• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.2 s.93
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• pp.189-193
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• 2005

In this paper, we propose a direct conversion double-balanced down-converter fer MB-OFDM W system, which is implemented using $0.18\;{\mu}m$ CMOS technology and its measurement results are shown. The proposed down-converter adopts a resistive current-source instead of general transconductance stage using MOS transistor to achieve wideband characteristics over RF input frequency band $3\~5\;GHz$ with good gain flatness. The measured conversion gain is more than +3 dB, and gain flatness is less than 3 dB for three UWB channels. The dc consumption of this work is only 0.89 mA from 1.8 V power supply, leading to the low-power W application.

• Tribology and Lubricants
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• v.35 no.3
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• pp.190-198
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• 2019

Gas foil bearings (GFBs) enable small- to medium-sized turbomachinery to operate at ultra-high speeds in a compact design by using ambient air or process gas as a lubricant. When using air or process gas, which have lower viscosity than lubricant oil, the turbomachinery has the advantage of reduced power loss from bearing friction drag. However, GFBs may have high Reynolds number, which causes turbulent flows due to process gas with low viscosity and high density. This paper analyzes gas foil journal bearings (GFJBs) with high Reynolds numbers and studies the effects of turbulent flows on the static and dynamic performance of bearings. For comparison purposes, air and R-134a gas lubricants are applied to the GFJBs. For the air lubricant, turbulence is dominant only at rotor speeds higher than 200 krpm. At those speeds, the journal eccentricity decreases, but the film thickness, power loss, and direct stiffness and damping coefficients increase. On the other hand, the R-134a gas lubricant, which that has much higher density than air, causes dominant turbulence at rotor speeds greater than 10 krpm. The turbulent flow model predicts decreased journal eccentricity but increased film thickness and power loss when compared with the lamina flow model predictions. The vertical direct stiffness and damping coefficients are lower at speeds below 100 krpm, but higher beyond that speeds for the turbulent model. The present results indicate that turbulent flow effects should be considered for accurate performance predictions of GFJBs with high Reynolds number.

• 연구논문집
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• s.27
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• pp.87-99
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• 1997

Present paper describes on/off design performance of a 50KW turbogenerator gas turbine engine for hybrid vehicle application. For optimum design point selection, relevant parameter study is carried out. The turbogenerator gas turbine engine for a hybrid vehicle is expected to be designed for maximum fuel economy, ultra low emissions, and very low cost. Compressor, combustor, turbine, and permanent-magnet generator will be mounted on a single high speed (82,000 rpm) shaft that will be supported on air bearings. As the generator is built into the shaft, gearbox and other moving parts become unnecessary and thus will increase the system's reliability and reduce the manufacturing cost. The engine has a radial compressor and turbine with design point pressure ratio of 4.0. This pressure ratio was set based on calculation of specific fuel consumption and specific power variation with pressure ratio. For the given turbine inlet temperature, a rather conservative value of $1100^\circK$ was selected. Designed mass flow rate was 0.5 kg/sec. Parametric study of the cycle indicates that specific work and efficiency increase at a given pressure ratio and turbine inlet temperature. Off design analysis shows that the gas turbine system reaches self operating condition at N/$N_{DP}$ = 0.53. Bleeding air for turbine stator cooling is omitted considering low TIT and for a simple geometric structure. Various engine performance simulations including, ambient temperature influence, surging at part load condition. Transient analysis were performed to secure the optimum engine operating characteristics. Surge margin throughout the performance analysis were maintained to be over 80% approximately. Validation of present results are yet to be seen as the performance tests are scheduled by the end of 1998 for comparison.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.6
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• pp.1150-1158
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• 2010

In this paper, a new reliable portable activity monitoring device implemented with the buddhist-style bowing activity and walking step detection algorithm, is presented. In order to monitor the bowing and walking activities, miniaturized 3-axis accelerometer sensor with the sensitivity of 800 mV/g was used. After initial signal conditioning, vector magnitude of accelerometer signals was calculated. Syntactic peak detection method was used in order to feature points. All signal processing algorithms were implemented in ultra-low power microcontroller MSP430 with double precision floating point arithmetic. For evaluation, 19 young man($24.22\pm5.22$ yrs) and woman($22.28\pm2.72$ yrs) were involved. The accuracy of the proposed algorithms were 98.91 %($\pm0.011$) for walking step detection and 98.25 %($\pm0.023$) for buddhist-style bowing activity. Comparing to the commercialized pedometer accuracy, 87.1 %($\pm0.058$), the proposed walking step detection algorithms show more reliable accuracy.

• Journal of Astronomy and Space Sciences
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• v.34 no.2
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• pp.111-118
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• 2017

A ultra low frequency (ULF) wave, Pi2, has been reported to occur during periods of extremely quiet magnetospheric and solar wind conditions. And no statistical study on the Pi2 has been performed during extremely quiet conditions, using satellite observations to the author's knowledge. Also Pi2 pulsations in the space fluxgate magnetometers near perigee failed to attract scientist's attention previously. In this paper, Pi2 pulsations detected by the Van Allen probe satellites (VAP-A & VAP-B) were investigated statistically. During the period from October 2012 to December 2014, ninety six Pi2 events were identified using VAP when Kp = 0 while using Kakioka (KAK, L = 1.23) as a reference ground station. Seventy five events had high coherence between VAP-Bz and H components at KAK station. As a result, it was found that 77 % of the events had power spectra between 5 and 12 mHz, which differs from the regular Pi2 band range of from 6.7 to 25 mHz. In addition, it was shown that it is possible to observe Pi2 pulsations from space fluxgate magnetometers near perigee. Twenty two clean Pi2 pulsations were found where L < 4 and four examples of Pi2 oscillations at different L shells are presented in this paper.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.266-267
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• 2006

A coupling capacitor voltage transformer (CCVT) is used in extra high voltage and ultra high voltage transmission systems to obtain the standard low voltage signal for protection and measurement. To obtain the high accuracy at the power system frequency, a tuning reactor is connected between a capacitor and a voltage transformer (VT). Thus, no distortion of the secondary voltage is generated when no fault occurs. However, when a fault occurs, the secondary voltage of the CCVT has some errors due to the transient components resulting from the fault. This paper proposes an algorithm for compensating the secondary voltage of the CCVT in the time domain. With the values of the secondary voltage of the CCVT, the secondary and the primary currents are obtained; then the voltage across the capacitor and the tuning reactoris calculated and then added to the measured secondary voltage. The proposed algorithm includes the effect of the non-linear characteristic of the VT and the influence of the ferro-resonance suppression circuit. Test results indicate that the algorithm can successfully compensate the distorted secondary voltage of the CCVT irrespective of the fault distance, the fault inception angle and the fault impedance.

• Proceedings of the KIEE Conference
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• 2006.10c
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• pp.139-141
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• 2006

Quantum-dot Cellular Automata (QCA) is one of the most promising next generation nano-electronic devices which will inherit the throne of CMOS which is the domineering implementation technology of large scale low power digital systems. In late 1990s, the basic operations of the QCA cell were already demonstrated on a hardware implementation. Also, design tools and simulators were developed. Nevertheless, its design technology is not quite ready for ultra large scale designs. This paper proposes a new approach which enables the QCA designs to inherit the verification methodologies and tools of CMOS designs, as well. First, a set of disciplinary rules strictly restrict the cell arrangement not to deviate from the predefined structures but to guarantee the deterministic digital behaviors. After the gate and interconnect structures of the QCA design are identified, the signal integrity requirements including the input path balancing of majority gates, and the prevention of the noise amplification are checked. And then the digital logic is extracted and stored in the OpenAccess common engineering database which provides a connection to a large pool of CMOS design verification tools. Towards validating the proposed approach, we designed a 2-bit QCA adder. The digital logic is extracted, translated into the Verilog net list, and then simulated using a commercial software.

• Convergence Security Journal
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• v.15 no.2
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• pp.81-89
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• 2015

HIGHT is an 64-bit block cipher, which is suitable for low power and ultra-light implementation that are used in the network that needs the consideration of security aspects. This paper presents a key scheduler that employs the presented LFSR and reverse LFSR that can generate four outputs simultaneously. In addition, we construct new key scheduler that generates 4 subkey bytes at a clock since each round block requires 4 subkey bytes at a time. Thus, the entire HIGHT processor can be controlled by single system clock with regular control mechanism. We synthesize the HIGHT processor using the VHDL. From the synthesis results, the logic size of the presented key scheduler can be reduced as 9% compared to the counterpart that is employed in the conventional HIGHT processor.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.5
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• pp.504-510
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• 2015

This paper presents a power and area efficient SAR ADC for multi-channel near threshold-voltage (NTV) applications such as neural recording systems. This work proposes a split dual-capacitive-array (S-DCA) structure with shifted input range for ultra low-switching energy and architecture of multi-channel single-ended SAR ADC which employs only one comparator. In addition, the proposed ADC has the same amount of equivalent capacitance at two comparator inputs, which minimizes the kickback noise. Compared with conventional SAR ADC, this work reduces the total capacitance and switching energy by 84.8% and 91.3%, respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.947-952
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• 1997

The magnetic polishing is the useful method to finish using magnetic power of a magnet. The time hasn't been that long since the magnetic polishing method was introduced to korea as one of precision polishing techniques. However, the reasons for not being spreaded widely are the magnetic polishing method don't have mediocrity for machine, the efficiency of magnet-abrasive is confined as a bad polishing, and there are not many researchers in this field. The mechanism of this R&D is dealing with the dynamic state of magnet-abrasive. This paper deals with mediocritizing magnetic polishing device into regular lathe and this experiment was conducted in order to get a best surface roughness with low cost. Beside the subsidiary experiment was performed using the mixed magnet-abrasive with general alumina, barium. This paper introduced the main reason for difficulty using this method in industrial field. It needs more continues research on it. This paper contains the result of experiment to acquire the best surface roughness, not using the high-cost polishing material in processing. The average diameters of magnet-abrasive are the particles of 150 $\mu\textrm{m}$, 250 $\mu\textrm{m}$.