• 한국산학기술학회논문지
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• 제14권4호
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• pp.1982-1987
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• 2013

본 논문에서는 1.7-2.7 GHz 대역에서 동작하는 이동통신 기지국용 광대역 직렬 급전 다이폴 쌍 (SDP) 안테나에 대하여 2.4-2.484 GHz 무선랜(WLAN) 대역에서 저지 특성을 가지기 위한 설계 방법을 연구하였다. 대역 저지 특성은 SDP 안테나의 두 다이폴 소자를 연결하는 코플래너 스트립 선로 상에 U자형 슬롯을 삽입함으로써 얻을 수 있다. 슬롯의 위치와 구조에 따른 저지 대역의 특성 변화를 분석하였다. 최적화된 WLAN 대역 저지 SDP 안테나를 FR4 기판 상에 제작하고 특성을 실험한 결과 VSWR < 2 인 대역은 1.65-2.78 GHz (51.0%) 이고, 저지 대역은 2.39-2.54 GHz로 원하는 대역 저지 성능을 갖는 것을 확인하였다.

• Membrane and Water Treatment
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• 제3권1호
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• pp.25-34
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• 2012

Carboxylated polysulfone (CPS), poly (1,4-phenylene ether ethersulfone) (PPEES), membranes were prepared and used for the separation of NaCl and $CaCl_2$, in efficient way with less energy consumption. In this work, nanofiltration and reverse osmosis membranes were employed to the salt rejection behavior of the different salt solutions. The influence of applied pressure (1-12 bar), on the membrane performance was assessed. In CM series of membranes, $CM_1$ showed maximum of 97% water uptake and 36% water swelling, whereas, $CM_4$ showed 75% water uptake and 28% water swelling. In RCM series, $RCM_1$ showed 85% water uptake and 32% water swelling whereas, in $RCM_4$ it was 68% for water uptake and 20% for water swelling. Conclusively reverse osmosis membranes gave better rejection whereas nanofiltration membrane showed enhanced flux. CM1 showed 58% of rejection with 12 L/($m^2$ h) flux and $RCM_1$ showed 55% of rejection with 15 L/($m^2$ h) flux for 0.1 wt.% NaCl solution. Whereas, in 0.1 wt.% $CaCl_2$ solution, membrane $CM_1$ showed 78% of rejection with 12 L/($m^2$ h) flux and $RCM_1$ showed 63% rejection with flux of 9 L/($m^2$ h).

• 제어로봇시스템학회논문지
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• 제3권1호
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• pp.9-16
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• 1997

The method of designing robust two degree of freedom(2 DOF) controllers for linear systems with parameter uncertainties and unmodeled dynamics is presented in this paper. Robust performance condition that accounts for robust model matching of closed loop system and disturbance rejection is derived. Using the robust performance condition, the feedback controller is designed to meet robust stability and disturbance rejection specifications, while prefilter is used to improve the robust model matching properties. The $H^{\infty}$ and $\mu$ controller for six degree of freedom vehicle with parameter variations are designed and compared. Simulations for hydrodynamic parameter variations and disturbance are presented to demonstrate the achievement of good robust performance.

• 대한전자공학회논문지TC
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• 제45권8호
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• pp.47-52
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• 2008

좌우현 합성 선로 메타재질구조 쎌 형식인 UWB 대역통과여파기의 저지특성을 향상시키기 위해, 메타재질특성을 유지하면서도 소형화라는 설계목적에 적합한 저역통과여파기 개념을 제안한다. 따라서 대역통과여파기 자체는 파장의 0.25배보다 훨씬 작게 만들어지고, 이는 인터디지틀 결합기와 접지된 스텁으로 구성되며, 전후에 대칭형 소형 저역통과 블록을 가진다. 설계결과는, 예상대로, 관내파장의 1/8의 크기, 대역폭 100%, 1dB 이하의 삽입손실, 평탄한 군지연, 우수한 반사손실 특성을 보인다.

• 전력전자학회논문지
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• 제27권5호
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• pp.367-375
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• 2022

Generally, a proportional-resonant controller is used to eliminate steady-state errors during the voltage-current control of a double-conversion uninterruptible power supply (UPS) in a stationary reference frame. Additionally, the feed-forward control compensating for the load current, which can be considered a disturbance of the voltage controller, can be used to improve the disturbance rejection performance. However, during the parallel operation of UPSs, circulating current can occur between UPS modules when performing both feed-forward control and droop control because feed-forward control reduces the circulating current impedance. This study proposes a feed-forward compensation technique that considers the impedance of circulating current. An additional feed-forward compensation technique is developed to enhance the disturbance rejection performance. The validity of the proposed feed-forward compensation technique is verified by the experiment results of the parallel operation of a 500 W double-conversion UPS module.

• Membrane and Water Treatment
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• 제13권4호
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• pp.191-199
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• 2022

In industrial production, the development of traditional polyamide nanofiltration (NF) membrane was limited due to its poor oxidation resistance, complex preparation process and high cost. In this study, a composite NF membrane with high flux, high separation performance, high oxidation resistance and simple process preparation was prepared by the method of dilute solution dip coating. And the sulfonated polysulfone was used for dip coating. The results indicated that the concentration of glycerin, the pore size of the based membrane, the composition of the coating solution, and the post-treatment process had important effects on the structure and performance of the composite NF membrane. The composite NF membrane prepared without glycerol protecting based membrane had a low flux, when the concentration of glycerin increased from 5% to 15%, the pure water flux of the composite NF membrane increased from 46.4 LMH to 108.2 LMH, and the salt rejection rate did not change much. By optimizing the coating system, the rejection rate of Na₂SO₄ and PEG1000 was higher than 90%, the pure water flux was higher than 40 LMH (60psi), and it can withstand 20,000 ppm.h NaClO solution cleaning. When the post treatment processes was adjusted, the salt rejection rate of NaCl solution (250 ppm) reached 45.5%, and the flux reached 62.2 LMH.

• ETRI Journal
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• 제36권3호
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• pp.510-513
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• 2014

A Q-band pHEMT image-rejection low-noise amplifier (IR-LNA) is presented using inter-stage tunable resonators. The inter-stage L-C resonators can maximize an image rejection by functioning as inter-stage matching circuits at an operating frequency ($F_{OP}$) and short circuits at an image frequency ($F_{IM}$). In addition, it also brings more wideband image rejection than conventional notch filters. Moreover, tunable varactors in L-C resonators not only compensate for the mismatch of an image frequency induced by the process variation or model error but can also change the image frequency according to a required RF frequency. The implemented pHEMT IR-LNA shows 54.3 dB maximum image rejection ratio (IRR). By changing the varactor bias, the image frequency shifts from 27 GHz to 37 GHz with over 40 dB IRR, a 19.1 dB to 17.6 dB peak gain, and 3.2 dB to 4.3 dB noise figure. To the best of the authors' knowledge, it shows the highest IRR and $F_{IM}/F_{OP}$ of the reported millimeter/quasi-millimeter wave IR-LNAs.

• Membrane and Water Treatment
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• 제12권1호
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• pp.1-9
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• 2021

This study optimized the chemical cleaning process of discarded RO membranes for reuse in less demanding separation processes. The effect of physicochemical parameters, including the temperature, cleaning time, pH of the cleaning solution, and addition of additives, on the cleaning process was investigated. The membrane performance was evaluated by testing the flux recovery rate and salt rejection before and after the cleaning process. High temperatures (45-50 ℃) resulted in a better flux recovery rate of 71% with more than 80% salt rejection. Equal time for acid and base cleaning 3-3 h presented a 72.43% flux recovery rate with salt rejection above 85%. During acid and base cleaning, the best results were achieved at pH values of 3.0 and 12.0, respectively. Moreover, 0.05% concentration of ethylenediaminetetraacetic acid presented 72.3% flux recovery, while 69.2% flux was achieved using sodium dodecyl sulfate with a concentration of 0.5%; both showed >80% salt rejection, indicating no damage to the active layer of the membrane. Conversely, 0.5% concentration of sodium percarbonate showed 83.1% flux recovery and 0.005% concentration of sodium hypochlorite presented 85.2% flux recovery, while a high concentration of these chemicals resulted in oxidation of the membrane that caused a reduction in salt rejection.

• 대한전자공학회논문지TC
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• 제41권11호
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• pp.9-15
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• 2004

다중 안테나를 사용한 다중 반송파 대역확산 다중접속 (MIMO MC-CDMA) 시스템에 대한 V-BLAST의 수신 성능을 개선하기 위해 기존에 제안된 다단계 병렬 널링 및 병렬 부분 간섭 제거 수신기 (MPN-PPIC)의 성능을 보다 향상시키기 위한 방법으로, 최적의 간섭 제거 가중치를 구하는 방법을 제안한다. [1]에서 제안된 MPN-PPIC 방법은 병렬 간섭 제거 기법과 실험적으로 구한 최적의 간섭 제거 가중치를 이용하여 다중 사용자 환경에서 기존의 V-BLAST의 단점을 효과적으로 개선할 수 있었다. 하지만, 실험적으로 구한 가중치는 시스템에 적응적으로 적용할 수 없다는 단점이 있기 때문에, 본 논문에서는 수신신호의 신호대 간섭 및 잡음비 (SINR)을 이용한 최적의 간섭 제거 가중치를 구하는 방법을 보이고, 이를 [1]에서의 결과와 비교하기 위해 컴퓨터 모의 실험을 수행한다. 컴퓨터 모의 실험 결과, 제안한 방법이 기존의 방법에 비해 10/sup -3/의 BER에 대해서 2.5～5dB 정도의 성능 이득을 얻을 수 있음을 확인할 수 있었다.

• 산업기술연구
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• 제22권B호
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• pp.185-190
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• 2002

This paper describes a design of an induction motor control system using a 2 degree-of-freedom PI controller to compensate the effects of disturbance without degrading tracking performance. On the basis of vector control principle, the control system is simulated by using the ACSL and implemented on a DSP system(TMS320C31). In designing the 2 DOF controller, we can tune the performance of either the tracking or disturbance rejection independently without affecting the other. With the experimental results, the 2 DOF controller has shown a better performance in command tracking and disturbance rejection than a conventional PI controller.