Computational electromagnetics

About: Computational electromagnetics is a research topic. Over the lifetime, 6412 publications have been published within this topic receiving 113727 citations. The topic is also known as: Electromagnetic field analysis.

An accelerated time domain finite difference simulation scheme for three‐dimensional transient electromagnetic modeling using geometric multigrid concepts

Abstract: The fact that the transient electromagnetic (TEM) field is smoothed gradually in space with time allows for a reduced spatial sampling rate of the EM field. On the basis of concepts known from multigrid methods, we have developed a restriction operator in order to map the EM field and the material properties from a fine to a coarser finite difference mesh during a forward field simulation with an explicit time-stepping scheme. Two advantages follow. First, the grid size can be reduced. Field restriction involves reducing the number of grid nodes by a factor of 2 for each Cartesian direction. Second, as can be seen from the Courant-Friedrichs-Levy condition, the larger grid spacing allows for proportionally larger time step sizes. After field restriction, a material averaging scheme is employed in order to calculate the underlying effective medium on the coarse simulation grid. Example results show a factor of up to 5 decrease in solution run time, compared to a scheme that uses a constant grid. Key to the accuracy of the approach is knowledge of the proper time range to restrict the fields. An adequate criterion to decide during run time when to restrict involves an error measure for the locations of interest between the fields on the fine mesh and the restricted fields.

High Order Finite Difference Approximations of Electromagnetic Wave Propagation Close to Material Discontinuities

Abstract: Electromagnetic wave propagation close to a material discontinuity is simulated by using summation by part operators of second, fourth and sixth order accuracy The interface conditions at the discontinuity are imposed by the simultaneous approximation term procedure Stability is shown and the order of accuracy is verified numerically

Fast Electromagnetic Analysis of MRI Transmit RF Coils Based on Accelerated Integral Equation Methods

Abstract: A fast frequency domain full-wave electromagnetic simulation method is introduced for the analysis of MRI coils loaded with the realistic human body models. The approach is based on integral equation methods decomposed into two domains: 1) the RF coil array and shield, and 2) the human body region where the load is placed. The analysis of multiple coil designs is accelerated by introducing the precomputed magnetic resonance Green functions (MRGFs), which describe how the particular body model used responds to the incident fields from external sources. These MRGFs, which are precomputed once for a given body model, can be combined with any integral equation solver and reused for the analysis of many coil designs. This approach provides a fast, yet comprehensive, analysis of coil designs, including the port S-parameters and the electromagnetic field distribution within the inhomogeneous body. The method solves the full-wave electromagnetic problem for a head array in few minutes, achieving a speed up of over 150 folds with root mean square errors in the electromagnetic field maps smaller than 0.4% when compared to the unaccelerated integral equation-based solver. This enables the characterization of a large number of RF coil designs in a reasonable time, which is a first step toward an automatic optimization of multiple parameters in the design of transmit arrays, as illustrated in this paper, but also receive arrays.

Electromagnetic Model Reliably Predicts Radar Scattering Characteristics of Airborne Organisms

Abstract: The radar scattering characteristics of aerial animals are typically obtained from controlled laboratory measurements of a freshly harvested specimen. These measurements are tedious to perform, difficult to replicate, and typically yield only a small subset of the full azimuthal, elevational, and polarimetric radio scattering data. As an alternative, biological applications of radar often assume that the radar cross sections of flying animals are isotropic, since sophisticated computer models are required to estimate the 3D scattering properties of objects having complex shapes. Using the method of moments implemented in the WIPL-D software package, we show for the first time that such electromagnetic modeling techniques (typically applied to man-made objects) can accurately predict organismal radio scattering characteristics from an anatomical model: here the Brazilian free-tailed bat (Tadarida brasiliensis). The simulated scattering properties of the bat agree with controlled measurements and radar observations made during a field study of bats in flight. This numerical technique can produce the full angular set of quantitative polarimetric scattering characteristics, while eliminating many practical difficulties associated with physical measurements. Such a modeling framework can be applied for bird, bat, and insect species, and will help drive a shift in radar biology from a largely qualitative and phenomenological science toward quantitative estimation of animal densities and taxonomic identification.

Particle-Swarm Optimization in Antenna Design: Optimization of Log-Periodic Dipole Arrays

Abstract: This paper presents a short tutorial and overview of optimization algorithms based on particle-swarm schemes, and their application to solving electromagnetic problems. As a practical example, a particle-swarm optimization (PSO) tool has been applied in conjunction with the Numerical Electromagnetics Code (NEC) to get the design curves of optimized log-periodic dipole arrays (LPDAs). The graphs show the performance of several radiation parameters (directive gain, front-to-back ratio, bandwidth, SWR, and half-power beamwidth in the E and H planes) as a function of typical design parameters of log-periodic dipole arrays (geometrical parameters and characteristics of the feed). Examples of optimized antennas are given, and their performance is compared to that of standard log-periodic dipole arrays.