• Title/Summary/Keyword: Green's function

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Time-reversal microwave focusing using multistatic data

  • Won-Young Song;Soon-Ik Jeon;Seong-Ho Son;Kwang-Jae Lee
    • ETRI Journal
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    • v.46 no.2
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    • pp.333-346
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    • 2024
  • Various techniques for noninvasively focus microwave energy on lesions have been proposed for thermotherapy. To focus the microwave energy on the lesion, a focusing parameter, which is referred to as the magnitude and phase of microwaves radiated from an external array antenna, is very important. Although the finite-difference time-domain (FDTD)-based time-reversal (TR) focusing algorithm is widely used, it has a long processing time if the focusing target position changes or if optimization is needed. We propose a technique to obtain multistatic data (MSD) based on Green's function and use it to derive the focusing parameters. Computer simulations were used to evaluate the electric fields inside the object using the FDTD method and Green's function as well as to compare the focusing parameters using FDTD- and MSD-based TR focusing algorithms. Regardless of the use of Green's function, the processing time of MSD-based TR focusing algorithms reduces to approximately 1/2 or 1/590 compared with the FDTD-based algorithm. In addition, we optimize the focusing parameters to eliminate hotspots, which are unnecessary focusing positions, by adding phase-reversed electric fields and confirm hotspot suppression through simulations.

GREEN'S FUNCTION APPROACH TO THERMAL DEFLECTION OF A THIN HOLLOW CIRCULAR DISK UNDER AXISYMMETRIC HEAT SOURCE

  • GAIKWAD, KISHOR R.;NANER, YOGESH U.
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.25 no.1
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    • pp.1-15
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    • 2021
  • A Green's function approach is adopted to solve the two-dimensional thermoelastic problem of a thin hollow circular disk. Initially, the disk is kept at temperature T0(r, z). For times t > 0, the inner and outer circular edges are thermally insulated and the upper and lower surfaces of the disk are subjected to convection heat transfer with convection coefficient hc and fluid temperature T∞, while the disk is also subjected to the axisymmetric heat source. As a special case, different metallic disks have been considered. The results for temperature and thermal deflection has been computed numerically and illustrated graphically.

Influence of impulsive line source and non-homogeneity on the propagation of SH-wave in an isotropic medium

  • Kakar, Rajneesh
    • Interaction and multiscale mechanics
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    • v.6 no.3
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    • pp.287-300
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    • 2013
  • In this paper, the effect of impulsive line on the propagation of shear waves in non-homogeneous elastic layer is investigated. The rigidity and density in the intermediate layer is assumed to vary quadratic as functions of depth. The dispersion equation is obtained by using the Fourier transform and Green's function technique. The study ends with the mathematical calculations for transmitted wave in the layer. These equations are in complete agreement with the classical results when the non-homogeneity parameters are neglected. Various curves are plotted to show the effects of non-homogeneities on shear waves in the intermediate layer.

SH-wave propagation in a heterogeneous layer over an inhomogeneous isotropic elastic half-space

  • Kakar, Rajneesh
    • Earthquakes and Structures
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    • v.9 no.2
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    • pp.305-320
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    • 2015
  • The present paper is devoted to study SH-wave propagation in heterogeneous layer laying over an inhomogeneous isotropic elastic half-space. The dispersion relation for propagation of said waves is derived with Green's function method and Fourier transform. As a special case when the upper layer and lower half-space are homogeneous, our derived equation is in agreement with the general equation of Love wave. Numerically, it is observed that the velocity of SH-wave increases with the increase of inhomogeneity parameter.

Analysis of Coplanar Waveguide Discontinuities Using Accurate Closed-Form Green's function (정확한 Closed-Form 그린함수를 이용한 코플래너 도파로 불연속 해석)

  • Kang, Yeon-Duk;Song, Sung-Chan;Lee, Taek-Kyung
    • Journal of Advanced Navigation Technology
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    • v.7 no.2
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    • pp.180-190
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    • 2003
  • By using accurate closed-form Green's functions obtained from real-axis integration method, the full-wave analysis of CPW discontinuities are performed in space domain. In solving MPIE(Mixed Potential Integral Equation), Galerkin's scheme is employed with the linear basis functions on the triangular elements in air-dielectric boundary. In the singular integral arising when the observation point and source point coincides, the surface integral is transformed into the line integral and the integral is evaluated by regular integration. By using the Green's function from the real-axis integration method, the discontinuities are characterized accurately.

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A four-port stripline circulator using a single ferrite disk (단일 페라이트 공진기를 이용한 4단자 스트립라인 서큘레이터)

  • Kim, Hye-Jin;Nam, Min-Hee;Lee, Jae-Hyun
    • Journal of Satellite, Information and Communications
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    • v.4 no.2
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    • pp.52-56
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    • 2009
  • The design method of a four-port stripline circulator with a single ferrite disk is proposed using Green's function method. The four-port circulator gives the flexibility of the design of the communication system. Two cascaded three-port circulators has been used as a four-port circulator. However, if a four-port circulator with a single ferrite disk replace the present four-port circulator, then it will give less weight and volume and so has the advantage in satellite application.

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A New Analysis of Waveguide Structure Using the Iterative Green's Function Method Applicable to the Electromagnetics Instruction (전파 교육에 적용할 수 있는 반복 그린함수 방법을 이용한 전자파 도파관 구조의 새로운 해석법)

  • 조용희
    • Proceedings of the Korea Contents Association Conference
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    • 2003.05a
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    • pp.403-405
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    • 2003
  • An iterative Green's function method (IGFM) is introduced to analyze complex electromagnetic waveguide structures in view of the university student. The IGFM utilizes the Green's function and iteration scheme. The physical mechanism with simple mathematical equations is used to formulate the IGFM. Scattering characteristics of a standard E-plane T-junction in a parallel-plate waveguide are theoretically investigated in terms of the IGFM. Numerical computations illustrate the characteristics of resection and transmission powers versus frequency. A dominant-mode solution is presented and compared with the higher-mode solutions.

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Green's Function of Semi-Infinite Straight Interfacial Crack Problems (반무한 직선 계면균열문제에 관한 그린함수)

  • 최성렬;강기주
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.5
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    • pp.1530-1537
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    • 1991
  • 본 연구에서는 반무한 직선 계면균열의 상하면에 임의로 분포하는 어떠한 하 중에 대해서도 그 해석이 가능한 그린함수(Green's function)를 구하고자 한다. 이 를 위하여 반무한 직선 계면균열상의 임의의 한 점에 평면 집중하중이 작용하는 문제 와 비평면 집중전단하중이 작용하는 문제를 각각 택하였고, 이때 계면균열의 선단은 열려있다고 가정하였다. 이 문제를 풀므로써 균열선단부근의 응력성분을 결정하고 이로부터 그린함수의 의미를 지니는 응력강도계수에 대한 폐형해를 얻었다.

EXPLICIT EXPRESSION OF THE KRAWTCHOUK POLYNOMIAL VIA A DISCRETE GREEN'S FUNCTION

  • Kim, Gil Chun;Lee, Yoonjin
    • Journal of the Korean Mathematical Society
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    • v.50 no.3
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    • pp.509-527
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    • 2013
  • A Krawtchouk polynomial is introduced as the classical Mac-Williams identity, which can be expressed in weight-enumerator-free form of a linear code and its dual code over a Hamming scheme. In this paper we find a new explicit expression for the $p$-number and the $q$-number, which are more generalized notions of the Krawtchouk polynomial in the P-polynomial schemes by using an extended version of a discrete Green's function. As corollaries, we obtain a new expression of the Krawtchouk polynomial over the Hamming scheme and the Eberlein polynomial over the Johnson scheme. Furthermore, we find another version of the MacWilliams identity over a Hamming scheme.