• 한국전자통신학회논문지
• /
• 제2권4호
• /
• pp.199-202
• /
• 2007

본 논문에서는 UHF 대역(860~960 MHz의 수동 RFID 태그 안테나 제안하여 해석하였다. 제안한 안테나는 루프구조에 의한 UHF 대역 초소형 수동 RFID 태그 안테나이다. 제안한 안테나는 단일 평면 구조 형태로 인쇄 기판에 손쉽게 인쇄할 수 있어 생산비 절감을 통한 대량 생산이 용이하며, Pareto 유전자 알고리즘과 IE3D 시뮬레이션 툴로 최적화하여 안테나의 크기를 소형화 하였다. 최적화 한 RFID 태그 안테나의 성능을 검증하기 위하여 몇 개의 표본 안테나를 제작하고 반사 손실, 복사 효율, 복사 패턴 등을 측정하였다. 상용태그 와 고정형 리더 시스템을 이용하여 제작된 태그 안테나의 인식 거리를 측정하였고, 약 1~3 m의 인식거리를 가지는 것을 확인하였다.

• 대한전자공학회논문지TC
• /
• 제48권1호
• /
• pp.38-44
• /
• 2011

수중 환경의 복잡성 때문에 수중통신은 대기중에서의 통신과는 그 차이가 상당한 여러 가지 어려움들을 가지고 있다. 신호는 수중에서 많은 불규칙 소음들에 의해 저하된다. 뿐만 아니라 대역폭의 한계는 수중 통신에서 매우 큰 이슈이다. 그러므로 배열신호 처리 기법은 SNR을 개선에 적당하다. 이 논문에서 소스 추적기법에 기반한 수중 통신을 목적으로 하는 potential 기법을 제안하고자 한다. 또한 다중배열 소나를 이용한 새 추적 모델과 동 소나의 세부 구성을 제시했다. 실험들에서는 샘플 모델과 본 모델상에서 추적 결과의 차이점을 도출해 냈다. 실험 결과, 특히 수중환경에서 통신 문제들을 해결할 가능성이 수신기 구성이라는 것을 시연하였다.

• 천문학논총
• /
• 제19권1호
• /
• pp.129-133
• /
• 2004

In the past, radio astronomers have sought isolation from man-made signals by placing their telescopes in remote locations. These measures may no longer safeguard scientific observations, since NGSO satellite systems, particularly low-Earth orbit (LEO) systems, are usually designed to provide global or wide regional coverage. Further, radio astronomers have historically made their observations in the frequency bands allocated for their use by the member countries of the International Telecommunication Union (ITU). The science of radio astronomy could be adversely impacted by the deployment of large constellations of new non-geostationary orbiting (NGSO) satellites for telecommunications, navigation and Earth observation, and the proliferation of new, high-power broadcasting and telecommunication satellites in geostationary (GSO) orbits. Radio telescopes are extremely sensitive, and, in certain situations, signals from satellites can overwhelm the signals from astronomical sources. This paper describes the problem in detail and identifies ways to mitigate it without adversely affecting the continued vigorous growth of commercial space-based telecommunications.

• Journal of Electrical Engineering and Technology
• /
• 제10권3호
• /
• pp.1015-1024
• /
• 2015

This paper introduces a low cost, high efficiency, high performance three-phase unified power quality conditioner (UPQC) by using four-switch three-phase inverters (FSTPIs) and an extra capacitor in the shunt active power filter (APF) side of the UPQC. In the proposed UPQC, both shunt and series APFs are developed by using FSTPIs so that the number of switching devices is reduced from twelve to eight devices. In addition, by inserting an additional capacitor in series with the shunt APF, the DC-link voltage in the proposed UPQC can also be greatly reduced. As a result, the system cost and power loss of the proposed UPQC is significantly minimized thanks to the use of a smaller number of power switches with a lower rating voltage without degrading the compensation performance of the UPQC. Design of passive components for the proposed UPQC to achieve a good performance is presented in detail. In addition, comparisons on power loss, overall system efficiency, compensation performance between the proposed UPQC and the traditional one are also determined in this paper. Simulation and experimental studies are performed to verify the validity of the proposed topology.

• Journal of Power Electronics
• /
• 제16권2호
• /
• pp.436-446
• /
• 2016

A novel step-up DC-DC converter with a switched-coupled-inductor-capacitor (SCIC) which successfully integrates three-winding coupled inductors and switched-capacitor techniques is proposed in this paper. The primary side of the coupled inductors for the SCIC is charged by the input source, and the capacitors are charged in parallel and discharged in series by the secondary windings of the coupled inductor to achieve a high step-up voltage gain with an appropriate duty ratio. In addition, the passive lossless clamped circuits recycle the leakage energy and reduce the voltage stress on the main switch effectively, and the reverse-recovery problem of the diodes is alleviated by the leakage inductor. Thus, the efficiency can be improved. The operating principle and steady-state analyses of the converter are discussed in detail. Finally, a prototype circuit at a 50 kHz switching frequency with a 20-V input voltage, a 200-V output voltage, and a 200-W output power is built in the laboratory to verify the performance of the proposed converter.

• 대기
• /
• 제21권1호
• /
• pp.95-108
• /
• 2011

The effects of an apartment complex on flow and pollutant dispersion in an urban area are numerically investigated using a computational fluid dynamics (CFD) model. The CFD model is based on the Reynolds-averaged Navier-Stokes equations and includes the renormalization group k-${\varepsilon}$ turbulence model. The geographic information system (GIS) data is used as an input data of the CFD model. Eight numerical simulations are carried out for different inflow directions and, for each inflow direction, the effects of an apartment complex are investigated, comparing the characteristics of flow and dispersion before and after construction of the apartment complex in detail. The observation data of automatic weather system (AWS) is analyzed. The windrose analysis shows that the wind speed and direction after the construction of the complex are quite different from those before the construction. The construction of the apartment complex resulted in the decrease in wind speed at the downwind region. It is also shown that the wind speed increased partially inside the apartment complex due to the channeling effect to satisfy the mass continuity. On the whole, the wind speed decreased at the downwind region due to the drag effect by the apartment complex. As a result, the passive pollutant concentration increased (decreased) near the downwind region of (within) the apartment complex compared with that before the construction.

• 한국초등과학교육학회지:초등과학교육
• /
• 제39권3호
• /
• pp.353-368
• /
• 2020

This study analyzed the teacher's perception for influence of behavioral characteristics of scientifically-gifted students on general students in elementary school science class. To do this, we selected the eight elementary school teachers who were conducting the regular science classes including scientifically-gifted students belonging to the gifted education institutes in Seoul and conducted individual in-depth interviews. The analysis of the results reveal that the teachers mentioned seven behavioral characteristics of scientifically-gifted students in general elementary school science classes.: 'excellent in designing and performing experiments', 'playing a leading role in experiments', 'expressing their abundant prior knowledge frequently', 'attempting their tasks with curiosity and persistence', 'displaying scientific creativity', 'often asking scientific questions in detail', and 'expressing their opinions logically'. These behavioral characteristics of scientifically-gifted students had positive effects on general students, such as 'providing them with a successful experience in conducting experiments', 'improving understanding of science class contents', 'developing scientific thinking and reflective thinking', and 'improving their students' positive experiences about science'. However, the excessive learning-driven behaviors of scientifically-gifted students had negative effects on general students, such as 'limiting opportunities for general students to participate in classes', 'conducting passive exploration centered on results', and 'causing conflicts with general students'. Educational implications of these findings are discussed.

• Journal of Power Electronics
• /
• 제16권3호
• /
• pp.832-839
• /
• 2016

In this study, the performance of a direct current (DC)-DC buck converter is analyzed in the presence of non-idealities in passive components and semiconductor devices. The effect of these non-idealities on the various design issues of a DC-DC buck converter is studied. An improved expression for duty cycle is developed to compensate the losses that occur because of the non-idealities. The design equations for inductor and capacitor calculation are modified based on this improved expression. The effect of the variation in capacitor equivalent series resistance (ESR) on output voltage ripple (OVR) is analyzed in detail. It is observed that the value of required capacitance increases with ESR. However, beyond a maximum value of ESR (r_c,max), the capacitor is unable to maintain OVR within a specified limit. The expression of r_c,max is derived in terms of specified OVR and inductor current ripple. Finally, these theoretical studies are validated through MATLAB simulation and experimental results.

• Corrosion Science and Technology
• /
• 제16권2호
• /
• pp.69-75
• /
• 2017

Zinc coating on carbon steels give the higher corrosion resistance in chloride containing environments and in carbonated concrete. However, hydrogen evolution accompanies the corrosion of zinc in the initial activity in fresh concrete, which can lead to the formation of a porous structure at the reinforcement -concrete interface, which can potentially reduce the bond-strength of the reinforcement with concrete. The present study examines the mechanism of the corrosion of hot-dip galvanized steel in detail, as in the model pore solutions and real concrete. Calcium ion plays an important role in the corrosion mechanism, as it prevents the formation of passive layers on zinc at an elevated alkalinity. The corrosion rate of galvanized steel decreases in accordance with the exposure time; however, the reason for this is not the zinc transition into passivity, but the consumption of the less corrosion-resistant phases of hot-dip galvanizing in the concrete environment. The results on the electrochemical tests have been confirmed by the bond-strength test for the reinforcement of concrete and by evaluating the porosity of the cement adjacent to the reinforcement.

• 한국정보통신학회:학술대회논문집
• /
• 한국해양정보통신학회 2006년도 춘계종합학술대회
• /
• pp.685-688
• /
• 2006

본 논문에서는 초전도에너지저장 시스템에 적합한 간략한 회로 구성과 높은 신뢰성을 가지는 단상 무정전 전원공급장치를 제안한다. 제안된 시스템은 공통암 방식을 적용하여 스위칭 소자수를 저감한다. Normal, Stored-energy, Bypass의 세 가지 동작 모드에 대하여 상세히 설명한다. 사용되는 스위칭 소자수를 저감시키거나 수동소자로 대체시킬 경우 제어가 복잡해지고 자유도를 감소키는 문제점이 있지만 고성능의 디지털 제어기를 통해 추가적인 부담 없이 해결할 수 있다. 제안된 시스템의 타당성 검증을 위해 시뮬레이션 결과를 제시한다.