• Journal of the Korean Institute of Gas
• /
• v.22 no.1
• /
• pp.1-8
• /
• 2018

FCV is installed with a automatic valve attached in an high pressure cylinder to control the hydrogen flow. The supply of hydrogen from the cylinder into the fuel cell stack is controlled via the on/off operation of a solenoid attached to the automatic valve. The solenoid needs to provide the necessary attraction force even at any saturation temperature caused by drive of the vehicle. In this study, the simplified prediction equations for the saturation temperature are suggested. The finite element analysis was performed by steady state technique, according to the boundary condition in order to predict the saturation temperature and attraction force. Finally, the saturation temperature was validated through comparison between the analysis results and measurement results. From the results, the measured saturation temperature $5.9^{\circ}C$ lower with respect to the analysis results. And the error of attraction force ranged from 1.0 to 2.1 N at testing conditions.

• Journal of the Korean Magnetics Society
• /
• v.4 no.2
• /
• pp.135-141
• /
• 1994

With the variation of Cr content and $N_2$ flow ratio, the soft magnetic properties, corrosion resistance and reactivity of the sputtered nanocrystalline FeZrCrN thin flims were investigated. In case of FeZrCrN thin films, a saturation magnetization was decreased with increasing $N_2$ flow ratio. In addition, good soft magnetic properties were obtained at the flow ratio of 3% $N_2$. The $Fe_{64.9}Zr_{8.8}Cr_{5.8}N_{20.5}$ nanocrystalline thin film after annealing at $550^{\circ}C$ exhibited the saturation magnetization of 12.5kG, low coercivity of 0.4 Oe and high permeability of 2600 at 5 MHz. Films containing up to 7.5% Cr showed an enhanced corrosion resistance and reduced reactivity with the bonding glass without degradation of soft magnetic properties, although the saturation magnetization was decreased slightly with the Cr addtion.

• Journal of the Korean Magnetics Society
• /
• v.4 no.4
• /
• pp.347-354
• /
• 1994

The structural change and magnetic properties of mechanically milled Fe-N and Mn-Al alloy powders have been investigated by XRD, TEM, VSM, $M\"{o}ssbauer$ spectroscopy and inelastic neutron scattering measurements. During milling of ${\gamma}'-Fe_{4}N$ powders, and fcc ${\gamma}'-Fe_{4}N$ phase is transformed to a bct ${\alpha}'-Fe(N)$ phase by stress-induced martensitic transformation, being accompanied by an initial increase in saturation magnetization. During annealing the bct ${\alpha}'-Fe(N)$ nanocrystalline phase which is obtained by mechanical grinding for a long time, an ${\alpha}'-Fe_{16}N_{2}$ phase partially appears as an intermediate phase at 673~773 K, causing an increase in saturation magnetization. During milling of Mn-45, 70 and 85 at.% Al mixed powders, Al atoms are partially solubilized into an ${\alpha}-Mn$ phase. The Al supersaturated ${\alpha}-Mn-type$ phases change from paramagnetic to ferromagnetic : the saturation magnetization is 11 emu/g for the as-milled Mn-70 at.% Al powders. Moreover, by removing almost all Al atoms from the as-milled Mn-85 at.% Al powders using chemical leaching, the saturation magnetization increases up to 36 emu/g. The above bct ${\alpha}'-Fe(N)$ and ferromagnetic ${\alpha}-Mn$ type alloys are the magnetic materials found for the first time, by using the present mechanochemical process.

• Journal of the Korean institute of surface engineering
• /
• v.44 no.6
• /
• pp.255-259
• /
• 2011

The thickness dependence of magnetic properties was experimentally investigated in nanocrystalline Fe-Hf-N thin films fabricated by a RF magnetron sputtering method. In order to investigate the thickness effect on their magnetic properties, the films are prepared with different thickness ranges from 90 nm to 330 nm. It was revealed that the coercivity of the thin film increased with film thickness. On the contrary, the saturation magnetization decreased with film thickness. On the basis of the SEM and TEM, an amorphous phase forms during initial growth stage and it changes to crystalline structure after heat treatment at $550^{\circ}C$. Nanocrystalline Fe-Hf-N particles are also generated.

• Korean Journal of Metals and Materials
• /
• v.50 no.3
• /
• pp.248-255
• /
• 2012

AlN thin films containing various amounts of Co, AlN-Co, and Al-Co alloy particles were prepared using a two-facing-target type dc reactive sputtering (TFTS) system. The as-deposited films exhibited the variable nature expected from an AlN-rich phase, and an amorphous-like phase, depending on the Co content in the films. Specific favorable microstructures were prepared by optimizing annealing conditions. Those microstructures and their magnetic properties and resistivity were investigated. As-deposited films showed very small saturation magnetization and an amorphous-like structure. However, when annealed, the as-deposited amorphous-like phase decomposes into phases of AlN, Co and Al-Co. These annealing induced changes in the microstructure improve the magnetization and resistivity of the films. Further improvement of soft magnetic properties could lead to the material being used for high density magnetic recording head material.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.50 no.9
• /
• pp.55-59
• /
• 2013

A new method using RF Ids determined from measured S-parameters is proposed to extract the gate-voltage dependent effective carrier velocity of bulk MOSFETs in the saturation region without additional dc Ids measurement data suffering parasitic resistance effect that becomes larger with continuous down-scaling to sub-$0.1{\mu}m$. This method also allows us to extract the carrier velocity in the saturation region without the difficult extraction of bias-dependent parasitic gate-source capacitance and effective channel length. Using the RF technique, the electron velocity overshoot exceeding the bulk saturation velocity is observed in bulk N-MOSFETs with a polysilicon gate length of $0.065{\mu}m$.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.38 no.7
• /
• pp.464-472
• /
• 2001

Asymmetric n-MOSFET＇s for improving packing density have been fabricated with 0.35 ${\mu}{\textrm}{m}$ CMOS process. Electrical characteristics of asymmetric n-MOSFET show a lower saturation drain current and a higher linear resistance compared to those of symmetric devices. Substrate current of asymmetric MOSFET is lower than that of symmetric devices. Asymmetric n-MOSFET＇s have been modeled using a parasitic resistance associated with abnormally structured drain or source and a conventional n-MOSFET model. MEDICI simulation has been done for accuracy of this modeling. Simulated values of reverse as we11 as forward saturation drain current show good agreement with measured values for asymmetric device.

• Journal of Electrical Engineering and Technology
• /
• v.11 no.4
• /
• pp.939-942
• /
• 2016

One of the most important characteristic curves of a solar cell is its current density-voltage (J-V) curve under AM1.5G insolation. Solar cell can be considered as a semiconductor diode, so a diode equivalent model was used to estimate its parameters from the J-V curve by numerical simulation. Active layer plays an important role in operation of a solar cell. We investigated the effect thicknesses and defect densities (N_d) of the active layer on the J-V curve. When the active layer thickness was varied (for N_d = 8×10¹⁷ cm^-3) from 800 nm to 100 nm, the reverse saturation current density (J_o) changed from 3.56×10^-5 A/cm² to 9.62×10^-11 A/cm² and its ideality factor (n) changed from 5.28 to 2.02. For a reduced defect density (N_d = 4×10¹⁵ cm^-3), the n remained within 1.45≤n≤1.92 for the same thickness range. A small increase in shunt resistance and almost no change in series resistance were observed in these cells. The low reverse saturation current density (J_o = 9.62×10^-11 A/cm²) and diode ideality factor (n = 2.02 or 1.45) were observed for amorphous silicon based solar cell with 100 nm thick active layer.

• Solar Energy
• /
• v.8 no.2
• /
• pp.12-18
• /
• 1988

The effect of surface recombination current density on the saturation current density in Si solar cell has been studied. Theoretical model for surface recombination current was set up from emitter transparent model of M.A. Shibib, and saturation current of Si solar cell made by ion implantation method was also measured by digital electrometer. The theoretical surface recombination current density which is the same as saturation surface recombination current density in Shibib model was $10^{-11}[A/cm^2]$ and the measured value was ranged from $8{\times}10^{-10}$ to $2{\times}10^{-9}[A/cm^2]$. Comparing with the ideal p-n junction of Shockley, transparent emitter model shows improved result by $10^2$ order of saturation current density. But there still exists $10^2$ order of difference of saturation current density between theoretical and actual values, which are assumed to be caused by 1) leakage current through solar cell edge, 2) recombination of carriers in the depletion layer, 3) the series resistance effect and 4) the tunneling of carriers between states in the band gap.

• Geophysics and Geophysical Exploration
• /
• v.18 no.3
• /
• pp.125-132
• /
• 2015

The water saturation ($S_w$), which is very important to estimate hydrocarbon reserves in the reservoir, has been determined from resistivity index (RI) by using the Archie's formula. However, in many cases, it has been reported that n is not constant for a given formation and it could be varied with water saturation. In addition, it frequently happens that the line obtained by linear regression analysis on log-log scale does not pass through the origin. In order to overcome these drawbacks, we suggested a modified Archie's formula, which can handle almost all the RI vs. $S_w$ cross-plots whether the trend is straight or curved and whether it passes through the origin or not. We also demonstrated that how to determine conductivity exponent ${\mu}$, critical water saturation $S_c$, and saturation distribution factor b in the laboratory to use the modified Archie's formula. Since the modified Archie's formula takes into account pore structure, pore water distribution, and wettability of reservoir such as clean sandstone and carbonate rocks, it might improve field applicability.