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ACES Journal February 2013

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ACES Journal Paper
Year: 2013      Volume: 28      Number: 2
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ACES Journal November 2017 Full

ACES Journal Paper
Year: 2017      Volume: 32      Number: 11
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ACES Journal June 2013 Full Issue

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ACES Journal Paper
Year: 2013      Volume: 28      Number: 6
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ACES June 2011 Full Journal

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ACES Journal Paper
Year: 2011      Volume: 26      Number: 6
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ACES Journal September 2012

ACES
ACES Journal Paper
Year: 2012      Volume: 27      Number: 9
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Numerical Solution of Electromagnetic Integral Equations by the Meshfree Collocation Method

B. Honarbakhsh, A. Tavakoli
ACES Journal Paper
Year: 2012      Volume: 27      Number: 9
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This paper presents guidelines for mesh free numerical solution of electromagnetic integral equations. Both static and dynamic problems are considered, including the EFIE and the MPIE for dynamic case. Different choices of the kind of meshfree method, shape functions and their parameters are studied and proper choices are suggested by logical deduction, experience or previous reports. The final configuration is applied to classical problems in one and two dimensions such as electric charge (density) and electric current (density) distributions over a line and flat plates, respectively. The method is validated by convergence analysis and is compared with MoM. In addition, suggestions are made for bypassing numerical integrations that make the construction of the coefficient matrix integration free.

Polarimetric Scattering from a 3-D Rectangular Crack in a PEC Covered by a Dielectric Layer

M. Bozorgi, A. Tavakoli
ACES Journal Paper
Year: 2011      Volume: 26      Number: 6
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A novel direct approach for calculation of the polarimetric scattering fields from a narrow 3-D rectangular crack in an infinite ground plane underneath a dielectric layer is presented. Since the electromagnetic fields are directly calculated and thus the approach in inversible, this technique is suitable for microwave NDT applications where cracks of narrow width, arbitrary length and depth under a dielectric layer are frequently encountered. A set of coupled field integral equations (FIE) with logarithmic and hypersingular kernels are derived and then descritized by a collocation method based on Chebyshev polynomials. The results of this direct approach are in good agreement with noninversible full numerical FEM and MoM results.

ACES Journal July 2012

ACES
ACES Journal Paper
Year: 2012      Volume: 27      Number: 7
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Analysis of Thin Microstrip Antennas by Meshless Methods

B. Honarbakhsh, A. Tavakoli
ACES Journal Paper
Year: 2012      Volume: 27      Number: 12
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In this paper, different meshless methods are applied to the analysis of microstrip antennas with thin substrate. Comparison is made between the performance of the methods with respect to convergence, CPU time and condition number of final coefficient matrix. The exact modal solution and method of moments are used for validation. The input impedance results of all methods are in agreement with each other.

ACES Journal December 2012

ACES
ACES Journal Paper
Year: 2012      Volume: 27      Number: 12
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The Meshless Local Boundary Equation Method

B. Honarbakhsh, A. Tavakoli
ACES Journal Paper
Year: 2012      Volume: 27      Number: 7
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A method similar to the local boundary integral equation method that preserves its properties and is free from singular integrals is proposed. The approach is based on selection of the weighting functions from a homogeneous solution of the problem rather than the fundamental solution. Many examples of 2D Laplace and Helmholtz equations and 3D vector wave equation are presented for verification. The method shows optimistic performance over piecewise smooth boundaries. Radial basis functions of thin plate spline type are used for meshless discretization. The dependable performance of the proposed method provides a hopeful applicability to numerical solutions of partial differential equations.

ACES Journal January 2014 Full Issue

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ACES Journal Paper
Year: 2014      Volume: 29      Number: 1
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Application of an IE-Based Domain Decomposition Method for Analysis of Planar Microstrip Array Structures: Meshless Approach

B. Honarbakhsh, A. Tavakoli
ACES Journal Paper
Year: 2015      Volume: 30      Number: 8
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In this paper, application of an integral equation based domain decomposition method (DDM), developed for numerical solution of one-dimensional Fredholm integral equations of the second kind, is extended to electric field and mixed potential integral equations in two dimensions. Even though the original DDM was developed based on the Nyström method, results of the present work shows that meshfree approach can also be utilized. The extended DDM is employed for efficient meshfree analysis of planar microstrip array structures in the sense of reduced-size shape function and stiffness matrices. Results are validated by method of moments.

Reduction of Mutual coupling in Microstrip Array Antenna using Polygonal Defected Ground Structure

A. Farahbakhsh, G. Moradi, S. Mohanna
ACES Journal Paper
Year: 2011      Volume: 26      Number: 4
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The surface wave propagation is a significant problem in microstrip array antennas. Several methods have been reported to suppress the propagation of surface wave such as defected ground structure (DGS). The main problem in DGS is to determine the shape of ground slot. In this paper, a new method is proposed in which the slot is assumed to be a polygon and its shape is obtained by enhanced genetic algorithm (GA) and ant colony optimization (ACO) to have an array antenna with good gain and the least amount of return loss and mutual coupling.

Ultra Low RCS Measurement Using Doppler Frequency Shift

E. S. Kashani, Y. Norouzi, A. Tavakoli, P. Dehkhoda
ACES Journal Paper
Year: 2014      Volume: 29      Number: 1
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A new clutter removal method is proposed for ultra-low RCS measurement in anechoic chamber. In the proposed method, the target is moved along the line of sight of the radar in a sinusoidal manner. This movement generates some Doppler frequency shift. At the receiver, a filter matched to this Doppler shifter signal is implemented digitally. While the matched filter removes clutter signal largely it preserves the echo from the moving target. As it is shown through analytic estimation as well as simulations, the method can attenuate the clutter and noise level far beyond previously suggested methods. It also removes some of the difficulties in higher frequencies that exist in previous methods.

A Comparative Study of Opposition-Based Differential Evolution and Meta-Particle Swarm Optimization on Reconstruction of Three Dimensional Conducting Scatterers

M. Maddahali, A. Tavakoli, M. Dehmollaian
ACES Journal Paper
Year: 2017      Volume: 32      Number: 9
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In this paper, opposition-based differential evolution and Meta-particle swarm optimization is applied to reconstruct three dimensional conducting scatterers. Rational Bezier surfaces are utilized to model the shape of the scatterers. The mathematical representation of this surfaces are expanded in terms of Bernstein polynomials. The unknown coefficients of these polynomials depend on a few control points in space. An optimization method is used to find the location of the control points such that a specific measure of the difference between radar cross section (RCS) of the reconstructed and the original target is minimized. Physical optics (PO) approximation is used to find the RCS of a reconstructed scatterer in each iteration of the proposed algorithm. Simulation results show that these algorithms are very stable in the presence of noise.

ACES Journal November 2016 Full

ACES
ACES Journal Paper
Year: 2016      Volume: 31      Number: 11
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ACES April 2011 Full Journal

ACES
ACES Journal Paper
Year: 2011      Volume: 26      Number: 4
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A Three-Conductor Transmission Line Model for MOS Transistors

F. Daneshmandian, A. Abdipour, R. Mirzavand
ACES Journal Paper
Year: 2015      Volume: 30      Number: 6
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An accurate high frequency small signal model for MOS transistors is presented. In the proposed model, by considering the layout of the MOS transistor, it is considered as a three-conductor transmission line. Then, a set of current-voltage equations are derived for the structure using the transmission line theory. These coupled equations are solved by the Finite-Difference Time-Domain (FDTD) technique in a marching-in-time process. To verify the model, the scattering parameters of a 0.13 m transistor are extracted from the time domain results over the 1–100 GHz frequency band and compared with the results obtained from the available models and commercial simulator. The suggested model can be useful in design of various types of high frequency integrated circuits.

Analytical Solution of Scattering by a 2D Dielectric Filled Crack in a Ground Plane Coated by a Dielectric Layer: TM Case

B. Ghalamkari, A Tavakoli, M. Dehmollaian
ACES Journal Paper
Year: 2013      Volume: 28      Number: 6
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In this paper, KP method is applied to study the scattering of a 2D loaded crack on a ground plane, coated by a dielectric layer for TM case. For simplicity, the geometry is divided into three regions, whose fields are expressed in terms of Bessel eigen functions. The governing equations involve several infinite summations with infinite number of unknown coefficients. By the use of Weber-Schafheitlin discontinuous integrals, these infinite summations could efficiently be truncated with high numerical accuracy. Boundary conditions are applied to determine unknown coefficients. We employ finite element method (FEM) and convergence analysis to confirm our results. Finally, the influence of coating dielectric layer and filling material is investigated on the scattered field.

Analytical Solution of Scattering by a 2D Dielectric Filled Crack in a Ground Plane Coated by a Dielectric Layer: TE Case

B. Ghalamkari, A. Tavakoli, M. Dehmollaian
ACES Journal Paper
Year: 2012      Volume: 27      Number: 11
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Analytical solution of scattering by a 2D loaded crack on a ground plane, coated by a dielectric layer for TE case is studied theoretically using Kobayashi and Nomura's (Kobayashi Potential) method. The geometry is divided into three regions whose fields are expressed in terms of Bessel eigenfunctions. The problem is reduced to a system of equations involving truncated summations with an infinite number of unknowns. Excitation coefficients are determined by applying the boundary conditions. By applying Weber- Schafheitlin discontinuous integrals, the infinite summations could efficiently be truncated with high numerical accuracy. For validation, in addition to convergence analysis, near-field magnetic current densities on the crack and the radar cross section (RCS) results are compared with those of Finite Element Method (FEM). Having the analytical method, the influence of the filling and the dielectric layer is investigated.

Efficient Electromagnetic Scattering Analysis of Open-ended Circular Cavities with Modal MoM Method

A. Aghabarati, P. Dehkhoda, A. Tavakoli
ACES Journal Paper
Year: 2016      Volume: 31      Number: 11
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An efficient and accurate technique is introduced to calculate the scattered electromagnetic (EM) fields from an open-ended circular cavity (OECC). In this paper, it is assumed that the OECC is perforated in an infinite perfect electric conductor (IPEC). Then, the scattered fields are calculated using modal Method of Moments. The complexity and computational cost of the encountered quadruple integrals are addressed in detail. Here, the singularities are extracted and resolved. Next, the scattered far field of a circular PEC plate of the same size is calculated by physical optics approximation. The final OECC scattered field is the sum of these two solutions. A very good agreement is observed between the results of this method and full wave numerical simulations and measurements. The proposed approach is highly efficient and accurate over a wide range of frequencies and incidence angles, making it appealing for analysis of large frequency dispersive structures.

Forward Scattering from a Three Dimensional Layered Media with Rough Interfaces and Buried Object(s) by FDTD

S. H. Mirjahanmardi, P. Dehkhoda, A. Tavakoli
ACES Journal Paper
Year: 2017      Volume: 32      Number: 11
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In this paper, the finite difference time domain (FDTD) method is implemented to analyze the scattered field from a three dimensional structure including two-layer rough interfaces with or without buried object(s). The effects of different parameters such as rough interface correlation length as well as its root mean square (rms) height, the moisture content of the soil, also the buried object position and size on the scattered field are studied. Simulations show that by increasing the soil moisture, the level of scattering from the structure (without the buried object) is increased. In addition, it is shown that the same amount of moisture change, but in different percentage level, shows completely different effect on the scattering level. Furthermore, it is observed that changing the correlation length in the small perturbation range does not have a significant effect on the scattering coefficients. Moreover, images from the buried objects are obtained to show the visualization of object observation with different materials in a background. The solution has been validated by the finite integration based commercial software, CST.

Shape Reconstruction of Three Dimensional Conducting Objects Using Opposition-Based Differential Evolution

M. Maddahali, A. Tavakoli, M. Dehmollaian
ACES Journal Paper
Year: 2017      Volume: 32      Number: 1
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In this paper, shape reconstruction of three dimensional conducting objects using radar cross section (RCS) of the scatterer and opposition-based differential evolution is investigated. The shape of the scatterer is modeled with nonuniform rational B-spline (NURBS) surfaces composed of more than one Bezier patches. NURBS are piecewise polynomial with unknown coefficients that are determined in the procedure of shape reconstruction. Opposition-based differential evolution (ODE) is then employed as an optimization tool to find the unknown coefficients. Physical optics approximation is used to predict RCS of the large conducting scatterer in various directions and at multiple frequencies. The effect of noise is also considered in the inverse process.

Eccentricity Compensation in Switched Reluctance Machines via Controlling Winding Turns/Stator Current: Theory, Modeling, and Electromagnetic Analysis

E. Afjei, M. R. Tavakoli, H. Torkaman
ACES Journal Paper
Year: 2013      Volume: 28      Number: 2
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In this paper, a new eccentricity compensation method for Switched Reluctance Machines (SRMs) is presented. In this regard, the dependency of radial force (RF) on variation of number of turns for stator coils and fault level is demonstrated analytically and principle of the new compensation strategy is introduced as well. This strategy is implemented on an SRM utilizing Finite Element Method (FEM) under different fault conditions. This approach is accomplished through switching among the various arrangements in the number of turns for the coils on the stator poles; hence, unbalanced magnetic force (UMF) is controlled without additional auxiliary coils. Simultaneously, regulating the stator currents guarantees the motor torque is not diminished. This comprehensive approach is suitable for different types and structures of SRMs and will compensate or control eccentricities in a wide range of eccentricity faults namely 10%-70% while motor performance is not impaired.

Scattering by a 2D Crack: The Meshfree Collocation Approach

B. Honarbakhsh, A. Tavakoli
ACES Journal Paper
Year: 2012      Volume: 27      Number: 3
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In this paper, the meshfree collocation method is applied to the problem of EM scattering by a 2D crack in a PEC plane. The hybrid PDE-IE formulation is the mathematical statement of the problem. Consequently, the geometry and the filling material of the cavity is arbitrary. Validations are based on convergence analysis, modal solution and measurement results. Furthermore, elliminating numerical integrations has lead to a fast, accurate, and general meshfree solution.

A Closed-Form Spatial Green’s Function for the Thick Microstrip Substrate: The Meshless Interpolation Approach

B. Honarbakhsh, A. Tavakoli
ACES Journal Paper
Year: 2013      Volume: 28      Number: 2
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n this paper the Green’s functions (GFs) of a thick microstrip in the spatial-domain is computed based on expanding the corresponding spectral-domain functions over inverse quadric (IQ) radial basis functions (RBFs). The scattered data interpolation ability of RBFs is exploited for efficient sampling of the Sommerfeld integration path (SIP), passing from close vicinity of singularities in the complex k? plane. By this, the information content of spectral-domain GFs is preserved, which makes it possible to compute the far-fields accurately. Thus, the method can be applied to the analysis of electrically large structures near layered media. The proposed method is direct with only one approximation level.

Analysis of Thick Microstrip Antennas by the Meshfree Collocation Method

B. Honarbakhsh, A. Tavakoli
ACES Journal Paper
Year: 2013      Volume: 28      Number: 2
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A meshless integration free approach is applied to numerical solution of the mixed potential integral equation (MPIE) governing various microstrip resonators/antennas. The idea behind the discrete complex image method (DCIM) is exploited to provide closed form expressions for all of the integrals, leading to an efficient spectral-domain meshless integral equation (IE) solver. The proposed meshfree method (MFM) is compared with low order method of moments (MoM) from the aspects of memory usage and simulation time, which shows superior performance of the MFM.

Design and Electromagnetic Analysis of a New Rotary-Linear Switched Reluctance Motor in Static Mode

M. M. Nezamabadi, E. Afjei, H. Torkaman
ACES Journal Paper
Year: 2016      Volume: 31      Number: 2
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A newly designed rotary-linear switched reluctance (RLSRM) motor is presented and electromagnetically analyzed in this paper. The motor has an integrated structure and can control both linear and rotary motions. It is mainly designed to control the engagement of a rotating gear. For this purpose a twosection motor comprised of a rotary and a linear SRM is designed. In the middle part of the motor assembly, a three-phase rotary SRM with 6 stator and 4 rotor poles creates rotary motion. The linear section which is a transverse flux two-phase SRM is composed of two parts placing at each side of the rotary section. The cylindrical translators inside the linear stator poles provide short magnetic flux paths which reduce the core losses and increase the force per volume. The motor parameters derived from the motor design procedure are evaluated using 3-dimensional finite element analysis (3DFEA). The motor performance indices such as flux linkages, flux density, mutual flux, static torque and force for various loads are obtained and assessed for rotary and linear motions. Finally, a comparative study is performed and 3DFEA results are compared with two different RLSRM structures. The comparison shows that the proposed structure has the highest force per motor volume.

ACES Journal November 2016 Front/Back Matter

ACES
ACES Journal Paper
Year: 2016      Volume: 31      Number: 11
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Real-Coded Genetic Algorithm with Differential Evolution Operator for Terahertz Quasi-Optical Power Divider/Combiner Design

F. Zhang, K. Song, Y. Fan
ACES Journal Paper
Year: 2017      Volume: 32      Number: 10
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This paper describes a modified real-coded genetic algorithm with a differential evolution operator (RGA-DE) for a shaped reflector of terahertz (THz) quasi-optical power divider/combiner. The real-coded genetic algorithm (RGA) is more convenient to define the reflector surfaces as compared to other coding methods. Interpolation method is applied to smooth the sophisticated surfaces. A better searching ability is obtained in a small number of individuals by using the differential evolution operator instead of the conventional crossover operator. So a bionics algorithm combining real-coded genetic algorithm and differential evolution (DE) algorithm has been presented to design the THz quasi-optical multiple-way holographic power-combining circuits. The RGA-DE has been utilized to optimize the coupling coefficient kappa of the field distribution to get close to 1. Two real-world examples operating at 380 GHz and 450 GHz respectively are described. The computed results are verified by using the commercial software FEKO Suite.

ACES Journal October 2017 Full

ACES Journal Paper
Year: 2017      Volume: 32      Number: 10
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ACES

ACES Journal November 2017 Front/Back Matter

ACES Journal Paper
Year: 2017      Volume: 32      Number: 11
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An Interpolation Scheme for Green’s Function and its Application in Method of Moment

Y. Xu, H. Yang, X. Liu, R. Shen
ACES Journal Paper
Year: 2018      Volume: 33      Number: 7
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An interpolation scheme is put forward to accelerate the calculation of free space Green’s function. Through theoretical analysis, a universal rule on how to build value lists for the phase item of Green’s function is discussed. And this rule can guarantee accuracy of the interpolation scheme. Accuracy and efficiency of the scheme are verified in the calculation of impedance matrix for method of moment. Besides, this scheme can also be applied to other applications which contain the calculation of Green’s functions and is especially useful for the analysis of large scale problems. Moreover, this scheme can be combined with other existing improved approaches of method of moment.

ACES Journal January 2017 Full

ACES
ACES Journal Paper
Year: 2017      Volume: 32      Number: 1
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