• Journal of the Korean institute of surface engineering
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• v.47 no.4
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• pp.168-173
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• 2014

The paper presents the comparative results of TiAlN coatings deposited by DC and pulsed DC asymmetric bipolar magnetron sputtering systems. The results show that, with the decreasing duty cycle and increasing pulse frequency, the coating morphology changes from a columnar to a dense structure, with finer grains. Pulsed sputtered TiAlN coatings showed higher hardness, higher residual stress, and smaller grain sizes than dc prepared TiAlN coatings. Moreover residual stress of pulsed sputtered TiAlN coatings increased on increasing pulse frequency. Meanwhile, the surface roughness decreased continuously with increasing pulsed DC frequency up to 50 kHz.

• Journal of Powder Materials
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• v.9 no.2
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• pp.124-132
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• 2002

Nano Cu powders, synthesized by Pulsed Wire Evaporation (PWE) method, have been compacted by Magnetic Pulsed Cojpaction(MPC) method. The microstructure and mechanical properties were analyzed. The optimal condition for proper mechanical properties with nanostructure was found. Both pure nano Cu powders and passivated nano Cu powders were compacted, and the effect of passivated layer on the mechanical properties was investigated. The compacts by MPC, which had ultra-fine and uniform nanostructure, showed higher density of 95% of theoretical density than that of static compaction. The pur and passivated Cu compacted at $300^{\circ}C$ exhibited maximum hardnesses of 248 and 260 Hv, respectively. The wear resistance of those compacts corresponded to the hardness.

• Journal of the Korean institute of surface engineering
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• v.48 no.4
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• pp.136-141
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• 2015

The paper presents the comparative results of NbN coatings deposited by DC and pulsed DC asymmetric bipolar magnetron sputtering systems. The results show that, with the decreasing duty cycle and increasing pulse frequency, the coating morphology changes from a columnar to a dense structure, with finer grains. The Pulsed sputtered NbN coatings showed higher hardness, higher residual stress, and smaller grain sizes than those of DC prepared NbN coatings. Moreover residual stress of pulsed sputtered NbN coatings increased on increasing pulse frequency. Meanwhile, the surface roughness decreased continuously with increasing pulsed DC frequency up to 50 kHz.

• Journal of the Korean institute of surface engineering
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• v.49 no.5
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• pp.461-466
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• 2016

Nanocrystalline vanadium nitride (VN) coatings were deposited using asymmetric bipolar pulsed dc sputtering to further understand the influence of the pulsed plasmas on the crystal structure, microstructure and mechanical properties. Properties of VN coatings were investigated with FE-SEM, XRD and nanoindentation. The results show that, with the increasing pulse frequency and decreasing duty cycle, the coating morphology changed from a porous columnar to a dense structure, with finer grains. Asymmetric bipolar pulsed dc sputtered VN coatings showed higher hardness, elastic modulus and residual compressive stress than dc sputtered VN coatings. The results suggest that asymmetric bipolar pulsed dc sputtering technique is very beneficial for the reactive sputtering deposition of VN coatings.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.2
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• pp.87-93
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• 2020

This study proposes a gate driver that operates semiconductor switches in the bipolar pulsed power modulator. The proposed gate driver was designed to receive isolated power and synchronized signals through the gate transformer. The gate circuit has a separate delay in the on-and-off operation to prevent a short circuit between the top and bottom switches of each leg. On the basis of the proposed gate circuit, a bipolar pulsed power modulator prototype with a 2.5 kV/100 A rating was developed. Finally, the bipolar pulsed power modulator was tested under resistive load and plasma reactor load conditions. It is verified that the proposed gate driver can be applied to a bipolar pulsed power modulator.

• Korean Journal of Materials Research
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• v.26 no.9
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• pp.486-492
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• 2016

Tungsten (W) thin film was deposited at $400^{\circ}C$ using pulsed chemical vapor deposition (pulsed CVD); film was then evaluated as a nucleation layer for W-plug deposition at the contact, with an ultrahigh aspect ratio of about 14~15 (top opening diameter: 240~250 nm, bottom diameter: 98~100 nm) for dynamic random access memory. The deposition stage of pulsed CVD has four steps resulting in one deposition cycle: (1) Reaction of $WF_6$ with $SiH_4$. (2) Inert gas purge. (3) $SiH_4$ exposure without $WF_6$ supply. (4) Inert gas purge while conventional CVD consists of the continuous reaction of $WF_6$ and $SiH_4$. The pulsed CVD-W film showed better conformality at contacts compared to that of conventional CVD-W nucleation layer. It was found that resistivities of films deposited by pulsed CVD were closely related with the phases formed and with the microstructure, as characterized by the grain size. A lower contact resistance was obtained by using pulsed CVD-W film as a nucleation layer compared to that of the conventional CVD-W nucleation layer, even though the former has a higher resistivity (${\sim}100{\mu}{\Omega}-cm$) than that of the latter (${\sim}25{\mu}{\Omega}-cm$). The plan-view scanning electron microscopy images after focused ion beam milling showed that the lower contact resistance of the pulsed CVD-W based W-plug fill scheme was mainly due to its better plug filling capability.

• Journal of International Academy of Physical Therapy Research
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• v.5 no.2
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• pp.752-756
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• 2014

This study investigated the effects of changes to the pulsation factor of pulsed direct currents on wound healing. Patients with a pressure ulcer at a care hospital for the elderly were randomly divided into three groups: Group 1 involved the application of $100{\mu}s$ in pulse duration, 10 ms in pulse period, 100 pps in a pulsation factor, 15 mA in pulse amplitude, and polarity red+ by using pulsed direct currents; Group 2 involved a change of pulse period to 8 ms; and Group 3 received general wound management. Although there were no statistically significant differences in the changing stages of pressure ulcers among the groups, all the groups dropped in numerical stages. In the two groups to which pulsed direct currents were applied, there was a statistically significant reduction in the stages of pressure ulcers from the initial assessment to the 12-week assessment (p<.05). Even though there were no statistically significant differences in changes to the area of pressure ulcers among the groups, a statistically significant decrease was found in pulsed direct current group 2 whose pulse period was shortened (p<.05). There was no difference in the healing rate of pressure ulcers among the groups, but it made a numerical increase in pulsed direct current group 1 and group 2 and a numerical decrease in group 3. There were no significant differences in the characteristics of those who had a full recovery among the groups. Those findings indicate that pulsed direct currents have positive effects on the wound healing of patients with a pressure ulcer and that a treatment with pulsed direct currents whose pulsation factor is raised by reducing the pulse duration is especially effective.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.3
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• pp.380-388
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• 2011

In this paper, we developed the X-band 63 watt pulsed SSPA(Solid State Power Amplifier) by using HMIC(Hybrid Microwave Integrated Circuits). The pulsed SSPA consists of power supply and 3-stage amplifier modules : pre-amplifier stage, driver-amplifier stage, final-amplifier stage. The developed pulsed SSPA provides more than 63 watts of output power with a short pulse width and the duty cycle of up to 1.2 % at $70^{\circ}C$. The fabricated module offers great than 37 dB of saturated gain across the operating band. Input and output VSWR is <1.5:1. This module has an average current of 400 mA typical and operates at a +28 $V_{dc}$ supply. The developed SSPA in this paper can apply to pulsed Doppler radar with high speed operation.

• Journal of Welding and Joining
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• v.32 no.6
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• pp.47-55
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• 2014

The purpose of the study is to produce a mechanically improved weld and minimum variation of color through comparing unpulsed and pulsed GTAW (Gas Tungsten Arc Welding) for pure titanium (CP grade7) tube. Pulsed GTAW using 60 A peak current and 20 A background current (1:9) achieved the wider window of welding conditions having part and full penetration without burn-through than the case of unpulsed GTAW. Moreover, the pulsed welding reduced a discoloration on the back bead of the weld and the size of microstructures (basket weave and serrated ${\alpha}$). That is because the pulsed welding has it's a low heat input and severe weld flow induced from electric current variation. Furthermore, the pulsed welding improved the bending property of the welded Ti tube. The enhanced bending property for the pulsed GTAW was due to the insignificant discoloration on the weld surface with maintaining the metal polish.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.2
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• pp.174-180
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• 2008

The pulsed amplifier which switches the main supply voltage of RF amplifier according to input pulse signal has good efficiency and low noise level between pulses. And it has simple structure because it doesn't need a pulse modulator at input port. The pulsed amplifier using the conventional switching circuit has slow fall time compared to rise time. We proposed the novel switching circuit for improving the fall time of pulsed amplifier The proposed switching circuit is implemented by replacing FET of conventional circuit with BJT. As a result of appling this circuit to RF pulsed amplifier, the rise and fall time are 5.7 ns and 21.9 ns at 27 dBm output power, respectively.