• Journal of electromagnetic engineering and science
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• v.1 no.1
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• pp.73-77
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• 2001

We studied the fabrication of GaAs-based pseudomorphic high electron mobility transistors(PHEMT`s) for the purpose of millimeter- wave applications. To fabricate the high performance GaAs-based PHEMT`s, we performed the simulation to analyze the designed epitaxial-structures. Each unit processes, such as 0.1 m$\mu$$\Gamma$-gate lithography, silicon nitride passivation and air-bridge process were developed to achieve high performance device characteristics. The DC characteristics of the PHEMT`s were measured at a 70 $\mu$m unit gate width of 2 gate fingers, and showed a good pinch-off property ($V_p$= -1.75 V) and a drain-source saturation current density ($I_{dss}$) of 450 mA/mm. Maximum extrinsic transconductance $(g_m)$ was 363.6 mS/mm at $V_{gs}$ = -0.7 V, $V_{ds}$ = 1.5 V, and $I_{ds}$ =0.5 $I_{dss}$. The RF measurements were performed in the frequency range of 1.0~50 GHz. For this measurement, the drain and gate voltage were 1.5 V and -0.7 V, respectively. At 50 GHz, 9.2 dB of maximum stable gain (MSG) and 3.2 dB of $S_{21}$ gain were obtained, respectively. A current gain cut-off frequency $(f_T)$ of 106 GHz and a maximum frequency of oscillation $(f_{max})$ of 160 GHz were achieved from the fabricated PHEMT\\`s of 0.1 m$\mu$ gate length.h.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.1
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• pp.9-14
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• 2016

This study evaluated a digital locking device design using detection distance of 13.4mm of a human body sensing type magnetic field coil. In contrast to digital locking devices that are used nowadays, the existing serial number entering buttons, lighting, number cover, corresponding pcb, exterior case, and data delivery cables have been deleted and are only composed of control ON/OFF power switches and emergency terminals. When the magnetic field coil substrates installed inside the inner case detects the electric resistance delivered from the opposite side of the 12mm interval exterior contacting the glass body part, the corresponding induced current flows. At this time, the magnetic field coil takes the role as a sensor when coil frequency of the circular coil is transformed. The magnetic coil as a sensor detects a change in the oscillation frequency output before and after the body is detected. This is then amplified to larger than 2,000%, transformed into digital signals, and delivered to exclusive software to compare and search for embedded data. The detection time followed by the touch area of the body standard to a $12.8{\emptyset}$ magnetic field coil was 30% contrast at 0.08sec and 80% contrast at 0.03sec, in which the detection distance was 13.4mm, showing the best level.

• Journal of the Korean earth science society
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• v.36 no.1
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• pp.68-81
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• 2015

In this study, the correlation between the frequency of summer tropical cyclones (TC) affecting areas around Korea over the last 37 years and the western North Pacific monsoon index (WNPMI) was analyzed. A clear positive correlation existed between the two variables, and this high positive correlation remained unchanged even when excluding El Ni$\tilde{n}$o-Southern Oscillation (ENSO) years. To investigate the causes of the positive correlation between these two variables, ENSO years were excluded, after which the 8 years with the highest WNPMI (positive WNPMI phase) and the 8 years with the lowest WNPMI (negative WNPMI phase) were selected, and the average difference between the two phases was analyzed. In the positive WNPMI phase, TCs usually occurred in the eastern waters of the tropical and subtropical western North Pacific, and tended to pass the East China Sea on their way north toward Korea and Japan. In the negative WNPMI phase, TCs usually occurred in the western waters of the tropical and subtropical western North Pacific, and tended to pass the South China Sea on their way west toward the southeastern Chinese coast and the Indochina peninsula. Therefore, TC intensity was higher in the positive WNPMI phase, during which TCs are able to gain sufficient energy from the sea while moving a long distance to areas nearby Korea. TCs also tended to occur more often in the positive WNPMI phase. In the difference between the two phases regarding 850 and 500 hPa streamline, anomalous cyclones were reinforced in the tropical and subtropical western North Pacific, while anomalous anticyclones were reinforced in mid-latitude East Asian areas. Due to these two anomalous pressure systems, anomalous southeasterlies developed in areas near Korea, with these anomalous southeasterlies playing the role of anomalous steering flows making the TCs head toward areas near Korea. Also, due to the anomalous cyclones developed in the tropical and subtropical western North Pacific, more TCs could occur in the positive WNPMI phase.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.2
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• pp.207-212
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• 2012

In this work, a 70/140 GHz dual-band push-push voltage controlled oscillator(VCO) has been developed based on a 0.18-${\mu}m$ SiGe BiCMOS technology. The lower band and the upper band oscillation frequency varied from 67.9 GHz to 76.9 GHz and from 134.3 GHz to 154.5 GHz, respectively, with tuning voltage swept from 0.2 to 2 V. The calibrated maximum output power for each band was -0.55 dBm and -15.45 dBm. The VCO draws DC current of 18 mA from 4 V supply.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.1
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• pp.1-7
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• 2014

A stretchable polymeric membrane shaped diffuser was used to homogenize the coherent laser beam. The developed RGB module was used to focus and defocus test by beam combiners. Average oscillation frequency was set at 180Hz~300Hz and it resulted in the best homogenization effect in visual range. The blue laser module turned out to be the worst case for the transmission and primary reason is believed to be the short length of irradiated laser beam. The developed system removed the speckling and the brightness was decreased by 10 ~ 20% for the RGB laser. Overall the brightness was decreased by 13% and homogenity with respect to the temporal axis was improved from 30fs to 110fs.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.11
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• pp.9-14
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• 2007

In this article, the organic integrated circuits such as inverter, ring oscillator, NAND and NOR gates, and rectifier have been fabricated on PEN substrate by using pentacene TFTs, The OTFTs used bottom contact structure and produced the average mobility of 0.26 $cm^2/V.sec$ and on/off current ratio of $10^5$. All circuits successfully worked as the simulation results. Especially, the rectifier was able to operate up to 1 MHz input AC signals, and ring oscillator exhibited oscillation frequency of 1MHz at 40 V. Based on the results of organic integrated circuits we could confirm the possibility of the low cost RFID tags and flexible display with OTFTs.

• Journal of The Korean Astronomical Society
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• v.36 no.spc1
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• pp.75-81
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• 2003

Changes in the earth's climate depend on changes in the net sunlight reaching us. The net depends on the sun's output and earth's reflectance, or albedo. Here we develop the limits on the changes in the sun's output in historical times based on the physics of the origin of solar cycle changes. Many have suggested that the sun's output could have been $0.5\%$ less during the Maunder minimum, whereas the variation over the solar cycle is only about $0.1\%$. The frequencies of solar oscillations (f- and p-modes) evolve through the solar cycle, and provide the most exact measure of the cycle-dependent changes in the sun. But precisely what are they probing? The changes in the sun's output, structure and oscillation frequencies are driven by some combination of changes in the magnetic field, thermal structure and velocity field. It has been unclear what is the precise combination of the three. One way or another, this thorny issue rests on an understanding of the response of the solar structure to increased magnetic field, but this is complicated. Thus, we do not understand the origin of the sun's irradiance increase with increasing magnetic activity. Until recently, it seemed that an unphysically large magnetic field change was required to account for the frequency evolution during the cycle. However, the problem seems to have been solved (Dziembowski, Goode & Schou 2001) using f-mode data on size variations of the sun. From this and the work of Dziembowski & Goode (2003), we suggest that in historical times the sun couldn't be much dimmer than it is at activity minimum.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.12
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• pp.691-698
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• 2014

An L-band single side band(SSB) mixer with CMOS switches and a C-band quadrature voltage-controlled oscillator(QVCO) have been developed using the TowerJazz 0.18-um RFCMOS process. The SSB mixer exhibits a conversion gain of 6.6 ~ 7.5 dB with a 70-dBc image rejection ratio and 65-dBc port isolation. The oscillation frequency range of the QVCO is 6.2 ~ 6.7 GHz with an output power of 4~6 dBm. For measurement, 1.8 V supply voltage is used while drawing 36 mA for the mixer and 23 mA for the QVCO.

• Atmosphere
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• v.20 no.4
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• pp.451-466
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• 2010

This edition has continued since 2006 tropical cyclone season our effort to provide standard tropical cyclone summaries by the western North Pacific basin and detailed reviews of operationally or meteorologically significant tropical cyclones to document significant challenges and shortfalls in the tropical cyclone warning system to serve as a focal point for research and development efforts. The tropical cyclone season of 2009 in the western North Pacific basin is summarized and the main characteristics of general atmospheric circulation are described. Also, the official track and intensity forecasts of these cyclones are verified. The total number is less than 59-year (1951~2009) average frequency of 26.4. The 2009 western North Pacific season was an inactive one, in which 22 tropical storms generated. Of these, 13 TCs reached typhoon (TY) intensity, while the rest 9 TCs only reached severe tropical storm (STS) and tropical storm (TS) intensity - three STS and six TS storms. On average of 22 TCs in 2009, the Korea Meteorological Administration official track forecast error for 48 hours was 219 km. There was a big challenge for individual cyclones such as 0902 CHAN-HOM, 0909 ETAU, and 0920 LUPIT resulting in significant forecast error, with both intricate tracks and irregular moving speed. There was no tropical cyclone causing significant direct impact to the country. The tropical cyclone season in 2009 began in May with the formation of KUJIRA (0901). In September and October, ten TSs formed in the western North Pacific in response to enhanced convective activity. On the other hand, the TC activity was very weak from June to July. It is found that the unusual anti-cyclonic circulation in the lower level and weak convection near the Philippines are dominant during summertime. The convection and atmospheric circulation in the western North Pacific contributed unfavorable condition for TC activity in the 2009 summertime. Year 2009 has continued the below normal condition since mid 1990s which is apparent in the decadal variability in TC activity.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.15-20
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• 2005

Two-dimensional incompressible Navier-Stokes flow solver is developed using SIMPLER method to study the unsteady viscous flow physics over two-dimensional ellipses. Unsteady viscous flows over various thickness-to-chord ratios of 0.6, 0.8, 1.0, and 1.2 elliptic cylinders are simulated at different Reynolds numbers of 200, 400, and 1,000. This study is focused on the understanding the effects of Reynolds number and elliptic cylinder thickness on the drag and lift forces. The present numerical solutions are compared with available experimental and numerical results and show a good agreement. Through this study, it is observed that the Reynolds number and the cylinder thickness affect not only the frequency of the force oscillations but also the mean values and the amplitudes of the total drag and lift forces significantly.