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Fresnel zone
About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.
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23 Sep 2020
TL;DR: In this paper, a wideband worst case model to account for the diffraction of a plane electromagnetic (EM) wave by a system hull made of a conductive material is developed, which can be used for estimating the amplitudes of electric and magnetic fields in places of antenna mounting on the hull of an airborne vehicle.
Abstract: A wideband worst case model to account for the diffraction of a plane electromagnetic (EM) wave by a system hull made of a conductive material is developed. The model can be used for estimating the amplitudes of electric and magnetic fields in places of antenna mounting on the hull of an airborne vehicle (aircraft, helicopter, etc.). The model is based on consideration of the fields radiated by electric dipole in a low-frequency range and on the Fresnel approach to analysis of the diffraction in resonance- and high-frequency ranges. The use of analytical methods provides the high computational efficiency of the model. The developed model is validated by comparison of calculation results obtained by the model with results of numerical simulation performed in framework of FDTD and MOM (the ratio of the wavelength to the obstacle dimension is varied from 100 to 0.5).
01 Aug 2016
TL;DR: In this paper, the intensity distribution in the vicinity of the focus of a circular Fresnel zone plate formed by a Bessel-Gauss beam is studied, and the width and the length of the central hollow of a central hollow depending on the order of the beam and the number of plate zones.
Abstract: The intensity distribution in the vicinity of the focus of circular Fresnel zone plate formed by Bessel-Gauss beam is studied. Dark hollow beams are obtained near focus under the illumination of high order Bessel-Gauss beam, the width and the length of central hollow depends on the order of the beam and the number of plate zones. These beams with special intensity distribution in the field of laser processing and trapping particles have potential application value.
21 Oct 2004
TL;DR: In this paper, the authors define a generalized Fresnel zone plate as a diffraction grating device that diffracts a predetermined wave front into a spherical converging one, which is constructed as the intersection of a family of refracting profiles with an arbitrary shaped surface.
Abstract: We define a generalized Fresnel zone plate as a diffraction grating device that diffracts a predetermined wave front into a spherical converging one. The device is constructed as the intersection of a family of refracting profiles with an arbitrary shaped surface. The refracting profiles are obtained as envelopes of specific families of Cartesian ovals. The classical Fresnel zone plate is a particular case of this class. This construction has several interesting applications.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
02 Jul 2018
TL;DR: In this paper, a variational statement of synthesis problem according to the prescribed amplitude pattern for the plane arrays is formulated in the variational statements, and the corresponding Euler equation of functional is obtained and the successive approximation method is used for its numerical solving.
Abstract: The approach that takes into account the requirements to the electromagnetic field (EM) characteristics in Fresnel zone while statement of synthesis problem according to prescribed amplitude pattern for the plane arrays is proposed. The synthesis problem is formulated in the variational statement. The optimizing functional contains the term, which provides the possibility to minimize the EM field amplitude in near zone of array. The respective Euler equation of functional is obtained and the successive approximation method is used for its numerical solving. The computational results are discussed.
24 Aug 2009
TL;DR: In this article, the authors proposed a common reflection surface (CRS) stack to estimate the optimum aperture size for zero-offset and its dislocation with varying offset, which is the smallest aperture providing interpretable amplitudes along with the highest possible S/N ratio and the minimum number of required summations.
Abstract: Summary In Kirchhoff migration, the proper choice of the aperture is essential: the optimum aperture is the limited aperture defined by the first projected Fresnel zone. This is the smallest aperture providing interpretable amplitudes along with the highest possible S/N ratio and the minimum number of required summations. In addition, limited-aperture migration naturally prevents operator aliasing. The commonreflection-surface (CRS) stack provides kinematic wavefield attributes which allow to estimate the optimum aperture size for zero-offset and its dislocation with varying offset. The aperture is centered around the stationary point, but this point has to be associated with the corresponding point in the migrated domain in an additional process. Kirchhoff migration itself implicitly connects the stationary point and the image point in depth by collecting the energy in the vicinity of the former and assigning it to the latter. In principle, any smoothly varying property can be migrated “on top” of the seismic data themselves by applying multiple weighted diffraction stacks. The most generic property to be migrated in this way is the source/receiver midpoint which yields the lateral position of the stationary point mapped to the image location in depth. We investigate the validity and accuracy of this approach for simple synthetic data and apply it to a real land data set. A straightforward extension is introduced to solve some of the numerical problems inherent to this approach and CRSbased strategies are transferred from the time domain to the depth domain to identify the reflector images and to attenuate migration noise. Finally, the approach is compared to another CRS-based approach which directly evaluates the tangency criterion.