• 한국광학회지
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• 제8권2호
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• pp.116-121
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• 1997

주위온도에 따른 레이저다이오드의 광출력의 변화는 정전류로 구동하는 경우와 정전압으로 구동하는 경우에 서로 다르다. 레이저다이오드를 정전류로 구동하는 경우에는 온도증가에 따라 밀도반전이 감소하므로 광출력이 감소한다. 그러나 정전압으로 구동하는 경우에는 이러한 열효과에 의한 광출력의 감소이외에 내부저항과 임계전압의 감소에 의한 주입전류의 증가효과가 있어서 열효과를 일부 상쇄하므로 광출력의 변화가 정전류로 구동할 때보다 적다. 특히 정전압으로 레이저다이오드를 구동하는 경우에 이 두가지 효과에 의한 광출력의 변화폭이 비슷하여 서로 상쇄되는 동작점 부근에서는 온도에 따른 광출력의 변화가 아주 적어져 정전류로 구동하는 때보다 훨씬 광출력이 안정함을 실험적으로 확인하였다.

• Advances in materials Research
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• 제2권3호
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• pp.141-153
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• 2013

Nanocrystalline Barium niobate ($BaNbO_3$) has been synthesized by a novel auto-igniting combustion technique. The X-Ray diffraction studies reveals that $BaNbO_3$ posses a cubic structure with lattice constant $a=4.071{\AA}$. Phase purity and structure of the nano powder are further examined using Fourier-Transform Infrared and Raman spectroscopy. The average particle size of the as prepared nano particles from the Transmission Electron Microscopy is 20 nm. The UV-Vis absorption spectra of the samples are recorded and the calculated average optical band gap is 3.74eV. The sample is sintered at an optimized temperature of $1425^{\circ}C$ for 2h and attained nearly 98% of the theoretical density. The morphology of the sintered pellet is studied with Scanning Electron Microscopy. The dielectric constant and loss factor of a well-sintered $BaNbO_3$ at 5MHz sample is found to be 32.92 and $8.09{\times}10^{-4}$ respectively, at room temperature. The temperature coefficient of dielectric constant was $-179pp/^{\circ}C$. The high dielectric constant, low loss and negative temperature coefficient of dielectric constant makes it a potential candidate for temperature sensitive dielectric applications.

• 융합신호처리학회논문지
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• 제22권3호
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• pp.116-121
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• 2021

에너지를 절약하기 위해 고효율 히트펌프를 개발하기 위한 많은 연구가 이루어지고 있으며, 실외기 코일에 발생하는 서리가 발생하는 현상을 줄이거나 없애기 위한 연구도 동시에 이루어지고 있다. 계절과 관계없이 히트펌프의 실외기에 서리가 발생하지 않는 연구를 진행할 수 있도록 자연 상태와 동일한 조건에서 실험할 수 있는 곡선형 항온챔버를 구축하였다. 이러한 곡선형 항온챔버가 실험 장치로서 타당성을 갖추고 있는지 검증하기 위해 시뮬레이션을 하였다. CFD 조건은 곡선형 항온챔버 내에 위치한 실외기 앞의 직선형 덕트 길이를 덕트 관경의 1배, 5배, 10배, 15배로 하였다. 그 결과 덕트 관경의 10배 길이로 시뮬레이션했을 때 자연 상태와 가장 유사하다는 것을 알게 되었다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.28-31
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• 1997

This paper describes the quick and precise controlling method for home-applied refrigerator. The proposed controller is based on the fuzzy logic control method and is designed for better performance in maintaining the constant temperature of the refrigerator. The temperature of the refrigerator is controlled by the cooling air blowing fan motor which is put on, off according to fuzzy logic controller. Finally, I study the performance of the proposed controller through the computer simulation about the approximated model of the refrigerator.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1250-1251
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• 2008

In this study, the dielectric ceramics with low loss were investigated for high frequency application. All sample of the $Ba_5M_4O_{15}$ (M=Ta, Nb) ceramics were prepared by the conventional mixed oxide method and sintered at $1325{\sim}1575^{\circ}C$. The bulk density and dielectric constant of the $Ba_5Ta_4O_{15}$ ceramics were increased continuously with increasing of sintering temperature. The quality factor was increased in the sintering temperature of $1375{\sim}1475^{\circ}C$ but decreased at the temperature above 1475$^{\circ}C$. In the case of $Ba_5Nb_4O_{15}$ ceramics, the bulk density, dielectric constant and quality factor were increased with sintering temperature but decreased above temperature of 1400$^{\circ}C$. The dielectric constant, quality factor and temperature coefficient of the resonant frequency (TCRF) of the $Ba_5Ta_4O_{15}$ and $Ba_5Nb_4O_{15}$ ceramics, sintered at 1475$^{\circ}C$ and 1400$^{\circ}C$, were 25.15, 53105 GHz, -3.06 ppm/$^{\circ}C$ and 39.55, 28052 GHz, 5.7 ppm/$^{\circ}C$, respectively.

• Journal of Advanced Marine Engineering and Technology
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• 제23권3호
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• pp.300-310
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• 1999

A constant-volume combustion chamber is developed to measure the burnt gas temperature over the wide ranges of equivalence ratio from 1.5 to 2.7 and pressure from 0.1 to 2.7 and pressure from 0.1 to 6 MPa by two-color method. The combustion temperature is also calculated by the conventional two-region model. The premixed fuel rich propane-oxygen-inert gas mixtures under high pressures are simultaneously ignited by eight spark plugs located on the circumference of combustion chamber with 45 degree intervals. The eight converging flames compress the end gases to high pressures. The transmissiv-ity in the chamber center during the final stage of combustion at the highest pressure is measured by in situ laser extinction method. Comparisons are made with the combustion temperatures between two-color method and two-region model. It is found that the burnt gas temperature mea-sured by two-color method is higher than that calculated by two-region model because of being the negative temperature gradient on the calculation and the temperature distribution of light path-length on the measurement and the burnt gas temperature for the turbulent combustion is higher than that of the laminar combustion under the same conditions because the heat loss for turbulent combustion is lower due to the shorter combustion period.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권3호
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• pp.110-114
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• 2001

$0.7Ba(Mg{\frac}_{1}{3}Ta{\frac}_{1}{3})O_3-0.3Ba({\frac}_{1}{3}Nb{\frac}_{1}{3})O_3ceramics$ were prepared by the conventional mixed oxide method. The ceramics were sintered at the temperature of $1500{\sim}1575[^{\circ}C]$ for 5 hours in air. The microwave dielectric properties of the specimens were investigated with sintering temperature. The 0.7BMT-0.3BCN ceramics showed typical XRD patterns of the complex perovskite structure. Dielectric constant and quality factor were increased with increasing the sintering temperature. In the case of the specimens sintered at $1575[^{\circ}C]$ for 5 hours, dielectric constant, quality factor and temperature coefficient of resonant frequency were good values of 28,23545 at 10[㎓] and -1.2 $[ppm/^{\circ}C]$, respectively.

• E2M - 전기 전자와 첨단 소재
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• 제8권2호
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• pp.224-228
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• 1995

0.15(B $a_{0.95}$ S $r_{0.05}$)O-0.15S $m_{2}$ $O_{3}$-0.7Ti $O_{2}$ ceramics were fabricated by the mixed-oxide method. Microwave dielectric properties were investigated with sintering conditions. Increasing the sintering temperature from 1300 to 1375[.deg. C], the sintered density was increased from 5.44 to 5.63[g/c $m^{3$]. Increasing the sintering temperature, dielectric constant and quality factor were increased and temperature coefficient of resonant frequency was independent of sintering temperature. In the specimen sintered at 1375[.deg. C], dielectric constant, quality factor and temperature coefficient of resonant frequency were 80.79, 2784(at 3[GHz]), +11.07[ppm/.deg. C], respectively..

• Journal of Biosystems Engineering
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• 제11권1호
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• pp.52-63
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• 1986

This study was performed to find out drying characteristics and develop drying model for the design of an efficient dryer or drying system of red peper. The basic model which describes drying phenomenon of red pepper was firstly established, and drying tests were conducted at 14-different drying conditions. In this test, the effects of drying air temperature and relative humidity on the rate of drying were undertaken. Finally, a new drying model based on these experimental results was developed to describe the drying characteristics of red pepper. The results from this study may be summarized as follows. 1. Drying constant of the basic model established from Lewis' experimental model and diffusion equation was theoretically deduced as a function of moisture content and inner-temperature of red pepper. 2. From the results of drying tests, drying air temperature was found to have the greatest effect on the rate of drying. However, the effect of temperature was small for the condition of high relative humidity, and for low temperature, the effect of relative humidity was found to be large even though the range of relative humidity was low. 3. Modified Henderson equation was found to be better than Chung equation as the EMC model for the estimation of the equilibrium moisture content of red Pepper. 4. Constant-rate drying period did not exist in the red pepper drying test. And falling-rate drying period was divided into three distinct phases. Drying rate was dependent on the moisture content, the inner-temperature of red pepper and the change of physical property due to drying. 5. Drying constant increased with decrease of free moisture content, but it decreased at the end of the drying period. Also, drying constant was dependent on the drying air temperature and relative humidity. 6. The new drying model developed in this study was found to be most suitable in describing the drying characteristics of red pepper. Therefore, it may be concluded that drying time could be accurately estimated by the new drying model.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.386-389
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• 2001

In this study, development of a new LTCC material using non-glassy system was attempted with repsect to reducing the fabrication process steps and cost down. Lowering the sintering temperature can be achieved by liquid phase sintering. However, presence of liquid phases usually decrease dielectric properties, especially the quality factor. Therefore, the starting material must have quality factor as high as possible in microwave frequency range. And also, the material should have a low dielectric constant for enhancing the signal propagation speed. Regarding these factors, dielectric constants of various materials were estimated by the Clausius-Mosotti equation. Among them, $ZnWO_4$ was turned out the suitable LTCC material. $ZnWO_4$ can be sintered up to 98% of full density at $1050^{\circ}C$ for 3 hours. It's measured dielectric constant, quality factor, and temperature coefficient of resonant frequency were 15.5, 74380GHz, and $-70ppm/^{\circ}C$, respectively. In order to modify the dielectric properties and densification temperature, $B_{2}O_{3}$ and $V_{2}O_{5}$ were added to $ZnWO_4$. 40 mol% $B_{2}O_{3}$ addition reduced the dielectric constant from 15.5 to 12. And the temperature coefficient of resonant frequency was improved from -70 to $-7.6ppm/^{\circ}C$. However, sintering temperature did not change due to either lack of liquid phase or high viscosity of liquid phase. Incorporation of small amount of $V_{2}O_{5}$ in $ZnWO_{4}-B_{2}O_{3}$ system enhanced liquid phase sintering. 0.1 wt% $V_{2}O_{5}$ addition to the $0.6ZnWO_{4}-0.4B_{2}O_{3}$ system, reduced the sintering temperature down to $950^{\circ}C$. Dielectric constant, quality factor, and temperature coefficient of resonant frequency were 9.5, 16737GHz, and $-21.6ppm/^{\circ}C$, respectively.