TECHNOLOGY OF MANUFACTURE OF RADIO ABSORPTION CERAMICS

The object of the work is the technology of manufacturing radio-absorbing ceramics on the basis of facing tiles with the addition of silicon carbide. The method of hydrostatic weighing in water was used to determine the physical properties. X-ray phase analysis and spectral characteristics - transmission and reflection coefficients, in the frequency range 25.8 – 37.5 GHz were also determined. Tiles consist of two layers. First, separately obtain a press powder for the I and II layer of raw materials in a given amount, which were weighed, moistened, ground in a ball mill; the slip was dried in an oven, then ground and passed through a suitable sieve. The moistened press powder for the first layer was weighed and poured into a mold for pressing, after which the moistened press powder for the second layer was weighed and poured into the mold for pressing. The resulting raw material was dried. The semi-finished product was covered with watering and placed in an oven. The finished semi-finished product was fired in a silite furnace. The two-layer tile with an irrigated covering made on the developed technology was characterized by the following characteristics: water absorption – 9,8 %, imaginary density – 1,90 g/cm3. The developed ceramics, according to the classification, can be referred to the class of radio-absorbing ceramics.

Rigorous Bounds on Transmission, Reflection, and Bogoliubov Coefficients

<p>This thesis describes the development of some basic mathematical tools of wide relevance to mathematical physics. Transmission and reflection coefficients are associated with quantum tunneling phenomena, while Bogoliubov coefficients are associated with the mathematically related problem of excitations of a parametric oscillator. While many approximation techniques for these quantities are known, very little is known about rigorous upper and lower bounds. In this thesis four separate problems relating to rigorous bounds on transmission, reflection and Bogoliubov coefficients are considered, divided into four separate themes: Bounding the Bogoliubov coefficients; Bounding the greybody factors for Schwarzschild black holes; Transformation probabilities and the Miller-Good transformation; Analytic bounds on transmission probabilities.</p>

Rigorous Bounds on Transmission, Reflection, and Bogoliubov Coefficients

<p>This thesis describes the development of some basic mathematical tools of wide relevance to mathematical physics. Transmission and reflection coefficients are associated with quantum tunneling phenomena, while Bogoliubov coefficients are associated with the mathematically related problem of excitations of a parametric oscillator. While many approximation techniques for these quantities are known, very little is known about rigorous upper and lower bounds. In this thesis four separate problems relating to rigorous bounds on transmission, reflection and Bogoliubov coefficients are considered, divided into four separate themes: Bounding the Bogoliubov coefficients; Bounding the greybody factors for Schwarzschild black holes; Transformation probabilities and the Miller-Good transformation; Analytic bounds on transmission probabilities.</p>

DKP equation with smooth barrier

In this paper, we study the Duffin–Kemmer–Petiau (DKP) equation in the presence of a smooth barrier in dimensions space–time (1+1) dimensions. The eigenfunctions are determined in terms of the confluent hypergeometric function [Formula: see text]. The transmission and reflection coefficients are calculated, special cases as a rectangular barrier and step potential are analyzed. A numerical study is presented for the transmission and reflection coefficients graphs for some values of the parameters [Formula: see text] are plotted.

Anisotropy Characterization of Metallic Lens Structures

This paper presents a full electromagnetic (EM) characterization of metallic lenses. The method is based on the utilization of free-space transmission and reflection coefficients to accurately obtain lenses’ tensorial EM parameters. The applied method reveals a clear anisotropic behavior with a full tensorial directional permittivity and permeability and noticeably dispersive permeability and wave impedance. This method yields accurate values for the effective refractive index, wave impedance, permittivity, and permeability, unlike those obtained by simple methods such as the eigenmode method. These correct cell parameters affect their lens performance, as manifested in a clear level of anisotropy, impedance matching, and losses. The effect of anisotropy caused by oblique incidence on the performance and operation of lens designs is illustrated in a lens design case.

Y-Shaped Demultiplexer Photonic Circuits Based on Detuned Stubs: Application to Radiofrequency Domain

We present a theoretical and experimental study of photonic demultiplexers based on detuned stubs. The demultiplexers consist of Y-shaped structures with one input line and two output lines. Two different types of structures are proposed to achieve a selective transfer of a single mode in one output line without disturbing the second one. (i) In the first platform each output contains two different stubs attached at two different sites (U-shaped resonators). We derive in closed form the geometrical parameters of the stubs to achieve a selected frequency in each line while keeping the other line unaffected. The frequency selection can be made on the basis of two different mechanisms, namely a Fano or an electromagnetic induced transparency (EIT) resonance. Consequently, different demultiplexing schemes can be designed by a combination of the two mechanisms, such as Fano-Fano, Fano-EIT or EIT-EIT. In particular, the width of the Fano or EIT resonances can become zero for an appropriate choice of the stubs’ lengths, giving rise to trapped modes also called bound in continuum states (BICs) with infinite quality factors. We also show that the crosstalk between the two outputs can reach minimum values around −45 dB. (ii) In the second platform, each output line contains a photonic comb with a defect stub. The latter is appropriately designed to filter one or a few frequencies in the bandgap of the photonic comb. The analytical calculations are performed with the help of the Green’s function method which enables us to derive the transmission and reflection coefficients as well as the density of states (DOS). These results are confirmed by experimental measurements using coaxial cables in the radio frequency domain.

A hybrid method of predicting the acoustical properties of multi-layered materials

Many numerical and measuring approaches are widely used in predicting and analysing the acoustic performances of laminated materials for noise control applications. However, numerical methods generally require a set of non-acoustic parameters, and the measuring methods are not available for exceedingly thick materials. The main aim of this article is to address a hybrid approach of evaluating the normal incidence sound transmission loss and absorption coefficients of multi-layered materials. This method is performed with some special parameters that contain the sound transmission and reflection coefficients of each sub-layer of a multi-layer specimen and can be measured by a standing wave tube system. The accuracy and feasibility of the present method are validated by the experimental and numerical comparisons between different methods and samples. Moreover, this present approach can be applied as a numerical tool of estimating the acoustical behaviours of multi-layered structures in noise control treatments, such as automotive, building and aerospace industries.

Modeling and Imaging of Ultrasonic Array Inspection of Side Drilled Holes in Layered Anisotropic Media

There has been an increase in the use of ultrasonic arrays for the detection of defects in composite structures used in the aerospace industry. The response of a defect embedded in such a medium is influenced by the inherent anisotropy of the bounding medium and the layering of the bounding medium and hence poses challenges for the interpretation of the full matrix capture (FMC) results. Modeling techniques can be used to understand and simulate the effect of the structure and the defect on the received signals. Existing modeling techniques, such as finite element methods (FEM), finite difference time domain (FDTD), and analytical solutions, are computationally inefficient or are singularly used for structures with complex geometries. In this paper, we develop a novel model based on the Gaussian-based recursive stiffness matrix approach to model the scattering from a side-drilled hole embedded in an anisotropic layered medium. The paper provides a novel method to calculate the transmission and reflection coefficients of plane waves traveling from a layered anisotropic medium into a semi-infinite anisotropic medium by combining the transfer matrix and stiffness matrix methods. The novelty of the paper is the developed model using Gaussian beams to simulate the scattering from a Side Drilled Hole (SDH) embedded in a multilayered composite laminate, which can be used in both immersion and contact setups. We describe a method to combine the scattering from defects with the model to simulate the response of a layered structure and to simulate the full matrix capture (FMC) signals that are received from an SDH embedded in a layered medium. The model-assisted correction total focusing method (MAC-TFM) imaging is used to image both the simulated and experimental results. The proposed method has been validated for both isotropic and anisotropic media by a qualitative and quantitative comparison with experimentally determined signals. The method proposed in this paper is modular, computationally inexpensive, and is in good agreement with experimentally determined signals, and it enables us to understand the effects of various parameters on the scattering of a defect embedded in a layered anisotropic medium.

Transmission, Reflection and Dissipation of Microwaves in Magnetic Composites with Nanocrystalline Finemet-Type Flakes

The microwave properties of a composite material containing flakes of finemet-type nanocrystalline alloy placed in the epoxy matrix have been investigated. Two compositions have been studied: with 15% and 30% flakes. Frequency dependences of transmission and reflection coefficients are measured in the frequency range from 12 to 38 GHz. The dielectric permittivity and magnetic permeability are obtained, and the microwave losses are calculated. The dependences of transmission and reflection coefficients have been drawn as functions of wave frequency and thickness of the composite material, taking into account the frequency dependences of permittivity and permeability. The regions of maximal and minimal microwave absorption have been defined. The influence of wave interference on the frequency dependence of microwave absorption is studied.

The Efficiency of Upward Wave Propagation Near the Tropopause

&lt;p&gt;Extreme states of the polar stratospheric vortex are typically followed by anomalous surface circulation. These extreme stratospheric vortex states are in turn often associated with extreme heat flux between the tropopause and 100 hPa.&amp;#160;&lt;/p&gt;&lt;p&gt;The goal of this work is to better understand upward wave propagation between the tropopause and the bottom of the vortex near 100 hPa using both theory and reanalysis data.&lt;/p&gt;&lt;p&gt;Following Charney and Drazin (1961) we analytically solve a quasi-geostrophic planetary-scale model with three different layers: troposphere, tropopause inversion layer (TIL) and stratosphere. We allow for different buoyancy frequencies in each layer and show the dependence of transmission and reflection coefficients on the buoyancy frequencies, TIL depth and mean-state zonal wind. The dependence of heat flux in the TIL and stratosphere, as well as phase-lines for the wave solution, are presented. This analysis highlights the key role that the TIL and jumps in buoyancy frequency play for upward wave propagation.&lt;/p&gt;&lt;p&gt;We then use reanalysis data to consider the importance of this effect in observations. Four different specifications of the index of refraction are compared: that derived by Charney and Drazin in 1961, that derived by Matsuno in 1970, and two that relax some of the assumptions used in the derivations of the first two. The Charney and Drazin index of refraction includes terms ignored by Matsuno that are critical for understanding upward wave propagation just above the tropopause in both the climatology and associated with extreme heat flux events. By adding these ignored terms to the Matsuno index of refraction, it is possible to construct a useful tool that describes wave flux immediately above the tropopause and at the same time also describes the role of meridional gradients within the stratosphere. Specifically, a stronger tropopause inversion layer (TIL) tends to restrict upward wave propagation. It is also shown that while only 38% of extreme wave-1 Eliassen-Palm flux vertical component (F&lt;sub&gt;z&lt;/sub&gt;) at 100hPa events are preceded by extreme F&lt;sub&gt;z&lt;/sub&gt; at 300hPa, there are almost no extreme events at 100hPa in which the anomaly at 300hPa is of opposite sign or very weak. &amp;#160;&lt;/p&gt;