• Progress in Superconductivity
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• v.6 no.1
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• pp.89-94
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• 2004

The policrystalline$SmBa_2$$Cu_2$$O_{y}$ was synthesized by the solid state reaction method. The dependence of AC susceptibility on temperature and applied ac field was studied. The critical temperature $T_{c}$ is about 92 K. As the ac field is increased, the slope and the value of real part of susceptibility become smaller and the peak position of imaginary part $T_{P}$ was shifted to a lower temperature with peak broadening. Using Bean's model, we determined intergrain critical current density $J_{c}$ and obtained $44 A/{cm}^2$ at 75 K. From the relation of the $J_{c}$ (T)=($1-T/T_{c}$ )$^{\beta}$ we obtained $\beta$=0.8 and found that the Josephson junction type of the $SmBa_2$$Cu_2$$O_{y}$ is SIS junction. The peak of the imaginary part shifts to higher temperature with increasing frequency, f. from Arrhenius plot, we obtained the activation energy of about 0.96 eV.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.12
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• pp.57-63
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• 2010

The efficiency of LED package is increasing by applying the high power, and a existing lighting is changing as the LED lighting. However, many problems have appeared by heat. Therefore, in order to solve thermal problems, LED lighting is designing in several ways, but the advantages of LED lighting is fading due to increase the prices and volumes. In this study, we try to improve the thermal performance by formation of via holes. The junction temperature and thermal resistance in the FR4-PCB with via-holes of 0.6[mm] was excellent in experiment and FR4-PCB with Via-holes of 0.6[mm] was excellent in simulation without solder. Further, the thermal resistance and the optical properties can be improved through a formation of via-holes.

• International Journal of Internet, Broadcasting and Communication
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• v.7 no.2
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• pp.161-167
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• 2015

The performance of high power LEDs highly depends on the junction temperature. Operating at high junction temperature causes elevation of the overall thermal resistance which causes degradation of light intensity and lifetime. Thus, appropriate thermal management is critical for LED packaging. The main goal of this research is to improve thermal resistance by optimizing and comparing nano-pore silicon-based thermal substrate to insulated metal substrate and direct bonded copper thermal substrate. The thermal resistance of the packages are evaluated using computation fluid dynamic approach for 1 W single chip LED module.

• Journal of IKEEE
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• v.24 no.3
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• pp.677-684
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• 2020

In this paper, the energy efficiency of a 4H-SiC UMOSFET with a local floating superjunction (LFS UMOSFET) was compared with a conventional P-shielding UMOSFET. For analysis, P-shielding UMOSFET and LFS UMOSFET were modeled for energy loss and junction temperature. As a result, LFS UMOSFET showed switching loss reduction of 20.6%. In addition, it was confirmed that LFS UMOSFET is applied to a 3-phase inverter, resulting in 33.2% lower power efficiency and 28.1% lower junction temperature than P-shielding UMOSFET. Electrical characteristics were simulated using Sentaurus TCAD, and the power circuit was simulated with the modelled UMOSFET using PSIM, a power circuit simulator.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.443-444
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• 2006

The influence of the heat sources on LED junction temperature are Engine room air, Back plate, Electric power device, and so on. LED lamp cooling system is considered to be an important subject fur high light efficiency. Because LED Chip will be problem When LED junction temperature be over $135^{\circ}C$, In this Study, The Looped Heat Pipe System is considered to prevent LED Chip fall. The LHPS is consist of evaporator part, condenser part, heat pipe part. The working fluid of LHPS is HCFC-123. In this study, to prevent LED Chipfall, we study thermal characteristics for Looped Heat Pipe System with LED lamp.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.268-268
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• 2011

열전소자를 사용하여 발광다이오드의 발열을 개선한다. 열전소자(Thermoelectric device: TED)의 펠티에효과(Peltier effect)를 이용하여 발광다이오드(Light Emitting Diodes: LED)의 접합온도 (Junction Temperature)를 제어한다. 열전소자의 구동 전력을 제어하여, 발광다이오드의 사용 전류에 대한 접합온도의 특성을 조사한다. 열전소자의 입력 전력 0.2W에 대하여, 일반 조명용 또는 표시 장치로 사용되는 1W급 고전력 LED를 정격전류(350 mA)로 구동할 때 접합온도를 최저 $69^{\circ}C$로 유지할 수 있다. 열전소자의 구동 전력이 0.2W일 때, 발광다이오드의 접합온도 $110^{\circ}C$에 대하여 최대 사용 가능 전류는 560 mA로 예측된다.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.847-848
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• 2006

R-type thermocouple(TC) interface circuits with cold-junction compensator(CJC) and its broken wires detection was developed. The circuit consists of a CJC device, a instrumentation amplifier(IA), and two resistor and a diode for broken wire detection. The experiment results show that the interface circuit has a good CJC function on the temperature range for $20^{\circ}C$ to $1400^{\circ}C$. At the range the output voltage of the IA was -14V when the TC was broken. At normal operation condition the output voltage of IA was 0V to 10V for the temperature range.

• Progress in Superconductivity
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• v.3 no.1
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• pp.87-90
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• 2001

We designed a high temperature superconducting rapid single flux quantum(RSFQ) T flip-flop(TFF) circuit using Xic and WRspice. According to the optimized circuit parameters, we fabricated the TFF circuit with $Y_1$$Ba_2$Cu$_3$$O_{7-x}$(YBCO) interface-controlled Josephson junctions. The whole circuit was comprised of five epitaxial layers including YBCO ground plane. The interface-controlled Josephson junction was fabricated with natural junction barrier that was formed by interface-treatment process. In addition, we report second design for a new flip-flop without ground palne.e.

• Progress in Superconductivity
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• v.1 no.2
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• pp.146-150
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• 2000

Step edge Josephson junctions in c-axis oriented $YBa_2Cu_3O_7$ films were fabricated on $CeO_2$ buffered sapphire substrates. The step angle was controlled in the wide range of $20^{\circ}\sim75^{\circ}$ by the Ar ion milling technique. I-V curves of junction fabricated on the thickness ratio of $\sim$0.8 and the step angle of $35^{\circ}$ were exhibited RSJ-like behavior with $I_CR_N$ product of $\sim250{\mu}A$ and critical current density of $\sim2\times10^4A/cm^2$ at 77 K. Critical current of step edge junction was increased linearly with decreasing temperature but the normal resistance was almost constant. Total samples of step edge Josephson junction was satisfied a scaling behavior of $I_CR_N{\propto}(J_C)^{0.5}$.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.3
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• pp.302-312
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• 2012

Underwater vehicles play a very important role in underwater engineering. Water-tight junction box (WJB) is one of the key components in underwater vehicle. This paper puts forward a pressure self-adaptive water-tight junction box (PSAWJB) which improves the reliability of the WJB significantly by solving the sealing and pressure problems in conventional WJB design. By redundancy design method, the pressure self-adaptive equalizer (PSAE) is designed in such a way that it consists of a piston pressure-adaptive compensator (PPAC) and a titanium film pressure-adaptive compensator (TFPAC). According to hydro-mechanical simulations, the operating volume of the PSAE is more than or equal to 11.6 % of the volume of WJB liquid system. Furthermore, the required operating volume of the PSAE also increases as the gas content of oil, hydrostatic pressure or temperature difference increases. The reliability of the PSAWJB is proved by hyperbaric chamber tests.