Electro-acoustic Scattering from a Pulsating Sphere

In this paper, we show the RCS enhancement due to the acoustic disturbances around a pulsating sphere. The acoustic variation is modeled with the dielectric inhomogeneities around the sphere caused by the pressure fluctuations due to the acoustic source. RCS is computed for the modeled dielectric pulsating sphere, a cube, and a cone on a cylinder across a frequency band using Finite Difference Time Domain (FDTD) method. The RCS of the pulsating sphere and other objects considered are dominated by the background scattering from the pulsating object. In this work, we show that the dielectric variation due to the acoustic source can be detected even if there is no scattering from the object. The scattering from the dielectric variation leads to the detection of Bragg scattering along with a significant increase in RCS.Comment: 8 Page

Application of computational physics within Northrop

An overview of Northrop programs in computational physics is presented. These programs depend on access to today's supercomputers, such as the Numerical Aerodynamical Simulator (NAS), and future growth on the continuing evolution of computational engines. Descriptions here are concentrated on the following areas: computational fluid dynamics (CFD), computational electromagnetics (CEM), computer architectures, and expert systems. Current efforts and future directions in these areas are presented. The impact of advances in the CFD area is described, and parallels are drawn to analagous developments in CEM. The relationship between advances in these areas and the development of advances (parallel) architectures and expert systems is also presented

Reduction of the radar cross section of arbitrarily shaped cavity structures

The problem of the reduction of the radar cross section (RCS) of open-ended cavities was studied. The issues investigated were reduction through lossy coating materials on the inner cavity wall and reduction through shaping of the cavity. A method was presented to calculate the RCS of any arbitrarily shaped structure in order to study the shaping problem. The limitations of this method were also addressed. The modal attenuation was studied in a multilayered coated waveguide. It was shown that by employing two layers of coating, it was possible to achieve an increase in both the magnitude of attenuation and the frequency band of effectiveness. The numerical method used in finding the roots of the characteristic equation breaks down when the coating thickness is very lossy and large in terms of wavelength. A new method of computing the RCS of an arbitrary cavity was applied to study the effects of longitudinal bending on RCS reduction. The ray and modal descriptions for the fields in a parallel plate waveguide were compared. To extend the range of validity of the Shooting and Bouncing Ray (SBR) method, the simple ray picture must be modified to account for the beam blurring

Lorenz-Mie theory for 2D scattering and resonance calculations

This PhD tutorial is concerned with a description of the two-dimensional generalized Lorenz-Mie theory (2D-GLMT), a well-established numerical method used to compute the interaction of light with arrays of cylindrical scatterers. This theory is based on the method of separation of variables and the application of an addition theorem for cylindrical functions. The purpose of this tutorial is to assemble the practical tools necessary to implement the 2D-GLMT method for the computation of scattering by passive scatterers or of resonances in optically active media. The first part contains a derivation of the vector and scalar Helmholtz equations for 2D geometries, starting from Maxwell's equations. Optically active media are included in 2D-GLMT using a recent stationary formulation of the Maxwell-Bloch equations called steady-state ab initio laser theory (SALT), which introduces new classes of solutions useful for resonance computations. Following these preliminaries, a detailed description of 2D-GLMT is presented. The emphasis is placed on the derivation of beam-shape coefficients for scattering computations, as well as the computation of resonant modes using a combination of 2D-GLMT and SALT. The final section contains several numerical examples illustrating the full potential of 2D-GLMT for scattering and resonance computations. These examples, drawn from the literature, include the design of integrated polarization filters and the computation of optical modes of photonic crystal cavities and random lasers.Comment: This is an author-created, un-copyedited version of an article published in Journal of Optics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

A fast 2-D parallel multilevel fast multipole algorithm solver for oblique plane wave incidence

We present a multilevel fast multipole algorithm (MLFMA) implementation to numerically solve Maxwell's equations for large two-dimensional geometries illuminated by an arbitrary plane wave in three-dimensional space. The solver's capabilities are augmented by means of an asynchronous and hierarchical parallelization. Its accuracy is demonstrated by comparing the analytical and numerically obtained scattering width of several canonical examples with a size of 700,000 wavelengths

Multilevel fast multipole algorithm for fields

An efficient implementation of the multilevel fast multipole algorithm is herein applied to accelerate the calculation of the electromagnetic near- and far-fields after the equivalent surface currents have been obtained. In spite of all the research efforts being drawn to the latter, the electric and/or magnetic fields (or other parameters derived from these) are ultimately the magnitudes of interest in most of the cases. Though straightforward, their calculation can be computationally demanding, and hence the importance of finding a sped-up accurate representation of the fields via a suitable setup of the method. A complete self-contained formulation for both near- and far-fields and for problems including multiple penetrable regions is shown in full detail. Through numerical examples we show that the efficiency and scalability of the implementation leads to a drastic reduction of the computation time.Ministerio de Economía y Competitividad | Ref. MAT2014-58201-C2-1-RMinisterio de Economía y Competitividad | Ref. MAT2014-58201-C2-2-RGobierno Regional de Extremadura | Ref. IB1318

The finite element solution of inhomogeneous anisotropic and lossy dielectric waveguides

This thesis presents a new variational finite element formulation and its implementation for the analysis of microwave and optical waveguide problem with arbitrarily- shaped cross section, inhomogeneous, transverse-anisotropic, and lossy dielectrics. In this approach, the spurious, nonphysical solutions, which ordinarily appear interspersed with the correct results of earlier vectorial finite element methods and thus have been the most serious problem in finite element analysis of waveguides, are totally eliminated. In this formulation either the propagation constant or the frequency may be treated as eigenvalues of the resulting generalized eigenvalue problem. This formulation also has the capability to find complex modes of lossless waveguides. Furthermore, the numerical efficiency of the solution is maximized since this formulation uses the most economical representation of a problem, in terms of only two vector components. This is achieved without losing the sparsity of the matrices of the resultant eigenvalue equation, which only depends on the topology of mesh used. This property is very important for solving large-size problems by efficient sparse matrix algorithms. In this work, a basic vector wave equation which involves only transverse components of magnetic field is straightforwardly derived from Maxwell equations. This differential equation incorporates the divergence condition V.B = 0 and leads to a canonical form of the resultant eigenvalue equation. The Local Potential Method is used to obtain the variational formulation. When implementing the finite element method, the Rayleigh-Ritz procedure is used to find stationary values of the functional to get the resulting generalized matrix eigenvalue equation. To show the validity and applicability of the method, a series of examples of microwave and optical waveguides including inhomogeneity, anisotropy and loss are studied. These examples show good accuracy and complete absence of spurious modes, demonstrating the effectiveness of the new formulation developed

Analytic pulse technique for computational electromagnetics

Numerical modeling of electromagnetic waves is an important tool for understanding the interaction of light and matter, and lies at the core of computational electromagnetics. Traditional approaches to injecting and evolving electromagnetic waves, however, can be prohibitively expensive and complex for emerging problems of interest and can restrict the comparisons that can be made between simulation and theory. As an alternative, we demonstrate that electromagnetic waves can be incorporated analytically by decomposing the physics equations into analytic and computational parts. In particle-in-cell simulation of laser--plasma interaction, for example, treating the laser pulse analytically enables direct examination of the validity of approximate solutions to Maxwell's equations including Laguerre--Gaussian beams, allows lower-dimensional simulations to capture 3-D--like focusing, and facilitates the modeling of novel space--time structured laser pulses such as the flying focus. The flexibility and new routes to computational savings introduced by this analytic pulse technique are expected to enable new simulation directions and significantly reduce computational cost in existing areas.Comment: 26 pages, 9 figure