F. Olyslager

INRIM Istituto Nazionale di Ricerca Metrologica, Torino, Piedmont, Italy

Are you F. Olyslager?

Claim your profile

Publications (196)164.48 Total impact

  • Source
    D. Pissoort, D. Vande Ginste, F. Olyslager
  • Source
    Jan Fostier, Femke Olyslager
    [Show abstract] [Hide abstract]
    ABSTRACT: In this contribution, we demonstrate that recent improvements in “fast methods” allow for fully error-controlled full-wave simulations of two-dimensional objects with sizes over a million wavelengths using relatively simple computing environments. We review how a fully scalable parallel version of the Multilevel Fast Multipole Algorithm (MLFMA) is obtained to accelerate a two-dimensional boundary integral equation for the scattering by multiple large dielectric and/or perfectly conducting objects. Several complex and large-scale examples demonstrate the capabilities of the algorithm. This implementation is available as open source under GPL license (http://www.openfmm.net).
    IEEE Antennas and Propagation Magazine 11/2010; · 1.18 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A well-conditioned coupled set of surface (S) and volume (V) electric field integral equations (S-EFIE and V-EFIE) for analyzing wave interactions with densely discretized composite structures is presented. Whereas the V-EFIE operator is well-posed even when applied to densely discretized volumes, a classically formulated S-EFIE operator is ill-posed when applied to densely discretized surfaces. This renders the discretized coupled S-EFIE and V-EFIE system ill-conditioned, and its iterative solution inefficient or even impossible. The proposed scheme regularizes the coupled set of S-EFIE and V-EFIE using a Calderón multiplicative preconditioner (CMP)-based technique. The resulting scheme enables the efficient analysis of electromagnetic interactions with composite structures containing fine/subwavelength geometric features. Numerical examples demonstrate the efficiency of the proposed scheme.
    IEEE Transactions on Antennas and Propagation 09/2010; · 2.33 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Calderon preconditioners have recently been demonstrated to be very successful in stabilizing the electric field integral equation (EFIE) for perfect electric conductors at lower frequencies. Previous authors have shown that, by using a dense matrix preconditioner based on the Calderon identities, the low frequency instability is removed while still maintaining the inherent accuracy of the EFIE. It was also demonstrated that the spectral properties of the Caldero-n preconditioner are conserved during discretization if the EFIE operator is discretized with Rao-Wilton-Glisson expansion functions and the preconditioner with Buffa-Christiansen expansion functions. In this article we will show how the Calderon multiplicative preconditioner (CMP) can be combined with fast multipole methods to accelerate the numerical solution, leading to an overall complexity of O ( N log N ) for the entire iterative solution. At low frequencies, where the CMP is most useful, the traditional multilevel fast multipole algorithm (MLFMA) is unstable and we apply the nondirectional stable plane wave MLFMA (NSPWMLFMA) that resolves the low frequency breakdown of the MLFMA. The combined algorithm will be called the CMP-NSPWMLFMA. Applying the CMP-NSPWMLFMA at open surfaces or very low frequencies leads to certain problems, which will be discussed in this article.
    IEEE Transactions on Antennas and Propagation 05/2010; · 2.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The present paper numerically investigates the micromagnetic behavior of permalloy nanostrips, starting from the space-time integration of the Landau-Lifshitz-Gilbert equation. The analysis is performed on objects with variable longitudinal size of the order of some hundreds of nanometers. The attention is focused on the role of geometrical properties (e.g., scaling factor and end shape) and of thermal agitation on magnetization reversal processes. The thermal effects are included in the model following the Langevin approach.
    IEEE Transactions on Magnetics 03/2010; · 1.42 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Micromagnetic hysteresis models for large, bulk like samples are useful for the identification of relations between microscopic material properties and macroscopic magnetic behavior. To bridge the gap between the nanometer space scale of the micromagnetic theory and the large sample dimensions, time and memory efficient numerical schemes are needed. In micromagnetic computations, fast Fourier transforms (FFTs) have been widely adopted to speed up magnetostatic field computations. In this paper, two FFT schemes are compared. The first scheme evaluates the magnetostatic field directly starting from the magnetization and has a large accuracy, while in the second scheme the magnetostatic field is derived from the scalar magnetic potential resulting in a reduced accuracy but also in a CPU time reduction for a magnetostatic field evaluation to 65% and a reduction of memory requirements to 55%. The influence of the low accuracy evaluations on the simulated macroscopic hysteresis behavior is studied. Therefore, comparison is made with the influence of thermal effects in hysteresis simulations. It is found that the resulting changes in macroscopic hysteresis behavior are of the same order of magnitude as the ones obtained when thermal fluctuations are taken into account in the high accuracy computations.
    Journal of Magnetism and Magnetic Materials 02/2010; 322:469-476. · 2.00 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In finite ferromagnetic wires, the demagnetizing effects along the wire axis have a substantial influence on the reversal processes. By considering infinite wires, these effects are annihilated and only the sample dimensions, cross-sectional geometry, and material properties determine the magnetization reversal. The magnetization reversal is now initiated by small thermal fluctuations. With decreasing cross-sectional dimensions, three different reversal modes can be distinguished: reversal with (i) domain formation; (ii) vortex formation; and (iii) precessional switching combined with buckling. For different cross-sectional dimensions and lattice axes orientations, the 3-D magnetization dynamics and evolution of the different micromagnetic energy terms are investigated, resulting in a clear understanding of the reversal modes.
    IEEE Transactions on Magnetics 12/2009; · 1.42 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Magnetic field integral equation (MFIE) and Calderon preconditioned electric field integral equation (EFIE) operators applied to toroidal surfaces have nontrivial nullspaces in the static limit. The nature of these nullspaces is elucidated and a technique for generating a basis for them presented. In addition, the effects of these nullspaces on the numerical solution of both frequency and time-domain MFIE and CalderOacuten preconditioned EFIEs are investigated. The theoretical analysis is accompanied by corroborating numerical examples that show how these operators' nullspaces affect real-world problems.
    IEEE Transactions on Antennas and Propagation 11/2009; · 2.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A Calderon multiplicative preconditioner (CMP) for the combined field integral equation (CFIE) is developed. Just like with previously proposed Calderon-preconditioned CFIEs, a localization procedure is employed to ensure that the equation is resonance-free. The iterative solution of the linear system of equations obtained via the CMP-based discretization of the CFIE converges rapidly regardless of the discretization density and the frequency of excitation.
    IEEE Transactions on Antennas and Propagation 11/2009; · 2.33 Impact Factor
  • K. Coolst, F.P. Andriulli, F. Olyslager
    [Show abstract] [Hide abstract]
    ABSTRACT: Electromagnetic scattering by dielectric bodies can be described by two integral equations: the PMCHWT equation and the Muller equation. The spectral properties of the former resemble those of the EFIE, while the spectral properties of the latter resemble those of the MFIE. Indeed, the PMCHWT equation is susceptible to the low frequency and dense grid breakdowns. Recently, a solution for the dense grid breakdown of the EFIE has been proposed: Calderoacuten preconditioning. In this contribution, the Calderoacuten preconditioning scheme is extended to the PMCHWT equation. the well-posedness of this new formulation is proven and numerical results testifying to the scheme's validity are presented.
    Electromagnetics in Advanced Applications, 2009. ICEAA '09. International Conference on; 10/2009
  • Source
    I. Bogaert, F. Olyslager
    [Show abstract] [Hide abstract]
    ABSTRACT: The Multilevel Fast Multipole Algorithm (MLFMA) is widely used for the acceleration of matrix-vector products in the iterative solution of scattering problems. The MLFMA, however, suffers from a low-frequency (LF) breakdown. This breakdown is usually avoided by hybridizing the MLFMA with a method that does not fail at LF. For example, the Green function can be decomposed using the spectral representation or multipoles. Recently, a novel decomposition was presented, which uses so-called pseudospherical harmonics in the translation operator. In this contribution, the coupling of this method and the MLFMA will be investigated in detail.
    Electromagnetics in Advanced Applications, 2009. ICEAA '09. International Conference on; 10/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: Time domain electric field integral equations often are used to analyze transient scattering from perfect electrically conducting objects. When discretized using marching-on-in-time recipes they give rise to linear systems of equations that can be solved for the induced currents for all time steps. Unfortunately, when the scatterer is approximated by increasingly dense meshes, the condition number of these systems grows rapidly, slowing down the convergence of iterative solvers. Here, time domain Calderon identities are derived and subsequently used to construct a Calderon-preconditioned time domain electric field integral equation that can be discretized even with dense meshes using Buffa-Christiansen basis functions. Numerical results that demonstrate the effectiveness and accuracy of the proposed method are presented.
    IEEE Transactions on Antennas and Propagation 09/2009; · 2.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Novel time domain integral equations for analyzing scattering from perfect electrically conducting objects are presented. They are free from DC and resonant instabilities plaguing standard electric field integral equation. The new equations are obtained using operator manipulations originating from the Calderon identities. Theoretical motivations leading to the construction of the new equations are explored and numerical results confirming their theoretically predicted behavior are presented.
    IEEE Transactions on Antennas and Propagation 09/2009; · 2.33 Impact Factor
  • J. Peeters, F. Olyslager
    [Show abstract] [Hide abstract]
    ABSTRACT: Calderon preconditioning is very succesful in stabilising the EFIE and the use of BC functions makes the formalism valid on open surfaces. Through applying a broadband fast multipole method, the complexity can be reduced from O (N<sup>2</sup>) to O(N log N), allowing the simulation of very large structures. In the high frequency case a localised version of the preconditioner must be used to avoid excessive scattering of the eigenvalues of the combined operator.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: The scattering of time-harmonic electromagnetic waves by perfect electrical conductors (PECs) can be modelled by several boundary integral equations, the magnetic and electric field integral equations (MFIE and EFIE) being the most prominent ones. These equations can be discretized by expanding current distributions in terms of Rao-Wilton-Glisson (RWG) functions defined on a triangular mesh approximating the scatterer's surface and by testing the equations using the same RWG functions. The main advantage of the MFIE is that it is well-posed in the easy-to-understand L2-norm. Discretization of the MFIE leads to systems that can be solved efficiently using iterative solution techniques. In this contribution, the cause for the MFIE's inaccuracy is discussed, and a new discretization scheme is proposed. Numerical results are presented that demonstrate the improvement realized by the new scheme over the classical one.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • Source
    I. Bogaert, F. Olyslager
    [Show abstract] [Hide abstract]
    ABSTRACT: Integral equations arising from the time-harmonic Maxwell equations contain the Green function of the Helmholtz equation as the integration kernel. The structure of this Green function has allowed the development of so-called fast multipole methods (FMMs), i.e. methods for accelerating the matrix-vector products that are required for the iterative solution of integral equations. Arguably the most widely used FMM is the multilevel fast multipole algorithm (MLFMA). It allows the simulation of electrically large structures that are intractable with direct or iterative solvers without acceleration. The practical importance of the MLFMA is made all the more clear by its implementation in various commercial EM software packages such as FEKO and CST Microwave studio.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • D. Beke, K. Cools, F. Olyslager, E. Michielssen
    [Show abstract] [Hide abstract]
    ABSTRACT: Scattering of time-harmonic electromagnetic waves by perfect electrical conductors (PECs) can be modelled by electric field integral equations (EFIEs). If the If the scatterer is wire-like, the EFIE often is constructed using the thin wirescatterer is wire-like, the EFIE often is constructed using the thin wire approximation. The systems of linear equations resulting upon discretization of the EFIE can be of very high dimension. The time of matrix-vector multiplications can be reduced by using multilevel multipole algorithms. To reduce the number of matrix-vector multiplications necessary, the system needs to be preconditioned. In this paper, a physically inspired preconditioner for systems that originate from the discretization of scattering by wire structures is presented. The method used here is more efficient than algebraic preconditioning techniques, and applies to structures containing wire-wire junctions.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • F. Olyslager, H. Rogier, D. De Zutter
    [Show abstract] [Hide abstract]
    ABSTRACT: In the mode matching technique is extended to the evaluation of the far field radiation pattern of waveguide discontinuities and in the idea is used to study discontinuities in finite planar substrates. In the properties of the PML closed waveguide are extensively studied from a theoretical point of view. The completeness of the modal set is studied as well as formulas to estimate the locations of the solutions for the pseudo-leaky eigenmodes and the PML eigenmodes. Also the convergence properties of the modal series expansions for the Green functions are studied and improved. In the complex coordinate idea is used to terminate infinite periodic waveguides by continuing the periodic structure a few periods into complex space. It also deal with the use of the PML series expansion of the Green function for the MLFMA.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: Combined field integral equation (CFIE) solvers are widely used for analyzing electromagnetic interactions with perfect electrically conducting (PEC) closed surfaces because, unlike electric field equation (EFIE) solvers, they do not suffer from internal resonance problems. However, they are unbounded as their EFIE components contain a hypersingular term. This renders the matrix systems resulting from discretization of CFIEs ill-conditioned, and their iterative solution inefficient or even impossible when the discretization is dense across part of, or the entire, surface. The unbounded nature of EFIEs can be remedied by leveraging the well-known Calderon identities. However, since Calderon-preconditioned EFIEs exhibit the same resonances as magnetic field integral equations (MFIEs), CFIEs obtained by combining them are not resonance-free. In this work, the Calderon multiplicative preconditioner (CMP) is combined with the localization technique to render CFIEs bounded and resonance-free. The proposed technique easily can be implemented in existing (fast) method-of-moments (MOM) codes. Numerical results show that the iterative solution of the preconditioned CFIE-MOM system converges rapidly regardless the discretization density and frequency of excitation.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effectiveness of the proposed CMP-based regularization is demonstrated via the characterization of a hemispherical dielectric resonator antenna with an air gap. The resonator is excited by a feed probe. The need for fine discretization around the feed is justified by the need for properly modeling the curvature of the feed probe and the distribution of fields around it. The article demonstrates the benefits of the proposed approach by comparing the residual error versus iteration number recorded by a TFQMR solver for the systems produced by standard MOM and CMP-based discretizations.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009

Publication Stats

2k Citations
164.48 Total Impact Points

Institutions

  • 2010
    • INRIM Istituto Nazionale di Ricerca Metrologica
      Torino, Piedmont, Italy
  • 2008–2010
    • University of Michigan
      • Department of Electrical Engineering and Computer Science (EECS)
      Ann Arbor, MI, United States
  • 195–2010
    • Ghent University
      • • Department of Information Technology
      • • Department of Electrical Energy, Systems and Automation
      Gent, VLG, Belgium
  • 1997–2009
    • INTEC
      Belgium, Wisconsin, United States
  • 2007–2008
    • Concordia University–Ann Arbor
      Ann Arbor, Michigan, United States
  • 2004
    • University of Illinois, Urbana-Champaign
      Urbana, Illinois, United States