• Korean Journal of Crystallography
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• v.14 no.2
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• pp.79-83
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• 2003

The microstructure of bulk electrolytic MnO₂ (EMD) was studied using x-ray diffraction and transmission electron microscopy (TEM). The bulk sample showed a typical powder x-ray diffraction pattern of EMD materials. TEM study showed that the structure of EMD is present at two length scales;grains, ∼0.2 ㎛ in diameter, and ∼10 nm crystallites within the grain. The electron beam microdiffraction study revealed that each grain is an assemblage of multiphase with a common crystallographic orientation, and_that ∼50% of the crystallites are Ramsdellite, ∼30% are ε-MnO₂, and ∼15% are Pyrolusite. The ｛1120｝peak located at about 67° in powder XRD pattern as well as a high-resolution electron microscope (HREM) image of (0001) plane support the existence of ε-MnO₂ phase.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.7
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• pp.36-42
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• 2000

Some polarization characteristics of reflection type photopolymer are investigated. Photopolymer on a Mylar substrate alters an incoming linearly polarized laser beam to an elliptical polarization. Due to the rotation of the polarization, the recording gratings show different diffraction efficiencies. The rotation angle is of order of 10-50% for the tested samples. It is found that the polymer layer does not changes the polarization direction but the Mylar substrate alone distorts the incoming polarization to a comparable degree. As align the polarization states of photopolymers to be parallel with a laser using a He-Ne laser(633nm), which is not sensitive to that material, it was possible to make high diffraction efficiency gratings.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.5 s.96
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• pp.465-471
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• 2005

A method of calculation fur propagating and focusing of focused beams generated in antenna arrays, using BPM(Beam Propagation Method), is presented in this paper. Based on the diffraction theory, the beam focusing and Propagation is studied specially for the case of the antenna way fed by the Rotman lens that is able to focus microwave power on its focal arc or generate multiple beams. There are difficulties in performing a full-wave simulation using a commercial EM simulation tool for propagating and focusing of beams because of the structural complexity and the feeding assignment of the antenna array. Therefore, as an alternative solution, the BPM is presented to calculate the beam propagation from the aperture-type antennas. From the point of view of optics, the propagations of the lens have been simplified from the Fresnel diffraction integral to the Fourier transform. Using Fourier Transform, a beam propagation method is developed to show improvement of the resolution by controlling the wavefront of wave Propagating from an aperture-type antenna array. The beam width(or spot size) and the intensity are calculated for a focused beam propagating from an array having $10\lambda$ of its size. For the beams with $20\lambda,\;30\lambda$, and $50\lambda$ of geometrical focal length, the half-power beam widths(or spot size) are about 1.1\lambda,\;1.3\lambda,\;and\;1.9\lambda$ respectively.

• Korean Journal of Optics and Photonics
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• v.6 no.2
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• pp.108-114
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• 1995

규칙적인 간격이 $M\timesN$ 이차원패턴과 임의 모양 빔 스폿을 발생시키기 위해 일반적인 이차원 Dammann 격자보다 재구성 에러가 작고, 높은 효율을 보이는 줄무늬형 격자를 설계하였다. 회절효율은 일반적인 이차원 Dammann 격자의 효율보다 평균 15-20% 정도 높은 60% 이상을 얻었다. 설계된 격자는 컴퓨터 시뮬레이션을 통해 회절특성을 확인하였으며 우수한 패턴 발생 결과가 확인되었다. $3\times3에서 11\times11$까지의 규칙적인 스폿 배열과 문자열에 대한 효율, 계산 시간 및 표준편차를 비교분석하였다.

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.127-128
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• 2007

• Proceedings of the Optical Society of Korea Conference
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• 2001.08a
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• pp.84-85
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• 2001

• Proceedings of the Optical Society of Korea Conference
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• 2001.08a
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• pp.88-89
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• 2001

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.3
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• pp.217-224
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• 2003

In this study, the adaptive triangular beam method(ATBM) considering different sound reflection coefficients and angles of a triangular beam on two or more planes as well as diffraction effect is suggested. The ATBM, subdividing a tracing triangular beam into multiple triangular beams on reflection planes, gives reliable and convergent sound-field analysis results without the dependancy on the number of initial triangular beam segmentation to search sound propagation paths from source to receiver. The validity of the method is verified by the comparison of numerical and experimental results for energy decay curve and steady-state sound pressure level of rooms having direct, reflective and diffractive sound paths.

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.315-319
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• 1997

In photorefractive crystals, light deflection is achieved by dynamic photorefractive volume grating, which is induced by the interference of two writing beams. In this paper, we implemented and analyzed the light deflector using Ce-SBN:60 crystals, which is doped with CeO$_2$ and photorefractive effect is induced by low intensity. And we measured maximum coupling coefficient, effective charge density, diffraction efficiency as the intensity ratio and response time.

• Applied Microscopy
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• v.33 no.3
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• pp.179-185
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• 2003

The operating accelerating voltage in the electron microscopy may differ from the nominal voltage specified by the manufacture. Thus it is necessary, at least once, to determine the wavelength of electron beam for the nominal accelerating voltage. Particularly in QCBED technique, the wavelength of the incident electron beam on a specimen must be determined as accurately as possible. In this paper we present a simple method to determine accurately the wavelength of electrons from LACBED patterns of a known crystalline materials, which is analogous to a method based on Kikuchi patterns reported previously. This method is to utilize three diffraction lines not belonging to the same zone, which nearly intersect at the same point. For an application of the method, the wavelength of electrons for the 200 kv nominal acceleration voltage of JEM2010 is determined to be 0.002496(3) nm ($201.5{\pm}0.4$ kv) with an uncertainty of 0.12%.