• The Korean Journal of Ceramics
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• v.5 no.3
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• pp.235-238
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• 1999

In a ceramic green body, some degree of nonuniformity in density always presents. These differences in green density will appear as nonuniform shrinkage after sintering takes place. For the complex ceramic bodies with various curves and angles, therefore, it is quite difficult to foresee the final dimensions precisely after sintering. This simulation study shows that, considering the sintering process as a thermal shrinkage phenomenon, the use of NASTRAN enables to predict the precise shape of a sintered body. Based on this result, 'the reverse engineering technique' has been developed that can unfold the exact dimensions of a green body to have the desired shape after sintering. This approach will provide a simple and useful tool for ceramic engineers to fabricate complicate bodies with tight dimensional tolerances.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.211-218
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• 2000

Off-design experimental performance was investigated for a small centrifugal compressor, whose impeller diameter is about 125mm, used in an industrial gas turbine. Test rig was designed and manufactured with a radial inflow turbine and a combustor to supply driving power to the compressor. Static pressure was measured on the casing of the impeller, vaneless diffuser, vaned diffuser and volute. Total pressure was obtained using specially fabricated rakes at the vaned diffuser throat and exit. Circumferential nonuniformity was found, near surge, in the Impeller, vaned diffuser and volute region. Spanwise nonuniform flow from the impeller affected the total pressure defects in the vaned diffuser region. Static pressure distortion in the circumferential direction in the volute was found near surge, where the minimum occurred near 140 degree position.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.8 s.179
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• pp.1923-1930
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• 2000

A bar with periodically nonuniform material properties is selected as a one-dimensional model of a flat-panel speaker. This paper describes a theoretical approach to the bending waves propagating i n the nonuniform bar. The phase speed of the wave is obtained using perturbation techniques for small amplitude, sinusoidal modulation of the flexural rigidity and mass density. It is shown that the wave speed is decreased due to the nonuniformity of the material properties by the amount proportional to the square of the modulation amplitude. The resonance occurring when the wavelength is half of the period of the material properties is analyzed by the method of multiple scales. It is also shown that the wave speed at the resonance mode is decreased by the amount proportional to the modulation amplitude but the wave of this mode does not propagate far enough due to attenuation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.854-857
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• 2000

Chemical Mechanical Polishing(CMP) has been accepted as one of the essential processes for VLSI fabrication. However, as the polishing process continues, pad pores get to be glazed by polishing residues, which hinder the supply of new slurry. This defect makes removal rate decrease with a number of polished wafer and the desired within-chip planarity, within wafer and wafer-to-wafer nonuniformity are unable to be achieved. So, pad conditioning is essential to overcome this defect. The eletroplated diamond grit disk is used as the conventional conditioner, And alumina long fiber, the .jet power of high pressure deionized water and vacuum compression are under investigation. But, these methods have the defects like scratches on wafer surface by out of diamond grits, subsidences of pad pores by over-conditioning, and the limits of conditioning effect. To improve these conditioning methods. this paper presents the Characteristics of Ultrasonic conditioning aided by cavitation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.464-473
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• 2000

The method is presented which predicts voltage waveforms at each nodes inter-connected arbitrarily on the coupled transmission lines by extracting the node connection condition to be included in the modal telegrapher's equation, hence analyzing the mechanism of waveform propagation on transmission lines. It is shown that it is also possible to analyze efficiently the coupled nonuniform lines. And then the nonuniformity of coupled lines is demonstrated for suppressing the crosstalk spikes using the one-dimensional inverse-scattering control theory. The predicted waveforms by presented method are analyzed and verified by comparison with those by the generalized S-parameter technique.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.573-578
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• 2000

A bar with periodically nonuniform material properties is selected as a one-dimensional model of a flat-panel speaker. This paper describes a theoretical approach to the bending waves propagating in the nonuniform bar. The phase speed of the wave is obtained using perturbation techniques for small amplitude, sinusoidal modulation of the flexural rigidity and mass density. It is shown that the wave speed is decreased due to the nonuniformity of the material properties by the amount proportional to the square of the modulation amplitude.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.151-156
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• 2003

We performed the numerical study on the characteristics of the airflow and cross contamination in the photolithography process cleanroom. The nonuniformity, the deflection angle and the global cross contamination were used for analyzing the characteristics and performances of cleanroom. We knew that the airflow characteristics of the cleanrooms are largely affected by the porosity of panel and the adjustment of dampers. And the numerical result showed that the global cross contamination varies with the location of source and the passage of time.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.167-170
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• 2002

We have proposed new pixel structures for Active Matrix OELD (AMOELD) to improve the uniformity of luminance and manufactured a full-color 3.6-inch QVGA AMOELD. The proposed pixel structures, composed of four TFTs and one capacitor, can display 64 gray scales by compensating threshold voltage (Vth) variation of driving TFTs. Nonuniformity and peak intensity of measured luminance are under 14% and over $200cd/m^2$, respectively.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.5 s.98
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• pp.40-47
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• 1999

In CMP for semiconductor wafer films, the acceptable within-chip planarity, within-wafer and wafer-to-wafer nonuniformity could be achieved by conditioning. The role of conditioning is to remove continuously polishing residues from pad and to maintain the initial pad surface pores. To reach these requirements, the diamond grits disk has been considered as a conventional conditioner. However, we have investigated many defects as scratch on wafers out of diamond grits shedding, contaminations from bonding materials, and pad pore subsidences by over-conditioning. So, this paper studies the effect of ultrasonic vibration in CMP conditioning as a representative. The effect of ultrasonic vibration was certified through ILD, Metal CMP.

• KSTLE International Journal
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• v.7 no.2
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• pp.56-60
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• 2006

By the increasing amount of vehicles, the increase of car accident served as a major momentum for remind the importance of braking system. The adequate design of a passenger car braking system, which is directly related to the safety of a car, is very important since the safety is an essential design parameter of a car to keep men and car from the damage. The thermal behaviors of the ventilated disk has been investigated based on the air cooling effects during repeat braking operations. In this study, the temperature and velocity fields of 3-D unsteady simulated model are obtained using a software package "FLUENT". The numerical results show that there exits a temperature nonuniformity between the disk faces contacting with pads.