• The Journal of the Convergence on Culture Technology
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• v.9 no.3
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• pp.641-646
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• 2023

In this paper, TM(transverse magnetic) scattering problems by a resistive strip grating between a double dielectric layer are analyzed by using the FGMM(fourier galerkin moment method) known as a numerical method of electromagnetic fileld. The boundary conditions are applied to obtain the unknown field coefficients, the scattered electromagnetic fields are expanded in a series of Floquet mode functions, and the resistive boundary condition is applied to analysis of the resistive strip. Overall, as the uniform resistivity of the resistive strip increased, the size of the current density induced in the resistance band decreased, the reflected power decreased, and the transmitted power increased. In addition, As the thickness of the dielectric layer increased, the reflected power increased and the transmitted power relatively decreased. The numerical results of the structure proposed in this paper are shown in good agreement compared to the results of PMM, a numerical analysis method of the existing paper.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.12
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• pp.53-62
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• 1999

Center of photon mass(CPM), defined as the center of axial photon distribution, is proposed as a unified design parameter, which contains information about both threshold gain and nonuniformity of axial photon distribution in DFB lasers with low and high-reflection facets. The CPM is inversely proportional to threshold gain and is 0.5 when axial photon distribution is the most uniform. Therefore, a general rule of single-frequency leser design is that main mode CPM should be around 0.5 for-uniform axial photon distribution and side mode CPM should be minimized to maximize the threshold gain difference.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.2
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• pp.415-421
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• 2005

The radiating or receiving characteristics of array elements (i.e., antennas) are changed from those of isolated elements due to mutual coupling effects and the array performance becomes different from those originally designed by assuming isolated elements. The effects of mutual coupling on the performance of a rectangular array with triangular grid geometry of dipoles above a ground plane are discussed with respect to element pattern. The concept of element gain function is used to examine the effects of mutual coupling on the array performance in terms of sidelobe level in the uniformly spaced and space-tapered rectangular arrays with triangular grid geometry of dipoles. It was shown that the sidelobe performance improved in the space-tapered array compared to the uniformly spaced array in the presence of mutual coupling effects. Computer simulation results are presented.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.2
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• pp.331-337
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• 1994

The scatting problem by E-polarized plane wave with obique incidence on a tapered resistive strip grating with zero resistivity(perfectly conducting) at strip-edges is analyzed by the method of moments in the spectral domain. Then the induced surface current density on the strip is expanded in a series of Chebyshev polynomials of the second kind. The expasion coefficients are calculated numerically in the spectral domain, the numerical results of the geometric-optical reflection coefficient for the tapered resistivity in this paper are compared with those for the existing uniform resistivity. And the position of sharp variation points in the magnitude of the geometric-optical reflection coefficient can be moved by varying the incident angle and the strip spacing, It is found out that these sparp variation points are due to the transition of higher mode between the propagation mode and the evanescent mode.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.2
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• pp.81-92
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• 1990

We developed the technologies of wuperlattice and HEMT structures grown by MOCVD, and their characterization. In the case of GaAs/AlGaAs superlattice, the periodicity, interface abruptness and Al compositional uniformity were confirmed through the shallow angle lapping technique and double crystal x-ray measurement. Photoluminesence spectra due to quantum size effect of isolated quantum wells were also observed. The heterojunction abruptness was estimated to be within 1 monolayer fluctuation by the analysis of the relation between PL FWHM(Full Width at Half Maximum) and well width. HEMT structure was successfully grown by MOCVD. The 2 dimensional electron gas formation at heterointerface in HEMT structure were evidenced through the C-V profile, SdH (Shubnikov-de Haas)oscillation and low temperature Hall measurement. Low field mobility were as high as $69,000cm^2/v.sec$ for a sheet carrier density of $5.5{\times}10^{11}cm^-2$ at 15K, and $41,200cm^2/v.sec$ for a sheet carrier density of $6.6{\times}10^{11}cm^-2$ at 77K. In addition, well defined SdH oscillation and quantized Hall plateaues were observed.

• Korean Journal of Materials Research
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• v.8 no.11
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• pp.999-1004
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• 1998

$SrAl_2O_4$:$Eu^{2+}, Dy^{3+}$ 축광성 형광체의 합성에 있어서 $B_2O_3$는 일반적으로 고상반응의 촉진을 위한 플럭스로서 첨가된다. 본 연구에서는 플럭스로 첨가되는 $B_2O_3$가 $SrAl_2O_4$:$Eu^{2+}, Dy^{3+}$ 형광체의 결정구조 및 잔광 특성에 미치는 영향을 조사하였다. 합성된 $SrAl_2O_4$:$Eu^{2+}, Dy^{3+}$ 형광체는 520nm에서 최대 피크를 갖는 폭넓은 발광 스펙트럼을 나타내었고, $B_2O_3$ 첨가량의 5wt%일 때 최대값을 나타내었다. $B_2O_3$의 첨가에 의해 $SrAl_2O_4$:$Eu^{2+}, Dy^{3+}$ 결정 내부에는 균일 변형(uniform strain)이 발생하였고 이 결과로 결정격자의 a축과 c축의 길이 및 $\beta$각이 감소하여다. 그리고 $SrAl_2O_4$ 결정내부의 균일 변형은 $Eu^{2+}$이온의 여기과정에서 발생하는 정공(hole)의 포획 사이트인 음이온 결함(negative defect)을 다량 발생시키는 원인이 되고, 결과적으로 $SrAl_2O_4$:$Eu^{2+}, Dy^{3+}$ 결정의 잔광 특성을 향상시키는 것으로 생각되었다.

• Korean Chemical Engineering Research
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• v.43 no.1
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• pp.71-75
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• 2005

$La_{0.5}Ca_{0.5}MnO_3$ colossal magnetoresistance (CMR) powders and pellets were synthesized by sol-gel process. The structural changes were investigated by FT-IR, CP/MAS $^{13}C$ solid state NMR spectroscopy and XRD. The particle characterization, microstructure of sintered samples, and cation composition of gel powders were studied by FE-SEM/EDS, TEM and ICP-AES. The structure refinement reveals that $La_{0.5}Ca_{0.5}MnO_3$ has orthorhombic, perovskite type unit cell. The magnetic characterizations were identified through measurement of magnetic moment by VSM.

• Journal of Advanced Navigation Technology
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• v.18 no.4
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• pp.371-375
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• 2014

In this paper, the solutions of TE(transverse electric) scattering problems by a resistive strip grating over a grounded dielectric layer are analyzed by applying the PMM(point matching method) known as a numerical method of electromagnetic fileld. The boundary conditions are applied to obtain the unknown field coefficients and the resistive boundary condition is used for the relationship between the tangential magnetic field and the induced surface current density on the resistive strip. The induced surface current density of resistive strip is obtained by difference of the up and down of the magnetic field in two boundary areas of the resistive strip. The numerical results for reflected power of zeroth order mode analyzed by according as the resistivity, the width and spacing of resistive strip, the relative permittivity and thickness of dielectric layer, and incident angles. The numerical results shown in good agreement compared to those of the existing papers using FGMM(fourier galerkin moment method).

• Proceedings of the Optical Society of Korea Conference
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• 2002.07a
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• pp.62-63
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• 2002

파장가변 색소 레이저 발진기는 반사형 회절격자에 비스듬히 입사하는 Grazing Incidence형 공진기 구조로 설계되었다.[1-2] 색소용액이 고속으로 순환되는 색소 셀에 여기광인 레이저 광원을 입사시키는 방법은 색소 셀과 색소 용액 순환방향 및 펌핑 광의 방향이 서로 수직을 이루도록 구성되어 있다. 또한, 두 개의 펌핑 광을 양방향에서 동시에 입사시킬 수 있도록 함으로써, 색소 셀 내부의 색소 용액이 여기 광을 균일하게 흡수하도록 설계하였다. (중략)

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.29.1-29.1
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• 2010

ZnO 는 톡특한 물리적 화학적 성질을 가지고 있는 반도성 물질이기 때문에 최근 광전자 소자인 LED, TFT, 광센서 등에 적용하려는 연구가 많은 관심을 받고 있다. 특히 1차원 ZnO 나노구조는 박막보다 높은 결정성과 물리, 화학적으로 안정하고 표면적이 매우 넓어 많은 연구가 진행되고 있지만, 대량으로 간단하며 저렴하게 생산하기 위해서 친환경적이며 적은 시간으로 합성을 해야 한다. 그래서 최근 수열 합성법을 이용하여 합성이 많이 이루어지고 있지만, ZnO 나노막대 제조 중 기존에 보고된 방법은 대부분 aspect ratio가 낮으며, 저가의 용액 기반으로 높은 aspect ratio를 가지는 나노 선을 제작하기 어려운 실정이다. 또한 용액기반의 성장에서는 기판과의 격자 상수와 열팽창 계수의 차이로 인해 기판과의 adhesion 이 매우 낮아 adhesion layer를 증착 하여 나노 막대을 제작하는 것이 발표가 되고 있다. 하지만 또 하나의 공정이 더해지기 때문에 복잡해지고, 소자에 응용하기에는 한계점이 보인다. 그렇기 때문에 이번 연구에서는 성장 시 Zn 소스가 소모가 다 되었을 시 성장 용액을 교체하는 과정에서 성장 온도와 같이 유지 시킨 뒤에 성장을 하는 방법으로 수직 방향으로 10 um 의 길이를 가지는 ZnO 나노막대의 합성을 가능하게 하였다.