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Stable Stretchable Silver Electrode Directly Deposited on Wavy Elastomeric Substrate
Jaewook Jeong,Sangwoo Kim,Junhee Cho,Yongtaek Hong IEEE 2009 IEEE electron device letters Vol.30 No.12
<P>We demonstrated a stable operation of stretchable silver (Ag) electrodes under fast cycling strain stress conditions. Relatively thick Ag electrodes (700 nm) were directly deposited on an elastomeric polydimethylsiloxane (PDMS) substrate with vertical wavy patterns that were formed by using an aluminum mold. The large surface roughness of PDMS substrate that was transferred from an intentionally roughened mold surface enhanced the adhesion between thick electrode and PDMS layer. Top PDMS layer was coated on the Ag electrode for encasement. During a slow stretching test (16.7 mum/s), the resistance of the Ag electrode on the wavy substrate was increased only by three times for 50% tensile strain. The change in Ag electrode resistance was monitored during 10 000 times of fast (1 mm/s) cycling of 10% tensile strain. The maximum resistance was increased by less than five times during the stress test and returned to its initial value after the stress was removed.</P>
Variable step-size sign subband adaptive filter with subband filter selection
Cho, Jaegeol,Baek, Hyun Jae,Park, Bum Yong,Shin, JaeWook Elsevier 2018 Signal processing Vol.152 No.-
<P><B>Abstract</B></P> <P>This letter proposes a novel sign subband adaptive filtering (SSAF) algorithm with a subset selection for subband filters, called the SS-SSAF. The proposed algorithm achieves the fast convergence performance and reduces the computational complexity by a proposed sufficient condition. The condition associated with each subband immediately ensures the decrease of the mean square deviation (MSD) value at every iteration. Furthermore, we suggest the variable step-size algorithm for SS-SSAF to achieve both fast convergence speed and small steady-state errors. Simulation results show that the proposed algorithm with fixed step-size performs better than the conventional SSAF and the other improved SSAF algorithms in terms of the convergence rate. In addition, the performance of proposed variable step-size algorithm is demonstrated in the system identification compared with recent variable step-size SSAFs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We proposes a novel SSAF algorithm with subband filter selection (SS-SSAF). </LI> <LI> We suggest the variable step-size algorithm for SS-SSAF. </LI> <LI> The proposed algorithms have fast convergence speed than SSAF. </LI> <LI> The proposed algorithms have reduced average computational complexity than SSAF. </LI> <LI> The proposed algorithms show demonstrated in the system identification. </LI> </UL> </P>
Jaewook Shin,Min-Oh Kim,Sungmin Cho,Dong-Hyun Kim IEEE 2017 IEEE transactions on medical imaging Vol.36 No.8
<P>Magnetic resonance electrical property tomography (MREPT) is a technique used to extract the electrical properties of tissues (conductivity in particular) using a magnetic resonance imaging system. In this paper, we propose an improved data acquisition scheme for the electrical property tomography technique by utilizing T-2 modulation in fast spin echo (FSE) imaging. This technique was motivated by a numerical analysis of conductivity reconstruction in the frequency domain; results reveal the spatial frequency-dependent noise texture of conventional methods. A data-acquisition scheme using the FSE sequence was formulated to concentrate the signal within a specific frequency range where notable noise amplification is observed in the conventional method. Through numerical studies, the performance of the proposed acquisition was investigated. Furthermore, a compensation scheme was applied to reduce quantification errors due to tissuespecific T-2 modulation, which is inherent in FSE imaging. The technique was applied to phantom and in vivo experiments. Results showed improved conductivity contrasts in both experiments, as compared with conventional MREPT methods.</P>
Two-Dimensional Atomic-Layered Alloy Junctions for High-Performance Wearable Chemical Sensor
Cho, Byungjin,Kim, Ah Ra,Kim, Dong Jae,Chung, Hee-Suk,Choi, Sun Young,Kwon, Jung-Dae,Park, Sang Won,Kim, Yonghun,Lee, Byoung Hun,Lee, Kyu Hwan,Kim, Dong-Ho,Nam, Jaewook,Hahm, Myung Gwan American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.30
<P>We first report that two-dimensional (2D) metal (NbSe2) semiconductor (WSe2)-based flexible, wearable, and launderable gas sensors can be prepared through simple one-step chemical vapor deposition of prepatterned WO3 and Nb2O5. Compared to a control device with a Au/ WSe2 junction, gas-sensing performance of the 2D NbSe2/ WSe2 device was significantly enhanced, which might have resulted from the formation of a NbxW1xSe2 transition alloy junction lowering the Schottky barrier height. This would make it easier to collect charges of channels induced by molecule adsorption, improving gas response characteristics toward chemical species including NO2 and NH3. 2D NbSe2/WSe2 devices on a flexible substrate provide gas-sensing properties with excellent durability under harsh bending. Furthermore, the device stitched on a T-shirt still performed well even after conventional cleaning with a laundry machine, enabling wearable and launderable chemical sensors. These results could pave a road toward futuristic gas-sensing platforms based on only 2D materials.</P>
Jaewook Kim,Wonsik Yu,SeongHwan Cho IEEE 2012 IEEE transactions on microwave theory and techniqu Vol.60 No.10
<P>In this paper, we present a 0.2-1.8-GHz digital-intensive receiver front-end using a voltage-controlled oscillator (VCO)-based analog-to-digital converter (ADC) running at 1.4 Gs/s in 90-nm CMOS. To improve the out-of-band rejection, we propose a second-order anti-aliasing Sinc filter that can be embedded in the ADC, which exploits the integrating nature of a VCO. the nonideal effect of the proposed architecture is analyzed with regard to the waveform imperfection due to device mismatch. The proposed receiver achieves -94 dBm of sensitivity at 1-MHz bandwidth and - 6.8 dBm of IIP3, while providing 50-dB rejection of aliased signals.</P>
손재욱(Jaewook Son),이응찬(Eungchan Lee),강훈(Hoon Kang),김용찬(Yongchan Kim),김정규(Jung-Kyu Kim),조성열(Sung-Youl Cho),박재홍(Jae-Hong Park) 대한기계학회 2012 大韓機械學會論文集B Vol.36 No.6
판형열교환기는 높은 효율로 인하여 다양한 산업 분야에 사용되고 있으며, 판형열교환기의 성능특성을 파악하기 위해 많은 연구가 이루어 졌다. 하지만 세브론 각을 제외한 판형열교환기의 기구적 설계변수에 따른 성능특성 파악은 상대적으로 많이 부족한 실정이다. 본 연구는 판형열교환기의 기구적 설계변수에 따른 열전달 및 압력강하 성능특성을 파악하기 위해서 세브론 각, 전열판 골 깊이, 전열판골 길이, 전열판 개수 등을 변화시키며 실험을 수행하였다. 실험결과를 바탕으로 판형열교환기의 다양한 기구적 설계변수를 반영한 열전달 및 압력강하 성능특성 상관식을 제안하였다. 실험 데이터와 제안된 판형열교환기 상관식을 이용해 예측된 데이터를 비교한 결과 약 95% 이상의 데이터가 ±10% 오차범위 내에 존재함을 알 수 있었다. Plate heat exchangers have been widely used in many industrial applications because of their compactness and high efficiency. Even though plate heat exchangers have been investigated extensively, studies on the effects of geometric parameters other than the chevron angle are very limited in the open literature. In this study, the effects of the chevron angle, corrugation length, corrugation depth, and the number of plates on the heat transfer and pressure drop characteristics of plate heat exchangers were investigated experimentally. Based on the experimental results, empirical correlations were proposed. More than 95% of the predictions made based on the correlations had relative deviations of less than ±10% when compared with the measured data.