Fresnel zone

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

Fresnal Zones in Wireless Links, Zone Plate Lenses and Antennas

Abstract: From the Publisher: The first book devoted solely to Fresnel zones in microwave/mm-wave electromagnetics, this comprehensive survey covers theory, design and practical applications. Whether you are an experienced electromagnetics specialist or a newcomer to the field, whether you need practical design guidelines or a clear and concise exposition of the fundamentals, you'll find this book invaluable. Written by an acknowledged expert, the volume includes a detailed description of the application of Fresnel zones to microwave wireless communication links as well as a comprehensive description of the state-of-the-art in newly created zone plate lens and antenna technologies. It also contains an overview of the basic electromagnetic equations for time harmonic fields, and a thorough treatment of the Fresnel-Kirchoff diffraction theory. If you are a researcher, practising engineer or student in wireless/electromagnetics, this authoritative resource will help you to understand Fresnel zones, zone plate devices and their practical uses, in particular the analysis and design of microwave communication links, Fresnel zone antennas for DBS, Fresnel zone plate lenses for radio telescopes, and conformal curvilinear zone plate antennas. The work is generously illustrated.

Global surface wave diffraction tomography

Abstract: [1] We determine the effect of replacing geometrical ray theory in surface wave tomography with scattering theory. We describe a tomographic method based on a simplified version of the scattering sensitivity kernels that emerge from the Born or Rytov approximations in which surface wave travel times are a weighted average of phase or group slowness over the first Fresnel zone of the wave. We apply this “diffraction tomography” to Rayleigh and Love wave group velocity measurements to produce group velocity maps from 20 to 150 s period on a 2° × 2° grid globally. Using identical data and damping parameters, we also produce maps using “Gaussian tomography” which is based on ray theory with intuitive Gaussian smoothing constraints. Significant differences in the amplitude and geometry of the imaged features appear primarily at long periods but exist even in the short-period maps in regions where average path lengths are large. Diffraction tomography, therefore, is significant in most oceanic regions at all periods, but it is also important on continents at long periods at least. On average, diffraction tomography produces larger velocity anomalies in a period-dependent band of spherical harmonic degrees, and diffraction and Gaussian tomography maps decorrelate past a critical spherical harmonic degree that also depends on period. The widths of resolving kernels that emerge from diffraction tomography are systematically larger than those from Gaussian tomography. Finally, mantle features inferred from diffraction tomography tend to have larger amplitudes and extend deeper than those from Gaussian tomography.

Real space soft x-ray imaging at 10 nm spatial resolution.

Abstract: Using Fresnel zone plates made with our robust nanofabrication processes, we have successfully achieved 10 nm spatial resolution with soft x-ray microscopy. The result, obtained with both a conventional full-field and scanning soft x-ray microscope, marks a significant step forward in extending the microscopy to truly nanoscale studies.

Fresnel volume ray tracing

Abstract: The concept of “Fresnel volume ray tracing” consists of standard ray tracing, supplemented by a computation of parameters defining the first Fresnel zones at each point of the ray. The Fresnel volume represents a 3-D spatial equivalent of the Fresnel zone that can also be called a physical ray. The shape of the Fresnel volume depends on the position of the source and the receiver, the structure between them, and the type of body wave under consideration. In addition, the shape also depends on frequency: it is narrow for a high frequency and thick for a low frequency. An efficient algorithm for Fresnel volume ray tracing, based on the paraxial ray method, is proposed. The evaluation of the parameters defining the first Fresnel zone merely consists of a simple algebraic manipulation of the elements of the ray propagator matrix. The proposed algorithm may be applied to any high‐frequency seismic body wave propagating in a laterally varying 2-D or 3-D layered structure (P, S, converted, multiply reflected, et...

Aperture averaging of optical scintillations in the turbulent atmosphere

Abstract: We have developed approximate expressions for the aperture-averaging factor of optical scintillation in the turbulent atmosphere. For large apertures and weak path-integrated turbulence with a small inner scale, the variance of signal fluctuations is proportional to the -7/3 power of the ratio of the aperture diameter to the Fresnel zone size. If the inner scale is large, the variance is proportional to the -7/3 power of the ratio of the aperture diameter to the inner scale. In strong path-integrated turbulence, two scales develop. That portion of the variance associated with the smaller scale is proportional to the -2 power of the ratio of the aperture diameter to the phase coherence length. That portion of the variance associated with the larger scale is proportional to the -7/3 power of the ratio of the aperture diameter to the scattering disk. These simple approximations are within a factor of 2 of the measurements.