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.

Finite-difference time-domain modeling of nonperfectly conducting metallic thin-film gratings

Abstract: A simulation tool based on the finite-difference time-domain (FDTD) technique is developed to model the electromagnetic interaction of a focused optical Gaussian beam in two dimensions incident on a simple model of a corrugated dielectric surface plated with a thin film of realistic metal The technique is a hybrid approach that combines an intensive numerical method near the surface of the grating, which takes into account the optical properties of metals, with a free-space transform to obtain the radiated fields A description of this technique is presented along with numerical examples comparing gratings made with realistic and perfect conductors In particular, a demonstration is given of an obliquely incident beam focused on a uniform grating and a normally incident beam focused on a nonuniform grating The gratings in these two cases are coated with a negative-permittivity thin film, and the scattered radiation patterns for these structures are studied Both TE and TM polarizations are investigated Using this hybrid FDTD technique results in a complete and accurate simulation of the total electromagnetic field in the near field as well as in the far field of the grating It is shown that there are significant differences in the performances of the realistic metal and the perfect metal gratings

Near-field far-field transformations using spherical-wave expansions

Abstract: Spherical-wave expansions are a well-known technique of expressing electromagnetic field data. However, most previous work has been restricted to idealized cases in which the expansion coefficients are obtained analytically. In this paper spherical-wave expansions are used as a numerical technique for expressing arbitrary fields specified by analytical, experimental, or numerical data. Numerical results on the maximum wave order needed to expand fields arising from a source of a given size are given for two practical cases, and it is found that the generally accepted wave order cutoff value corresponds to 99.9 percent or more of the power in the input pattern. Near-field patterns computed from far-field data are compared to measured data for the two cases, demonstrating the excellent numerical accuracy of the technique.

Self-Assembled Plasmonic Core–Shell Clusters with an Isotropic Magnetic Dipole Response in the Visible Range

Abstract: We theoretically analyze, fabricate, and characterize a three-dimensional plasmonic nanostructure that exhibits a strong and isotropic magnetic response in the visible spectral domain. Using two different bottom-up approaches that rely on self-organization and colloidal nanochemistry, we fabricate clusters consisting of dielectric core spheres, which are smaller than the wavelength of the incident radiation and are decorated by a large number of metallic nanospheres. Hence, despite having a complicated inner geometry, such a core–shell particle is sufficiently small to be perceived as an individual object in the far field. The optical properties of such complex plasmonic core–shell particles are discussed for two different core diameters.

Accurate computation of wide-band response of electromagnetic systems utilizing narrow-band information

Abstract: Cauchy's technique for interpolating a rational function from samples of frequency responses and/or their derivatives is investigated. This technique can be used to speed up the numerical computations of parameters, including input impedance and RCS of any linear time-invariant electromagnetic system. This technique is utilized to find the far field of a slit conducting cylinder (TM incidence) over a bandwidth utilizing the information about the current and its derivatives at a few sample points. The numerical results are presented are in good agreement with exact computational data. This technique is a true interpolation/extrapolation technique as it provides the same defective result as the original electric field integral equation at a frequency which corresponds to the internal resonance of the closed structure. >