Equivalent Reflector Research Articles

UWB full polarization single-plane monopulse reflector antenna

ABSTRACT UWB dual polarization azimuth plane monopulse feed-reflector antenna is presented. Quadridge ‎open ended waveguide working in frequency range from 6 to 12 GHz is proposed as feed for Cassegrain ‎reflector. The feed phase center distance is 0.65 and 1.3 at lowest and highest operating ‎frequency respectively. Sum (Σ) and Diff (Δ) radiation pattern of the feed array are measured in ‎anechoic chamber using same electrical length coaxial cable and 180°Coupler. The results are in good ‎agreement (vertical and horizontal polarizations) with numerical simulation especially for the main ‎beam. To enhance gain value, 50 cm reflector antenna has been used. A proper crossover is achieved ‎by controlling F/D ratio of the equivalent reflector. A compact Cassegrain reflector compatible to feed ‎array is designed and fabricated. The radiation characteristics measurements of the feed-reflector ‎system have been performed using outdoor measurement setup. By ignoring coupler insertion loss, ‎Sum (Diff) gain range is between 24.8 (17) dBi at 6 GHz and 31.7 (29.5) dBi at 12 GHz. Cross pol and null ‎depth better than −31.5 and −24 have been obtained. ‎

Multiple-wavelength conversion based on the anomalous Doppler effect induced by dynamic tuning in a self-collimation photonic crystal

The Doppler effect of relative motion-induced frequency shift as an interesting fundamental wave phenomenon draws significant research interest in many applied aspects of physics and engineering. Photonic settings represent an important class of platforms to observe and manipulate this effect. Here, an anomalous Doppler effect via dynamic index tuning in a photonic crystal (PhC) is proposed and investigated theoretically by considering the guided reflection of light from a moving front at near the speed of light. A virtual waveguide constructed in a square lattice PhC slab utilizing the self-collimation effect is proposed, and the moving equivalent reflector is realized by photonic band shift induced by a pump light for changing the refractive index dynamically. The anomalous Doppler shift occurs at multiple wavelengths, which depends on the Bloch nature of this photonic crystal and its band structure. Moreover, another kind of small spectral shift caused by adiabatic wavelength conversion is also observed. This nonstationary procedure is studied combining the full-wave numerical simulation and wavelet transform analysis. This work sheds light on the emergence of anomalous Doppler effect and wavelength conversion via dynamic index tuning in photonic crystals and can be important for manipulating such effects in practical photonic devices.

Modelled and measured effects of clouds on UV Aerosol Indices on a local, regional, and global scale

Abstract. The UV Aerosol Indices (UVAI) form one of very few available tools in satellite remote sensing that provide information on aerosol absorption. The UVAI are also quite insensitive to surface type and are determined in the presence of clouds – situations where most aerosol retrieval algorithms do not work. The UVAI are most sensitive to elevated layers of absorbing aerosols, such as mineral dust and smoke, but they can also be used to study non-absorbing aerosols, such as sulphate and secondary organic aerosols. Although UVAI are determined for cloud-contaminated pixels, clouds do affect the value of UVAI in several ways: (1) they shield the underlying scene (potentially containing aerosols) from view, (2) they enhance the apparent surface albedo of an elevated aerosol layer, and (3) clouds unpolluted by aerosols also yield non-zero UVAI, here referred to as "cloudUVAI". The main purpose of this paper is to demonstrate that clouds can cause significant UVAI and that this cloudUVAI can be well modelled using simple assumptions on cloud properties. To this aim, we modelled cloudUVAI by using measured cloud optical parameters – either with low spatial resolution from SCIAMACHY, or high resolution from MERIS – as input. The modelled cloudUVAI were compared with UVAI determined from SCIAMACHY reflectances on different spatial (local, regional and global) and temporal scales (single measurement, daily means and seasonal means). The general dependencies of UVAI on cloud parameters were quite well reproduced, but several issues remain unclear: compared to the modelled cloudUVAI, measured UVAI show a bias, in particular for large cloud fractions. Also, the spread in measured UVAI is larger than in modelled cloudUVAI. In addition to the original, Lambert Equivalent Reflector (LER)-based UVAI algorithm, we have also investigated the effects of clouds on UVAI determined using the so-called Modified LER (MLER) algorithm (currently applied to TOMS and OMI data). For medium-sized clouds the MLER algorithm performs better (UVAI are closer to 0), but like for LER UVAI, MLER UVAI can become as large as −1.2 for small clouds and deviate significantly from zero for cloud fractions near 1. The effects of clouds should therefore also be taken into account when MLER UVAI data are used. Because the effects of clouds and aerosols on UVAI are not independent, a simple subtraction of modelled cloudUVAI from measured UVAI does not yield a UVAI representative of a cloud-free scene when aerosols are present. We here propose a first, simple approach for the correction of cloud effects on UVAI. The method is shown to work reasonably well for small to medium-sized clouds located above aerosols.

An Analysis of Reflector Homogenization Techniques for Full Core Diffusion Calculations

Today’s reactor core calculations are done in diffusion with a few coarse groups and require the homogenization of the core assemblies as well as a correct representation of the reflector. In industrial applications a homogeneous reflector is often used with cross sections obtained from transport calculations and adjusted to fit in-core measurements. However, the need for better precision in the core diffusion calculations and the emergence of new reflector concepts, such as for the European Pressurized Reactor (EPR), require an increase in the number of coarse groups for novel loading patterns and a rethinking of how to define the equivalent reflector. In this work we analyze and extend current techniques for the reflector homogenization for core calculations. Following the adopted industrial methodology, we have perfected a technique for the determination of an equivalent homogenous reflector by implementing a Particle Swarm Optimization Algorithm and showed its limitations through the analysis of an academic slab reactor model and of a realistic two-dimensional representation of the EPR. We have compared the precision of the resulting core calculations to transport reference calculations as well as to diffusion calculations using a multigroup albedo boundary condition. We have also explored the use of current-preserving flux discontinuity coefficients at the core-reflector interface in conjunction with an equivalent reflector.

Equivalent hyperboloid (ellipsoid) and its application

Analogous to the equivalent paraboloid, the equivalent hyperboloid (ellipsoid) for dual quadratic surface reflector antennas is derived. The condition that the equivalent reflector is center fed is also derived. The numerical example shows that a reflector geometry that satisfies this center fed condition is a good initial antenna geometry to design a shaped dual reflector antenna.

Fiber optic displacement sensor with subangstrom resolution

A simple Fabry-Perot interferometer that uses a singlemode bidirectional fiber coupler as a beam splitter is described. With light from a high stability He-Ne laser focused on the optic fiber, noise levels of 0.5-A rms equivalent reflector displacements were obtained in a bandwidth of 0.02-1 kHz.

An original circularly polarized backfire antenna with high gain

In this paper, a circularly polarized backfire antenna with an original structure and excellent properties is presented. It is designed on the basis of “Equivalent Reflector Method” proposed by the author.

Application and Verification of the Simplified Equivalence Theory for Burnup States

The efficient use of nodal methods for three-dimensional two-group reactor calculations requires homogenization over large volumes or nodes. This homogenization removes the internal structure of the nodes. On the other hand, accurate pinwise power distributions are indispensable for light water reactor design. A homogenization and dehomogenization procedure called the simplified equivalence theory (SET) has been proposed, which allows the accurate and inexpensive determination of pinwise power distributions of fresh reactor cores. The SET procedure is extended to burnup and parameter dependencies. For the case of fuel assembly homogenization and dehomogenization, this extension is validated by a procedure that allows assessment of the accuracy of the method, referring exclusively to the spectral geometry of the assembly. For the validation of the equivalent reflector model, a nodal reactor test problem is set up which shows that this model is adequate to describe core/reflector interactions under burnup conditions.

A high-angle one-way wave equation for seismic wave propagation along rough and sloping interfaces

A model of acoustic propagation in solid media has been derived. It is a one-way wave equation based on a high-order approximation, called a Padé approximation, to the square-root function. The physical properties of the environment are modeled as stratified, thin, homogenous layers. The model can be applied to obtain an approximate solution in range-dependent environments by allowing the properties of the layers to vary in range. Furthermore, the effects of rough or sloping reflecting interfaces can be approximated using an equivalent reflector, consisting of two thin layers whose properties vary in range.

Shear high angle PE (shape): A PE‐type wave equation for seismic wave propagation

A model of acoustic propagation in solid media has been derived. It is a one‐way wave equation based on a high‐order Pade approximation to the square root function. The physical properties of the environment are modeled as thin stratified layers. A generalization of the equations to range‐dependent environments is easily implemented by allowing the material properties of the layers to vary in range. Furthermore, reflecting interfaces of variable depth can be approximated by using an equivalent reflector, consisting of two thin layers whose material properties vary in range.

Comparison of ultrasonically and metallographically indicated sizes of steelmaking defects in a large 3·5Ni-Cr-Mo-V rotor forging

AbstractFracture-mechanics acceptance procedures for steelmaking defects in components require an accurate non-destructive determination of the defect size. In large components this is only possible using ultrasonics and the equivalent reflector (AVG) system has become accepted for this purpose in cases, such as steam turbine and generator rotors, where the critical defect size is significantly smaller than the ultrasonic beam diameter. To assist in evaluating the AVG procedure, detailed metallographic and ultrasonic examinations of eight non-metallic inclusions in a low-pressure steam turbine rotor forging have been carried out. Simple inclusions were accurately sized by the AVG system, but more complex groupings of inclusions were underestimated in size by factors of up to 5 in equivalent diameter if assumed circular. Infact, the defects examined were elliptical with a typical aspect ratio of 1:3, comparable to that normally assumed for fracture-mechanics calculations.