• 한국정보전자통신기술학회논문지
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• 제4권1호
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• pp.46-52
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• 2011

본 논문에서는 이중 LTE 대역의 MIMO 안테나를 제안하였다. 제안된 안테나는 FR-4 기판 (${\epsilon}_r=4.4$, 두께 = 0.8 mm)의 윗 면에 설계되어졌다. 제안된 구조는 안테나의 소형화를 위하여 미엔더 구조와 폴디드 구조가 적용된 PIFA 형태로 설계되었으며, 두개의 안테나를 공통 접지면 상단에 대칭으로 위치시키고 접지면에 두개의 슬릿을 부설하여 이중 LTE 대역에서 격리도를 향상시켰다. 제작된 안테나의 측정결과 LTE 13 (0.748 GHz ~ 0.787 GHz)과 LTE 7 (2.5 GHz ~ 2.69 GHz)대역을 동시에 만족시키며 두 안테나 사이의 격리도는 LTE 13과 LTE 7 대역에서 각각 -18 dB, -13 dB를 나타내었다. LTE 13대역에서 평균 이득과 효율은 각각 - 4.1 dBi, 41%이고, LTE 7대역에서는 -1 dBi, 81% 값을 나타내었다. 따라서 제안된 안테나는 LTE 시스템에 적용될 수 있을 것으로 사료된다.

• 한국산학기술학회논문지
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• 제7권3호
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• pp.332-337
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• 2006

기판전면에 패턴 없이 15 nm Co/15 nm Ni/70 nm polysilicon/200 nm $SiO_2$/Si(100) 구조로 적층된 구조로부터 급속열처리기 (rapid thermal annealer : RTA)를 이용하여 40초간 700, 900, $1000^{\circ}C$의 실리사이드화 온도를 변화시키면서 CoNi 복합실리사이드를 형성하였다. 완성된 두께 100 nm 정도의 CoNi 복합실리사이드층으로 배선층을 만든다고 상정하여, 이중 집속이온빔(dual beam focused ion beam : FIB)을 써서 30 kV에서 표면전류를 $1{\sim}100$ pA 범위에서 조절하면서 나노급 선폭제작의 가능성을 확인하였다. 각 온도별 복합실리사이드에 동일한 이온빔 조건으로 $100{\mu}m$ 길이의 패턴을 만들고, 이온빔으로 양 끝단에 트렌치를 만들어 FE-SEM으로 각 조건에서의 선폭, 두께, 최종 에칭형상을 확인하였다. 기존 형상변형이 많아서 나노급 선폭 구현이 불리한 폴리사이드 공정에 비해서, 최초로 새로운 저저항 복합실리사이드에 대해서 100 nm 이하의 나노급 피치를 가진 선폭 제작이 $30kV{\sim}30pA$ 범위에서 가능하였다.

• 한국방사선학회논문지
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• 제13권7호
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• pp.941-946
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• 2019

환자의 진단 및 치료를 결정할 때 전산화단층촬영 (computed tomography; CT)은 우수한 해부학 정보를 제공하기 때문에 진단에 큰 도움이 되어 있다. 그에 따른 사용빈도가 증가하고 있으며, 활용 및 응용범위도 확대되어가는 추세이다. 저관전압을 사용해서 CT 검사를 하면 노이즈가 증가한다. 기존의 여러 연구에서는 영상재구성법에 대한 노출조건을 조절하는 방법 등을 시도해서 최적의 화질을 찾는 방법을 찾고 있으나 근본적 문제해결은 되지 못한다. 입력 영상의 신호를 유지하고 노이즈만을 최대한 제거하기 위해서 이중 트리웨이블릿 알고리즘을 적용하였다. 실험결과 100kVp, 회전시간 0.5sec의 영상에서 complex oriented 2d 방을 사용 할 경우 노이즈는 8.53에서 4.51로 줄어들었다. 본 연구를 통해서 저관전압 두부 CT에서 발생하는 높은 수준의 노이즈를 최적의 노이즈제거 알고리즘으로 노이즈를 제거하고 환자선 량을 낮출 수 있었다. 본 연구결과를 임상에서 사용 시 저선량의 CT 사용이 가능하고 환자 피폭을 줄일 것으로 판단한다.

• 한국전자파학회논문지
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• 제21권10호
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• pp.1154-1160
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• 2010

본 논문에서는 이동 통신 기기에 적합하고 다중 대역을 지원하는 무선 USB 동글(dongle)용 내장형 안테나를 제안하였다. 제안된 무선 USB 동글용 안테나는 프린트형 미앤더 모노폴 안테나를 사용하여 이중 광대역 특성을 구현하였고, $50-{\Omega}$ 동축 케이블을 이용하여 급전하였다. 안테나는 두께가 1 mm, 비유전율이 4.6인 FR-4 기판 위에 설계되었고, 전체 크기는 $10{\times}50mm^2$로 내장형 안테나에 적합하다. 제작된 안테나는 측정 결과, VSWR<2 기준으로 2.3~2.7 GHz, 5.15~5.825 GHz의 이중 대역을 만족시킨다. 따라서 제안된 안테나는 WiBro, Bluetooth/ISM, WLAN, S-DMB, WiMAX의 대역을 만족하는 무선 USB 동굴용 안테나로 유용하게 활용될 수 있을 것이라 사료된다.

• 한국전자파학회논문지
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• 제20권11호
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• pp.1194-1200
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• 2009

1 cc 체적을 갖는 휴대폰 내장형 안테나를 FPCB(Flexible Printed Circuit Board)로 구현하였다. 안테나 전류의 방향이 가급적 일정하도록 설계함으로써 소형이지만 효율을 높여 이득을 증가시켰다. GSM 대역의 공진을 위한 짧은 길이의 보상은 맴돌이 인덕터를 FPCB상에 구현하여 보상하였다. 2개 맴돌이 인덕터를 적용하여 GSM 대역의 대역폭을 넓혔다. DCS 대역의 방사 소자는 FPCB와 수직인 형태의 도체 패턴을 부설하여 설계하였다. 비유전율 4.4를 갖는 두께 0.05 mm의 FPCB로 구현하고 길이$\times$폭$\times$높이=$30{\times}7{\times}5$ mm인 캐리어(carrier)에 부착하여 안테나를 제작하였다. 제작된 안테나를 측정한 결과, GSM 대역에서 VSWR 2:1 이하, 효율 42.49~60.95 % 및 평균 이득 -3.72~-2.15 dBi를 보였고, DCS 대역에서 VSWR 2:1 이하, 효율 47.95~73.21 % 및 평균 이득 -3.19~-1.35 dBi가 나타나 2대역 공히 우수한 특성을 보였다. 방사 패턴은 2대역 모두 H-면 전방향성 특성을 보였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 춘계학술대회 논문집
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• pp.9-9
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• 2009

Coated conductor is required to have good critical current property for high efficiency of electric power applications. Until now, long coated conductor does not show high Jc over 3 MA/$cm^2$ in thick superconducting layer because of texture degradation by thick superconducting layer. In this study, in order to overcome this issue, thicker superconducting layer was deposited with optimized conditions to reduce the degradation of critical current density. SmBCO superconducting coated conductor was deposited with 1~3 um of thickness at $750\sim850^{\circ}C$ under 15~20 mTorr of oxygen partial pressure using batch type EDDC( evaporation using drum in dual chamber). The buffered substrate for superconducting layer deposition was used IBAD-MgO template with the architecture of $LaMnO_3/MgO/Y_2O_3/Al_2O_3$/Hastelloy. After fabrication of coated conductor, critical current was measured by 4-prove method under self-magnetic field and 77K. In addition, surface morphology and texture were analyzed by SEM and XRD, respectively. 3 um thick SmBCO coated conductor shows highest $I_C$ values of 638A/cm-w in 1 m long in the world.

• Journal of Welding and Joining
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• 제35권2호
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• pp.23-29
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• 2017

Mechanical properties and hardness distributions in arc brazed joints of Dual phase steel using Cu-Al insert metal were investigated. The maximum tensile shear load was 10.4kN at the highest brazing current. It was about 54% compared to tensile load of base metal. This joint efficiency is higher than that of joint of DP steel using Cu-based filler metals which are Cu-Si, Cu-Sn. Fracture positions can be divided into two types. Crack initiation commonly occurred at three point junction among upper sheet, lower sheet and the fusion zone. However crack propagations were different with increasing the brazing current. In case of the lower current, it instantaneously propagated along with the interface between fusion zone and upper base material. On the other hand, in case of higher current, a crack propagation occurred through fusion zone. When the brazing current is low (60, 70A), the interface shape is flat type. However the interface shape is rough type, when the brazing current is high (80A). It is thought that the interface shapes were the reason why the crack propagations were different with brazing current. The interface was the intermetallic compounds which consisted of $(Fe,Al)_{0.85}Cu_{0.15}$ IMC formed by crystallization at $1200^{\circ}C$during cooling. Therefore the maximum tensile shear load and the fracture behavior were determined by a interface shape and effective sheet thickness of the fracture position.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.379-380
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• 2007

The characteristics of a co-sputtered indium zinc tin oxide (IZTO) films prepared by dual target dc magnetron sputtering from IZO and ITO targets at a room temperature are investigated. Film properties, such as sheet resistance, optical transmittance, surface work function and surface roughness were examined as a function of ITO dc power at constant IZO dc power of 100 W. It was shown that the increase of the ITO dc power during co-sputtering of ITO and IZO target resulted in an increase of sheet resistance of the IZTO films. This can be attributed to high resistivity of ITO film prepared at room temperature. Surface smoothness and roughness were investigated by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The synchrotron x-ray scattering results obtained from IZTO film with different ITO contents showed that introduction of ITO atoms into amorphous IZO film resulted in a crystallization of IZTO film with (222) preferred orientation due to low alc transition temperature of ITO film. However, the transmittance of the IZTO films with thickness of 150 nm is between 80 and 85 % at wavelength of 550 nm regardless of ITO content. Possible mechanism to explain the ITO and IZO co-sputtering effect on properties of IZTO is suggested.

• Restorative Dentistry and Endodontics
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• 제25권2호
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• pp.180-192
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• 2000

One bottle system was recently developed in order to simplify the clinical skills and save chair time after continuous improvements on dentin bonding agents. There has been many studies to measure the bond strength of one bottle systems but no actual work has been done on micromorphologic study of resin-dentin interdiffusion zone after one bottle system application. To evaluate the bonding patterns of various commercially available one bottle systems to dentin, observation of resin-dentin interdiffusion zone under TEM was performed. Caries-free human third molars within one month of extractions were chosen for the experiments. The molars were sectioned 1mm above the cementoenamel junction and got rid of the root portions. Crown portions of the teeth were sectioned parallel to occlusal surface so that dentin discs of 1mm in thickness were remained. 7 one bottle systems and 1 two bottle system were applied according to manufacturer's instructions and followings were the results. 1. In every experimental groups, cross bandings of collagen fiber were distinguishable and tight bon dings between the bonding agents and dentin were observed. 2. Hybrid layer was clearly observed in ONE-STEP$^{(R)}$, Prime & Bond$^{(R)}$ 2.1, Syntac$^{(R)}$ SC, MAC-BOND II groups but it was not clear in Single Bond, D-Liner Dual PLUS, ONE COAT BOND groups. 3. Electron-density of hybrid layer was uniform in pattern in MAC-BOND II, Prime & Bond$^{(R)}$ 2.1 groups but not so uniform in ONE-STEP$^{(R)}$ group. 4. Electron-dense amorphous phase in most superior layer of the resin-dentin interdiffusion zone was characteristically observed in Single Bond, Syntac$^{(R)}$ SC, ONE COAT BOND groups. It can be concluded that bondings between the dentin bonding agents and dentin can be various in pattern according to their chemical compositions and the condition during applications.

• Restorative Dentistry and Endodontics
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• 제39권4호
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• pp.296-302
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• 2014

Objectives: It is difficult to achieve adhesion between resin cement and zirconia ceramics using routine surface preparation methods. The aim of this study was to evaluate the effects of $CO_2$ and Er:YAG laser treatment on the bond strength of resin cement to zirconia ceramics. Materials and Methods: In this in-vitro study 45 zirconia disks (6 mm in diameter and 2 mm in thickness) were assigned to 3 groups (n = 15). In control group (CNT) no laser treatment was used. In groups COL and EYL, $CO_2$ and Er:YAG lasers were used for pretreatment of zirconia surface, respectively. Composite resin disks were cemented on zirconia disk using dual-curing resin cement. Shear bond strength tests were performed at a crosshead speed of 0.5 mm/min after 24 hr distilled water storage. Data were analyzed by one-way ANOVA and post hoc Tukey's HSD tests. Results: The means and standard deviations of shear bond strength values in the EYL, COL and CNT groups were $8.65{\pm}1.75$, $12.12{\pm}3.02$, and $5.97{\pm}1.14MPa$, respectively. Data showed that application of $CO_2$ and Er:YAG lasers resulted in a significant higher shear bond strength of resin cement to zirconia ceramics (p < 0.0001). The highest bond strength was recorded in the COL group (p < 0.0001). In the CNT group all the failures were adhesive. However, in the laser groups, 80% of the failures were of the adhesive type. Conclusions: Pretreatment of zirconia ceramic via $CO_2$ and Er:YAG laser improves the bond strength of resin cement to zirconia ceramic, with higher bond strength values in the $CO_2$ laser treated samples.