• Proceedings of the Korea Electromagnetic Engineering Society Conference
• /
• 2001.11a
• /
• pp.300-303
• /
• 2001

개방단말 동축선 프로브는 임의의 매질에 접촉하여 복소 유전율을 구하므로 사용이 용이한 측정법이다. 복소 유전율의 측정 과정은 두 단계로 구성된다. 먼저 프로브의 개구면을 미지의 매질에 접촉시켜서 반사계수를 측정한다. 다음에는 반사계수를 환산모델에 대입하여 복소 유전율을 구한다. 그러나 실제 측정시 발생하는 오차들에 대해 취약하다는 단점을 가지고 있다. 정확성을 떨어뜨리는 주요 오차 요인으로는 프로브의 개구면과 측정매질 사이의 공극으로 인한 불완전 접촉오타와 프로브의 제작 한계로 인한 오차를 들 수 있다. 본 논문에서는 이런 오차상황에서 유한 차분 시간영역법으로 반사계수를 계산하고나서 환산모델에 의해 복소 유전율로 환산함으로써 오차에 대한 환산모델들간의 안정성을 살펴보고자 한다.

• Proceedings of the Korean Society of Computer Information Conference
• /
• 2013.01a
• /
• pp.3-6
• /
• 2013

반도체 공정에서 소자의 제조 비용 감소를 위해 제조 공정 검증을 위한 시뮬레이션을 수행하게 된다. 이 시뮬레이션은 반도체 소자 내부의 물리량 계산을 통해 반도체 소자 내부의 불순물의 거동을 해석하게 된다. 이를 위해 사용되는 알고리즘으로 3차원적 형상을 표현하는 물리적 미분 미분방정식을 계산하게 되는데, 정확한 계산을 위해 유한 차분 시간 영역법(이하 FDTD)과 같은 수치해석 기법을 이용한다. 실제적으로 반도체 공정의 시뮬레이션에서 FDTD연산의 실행 시간은 90% 이상을 소요하게 된다. 이러한 연산에서 더욱 빠른 성능을 확보하기 위해 본 논문에서는 기존의 CUDA(Compute Unified Device Architecture)로 구현된 FDTD알고리즘을 OpenMP를 통한 다중 GPU제어를 이용하여 연산 수행시간을 감소하고, 그 결과물을 통하여 성능 향상도를 측정한다.

• Geophysics and Geophysical Exploration
• /
• v.3 no.2
• /
• pp.39-47
• /
• 2000

A great deal of computing time and a large computer memory are needed to solve wave equation in a large complex subsurface layers using the finite difference method. The computing time and memory can be reduced by decreasing the number of grid points per minimum wave length. However, the decrease of grids may cause numerical dispersion and poor accuracy. In this study we performed the grid dispersion analysis for several rotated finite difference operators, which was commonly used to reduce grids per wavelength with accuracy in order to determine the solution for the acoustic wave equation in frequency domain. The rotated finite difference operators were to be extended to 81, 121 and 169 difference stars and studied whether the minimum grids could be reduced to 2 or not. To obtain accuracy (numerical errors less than $1\%$) the following was required: more than 13 grids for conventional 5 point difference stars, 9 grids for 9 difference stars, 3 grids for 25 difference stars, and 2.7 grids for 49 difference stars. After grid dispersion analysis for the new rotated finite difference operators, more than 2.5 grids for 81 difference stars, 2.3 grids for 121 difference stars and 2.1 grids for 169 difference stars were needed. However, in the 169 difference stars, there was no solution because of oscillation of the dispersion curves in the group velocity curves. This indicated that the grids couldn't be reduced to 2 in the frequency acoustic wave equation. According to grid dispersion analysis for the determination of grid points, the more rotated finite difference operators, the fewer grid points. However, the more rotated finite difference operators that are used, the more complex the difference equation terms.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2000.05a
• /
• pp.147-151
• /
• 2000

This paper presents an analysis of a slot on the broad wall of a rectangular waveguide using the 3D FDTD method. In order to reduce the reflection loss, Mur's 2nd absorbing boundary condition is used. To realize the optimum design by FDTD, the effects of time step, excitation aperture size, analysis region and excitation position in model are derived. The analysis results are compared with the experimental results and they show a good agreement with each other.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2008.10a
• /
• pp.51-56
• /
• 2008

The waveform inversion for isotropic media has ever been studied since the 1980s, but there has been few studies for anisotropic media. We present a seismic waveform inversion algorithm for 2-D heterogeneous transversely isotropic structures. A cell-based finite difference algorithm for anisotropic media in time domain is adopted. The steepest descent during the non-linear iterative inversion approach is obtained by backpropagating residual errors using a reverse time migration technique. For scaling the gradient of a misfit function, we use the pseudo Hessian matrix which is assumed to neglect the zero-lag auto-correlation terms of impulse responses in the approximate Hessian matrix of the Gauss-Newton method. We demonstrate the use of these waveform inversion algorithm by applying them to a two layer model and the anisotropic Marmousi model data. With numerical examples, we show that it's difficult to converge to the true model when we assumed that anisotropic media are isotropic. Therefore, it is expected that our waveform inversion algorithm for anisotropic media is adequate to interpret real seismic exploration data.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.12 no.4
• /
• pp.521-531
• /
• 2001

This paper presents the extraction scheme of the scattered waves by a target above the ground using the buried antenna in a lossy and dispersive medium. The half wave dipole antennas are used to transmit and to receive a signal. The transmission line model as a feeding model is considered to take into account the effect of transmission line in a real system. The ground is modeled by the 2nd order Debye approximation with the dispersion and loss. PLRC algorithm and DPML as absorbing boundary condition are utilized to apply the 2nd order Debye approximation to FDTD. To extract the scattered wave, in addition, we employed the delay time extraction algorithm. The simulations are conducted to observe the variation of magnitude in scattered wave and detection of target position according to the change of moisture content of the lossy medium.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.48 no.11
• /
• pp.83-88
• /
• 2011

The spectral field data on the observation planes inside a mode stirred chamber have been computed by using the FDTD method. They can describe the directional dependence of all supported modes in the reverberation chamber (RC). Correlation coefficients have been found to evaluate the stirring effects. The correlation coefficients were obtained and compared for three different sizes of stirrers and statistical uniformity was investigated.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.3
• /
• pp.347-352
• /
• 2015

Time domain reflectometry (TDR) is widely used for wire failure detection. It transmits a pulse that is reflected at the boundaries of different characteristic impedances. By analyzing the reflected signal, TDR makes it possible to locate the failure. In this study, TDR was used to detect the water leakage at a pipe joint. A wire attached to the pipe surface was soaked by water when a leak occurred, which affected the characteristic impedance of the wet part, resulting in a change in the reflected signal. To infer the leakage from the TDR signal, we first developed a finite difference time domain-based forward model that provided the output of the TDR signal given the configuration of the transmission line. Then, by solving the inverse problem, the locations of the leaks were found.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.41 no.4
• /
• pp.29-40
• /
• 2004

This paper reports the frequency characteristics and the time response of parallel adjacent-transmission lines, crossed adjacent-transmission lines and parallel adjacent-transmission lines which are on the different planes by using FDTD-PML method. In the parallel adjacent-transmission lines, the crosstalks as a function of horizontal distance are calculated and in the crossed adjacent- transmission lines, the crosstalks as a function of vertical distance are simulated. Also, the crosstalks as functions of horizontal and vertical distances are measured and analyzed in the parallel adjacent-transmission lines which are on the different planes.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.29 no.3
• /
• pp.225-232
• /
• 2018

This paper proposed the optimization method of the extremely low numerical-dispersion finite-difference time-domain (ELND-FDTD) method based on the H(2,4) scheme for wideband and extremely accurate electromagnetic properties of lossy material, which has a constant conductivity and relative permittivity. The optimized values of three variables are calculated for the minimum numerical dispersion errors of the proposed FDTD method. The excellent accuracy of the proposed method is verified by comparing the calculated results of three different FDTD methods and the analytical results of the two-dimensional dielectric cylinder scattering problem.