Si-Yuan He

Using Genetic Algorithm to Reduce the Radar Cross Section of Three-Dimensional Anisotropic Impedance Object

This paper focuses on the radar cross section (RCS) reduction for the three-dimensional object with anisotropic impedance coating. In this work, a genetic algorithm is adopted to optimize the RCS of the anisotropic impedance object in desired angle range. The surface impedances are considered as the optimized parameters and the scattering of the object is computed by the PO method. The optimization process is demonstrated by considering the RCS reduction of two typical targets: the cone and the cone/cylinder composite structure. It is found that the optimization process can reduce the RCS of the targets remarkably and the anisotropic impedance coating has better RCS reduced effect than the isotropic impedance coating.

Numerical Simulation of Vector Wave Scattering From the Target and Rough Surface Composite Model With 3-D Multilevel UV Method

Numerical simulation of vector wave scattering from three-dimensional (3-D) target and rough surface composite model is investigated with a 3-D multilevel UV method. Due to the adoption of RWG basis functions for accurate modeling of vector current, the oscillation of the interaction matrix elements brings difficulty to directly apply the UV decomposition method. Based on the reordering of the interaction strength and the sampling according to the characteristics distribution of the interaction, an EM-interaction-based sampling algorithm is developed for the accurate reconstruction of the far interaction submatrix with UV decomposition method. Combined with multilevel division of the total composite model, the 3-D multilevel UV method incorporating the new sampling algorithm is developed for vector wave scattering from 3-D complex target above or on a random rough surface. The 3-D multilevel UV method yields a complexity of O(N log N) for the setup time of the impedance matrix, the solve time of the matrix iterative solution and also for the memory requirements. The accuracy and the efficiency of the 3-D multilevel UV method is compared and validated with the full MOM method and the ACA method in the tested cases. Finally, the applications of a target above or on the rough surface, for example, a ship on the sea surface, have been accomplished and analyzed.

The BCGS-FFT Method Combined With an Improved Discrete Complex Image Method for EM Scattering From Electrically Large Objects in Multilayered Media

This paper presents an efficient algorithm combining the stabilized biconjugate gradient fast Fourier transform (BCGS-FFT) method with an improved discrete complex image method (DCIM) for electromagnetic scattering from electrically large objects in both lossless and lossy multilayered media. The required spatial Greens functions obtained by the improved DCIM are accurate both in the near- and far-field regions without any quasi-static and surface-wave extraction. Then, the scattering by buried objects is considered using the BCGS-FFT method combined with the improved DCIM. Numerical results show the improved DCIM can save tremendous CPU time in scattering involving buried objects.

Range Profile Analysis of the 2-D Target Above a Rough Surface Based on the Electromagnetic Numerical Simulation

In this paper, 1-D range profiles of a 2-D perfect electric conductor (PEC) target above a 2-D PEC rough surface are investigated with numerical solutions for the electric field integral equations (EFIEs) of the combined scattering model. The backscattering is computed accurately by the reradiation of the induced surface currents on the target and the rough surface. Using a stepped frequency waveform (SFW), 1D high-resolution range profiles (HRRPs) of the target above a rough surface are obtained by performing the inverse discrete Fourier transform (IDFT) on the wideband backscattered field. Plots of range profiles show that the multiple interactions between the target and the bottom surface lead to a series of equivalent range profiles, especially when the bottom surface is smooth. Range locations of the equivalent range profiles are in good agreement with the results expected from the ray theory. The range profiles could be understood and analyzed based on the knowledge of the scattering mechanisms. Thus, the connection between the numerically simulated range profiles and the scattering mechanisms is established.

Geodesic Computation on NURBS Surfaces for UTD Analysis

One of the great challenges in calculating the uniform geometrical theory of diffraction (UTD) surface diffracted fields on NURBS surfaces is due to the difficulty in determining the geodesic paths along which the creeping waves propagate. On one single parametric surface patch, the geodesic computation needs to be performed by solving the geodesic equations numerically. Furthermore, realistic objects are generally modeled as the union of several connected NURBS patches. Due to the discontinuity of parameter between patches, it is more complicated to compute geodesic paths on several connected patches than on one single patch. Therefore, this letter develops an adjustable modeling scheme that can adjust the parameterizations of several connected patches to support the geodesic computation throughout these patches. Based on the geodesic computation, the UTD diffractions by NURBS models can be analyzed.

Ray-tracing method for creeping waves on arbitrarily shaped nonuniform rational B-splines surfaces

An accurate creeping ray-tracing algorithm is presented in this paper to determine the tracks of creeping waves (or creeping rays) on arbitrarily shaped free-form parametric surfaces [nonuniform rational B-splines (NURBS) surfaces]. The main challenge in calculating the surface diffracted fields on NURBS surfaces is due to the difficulty in determining the geodesic paths along which the creeping rays propagate. On one single parametric surface patch, the geodesic paths need to be computed by solving the geodesic equations numerically. Furthermore, realistic objects are generally modeled as the union of several connected NURBS patches. Due to the discontinuity of the parameter between the patches, it is more complicated to compute geodesic paths on several connected patches than on one single patch. Thus, a creeping ray-tracing algorithm is presented in this paper to compute the geodesic paths of creeping rays on the complex objects that are modeled as the combination of several NURBS surface patches. In the algorithm, the creeping ray tracing on each surface patch is performed by solving the geodesic equations with a Runge-Kutta method. When the creeping ray propagates from one patch to another, a transition method is developed to handle the transition of the creeping ray tracing across the border between the patches. This creeping ray-tracing algorithm can meet practical requirements because it can be applied to the objects with complex shapes. The algorithm can also extend the applicability of NURBS for electromagnetic and optical applications. The validity and usefulness of the algorithm can be verified from the numerical results.

A spectral domain approach for the calculation of the scattering of the stratified uniaxial electric anisotropic media under point source excitation with arbitrary orientation

A method for the calculation of the scattering of the stratified uniaxial electric anisotropic media (UEAM) under point source excitation with arbitrary orientation is presented. In this method, the total field is decomposed into three parts, the radiated field of the point source in free space, the reflected field from the top interface of the UEAM and the transmitted field after multiple reflections in the anisotropic layer. The three parts are derived in spectral domain respectively and can be expressed by using Fourier transform. Then the saddle point technique (SPT) is introduced to obtain an asymptotic solution of the scattered field. Results from the asymptotic solution are compared with the results calculated by the method of moments (MOM) and the comparison shows good agreement.

Investigation of range profiles from buried 3-D object based on the EM simulation

The 1-D range profiles are suitable features for target identification and target discrimination because they provide discriminative information on the geometry of the target. To resolve features of the buried target, the contribution from individual scattering centers of the buried target in the range profiles need to be identified. Thus, the study of complex scattering mechanisms from which the range profiles are produced is of great importance. In order to clearly establish the relationship between the range profile characteristics and the complicated electromagnetic (EM) scattering mechanisms, such as reflections and diffractions, a buried cuboid possessing straight edges is chosen as the buried target in this paper. By performing an inverse discrete Fourier transform (IDFT) on the wideband backscattered field data computed with an accurate and fast EM method, the 1-D range profiles of the buried cuboid is successfully simulated. The simulated range profiles provide information about the position and scattering strength of the cuboids scattering centers along the range direction. Meanwhile, a predicted distribution of the scattering centers is quantitatively calculated for the buried cuboid based on the ray path computation. Good agreement has been found between simulated and predicted locations of the range profiles. Validation for amplitudes of the range profiles is further provided in the research. Both the peak amplitudes and locations of the range profiles could be understood and analyzed based on the knowledge of the scattering mechanisms. The formation of the 1-D range profiles has been revealed clearly from the full analysis of the scattering mechanisms and contributions. The problem has been solved for both near and far field regions. Finally, the buried depth and the characteristic size of the object are reasonably deduced from the simulated range profiles.

Evaluation of Scattering From Electrically Large and Complex PEC Target Coated With Uniaxial Electric Anisotropic Medium Layer Based on Asymptotic Solution in Spectral Domain

This paper presents a novel and original approach for the evaluation of electromagnetic (EM) scattering from electrically large and complex target coated with uniaxial electric anisotropic medium (UEAM) layer. The evaluation includes two indispensable aspects, the geometry modeling of the target and the determination of the surface currents. Once the equivalent surface currents (ESCs) induced on the outer surface of the coated target are determined, the scattered field could be calculated by the corresponding radiation integrals. First, the outer surface of the arbitrarily shaped target is discretized using flat triangle facets. Second, the ESCs on any facet are deduced from the surface fields, which involve a complicated coupling of type I and type II waves existing in the UEAM. Thus, the determination of the surface fields and the ESCs on the surface of the target with large radius of curvature is the crux of the whole evaluation. By making the tangent plane approximation, used in the physical optics (PO) method, any discretized flat facet could be approximated as an infinite PEC plate coated with a homogenous UEAM layer. Thereafter, the scattering from the infinite coated plate is asymptotically calculated by using the proposed spectral domain method combined with saddle point evaluation (SDM-SPE). Ultimately, comparisons of the proposed asymptotic solution with the reference solutions calculated numerically confirm the validity and efficiency of the proposed SDM-SPE. Numerical results of several canonical and complex targets coated with UEAM layer are given by the proposed approach for the first time.

Creeping Ray Tracing Algorithm for Arbitrary NURBS Surfaces Based on Adaptive Variable Step Euler Method

Although the uniform theory of diffraction (UTD) could be theoretically applied to arbitrarilyshaped convex objects modeled by nonuniform rational B-splines (NURBS), one of the great challenges in calculation of the UTD surface diffracted fields is the difficulty in determining the geodesic paths along which the creeping waves propagate on arbitrarilyshaped NURBS surfaces. In differential geometry, geodesic paths satisfy geodesic differential equation (GDE). Hence, in this paper, a general and efficient adaptive variable step Euler method is introduced for solving the GDE on arbitrarilyshaped NURBS surfaces. In contrast with conventional Euler method, the proposed method employs a shape factor (SF) to efficiently enhance the accuracy of tracing and extends the application of UTD for practical engineering. The validity and usefulness of the algorithm can be verified by the numerical results.