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부분대역 간섭이 존재하는 직교 멀티캐리어 시스템의 성능 개선에 관한 연구
정재필 京畿專門大學 1998 京畿專門大學 論文集 Vol.- No.26
The orthogonal multicarrier modulation is considered as an effective technique in high speed digital transmission under the multipath fading. In this paper, we theoretically analyze the bit error rate (BER) and has evaluated the performance improvement of orthogonal multicarrier QDPSK system with partial-band interference using BCH coding in a frequency selective fading environment. The result shows that when D/U=10 dB in the SNR of 30 dB, multicarrier QDPSK system adopting BCH coding technique presents better error performance in terms of partial-band interference (γ=0.5).
임펄스성 잡음과 페이딩이 존재하는 채널에서 OFDM시스템의 성능 분석
정재필 京畿專門大學 2000 京畿專門大學 論文集 Vol.- No.28
In this paper, we analyze the BER performance of OFDM system and improve its performance adopting convolutional coding as a performance improvement technique in frequency selective Rayleigh fading channel with impulsive noise. When the channel delay time is shorter than the guard band, OFDM system shows good BER performance, however when the channel delay time becomes longer than the guard band, its BER performance is abruptly degraded in frequency selective Raylelgh fading channel with impulse noise. Moreover, when contaminated by strong impulsive noise in the channel, BER performance falls to about 10^(-1).
강과 스테인레스강 brazing 부의 전단 강도에 미치는 Sn, P의 영향 연구
정재필,이보영,강춘식 대한용접접합학회 1989 대한용접·접합학회지 Vol.7 No.3
The furnace brazing in a Ar of copper to martensitic stainless steel(13.5Cr) using Cu-(5~8%)P-(0~8%)Sn powders was investigated. Shear strength, wettability, reacted layer, defect ratio at the stainless steel interface was evaluated. As Sn was added to the Cu-P powders, defect ratio and P content at the stainless steel interface decreased. And also as Sn was added, defect form at the stainless steel interface changed from the continuous layer to the discrete type, and shear strength of the brazed joint increased.
정재필 서울市立大學校 1997 論文集 Vol.31 No.-
최근 MAG (Metal Active Gas) 용접의 생산성을 향상시키는 것이 중요한 연구관심 분야화 되고 있다. 본 연구에서는 보호가스 조성이 용접부의 형상과 기계적 성질, 스패터 발생에 미치는 영향을 조사하여, 고속용접 조건을 찾는데 활용하고자 하였다. 실험을 위해 보호가스로써 Ar + (0-100)%CO₂를 사용하였다. 연구결과, 용접전류를 110A, 130A, 170A로 하였을 때, CO₂함량을 18%까지 증가시킴에 따라 비드 폭, 용입이 증가되었다. Charpy V-notch 충격 에너지는 용접전류를 250A로 하였을 때, CO₂함량을 18%까지 증가시킴에 따라 증가되었다. 용접부는 Ar+(0-100)% CO₂ 보호가스 범위내에서 언더 컷 없이 2.4m/min 까지 용접이 가능하였다. Increasing welding productivity for Metal Active Gas (MAG) welding becomes one of important theme in these days. In this study the effect of shielding gas composition on the bead shape, mechanical properties of welded joint and number of spatter during MAG welding was investigated. For the experiment, mixed gases, Ar + (0-100)%CO₂, were used as shielding gases. As results, at the welding current of 110A, 130A, and 170A, bead width and penetration were increased with increasing CO₂content up to 18%. Charpy V-notch impact energy was increased also with increasing CO₂content up to 18% at welding current of 250A. The joint can be welded up to 2.4m/min without undercut in the range of Ar + (0-40)%CO₂shielding gas.
Plasma Electrolytic Oxidation in Surface Modification of Metals for Electronics
정재필 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.3
This paper presents a brief summary on a relatively new plasma aided electrolytic surface treatmentprocess for light metals. A brief discussion regarding the advantages, principle, process parameters andapplications of this process is discussed. The process owes its origin to Sluginov who discovered an arcdischarge phenomenon in electrolysis in 1880. A similar process was studied and developed by Markovand coworkers in 1970s who successfully deposited an oxide film on aluminium. Several investigationthereafter lead to the establishment of suitable process parameters for deposition of a crystalline oxide filmof more than 100μm thickness on the surface of light metals such as aluminium, titanium and magnesium. This process nowadays goes by several names such as plasma electrolytic oxidation (PEO), micro-arcoxidation (MOA), anodic spark deposition (ASD) etc. Several startups and surface treatment companieshave taken up the process and deployed it successfully in a range of products, from military grade riflesto common off road sprockets. However, there are certain limitations to this technology such as theformation of an outer porous oxide layer, especially in case of magnesium which displays a PilingBedworth ratio of less than one and thus an inherent non protective oxide. This can be treated further butadds to the cost of the process. Overall, it can be said the PEO process offers a better solution than theconventional coating processes. It offers advantages considering the fact that he electrolyte used in PEOprocess is environmental friendly and the temperature control is not as strict as in case of other surfacetreatment processes.
Rene80/B/Rene80계의 액상확산 접합과정 -B분말 도포법을 이용한 액상확산접합
정재필,강춘식 대한용접접합학회 1995 대한용접·접합학회지 Vol.13 No.2
Rene80 superalloy was liquid phase diffusion bonded by using boron(B) as an insert material, where B has high diffusivity and higher melting point as an insert material. Bonding procedure and bonding mechanism of Rene80/B/Rene80 joint were investigated. As results, liquid metal was produced by solid state reaction between base metal and insert material on bonding zone. The liquid metal was produced preferentially at the grain boundary. Except for production of liquid metal, other bonding procedure was nearly same as TLP(Transient Liquid Phase) bonding. Bonding time, however, was reduced compared to prior result of TLP bonding. By bonding S.4ks at l453K, Ren80/B/Rene80 joint was isothermally solidified and homogenized where thickness of insert material was 7.5.mu.m.
페이딩 채널 환경에서 MC-CDMA/QPSK 시스템의 성능분석
정재필 京畿專門大學 1999 京畿專門大學 論文集 Vol.- No.27
This paper has analyzed the Error performance of MC-CDMA/QPSK system adopting error control coding and diversity reception techniques in fading channel Environment. Also, this paper has compared the Error performance of MC-CDMA/QPSK system with that of DS-CDMA/QPSK system. From the obtained results it is found that the Error performance of MC-CD77A/QPSK system has been improved considerably by convolutional coding and MRC diversity reception techniques. Also, it is confirmed that MC-CDMA/QPSK system produces better Error performance than DS-CDMA/QPSK system in fading channel Environment as the number of users increases.