• Journal of electromagnetic engineering and science
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• v.9 no.2
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• pp.78-84
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• 2009

This paper represents the effects of drain bias on the linearity and efficiency of an analog pre-distortion power amplifier(PA) for wideband code division multiple access(WCDMA) repeater applications. For verification, an analog predistorter(APD) with three-branch nonlinear paths for memory-effect compensation is implemented and a class-AB PA is fabricated using a 30-W Si LOMaS. From the measured results, at an average output power of 33 dBm(lO-dB back-off power), the PA with APD shows the adjacent channel leakage ratio(ACLR, ${\pm}$5 MHz offset) of below -45.1 dBc, with a drain efficiency of 24 % at the drain bias voltage($V_{DD}$) of 18 V. This compared an ACLR of -36.7 dEc and drain efficiency of 14.1 % at the $V_{DD}$ of 28 V for a PA without APD.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.118-121
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• 2003

A new approach, using MEMS, for improving the performance of high efficiency amplifiers is proposed in this paper. The MEMS tuning element is described as a variable-length shorted CPW stub. Class-E amplifiers can be optimally tuned by these MEMS tuning elements because their operation varies with the impedance of the output tuning circuit. A MEMS tuning element was simulated using full-wave EM simulators to obtain its S-parameters. A Class-E amplifier with the MEMS was designed at 8GHz. The non-linear operation of this amplifier was simulated to explore the effect of the MEMS tuning. Comparing the initially designed amplifier without MEMS, the Power Added Efficiency (PAE) of the amplifier with MEMS is improved from 46.3% to 66.9%. For the amplifier with MEMS, the nonlinear simulation results are PAE = 66.90%, $\eta$(drain efficiency) = 75.89%, and $P_{out}$ = 23.37 dBm at 8 GHz. In this paper, the concept of the MEMS tuning element is successfully applied to the Class E amplifier designed with transmission lines.

• Computers and Concrete
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• v.22 no.5
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• pp.493-500
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• 2018

Due to the fact that the ratio of their height to their openings is very large compared to normal beams, there are difficulties in the design and analysis of deep beams, which differ in behavior. In this study, the optimum horizontal and vertical reinforcement diameters of 5 different beams were determined by using genetic algorithms (GA) due to the openness/height ratio (L/h), loading condition and the presence of spaces in the body. In this study, the effect of different mutation operators and improved double times sensitive mutation (DTM) operator on GA's performance was investigated. In the study following random mutation (RM), boundary mutation (BM), non-uniform random mutation (NRM), Makinen, Periaux and Toivanen (MPT) mutation, power mutation (PM), polynomial mutation (PNM), and developed DTM mutation operators were applied to five deep beam problems were used to determine the minimum reinforcement diameter. The fitness values obtained using developed DTM mutation operator was higher than obtained from existing mutation operators. Moreover; obtained reinforcement weight of the deep beams using the developed DTM mutation operator lower than obtained from the existing mutation operators. As a result of the analyzes, the highest fitness value was obtained from the applied double times sensitive mutation (DTM) operator. In addition, it was found that this study, which was carried out using GAs, contributed to the solution of the problems experienced in the design of deep beams.

• Korean Journal of Construction Engineering and Management
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• v.3 no.1 s.9
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• pp.65-73
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• 2002

By its nature, software part of the construction industry such as engineering and so forth has been kept secret to outside, as it determines a company$^{\circ}{\phi}s$ competitiveness. As a result, construction field knowledge usually disappears with the end of a project. The objective of this study is to develop the knowledge management (BM) learning model tuned in to construction area in order to manage project-related knowledge and promote the knowledge management. This study presented a learning model for knowledge management in the construction field, with the aim to integrate a series of processes. The model is composed of EIP, EDMS, knowledge and failure cases management, CoP and e-Learning.

• Korean Chemical Engineering Research
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• v.55 no.1
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• pp.19-26
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• 2017

Increasing global energy demand has resulted in an energy crisis. The dye sensitizer solar cell (DSSC) is an alternative source because of its ability to convert the sun's energy into electrical energy. Our aim was to determine the effect of synthesized Ni(II)-Chlorophyll for enhancing the efficiency of solar cells based DSSC. Complex compound Ni(II)-Chlorophyll was successfully synthesized as a dye sensitizer of $Ni(NO_3)_2.6H_2O$ and chlorophyll ligand with saponification method. Characterization results with spectrophotometer UV-Vis showed that the complex compounds of Ni(II)-Chlorophyll have a maximum wavelength of 295.00 nm, 451.00 and 665.00 nm. The bond between the ligand and metal appears in the vibration Ni-O at wave number $455.2cm^{-1}$. Complex compoun Ni(II)-Chlorophyll has a magnetic moment 7.10 Bohr Magneton (BM). The performance of complex compound Ni(II)-Chlorophyll as a dye sensitizer shows the value of short-circuit current (Jsc) at $3.00mA/cm^2$, open circuit voltage (Voc) at 0.15 V and the efficiency (${\eta}$) 0.20%.

• Journal of the Optical Society of Korea
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• v.13 no.3
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• pp.354-360
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• 2009

We investigate theoretically the tolerance of 40 Gbps phase-modulated (PM) duobinary signals using a vestigial sideband (VSB) filter on impairments which occurred in dense wavelength-division multiplexing (DWDM) systems, compared to the conventional duobinary signals. Our simulation results show that PM duobinary signals can't have the gain on the spectral efficiency achieved by utilizing the VSB filtering technique. In order to increase the spectral efficiency, they indispensably require to be transmitted at the optimum bandwidth of multiplexer (MUX) and demultiplexer (DEMUX) since they are susceptible to inter-channel crosstalk. It is also shown that the PM duobinary modulation format has a large tolerance on self-phase modulation (SPM) and cross-phase modulation (XPM) under the condition which MUX and DEMUX have been tuned at an optimum bandwidth; it has 1.2 dB power penalty at the fiber launching power (FLP) of 15 dBm and the channel spacing of 50 GHz.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.633-633
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• 2013

직접쓰기 기술은 재료의 낭비가 적고, 생산가격의 절감, 빠른 공정속도 및 유독물질 발생 없이 친환경적인 공정이 가능하여 디스플레이 및 인쇄전자 산업 등 다양한 분야에서 적용이 가능한 기술로 평가 받고 있다. 특히 EHD (Electro-Hydro-Dynamics) 기술을 이용한 잉크젯 방식의 경우 기존의 직접쓰기 기술에서는 어려운 고해상도의 패터닝이 가능하고 다양한 특성의 잉크에 적용 가능하다는 장점을 지니고 있어 크게 각광받고 있다. 본 연구는 내경 $60{\mu}m$, 외경 100 ${\mu}m$인 지르코니아 재질의 세라믹 노즐을 사용하여 EHD 잉크젯에서의 인가전압과 기판속도 변화에 의한 토출 현상을 연구하였다. BM 잉크를 이용하여 전압을 1.7~2.25 kV 증가하여 토출 시 구현된 라인의 선폭은 22~38 ${\um}m$까지 커졌고, AMO 잉크를 이용하여 기판속도를 25~500 mm/s 증가시켜 토출 시 구현된 라인의 선폭은 $91{\sim}21{\mu}m$로 줄어들며 라인의 두께는 400~110 nm얇아지는 것을 확인하였다. 이처럼 노즐에 인가되는 전압과 기판 속도에 따라 토출의 양상이 달라지므로 이를 적절히 조합하면 안정적으로 원하는 토출을 구현할 수 있다.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.505-506
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• 2006

In this paper, the linearization technique for CMOS low-noise amplifier (LNA) using the derivative superposition method through the multiple gated transistors configuration is presented. LNA based on 0.13um RF CMOS process has been implemented with a modified cascode configuration using multiple gated common source transistors to fulfill a high linearity. Compared with a conventional cascode type LNA, the third order input intercept point (IIP3) per DC power consumption (IIP3/DC) is improved by 3.85 dB. The LNA achieved 2.5-dBm IIP3 with 13.4-dB gain, 3.6 dB NF at 2.4 GHz consuming 8.56 mA from a 1.5-V supply.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.495-498
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• 2006

This paper reports a high power 60 GHz push-push oscillator fabricated using 0.12 um metamorphic high electron-mobility transistors (mHEMTs). The devices with a $0.1{\mu}m$ gate-length exhibited good DC and RF characteristics such as a maximum drain current of 700 mA/mm, a peak gm of 660 mS/mm, and an $f_T$ of 170 GHz. By combining two sub-oscillators having $6{\times}50{\mu}m$ periphery mHEMT, the push-push oscillator achieved a 6.3 dBm of output power at 59.5 GHz with more than -35 dBc fundamental suppression. This is one of the highest output power obtained using mHEMT technology without buffer amplifier, and demonstrates the potential of mHEMT technology for cost effective millimeter-wave commercial applications.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.553-554
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• 2006

In this paper, 77 GHz CPW power amplifier MMIC, which are consisted of a 2 stage driver stage and a power stage employing $8{\times}50um$ gate width, have been successfully developed by using 120nm $In_{0.4}AlAs/In_{0.35}GaAs$ Metamorphic high electron mobility transistors (MHEMTs). The devices show an extrinsic transconductance $g_m$ of 660 mS/mm, a maximum drain current of 700 mA/mm, and a gate drain breakdown voltage of -8.5 V. A cut-off frequency ($f_T$) of 172 GHz and a maximum oscillation frequency ($f_{max}$) of over 300 GHz are achieved. The fabricated PA exhibited high power gain of 20dB only with 3 stages. The output power is measured to be 12.5 dBm.