• Journal of Welding and Joining
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• 제16권2호
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• pp.40-47
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• 1998

In the present study, depressions of the GMA weld pool due to the impact of droplet are numerically investigated. The numerical simulation is conducted on the basis of the Navier-Stokes equation and the volume of fluid(VOF) functions. The kinetic energy of transferring droplet makes a depression of the weld pool surface. The surface active element affects the depression of the weld pool. The droplets transferred efficiently to the bottom of the weld pool, along with electromagnetic force make the finger shape penetration at the high current GMAW.

• Current Optics and Photonics
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• 제2권4호
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• pp.378-382
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• 2018

In most previous investigations of plasmonic and metamaterial applications, the metallic film has been regarded as a perfect electrical conductor. Here we demonstrate the resonance characteristics of THz metamaterials fabricated from metal film that has a finite dielectric constant, using finite-difference time-domain simulations. We found strong redshift and spectral broadening of the resonance as we decrease the metal's plasma frequency in the Drude free-electron model. The frequency shift can be attributed to the effective thinning of the metal film, originating from the increase in penetration depth as the plasma frequency decreases. On the contrary, only peak broadening occurs with an increase in the scattering rate. The metal-thickness dependence confirms that the redshift and spectral broadening occur when the effective metal thickness drops below the skin-depth limit. The electromagnetic field distribution illustrates the reduced field enhancement and reduced funneling effects near the gap area in the case of low plasma frequency, which is associated with reduced charge density in the metal film.

• ETRI Journal
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• 제28권2호
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• pp.247-249
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• 2006

In the development of a new wireless communications system, a versatile and accurate radio channel for indoor communications is needed. In particular, the investigation of radio transmission into buildings is very important. In this letter, we present an improved three-dimensional electromagnetic wave propagation prediction model for indoor wireless communications that takes into consideration building penetration loss. A ray tracing technique based on an image method is also employed in this study. Three-dimensional models can predict any complex indoor environment composed of arbitrarily shaped walls. A speed-up algorithm, which is a modified deterministic ray tube method, is also introduced for efficient prediction and computation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1518-1519
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• 2007

본 논문에서는 두 개의 무한도체 평판에 폭이 좁은 개구가 존재할 때, 개구를 통해서 침투하는 침투전자파의 크기를 두 무한도체 평판사이에 여러 가지 특성을 가지는 손실판을 장하하여 개구면 전계분포를 제어하여 침투 전자파의 크기를 저감시키는 방법을 제안하고 있다. 개구면에 평면파가 입사할 때, 손실판에 의해 개구면 전계분포가 제어된다. 두 개의 무판도체 평판 사이에 손실판을 장하하면 개구면의 전계분포 및 침투전자파가 효과적으로 제어됨을 확인하고 있다.

• 한국전자파학회논문지
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• 제24권1호
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• pp.98-105
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• 2013

본 논문에서는 초광대역 벽 투과 레이더를 이용한 벽 내부 진단에 대한 유한차분 시간영역(finite-difference time-domain, FDTD) 시뮬레이션과 데이터 처리 기술에 대한 연구를 소개한다. 본 연구에서는 2차원 FDTD 기법을 이용하여 실제 측정과 유사한 조건으로 시뮬레이션을 수행하기 위해 우선 전파의 감쇄, 투과 특성, 해상도 등을 고려하여 0.3~7 GHz의 초광대역을 갖는 반대 극성 비발디 안테나(anti-podal vivaldi antenna)를 설계/제작하였다. 다음으로 제작된 안테나의 방사 패턴을 측정한 후 이것을 FDTD 시뮬레이션의 소스로 사용하여 콘크리트 벽 경계면과 벽 내부의 금속으로부터 반사된 데이터를 얻었다. 다음으로 이 데이터를 처리하고 레이더 영상을 생성하여 벽 내부를 관찰하였다. FDTD 시뮬레이션에서는 일반적으로 사용되고 있는 등방성 점 소스와 다항식으로 측정된 방사 패턴을 근사화하여 소스로 적용한 2가지 경우에 대해 비교하였으며, 그 결과, 안테나 패턴을 적용했을 경우 등방성 점 소스를 사용한 경우에 비해 최대 약 2.5 dB 높은 신호 대 잡음비를 얻을 수 있었다.

• 한국전자파학회논문지
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• 제19권2호
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• pp.200-206
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• 2008

군 전술이 운영되는 산악 지형에 WiBro 시스템을 도입하기 위해서는 산악 지형에 대한 전파 예측 모델이 필요하다. 기존의 전파 모델은 도심 지역에 대한 모델이 대부분이며, 도심 지역과는 전파 환경이 다른 산악 지형에 대한 전파 모델은 부족하다. 본 논문에서는 군 전술 환경의 주를 이루는 산악 지형을 전파의 기본 메커니즘을 바탕으로 개활지, 수풀 지역, 산마루 회절 지역으로 분류하였으며, 분류된 환경에 대하여 측정을 수행하였다. 측정 결과를 바탕으로 모델링을 수행하였으며, 모델링 결과로부터 산악 지형에 적합한 전파 모델을 제시하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 3차
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• pp.24-30
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• 2010

The void ratio and elastic moduli are design parameters used in geotechnical engineering to understand soil behavior. Elastic and electromagnetic waves have been used to evaluate the various soil characteristics due to high resolution. The objective of this study is to evaluate the void ratio and elastic moduli based on elastic wave velocities and electrical resistivity. The Field Velocity Resistivity Probe (FVRP) is developed to obtain the elastic and electromagnetic wave profiles of soil during penetration. The Piezoelectric Disk Elements (PDE) and Bender Elements (BE) are used as transducers for measuring the elastic wave velocities such as compressional and shear wave velocities. The Electrical Resistivity Probe (ERP) is also installed for capturing the electrical resistivity profile. The application test is carried out on the southern coast of the Korean peninsula. The field tests are performed at a depth of 6~20 m, at 10 cm intervals for measuring elastic wave velocities and at 0.5cm intervals for measuring electrical resistivity. The elastic moduli such as constraint and shear moduli are calculated by using measured elastic wave velocities. The void ratios are also evaluated based on the elastic wave velocities and the electrical resistivity. Furthermore, the converted void ratios by using FVRP are compared with the volumetric void ratio obtained by a standard consolidation test. The comparison shows that the void ratios based on the FVPR match the volume based void ratio well. This study suggests that the FVRP may be a useful device to effectively determine the elastic moduli and void ratio in the field.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.32-37
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• 2001

As increasing underground facilities, more effective management is needed nowadays. It is important to get an accurate information of underground facilities to manage that, so some methods of detecting location - electromagnetic induction method, ground penetration radar method, sonic method - are used to obtain the information of underground facilities. In this study, a magnetic method to detect underground facilities was developed. In the magnetic method, underground facilities are detected by a detector and the magnetic marker which is a permanent magnet and used to marking the location by attaching underground facilities. A proper characteristic of the magnetic marker was optimized by maxwell 20 magnetic field analysis tool, a test field was constructed with the magnetic marker, PVC pipe, and steel pipe under ground 1.5m, and the detector was made by modifying a common ferromagnetic detector. Magnetic strengths of the magnetic marker were measured by the detector at each location in the test field, and analyzed by magnetic field analysis tool in the same condition. In the result, the underground pipes were detectable within the deviation ${\pm}20cm$ at PVC pipe and ${\pm}10cm$ at steel pipe respectively. The steel pipe was more detectable by ferromagnetism. The developed magnetic method can be applied to maintain and manage underground facilities.

• 한국정밀공학회지
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• 제20권9호
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• pp.63-69
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• 2003

As increasing underground facilities, more effective management is needed nowadays. It is important to get an accurate information of underground facilities to manage that, so some methods of detecting location - electromagnetic induction method, ground penetration radar method, sound wave method - are used to obtain the information of underground facilities. In this study, a magnetic method to detect underground facilities was developed. In the magnetic method, underground facilities are detected by a detector and the magnetic marker which is a permanent magnet and used to marking the location by attaching underground facilities. A test field was constructed for experiment with the magnetic marker, PVC pipe, and steel pipe under ground 1.5m, and a ferromagnetic detector was used for measurement. Magnetic strengths of the magnetic marker were measured by the detector at each location in the test field, and analyzed by magnetic field analysis tool in the same condition. In the result, the underground pipes of 1.5m below were detectable within the deviation $\pm$0.2m. When For applying this method, it should be considered that ferromagnetic materials around the detector could affect a measured value.

• Journal of the korean society of oceanography
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• 제36권1호
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• pp.1-8
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• 2001

An in-situ four-electrode contact resistivity probe system was designed, and field-tested in submarine sediments. Seismic survey was also performed to support and compare the results of electric survey. The probe was designed to be driven to selected depths below the seafloor using a Vibracore system. The four insulated electrodes were, spaced equidistant across the wedge, were extended beyond the probe tip to minimize effects of sediment disturbance by the wedge insertion. In-situ measurements of resistivity were recorded on board by precision electronic equipment consisting of signal generators and processors, and by temperature-monitoring systems. Overall limits of Uncertainty at respective depths below the seafloor are up to ${\pm}$10 of the measured values. Best estimates of conductivity are considered to be ${\pm}$3 percent of the reported values. Resistivity measurements were made at six sites in carbonate sediments to a maximum depth of penetration of about 5 m. Average values of conductivity range between 0.88 and 1.21 mho/m. The results show the seabed is composed of alternating layers of relatively high-conductivity material (0.8 to 1.4 mho/m) in thicknesses of more or less one meter and layers about 30 cm thick having relatively low conductivities (0.4 to 0.8 mho/m).