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친수성과 소수성이 복합된 마이크로/나노 혼합 구조 표면에서의 수조비등 연구
조학래(Hak Rae Cho),김영현(Young Hyun Kim),장진규(Jin Gyu Jang),Narayan Pandurang Sapkal,박수청(Su Cheong Park),주형민(Hyeong Min Joo),유동인(Dong In Yu) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12
Surface roughness and wettability is important to enhance not only critical heat flux (CHF) but also boiling heat transfer coefficient (HTC). Generally hydrophilic micro/nano structures contribute on enhancing liquid supply to dry spot and delay CHF and hydrophobic surface contribute on promoting nucleation and enhancing HTC. Therefore, excellent pool boiling performance can be achieved by combining hydrophilic structures and hydrophobic structures. In this study, we fabricated hydrophilic micro pillar (MP) surface, biphilic micro pillar (BMP) surface, hydrophilic micro/nano pillar (MNP) surface and biphilic micro/nano pillar (BMNP) surface. To investigate the effect of surface roughness and heterogeneous wettability on critical heat flux phenomena, pool boiling experiments were conducted using fabricated surfaces and bare surface.
LTCC 수동소자 라이브러리를 활용한 5G 대역 일립틱 LPF 구현
조학래 ( Hak-rae Cho ),구경헌 ( Kyung Heon Koo ) 한국항행학회 2020 韓國航行學會論文誌 Vol.24 No.6
본 논문에서는 회로의 기본 구성요소인 인덕터와 커패시터를 LTCC 다층 기판에서 활용이 가능한 형태로 구성하여 각각의 특성을 분석하였다. 분석을 위해 사용된 인덕터와 커패시터는 유전율 7인 유전체 내부에 각각 사각형 나선 구조와 MIM 구조로 설계되었으며, 인덕터의 감은 수와 커패시터의 적층 수를 달리하여 제작하고 측정하였다. 측정된 결과는 커브피팅 방식을 이용하여 논문에서 제안한 등가회로의 각 소자 값을 추출하였고 추출된 결과를 토대로 제안한 등가회로의 타당성을 검증하였다. 분석된 인덕터와 커패시터는 라이브러리 형태로 구현하였으며 일립틱 타입의 5차 LPF 설계에 적용하여 그 활용성을 입증하였다. LPF는 실제 제작을 통해 측정되었으며, 결과적으로 통과 대역인 DC ~ 3.7 GHz 대역에서 삽입손실이 최대 1.0 dB, 반사손실이 19.2 dB, 저지 대역에서의 감쇄 값이 23.9 dB로 모든 항목에서 설계 목표치에 근접한 결과를 보였다. In this paper, the characteristics of the inductor and capacitor, which are the basic components of the circuit, are constructed in a form that can be used in the LTCC multilayer. The inductors and capacitors used for the analysis were designed with rectangular spiral structures and MIM structures inside dielectrics with a dielectric constant of 7, respectively. The measured results were extracted from each element of the equivalent circuit proposed by the curve fitting method and verified the validity of the proposed equivalent circuit based on the extracted results. The analyzed inductor and capacitor were implemented in the form of library and proved its usefulness by applying to Elliptical type 5th LPF design. The LPF was measured through practical production, and as a result, the insertion loss in the passband DC ~ 3.7 GHz was up to 1.0 dB, the return loss was 19.2 dB, and the attenuation in the rejection band was 23.9 dB, which was close to the design goal.
조학래 ( Cho¸ Hak-rae ) 현대영미어문학회 1990 현대영미어문학 Vol.8 No.-
Herman Melville carried out one of the impressive performances in the history of American letters when he crowded into only six years the writing and publishing of seven long narratives, beginning with Typee (1846) and ending with Pierre(1852). The ordeal of writing and revising the epical Moby Dick brought him to the verge of nervous and physical collapse ; he admitted as much. But he could not stop writing, and the frist draft of Pierre was begun and finished before Moby Dick could be printed and published. The purpose of this paper is to scrutinize ‘Mythic Irony in the Man or World.’ From the point of view of literary technique, Christian myth function in the work. In Pierre, it is used ironically, to mock human pride. For example, Pierre’s notion that he is christ-like makes his bitterness toward his father monstrous ; Mrs. Glendinning’s madonna-like beauty has the effect of an evil disguise ; the protecting angel Lucy has a major part in bringing about Pierre’s downfall. Although the art theme is major only in Pierre, it is important in the evolution of the later novels. Fundamental to the question of moral responsibility is the question of what we can know. Melville’s treatment of the latter problem is expressed through art ; in Pierre, it is the artist who has revelation, not the saint. But Melville’s idea of knowledge has a deeply religious cast. The intention of the truth-seeker is to discover ultimate truths ; his method is intuitive and mystical rather than scientific. Moreover, Melville’s interpretation of the artist role is tinged with Calvinistic doubts ; Pierre is both heroic and Satanic. Heroic because he searches after ultimate truths. Satanic because he attempts as an artist, to escape his experience, to deny its subjective limitations and see the picture whole, like God. What Melville seem to express is that art, like other human activities, must con fine itself to humanly appropriate goals. But Melville was not wholly committed to the theme of limitation. It is this ambivalence which makes Pierre and unbalanced book. The symbolism of the manor world is predominantly but not exclusively Christian. There are, for example, many Pierres in Melville’s novel ; he is at various times Adam, Romeo, Phaeton, Hamlet, Pluto, Memmon, Christ, Ishmael, Manfred, Dantean Sinner, Satan, Zeus, Enceladus and, finally Cain. To assimilate these associations in a single figure suggests one of the major artistic difficulties of the novel. However, in the opening sections, there are two mystic references that are particularly important in relation to the preceding analysis ; for they are used in much the same way as the Christian myth to emphasize the disparity between Pierre’s aspirations and his true capacity.
조학래(Hak-Rae Cho),서수덕(Soo-Duk Seo),구경헌(Kyung Heon Koo) 대한전자공학회 2019 전자공학회논문지 Vol.56 No.5
본 논문에서는 비교적 낮은 유전율을 갖는 LTCC 소재를 이용하여 비대역폭 3% 이하인 5차 협대역 필터를 설계하였다. 협대역 필터의 기능과 성능을 개선하기 위하여 교차결합 원리를 적용하여 인접대역의 차단 특성을 향상시켰다. 높은 차단과 낮은 삽입손실 특성은 서로 인접하지 않은 공진기 간에 결합 구조를 추가하여 얻었다. 필터를 구성하는 결합공진기 사이에 전자기 교차 결합 구조를 갖는 작은 스트립선로 패치를 추가하여, 공진기 차수를 감소시키고 차단 특성을 개선할 수 있는 LTCC 대역통과 필터가 구현되었다. 제작 과정에 있어서 NH20M4 유전체 파우더를 사용한 LTCC 필터 구조 내에 Namics의 7251S 전극을 2겹으로 인쇄함으로써 최상의 필터 특성을 얻었다. 이 경우, 설계에 사용된 매체의 유전율은 21.5이며, 구현된 크기는 0.8㎓ 대역에서 6×5×3 [㎣]이다. This paper has presented the design of a narrow band filter with less than 3% bandwidth and the filter order of 5, using a relatively low permittivity LTCC material. The cross-coupling principle is applied to improve the function and performance of the narrow band filter, and the blocking characteristics of the adjacent band have been enhanced. High blocking and low insertion loss characteristics are obtained by adding coupling structures between resonators that are not adjacent to each other. By adding a small strip line patch with an electromagnetic cross-coupling structure between the coupled resonators constituting the filter, the LTCC band pass filter is realized which can reduce the resonator-order and improve the blocking characteristics. In the fabrication process, Namics’ 7251S electrode was printed twice in the LTCC filter structure using NH20M4 dielectric powder, and the best filter characteristics have been obtained. In this case, the dielectric constant of the material used in the design is 21.5, and the implemented size is 6×5×3 [㎣] for the 0.8 ㎓ band.
Metamaterial 전송선로를 이용한 4출력 90°위상 분배기
조학래 ( Hak-rae Cho ),김정표 ( Jeong-pyo Kim ),구경헌 ( Kyung-heon Koo ) 한국항행학회 2018 韓國航行學會論文誌 Vol.22 No.2
본 논문에서는 90° 위상차를 갖는 GNSS (global navigation satellite system)용 광대역 4출력 분배 회로를 제안한다. 제안하는 분배회로는 1개의 발룬과 2개의 90° 위상 분배기로 이루어진다. 발룬은 wilkinson 분배기와 두 출력단에 각각 ±90° metamaterial 전송선 위상 천이기를 이용하여 구현된다. 90° 위상 분배기의 경우, 발룬과 구조는 같으나, 두 개의 출력단에 각각 ±45° metamaterial 전송선 위상 천이기가 적용된다. Metamaterial 전송선은 LCL-TL (LC loaded transmission line) 단위 셀을 이용하여 구현하였으며, 요구되는 위상 천이 특성을 구현하기 위해 5셀을 갖도록 하였다. 구현된 4출력 90° 위상 분배기는 GNSS 대역인 1.165 -1.61 GHz의 넓은 대역에서 각 포트별 90° ± 10°의 위상차를 갖는다. We propose a wideband 4-way quadrature divider for global navigation satellite system (GNSS). The proposed divider consists of one balun and two 2-way quadrature dividers. In the balun, the input power is divided by a wilkinson divider and the out of phase characteristic is achieved by ±90° metamaterial transmission line phase shifters applied two output ports. The structures of two quadrature dividers is similar to that of the balun, but the phase shifters of two output ports are exchanged by ±90° metamaterial transmission line. Metamaterial transmission lines are designed by using five LC loaded transmission line (LCL-TL) unit cells. The fabricated 4 way quadrature divider has the phase characteristic of 90° ± 10° in 1.165 - 1.61 GHz.