A method and system for calculating electromagnetic scattering field of a moving target coated with a chromatic dispersion medium

Abstract

The application belongs to the technical field of electromagnetic field calculation, and discloses a kind of coated with lossy dispersive medium moving target electromagnetic scattering field calculation method and system.The method of the application first adopts triangular facet to carry out three-dimensional modeling to target surface to form model file, then model file is imported into main program to obtain the geometric feature data of target;Secondly, the Lorentz transformation is used to carry out the relative coordinate conversion of space-time component, and the dynamic problem is mapped to the inertial coordinate system synchronized with the target;Then, the transmission matrix method is used to establish the equivalent reflectivity model of the region coated with lossy dispersive medium;Subsequently, the time-domain physical optics method is used to efficiently solve the transient scattering field in the moving coordinate system;Finally, the calculation results are reconstructed to the laboratory coordinate system through inverse Lorentz transformation, and the electromagnetic field distribution under dynamic scene is output.The method of the application can realize the fast calculation of electromagnetic scattering field of moving target coated with lossy dispersive medium.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic field calculation, and particularly relates to a method and system for calculating electromagnetic scattering field of a moving target coated with a lossy dispersive medium. BACKGROUND

[0002] With the increasing application of high-speed vehicles, underwater vehicles and other moving carriers in complex electromagnetic environments, the surfaces of the moving carriers are often coated with lossy dispersive media, such as plasma sheath, seawater, soil composite layer and the like. Such media exhibit significant energy dissipation characteristics and frequency variation characteristics, i.e. dispersion, which causes the permittivity and conductivity to vary with frequency, which will affect the electromagnetic scattering characteristics of the target and further affect the detection and communication of the target. Therefore, it is necessary to design a method for calculating electromagnetic scattering field of a moving target coated with a lossy dispersive medium.

[0003] In addition, electromagnetic calculation methods for high-speed moving conductor and medium targets have begun to appear, such as Lorentz-FDTD method, relativistic boundary condition RBC method, however, these calculation methods consume too much computing time and memory computing resources. In contrast, the time-domain physical optics method, i.e. TDPO algorithm, has the advantages of less unknowns, simple and easy to understand, and fast calculation speed, and has been widely applied to the calculation and analysis of electromagnetic field scattering problems of high-frequency electrically large targets. SUMMARY

[0004] The application aims to provide a method for calculating electromagnetic scattering field of a moving target coated with a lossy dispersive medium, which is based on the time-domain physical optics method, the lossy dispersive medium model, and combined with Lorentz transformation, and can realize fast calculation of electromagnetic scattering field of a moving target coated with a lossy dispersive medium, greatly shorten the running time, and improve the resource utilization.

[0005] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0006] A method for calculating electromagnetic scattering field of a moving target coated with a lossy dispersive medium, comprising the following steps:

[0007] Step 1. Triangular facet division is performed on the target surface in the laboratory coordinate system by using a 3D modeling software to obtain a model file, and then the geometric feature data of the target is obtained;

[0008] Step 2. The parameters are initialized in the laboratory coordinate system, and the motion parameters are inputted;

[0009] Step 3. The spatial and time components in the moving coordinate system are obtained by using the Lorentz transformation formula in combination with the target space grid components in the model file parameters and the time components in the running parameters;

[0010] Step 4. According to the space and time components in the moving coordinate system obtained in step 3, the angular frequency and amplitude of the incident wave in the moving coordinate system are determined, so as to determine the incident wave in the moving coordinate system;

[0011] Step 5. According to the electromagnetic parameters of the lossy dispersive medium and the angular frequency of the incident wave in the moving coordinate system obtained in step 4, the relative permittivity of the lossy dispersive medium in the moving state is determined;

[0012] Step 6. The angle between the incident wave and each irradiated triangular facet is calculated, and the reflection coefficient of each triangular facet in the layered medium region is calculated by the transfer matrix method, and an equivalent reflectivity model of the lossy dispersive medium coated target is constructed;

[0013] Step 7. In the moving coordinate system, the time domain scattering field of each triangular facet is calculated by using the TDPO algorithm, and multiplied by the corresponding reflection coefficient, and then the time domain scattering field of the whole target is obtained;

[0014] Step 8. The time domain scattering field of the whole target in the moving coordinate system obtained in step 7 is subjected to inverse Lorentz transformation to obtain the far zone scattering field data in the laboratory coordinate system, and the far zone scattering field data in the laboratory coordinate system is output as the result.

[0015] In addition, on the basis of the electromagnetic scattering field calculation method of the lossy dispersive medium coated moving target, the application further provides a lossy dispersive medium coated moving target electromagnetic scattering field calculation system which is suitable for the method, and the technical scheme is as follows:

[0016] A lossy dispersive medium coated moving target electromagnetic scattering field calculation system comprises:

[0017] A geometric feature acquisition module is used to divide the target surface in the laboratory coordinate system into triangular facets by using a 3D modeling software, obtain a model file, and then acquire the geometric feature data of the target;

[0018] A parameter initialization module is used to initialize the parameters in the laboratory coordinate system and input the motion parameters;

[0019] A component transformation module is used to combine the target space grid components in the model file parameters and the time components in the running parameters, and obtain the space and time components in the moving coordinate system by using the Lorentz transformation formula;

[0020] An incident wave determination module is used to determine the angular frequency and amplitude of the incident wave in the moving coordinate system according to the space and time components in the moving coordinate system obtained by the component transformation module, so as to determine the incident wave in the moving coordinate system;

[0021] A relative dielectric constant determination module is configured to determine the relative dielectric constant of the lossy dispersive medium in the moving state according to the electromagnetic parameters of the lossy dispersive medium and the angular frequency of the incident wave obtained by the incident wave determination module.

[0022] A reflection coefficient calculation module is configured to solve the included angle between the incident wave and each irradiated triangular facet element, and then calculate the reflection coefficient of the layered medium region where each triangular facet element is located by using the transfer matrix method, so as to construct an equivalent reflectivity model of the lossy dispersive medium coated target.

[0023] A time-domain scattering field solving module is configured to calculate the time-domain scattering field of each triangular facet element in the moving coordinate system by using the TDPO algorithm, and multiply the corresponding reflection coefficient, so as to obtain the time-domain scattering field of the entire target in the moving coordinate system.

[0024] A result output module is configured to perform inverse Lorentz transformation on the time-domain scattering field of the entire target in the moving coordinate system obtained by the time-domain scattering field solving module, so as to obtain the far-zone scattering field data in the laboratory coordinate system, and output the far-zone scattering field data as the result.

[0025] The present application has the following advantages:

[0026] As described above, the present application discloses a method for calculating the electromagnetic scattering field of a lossy dispersive medium coated moving target. The method is based on the time-domain physical optics method, the lossy dispersive medium model, the multi-layer medium model and the Lorentz transformation. First, the incident field is subjected to Lorentz transformation, and the angular frequency component in the lossy dispersive medium is changed by means of the Lorentz transformation, so as to construct an accurate model of the lossy dispersive medium in the moving state. Then, the reflection coefficient of the multi-layer medium is calculated by using the transfer matrix method (TMM), and an equivalent reflectivity model of the lossy dispersive medium coated target is established. Finally, the time-domain electromagnetic scattering field of the lossy dispersive medium coated moving target is calculated quickly under the framework of the TDPO algorithm. The method of the present application is especially suitable for calculating the time-domain electromagnetic scattering field of a large-size moving three-dimensional target coated with a lossy dispersive medium. By using the method, the influence of target movement on the received time-domain scattering field can be observed in the time domain, including the changes of key parameters such as time delay, angular frequency, pulse width and amplitude. In addition, the method of the present application has the advantages of fast calculation speed, accurate calculation result and wide application range. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The flowchart of the method for calculating the electromagnetic scattering field of a lossy dispersive medium coated moving target in the embodiment of the present application is shown.

[0028] Figure 2 The schematic diagram of the method for calculating the electromagnetic scattering field of a lossy dispersive medium coated moving target in the embodiment of the present application is shown.

[0029] Figure 3 A schematic diagram of a target irradiated by an incident wave in an embodiment of the present application.

[0030] Figure 4 A schematic diagram of a time-domain waveform of an incident wave in an embodiment of the present application.

[0031] Figure 5 A schematic diagram of a layered medium in an embodiment of the present application.

[0032] Figure 6 A schematic diagram of a time-domain scattering field of a moving target coated with a lossy dispersive medium in an embodiment of the present application. DETAILED DESCRIPTION

[0033] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0034] Embodiment 1

[0035] This embodiment describes a method for calculating an electromagnetic scattering field of a moving target coated with a lossy dispersive medium, which is based on a time-domain physical optics method, a lossy dispersive medium model and Lorentz transformation. The electromagnetic scattering field calculation method of the present application can achieve fast and accurate calculation of the time-domain scattering field of a moving target coated with a lossy dispersive medium.

[0036] The electromagnetic scattering field calculation method of a moving target coated with a lossy dispersive medium proposed in the present application generally includes the following processes: First, a three-dimensional model of the target surface is formed by using triangular facet elements to form a model file, and then the model file is imported into the main program to obtain the geometric feature data of the target. Second, the Lorentz transformation is used to perform a relativistic coordinate transformation on the space-time components, mapping the dynamic problem to the inertial coordinate system synchronized with the target. Third, the Transfer Matrix Method (TMM) is used to establish an equivalent reflectivity model for the region coated with a lossy dispersive medium. Fourth, the time-domain physical optics method TDPO is used to efficiently solve the transient scattering field in the moving coordinate system. Finally, the inverse Lorentz transformation is used to reconstruct the calculation results to the laboratory coordinate system, and the electromagnetic field distribution under the dynamic scene is output.

[0037] The electromagnetic scattering field calculation method of a moving target coated with a lossy dispersive medium proposed in the present application will be described in detail below.

[0038] As shown in Figure 1 A method for calculating an electromagnetic scattering field of a moving target coated with a lossy dispersive medium, which specifically includes the following steps:

[0039] Step 1. Use a 3D modeling software to model the target in the laboratory coordinate system The target surface in the laboratory coordinate system is divided into triangular facets to obtain a model file. The model file is imported into a main program folder, and when the main program is run, the model file parameters are read by the main program to obtain the geometric feature data of the target.

[0040] Specifically, the moving target coated with a lossy dispersive medium in the laboratory coordinate system is modeled by a 3D modeling software, the target surface is divided into triangular facets, and a model file of the target, i.e., a grid model file obj.stl, is exported.

[0041] The model file parameters include normal vectors and vertex coordinates of all triangular facets. The normal vectors are used to determine the orientation of the triangular facets and the light calculation. The vertex coordinates are used to define the shape and position of the triangular facets.

[0042] The grid model file obj.stl is imported into the main program folder.

[0043] When the main program is run, the model file parameters in the grid model file obj.stl are read by the main program and processed to obtain the geometric feature data of the target, i.e., the geometric parameters of the model obj.Area, obj.center and obj.coord.

[0044] Among them, obj.Area is used to store the area of each triangular facet, obj.center is used to store the normal vector of each triangular facet, and obj.coord is used to store the vectors of the three edges of each triangular facet.

[0045] Step 2. In the laboratory coordinate system , the parameters in the main program are initialized, and the motion parameters are input.

[0046] The process of initializing the parameters in the main program in step 2 is as follows: the main program initializes the electromagnetic parameters, sets the position information of the observation point and the target, the speed of the target motion, and the sampling time length of the incident wave and the scattered wave.

[0047] In this embodiment, the sphericon target is set to be located at the coordinate origin, and the observation point is set at (1000m, 0, 0). The target motion speed is 0.05c. The calculation schematic diagram is shown in Figure 2 , wherein represents the origin of the laboratory coordinate system, the sphericon target is 1m long, the bottom surface has a radius of 0.5m, and the uniform lossy dispersive medium is coated with a thickness of 0.02m. The light schematic diagram is shown in Figure 3 , wherein , , represent the coordinate axes in the horizontal, longitudinal and vertical directions in the laboratory coordinate system, respectively.

[0048] Step 3. In the main program, the space grid components in the model file parameters and the time components in the running parameters are combined to obtain the space and time components in the moving coordinate system using the Lorentz transformation formula.

[0049] There are two coordinate systems when analyzing the electromagnetic scattering characteristics of moving targets using Lorentz transformation: one is the laboratory coordinate system which remains stationary with the ground, and the other is the moving coordinate system which remains relatively stationary with the moving target.

[0050] The transformation relationship between the space and time components of the laboratory coordinate system and the moving coordinate system is:

[0051] (1)

[0052] (2)

[0053] (3)

[0054] (4)

[0055] where, , , represent the space components in the horizontal, longitudinal, and vertical directions in the laboratory coordinate system , respectively. , , represent the space components in the horizontal, longitudinal, and vertical directions in the moving coordinate system , respectively.

[0056] represents the time component in the laboratory coordinate system , represents the time component in the moving coordinate system .

[0057] , , represent the components of the target's moving speed in the x, y, and z directions, respectively.

[0058] , , represent the speed of light in vacuum.

[0059] represents the unit vector of the scattering direction, unit vector representing velocity.

[0060] .

[0061] wherein, is the velocity vector of the target, , , are unit vectors in the three directions, respectively.

[0062] (5)

[0063] wherein, is the angle between the velocity of the target in the laboratory coordinate system and the positive half-axis of the axis. is the angle between the projection of the direction of the target in the laboratory coordinate system onto the plane and the positive half-axis of the axis.

[0064] Step 4. According to the space and time components in the moving coordinate system obtained in step 3, the angular frequency and amplitude of the incident wave in the moving coordinate system are determined, so as to determine the incident wave in the moving coordinate system .

[0065] The incident wave in the laboratory coordinate system is determined, and the amplitude of the incident wave in the laboratory coordinate system is defined as 1V / m, the angular frequency , and the time-domain waveform of the incident wave is shown in Figure 4 .

[0066] The angular frequency and amplitude of the incident wave in the moving coordinate system after Lorentz transformation are:

[0067] (6)

[0068] (7)

[0069] wherein, and are the angular frequency and amplitude of the incident wave in the laboratory coordinate system , respectively. and are the angular frequency and amplitude of the incident wave in the moving coordinate system , respectively. ​denotes the unit vector of the incident wave. denotes the magnetic field in the laboratory coordinate system . denotes the angle between the electric field vector and the velocity vector.

[0070] .

[0071] wherein, denotes the unit vector of the electric field.

[0072] According to the angular frequency and the amplitude of the incident wave in the moving coordinate system , the incident wave in the moving coordinate system is determined as .

[0073] Step 5. According to the electromagnetic parameters of the lossy dispersive medium and the angular frequency of the incident wave in the moving coordinate system obtained in Step 4, the relative permittivity of the lossy dispersive medium in the moving state is determined.

[0074] According to the electromagnetic parameters of the Debye lossy dispersive medium model and the angular frequency of the incident wave in the moving coordinate system obtained in Step 4, the lossy dispersive medium in the moving state is modeled to obtain the relative permittivity of the lossy dispersive medium in the moving state .

[0075] (8)

[0076] wherein, denotes the vacuum permittivity, is the static relative permittivity of the medium, is the relative permittivity when the angular frequency is infinite, is the relaxation time, is the conductivity, is the imaginary unit.

[0077] In this embodiment, the parameters of the lossy dispersive medium are set as:

[0078] , , , .

[0079] Step 6. The angle between the incident wave and each irradiated triangular facet element is solved, and the reflection coefficient of each triangular facet element in the layered medium region is calculated by the transfer matrix method to construct an equivalent reflectivity model of the lossy dispersive medium coated target.

[0080] For the target coated with layered lossy dispersive medium, each triangular facet region is regarded as a multi-layered medium model. The incident angle is solved between the incident wave and each illuminated triangular facet

[0081] (9)

[0082] where, is the unit normal vector of the illuminated triangular facet, the unit normal vector points to the outside of the target.

[0083] Given the electromagnetic parameters of the lossy dispersive medium and the angular frequency of the incident wave, each triangular facet region is regarded as a layered medium region, as shown in Figure 5 , where represents the perpendicular polarization component, whose electric field direction is perpendicular to the incident plane, and represents the parallel polarization component of the incident wave and the reflected wave, whose electric field direction is parallel to the incident plane. The transfer matrix method is used to calculate the reflection coefficient of each triangular facet region in the layered medium.

[0084] When the electromagnetic wave propagates in the medium, it is assumed that the electromagnetic wave is incident to the h+1th layer medium from the hth layer medium with an incident angle , where h ∈ [1, N], N represents the number of layers of the multi-layered medium model. The wavelength of the electromagnetic wave is .

[0085] After the incident angle between the incident wave and the triangular facet is known, the incident angle of the electromagnetic wave incident from the h+1th layer medium to the h+2th layer medium can be obtained by Snell's law:

[0086] (10)

[0087] where, is the refractive index of the hth layer medium, is the refractive index of the h+1th layer medium. h ∈ [1, N]. N represents the number of layers of the multi-layered medium model. represents the incident angle of the electromagnetic wave incident from the hth layer medium to the h+1th layer medium.

[0088] The wavelength of the electromagnetic wave is . The wave impedance , the phase constant and the wave number of the hth layer medium are respectively represented as:

[0089] (11)

[0090] (12)

[0091] (13)

[0092] where, is the permeability of the hth layer medium, is the permittivity of the hth layer medium in the moving coordinate system is the conductivity of the hth layer medium.

[0093] The transmission matrix of the hth layer medium in the moving coordinate system is given by:

[0094] (14)

[0095] where, is the thickness of the hth layer medium.

[0096] For a multi-layer medium model consisting of N layer media, the total transmission matrix M is given by the product of the individual transmission matrices:

[0097] (15)

[0098] where, to are the transmission matrices of the 1st to Nth layer media, respectively, is the inverse of the transmission coefficient of the forward wave, is the coupling contribution of the backward wave to the forward wave, is the coupling contribution of the forward wave to the backward wave, is the inverse of the transmission coefficient of the backward wave.

[0099] The reflection coefficient R s is given by:

[0100] (16)

[0101] where, is the wave impedance of the incident medium, is the wave impedance of the last layer medium.

[0102] Step 7. In the moving coordinate system , the time-domain scattering field of each triangular facet is calculated using the TDPO algorithm, and multiplied by the corresponding reflection coefficient, to obtain the time-domain scattering field of the entire target.

[0103] Specifically, in the moving coordinate system , the time-domain scattering field of each triangular facet is calculated using the TDPO algorithm, and multiplied by the corresponding reflection coefficient R s ​, and then the time-domain scattering electric field of the whole target is obtained is:

[0104] (17)

[0105] where, is the position vector of the observation point in the moving coordinate system , is the position vector of the integral point in the moving coordinate system , and are respectively the and are respectively the and calculated according to formulas (1) to (3), is the wave vector of the incident wave, is the wave vector of the scattered wave.

[0106] represents the propagation direction, represents the unit vector in the direction, represents the reflection coefficient of the layered medium region where each triangular facet element is located. The integral surface is the part of the target surface irradiated. is the triangular facet element at

[0107] The unit vector of the incident direction satisfies the condition of being perpendicular to the propagation direction:

[0108] .

[0109] The scattered wave magnetic field in the moving coordinate system is obtained from the electric field :

[0110] (18)

[0111] where, and respectively represent the magnetic permeability and the dielectric constant of the medium.

[0112] Step 8. Perform inverse Lorentz transformation on the time-domain scattering field of the whole target in the moving coordinate system obtained in step 7 to obtain the far-zone scattering field data in the laboratory coordinate system , and output it as the result.

[0113] Perform inverse Lorentz transformation on the electromagnetic field in the moving coordinate system to transform the electromagnetic field values to the laboratory coordinate system​​ The formula in the text is:

[0114] (19)

[0115] (20)

[0116] in, and Representing the laboratory coordinate system Electric and magnetic fields in and Representing the motion coordinate system electric field and magnetic field .

[0117] Finally, the time-domain electromagnetic scattering field covering the lossy dispersive moving target is obtained and output as the result.

[0118] like Figure 6 As shown, the output results of the method of the present invention were compared with the time-domain scattering fields of metallic targets and targets coated with lossy dispersive media in a static state. The mesh size of the moving target coated with the medium was 5324. The computer configuration was Intel i7-12700K, 2.1GHz, 12 cores, 64GB DDR4 2400MHz + Samsung SSD 980. The single run time of the MATLAB software was 80.9 seconds, demonstrating the high efficiency of the electromagnetic scattering field calculation method of the present invention for moving targets coated with lossy dispersive media.

[0119] Furthermore, the method of this invention includes, but is not limited to, moving metal spheres, metal cylinders, metal cones, etc., coated with a lossy dispersive medium. For example, it may also include multilayered medium targets with complex shapes, such as combinations of cones and hemispheres, and multilayered medium plates. The method of this invention can rapidly calculate the electromagnetic scattered waves of moving targets coated with a lossy dispersive medium, especially the electromagnetic scattered waves of large-sized targets.

[0120] Example 2

[0121] This embodiment 2 describes a system for calculating the electromagnetic scattering field of a moving target coated with a lossy dispersive medium. This system is based on the same inventive concept as the method for calculating the electromagnetic scattering field of a moving target coated with a lossy dispersive medium in embodiment 1.

[0122] Specifically, the electromagnetic scattering field calculation system for a moving target covered by a lossy dispersive medium includes the following modules:

[0123] The geometric feature acquisition module is used to divide the target surface in the laboratory coordinate system into triangular elements using 3D modeling software to obtain model files, and then obtain the geometric feature data of the target.

[0124] A parameter initialization module is configured to initialize the parameters in the laboratory coordinate system while inputting the motion parameters.

[0125] A component transformation module is configured to combine the target space grid components in the model file parameters and the time components in the operation parameters, and obtain the space and time components in the motion coordinate system by using the Lorentz transformation formula.

[0126] An incident wave determination module is configured to determine the angular frequency and amplitude of the incident wave in the motion coordinate system according to the space and time components in the motion coordinate system obtained by the component transformation module, so as to determine the incident wave in the motion coordinate system.

[0127] A relative dielectric constant determination module is configured to determine the relative dielectric constant of the lossy dispersive medium in the motion state according to the electromagnetic parameters of the lossy dispersive medium and the angular frequency of the incident wave in the motion coordinate system obtained by the incident wave determination module.

[0128] A reflection coefficient calculation module is configured to solve the included angle between the incident wave and each irradiated triangular facet element, and then calculate the reflection coefficient of each triangular facet element in the layered medium region by using the transfer matrix method, so as to construct an equivalent reflectivity model of the lossy dispersive medium target.

[0129] A time-domain scattering field solving module is configured to calculate the time-domain scattering field of each triangular facet element in the motion coordinate system by using the TDPO algorithm, and multiply the corresponding reflection coefficient, so as to obtain the time-domain scattering field of the entire target.

[0130] A result output module is configured to perform inverse Lorentz transformation on the time-domain scattering field of the entire target in the motion coordinate system obtained by the time-domain scattering field solving module, so as to obtain the far-zone scattering field data in the laboratory coordinate system, and output the far-zone scattering field data as the result.

[0131] Of course, the above description is only for the preferred embodiments of the present application, and the present application is not limited to the above-described embodiments. It should be noted that any person skilled in the art can make all equivalent replacements and obvious modifications under the teaching of the present application, and all the replacements and modifications fall within the scope of the present application, and should be protected by the present application.

Claims

1. A method for calculating the electromagnetic scattering field of a moving target coated with a chromatic dispersion medium, characterized in that, Comprise the following steps: Step 1. Triangular facet division is performed on the target surface in the laboratory coordinate system using 3D modeling software to obtain a model file, and then the geometric feature data of the target is obtained; Step 2. In the laboratory coordinate system, the parameters are initialized, and the motion parameters are inputted; Step 3. The spatial and time components in the motion coordinate system are obtained by using the Lorentz transformation formula in combination with the target space grid component in the model file parameter and the time component in the running parameter; Step 4. The angular frequency and amplitude of the incident wave in the motion coordinate system are determined according to the spatial and time components in the motion coordinate system obtained in step 3, so as to determine the incident wave in the motion coordinate system; Step 5. The relative permittivity of the lossy dispersive medium in the motion state is determined according to the electromagnetic parameters of the lossy dispersive medium and the angular frequency of the incident wave in the motion coordinate system obtained in step 4; Step 6. The angle between the incident wave and each irradiated triangular facet is solved, and then the reflection coefficient of each triangular facet in the layered medium region is calculated by the transfer matrix method to construct an equivalent reflectivity model of the target coated with a lossy dispersive medium; Step 7. In the motion coordinate system, the time-domain scattering field of each triangular facet is calculated by using the TDPO algorithm, and then multiplied by the corresponding reflection coefficient to obtain the time-domain scattering field of the entire target; Step 8. The inverse Lorentz transformation is performed on the time-domain scattering field of the entire target in the motion coordinate system obtained in step 7 to obtain the far-zone scattering field data in the laboratory coordinate system, which is outputted as the result.

2. The electromagnetic scattering field calculation method of the moving target coated with a lossy dispersive medium according to claim 1, characterized in that, Step 1 is specifically: A 3D modeling software is used to model the moving target coated with a lossy dispersive medium in the laboratory coordinate system, triangular facet division is performed on the target surface, and a model file, i.e. a grid model file obj.stl, of the target is derived; The model file parameter includes the normal vector and vertex coordinates of all triangular facets; the normal vector is used to determine the orientation and lighting calculation of the triangular facet; the vertex coordinates are used to define the shape and position of the triangular facet; The grid model file obj.stl is imported into the main program folder; When the main program is run, the model file parameter in the grid model file obj.stl is read and processed by the main program to obtain the geometric feature data of the target, i.e. the geometric parameters of the model obj.Area, obj.center and obj.coord; Among them, obj.Area is used to store the area of each triangular facet, obj.center is used to store the normal vector of each triangular facet, and obj.coord is used to store the vector of each triangular facet.

3. The electromagnetic scattering field calculation method of the moving target coated with a lossy dispersive medium according to claim 1, characterized in that, In step 2, the process of initializing the parameters in the main program is specifically: The electromagnetic parameters are initialized by the main program, and the position information of the observation point and the target, the velocity of the target motion, and the sampling time length of the incident wave and the scattered wave are set.

4. The electromagnetic scattering field calculation method of a moving target coated with a lossy dispersive medium according to claim 1, wherein, In step 3, the laboratory coordinate system has a spatial and temporal component transformation relationship with the motion coordinate system ​ (1) (2) (3) (4) wherein , , respectively represent the spatial components in the horizontal, longitudinal, and vertical directions in the laboratory coordinate system ; , , respectively represent the spatial components in the horizontal, longitudinal, and vertical directions in the moving coordinate system ; denotes the time component in the laboratory frame denotes the time component in the laboratory frame denotes the time component in the moving frame denotes the time component in the moving frame , , respectively the velocity of the movement of the target components in the x, y, z directions; , , denotes the speed of light in vacuum; unit vector representing the scattering direction, unit vector representing the velocity; ； wherein a movement velocity vector of the target, , , respectively represent unit vectors in three directions; (5) wherein denotes the laboratory coordinate system the angle of the velocity of the target in the laboratory coordinate system the angle of the direction of the target in the laboratory coordinate system denotes the laboratory coordinate system the angle of the direction of the target in the laboratory coordinate system the angle of the direction of the target in the laboratory coordinate system the angle of the direction of the target in the laboratory coordinate system 5. The electromagnetic scattering field calculation method of a moving target coated with a lossy dispersive medium according to claim 4, wherein, In step 4, the incident wave in the laboratory coordinate system is determined and the angular frequency and amplitude of the incident wave in the moving coordinate system after Lorentz transformation are defined. are given by​ (6) (7) where and denote the angular frequency and amplitude of the incident wave in the laboratory frame ; and denote the angular frequency and amplitude of the incident wave in the moving frame ; denotes the unit vector of the incident wave; denotes the magnetic field in the laboratory frame ; denotes the angle between the electric field vector and the velocity vector; ； wherein e represents the unit vector of the electric field; According to the motion coordinate system The angular frequency of the incident wave And the amplitude , determine the incident wave in the motion coordinate system Is .

6. The electromagnetic scattering field calculation method of a moving target coated with a lossy dispersive medium according to claim 5, wherein, the step 5 is specifically: The electromagnetic parameters of Debye lossy dispersive medium model and the moving coordinate system obtained in step 4 The relative permittivity of Debye lossy dispersive medium model in the moving state is obtained by modeling the lossy dispersive medium in the moving state with the angular frequency of the incident wave is: (8) wherein represents the vacuum permittivity, is the static relative permittivity of the medium, is the relative permittivity at an angular frequency of infinity, is the relaxation time, is the electrical conductivity, is the imaginary unit.

7. The electromagnetic scattering field calculation method of a moving target coated with a lossy dispersive medium according to claim 6, wherein, the step 6 is specifically: For the target coated with layered lossy dispersive medium, each triangular facet region is regarded as a multi-layered medium model; the angle between the incident wave and each illuminated triangular facet is solved is: (9) wherein is the unit normal vector of the illuminated triangle facet, the unit normal vector pointing outward the target; Upon learning the angle between the incident wave and the triangular facet element After that, the incident angle of the electromagnetic wave from the h+1 layer medium to the h+2 layer medium is obtained by Snell's law is: (10) wherein, is the refractive index of the hth medium, is the refractive index of the h+1th medium; h e [1, N]; N represents the number of layers of the multilayer medium model; represents the incidence angle of the electromagnetic wave from the hth medium to the h+1th medium; The angle frequency of the incident wave in the moving coordinate system and the electromagnetic parameters of the lossy dispersive medium in the moving coordinate system are known, the area where each triangular facet element is located is regarded as a multi-layer medium model, and the reflection coefficient of the layered medium area where each triangular facet element is located is calculated by using the transfer matrix method, so as to establish an equivalent reflectivity model of the target coated with the lossy dispersive medium in the moving state. The wavelength of the electromagnetic wave is ; the wave impedance of the hth medium , the phase constant and the wave number are respectively expressed as: (11) (12) (13) wherein is the magnetic permeability of the hth medium, denotes the dielectric constant of the hth medium in the moving coordinate system denotes the dielectric constant of the hth medium in the moving coordinate system denotes the electrical conductivity of the hth medium; Transmission matrix in the hth medium is represented as: (14) wherein represents the thickness of the hth medium layer; For a multi-layer medium model composed of N layers of media, the total transfer matrix M is represented by the product of each transfer matrix: (15) wherein, to T1, T2,..., TNrepresent the transmission matrices of the 1st to Nth layer medium, respectively, represents the inverse of the transmission coefficient of the forward wave, represents the coupling contribution of the backward wave to the forward wave, represents the coupling contribution of the forward wave to the backward wave, represents the inverse of the transmission coefficient of the backward wave; Reflection coefficient R s The formula for calculating R is: (16) wherein, represents the wave impedance of the incident medium, represents the wave impedance of the last medium.

8. The electromagnetic scattering field calculation method of a moving target coated with a lossy dispersive medium according to claim 7, wherein, the step 7 is specifically: In the motion coordinate system In this study, the time-domain scattering field of each triangular facet element is calculated using the TDPO algorithm and multiplied by the corresponding reflection coefficient R. s Then, the time-domain scattering electric field of the entire target can be obtained. for: (17) wherein is the position vector of the observation point in the moving coordinate system , is the position vector of the integration point in the moving coordinate system , and are respectively calculated from and and according to formula (1) to formula (3), is the wave vector of the incident wave, is the wave vector of the scattered wave; denotes the direction of propagation, denotes the unit vector in the direction of propagation, denotes the reflection coefficient of the layered medium region in which each triangular facet lies; the integration surface is the portion of the target surface that is illuminated; is the triangular facet at ; unit vector of the direction of incidence satisfies the condition of being perpendicular to the direction of propagation: ； Scattered wave magnetic field in a moving coordinate system By electric field Yields: (18) wherein, and denote the magnetic permeability and the dielectric constant of the medium, respectively.

9. The electromagnetic scattering field calculation method of a moving target coated with a lossy dispersive medium according to claim 8, wherein, the step 8 is specifically: The inverse Lorentz transformation of the electromagnetic field in the moving coordinate system to the laboratory coordinate system is given by the formula (19) (20) where and denote the electric and magnetic field in the laboratory coordinate system , and denote the electric and magnetic field in the moving coordinate system . .​ 10. A system for computing the electromagnetic scattering field of a moving target coated with a chromatic dispersive medium, characterized in that, including: a geometric feature acquisition module, configured to perform triangular facet element division on a target surface in a laboratory coordinate system by using a 3D modeling software, obtain a model file, and then acquire geometric feature data of the target; a parameter initialization module, configured to initialize parameters in the laboratory coordinate system, and input motion parameters; a component transformation module, configured to combine the target space grid component in the model file parameter and the time component in the running parameter, and obtain the space and time components in the moving coordinate system by using a Lorentz transformation formula; an incident wave determination module, configured to determine the angle frequency and amplitude of the incident wave in the moving coordinate system according to the space and time components in the moving coordinate system obtained by the component transformation module, and determine the incident wave in the moving coordinate system; a relative permittivity determination module, configured to determine the relative permittivity of the lossy dispersive medium in the moving state according to the electromagnetic parameters of the lossy dispersive medium and the angle frequency of the incident wave in the moving coordinate system obtained by the incident wave determination module; a reflection coefficient calculation module, configured to solve the included angle between the incident wave and each irradiated triangular facet element, calculate the reflection coefficient of the layered medium area where each triangular facet element is located by using the transfer matrix method, and construct an equivalent reflectivity model of the target coated with the lossy dispersive medium; a time domain scattering field solving module, configured to calculate the time domain scattering field of each triangular facet element in the moving coordinate system by using a TDPO algorithm, multiply the corresponding reflection coefficient, and then obtain the time domain scattering field of the entire target; and a result output module, configured to perform inverse Lorentz transformation on the time domain scattering field of the entire target in the moving coordinate system obtained by the time domain scattering field solving module, obtain far zone scattering field data in the laboratory coordinate system, and output the far zone scattering field data as a result.

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