• Journal of electromagnetic engineering and science
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• 제9권1호
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• pp.46-52
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• 2009

This paper conducts a study on the frequency-dependent filtering and blocking effects of a variety of periodic structures, dubbed frequency selective surface(FSS). The periodic structures of interest are 1D and 2D repeated patterns of metal patches or slots sitting on the interface between the two different regions in the layered media which will show the capacitive or inductive behaviors and incorporated with the electromagnetic bandgap(EBG) geometry as another stratified media. Besides the normal substances so called double positive(DPS)-type in the layered media, metamaterials of double negative(DNG) are considered as layering components on the purpose of investigating the unusual electromagnetic phenomena. Frequency responses of transmission(absorption in terms of scattering) and reflection will be calculated by a numerical analysis which can be validated by the comparison with the open literature and demonstrated for the periodic structures embedding metamaterials or not. Most importantly, numerous examples of FSS will present the useful guidelines to have absorption or reflection properties in the frequency domain.

• 한국산학기술학회논문지
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• 제5권5호
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• pp.385-388
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• 2004

본 논문에서는 격자구조의 유전체에 수직으로 입사된 전자기파의 산란, 투과 특성을 얇은 위상 막 근사화 이론을 이용하여 분석하였다. 위상 막 근사화 이론은 격자구조가 입사되는 전자기파의 위상 변화만을 주는 것으로 간주하는 것으로 이를 이용하여 격자구조를 통과한 직후인 근거리 필드 분포를 TE 모드에서 계산하였다. 기존의 제시된 이론에 비해 비교적 간단하고 빠르게 산란 필드를 분석할 수 있다.

• 한국전자파학회논문지
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• 제10권1호
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• pp.109-121
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• 1999

본 논문에서는 HF 대의 대수주기 다이폴 안테나(LPDA: Log-Pericx:lic Dipole Antennas)와 변형된 대수 주기 다이폴 안테나(MLPDA: Mcx:lified Log-Periodic Dipole Antennas)를 대지의 매질 종류에 따라 자유공 간이나 완전도체에 놓인 것으로 큰사화하지 않고, 실제 대지의 매질을 고려하여 모멘트볍을 적용함으로써 복 사전계를 해석하였다 대지에 섣치된 LPDA와 MLPDA에 대하여 주파수. 안테나 높이, 경사각에 따른 복사 패턴과 이득의 변화를 나타내고 대지가 안테나 특성에 미치는 영향을 고찰하였다. 그 결과 MLPDA가 LPDA보다 주파수에 따른 복사패턴 및 이득의 변화가 적고 최대 빔 방향이 다소 높게 나타났으며, 또한 LPDA와 MLPDA 모두 대지의 매질 종류와 안테나의 높이가 안테나이득 변화에 주로 관계함을 확인하였다.

• 대한기계학회논문집B
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• 제21권12호
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• pp.1668-1678
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• 1997

Numerical analyses were performed to investigate the characteristics of regenerator in oscillating flow by using moving boundary method and Darcy model. In this work, periodic adiabatic boundary condition was suggested as the boundary condition of adiabatic part so that the effects of the thermal inertia of the wall could be considered. In carrying out numerical analyses, two models were applied and compared. One called isotropic model has the same thermal conductivity in radial and axial directions within a porous media. The other called aeolotropic model has different conductivity in each directions. Isotropic model could not show the advantage of energy reduction which needs to maintain constant wall temperature difference between heater and cooler. But aeolotropic model could simulate the reduction of energy consumption.

• 센서학회지
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• 제5권5호
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• pp.85-95
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• 1996

Based on the transmission of coupled gap solitons in nonlinear periodic media, we present an all-optical switching scheme which has a novel architecture and principle. The proposed switch with an extremely small switching element can be realized on a semiconductor waveguide. We here investigate the switching performance with a GaAs waveguide in order to give criteria for the experimental realization of the all-optical switching phenomena. We also suggest a variation of an index-matching scheme to solve the technical problem such as the input-energy coupling into a periodic waveguide.

• Journal of Communications and Networks
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• 제17권2호
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• pp.203-209
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• 2015

Although mobile applications are an essential characteristic of wireless sensor networks, most existing media access control (MAC) protocols focus primarily on static networks. In these protocols, fixed periodic neighbor discovery and schedule updating are used to connect and synchronize neighbors to provide successful data transmission; however, they cannot adapt to mobile speed variation and degrade the network performance dramatically. In this paper, we propose a mobile-supporting mechanism for MAC protocols, in which the decision to update the neighbors of a mobile node is made adaptively according to the mobile speed. Analysis and simulation results demonstrate that the mechanism efficiently avoids the disconnection of amobile node from its neighbors and achieves a better performance as compared with fixed periodic neighbor discovery.

• 전기전자학회논문지
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• 제25권1호
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• pp.32-36
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• 2021

This paper presents a novel collided tag signals's periodic characteristic based radio frequency identification (RFID) tag collision detection method for the ultra high frequency (UHF) RFID. The proposed method utilizes that periodicity of tag signals is maintained even under tag collision. In the proposed method, the correlation between received signal and reference edge signal is used. Simulation result shows that the detection performance using the proposed method is about 10 dB better than that of existing method. In addition, the detection performances with different magnitude difference, phase difference, delay, number of tags are analyzed.

• Environmental Engineering Research
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• 제24권3호
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• pp.456-462
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• 2019

Hydrocarbon contamination is among the most challenging problems in soil remediation. Electrokinetic method can be a promising method to remediate hydrocarbon-contaminated soils. Electrokinetic method consists of different transport phenomena including electro-migration, electrophoresis, and electroosmotic flow. Electroosmotic flow is the main transport phenomenon for hydrocarbon removal in soil porous media. However, the main component of hydrocarbons is the hydrophobic organic which indicates low water solubility; therefore, it makes the electroosmotic flow less effective. The objective of the present study is to enhance electrokinetic remediation of diesel-contaminated silty sand by increasing the solubility of the hydrocarbons in the soil and then increase the efficiency. For this purpose, sodium dodecyl sulfate (SDS) was used as a catholyte. In this content, SDS 0.05 M was used as catholyte and $Na_2SO_4$ 0.1 M was used as an anolyte. Low (1 V/cm) and high (2 V/cm) voltage gradients were used in periodic and continuous forms. The best removal efficiency was observed for high voltage gradient (2 V/cm) in a periodic form, which was 63.86. This result showed that a combination of periodic voltage application in addition to the employment of SDS is an effective method for hydrocarbon removal from low permeable sand.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2061-2066
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• 2007

Recently, ultra-lightweight materials with open, periodic cell structures take much attention owing to its potential for multi-functionality such as load bearing, thermal dissipation, and actuation. This paper presents experimental results on the hydraulic and heat transfer characteristics for the Wire-woven Bulk Kagome(WBK) composed of aluminum 1100 wires. The overall pressure drop and heat transfer of the WBK specimen have been experimentally investigated under forced air convection condition. The pressure loss and heat transfer performance of the aluminum WBK are compared with other heat dissipation media. It was shown that heat transfer depended on relative density and surface area density. Comparison with metal foams and other heat dissipation media such as packed beds, lattice frame materials, louvered fins, and other materials suggests that the aluminum WBK competes favorably with the best available heat dissipation media in heat transfer performance.

• 대한기계학회논문집B
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• 제32권1호
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• pp.15-22
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• 2008

Recently, ultra-lightweight materials with open, periodic cell structures take much attention owing to its potential for multi-functionality such as load bearing, thermal dissipation, and actuation. This paper presents experimental results on the fluid flow and heat transfer characteristics for the Wire-woven Bulk Kagome (WBK) composed of aluminum 1100 wires. The overall pressure drop and heat transfer of the WBK specimen was experimentally investigated under forced air convection condition. The pressure loss and heat transfer performance of the aluminum WBK were compared with other heat dissipation media. It was shown that heat transfer characteristics depended on relative density and surface area density. Comparison with metal foams and other heat dissipation media such as packed beds, lattice frame materials, louvered fins, and others suggests that the aluminum WBK competes favorably with the best available heat dissipation media in heat transfer performance.