• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.4
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• pp.667-673
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• 2000

This paper presents the modeling method of nonlinear circuits with lumped elements by using a hybrid Haar -wavelet MRTD/FDTD techniques. To analyze nonlinear circuits with lumped elements, the Haar-wavelet MRTD scheme is applied to the entire structure of interest and the conventional FDTD scheme is locally used to describe the characteristics of the lumped elements. To validate the scheme, microstrip structure with lumped elements and a single diode mixer are simulated.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.130-134
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• 2000

본 논문에서는 확장된 시간영역 유한차분법(Extended finite difference time domain method)을 이용하여 마이크로파 중폭기를 해석하였다. 회로에 포함되어 있는 능동 소자는 고주파 등가 회로를 이용하여 모델링 하였다. 고주파 등가 회로를 통하여 계산한 게어트와 드레인의 전류를 FDTD의 전계 계산식에 첨가향으로개 마이크로스트립 회로의 전자기파와 능동 소자와의 상호 작용을 특성 지었다. 해석 결과는 주파수 영역 회로 해석법(Frequency-domain circuit analysis)을 이용한 결과와의 비교를 통하여 정확성을 입증했다.

• 한국전산유체공학회:학술대회논문집
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• 1995.10a
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• pp.197-202
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• 1995

비정상(unsteady) 압축성(compressible) 유동에 의한 공력음향(aeroacoustics)을 모사하여 공력소음원을 해석하기 위해서는 고차(high order)의 정확도와 높은 해상도(resolution)를 가지며, 상대적으로 계산시간을 많이 필요로 하지 않는 외재적(explicit) 유한차분법이 필수적으로 요구된다. 이것은 주어진 차분방식과 격자계로써 공간과 시간상에 존재하는 미소크기의 파동성분들을 충분히 구현하여야 만족할 만한 수치해를 얻을 수 있기 때문이다. 본 연구에서는, 그러한 유한차분법 중 최근에 관심의 대상이 되고있는 삼각(tridiagonal)또는 오각(pentadiagonal) 집적유한차분법(compact finite difference scheme)이 최대의 해상도를 갖도록 하는 수학적인 방법을 개발하고, 이 방법으로써 새롭게 집적유한차분법을 최적화하였다. 개발된 최적화 방법은, 푸리에 해석법(Fourier analysis)을 통하여 파동수(wavenumber) 영역에서 수학적으로 계산된 위상오차(phase error)를 최소화하는 것이며, 이러한 개념과 방법은 본 연구에서 처음으로 집적유한차분법에 적용되었다. 여러가지 절단정확도(truncation order)에 대해서 최적화 된 집적유한차분법들이 실제 공간과 시간상에서 보여주는 정확도와 오차특성을 알아보기 위하여, 이 방법들을 1차원 선형파동방정식에 적용하였고, 이 결과를 통하여 가장 정확하고 효과적인 절단정확도의 집적유한차분법을 선별하였다. 특히, 오각(pentadiagonal)법에 비해 더욱 효율적인 6차 삼각(tridiagonal)법을 1차원 Euler방정식에 적용하여, 비선형 파동에 대한 모사를 수행할 수 있었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.8
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• pp.1595-1611
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• 1994

In this paper, the numerical wave propagation properties of the finite difference-time domain(FD-TD) method is investigated as a discrete model describing electromagnetic(EM) wave propagation phenomena. The leap-frog approximation of Maxwell's curl equations in time-space simulates EM wave propagation in terms of the numerical characteristic and the domain of dependence. A geometrical interpretation of the FD-TD numerical procedure is presented. The numerical dispersion error due to the leap-frog approximation and its dependence on the stability factor are illustrated. The FD-TD method using the leap-frog approximation is inherently a descriptive model. Thus, not only any physical picture about EM wave propagation phenomena can be drawn through this model, but also physical or engineering parameters in the frequency domain can be extracted from descriptive results. E-plane filter characteristics in the WR-28 rectangular waveguide and reflection property of an inductive iris in the WR-90 rectangluar waveguide extracted from simulation of the FD-TD model is included.

• Geophysics and Geophysical Exploration
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• v.6 no.2
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• pp.77-86
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• 2003

We designed a new time-domain, finite-difference, elastic wave modeling technique, based on a displacement formulation. which yields nearly correct solutions to Lamb's problem. Unlike the conventional, displacement-based, finite-difference method using a node-based grid set (where both displacements and material properties such as density and Lame constants are assigned to nodal points), in our new finite-difference method, we use a cell-based grid set (where displacements are still defined at nodal points but material properties within cells). In the case of using the cell-based grid set, stress-free conditions at the free surface are naturally described by the changes in the material properties without any additional free-surface boundary condition. Through numerical tests, we confirmed that the new second-order finite differences formulated in the cell-based grid let generate numerical solutions compatible with analytic solutions unlike the old second-order finite-differences formulated in the node-based grid set.

• Geophysics and Geophysical Exploration
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• v.20 no.3
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• pp.121-128
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• 2017

Interpretation of time-domain electromagnetic (TEM) data has been made mostly based on one-dimensional (1-D) inversion scheme in Korea. A proper interpretation of TEM data should employ 3-D TEM forward and inverse modeling algorithms. This study developed a 3-D TEM modeling algorithm using a finite difference time-domain (FDTD) method with staggered grid. In numerically solving Maxwell equations, fictitious displacement current is included based on an explicit FDTD method using a central difference approximation scheme. The developed modeling algorithm simulated a small-coil source configuration to be verified against analytic solutions for homogeneous half-space models. Further, TEM responses for a 3-D anomaly are modeled and analyzed. We expect that it will contribute greatly to the precise interpretation of TEM data.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.9
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• pp.1847-1853
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• 2011

Analysis of an indoor propagation channel has conventionally used the ray-tracing method. But, in this paper, we had modelling the channel for three dimensional indoor structure by the finite difference time domain method for three dimensional full wave analysis. An excitation signal of the FDTD method used plane wave. The plane wave was excited using the total field/scattered field method. And absorbing boundary condition used the perfectly matched layer method with 7 layers. An living room for the simulation of indoor channel modeling is surrounded the wall that be composed of the wood, the conductor, the glass and concrete. When there are furniture in the living room or not, it were simulated, respectively. As simulation results, we could identify the fading effect of multipath at indoor propagation environment, calculated mean excess delay and rms delay spread for the receiver design.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.9
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• pp.1975-1984
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• 1997

In this paper, we analyzed the frequency characteristics and the crosstalk of the adjacent parallel lines and the crossed lines in high-speed packaging interconnections by using the three-dimensional finite difference time domain (3D FDTD) method. To analyze the actual crosstalk phenomena in the transmission of the high-speed digital sgnal, the step pulse with fast rise time was used for the source excitation signal instead of using the Gaussian pulse that is generally used in FDTD. To veify the theoretical resutls, the experimental interconnection lines that were fabricated on the Duroid substrate($\varepsilon_{r}$=2.33, h=0.787 [mm]) were tested by TDR(time domain reflectometry). The results show good agreement between the analyzed results and the tested outcomes.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2005.11a
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• pp.169-174
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• 2005

In this paper, we proposed a new algorithm of the inverse scattering for the reconstruction of unknown dielectric scatterers using the finite-difference time-domain method and the design sensitivity analysis. We introduced the design sensitivity analysis based on the gradient for the fast convergence of the reconstruction. By introducing the adjoint variable method for the efficient calculation, we derived the adjoint variable equation. As an optimal algorithm we used the steepest descent method and reconstructed the dielectric targets using the iterative estimation. To verify our algorithm we will show the numerical examples for the two-dimensional $TM^2$ cases.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.4
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• pp.653-660
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• 1998

The purpose of this paper is to analyze the electromagnetic field characteristics of microstrip array antenna with the FDTD(finite difference-time domain method). Finite difference equations of Maxwell's equations are defined in rectangular coordinate systems. To simulate the unbounded problem like a free space, the Mur's absorbing boundary condition is also used. After modeling the microstrip array antenna with the grid structure, the transient response of the field distribution is depicted in the time domain.