• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.3
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• pp.258-264
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• 2004

In this paper, MMIC double balanced star mixer for 40 ㎓ was implemented on GaAs substrate with backside vias. In the design of the MMIC mixer, the design of balun and diode was required. A novel balun structure using microstrip to CPS was presented. The 40 ㎓ balun was designed based on the design experience of the scale-down balun by 2 ㎓. The balun may be suitable for fabrication in MMIC process with backside via and can easily be applied for DBM(Double Balanced Mixer). A Schottky diode was designed and implemented using p-HEMT process considering the compatability with other high frequency MMIC's fabricated on p-HEMT base process. Finally, the double balanced star mixer was fabricated using the balun and the p=HEMP Schottky diode. The measured performance of mixer shows 30 ㏈ conversion loss at 18 ㏈m LO power. This insufficient performance is caused by the unwanted diode at AlGaAs junction in vertical structure of p-HEMT. If the p-HEMT's gate is recessed to AlGaAs layer, and so the diode is eliminated, the mixer's performances will be improved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10A
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• pp.847-851
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• 2011

In this paper, we reported on a high performance MMIC star mixer for millimeter-wave applications. The star mixer was fabricated using drain-source-connected pseudomorphic high electron mobility transistor (PHEMT) diodes considering the PHEMT MMIC full process on 2 mil thick GaAs substrate. The average conversion loss of 13 dB was measured in the RF frequency range of 81 GHz to 86 GHz at LO frequency of 75 GHz with LO power of 10 dBm. The RF-LO isolation characteristics are greater than 30 dB and the input 1-dB compression are approximately 4 dBm. The total chip size is 0.8 mm ${\times}$ 0.8 mm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.6
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• pp.608-618
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• 2004

In this paper, modifying the diode star double balanced mixer of Maas, a novel resistive 60 GHz pHEMT MMIC star mixer is suggested. Due to star configuration, troublesome IF balun for ring configuration FET mixer is not necessary. In addition, the sysematic design method of dual balun through EM simulation is suggested rather than the design by inspection as Maas. The mixer circuit is fabricated as MMIC on CPW base using 0.1 um GaAs pHEMT Library of MINT in Dongguk University. The size is 1.5 ${\times}$ 1.5 $\textrm{mm}^2$ and its performance is adjustable by DC supply. It can be operated as both up and down converters and it shows the conversion loss of about 13∼18 ㏈ over the full V-band frequencies.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.630-637
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• 2003

In this paper, a DBM(double balanced mixer) of 2 GHz is implemented on FR4(h=1.6mm, ${\epsilon}_r=4.6$) substrate. The structure of double balanced mixer requires, in general, two talons and a quad diode. For balun, a novel planar balun using microstrip to CPS(Coplanar Strip) is suggested and designed. The suggested balun shows the phase imbalance of $180^{\circ}{\pm}1.5^{\circ}$ and the amplitude imbalance of ${\pm}0.2 dB$ for 1.5 to 2.5 GHz. Using the balun, DBM is successfully implemented, and the measured conversion loss of up/down converter show about 6 dB over the bandwidth. The balun may be applicable for MMIC(Monolithic Microwave Integrated Circuit) DBM with the process supporting backside via though more study.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.1
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• pp.44-50
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• 2004

In this paper, a DBM(Doubly Balanced Mixer) of 2 GHz is implemented on FR4 substrate. The structure of doubly balanced mixer requires, in general, two batons and a quad diode. For balun, a novel planar balun using microstrip to CPS is suggested and designed. The suggested balun shows the phase imbalance of 180$^{\circ}$${\pm}$ 1.5$^{\circ}$and the amplitude imbalance of ${\pm}$ 0.2 ㏈ for 1.5 to 2.5 GHz. Using the balun, DBM is succesfully implemented, and the measured conversion loss of up/down converter show about 6 ㏈ over the bandwidth. The balun may be applicable for MMIC DBM with the process supporting backside via thourgh more study.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.4
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• pp.50-55
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• 2001

To simulate the combustion process under stratified charged conditions, like GDI engines, the new combustion model is proposed, which is based on Welter's FAE model and Peters' PDF model for considering primary reactions. In addition to these models, the new laminar burning velocity correlation and diffusion flame model are also included in the proposed model. The former can be applicable to much wider range of equivalence ratio, pressure and temperature than the others, such as Keck's and Guilder's models, and the latter has been derived from water-gas shift reaction and hydrogen oxidation, by which the secondary reactions can be considered after primary reactions. 3-D computation has been performed by using STAR-CD v3.05 in the simple cylindrical geometry under stratified charged condition. Judging from the calculated results, the present model proves to be reasonable to simulate the characteristics of flame propagation and concentrations of products in burned regions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.2
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• pp.103-109
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• 2013

In this study, we performed a numerical study of hydrogen/air combustion in the combustion chamber of an ultra micro gas turbine. The supply flow rate and equivalence ratio are used as variables, and the commercial computational fluid dynamic program (STAR-CCM) is used for the numerical study of the combustion. The flow rate significantly affects the flame position, flame temperature, and pressure ratio between the inlet and the outlet. The flame position is close to the outlet in the combustion chamber, and the flame temperature and pressure ratio monotonously increases with the supply flow rate. The change in the equivalence ratio does not affect the flame position. The maximum flame temperature occurs under stoichiometric conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1257-1264
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• 2011

This paper presents 3D simulation by STAR-CCM+ for lean premixed combustion in a stationary gas turbine combustor with separate pilot and main nozzles. The constant for the source term in the flame area density transport equation was modified to account for a low global equivalence ratio and validated against measurement data. A Partially-premixed Coherent Flame Model(PCFM) involves propagation of a laminar premixed flame with the predicted flame surface density and equilibrium assumption in the burned gas with spatial inhomogeneity. The conditions for cooling by radiation and convection are considered for accurate determination of the heat flux on the wall. A parametric study is of the pilot-fuel-to-total-fuel-ratio is carried out. A chemical reactor network (CRN) was constructed on the basis of the 3D simulation results and compared against measurements of NOx.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.1 s.244
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• pp.32-41
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• 2006

We analyzed the non-Newtonian and non-isothermal flow in the melt conveying zone in co-rotating and counter-rotating screw extruder system with the commercial code, STAR-CD, and compared the mixing performance with respect to screw speed and rotating direction. The viscosity of fluid was described by power-law model. The dynamics of mixing was studied numerically by tracking the motion of particles in a twin screw extruder system. The extent of mixing was characterized in terms of the residence time distribution and average strain. The results showed that high screw speed decreases the residence time but increases the shear rate. Therefore higher screw speed increases the strain and has better mixing performance. Counter-rotating screw extruder system and co-rotating screw extruder has the similar shear rate with the same screw speed in spite of different rotating direction. However, the counter-rotating screw has good mixing performance, which is resulted from longer residence time than that of co-rotating screw extruder.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.704-709
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• 2000

Laminar burning velocities of propane- and iso-octane-air mixtures have been numerically modelled over a wide range of equivalence ratio, pressure and temperature. These correlations are applicable to the modelling of stratified charged combustion like that of lean bum and GDI engine combustion. The numerical models are based on the results calculated by PREMIX code with Sloane's detailed chemical reaction mechanism for propane and FlameMaster code with Peters' for iso-octane. Laminar burning velocity for two fuels showed a pressure and temperature dependence in the following form, in the range of $0.1{\sim}4MPa$, and $300{\sim}1000K$, respectively. $S_L={\alpha}\;{\exp}[-\xi({\phi}-{\phi}_m)^2-{\exp}\{-{\xi}({\phi}-{\phi}_m)\}-{\xi}({\phi}-{\phi}_m)]$ where ${\phi}_m=1.07$, and both of ${\alpha}$ and ${\xi}$ are functions of pressure and temperature. Compared with the results of the existing models, those of the present one showed the good agreement of the recent experiment data, especially in the range of lean and rich sides. Judging from the calculated results of the stratified charged combustion by using STAR-CD, the above modelling prove to be more suitable than the other ones.