• Applied Chemistry for Engineering
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• v.23 no.2
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• pp.241-246
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• 2012

Cr(VI)-heterocyclic complex (2,2'-bipyridinium dichromate) was synthesized by the reaction between of 2,2'-bipyridine and chromium trioxide in $H_2O$, and characterized by IR and ICP. The oxidation of benzyl alcohol using 2,2'-bipyridinium dichromate in various solvents showed that the reactivity increased with the increase of the dielectric constant, in the order: cyclohexene < chloroform < acetone < N,N-dimethylformamide. In the presence of DMF solvent with acidic catalyst such as $H_2SO_4$ solution, 2,2'-bipyridinium dichromate oxidized the benzyl alcohol and its derivatives (p-$p-OCH_3$, $m-CH_3$, H, $m-OCH_3$, m-Cl, $m-NO_2$). Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant was -0.66 (303 K). The observed experimental data was used to rationalize the hydride ion transfer in the rate-determining step.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.12
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• pp.897-903
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• 2019

This paper represents an simplified design method of hybrid composites. The proposed method is very simple compared to conventional design approaches and easy to apply to practical design problems. The method is based on not complex optimization approaches but conventional theories. The equivalent dielectric properties concept and multi-layered dielectric slab theory are an important theoretical background of the proposed method. This approach divide the design domain into several domain which have theoretically different electro- agnetic functionality. Then, the domains are expressed by equivalent dielectric properties. Numerical analysis are performed several types of design candidates. S-parameter test for final design was conducted for validate the proposed approach indirectly.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.4
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• pp.515-523
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• 2012

In this paper, the resonance characteristics and radiation characteristics of a spherical patch on a dielectric sphere are analyzed. Resonance characteristics can be obtained from the resonant frequency and the quality factor. Radiation characteristics can be also analyzed from the E-field in the far region. In order to calculate these parameters, spectral domain analysis method is applied. Algebraic equation can be obtained in spectral domain through Vector Legendre transform pair and Galerkin's method. So, efficient calculation is possible numerically. It is investigated that radius, curvature of a spherical patch, and dielectric constant of a dielectric sphere have an effect on characteristics of a spherical patch.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05b
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• pp.75-81
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• 2003

This study evaporates ZnO layer thickness differently with RF sputtering method on Si Wafer(n-100). This study is performed to examine the characteristics of photon energy and dielectric loss according to the thickness of ZnO and increase the reliability and reproduction of ZnO thin film. It is confirmed that the variation of electric Permittivity by frequency is resulted from the formation of particles within thin film, the particle size and the polarization on grain boundary. Peak of electric Permittivity value of thin film has slower and less value in early low wavelength by the coulomb force involved in carrier combination according to the increase of frequency. Reversal of electric Permittivity values is induced by dipole polarization shown in the dielectric of thin film. Complex electric constant $({\varepsilon}_1{\varepsilon}_2)$ has larger peak values as it’s thickness is thinner and then it is larger according to the increase of frequency. Electric Permittivity by photon energy has large value in imaginary number and is reduced exponentially by the increase of carrier density according to that of photon energy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.08a
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• pp.73-79
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• 2002

This study evaporates ZnO layer thickness' differently with RF sputtering method on Si Wafer(n-100). This study is performed to examine the characteristics of photon energy and dielectric loss according to the thickness of ZnO and increase the reliability and reproduction of ZnO thin film. It is confirmed that the variation of electric Permittivity by frequency is resulted from the formation of particles within thin film, the particle size and the polarization on grain boundary. Peak of electric Permittivity value of thin film has slower and less value in early low wavelength by the coulomb force involved in carrier combination according to the increase of frequency. Reversal of electric Permittivity values is induced by dipole polarization shown in the dielectric of thin film. Complex electric constant $({\varepsilon}_1,{\varepsilon}_2)$ has larger peak values as it's thickness is thinner and then it is larger according to the increase of frequency. Electric Permittivity by photon energy has large value in imaginary number and is reduced exponentially by the increase of carrier density according to that of photon energy.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.2
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• pp.385-394
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• 2021

In this paper, a new equation of electromagnetic wave transmission matrix was proposed to calculate the reflected power and transmitted power for the multi-layered planar lossy structure. The applied human leg was modeled as a four-layer planar structure of skin, fat, muscle and bone. The complex dielectric constant to consider the loss of each of these layers was calculated using the 4-pole cole-cole model parameter. When electromagnetic waves were incident on the skin surface, total reflected and transmitted power, and human body loss were calculated for a frequency band of 0.1 to 20.0 GHz. And for various muscle thicknesses, the power reflected only from the outermost bone and re-radiated from the skin was calculated. It was confirmed that at the muscle thickness of 3.0 mm and the frequency of 4.6 GHz the return loss was -6.13 dB, which was 3.42 dB lower than the average value.

• Journal of the Korean Magnetics Society
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• v.15 no.3
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• pp.202-206
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• 2005

The present investigation provides an electromagnetic radiation absorptive composition which comprises silver-coated ferrite microspheres dispersed in silicon rubber matrix for the aim of thin microwave absorber in GHz frequencies. Ni-Zn ferrite spheres with $50{\mu}m$ size in average were prepared by spray-drying and sintering at $1130^{\circ}C$. Conductive silver layer was plated on ferrite spheres by electroless plating. Conductive Ni-Zn ferrite sphere with uniform silver layer were obtained in the concentration of 10 g/L $AgNO_3$ per 20 g ferrite spheres. For this powder, electrical resistance is reduced as low as $10^{-2}\~10^{-3}\;\Omega$. The most sensitive material parameters with silver plating is real and imaginary parts of complex permittivity. The conductive Ni-Zn ferrite spheres have large values of dielectric constant. Due to this high dielectric constant of microspheres, matching thickness is reduced to as low as 2 mm at the frequency of 7 GHz, which is much thinner than conventional ferrite absorbers.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.136-144
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• 1999

Crystal structures of tungsten-bronze type microwave dielectric ceramics, $BaOLa_2O_34TiO_2$ (BLT) and $BaO(Nd_{0.77}Y_{0.23})_4TiO_2$ (B(NY)T), were analysed using the Rietveld method. The most relibale refinement was obtained by refining the cation and anion positions from the x-ray and neutron diffraction data, respectively. The ambiguites inherent in the refined crystal structure by Mateeva et al. were resolved. The $BaORe_2O_34TiO_2$ structure consiste of $3\times2$ perovskite blocks and 4 pentagon-channels. The Ti-O6 octahedrons are distroted and tilted, which, consequently, induces the displacements of Ba and Re ions producing the superlattics (c$\approx$ 7.6 $\AA$). The B(NY)T showed more severely tilted Ti-O6 octahedrons. The relative dielectric constant $\varepsilon_{\gamma}$ and temperature coefficient $\tau_\varepsilon$ are 109.5 and-$180 ppm/^{\circ}C$ in BLT, 76 and $+40 ppm/^{\circ}C$ in B(NY)T, respectively. The small Re ions produced a positive $\tau_\varepsilon$. The relation between $\tau_\varepsilon$ and the octahedron tilting in complex perovskite is discussed for the tungsten bronze type structure.

• Journal of the Korean Ceramic Society
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• v.37 no.3
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• pp.256-262
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• 2000

The dielectric properties of complex perovskite ($Pb_{1-x}Ca_{x}$)($Fe_{0.5}Ta_{0.5}$)$O_{3}$ with >($0.5{\le}x{\ge}0.65$ were investigated at microwave frequencies. Dilectric constant decreased with increasing Ca content, and was directly proportional to the cube of average ionic ra야 of A-site. For the specimen of x=0.6 sintered at $1250^{\circ}C$ for 3 h in air, dielectric constant (k) of 63, QF of 11000 GHz, and the temperature coefficient of resonant frequency(TCF) of -14ppm/$^{\circ}C$ were obtained. As Ca content increased, TCF of the specimen negatively increased due to the reduction of the tolerance factor(t). Changes in intrinsic loss with varying Ca content was investigated by the infrared reflectivity spectra ranging 50 to 4000 $cm^{-1}$, which were calculated by the Kramers-Kronig analysis and classical oscillator model. The relative tendency of microwave dielectric properties of the ($Pb_{1-x}Ca_{x}$)($Fe_{0.5}Ta_{0.5}$)$O_{3}$ specimens calculated from the reflectivity data were in good agreement with the results by the post resonant method.

• 전기의세계
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• v.25 no.1
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• pp.95-100
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• 1976

The main purpose of this paper is to study on the transient current due to the change of environmental temperature under no external field in the arrangement of M$_{1}$(metal)-P(polyver)-M$_{2}$(metal). The specimer of polymeric insulator sandwiched by two metal electrodes composes a parallel-plate condenser represented by Maxwell-model. The behaviors of short circuit current flowing in M-P-M arrangement are very complex and the analysis of its conduction mechanism appears to be much complicated. In this paper we can suggest that a contact potential difference as an energetic state exists in the thin film specimen both sides of which are contacted by two different metals having different cook functions. Futhermore the contact potential difference appears to be constant through the course of temperature change, however, the dielectric constant and caparitance of the specimen must be temperature dependent. Accordingly the charge difference induced on both sides of electrodes may be a cause for the shory circuited transient current flowing through the external circuit. It is also suggestive that the results of the observation must be considered in cases of insulation design of electrical machines and D.C. cable for high voltage use.