• The Journal of the Acoustical Society of Korea
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• v.24 no.8
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• pp.441-446
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• 2005

This paper presents the changes of acoustic scattering pattern from a single cylinder and two identical cylinders in both theoretical calculations and experimental measurements. Bi-static scattering pattern by single cylinder and two parallel cylinders (length 2m, radius 30mm) was measured in $5m\times5m\times5m$ water tank using high frequency projector (120 kHz) and hydrophone. The results show similar agreement between experiment and theory. In case of single cylinder scattering. omni-directional pattern was observed in backward but there are fluctuations or target strength in forward. Interference between each cylinder's scattering fields produce fluctuations of target strength in all directions of two cylinders.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.10
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• pp.1454-1460
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• 1993

The scattering pattern, due to an E-Polarized wave incident on M circular parallel dielectric cylinders, is computed. The multiply-scattered fields between the cylinders are considered. Modeling of infinite cylindrical scatterer of arbitrary cross sections by a number of circular cylinders is executed. By enforcing the boundary conditions on the surface of each cylinder, an infinite set of equations is obtained. The first order of scattering results from the excitation of each cylinder by only the incident wave. The second order results from the excitation of each cylinder by the first order of scattering from the remaining cylinders, and so no to an infinite order of scattering. Although the resulting equation is of infinite size, proper truncation yields very accurate numerical results.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.62-70
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• 2001

Based on the recently developed resonance scattering theory for elastic waves, a relationship between the stress components, which may be measured using ultrasonic transducers, of partial waves scattered from cylindrical fluid scatterer, cavity, and resonance scatterer has been derived. The computed resonance scattered stresses exhibit frequency behaviors similar to the corresponding scattering coefficients: particularly, abrupt changes in phase by 180°near the resonant frequencies. By studying the behavior of pressure in the fluid scatterer, the physics of the theory has been further understood. Using the method studied and developed in this paper, nondestructive characterization of fluid inclusions in elastic media is expected to become more reliable.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.171-174
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• 2004

표적강도는 수중 산란체의 능동 탐지 확률을 좌우하는 중요한 변수중 하나이며 산란체의 기하학적 형상에 의해 결정이 되기 때문에 수치해석을 통한 해석 및 예측이 가능하다. 수치해석 기법은 현재 여러 가지가 알려져 있으며, 그중 Kirchhoff approximation이 다른 해석 기법에 비해 거울면 반사특성의 산란해석에 적합하며, 프로그램으로의 적용이 용이하다는 장점으로 인해 많이 사용되고 있다. 본 연구에서는 이러한 장점에 의거하여 Kirchhoff approximation을 이용하여 표적강도 수치해석 프로그램을 개발 및 검증하였다. 프로그램의 성능 검증은 원통형 산란체에 대한 이론해 검증과 원통형 실험 산란체를 통한 실험 검증을 수행하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.6
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• pp.939-945
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• 2000

A cylindrical object buried in the lossy half space is reconstructed from the measured scattered fields above the lossy half space. The position, the size and the medium parameters i.e. relative dielectric constants and conductivity of the buried object as well as the medium parameters of the background lossy half space are obtained from the scattered fields by using the iterative inversion method and the optimization hybrid algorithm combining the genetic algorithm and the Levenberg-Marquardt algorithm. Illposedness of the inversion due to the measurement errors in the scattered fields are regularized by filtering out the evanescent modes in the spatial frequency spectrum domain.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.2 no.1
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• pp.63-70
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• 2003

Resonance Scattering Theory (RST) offers us an interpretation of the resonance phenomena in the scattered field. It is shown 1.hat the scattered field consists of the resonance and background components in the RST. The suitable background is necessary in order to obtain the resonance component. In this study, the background coefficients are investigated to obtain resonance components from electromagnetic scattering field for cylindrical object with different permittivities. We show some valid results valid for two models; cavity and dielectric cylinder.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.113-117
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• 2002

최근 산란함수의 곱셈전개에 근거를 둔 새로운 공명 산란이론이 개발되어 공명성분의 크기와 위상을 수치적으로 정확하게 얻게 해 주었다. 또한 음파분야에서는 공명스펙트럼을 얼기 위해 MIIR 라는 실험방법을 개발되어 사용하여 왔다. 본 논문에서는 원통형 유전체에 의한 산란장 문제에 공진 산란이론을 적용하여 공진 주파수를 얻고, MIIR 의 실험 모델에 수치 해석방법인 FDTD를 적용하여 이로부터 역으로 유전율 등에 관한 정보를 얻기 위한 산란장 스펙트럼을 예측하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.1
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• pp.87-93
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• 2002

The previous RST postulates that the scattering field, within each modal partial wave, comprise of the resonance and the background components. The new RST is recently developed by the product expansion of the scattering functions in the field of acoustics. The new formulation suggests that the scattering coefficients consist of resonance, non-resonance, and their interactional portions. In the scattering problems of acoustic waves, the moduli and phase of the resonance coefficient are obtained correctly by the new RST. In our recent works the new RST was successfully applied to the scattering problem of electromagnetic waves for coated conducting cylinder and sphere. In this paper, the new RST is extended to the 2-dimensional scattering problem of electromagnetic waves for a homogeneous dielectric cylinder, and the numerical results are compared with the previous RST.

• Journal of radiological science and technology
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• v.14 no.2
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• pp.45-53
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• 1991

SPECT 영상에서 콤프톤 산란 광자는 공간분해능의 감소와 그 양을 측정하는데 있어 정확성과 정밀성을 감소시킨다. 이와같은 콤프톤 산란의 영향을 감소시키기 위하여 사용하는 대부분의 보정방법은 선원의 위치로부터 거리의 단일지수함수로 대칭인 산란분포함수를 고려하게 된다. 본 연구는 균등 및 불균등 산란에 대한 산란분포함수를 얻기 위하여 보다 현실적인 접근방법을 시도하였다. 산란 및 비산란광자의 공간분포와 에너지분포를 얻기 위하여 뼈, 폐, 물의 균등 및 불균등 분포로 된 원통형의 팬톰 속에 $^{99m}Tc$의 선선원 및 점선원을 놓고 Monte Carlo Simulation을 하였으며, 깊이의 함수, media의 접촉영역으로부터 선원거리 및 산란체의 밀도의 변화로 표현한 산란분포함수(SDF)를 얻었다. 산란분포함수는 균등한 뼈, 폐, 물에서는 선원위치로부터 거리의 단일지수함수(single exponential functions)로 대칭으로 나타났으며, 두 물체의 조합에서는 2중지수함수(dual exponential functions)로 비대칭으로 나타났다. 산란분율은 20% window photopeak에서 총 계수의 8%에서 53%까지 다양한 변화가 있었으며, 지수함수의 기울기는 $0.1{\sim}0.9\;cm^{-1}$의 범위로 나타났다. 불균등 산란체에서 얻은 산란분포함수는 SPECT 영상에 있어 콤프톤 산란의 감소에 대한 보다 정확한 보정방법의 개발에 필요한 정보를 제공할 것이다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.7
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• pp.647-652
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• 2016

Guided waves can be used for the inspection of long range pipelines. Surface corrosion is often found as a major defect type in pipelines. The reciprocity relation is a well-established theorem by which one can simplify complicated mathematical expressions. The approach has been already applied to plate and half-space structures to obtain the closed-form solutions of scattered amplitude. However, results for the case of cylindrical structures have not been reported yet. In this paper, the scattering of torsional waves, which is widely used in commercial applications, is explored by the reciprocity theorem approach. Obtaining closed-form solutions of the amplitudes of propagating waves is much simplified by using the reciprocal relation. The scattered amplitudes for elliptical and rectangular defect shapes are calculated with respect to defect depth and width, at frequencies between 0 and 500 kHz. The amplitude shows the periodic result as a function of frequency. The derived closed-form solutions can play a significant role in quantitative signal interpretation.