• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.55-55
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• 2009

Silicon Carbide (SiC) is a material with a wide bandgap (3.26eV), a high critical electric field (~2.3MV/cm), a and a high bulk electron mobility (${\sim}900cm^2/Vs$). These electronic properties allow high breakdown voltage, high frequency, and high temperature operation compared to Silicon devices. Although various SiC DMOSFET structures have been reported so far for optimizing performances. the effect of channel dimension on the switching performance of SiC DMOSFETs has not been extensively examined. In this paper, we report the effect of the interface states ($Q_s$) on the transient characteristics of SiC DMOSFETs. The key design parameters for SiC DMOSFETs have been optimized and a physics-based two-dimensional (2-D) mixed device and circuit simulator by Silvaco Inc. has been used to understand the relationship with the switching characteristics. To investigate transient characteristic of the device, mixed-mode simulation has been performed, where the solution of the basic transport equations for the 2-D device structures is directly embedded into the solution procedure for the circuit equations. The result is a low-loss transient characteristic at low $Q_s$. Based on the simulation results, the DMOSFETs exhibit the turn-on time of 10ns at short channel and 9ns at without the interface charges. By reducing $SiO_2/SiC$ interface charge, power losses and switching time also decreases, primarily due to the lowered channel mobilities. As high density interface states can result in increased carrier trapping, or recombination centers or scattering sites. Therefore, the quality of $SiO_2/SiC$ interfaces is important for both static and transient properties of SiC MOSFET devices.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(2)
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• pp.61-64
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• 2002

We have optimally designed and implemented by a monolithic microwave integrated circuit(MMIC) the low noise amplifier(LNA) of 5.8GHz band composed of receiver front-end(RFE) in a on-board equipment system for dedicated short range communication using a depletion-mode GaAs MESFET. The LNA is provided with two active devices, matching circuits, and two drain bias circuits. Operating at a single supply of 3V and a consumption current of 18㎃, The gain at center frequency 5.8GHz is 13.4dB, Noise figure(NF) is 1.94dB, Input 3rd order intercept point(lIPS) is 3dBm, and Input return loss(5$_{11}$) and Output return loss(S$_{22}$) is -l8dB and -13.3dB, respectively. The circuit size is 1.2$\times$O.7$\textrm{mm}^2$.EX>.>.

• 한국초전도ㆍ저온공학회논문지
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• 제6권4호
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• pp.27-31
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• 2004

This paper describes the development and fabrication of a high temperature superconducting motor which consists of HTS rotor and air-core stator. The machine was designed for the rated power of 100hp at 1800 rpm. The HTS field windings are composed of the double-pancake coils wound with AMSC's SUS-reinforced Bi-2223 tape conductor. These were assembled on the support structure and fixed by a bandage of glass-fiber composite. The cooling system is based on the heat transfer mechanism of the thermosyphon by using GM cryocooler as cooling source. The cold head is in contact with the condenser of a Ne-filled thermosyphon. The rotor assembly was tested independently at the stationary state and combined with stator. Characteristic parameters such as reactances, inductances, and time constants were determined to obtain a consistent overview of the machine operation properties. This motor has met all design parameters by demonstrating HTS field winding, cryogenic refrigeration systems and an air-core armature winding cooled with air. The HTS field winding could be cooled down below 30K. No-load test of open-circuit characteristics(OCC) and short-circuit characteristics(SCC) and load test with resistive load bank were conducted in generator mode. Maximum operating current of field winding at 30K was 120A. From OCC and SCC test results synchronous inductance and synchronous reactance were 2.4mH, 0.49pu, respectively. Efficiency of this HTS machine was 93.3% in full load(100hp) test. This paper will present design, construction, and basic experimental test results of the 100hp HTS machine.

• 한국재료학회지
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• 제32권11호
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• pp.508-514
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• 2022

Piezoelectric composite films which are enabled by inorganic piezoelectric nanomaterials-embedded polymer, have attracted enormous attention as a sustainable power source for low powered electronics, because of their ease of fabrication and flexible nature. However, the absorption of applied stress by the soft polymeric matrices is a major issue that must be solved to expand the fields of piezoelectric composite applications. Herein, a flexible and porous piezoelectric composite (piezoelectric sponge) comprised of BaTiO₃ nanoparticles and polydimethylsiloxane was developed using template method to enhance the energy conversion efficiency by minimizing the stress that vanishes into the polymer matrix. In the porous structure, effective stress transfer can occur between the piezoelectric active materials in compression mode due to direct contact between the ceramic particles embedded in the pore-polymer interface. The piezoelectric sponge with 30 wt% of BaTiO₃ particles generated an open-circuit voltage of ~12 V and a short-circuit current of ~150 nA. A finite element method-based simulation was conducted to theoretically back up that the piezoelectric output performance was effectively improved by introducing the sponge structure. Furthermore, to demonstrate the feasibility of pressure detecting applications using the BaTiO₃ particles-embedded piezoelectric sponge, the composite was arranged in a 3 × 3 array and integrated into a single pressure sensor. The fabricated sensor array successfully detected the shape of the applied pressure. This work can provide a cost-effective, biocompatible, and structural strategy for realizing piezoelectric composite-based energy harvesters and self-powered sensors with improved energy conversion efficiency.

• 한국기계가공학회지
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• 제21권5호
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• pp.9-15
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• 2022

Discarded bio-wastes, such as seeds and rinds, cause environmental problems. Multiple studies have recycled bio-wastes as eco-friendly energy sources to solve these problems. This study uses bio-waste to fabricate a mandarin peel powder based triboelectric nanogenerator (MPP-TENG). The MPP-TENG is based on the contact separation mode. It generates an open-circuit voltage and short-circuit current of 156V and 2µA, respectively. In addition, MPP-TENG shows stable operation over continuous 3000s without any deviation in output. Also, the device exhibits maximum power density of 5.3㎼/cm² when connected to a resistance of 100MΩ. In an energy storage capacity test for 1000s, the MPP-TENG stores an energy of 171.6µJ in a 4.7µF capacitor. The MPP-TENG can power 9 blue LEDs and 54 green lettering LEDs. These results confirm that the MPP-TENG can provide a new avenue for eco-friendly energy harvesting device fabrication.

• Journal of Welding and Joining
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• 제11권3호
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• pp.22-33
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• 1993

Arc sensor is indispensable to arc welding robot systems for compensating the joint misalignment such as mismatch of the workpiece, ill-conditioned positioner and thermal deformation during welding. Furthermore, the amount of these mismatches cannot be preivously expected, and changes from time to time. There are many kinds of seam trackers for correcting the welding path of the robot, where non-contact type sensors arc prevalently used in arc welding robot systems. In this study, an arc sensor was developed for GMA and FCA welding robot system. Since the arc sensor uses the arc characteristics during welding, the operating principle of the arc sensor must be adjusted according to the welding condition. Especially in GMA welding with the $CO_{2}$ shielding gas, the welding arc is not stable because of the short circuit and non-axial globular transfer mode of the molten droplet. In this study, the 2nd order least square curve fitting algorithm was adopted and the applicability of this algorithm was investigated for robot welding systems. For easy usage of the arc sensor, the operating parameters for arc sensor were limited to eight which can be easily determined by the operator.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 B
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• pp.1118-1120
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• 2004

For the first time in Korea, a 100hp high Tc superconducting(HTS) motor has been designed, developed and successfully tested recently. The design was based on 2-dimensional electromagnetic field analysis of cylindrical coordinate. The field winding of rotor was wound with Bi-2223 tapes and tested after assembled with other rotor components. The stator had air-gap type armature windings which allow higher terminal voltage and more sinusoidal voltage waveform than conventional iron cored machines. Steady state open & short-circuit test and resistive load test were conducted also in generator mode. The fabrication and test results of this machine were discussed in this paper.

• 대한기계학회논문집A
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• 제37권8호
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• pp.983-989
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• 2013

본 연구에서 제안한 압전 진동 에너지 수확 장치는 기존 외팔보의 직사각형 면이 대각선을 따라 분할되어 2 개의 에너지 수확 단위로 구성되어 있다. 부 구조물은 주 구조물이 진동 에너지 원에 부착되는 방향과 반대 방향으로 주 구조물의 끝단에 부착되어 있으며, 각 에너지 수확 단위는 폐회로 상태의 고유 진동수가 일치하도록 설계되었다. 동일한 고유 진동수를 갖는 2 개의 구조물이 연결될 때 관찰되는 일반적인 현상과 달리, 제안된 구조에서는 고유 진동수 분리가 작으며, 1 차 및 2 차 모드의 순서가 바뀌어 나타난다. 이로 인해 출력 전력 역시 특정 주파수 근처에서 집중 생성된다. 상용 유한 요소 해석 소프트웨어를 사용하여 제안된 진동 에너지 수확 장치의 최대 생성 전력이 동일한 설치 영역 및 끝단 질량을 갖는 기존 외팔보 형태의 장치에 비해 실질적으로 향상됨을 보였다.

• 대한전자공학회논문지SD
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• 제45권12호
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• pp.1-7
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• 2008

Magnetic Tunnel Junction (MTJ)는 비휘발성 소자로서 그간 기억소자분야에 국한되어왔으나, 최근 다양한 연구들에 의하여 자기논리 (magneto-logic) 회로에 사용되면서 기존 트랜지스터 기반의 논리연산자를 대체할 수 있는 가능성을 보이고 있으며, 논리회로까지 확장 적용되어 스핀전자공학 분야의 새로운 장을 열 것으로 기대되어지고 있다. 자체 저장 능력을 갖는 MTJ 소자로 구현된 자기논리 회로는 전원이 꺼져도 정보가 그대로 유지되고, 또한, 불 (Boolean) 연산 수행 시 단순한 입력변화만으로 다양한 논리 연산자 구현이 가능한 구조적인 유연성을 보이므로, 물리적으로 완성된 회로 내에서 얼마든지 재구성이 가능한 자기논리 회로를 구현할 수 있다. 본 논문에서는 단순한 조합논리나 순차논리 회로의 동작을 넘어서, 임의의 3비트 논리회로 동작을 모두 수행할 수 있는 자기논리 회로를 제안한다. 이를 위해 3비트 논리회로 중에서 최대의 복잡성을 갖는 논리회로를 MTJ 소자를 사용하여 설계하였고, 그 동작을 이전 논문에서 제안된 바 있는 macro-model을 보완 적용하여 검증하였다. 제안된 회로는 3비트로 구현할 수 있는 가장 복잡한 논리회로의 동작을 수행할 뿐만 아니라, 전류구동회로의 게이트 신호들을 변화시킴으로써 임의의 3비트 논리 회로의 동작을 모두 수행하는 것이 가능하다.

• 한국전자파학회논문지
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• 제21권9호
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• pp.987-994
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• 2010

본 논문에서는 간단하면서도 효과적인 능동적인 로드 풀(active load-pull) 방법을 제시하고, 고조파의 임피던스 성분을 제어하는 회로를 사용하여, X-대역 전력 증폭기의 효율을 개선시킬 수 있는 방법에 관하여 연구하였다. 제안된 능동적인 로드 풀 시스템은 크게 방향성 결합기와 위상 변위기, 단락 회로, 그리고 전력 증폭기로 구성되어 있으며, 전통적인 능동적인 로드 풀 방법에 비해 반사 계수가 1인 지점까지 임피던스를 쉽게 가져다 놓을 수 있다. 본 논문에서 사용된 소자는 Mitsubishi사의 GaAs FET인 MGF1801이며, 9 GHz의 동작 주파수에서 class-A일 때, 21.65 dBm의 출력 전력과 24.9 %의 드레인 효율을 얻었고, class-AB일 때, 21.46 dBm의 출력 전력과 53.3%의 드레인 효율을 얻었다. 고조파 제어 회로는 실험에 사용된 초고주파 부품의 주파수 대역폭의 한계로 인해, 2차와 3차 항 성분까지만 고려하여 설계하였으며, class-AB에서, 6.4 %의 효율이 증가된 것을 확인하였다.