Radiation and scattering from ferrite-tuned cavity-backed slotantennas: theory and experiment

A three-dimensional finite-element method hybridized with the spectral/spatial domain method of moments is presented for the analysis of ferrite-tuned cavity-backed slot antennas. The cavity, which is partially filled with magnetized ferrite layers, is flush mounted on an infinite ground plane with possible dielectric or magnetic overlay. The antenna operates primarily in the ultrahigh-frequency band. The finite-element method is used to solve for the electric-field distribution inside the cavity, whereas the spectral-domain approach is used to solve for the exterior region. An asymptotic extraction of the exponential behavior of the Green's function followed by a spatial evaluation of the resulting integral is used to improve computational speed. Radar cross section, input impedance, return loss, gain, and efficiency of ferrite-tuned cavity-backed slots (CBS) are calculated for various biasing conditions. Numerical results are compared with experimental data     

RCS measurements, transformations, and comparisons undercylindrical and plane wave illumination

Monostatic RCS measurements of a long bar (at X-band) and of a scale model aircraft (at C-band) were performed under the quasi-plane wave illumination produced by a dual parabolic-cylinder CATR. At Arizona State University's ElectroMagnetic Anechoic Chamber (EMAC) facility, these measurements were repeated under the cylindrical wave illumination produced by a March Microwave Single-Plane Collimating Range (SPCR). The SPCR measurements were corrected using the “reference target method.” the corrected SPCR measurements are in good agreement with the CATR measurements     

Radar cross section of trihedral corner reflectors using PO and MEC

Physical optics (po) and the method of equivalent currents (mec) are used for the formulation and calculation of the backscatter cross section of both the triangular and square trihedral corner reflectors. Scattering from a trihedral corner reflector is dominated by single, double, and triple reflections by the interior walls. A physical optics integration is performed on the entire surface of each plate for the evaluation of the singly reflected fields. Doubly and triply reflected fields are evaluated by first using geometrical optics (go) at initial reflections to calculate the incident plane wave on the plate where the last reflection occurs. Physical optics is then applied on the illuminated area of that plate. First-order diffractions, which are based on the fringe current expressions for the exterior edges of the trihedral, are also included in the analysis. Predictions compare very well with both experimental and fdtd data.     

Radiation effects on the microstructure of a 9Cr-ODS alloy

Oxide dispersion strengthened (ODS) steels are prime candidates for high-temperature, high-dose cladding in advanced nuclear reactors. When a 9Cr-ODS alloy was irradiated with 5 MeV nickel ions at temperatures of 500–700°C to doses up to 150 dpa, there was no significant change in the dislocation arrangement. For oxide particles, there is a small shrinkage in size and increase in density with increasing irradiation dose. This work confirms that oxide particles and the microstructure of the 9Cr-ODS show minimal changes under irradiation at temperatures up to 700°C and doses up to 150 dpa.     

Ferrite-loaded cavity-backed antennas including nonuniform and nonlinear magnetization effects

A method of analyzing both the electromagnetic and the magnetostatic phenomena involved in ferrite-loaded cavity-backed antennas is presented. The high-frequency modeling of the antenna is based on a hybrid of the finite element method (FEM) with the method of moments (MoM). The (magnetostatic) demagnetizing process of the finite ferrite loadings is modeled with the use of a nonlinear static FEM. The results of the magnetostatic analysis are used to compute the internal field of the ferrite samples. Through the use of an appropriate ferrite permeability tensor, the nonuniform internal bias field is incorporated into the high-frequency FEM/MoM analysis. The input impedance characteristics of two different ultrahigh-frequency (UHF) antennas are presented using different ferrite models. Results for the tuning range and sensitivity are presented for different bias directions. The numerical results are also compared with experimental data.     

Neutron irradiation effects on the mechanical properties of organic composite materials

Neutron irradiations with low γ-ray flux in the Intense Pulsed Neutron Source were carried out on four kinds of cloth-filled organic composites (filler: E-glass or carbon fiber; matrix: epoxy or polyimide resin) and a unidirectional alumina fiber/epoxy composite. These composites were examined with regard to the mechanical properties at room temperature. Following irradiation at room temperature, the Young's (tensile) modulus of these composites remains practically unchanged up to a total neutron fluence of $\text{5.0 × 10}{}^{18}\text{n/cm}{}^2$ ($\text{1.4 × 10}{}^{18}\text{n/cm}{}^2$ for $\text{E > 0.1 MeV}$). The shear modulus and the ultimate strength, on the other hand, decrease significantly at this neutron fluence for the glass/epoxy and glass/polyimide composites, whereas for the other composites both properties do not degrade. This result is most likely ascribed to the radiation damage at fiber/matrix interface due to recoil particles produced by a ${}^{10}\text{B(n,α)}{}^7$ Li reaction in the boron-containing E-glass fibers. Only for the E-glass fiber composites, in fact, the fracture propagation energy is appreciably increased by irradiation, while for the other composites the propagation energy is scarcely changed, thus confirming the significant contribution due to the ¹⁰B reaction. As to the 5 K irradiation, degradation of the present composites was not observed up to a total neutron fluence of $\text{1.0 × 10}{}^{18}\text{n/cm}{}^2$ ($\text{7.0 × 10}{}^{17}\text{n/cm}{}^2$ for $\text{E > 0.1}\text{MeV}$) when tested at room temperature.     

Numerical and experimental studies of current distributions on thinmetallic posts inside rectangular waveguides

A fast converging and stable moment method solution for the current distribution on arbitrary size rectangular obstacles mounted transversely inside the rectangular waveguide has been developed. A special arrangement of piecewise sinusoidal and pulse basis functions has been utilized to determine the transverse current distributions on the obstacles and their scatterings in the waveguide. The method has been compared well with the Marcuvitz's results for the inductive and capacitive posts and the experimental data of an arbitrary size rectangular obstacle     

Analytical evaluation of the asymptotic impedance matrix of agrounded dielectric slab with roof-top functions

An analytical technique is derived to solve the asymptotic part of impedance matrix elements for printed circuit structures using roof-top subdomain expansions. The key to this problem is the analytical transformation from an infinite double integral to a suitable finite one-dimensional (1-D) integral. The newly developed formula is applied to the monostatic radar cross section (RCS) of a microstrip patch. Comparisons are made with measurements and conventional method of moments predictions