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Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
fresh fuel nuclear fuel which has never participated in a nuclear reaction and is thus only slightly radioactive. Fresnel region the region in space around an antenna at which the fields have both transverse and radial components and the antenna pattern is dependent on the distance from the antenna. The Fresnel, or near-field, region is typically taken to be r < 2D 2 /, where r is the distance from the antenna, D is the maximum dimension of the antenna, and is the wavelength. Fresnel zone an indicator of the significant volume of space occupied by a radio wave propagating along a line-of-sight path between the transmitter and receiver. At an arbitrary point which is at distance d1 from the transmitter and at distance d2 from the receiver, along the axis joining the transmitter and the receiver, a radio wave with wavelength occupies a volume, which at that point between the transmitter and the receiver, has a radius which is given by the radius of the first Fresnel zone. The radius of the first Fresnel zone is given by R= d1 d2 d1 + d2
Propagation Prediction for Urban Systems
Published in Lal Chand Godara, Handbook of Antennas in Wireless Communications, 2018
Henry L. Bertoni, Saúl A. Torrico
By using the logarithmic scale for the horizontal separation R in Fig. 3.8, it is clearly seen that the variation of the received signal has two distinct slopes separated by a break point RB that lies near the last peak in the two ray model. Before the RB, the radio signal oscillates severely because of alternating regions of destructive and constructive combination of the two rays, whereas after the RB it decreases more rapidly with distance due. The break point distance can be understood in terms of the first Fresnel zone clearance. The first Fresnel zone is an ellipsoid of revolution having the two antennas as foci, and is such that the distance from one antenna to a point on the ellipsoid and back to the other antenna is λ/2 greater than the direct path distance between the antennas.
Theory and practices involved in depth and source localization of anisotropy
Published in Rajib Biswas, Recent Developments in Using Seismic Waves as a Probe for Subsurface Investigations, 2023
To estimate the lateral resolution of an unmigrated stacked core refractive wave data, often seismologists use the concept of Fresnel zone (Lindsey, 1989; Sheriff, 1996). Fresnel zone determines the spatial resolving power for unmigrated seismic data, for which important lithological changes may be analysed along with the seismic profile direction. Fresnel zone is an area of the reflector dependent on the frequency and range from which most of the energy of a reflection is returned where the arrival times differ by less than half a period of time from the first break. These waves after reflection from the Fresnel zone (with such arrival times) will interfere constructively and detected as a single arrival. Subsurface features cannot be detected using seismic waves if they have wavelengths smaller than the Fresnel zone. The zone which indicates the part of a reflector (Figure 3.1) from which energy of a reflection can reach a detector where the waves travel with a one-fourth wavelength is called the first Fresnel zone. In the second Fresnel zone, the energy comes delayed one-half to one cycle adding destructive to the energy from the first zone. There is a third Fresnel zone and so on. The size of the Fresnel zone determines the minimum size feature that can be resolved from the seismic data (Dewangan et al., 2007). The radius of the Fresnel zone for zero offset is: R=12√(VλT)
Development of projection X-ray microscope with 100 nm spot size
Published in Nondestructive Testing and Evaluation, 2022
Norihito Matsunaga, Tomoya Sato, Kota Higuchi, Atsushi Yamada
Since Wilhelm Röntgen’s discovery of X-rays in 1895, High-resolution CT system using X-rays has been widely used in non-destructive inspection of industrial samples, material science and life science. In such situations, X-ray microscopes are often used as measurement systems because the short wavelength performance of X-rays makes it easy to achieve high spatial resolution. Through research conducted at the Synchrotron Radiation Facility, X-ray microscope technology has made remarkable progress [1–6]. These state-of-the-art X-ray microscopes contribute significantly to advanced research in life sciences [4,5,7] and materials sciences [6,8,9]. Generally, these microscopes realise high spatial resolution by using an imaging optical element such as a Fresnel Zone Plate or a reflection mirror (For example [1–4,6,9]).
High-diffraction-efficiency Fresnel lens based on annealed blue-phase liquid crystal–polymer composite
Published in Liquid Crystals, 2019
Hua-Yang Lin, Nejmettin Avci, Shug-June Hwang
In this study to effectively purify the BPLC domain, a thermal annealing process is proposed that expels the remaining monomer from the odd regions and ameliorates the purity of the LC-rich regions. This purification method is similar to the principle of temperature-induced phase separation (TIPS) [23,24]. Based on the temperature difference, the phase separation of the BPLC and the photo-sensitive monomer is induced. When the thermal annealing treatment is thoughtfully controlled, more coalescence of BPLC droplets can be progressively obtained and make the remained monomers gradually expelled out of the BPLC domains. As a result, a perfect BPLC–polymer binary Fresnel zone with well phase separation is successfully achieved. According to the experimental results, the great success of the proposed TIPS annealing technique significantly improves the optical diffraction efficiency and response time of the BPLCFL. Therefore, we claim that the proposed annealing technique is extremely prospective for constructing the polymer–BPLC composite Fresnel lens device.
Sparsity-assisted phase retrieval in the Fresnel zone
Published in Journal of Modern Optics, 2019
In conclusion, we have demonstrated the possibility of single-shot phase retrieval from Fresnel zone intensity data. The performance of the traditional Gerchberg–Saxton (GS) and a sparsity-assisted GS algorithm for this problem is tested. It is shown that the proposed sparsity-assisted phase retrieval algorithm can provide excellent phase reconstruction with single-shot near zone diffraction intensity data. The system can have high resolution and wide field of view purely guided by sensor chip specifications. The near zone intensity data typically has no strong peaks as is often the case with the strong dc peak in the far-field diffraction data. The data collection thus does not face difficulties associated with a dynamic range of sensors. The proposed method is shown to be robust to noise. A discussion regarding sampling considerations for enabling good phase recovery has also been provided which is an important point to consider when designing a practical compact phase imaging system. Our results suggest the possibility of a compact single-shot less-less phase imaging system that can have applications in multiple areas such as microscopy, point-of-care diagnostics, wavefront sensing, optical metrology, spatial mode structure determination from waveguides, etc. as we will explore in future.