Using WCS‐FDTD method to simulate various cylindrical metallic enclosures

The weakly conditionally stable (WCS) finite‐difference time‐domain (WCS‐FDTD) method in the cylindrical coordinate system is employed to compute the electromagnetic coupling and shielding of various cylindrical enclosures. In the WCS‐FDTD method, a larger time‐step size than that allowed by the Courant–Friedrich–Levy stability condition limitation can be set because the algorithm of this method is WCS. Consequently, an increase in computational efforts caused by fine cells due to thin sots can be prevented. The results from the WCS‐FDTD method agree well with the results from the conventional FDTD method, and the required CPU time for the WCS‐FDTD method is much shorter than that for the FDTD method. Careful investigation of different aspects of the shielding properties of the cylindrical enclosures is performed, and the shielding performance of the cylindrical enclosure and rectangular enclosure is compared. The result obtained in this paper can be used to design a practical cylindrical shielding enclosure. Copyright © 2010 John Wiley & Sons, Ltd.     

Modeling of ultra‐wideband indoor channels with the modified leapfrog ADI‐FDTD method

Full‐wave time‐domain electromagnetic methods are usually effective in rigorously modeling and evaluating ultra‐wideband (UWB) wireless channels. However, their computational expenditures are expensive, when they are used to deal with electrically large‐size problems consisting of fine structures. In order to reduce computational time, the unconditionally stable leapfrog alternating‐direction implicit finite‐difference time‐domain (leapfrog ADI‐FDTD) method has been proposed recently. In this paper, the leapfrog ADI‐FDTD algorithm is developed for simulating lossy objects, such as office walls, floors, and ceilings, for UWB communication channel characterization. It leads to effective UWB channel characterization with power‐decay time constant, path loss exponent, and probability distribution of power gain. In comparison with the conventional FDTD, the proposed method can achieve 60% saving in computational time while retaining good accuracy. Copyright © 2014 John Wiley & Sons, Ltd.     

FDTD method for site attenuation analysis of compact anechoic chamber using large‐cell concept

In this paper, the FDTD method has been applied to analyze the site attenuation of an anechoic chamber at 100 MHz or less where the ray tracing method is not applicable. To calculate site attenuation by a personal computer, the dipole antenna and the EM absorber were modeled using a large cell which was larger than the diameter of the antenna element and the thickness of the EM absorber. The equivalent diameter of the antenna element was determined so that the calculated site attenuation in free space agreed with that by the method of moments, and the equivalent dielectric constant and permeability of the absorber were determined so that the reflection coefficient agreed with that by the transmission theory. The site attenuation of the compact anechoic chamber was calculated for frequencies from 30 MHz to 100 MHz and compared with the measured one to confirm the validity of the proposed modeling method. The results indicated that the deviation between the calculated values and the measured ones was within 2 dB. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(4): 9–16, 2008; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20411     

Efficient analysis of ridged cavity by modal FDTD method

A modal finite‐difference time‐domain (FDTD) method is extended for the analysis of ridged cavities, which are uniform in the z‐direction. Assuming that the end surfaces of cavity are the perfect conductor, thus, the fields along the z‐axis can be described by k_z. Therefore, three‐dimensional (3‐D) problems can be simulated by the use of a two‐dimensional model. Besides, to achieve a faster computation, the field components are expressed by two pairs of equations—sine and cosine. To validate the utility and efficiency of proposed method, we analyzed two ridged cavities. Numerical results show that less than one‐tenth memory and CPU requirements are needed by the modal FDTD as compared with conventional 3‐D FDTD method. Copyright © 2012 John Wiley & Sons, Ltd.     

Wide‐band modelling of CMOS interconnections and voiding damages with the lumped element LE‐FDTD method

This paper illustrates the application of a lumped element‐finite difference time domain (LE‐FDTD) simulator to the wide‐band modelling of CMOS interconnections. To achieve very accurate results the short‐open calibration (SOC) technique has been adopted. Specific parameters of a CMOS interconnection laterally screened by a stack of metal vias have been extracted in the two cases of an unperturbed and a purposely damaged metal line. The behaviour of void‐like defects in the metal line has been also studied using the fully three‐dimensional capabilities of the simulator. It has been demonstrated that, at least in the simulated cases, only the specific resistance is affected by damaging. Copyright © 2004 John Wiley & Sons, Ltd.     

Modified Z‐transform‐based FDTD algorithm for the anisotropic perfectly matched layer

A modified Z‐transform‐based algorithm for implementing the D‐H anisotropic perfectly matched layer (APML) is presented for truncating the finite‐difference time‐domain (FDTD) lattices. The main advantage is that, as compared with the previous Z‐transform‐based implementation for the D‐H APML, the proposed algorithm requires less auxiliary variables in the PML regions, and thus the memory requirement and the computational time are saved. These formulations are simple and independent of the material properties of the FDTD computational domain. Two numerical tests have been carried out to validate these formulations. Copyright © 2007 John Wiley & Sons, Ltd.     

Exact stability conditions in upwinding‐scheme FDTD for the Boltzman transport equation

An in‐depth stability analysis of the FDTD method under the upwinding scheme for the Boltzmann transport equation (BTE) under the relaxation time approximation is provided. Both time forward and time backward difference equations are considered. In the time forward differencing case, a sufficient stability condition is derived for the BTE with variable coefficients, and a necessary and sufficient condition is derived for the BTE with constant coefficients. In the time backward differencing case, it is shown that the differencing equations are unconditionally stable. It is shown numerically that the previously reported stability conditions in the literature are not accurate. Copyright © 2013 John Wiley & Sons, Ltd.     

PML absorbing boundary condition for the integral‐based high‐order FV24 FDTD algorithm

An integral equations‐based perfectly matched layers (PML) implementation is presented for the highly phase‐coherent FV24 finite‐difference time‐domain (FDTD) algorithm. The implementation allows including field values off the grid axes in the split‐field PML formulation conserving in the process the continuity and phase coherency of the FV24 algorithm when modeling absorbing boundary conditions (ABCs). It also eliminates the need for cumbersome subgridded low‐order FDTD subregions that until now were required to model PML ABCs within integral‐based high‐order FDTD simulations. The developed approach was numerically tested and found to match the PML behavior of the standard FDTD method at normal wave incidence on ABC boundaries and exceeds it at highly oblique wave incidence. This development serves to improve the capability and practicality of the computationally efficient FV24 algorithm when modeling electrically large structures in 3‐D space. Copyright © 2010 John Wiley & Sons, Ltd.     

Broadband characteristics analysis of semicircle‐type bow‐tie antenna with hole slots

For electromagnetic compatibility, broadband antennas are important for measurements of fast pulse transient electromagnetic phenomena and broadband characteristics due to noise and high‐frequency interference. We analyzed the characteristics of a semicircle type bow‐tie antenna with various slots using the FDTD method. It was shown from the simulation results that the shape and position of the slot influenced greatly the broadband characteristics of the antenna. We confirmed that a semicircle type bow‐tie antenna with a triangle slot was effective for a broadband antenna. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 47–53, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20252     

Fourth‐order hybrid implicit and explicit‐FDTD method

A fourth‐order hybrid implicit and explicit finite‐difference time‐domain Method has been presented in this paper. This new method investigates the use of a second‐order accurate in time and a fourth‐order accurate in space. The 2D formulation of the method is presented and the time stability condition of the method is certified. The maximum time step size in this method is only determined by one spatial discretization. The numerical dispersion is discussed. Numerical examples demonstrate that when this method is used to solve electromagnetic problems, higher computational efficiency and less dispersion error can be obtained by comparing with the traditional finite‐difference time‐domain algorithm. Copyright © 2015 John Wiley & Sons, Ltd.     

Extending the enlarged cell and uniformly stable conformal techniques to modeling curved conductors in two‐dimensional high‐order finite‐difference time‐domain algorithms

The critical tool of modeling irregularly shaped perfect conductors is developed for the extended‐stencil high‐order two‐dimensional M24 variant of the finite‐difference time‐domain (FDTD) method. Two standard FDTD conformal approaches are analyzed and successfully extended to work accurately with M24. They both afford higher order convergence with respect to mesh density than a previously developed technique, which better matches M24's characteristics. Both approaches rely on borrowing weighted electromotive forces from nearby extended‐stencil cells to ensure accuracy and numerical stability while the overall algorithm is efficiently operated at the maximum allowable time steps by FDTD and M24 theories. Validation examples demonstrate that M24's amplitude and phase accuracies using coarse numerical meshes were not compromised. Copyright © 2012 John Wiley & Sons, Ltd.     

Numerical analysis of electrical logging‐while‐drilling tool using propagator matrix method

In this paper, a propagator matrix method applied to logging‐while‐drilling tools is introduced and extended to deal with the anisotropic and radially inhomogeneous earth formations. This method expands the Maxwell's equations in the transverse direction, constructs the relationship between propagator matrix and reflection matrix, and obtains the solution by using the reflection matrix. We systematically derived the formulas of propagator matrix method in isotropic media, uniaxially anisotropic media, fully anisotropic media, and radially inhomogeneous media respectively. In order to obtain the propagator matrix in complex media, we used the fourth‐order Runge–Kutta scheme. Numerical experiments show that, compared with traditional methods, the propagator matrix method has wide range of applications while maintaining low computational costs and high accuracy. All algorithms presented in the paper have been parallelized and implemented on a high‐performance computing platform. Copyright © 2012 John Wiley & Sons, Ltd.     

The method of lines for the analysis of composite‐metal lossy microstrip lines

A full‐wave analysis of the composite‐metal microstrip lines is presented. The effects of the composite metal to the loss of the microstrip lines are accurately investigated, which are often avoided by other methods. The metal layers of the microstrip lines are considered as lossy inhomogeneous layers. The effects of the thickness of the Au layer and Ti layer are given, respectively. And the reasons that lead to the differences between them are discussed for the first time by analyzing the longitudinal electric field on the strip. The results are compared with other published data. Copyright © 2010 John Wiley & Sons, Ltd.     

Data‐Driven Controller Tuning for Nonminimum Phase Plants with Stability Constraints

This paper addresses the model reference control problem, which is a typical control problem found in data‐driven controller tuning methods. For nonminimum phase plants, the unstable zeros of the plant should be included in the reference to avoid destabilization of the resulting closed‐loop system and improve tracking performance. First, we propose a data‐driven controller tuning method with closed‐loop stability taken into consideration and with the tuned controller parameters in the time domain. If the plant has unstable zero(s), the proposed method would not lead to destabilizing controller in the worst case. Closed‐loop stability is checked using linear inequalities described with input/output data. This contributes to reducing computation in the proposed method. Moreover, this paper proposes a data‐driven controller tuning method for nonminimum phase plants estimating the unstable zero(s) using a flexible reference model at each parameter update and reflecting them into the resulting reference model. The effectiveness of the proposed method is confirmed through numerical experiments.     

Transient analysis of printed lines using finite‐difference time‐domain method

Comprehensive studies of ultra‐wideband pulses and electromagnetic coupling on printed coupled lines have been performed using full‐wave 3D finite‐difference time‐domain analysis. Effects of unequal phase velocities of coupled modes, coupling between line traces, and the frequency dispersion on the waveform fidelity and crosstalk have been investigated in detail. To discriminate the contributions of different mechanisms into pulse evolution, single and coupled microstrip lines without (ϵ_r = 1) and with (ϵ_r > 1) dielectric substrates have been examined. To consistently compare the performance of the coupled lines with substrates of different permittivities and transients of different characteristic times, a generic metric similar to the electrical wavelength has been introduced. The features of pulse propagation on coupled lines with layered and pedestal substrates and on the irregular traces have been explored. Physical interpretations of the simulation results are discussed in the paper. Copyright © 2012 John Wiley & Sons, Ltd.     

Investigation of numerical time‐integrations of Maxwell's equations using the staggered grid spatial discretization

The Yee‐method is a simple and elegant way of solving the time‐dependent Maxwell's equations. On the other hand, this method has some inherent drawbacks too. The main one is that its stability requires a very strict upper bound for the possible time‐steps. This is why, during the last decade, the main goal was to construct such methods that are unconditionally stable. This means that the time‐step can be chosen based only on accuracy instead of stability considerations. In this paper we give a uniform treatment of methods that use the same spatial staggered grid approximation as the classical Yee‐method. Three other numerical methods are discussed: the Namiki–Zheng–Chen–Zhang alternating direction implicit method (NZCZ), the Kole–Figge‐de Raedt method (KFR) and a Krylov‐space method. All methods are discussed with non‐homogeneous material parameters. We show how the existing finite difference numerical methods are based on the approximation of a matrix exponential. With this formulation we prove the unconditional stability of the NZCZ method without any computer algebraic tool. Moreover, we accelerate the Krylov‐space method with a skew‐symmetric formulation of the semi‐discretized equations. Our main goal is to compare the methods from the point of view of the computational speed. This question is investigated in ID numerical tests. Copyright © 2005 John Wiley & Sons, Ltd.     

A uniformly stable conformal FDTD‐method in Cartesian grids

A conformal finite‐difference time‐domain algorithm for the solution of electrodynamic problems in general perfectly conducting 3D geometries is presented. Unlike previous conformal approaches it has the second‐order convergence without the need to reduce the maximal stable time step of conventional staircase approach. A novel proof for the local error rate for general geometries is given, and the method is verified and compared to other approaches by means of several numerical 2D examples. Copyright © 2003 John Wiley & Sons, Ltd.     

A locally conformal FDTD analysis of a thin printed antenna for wideband wireless applications

A compact wideband planar‐printed antenna for wireless communications is presented. A suitable shape of the antenna arms and a proper tapering of the feeding line are employed to achieve an impedance bandwidth of more than 10 GHz useful to meet the requirements of several wireless communication standards. An enhanced locally conformal finite‐difference time‐domain (FDTD) numerical procedure, based on a suitable normalization of the electromagnetic field‐related quantities together with a near‐to‐far‐field transformation, is developed to perform the full‐wave analysis of the radiating structure. The proposed numerical procedure allows the accurate evaluation of the electromagnetic field distribution from the FDTD domain up to the far‐field region, achieving a reduced computational burden compared with conventional FDTD formulations. Using the proposed technique, the electromagnetic and circuital behaviour of the antenna is then derived and analyzed in detail. Numerical results concerning the antenna parameters are in good agreement with experimental measurements. Copyright © 2010 John Wiley & Sons, Ltd.     

Large‐scale magnetic field analysis by the hybrid finite element‐boundary element method combined with the fast multipole method

This paper describes a large‐scale magnetic field analysis by means of the hybrid finite element‐boundary element (FE‐BE) method. The hybrid FE‐BE method is well‐suited for solving open electromagnetic field problems that comprise movement, nonlinear media, and eddy current. In general, however, large memory and computational costs are required due to the dense blocks in the system matrix generated by the BE part of the hybrid formulation. In order to overcome the above difficulties, we introduce the fast multipole method (FMM) to the hybrid FE‐BE formulation developed by ourselves. Furthermore, we propose a novel preconditioning technique suitable for the hybrid FE‐BE method with the FMM. Some numerical results that demonstrate the effectiveness of the proposed approach are also presented. ©2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(1): 73–80, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20508     

Convergence properties of bias‐eliminating algorithms for errors‐in‐variables identification

This paper considers the problem of dynamic errors‐in‐variables identification. Convergence properties of the previously proposed bias‐eliminating algorithms are investigated. An error dynamic equation for the bias‐eliminating parameter estimates is derived. It is shown that the convergence of the bias‐eliminating algorithms is basically determined by the eigenvalue of largest magnitude of a system matrix in the estimation error dynamic equation. When this system matrix has all its eigenvalues well inside the unit circle, the bias‐eliminating algorithms can converge fast. In order to avoid possible divergence of the iteration‐type bias‐eliminating algorithms in the case of high noise, the bias‐eliminating problem is re‐formulated as a minimization problem associated with a concentrated loss function. A variable projection algorithm is proposed to efficiently solve the resulting minimization problem. A numerical simulation study is conducted to demonstrate the theoretical analysis. Copyright © 2005 John Wiley & Sons, Ltd.