• 전자공학회논문지
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• 제50권12호
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• pp.197-204
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• 2013

본 논문에서는 주파수 영역에서 협대역 신호를 광대역으로 확장하는 새로운 인공 대역 확장 기술을 제안한다. 제안한 기술은 협대역 신호를 여기 신호와 스펙트럼 포락선 성분으로 분리하고, 주파수 영역에서 각각 독립적인 방법으로 확장한다. 여기 신호는 저대역의 하모닉 구조가 고대역에서 유지되도록 확장하고, 스펙트럼 포락선은 부대역별 에너지를 기반으로 NMF방법으로 확장한다. 마지막으로 시간 축에서 프레임 사이의 상관관계를 기반으로 스펙트럼 위상을 결정하여 최종 광대역 신호를 생성한다. 주관적 청취 평가를 통하여 제안한 방법으로 대역 확장된 신호가 원 협대역 신호보다 음질이 향상된 것을 확인하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 학술대회 논문집 전문대학교육위원
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• pp.88-93
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• 2002

$Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}$ and $Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}:Co^{2+}$ + single crystals were grown by CTR method. The grown single crystals have defect chalcopyrite structure with lattice constant a= 5.5966A. c= 10.8042${{\AA}}$ for the pure. a= 5.6543${{\AA}}$. c= 10.8205${{\AA}}$ for the Co-doped single crystal. respectively. The optical energy band gap was given as indirect band gap. The optical energy band gap was decreased according to add of Co-impurity. Temperature dependence of optical energy band gap was fitted well to the Varshni equation. From this relation. we can deduced the entropy. enthalpy and heat capacity. Also. we can observed the Co-impurity optical absorption peaks assigned to the $Co^{2+}$ ion sited at the $T_d$ symmetry lattice and we consider that they were attributed to the electron transitions between energy levels of ions.

• 한국위성정보통신학회논문지
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• 제12권2호
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• pp.89-93
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• 2017

본 논문은 Buck-Boost DC-DC 변환기를 이용하여 다중 대역으로 존재하는 RF 신호를 수집하여 에너지를 생성하는 에너지 수집 시스템에 대하여 소개한다. 수집된 전기에너지를 사용하는 부하의 저항이 지속적으로 변하는 환경에서는 부하 저항이 변하여도 DC-DC 변환기의 입력저항이 변하지 않는 Buck-Boost DC-DC 변환기를 사용하였다. 입력으로 들어오는 RF 신호의 주파수 대역이 다양하므로 다중대역을 다 처리 할 수 있도록 정류기를 대역별로 설계하고 정류기 앞에 각 대역별로 매칭 회로를 추가하였다. 크기가 매우 작은 RF 신호를 효과적으로 수집하기 위한 정류기를 위하여 각 대역에서 수집하여 발생시킨 전압을 계속 누적하여 축적하는 방법을 고안하여 매우 작은 크기의 입력 신호에도 일정한 전압이 출력되게끔 회로를 설계하였다. 입력이 -20 dBm의 크기를 가진 RF 신호에도 출력 효율이 20% 정도까지 낼 수 있음을 확인하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 제4회 영호남학술대회 논문집
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• pp.92-96
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• 2002

Hot wall epitaxy 방법을 이용하여 chalcopyrite 구조를 가진 고품질의 $AgInS_{2}$ 박막을 성장 하였다. 광전류 스펙트럼을 측정한 결과， 30K에서 300K까지는 단지 A 와 B 두개의 봉우리가 관측되었고 반면에 10K에서는 A,B,C 세 개의 봉우리가 관측되었다. 이때 이들 봉우리들은 band-to-band 전이에 기인하는 것으로 관측되었다. 광전류 측정으로부터 $AgInS_{2}$의 가전자대 갈라짐이 측정되었고 이로부터 10k에서 결정장에 의한 갈라짐 $D_{cr}$과 스핀궤도에 의한 갈라짐 $D_{so}$은 각각 0.150eV와 0.009eV로 관측되었다. 또한 에너지 밴드갭의 온도 의존성 $E_{g}(T)$에 대하여 연구하였고 성장된 $AgInS_{2}$ 박막의 에너지 밴드갭은 1.868eV 임을 알았다.

• Nuclear Engineering and Technology
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• 제34권3호
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• pp.202-210
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• 2002

The details of the electronic structure of the perfect crystal provides a critically important foundation for understanding the various defect states in uranium dioxide. In order to understand the local defect and impurity mechanism, the calculation of electronic structure of UO$_2$ in the one-electron approximation was carried out, using a semi-empirical tight-binding formalism(LCAO) with and without f-orbitals. The energy band, local and total density of states for both spin states are calculated from the spectral representation of Green’s function. The bonding mechanism in Perfect lattice of UO$_2$ is discussed based upon the calculations of band structure, local and total density of states.

• E2M - 전기 전자와 첨단 소재
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• 제7권6호
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• pp.504-510
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• 1994

In this work the crystal structure, optical absorption and photoluminescence of Cd$_{4}$GeSe$_{6}$ single srystals grown by the vertical bridgman method are investigated. From the observed results of the PICTS, we proposed on energy band model which contains deep levels between the conduction band and the valence band. The energy band model permit us to explain the mechanism of the radiative recombination for the Cd$_{4}$GeSe$_{6}$ single crystals.als.

• 한국정밀공학회지
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• 제9권3호
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• pp.117-121
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• 1992

There have been many studies on chatter vibration in machining but there seems to be no regulations to decide the commencing point of chatter objectively. The development of an objective method which can estimate and detect chatter commencement is very much in need for automatic manufacturing systems, dynamic performance tests for machine tools, and so on. In this study, an approach for in-process monitoring and for deciding commencing point of the chatter vibration using the frequency band-energy method was proposed. From this method, in-process monitoring system for detection the chatter vibration was developed, and investigated its practical possibility. As a result, it is shown by experiments that the chatter vibtation can be detected accurately. Since the changing pattern of the signal energy in certain frequency band during chattering is seldom affected by the variation of cutting conditions, if adequate pre-measures are taken, this method can be widely used in most machining processes.

• 정보통신설비학회논문지
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• 제8권1호
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• pp.18-23
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• 2009

The conventional channel selection method for a ZigBee communication network basically detects the energy values in all channels. In the ISM band, no license is required to use channels in this band, so there may exist various interference factors in this band. It is well known that WLAN is the major interference factor degrading the performance of ZigBee in the ISM band. In this paper, we propose an efficient channel selection algorithm which uses the pattern of two types of WLAN channel uses as the a priori information of IEEE 802.11 band IEEE 802.11g. By using the proposed algorithm, we may save the time required to select channels for the ZigBee communications.

• 한국수소및신에너지학회논문집
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• 제24권2호
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• pp.107-112
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• 2013

The ZnO is able to produce hydrogen from water however it can only absorb ultraviolet region due to its 3.37eV of wide band gap. Therefore efficiency of solar hydrogen production is low. In this work we report investigation results of improved visible light photo-catalytic properties of CdSe quantum dots(QDs) sensitized ZnO nanorod heterostructures. Hydrothermally vertically grown ZnO nanorod arrays on FTO glass were sensitized with CdSe by using SILAR(successive ionic layer adsorption and reaction) method. Morphology of grown ZnO and CdSe sensitized ZnO nanorods had been investigated by FE-SEM that shows length of $2.0{\mu}m$, diameter of 120~150nm nanorod respectively. Photocatalytic measurements revealed that heterostructured samples show improved photocurrent density under the visible light illumination. Improved visible light performance of the heterostructures is resulting from narrow band gap of the CdSe and its favorable conduction band positions relative to potentials of ZnO band and water redox reaction.

• 한국세라믹학회지
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• 제43권1호
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• pp.22-27
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• 2006

The electronic band structures of Metal-doped titanium dioxide, M-doped $TiO_2$ (M=Co, Cr, Fe), have been studied by using XRD, UV-vis diffuse reflectance spectrometer and FP-LAPW (Full-Potential Linearized Augmented-Plane-Wave) method. The UV-vis of M-doped $TiO_2$ (M=Co, Cr, Fe) showed two absorption edges; the main edge due to the titanium dioxide at 387 nm and a shoulder due to the doped metals at around 560 nm. The band gap energies of Co, Cr and Fe-doped $TiO_2$ calculated by FP-LAPW method were 2.6, 2.0, and 2.5 eV, respectively. The theoretically calculated band gap energy of $TiO_2$ by using FP-LAPW method was the same as experimental results. FP-LAPW method will be useful for fabrication and development of photo catalysts working under visible light.