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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.


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Journal ArticleDOI
TL;DR: In this article, the authors provide a brief historical review of how near-field microscopy has developed, including a review of visible and infrared near field microscopy in the context of the main theme, the principles and applications of near-Field microscopy using millimeter to micrometer electromagnetic waves.
Abstract: Conventional optics in the radio frequency (rf) through far-infrared (FIR) regime cannot resolve microscopic features since resolution in the far field is limited by wavelength. With the advent of near-field microscopy, rf and FIR microscopy have gained more attention because of their many applications including material characterization and integrated circuit testing. We provide a brief historical review of how near-field microscopy has developed, including a review of visible and infrared near-field microscopy in the context of our main theme, the principles and applications of near-field microscopy using millimeter to micrometer electromagnetic waves. We discuss and compare aspects of the remarkably wide range of different near-field techniques, which range from scattering type to aperture to waveguide structures.

262 citations

Journal ArticleDOI
TL;DR: This work has shown how input impedance, far-field radiation pattern, radiation efficiency, and the magnitude of the near field are affected by the presence of the human body.
Abstract: This work deals with the influence the presence of a person has on the performance of antennas for hand-held portable telephones. It is shown how input impedance, far-field radiation pattern, radiation efficiency, and the magnitude of the near field are affected by the presence of the human body. The investigations have been carried out by applying the finite-difference time-domain (FDTD) technique to a model of the telephone with a lambda /4 monopole antenna and a simple hand-head model of the operator. Results from this configuration are compared with results for the telephone box and antenna alone. Measurements have been performed to verify the results obtained by simulations. The results show that a shadow effect in the far-field pattern occurs in the direction of the person and that the radiation pattern, including polarization, changes considerably from the telephone with the antenna alone. The impedance results show a change in resonance frequency when the telephone is placed next to a person. Results for radiation efficiency show that close to half of the energy is absorbed by hand and head. On average a system loss of 3-4 dB should be included in a link budget, and there is considerable fading, even in a radio-anechoic chamber, when persons move around in a natural manner. >

261 citations

PatentDOI
TL;DR: In this paper, a microwave near field microscope has a novel microwave probe structure wherein the probing field of evanescent radiation is emitted from a sharpened metal tip instead of an aperture or gap.
Abstract: A microwave near field microscope has a novel microwave probe structure wherein the probing field of evanescent radiation is emitted from a sharpened metal tip instead of an aperture or gap. This sharpened tip, which is electrically and mechanically connected to a central electrode, extends through and beyond an aperture in an endwall of a microwave resonating device such as a microwave cavity resonator or a microwave stripline resonator. Since the field intensity at the tip increases as the tip sharpens, the total energy which is radiated from the tip and absorbed by the sample increases as the tip sharpens. The result is improved spatial resolution without sacrificing sensitivity.

260 citations

Journal ArticleDOI
TL;DR: In this article, an electric field integral equation (EFIE) is developed to relate the near fields to the equivalent magnetic currents, and the method of moments is used to transform the integral equation into a matrix one.
Abstract: An alternative method is presented for computing far-field antenna patterns from near-field measurements. The method utilizes the near-field data to determine equivalent magnetic current sources over a fictitious planar surface that encompasses the antenna, and these currents are used to ascertain the far fields. Under certain approximations, the currents should produce the correct far fields in all regions in front of the antenna regardless of the geometry over which the near-field measurements are made. An electric field integral equation (EFIE) is developed to relate the near fields to the equivalent magnetic currents. The method of moments is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient method, and in the case of a rectangular matrix, a least-squares solution for the currents is found without explicitly computing the normal form of the equation. Near-field to far-field transformation for planar scanning may be efficiently performed under certain conditions. Numerical results are presented for several antenna configurations. >

260 citations

Journal ArticleDOI
TL;DR: The experimental confirmation of the focusing properties and field enhancement effect of plasmonic lens made of multiple concentric annular rings using a collection mode near field scanning optical microscope.
Abstract: Optimal plasmonic focusing can be achieved through matching the rotational symmetry of the plasmonic lens to the polarization symmetry of a radially polarized illumination. In this letter, we report the experimental confirmation of the focusing properties and field enhancement effect of plasmonic lens made of multiple concentric annular rings using a collection mode near field scanning optical microscope. Surface plasmons excited at all azimuthal directions propagate toward the geometric center and constructively interfere at the focus to create a strongly enhanced evanescent optical “needle” field that is substantially polarized vertically to the plasmonic lens surface. The field enhancement factor can be improved through adding more rings while maintaining the plasmonic focal spot size. Strategy for optimizing the field enhancement factor is studied with both analytical and numerical methods.

258 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023132
2022281
2021376
2020460
2019640
2018604