Seok-Hwan Moon

Compact fiber-pigtailed InGaAs photoconductive antenna module for terahertz-wave generation and detection

We propose a compact fiber-pigtailed InGaAs photoconductive antenna (FPP) module having an effective heat-dissipation solution as well as a module volume of less than 0.7 cc. The heat-dissipation of the FPP modules when using a heat-conductive printed circuit board (PCB) and an aluminium nitride (AlN) submount, without any cooling systems, improve by 40% and 85%, respectively, when compared with a photoconductive antenna chip on a conventional PCB. The AlN submount is superior to those previously reported as a heat-dissipation solution. Terahertz time-domain spectroscopy (THz-TDS) using the FPP module perfectly detects the absorption lines of water vapor in free space and an α-lactose sample.

Development of the micro capillary pumped loop for electronic cooling

Electronic devices have been minimized but the performance of those is becoming better and better. Therefore it is needed to develop new cooling methods suitable for a thin packaging structure with high thermal density. The thin flat plate type micro CPL(capillary pumped loop) with the thickness less than 2 mm was developed in this study. The proposed micro CPL has two staged grooves in evaporator instead of poles for preventing backflows of the vapor bubble and the simpler structure than that of a micro CPL with the poles. Also a large vapor space from the evaporator to the condenser was constructed in the middle plate therefore flow resistance of the vapor could be reduced. The micro CPL was fabricated using MEMS technology. The micro CPL was composed of lower, middle and upper substrates. The lower substrate was made of silicon and the middle and upper substrates are made of Pyrex glass for visualization. Through a preliminary test it was checked that there was no leakage at the adhesion interface between lower and middle or upper substrates and at the bonding interface between lower substrate and fill tube. Although the experimental studies for the micro CPL have been poor till now, we have obtained the reasonable experimental results in this study. The performance test result has showed 8.5 W of the heat transfer rate for the micro CPL and we could observe the operating characteristics of circulating or evaporating and condensing by visualization. Pure distilled water was used as the working fluid.

Micro Capillary Pumped Loop for Electronic Cooling

Electronic devices have been minimized, but their performance is becoming better and better. Their heat flux has been significantly increased and has already exceeded about 100 W/cm2 recently. The insufficient dissipating of the heat flux may lead to performance decrease or failure of the electronic device and components. Heat flux in laptop computers has not been questioned; therefore, only a heat sink has been applied on cooling them. Recently, however, a more powerful cooling solution is sought for high heat flux. Solid materials with high thermal conductivity have been mainly used in low heat flux applications, whereas small-sized heat pipes have been utilized in high heat flux applications. The use of small-sized heat pipes in electronic devices like laptop computers has only been developed recently. For example, the use of heat pipes with diameter of 3–4 became common in laptop and desktop computers only during the early 2000s. Recently, as electronic devices have started to become smaller and thinner, heat pipes with diameter of 3–4 mm have been pressed to fit the form factor to them. However, a lot of problems were encountered in their thermal performance, thus micro heat pipes (MHPs) were developed to solve them. Specifically, a flat plate micro heat pipe (FPMHP) with diameter of less than 1.5 mm was developed by Moon (Moon et al., 2002). FPMHPs are being used mainly in display panel BLU applications and are being prepared to be used in the LED headlight of vehicles. However, in spite of their thermal performance and broad applications, FPMHPs may still show degradation in thermal performance in the case of thinner applications. If we consider phase-change cooling devices like heat pipes that have thermal conductivity that is 500 times larger than copper rods for small-sized and thin electronic devices, there is a need to develop new cooling methods suitable for them. A thin flat plate type micro capillary pumped loop (CPL) with thickness of less than 2 mm was developed by Moon as a trial product. The proposed micro CPL has two-staged grooves in the evaporator, instead of poles, for preventing the backflow of the vapor bubbles; this is a simpler structure compared to that of a micro CPL with poles. A large vapor space from the evaporator to the condenser was also constructed in the middle plate to allow for the reduction of the flow resistance of the vapor. The micro CPL was fabricated using MEMS technology and was composed of lower, middle, and upper substrates. The lower substrate was composed of silicon, while the middle and upper substrates were made from Pyrex glass for visualization. Through a preliminary test, it was verified that there was no leakage at the adhesion interface between the lower and the middle or upper substrates

Thermal Analysis and Testing of a Heat Pipe With Woven Wired Wick

The heat generation of electronic systems has been increasing because of the increase in the speed and density of such systems. High-power light-emitting diode and power semiconductor modules are examples of electronic systems that exhibit the aforementioned thermal problem. Recently, microsized cooling devices that are developed using the semiconductor process of silicon and glass have been used as electronic cooling solutions. However, microsized cooling devices with an equivalent diameter of less than 1 mm have low cooling capability close to 10 W. Therefore, cooling devices that have high cooling capability are needed in the field of electronic cooling. In this paper, a woven wire wick with a high capillary limit and high productivity was developed, and small-sized heat pipes with outer diameters of 3 and 4 mm were designed, manufactured, and tested. Performance test results show the maximum cooling capability of 27.9 W at a working temperature of 90 °C for the small-sized heat pipe with length of 300 mm and outer diameter of 4 mm. The capillary radius distributions in the vapor-liquid meniscus and the pressure distributions in the vapor and liquid paths were obtained through numerical analysis. The obtained maximum cooling capability at various working temperatures was compared with the experimental results. The maximum cooling capability was compared with that of other wick structures as well.

Development of a heat pipe heat dissipation method for CPV application

Even when there is a sufficient heat dissipation area from the heat sink to the environment, if the heat flux in the chip package substrate cannot be transferred rapidly to the heat sink, a thermal problem may occur.[1] In this study, a relatively thin CPV module compared to general models was considered. Because four solar chips are mounted on a center column in the CPV module, heat can accumulate rapidly. Therefore, a heat pipe with high thermal conductivity was considered as the heat dissipation method.[2] The heat pipe adopted in the present study is commercially available and has a circular type sintered wick in it. To apply the heat pipe to the CPV module with thin thickness and a central column with 4 solar cells, it should be pressed and bent. The thermal characteristics of the pressed and bent heat pipe was investigated experimentally.

PowerField: a transient temperature-to-power technique based on Markov random field theory

Transient temperature-to-power conversion is as important as steady-state analysis since power distributions tend to change dynamically. In this work, we propose PowerField framework to find the most probable power distribution from consecutive thermal images. Since the transient analysis is vulnerable to spatio-temporal thermal noise, we adopted a maximum-a-posteriori Markov random field framework to enhance the noise immunity. The most probable power map is obtained by minimizing the energy function which is calculated using an approximated transient thermal equation. Experimental results with a thermal simulator shows that PowerField outperforms the previous method in transient analysis reducing the error by half on average. We also applied our method to a real silicon achieving 90.7% accuracy.