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.

Near-Field Antenna Measurement Techniques

Abstract: A complete description of the near-field antennameasurement techniques is provided in this chapter. After a discussion of the state of the art, the key steps of the classical near-field–far-field (NF-FF) transformations with plane-rectangular, cylindrical, and spherical scannings, in their probe-uncompensated and probe-compensated versions, are summarized, by also providing some analytical details on the wave expansions commonly adopted to represent the antenna radiated field. The nonredundant sampling representations of electromagnetic field are then introduced and applied to drastically reduce the number of required NF data and related measurement time with respect to the classical NF-FF transformations. At last, the NF-FF transformations with innovative spiral scannings, allowing a further measurement time saving, are described.

Illustration of the role of multiple scattering in subwavelength imaging from far-field measurements

Abstract: Recently it has been proposed that the classical diffraction limit could be overcome by taking into account multiple scattering effects to describe the interaction of a probing wave and the object to be imaged [Phys. Rev. E73, 036619 (2006)]. Here this idea is illustrated by considering two point scatterers spaced much less than a wavelength apart. It is observed that while under the Born approximation the scattered field pattern is similar to that of a monopole source centered between the scatterers, multiple scattering leads to a more complicated pattern. This additional complexity carries information about the subwavelength structure and can lead to superresolution in the presence of large noise levels. Moreover, it is pointed out that the additional information due to multiple scattering is interpreted as a form of coherent noise by inversion algorithms based on the Born approximation.

Perforated Semishells: Far-Field Directional Control and Optical Frequency Magnetic Response

Abstract: Reduced-symmetry plasmonic nanostructures can be designed to support a range of novel optical phenomena, such as nanoscale control of the far-field scattering profile and magnetic resonances at optical frequencies. A family of reduced-symmetry nanostructures—plasmonic semishells with specifically shaped and oriented perforations introduced into the metallic shell layer—can be tailored to control these effects. Unlike core−shell nanoparticles, perforated semishells can be fabricated using a combination of clean-room techniques. For a semishell with a single spherical perforation positioned on its symmetry axis, we examine how the resonant modes of the structure depend on hole size and shape. Placing the perforation off the symmetry axis allows a family of higher-order modes to be excited in the nanostructure, along with complex near-field charge distributions for the various resonant modes. This reduced-symmetry case provides a platform for optical studies, which agree quite well with theoretical analysis....

Computational Lens for the Near Field

Abstract: A method is presented to reconstruct the structure of a scattering object from data acquired with a photon scanning tunneling microscope . The data may be understood to form a Gabor type near-field hologram and are obtained at a distance from the sample where the field is defocused and normally uninterpretable. Object structure is obtained by the solution of the inverse scattering problem within the accuracy of a perturbative, two-dimensional model of the object.