• Proceedings of the KIEE Conference
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• 1994.11a
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• pp.231-233
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• 1994

We have studied a properly of N-docosyl pyridinium(TCNQ) Langmuir-Blodgett film at room temperature with the $NO_2$ gas-detection characteristics. As a result, we have found that their conductivities were increased by 6 times at 5 layers(about $250{\AA}$ thickness) LB film. However, their reproducibility was not able to be measured at room temperature. Therefore, we must find their working temperature which was able to activate gas-detection characteristics. The $NO_2$ gas response experiments under 200 ppm concentration in $50^{\circ}C$ show that :here are increment of electrical conductivity by 8 times and 100 seconds of response time, and 200 seconds of recovery times at $60^{\circ}C$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.10 s.113
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• pp.920-928
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• 2006

Fiber-reinforced composites transmitting microwaves of certain frequencies or bands were proposed. These frequency selective fabric composites(FSFCs) are fabricated by weaving carbon fibers and dielectric fibers that build periodic patterns. Design parameters affecting the electromagnetic characteristics of FSFCs were widely discussed, Then the electromagnetic characteristics of a fabricated plain-weave FSEC were investigated with regard to the electrical conductivities of carbon roving, the fiber undulation, and the aperture-to-cell ratio, for the electrical conductivities, its dependence on frequency as well as on the fiber volume fraction of carbon roving was taken into account. Constituent material properties and the fiber undulation had little effect on the EM properties of the fabricated FSFC, while the aperture-to-cell ratio made a profound effect on them.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.1075-1080
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• 2015

A hybrid electric vehicle (HEV) powertrain has more than one energy source including a high-voltage electric battery. However, for a high voltage electric battery, the average current is relatively low for a given power level. Introduced to increase the voltage of a HEV battery, a compact, high-efficiency boost converter, sometimes called a step-up converter, is a dc-dc converter with an output voltage greater than its input voltage. The inductor occupies more than 30% of the total converter volume making it difficult to get high power density. The inductor should have the characteristics of good thermal stability, low weight, low losses and low EMI. In this paper, Mega Flux^® was selected as the core material among potential core candidates. Different structured inductors with Mega Flux^® were fabricated to compare the performance between the conventional air cooled and proposed potting structure. The proposed inductor has reduced the weight by 75% from 8.8kg to 2.18kg and the power density was increased from 15.6W/cc to 56.4W/cc compared with conventional inductor. To optimize the performance of proposed inductor, the potting materials with various thermal conductivities were investigated. Silicone with alumina was chosen as potting materials due to the high thermo-stable properties. The proposed inductors used potting material with thermal conductivities of 0.7W/m·K, 1.0W/m·K and 1.6W/m·K to analyze the thermal performance. Simulations of the proposed inductor were fulfilled in terms of magnetic flux saturation, leakage flux and temperature rise. The temperature rise and power efficiency were measured with the 40kW boost converter. Experimental results show that the proposed inductor reached the temperature saturation of 107℃ in 20 minutes. On the other hand, the temperature of conventional inductor rose by 138℃ without saturation. And the effect of thermal conductivity was verified as the highest thermal conductivity of potting materials leads to the lowest temperature saturations.

• Bulletin of the Korean Chemical Society
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• v.15 no.12
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• pp.1058-1064
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• 1994

Mn/In$_2O_3$ systems with a variety of Mn mol${\%}$ were prepared to investigate the effect of Mn-addition on the catalytic activity of Mn/In$_2O_3$ in the oxidative coupling of methane. The oxidative coupling of methane was examined on pure In$_2O_3$ and Mn/In$_2O_3$ catalysts by cofeeding gaseous methane and oxygen under atmospheric pressure between 650 and 830 $^{\circ}C$. Although pure In$_2O_3$ showed no C$_2$ selectivity, both the C$_2$ yield and the C$_2$ selectivity were increased by Mn-doping. The 5.1 mol${\%}$ Mn-doped In$_2O_3$ catalyst showed the best C$_2$ yield of 2.6${\%}$ with a selectivity of 19.1${\%}$. The electrical conductivities of pure and Mn-doped In$_2O_3$ systems were measured in the temperature range of 25 to 100 $^{\circ}C$ at PO$_2$'S of 1 ${\times}$ 10$^{-7}$ to 1 ${\times}$ 10 $^{-1}$ atm. The electrical conductivities were decreased with increasing Mn mol${\%}$ and PO$_2$, indicating the specimens to be n-type semiconductors. Electrons serve as the carriers and manganese can act as an electron acceptor in the specimens. Manganese ions doped in In$_2O_3$ inhibit the ionization of neutral interstitial indium or the transfer of lattice indium to interstitial sites and increase the formation of oxygen vacancy, giving rise to the increase of the concentration of active oxygen ion on the surface. It is suggested that the active oxygen species adsorbed on oxygen vacancies are responsible for the activation of methane.

• Korean Journal of Materials Research
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• v.7 no.1
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• pp.81-88
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• 1997

Vanadate glasses using $B_2O_3$ as a network former and with CuO additive were mainly investigated in relation to electrical properties. Crystalline phases formed by heat-treatment in each composition were examined and dc electrical conductivity changes of the glasses were analyzed. Crystalline phases were identified as $V_3O_5,\;a-CuV_2O_6\;and\;{\beta}-CuV_2O_6$ by XRD analysis. Crystallization degrees of $V_2O_5$ and ${\beta}-CuV_2O_6$ were little changed with heat-treatment time, but those of ${\alpha}u-CuV_2O_6$ were changed sharply with heat-treatment time. The more crystallization of ${\alpha}u-CuV_2O_6$ occurred, the higher electrical conductivity was observed. Electrical conductivities with $10^{-2}~10^{-4}/{\Omega}/cm$ at room temperature(303K) could be obtained by controlling the glass compositions. The electrical conductivities were increased with increasing of $V_20_5$ content and decreasing of alkality($CuO/B_2O_3$). In this study, electron was proved to be charge carrier by seebeck coefficient measurement. Accordingly, the glasses are believed to be n-type semiconductor. Calculated activation energies for the conduction were in the range 0.098-0.124 eV. Electrical conduction mechanism was small polaron hopping without showing variable range hopping in the temperature range $30~200^{\circ}C$.

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.329-336
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• 2010

The paper describes the electrical and optical properties of underwater discharges in highly inhomogeneous electric fields caused by 1.2/50 ${\mu}s$ impulse voltages as functions of the polarity and amplitude of the applied voltage, and various water conductivities. The electric fields are formed by a point-to-plane electrode system. The formation of air bubbles is associated with a thermal process of the water located at the tip of the needle electrode, and streamer coronas can be initiated in the air bubbles and propagated through the test gap with stepped leaders. The fastest streamer channel experiences the final jump across the test gap. The negative streamer channels not only have more branches but are also more widely spread out than the positive streamer channels. The propagation velocity of the positive streamer is much faster than that of the negative one and, in fact, both these velocities are independent of the water conductivity; in addition the time-lag to breakdown is insensitive to water conductivity. The higher the water conductivity the larger the pre-breakdown energy, therefore, the ionic currents do not contribute to the initiation and propagation of the underwater discharges in the test conditions considered.

• The Korean Journal of Ceramics
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• v.4 no.2
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• pp.83-89
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• 1998

The structure refinements and the electrical and magnetoelectric measurements were performed for BIT.1BF and BIT.2BT. The tetragonal distortion of the ab plane became lessened with the addition of $4BiFeO_3 into Bi_4Ti_3O_{12}$ significantly. However, the tilting of the outer-oxygen octahedra of the perovskite unit and the elongatin of the $(Bi_2O_2)^{2+}$ layers became more pronounced. For the both phases, the bariations of dielectric properties and electrical conductivities at high temperatures showed that the ferroelectic I-rerroelectric II phase transition existed before reaching the Curie temperature. The electrical conductivity became higher with the increase of $Fe^{3+}$ ions, implying that the electron transfer increased correspondingly. The magnetoelectric effect was observed linear up to ~8 kOe, which was stronger in BIT.1BF than BIT.2BF. This behavior indicates that the distortion of the ab plane may affect the induced polarization as well as magnetic moment.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.629-632
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• 2013

Many properties of inorganic compounds are sensitive to changes in the point-defect concentrations. In minerals, such changes are influenced by temperature, pressure, and chemical impurities. Olivines form an important class of minerals and are magnesium-rich solid solutions consisting of the orthosilicates forsterite $Mg_2SiO_4$ and the fayalite $Fe_2SiO_4$. Orthosilicates have an orthorhombic crystal structure and exhibit anisotropic electronic and ionic transport properties. We examined the anisotropy of the electrical conductivity of $Fe_2SiO_4$ under the assumption that the electronic conduction in $Fe_2SiO_4$ occurs via a small polaron hopping mechanism. The anisotropic electrical conductivity is well explained by the electron transfer integrals obtained from the spin dimer analysis based on tight-binding calculations. The latter analysis is expected to provide insight into the anisotropic electrical conductivities of other magnetic insulators of transition metal oxides.

• Korean Journal of Materials Research
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• v.17 no.10
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• pp.526-531
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• 2007

The sintering behavior and electrical property of $Ce_{0.8}Gd_{0.2}O_{1.9}$ ceramics were investigated with the iron oxide concentration ranging from 0 to 5 mol%. Both the sintered density and grain size were found to increase up to 2 mol% $Fe_2O_3$, and then to decrease with further additions. At a higher $Fe_2O_3$ content above 3 mol%, grain size decreased by a pinning effect induced by different shape grains. The electrical conductivity was also increased with increasing $Fe_2O_3$ content up to 2 mol%. Total conductivity of 2 mol% $Fe_2O_3-added$ specimen showed the maximum conductivity of $2{\times}10^{-2}{\Omega}{\cdot}cm^{-1}$ at $500^{\circ}C$. The addition of $Fe_2O_3$ was found to promote the sintering properties and electrical conductivities of $Gd_2O_3-dope\;CeO_2$.

• Journal of the Korean Ceramic Society
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• v.30 no.5
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• pp.373-380
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• 1993

Li2O-B2O3-P2O5 glasses with high lithium content were analysed by electrical characterization. The electrical conductivity increase with Li content and exhibits a maximum value of 1.2$\times$10-4S/cm near B2O3/P2O5=1 at 15$0^{\circ}C$. Glass transitiion temperature increased with conductivity. Concentration of charge carrier and distribution of relaxation time were independent of temperature. In this system the variation of conductivity with the composition was depend on mobility of lithium ion. Basically, it is attribute to primitive activation energy. Enhancement of conductivities was related to be formation of (B-O-P)-, di-, and metaborate group, which give additional available sites for Li+ diffusion.