• 한국분무공학회지
• /
• 제27권1호
• /
• pp.26-35
• /
• 2022

Electrospray is a method of atomizing fluid using high voltage supply and capable of generating continuous flow and coherent size of droplets. Electrical system and properties of fluids has enabled electrospray to have various spray modes. However, its studies have been confined only in Cone jet, which is more stable and easier to manipulate droplets' size than other spraying modes. Therefore, it is necessary to investigate and compare other spraying modes based on experimental parameters and physical properties of fluids. This research paper identified nine different spray modes. It was found out that Sauter Mean Diameter (SMD) is proportional to flow rate of fluids and maximum difference among spray modes was 1.7 times. On the other hand, SMD standard deviation had low variations on specific flow rates of fluids. Pulsed jet mode recorded the largest SMD standard deviation, while Spindle recorded the lowest.

• 대한기계학회논문집A
• /
• 제31권10호
• /
• pp.981-985
• /
• 2007

We present a MEMS-based portable Direct Methanol Fuel Cell (micro-DFMC), featured by a platinum sputtered microcolumn electrode and a built-in fuel chamber containing a limited amount of methanol fuel. Also presented is a micro-DMFC stack structure having a common electrolyte sandwiched by the microcolumn electrodes. The single cells with ME16 and PE16 electrodes show the maximum power densities of $31.04{\pm}0.29{\mu}W/cm^2$ and $9.75{\pm}0.29{\mu}W/cm^2$, respectively; thus indicating the microcolumn electrode (ME16) generates the power density (3.2 times) higher than the planar electrode (PE16). The single cell tests of ME16 and ME4 electrodes (Fig.8) show the maximum power of $31.04{\pm}0.29{\mu}W/cm^2$, and $25.23{\pm}2.7{\mu}W/cm^2$, respectively; thus demonstrating the increased window frame reduces the normalized standard power deviation (standard deviation over the average power). The normalized deviation of 0.11 in ME4 cell has been reduced to 0.01 in ME16 cell due to the increased window frames. The maximum power density of 4-cell stack is 15.7 times higher than that of the single cell. 4-cell stack produces the power capacity of 20.3mWh/g during 980min operation at the voltage of 450mV with the load resistance of $800{\Omega}$.

• 센서학회지
• /
• 제25권2호
• /
• pp.124-130
• /
• 2016

NDIR $CO_2$ gas sensor was built with ASIC implemented thermopile sensor which included temperature sensor and unique elliptical waveguide structures in this paper. The temperature dependency of dual infrared sensor module ($CO_2$ and reference IR sensors) has been characterized and its output voltage characteristics according to the temperature and gas concentration were proposed for the first time. NDIR $CO_2$ gas and reference IR sensors showed linear output voltages according to the variation of ambient temperatures from 243 K to 333 K and their slopes were 14.2 mV/K and 8.8 mV/K, respectively. The output voltages of temperature sensor also presented a linear dependency according to the ambient temperature and could be described with V(T)=-3.191+0.0148T(V). The output voltage ratio between $CO_2$ and reference IR sensors revealed irrelevant to the changes of ambient temperatures and gave a constant value around 1.6255 with standard deviation 0.008 at 0 ppm. The output voltage of $CO_2$ gas sensor at zero ppm $CO_2$ gas consisted of two components; one is caused by the HPB (half pass-band) of IR filter and the other is attributed to the part of $CO_2$ absorption wavelength. The characteristics of output voltages of $CO_2$ gas sensor could be accurately modeled with three parameters which are dependent upon the ambient temperatures and represented small average error less than 1.5% with 5% standard deviation.

• 한국방사선학회논문지
• /
• 제12권1호
• /
• pp.79-83
• /
• 2018

본 논문에서는 OSL 도트 선량계의 교정인자, 흡수선량 선형성, 피크전압 선형성, 각도 변화에 의한 흡수선량 변화를 측정하고 분석했다. 의료용 X 선발생 장치를 사용하여 조사에 노출 선량 보정 계수, 흡수선량 선형성, 피크 전압 선형성은 모두 IEC-62387-1 (2007) 기준을 만족하였다. 기준 방사선 노출과 관련하여 0도, 30도 및 60도에서 선량계 방향에 대한 기준은 -29 % (${\pm}30^{\circ}$) 및 + 67 % (${\pm}60^{\circ}$)이었다. 30도에서 측정된 값은 기준보다 -8 % 낮고 60도에서 기준보다 -18 % 낮게 나타났다. 그러므로 OSL 도트 선량계 사용 시 방향에 따른 영향을 보정하여야 한다.

• 지질공학
• /
• 제18권3호
• /
• pp.311-319
• /
• 2008

주파수 인피던스를 이용하는 ThetaProbe ML2x인 ADR 형식의 토양함수비센서를 적용하여 주문진 표준사, 상주 화강 풍화토, 장수 편마암풍화토을 대상으로 실험을 수행하였다. 시험의 목적은 측정센서의 측정 정밀도를 측정로드부 삽입 깊이에 따른 변화 양상을 파악하였다. 흙매질은 체적함수비 함량과의 관계를 비교하기 위하여 건조상태와 습윤상태로 구분하여 수행하였다. 측정결과에서 측정로드부가 흙매질 내 5cm 이상 삽입되면 측정전압의 변화폭이 크게 감소하는 것을 파악하였다. 또한, 표준사와 같이 균질한 입자를 가진 흙보다는 점토와 실트 등과 같은 세립질을 함유한 화강풍화토와 편마암풍화토에서 측정전압이 안정적인 형태를 갖는 것으로 나타났다. 따라서, 측정치는 측정로드부가 다공질매질과의 접촉 면적이 커질수록 안정적인 값을 제공한다.

• 대한전자공학회논문지SD
• /
• 제45권1호
• /
• pp.28-36
• /
• 2008

이번 논문은 implantable cardiac 페이스메이커의 검출 단 로서 저전압, 저전력 단일-비트 삼차 델타-시그마 모듈레이터를 구현하였다. 1V이하의 전원 전압에서 효과적으로 동작하기 위하여 distributed feedforward구조와 벌크-드리븐 OTA를 활용하였다. 설계된 모듈레이터는 0.8V의 전원 전압에서 49dB의 dynamic range를 가지면서 816nW의 파워를 소모하였다. 파워 소모를 획기적으로 줄임으로서 페이스메이커뿐만 아니라 제한된 배터리에서 동작하는 implantable 의료 기기에서 다양한 활용이 가능할 것으로 생각된다. 본 모듈레이터의 칩 크기는 $1000{\mu}m{\times}500{\mu}m$로서 $0.18{\mu}m$ CMOS standard 공정으로 제작되었다.

• 한국통신학회논문지
• /
• 제27권6C호
• /
• pp.619-624
• /
• 2002

본 논문에서는 50%의 duty cycle 출력을 가지며, 디지털 방식으로 분주수를 제어할 수 있는 새로운 분주기 구조를 제안하였다. 그리고 0.25$\mu\textrm{m}$ 2-poly, 5-metal CMOS 공정 파라미터를 이용한 HSPICE 모의실험을 통해서 제안한 주파수 분주기를 이용한 900MHz 주파수 합성기를 설계하였다. 제안한 주파수 분주기의 동작은 0.657m 2-poly, 2-metal CMOS 공정을 사용하여 제작한 칩을 측정하여 확인하였다. 설계한 전압제어발진기(VCO)는 2.5V 전원전압 하에서 900Mh의 충간주파수, $\pm$10%의 동작 범위, 154MHz/V의 이득을 가진다. 또한 모의실험 결과 주파수 합성기의 settling time은 약 $1.5\mu\textrm{m}$이고 짝수와 홀수 분주시 50%의 duty cycle과 820MHz~1GHz의 동작 주파수 범위를 갖으며, 전력소모는 대략 70mW 임을 확인하였다.

• Progress in Superconductivity
• /
• 제4권1호
• /
• pp.1-9
• /
• 2002

Transferring single flux quanta across a Josephson junction at an exactly determined rate has made highly precise voltage measurements possible. Making use of self-shunted Nb-based SINIS junctions, programmable fast-switching DC voltage standards with output voltages of up to 10 V were produced. This development is now extended from fundamental DC measurements to the precise determination of AC voltages with arbitrary waveforms. Integrated RSFQ circuits will help to replace expensive semiconductor devices for frequency control and signal coding. Easy-to-handle AC and inexpensive quantum voltmeters of fundamental accuracy would be of interest to industry. In analogy to the development in the flux regime, metallic nanocircuits comprising small-area tunnel junctions and providing the coherent transport of single electrons might play an important role in quantum current metrology. By precise counting of single charges these circuits allow prototypes of quantum standards for electric current and capacitance to be realised. Replacing single electron devices by single Cooper pair circuits, the charge transfer rates and thus the quantum currents could be significantly increased. Recently, the principles of the gate-controlled transfer of individual Cooper pairs in superconducting A1 devices in different electromagnetic environments were demonstrated. The characteristics of these quantum coherent circuits can be improved by replacing the small aluminum tunnel Junctions by niobium junctions. Due to the higher value of the superconducting energy gap ($\Delta_{Nb}$ ＝ $7\Delta_{Al}$), the characteristic energy and the frequency scales for Nb devices are substantially extended as compared to A1 devices. Although the fabrication of small Nb junctions presents a real challenge, the Nb-based metrological devices will be faster and more accurate in operation. Moreover, the Nb-based Cooper pair electrometer could be coupled to an Nb single Cooper pair qubit which can be beneficial for both, the stability of the qubit and its readout with a large signal-to-noise ratio..

• 조명전기설비학회논문지
• /
• 제29권4호
• /
• pp.11-17
• /
• 2015

While most switching devices are based on PN junctions, a single layer can realize a switching device in the case of vanadium dioxide($VO_2$) thin films. In this paper, bidirectional current triggering(switching) is demonstrated in a two-terminal planar device based on a $VO_2$ thin film by illuminating the film with an infrared laser at 1550nm. To begin with, a two-terminal planar device, which had a $30{\mu}m$-wide $VO_2$ conducting layer and an electrode separation of $10{\mu}m$, was fabricated. A specific bias voltage range for stable bidirectional laser triggering was experimentally obtained by measuring the current-voltage characteristics of the fabricated device in a current-controlled mode. Then, by constructing a test circuit composed of the device, a standard resistor, and a DC voltage source, connected in series, the transient response of laser-triggered current and its response time were investigated with a DC bias voltage, included in the above specific bias voltage range, applied to the device. In the test circuit with a DC voltage source of 3.35V and a $10{\Omega}$ resistor, bidirectional laser triggering could be realized with a maximum on-state current of 15mA and a switching contrast of ~78.95.

• 한국산학기술학회논문지
• /
• 제15권11호
• /
• pp.6821-6829
• /
• 2014

자동차에서 반도체 소자의 사용이 증가하고 있으며 특히 친환경자동차의 구동장치 부품으로서 고내압 스위칭 사용 증가가 예상된다. 그러나 고내압 소자의 경우는 신뢰성 시험을 하기 위한 장비가 국산화 되어 있지 않다. 그러므로 고내압 소자를 시험하기 위한 전원장치의 개발을 위하여 관련 시험규격을 분석하였다. 특히 자동차용 반도체 신뢰성 시험을 위한 AEC(Automotive Electronic Council) Q101에서 시험항목을 분석하여 개발이 필요한 전원장치의 사양을 결정하였다. 주회로는 풀브리지 컨버터로 선정하였으며 주어진 장치 사양에 따라 각종 변수를 설계하였고, 회로 변수의 적절성은 시뮬레이션을 통하여 검증하였다. 또한 전력부의 병렬운전. 패턴 운전을 위한 인터페이스를 설계하였다. 이를 통해 개발된 제품은 시험을 통하여 특성을 검증하였다.