F. Obelleiro

The generalized forward-backward method for analyzing the scattering from targets on ocean-like rough surfaces

The iterative forward backward (FB) method has been proposed to solve the magnetic field integral equation for smooth one-dimensional rough surfaces. This method has proved to be very efficient, converging in a very small number of iterations. Nevertheless, this solution becomes unstable when some obstacle, like a ship or a large breaking wave, is included in the original problem. In this paper we propose a new extension of the FB method: the generalized forward backward (GFB) method, to solve such kinds of composite problems.

MLFMA-FFT PARALLEL ALGORITHM FOR THE SO- LUTION OF LARGE-SCALE PROBLEMS IN ELECTRO- MAGNETICS (INVITED PAPER)

MLFMA-FFT PARALLEL ALGORITHM FOR THE SO-LUTION OF LARGE-SCALE PROBLEMS IN ELECTRO-MAGNETICS (INVITED PAPER)J. M. TaboadaDepartment Tecnolog¶‡as de los Computadores y de lasComunicaciones, Escuela Polit¶ecnicaUniversidad de ExtremaduraC¶aceres 10071, SpainM. G. Araujo¶ and J. M. B¶ertoloDepartment Teor¶‡a do Sinal e Comunicaci¶ons, E.T.S.E.Telecomunicaci¶onUniversidade de VigoVigo (Pontevedra) 36310, SpainL. LandesaDepartment Tecnolog¶‡as de los Computadores y de lasComunicaciones, Escuela Polit¶ecnicaUniversidad de ExtremaduraC¶aceres 10071, SpainF. Obelleiro and J. L. RodriguezDepartment Teor¶‡a do Sinal e Comunicaci¶ons, E.T.S.E.Telecomunicaci¶onUniversidade de VigoVigo (Pontevedra) 36310, SpainAbstract|An e–cient hybrid MPI/OpenMP parallel implementationof an innovative approach that combines the Fast Fourier Transform(FFT) and Multilevel Fast Multipole Algorithm (MLFMA) has beensuccessfully used to solve an electromagnetic problem involving 620millions of unknowns. The MLFMA-FFT method can deal withextremely large problems due to its high scalability and its reducedcomputational complexity. The former is provided by the use of the

Method-of-moments formulation for the analysis of plasmonic nano-optical antennas

We present a surface integral equation (SIE) to model the electromagnetic behavior of metallic objects at optical frequencies. The electric and magnetic current combined field integral equation considering both tangential and normal equations is applied. The SIE is solved by using a method-of-moments (MoM) formulation. The SIE-MoM approach is applied only on the material boundary surfaces and interfaces, avoiding the cumbersome volumetric discretization of the objects and the surrounding space required in differential-equation formulations. Some canonical examples have been analyzed, and the results have been compared with analytical reference solutions in order to prove the accuracy of the proposed method. Finally, two plasmonic Yagi-Uda nanoantennas have been analyzed, illustrating the applicability of the method to the solution of real plasmonic problems.

Toward Ultimate Nanoplasmonics Modeling

Advances in the field of nanoplasmonics are hindered by the limited capabilities of simulation tools in dealing with realistic systems comprising regions that extend over many light wavelengths. We show that the optical response of unprecedentedly large systems can be accurately calculated by using a combination of surface integral equation (SIE) method of moments (MoM) formulation and an expansion of the electromagnetic fields in a suitable set of spatial wave functions via fast multipole methods. We start with a critical review of volume versus surface integral methods, followed by a short tutorial on the key features that render plasmons useful for sensing (field enhancement and confinement). We then use the SIE-MoM to examine the plasmonic and sensing capabilities of various systems with increasing degrees of complexity, including both individual and interacting gold nanorods and nanostars, as well as large random and periodic arrangements of ∼1000 gold nanorods. We believe that the present results and methodology raise the standard of numerical electromagnetic simulations in the field of nanoplasmonics to a new level, which can be beneficial for the design of advanced nanophotonic devices and optical sensing structures.

Gold Nanorod–pNIPAM Hybrids with Reversible Plasmon Coupling: Synthesis, Modeling, and SERS Properties

The thermoresponsive optical properties of Au nanorod-doped poly(N-isopropylacrylamide) (Au NR-pNIPAM) microgels with different Au NR payloads and aspect ratios are presented. Since the volume phase transition of pure pNIPAM microgels is reversible, the optical response reversibility of Au NR-pNIPAM hybrids is systematically analyzed. Besides, extinction cross-section and near-field enhancement simulations for Au NR-microgel hybrids are performed using a new numerical method based on the surface integral equation method of moments formulation (M3 solver). Additionally, the Au NR-microgel hybrid systems are expected to serve as excellent broadband surface-enhanced Raman scattering (SERS) substrates due to the temperature-controlled formation of hot spots and the tunable optical properties. The optical enhancing properties related to SERS are tested with three laser lines, evidencing excitation wavelength-dependent efficiency that can be easily controlled by either the aspect ratio (length/width) of the assembled Au NR or by the Au NR payload per microgel. Finally, the SERS efficiency of the prepared Au NR-pNIPAM hybrids is found to be stable for months.

Comparison of surface integral equation formulations for electromagnetic analysis of plasmonic nanoscatterers

The performance of most widespread surface integral equation (SIE) formulations with the method of moments (MoM) are studied in the context of plasmonic materials. Although not yet widespread in optics, SIE-MoM approaches bring important advantages for the rigorous analysis of penetrable plasmonic bodies. Criteria such as accuracy in near and far field calculations, iterative convergence and reliability are addressed to assess the suitability of these formulations in the field of plasmonics.

Surface integral equation formulation for the analysis of left-handed metamaterials

A surface integral equation (SIE) formulation is applied to the analysis of electromagnetic problems involving three-dimensional (3D) piecewise homogenized left-handed metamaterials (LHM). The resulting integral equations are discretized by the well-known method of moments (MoM) and solved via an iterative process. The unknowns are defined only on the interfaces between different media, avoiding the discretization of volumes and surrounding space, which entails a drastic reduction in the number of unknowns arising in the numerical discretization of the equations. Besides, the SIE-MoM formulation inherently includes the radiation condition at infinity, so it is not necessary to artificially include termination absorbing boundary conditions. Some 3D numerical examples are presented to confirm the validity and versatility of this approach on dealing with LHM, also providing some intuitive verifications of the singular properties of these amazing materials.

Optimization of an optical wireless nanolink using directive nanoantennas

Optical connects will become a key point in the next generation of integrated circuits, namely the upcoming nanoscale optical chips. In this context, nano-optical wireless links using nanoantennas have been presented as a promising alternative to regular plasmonic waveguide links, whose main limitation is the range propagation due to the metal absorption losses. In this paper we present the complete design of a high-capability wireless nanolink using matched directive nanoantennas. It will be shown how the use of directive nanoantennas clearly enhances the capability of the link, improving its behavior with respect to non-directive nanoantennas and largely outperforming regular plasmonic waveguide connects.

Spectral acceleration of the generalized forward-backward method

The generalized forward-backward (GFB) method was introduced as an iterative method of moments solution to compute the electromagnetic scattering from targets on ocean-like rough surfaces. In this paper, an existing spectral acceleration algorithm is adapted to the GFB. The spectral acceleration is presented for both polarizations and for perfect electrically conducting (PEC) and non-PEC surfaces. The accelerated scheme reduces the computational scaling cost of the GFB from O(N/sup 2/) to O(N) per iteration as the length of the sea surface increases linearly with the number of unknowns N. The numerical results demonstrate that the spectral acceleration introduces negligible error while greatly improving the efficiency of the GFB method.

Solution of large-scale plasmonic problems with the multilevel fast multipole algorithm.

A surface integral equation together with the multilevel fast multipole algorithm is successfully applied to fast and accurate resolution of plasmonic problems involving a large number of unknowns. The absorption, scattering, and extinction efficiencies of several plasmonic gold spheres of increasing size are efficiently obtained solving the electric and magnetic current combined-field integral equation. The numerical predictions are compared with reference analytic results to demonstrate the accuracy, suitability, and capabilities of this approach when dealing with large-scale plasmonic problems.