High-frequency Approximation Method Research Articles

Scattering of arbitrarily incident Laguerre-Gaussian vortex electromagnetic beams by electrically large-scaled complex targets.

We implement an algorithm, termed parallel-processing physical optics, providing an efficient high-frequency approximation method to characterize the scattering of Laguerre-Gaussian (LG) vortex electromagnetic (EM) beams by electrically large-scaled complex targets. The incident beam is described by vector expressions in terms of electric and magnetic fields, and it is combined with rotation Euler angles to achieve an arbitrary incidence of the vortex beam. The validity and capability of the proposed method are illustrated numerically, and the effects of various beam parameters as well as target geometric models such as a blunt cone and Tomahawk-A missile on monostatic and bistatic radar cross section distributions are investigated. Results show that the scattering features of the vortex beam vary significantly with the parameters of the vortex beam and the target. These results are helpful to reveal the scattering mechanism of LG vortex EM beams and provide a reference for the application of vortex beams to detect electrically large-scaled targets.

A Fast, Hybrid, Time-Domain Discontinuous Galerkin-Physical Optics Method for Composite Electromagnetic Scattering Analysis

To accelerate the solution of transient electromagnetic scattering from composite scatters, a novel hybrid discontinuous Galerkin time domain (DGTD) and time-domain physical optics (TDPO) method is proposed. The DGTD method is used to solve the accurate scattering field of the multi-scale objects region, and a hybrid explicit-implicit time integration method is also used to improve the efficiency of multi-scale problems in the time domain. Meanwhile, the TDPO method is used to accelerate the speed of surface current integration in an electrically large region. In addition, the DGTDPO method considers the mutual coupling between two regions, and effectively reduces the number of numerical calculations for the other space of the composite target, thereby significantly reducing the computer memory consumption. Numerical results certified the high efficiency and accuracy of the hybrid DGTDPO. According to the results, in comparison with the DGTD algorithm in the entire computational domain, the DGTDPO method can reduce computing time and memory by 90% and 70% respectively. Meanwhile, the normalized root mean square deviation (NRMSD) of the time-domain, high-frequency approximation method is over 0.2, and that of the DGTDPO method is only 0.0971. That is, compared with the approximation methods, the hybrid method improves the accuracy by more than 64%.

Fast Modeling Methods for Estimating Imaging Performance of Whole Body Screening

The simulation of the millimeter wave imaging system for whole body screening before a safety inspection manufactured is a challenging work. The conventional physical optics (PO) method is a proper high-frequency approximation method to solve the forward problem of imaging. In this letter, a modified PO method is used to calculate not only metal scatterer but also nonmetal dielectric medium. A ray tracing method and its modification are proposed to further fast estimate the performance of the multiple-input-multiple-output (MIMO) imaging system. The radiation pattern of transmitter or receiver is taken into account, then the rough imaging performance of arbitrary MIMO system on arbitrary human posture can be acquired in seconds to make the system design flexible and convenient. The image reconstruction of the proposed method for a human body model with dielectric skin medium and metal pistol has demonstrated the applicability to real-life applications.

A Shooting and Bouncing Ray (SBR) Modeling Framework Involving Dielectrics and Perfect Conductors

A parallel computing architecture based on NVIDIA’s compute unified device architecture (CUDA) for the modeling of electromagnetic wave propagation by means of the high-frequency approximation method, shooting and bouncing rays (SBRs), is introduced and evaluated. The algorithm provides a reliable treatment of problems involving bulky and nonperfectly conducting materials. The general case of wave propagation through arbitrary dielectric materials also considering evanescent waves is presented in a concise way and a simplified treatment of the practically important case of thin dielectric layers over perfectly electrically conducting (PEC) bodies is considered. The resulting hybrid SBR approach is capable of dealing with PEC and the various dielectric object cases in a unified manner. A wide variety of scattering problems is considered, and scattered field predictions are compared to exact method of moments (MoM) and finite-element method (FEM) results. In particular, the benefits of the SBR within bulky dielectrics are highlighted.

Optimized Conformal FDTD (2, 4) Method for Calculating Reflected and Diffracted Electromagnetic Fields of Perfectly Conducting Wedges

An optimized conformal finite-difference time-domain (FDTD) (2, 4) method is proposed for calculating reflected, diffracted, and total fields of two- and three-dimensional (2- and 3-D) perfectly conducting (PEC) wedges with an electromagnetic pulse (EMP) incidence, where one low-cost coefficient-modification (CM) technique is implemented for effectively reducing its numerical dispersion error. For the 2-D geometries, both reflected and diffracted fields are extracted from the whole calculation domain of FDTD (2, 4), and excellent agreement is achieved between the calculated diffraction coefficient and the analytical one obtained by high frequency approximation method of UTD. While for the 3-D wedges, even with the coarse FDTD cells adopted, such an optimized method still possesses the capability for getting more accurate diffracted fields in comparison with the conventional FDTD.

COMPOSITE SCATTERING OF SHIP ON SEA SURFACE WITH BREAKING WAVES

The composite backscattering of the ship model on sea surface is investigated with the spilling breaking waves and ship bow waves. The spilling breakers are approximately modeled with the wedge-like waves, and the ship bow waves are simulated based on the Kelvin model. With the modifled four-path model, each scattering component is evaluated with the high frequency approximation methods for the total composite scattering. Due to the volume scattering, the composite scattering at large incidence angles is strongly enhanced by the non-Bragg scattering. The relationship of the composite scattering and the ship motion is analyzed. The numerical results of sea surface scattering agree with the measured data well, and the complex physical mechanism of the low-grazing-angle composite scattering is explicitly evaluated in this paper.

STUDY OF FOCUSING OF FIELD REFRACTED BY THE QUARTIC WOOD LENS INTO AN UNIAXIAL CRYSTAL

A geometrical high-frequency approximation method for solving the propagation of electromagnetic wave through the quartic Wood lens into an uniaxial crystal is presented in this paper. Caustic problem of electromagnetic wave is translated into non-caustic problem by using the hybrid space. The drawback that the solution in the caustic region cannot be obtained with geometrical optics is overcome by this method known as Maslov's method. The high-frequency approximation solution that is valid around caustic region is obtained by using this method which combines the simplicity of ray and generality of the transform method. And the results are compared with those obtained by Huygens-Kirchhoff's expression.

Solving the propagation of electromagnetic wave in a simple two-dimensional inhomogeneous medium based on symplectic geometrical theory

A new symplectic geometrical high-frequency approximation method for solving the propagation of electromagnetic waves in the two-dimensional inhomogeneous media is presented in this paper. The propagating caustic problem of electromagnetic wave is translated into non-caustic problem by the coordinate transform on the symplectic space. The high-frequency approximation solution that includes the caustic region is obtained with the method combining the geometrical optics. The drawback that the solution in the caustic region can't be obtained with geometrical optics is overcome by this method. The results are compared with those obtained by finite elements method; it proves to be satisfactory.