Full-wave Model Research Articles

Electromagnetic wave propagation in general relativistic situations: A general solution of the problem

[1] The exact full-wave modeling and computation of the electromagnetic signals propagating through curved space-time is important from theoretical and practical aspects (e.g., for satellite positioning systems). In this paper a general solution method is presented for these problems. Beside this, it is demonstrated that the Method of Inhomogeneous Basic Modes is a natural consequence of Maxwell's equations in the general relativity.

Global modeling of nonlinear circuits using the finite-difference Laguerre time-domain/alternative direction implicit finite-difference time-domain method with stability investigation

This paper describes a new unconditionally stable numerical method for the full-wave physical modeling of semiconductor devices by a combination of the finite-difference Laguerre time-domain (FDLTD) and alternative direction implicit finite-difference time-domain (ADI-FDTD) approaches. The unconditionally stable method by using FDLTD scheme for the electromagnetic model and semi-implicit ADI-FDTD approach for the active model leads to a significant decrease in the full-wave simulation time. Numerical simulations of an example transistor and a power amplifier show the efficiency of presented method for the full-wave simulation of mm-wave active circuits. Copyright © 2012 John Wiley & Sons, Ltd.

On the choice between walls and berms for road traffic noise shielding including wind effects

A numerical comparison is made between the road traffic noise shielding provided by 4-m high vertically erected walls and (earth) berms, averaged over large zones behind them. A previously developed and validated full-wave numerical sound propagation model was used. In absence of wind, a noise screen is preferred when it can be placed at the same position as the foot of the berm at the source side. In case of a fixed top position for both the wall and berm, an acoustically soft berm with a flat top gives similar shielding as the wall. In case of downwind sound propagation (i.e. a worst-case situation), the noise wall efficiency largely decreases. Strong wind might lead to an almost complete loss of noise wall shielding when compared to sound propagation over unobstructed terrain in absence of wind. In contrast, with decreasing berm slope angle, downward refraction by wind can become very small. In case of berms with a slope of 1:3, or berms with steeper slopes but with a flat top, the averaged wind effect can be smaller than 1dBA because of the limited magnitude of vertical gradients in the horizontal component of the wind speed near such more streamlined obstacles. When looking at long-term equivalent noise levels, including periods with wind, acoustically soft and shallow berms should be chosen upon vertically erected noise walls. In addition, there are clear non-acoustical benefits associated with the use of such natural berms. Wind-breaking vegetation has not been considered in this study.

AN ACTIVE RING SLOT WITH RF MEMS SWITCHABLE RADIAL STUBS FOR RECONFIGURABLE FREQUENCY SELECTIVE SURFACE APPLICATIONS

An active ring slot resonator loaded by switchable radial stubs is investigated. It is shown that this element can be used as the unit cell of a switchable reconflgurable frequency selective surface (RFSS). Equivalent circuit and full-wave mathematical models are obtained to evaluate the re∞ection characteristics of the RFSS based on this element. The possibility to obtain difierent resonant transmission frequencies is discussed. The mathematical model developed is used to design an X band RFSS capable of obtaining resonant frequencies at 9.65, 10.28, 10.83 and 12.05GHz. Commercially available RF MEMS switches are used to evaluate the efiect of the ofi-state capacitances over the response of the periodic structure. To validate the numerical simulation results, difierent active and passive diaphragms were designed, fabricated, and tested using the waveguide simulator. A good agreement between numerical and measured results was found.

Quasi-Dynamic Green’s Functions for Efficient Full-Wave Integral Formulations for Microstrip Interconnects

Integral formulations are widely used for full-wave analysis of microstrip interconnects. A weak point of these formulations is the inclusion of the proper planar-layered Green’s Functions (GFs), because of their computational cost. To overcome this problem, usually the GFs are decomposed into a quasi-dynamic term and a dynamic one. Under suitable approximations, the ?rst may be given in closed form, whereas the second is approximated. Starting from a general criterion for this decomposition, in this paper we derive some simple criteria for using the closed-form quasi-dynamic GFs instead of the complete GFs, with reference to the problem of evaluating the full-wave current distribution along microstrips. These criteria are based on simple relations between frequency, line length, dielectric thickness and permittivity. The layered GFs have been embedded into a full-wave transmission line model and the results are ?rst benchmarked with respect to a full-wave numerical 3D tool, then used to assess the proposed criteria.

Scattering of ECRF waves by edge density blobs and fluctuations in tokamak plasmas

There are two basic approaches to studying the effects of density blobs and edge fluctuations on the coupling of electron cyclotron (EC) radio frequency waves to the core of tokamak plasmas. The first is the geometric optics approach in which the effect of fluctuations is to change the refractive properties of the EC beam or rays. There are two consequences of refractive scattering - diffusion in real space leading to a spatial deflection of the rays and diffusion in wave vector space leading to the broadening of the launched spectrum. The geometric optics approach is limited to small density fluctuations of 10% or less. The second approach to studying the effect of blobs on EC fields is using the full wave approach. This approach extends the range of validity well beyond that of geometric optics; however, it is theoretically and computationally much more challenging. In this paper a full wave model for scattering of radio frequency waves is developed. Results from the model demonstrate diffractive scattering of EC waves by density blobs and the enhancement of the electric fields near the surface of the blob.

MoM solutions to building blockage of mobile satellite communications

This article presents a full-wave propagation model for arbitrary profile of building blockage in mobile satellite communications, by solving the electric field integral equation for induced surface currents using the method of moments. Asymptotic expressions are used to simplify the integrals. Scattered fields are then found by the radiation equations derived from Maxwell equations. The total received fields around different profiles of buildings are calculated as a function of space, elevation angle and frequency. The results agree well with measurements and other published data. Various useful parameters for designing robust and reliable communication systems like frequency response, average fade duration and coherence bandwidth are found. Performance of mobile satellite system is evaluated in terms of bit error rate of mobile satellite system in frequency non-selective, slowly fading channel.

Gravity wave heating and cooling of the thermosphere: Sensible heat flux and viscous flux of kinetic energy

[1] Total wave heating is the sum of the convergence of the sensible heat flux and the divergence of the viscous flux of wave kinetic energy. Numerical simulations, using a full-wave model of the viscous damping of atmospheric gravity waves propagating in a nonisothermal atmosphere, are carried out to explore the relative contributions of these sources of wave heating as a function of wave properties and altitude. It is shown that the sensible heat flux always dominates in the lower thermosphere, giving a lower region of heating and an upper stronger region of cooling. The heating due to the divergence of the viscous flux of kinetic energy is significant only for fast waves (horizontal phase speed greater than about 120 m s−1). The faster the wave is, the greater the heating in the upper thermosphere can be. The viscous heat source in per unit mass terms can greatly exceed the sensible heat source for fast waves and might be a significant heat source for the middle and upper thermosphere.

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We demonstrate the feasibility of using effective medium theory to reduce the computational complexity of full-wave models of inductors that are placed over interconnects. Placing inductors over interconnects is one way that designers can tackle the problem of reducing overall chip size, however this has heretofore been a difficult option to evaluate because of the prohibitive memory requirements and run times for detailed simulations of the inductor. Here we replace the interconnects with a homogeneous equivalent layer that mimics their impact on the inductor to within 2% error, but reducing runtime and memory use by 90% or more.

Image and Exact Models of a Vertical Wire Penetrating a Two-Layered Earth

In this paper, we investigate the validity of image theory in modeling a vertical wire penetrating a uniform or two-layered earth. First, a rigorous full-wave electromagnetic model is described that may be used as a standard for comparison. The model is based on the method of moments (MoM) and exact Green functions for the layered earth that involve Sommerfeld-type integrals. Next, we derive the image model from the exact model and analyze the approximations. We compare the current along a vertical wire as computed by the MoM using the exact Green functions, with the current computed using the image Green functions. The image model is accurate at dc, and the error is generally low at low frequencies but rises at high frequencies. We show that the image model leads to smaller errors when the wire is embedded in one layer. However, the error is larger in cases of penetration through different layers. We also show a strong dependence of the error on the resonant frequencies.

Prediction of Radiated Emissions Using Near-Field Measurements

A procedure is developed to predict electromagnetic interference from electronic products using near-field scan data. Measured near-field data are used to define equivalent electric and magnetic current sources characterizing the electromagnetic emissions from an electronic circuit. Reconciliation of the equivalent sources is performed to allow the sources to be accurately applied within full-wave numerical modeling tools like finite-difference time domain (FDTD). Results show that the radiated fields must typically be represented by both electric and magnetic current sources if scattering and multiple-reflections from nearby objects are to be taken into account. The accuracy of the approach is demonstrated by predicting the fields generated by a microstrip trace within and outside of a slotted enclosure, and by predicting the fields generated by the microstrip trace close to a long wire. Values predicted from near-field scan data match those from full-wave simulations or measurements within 6 dB.

Multipoint Full-Wave Model Order Reduction for Delayed PEEC Models With Large Delays

The increase of operating frequencies requires 3-D electromagnetic (EM) methods, such as the partial element equivalent circuit (PEEC) method, for the analysis and design of high-speed circuits. Very large systems of equations are often produced by 3-D EM methods and model order reduction (MOR) techniques are used to reduce such a high complexity. When signal waveform rise times decrease and the corresponding frequency content increases, or the geometric dimensions become electrically large, time delays must be included in the modeling. A PEEC formulation, which include delay elements called τ PEEC method, becomes necessary and leads to systems of neutral delayed differential equations (NDDE). The reduction of large NDDE is still a very challenging research topic, especially for electrically large structures, where delays among coupled elements cannot be neglected or easily approximated by rational basis functions. We propose a novel model order technique for τ PEEC models that is able to accurately reduce electrically large systems with large delays. It is based on an adaptive multipoint expansion and MOR of equivalent first-order systems. The neutral delayed differential formulation is preserved in the reduced model. Pertinent numerical examples based on τ PEEC models validate the proposed MOR approach.

A linearized contrast source method for full-wave modeling of nonlinear acoustic wave fields in homogeneous media

Many novel medical echography modalities, like super harmonic imaging (SHI), employ imaging of higher harmonics arising from nonlinear propagation. Design optimization of dedicated imaging probes for these modalities requires accurate computation of the higher harmonic beam profiles. The existing iterative nonlinear contrast source method can perform such simulations. With this method, the nonlinear term of the Westervelt equation is considered to represent a distributed contrast source in a linear background medium. The full transient nonlinear acoustic wave field follows from the Neumann iterative solution of the corresponding integral equation. Each iteration involves the spatiotemporal convolution of the background Green's function with an estimate of the contrast source, and appropriate filtering enables a discretization approaching two points per smallest wavelength or period. To further reduce the computational load and to anticipate extension of the method, in this presentation, the effect of linearizing the nonlinear contrast source is investigated. This enables the replacement of the Neumann scheme by more efficient schemes. Numerical simulations show that for design purposes the effect of linearization on the harmonic components involved with SHI remains sufficiently small. Moreover, it is shown that a significant decrease in computational costs may be achieved by using a Bi-CGSTAB scheme.

A linearized contrast source method for full-wave modeling of nonlinear acoustic wave fields in media with strong and inhomogeneous attenuation

The iterative nonlinear contrast source (INCS) method is a numerical method originally developed for modeling transient nonlinear acoustic wave fields in homogeneous (i.e., spatially independent) lossless or lossy media. This method is based on the Westervelt equation and assumes that the nonlinear term describes a distributed contrast source in a linear background medium. Next, the equivalent nonlinear integral equation is iteratively solved by means of a Neumann scheme. In medical diagnostic ultrasound, the observed acoustic nonlinearity is weak, resulting in a weak nonlinear contrast source and a fast convergence of the scheme. To model spatially dependent attenuation, the Westervelt equation has recently been extended with an attenuative contrast source. This presentation deals with the situation of strong local attenuation. In that case, the attenuative contrast source is large and the Neumann scheme may fail to converge. By linearizing the nonlinear contrast source, the integral equation becomes linear and can be solved with more robust schemes, e.g., Bi-CGSTAB. Numerical simulations show that this approach yields convergent results for nonlinear acoustic fields in realistic media with strong local attenuation. Moreover, it is shown that in practical situations, the error due to the linearization remains sufficiently small for the first few harmonics.

Simulation of complex plasmonic circuits including bends

Using a finite-element, full-wave modeling approach, we present a flexible method of analyzing and simulating dielectric and plasmonic waveguide structures as well as their mode coupling. This method is applied to an integrated plasmonic circuit where a straight dielectric waveguide couples through a straight hybrid long-range plasmon waveguide to a uniformly bent hybrid one. The hybrid waveguide comprises a thin metal core embedded in a two-dimensional dielectric waveguide. The performance of such plasmonic circuits in terms of insertion losses is discussed.

Evidence of guided resonances in photonic quasicrystal slabs

We report on the experimental evidence of Fano-type guided resonances (GRs) in aperiodically-ordered photonic quasicrystal slabs. With specific reference to the Ammann-Beenker (8-fold symmetric, quasiperiodic) octagonal tiling geometry, we present our experimental results on silicon-on-insulator devices operating at near-infrared wavelengths, and compare them with the full-wave numerical predictions based on periodic approximants. Our results indicate that spatial periodicity is not strictly required for the GR excitation, and may be effectively surrogated by weaker forms of long-range aperiodic order which intrinsically provide extra degrees of freedom (e.g., higher-order rotational symmetries, richer defect states and phase-matching conditions, etc.) to be exploited in the design and performance optimization of nanostructured dielectric slabs operating in the out-of-plane configuration. The essential spectral features may be qualitatively understood in terms of phase-matching conditions derived from approximate homogenized models, and turn out to be effectively captured by full-wave modeling based on suitably-sized periodic approximants.

Dynamic full-wave modeling of storm microseism propagation in an oceanic environment

The full-wave modeling of storm seismoacoustic field propagation in oceanic waveguides and at the ocean-continent border in the low-frequency range from 0.01 to 1 Hz using the numerical grid method is considered. The 2D model proposed by Press and Ewing for planar waveguides above the homogeneous elastic halfspace was chosen as a basis. The influence of a layer of deposits and features of the crust of the oceanic- and continent-type was taken into account in the more complex model. The effects of the carrier frequency, orientation of directivity diagram of the signal source, and steepness of the continental slope were investigated. A system of the second-order linear partial differential equations of hyperbolic type was solved in the process of modeling. The inertia properties and attenuation in the medium were taken into consideration. Fast-operating locally recursive nonlocally asynchronous parallel algorithms were used in the modeling, which were developed at the Keldysh Institute of Applied Mathematics of the Russian Academy of Sciences for modeling of plasma processes. At present, these algorithms are adapted for modeling of geophysical fields. A computing system consisting of two computers based on eight-core processors is used for computations. As a result, instantaneous pictures of microseism field propagation were constructed at the specified cross sections of the medium at sequential time moments, and the microseism’s frequency spectra and synthetic seismograms were obtained for some characteristic points of aqueous medium, bottom sediment, and land. The considered algorithms of full-wave numerical modeling and the computing system can be easily adapted to the 3D variant of anisotropic and inhomogeneous media specified by analytical expressions.

Improving the Accuracy of FDTD Approximations to Tangential Components of the Coupled Electric and Magnetic Fields at a Material Interface

The finite-difference time-domain (FDTD) method is one of the most popular tools used for modeling important electromagnetic wave propagation and scattering problems. Of the many variations on the basic formulation, conventional orthogonal schemes remain prevalent because of their high level of accuracy and relative ease of implementation. Inaccuracies do persist, however, and in this paper a simple, computationally efficient remedy to an error that occurs when simulating waves that impinge on a material interface is identified. The detail of when and how the error occurs is illustrated using a simplistic interface scenario, with an analytic electric field being used to drive a single FDTD magnetic field update step. The resulting FDTD approximations are compared to the analytic solution to reveal the extent of the error. The proposed modification is then introduced and its remedial effect shown by repeating the above comparison using the modified FDTD equations. The broader effects of the proposed modification are demonstrated using a practical, 3D, full-wave FDTD forward modeling tool, taking scenario examples from the application area of ground penetrating radar (GPR). It is concluded that the overall accuracy of conventional, orthogonal FDTD schemes is improved, without unduly increasing their computational burden or algorithmic complexity.

Full-wave modeling of the O–X mode conversion in the Pegasus toroidal experiment

The ordinary–extraordinary (O–X) mode conversion is modeled with the aid of a 2D full-wave code in the Pegasus toroidal experiment as a function of the launch angles. It is shown how the shape of the plasma density profile in front of the antenna can significantly influence the mode conversion efficiency and, thus, the generation of electron Bernstein waves (EBWs). It is therefore desirable to control the density profile in front of the antenna for successful operation of an EBW heating and current drive system. On the other hand, the conversion efficiency is shown to be resilient to vertical displacements of the plasma as large as ±10 cm.

Study of an optical nanolens with the parallel finite difference time domain technique

[1] In this paper a three-dimensional dispersive finite difference time domain based on the message passing interface architecture is applied for the full wave modeling of a metallic nanolens operating at optical frequencies. The subwavelength imaging potential of the nanodevice is thoroughly studied. The issue of symmetry in the nanolens is exploited, which is shown to have a direct result at the dynamic behavior of the nanolens.