Comparison of surface integral equations for left-handed materials

A wide analysis of left-handed material (LHM) spheres with di®erent constitutive parameters has been carried out employ- ing di®erent integral-equation formulations based on the Method of Moments. The study is focused on the accuracy assessment of for- mulations combining normal equations (combined normal formula- tion, CNF), tangential equations (combined tangential formulation, CTF, and Poggio-Miller-Chang-Harrington-Wu-Tsai formulation, PM- CHWT) and both of them (electric and magnetic current combined ¯eld integral equation, JMCFIE) when dealing with LHM's. Relevant and informative features as the condition number, the eigenvalues dis- tribution and the iterative response are analyzed. The obtained results show up the suitability of the JMCFIE for this kind of analysis in con- trast with the unreliable behavior of the other approaches.Ministerio de Ciencia e Innovación | Ref. TEC2008-06714-C02-01Ministerio de Ciencia e Innovación | Ref. TEC2008-06714-C02-02Ministerio de Ciencia e Innovación | Ref. CSD2008-00068Xunta de Galicia | Ref. INCITE08PXIB322250P

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 elec- tric andmagnetic 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

Improving condition number and convergence of the surface integral-equation method of moments for penetrable bodies

Most of the surface integral equation (SIE) formulations for composite conductor and/or penetrable objects suffer from balancing problems mainly because of the very different scales of the equivalent electric and magnetic currents. Consequently, the impedance matrix usually has high- or ill-condition number due to the imbalance between the different blocks. Using an efficient left and right preconditioner the elements of the impedance matrix are balanced. The proposed approach improves the matrix balance without modifying the underlying SIE formulation, which can be selected solely in terms of accuracy. The numerical complexity of this preconditioner is O(N) with N the number of unknowns, and it can be easily included on any existing SIE code implementation.Ministerio de Ciencia e Innovación | Ref. TEC2011-28784-C02-01Ministerio de Ciencia e Innovación | Ref. TEC2011-28784-C02-0

Multilevel fast multipole algorithm for fields

An efficient implementation of the multilevel fast multipole algorithm is herein applied to accelerate the calculation of the electromagnetic near- and far-fields after the equivalent surface currents have been obtained. In spite of all the research efforts being drawn to the latter, the electric and/or magnetic fields (or other parameters derived from these) are ultimately the magnitudes of interest in most of the cases. Though straightforward, their calculation can be computationally demanding, and hence the importance of finding a sped-up accurate representation of the fields via a suitable setup of the method. A complete self-contained formulation for both near- and far-fields and for problems including multiple penetrable regions is shown in full detail. Through numerical examples we show that the efficiency and scalability of the implementation leads to a drastic reduction of the computation time.Ministerio de Economía y Competitividad | Ref. MAT2014-58201-C2-1-RMinisterio de Economía y Competitividad | Ref. MAT2014-58201-C2-2-RGobierno Regional de Extremadura | Ref. IB1318

Accurate EMC engineering on realistic platforms using an integral equation domain decomposition approach

This article investigates the efficiency, accuracy and versatility of a surface integral equation (SIE) multisolver scheme to address very complex and large-scale radiation problems including multiple scale features, in the context of realistic electromagnetic compatibility (EMC)/electromagnetic interference (EMI) studies. The tear-and-interconnect domain decomposition (DD) method is applied to properly decompose the problem into multiple subdomains attending to their material, geometrical, and scale properties, while different materials and arbitrarily shaped connections between them can be combined by using the so-called multiregion vector basis functions. The SIE-DD approach has been widely reported in the literature, mainly applied to scattering problems or small radiation problems. Complementarily, in this article, the focus is placed on realistic radiation problems, involving tens of antennas and sensors and including multiscale ingredients and multiple materials. Such kind of problems are very demanding in terms of both convergence and computational resources. Throughout two realistic case studies, the proposed SIE-DD approach is shown to be a powerful electromagnetic modeling tool to provide the accurate and fast solution which is indispensable to rigorously accomplish real-life EMC/EMI studies.Agencia Estatal de Investigación | Ref. TEC2017-85376-C2-1-RAgencia Estatal de Investigación | Ref. TEC2017-85376-C2-2-

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.Ministerio de Ciencia e Innovación | Ref. TEC2011-28784-C02-01Ministerio de Ciencia e Innovación | Ref. TEC2011-28784-C02-0

HF broadband antenna design for shipboard communications: Simulation and measurements

The objective pursued in this work is to highlight the convenience of using electromagnetic simulation software as an alternative to the traditional scale model measurement when dealing with the design of HF antennas on real complex platforms. The experience was developed during the building process of a real vessel. A low and a medium band antennas (fan-wire type) were designed ad-hoc for this project. The HF broadband antennas’ study covered from the preliminary design stages to the final verification measurements completed onboard the ship. The experiment has demonstrated that more accurate results can be obtained when using an adequate electromagnetic simulation code, which, besides, brings important advantages in flexibility and usability. These advantages, inherent to the use of virtual models, hinge on the ability of the simulation tools to properly handle any modification of the vessel’s structure that might arise during the platform construction

Tear-and-interconnect domain decomposition scheme for solving multiscale composite penetrable objects

In this work, the tear-and-interconnect (T&I) surface-integral-equation (SIE) domain-decomposition (DD) approach-previously developed for non-penetrable bodies-, is extended to composite piecewise homogeneous penetrable objects including multiple materials and multiscale features. The main advantage of the proposed T&I scheme, with respect to conventional DD approach, is that it obviates the definition of large artificial surfaces (required for splitting the volumetric regions) with additional redundant unknowns, which avoids a significant increase in the computational cost, especially when dealing with large volumetric regions. In this sense, it has been shown that the T&I approach is an efficient and accurate alternative, which besides complements the conventional DD approach, since both are compatible and can be easily combined, which gives the possibility of applying one or the other as appropriate, depending on the specific characteristics of the problems to be solved in each case.Agencia Estatal de Investigación | Ref. TEC2017-85376-C2-1-RAgencia Estatal de Investigación | Ref. TEC2017-85376-C2-2-RGobierno Regional de Extremadura | Ref. IB18073Gobierno Regional de Extremadura | Ref. GR1805

MLFMA-MoM for solving the scattering of densely packed plasmonic nanoparticle assemblies

In this paper, we present a judicious combination of two renowned surface integral equation (SIE)-based techniques, namely, the multilevel fast multipole algorithm (MLFMA) and the method of moments (MoM), which synergize into a hybrid method that allows to address the analysis of large densely packed particle assemblies in an efficient and accurate way. This hybridization takes advantage of the repetition pattern inherent to these kinds of structures. Basically, the repeated self-coupling problems are squarely solved throughout the factorization of their MoM impedance matrix, whereas the cross-couplings through the surrounding medium are expedited via the MLFMA in the framework of a global iterative scheme. Some results are presented here to demonstrate the suitability of the proposed hybrid method to address large-scale nanoparticle arrays in the framework of nanoplasmonic biosensing applications.Ministerio de Ciencia e Innovación | Ref. TEC2011-28784-C02-01Ministerio de Ciencia e Innovación | Ref. TEC2011-28784-C02-0

Plasmonic substrates comprising gold nanostars efficiently regenerate cofactor molecules

The light harvesting capacity of plasmonic nanoparticles is a fundamental feature for catalysing chemical reactions close to their surface. The efficiency of the photochemical processes depends not only on the geometrical aspects on a single particle level but also on the complexity of the multiparticle architectures. Although, the effect of the particle geometry is progressively understood in the relevant photochemical processes (water splitting and hydrogen evolution), there are experimental and theoretical needs for understanding the role of the shape in the multiparticle systems in the photocatalytic processes. Here we have shown that macroscopic plasmonic substrates comprising gold nanostars exhibit better efficiencies than nanorods or cubes in the photoregeneration of cofactor molecules. We performed photochemical and photoelectrochemical measurements, supported by theoretical simulations, showing that the unique geometry of nanostars – radially distributed spikes – contributes to stronger light absorption by the plasmonic film containing that type of nanoparticles.La capacidad de recolección de luz de nanopartículas plasmónicas es una característica fundamental para catalizar reacciones químicas cerca de su superficie. La eficiencia de los procesos fotoquímicos depende no solo de los aspectos geométricos en un solo nivel de partículas, sino también de la complejidad de las arquitecturas multipartículas. Aunque el efecto de la geometría de la partícula se entiende progresivamente en los procesos fotoquímicos relevantes (división del agua y evolución del hidrógeno), existen necesidades experimentales y teóricas para comprender el papel de la forma en los sistemas de múltiples partículas en los procesos fotocatalíticos. Aquí hemos demostrado que los sustratos plasmónicos macroscópicos que comprenden nanoestrellas de oro exhiben mejores eficiencias que nanorods o cubos en la fotorregeneración de moléculas de cofactor. Realizamos mediciones fotoquímicas y fotoelectroquímicas, respaldadas por simulaciones teóricas, que muestran que la geometría única de las nanoestrellas (picos distribuidos radialmente) contribuye a una mayor absorción de la luz por la película plasmónica que contiene ese tipo de nanopartículas.• Ministerio de Economía y Competitividad. Proyectos MAT2013-49375-EXP y BIO2014-59741-R • Fundación BBVA. Primera convocatoria de ayudas para investigadores, innovadores y creadores culturales • Ministerio de Economía y Competitividad y Fondos FEDER. Proyectos MAT2014-58201-C2-1-R, MAT2014-58201-C2-2-R, para Diego Martínez Solís, José Manuel Taboada Varela y Fernando Obelleiro Basteiro • Xunta de Galicia, Centro Atlántico de Investigación en Tecnologías de la información y la Comunicación (AtlantTIC) y Fondos FEDER, para Diego Martínez Solís, José Manuel Taboada Varela y Fernando Obelleiro Basteiro • Junta de Extremadura y Fondos FEDER. Proyecto IB13185peerReviewe