• Journal of the Korean Ceramic Society
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• v.40 no.1
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• pp.98-103
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• 2003

The effect of glass addition on the low-temperature sintering and microwave dielectric properties in $BaO-Nd_2O_3-TiO_2$ dielectric ceramics were studied. When 10~30 wt% of alkali lithium borosilicate glass was added, the sintering temperature decreases from $1300^{\circ}C$;to;1000^{\circ}C$ and the relative density more than 95% was obtained. When the added amount of glass increased above 10 wt%, the density as well as dielectric properties changed, which was attributed to the second phase formation. When the sample was sintered at 100$0^{\circ}C$ with l0wt% of glass, the dielectric properties of $Qxf_o{ge}2800,;{varepsilon}_r{ge}65;and;{ au_f=+55 ppm/^{\circ}C$ were obtained.

• Journal of the Korea Society of Computer and Information
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• v.17 no.4
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• pp.1-9
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• 2012

As we are turnning into the aged society, accidents by falling down are increasing in the aged people's group. In this paper, we design the system with the 3-Axis acceleration sensor which is composed by a single chip. The body activity signal is measured with the signal detector and RF communicator in this proposed system and the and falling by the entering signal pattern analysis with 3-Axis acceleration sensor. For the RF communication, we are using nRF24L01p and 8bits ATmega uC for the processor. The error of energy expenditure estimation between motor driven treadmill and proposed a body activity module was 7.8% respectively. Human activities and falling is monitored according to analyze and judge the critical value of the Signal Vector. as falled down if they don't turn off the alarm after specific period and the aged person's after falling down activities are their position and more.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.8-14
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• 1995

The magnetic properties of an $Fe_{87}Zr_{7}B_{5}Ag_{1}$(at.%) amorphous alloy have been investigated as a function of annealing temperatures to clarify its application potential as a core material for high-frequency use by adding a small amount of insoluble element of Ag. A new excellent soft magnetic material was developed. The amorphous alloy produced by relatively low temperature annealing at $T_{a}=400^{\circ}C$ exhibited very high initial permeability$(\mu_{i})$ of 288,000 at 1kHz and 2mOe, very low coercivity$(H_{c})$ of 15mOe and low core loss$(W_{c})$ of 50W/kg at 100kHz and 1,000G which is comparable with Co-based amorphous alloys, respectively. It is notable that the values obtained in the present study are the best magnetic properties among various kinds of Fe-based soft amorphous materials reported up to date. The reasons for the achievement of good soft magnetic properties are presumably due to the homogeneous formation of very fine $\alpha$-Fe clusters with the size of 2~3nm in an amorphous matrix, which can be deduced from the increase of resistivity and the TEM observation. The very fine $\alpha$-Fe clusters embedded in an amorphous matrix had a great influence on reduction of magnetostriction and refinement of magnetic domain.

• Journal of the Korean Magnetics Society
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• v.25 no.4
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• pp.129-137
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• 2015

The Cu(radius ra = $95{\mu}m$)/$Ni_{80}Fe_{20}$(outer radius $r_b$ = $120{\mu}m$) core/shell composite wire is fabricated by electrodeposition. The two diagonal components of impedance tensor for the Cu/$Ni_{80}Fe_{20}$ core/shell composite wire in cylindrical coordinates, $Z_{zz}$ and $Z_{{\theta}{\theta}}$, are measured as a function of frequency in 10 kHz~10 MHz and external static magnetic field in 0 Oe~200 Oe. The equations expressing the diagonal $Z_{zz}$ and $Z_{{\theta}{\theta}}$ in terms of diagonal components of complex permeability tensor, ${\mu}^*_{zz}$ and ${\mu}^*_{{\theta}{\theta}}$, are derived from Maxwell's equations. The real and imaginary parts of ${\mu}^*_{zz}$(f) and ${\mu}^*_{{\theta}{\theta}}$(f) spectra are extracted from the measured $Z_{zz}$(f) and $Z_{{\theta}{\theta}}$(f) spectra, respectively. It is presened that the extraction of ${\mu}^*_{zz}$(f) and ${\mu}^*_{{\theta}{\theta}}$(f) spectra from the diagonal impedance spectra can be a versatile tool to investigate dymanic magnetization process in the core/shell composite wire.

• Journal of the Korean Magnetics Society
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• v.25 no.4
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• pp.123-128
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• 2015

The iron is an element having a high yield strength, mechanical hardness, good electrical conductivity, and also it has been used in various fields because of ease machining. In bridges have been used tendon made of a steel wire for large loads and light weight. Tension measurement of tendon employed in PreStressed Concrete (PSC) bridge is very important for the bridge safety check. NDT (Non-Destructive Testing) is essential for the safety check, however, magnetic NDT is difficult to apply due to the non-linear magnetization curve and hysteresis loop in the magnetic properties. In this work, for basic study of magnetic NDT application, we have constructed a B-H loop measuring system for 7-strand tendon of which diameter is 15.5 mm, and which can apply tensile stress up to 2.0 GPa. We have measured hysteresis loops of two kinds of tendons under different tensile stress. Amplitude permeability and maximum magnetic induction near knee show the most sensitive and high linearity depends on tensile stress. Relative amplitude permeability was decreased from 500 to 200 and maximum magnetic flux density changed 0.6 T.

• Journal of the Korean Magnetics Society
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• v.22 no.1
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• pp.15-18
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• 2012

The olivine structured $LiFe_{0.9}Mn_{0.1}PO_4$ material was prepared by solid state method, and was analyzed by x-ray diffractometer (XRD), superconducting quantum interference devices (SQUID) and Mossbauer spectroscopy. The crystal structure of $LiFe_{0.9}Mn_{0.1}PO_4$ was determined to be orthorhombic (space group: Pnma) by Rietveld refinement method. The value of N$\acute{e}$el temperature ($T_N$) for $LiFe_{0.9}Mn_{0.1}PO_4$ was determined 50 K. The temperature dependence of the magnetization curves showed magnetic phase transition from paramagnetic to antiferromagnetic at $T_N$ by SQUID measurement. M$\ddot{o}$ssbauer spectra of $LiFe_{0.9}Mn_{0.1}PO_4$ showed 2 absorption lines at temperatures above $T_N$ and showed asymmetric 8 absorption lines at temperatures below $T_N$. These spectra occurred due to the magnetic dipole and electric quardrupole interaction caused by strong crystalline field at asymmetric $FeO_6$ octahedral sites.

• Journal of the Korean Magnetics Society
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• v.17 no.1
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• pp.10-13
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• 2007

Single crystalline, $LuFe_2O_4$, was grown by the floating zone method. The crystal structure was a two-dimensional layered-type rhombohedral($R\={3}mh$) structure, with an $a_0=3.440(2)\;{\AA}\;and\;a\;c_0=25.263(2)\;{\AA}$. The magnetic $N\'{e}el$ temperature($T_N$) was determined to be 250 K. The $M\"{o}ssbauer$ spectrum at 12 K was fitted with four sextet sets which was resulted from the crystal structure. The spectrm at room temperature consisted of three singlets and a doublet with the electric quadrupole splitting. The isomer shift($\delta$) value of the singlet was $0.20{\pm}0.01mm/s$ relative to the Fe metal indicating the $Fe^{3+}$ valence state, and the value of the doublet was $0.70{\pm}0.01mm/s$ indicating $Fe^{2+}$. The $M\"{o}ssbauer$ absorption area ratio between $Fe^{3+}$ and $Fe^{2+}$ at room temperature was 1:1. The doublet phase of spectra gradually disappears by up to 360 K. At 360 K, the spectrum shows the singlet phase. We suggested that the spontaneous polarization effect of $LuFe_2O_4$ was caused by the change of iron behavior.

• Journal of the Korean Magnetics Society
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• v.20 no.1
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• pp.13-17
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• 2010

Fe-3, 4.2 and 6.8% Si compressed cores were fabricated, and then electrical resistivity, AC and DC magnetic properties, microhardness, and other properties were analyzed in order to know whether best soft magnetic properties could be also obtained in an Fe-Si compressed core with the well-known composition of Fe-6.5% Si. With increasing the silicon content, eddy current loss and hysteresis loss decreased and increased, respectively, so that a minimum total loss was not obtained in the well-known Fe-6.8 % Si cores, but obtained in the Fe-4.2 % Si cores. Also electrical resistivity of the cores and hardness of the particles increased monotonously with silicon content so that compaction ratio of the cores decreased. B2 and $DO_3$ ordered phase could be observed only in Fe-6.8% Si powder. A minimum loss and highest permeability of the Fe-4.2 % Si cores can be explained by the ratio of specific electrical resistivity of insulator to that of magnetic particles, micro-hardness, compaction ratio and demagnetization coefficient of the Fe-Si powder particles with silicon content.

• Journal of Korea Port Economic Association
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• v.27 no.3
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• pp.41-64
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• 2011

This article investigates the interrelationships in daily returns using fractionally integrated error correction term and volatilities using constant conditional correlation and dynamic conditional correlation GARCH with asymmetries between Capesize and Panamax markets. Our findings are as follows. First, for the fractionally cointegrated error correction model, there is a unidirectional relationship in returns from the Panamax market to the Capesize market, but a bidirectional causal relationship prevails for the traditional error correction models. Second, the coefficients for the error correction term are all statistically significant. Of particular interest are the signs of the estimates for the error correction term, which are all negative for the Capesize return equation and all positive for the Panamax return. Third, there are bidirectional volatility spillovers between both markets and the direction of the information flow seems to be stronger from Panamax to Capesize. Fourth, the coefficients for the asymmetric term are all significantly positive in the Capesize market, but the Panamax market does not have a significant effect. However, the coefficients for the asymmetric term are all significant, implying that the leverage effect does exist in the Capesize and Panamax markets.

• Korean Journal of Materials Research
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• v.17 no.8
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• pp.447-451
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• 2007

We investigated the dependence of the various annealing conditions and thickness ($6\sim45nm$) of the Ti-doped $Al_2O_3$ coating on the electrochemical properties and the capacity fading of Ti-doped $Al_2O_3$ coated $LiCoO_2$ films. The Ti-doped-$Al_2O_3$-coating layer and the cathode films were deposited on $Al_2O_3$ plate substrates by RF-magnetron sputter. Microstructural and electrochemical properties of Ti-doped-$Al_2O_3$-coated $LiCoO_2$ films were investigated by transmission electron microscopy (TEM) and a dc four-point probe method, respectively. The cycling performance of Ti-doped $Al_2O_3$ coated $LiCoO_2$ film was improved at higher cut-off voltage. But it has different electrochemical properties with various annealing conditions. They were related on the microstructure, surface morphology and the interface condition. Suppression of Li-ion migration is dominant at the coating thickness >24.nm during charge/discharge processes. It is due to the electrochemically passive nature of the Ti-doped $Al_2O_3$ films. The sample be made up of Ti-doped $Al_2O_3$ coated on annealed $LiCoO_2$ film with additional annealing at $400^{\circ}C$ had good adhesion between coating layer and cathode films. This sample showed the best capacity retention of $\sim92%$ with a charge cut off of 4.5 V after 50 cycles. The Ti-doped $Al_2O_3$ film was an amorphous phase and it has a higher electrical conductivity than that of the $Al_2O_3$ film. Therefore, the Ti-doped $Al_2O_3$ coated improved the cycle performance and the capacity retention at high voltage (4.5 V) of $LiCoO_2$ films.