액상환원공정을 이용한 황산코발트로부터의 코발트 나노분말 합성

안세환,김세훈,이진호,홍현선,김영도,An, Se-Hwan,Kim, Se-Hoon,Lee, Jin-Ho,Hong, Hyun-Seon,Kim, Young-Do 한국재료학회 2011 한국재료학회지 Vol.21 No.6

Nanostructured cobalt materials have recently attracted considerable attention due to their potential applications in high-density data storage, magnetic separation and heterogeneous catalysts. The size as well as the morphology at the nano scale strongly influences the physical and chemical properties of cobalt nano materials. In this study, cobalt nano particles synthesized by a a polyol process, which is a liquid-phase reduction method, were investigated. Cobalt hydroxide ($Co(OH)_2$), as an intermediate reaction product, was synthesized by the reaction between cobalt sulphate heptahydrate ($CoSO_4{\cdot}7H_2O$) used as a precursor and sodium hydroxide (NaOH) dissolved in DI water. As-synthesized $Co(OH)_2$ was washed and filtered several times with DI water, because intermediate reaction products had not only $Co(OH)_2$ but also sodium sulphate ($Na_2SO_4$), as an impurity. Then the cobalt powder was synthesized by diethylene glycol (DEG), as a reduction agent, with various temperatures and times. Polyvinylpyrrolidone (PVP), as a capping agent, was also added to control agglomeration and dispersion of the cobalt nano particles. The optimized synthesis condition was achieved at $220^{\circ}C$ for 4 hours with 0.6 of the PVP/$Co(OH)_2$ molar ratio. Consequently, it was confirmed that the synthesized nano sized cobalt particles had a face centered cubic (fcc) structure and with a size range of 100-200 nm.

Hybrid Coupler 제거와 부하 최적화를 이용한 고효율 및 고선형성 전력 증폭기의 관한 연구

안세환,서철헌,An, Se-Hwan,Seo, Chul-Hun 대한전자공학회 2006 電子工學會論文誌-TC (Telecommunications) Vol.43 No.2

본 논문은 일반적인 Doherty amplifier보다 더 작은 부하저항을 갖도록 설계하였으며 출력 정합 회로에 PBG구조를 적용하여 IMD(Inter-modulation Distortion)를 억제 시키고 PAE (Power Added Efficiency)를 향상시켰다. 본 논문에서 제안된 전력 증폭기는 기존의 Doherty 전력 증폭기를 기준으로 IMD3는 5.5 dEC, PAE는 $5\%,$ 최대 출력 전력은 8dB back-off point 에서 $18\%$의 성능 개선을 시켰다. In this paper, smaller load has been used compared with the conventional Doherty amplifier and PBG structure have been employed to suppress IMD (Inter-modulation Distortion) and improve PAE (Power Added Efficiency). And The PBG structure has been employed on the output macthing network of Doherty amplifier. The proposed power amplifier has been improved more the IMD3 by 5.5 dBc, and the average PAE by $5\%,$ at peak output power, $18\%$ at 8dB back-off point respectively than the conventional Doherty power amplifier.

소아에서 마이코플라스마 폐렴과 바이러스 폐렴의 임상적 특징 비교: 다기관 단면연구

안세환 ( Se Hwan An ),조홍제 ( Hong Je Cho ),백혜성 ( Hey-sung Baek ),성명순 ( Myong Soon Sung ),윤정원 ( Jung Won Yoon ),최선희 ( Sun Hee Choi ),신윤호 ( Youn Ho Sheen ),한만용 ( Man Yong Han ) 대한천식알레르기학회(구 대한알레르기학회) 2018 Allergy Asthma & Respiratory Disease Vol.6 No.3

Purpose: This study was conducted to compare clinical features between Mycoplasma pneumonia and viral pneumonia. Methods: We retrospectively analyzed the medical records of 428 patients requiring hospitalization among children younger than 18 years of age in 5 hospitals in Seoul and Gyeonggi-do. There were 131 patients with M. pneumonia and virus coinfection, 167 patients with M. pneumonia without virus coinfection, and 130 patients with viral pneumonia. All subjects had radiographic evidence of pneumonia with specimens available for both M. pneumonia and viral testing. Virus was identified using the polymerase chain reaction assay in a nasopharyngeal or oropharyngeal swab. M. pneumoniae pneumonia was diagnosed serologically. Results: Human rhinovirus was detected in 60.3% (79 of 131) of children with M. pneumonia accompanied by virus coinfection. Respiratory syncytial virus (RSV) was detected in 38.2% (50 of 130) of children with viral pneumonia. The mean age was significantly lower in the viral pneumonia group than in the M. pneumonia group with and without virus coinfection. The sex distribution did not differ significantly among the 3 study groups. The procalcitonin level was higher in viral pneumonia and erythrocyte sedimentation rate level was higher in the M. pneumonia group although no significant difference was found in C-reactive protein level between the M. pneumonia and viral pneumonia groups. Conclusion: Clinical features and inflammatory markers between M. pneumonia and viral pneumonia may be useful for the treatment of community-acquired pneumonia. (Allergy Asthma Respir Dis 2018;6:155-160)

Ka 대역 탐색기용 다기능 초소형 주파수 합성기

안세환(Se-Hwan An),이만희(Man-Hee Lee),김홍락(Hong-Rak Kim) 한국전자파학회 2016 한국전자파학회논문지 Vol.27 No.10

본 논문에서는 다기능 Ka 대역 탐색기용 초소형 주파수 합성기를 제안하였다. 제작된 주파수 합성기는 다양한 파형생성과 고속의 파형 및 주파수 전환을 위해 DDS를 적용하였고, 소형화를 위해 파형발생 모듈과 주파수 상향 변환 모듈을 통합하여 설계하였다. 본 논문의 주파수 합성기는 저속 및 고속 표적 탐지 추적용 파형 과 고속표적의 정밀 탐지 추적용 파형발생이 가능하고, 주파수 전환 속도 0.45 μsec, 1 kHz 오프셋(offset)에서 —93.69 dBc/Hz의 위상잡음이 측정되었고, 이를 120(width) mm×120(length) mm×22(height) mm 크기로 구현하였다. In this paper, we designed a compact frequency synthesizer with multi-function for Ka-band seeker. DDS(Direct Digital Synthesizer) is applied to generate various waveform and to cover high-speed frequency sweep. In order to reduce size, waveform generator and frequency up-converter are integrated in one module. Proposed frequency synthesizer provides precise detection and tracking waveform for low and high speed targets. It is observed that fabricated synthesizer performs 0.45 μsec frequency switching time and —93.69 dBc/Hz phase noise at offset 1 kHz. The size of the synthesizer is kept within 120 mm width, 120 mm length and 22 mm height.

AESA 레이더 광각 빔조향 특성을 고려한 복사소자 설계 기법

김영완,채희덕,안세환,주지한,Kim, Young-Wan,Chae, Hee-Duck,An, Se-Hwan,Joo, Ji-Han 한국인터넷방송통신학회 2022 한국인터넷방송통신학회 논문지 Vol.22 No.5

In this paper, a study was conducted on the design of an array element that can be applied to the AESA radar for seeker. An antenna for application to AESA radar should choose an optimal radiation element to be applied to an array antenna in order to secure electronical beam steering characteristics, and consider beam steering characteristics when designing. In particular, in order to satisfy the wide-angle beam steering characteristics, the wide-angle impedance matching technique should be used to minimize the scan blindness region that may occur during wide-angle steering. As such, securing the stability of system operation is becoming an important design consideration for AESA radar. In this paper, WAIM is applied to the end of the radiation element to improve the characteristics of the radiation element applied to the AESA radar antenna device, and the change in the performance of the active reflection coefficient, which is a stable operation index of the system, is reviewed. The final performance result verified the validity of the proposed method by mathematically synthesizing the simulation data.

Ka-대역 추적 레이더용 전원공급기 개발

이동주,안세환,주지한,권준범,서미희,Lee, Dongju,An, Se-Hwan,Joo, Ji-Han,Kwon, Jun-Beom,Seo, Mihui 한국인터넷방송통신학회 2022 한국인터넷방송통신학회 논문지 Vol.22 No.5

밀리미터파 추적 레이더는 다양한 환경조건에서 운용하므로 입력전압의 큰 변동에도 안정적인 출력전원을 공급하는 전원공급기가 필요하며, 송수신기에 고품질의 전원공급을 위해 낮은 잡음레벨 특성을 가져야 한다. 본 논문에서는 Ka-대역 추적 레이더에 적용하기 위한 최대 출력 727 W급의 소형 전원공급기 설계 및 구현방안에 대해 기술한다. 전압안정도 및 효율 요구사항을 충족하기 위해 buck 타입의 DC-DC 컨버터의 윗면이 전원공급기의 커버와 맞닿게 배치하여 방열효율을 극대화하였다. 최대 부하 조건에서 시스템 효율 88.4 %, 전압정밀도 ±2 %, 잡음레벨은 전압값의 1 % 이내임을 확인하였다.

Ka 대역 고출력 고효율 도파관 공간 결합기 설계 및 제작

김효철,조흥래,이주흔,이덕재,안세환,이만희,주지한,김홍락,Kim, Hyo-Chul,Cho, Heung-Rae,Lee, Ju-Heun,Lee, Deok-Jae,An, Se-Hwan,Lee, Man-Hee,Joo, Ji-Han,Kim, Hong-Rak 한국인터넷방송통신학회 2021 한국인터넷방송통신학회 논문지 Vol.21 No.5

본 논문에서는 고출력 저손실의 도파관 공간결합 구조를 제안하였다. 제안하는 공간결합구조는 각 포트의 중심에서 원형 도파관을 통해 결합하는 방식으로 구현 하였다. 특히 도파관의 모드 중 전송 선로 손실이 가장 적은 TE01모드를 이용하여 저 손실을 구현하고, 새로운 모드 변환 방식을 적용하여 소형화를 이루었다. 또한 전계 분석을 통해 새로운 모드 변환 구조의 절연 파괴 전압을 계산하여 고출력에 적합함을 확인하였다. 최종 8-way 도파관 공간 결합기를 설계, 제작하여 삽입 손실은 0.4dB 이하 결합효율 97% 이상의 결과를 얻어 평면 결합 방식 대비 전기적 성능이 매우 우수함을 확인하였다. This report proposes a waveguide spatial combiner with high power low loss. The proposed spatial combiner implements high power by combining from the center of each port through a waveguide. In particular, we implement low loss using TE01 mode, which has the lowest transmission track loss among modes of circular waveguide, and miniaturization is achieved by applying a new mode conversion method. IIn addition, it was confirmed that it was suitable for high output by calculating the insulation breakdown voltage of the new mode conversion structure through E-field analysis. The final 8-way waveguide spatial combiner was designed and manufactured, and the insertion loss was less than 0.4dB and the combining efficiency was 97% or more, confirming that the electrical performance was very good compared to the planar combining method.

Ka 대역 고출력 저손실 도파관 결합기 설계 및 제작

김효철,조흥래,이주흔,이덕재,안세환,이만희,주지한,권준범,정해창,김소수,Kim, Hyo-Chul,Cho, Heung-Rae,Lee, Ju-Heun,Lee, Deok-Jae,An, Se-Hwan,Lee, Man-Hee,Joo, Ji-Han,Kwon, Jun-Beom,Jeong, Hae-Chang,Kim, So-Su 한국인터넷방송통신학회 2021 한국인터넷방송통신학회 논문지 Vol.21 No.3

초고주파 대역에서 TWTA(Traveling Wave Tube Amplifier)를 대체하기 위한 증폭기 연구가 활발히 이루어지고 있다. 반도체형 소자를 결합하여 높은 출력을 얻는 SSPA(Solid State Power Amplifier)의 경우 상대적으로 낮은 단일 소자의 출력으로 요구 출력을 충족하기 위해서는 저손실, 고효율의 결합 기술이 필요하다. 본 논문을 통해 8-way 도파관 결합기를 설계, 제작하여 20dB 이상의 반사 손실과 85% 이상의 결합 효율을 확인하였다. 전계 분석을 통해 결합기 내부의 임계 전력을 계산하여 안정적인 Power Rating을 확보하였고 전력 모니터링을 위한 커플러를 내장하여 소형화 및 경량화를 이루었다. The research of amplifier have been actively conducted to replace the Traveling Wave Tube Amplifier (TWTA) in the mmWave. For Solid State Power Amplifiers (SSPA), which combine semiconductor-type devices to obtain high output, Low-loss, high-efficiency combination techniques are required to meet the required output as the output of a single relatively low device is relatively low. In this paper, we design and produce an 8-way waveguide combiner and a reflective loss of more than 20dB and a binding efficiency of 85% or more were identified. Field analysis calculates the critical power inside the combiner. It secured stable Power Ratings and built-in coupler for power monitoring to achieve miniaturization and light weight.

TM₀₁ 모드 변환을 이용한 Ka 대역 고출력 고효율 공간 결합기 설계 및 제작

김효철,조흥래,이주흔,이덕재,안세환,이만희,주지한,김홍락,Kim, Hyo-Chul,Cho, Heung-Rae,Lee, Ju-Heun,Lee, Deok-Jae,An, Se-Hwan,Lee, Man-Hee,Joo, Ji-Han,Kim, Hong-Rak 한국인터넷방송통신학회 2021 한국인터넷방송통신학회 논문지 Vol.21 No.6

본 논문에서는 비교적 구현이 쉽고, 최종 결합 포트의 전송 선로 길이를 짧게 구현할 수 있는 모드 변환기에 대해 제안하고, 8-way 공간 결합기에 적용하여 제작 및 시험을 하였다. 제안하는 모드 변환기는 그라운드와 연결되어 있는 Doorknob 형태의 원형 디스크에서 변환된 신호를 원형 도파관 내에서 개방을 시켜 TM₀₁ 모드로 변환이 이루어진다. 8-way 도파관 공간 결합기는 H-평면에서 입력된 8개의 신호를 중심의 원형 도파관에서 결합이 이루어지고, 최종 결합 모드는 TM₀₁이 되도록 설계를 하였다. 시험 결과는 삽입손실 0.4dB 이하, 결합효율 95%이상의 우수한 성능을 확인하였다. 또한 전계 분석을 통해 새로운 모드 변환 구조의 절연 파괴 전압 및 방전 임계전력을 계산하여 고출력에 적합함을 확인하였다. 본 연구를 통해 확인된 결과는 향후 고출력 고효율 SSPA에 다방면으로 적용이 가능할 것으로 기대된다. In this study, it proposes a mode converter that is relatively easy to implement and can shorten the transmission line length of the final combining port and it was fabricated and tested by applying it to an 8-way spatial combiner. The proposed mode converter converts the signal converted from the doorknob-shaped circular disk connected to the ground into the TM₀₁ mode by opening it in the circular waveguide. The 8-way waveguide spatial combiner is designed and implemented so that 8 signals input from the H-plane are combined in a circular waveguide at the center, and the final combining mode is TM₀₁. The test results confirmed excellent performance with an insertion loss of less than 0.4dB and a combining efficiency of 95% or more. In addition, it was confirmed that it is suitable for high output by calculating the breakdown voltage and discharge threshold power of the new mode conversion structure through electric field analysis. The results confirmed through this study are expected to be applicable to high-power, high-efficiency SSPA in various fields in the future.

해양구조물용 고강도 주강품의 용접성 평가

하종문(Jong-Moon Ha),권희경(Hee-Kyung Kwon),안세환(Se-Hwan An) 대한용접·접합학회 2016 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2016 No.11