Method Of Moments Simulation Research Articles

A Novel Method of Conductivity Measurements for Carbon-Fiber Monopole Antenna

The relation between loss resistance and conductivity for monopole antennas over a ground plane is derived. Its accuracy was confirmed by good agreement between it and finite element and method of moments simulations. This relation may be used to calculate conductivity of any material that radiates. A Wheeler Cap system was setup. System losses were determined by equating the loss resistance of a 70 mm long × 1.17 mm diameter copper monopole at resonance with that predicted using the published conductivity for this material. The loss resistance of a 70 mm long × 2 mm wide × 2 mm thick monopole antenna manufactured from an aerospace grade carbon fibre reinforced plastic (CFRP) laminate, IM7/977-3 prepreg tape with a [0 45 90-45]2s stacking sequence, was measured then corrected for system loss. The conductivity of the CFRP laminate was calculated to be 51,000 S/m at 980 MHz.

Using GPU With CUDA to Accelerate MoM-Based Electromagnetic Simulation of Wire-Grid Models

In this letter, a CUDA-enabled graphics processing unit (GPU) accelerated implementation of the method of moments (MoM) for electromagnetic simulation of wire-grid models of arbitrary configurations of conducting surfaces and wires is presented. The solution based on the frequency-domain electric field integral equation (EFIE) discretized using piecewise-linear (triangular) functions for expansion and testing is considered. Some issues pertinent to porting a single-CPU sequential code to an inherently parallel GPU platform are addressed. The GPU numerical results for a user-created benchmark structure are backed up with comparison to CPU results. A noticeable speedup (about 6t) of the overall MoM simulation is achieved due to employing GPU.

IMPLICIT SPACE MAPPING APPLIED TO THE SYNTHESIS OF ANTENNA ARRAYS

This paper introduces a novel technique for efficiently combining implicit space mapping (ISM) with method of moments (MoM) for the synthesis of antenna arrays and explores several example applications of the ISM approach. The antenna arrays geometric parameters are extracted to be optimized by ISM, and a fitness function is evaluated by MoM simulations to represent the performance of each candidate design. A coarse-mesh MoM and a fine-mesh MoM solver are used for the coarse and the fine models, respectively. To achieve the parameter extraction, the auxiliary parameter is selected and the approximation between the two models is accomplished by particle swarm optimization (PSO). The results show that the running time of the ISM algorithm is 2 ∼ 3 times faster than that of other optimization algorithms (e.g., PSO).

Transmission properties of thick-screen frequency selective surface having circular hole elements

A thick-screen frequency selective surface (FSS) with circle slot elements is designed. Based on the moment method simulation, we investigate mainly the transmission properties of this structure under no dielectric condition, when some parameters, including the element diameter, unit distribution period and incidence angle of electromagnetic wave,are changed. The result of numerical analysis show that the unit diameter, unit spacing and incidence angle have great influence on the transmission properties of the thick-screen FSS,but unit diameter has little influence on the center frequency.

Optimum Design for External Seismic Stability of Geosynthetic Reinforced Soil Walls: Reliability Based Approach

In this paper, an analytical study considering the effect of uncertainties in the seismic analysis of geosynthetic-reinforced soil (GRS) walls is presented. Using limit equilibrium method and assuming sliding wedge failure mechanism, analysis is conducted to evaluate the external stability of GRS walls when subjected to earthquake loads. Target reliability based approach is used to estimate the probability of failure in three modes of failure, viz., sliding, bearing, and eccentricity failure. The properties of reinforced backfill, retained backfill, foundation soil, and geosynthetic reinforcement are treated as random variables. In addition, the uncertainties associated with horizontal seismic acceleration and surcharge load acting on the wall are considered. The optimum length of reinforcement needed to maintain the stability against three modes of failure by targeting various component and system reliability indices is obtained. Studies have also been made to study the influence of various parameters on the seismic stability in three failure modes. The results are compared with those given by first-order second moment method and Monte Carlo simulation methods. In the illustrative example, external stability of the two walls, Gould and Valencia walls, subjected to Northridge earthquake is reexamined.

Broadband patch antenna design using differential evolution algorithm

AbstractA novel evolutionary algorithm for broadband patch antenna design is presented. The differential evolution algorithm (DE) and the method of moments (MOM) are combined to achieve the optimum antenna satisfying a certain design criterion. The antenna geometric parameters are extracted to be optimized by DE, and a fitness function is evaluated by MOM simulations to represent the performance of each candidate design. A broadband patch antenna is designed using the optimizer. The optimized patch antenna is fabricated and measured to validate the robustness of the algorithm. The measured 38.6% bandwidth exhibits the prospect of the DE/MOM algorithm in practical patch antenna design. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1692–1695, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24423

Optimization of an Innovative Type of Compact Frequency-Reconfigurable Antenna

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a novel patch antenna geometry that is well suited to frequency reconfigurability, achieved through the use of switches connecting metal portions to the ground plane. An optimization methodology is presented that allows operating without gaps in the 1.7–2.7 GHz band with sizes bounded by 0.17 wavelengths at the lowest frequency. The optimization procedure combines a global optimizer (genetic algorithm), and a local optimizer (1-bit neighborhood) for the geometry, and exhaustive search for the switching patterns. During optimization, performances are evaluated by method of moments simulation. The resulting structure has very attractive characteristics, such as small size, space filling, and good Return Loss (at 50 <formula formulatype="inline"> <tex Notation="TeX">$\Omega$</tex></formula>). A proof-of-concept prototype has been fabricated and measured, with switches simulated by soldering. Inclusion in simulation of the detailed behavior of commercial microelectromechanical systems devices is also reported. </para>

Observing bifurcation and resonance in a mean-field coupled periodically driven noisy overdamped oscillators by the method of moments

A method of moments for calculating long-term order parameter dynamics of mean-field coupled periodically driven overdamped oscillators is described based on nonlinear Fokker–Planck equation. Using this technique the bifurcation behavior and stochastic resonance of the order parameter is observed, and the accuracy is verified by comparing with Gaussian moment method and stochastic simulation. The technique can be used in nonharmonic external excitation case.

MPSO-MOM: A Hybrid Modified Particle Swarm Optimization and Method of Moment Algorithm for Smart Antenna Synthesis

In this article, a modified version of particle swarm optimization (MPSO) and the method of moment (MOM) are combined to achieve the beamforming objective of a practical smart antenna array. The hybrid approach (MPSO–MOM) is illustrated by application to a planar uniform circular array (PUCA) with 30 elements of half-wave dipoles. The array feeding is optimized by MPSO, and the fitness function is evaluated by MOM simulations. The MOM is used to calculate the response of the array in a mutual coupling environment. The performance of the adaptive array using discrete (quantized) feedings is studied. Also in this article, the convergence capability of the MPSO is compared with that of the classical particle swarm optimization and other recent evolutionary-based algorithms using benchmark examples and a linear array synthesis problem.

Modal Propagation and Excitation on a Wire-Medium Slab

A grounded wire-medium slab has recently been shown to support leaky modes with azimuthally independent propagation wavenumbers capable of radiating directive omnidirectional beams. In this paper, the analysis is generalized to wire-medium slabs in air, extending the omnidirectionality properties to even modes, performing a parametric analysis of leaky modes by varying the geometrical parameters of the wire-medium lattice, and showing that, in the long-wavelength regime, surface modes cannot be excited at the interface between the air and wire medium. The electric field excited at the air/wire-medium interface by a horizontal electric dipole parallel to the wires is also studied by deriving the relevant Green's function for the homogenized slab model. When the near field is dominated by a leaky mode, it is found to be azimuthally independent and almost perfectly linearly polarized. This result, which has not been previously observed in any other leaky-wave structure for a single leaky mode, is validated through full-wave moment-method simulations of an actual wire-medium slab with a finite size.

Using the Milliken Moment Method and dynamic simulation to evaluate vehicle stability and controllability

The Milliken Moment Method (MMM) effectively organises kinematically constrained vehicle test results. The authors present a method for evaluating vehicle handling; assessing the overall performance capability with the MMM then using the closed-loop dynamic simulation to determine how much of that performance is used for a real manoeuvre. By mapping the simulation data onto the yaw moment-lateral acceleration diagram from the MMM, this method explicitly quantifies the tradeoff between vehicle controllability and stability. Results from a design case study and comparison of the stability measure to phase plane analysis are presented and show the potential efficacy of the proposed approach.

A MOMENT METHOD SIMULATION OF ELECTROMAGNETIC SCATTERING FROM CONDUCTING BODIES

In this paper a moment method simulation of electromag- netic scattering problem is presented. An effective numerical method for solving this problem based on the method of moments and using block-pulse basis functions is proposed. Some examples of engineer- ing interest are included to illustrate the procedure. The scattering problem is treated in detail, and illustrative computations are given for some cases. This method can be generalized to apply to objects of arbitrary geometry and arbitrary material.

Accurate Evaluation of Magnetic- and Electric-Field Losses in Ground Systems

The efficiency of ground-based antennas is highly determined by the power dissipated in the ground plane, which can be separated into H-field and E-field losses. In this paper, a new approach is presented for the separation of ground losses that is based on Joule's law. It is theoretically valid at any frequency. Nevertheless, some simplifications can be applied in the low-and medium-frequency bands, where the Earth's soil behaves like a good conductor. In the analysis, the antenna's ground plane has been divided into two zones: a) the artificial ground plane, where a radial-wire ground screen was used; and b) the natural ground plane or bare soil, up to a circular boundary a half wavelength from the antenna's base. In order to avoid overestimating the penetration of fields in the artificial ground plane, the previous theory has been extended by introducing the concept of effective skin depth. The monopole's nonzero equivalent radius effect has been taken into account by means of a modified current distribution. Also, the case of short top-loaded antennas has been treated. H-field and E-field losses have been analyzed by means of equivalent resistances and computed numerically as functions of frequency in the LF and MF bands for different antenna dimensions, ground screens, and soil physical conditions. Some results have also been obtained by Moment-Method simulations.

A Statistical Integral Equation Model for Shadow-Corrected EM Scattering From a Gaussian Rough Surface

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We propose a statistical model in conjunction with the integral equation formalism for electromagnetic scattering from Gaussian rough surfaces with small to moderate heights and Gaussian power spectra where we include the statistical features of the surface slopes and the effect of shadowing. In evaluating the Kirchhoff incoherent power, for the correlated term due to correlation between the normal vectors of two neighboring points on the surface, an approximation scheme based on the decomposition of the covariance matrix is proposed. For the cross and complementary incoherent powers, due to their subdominant nature, the cross correlations between the surface slopes at different points on the surface are neglected to reduce the computational complexity. The validity of the proposed statistical integral equation model is demonstrated through agreement between its theoretical predictions and method of moment simulations. Moreover, all the simulated cases are outside the regions of validity of the small perturbation method and the conventional Kirchhoff model, which indicates that the statistical model holds the potential of bridging the gap between these two traditional models. </para>

Cable Trays in EMC: Measurement and Modeling to 30 MHz

Common mode (CM) currents are a major source of interference in electrical and electronic systems. Cable trays are often used to shield cables from unwanted CM electromagnetic interference, and their shielding characteristics are defined in terms of transfer impedance. We present the measurement and modeling of nonmagnetic U-shaped cable trays from 300 kHz to 30 MHz. A calibrated vector network analyzer in a screened environment is required for the high dynamic range measurements. We use method of moments simulations to determine the transfer impedance and mutual inductance within the interior region of a cable tray. We refined the modeling after detailed attention to the code. The computational and measured data are in good agreement. We propose the simulation as a means to predict the magnetic fields, mutual inductance, and transfer impedance associated with victim cable loops in the cross section of nonmagnetic cable trays to frequencies well beyond our studied range of 30 MHz.

High Directivity Antenna Using a Modified Peano Space-Filling Curve

In this letter, a high directivity space-filling curve antenna is proposed. The antenna configuration is based on a second iteration Peano space-filling curve, where some modification is performed such that the final antenna operates as an array of dipoles having the same current phases. This is achieved by the insertion of a folded section of the wire antenna that provides a 180deg phase shift at some points, so that the current over the dipole segments is kept in phase. Three antenna structures are proposed and compared regarding; used area, directivity, radiation pattern and cross polarization. The proposed antenna structures have been simulated using the moment method simulation software IE3D. The designed antenna has a very narrow bandwidth (S11 40 dB, and dimensions of 8/3lambdatimes4/3lambda.

Simplified calculation of ground losses in low- and medium-frequency antenna systems

Calculations of ground losses are paramount in obtaining the best performance of a monopole antenna in the low- (LF) and medium-frequency (MF) bands. Ground losses are usually computed numerically, due to difficulties in the mathematical formalism. The novel approach here permits obtaining simple analytical expressions for ground-loss calculations that can be useful for determining the behavior of the ground plane. As a first approximation, the monopole antenna is placed on a perfect electrically conducting (PEC) ground plane in order to obtain the antenna current distribution and the near magnetic field, taking into account the non-zero-radius effect of the monopole. Next, the near magnetic field is used to determine the surface-current density on the ground plane below the antenna. This is divided into two zones: (1) the artificial ground plane, where either a radial-wire ground screen or a metallic layer is used to increase the soil's conductivity; and (2) the natural ground plane or bare soil up to a circular boundary a half wavelength from the antenna's base. The power dissipation is calculated from the artificial and natural ground-plane surface-current densities, and the ground-plane loss resistance is obtained. Also, an effective conductivity is defined as a measure of the ground plane's effectiveness, and the cases of quarter-wave monopoles and short top-loaded antennas are analyzed. Some results are validated by means of numerical computations and moment method simulations

On the Crossed Field Antenna Performance

Lately, short antennas and Crossed Field Antennas (CFA) have attracted broadcast and amateur community attention. The CFA antenna has been developed in the last decade of the 20th century, trying to obtain a compact transmitting antenna for low and medium frequency AM bands. The CFA is intended to be used in order to get a low profile antenna and a supposed performance similar or better compared to a quarter-wave monopole. The CFA has a short monopole and a metallic disk close to the monopole base, both mechanical structures being fed by means of two separated generators. Thus, the CFA has two ports and can be analyzed from the Network Theory point of view. In this paper, the CFA has been studied exhaustively using the Transmission Line Method (TLM) in order to obtain an equivalent network and the antenna performance. Due to the lack of theoretical data to explain the CFA antenna behavior, the TLM has been validated by means of Moment Method simulations and some available experimental data

An Application of Sampling Theorem to Moment Method Simulation in Surface Scattering

The method of moment (MoM) is a numerical procedure for solving the equation Lf = g, where L is a continuous linear operator, f is the unknown function to be determined and g is a known excitation. In essence, the procedure converts the linear equation into a matrix equation and determines the unknown function in the form of a set of samples of the function through matrix inversion. It is well known that the sampling theorem states that to completely represent a function, one requires a minimum of two samples per wavelength, when the basis function is the Sinc function. Thus, by choosing the Sinc function as the testing and basis function in MoM implementation, we should have the smallest possible size for the matrix. To test the above stated approach, we calculate the scattering coefficient from a 2-D rough surface with a Gaussian distribution. The standard point matching approach is also used so that comparisons can be made between the two results. By comparing these numerical calculations with the IEM model, it is found that to achieve the same degree of accuracy, the number of unknowns used in the point matching method is an order of magnitude more than when the Sinc function is used as the basis function. This reduction in matrix size is specially significant in a three dimensional surface scattering problem, because we shall be able to reduce the matrix size by two orders of magnitude

An Estimation Method for the Free-Space Antenna Factor of VHF EMI Antennas

A novel numerical method is developed for theoretically estimating the free-space antenna factor of an electromagnetic interference (EMI) antenna, especially for the very high frequency (VHF) range where traditional methods are difficult to apply. It requires conventional EMI antenna calibration such as the standard antenna method to obtain the antenna factor of an antenna under calibration as a function of the antenna height. Then, a nonlinear least-squares method is applied to the calibration results to estimate the free-space antenna factor. It is found that the proposed method can yield more accurate estimates of the free-space antenna factor than the averaging method. Attainable accuracy of this method is better than 0.2 dB for tuned dipole antennas and 0.1 dB for biconical antennas and biconi-log antennas. The paper outlines the theoretical background and the validity of this method, with the attainable accuracy demonstrated using method of moments simulations.