An FFT-based footprint pattern synthesis from a rectangular planar array of isotropic antennas by modifying the amplitude, phase and the state (‘on’/‘off’) of the array elements using differential evolution algorithm has been presented. Three different footprints of rectangular, square and circular boundaries are generated from the array while maintaining a satisfactory lower peak sidelobe level and ripple. The method greatly reduces the computational time than the conventional method of calculating beam patterns. The dynamic range ratio of the excitation amplitudes are kept below a threshold level to reduce the design complexity of the attenuators at the feed network level and to minimize the effect of mutual coupling among the array elements. Copyright © 2013 John Wiley & Sons, Ltd.

The effects of thermal-dissipation structure on the thermal performance of nanoscale InGaP/GaAs collector-up heterojunction bipolar transistors were investigated by using the advanced hybrid optimization technique, a combination of the three-dimensional finite-element method for temperature-distribution analysis and the technology computer-aided design tool for power-performance evaluation. Through adequately locating the thermal-dissipation structure at the rear side of the transistor and via effective thickness-thinning procedures, which reduce foundry cost, the thermal coupling between collector fingers has been greatly ameliorated and a power-added efficiency of 45% is achieved. Copyright © 2013 John Wiley & Sons, Ltd.

The convergence rate of iterative methods can vary in an unpredictable way. It is related to the matrix condition number, which is notoriously bad for the electric field integral equation in the large-scale electromagnetic problems. Therefore, an efficient direct solution—a multilevel compressed block decomposition (MLCBD) algorithm based on the adaptive cross-approximation algorithm—is applied to overcome this problem; it is very efficient for the monostatic problems. Simulation results of the objects up and below ground in half space demonstrate that the proposed MLCBD method is efficient for analyzing electromagnetic problems. Copyright © 2013 John Wiley & Sons, Ltd.

This paper presents two sequential sampling algorithms for the macromodeling of parameterized system responses in model-dependent sampling frameworks. The construction of efficient algorithms for the automatic selection of samples for building scalable macromodels of frequency-domain responses is addressed in this paper. The sequential sampling algorithms proposed here are tailored toward the application of local scalable macromodeling schemes on unstructured design space grids. Two pertinent examples are considered. For the first one, different algorithms are applied, and a comparison is made in terms of the number of samples generated, accuracy and CPU time. As a second example, four design variables are taken into account with one of the proposed algorithms, and the generated model is used in a frequency-domain optimization. Copyright © 2013 John Wiley & Sons, Ltd.

A comprehensive study on semiconductor laser characteristics under gigabit-per-second digital modulation is presented. Comparison of the modulation characteristics under both formats of the return to zero (RZ) and non-return to zero (NRZ) bit formats is introduced. The modulation characteristics include the eye diagram, turn-on jitter (TOJ) and frequency chirp. The study elucidates how the laser modulation performance changes with variation of the modulation bit rate relative to the maximum bit rate and the setting bit rate of the relaxation oscillations. The relative contributions of the intrinsic noise of the laser and the pseudorandom bit-pattern effect to the modulation characteristics are differentiated. The results showed that when the bit rate is higher than the setting bit rate, the eye diagram is partially closed and becomes completely closed when the bit rate increases beyond the maximum bit rate. When the bit rate is higher than 2.25 Gbps, the TOJ values under NRZ modulation are smaller than those under RZ modulation near the threshold level. Under both RZ and NRZ formats, chirp increases with the bit rate with the chirp under the RZ format being higher than that under the NRZ format. Copyright © 2013 John Wiley & Sons, Ltd.

In the framework of silicon (Si) technology, evolution towards high-frequency analog applications – which involves innovative solutions such as SiGe BiCMOS and FinFET devices – wide bandgap semiconductors grown on Si substrates are likely to represent a valid option in those cases wherever high-power handling and low noise figures are required. Although such active devices have been extensively investigated in the last years, much of interest has been devoted in developing nonlinear models for high-power applications, whereas reliable noise models still lack, in particular, the validity of traditional (i.e. equivalent temperature-based) approaches for noise modeling of wide bandgap devices has not been sufficiently probed yet.

In this contribution, a quite general, black box noise model of active devices is proposed and applied to a family of gallium nitride-on-Si high-electron-mobility transistors fabricated by Selex ES. The model is based on a polynomial approximation of the device correlation matrix and does not require that an accurate small-signal equivalent circuit is available; instead, it can be extracted from multifrequency source pull data. Experimental results demonstrate that a typical behavior of the noise parameters is obtained, both versus frequency and gate periphery. Copyright © 2013 John Wiley & Sons, Ltd.

Because the permittivity, permeability, and chirality parameters of chiral metamaterials (CMMs) are frequency dependent, the wave equations that describe the characters of electromagnetic wave propagation in CMMs are presented and discretized on the basis of auxiliary differential equation technique in finite-difference time-domain method. The total-field/scattered-field, Mur's first-order absorbing and dielectric boundary conditions for CMMs slab are discussed in the paper. Numerical results show that the cross-polarized reflected coefficient of the CMMs slab is zero. Negative index of refraction phenomenon and optical property of giant optical activity in CMMs slabs are illustrated with 1D auxiliary differential equation–finite-difference time-domain method. The effects to positive or negative phase velocity caused by media parameters of CMMs are studied. Copyright © 2013 John Wiley & Sons, Ltd.

In this article, quantum-dot semiconductor optical amplifiers (QD-SOAs) have been modelled using state space method. To derive this model, we have manipulated the rate equation model of the QD-SOA, where the average values of the occupation probabilities along the QD-SOA cavity are considered as the state variables of the system. Using these variables, the distance dependence of the rate equations is eliminated. The derived state space model gives the optical gain and output signal of the amplifier with a high accuracy. Simulation results show that the derived model is not only much simpler and faster than conventional rate equation models, but also the optical gain and output signal of the investigated QD-SOA are calculated with a higher precision compared to the rate equation model. Copyright © 2013 John Wiley & Sons, Ltd.

A novel algorithm is proposed for solving coupled Maxwell and Schrödinger equations relying on the use of a length gauge form of the coupling between an electromagnetic field and electrons. Numerical simulations using codes implemented with the proposed and conventional algorithms have been performed for a harmonic model of a nanoplate subjected to a pulsed laser field whose central frequency is close to the plasmon frequency. We verify that the proposed algorithm can reduce computational time almost by half as compared with the conventional method. Copyright © 2013 John Wiley & Sons, Ltd.

We establish the deflection functions of electrostatically actuated micro beams by an approximate finite element method (AFEM), in which the beam and the electrostatic load are discretized. The beam is replaced with a series of beam elements by traditional FEM. Using the total differential of the distributed electrostatic force, we represent such a force with the nodal forces on the beam elements. We calculate the deformation curve of the beam by gradually loading voltage in small increments, and pull-in behavior is identified when the convergence of the deflection iteration cannot be achieved after voltage increment. The proposed method considers the effect of deformation on stiffness by establishing a new equivalent stiffness matrix for each voltage step based on of the results of previous steps. Through this approach, we prevent the approximate errors of the stiffness matrix from accumulating. The AFEM results on micro beams with different geometries indicate good agreement with those obtained by other studies and those derived using commercial FE software. Copyright © 2013 John Wiley & Sons, Ltd.

In the paper, an electrothermal compact model of monolithic switching-mode voltage regulators belonging to the TOPSwitch family is proposed. The description of this model and some results of the experimental verification of its correctness on the example of the regulator TOP222Y are presented. The proposed model can be used to calculate the terminal voltages and currents of the investigated device and the internal temperature of this regulator, too. The satisfying agreement between the calculated and measured characteristics of the switching-mode power supply including the considered integrated circuit was reached. Copyright © 2013 John Wiley & Sons, Ltd.

On the basis of the exact solution of Poisson's equation and Pao–Sah double integral for long-channel bulk MOSFETs, a continuous and analytic drain current model for the undoped gate stack (GS) surrounding-gate (SRG) metal–oxide–semiconductor field-effect transistor (MOSFET) including positive or negative interface fixed charges near the drain junction is presented. Considering the effect of the interface fixed charges on the flat-band voltage and the electron mobility, the model, which is expressed with the surface and body center potentials evaluated at the source and drain ends, describes the drain current from linear region to saturation region through a single continuous expression. It is found that the surface and body center potentials are increased/decreased in the case of positive/negative interface fixed charges, respectively, and the positive/negative interface fixed charges can decrease/increase the drain current. The model agrees well with the 3D numerical simulations and can be efficiently used to explore the effects of interface fixed charges on the drain current of the gate stack surrounding-gate MOSFETs of the charge-trapped memory device. Copyright © 2013 John Wiley & Sons, Ltd.

Microring resonator (MRR)-based channel dropping filters have been extensively explored because of the high quality factor, compact size, and easy integration of fabrication. In order to design an excellent MRR wavelength filter, optimization of the design parameters are essential. In this paper, the design trade-off of MRR-based channel dropping filter was statistically studied by employing the Taguchi method. Four control factors considered were width of rings and channels, radii of the microring, upper rib waveguide height, and gap size. The analysis of variance was adopted to analyze significant trends that occurred on the free spectral range (FSR) and insertion loss (IL) performance under different sets of control factor combinations. The best parametric combination of control factors was identified in order to achieve a balance performance between large FSR and low IL using Finite-Difference Time Domain (FDTD) simulation by RSoft Inc. After optimization, the value of FSR and IL obtained was 17 nm and 0.245 dB, respectively. Confirmation tests were carried out to verify the optimized parametric combinations and a new parametric combination considering both outputs were 16 nm and 0.215 dB. The optimal combinations were 6 µm ring radius with the separation gap of 50 nm and 350 nm × 350 nm rib waveguide cross section. Copyright © 2013 John Wiley & Sons, Ltd.

This paper describes the shaped-beam synthesis of phased arrays using the cross entropy (CE) method. The CE method is a general stochastic optimization technique based on minimizing the CE (or Kullback–Leibler divergence) between sets of probability distributions to solve complex multi-extremal, multi-objective optimization problems. In this work, the CE method will be utilized to choose the complex weights of array element excitations to control the shape of far-field radiation pattern side lobe power, main lobe beamwidth, and introduce side lobe notches using amplitude-only and complex weight synthesis. Compared with similar stochastic techniques previously used to solve this problem, such as the genetic algorithm and particle swarm optimization, the CE method is a competitive alternative, possessing attractive convergence properties. Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, a full-band Monte Carlo simulator is employed to study the dynamic characteristics and high-frequency noise performances of a double-gate (DG) metal–oxide–semiconductor field-effect transistor (MOSFET) with 30 nm gate length. Admittance parameters (Y parameters) are calculated to characterize the dynamic response of the device. The noise behaviors of the simulated structure are studied on the basis of the spectral densities of the instantaneous current fluctuations at the drain and gate terminals, together with their cross-correlation. Then the normalized noise parameters (P, R, and C), minimum noise figure (NF_min), and so on are employed to evaluate the noise performances. To show the outstanding radio-frequency performances of the DG MOSFET, a single-gate silicon-on-insulator MOSFET with the same gate length is also studied for comparison. The results show that the DG structure provides better dynamic characteristics and superior high-frequency noise performances, owing to its inherent short-channel effect immunity, better gate control ability, and lower channel noise. Copyright © 2013 John Wiley & Sons, Ltd.

Interturn short circuit faults are the leading cause of power transformer failures. If not quickly detected, these faults usually develop into more serious faults, which would result in irreversible damage to the transformer, unexpected outages, and consequential costs. The aim of this research is to obtain a better understanding of the physical behavior of the power transformers in the presence of interturn faults as well as to discover the best indicators for detection of interturn short circuit faults. To this end, a time stepping finite element model of power transformer has been developed to analyze the transient behavior of a real power transformer when the transformer is working under winding short circuit fault conditions. The transient model, coupled with external circuit equations, allows us to simulate the dynamic behavior of the transformer with the real power supply and external loads connections. The FEM computations show the ability of the electromagnetic flux inside the transformer, transformer terminal currents, and circulating current in the shorted turns as useful monitoring parameters for transformer fault detection. Copyright © 2013 John Wiley & Sons, Ltd.

The interconnect layouts of chips can be modeled by large resistor networks. In order to be able to speed up simulations of such large networks, reduction techniques are applied to reduce the size of the networks. For some class of networks, an existing reduction strategy does not provide sufficient reduction in terms of the number of resistors appearing in the final network. In this paper, we propose an approach for obtaining a further reduction in the amount of resistors. The suggested approach improves sparsity of the conductance matrix by neglecting resistors that do not contribute significantly to the behavior of the circuit. Explicit error bounds, which give an opportunity to control the errors due to approximation, have been derived. Numerical examples show that the suggested approach appears promising for multi-terminal resistor networks, and in combination with the existing reduction strategy, leads to better reduction. Copyright © 2013 John Wiley & Sons, Ltd.

Infrared (IR) sensors are widely used in thermal imaging and sensor applications. The performance of IR sensor is strongly dependent on the noise currents of the sensor. If characteristics of the noise currents are known prior to the costly and time-consuming sensor production phase, high performance IR sensors could be obtained rapidly and cost effectively. In this study, a p–n long-wave IR mercury cadmium telluride sensor is evaluated at 77 K using a physics-based numerical modeling and simulation approach. Results of the study showed that 1/f noise originating from the trap-assisted tunneling dominates as the cut-off wavelength and the magnitude of the applied reverse bias voltage increase. Copyright © 2013 John Wiley & Sons, Ltd.

This paper investigates the electrical performance of innovative carbon-based nano-interconnects made by carbon nanotubes and graphene nanoribbons. The electronic transport in the carbon materials is modeled in the frame of the Transmission Line theory, where the classical per-unit-length circuital parameters are corrected by new terms arising from the quantistic nature of the transport. These parameters are related to the number of the conducting channels and the mean free path, which in turn, are expressed as functions of temperature and size. By coupling this model to the heat equation, a simple electro-thermal model is derived. Case-studies are carried out with reference to 22-nm technology node applications. Copyright © 2013 John Wiley & Sons, Ltd.

A simple generalized theory is developed for optical gain of nonparabolic semiconductor lasers based on the three-band model of Kane, by taking into account the wave-vector () dependence of the optical matrix element. The gain in laser of nonparabolic semiconductors is demonstrated, by taking InAs, InSb, Hg_1−xCd_xTe and In_1−xGa_xAs_yP_1−y lattice matched to InP as examples, and it has been found that the peak of the gain spectra for a given carrier density is higher in the three-band model of Kane than those with parabolic energy band approximations in all the cases. The difference between the peak of gain spectra for three-band model and the parabolic band model is greater for laser of narrow band gap materials in comparisons with that of laser of wide band gap materials, thereby reveals the necessity for inclusion of the nonparabolicity in modeling lasers of small band gap materials. The well-known results for wide band gap materials having parabolic energy bands has also been obtained from our generalized formulation under certain limiting condition. Copyright © 2013 John Wiley & Sons, Ltd.

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.

This paper presents a novel predictive direct torque control for doubly fed induction machine based on indirect matrix converter (IMC), which is characterized by its simple structure, minimal-torque ripple, and constant switching frequency. Nowadays, the control strategies based on predictive methods have proved their efficiency to improve drive systems capabilities. So, in this paper, one of the best predictive methods that have recently been suggested for doubly fed induction machine drive systems is applied to IMC. The purpose of this combination is to modify the control parameters and size/volume reduction of drive system structure, which is difficult to achieve in conventional systems based on voltage source inverters. The good tracking behavior with reduced torque and flux ripple for both motoring and generating modes as well as removing bulky electrolytic capacitor from the DC link of a converter resulted by using three vectors, two active vectors together with one zero vector per switching period, and applying these vectors to the inverter stage of IMC. To improve the motor drive system performance and reduce losses caused by snubber circuits, the rectifier four-step commutation method in rectifier bridge is used. In the inverter stage, the predictive direct torque control method is employed. The simulation results of the proposed model confirm its effectiveness and accuracy. Copyright © 2013 John Wiley & Sons, Ltd.

In this paper, a numerical model of electromagnetic left-handed metamaterials is proposed. The dispersive properties of these materials are accounted for in the time domain by using the transmission-line matrix method based on Z-transforms. The close agreements obtained between the analytic and numerical results verify the validity, accuracy and stability of the approach. Copyright © 2013 John Wiley & Sons, Ltd.

An effective device structure for thermal management of multifinger InGaP/GaAs collector-up heterojunction bipolar transistors (HBTs), compelling active components in high-efficiency handset power amplifiers, is presented for the first time. From the unique 3-D thickness-adjusting numerical analysis, based on a finite element model, the miniaturized device can lead to a greater than 40% reduction in the thickness of plated gold layer. Above all, this is quite different from previous attempts, in which the thermal resistance was reduced by increasing the thickness of plated gold layer. Compared with literature works, the thermally stable design with an innovative heat-spread configuration shows a 50% reduction in thermal resistance and demonstrates favorable power performance. Copyright © 2013 John Wiley & Sons, Ltd.

A reliable methodology for accurate modeling of microwave filter is presented. Our approach exploits co-kriging that utilizes low-fidelity and high-fidelity electromagnetic simulation data and combines them into a single surrogate model. Densely sampled low-fidelity data determine a trend function, which is further corrected by sparsely sampled high-fidelity simulations. Low-fidelity electromagnetic data are also enhanced by using a frequency scaling to reduce its misalignment with the high-fidelity model. With our method, accurate models can be obtained at a fraction of the cost required by conventional approximation models that are exclusively based on high-fidelity simulations. Three examples of microstrip filters are considered for verification purposes. We also provide comparisons with conventional approximation models and include an application of co-kriging models for filter design optimization. Copyright © 2013 John Wiley & Sons, Ltd.

A novel stable anisotropic finite-difference time-domain (FDTD) algorithm based on the overlapping cells is developed for solving Maxwell's equations of electrodynamics in anisotropic media with interfaces between different types of materials, such as the interface between anisotropic dielectrics and dispersive medium or perfect electric conductor (PEC). The previous proposed conventional anisotropic FDTD methods suffer from the late-time instability due to the extrapolation of the field components near the material interface. The proposed anisotropic overlapping Yee FDTD method is stable, as it relies on the overlapping cells to provide the collocated field values without any interpolation or extrapolation. Our method has been applied to simulate electromagnetic invisibility cloaking devices with both anisotropic dielectrics and PEC included in the computational domain. Numerical results and eigenvalue analysis confirm that the conventional anisotropic FDTD method is weakly unstable, whereas our method is stable. Copyright © 2013 John Wiley & Sons, Ltd.

The electromagnetic modeling of antennas and radio frequency devices has become increasingly challenging as the applications demand intricate and complex designs, such as fine features embedded in electrically large structures or integrated systems (e.g., antennas on vehicles). Often the design stage is further challenged by the need to find an optimal solution, which results in a numerically intensive problem. The objective of this paper is to investigate the use of graphics processing units (GPUs) in such challenging design and optimizations. Two full-wave approaches (method of moments and rigorous coupled wave analysis) are discussed along with a bio-inspired optimization technique, namely the particle swarm optimization. The inherent parallel nature of the GPUs is utilized in implementing the most numerically intensive parts of these full-wave methods. Furthermore, the independent search mechanism employed by the particle swarm optimization in its agent-based search renders itself to parallelism offered by GPUs. The paper demonstrates the acceleration achieved by the GPUs in designing a variety of radio frequency structures such as reconfigurable patch antennas and antireflective surfaces. Copyright © 2013 John Wiley & Sons, Ltd.

The meshless radial point interpolation method (RPIM) in frequency domain for electromagnetic scattering problems is presented. This method promises high accuracy in a simple collocation approach using radial basis functions. The treatment of high-order non-reflecting boundary conditions for open waveguides is discussed and implemented up to fourth-order. RPIM allows the direct calculation of high-order spatial derivatives without the introduction of auxiliary variables. High-order absorbing boundary conditions offer a choice of absorbing angles for each degree of spatial derivatives. For general applications, a set of these absorbing angles is calculated using global optimization. Numerical experiments show that at the same computational cost, the numerical reflections of the absorbing boundary conditions are much lower than conventional perfectly matched layers, especially at high angles of incidence. Copyright © 2013 John Wiley & Sons, Ltd.

This paper proposes a new technique to train neural network (NN); with the result, we can solve some real-world application problems such as microwave components modeling and optimization. Its major advance is achieved in avoiding the testing error falling into local minimum. After the generalization, the ability of three-layer and four-layer NN is also checked; our investigations show that four-layer NN trained by the proposed training method can map the electromagnetic simulation of microwave components better than its counterpart. Besides, the modeling of microwave circuits and slotted patch antennas is examined to demonstrate the validity of this technique. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we present a free and open source platform by using the equivalent-circuit finite-difference time-domain (FDTD) method adapted to cylindrical coordinates to efficiently model cylindrically shaped objects. We will address the special characteristics of a cylindrical FDTD mesh such as the mesh singularity at r = 0 and discuss how cylindrical subgrids for small radii can reduce the simulation time considerably. Furthermore, we will demonstrate the applicability and advantages of this cylindrical equivalent-circuit FDTD method to evaluate new types of conformal ring antennas used in the context of high-field (7T) traveling wave magnetic resonance imaging (MRI). Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, the design and simulation of a tactile display that is based on a capacitive micromachined ultrasonic transducer (CMUT) array is presented. The array implements a ‘pixel’ of the display and is used to focus airborne ultrasound energy on the skin surface. The pressure field generated by the focused ultrasound waves excites the mechanoreceptors under the skin and transmits tactile information. The geometry of the individual transducer and the array are optimized so that the medium presents maximum impedance and the membrane oscillates with maximum deflection. Optimization is achieved using an electrical equivalent circuit model and the Berkeley Simulation Program with Integrated Circuit Emphasis (SPICE) code. Finite element analysis of the CMUT and the CMUT phased array is used to verify the SPICE results. The pressure at focal point is compared with the pressure threshold required for mechanoreceptor excitation in order to verify the feasibility of the design. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we propose the optimization of the parameters of a hybrid antenna for wireless applications by using a multi-objective evolutionary programming (EP). Specifically, the antenna proposed is formed by a planar inverted-F antenna and a coplanar patch, in the same structure. The objective functions to carry out the optimization process are related to the antenna's bandwidth and the gain requirements in the wireless applications considered. In fact, the antenna is intended to be used in mobile and WIFI applications simultaneously. To be concise, we have utilized an improved fast EP optimization approach that includes a selection mechanism based on nondominated ranking procedure with crowding distance to maintain diversity in the population. In the experimental part of the paper, we show that the multi-objective EP–improved fast EP is able to obtain excellent results in the parameters' design of this hybrid device, with reasonable values of both bandwidth and gain values. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, electrical–thermal modeling of through-silicon via (TSV) arrays is presented. In order to address the thermal effect on TSVs, TSV array design and modeling need to take into account the effect of realistic system thermal profile to meet design budget. To obtain temperature estimation for a 3D system, cascadic multigrid method is employed using an initial guess obtained by simulation using equivalent thermal conductivity to represent critical regions. By considering the thermal effect on electrical conductivities of TSV conductor and silicon substrate, the electrical–thermal modeling of TSV array in the interposer is carried out using cylindrical modal basis functions. The temperature effect on TSV insertion loss, crosstalk, and RLCG parameters are discussed with examples along with correlation with measurements. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents a multiobjective differential evolution (MODE) algorithm for designing concentric ring arrays with three-dimensional (3D) beam scanning. The problem formulation of the concentric ring arrays with 3D beam scanning based on the optimization of the array geometry is a constrained multiobjective optimization problem. To obtain 3D beam scanning, concentric ring array geometries are optimized. The design tradeoffs, namely, the directivity, peak sidelobe level, and the total number of elements of the concentric ring array, are captured by using MODE. MODE adopts an external archive to retain nondominated solutions that are found during the evolutionary process. The method yields the distribution of the objective function values and the corresponding array configurations. In addition, the nondominated sorting genetic algorithm-II (NSGA-II), which is a well-known multiobjective evolutionary algorithm, is also employed to optimize the proposed problems. The comparison with the results of NSGA-II reveals the superiority of the MODE approach and confirms its potential for the array synthesis problems. Copyright © 2012 John Wiley & Sons, Ltd.

The aim of this manuscript is to present the application of an iterative method based on the concept of transverse wave to analyze the packaging (passive element and substrate) miniaturization effect on the characteristics of an active planar circuit structure. This approach consists in the substitution of the active element by one auxiliary source, and connection is assumed by microstrip line as passive element deposited on one unique substrate. An implementation of the presented theory is shown by extraction of S-parameters and impedances of the active circuit using MATLAB program codes. Copyright © 2012 John Wiley & Sons, Ltd.

The commutating machines have a notable effect on the exchanges in brush–commutator contact area, which is particularly obvious when determining the intensity of sparks located on the brush. With time, higher current density at the descending edge promote sparks excitation, which itself increases intensity of the electrical erosion, brush temperature and thus also the wear. So in order to make an analytical study of commutation phenomenon, the coupled circuit method was developed. Therefore, a generalized mathematical model of the commutation, for brush–commutator, is established and can be extended for any other types of commutation on the basis of electromagnetic field (e.g. transformers and phase shift transformer. This model provides a greater efficiency to explain the impact of the electromagnetic fluxes surrounding brush area (or switch), specially for the current transition of the commutation process. Successful commutation is defined as operation in normal service, with no serious damages to the commutator, brushes or switches due to sparking that might require abnormal maintenance. It is recognized that some visible sparking are not evidence of unsuccessful commutation. The recommendation to improve the commutation (to achieve longer brush life) is the implementation of the proposal (slotted brush), which provides a linear and a sweet transition of currents in the coils of commutation. Copyright © 2012 John Wiley & Sons, Ltd.

The solution of large and complex electromagnetic (EM) problems often leads to a substantial demand for high-performance computing resources and strategies. This is true for a wide variety of numerical methods and applications, ranging from EM compatibility to radio-coverage, circuit modeling, and optimization of components. In the last decades, graphics processing units (GPUs) have gained popularity in scientific computing as a low-cost and powerful parallel architecture. This paper gives an overview of the main efforts of researchers to port computational electromagnetics (CEM) codes to GPU. Moreover, GPU implementation aspects of two well-known techniques, namely the finite-difference time domain (FDTD) and the method of moments (MoM), are investigated. The impressive speed-ups achieved (up to 60× and 25× for FDTD and MoM, respectively) demonstrate the effectiveness of GPUs in accelerating CEM codes. Copyright © 2012 John Wiley & Sons, Ltd.

The use of graphic processor units (GPUs) has been recently proposed in computational electromagnetics to accelerate the solution of the electric field integral equation. In these methods, the linear systems obtained by using boundary elements are considered, and then an accelerated solution for a specific excitation is obtained. The existing studies are mostly focused on speeding up the filling time or the LU decomposition of that matrix. This limits the application to simple simulation scenarios if a fast method is not employed. In this paper, we propose a GPU acceleration for FFT-based integral equation solvers. We will investigate the operations involved in the solver, and we will motivate the use of GPUs. Results of numerical tests will be reported firstly on a perfect electric conductor sphere with different radii; then a realistic aircraft will be considered. We found that using GPUs for FFT-based methods allows achieving a reasonable speed-up. Copyright © 2012 John Wiley & Sons, Ltd.

An indirect boundary element method that is geared to electrostatic field analysis in voxel models is accelerated by graphics processing units (GPUs). The method considers square walls on cubic voxels as boundary surface elements and uses the fast multipole method (FMM) to analyze large-scale models. On the basis of two conventional CPU codes, three GPU codes are programmed in search of higher computing performance. These GPU codes are designed as follows: In GPU code 1, direct and far fields in the FMM are simultaneously calculated on the GPU and the CPU, respectively; in GPU code 2, both fields are calculated on the GPU with a rotation-coaxial translation–rotation decomposition algorithm; and in GPU code 3, both fields are calculated on the GPU with a diagonal translation scheme. The electric fields in human models are generated by applying a 50-Hz magnetic field or by injecting direct-current (DC) current through two electrodes and they were calculated successfully using a personal computer with three GPUs and six CPU cores. An analysis with 3.9 million surface elements took 89.4 s to solve its governing linear system with double-precision floating-point arithmetic. GPU codes 1, 2, and 3 demonstrated the least memory usage, the greatest speed-up ratio, and the fastest calculation time, respectively. These results show an example of the trade-off relationships of computation performances on a heterogeneous CPU–GPU system. Copyright © 2013 John Wiley & Sons, Ltd.

The evolution of processors into multi-core architectures has led to the acceleration of scientific codes using numerous highly specialized processors, that is, multi-core central processing units (CPUs), graphics processing units (GPUs) and also devices that merge both technologies in a single-die chip. Development of parallel codes that are both scalable and portable between the processor architectures is challenging. To overcome this limitation, we investigated the acceleration of the finite-difference time-domain (FDTD) method in computational electromagnetics on modern computing architectures, that is, multi-core CPUs and GPUs, through the use of Open Computing Language (OpenCL). Further extension of the OpenCL parallel programing model with the Message Passing Interface allows for the targeting of standard distributed memory computer clusters as well as clusters accelerated by GPUs. Portability between hardware manufactured by different vendors and highly specialized and parallel computing architectures is the main advantage of the developed FDTD solvers. The codes were coupled with a commercial simulation platform to evaluate the performance of the solvers in real-world industrial scenarios. Although the portability resulted in a slightly reduced performance (10–35%) of the OpenCL-accelerated FDTD simulations compared with the native Compute Unified Device Architecture or Open Multiprocessing implementations, the obtained benchmarking results of the OpenCL FDTD solvers on distributed memory systems show that the communication overhead can be hidden by computations for sufficiently large simulation domains with a scaling efficiency higher than 90%. Copyright © 2012 John Wiley & Sons, Ltd.

We have developed a micromagnetic simulator for graphical processing units (GPU), using the CUDA framework. In this paper, we discuss the optimization of the effective field calculation, both from a mathematical and from a hardware-specific point of view. By using a finite-difference discretization scheme, the long-range magnetostatic field can be calculated using fast Fourier transforms, an approach well suited for the GPU. We show how the implementation can be tuned to the GPU hardware and how the performance can be further increased by dealing with the large number of zeros that typically occurs in the micromagnetic field computation. Additionally, we show how the ferromagnetic exchange interaction can be readily included in the magnetostatic field calculation without any additional computational cost. The resulting high-performance software can be used to run large-scale simulations that would have been very time-consuming on regular CPU hardware. As an example, we present a case study on the de-pinning of domain walls in racetrack memory devices. Copyright © 2012 John Wiley & Sons, Ltd.

This paper discusses the practical implementation on graphics processing unit (GPU) of a computer code for the analysis of electromechanical devices. The software is based on a low frequency integral formulation of the Maxwell equations coupled with the rigid body dynamic equations. The formulation here considered is based on the development of an equivalent network whose parameters are functions of the relative positions and of the velocities of the subparts of the device. Positions and velocities on their turn depend on the force between them that are functions of the electromagnetic quantities. The choice of the numerical methods to manage such a complex coupled problem is an open issue in the electromagnetic community. The use of multicore CPUs can reduce the computation times, but a true breakthrough is achieved by running these codes on GPUs. The practical implementation of an existing code is used as a case study for discussing a number of issues that may arise in the implementation of other GPU-accelerated electromagnetic codes. The implementation here reported has been designed for a multi-GPUs environment where the efficient cooperation between GPUs is a further aspect to be considered. The overall performance of the accelerated code has been evaluated by considering the dynamic analysis of a passive magnetic bearing. Copyright © 2012 John Wiley & Sons, Ltd.

Physics-based fluid simulation has been widely used in manufacture and entertainment industry. However, numerically solving the three-dimensional incompressible fluid equation is an expensive computation task. Recently, the general purpose graphics hardware allows to speed up the numerical computations. To this end, we explore a new unified particle model on a multi-graphics processing unit (GPU) platform for interactive fluid simulation. In this paper, we present a parallel framework for fluid simulation with smoothed particle hydrodynamics. To begin with, we discuss the characteristics of storage dependence, data dependence, and decomposition method based on particles. And then, we design the computation model of simulation including kernel functions, adaptive time step, force, and pressure equations. The unified particle model not only ensures the mass and momentum conservation of simulation but also protects the volume of fluid and allows larger time steps, thus alleviating the calculation burden, contributing to the real-time simulation. Moreover, an effective parallel architecture based on the multi-GPU is implemented. For the fluid scene, the spatial domain is automatically partitioned into grid layers and assigned to multiple GPUs subsequently. A dynamic load balancing algorithm and an asynchronous data transferring strategy are proposed and implemented. Furthermore, we propose an adaptive density model for particle surface reconstruction. Finally, the quality and performance of the method are demonstrated using multiple scenes with different numbers of particle. Copyright © 2013 John Wiley & Sons, Ltd.

General purpose computation on graphics processing units is becoming very important as a means for speeding up numerical computations. In this research, nVidia's Compute Unified Device Architecture (CUDA) language is used along with a graphics processing unit to accelerate the generation of the system matrix for the numerical solution of a partial differential equation employing radial basis functions. Details of the CUDA implementation as well as speedup curves using several different graphics processing units will be discussed. Copyright © 2012 John Wiley & Sons, Ltd.