Near and far field

About: Near and far field is a research topic. Over the lifetime, 15922 publications have been published within this topic receiving 220571 citations.

A fast integral-equation solver for electromagnetic scattering problems

Abstract: We describe a new fast integral-equation solver applicable to large-scale electromagnetic scattering problems. In our approach, the field generated by a given current distribution M decomposed into near and far field components. The near field is computed using the conventional method of moments technique with the Galerkin discretization. The far field is calculated by approximating the original current distribution by an equivalent current distribution on a regular Cartesian grid, such that the two currents have identical multipole moments up to a required order m. As the result of this discretization, the original full impedance matrix is decomposed into a sum of a sparse matrix (corresponding to the near field component) and a product of sparse and Toeplitz matrices (corresponding to the far field component). Because of the convolution nature of the Toeplitz kernel, the field generated by the equivalent current distribution can be then obtained by means of discrete fast Fourier transforms. The single computational domain solver based on our formulation requires both memory and computation time of order O(N log N) (in volume problems) or O(N/sup 3/2/) (in surface problems), where N is the number of unknown current elements. In the domain-decomposed parallelized version of the solver, with the number P of processors equal to the number of domains, the total memory required in surface problems is reduced to O(N/sup 3/2//P/sup 1/2/). The corresponding speedup factor is equal to the number of processors P. During the talk, applications of the solver to 2- and 3-dimensional electromagnetic volumetric and boundary-value problems will be presented. >

Observation of near-field dipolar interactions involved in a metal nanoparticle chain waveguide.

Abstract: We present near-field measurements of transverse plasmonic wave propagation in a chain of gold elliptical nanocylinders fed by a silicon refractive waveguide at optical telecommunication wavelengths. Eigenmode amplitude and phase imaging by apertureless scanning near-field optical microscopy allows us to measure the local out-of-plane electric field components and to reveal the exact nature of the excited localized surface plasmon resonances. Furthermore, the coupling mechanism between subsequent metal nanoparticles along the chain is experimentally analyzed by spatial Fourier transformation on the complex near-field cartography, giving a direct experimental proof of plasmonic Bloch mode propagation along array of localized surface plasmons. Our work demonstrates the possibility to characterize multielement plasmonic nanostructures coupled to a photonic waveguide with a spatial resolution of less than 30 nm. This experimental work constitutes a prerequisite for the development of integrated nanophotonic devices.

Gold elliptical nanoantennas as probes for near field optical microscopy

Abstract: We investigate the light scattering by individual nanometer-sized gold particles attached at the apex of fiber-based probes for near field optical microscopy. The dependence of the light scattering by the gold nanoparticle on the wavelength, the shape, and the surrounding medium dielectric profile are theoretically described and experimentally investigated, demonstrating that the tuning of the particle’s size and shape plays a crucial role in the light scattering process. In the case of gold spherical nanostructures, the plasmon resonance occurs at 540 nm in air, and 600 nm in water. A higher surrounding medium refraction index leads to a redshift of the plasmon resonance in the gold particle. Moreover, for elliptical structures, the orientation of the polarization of the incident field, as well as the relative ratio of the ellipse dimensions along its main axis, govern the position of the plasmon resonances. The light transmission spectrum for several probes where a single elliptical gold particle has be...

Propagation of half-cycle far infrared pulses

Abstract: We have studied the propagation of half-cycle (i.e., unipolar) electromagnetic pulses centered at terahertz frequencies, in free space, through apertures, and through focusing optics. The temporal pulse shape of an apertured half-cycle pulse is significantly altered during propagation, but retains much of its unipolar character after traveling more than 20 times the aperture dimension. When focused by an achromatic lens, a half-cycle pulse evolves into a single-cycle pulse at the focal waist and an inverted half-cycle pulse in the far field.

Low-Cost Nonuniform Metallic Lattice for Rectifying Aperture Near-Field of Electromagnetic Bandgap Resonator Antennas

Abstract: This article addresses a critical issue, which has been overlooked, in relation to the design of phase-correcting structures (PCSs) for electromagnetic bandgap (EBG) resonator antennas (ERAs). All the previously proposed PCSs for ERAs are made using either several expensive radio frequency (RF) dielectric laminates or thick and heavy dielectric materials, contributing to very high fabrication cost, posing an industrial impediment to the application of ERAs. This article presents a new industrial-friendly generation of PCS, in which dielectrics, known as the main cause of high manufacturing cost, are removed from the PCS configuration, introducing an all-metallic PCS (AMPCS). Unlike existing PCSs, a hybrid topology of fully metallic spatial phase shifters are developed for the AMPCS, resulting in an extremely lower prototyping cost as that of other state-of-the-art substrate-based PCSs. The APMCS was fabricated using laser technology and tested with an ERA to verify its predicted performance. The results show that the phase uniformity of the ERA aperture has been remarkably improved, resulting in 8.4 dB improvement in the peak gain of the antenna and improved sidelobe levels (SLLs). The antenna system including APMCS has a peak gain of 19.42 dB with a 1 dB gain bandwidth of around 6%.