• 한국전자파학회논문지
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• 제29권4호
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• pp.266-269
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• 2018

본 논문에서는 Q 대역에서 사용가능한 무인항공기 라디오미터 응용 소형 도파관-마이크로스트립 전이구조를 제안하였다. 제안된 전이구조는 간단하면서도 소형이며, 쉽게 정합이 되고, 크기와 제작 오차에 덜 민감한 특징을 가진다. E 평면 패치형태를 가지는 제안된 전이구조는 캐비티 장착뿐 아니라, 도파관-마이크로스트립 기판의 정렬오차에도 덜 민감한 것이 특징이다. 주요파라미터의 최적화에는 3차원 시뮬레이터인 ANSYS사의 HFSS를 사용하였다. Back-to-back 구조에 대하여 중심 주파수에서 20 dB 이상의 반사손실과 1 dB 이하의 삽입손실을 가졌으며, 36 GHz에서 42 GHz까지 반사손실 15 dB 이상의 우수한 성능을 가졌다.

• 한국전기전자재료학회논문지
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• 제17권7호
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• pp.691-696
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• 2004

The electronic state and chemical bonding of $\beta$-MnO$_2$ with transition metal dopants were theoretically investigated by DV-X$_{\alpha}$ (the discrete variational X$_{\alpha}$) method, which is a sort of the first principles molecular orbital method using the Hartree-Fock-Slater approximation. The calculations were performed with a $_Mn_{14}$ MO$_{56}$ )$^{-52}$ (M = transition metals) cluster model. The electron energy level, the density of states (DOS), the overlap population, the charge density distribution, and the net charges, were calculated. The energy level diagram of MnO$_2$ shows the different band structure and electron occupancy between the up spin states and down spin states. The dopant levels decrease between the conduction band and the valence band with the increase of the atomic number of dopants. The covalency of chemical bonding was shown to increase and ionicity decreased in increasing the atomic number of dopants. Calculated results were discussed on the basis of the interaction between transition metal 3d and oxygen 2p orbital. In conclusion it is expected that when the transition metals are added to MnO$_2$ the band gap decreases and the electronic conductivity increases with the increase of the atomic number of dopants. the atomic number of dopants.

• 한국인터넷방송통신학회논문지
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• 제15권4호
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• pp.185-190
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• 2015

본 논문에서는 5세대 이동통신 시스템에 적용하기 위한 V-밴드 내 57-65GHz 대역에서의 앤티포달 핀라인(antipodal finline) 도파관 변환기의 특성을 분석하고, 변환기를 설계하였다. 특히, 핀라인 테이퍼 형태를 설계하기 위해 선형 테이퍼에 곡률변수를 통해 곡률을 추가시켜 스플라인(spline) 테이퍼를 구하는 방식을 제안하였다. 이 방식을 통해 최적화에 부적절한 영역을 최적화 영역에서 제외함으로써 보다 효율적으로 최적화를 할 수 있었다. 앤티포달 핀라인 변환기의 반사손실과 삽입손실은 핀라인 테이퍼 형태에 가장 크게 좌우되었다. 핀라인 변환기 구조에서 발생되는 공진은 변환기의 성능을 저해하는 가장 큰 적이었으며 반원 모양의 패치(patch)를 사용하여 완화시켰다. 설계한 앤티포달 핀라인 변환기는 사용하고자 하는 대역(57-65GHz)에서 반사손실은 -24.2dB이하이고 삽입손실은 -0.24dB 이하로서 매우 양호한 특성을 나타냈다.

• 한국전자파학회논문지
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• 제30권2호
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• pp.95-103
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• 2019

본 논문에서는 위성통신 대역인 Ku-대역에서 사용할 수 있는 마이크로스트립 선로 입출력의 기판 집적 도파관 및 빈 공간 기판 집적 도파관의 천이 구조를 제공한다. 기판 집적 도파관의 유전체 부분을 제거한 빈 공간 기판 집적 도파관의 효율적 활용을 위해 마이크로스트립 선로로의 천이 구조를 설계 및 제작하고, 그 결과를 기판 집적 도파관 천이 구조와 비교하였다. Back-to-back 구조의 마이크로스트립 선로 입출력의 기판 집적 도파관 천이 구조는 12~18 GHz에서 20 dB 이상의 반사 손실과 $1.5{\pm}0.2dB$의 삽입 손실이 측정되었고, back-to-back 구조의 빈 공간 기판 집적 도파관 천이 구조는 15 dB의 반사 손실과 $0.55{\pm}0.2dB$의 삽입 손실이 측정되었다.

• 한국진공학회지
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• 제9권2호
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• pp.130-135
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• 2000

Photoluminescence(PL)와 photoreflectance(PR)를 이용하여 $Al_{0.25}/Ga_{0.75}/As/In_{0.15}/Ga_{0.85}$/AS/GaAS 슈우도형 고 전자 이동도 트랜지스터 구조에 대한 특성을 조사하였다. 온도 10K의 PL측정에서 InGaAs 양자우물에 의한 e2-hl 및 e2-hl 전이 피크가 각각 1.322 및 1.397 eV에서 관측되었다. 온도 의존성으로부터 첫번째 가전자 띠와 두번째 가전자 띠의 에너지 차이는 약 23'meV로 나타났다. 또한 300 K에서의 PR 측정으로 e2-h2및 e2-hl 전이에 의한 피크를 관측하였고, 두번째 전도 띠의 에너지 준위에 의한 피크가 띠 채움으로 인해 첫번째 전도 띠의 에너지 준위에 의한 피크보다 상대적으로 우세하였다. 반면에 PL 측정에서는 전자 가리개 효과 때문에 첫번째 전도 띠에 의한 피크가 우세하였다.

• Bulletin of the Korean Chemical Society
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• 제32권11호
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• pp.4005-4010
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• 2011

We investigated thermal behavior of spin-coated films of P(HB-co-HHx)/PEG blends by using infraredreflection absorption (IRRAS) spectroscopy and 2D correlation spectroscopy. Based on 2D IRRAS correlation spectra, we could determine the sequence of spectral intensity changes with increasing temperature that PEG band changes first and then a band for crystalline component of P(HB-co-HHx) changes before a band for amorphous component. The intensities of bands for PEG and amorphous P(HB-co-HHx) were changed greatly as PEG weigh % of P(HB-co-HHx)/PEG blends increased. Transition temperatures of P(HB-co-HHx)/PEG blends were successfully determined by 2D gradient mapping method. The transition temperature of spincoated films of 98/2 and 90/10 P(HB-co-HHx)/PEG blends and 80/20 P(HB-co-HHx)/PEG blend determined by 2D gradient map are, respectively, about 137.5 and $132.5^{\circ}C$. Furthermore, P(HB-co-HHx)/PEG blends show an additional transition temperature that have been interpreted in terms of different lamellar thicknesses in spin coated films.

• Applied Microscopy
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• 제47권3호
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• pp.187-202
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• 2017

The classical electron band theory is a powerful tool to describe the electronic structures of solids. However, the band theory and corresponding density functional theory become inappropriate if a system comprises localized electrons in a scenario wherein strong electron correlations cannot be neglected. $SrRuO_3$ is one such system, and the partially localized d-band electrons exhibit some interesting behaviors such as enhanced effective mass, spectral incoherency, and oppression of ferromagnetism and itinerancy. In particular, a Metal-Insulator transition occurs when the thickness of $SrRuO_3$ approaches approximately four unit cells. In the computational studies, irrespective of the inclusion of on-site Hubbard repulsion and Hund's coupling parameters, correctly depicting the correlation effects is difficult. Because the oxygen atoms and the symmetry of octahedra are known to play important roles in the system, scrutinizing both the electronic band structure and the lattice system of $SrRuO_3$ is required to find the origin of the correlated behaviors. Transmission electron microscopy is a promising solution to this problem because of its integrated functionalities, which include atomic-resolution imaging and electron energy loss spectroscopy.

• 세라미스트
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• 제22권4호
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• pp.350-356
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• 2019

Recently, transition metal dichalcogenide (TMDC) monolayers have been the subject of research exploring the physical phenomenon generated by low dimensionality and high symmetry. One of the keys to understanding new physical observations is the electronic band structure of 2D TMDCs. Angle-resolved photoelectron spectroscopy (ARPES) is, to this point, the best technique for obtaining information on the electronic structure of 2D TMDCs. However, through ARPES research, obtaining the long-range well-ordered single crystal samples always proves a challenging and obstacle presenting issue, which has been limiting towards measuring the electronic band structures of samples. This is particularly true in general 2D TMDCs cases. Here, we introduce the approach, with a mathematical framework, to overcome such ARPES limitations by employing the high level of symmetry of 2D TMDCs. Their high symmetry enables measurement of the clear and sharp electronic band dispersion, which is dominated by the band dispersion of single-crystal TMDCs along the two high symmetry directions Γ-K and Γ-M. In addition, we present two important studies and observations for the direct measuring of the exciton binding energy and charge transfer of 2D TMDCs, both being established by the above novel approach.

• Journal of the Korean Physical Society
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• 제73권11호
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• pp.1729-1734
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• 2018

Organic-inorganic halide perovskite single crystals undergo phase transition of being cubic, tetragonal, or orthorhombic depending on the temperature. We investigated the $CH_3NH_3PbBr_{3-x}I_x$ single crystals grown by the inverse temperature crystallization method with temperature-dependent UV-Vis absorption and photoluminescence. From the temperature-dependent absorption measurement, the optical band gap is extracted by derivation of absorption spectrum fitting and Tauc plot. In our results, $CH_3NH_3PbBr_{3-x}I_x$ single crystals show that an abrupt change in optical band gap, PL peak position and intensity appears around 120 K - 170 K regions, indicating the phase transition temperature.

• 한국자기공명학회논문지
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• 제27권4호
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• pp.28-34
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• 2023

We study the linear-nonlinear quantum transport theory of Wannier-Landau transition system in the confinement of electrons by a square well confinement potential. We use the projected Liouville equation method with the ensemble density projection technique. We select the dynamic value under a linearly oscillatory external field. We derive the dynamic value formula and the memory factor functions in three electron phonon coupling systems and electron impurity coupling systems of two transition types, the intra-band transitions and inter-band transitions. We obtain results that can be applied directly to numerical analyses. For simple example of application, we analyze the absorption power and line-widths of ZnO, through the numerical calculation of the theoretical result in the Landau system.