• 전기의세계
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• v.14 no.5
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• pp.20-27
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• 1965

There are several methods of speed control in induction motors. One of which is to change the frequency of source but was not used frequently because of the difficulty of frequency-change. Then, the development of frequency changer using semiconductor enables the method useful. In this paper the speed characteristics of mechanical output, secondary input torque and secondary power factor are described when the frequency of source and voltage which is proportional to the frequency of source in order to make the flux in the air gap in constant, are changed. The above characteristics are searched on the basis of the rated characteristics of the motor. Because the ratio of these is proportional to that of the secondary current or the square value of it. To get the ratio of the secondary current, a current circle diagram is introduced, and the magnitude of the ratio from this diagram is accurate and simple. Experimental results are in good agreement with theoretical predictions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.157-162
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• 2003

This Paper presents a robust design of an Electrorheological(ER) damper using Taguchi method. Taguchi method is a robust design method that determines control parameters in the presence of noise effect. Electrode length, electrode gap, base oil viscosity and the weight ratio of ER particles are chosen for the control parameters and the temperature is considered to be a noise factor. The sensitivity of each factor with signal-to-noise(S/N) ratio and analysis of variance are investigated. The analysis results show that the electrode length and base oil viscosity of the ER fluid mostly affect the damping force in the absence of electric field. On the other hand, when the voltage is applied to the ER damper, the electrode length and the weight ratio of ER fluid exhibit significant effect. Based on the Taguchi method, an optimal configuration was designed and the robustness of the designed ER damper was validated by comparing the analysis and experimental results.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1391-1392
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• 2007

A selective reset waveform which can improve the dark room contrast ratio in a large sustain gap structure is suggested in this paper. When conventional selective reset discharge is performed, frequent unexpected misfiring happens because of high Vxb and much quantity of negative wall charge formed on Y electrode during final sustain period. The misfiring between sustain electrode and address electrode can be removed by lowering Vxb value and the misfiring between address electrode and scan electrode can be prevented by applying last sustain pulse of 40us and rectangular pulse of Vscan on Y electrode. When the selective reset waveform has one time reset per 8 subfields, black luminance of 1.55 cd/m2 can be obtained without any misfiring.

• Journal of electromagnetic engineering and science
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• v.13 no.4
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• pp.214-223
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• 2013

This paper proposes a theoretical analysis of hidden device detection and a design of multiband circular polarization patch array antenna for non-linear junction detector system application. A good axial ratio of circular polarization patch antenna is realized by a new approach that employs inclined slots, two rectangular grooves and a truncated ground for the conventional antenna. A good axial ratio of the 1.5 dB lower is measured by having an asymmetric gap distance between the ground planes of the coplanar waveguide feeding structure. The common ground plane of the linear array has an optimum trapezoidal slot array to reduce the mutual coupling without increasing the distance between the radiators. The higher gain of about 1 dBi is realized by using the novel common ground structure. The measured return loss, gain, and axial ratio of the proposed single radiator, as well as the proposed array antennas, showed a good agreement with the simulated results.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1974-1976
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• 1996

An electrostatically driven comb actuator with $525{\mu}m$ height was fabricated using (110) Si anisotropic etching in the Potassium Hydroxide(KOH) solution. The etch-rate and etch-rate ratio are strongly dependent on the weight % and temperature of KOH solution. We developed the optimal condition for the anisotropic etching on (110) wafer with varying these conditions. The force that the comb-drive actuator generates is inversely proportional to the distance of gap and proportional to the height of the comb electrodes. The electrodes must have the high aspect ratio. The (110) Si anisotropic etching is very useful to get a high aspect ratio structure.

• Korean Journal of Materials Research
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• v.9 no.2
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• pp.111-116
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• 1999

The microstructure of vitreous bonded abrasives, which are used as the essential materials in the precise grinding, was investigated theoretically using two particle model. In this paper, a general equation applicable for a case in which there is a gap between abrasive grits is suggested. As a result, it was known that both the volume ratio of grit to glassy bond(V\ulcorner/V\ulcorner) and porosity(V\ulcorner) are the function of $\alpha$(the ratio of distance between grit to diameter of grit) and $\theta$(the angle from the center of pore to that of grit). Because the value $\alpha$ and $\theta$ can be get easily by using these suggested equations, the microstructure could be explained quantitatively. Also the raised error with the increasing amount of bond was modified by the simple assumption. As a result, in that case, both V\ulcorner/V\ulcorner and V\ulcorner were known to be the function of $\alpha$ and $\theta$(the ratio diameter of pore to that of grit).

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1586-1588
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• 2003

The Pb$(Zr{_{0.7}}Ti_{0.3})O_3$[PZT(70/30)] thin films were fabricated on Pt/$TiO_2/SiO_2$/Si substrate by RF sputtering method. The effects of Ar/$O_2$ ratio on the structural and dielectric properties of PZT thin fillms were investigated. In the case of the PZT thin films deposited with condition of 50/50$(Ar/O_2) $ ratio, the grain of the PZT thin films were fine and uniform. Increasing of $O_2$ ratio, the dielectric constant was increased. In this case the dielectirc constant and dielectric loss of PZT thin fims were about 627 and 0.010, respectively.

• Proceedings of the KIEE Conference
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• 2001.11a
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• pp.62-64
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• 2001

In this paper, we present the fabrication and performance of tunable capacitors with various structural geometry of plates. Experimental devices have been fabricated using Cu-electroplating techniques and standard MEMS techniques. In particular, the thickness of electroplated Cu is designed below $0.5{\mu}m$ for lower actuation voltage. The fabricated tunable capacitors has been tested from $OV{\sim}42V$ and achieves a tuning ratio of $46%{\sim}64.2%$.

• Journal of Digital Contents Society
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• v.10 no.3
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• pp.389-393
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• 2009

In this paper, the single patch microstrip antenna and gap coupled broadband microstrip patch antenna using FDTD(Finite Difference Time Domain method) are analyzed. Mur's 2nd absorbing boundary condition to minimize reflected wave is applied. Return loss, voltage standing wave ratio, and input impedance by the length and width of driving patch, the length and width of parasitic patch, and the distance between driving patch and parasitic patch have been analyzed. Design parameters and radiation patterns of broadband antenna have been also shown.

• Nuclear Engineering and Technology
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• v.48 no.2
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• pp.533-544
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• 2016

This paper provides a reference to determine the seal performance of metallic O-rings for a reactor pressure vessel (RPV). A nonlinear elastic-plastic model of an O-ring was constructed by the finite element method to analyze its intrinsic properties. It is also validated by experiments on scaled samples. The effects of the compression ratio, the geometrical parameters of the O-ring, and the structure parameters of the groove on the flange are discussed in detail. The results showed that the numerical analysis of the O-ring agrees well with the experimental data, the compression ratio has an important role in the distribution and magnitude of contact stress, and a suitable gap between the sidewall and groove can improve the sealing capability of the O-ring. After the optimization of the sealing structure, some key parameters of the O-ring (i.e., compression ratio, cross-section diameter, wall thickness, sidewall gap) have been recommended for application in megakilowatt class nuclear power plants. Furthermore, air tightness and thermal cycling tests were performed to verify the rationality of the finite element method and to reliably evaluate the sealing performance of a RPV.