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Kim D.C.,ETRI | Kown O.-K.,ETRI | Kim H.-S.,ETRI | Kim K.S.,ETRI | And 8 more authors.
IEEE Photonics Technology Letters | Year: 2010

We report on the signal monitoring characteristics in a reflective semiconductor optical amplifier (RSOA) transistor outline can with a monitor-photodiode, thermoelectric cooler, and thermistor. Because of spatial hole-burning in the RSOA cavity, a front-side signal-monitoring module exhibits wider windows and better linearity in monitor current to signal power ratio (MCSPR) than a rear-side signal-monitoring module for current variations. In C-band, the average of the MCSPR is about 0.150 A/W and the MCSPR variation on wavelength is about ±0.038 A/W. © 2006 IEEE.

Oh S.-S.,Chosun University | Lee Y.-H.,ETRI | Kim W.-S.,KEIT
Microwave and Optical Technology Letters | Year: 2015

We propose a low-cost measurement technique of commercially available base-station antenna in a compact experimental setting, which may be considerably smaller than the far-field distance. An α-variable positioner was utilized with Fresnel-to-far-field transformation method. Compared with conventional near-field measurements, the technique described here allows for more rapid scanning and transformations. The experimental results show good agreement between the results measured at the far-field and that found using the Fresnel-to-far-field transformation. The experimental validity for commercial base-station antenna has been successfully shown for the first time as far as our knowledge, so that the proposed technique can be easily applied in small anechoic chambers, which are typically possessed by small-/medium-sized companies. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2617-2622, 2015.

News Article | November 18, 2016

A new research, affiliated with UNIST has presented a novel strategy for non-precious metal catalyst that can replace rare and expensive platinum(Pt)-based catalyst, currently used in hydrogen fuel cell. In their study, published in the November issue of the Journal of the American Chemical Society, Professor Sang Hoon Joo of Energy and Chemical Engineering and his team have devised a new synthetic strategy to boost the activity of iron- and nitrogen-doped carbon (Fe-N/C) catalyst that can realize low-cost hydrogen fuel cell. Hydrogen fuel cell generates electricity with hydrogen and oxygen, producing water as a byproduct. Precious platinum(Pt) has been used in commercialized fuel cell. However, the high cost of Pt (>40$ per g) hampers widespread application of the fuel cell. The research team has attempted to develop high-performance non-precious metal catalyst which can substitute for state-of-the-art Pt-based catalysts. In this research, they focused on carbon-based catalyst with iron and nitrogen due to low cost and high activity (Fe-N/C catalyst). During the preparation of the Fe-N/C catalysts, high-temperature heat-treatment at over 700 ? is commonly required to endow high catalystic activity, but unfortunately this treatment also diminishes the number of active site. The active site refers to the place where rate-determining catalytic reaction occurs. To solve the problem, they have introduced 'silica-protective-layer' approach. The silica layer effectively preserved the active site at high-temperature, preventing the destruction of the active site. The novel Fe-N/C catalyst prepared by 'silica-protective-layer' approach showed very high oxygen reduction reaction (ORR) activity which is comparable to Pt catalyst. ORR is an electrochemical reaction at the cathode of hydrogen fuel cell. Due to 1-million-times slower reaction kinetics of ORR at the cathode compared with hydrogen oxidation reaction at the anode, ORR is a major factor for a large drop of the efficiency of fuel cell. Up to date, expensive Pt has been used primarily as an efficient ORR catalyst. The research team realized a record high activity by employing their catalyst as the cathode catalyst of alkaline membrane fuel cell (one type of hydrogen fuel cell). The team also demonstrated very high performance in proton exchange membrane fuel cell (PEMFC), in which the developed catalyst showed the activity of 320 A cm-3, exceeding 2020 US Department of Energy (DOE) activity target for non-precious metal catalyst (300 A cm-3). "Our novel strategy for high-performance catalyst is expected to hasten the commercialization of hydrogen fuel cell, and the catalyst design can be also applied to other energy storage and conversion devices." says Prof. Joo. This research has been published on November 2nd in JACS (Journal of the American Chemical Society), a world renowned journal in the field of chemistry. This work has been supported by the Korea Evaluation Institute Of Industrial Technology (KEIT) funded by the Ministry of Trade, Industry and Energy, and by the National Research Foundation (NRF) of Korea funded by the Ministry of Science, ICT and Future Planning. Young Jin Sa and Sang Hoon Joo et al. "A General Approach to Preferential Formation of Active Fe-Nx Sites in Fe-N/C Electrocatalysts for Efficient Oxygen Reduction Reaction", JACS, (2016).

News Article | December 13, 2016

A new approach developed by a team of researchers, led by Prof. Jaephil Cho (School of Energy and Chemical Engineering) could hold the key to greatly improving the performance of commercial lithium-ion batteries. Prof. Cho and his research team have developed a new type anode material that would be used in place of a conventional graphite anode, which they claim will lead to lighter and longer-lasting batteries for everything from personal devices to electric vehicles. In the study, the research team has demonstrated the feasibility of a next-generation hybrid anode using silicon-nanolayer-embedded graphite/carbon. They report that this architecture allows compatibility between silicon and natural graphite and addresses the issues of severe side reactions caused by structural failure of crumbled graphite dust and uncombined residue of silicon particles by conventional mechanical milling. This newly-developed anode material has been manifactured with increase in graphite content in composite by 45%. The research team has also developed new equipment, which is capable of producing 300kg in 6 hours per batch using a small amount of silane gas (SiH4). Such simple procedure is highly esteemed, as it ensures competitive price. They report that the silicon/graphite composite is mass-producible and it has superior battery performances with industrial electrode density, high areal capacity, and low amounts of binder. The findings of the research have been published in the August issue of the prestigious energy journal Nature Energy. This work has been supported by the IT R&D programme of the Ministry of Trade, Industry & Energy (MOTIE) and Korea Evaluation Institute of Industrial Technology (KEIT), 2016 Research Fund of UNIST, and by the Office of Vehicle Technologies, Battery Materials Research Program of the US Department of Energy. Journal Reference: Minseong Ko, Sujong Chae, Jiyoung Ma, Namhyung Kim, Hyun-Wook Lee, Yi Cui, and Jaephil Cho, "Scalable synthesis of silicon-nanolayer-embedded graphite for high-energy lithium-ion batteries." Nature Energy, (2016).

« ENGIE joins Michelin in investing in Symbio FCell | Main | JetBlue enters 10-year renewable HEFA SPK jet fuel purchase agreement with SG Preston; 33M gallons of 30% blend per year » Researchers affiliated with Ulsan National Institute of Science and Technology (UNIST), South Korea, and Stanford University have demonstrated the feasibility of a next-generation hybrid anode for high-capacity Li-on batteries using silicon-nanolayer-embedded graphite/carbon. This architecture allows compatibility between silicon and natural graphite and addresses the issues of severe side reactions caused by structural failure of crumbled graphite dust and uncombined residue of silicon particles by conventional mechanical milling. A paper describing the work is published in the journal Nature Energy. The new material shows a high first-cycle Coulombic efficiency (92%) and a rapid increase of the Coulombic efficiency to 99.5% after only 6 cycles with a capacity retention of 96% after 100 cycles, with an industrial electrode density of >1.6 g cm−3; areal capacity loading of >3.3 mAh cm−2; and As a result, a full cell using LiCoO has demonstrated a higher energy density (1,043 Wh l−1) than with standard commercial graphite electrodes. The researchers prepared the Si-nanolayer-embedded-graphite/carbon hybrids (SGC) using a chemical vapor deposition(CVD) process with a scalable furnace. This design has been demonstrated to produce 5 kg per batch using a small amount of silane gas (SiH ), and uniformly distributes Si nanolayers on graphite powder. The material showed an enhanced reversible capacity (517 mAh g−1) with high CE (92%) at the first cycle. The hybrid overcomes the electrode expansion problem even in high electrode density cases. The production equipment is capable of producing 300 kg of material in 6 hours per batch. The work was supported by the IT R&D program of the Ministry of Trade, Industry & Energy (MOTIE) and Korea Evaluation Institute of Industrial Technology (KEIT), 2016 Research Fund of UNIST, and by the Office of Vehicle Technologies, Battery Materials Research Program of the US Department of Energy.

Jeong G.-T.,Inha University | Kim W.-S.,KEIT | Kwak K.-S.,Inha University
IEEE Antennas and Wireless Propagation Letters | Year: 2012

Design of a compact modified inverted-L antenna with a ground stub is proposed for Wi-Fi applications. With the ground stub structure, the impedance bandwidth for 2.45-GHz band enhances from 13.1% to 15.7%, and the impedance bandwidth for 5.2/5.8-GHz bands improves from 10.1% to 19.9%. The performances of the antenna with optimized parameters are characterized in terms of reflection coefficient, gain, and radiation pattern measurements in an anechoic chamber. The measured result satisfies Wi-Fi frequency specifications. © 2011 IEEE.

Yoon C.,Inha University | Lee W.-J.,Inha University | Kim W.-S.,KEIT | Lee H.-C.,Chodang University | Park H.-D.,Inha University
Microwave and Optical Technology Letters | Year: 2012

A compact and simple design of a printed antenna for ultra-wideband (UWB) application with band-notch characteristics are presented.The antenna size is 30 × 36 × 0.4 mm3 and operates over an extremely wide band of 2.82-13.95 GHz. The desired band-notched UWB operation can be obtained by choosing the size of the inverted L-slit. The proposed design consists of an inverted L-slit as the radiator and a coplanar ground plane. The proposed antenna has advantages of low cost, compact size, thin substrate, and easy design. The measured impedance bandwidth defined by VSWR ≤ 2 of 11.13 GHz (2.82-13.95 GHz), with the band-notched of 4.85-6.04 GHz, is obtained. Moreover, omnidirectional radiation patterns with appreciable gain across the operating band can be obtained. © 2011 Wiley Periodicals, Inc.

Yoon C.,Inha University | Hwang S.-G.,Inha University | Lee G.-C.,Inha University | Kim W.-S.,KEIT | And 2 more authors.
Microwave and Optical Technology Letters | Year: 2013

In this article, a broadband antenna for LTE, GSM, DCS, PCS, and WCDMA is proposed.The antenna consists of a T-shape strip and a shorted strip with capacitive coupling is excited. The capacitively coupled shorted strip shows resonance at the lower band, and the T-shape strip presents good matching at the higher band because the characteristics of input impedance are affected by the coupling. Moreover, by optimizing the dimensions of the L-shape strip, the total bandwidth of the antenna can be greatly improved. Copyright © 2013 Wiley Periodicals, Inc.

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