Fresnel zone

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

Common-shot Fresnel beam migration based on wave-field approximation in effective vicinity under complex topographic conditions

Abstract: Gaussian beam migration is a versatile imaging method for geologically complex land areas, which overcomes the limitation of Kirchhoff migration in imaging multiple arrivals and has no steep-dip limits of one-way wave-equation migration. However, its imaging accuracy depends on the geometry of Gaussian beam that is determined by the initial parameter of dynamic ray tracing. As a result, its applications in exploration areaswith strong variations in topography and near-surface velocity are limited. Combined with the concept of Fresnel zone and the theory of wave-field approximation in effective vicinity, we present a more robust common-shot Fresnel beam imaging method for complex topographic land areas in this paper. Compared with the conventional Gaussian beam migration for irregular topography, our method improves the beam geometry by limiting its effective half-width with Fresnel zone radius. Moreover, through a quadratic travel-time correction and an amplitude correction that is based on the wave-field approximation in effective vicinity, it gives an accurate method for plane-wave decomposition at complex topography, which produces good imaging results in both shallow and deep zones. Trials of two typical models and its application in field data demonstrated the validity and robustness of our method.

Depth resolution enhancement in double-detection optical scanning holography

Abstract: We propose an optical scanning holography system with enhanced axial resolution using two detections at different depths. By scanning the object twice, we can obtain two different sets of Fresnel zone plates to sample the same object, which in turn provides more information for the sectional image reconstruction process. We develop the computation algorithm that makes use of such information, solving a constrained optimization problem using the conjugate gradient method. Simulation results show that this method can achieve a depth resolution up to 1 μm.

Theory of diffraction of vortex beams from structured apertures and generation of elegant elliptical vortex Hermite–Gaussian beams

Abstract: In this work, a comprehensive analytic study of the diffraction of vortex beams from structured apertures is presented. We formulate the near- and far-field diffraction of a vortex beam from an aperture having an arbitrary functionality in the Cartesian coordinates by two general and different approaches. We show that each of the resulting diffraction patterns can be determined by a number of successive derivatives of the 2D Fourier transform of the corresponding hypothetical aperture function or equally can be obtained by a summation of 2D Fourier transforms of the corresponding modified aperture function. We implement both introduced analytic approaches in predicting the diffraction of a vortex beam from an elliptic Gaussian aperture, an elliptic Gaussian phase mask, and a hyperbolic Gaussian phase mask in the near- and far-field regimes. It is shown that the predicted diffraction patterns by both these approaches are exactly the same. It is shown that the diffraction of a vortex beam from an elliptic Gaussian aperture at the far-field regime forms a light beam that belongs to a family of light beams we call elegant elliptical vortex Hermite–Gaussian beams. In addition, the diffractions of a vortex beam from a Fresnel zone plate in general form for the on- and off-axis situations are formulated, and sinusoidal and binary zone plates are investigated in detail. Our general analytic formula can be used for a large variety of apertures including off-center situations and asymmetrical cases.

Multipath tolerant cellular communication system and method

Abstract: A method for deploying a PCS system wherein radio transceivers are deployed at spacings which correspond to a diameter of a first Fresnel zone and set output powers of the transceivers to define cells which correspond to the first Fresnel zone of the transceivers. A PCS system having radio transceivers deployed at spacings corresponding to a diameter of a first Fresnel zone and operating at output powers which define cells corresponding to the first Fresnel zones of the transceivers. A handoff area surrounds the first Fresnel zone breakpoint.