• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.12
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• pp.1435-1444
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• 2008

In this paper, we designed a reduced height waveguide(WG) to microstrip mode converter with a short transition length. The mode converter is composed of a mode converter using E-plane probe and a modified impedance transformer. The mode converter was designed using a probe shorted to top of a 50 ohm ridge WG. The modified impedance transformer was designed to connect the mode converter to the reduced height WG. For wide bandwidth operation, the coupling of the two parts was tuned. The structure of the mode converter was optimized for low loss and wide bandwidth, and the optimized mode converter was fabricated. The performance of the mode converter was extracted using the thru and line S-parameters for back-to-back connections, and the connector loss was calibrated. The mode converter has a right angle structure and short transition length, 7.2 mm. The mode converter shows excellent performances; the insertion loss of 0.12 dB at 15 GHz, and the return loss above 10 dB for the full Ku-band.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.638-646
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• 2023

Recently, active research has been conducted to enhance the power characteristics and thermal stability of lithium-ion batteries (LiBs) by modifying separators using a ceramic coating method. However, since the thermal properties and surface features of the separator vary depending on the characteristics of the ceramic powders applied to the separator, it is crucial to manufacture ceramic powders optimized for the separator's performance. In this study, we evaluated the characteristics of three types of α-alumina (A-1, A-2, and A-3) produced with varying dispersant contents and milling times, in addition to commercial α-alumina (AES-11). Subsequently, the optimized powders (A-3) were coated onto the separator using an aqueous binder for comparison with the characteristics of an AES-11 coated separator and an uncoated PE separator. The A-3 coated separator improved electrolyte wettability with a low contact angle (44.69°) and increased puncture strength (538 gf). Furthermore, it exhibited excellent thermal stability, with a shrinkage value of 5.64% when exposed to 140℃ for 1 hour, compared to the AES11 coated separator (6.09%) and the bare PE separator (69.64%).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.865-873
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• 2013

The deep drawing and ironing (DDI) process involving the use of a high-capacity horizontal press is used for manufacturing acompressed natural gas (CNG) pressure vessel. However, some variables of the DDI process have been determined based on the experiences of workers, and the short die life needs to be improved for manufacturing the pressure vessel withhighquality and lowcost. In this study, process variables such as the draw ratio, distance between dies, radius of rounding of drawing die, and angle of ironing die are chosen to enhance the reliability and improve the die life based on previous studies and experiences. The draw ratio limits at which no tearing or wrinkling occurs are determined using FEA, and the distances between dies, radius of rounding of drawing die, and angle of ironing die are optimized by the DOE method. The results of the optimal process variables are compared with those of the existing DDI process for verifying their effectiveness.

• Investigative Magnetic Resonance Imaging
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• v.13 no.2
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• pp.117-126
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• 2009

Purpose : A numerical method of designing a multiple quantum filter (MQF) is presented for the optimum detection of myo-inositol (mI), an important brain metabolite, by using in vivo proton nuclear magnetic resonance spectroscopy ($^1$-HMRS). Materials and Methods : Starting from the characterization of the metabolite, the filter design includes the optimization of the sequence parameters such as the two echo times (TEs), the mixing time (TM), and the flip angle and offset frequency of the 3rd $90^{\circ}$ pulse which converts multiple quantum coherences (MQCs) back into single quantum coherences (SQCs). The optimized filter was then tested both in phantom and in human brains. Results : The results demonstrate that the proposed MQF can improve the signal-to-background ratio of the target metabolite by a factor of more than three by effectively suppressing the signal from the background metabolites. Conclusion : By incorporating a numerical method into the design of MQFs in $^1$-HMRS the spectral integrity of a target metabolite, in particular, with a complicated spin system can be substantially enhanced.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.9 s.112
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• pp.900-912
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• 2006

A GPS receiving antenna installed in the missile's warhead is designed and fabricated at a center frequency 1.575 GHz. The circular shaped antenna is installed in the middle of the warhead where the antenna's patch and the ground plane are connected with a hollow cylindrical shaped short pin. Using the dual feeding and phase difference method, an omni-directional radiation pattern which direction is normal to the missile's axis(H-plane) is obtained. The optimized diameters of the circular patch and the cylindrical ring typed shorting pin of the GPS receiving antenna which use the FR4.material(dielectric constant $\varepsilon_r=4.6$) are 59.5 mm and 14 mm, respectively. The cylindrical body with diameter 100 mm and height 500 mm is attached to the lower part of the warhead in order to complete the missile figure. The radiation patterns are measured by changing the angle and phase between the dual feeding points. When the phase difference of dual feeding is $100^{\circ}$ and the angle between the dual feeding points is $100^{\circ}$, the nearly omni-directional radiation pattern in the H-plane is obtained. In this case, the antenna gain is -5.55 dBd and the relative level difference between the maximum and the minimum radiation intensity is 3.98 dB.

• Clean Technology
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• v.23 no.1
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• pp.42-53
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• 2017

Numerical analysis was done to evaluate the fluid distribution inside of the mixing quencher to increase the reaction efficiency of the aqueous hydrogen peroxide solution in the scrubbing column which is used for simultaneous desulfurization and denitrification. Effective injection of the aqueous hydrogen peroxide ($H_2O_2$) solution in the mixing quencher has major effects for improving the reaction efficiency in the scrubbing column by enhancing the mixing of the aqueous $H_2O_2$ solution with the exhaust gas. The current study is to optimize the array of nozzles and the spray angles of the aqueous $H_2O_2$ solution in the mixing quencher by using the computational method. Main concerns of the analysis are how to enhance the uniformity of the $H_2O_2$ concentration distribution in the internal flow. Numerical analysis was done to check the distribution of the internal flow in the mixing quencher in terms of RMS values of the $H_2O_2$ concentration at the end of quencher. The concentration distribution of $H_2O_2$ at the end of is evaluated with respect to the different array of the nozzle pipes and the nozzle tip angles, and we also analyzed the turbulence formation and fluid mixing in the zone. The effect of the spray angle was evaluated with respect to the mixing efficiency in different flow directions. The optimized mixing quencher had the nozzle array at location of 0.3 m from the inlet duct surface and the spray angle is $15^{\circ}$ with the co-current flow. The RMS value of the $H_2O_2$ concentration at the end of the mixing quencher was 12.4%.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.46-49
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• 2003

Cu have been widely used as signal transmission materials for electrical electronic components owing to its high electrical conductivity. However, it's size have been limited to small ones due to its poor mechanical properties, Until now, strengthening of the copper at toy was obtained either by the solid solution and precipitation hardening by adding alloy elements or the work hardening by deformation process. Adding the at toy elements lead to reduction of electrical conductivity. In this aspect, if carbon nanofiber is used as reinforcement which have outstanding mechanical strength and electric conductivity, it is possible to develope Cu matrix nanocomposite having almost no loss of electric conductivity. It is expected to be innovative in electric conduct ing material market. The unidirectional alignment of carbon nanofiber is the most challenging task developing the copper matrix composites of high strength and electric conductivity In this study, the unidirectional alignment of carbon nanofibers which is used reinforced material are controlled by drawing process in order to manufacture the intermediary materials for the carbon nanofiber reinforced Cu matrix nanocomposite and align mechanism as well as optimized drawing process parameters are verified via experiments and numerical analysis. The materials used in this study were pure copper and the nanofibers of 150nm in diameter and of $10~20\mu\textrm{m}$ In length. The materials have been tested and the tensile strength was 75MPa with the elongation of 44% for the copper it is assumed that carbon nanofiber behave like porous elasto-plastic materials. Compaction test was conducted to obtain constitutive properties of carbon nanofiber. Optimal parameter for drawing process was obtained by experiments and numerical analysis considering the various drawing angles, reduction areas, friction coefficient, etc Lower reduction areas provides the less rupture of cu tube is not iced during the drawing process. Optimal die angle was between 5 degree and 12 degree. Relative density of carbon nanofiber embedded in the copper tube is higher as drawing diameter decrease and compressive residual stress is occurred in the copper tube. Carbon nanofibers are moved to the reverse drawing direct ion via shear force caused by deformation of the copper tube and alined to the drawing direction.

• Journal of the Korea Computer Graphics Society
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• v.23 no.5
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• pp.9-17
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• 2017

Filming using multiple cameras is required for the production of the multi-screen content. It can fill the viewer's field of view (FOV) entirely to provide an increased sense of immersion. In such a filming scenario, it is very important to monitor how images captured by multiple cameras are displayed as a single content or how the content will be displayed in an actual theatre. Most recent studies on creating the content of special format have been focused on their own purposes, such as stereoscopic and panoramic images. There is no research on content creation optimized for theatres that use three screens that are spreading recently. In this paper, we propose a novel content production system with a rig that can control three cameras and monitoring software specialized for multi-screen content. The proposed rig can precisely control the angles between the cameras and capture wide angle of view with three cameras. It works with monitoring software via remote communication. The monitoring software automatically aligned the content in real time, and the alignment of the content is updated according to the angle of camera rig. Futher, the producion efficiency is greatly improved by making the alignment information available for post-production.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.7
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• pp.445-454
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• 2022

Ice accretion on the aircraft components, such as wings, fuselage, and empennage, can occur when the aircraft encounters a cloud zone with high humidity and low temperature. The prevention of ice accretion is important because it causes a decrease in the aerodynamic performance and flight stability, thus leading to fatal safety problems. In this study, a shape design optimization of a multi-element airfoil is performed to minimize the amount of ice accretion on the high-lift device including leading-edge slat, main element, and trailing-edge flap. The design optimization framework proposed in this paper consists of four major parts: air flow, droplet impingement and ice accretion simulations and gradient-free optimization algorithm. Reynolds-averaged Navier-Stokes (RANS) simulation is used to predict the aerodynamic performance and flow field around the multi-element airfoil at the angle of attack 8°. Droplet impingement and ice accretion simulations are conducted using the multi-physics computational analysis tool. The objective function is to minimize the total mass of ice accretion and the design variables are the deflection angle, gap, and overhang of the flap and slat. Kriging surrogate model is used to construct the response surface, providing rapid approximations of time-consuming function evaluation, and genetic algorithm is employed to find the optimal solution. As a result of optimization, the total mass of ice accretion on the optimized multielement airfoil is reduced by about 8% compared to the baseline configuration.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.3
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• pp.89-95
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• 2022

In this study, glassy carbon coating was performed on the graphite using a phenolic resin and a curing agent was mixed with ethylene glycol as an additive to form the uniform surface. The phenolic resin was dried and cured under the environments of hot air, then converted into a glassy carbon layer by pyrolysis at 500~1,500℃. FTIR, XRD, SEM analysis, and density/porosity/contact angle measurement were performed for characterization of glassy carbon. The pyrolysis temperature for high-quality glassy carbon was optimized to be about 1,000℃. As the content of the additive increased, the effect of reducing surface defects on the coated surface, reduction of porosity, increase of contact angle, and increase of density were investigated in this study. The method of forming a glassy carbon coating layer through an additive is expected to be applicable to graphite coating and other fields.