• Journal of electromagnetic engineering and science
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• 제3권1호
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• pp.57-61
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• 2003

The effects of high frequency noises on a perturbational inversion technique for a stratified dispersive medium are investigated in this paper. It is shown that the perturbational solution becomes unstable under high frequency noises. The physical origin of this instability is described. In order to enhance the robustness of the perturbational inverse scattering solution, a parametric inversion technique is introduced. The examples for the 2-pole and the 3-pole reflection coefficients are compared and contrasted, and improvement of the robustness of the solutions is shown.

• 한국전자파학회논문지
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• 제22권10호
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• pp.1005-1011
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• 2011

본 논문에서는 일반적인 분산 매질의 전자기 과도 응답을 해석하기 위하여 헬름홀츠 방정식에 근거한 MODFDM(Marching-on-in-Degree Finite Difference Method) 기법을 제안한다. 라게르 함수의 특성을 이용하여 시간에 대한 미분항과 상승 적분(convolution integral)의 근사를 해석적으로 처리하였다. 본 기법의 기본적인 독창성은 전장과 전속 밀도, 유전율 등을 모두 라게르 함수로 전개한 다음, 갤러킨 시험 과정을 적용하여 시간 변수를 완전히 제거하였을 뿐만 아니라, 기존의 FDTD(Finite Difference Time-Domain) 방법과 달리 최종 계산식에 공간적인 유한 차분만을 적용하는데 있다. 일반적인 분산 매질의 해석에 적용 가능함을 보이기 위하여 대표적인 드바이, 드루드 및 로렌츠 분산 매질에 대한 전자기 과도 응답을 수치예로 보인다.

• 한국광학회지
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• 제16권6호
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• pp.494-499
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• 2005

코어가 확산된 단일모드 광섬유와 외부 물질 사이의 분산 특성의 차이를 이용하여 차단 특성이 우수한 단파장 통과 필터(short-pass filter)를 구현하였다. 두 물질의 결합 방법으로 측면 연마 기법을 도입하였다. 실험 결과 소자의 대역경계 파장(band edge wavelength)은 코어의 확산 정도로 조절이 가능하였다. 일반 통신용 단일 모드 대신에 열확산 코어 확산 광섬유를 도입함으로써 더 예리한 파장응답을 얻을 수 있었다. 열광학 효과를 이용하여 경계 파장을 400nm 이상 가변 할 수 있음을 관측하였다.

• ETRI Journal
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• 제31권4호
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• pp.387-392
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• 2009

This paper introduces a novel parallel shift operator finite-difference time-domain (SO-FDTD) method for plasma in the dispersive media. We calculate the interaction between the electromagnetic wave of various frequencies and non-magnetized plasma by using the parallel SO-FDTD method. Then, we compare the results，which are calculated with serial and parallel SO-FDTD executions to obtain the speedup ratio and validate the parallel execution. We conclude that the parallel SO method has almost the same precision as the serial SO method, while the parallel approach expands the scope of memory and reduces the CPU time.

• 암석학회지
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• 제6권2호
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• pp.88-95
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• 1997

High pressure X-ray diffraction study was carried out on a polycrystalline graphite to investigate the phase transition(s) at room temperature. Energy dispersive X-ray diffraction method was employed using a Mao-Bell type diamond anvil cell with an Wiggler synchrotron Radiation at the National Synchrotron Light Source. Sodium chloride power was used as the internal pressure sensor for the high pressure determinations as well as the pressure medium for quasihydrostatic pressure environment. Graphite transforms into a hexagonal didose not agree with the previously reported observations and this phase persists when pressure is released down to 0.1 MPa. This result dose not agree with the previously reported observations and this discrepancy would be due to the kinetics in phase transition as well as the uniaxially oriented pressure field in the diamond anvil cell.

• 한국전자파학회논문지
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• 제9권4호
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• pp.483-490
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• 1998

The reflectivity of a grid ferrite electromagnetic wave absorber is analyzed using finite difference time domain (FDTD) method, which is usually used in anechoic chambers for EMI / EMS test. The frequency dispersive characteristics of ferrite medium and its boundary condition are modeled using magnetic flux in addition to E- and H-fields. By applying Floquets theorem, FDTD analysis of the grid ferrite absorber with periodic infinite array is simplified as a unit cell problem. The method of homogenization which is mainly utilized in the calculation of absorber reflectivity as a low frequency technique takes only into account volume fraction of the unit cell of the absorber except for the structure of medium geometry. However, the presented method in this paper can analyze the geometry effect of the unit cell with its medium characteristics up to high frequency region.

• 센서학회지
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• 제15권4호
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• pp.263-268
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• 2006

We have demonstrated a highly sensitive temperature sensor using an etched single mode fiber with a thermally expanded core region. Large core size of thermally expanded core facilitates access to evanescent wave by the wet etching. The etched region was surrounded by a low dispersive external medium with high thermo-optic coefficient. Due to the large difference between the dispersion property of the fiber and that of the external medium, the device reveals a cut-off properties at spectral region. The cut-off wavelength was shifted by the variations of the environmental temperatures because of thermo-optic effect of the external medium. The sensitivity of the fabricated device was found to be $45nm/^{\circ}C$.

• 한국전자파학회논문지
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• 제15권10호
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• pp.977-982
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• 2004

본 논문에서는 유한 시간 차분법(FDTD) 내에서 PLRC(Piecewise Linear Recursive Convolution)법을 이용한 분산성 물질에 대한 비등방성 흡수체(APML)를 제안한다. 제안된 흡수체는 비선형, 분산성 매질 해석시 무한 경계조건을 표현하기 위해 사용될 수 있다. 제안된 흡수체는 기존의 APML 정식화 과정에서 분산 특성을 고려한 것이며 PLRC법의 장점인 빠른 계산시간, 저 메모리 사용, 다극 감수율의 간편한 정식화 등의 장점을 가지고 있다. 개발된 분산성 APML은 드바이(Debye)매질과 로렌츠(Lorentz) 매질 등의 분산성 물질의 해석에 적용하였으며 수치실험을 통해 흡수경계에서 뛰어난 흡수율을 가짐을 보였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 C
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• pp.2348-2350
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• 2005

LHM (Left Handed Material)은 특정 주파수 범위에서 음의 유전율과 투자율을 가지는 물질이며 유효 유전율과 투자율은 분산 특성을 가지고 로렌츠(Lorentz) 물질과 비슷한 형태를 가진다. 본 논문에서는 FDTD (Finite Difference Time Domain) 법을 바탕으로 한 PLRC (Piecewise Linear Recursive Convolution) 법을 이용하여 LHM 내의 유효 전파특성을 모의한다. 모의실험 결과는 음의 유전율과 투자율을 가지는 주파수 범위를 보여준다.

• Geomechanics and Engineering
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• 제7권6호
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• pp.649-663
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• 2014

In past few years, the use of bacterial calcium carbonate precipitation (biocementation) has become popular as a ground improvement technique for sandy soil. However, this technique was not applied to organic soil. This study focused on bacterial calcium carbonate precipitation and its effect on permeability in organic soil. A special injection system was prepared for inducing bacterial solution to the samples. The bacterial solution supplied to the samples by gravity for 4 days in specific molds designed for this work. Calcite precipitation was observed by monitoring pH value and measuring amount of calcium carbonate. Change in the permeability was measured before and after biocementation. The test results showed that the pH values indicates that the treatment medium is appropriate for calcite precipitation, and amount of precipitated calcium carbonate in organic soil increased about 20% from untreated one. It was also found that the biocementation can be considered as an effective method for reducing permeability of organic soil. The results were supported by Scanning electron microscopy (SEM) analysis and energy-dispersive x-ray (EDX) analysis.