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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.


Papers
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Journal ArticleDOI
TL;DR: In this article, an asymptotic solution for the electromagnetic diffraction by a perfectly conducting strip illuminated at grazing incidence is obtained by an extension of the uniform GTD for plane, cylindrical, and spherical wave illuminations.
Abstract: An asymptotic solution for the electromagnetic diffraction by a perfectly conducting strip illuminated at grazing incidence is obtained by an extension of the uniform GTD. Uniform expressions for the scattered field are given for plane, cylindrical, and spherical wave illuminations. Outside the transition regions these essentially reduce to results obtained by an ordinary application of the uniform GTD augmented by slope diffraction. In the case of plane wave illumination a very simple closed form expression is provided for the scattered far field. Numerical results are presented and compared with those calculated from a moment method solution.

87 citations

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate a technique for optical trapping of single particles in a fluid, which is based on the intense near-field gradients around small apertures in a metal film.
Abstract: In recent years, optical micromachines based on forces exerted by strongly focused beams of light have started to provide unprecedented access to nonintrusive measurement and manipulation of matter on submicron length scales. However, the sharpness of the present optical tweezers is restricted by the spatial gradients of light attainable with diffraction-limited optics. Here, we demonstrate a technique for optical trapping of single particles in a fluid, which is based on the intense near-field gradients around small apertures in a metal film. Our scheme should be able to trap smaller particles with a fraction of the laser intensity required by conventional optical tweezers. Detailed simulations of the electromagnetic fields near apertures and the resulting forces they can produce are described. We also present a proof-of-principle experiment in which the trapping of latex beads is demonstrated by following the time evolution of their fluorescence. Our scheme allows containment of particles in free soluti...

87 citations

Journal ArticleDOI
15 Jun 1987
TL;DR: In this article, the four-point bivariate Lagrange interpolation algorithm was applied to near-field antenna data measured in a plane-polar facility, and the results were sufficiently accurate to permit the use of the FFT (fast Fourier transform) algorithm to calculate the far-field patterns of the antenna.
Abstract: The four-point bivariate Lagrange interpolation algorithm was applied to near-field antenna data measured in a plane-polar facility. The results were sufficiently accurate to permit the use of the FFT (fast Fourier transform) algorithm to calculate the far-field patterns of the antenna. Good agreement was obtained between the far-field patterns as calculated by the Jacobi-Bessel and the FFT algorithms. The significant advantage in using the FFT is in the calculation of the principal plane cuts, which may be made very quickly. Also, the application of the FFT algorithm directly to the near-field data was used to perform surface holographic diagnosis of a reflector antenna. The effects due to the focusing of the emergent beam from the reflector, as well as the effects of the information in the wide-angle regions, are shown. The use of the plane-polar near-field antenna test range has therefore been expanded to include these useful FFT applications. >

86 citations

Patent
07 Jun 1995
TL;DR: In this article, the magnetic sensor is placed at a right angle to the sensor electronics to provide a smaller surface area across the diameter of the sensor, and the magnet that charges the object to be detected is manufactured as a part of a sensor encapsulant.
Abstract: A method and apparatus for sensing proximity of an object using near-field effects or magnetic effects. The sensor chips are designed to accommodate numerous sensing elements. In the electromagnetic sensor, radio frequency energy is fed to an antenna. The antenna radiates this radio frequency energy to charge the surface of an object. When the position of the object changes, the impedance of the antenna due to near-field effects changes. This impedance change is detected to provide an indication of the object's movement. In the magnetic sensor, the sensing element is placed at a right angle to the sensor electronics to provide a smaller surface area across the diameter of the sensor. The magnet that charges the object to be detected is manufactured as a part of the sensor encapsulant. The sensing device may be packaged to be inserted into a wall to provide a sensor having a leak-free seal.

86 citations

Journal ArticleDOI
TL;DR: In this article, a plasmonic quantum cascade laser antenna that confines coherent mid-infrared radiation well below the diffraction limit was presented. But the antenna was fabricated on the facet of a midinfrared quantum cascade (QC) laser and consisted of a pair of gold nanorods separated by a gap.
Abstract: We report a plasmonic quantum cascade laser antenna that confines coherent midinfrared radiation well below the diffraction limit. The antenna was fabricated on the facet of a midinfrared quantum cascade laser and consists of a pair of gold nanorods separated by a gap. The antenna near field was characterized by an apertureless near-field scanning optical microscope; field confinement of about 100 and 70nm, limited by the gap size, was demonstrated at wavelengths of 7.0 and 5.3μm, respectively. This device may find important applications in midinfrared subwavelength chemical and biological imaging and spectroscopy.

86 citations


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