Fresnel zone

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

Estimation of target size using two passive infrared sensors

Abstract: Passive infrared (PIR) sensors are widely used as a part of unattended ground sensor suite for situational awareness. Currently, the PIR sensor is mainly used as a wakeup sensor for the imaging sensor in order to conserve power. Since the PIR sensor mainly responds to the thermal radiation from the target, animals in the vicinity of the sensor can cause many false alarms. The number of false alarms can be cut drastically, if the target’s size can be estimated and a decision is made based on target size. For example, if the target is 5 ft 9 in tall and 1.5 ft wide, it is most likely a human being as opposed to an animal. In this paper, we present a technique to estimate target size using two PIR sensors with Fresnel lens arrays. One of the PIR sensors is mounted such that its Fresnel zones are horizontal to the ground, and the second PIR sensor is mounted such that its Fresnel zones are at a slant angle to the horizontal plane. The former is used to estimate the width/length, while the latter is used to estimate the height of the target. The relative signal strength between the two sensors is used to estimate the distance of the target from the sensor. The time it takes to cross the Fresnel zones is used to estimate the speed of the target. The algorithm is tested using the data collected in the woods, where several animals are observed roaming.

Fresnel zone plates made by holography in the extreme ultraviolet region

Abstract: We present the fabrication of Fresnel zone plates (FZP) by holography that yields FZPs completely free from imperfections such as zone placement errors and finite pixel size effects found in serial writing techniques such as e-beam lithography (EBL). Our holographic scheme is based on the interference of a spherical wave and a plane wave. A partially transparent membrane containing a pinhole is illuminated by a fully coherent plane wave (λ = 13.4 nm). The spherical wave, obtained by diffraction from the pinhole, interferes with the plane reference wave that is transmitted by the membrane. The interference pattern, which is a hologram of the pinhole, is recorded on a photoresist film and used to fabricate a FZP that has resolution similar to the size of the pinhole.

High Numerical Aperture Diffractive Optics for Imaging Applications at 0.6 THz Frequency

Abstract: High numerical aperture diffractive lenses such as conventional and combined zone plates, silicon based multilevel phase Fresnel zones were developed for high resolution THz imaging at the frequency range of 0.6 THz. Spectral features, spatial profiles, and focal depth characteristics are discussed, demonstrating the results to be in a good agreement with simulation data. In addition, new technique of the bifocal THz imaging is proposed.

Beamforming in high resolution single-position imaging radars

Abstract: The results of beamforming processes by antennas of single-position imaging radars investigation are presented. Taking into account the high effective antenna surface, which is need for ensuring of the high spatial resolution, the peculiarity of these processes consists in disposition of the objects in Fresnel zone, where the antenna pattern is not formed yet. However, on the potential possibility to provide high spatial resolution, the near-zone imaging radar can be characterized by the presence of high distortions in the image formation channel. In this paper a characteristic of the distortions caused by beamforming features is described and the spread function of the channel of a single-position imaging radar was analytically established. The results allow one to reasonably create an optimal algorithm for spatio-temporal signal processing in single-position imaging radars.