• 전자공학회논문지A
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• 제31A권9호
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• pp.104-113
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• 1994

We have fabricated n-p-n HBTs using 3-inchAlgaAs/GaAs hetero structure epi-wafers grown by MBE. DC and AC characteristics of HBT devices were measured and analyzed. For HBT epi-structure, Al composition of emitter was graded in the region between emitter cap and emitter. And base layer was designed with concentration of 1${\times}10^{19}/cm^{3}$ and thickness of 50nm, and Be was used as the p-type dopant. Principal processes for device fabrication consist of photolithography using i-line stepper, wet mesa etching, and lift-off of each ohmic metal. The PECVD SiN film was used as the inslator for the metal interconnection. HBT device with emitter size of 3${\times}10{\mu}m^{2}$ resulted in cut-off frequency of 35GHz, maximum oscillation frequency of 21GHz, and current gain of 60. The distribution of the ideality factor of collector and base current was very uniform, and the average values of off-set voltage and current was very uniform, and the average values of off-set voltage and current gain were 0.32V and 32 within a 3-inch wafer.

• 한국산업융합학회 논문집
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• 제24권4_1호
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• pp.377-385
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• 2021

High voltage direct current(HVDC) systems has been an alternative method of a power transmission to replace high voltage alternate current(HVAC), which is a traditional AC transmission method. Due to technical limitations, Line commutate converter HVDC(LCC-HVDC) was mainly used. However, result from many structural problems of LCC-HVDC, the voltage source converter HVDC(VSC-HVDC) are studied and applied recently. In this paper, after analyzing the reactive power and output voltage ripple, which are the main problems of LCC-HVDC, the characteristics of each HVDC are summarized. Based on this result, a new LCC-HVDC structure is proposed by combining LCC-HVDC with the MMC structure, which is a representative VSC-HVDC topology. The proposed structure generates lower reactive power than the conventional method, and greatly reduces the 12th harmonic, a major component of output voltage ripple. In addition, it can be easily applied to the already installed LCC-HVDC. When the proposed method is applied, the control of the reactive power compensator becomes unnecessary, and there is an advantage that the cut-off frequency of the output DC filter can be designed smaller. The validity of the proposed LCC-HVDC is verified through simulation and experiments.

• 한국통신학회논문지
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• 제25권5B호
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• pp.985-991
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• 2000

본 논문에서는 인덕터의 면적을 극소화시키고 인덕턴스와 Q값을 극대화시키기 위한 최적구조의 2GHz 자성박막 인덕터를 설계하고 제작하였다. Eddy-current 표피효과를 위해서 Co90Fe10와 SiO2의 multilayer를 사용하고, multilayer를 적용한 새로운 lumped 소자모델을 고려하여 최적설계를 수행하였다. 2GHz에서 동작하는 새로운 자성박막 인덕터는 photo-lithography와 lift-off기술을 이용하여 Si 기판위에 제작되었다. 50개 이상의 동일한 인덕터들의 주파수 특성은 RF Impedance Analyzer로, 자기공진주파수는 Vector Network 분석기(HP8510)로 측정되었다. 개발된 인덕터들은 1.8~2.3GHz 범위의 자기공진주파수, 47~68nH 범위의 L값, 그리고 1GHz이상의 주파수에서 70~80정도의 Q값을 가지므로 L과 Q가 극대화된 아주 우수한 최적구조의 소형(면적=30.8$\times$30.8mil2) 박막인덕터가 성공적으로 제작되었다.

• 한국자기학회지
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• 제11권6호
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• pp.239-244
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• 2001

최근 연구가 활발히 진행되고 있는 RF 대역에서 사용가능한 인덕터를 제조하여 특성을 평가하였다. 인덕턴스와 Q값을 높이기 위하여 5000 두께의 F $e_{78.81}$T $a_{8.47}$ $N_{12.71}$ 연자성박막을 삽입하였으며, 자성박막의 FMR 공진주파수를 인위적으로 확장시키기 위하여 pattern을 형성시켜 shape anisotropy를 증가시켰다. 또한 코일부분은 lift-off process를 이용하여 제조하였다. 제조된 인덕터의 디자인은 4턴의 rectangular spiral형태였으며, 측정된 특성은 Ti/Ag air-core의 경우 5 GHz까가지 공진이 없었으며 2GHz에서 Q값이 9, 인덕턴스 8.4nH였다. 자성박막을 이용한 경우 9 nH에 공진주파수는 약 700 MHz부근이었다.다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.21-25
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• 2017

우주 발사체에 사용되는 엄빌리칼 시스템은 지상의 유공압 및 전계장 라인들을 발사체로 연결하여 발사운용 과정에서 발사체 내부로 유공압의 공급 및 발사체와 전기적 연결들을 가능하도록 하다가 발사직전 또는 발사와 동시에 발사체로부터 분리되는 장치이다. 발사운용과정에서는 전기적 및 유공압적으로 확실히 연결되어 기밀 및 체결 성능을 보장하여야 하고 분리시점에는 확실한 분리특성을 보장하여야 한다. 따라서 체결력을 적절하게 선택하여 체결력과 분리성능 두가지를 모두 만족시키도록 하는 것이 엄빌리칼 시스템 설계의 핵심 요소이다. 이와 같은 장치 특성에 따라 엄빌리칼 시스템은 우주발사체 개발 초기부터 현재까지 다양한 형식의 엄빌리칼 장치들이 연구되고 발사체에 적용되어 왔다. 본 논문에서는 현재까지 주로 사용되었던 각 엄빌리칼 시스템들 그 특징과 그 작동개념별로 구분하여 기술하고 향후 한국형 발사체에 적용될 엄빌리칼 시스템의 개요에 대해 소개한다

• 대한기계학회논문집A
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• 제26권8호
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• pp.1599-1607
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• 2002

The purpose of this work is to suggest a new non-contact damage detection method for rotating ferromagnetic shafts. The presence and the location of a damage in rotating shafts are assessed by means of longitudinal elastic waves propagating along the shafts. These waves are measured by non-contact magnetostrictive sensors consisting of a coil and bias magnets. This paper shows the effectiveness of the sensors in the damage detection of rotating shafts. Several issues occurring in the application of the sensors to rotating shafts are carefully investigated.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.365-370
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• 2001

The purpose of this work is to suggest a new non-contact measurement method applicable to the diagnosis of rotating shafts. Longitudinal elastic waves propagating along the shafts are measured by magnetostrictive sensors that make use of the coupling phenomena between strains and magnetic induction in ferromagnetic shafts. These sensors have been successfully applied in pipes and others, but it appears that the present application of them to rotating shafts is made here for the first time. Several isssues appearing in the present application are carefully investigated and several experimental results are presented to address the usefulness of the present method.

• Advances in aircraft and spacecraft science
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• 제5권1호
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• pp.73-105
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• 2018

A particular type of constant speed helical trajectory, with variable ascension rate, is proposed. Such trajectories are candidates of choice as motion primitives in automatic airplane trajectory planning; they can also be used by airplanes taking off or landing in limited space. The equations of motion for airplanes flying on such trajectories are exactly solvable. Their solution is presented, together with an analysis of the restrictions imposed on the geometrical parameters of the helical paths by the dynamical abilities of an airplane. The physical quantities taken into account are the airplane load factor, its lift coefficient, and the thrust its engines can produce. Formulas are provided for determining all the parameters of trajectories that would be flyable by a particular airplane, the final altitude reached, and the duration of the trajectory. It is shown how to construct speed interval tables, which would appreciably reduce the calculations to be done on board the airplane. Trajectories are characterized by their angle of inclination, their radius, and the rate of change of their inclination. Sample calculations are shown for the Cessna 182, a Silver Fox like unmanned aerial vehicle, and the F-16 Fighting Falcon.

• Advances in aircraft and spacecraft science
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• 제7권1호
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• pp.53-78
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• 2020

Automatic trajectory planning is an important task that will have to be performed by truly autonomous vehicles. The main method proposed, for unmanned airplanes to do this, consists in concatenating elementary segments of trajectories such as rectilinear, circular and helical segments. It is argued here that because these cannot be expected to all be flyable at a same constant speed, it is necessary to consider segments on which the airplane accelerates or decelerates. In order to preserve the planning advantages that result from having the speed constant, it is proposed to do all speed changes at maximum deceleration or acceleration, so that they are as brief as possible. The constraints on the load factor, the lift and the power required for the motion are derived. The equation of motion for such accelerated motions is solved numerically. New results are obtained concerning the value of the angle and the speed for which the longest distance and the longest duration glides happen, and then for which the steepest, the fastest and the most fuel economical climbs happen. The values obtained differ from those found in most airplane dynamics textbooks. Example of tables are produced that show how general speed changes can be effected efficiently; showing the time required for the changes, the horizontal distance traveled and the amount of fuel required. The results obtained apply to all internal combustion engine-propeller driven airplanes.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 II
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• pp.759-762
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• 2003

The epitaxially grown Mg-doped GaN thin film was prepared by MOCVD (Metal Organic Chemical Vapor Deposition) for a SAW(Surface Acoustic Wave) filter. Mg-doped GaN thin film had enough properties for a SAW filter which include crystallinity and morphology. The surface morphology and crystalline of the Mg-doped GaN thin films were characterized using AFM and an X-ray rocking curve. The SAW filter, which was fabricated by lift-off process and frequency response, was measured by HP 8753C network analyzer. Center frequency was 96.687 MHz and SAW velocity was 5801 m/s when wavelength(λ) was 60${\mu}{\textrm}{m}$. Insertion loss was over -10 dB, Q was factor over 200, and side lobe attenuation was over 22 dB which was suitable for use as a SAW filter. Electro-mechanical coupling coefficient (k$^2$) was calculated from the measured data. k$^2$ was from 1 % to 1.44 %. The fabricated SAW filter using Mg-doped GaN/sapphire structure has good qualities as a filter and will be used as a SAW filter for operating RF frequency.