Implementation of the stretched co‐ordinate‐based PML for waveguide structures in TLM

A novel implementation of the stretched co‐ordinate‐based perfectly matched layer (SCB PML) is presented to terminate waveguide structures in transmission‐line modelling (TLM). A generalized SCB PML, the complex frequency shifted PML (CFS PML) is also implemented to investigate its performance for evanescent waves. State variables in the Z‐domain are employed to obtain update equations for incident voltage pulses. Numerical results for a rectangular waveguide filled with a lossy medium as well as free space, and for a parallel plate waveguide are presented. Copyright © 2004 John Wiley & Sons, Ltd.     

Analysis of quadruple corner‐cut ridged elliptical waveguide by scaled boundary finite element method

The scaled boundary FEM (SBFEM) is a novel semi‐analytical approach, which combines the advantages of the FEM and BEM with appealing features of its own. In this paper, the method is applied to analyse the quadruple corner‐cut ridged elliptical waveguide. A quarter of the waveguide is adopted and divided into a few subdomains. SBFEM only discretizes the surface boundaries of the subdomains in the sense of FEM, and no discretization of side‐face boundaries is needed, leading to great flexibility in mesh generation with very few nodes. It transforms the governing PDEs to ODEs of the radial parameter by the variational principle. The radial differential equation is then solved fully analytically without adoption of any numerical scheme, which brings out the inherent advantage for solving a singularity problem. Based on the SBFEM governing equation and introducing the dynamic stiffness of waveguide, a generalised eigenvalue equation with respect to cut‐off wave number is formulated by a continued fraction solution without introducing an internal mesh. The numerical example demonstrates the simplicity, excellent computation accuracy and efficiency of the present SBFEM approach. Influences of corner‐cut ridge dimensions on the cut‐off wave numbers of modes are examined in detail. Therefore, these results provide an extension to the existing design data for ridged waveguides and are considered helpful in practical applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of quadruple corner‐cut ridged square waveguide by hybrid mode‐matching boundary‐element method

In this paper, the square waveguide with quadruple corner‐cut ridges is analyzed using the hybrid mode‐matching boundary‐element method. Because of its symmetry, only a quarter of its cross‐section needs to be considered and it is then divided into three regions. The electromagnetic field components in two regular regions can be obtained using the mode‐matching method and the third irregular region is discretized using the boundary‐element method. The combination of two methods produces one matrix equation, from whose determinant the cutoff wavenumbers of waveguide modes can then be computed. This hybrid technique takes advantage of the mode‐matching method's high efficiency and the boundary‐element method's versatility. The convergence of this hybrid method is studied, and numerical results are compared with the conventional boundary‐element method and commercial finite‐element software package, which shows that our hybrid method can achieve the same accuracy with much less time. The influence of the cut‐corners on the cutoff wavenumbers of the dominant and higher‐order modes is then examined. A simple approximate equation is found to accurately predict the cutoff wavenumber of TE₂₀ mode. The single‐mode bandwidth of a quadruple ridged square waveguide is calculated thereafter, which shows that this corner‐cut structure can provide a broader bandwidth compared to the one without cut‐corners. Copyright © 2010 John Wiley & Sons, Ltd.     

A comparison of numerical methods for the full‐wave analysis of flange mounted rectangular apertures

The analysis and design of small‐ and medium‐sized aperture antenna arrays is an important task in the development of many microwave systems, and is computationally heavy due to the typical requirements for efficiency and accuracy. Several approaches have already been proposed in the literature, but they have not been compared so far in terms of their computational efficiency. In this paper, we compare different methods, either based on rectangular waveguide modes to expand the field over the aperture, or based on Gegenbauer's polynomials for singular fields representation. Their numerical properties are studied, and their performance compared. It is concluded that similar accuracies are achieved, whilst the approach using the spectral‐domain rectangular waveguide mode formulation is the more robust, and should be considered for the development of general purpose software packages. Copyright © 2000 John Wiley & Sons, Ltd.     

Quasi‐TEM Rectangular Waveguides with Frequency Selective Surface Walls: Part II—Physical Mechanism

The physical mechanism of quasi‐TEM (transverse electromagnetic) waveguides with frequency selective surface (FSS) walls is established on the basis of an equivalent magnetic current technique in this paper. The equivalent magnetic current distributions in the slots of dielectric surfaces with dipole‐FSS walls and dielectric surface of bare‐slab, as well as hexagonal crystal FSS walls, are presented and discussed. This study shows that the electromagnetic fields in waveguide are mainly radiated from the concurrent magnetic current bands in longitudinal slots. The relationship between the uniformity of electromagnetic fields and the phase variation of longitudinal magnetic currents is discussed. The electrical properties and mechanism of quasi‐TEM rectangular waveguides with slotlines are also investigated to confirm the proposed mechanism. Three categories of periodic structure, which are potentially useful as artificial magnetic conductor, are investigated, and the required conditions to realize quasi‐TEM mode in rectangular waveguide are proposed. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Efficient optimization‐oriented design methodology of high‐order 3‐D filters using 2‐D and 3‐D electromagnetic simulators

This paper proposes a computationally highly efficient interface between two‐dimensional (2‐D) and three‐dimensional (3‐D) electromagnetic (EM) simulators for the optimization‐oriented design of high‐order 3‐D filters. In a first step, the novel optimization‐oriented design methodology aligns the 3‐D EM simulator response with the 2‐D EM simulator response of a low‐order 3‐D filter by using an inverse linear space mapping optimization technique. Then, a second mapping performs a calibration with the optimal 2‐D and 3‐D design parameters obtained from the first mapping. The optimization of high‐order filters is carried out using only the efficient 2‐D EM simulator, and the calibration equations directly give the design parameters of the 3‐D filter. The potential and the effectiveness of the proposed optimization‐oriented design methodology are demonstrated through the design of C‐band 3‐D evanescent rectangular waveguide bandpass filters with increasing orders from three to eight. Copyright © 2014 John Wiley & Sons, Ltd.     

A GSM analysis of E‐plane waveguide junctions filled with piecewise homogeneous dielectric

A specific generalized scattering matrix (GSM) approach to the analysis of a piecewise homogeneous E‐plane waveguide junction with plane interfaces is presented. The object is cascaded into homogeneously filled regions, whose GSMs are found in solving two uncoupled scalar problems related to longitudinal section electric and magnetic modes, and interfaces responsible for interaction of the said modes. The GSMs of irregular constituents are determined with the help of triangular blocks. Scattering parameters of the last ones are obtained by means of the domain‐product technique. The approach was successfully verified via test problems and was applied to the analysis of scattering of the TE₁₀ mode by an E‐plane slant interface between two dielectric media. Copyright © 2011 John Wiley & Sons, Ltd.     

Design and analysis of power‐CMOS‐gate‐based switched‐capacitor DC–DC converter with step‐down and step‐up modes

A unified multi‐stage power‐CMOS‐transmission‐gate‐based quasi‐switched‐capacitor (QSC) DC–DC converter is proposed to integrate both step‐down and step‐up modes all in one circuit configuration for low‐power applications. In this paper, by using power‐CMOS‐transmission‐gate as a bi‐directional switch, the various topologies for step‐down and step‐up modes can be integrated in the same circuit configuration, and the configuration does not require any inductive elements, so the IC fabrication is promising for realization. In addition, both large‐signal state‐space equation and small‐signal transfer function are derived by state‐space averaging technique, and expressed all in one unified formulation for both modes. Based on the unified model, it is all presented for control design and theoretical analysis, including steady‐state output and power, power efficiency, maximum voltage conversion ratio, maximum power efficiency, maximum output power, output voltage ripple percentage, capacitance selection, closed‐loop control and stability, etc. Finally, a multi‐stage QSC DC–DC converter with step‐down and step‐up modes is made in circuit layout by PSPICE tool, and some topics are discussed, including (1) voltage conversion, output ripple percentage, and power efficiency, (2) output robustness against source noises and (3) regulation capability of converter with loading variation. The simulated results are illustrated to show the efficacy of the unified configuration proposed. Copyright © 2003 John Wiley & Sons, Ltd.     

Absorbing boundary conditions for the FD‐TLM method : the perfectly matched layer and the one‐way equation technique

This paper investigates the absorbing boundary conditions for the frequency domain transmission line matrix method. Two approaches are presented, namely the perfectly matched layer (PML) technique and the one‐way wave equation. Concerning the PML technique, two‐dimensional and three‐dimensional transmission line matrix (TLM) nodes, already used in time domain, are exploited in frequency domain where a rigorous formulation of these PML–TLM nodes is presented. In addition, two types of one‐way wave operators are also transposed from time to frequency domain TLM approach: Taylor expansion and Higdon's boundary conditions. The simulation of a wideband matched load WR‐28 rectangular waveguide is presented for validation. Excellent results are obtained with a very thin PML layer. Results concerning one‐way operator techniques also show very good return loss performances. For instance, Higdon's boundary condition was extended beyond third‐order approximation, and a return loss better than 160 dB was obtained. Copyright © 2013 John Wiley & Sons, Ltd.     

Steady‐state stability of shaft torsional oscillation in an ac‐dc interconnected system with self‐commutated converters

Recent progress in power electronics technology makes it possible to consider applying self‐commutated converters using gate turn‐off thyristors (GTOs) to HVDC transmission systems. Since the self‐commutated converter can be operated stably without depending on ac‐side voltage, the magnitude and the phase angle of the converter output voltage can be controlled independently. Therefore, this type of converter will improve voltage stability at its ac side. On the other hand, shaft torsional oscillation of a thermal power plant caused by the interaction between the shaft‐generator system and the control system of the self‐commutated converter is still an open problem. In this paper, a linearized model for eigenvalue analysis of a power system, including HVDC interconnection with self‐commutated converters, is described to analyze the effect of the self‐commutated converter on the shaft torsional oscillation of a thermal power plant. Then, numerical results from the eigenvalue analysis of the shaft torsional oscillation are presented. Results obtained by the frequency response method are also reported. The numerical results make it clear that parameter regions of DC‐AVR and ACR control systems of self‐commutated converters exist where the shaft torsional oscillation may be caused. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 25–37, 1999     

Silicon nanorods‐based all‐dielectric waveguides with long decay‐length at the telecommunication band

We investigate subwavelength waveguides composed of silicon nanorods array in straight and nonstraight regimes deposited on a silica (SiO₂) substrate. It is shown that using all‐dielectric nanorods with high permittivity to design an all‐dielectric optical waveguide provides several advantages such as low‐dissipation coefficient and long decay length for the distributed fields. Exploiting silicon arrays in touching and nontouching arrangements, we examined the optical response of the structure to the guiding of magnetic and electric fields with transverse and longitudinal polarization modes. We studied the decay length for all propagated modes in both nanochain orientations numerically. Simulation results for straight arrays showed that the averaged decay length for the structure with dielectric particles in touching regime is 1.6 µm (for the waveguide with the length of 2.2 µm), and for the nontouching array is 2.2 µm (for the array with the length of 3.1 µm). Calculating transmission loss factors and considering decay length of the proposed waveguide, we verified the strong potential of the proposed structure to design all‐dielectric photonic devices to operate at telecommunication spectra (λ~1310 nm and 1550 nm). Also, we computed bending losses [dB] for the examined structures based on the bends degree. Copyright © 2015 John Wiley & Sons, Ltd.     

Technologies and applications of Al‐free high‐power laser diodes

We report high‐power technologies in 0.8‐µm Al‐free InGaAsP/InGaP laser diodes. To realize the high‐power operation, the improvement of catastrophic optical mirror damage (COMD) power density level is required. In addition to the use of low surface recombination velocity of Al‐free materials, optimization of waveguide thickness in broad waveguide structure with tensile‐strained barriers and current blocking structure near facets has led to high COMD power density level. Highly stable operation of Al‐free laser diodes with these structures has been obtained over 2500 hours at 2 W from a stripe width of µm. Applications of high‐power laser diodes are also described. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(1): 53–59, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20286     

Monte Carlo simulation for stochastic calculus of far‐field radiation from open‐ended waveguide arrays

In this paper, Monte Carlo (MC) simulation has been applied for the analysis and stochastic calculus of far‐field radiation from the small, large, and infinite open‐ended waveguide arrays. Elements of the arrays are excited by the fundamental TE₁₀ mode and with equal amplitude and linear phase. The simulated results from MC are compared closely with the finite element method (FEM). Numerical analysis based on FEM is performed using Ansoft High Frequency Structural Simulator to calculate the far‐field radiation characteristics of the arrays. The accuracy and the effectiveness of the aforesaid method, which is based on Monte Carlo integration technique, are also demonstrated in uniformly and nonuniformly spaced waveguide arrays for pattern synthesis or achieving side lobe level reduction. The arrays with arbitrary shapes are simply evaluated by MC method in equal spacing array. It is found that by applying MC simulation, the open‐ended waveguide arrays have the ability to produce the desired radiation pattern and could satisfy requirements for many applications. Copyright © 2016 John Wiley & Sons, Ltd.     

Performance Comparison of Scramjet‐Driven Experimental DCW‐MHD Generators with Different Cross‐Sections

The purpose of this study is to examine the influence of the shape of the cross‐section of a scramjet engine‐driven experimental diagonal conducting wall (DCW)‐MHD generator on generator performance by three‐dimensional numerical analyses. We have designed MHD generators with symmetric square and circular cross‐sections, based on an experimental MHD generator with an asymmetric square cross‐section. Under the optimum load conditions, the electric power output reaches 26.6 kW for the asymmetric square cross‐section, 24.6 kW for the symmetric square cross‐section, and 22.4 kW for the circular cross‐section. The highest output is obtained for the experimental generator with the asymmetric square cross‐section. The difference in the electric power output is induced by the difference of flow velocity and boundary layer thickness. For the generator with the asymmetric square cross‐section, the average flow velocity is highest and the boundary layer is thinnest. The compression wave is generated with dependence on the channel shape. The difference in the flow velocity and boundary layer thickness is induced by the superposition of the compression wave. © 2014 Wiley Periodicals, Inc. Electr Eng Jpn, 187(2): 9–16, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22403     

Time‐domain sensitivity analysis of planar structures using first‐order one‐way wave‐equation boundaries

An efficient adjoint variable method technique is developed for time‐domain sensitivity analysis of planar structures with transmission‐line modeling complemented by a first‐order one‐way wave‐equation absorbing boundaries. A backward‐running adjoint simulation is derived and solved. The validity of the technique is illustrated through three microstrip circuits. The examples demonstrate the efficiency and accuracy of the technique in comparison with the classical finite‐difference approaches to the estimation of the response sensitivities. Copyright © 2007 John Wiley & Sons, Ltd.     

GRO‐TDC with gate‐switch‐based delay cell halving resolution limit

In this paper, we propose a time‐to‐digital converter (TDC) with first‐order noise‐shaping. The proposed gated ring oscillator (GRO)‐TDC overcomes the limitation associated with GRO's intrinsic resolution by adopting two GROs, whose delay difference is equal to half the delay of a delay cell. The GRO is composed of 17 stages of a newly proposed delay cell, which utilizes a gate‐switched configuration to solve the charge redistribution problem. The proposed GRO‐TDC is designed using a 65‐nm process technology, with an area of 0.015 mm² and a supply voltage of 1 V. The sampling rate and the effective resolution of the proposed GRO‐TDC are 50 MS/s and 1.22 ps, respectively. Finally, the proposed GRO‐TDC consumes a power of 9.08 and 2.41 mW in the calibration and conversion modes, respectively. Copyright © 2017 John Wiley & Sons, Ltd.     

Analysis and realization of a switched fractional‐order‐capacitor integrator

Using fractional calculus, we analyze a classical switched‐capacitor integrator when a fractional‐order capacitor is employed in the feed‐forward path. We show that using of a fractional‐order capacitor, significantly large time constants can be realized with capacitances in the feedback path much smaller in value when compared with a conventional switched‐capacitor integrator. Simulations and experimental results using a commercial super‐capacitor with fractional‐order characteristics confirmed via impedance spectroscopy are provided. Copyright © 2016 John Wiley & Sons, Ltd.     

Interactive display of vector fields inside waveguides

The educational software package WGVMAP has been developed to enable students to plot interactively the electric and magnetic field lines of TE and TM propagating modes in cylindrical waveguides. The waveguide cross-sections considered are rectangular, circular, sectoral, and circular with a conducting baffle. The vector field display and generation of the field lines can be performed on a very modest configuration of an IBM PC or compatible computer, and plotted on an x-y plotter. Examples are presented to demonstrate the interactive procedure for generating the field lines     

An analytical model of triple‐material double‐gate metal–oxide–semiconductor field‐effect transistor to suppress short‐channel effects

This paper presents an analytical subthreshold model for surface potential and threshold voltage of a triple‐material double‐gate (DG) metal–oxide–semiconductor field‐effect transistor. The model is developed by using a rectangular Gaussian box in the channel depletion region with the required boundary conditions at the source and drain end. The model is used to study the effect of triple‐material gate structure on the electrical performance of the device in terms of changes in potential and electric field. The device immunity against short‐channel effects is evaluated by comparing the relative performance parameters such as drain‐induced barrier lowering, threshold voltage roll‐off, and subthreshold swing with its counterparts in the single‐material DG and double‐material DG metal–oxide–semiconductor field‐effect transistors. The developed surface potential model not only provides device physics insight but is also computationally efficient because of its simple compact form that can be utilized to study and characterize the gate‐engineered devices. Furthermore, the effects of quantum confinement are analyzed with the development of a quantum‐mechanical correction term for threshold voltage. The results obtained from the model are in close agreement with the data extracted from numerical Technology Computer Aided Design device simulation. Copyright © 2015 John Wiley & Sons, Ltd.