Finite-difference time-domain method in custom hardware?

While the finite-difference time-domain (FDTD) method is very successful in electromagnetics, it is computationally intensive. Reducing the runtime of these simulations, by an order of magnitude or more, would greatly increase the productivity of FDTD users and open new avenues of research. A dedicated hardware implementation that accelerates FDTD computations could provide a means to attain that goal. As the first step, we have implemented a one- and two-dimensional FDTD method in hardware. The experiment proved that computational speed can be increased by as much as two orders of magnitude, and is independent of the number of cells in the simulation.     

Finite-difference time-domain analysis of a stacked dual-frequencymicrostrip planar inverted-F antenna for mobile telephone handsets

We describe a stacked, dual-frequency microstrip planar inverted-F antenna (DF-PIFA) for mobile telephone handsets that can concurrently work in two frequency-bands, viz., those associated with the GSM and DCS 1800 systems operating at 0.9 GHz and 1.8 GHz, respectively. The proposed microstrip DF-PIFA is fed by a coaxial line, as opposed to two separated feed lines used in the conventional design. The design is carried out in a systematic manner and involves two steps. We begin with an initial configuration of the PIFA that is based on a standard design for a microstrip patch antenna fed by a coaxial line and is derived from an empirical approximation in conjunction with a transmission line model. Next, we employ a computer-aided design (CAD) tool, based on the nonuniform finite-difference time-domain (NU-FDTD) Maxwell solver, to optimize the performance characteristics of the DF-PIFA, including the return loss, the matching of the input impedance, and the far-field radiation patterns     

Finite-difference time-domain analysis of integrated ceramic ball grid array package antenna for highly integrated wireless transceivers

This paper presents a study of the integration of an antenna in a ceramic ball grid array package for highly integrated wireless transceivers. The study has been carried out on an 11/spl times/11.66 mm/sup 2/ small microstrip antenna in a thin 48-ball ceramic ball grid array package with the finite-difference time-domain (FDTD) method in C band. The impedance and radiation characteristics of the antenna are examined. More importantly, the loading effects of the complementary metal-oxide-semiconductor (CMOS) chip and bond wires on the performance of the antenna are investigated. It is found that the loading generally increases the impedance bandwidth but decreases the radiation efficiency of the antenna. To minimize detrimental loading, the shield of the antenna from the CMOS chip is considered. A new design has been realized. The new antenna achieves impedance bandwidth of 4.65%, radiation efficiency of 63%, and gain of 5.6 dBi at 5.52 GHz.     

Finite-difference time-domain implementation of surface impedanceboundary conditions

Surface impedance boundary conditions can be utilized to avoid using small cells, made necessary by shorter wavelengths in conducting media throughout the solution volume. The standard approach is to approximate the surface impedance over a very small bandwidth by its value at the center frequency, and then use that result in the boundary condition. In this paper, two implementations of the surface impedance boundary condition are presented. One implementation is a constant surface impedance boundary condition and the other is a dispersive surface impedance boundary condition that is applicable over a very large frequency bandwidth and over a large range of conductivities. Frequency domain results are presented in one dimension for two conductivity values and are compared with exact results. Scattering width results from an infinite square cylinder are presented as a two dimensional demonstration     

Finite-difference time-domain algorithm for solving Maxwell'sequations in rotationally symmetric geometries

In this paper, an efficient finite-difference time-domain algorithm (FDTD) is presented for solving Maxwell's equations with rotationally symmetric geometries. The azimuthal symmetry enables us to employ a two-dimensional (2-D) difference lattice by projecting the three-dimensional (3-D) Yee-cell in cylindrical coordinates (r, φ, z) onto the r-z plane. Extensive numerical results have been derived for various cavity structures and these results have been compared with those available in the literature. Excellent agreement has been observed for all of the cases investigated     

Finite-difference time-domain analysis of HF antennas on helicopterairframes

In this paper, the finite-difference time-domain (FDTD) method with the Berenger perfectly matched layer (PML) absorbing boundary condition (ABC) is used to model the radiation characteristics of high frequency (HF) antennas operating in the 2-30 MHz range on a full-scale helicopter. The computed input impedance of both antennas is compared with actual measurements from an operational full-scale helicopter and also with measurements on a scale model NASA generic advanced attack helicopter (GAAH). To study the coupling effects of the helicopter fuselage on the antenna systems, the S-parameters are computed and compared with measurements on the NASA GAAH scale model. Finally, computed gain patterns are compared with actual in-flight measurements of the antenna systems on an operational full-scale helicopter     

Finite-difference time-domain analysis of flip-chip interconnectswith staggered bumps

This paper presents finite-difference time-domain (FDTD) analysis of flip-chip interconnects. Transitions between coplanar waveguides on the chip and the mother board are investigated over a broad band of frequency by means of Fourier transform of the time-domain results. Objectives of the analysis include the evaluation of bump reflection and insertion loss as well as the reconfiguration of the transition to improve package performance. Novel designs have been developed and presented to reduce the effects of package discontinuities and asymmetry. Staggering the bumps has been found to reduce reflection and insertion loss over a broad band of frequency. A reduction In bump reflection of up to 8 dB per transition can be achieved by staggering the ground and signal connects. The degradation in package performance due to structure asymmetry is also studied. The present designs have also been found to reduce the effects of flip-chip asymmetry on insertion and reflection losses     

Finite-difference, time-domain analysis of lossy transmission lines

An active and efficient method of including frequency-dependent conductor losses into the time-domain solution of the multiconductor transmission line equations is presented. It is shown that the usual A+B√s representation of these frequency-dependent losses is not valid for some practical geometries. The reason for this the representation of the internal inductance the at lower frequencies. A computationally efficient method for improving this representation in the finite-difference time-domain (FDTD) solution method is given and is verified using the conventional time-domain to frequency-domain (TDFD) solution technique     

Finite-difference time-domain analysis of the Celestron-8 telescope

Electromagnetic interference analyses of large complex systems demand large computational resources and give limited information on general types of systems. A finite-difference time-domain (FDTD) code was used to determine the response of a “generic” optical system to microwave radiation. A plane wave with a Gaussian pulse excitation was used along with “point sensors” within the system model to determine time and frequency response. In the low-frequency region, ramped sinusoidal excitation from a point within the sensor was used to determine angles of high sensitivity and field distributions within the sensor. From these field distributions, resonance modes were identified that are similar to those found in a simple cylindrical cavity     

Finite-difference approach to the solution of time-domain integralequations for layered structures

A numerical algorithm for the analysis of transient electromagnetic fields in planar structures is proposed based on the time-domain magnetic-field integral equation (MFIE), electric-field integral equation (EFIE), and the marching-on-in-time approach. The field vectors are represented in terms of vector potential functions which are calculated either by integration or by the three-dimensional (3-D) wave equation according to the geometry of the structure. Thus, the algorithm combines the advantages of integral equation techniques and finite-difference schemes. While this approach is applicable to any geometries, it is especially suitable for multilayered planar structures and is competitive to the finite-difference time-domain (FDTD) method in the case of open and radiating problems. Theoretical results are verified by the analysis of a pulse propagation in a homogeneous open-end microstrip line     

Finite-difference time-domain (FDTD) analysis of magnetic diffusion

Problems with very slow waveforms or very long diffusion times may be difficult to treat using finite-difference time-domain techniques because of the Courant stability condition. Problems of this class, however, often prove to have a response which does not depend on the speed of light. The examples presented here show cases where internal fields do not change if c is reduced by as much as five orders of magnitude. This permits Δt to be proportionally increased. For simplicity much of this paper is restricted to one dimension, although generalization to three dimensions is also presented. The author considers an aluminum enclosure. Initially, the transient field will induce eddy currents on the enclosure which exactly cancel the external field and exclude it from the enclosure interior. This scheme has been, in fact, proposed to shield large systems which contain magnetic memories     

Finite-difference time-domain modeling of curved surfaces [EMscattering]

The finite-difference-time-domain (FDTD) method is generalized to include the accurate modeling of curved surfaces. This generalization, the contour path CP), method, accurately models the illumination of bodies with curved surfaces, yet retains the ability to model corners and edges. CP modeling of two-dimensional electromagnetic wave scattering from objects of various shapes and compositions is presented     

Finite-difference and pseudospectral time-domain methods applied to backward-wave metamaterials

Backward-wave (BW) materials that have simultaneously negative real parts of their electric permittivity and magnetic permeability can support waves where phase and power propagation occur in opposite directions. These materials were predicted to have many unusual electromagnetic properties, among them amplification of the near-field of a point source, which could lead to the perfect reconstruction of the source field in an image [J. Pendry, Phys. Rev. Lett. vol. 85, pp. 3966, 2000]. Often systems containing BW materials are simulated using the finite-difference time-domain technique. We show that this technique suffers from a numerical artifact due to its staggered grid that makes its use in simulations involving BW materials problematic. The pseudospectral time-domain technique, on the other hand, uses a collocated grid and is free of this artifact. It is also shown that when modeling the dispersive BW material, the linear frequency approximation method introduces error that affects the frequency of vanishing reflection, while the auxiliary differential equation, the Z-transform, and the bilinear frequency approximation method produce vanishing reflection at the correct frequency. The case of vanishing reflection is of particular interest for field reconstruction in imaging applications.     

Finite-difference time-domain solution of Maxwell's equations forthe dispersive ionosphere

The application of the finite-difference time-domain (FDTD) technique to problems in ionospheric radio wave propagation is complicated by the dispersive nature of the ionospheric plasma. In the time domain, the electric displacement is the convolution of the dielectric tensor with the electric field, and thus requires information from the entire signal history. It is shown that this difficulty can be avoided by returning to the dynamical equations from which the dielectric tensor is derived. By integrating these differential equations simultaneously with the Maxwell equations, temporal dispersion is fully incorporated. An FDTD approach utilizing the vector wave equation is also presented. The accuracy of the method is shown by comparison for a special case for which an analytic solution is available. The method is demonstrated with examples of pulse propagation in one and two dimensions. The computational limitations of present-generation computers are discussed. The application of this approach to the study of wave propagation in randomly structured ionization is addressed     

Finite-difference time-domain analysis of laser diodes integratedwith tapered beam-expanders

Waveguide properties of laser diodes integrated with horizontally tapered beam-expanders are analyzed by the finite-difference time-domain method. The taper length dependence of the radiation loss and fiber-coupling efficiency are clarified. Lower loss and higher fiber-coupling efficiency are achieved in the exponentially tapered beam-expander compared with a linearly tapered one having an equivalent length     

A hybrid method combining the multitemporal resolution time-domain method of moments with the time-domain geometrical theory of diffraction for thin-wire antenna problems

In this paper, a hybrid method combining a multitemporal resolution (MTR) enhanced time-domain method of moments (TD-MoM) with the TD geometrical theory of diffraction (GTD) is presented, which allows to efficiently calculate the transient fields radiated by antennas in presence of large objects. The MTR scheme tailors the time step size-and thus implicitly the duration of the temporal basis function-on the basis of the distance between source and test element. Additionally, the voltage induced by source elements far away from the test element is interpolated in time. The hybrid method is applied to calculate the radiation properties of thin-wire antennas in presence of perfectly conducting flat scatterers to demonstrate its basic features and advantages.     

圆环天线的时域有限差分分析

采用时域有限差分算法（FDTD）计算了圆环天线在高斯脉冲激励下的瞬时电流分布，通过付里叶变换，获得天线在不同频率下的稳态电流分布，经过进一步计算，得出天线在这组频率下的辐射方向图和输入阻抗。     

Finite-difference time-domain simulation of scattering from objectsin continuous random media

A three-dimensional (3D) finite-difference time-domain (FDTD) scheme is introduced to model the scattering from objects in continuous random media. FDTD techniques have been previously applied to scattering from random rough surfaces and randomly placed objects in a homogeneous background, but little has been done to simulate continuous random media with embedded objects where volumetric scattering effects are important. In this work, Monte Carlo analysis is used in conjunction with FDTD to study the scattering from perfectly electrically conducting (PEC) objects embedded in continuous random media. The random medium models under consideration are chosen to be inhomogeneous soils with a spatially fluctuating random permittivities and prescribed correlation functions. The ability of frequency averaging techniques to discriminate objects in this scenarion is also briefly investigated. The simulation scheme described in this work can be adapted and used to help in interpreting the scattered field data from targets in random environments such as geophysical media, biological media, or atmospheric turbulence     

基于FDTD的罗兰-C信号地波传播特性的时域分析

罗兰-C信号为载波调制的高斯脉冲,而传统方法对其传播特性预测均是基于100 kHz单频信号结果。文章采用FDTD方法计算了实际罗兰信号的时域特性,并和100 kHz连续单频信号结果进行了比较。结果显示:对于地形起伏不大的传播路径,两种信号结果吻合得很好,而对于地形起伏较大路径,脉冲信号结果与单频信号结果存在较大差异。该结果对地波传播特性工程测量与分析具有一定指导意义。     

一种新的无源偶极子天线辐射效率测量方法

提出一种无源超高频(UHF)射频偶极子标签天线在自由空间中辐射效率的测量方法并通过仿真和实验对其验证。辐射效率是标签天线的一个重要性能参数,通过测量标签天线的3个基本参数,即方向性系数、实际增益和功率传输系数得出结果,最后对比仿真与实测结果,两者取得良好的一致性,验证了该方法是可靠的。该方法的一个主要优点是可以在实际应用环境中对标签天线辐射效率进行测量,具有广阔的潜力。