Fresnel zone

About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.

Large-size local-domain basis function to embody the locality of high frequency diffraction in the Method of Moments

Abstract: The relation between the method of moments (MoM) and high frequency techniques are discussed in view of the locality of the scattering phenomena. Firstly, locality in the high frequency diffraction is embodied in the MoM in view of the method of stationary phase. Local-domain basis functions accompanied with the phase detour, which are not entire domain but are much larger than the segment length in the usual MoM, are introduced to enhance the cancellation of the mutual coupling over the local-domain; the off-diagonal elements in resultant reaction matrix evanesce rapidly. Secondly, the Fresnel zone threshold is proposed for simple and effective truncation of the matrix into the sparse band matrix; the way mitigating computational load of the MoM in high frequency problems is suggested. The extended use of the Fresnel zone threshold in PO-MoM hybrid methods is also mentioned.

Study of piezoelectric transducer for liquid ejection

Abstract: Self-focused acoustic transducers using using Fresnel zone plates have been fabricated and used to eject droplets of high-viscosity liquid, without nozzle, in the drop-on-demand mode. The Fresnel zone plate consists of a series of annular electrodes of half-wave-band source, and the acoustic waves are focused by constructive wave interference. Droplets of glycerin with a high-viscosity of 1400 cP can be ejected under a field of 200 kV/m and at a repetitive frequency of 120 Hz. The acoustic pressure distribution in the glycerin has been been simulated using an open-source computational fluid dynamic code OpenFOAM and measured using a needle-type hydrophone. Both the simulation and measurement give the location of two focal points which agree with the observations in the droplet ejection experiment.

Fresnel-Aperture PSDM

Abstract: A-34 FRESNEL-APERTURE PSDM Abstract 1 We introduce the Fresnel aperture which is the direct time-domain equivalent at the receivers’ surface of the subsurface Fresnel zone. Based on this concept we propose a new and efficient method for optimal aperture selection and Kirchhoff prestack depth migration. The problem with complex media is that multiple Fresnel apertures apparently exist for a given image point with just one of these corresponding to a possible real geological structure. Hence the contribution from these ‘false’ Fresnel apertures cause a noise-corrupted image of the subsurface. We propose a method by analogy with the velocity analysis where

Design of multi-beam reflectarray using mushroom-like structure

Abstract: Improving the propagation environment using a reflectarray has recently been proposed to eliminate blind zones or to improve the capacity of line of sight (LOS) multi-input and multi-output (MIMO) technology, which is a more significant factor at higher frequencies. For this purpose, the reflectarray must be able to scatter an arbitrary oblique incident wave (θi, φi) in an arbitrary oblique direction (θr, φr) in order to establish the reflectarray within a limited space outdoors. Moreover, a Fresnel zone multi-beam reflectarray is desired to achieve a large coverage area and high received level. This paper utilizes the fact that multiple in-phase surfaces are generated when a periodic mushroom structure is employed and proposes a novel multi-beam reflectarray using this characteristic. The design method is described and simulation and measured results are presented.