting the size of the electron density distribution function, changing the electron density distribution until the RCS was optimized to the optimal value.

[0057] The technical effects of the present invention were described in detail in combination with simulations.

[0058] The present invention utilized MATLAB 2021b and the commercial electromagnetic simulation software CST 2018 to design and simulate a study on the electron density distribution for the optimal reduction of the RCS of a metal plate by a non-uniform plasma.

[0059] A study on the electron density distribution for the optimal reduction of the RCS of a metal plate by a non-uniform plasma carried out an RCS reduction study and optimal RCS reduction optimization for a metal plate with dimensions of 200x175 mm in the frequency range of 10 - 18 GHz.

[0060] Scheme analysis and selection: According to the electromagnetic wave frequency range, initial parameters such as the electron density range, thickness, collision frequency, and electron density distribution of the non-uniform plasma were selected, and a numerical simulation based on ADE-FDTD was chosen, and the commercial software CST 2018 was used for simulation verification.

[0061] A study on the electron density distribution for the optimal reduction of the RCS of a metal plate by a non-uniform plasma selected a wide range of non-uniform plasma characteristic frequencies in the range of 5 - 36 GHz for simulation; in this embodiment, four simulations with different characteristic frequency ranges were given, namely 1 - 8 GHz, 5 - 14 GHz, 8 - 20 GHz, and 20 - 40 GHz, and the corresponding electron density ranges were 1.24×10 16 ~7.94×10 17 m -3 , 3.1×10 17 ~2.43×10 18 m -3 ,7.94×10 17 ~4.96×10 18 m -3 , and 4.96×10 18 ~1.99×10 19 m -3 . Additionally, the collision frequency was 10 GHz, the plasma thickness D = 50 mm, and the non-uniform plasma was set to 50 layers; Figure 2It is the RCS reduction diagram at a frequency of 10 - 18 GHz under different electron density ranges. It can be seen that different electron density distribution ranges have a particularly large impact on RCS reduction, and the characteristic frequency corresponding to the optimal RCS reduction is close to the electromagnetic wave range;

[0062] Select the non-uniform plasma thickness. A total of four thicknesses are set, which are 15 mm, 30 mm, 50 mm, and 100 mm respectively. The electron density range is: 7.94×10 17 ~4.96×10 18 m -3 , the distribution function adopts formula (2), the adjustable variable m = 1.5, and the specific simulation results can be seen Figure 5 ;

[0063] Set four collision frequencies: 5 GHz, 10 GHz, 15 GHz, and 20 GHz; by adjusting the size of the adjustable variable m, the electron density range, etc., to optimize the optimal RCS reduction.

[0064] Figure 3 It is the RCS reduction diagram at a frequency of 10 - 18 GHz under different electron distributions. It can be seen that under the fixed electron density distribution function, the distributions corresponding to the optimal RCS reduction, formulas (3)-(5)

[0065]

[0066] Provide a theoretical basis for finding the optimal distribution of RCS reduction; the optimal RCS reduction is as Figure 7 For the study of the electron density distribution of the optimal reduction of the RCS of a metal plate by non-uniform plasma, including the electromagnetic wave frequency range of 10 - 18 GHz, the study of the optimal electron density distribution for RCS reduction was carried out based on the genetic algorithm. The electron density distribution function can be selected as the following formula (6):

[0067]

[0068] Obtain the optimal reduction, with a reduction greater than 11 dB throughout the frequency range. Figure 6 It is the optimal RCS reduction result obtained by optimization.

[0069] In summary, through the processes of theoretical analysis, numerical calculation, and simulation verification of the present invention, it can be seen that in the entire frequency range of 10 - 18 GHz, the RCS reduction is greater than 11 dB. The optimal electron density distribution is as Figure 8As shown. The RCS reduction in the case of a metal plate coated with non-uniform plasma is analyzed in detail. The RCS reduction is affected by parameters such as the electron density range, distribution, plasma thickness, and collision frequency. After determining the electron density range, collision frequency, and non-uniform plasma thickness, the optimal electron density distribution can be obtained through genetic algorithm optimization to achieve the best RCS reduction, providing an important reference for the stealth of metal plates, spheres, or other complex aircraft.

Claims

1. A method for electron density distribution of non-uniform plasma to optimize RCS reduction of metal plate, characterized in that: The specific steps include: Step S1, making electromagnetic waves vertically incident on a metal plate 1 coated with non-uniform plasma; Step S2, selecting the non-uniform plasma electron density n according to the frequency of the incident electromagnetic wave e Optimization range: Step S3, according to the non-uniform plasma electron density n selected in step S2 e , select the optimal range of non-uniform plasma thickness; Step S4, determining an optimized range of the non-uniform plasma collision frequency; Step S5, according to the non-uniform plasma electron density n selected in step S2 e , design the electron density distribution function; Step S6, according to the non-uniform plasma electron density n selected in steps S2 to S5 e , non-uniform plasma thickness, non-uniform plasma collision frequency and electron density distribution function, and optimal RCS reduction is performed based on genetic algorithm.

2. The electron density distribution method for optimal reduction of RCS of a metal plate by non-uniform plasma according to claim 1, characterized in that: The non-uniform plasma electron density n selected in step S2 e and the characteristic frequency f of the inhomogeneous plasma p The following relationship exists: Among them, e is the charge carried by the electron, ε0 is the dielectric constant of vacuum, and m e is the mass of the electron; when the frequency of the electromagnetic wave is f L ~f H , then the corresponding characteristic frequency range of the inhomogeneous plasma is f pL ~f pH , the pre-set f pL <0.5f L , f pL >2f H .

3. The electron density distribution method for optimal reduction of RCS of a metal plate by non-uniform plasma according to claim 1, characterized in that: In step S3, the thickness of the non-uniform plasma is selected to be greater than 1 wavelength of the low frequency, and the greater the thickness of the plasma, the more obvious the RCS reduction.

4. The electron density distribution method for optimal reduction of RCS of a metal plate by non-uniform plasma according to claim 1, characterized in that: The non-uniform plasma collision frequency in step S4 is close to the frequency of the incident electromagnetic wave. The greater the collision frequency, the more obvious the RCS reduction effect.

5. The electron density distribution method for optimal reduction of RCS of a metal plate by non-uniform plasma according to claim 4, characterized in that: In step S4, the collision frequency of the non-uniform plasma is close to the frequency of the incident electromagnetic wave: collision frequency: electromagnetic wave frequency = 0.8-1.2:

1.

6. The electron density distribution method for optimal reduction of RCS of a metal plate by non-uniform plasma according to claim 1, characterized in that: The electron density distribution function in step S5 is: Among them, n emax is the maximum electron density, n emin is the minimum electron density, y L is the non-uniform plasma thickness, m is an adjustable variable, 0.01≤m≤3.

7. The electron density distribution method for optimally reducing the RCS of a metal plate by a non-uniform plasma according to claim 1, characterized in that: The specific method of step S6 is: e , electron density distribution function, non-uniform plasma collision frequency, and non-uniform plasma thickness are set as optimization parameters. The genetic algorithm is optimized through the Optimization module in the mathematical software. By adjusting the size of the electron density distribution function, the electron density distribution is changed until the RCS is optimized to the optimal value.

8. The electron density distribution method for optimal reduction of RCS of a metal plate by non-uniform plasma according to claim 1, characterized in that: The vertical incident electromagnetic wave frequency in step S1 and step 2 is selected to be 10-18 GHz; the non-uniform plasma electron density n in step S2 is e The optimization range is 1.24×10 16 m -3 ~1.99×10 19 m -3 ; The optimization range of the non-uniform plasma thickness in step S3 is selected as 15mm-100mm; the optimization range of the non-uniform plasma collision frequency in step S4 is selected as 5GHz-20GHz.

9. The electron density distribution method for optimal reduction of RCS of a metal plate by non-uniform plasma according to claim 1, characterized in that: The electron density distribution method for optimal RCS reduction of metal plates by non-uniform plasma is used in the field of RCS reduction of aircraft targets.

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