• 전기전자학회논문지
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• 제15권4호
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• pp.339-344
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• 2011

In this paper, we proposed an internal multi-band monopole antenna for mobile phone that can be used for smart phones. The proposed antenna has a small volume of $38{\times}8.5{\times}5\;mm^3$, ground size is $100{\times}60\;mm^2$, and covers the GSM900 (Global System for Mobile communications : 880-960 MHz), DCS (Digital Communications System : 1710-1880 MHz), K-PCS (Korea-Personal Communications Service : 1750-1870 MHz), US-PCS (US Personal Communications Service : 1850-1990 MHz), Bluetooth (2400-2483 MHz), Wibro (2300-2390 MHz) and WLAN (Wireless Local Area Network : 2400-2483.5 MHz) bands. The measured peak gains of the implemented antenna are 1.15 dBi at 920 MHz, 3.58 dBi at 1795 MHz, 3.46 dBi at 1810 MHz, 2.91 dBi at 1920 MHz, 5.18 dBi at 2345 MHz, 3.37 dBi at 2442 MHz.

• Journal of Electrical Engineering and Technology
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• 제1권3호
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• pp.343-350
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• 2006

This paper introduces a new high efficient bi-directional, non-isolated DC/DC converter. Through variations of the topology of the conventional Cuk converter, an optimum bi-directional DC/DC converter is proposed. Voltage and current in the proposed DC/DC converter are continuous. Furthermore, the efficiency in both step-up and step-down mode is improved over that of the conventional bi-directional converter. To prove the validation for the proposed converter, simulations and experiments are executed with a 300W bi-directional converter.

• 소성∙가공
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• 제13권1호
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• pp.78-83
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• 2004

High-temperature superconduction materials(Bi2223) possess electrical/electronic and magnetic properties. Because high-temperature superconduction materials is a ceramic powder, that cannot be produced singlehandedly. So Ag sheathed Bi-2223 wire was produced by drawing process using powder-in-tube(PIT) method. This superconductor has many difficulties to produce. The main difficulty is that the mechanical properties of the ceramic powder are very different from those of the Ag sheath. And by these properties, Bi2223 high-temperature superconductor, which has a single filament drawing process and multi-filament drawing process, has a defect like sausaging and bursting at a center. This study analyzed multi-filament drawing process by FEM, and a defect generated during multi-filament drawing was studied by FEH. Specially, in order to prevent a bursting at a center, this study presented a method that inserts a pure Ag at a center of multi-filament wire

• 한국재료학회지
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• 제7권1호
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• pp.40-49
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• 1997

기계적 합금화 공정과 가압소결법으로 $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ 열전재료를 제조하여, 가압소결온도 및 dopant첨가에 따른 미세구조와 열전특성의변화를 연구하였다. 평균 3.6mm 크기의 Bi, Te, Se granule을 볼과 원료금속의 무게비 5:1에서 3 시간 기계적 합금화 하므로써 $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ 합금분말의 형성이 완료되었다. $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$ 가압소결체의 성능지수는 $450^{\circ}C$ 이상의 온도에서 가압소결시 급격히 증가하였으며, $550^{\circ}C$에서 가압소결한 시편에서 $1.9{\times}10^{-3}/K$의 값을 얻었다. $550^{\circ}C$에서 가압소결한 $Bi_{2}(Te_{0.9}Se_{0.1})_{3}$의 성능지수는 acceptor dopant 인 Bi를 0.015wt %첨가함에 따라 $2.1{\times}10^{-3}/K$로 향상되었다.

• 한국분말재료학회지
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• 제22권4호
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• pp.254-259
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• 2015

$Bi_2Te_3$ related compounds show the best thermoelectric properties at room temperature. However, n-type $Bi_2Te_{2.7}Se_{0.3}$ showed no improvement on ZT values. To improve the thermolectric propterties of n-type $Bi_2Te_{2.7}Se_{0.3}$, this research has Cu-doped n-type powder. This study focused on effects of Cu-doping method on the thermoelectric properties of n-type materials, and evaluated the comparison between the Cu chemical and mechanical doping. The synthesized powder was manufactured by the spark plasma sintering(SPS). The thermoelectric properties of the sintered body were evaluated by measuring their Seebeck coefficient, electrical resistivity, thermal conductivity, and hall coefficient. An introduction of a small amount of Cu reduced the thermal conductivity and improved the electrical properties with Seebeck coefficient. The authors provided the optimal concentration of $Cu_{0.1}Bi_{1.99}Se_{0.3}Te_{2.7}$. A figure of merit (ZT) value of 1.22 was obtained for $Cu_{0.1}Bi_{1.9}Se_{0.3}Te_{2.7}$ at 373K by Cu chemical doping, which was obviously higher than those of $Cu_{0.1}Bi_{1.9}Se_{0.3}Te_{2.7}$ at 373K by Cu mechanical doping (ZT=0.56) and Cu-free $Bi_2Se_{0.3}Te_{2.7}$ (ZT=0.51).

• 한국재료학회지
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• 제12권12호
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• pp.911-917
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• 2002

0.5 at% $Na_2$Te-doped ($Pb_{0.7}Sn_{0.3}$)Te and ($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ powders were fabricated by mechanical alloying process. 0.5 at% Na$_2$Te-doped ($Pb_{0.7}Sn_{0.3}$)Te powders were charged at one end of mold and ($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ powders were charged at the other end of a mold. Then these powders were hot-pressed to form p-type ($Pb_{0.7}Sn_{0.3}$)Te/($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ functional gradient materials with the segment ratios (the ratio of ($Pb_{0.7}Sn_{0.3}$)Te to ($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ ) of 1:2, 1:1, and 2:1. Power generation characteristics of the ($Pb_{0.7}Sn_{0.3}$)Te/($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ were measured. When the temperature difference ΔT at both ends of the specimen was larger than $300^{\circ}C$, the ($Pb_{0.7}Sn_{0.3}$)Te/($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ with the segment ratios of 1:2 and 1:1 exhibited larger output power than those of the ($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ and 0.5 at% $Na_2$ Te-doped ($Pb_{0.7}Sn_{0.3}$)Te alloys. The maximum output power of the ($Pb_{0.7}Sn_{0.3}$)Te/($Bi_{0.2}Sb_{0.8}$)$_2$$Te_3$ predicted with the measured Seebeck coefficient and the estimated electrical resistivity was in good agreement with the measured maximum output power.

• 한국진공학회지
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• 제11권1호
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• pp.28-34
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• 2002

진공 증착한 $Sb_{2-x}Bi_xTe_3$ 박막은 Bi 농도에 관계없이 비정질 형태로 성장되었고, XPS 분석 결과 증착 물질과 거의 유사한 조성을 가짐을 알 수 있었다. 또한 박막의 광학적, 전기적 특성을 설명하기 위해 여러 미세구조 파라미터들을 계산하였다. 한편, 박막 내 Bi 농도가 증가함에 따라 전기 비저항은 급격히 감소하였고, 특히 높은 Bi 농도(x=1.0)에서는 전도 특성이 p-type에서 n-type으로 변화되었다. 또한 $Sb_{2-x}Bi_xTe_3$ 박막의 굴절 지수 및 광학적 밴드 갭은 Bi 농도에 따라 증가하였다.

• Journal of Magnetics
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• 제14권3호
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• pp.120-123
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• 2009

In this study, BiFe$O_3$-BaTi$O_3$ ceramics have been fabricated by a solid-state reaction method. The effects of BaTi$O_3$ content in the (1-x)BiFe$O_3$-xBaTi$O_3$ (x = 0.1, 0.2, 0.25, 0.3, 0.4, 0.5) system on crystal structure and magnetic, dielectric, and ferroelectric properties were investigated. Perovskite BiFe$O_3$ was stabilized through the formation of a solid solution with BaTi$O_3$. Rhombohedrally distorted structure (1-x)BiFe$O_3$-xBaTi$O_3$ ceramics showed strong ferromagnetism at x = 0.5. Dielectric and ferroelectric properties of the BiFe$O_3$-BaTi$O_3$ system also changed significantly upon addition of BaTi$O_3$. It was found that the maximum dielectric and ferroelectric properties were exhibited in the (1-x)BiFe$O_3$-xBaTi$O_3$ system at x = 0.25. This suggested the morphotropic phase boundary (MPB) with the coexistence of both rhombohedral and cubic phases of the (1-x)BiFe$O_3$-xBaTi$O_3$ system at x = 0.25.

• Journal of Magnetics
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• 제14권1호
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• pp.1-6
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• 2009

The magnetic properties of ${Bi_x}{Ca_{1-x}}{MnO_3}$ for x = 0.12, 0.13, 0.14, 0.15, and 0.16 were examined by measuring magnetic susceptibility, resistivity and electron magnetic resonance at different temperatures. ${Bi_x}{Ca_{1-x}}{MnO_3}$ showed complicated magnetic structure that varies with temperature and composition, particularly around Bi composition x. 0.15. The aim of this study was to determine how the magnetic and physical properties of ${Bi_x}{Ca_{1-x}}{MnO_3}$ change in this region. In addition, first principles calculations of the magnetic phase of ${Bi_x}{Ca_{1-x}}{MnO_3}$ for x = 0, 0.125, 0.25 were carried out, and the spin state, electric and magnetic characteristics are discussed.

• 한국전기전자재료학회논문지
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• 제22권4호
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• pp.290-296
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• 2009

$Bi_{4}Ti_{3}O_{12}$ (BiT) thin films were grown on the Pt/Ti/$SiO_2$/si substrate using a metal organic decomposition (MOD) method. Effects of oxygen annealing on the structural properties and dielectric properties of the BiT thin films were investigated. The BiT films were well developed when rapid thermal annealed at $>500^{\circ}C$ in oxygen ambient. For the film annealed at $700^{\circ}C$, no crystalline phase was observed under oxygen free annealing atmosphere while its crystallinity was significantly enhanced as the oxygen pressure increased. The BiT film also exhibited a smooth surface with defect free grains. A high dielectric constant and a low dielectric loss were achieved satisfactory in the frequency range from 75 kHz to 1 MHz. Especially, the BiT film, annealed at $700^{\circ}C$ and 10 torr oxygen pressure, showed good dielectric properties: dielectric constant of 51 and dielectric loss of 0.2 % at 100 kHz. Its leakage current was also considerably improved, being as $0.62\;nA/cm^2$ at 1 V. Therefore, it is considered that the oxygen annealing has effects on an enhancement of crystallinity and dielectric properties of the BiT films.