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Bagci, Hakan (200)

Ulku, Huseyin Arda (40)Michielssen, Eric (30)Li, Ping (27)Sayed, Sadeed B (22)View MoreDepartmentComputer, Electrical and Mathematical Sciences and Engineering (CEMSE) Division (200)Electrical Engineering Program (200)Computational Electromagnetics Laboratory (80)Physical Sciences and Engineering (PSE) Division (73)Center for Uncertainty Quantification in Computational Science and Engineering (SRI-UQ) (14)View MoreJournalIEEE Transactions on Antennas and Propagation (21)2014 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium) (9)Optics Express (7)2013 IEEE Antennas and Propagation Society International Symposium (APSURSI) (6)2013 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium) (5)View MoreKAUST Acknowledged Support UnitOffice of Sponsored Research (OSR) (2)Supercomputing Laboratory (2)Technology Innovation Center (1)KAUST Grant Number2016-CRG5-2953 (3)CRG-2953 (3)CRG5-2953 (1)KUS-C1-016-04 (1)RGC/3/2385-01 (1)PublisherInstitute of Electrical and Electronics Engineers (IEEE) (129)The Optical Society (11)EMW Publishing (5)American Physical Society (APS) (4)Springer Nature (4)View MoreSubjectCEM (15)Time-domain analysis (9)discontinuous Galerkin time-domain (DGTD) method (8)transient analysis (6)numerical analysis (5)View MoreTypeConference Paper (88)Article (77)Poster (32)Presentation (2)Abstract (1)Year (Issue Date)2019 (14)2018 (19)2017 (13)2016 (22)2015 (30)View MoreItem AvailabilityMetadata Only (113)Open Access (87)

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An explicit marching-on-in-time scheme for solving the time domain Kirchhoff integral equation.

Chen, Rui; Sayed, Sadeed B; Al-Harthi, Noha A.; Keyes, David E.; Bagci, Hakan (The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), 2019-10-09) [Article]

A fully explicit marching-on-in-time (MOT) scheme for solving the time domain Kirchhoff (surface) integral equation to analyze transient acoustic scattering from rigid objects is presented. A higher-order Nyström method and a PE(CE)m-type ordinary differential equation integrator are used for spatial discretization and time marching, respectively. The resulting MOT scheme uses the same time step size as its implicit counterpart (which also uses Nyström method in space) without sacrificing from the accuracy and stability of the solution. Numerical results demonstrate the accuracy, efficiency, and applicability of the proposed explicit MOT solver.

An explicit marching-on-in-time scheme for solving the time domain Kirchhoff integral equation.

A Novel Subdomain 2D/Q-2D Finite Element Method for Power/Ground Plate-Pair Analysis

Li, Ping; Jiang, Li Jun; Tang, Min; Zhang, Yao Jiang; Xu, Shuai; Bagci, Hakan (IEEE Transactions on Electromagnetic Compatibility, IEEE, 2019-10-07) [Article]

Upon excitation by a surface magnetic current, a power/ground plate-pair supports only $\mathrm{TM}^{z}$ modes. This means that the magnetic field has only azimuthal components permitting a simple but effective domain decomposition method (DDM) to be used. In the proximity of an antipad, field interactions are rigorously modeled by a quasi-two-dimensional (Q-2D) finite element method (FEM) making use of three-dimensional (3D) triangular prism mesh elements. Since high-order $\mathrm{TM}^{z}$ modes are confined in the close proximity of the antipad, field interactions in the region away from the antipad only involve the fundamental mode and are rigorously modeled by a 2D FEM. This approach reduces 3D computation domain into a hybrid 2D/Q-2D domain. The discretization of this hybrid domain results in a global matrix system consisting of two globally coupled matrix equations pertinent to 2D and Q-2D domains. In this article, these two matrix equations are “decoupled” using a Riemann solver and the information exchange between the two domains is facilitated using numerical flux. The resulting decoupled two matrix equations are iteratively solved using the Gauss–Seidel algorithm. The accuracy, efficiency, and robustness of the proposed DDM are verified by four representative examples.

Computation of Fields from a Magnetic Dipole in a Conductive Medium Using the QS-DGTD Method

Özakin, M. Burak; Chen, Liang; Ahmed, Shehab; Bagci, Hakan (Institute of Electrical and Electronics Engineers (IEEE), 2019-05-13) [Conference Paper]

Loop antennas are often used for field generation in low-frequency electromagnetic applications. Since the antenna dimensions are much smaller than the wavelength, the antenna can accurately be replaced by its equivalent magnetic dipole model in simulations. In this paper, low-frequency magnetic dipole radiation fields in a conductive medium are computed using a three-dimensional discontinuous Galerkin Time-Domain (DGTD) scheme. It is shown that this computation can be accelerated using a material scaling scheme under Quasi-Static (QS) approximation, i.e., time step size can be scaled up without sacrificing from the accuracy and the stability of the time marching scheme. Radiated fields from a magnetic dipole in a conductive medium computed by this accelerated scheme are compared to those obtained using analytical expressions. Results are in good agreement.

On Higher-Order Nyström Discretization of Scalar Potential Integral Equation for Penetrable Scatterers

Chen, Rui; Bagci, Hakan (Institute of Electrical and Electronics Engineers (IEEE), 2019-05-13) [Conference Paper]

The following topics are dealt with: finite difference time-domain analysis; Maxwell equations; finite element analysis; antenna radiation patterns; optimisation; time-domain analysis; electromagnetic wave scattering; plasmonics; computational electromagnetics; optical metamaterials.

A Discontinuous Galerkin Framework for Multiphysics Simulation of Photoconductive Devices

Chen, Liang; Bagci, Hakan (Institute of Electrical and Electronics Engineers (IEEE), 2019-05-13) [Conference Paper]

A discontinuous Galerkin (DG) framework is developed for multiphysics simulation of plasmonic photoconductive devices. The nonequilibrium steady state is modeled by the coupled system of Poisson and drift-diffusion (DD) equations and this system is solved using a nonlinear DG scheme. The optical-to-terahertz (THz) conversion process is modeled by the coupled system of Maxwell and time dependent DD equations and this system is solved using a time domain DG scheme. Numerical experiments show that the proposed scheme provides accurate results.

Mixed Discretization of CFIE in the Framework of MLFMA

Guler, S.; Yücel, A. C.; Bagci, Hakan; Ergül, O. (2018 Progress in Electromagnetics Research Symposium (PIERS-Toyama), Institute of Electrical and Electronics Engineers (IEEE), 2019-03-08) [Conference Paper]

The conventional combined-field integral equation (CFIE)using a Galerkin scheme suffers from inaccuracy issues due to the incorrect testing of the identity operator in the magnetic-field integral equation (MFIE). In this contribution, a mixed discretization scheme is used for correct testing of MFIE in the context of CFIE. The projection of testing spaces of EFIE and MFIE onto each other is required while solving CFIE numerically with the mixed discretization scheme. For this purpose, computations of the Gram matrix inversions are required to perform the projection operations. Such an operation can easily become computationally expensive, especially when solving large-scale problems using accelerated algorithms, such as the multilevel fast multipole algorithm (MLFMA). In this work, matrix decomposition methods and iterative solvers are used to solve Gram systems while solving CFIE with the mixed discretization scheme in the framework of MLFMA. The accuracy and efficiency of the results are compared, in the context of large-scale problems.

Numerical Modeling of Graphene Nano-Ribbon by DGTD Taking into Account the Spatial Dispersion Effects

Li, Ping; Jiang, L. J.; Bagci, Hakan (2018 Progress in Electromagnetics Research Symposium (PIERS-Toyama), Institute of Electrical and Electronics Engineers (IEEE), 2019-02-28) [Conference Paper]

It is well known that graphene demonstrates spatial dispersion properties [1]-[3], i.e., its conductivity is nonlocal and a function of spectral wave number (momentum operator) q. In this work, to fully account for effects of spatial dispersion on transmission of high speed signals along graphene nano-ribbon (GNR) interconnects, a discontinuous Galerkin time-domain (DGTD) algorithm is proposed. The atomically-thick GNR is modeled using a nonlocal transparent surface impedance boundary condition (SIBC) [4] incorporated into the DGTD scheme. Since the conductivity is a complicated function of q (and one cannot find an analytical Fourier transform pair between q and spatial differential operators), an exact time domain SIBC model cannot be derived. To overcome this problem, the conductivity is approximated by its Taylor series in spectral domain under low-q assumption. This approach permits expressing the time domain SIBC in the form of a second-order partial differential equation (PDE) in current density and electric field intensity. To permit easy incorporation of this PDE with the DGTD algorithm, three auxiliary variables, which degenerate the second-order (temporal and spatial) differential operators to first-order ones, are introduced. Regarding to the temporal dispersion effects, the auxiliary differential equation (ADE) method [4] is utilized to eliminates the expensive temporal convolutions. To demonstrate the applicability of the proposed scheme, numerical results, which involve characterization of spatial dispersion effects on the transfer impedance matrix of GNR interconnects, will be presented.

Computation of Electromagnetic Fields Scattered From Objects With Uncertain Shapes Using Multilevel Monte Carlo Method

Litvinenko, Alexander; Yucel, Abdulkadir C.; Bagci, Hakan; Oppelstrup, Jesper; Michielssen, Eric; Tempone, Raul (IEEE Journal on Multiscale and Multiphysics Computational Techniques, Institute of Electrical and Electronics Engineers (IEEE), 2019-02-06) [Article]

Computational tools for characterizing electromagnetic scattering from objects with uncertain shapes are needed in various applications ranging from remote sensing at microwave frequencies to Raman spectroscopy at optical frequencies. Often, such computational tools use the Monte Carlo (MC) method to sample a parametric space describing geometric uncertainties. For each sample, which corresponds to a realization of the geometry, a deterministic electromagnetic solver computes the scattered fields. However, for an accurate statistical characterization the number of MC samples has to be large. In this work, to address this challenge, the continuation multilevel Monte Carlo (CMLMC) method is used together with a surface integral equation solver. The CMLMC method optimally balances statistical errors due to sampling of the parametric space, and numerical errors due to the discretization of the geometry using a hierarchy of discretizations, from coarse to fine. The number of realizations of finer discretizations can be kept low, with most samples computed on coarser discretizations to minimize computational cost. Consequently, the total execution time is significantly reduced, in comparison to the standard MC scheme.

An Explicit MOT Scheme for solving the Nyström-Discretized TD-MFIE

Chen, Rui; Bagci, Hakan (2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting, Institute of Electrical and Electronics Engineers (IEEE), 2019-01-24) [Conference Paper]

A fully explicit marching-on-in-time scheme for solving the time domain magnetic field integral equation is proposed. The unknown current density induced on the surface of the scatterer is expanded using a higher-order Nyström method in space and Lagrange interpolation in time. The resulting system is cast in the form of an ordinary differential equation and integrated in time using a predictor-corrector scheme to obtain the unknown expansion coefficients. Numerical results demonstrate that the proposed explicit scheme can use the same time step size as its implicit counterpart without sacrificing stability and is five times faster under low-frequency excitation (i.e., for large time step).

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