• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 정기총회 및 창립40주년기념 학술대회 학회본부
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• pp.377-382
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• 1987

To obtain a high resolution microwave images, back scattering microwave fields from one, two, four poles on a rotating object is measured. A computation algorithm to reconstruct these poles images from measured data is programed. The program is tested for these poles on a rotating object for different frequency intervals in the X-Band. The more frequency data yield the reduction of side lobe level. The reconstructed image for the two pole objects having the diameter of 1cm and separated by 1 lamda, 2 lamda (lamda-3.75 cm) from the measured data is shown. And, the image of two objects having the different reflectivity coefficient from the measured data is also shown and it assumes that this reconstructing algorithm from the measured angular spectrum provides quite accurate images.

• 한국통신학회논문지
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• 제27권1B호
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• pp.114-124
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• 2002

본 논문에서는 실내 전파환경에서의 페이딩을 분석하기 위하여 영상법 기반의 3차원 광선추적법에 패치산란모델을 첨가한 모델을 제시하였다. 영상법 기반의 광선추적법은 정확한 경로를 얻을 수 있다는 장점 때문에, 안테나의 빔패턴 및 편파, 그리고 전파의 진행에 따른 편파를 고려함으로써 페이딩 특성 분석이 가능하다. 또한 실내 구조물을 모델링하기 위한 패치산란모델은 패치형태의 직사각형 평면에 대한 RCS (Radar Cross Section)를 이용하여 입사에 대한 산란현상을 정의한 것으로써, 책상이나 테이블 같은 평면적인 실내 구조물에 대한 산란현상을 각각의 구조물에 대한 영상 안테나를 발생시키는 복잡한 과정 없이 간단하게 해석하기 위한 것이다. 제안된 모델은 신호강도 뿐만 아니라 채널의 페이딩 특성을 예측할 수 있기 때문에 안테나 종류별 편파 다이버시티 기법의 성능을 분석하는데 이용될 수 있다.

• 대한전자공학회논문지TC
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• 제39권10호
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• pp.27-37
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• 2002

본 논문에서는 주파수 영역에서 3차원 임의형태의 유전체 산란 해석을 위하여 다양한 결합 적분방정식(combined field integral equation, CFIE)의 구성을 제안한다. 서로 다른 시험 함수의 조합으로 8 가지의 CFIE를 제안하였다. 본 논문의 목적 중의 하나는 제안된 모든 CFIE가 구조물의 내부공진 주파수에서 공진문제를 극복하지 못함을 보이는 것이다. 또한 이 8가지의 CFIE는 네 개의 항으로 구성되는데, 이 중에서 하나를 무시하는 방법으로 16가지의 새로운 CFIE를 제안하였다. 수치 예로서 유전체로부터의 원거리장과 레이다 단면적(radar cross section, RCS) 계산 결과들을 보이며, 제안되는 각 CFIE의 동작 특성을 비교하여 고찰하였다.

• 천문학회보
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• 제42권2호
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• pp.86.4-87
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• 2017

Symbiotic stars are binary systems composed of a hot white dwarf and a mass losing giant. Many symbiotic stars are known to exhibit broad wings around Balmer emission line. We show high resolution spectra of S-type symbiotic stars, Z Andromedae and AG Draconis, obtained with the ESPaDOnS and the 3.6 m Canada-France-Hawaii Telescope, in which we find prominent broad wings around Balmer lines. We adopt Monte-Carlo technique to consider two types of wing formation mechanisms, which are Thomson scattering by free electron in H II region and Raman scattering by atomic hydrogen in H I region. We find that Thomson wings of $H{\alpha}$ and $H{\beta}$ have the same widths in the Doppler space due to the cross section independent of wavelength. In contrast, Raman $H{\alpha}$ wings are 3 times broader widths than $H{\beta}$ counterparts, which is attributed to the different cross sections and branching ratios. Our CFHT data show that $H{\alpha}$ wings of Z Andromedae and AG Draconis are broader than $H{\beta}$ wings, lending strong support to the Raman scattering origin of Balmer wings in these objects.

• 천문학논총
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• 제30권2호
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• pp.65-67
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• 2015

The surfaces of most atmosphereless solar system objects are referred to as regolith, layers of loosely connected fragmentary debris, produced by meteorite impacts. Measurements of light scattered from such surfaces provides information about the composition and structure of the surface. A suitable way to characterize the scattering properties is to consider how the intensity and polarization of scattered light depends on the particle size, composition, porosity, roughness, wavelength of incident light and the geometry of observation. In the present work, the effect of porosity on bidirectional reflectance as a function of phase angle is studied for alumina powder with grain size of $0.3{\mu}m$ and olivine powder with grain size of $49{\mu}m$ at 543.5 nm. The optical constants of the alumina sample for each porosity were calculated with Maxwell Garnett effective medium theory. On using each of the optical constants of alumina sample in Mie theory with the Hapke model the variation of bidirectional reflectance is obtained as a function of phase angle with porosity as a parameter. Experimental reflectance data are in good agreement the model. For the olivine sample the effect of porosity is studied using Hapke (2008).

• 한국전자파학회논문지
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• 제15권10호
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• pp.961-968
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• 2004

본 논문에서는 임의 형상을 가지는 삼차원 유전체의 전자파 산란을 해석하기 위하여 모멘트법을 이용한 뮬러적분방정식의 새로운 해법을 제안한다. 매질이 균일한 유전체 표면을 평면 삼각형 패치로 모델링 하여, RWG (Rao, Wilton, Glisson)함수를 등가 전기 및 자기 전류밀도의 전개함수로 사용한다. 그리고 RWG 함수와 그 직교함수를 조합한 시험함수를 적용한다. 유전체구에 대하여 제안된 방법으로 계산된 수치 결과를 보이고 다른 공식에 의한 결과와도 비교한다.

• Journal of Electrical Engineering and information Science
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• 제3권3호
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• pp.348-354
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• 1998

The measured equation of invariance (MEI) method was introduced as a way to determine the electromagnetic fields scattered from discrete objects. Unlike more traditional numerical methods, MEI method over conventional methods over conventional methods are very substantial. In this work, Haar wavelets are applied to the measured equation of invariance (MEI) to solve two-dimensional scattering problem. We refer to "MEI method with wavelets" as "Wavelet MEI method". The proposed method leads to a significant saving in the CPU time compared to the MEI method that does not use wavelets as metrons. The results presented in this work promise that the Wavelet MEI method can give an accurate result quickly. We believe it is the first time that wavelets have been applied in conjunction with the MEI method to solve this scattering problem.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권9호
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• pp.412-417
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• 2003

In this Paper, we propose a time-domain magnetic field integral equation (TD-MFIE) formulation for analyzing the transient electromagnetic response from three-dimensional (3-D) dielectric bodies. The solution method in this paper is based on the Galerkin's method that involves separate spatial and temporal testing procedures. Triangular patch basis functions are used for spatial expansion and testing functions for arbitrarily shaped 3-D dielectric structures. The time-domain unknown coefficients of the equivalent electric and magnetic currents are approximated tv a set of orthonormal basis function that is derived from the Laguerre polynomials. These basis functions are also used for the temporal testing. Numerical results computed by the proposed method are presented and compared.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권1호
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• pp.41-46
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• 2004

In this paper, we present a new combined field integral equation (CFIE) formulation for the analysis of electromagnetic scattering from arbitrarily shaped three-dimensional perfectly conducting and piecewise homogeneous dielectric composite body. The conducting/dielectric structures are approximated by planar triangular patches, which have the ability to conform to any geometrical surface. The surface covering the conducting body is replaced by an equivalent surface electric current and the surface of the dielectric by equivalent electric and magnetic currents. The all equivalent currents are approximated in terms of RWG (Rao, Wilton, Glisson) functions. The objective of this paper is to illustrate that the CFIE is a valid methodology in removing defects, which occur at a frequency corresponding to an internal resonance of the structure. Numerical results are presented and compared with solutions obtained using other formulations.

• 한국세라믹학회지
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• 제54권6호
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• pp.470-477
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• 2017

Ceramic processing to fabricate 3D complex ceramic structures is crucial for structural, energy, environmental, and biomedical applications. A unique process is ceramic stereolithography, which builds ceramic green objects from CAD files from many thin liquid layers of powder in monomer, which are solidified by polymerization with a UV laser, thereby "writing" the design for each slice. This approach directly writes layers in liquid ceramic suspension and allows one to fabricate ceramic parts and products having more accurate, complex geometries and smooth surfaces. In this paper, both UV curable materials and processes are presented. We focus on the basic material principles associated with free radical polymerization and rheological behavior, cure depth and broadening of cured lines, scattering at ceramic interface and their corresponding simulation. The immediate potentials for ceramic AM to change industry fabrication are also highlighted.