• 대한전자공학회논문지TC
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• 제42권5호
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• pp.55-60
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• 2005

본 논문에서는 cascode 하모닉 발생기를 이용하여 V-band MIMIC (Millimeter-wave Monolithic Integrated Circuit) quadruple subharmonic 믹서를 설계 및 제작하였다. 고변환 이득 특성을 위하여 cascode 하모닉 발생기를 제안하였다. 제안된 cascode 하모닉 발생기는 기존의 multiplier 구조의 비해 평균 2.9 dB 및 최대 4 dB의 높은 4차 하모닉 출력 특성을 나타내었다. 제작된 V-band subharmonic 믹서의 측정결과 14.5 GHz LO 신호를 13 dBm의 크기로 입력하였을 때 3_4 dB의 높은 변환이득 특성을 얻었다. 또한 -53.6 dB의 LO-to-IF, -46.2 dB의 우수한 LO-to-RF 격리 특성을 나타내었다. 제작된 밀리미터파 subharmonic 믹서는 기존에 발표된 밀리미터파 대역의 subharmonic 믹서에 비해 우수한 변환이득 특성을 나타내었다.

• 전력전자학회논문지
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• 제7권3호
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• pp.262-271
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• 2002

견인전동기 구동시스템에 사용되는 PWM 인버터는 전력용량이 크기 때문에 스위칭주파수가 제한되며, 따라서 전자기적 가청소음이 발생한다. 이러한 가청소음을 줄이기 위하여 새로운 MRSF-PWM 방식을 제안한다. 제안한 MRSF-PWM 방식에서는 고조파를 확산시키기 위해 삼각파와 톱니파를 함께 운송파로 사용하며, 출력전압의 선형제어범위를 넓히기 위해 정현파에 3차 고조파를 주입한 파형을 기준파로 사용한다. MRSF-PWM 방식의 타당성을 검증하기 위하여 컴퓨터 시뮬레이션을 수행하였다. 그 결과, MRSF-PWM 방식이 선형성 및 고조파 확산면에서 다른 RPWM 방식보다 우수하며 가청소음 저감면에서 SPWM 방식보다 효과적임을 확인하였다.

• 비파괴검사학회지
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• 제29권4호
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• pp.344-350
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• 2009

본 연구의 목적은 탄성 표면파에서의 비선형 거동의 이론적 배경을 소개하고 실험적으로 검증하는 것으로서, 이론상의 표면파의 비선형 파라미터는 벌크파에서와 같이 전파된 표면파의 2차 고조파 성분과 기본파 성분 크기의 비에 의존한다. 이를 검증하기 위해 접촉식 탐촉자를 이용한 측정 시스템을 구축하였고, 표면파 전파거리와 인가전압 크기를 변화시키며 알루미늄 6061 합금의 비선형 파라미터를 측정하였다. 또한, 비선형 파라미터를 측정함에 있어서 주파수 의존적 감쇠의 영향을 고려하였다. 이러한 과정을 통한 결과는 탄성 표면파의 비선형 파라미터가 인가전압의 크기에 독립적이며, 2차 고조파 성분의 크기는 전파거리에 선형적으로 의존할 것이라는 이론적 예측과 일치한다.

• Journal of Power Electronics
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• 제16권3호
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• pp.1163-1175
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• 2016

In recent years, microgrids have been the focus of considerable attention in distributed energy distribution. Microgrids contain a large number of power electronic devices that can potentially cause negative impedance instability. Harmonic impedance is an important tool to analyze stability and power quality of microgrids. Harmonic impedance can also be used in harmonic source localization. Precise measurement of microgrid impedance and analysis of system stability with impedances are essential to increase stability. In this study, we introduce a new square wave current injection method for impedance measurement and stability analysis. First, three stability criteria based on impedance parameters are presented. Then, we present a new impedance measurement method for microgrids based on square wave current injection. By injecting an unbalanced line-to-line current between two lines of the AC system, the method determines all impedance information in the traditional synchronous reference frame d-q model. Finally, the microgrid impedances of each part and the overall microgrid are calculated to verify the measurement results. In the experiments, a simulation model of a three-phase AC microgrid is developed using PSCAD, and the AC system harmonic impedance measuring device is developed.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2002년도 학술대회 논문집
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• pp.189-192
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• 2002

In this study, The experimental open-tube-type and close-tube-type thermoacoustic refrigerator were constructed. The resonant characteristics of a thermoacoustic refrigerator were investigated. In order to determine the optimum resonant tube length and frequency, We changed the length of resonant tube from 400mm to 850mm and the frequency from 100Hz to 1000Hz. In case of first harmonic, the temperature difference of open-tube-type (1/4 wave) refrigerator was $41^{\circ}C$(resonator length :500mm). The temperature difference of close-tube-type (1/2 wave) refrigerator was $43^{\circ}C$(resonator length :850mm). In this experiments, the experimental 1/2 wave refrigerator is slightly cooler than the experimental l/4 wave refrigerator.

• 한국생산제조학회지
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• 제19권6호
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• pp.790-796
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• 2010

This paper designed the horn of half-wave needed for Ultrasonic meta) welding. The horn has to be designed and manufactured accurately, because measurements such as the shape, length, mass and etc. have effects on the resonant frequency and the vibration mode. Designed horn of half-wave has the feature of 40,000Hz of nature frequency, and maximizes vibration range in the Tip by resonance in the frequency of ultrasonic wave machine. In this study, we calculated and analyzed the natural frequency to find the optimal design of the horn that amplified the amplitude about double by the modal analysis and harmonic analysis using ANSYS. And we did FFT analysis of the manufactured horn.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.43.1-43.1
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• 2009

Electromagnetic radiation at the plasma frequency and its second harmonic, the so-called plasma emission, is fundamental process responsible for solar type II and III radio bursts. There have also been occasional observations of higher-harmonic plasma emissions in the solar-terrestrial environment. We will present that the simulation effort on characterizing the electron beam-generated plasma emission process at POSTECH. We have developed fully electromagnetic particle-in-cell (PIC) simulation code with three dimensions. We simulated harmonic plasma emission with various beam condition. Qualitative comparison with the traditional plasma frequency and second harmonic radiation theory is in good agreement. Higher harmonic emissions agree with the theory of coalescence of Langmuir and harmonic EM wave.

• 한국환경과학회지
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• 제23권4호
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• pp.661-672
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• 2014

Due to tidal force, it is very difficult to estimate the hydraulic parameters of high permeable aquifer near coastal area in Jeju Island. Therefore, to eliminate the impact of tidal force from groundwater level and estimate the hydraulic properties, tidal response technique has been mainly studied. In this study we have extracted 38 tidal constituents from groundwater level and harmonic constants including frequency, amplitude, and phase of each constituent using T_TIDE subroutine which is used to estimate oceanic tidal constituents, and then we have estimated hydraulic diffusivity associated with amplitude attenuation factor(that is the ratio of groundwater level amplitude to sea level amplitude for each tidal constituent) and phase lag(that is phase difference between groundwater level and sea level for each constituent). Also using harmonic constants for each constituent, we made the sinusoidal wave and then we constructed the synthesized wave which linearly combined sinusoidal wave. Finally, we could get residuals(net groundwater level) which was excluded most of tidal influences by eliminating synthesized wave from raw groundwater level. As a result of comparing statistics for synthesized level and net groundwater level, we found that the statistics for net groundwater level was more insignificant than those of synthesized wave. Moreover, in case of coastal aquifer which the impact of tidal force is even more than those of other environmental factors such as rainfall and groundwater yield, it is possible to predict groundwater level using synthesized wave and regression analysis of residuals.

• 조명전기설비학회논문지
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• 제27권1호
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• pp.99-108
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• 2013

The high-voltage pulse generator is consist of transformers of fundamental wave and harmonic waves, and shunt capacitances. The pulse has the fundamental wave and the harmonic waves that have been increased as a series circuit by the transformers to make high voltage pulse. This paper shows that pulse generator circuit is analyzed using Miller's theorem and network theory(ABCD Matrix) and simulated in frequency and time domain using Matlab program. The output voltage of pulse were obtained to 2.5kHz, 1.8kV. Output pulse voltage increases as $L_m$ increases in low voltage circuit. In high voltage circuit, outer capacitors are related to frequency band pass characteristics.

• 조명전기설비학회논문지
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• 제26권12호
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• pp.80-86
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• 2012

The high-voltage pulse generator is consist of transformers of fundamental wave and harmonic waves, and shunt capacitances. The pulse has the fundamental wave and the harmonic waves that have been increased as a series circuit by the transformers to make high voltage pulse. This paper shows the high-voltage pulse generator simulation using a circuit program with experiment data. In the equivalent circuit, magnetized inductances and loss resistances which affect output voltage, have been obtained. The output capacitor circuits have characteristics of band pass. The output voltages of the pulse width 50% and 25%(PWM) were obtained. The output of the high-voltage pulse generator is 2.5kHz, 1.8kV.