• 대한수학회논문집
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• 제17권2호
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• pp.349-361
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• 2002

The ill-posed elliptic wave propagation problems can be transformed into well-posed initial value problems of the reflection and transmission operators characterizing the material structure of the given model by the combination of wave field splitting and invariant imbedding methods. In general, the derived scattering operator equations are of first-order in range, nonlinear, nonlocal, and stiff and oscillatory with a subtle fixed and movable singularity structure. The phase space and path integral analysis reveals that construction and reconstruction algorithms depend crucially on a detailed symbol analysis of the scattering operators. Some information about the singularity structure of the scattering operator symbols is presented and analyzed in the transversely homogeneous limit.

• 한국자기학회지
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• 제18권1호
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• pp.36-38
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• 2008

축약 각운동량 전개(Reduced Angular Momentum Expansion) 을 사용하여 산란 진폭을 계산하였고, 평면파 근사와 비교하였다. Wentzel-Kramers-Brillouin(WKB) 방법을 써서 각 운동량이 영이 아닌 초기 파동의 곡률 효과를 주는 항이 광전자 또는 오제(Auger) 전자의 원심 퍼텐셜 에너지(centrifugal potential energy) 항이 됨을 보였으며, 이항은 평면파 근사에서 각 운동량에 의존하는 유효 파수 벡터가 됨을 보였다. 산란 진폭과 각 운동량과 관계를 구체적으로 보였다.

• 한국해안해양공학회지
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• 제19권3호
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• pp.183-193
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• 2007

부분반사 전면 및 완전반사 후면을 갖는 반무한 방파제 및 방파제 개구부에 의한 파의 산란 현상에 대한 해석 해를 유도하였다. 이는 수심이 일정하고 파가 방파제에 직각으로 입사하는 경우에 적용 가능하며, 선형파 이론에 근거하여 변수 변환 및 좌표 변환을 통해 지배 방정식을 상미분 방정식으로 전환하여 구하였다. 본 연구에서 유도된 해석 해는 유한 요소 수치 모델의 결과와 비교하여 그 정확도를 비교하였는데, 꽤 정확한 결과를 보인다는 것을 알 수 있었다. 유도된 해석 해를 이용하여 방파제에서의 반사율에 따른 항 입구에서의 정온도에 미치는 효과를 조사하였다.

• 한국전자파학회논문지
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• 제24권9호
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• pp.892-899
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• 2013

본 논문에서는 (서브)밀리미터파 대역에서 산란 계수 정밀 측정이 어려운 요인 및 보다 정확한 측정을 하기 위한 방안을 기술하였으며, G-band(140~220 GHz)에서의 측정 사례를 제시하였다. 우선 마이크로파 대역과 (서브)밀리미터파 대역에서 사용되는 산란 계수 측정시스템(벡터회로망 분석기)의 동작 원리에 대한 차이점을 파악하고, (서브)밀리미터파 대역 산란 계수 측정시스템을 보다 잘 운영하기 위한 방안을 기술하였다. 그리고 더 좋은 도파관 전송 특성 및 연결 반복도를 얻기 위한 방안과 반사 계수 크기가 작은 피측정기를 정밀 측정하기 위한 방안을 기술하였다.

• Structural Monitoring and Maintenance
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• 제2권3호
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• pp.213-236
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• 2015

The paper presents an investigation into the mode conversion and scattering characteristics of guided waves at delaminations in laminated composite beams. A three-dimensional (3D) finite element (FE) model, which is experimentally verified using data measured by 3D scanning laser vibrometer, is used in the investigation. The study consists of two parts. The first part investigates the excitability of the fundamental anti-symmetric mode ($A_0$) of guided wave in laminated composite beams. It is found that there are some unique phenomena, which do not exist for guided waves in plate structures, make the analysis become more complicated. The phenomena are observed in numerical study using 3D FE simulations. In the second part, several delaminated composite beams are studied numerically to investigate the mode conversion and scattering characteristics of the $A_0$ guided wave at delaminations. Different sizes, locations and through-thickness locations of the delaminations are investigated in detail. The mode conversion and scattering phenomena of guided waves at the delaminations are studied by calculating reflection and transmission coefficients. The results show that the sizes, locations and through-thickness locations of the delaminations have significant effects on the scattering characteristics of guided waves at the delaminations. The results of this research would provide better understanding of guided waves propagation and scattering at the delaminations in the laminated composite beams, and improve the performance of guided wave damage detection methods.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
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• pp.415-429
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• 2002

Various modeling techniques for ultrasonic wave propagation and scattering problems in finite solid media are presented. Elastodynamic boundary value problems in inhomogeneous multi-layered plate-like structures are set up for modal analysis of guided wave propagation and numerically solved to obtain dispersion curves which show propagation characteristics of guided waves. As a powerful modeling tool to overcome such numerical difficulties in wave scattering problems as the geometrical complexity and mode conversion, the Boundary Element Method(BEM) is introduced and is combined with the normal mode expansion technique to develop the hybrid BEM, an efficient technique for modeling multi-mode conversion of guided wave scattering problems.

• 한국통신학회논문지
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• 제26권4B호
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• pp.391-399
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• 2001

In this paper, electromagnetic wave scattering from a bianisotropicaly coated cylinder is formulated by using wave functions for bianisotropic media and boundary-value method. The cross section of the cylinder is made of a conducting core, a lossless dielectric layer which is both electrically magnetically bianisotropic, and a bianisotropic impedance sheet and a different uniaxial bianisotrpic coating. The solutions to arbitrary polarization angles are presented in two-dimensional. This paper presents and exact solution to the problem of scattering by a long composite circular cylinder using the boundary method. The validity of this solution is verified by comparing numerical results with those in literature. The numerical results for various geometrical and electrical parameters on bistatic scattering cross-section are presented.

• 한국지진공학회논문집
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• 제2권2호
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• pp.77-85
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• 1998

이방성 재료에서의 표면파 진행과 산란에 대한 연구를 수행하였다. 두 개의 이방성 4분 무한 영역의 계면에서의 표면파 산란거동을 해석하기 위한 이론을 제안하였다. Green 함수법을 이용하여 계면에서의 표면파 산란계수를 결정하기 위한 방정식을 유도하였다. 수치계산을 수행하였으며 이방성과 비균질성이 산란 거동에 미치는 영향을 비교하였다.

• 대한전기학회논문지
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• 제41권1호
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• pp.89-94
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• 1992

In this paper, the static limit of Helmholtz equation is discussed for the analysis of wave scattering in a wave scattering in a waveguide. Boundary integral equation method is used to formulato the scattering process in the exterior of the scatterer and finite element method in the interior of the scatterer. And hybrid ray-mode method is used to provide the Green's function in the waveguide. The proposed algorithm is applied algarithm is applied to a sample problem with arbitrary scatterer in a waveguide. The results are compared with those of static analysis.

• Journal of electromagnetic engineering and science
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• 제10권3호
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• pp.166-170
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• 2010

To numerically calculate electromagnetic scattering from the electrical-large three-dimensional(3D) objects, the high-frequency approaches have been usually applied, but the accuracy and feasibility of these geometrical and physical optics(GO-PO) approaches, to some extent, are remained to be improved. In this paper, a new framework is developed for calculation of the near-field scattering field of an electrical-large 3D target by using a multilevel fast multipole algorithm(MLFMA) and generation of radar images by using a fast back-projection(FBP) algorithm. The MPI(Message Passing Interface) parallel computing is carried out to multiply the calculation efficiency greatly. Finally, a simple example of perfectly electrical conducting(PEC) patch and a canonical case of Fighting Falcon F-16 are presented.