30 research outputs found
Numerical comparison of spectral properties of volume-integral-equation formulations
We study and compare spectral properties of various volume-integral-equation formulations. The equations are written for the electric flux, current, field, and potentials, and discretized with basis functions spanning the appropriate function spaces. Each formulation leads to eigenvalue distributions of different kind due to the effects of discretization procedure, namely, the choice of basis and testing functions. The discrete spectrum of the potential formulation reproduces the theoretically predicted spectrum almost exactly while the spectra of other formulations deviate from the ideal one. It is shown that the potential formulation has the spectral properties desired from the preconditioning perspective. (C) 2016 Elsevier Ltd. All rights reserved.Peer reviewe
On the Spectrum and Preconditioning of Electromagnetic Volume Integral Equations
Spectral properties of current-based volume integral equation of electromagnetic scattering are investigated in the case of isotropic and bi-isotropic objects. Using Helmholtz decomposition the spectrum is derived separately for the solenoidal, irrotational, and harmonic subspaces. Based on this analysis, preconditioning strategies of the matrix equation are discussed.Peer reviewe
Discretization of Electric Current Volume Integral Equation With Piecewise Linear Basis Functions
Peer reviewe
Positive and negative extinction of active particles
Using analytical Lorenz--Mie scattering formalism and numerical methods, we
analyze the response of active particles to electromagnetic waves. The
particles are composed of homogeneous, non-magnetic, and dielectrically
isotropic medium. Spherical scatterers and sharp and rounded cubes are treated.
The absorption cross-section of active particles is negative, thus showing gain
in their electromagnetic response. Since the scattering cross-section is always
positive, their extinction can be either positive, negative, or zero. We
construct a five-class categorization of active and passive dielectric
particles. We point out the enhanced backscattering phenomenon that active
scatterers display, and also discuss extinction paradox and optical theorem.
Finally, using COMSOL Multiphysics and an in-house Method-of-Moments code, the
effects of the non-sphericity of active scatterers on their electromagnetic
response are illustrated.Comment: preprint, 17 pages, 19 figure
Resonances in small scatterers with impedance boundary
With analytical (generalized Mie scattering) and numerical
(integral-equation-based) considerations we show the existence of strong
resonances in the scattering response of small spheres with lossless impedance
boundary. With increasing size, these multipolar resonances are damped and
shifted with respect to the magnitude of the surface impedance. The
electric-type resonances are inductive and magnetic ones capacitive.
Interestingly, these subwavelength resonances resemble plasmonic resonances in
small negative-permittivity scatterers and dielectric resonances in small
high-permittivity scatterers. The fundamental dipolar mode is also analyzed
from the point of view of surface currents and the effect of the change of the
shape into a non-spherical geometry
Realization of a spherical boundary by a layer of wave-guiding medium
In this paper the concept of wave-guiding medium, previously introduced for
planar structures, is defined for the spherically symmetric case. It is shown
that a quarter-wavelength layer of such a medium serves as a transformer of
boundary conditions between two spherical interfaces. As an application, the
D'B'-boundary condition, requiring vanishing of normal derivatives of the
normal components of D and B field vectors, is realized by transforming the
DB-boundary conditions. To test the theory, scattering from a spherical DB
object covered by a layer of wave-guiding material is compared to the
corresponding scattering from an ideal D'B' sphere, for varying medium
parameters of the layer
On the applicability of discrete dipole approximation for plasmonic particles
It has been recognized that the commonly used discrete dipole approximation (DDA) for calculating the optical properties of plasmonic materials may exhibit slow convergence for a certain region of the complex refractive index. In this work we investigate the quantitative accuracy of DDA for particles of different shapes, with silver as the plasmonic material. As expected, the accuracy and convergence of the method as a function of the number of dipoles is relatively good for solid spheres and rounded cubes whose size is of the same order as the wavelength of the localized surface plasmon resonance in silver. However, we find that for solid particles much smaller than the resonance wavelength, and for silver-silica core-shell particles in particular, DDA does not converge to the correct limit even for 10(6) dipoles. We also find that the slow convergence tends to be accompanied by strong, discretization dependent oscillations in the particle's internal electric field. We demonstrate that the main factor behind the slow convergence of the DDA is due to inaccuracies in the plasmonic resonances of the dipoles at the surface of the particles. (C) 2015 Elsevier Ltd. All rights reserved.Peer reviewe