A fast and accurate method for identifying the mutual coupling electromagnetic scattering region

Abstract

The application discloses a fast and accurate mutual coupling electromagnetic scattering area distinguishing method, belongs to the technical field of electromagnetic scattering characteristic calculation, determines the maximum boundary of the whole ship target, and decomposes the target into a plurality of local solid closed boundaries, positions each surface element, determines the array space to which each surface element belongs, and generates an incident ray tube for the directly visible surface element of the target, and all the ray tubes have triangular cross sections; the array space in which the surface element exists multiple scattering relationship with the reflection ray tracing of the first surface element is utilized to lock the search in the corresponding array space after decomposition; the surface element capable of generating multiple scattering with the first surface element is screened, and the improved Z-Buffer algorithm suitable for electromagnetic scattering calculation is adopted to perform shielding discrimination, so as to exclude two visible surface elements shielded by the intermediate surface element. The application greatly improves the calculation efficiency on the basis of ensuring the precision through adaptive ray tube division.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic scattering characteristic calculation, and more particularly relates to a fast and accurate mutual coupling electromagnetic scattering region discrimination method. BACKGROUND

[0002] The scattering field of a target is the result of the interaction of radar signals with the various structures of the target, and the algorithm for solving the scattering field of the target is the main means for predicting the electromagnetic scattering characteristics of the target. For multiple scattering analysis of the target, the basic idea is to use the ray tracing technique to judge the interaction between the structure surfaces. First, the initial reflection direction and reflection field are determined, and they are used as the incident direction and incident length of the next scattering; then the ray tracing method is used to determine the surface area illuminated by the incident wave of each scattering, and the reflection and shielding are determined by simulating the propagation path of the ray (light). Whether the radiation center of the surface current element passes through the second surface element and whether the two structure surfaces are both "visible surfaces" are determined to obtain the relationship between the ray vector and the normal vector of the two surface elements, so as to determine the echo direction. For complex multi-scale structures such as ships, how to analyze the mutual coupling scattering region is the premise of analyzing the interaction between multi-scale structures. In the traditional ray search discrimination process based on the center point of the surface element, the light ray tracing algorithm does not consider the structure of the target model during the equal-interval subdivision of the ray, so when the ray encounters a protrusion, a crack or other situations of the target model, it cannot effectively represent the true shape of the target model, and it also cannot accurately describe the visible region of the target model, thereby causing errors in the calculation results.

[0003] For large-size multi-scale structure targets such as ships, the shooting and bouncing ray (SBR) method is usually used to calculate the electromagnetic scattering characteristics thereof, and the basic idea is to divide the virtual aperture perpendicular to the incident wave direction into a plurality of mutually independent ray tubes, that is, to divide the virtual aperture perpendicular to the incident wave direction into a plurality of mutually independent ray tubes, and then to trace each ray tube according to the idea of ray tracing, and finally to calculate the result of the ray tracing by using geometric optics and physical optics integration, so as to obtain the electromagnetic scattering field. Among them, the number of ray tube division is directly related to the accuracy and efficiency of the algorithm. Considering the convergence of the calculation, the traditional ray tube division technique divides the virtual aperture according to one-tenth of the wavelength. This will lead to high-density grid subdivision of large flat areas on the target model, thereby causing a reduction in calculation efficiency and waste of computer resources.

[0004] At present, there is no mutual coupling electromagnetic scattering region discrimination method for fast and accurate calculation of the scattering field of a multi-scale structure target of a ship, and therefore, how to realize a mutual coupling electromagnetic scattering region discrimination method for a ship target based on fast beam tracing is a technical problem that needs to be solved at present. SUMMARY

[0005] In view of the problems of inaccurate mutual coupling scattering area tracking and low calculation efficiency in the calculation process of the scattering field of a ship target in the prior art, a fast beam tracking method is provided, which greatly improves the calculation efficiency on the basis of ensuring the accuracy through adaptive ray tube division.

[0006] To achieve the above object, the application provides a fast and accurate mutual coupling electromagnetic scattering area discrimination method, comprising:

[0007] The maximum boundary of the entire ship target is determined, and the target is divided into a plurality of local three-dimensional closed boundary areas, the closed boundary areas are embodied as a three-dimensional cubic array along the x, y and z directions, each face element is positioned to determine the array space to which each face element belongs, and incident ray tubes are generated for the directly visible face elements of the target, and all the ray tubes have triangular cross sections;

[0008] The array space in which the face element having multiple scattering relationship with the first face element is located is searched and locked in the corresponding array space after decomposition by using the reflected ray tracking of the first face element;

[0009] The face elements capable of generating multiple scattering with the first face element are screened, and an improved Z-Buffer algorithm suitable for electromagnetic scattering calculation is used for occlusion discrimination to exclude the two visible face elements occluded by the intermediate face element.

[0010] In some optional embodiments, the incident ray tube is generated for the directly visible face element of the target, comprising:

[0011] The coordinate system of the target is converted into an initial incident beam IIB coordinate system, wherein the direction of the incident wave is defined as the-z direction, the orthogonal projection on the incident plane is calculated for each face element hit by the incident wave, and the orthogonal projection is obtained in the IIB coordinate system by removing the Z coordinate of the vertex;

[0012] 2D polygon clipping is performed according to the depth order of facets, and polygons are clipped from the facets far away from the beam source;

[0013] Polygon minimum triangulation, each triangle is an initial grid, the initial triangular beam sent from the grid only hits one face element, the initial beam is reflected from the face element hit by them, and when the reflected beam hits the part of the target surface composed of multiple facets, the beam is reflected in multiple directions according to the direction of the facets.

[0014] In some optional embodiments, the array space in which the face element having multiple scattering relationship with the first face element is located is searched and locked in the corresponding array space after decomposition by using the reflected ray tracking of the first face element, comprising:

[0015] Computing the reflected beam direction, transforming the coordinate system to the reflected beam coordinate system to redefine the direction of the reflected beam as -z, computing the orthogonal projection of the facet facing the reflected beam;

[0016] Applying the hidden surface algorithm to the projected polygons according to the depth order of the facets, the polygons projected from the facets farther from the source of the reflected beam are clipped by the polygons closer;

[0017] Finding the intersection between the reflected beam and the projected polygons in the 2D plane, finding the part of the beam that does not hit any facet by subtracting the intersection of the beam polygon from the orthogonal projection of the beam;

[0018] Dividing the intersection into triangles, each triangle is the cross section of the next order reflected beam, recursively performing the beam splitting process for the next order reflected beam, and constructing a beam tree to describe the reflection aspect of each initial beam.

[0019] In some optional embodiments, the root node of the beam tree is the first order reflected beam, the beam tree has two kinds of child nodes, namely the facet hit by the beam and the child node derived from the facet, the intersecting child node of the nth order corresponds to the nth order reflected beam and will have child nodes, the non-intersecting child node represents the part of the parent beam that is not reflected from any facet, and they are leaf nodes.

[0020] Overall, compared with the prior art, the above technical solutions conceived by the present application can achieve the following beneficial effects:

[0021] (1) The construction process of the sub-ray tube of the present application is completely based on the grid information of the target model itself, so that each sub-ray tube obtained only corresponds to a certain triangular mesh on the target model, and the situation that a ray tube simultaneously irradiates two or more triangular facets or the situation that a ray tube irradiates the edge of the model will not occur. Therefore, the present application can effectively make up for the shortcomings of discarding ray tubes or being unable to accurately describe the visible region of the model in ray tracing;

[0022] (2) The present application adopts the idea of adaptive ray tube division, divides the visible surface into as few triangular facet ray tubes as possible according to the shape, assumes that adjacent rays have similar propagation paths, and uses a light column to simulate the propagation of a bundle of rays, effectively improving the efficiency of tracing and reducing the waste of computer resources;

[0023] (3) The calculation time of the present application depends on the number of constructed target facets, rather than the size of the target, which is very effective for electric large targets. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic diagram of a cubic array provided by an embodiment of the present application;

[0025] Figure 2 is a two-part overlapping quadrilateral diagram provided by an embodiment of the present application;

[0026] Figure 3 is an incident light pipe grid provided by an embodiment of the present application, wherein (a) is a traditional SBR; and (b) is a method proposed by the present application;

[0027] Figure 4 is a ray tracing search process top view provided by an embodiment of the present application;

[0028] Figure 5 is a reflection geometry provided by an embodiment of the present application, wherein (a) is a first-order reflection, and (b) is a second-order reflection;

[0029] Figure 6 is a representation of a beam tree for describing reflection aspects provided by an embodiment of the present application;

[0030] Figure 7 is a virtual grid without intersecting nodes provided by an embodiment of the present application;

[0031] Figure 8 is a beam tracing schematic diagram provided by an embodiment of the present application;

[0032] Figure 9 is a mutual coupling scattering area discrimination comparison provided by an embodiment of the present application, wherein (a) is a traditional mutual coupling scattering area discrimination; and (b) is a mutual coupling scattering area discrimination based on beam tracing proposed by the present application. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0034] The ship target mutual coupling scattering area discrimination is taken as an example for description.

[0035] For a ship multi-scale structure, the traditional discrimination process based on the center point of the facet only uses the reflection ray from the center point of the facet, which can miss other possible interacting facets, resulting in inaccurate or misjudged tracing results. To solve this problem, the present application proposes an analysis method of beam tracing to accurately extract the multiple scattering range as much as possible, including the following steps:

[0036] (1) Determine the maximum boundary of the entire ship target, and divide the target into several local solid closed boundaries, and the closed boundaries are represented as a three-dimensional cubic array along the x, y, and z directions, as shown in Figure 1 , and locate each face element, that is, it can be determined that each face element is contained in that array space;

[0037] In this embodiment, in order to improve efficiency, only the directly visible face elements of the target are generated for the incident ray tube, and in order to simplify the subsequent process, all ray tubes have a triangular cross section. As shown in Figure 2 , a simple target modeled using a set of triangular faces is considered. The traditional SBR represents this event as 11x12=132 ray tubes for a plane wave, but the method of the present application only needs six ray tubes, as shown in Figure 3 , thereby speeding up the calculation due to the reduction in the number of initial ray tubes.

[0038] In this embodiment, the steps of generating a light beam are:

[0039] 1) Convert the coordinate system of the target to the initial incident light beam IIB coordinate system, where the direction of the incident wave is defined as the -z direction, and the orthogonal projection on the incident plane is calculated for each face hit by the incident wave. In the IIB coordinate system, the orthogonal projection is obtained by simply removing the Z coordinate of the vertex;

[0040] 2) Perform 2D polygon clipping according to the depth order of the facets: clip the polygons projected from the facets farther from the light beam source from farther polygons;

[0041] 3) Polygon minimum triangulation, where each triangular face can only be hit by one light beam, and each triangle is an initial grid that roughly corresponds to the grid of the traditional SBR method, and the initial triangular beam sent from the grid only hits one face. The initial light beam is reflected from the surface it hits, and when the reflected light beam hits a part of the target surface composed of multiple facets, the light beam should be subdivided because it reflects in multiple directions according to the direction of the facets. The light beam tracing step recursively performs these subdivisions and subsequent tracing processes, and all initial light beams are sequentially calculated recursively.

[0042] (2) Use the reflected ray of the first face element to trace the array element space where the face element that may have multiple scattering relationships with the first face element, and lock the next search in the corresponding array element space after decomposition, reducing the time consumption caused by redundant judgments;

[0043] In this embodiment, the process of XZ plane ray tracing is as shown in Figure 4As shown, when the bounding box containing the center point of the preceding element is array element A, the reflected ray originating from A only intersects with a portion of the array elements. Unlike the traditional method of using a single ray for tracing, this invention uses two parallel rays originating from array elements B and C on either side of array element A. Considering the elements that interact with the current element between the rays, this invention ignores the elements in array elements 1, 2, and 3 by using only the reflected ray originating from the center point of the element. These elements may also experience multiple scattering, leading to inaccurate tracking results. Therefore, this invention uses beam tracking, which reduces the search range while ensuring tracking accuracy.

[0044] Beam tracing includes initial beam tracing and next-stage reflection beam tracing.

[0045] Initial beam tracing steps:

[0046] 1) Calculate the direction of the reflected beam;

[0047] 2) After transforming the coordinate system to the reflected beam coordinate system to redefine the direction of the reflected beam as -z, calculate the orthogonal projection of the small plane facing the reflected beam;

[0048] 3) Apply the hidden surface algorithm to the projected polygons according to the depth order of the facets: polygons projected from facets farther away from the reflected beam source are cut off by polygons closer to the source;

[0049] 4) Locate the intersection point between the reflected beam and the projected polygon in the 2D plane;

[0050] 5) Find the portion of the beam that did not hit any surface by subtracting the intersection points of the beam polygons from the orthogonal projection of the beam;

[0051] 6) Divide the intersection into as few triangles as possible. Each triangle is the cross-section of the next-order reflected beam.

[0052] The beam splitting process is recursively performed on the next-order reflected beam, and a beam tree is constructed to describe the reflection aspect of each initial beam. The root node of the beam tree is the first-order reflected beam. The beam tree proposed by this method has two types of child nodes: those originating from the plane hit by the beam (intersecting child nodes) and those originating from the plane, which are not non-intersecting child nodes. The intersecting child nodes of the nth order correspond to the nth-order reflected beam and will have child nodes. The non-intersecting child nodes represent the part of the parent beam that is not reflected from any surface; these are leaf nodes.

[0053] like Figure 5 As shown, for the initial triangular mesh P1P2P3, the root node is a first-order reflected beam, and its direction vector is... The cross-section is a triangle Q1Q2Q3, where (a) is a first-order reflection and (b) is a second-order reflection, as shown below. Figure 6 The second level consists of five child nodes. The leftmost node, R1R2R3, represents the second-order reflected beam, whose cross-section is P1P2P6, the intersection between the parent beam and the facet marked 2. The rightmost node, Q2Q4Q5, corresponds to a portion of the first-order reflected beam that does not reflect any facets. Each child node of the beam tree stores the reflection history, which blocks have reflected the beam and their coordinates in the IIB coordinate system.

[0054] like Figure 7 In this method, if the reflected beam from R1R2R6 does not reach any small plane, then R1R2R6 is a non-intersecting child node of the third level of the tree, and its scattered field is calculated by performing physical optical integration at the exit position according to the rules. A virtual grid ABC on the incident plane can be assumed by back-tracking, and the incident beam emitted from this virtual grid reflects a small plane at each reflection stage. Therefore, the output ray tube does not diffuse through the reflection process and is uniformly dispersed at the exit position. Despite using a relatively large ray beam, the method of this invention can satisfy the linear phase change approximation.

[0055] (3) After the previous step of screening, the face elements required for judgment are further simplified, and then according to... Figure 8 The criteria for selection are to identify face elements that can produce multiple scatterings with the first face element;

[0056] (4) Occlusion detection: In fact, two visible face elements are very likely to be occluded by a face element in the middle. Such face element pairs must be excluded, otherwise the calculation results will be greatly distorted. An improved Z-Buffer algorithm suitable for electromagnetic scattering calculation is used to detect occlusion.

[0057] Figure 9 The diagram shows the difference between beam tracing-based mutual scattering region discrimination and traditional methods, where (a) is the traditional mutual scattering region discrimination and (b) the beam tracing-based mutual scattering region discrimination proposed in this invention.

[0058] The present invention provides a method for identifying mutually coupled electromagnetic scattering regions of ship targets based on fast beam tracing, which has the following characteristics: (1) The construction process of sub-ray tubes is entirely based on the mesh information of the target model itself. Each sub-ray tube uniquely corresponds to a certain triangular mesh on the target model, which can accurately describe the visible area of ​​the target model; (2) Adaptive ray tube partitioning is adopted, and the visible surface is divided into as few triangular ray tubes as possible according to its shape. By assuming that adjacent light rays have similar propagation paths, a beam is used to simulate the propagation of a beam of light, which effectively improves the efficiency of tracking and reduces the waste of computer resources. It is mainly divided into two parts: beam formation and beam tracing.

[0059] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0060] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fast and accurate method for identifying mutually coupled electromagnetic scattering regions, characterized in that, include: The maximum boundary of the entire ship target is determined, and the target is decomposed into several local three-dimensional closed boundaries. The closed boundaries are represented as a three-dimensional cube array along the x, y, and z directions. Each face element is located to determine the array space to which each face element belongs, and incident ray tubes are generated for the directly visible face elements of the target, and all ray tubes have a triangular cross-section. By using the reflected rays of the first surface element to trace the array space where the surface element that has multiple scattering relationships with the first surface element is located, the search is locked within the array space corresponding to the decomposed surface element. Surface elements that can generate multiple scatterings with the first surface element are selected, and an improved Z-Buffer algorithm suitable for electromagnetic scattering calculations is used for occlusion discrimination to exclude two visible surface elements that are occluded by the middle surface element. To generate an incident ray tube for a directly visible surface of the target, including: The target's coordinate system is transformed into the initial incident beam IIB coordinate system, where the direction of the incident wave is defined as the -z direction. For each surface element hit by the incident wave, the orthogonal projection on the incident plane is calculated. In the IIB coordinate system, the orthogonal projection is obtained by removing the Z coordinate of the vertex. 2D polygon clipping is performed according to the depth order of the facets, clipping polygons projected from facets farther from the beam source from closer polygons; Minimal triangulation of polygons, where each triangle is an initial mesh, the initial triangular beams sent from the mesh hit only one facet, the initial beams start to reflect from the facets they hit, and when the reflected beams hit a portion of the target surface composed of multiple facets, the beams reflect in multiple directions according to the orientation of the facets; The array space containing facets that have multiple scattering relationships with the first facet is traced using the reflected ray from the first facet, including: Calculate the direction of the reflected beam, transform the coordinate system to the reflected beam coordinate system to redefine the direction of the reflected beam as -z, and then calculate the orthogonal projection of the small plane facing the reflected beam. The hidden surface algorithm is applied to the projected polygons according to the depth order of the facets. The polygons projected from the facets farther away from the reflected beam source are cut off by the closer polygons. Find the intersection between the reflected beam and the projected polygon in the 2D plane, and find the part of the beam that does not hit any face by subtracting the intersection of the beam polygon from the orthogonal projection of the beam. The intersection is divided into triangles, each triangle being the cross section of the next-order reflected beam. Beam splitting is recursively performed for the next-order reflected beam, and a beam tree is constructed to describe the reflection aspect of each initial beam.

2. The method according to claim 1, characterized in that, The root node of the beam tree is a first-order reflected beam. The beam tree has two types of child nodes: those originating from the plane hit by the beam and those originating from the plane. They are not non-intersecting child nodes. The intersecting child nodes of the nth order correspond to the nth-order reflected beam and will have child nodes. The non-intersecting child nodes represent the part of the parent beam that is not reflected from any surface; these are leaf nodes.

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