Fresnel zone

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

Liquid crystal variable focus lens based on Fresnel zone plate

Abstract: The liquid crystal (LC) variable focus lens combining LC Fresnel Zone Plate with spherical lens (FZP-S) presented in the paper is an electro-optical system using the applied voltages to control the variation of its focal length. Theoretical study for the mathematic model of the hybrid FZP-S lens shows that the focus length of the hybrid lens can use the similar method to that of the system with conventional refractive lens. The LC FZP with the electrodes widths vary as a FZP which was fabricated on a glass substrate with two layers of transparent electrodes in our experiment. The minimum of the electrodes width is 1.2um.The advantage of such system is that the focal length of which can be changed electrically without mechanical movement. The effect of the focus length variation was verified by the experiment results.

Image reconstruction algorithms for the microwave holographic vision system with reliable gap detection at theoretical limits

Abstract: We present a reliable image reconstruction algorithm suitable for a microwave holographic vision system with several sensors coupled to the spin-diode based microwave detector and a single emission source. An objective is, by reconstructing the spatial microwave scattering density on the scene, to detect the presence and the nature of road obstacles impeding driving in the near vehicle zone. The idea of holographic visualization is to reconstruct the spatial microwave scattering density of an object by detecting an amplitude and phase of a reflected signal by lattice of sensors. We discuss versions of an algorithm, determine and analyse its resolution limits for various distances with different number of sensors for a one-dimensional test problem of detecting two walls (or posts) separated by a gap at a fixed distance. The maximal interval between sensors needed for a reliable reconstruction equals approximately Fresnel zone width. We show that maximal resolution achieved by our algorithm with an appropriate number of sensors was about 40% of Fresnel zone width for wall detection and about 30% of zone width for gap detection.

A dual-polarized Fabry–Pérot antenna with high gain and wide bandwidth for millimeter-wave applications

Abstract: We introduce a dual-polarized (DP) Fabry—Perot cavity (FPC) antenna operating at the millimeter-wave (mmWave) frequency band with high-gain and wideband characteristics. A DP feeding source and a partially reflective surface (PRS) integrated with a Fresnel zone lens are suggested to realize dual-polarization wave radiation over a wide impedance bandwidth. The feeding source provides vertical and horizontal polarizations while keeping high isolation between the two polarizations. PRS is used to realize Fabry cavity to produce a directive beam radiation. The integrated Fresnel zone rings are introduced for phase correction, leading to a significant gain enhancement for the antenna. For verification, a 60-GHz FPC antenna prototype with DP radiation is designed and fabricated with measurement results. It consists of a feeding source, a PRS integrated with a Fresnel zone lens, a quasi-curved reflector, and four three-dimensional printed supporters. The results illustrate that the peak gains of vertical and horizontal polarizations are 18.4 and 17.6 dBi, respectively. The impedance matching bandwidth for the two polarizations is 14%. The performance ensures that the proposed DP FPC antenna is a promising candidate for the fifth-generation wireless communication systems in the mmWave band.