• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1120-1122
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• 1995

This paper presents a 2-stage, simple, power-efficient 3V CMOS operational amplifier and its equation based design optimization. Because of its simple structure, it is very suitable as a VLSI library cell in analog/digital mixed-mode systems. The op-amp, which contains a constant-$g_m$ rail-to-rail input stage and a simple feedforward class-AB rail-to-rail output stage, is analyzed and the results are presented in the form of design equations and procedures, which provide an insight into the trade-offs among performance requirements. The results of SPICE simulations are shown to agree very welt with the use of design equations.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.8
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• pp.65-71
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• 2008

This paper presents a transient heat transfer analysis of a drum brake shape. The transient heat transfer analysis of automotive drum brakes with frictional contact is performed by using the finite element method. The drum brake type studied in the page is the internally expanding one in which two shoes fitted externally with frictional material are forced outward against surface a rotating drum on the wheel unit. In this case, the braking power is produced by the friction force between a drum and a lining, and is converted into heat. The brake drum has constant material properties. The air inside the drum has temperature-dependent thermal conductivity and enthalpy. Radiation effects are ignored. The result explains the reason why hair crack and cause of drum failure occur. The temperature of drum is in proportion to the drum thickness and nonlinear changes at every points of drum. It's necessary for the decrease of the drum temperature to make the air inside drum flow.

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.385-396
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• 2012

Thermal shock test methods and thermal shock parameters for ceramics were reviewed from the following viewpoints: (1) The test methods should be based on the precise estimation of both temperature and thermal stress distributions in a specimen taking into account the temperature-dependent thermo-mechanical properties; (2) The thermal shock parameters must be defined as a physical property of the materials and described as a function of temperature at the fracture point of the specimen; (3) The relation between the strength and fracture toughness of brittle ceramics under a thermal shock load must be the same as the relation under a mechanical load. In addition, appropriate thermal shock parameters should be defined by the thermal shock strength and thermal shock fracture toughness based on stress and energy criteria, respectively. A constant heat flux method is introduced as a testing technique suitable for estimating these thermal shock parameters directly from the electric power charged.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.248-248
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• 2012

Synthesis graphene on Cu substrate by plasma-enhanced chemical vapor deposition (PE-CVD) is investigated and its quality's affection factors are discussed in this work. Compared with the graphene synthesized at high temperature in chemical vapor deposition (CVD), the low-temperature graphene film by PE-CVD has relatively low quality with many defects. However, the advantage of low-temperature is also obvious that low melting point materials will be available to synthesize graphene as substrate. In this study, the temperature will be kept constant in $400^{\circ}C$ and the graphene was grown in plasma environment with changing the plasma power, the flow rate of precursors, and the distance between plasma generator coil and substrates. Then, we investigate the effect of temperature and the influence of process variables to graphene film's quality and characterize the film properties with Raman spectroscopy and sheet resistance and optical emission spectroscopy.

• Journal of Korea Multimedia Society
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• v.18 no.4
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• pp.452-459
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• 2015

Three synchronization issues, i.e., phase, frequency, and symbol time, have to be properly controlled to achieve distributed beamforming gain. In this paper, the impacts of synchronization errors in distributed beamforming are analyzed for both single-carrier and OFDM systems. When the channel is constant over a symbol duration, the performance degradation due to phase offset is the same for both single-carrier and OFDM systems. For symbol timing offset in OFDM systems, high frequency subcarriers are more susceptible as compared to low frequency ones. Frequency offset is critical in OFDM systems since it leads to interference from the other subcarriers as well as power loss in the desired signal.

• Journal of Information Technology Services
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• v.13 no.1
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• pp.135-146
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• 2014

In this paper, an antenna has been proposed for the operation of mobile devices such as Zigbee. The presented rectenna operates at ISM (Industrial Scientific Medical) band of 2.45 GHz and consists of $2{\times}2$ array patch antenna and Villard voltage double rectifier circuit for high conversion efficiency. $2{\times}2$ array patch antenna is fabricated in FR4 substrate having thickness of 1.6mm and dielectric constant of 4.7. The proposed $2{\times}2$ array patch antenna resonates at 2.56GHz with return loss of 38.36dB, VSWR of 1.0244, and its impedance is matched to $50{\Omega}$. The fabricated rectenna has maximum conversion efficiency of 59.8% at an input power lever of 15dBm and load resistance of $500{\Omega}$.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.1
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• pp.1211-1217
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• 2001

This paper presnts a controller for the heat capacity of thermal storage systems using off-peak electricity which is composed of an identifier using neural networks and a storage time adjuster in order to store exactly the required thermal energy without loss. Since thermal storage systems have nonlinear characteristics and large time constant, even if we predict the heating load accurately, it is very difficult to store exactly the required thermal energy. Thus, in the neural network for the identifier, the adaptive learning rate for high learning speed and bit inputs based on state changes of thermal storage power source are used. Also a hardware for the controller using a microprocessor is developed. The performance of the proposed controller is shown by experiment.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.10
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• pp.806-811
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• 2001

The analysis and control algorithm of a new type unsymmetrical self-bearing step motor is presented. The motor actuator is used for both motor and bearing functionality without any redundant coil windings or redudant electromagnets for bearing functionality. Self bearing step motor layout and control current generation method for unsymmetrical position of electromagnets are described. This new current generation method without additional current for bearing functionality leads to minimize the power loss. As the result of the unbalance response approach, the constant torque is possible, even though the bearing functionality is added or not.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.509-514
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• 2004

This paper introduces the modified slip energy recovery system in order to improve its power factor and to reduce harmonics of line current waveforms. Twelve pulse line commutated converter with the chopper type IGBT is applied where the chopper is applied across the DC terminal and the chopped DC is fed to the converter operating as an inverter and then passed through the wye-wye and delta-wye transformer circuit. This scheme leads to be able to adjust the speed of the motor by the duty cycle of the chopper operating in PWM mode. The fuzzy logic controller is also introduced to the modified slip energy recovery system for keeping the motor speed to be constant when the load varies. The experimental results in testing the 0.22 kW wound rotor induction motor from no-load condition to rated condition show the effectiveness of the proposed control scheme.

• International Commerce and Information Review
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• v.11 no.3
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• pp.125-144
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• 2009

The purpose of this study is to research the investment environment of Vietnam and analyze the actual investment state of Korean enterprises in Vietnam and seek for the points at issue. In general, the investment environment in Vietnam shows both a positive side and negative side. However Vietnamese market is a attractive one as ever for direct investment of Korean enterprises considering their constant economy growth, investment increase of foreign company for Vietnam, China risk. And the point at issue in investment of Korean Enterprises is as follows. That is, inclining to manufacturing, preference of independence investment, small-sized investment by small and medium enterprises, preference of greenfield investment, restricted purpose of investment, insufficiency of infrastructure for logistics, electric power, legal system. The results of the study indicate mainly that the investment of Korean enterprise into Vietnam needs a switchover of the third service trade-tertiary industry, collaboration with Vietnamese enterprise through joint venture investment, a large-scale investment for Vietnam domestic market and neighboring countries' market, practical use of M&A with existing Vietnamese enterprise and diverse purpose for investment.