Physical Optics Approximation Research Articles

Coherent Backscattering by Large Ice Crystals of Irregular Shapes in Cirrus Clouds

All elements of the scattering matrix have been numerically studied for particles of irregular shapes whose size is much larger than incident wavelength. The calculations are performed in the physical optics approximation for a particle size of 20 μm at a wavelength of 0.532 μm. Here the scattered intensity reveals the backscattering coherent peak. It is shown that the polarization elements of the matrix reveal the surges within the backscattering peak. The angular width of the surges does not practically depend on particle shape, but depends on the particle size. It is shown that these surges are created by interference between the conjugate scattered waves propagating in the inverse directions. The results obtained are of interest for interpretation of lidar measurements in cirrus clouds.

Analysis of electromagnetic scattering from typical targets for orbital‐angular‐momentum waves: Theoretical model

The target scattering characteristics in microwave band are necessary to be researched for Orbital-Angular-Momentum (OAM) wave-based radar applications. A theoretical description of electromagnetic (EM) scattering from a typical target by OAM waves is proposed in this paper. First, OAM waves are decomposed into plane waves in the spectral domain with different elevation and azimuth angles. Then, the scattering form of each decomposed plane wave is determined through coordinate system transformation and physical optics approximation. Formulas and numerical results are presented for OAM-based radar scattering cross section of a perfect electric conductor and dielectric plate and a cylinder. Unlike the conventional results of EM plane wave scattering, the scattering properties of OAM waves from plate and cylinder are analysed with particular emphasis on OAM mode influence. The results provide insights into OAM wave-matter interactions and may find important applications in wave propagation and OAM wave-based radar detection and imaging.

On the Integration of Reconfigurable Intelligent Surfaces in Real-World Environments: A Convenient Approach for Estimation Reflection and Transmission

The use of reconfigurable intelligent surfaces (RISs) for optimization of propagation channels is one of the most promising and revolutionizing techniques for improving efficiency of the next generation of communications systems. In this article, we combine physical optics approximation and the theory of diffraction gratings to study the scattering properties of finite-size metasurfaces mounted on partially reflecting walls. We consider both reflective and refractive metasurfaces designed to control both the reflection and transmission of waves. We start the analysis under the assumption of uniform, plane-wave illumination, and then discuss nonuniform illuminations by directive antennas.

Scattering from a Truncated Metamaterial Layer Hosted by a Planar PEC Structure: Uniform Asymptotic Solution and Validation Tests

This research paper proposes an analytical approach for evaluating electromagnetic scattering from a planar complex object made of a perfect electric conductor, which hosts a double negative metamaterial half-layer on the lit face. The method is based on the physical optics approximation of equivalent sources and works in the framework of the uniform geometrical theory of diffracion, so that the scattered field in the surrounding free space is obtained by adding the reflected contribution and the diffracted one, which is originated by the surface break. The effectiveness of the proposed approach is tested and proved by using a full-wave numerical tool to generate reference values.

Physical Optics Scattering by A PEC Missile in Uniform Rectilinear Motion

Electromagnetic scattering by a perfect electric conductor (PEC) missile in uniform rectilinear motion is formulated and computed in X-band under the physical optics (PO) approximation. The missile dimensions are picked as 80 [cm] in length and 6.6 [cm] in radius as adapted from the well-known Soviet M-13 missile. We adopt a canonical structure simulated by a cylindrical body, an ellipsoid nose, and four planar tail fins. The surface of the missile is meshed using triangular facets. First, the formulation and computations are carried out for a stationary missile in MATLABTM and compared to simulations by the commercial full-wave simulator CSTTM. Good agreements that reveal the validity of PO formulation are observed. Finally, PO formulation and numerical results for a missile in uniform rectilinear motion are provided and discussed. These simulations are based on the principle of superposition of the formulas developed recently for scattering by a moving PEC flat plate.

A Solution for the Plane Wave Diffraction by the Discontinuity Between Two Co-Planar Metamaterial Sheets

A high-frequency approach is described to investigate the scattering by a junction between double negative metamaterial (DNG MTM) sheets. These last are lit by an incident plane wave and have same thickness, but different electric and magnetic parameters, thus assuring discontinuities of reflected and transmitted fields across the junction. The proposed methodology permits to evaluate the diffraction contribution as the sum of two independent terms arising from the scattering process including electric and magnetic equivalent sources under the physical optics (PO) approximation. The formulation of this wave contribution permits its use in the enclosure of the uniform geometrical theory of diffraction (UTD). Useful approximations and integral representations are adopted together with asymptotic evaluations to obtain the diffraction matrix elements. Accordingly, these last account for convenient reference systems, the approximated equivalent currents, and the typical function of the UTD. A full-wave numerical tool is exploited to assess the correctness of the proposed formulation.

Integrated Physical Optics for Calculating Electric-Large Metallic Sphere Scattering Irradiated by Vortex Wave in Microwave Frequency Band

In this letter, a novel integrated physical optics (PO) method for calculating high-frequency scattering of nonplane wave is proposed, and the orbital angular momentum (OAM) wave scattering upon an electric-large metallic sphere is illustrated. A high-order Bessel wave expanded by a series of plane wave angular spectra is selected to irradiate a perfect electric conductor sphere. Combining the PO approximation, the scattered field from the facet element is calculated, and the total scattered effect is obtained by vector superposition of the scattering from all facets. The calculated results are verified by the EM simulated software FEKO and scattering measurement experiment. Numerical results show that the scattered field of the vortex wave passing through the standard target still has the OAM characteristics, retaining the same topological charge. It can be seen that the proposed combined PO method is feasible at high frequency and can be extended to solve the scattering of other beams and objects, which has a broad range of applications.

A Discussion on Physical Optics Approximation for Edge Diffraction by A Conducting Wedge

A Discussion on Physical Optics Approximation for Edge Diffraction by A Conducting Wedge

Light Backscattering Properties of Distorted Hexagonal Atmospheric Ice Particles within the Physical Optics Approximation

Light Backscattering Properties of Distorted Hexagonal Atmospheric Ice Particles within the Physical Optics Approximation

On the Asymptotic Evaluation of the Physical Optics Approximation for Plane Wave Scattering by Circular Conducting Cylinders

In this paper, the scattering far-field from a circular electric conducting cylinder has been analyzed by physical optics (PO) approximation for both H and E polarizations. The evaluation of radiation integrations due to the PO current is conducted numerically and analytically. While non-uniform and uniform asymptotic solutions have been derived by the saddle point method, a separate approximation has been made for forward scattering direction. Comparisons among our approximation, direct numerical integration and exact solution results yield a good agreement for electrically large cylinders.

Physical optics approximation of electromagnetic field scattered from large PEC objects covered with chiral metamaterials

Electromagnetic scattering analysis from conducting objects comparable in size with the incident wavelength, using exact numerical approaches, always suffers from high computational complexity, especially when covered with composite penetrable materials. In this paper the asymptotic method of the physical optics (PO) is developed to predict the scattering patterns from conducting objects coated by chiral metamaterials (CMMs) as an absorber. In first stage, the backward ray-tracing is used to determine the lit region on the outer surface of the objects represented by flat elementary facets. Simple closed-form expressions are derived for the co- and cross-polarized reflection coefficients from a metal-backed CMM layer to approximate the equivalent currents on lit facets in terms of the geometrical-optics fields. Then, for stealth applications, a CMM layer with appropriate electromagnetic properties is suggested with reflected power lower than −20 dB in a wide aspect angle of incident ray from 0 to 57 degrees. Finally, the scattering patterns are calculated via the PO approximation and the equivalent currents. In order to check the accuracy of the proposed solutions, the simulation results of several objects will be compared with the experimental data and the results of the exact Mie theory and method of moment (MoM).

Modeling of Multiscale Wave Interactions Based on an Iterative Scheme of MoM-PO-EPA Algorithm

Electromagnetic modeling of multiscale wave interactions is a challenging task. This is because wave physics exhibit different characteristics at different length scales that require suitable modeling algorithms. Combining these algorithms to model multiscale wave physics requires careful design and tuning. In this study, we investigated a hybrid algorithm based on the method of moment (MoM), iterative physical optics (IPO) approximation, and the equivalence principle algorithm (EPA). EPA modeled targets with details, MoM modeled targets with moderate scales, and IPO modeled electrically large scatterers. The virtual equivalence surfaces in EPA worked as interfaces between relatively large and small scatterers. An iterative scheme is used to solve the targets instead of a matrix equation with large dimensions. This algorithm achieved a good balance between accuracy and efficiency. Numerical examples of modeling the plane-wave scattering of multiscale targets verify its performance for 2D and 3D problems. The iterative scheme can become faster and need less memory usage when solving the multiscale scatterers.

Light backscattering properties of atmospheric hexagonal ice particles with distorted shape within physical optics approximation

Light backscattering properties of atmospheric hexagonal ice particles with distorted shape within physical optics approximation

Forward and Inverse Scattering of Metallic Objects Through Focused Bessel-Shaped Fields

This paper deals with both forward and inverse electromagnetic scattering of metallic objects by focused Bessel-shaped incident field. After discussing the main features of this kind of field, it is shown that its focusing capabilities may offer new effective possibilities for the detection of metallic targets which are not so far extended with respect to the probing wavelength, i.e., not satisfying the hypotheses of physical optics approximation. Numerical examples are performed by means of full-wave simulations, and then inversion algorithms based on back-propagation and physical optics are exploited to show that more accurate reconstructions can be pursued using Bessel-shaped fields.

Considering Nonsurface Scattering in Physical Optics Approximations

This work addresses the issue of volume scattering effects within the context of the physical optics (PO) approach. This decreases the modeling and computational effort to simulate scattering from complex material compositions. It is shown that there is a natural progression from the classical PO for perfect electric conductors over the PO for dielectric scatterers toward the proposed formulation. Four specializations of the general algorithm are presented to emphasize the versatility of this approach. Details regarding the implementation of the proposed examples are described. Results for each of the special cases are shown and compared to commercially available full-wave solvers of CST and FEKO.

On physical optics approximation of stratified shear flows with eddy viscosity

We study a mathematical model of a perturbed stratified shear mean flow in the presence of eddy coefficients of turbulent viscosity. We adopt the standard Boussinesq approximation in the natural convection of the buoyancy-driven flow and neglect the influence of the eddy coefficients of turbulent diffusivity. Comprising both the vertical and horizontal viscosity effects, a model for the vertical velocity perturbation corresponds to a fourth-order Taylor–Goldstein (TG) differential equation. Considering only the latter, we obtained a modified TG equation with the same order as the classical, inviscid one. Under an assumption of the slowly varying Brunt–Väisälä frequency and background horizontal velocity, we discuss the corresponding geometrical and physical optics approximations of the modified TG equation using the WKB method. We further investigate the behavior of these asymptotic solutions near singular values of a turning point and critical level.

Improving Physical Optics Approximation Through Bessel Beam Scattering

In this letter, the scattering of a nondiffractive Bessel beam (BB) incident field by a perfect electric conducting circular cylinder is investigated and compared with the standard scattering solution by a plane wave. It is proven that the BB incident field improves the validity of standard physical optics approximation and possibly extends its range of applicability to cylinders, or more general scatterers, whose curvature radius is not much larger than the operating wavelength. This offers new effective possibilities in the solutions of different electromagnetic scattering problems.

An Iterative Hybrid JMCFIE-MSIE-PO Method for Analyzing EM Scattering From Complex Target Above Rough Surface

An iterative hybrid method is proposed for analyzing the electromagnetic (EM) scattering from complex target above rough surface. First, the electric/magnetic current-combined field integral equation (JMCFIE) is formulated to calculate the EM scattering from the complex target combining conductor and multiple dielectric objects. Then, the single integral equation (SIE) method for multiple dielectric objects in the complex target (MSIE) is applied to reduce one-half of the unknowns in dielectric regions, and the hybrid JMCFIE-MSIE method is formulated. Afterward, physical optics (PO) approximation is employed for computing the EM scattering on the rough surface, and the iterative hybrid based on the combination of JMCFIE-MSIE and PO is derived for composite scattering from complex target above rough surface. Furthermore, the multilevel fast multipole algorithm is utilized to accelerate the matrix-vector multiplications in the computation process. The equivalent edge currents method is applied to meliorate the result. Finally, the validation and applicability of the proposed iterative solution are demonstrated by several numerical examples.

Явное асимптотическое решение задачи дифракции на одиночном рассеивателе больших волновых размеров

The stated problem remains very relevant, despite the rapid development of numerical methods and computer technology. The fact, in particular, is that even when using the most efficient numerical methods and algorithms, the problem remains very time-consuming. The following is an approach to solving the above problem, based on the method of pattern equations. Presenting the scattered field as the sum of three terms - a current pattern in the approximation of physical optics and two patterns of so-called semi-shadow currents distributed in the neighborhood of the light-shadow boundary, the initial problem is reduced to solving the simpler problem of the interaction of two (small) diffusers located at a great distance from each other, which is already solved relatively easily and moreover in an explicit form.

Electromagnetic wave scattering by a half-plane with generalized semitransparent boundary conditions

ABSTRACT Hybrid and asymptotic methods of diffraction theory used when the electric size of a scatterer is large are based on the use of a solution for the radiation pattern of a cylindrical wave, which appears when a plane wave is scattered by an edge with a given boundary condition. The expression of the radiation pattern of a wave scattered by the edge of a half-plane with generalized semitransparent boundary conditions has not been obtained using the Sommerfeld integral technique. The use of the solution for the semitransparent case allows us to expand the asymptotic methods to scatterers with semitransparent edges. In this article, based on solving the problem of the scattering of a plane wave by a half-plane with the generalized semitransparent boundary conditions using the Sommerfeld integral technique, we derive a solution for the far-field of the cylindrical wave scattered by the semitransparent edge. Based on the obtained solution, we derive an expression for the calculation of an amendment to the physical optics approximation, which allows us to extend the physical theory of diffraction method to scatterers with semitransparent edges. We apply the uniform asymptotic theory of diffraction method to the problem of cylindrical-wave scattering by the semitransparent half-plane.