Fresnel zone

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

Study of non-zero offset Fresnel zone

Abstract: Fresnel zone is an important parameter of seismic lateral resolution The expressions of non-zero offset Fresnel zone for horizontal and dip reflectors were deduced Two numerical examples illustrated the theoretical results, and the ellipse features of non-zero offset Fresnel zone expounded the distribution of the main energy of seismic diffracted waves quantitatively The results show that offset is the main factor in changing the size and eccentricity of the Fresnel ellipse But the influence of interface dip is relatively small and can be omitted A considerable declinational departure of the ellipse's center from the reflection point may be caused by the reflector's dip, and the deflection grows rapidly with the dip increasing These results can be used for guiding the design of field survey project and the parameter selection in data processing It is also an expansion to the Fresnel zone in common sense

A simplified fabrication process of Fresnel zone plates with controlling proximity effect correction.

Abstract: Fresnel zone plates (FZPs) for soft X-ray microscopy with an energy range of 284 eV to 540 eV are designed and fabricated in a simple method. An adequate aspect ratio of the resist mold for electroplating was obtained by the proximity effect correction technology for an incident electron beam on a single thick layer resist. Without additional complicated reactive ion etching, a sufficient electro plating mold for nickel structures was fabricated. The overall fabrication procedures which involve a mix-and-match overlay technique for electron beam lithography and an optic exposure system that centers the membrane on the nanostructures, and hybrid silicon etching technology in junction with deep anisotropy and a KOH wet method in order to release the backside Si substrates of the Si3N4 membranes with no deformation of FZPs are introduced. High quality nanostructures with minimum outermost zone widths of 50 nm and diameters of 120 microm were fabricated with simplified fabrication process and with cost-effective.

Diffractive efficiency of terahertz zone plates with continuous phase

Abstract: We presented a design of the zone plate with continuous phase with Polytetrafluoroethylene (PTFE) based on scalar diffraction theory. Diffraction fields of the zone plate with continuous phase and the phase-correcting Fresnel zone plate with incidence of uniform plane wave were analyzed and compared. The effects of the focal length and diameter of the zone plate with continuous phase on the diffraction field were discussed. The simulations of intensity distribution on the focal plane and the optic axis based on Rayleigh-Sommerfeld diffraction formula were completed using Matlab. The results indicate that the zone plate with continuous phase performs better than the phase-correcting Fresnel zone plate. The intensity on the focus of the zone plate with continuous phase is 1.17, 1.35, 2.62 times stronger than that on 8-level, 4-level, 2-level phase-correcting Fresnel zone plate's respectively. The fabrication process might give rise to a phase error, such as groove depth error, surface roughness. The effects of the phase errors on the performance of the zone plate were discussed.

Optimum diversity separation for over-sea line-of-sight radio links

Abstract: Given the requirement for a line-of-sight link operating over a sea path and having established the clearance at the horizon over the appropriate range of k-values using standard procedure, a method is derived for determining the optimum spacing for worst case conditions between receiving antennas where dual space diversity is employed to reduce 2-path fading The means of calculating the minimum received signal, ie the deepest fade possible with destructive interference in the 2-path mode, is also included; as a check on performance if the optimum spacing cannot be realized or where the optimum value is used and the worst case conditions assumed in this determination do not apply in practicePrograms for these calculations are included which run on TI58 or TI59 pocket calculators A third program for the calculation of Fresnel zone numbers (cubic equation solution) is included The method is valid for any frequency band in which line-of-sight criteria apply and 2-path propagation occursAlthough consideration of the probability of occurrence of any particular propagation mode lies outside the scope of this paper, it is found that the correct 2-path diversity spacing also provides substantial protection in other adverse propagation circumstances