Bu çalışmada, sonlu kaynaklı elektromagnetik dalgaların, dielektrik kaplanmış silindirik bir yüzeyden optik gibi saçılması Fiziksel Optik (FO) yaklaşımı ile incelenmiştir. Sonlu kaynak, çizgisel ...elektrik akım kaynağı olarak seçilmiştir. Silindirik yüzeye ait yansıma katsayısı, Kırınımın Geometrik Teorisi (KGT) yaklaşımı kullanılarak bulunmuştur. Elde edilen bu katsayı kullanılarak yüzeyden saçılan alanlar ifade edilmiştir. Alan ifadeleri FO yaklaşımında kullanılmış ve yüzeye ait saçılma integrali belirlenmiştir. Bu integralin asimptotik olarak değerlendirilmesi sonucunda yüzeyden yansıyan alanlar ile yüzeye ait diverjans katsayısı hesaplanmıştır. Neticede, çalışmada elde edilen sonuçlar nümerik olarak değerlendirilmiş ve yüzey empedansının saçılan alanlara etkileri incelenmiştir. Yapılan çalışmada zaman faktörü j te? alınmıştır.
Bu çalışmada, sonlu kaynaklı elektromagnetik dalgaların, dielektrik kaplanmış silindirik bir yüzeyden optik gibi saçılması Fiziksel Optik (FO) yaklaşımı ile incelenmiştir. Sonlu kaynak, çizgisel ...elektrik akım kaynağı olarak seçilmiştir. Silindirik yüzeye ait yansıma katsayısı, Kırınımın Geometrik Teorisi (KGT) yaklaşımı kullanılarak bulunmuştur. Elde edilen bu katsayı kullanılarak yüzeyden saçılan alanlar ifade edilmiştir. Alan ifadeleri FO yaklaşımında kullanılmış ve yüzeye ait saçılma integrali belirlenmiştir. Bu integralin asimptotik olarak değerlendirilmesi sonucunda yüzeyden yansıyan alanlar ile yüzeye ait diverjans katsayısı hesaplanmıştır. Neticede, çalışmada elde edilen sonuçlar nümerik olarak değerlendirilmiş ve yüzey empedansının saçılan alanlara etkileri incelenmiştir. Yapılan çalışmada zaman faktörü j te? alınmıştır.
In this paper, linear field problems with a varying physical parameter are solved with the conjugate-gradient FFT method and a dedicated extrapolation procedure for generating the initial estimate. ...The scheme is formulated and illustrated for two simple example problems. The importance of the choice of the stop criterion and the step size are demonstrated for the case of a straight thin-wire segment. A brief summary is given of the applications that have appeared in the open literature until now, and actual three-dimensional scattering problems for a rectangular conducting plate and an inhomogeneous, dispersive dielectric body are discussed. Finally, the case where the medium surrounding the object of interest is no longer homogeneous is addressed for two representative examples: wire antennas over a layered half space and an inhomogeneous dielectric cylinder in a water-filled container.
Kısmen dielektrik yüklü dalga kılavuzları çok sayıda mikrodalga cihazında kullanılmaktadır. Kısmen
dielektrik yüklü dikdörtgen dalga kılavuzları ile malzemelerin karmaşık dielektrik ...geçirgenliklerinin
ve dielektrik yüklü metalik dalga kılavuzlarında propagasyon karakteristiklerinin belirlenmesi
birçok mühendislik uygulamasında önemlidir. Bu çalışma bahsedilen her iki alandaki mevcut
literatüre katkı yapılmasını amaçlamaktadır. Dielektrik yüklü metalik dalga kılavuzları için yansıma
iletim ölçmeleri ile malzemelerin karmaşık dielektrik geçirgenliklerinin belirlenmesi amacıyla
yapılmış olan çalışmalar nispeten basit durumları içermektedirler. Bu çalışmada, dikdörtgen dalga
kılavuzu içerisine yerleştirilen sütun şeklindeki dielektriğin geçirgenliğinin belirlenmesi ters saçılma
problemi olarak formüle edildi ve literatürdeki sınırlamalar ortadan kaldırıldı. Oldukça esnek
ve genel tipteki problemleri içerecek şekilde, doğru ve sayısal olarak verimli bir algoritma verildi.
Aynı zamanda bu çalışmada, kayıpsız periyodik yapılardaki birim hücrenin Genelleştirilmiş Saçılma
Matrisi için bir sakınım ilişkisi ortaya konuldu. Bu sakınım ilişkisi, tek Floquet modlu bölge içerisinde
yer alan iletim/durdurma band geçiş frekanslarını doğru olarak kestiren yeni bir yöntem
sağlamaktadır. Bu yöntem iletim durdurma band bölgeleri verilen/ölçülen periyodik yapıyı kullanarak
belirli topolojiler için birim hücre boyutlarının belirlenmesi ters problemine uygulanabilir niteliktedir.
Partially dielectric loaded waveguides have been
used in many microwave devices. Determination of
complex permittivity of materials with partially dielectric
loaded rectangular waveguides and propagation
characteristics of periodically dielectric
loaded metallic waveguides are important in many
engineering applications. This study aims to extend
the grounds thus far covered in both of the areas
mentioned above.
The methods reported in the literature on determination
of complex permittivity of materials via transmission/
reflection measurements for dielectric
loaded metallic waveguides include relatively simple
scenarios. These approaches either treat a simplified
scenario wherein the sample fills the entire crosssection
of the waveguide or in considering partial
filling they do not accurately account for interactions
between higher order modes. In this study the
determination of the complex permittivity of dielectric
posts in rectangular waveguides is formulated
as an inverse scattering problem and these limitations
are removed. An accurate and numerically efficient
algorithm is given which is quite flexible and
can easily be modified to address problems involving
more general types of inhomogeneous dielectric
loadings in waveguides. The predicted results are
compared with measurements and good agreement
is obtained. Propagation of waves in periodic structures
has long been an area of interest for physicists
and engineers. Periodically loaded waveguides can
be considered as one of the simplest subsets of periodic
structures which exhibit 1-D discrete translational
symmetry and which can be completely defined
by specifiying the loading over an interval
equal to the period p, or in other words by specifing
the unit cell of the structure. Propagation characteristics
of such waveguides play an important role in
the design problems encountered in many engineering
applications such as, slow-wave structures, filters,
phase shifters, polarizers, impedance matching
devices, antennas, antenna feeds, and pulse compressors.
Periodicity encountered in such devices is
comprised of a cascade of a limited number of unit
cells connected to appropriate terminations. Unit
cell approach of analysis then provides an approximate
description of device propagation characteristics,
the accuracy of which improves with the number
of unit cells utilized in the design. More then often
the actual device design involves a fine-tuning of
the parameters characterizing the unit cell and the
terminations via a multiparameter optimization
scheme. The generalized scattering matrix representation
of unit cell in terms of the modes of the uniform
waveguide provides a convenient and efficient
approach which has been used by several researchers
in addressing a fairly broad range of problems
involving periodically loaded waveguides. The results
reported in the literature on propagation in
periodically loaded waveguides also include investigations
of the features of the eigenvalue spectrum of
Floquet modes supported by such structures, as well
as derivations of certain conservation relations satisfied
by the generalized scattering matrix in the absence
of losses. Probably an interesting contribution
of this paper, from an applicational point of view, is
the formulation of an approximate relation between
the elements of the generalized scattering matrix of
a symmetric unit cell, which can be used to obtain
rather accurate estimates for stop-band/pass-band
transitions frequencies in single Floquet mode regions
of symmetric structures. The proposed approach
can be implemented in a very efficient manner,
without having to impose Floquet condition and
solve the resulting eigenvalue equation. The method
can be used in addressing the inverse problem of
determinating unit cell dimensions for a specified
topology using measured/given values of passband/
stopband regions. As a result, we believe that
the proposed method may effectively be used in the
design of microwave bandpass/stopband filter. In
order to demonstrate the validity and applicability of
the several points made in this paper we present
some typical results. We also investigate dependence
of estimated values of the band-edge frequencies
obtained via the proposed approximation scheme on
the parameters of the unit cell. For verification/
validation purposes we have compared our
mode matching generalized scattering matrix (MMGSM)
results with those calculated via an independent
commercial software package (HFSS). Numerical
results obtained for a typical periodically loaded
waveguide are in perfect agreement with the theory
and demonstrate the validity, applicability as well as
the numerical efficiency of the proposed approach.
To develop an enhanced understanding of an aspect of the charge transport mechanism in systems composed of solid-solid insulating contacts, the dynamic dielectric response of sand grains and of ...silica-silica rod contacts was investigated at dry and at 97% relative humidity (RH), in the frequency range $10^{-2}$ to $lO^5$ Hz. In dry atmosphere no appreciable amount of conductivity is observed, while in humidity the response follows a strongly dispersive behaviour. Sharp rise in capacitance gives a clear evidence for the storage of charge in the transport process. Collectively, the conductance of the sand grains increases super-linearly with the number of contacts suggesting filamentary conduction paths. The conductance G of the silica-silica contacts varies almost inversely with the number of contacts pointing towards a uniformly distributed conduction mechanism. It is found that the conduction process, despite a reduction in the geometrical area at the point of contact, is not significantly limited at the interface between the connecting surfaces.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
KHCO3 compound was characterized in three principle realms: for its dielectric properties as a function of temperature and frequency in the ranges 300-370 K and 50 Hz to 1 MHz, respectively; bulk ...conductivity as a function of temperature, via impedance technique; and relaxation time as function of temperature. Variations of the bulk conductivity and relaxation time with temperature have been found to yield two segments, with two different activation energies. The activation energy for the two segments due to bulk conductivity have been found as 1.96 eV and 1.85 eV, while the activation energy due to relaxation have been found to be 1.85 eV and 1.83 eV. The phase transition which was detected by DSC at T = 322 K has been verified by the dielectric and conductivity measurements.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
47.
Initiatory electrons in compressed gases in positive polarity TIOURSI, MustaDepartment, of Electrotechnics, Faculty of Electrical Engineering, Univercity of Science and Technology (USTO), P.O. Box 1505-El-mnaouar, Oran, Algeriapha; MESSAAD, Mohammed
Elektrik : Turkish journal of electrical engineering & computer sciences,
2003, Letnik:
11, Številka:
3
Journal Article
Recenzirano
Odprti dostop
This paper deals with the nature of seed electron sources in compressed N2 for positive polarity. We present an experimental procedure that provides evidence of the fact that collisional detachment ...from negative ions plays the most important role in the supply of seed electrons. Conditioning phenomena in compressed SF6, N2 and air have been simulated under positive lightning impulses for point-plane geometry.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Artificial neural networks (ANNs) have been promising tools for many applications. In recent years, a computer-aided design approach based on (ANNs) has been introduced to microwave modelling, ...simulation and optimization. In this work, the characteristic parameters of top shielded multilayered coplanar waveguides (CPWs) have been determined with the use of ANN models. These neural models were trained with Levenberg-Marquardt, resilient propagation, Bayesian regulation, quasi-Newton, and backpropagation learning algorithms. Better performance and learning speed with a simpler structure were achieved from these models. The results have shown that the estimated characteristic parameters are in very good agreement with the computed results by using conformal mapping theory. The Levenberg-Marquardt learning algorithm was found to be the best algorithm among all. As a result, ANN models presented in this work can be used easily, simply and accurately to determine the characteristic parameters of the top shielded multilayered CPWs.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Systems formed by the pyrene derivatives 3-hydroxypyrene and 1-aminopyrene with pyridine were studied. The thermodynamic and kinetic parameters of the systems were calculated using the changes in the ...absorption and emission spectra which occur due to hydrogen bond or complex formation.The decrease of the formation rate constant in the series methylcyclohexane, benzene, and o-chlorotoluene may be due to a more difficult formation of the hydrogen bond complex due to the increase of the dielectric constant in the solvent series.
Researchers have attempted to determine the dielectric constants of soil-water mixtures in order to establish relationships between dielectric constant and soil properties such as porosity. However, ...the suggested formulations were too complex to use for practical purposes. In order to effectively use the dielectric constant of soil-water mixtures, there is a need for a simple but well-defined formulation. In the first stage of this study, the dielectric constants of a natural sand and glass bead in two sizes at various porosities were determined at 13 MHz. Then the test results were compared with the independent data obtained on a wide range of soils, the second stage of the study. A linear relationship between the dielectric constant and porosity of soil-water mixtures was observed for both cases with coefficient of correlation values over 0.97. Based on the obtained results, it is suggested that the porosity of a soil-water mixture can be obtained using n = 0.0136 \varepsilon + 0.02.
