Fresnel zone

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

Fresnel Zone Plate Antenna

Abstract: The paper describes the design of a Fresnel zone plate suitable for use as an antenna in the centimetric or lower wavelength range. It has been shown that such antennas can be fabricated by using either metal or dielectric rings. Its properties have been analysed by employing the simple methods of electromagnetic diffraction. Experimental results are reported showing close agreement with the theory. A theory has been presented explaining the working of the dielectric ring zone plate. The investigation leads to the conclusion that both the metal and dielectric zone plates are useful as low gain antennas.

Fresnel-Zone-Plate Spectrometer with Central Stop*

Abstract: The marked chromatic aberration of a Fresnel-zone-plate lens can be used as a variable narrow-band optical filter, and thus a holographic spectrometer. The filtering properties of the zone plate are analyzed, with particular emphasis on the effect of a central stop over the low-order rings. It is shown that the central stop can markedly improve the rejection of frequencies outside the pass band without significant degradation of the spectrometer resolution.

Fresnel Interferometric Imager: ground-based prototype

Abstract: The Fresnel Interferometric Imager is a space-based astronomical telescope project yielding milli-arcsecond angular resolution and high contrast images with loose manufacturing constraints. This optical concept involves diffractive focusing and formation flying: a first “primary optics” space module holds a large binary Fresnel array, and a second “focal module” holds optical elements and focal instruments that allow for chromatic dispersion correction. We have designed a reduced-size Fresnel Interferometric Imager prototype and made optical tests in our laboratory in order to validate the concept for future space missions. The primary module of this prototype consists of a square, 8 cm side, 23 m focal length Fresnel array. The focal module is composed of a diaphragmed small telescope used as “field lens,” a small cophased diverging Fresnel zone lens that cancels the dispersion, and a detector. An additional module collimates the artificial targets of various shapes, sizes, and dynamic ranges to be imaged. We describe the experimental setup, different designs of the primary Fresnel array, and the cophased Fresnel zone lens that achieves rigorous chromatic correction. We give quantitative measurements of the diffraction limited performances and dynamic range on double sources. The tests have been performed in the visible domain, λ=400-700 nm. In addition, we present computer simulations of the prototype optics based on Fresnel propagation that corroborate the optical tests. This numerical tool has been used to simulate the large aperture Fresnel arrays that could be sent to space with diameters of 3 to 30 m, foreseen to operate from Lyman α (121 nm) to mid IR (25 μm).

Three-dimensional primary zero-offset reflections

Abstract: Zero‐offset reflections resulting from point sources are often computed on a large scale in three‐dimensional (3-D) laterally inhomogeneous isotropic media with the help of ray theory. The geometrical‐spreading factor and the number of caustics that determine the shape of the reflected pulse are then generally obtained by integrating the so‐called dynamic ray‐tracing system down and up to the two‐way normal incidence ray. Assuming that this ray is already known, we show that one integration of the dynamic ray‐tracing system in a downward direction with only the initial condition of a point source at the earth’s surface is in fact sufficient to obtain both results. To establish the Fresnel zone of the zero‐offset reflection upon the reflector requires the same single downward integration. By performing a second downward integration (using the initial conditions of a plane wave at the earth’s surface) the complete Fresnel volume around the two‐way normal ray can be found. This should be known to ascertain t...

Millimeter-Wave Left-Handed Extraordinary Transmission Metamaterial Demultiplexer

Abstract: In this work, by using an extraordinary transmission metamaterial prism and taking advantage of its inherent dispersive behavior, the feasibility of manufacturing a demultiplexer/multiplexer or even a spectrogram analyzer at millimeter-waves is shown. Depending on the incoming beam frequency, the outgoing beam suffers in a wedge-shaped configuration a different deflection (governed by Snell's law). Since the frequency dependent index of refraction of this metamaterial can go from negative values to almost zero for the first propagation band (cut-off regime) and also be positive for the second propagation mode (non-cut-off regime), different negative and positive outgoing angles can be obtained and then, diverse paths for each frequency, as the Fresnel zone experimental results confirm.