• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.24-29
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• 2002

In any rapid prototyping process, the layer by layer building process introduces an area error between the staircase and the surface line specified by the computer-aided design model. This affects the dimensional accuracy as well as the surface finish for different part build orientations. This paper describes a methodology for computing the area error for any orientation of the part built by the fused deposition modelling system. This technique can be applied to determine the best build orientation of the part, based on the minimum area error. This technique is verified by comparing the results with the experimental measurements of the area error of the parts built at different orientations.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.4
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• pp.7-15
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• 1989

A technique is suggested which enables the large signal current and voltage waveforms to be determined for a GaAs Schottky-Barrier diode mixer by extracting the algorithm for the nonlinear circuit analysis from the Gauss-Jacobi relaxation and the application of the Harmonic Balance Technique. Both the nonlinear and linear steps of the analysis are included. This analysis permitts accurate determination of the conversion loss for microwave mixer and the computer simulation provides an method applicable to MMIC design. The validity of the nonlinear and linear analysis is confirmed by comparing the simulation results with experimental data of the conversion loss.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.34C no.12
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• pp.20-27
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• 1997

In this paper, a multiplying digital-to-analog converter (MDAC) circuit for low-power high-resolution CMOS algorithmic A/D converters (ADC's) is proposed. The proposed MDAC is designed to operte properly at a supply at a supply voltge between 3 V and 5 V and employs an analog0domain power reduction technique based on a bias switching circuit so that the total power consumption can be optimized. As metal-to-metal capacitors are implemented as frequency compensation capacitors, opamps' performance can be varied by imperfect process control. The MDAC minimizes the effects by the circuit performance variations with on-chip tuning circuits. The proposed low-power MDAC is implementd as a sub-block of a 10-bit 200kHz algorithmic ADC using a 0.6 um single-poly double-metal n-well CMOS technology. With the power-reduction technique enabled, the power consumption of the experimental ADC is reduced from 11mW to 7mW at a 3.3V supply voltage and the power reduction ratio of 36% is achieved.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.861-870
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• 1999

An experimental study was carried out to investigate the effects of using various shapes of turbulence promoter on the heat-transfer enhancement of 2-D and 3-D arrays of rectangular modules in a rectangular channel for design of noiseless and low-powered cooling fan in the electronic systems. Measurements of heat/mass transfer coefficients were made using a naphthalene sublimation technique, and the friction factors were measured for Reynolds numbers in the range$3.3{\time}10^3$~$1.6{\time}10^4$. Flow visualization was peformed by oil-film method. It was found that heat transfer and pressure drop increased remarkably due to the existence of the promoter. The results of the performance evaluation based on equal pumping power were showed that substantial heat-transfer enhancement was obtained at low Reynolds number range by use of a turbulence promoter.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.673-676
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• 2001

In this paper, the improved zero-voltage transition(ZVT) PWM boost converter using an inductor feedback technique is proposed. The improved circuit uses a low-voltage zener diode to reduce the turn-off witching loss of the auxiliary witch and EMI noise. Using this technique, soft-witching for the auxiliary switch is guaranted at wide line and load ranges and some of the energy circulating in the auxiliary circuit is fed to the load Since the active switches are turned on and off softly, the witching losses and EMI noise are reduced significantly and the higher efficiency of the system is achieved. In this paper, the modes of converter operation are explained and analyzed, design guidelines are given, and experimental results of 1kW, 100kHz prototype system are presented.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.694-697
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• 2001

A optimal soft switching technique for A/DC full bridge converter is proposed. variable soft switching single stage AC/DC full bridge converter with unit power factor are presented in this paper. Using soft switching, we can reduce a switching losses. As a result, achieving good power factor and achieving a good efficiency. We search a optimal soft switching technique in this paper and to verify the theoretical analysis of the presented AC/DC full bridge converter, a design example is given with its Pspice and Psim simulation and experimental results.

• Nuclear Engineering and Technology
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• v.45 no.3
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• pp.361-366
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• 2013

An imaging technique to visualize the internal defects in a plate-type nuclear fuel specimen was developed by using an active optical interferometer for a nondestructive quality inspection. A periodic thermal wave having a sinusoidal intensity pattern induced a periodical strain variation for the specimen. The varying strain image was acquired using an optical laser interferometer. The strain distribution over the internal defects will be distorted in an acquired strain image because a part of the thermal wave will be reflected from these defects during propagation. In this paper, internal defects were efficiently visualized by sequentially accumulating the extracted defect components. The experimental results confirmed that the developed visualization system can be a valuable tool to detect the internal defects in plate-type nuclear fuel.

• ETRI Journal
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• v.43 no.2
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• pp.197-208
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• 2021

Single-carrier frequency division multiple access (SC-FDMA) is currently being used in long-term evolution uplink communications owing to its low peak-to-average power ratio (PAPR). This study proposes a new transceiver design for an SC-FDMA system based on Walsh-Hadamard transform (WHT). The proposed WHT-based SC-FDMA system has low-PAPR and better bit-error rate (BER) performance compared with the conventional SC-FDMA system. The WHT-based SC-FDMA transmitter has the same complexity as that of discrete Fourier transform (DFT)-based transmitter, while the receiver's complexity is higher than that of the DFT-based receiver. The exponential companding technique is used to reduce its PAPR without degrading its BER. Moreover, the performances of different ordered WHT systems have been studied in additive white Gaussian noise and multipath fading environments. The proposed system has been verified experimentally by considering a real-time channel with the help of wireless open-access research platform hardware. The supremacy of the proposed transceiver is demonstrated based on simulated and experimental results.

• 제어로봇시스템학회:학술대회논문집
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• 1987.10b
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• pp.631-636
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• 1987

The design of ultrasonic transducer energy processing systems requires highly reliable command featuring mechanical frequency tracking and constant velocity control of the ultrasonic transducer with an acoustic load. This paper presents a new conceptional instantaneous current resultant control base high-frequency inverter using self turn-off devices driving an electrostrictive ultrasonic transducer system and its optimum control technique, which is implemented by feed-back of the ultrasonic transducer applied voltage and instantaneous velocity of the transducer vibrating system through a Phase-Locked-Loop control scheme. The feedback voltage corresponding to instantaneous velocity is averaged over a half-period with respect to constant amplitude/constant velocity control strategy. Described are the theory of this signal detection technique and the experimental set-up.

• The Journal of the Acoustical Society of Korea
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• v.18 no.1
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• pp.16-24
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• 1999

Design of SAW ladder filters has been performed by a rather trial and error method, that is, by modifying the design variables step by step until designed performance of the filter satisfies given specifications. In this work, optimal design method has been developed that automatically determines the detailed pattern of the SAW ladder filter to meet the specification once desired performance is given. As a first step for the development, the analysis tool for the SAW ladder filter has been produced by means of the Smith equivalent circuit analysis technique, and its validity has been verified through comparison of its calculation result with experimental data. With the analysis tool, we have investigated the performance variation of the filter with the change of its design factors, and the result has led to the optimal design algorithm. Validity and efficiency of the algorithm has been checked through test design of several SAW ladder filter samples on the market.