• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.8
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• pp.411-416
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• 2006

A new method on the evaluation of insulation oil was proposed. Terahertz time-domain spectroscopy (THz-TDS) was applied to investigate the properties of the insulating oil. For the diagnostics of oil degradation, three kinds of oils have been analyzed by THz-TDS. The degraded oil showed different optical and electrical constants compared with a new one. Generally, the power absorption coefficient, the refractive index, the dielectric constant and loss $tan{\delta}$ of the oil increase as the aging of insulating oil proceed. And the characteristics of two kind of insulation oil, 1-4 and 7-4, was compared in terahertz spectral region. Difference in refractive index and complex dielectric constant has been observed between the samples. The results of this study suggest that THz-TDS is a promising new means for evaluating degradation and identification of insulating oil.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1738-1745
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• 2015

Radiation characteristics of a probe-fed rectangular microstrip patch antenna printed on a finite grounded high permittivity substrate are investigated systematically for various square grounded dielectric substrate sizes with several thicknesses and dielectric constants by experiment and full wave simulation. The effect of the substrate size on the radiation characteristics of a rectangular patch antenna is mainly determined by the effective dielectric constant of surface waves on a grounded dielectric substrate. As the effective dielectric constant of surface waves increases, the substrate sizes for the maximum broadside gain and the required onset for a large magnitude of squint angle decrease, while the variations of the broadside gain, the front-to-back ratio, and the magnitude of squint angle versus the substrate size increase due to the increase of the power of the surface wave.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.7
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• pp.1261-1267
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• 2007

Although LEDs have been used in various applications with improving the brightness and luminous efficacy, the electrical and optical characteristics of high power LED varies at different temperature and starting time. In this paper, optimal heat sink and apparatus design were conducted using IR camera and ICEPAK on the LED bulb consisting with fourteen LED array. The temperatures of heat sink and LED device of the designed LED bulb without cooling pan were $74^{\circ}C\;and\;96.8^{\circ}C$, respectively, showing in good themal characteristics. For high efficiency driving circuit of LED array adopted optimal heat sink design, driving circuits of constant voltage and current circuits were suggested and fabricated. As a result the efficacy of all driving circuits showed more than 20 lm/W. Also, the constant current circuits are suitable for signal lamp, hallway lamp, and flash lamp having short operating time(about 30 min). On the other hand, a reading light and indoor lamp having long operating time can be controlled by constant voltage circuit.

• Journal of Astronomy and Space Sciences
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• v.20 no.3
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• pp.163-174
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• 2003

The motion of 3C 120 Jet relative to the core is reasonably uniform and the VLBI scale jet connects outwards to a VLA ~ 100kpc scale. We measured the jet width variation from the center and found some indication of a power law which indicates the jet expands roughly with a constant opening angle and a constant flow velocity, $V_{f}{\cong}c$, from subparsec scales to ~ 100 kpc. With such a constant flow velocity and based on other physical parameters deduced from observed emission characteristics of the jet, we have established an equipartition jet model which might accommodate the basic parameters of the jet on subparsec scales, with which one can fit the radio intensities over all the scale of the jet even to ~100 kpc.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.2
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• pp.260-267
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• 2015

An LCL-type isolated dc-dc converter is analyzed, using ac approximation. Analyses to express characteristics on the proposed converter are derived under steady and ideal elements conditions in this paper. The two operating modes can be identified from the analysis results representing different device conduction sequences. This converter is capable of achieving required output voltage(step up or down) operations with inductance ratio while operated at fixed frequency with constant duty ratio-50%. Experimental results show that the designed converter based on Q has zero voltage switching and constant output voltage at different load variations to verify the analysis.

• Journal of the Korean Society of Safety
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• v.9 no.4
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• pp.58-68
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• 1994

A miniature size electrostatic induction motor has been fabricated and studied parameters Influencing dominantly to the motor speed, such as a voltage and frequency of the 3 phase ac power source supplied to the stator of fabricated motor, the surface resistivity and relative dielectric constant of the rotor surface materials and the concurrently calculated relaxation time constants. It is found that the higher resitivity and/or the higher relative dielectric constant, concurrently the longer relaxation time constant of the rotor surface materials make the motor speed get higher speed. In case of discrete coated rotor surface it is found that the motor speed was increased logarithmically as narrow as width of the discrete coated Ti. And the degree of width of discrete coated Ti to the axial direction of the rotor was 60$^{\circ}$ and 150$^{\circ}$, the motor has got a 125% higher than that at the degree of 0$^{\circ}$.

• ETRI Journal
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• v.32 no.1
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• pp.1-10
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• 2010

In this paper, we present a fast Fourier transform (FFT) processor with four parallel data paths for multiband orthogonal frequency-division multiplexing ultra-wideband systems. The proposed 128-point FFT processor employs both a modified radix-$2^4$ algorithm and a radix-$2^3$ algorithm to significantly reduce the numbers of complex constant multipliers and complex booth multipliers. It also employs substructure-sharing multiplication units instead of constant multipliers to efficiently conduct multiplication operations with only addition and shift operations. The proposed FFT processor is implemented and tested using 0.18 ${\mu}m$ CMOS technology with a supply voltage of 1.8 V. The hardware- efficient 128-point FFT processor with four data streams can support a data processing rate of up to 1 Gsample/s while consuming 112 mW. The implementation results show that the proposed 128-point mixed-radix FFT architecture significantly reduces the hardware cost and power consumption in comparison to existing 128-point FFT architectures.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.555-557
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• 2005

This paper proposed a hydraulic pump system that is driven by a variable SR drive. The operating pressure of hydric pump is limited by the pump speed and the mechanical structure. The operating of hydraulic pump is separated as constant pressure and constant flow region. Under fixed speed, the pressure can be controlled as constant value, and then decreased by increasing of pump speed. A 2.2[kW], 12/8-pole SR motor and DSP based digital controller are designed and tested for hydraulic pump system. The test results show that the system has some good features such as high efficiency and high response characteristics.

• Proceedings of the KIEE Conference
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• 2005.10a
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• pp.206-211
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• 2005

The LC filter design procedure of the inverter output filter is described. The transfer function of the filter output voltage to the load current is described with the capacitor value and the system time constant considering the system controller. By using the closed form of the relation between the filter capacitor value and the system time constant, the capacitor value can be calculated with the given system time constant and vice versa. It is more practical for the implementation of power and control circuit of inverter. And as the effect of the load current to the voltage distortion can be calculated from the closed form, it is possible to analyze the system how much the voltage waveform is distorted in case of the nonlinear load. All the proposed design procedure is verified with the simulation and experimental results.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2002.11a
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• pp.34-46
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• 2002

Si-O-C-H films with a low dielectric constant were deposited on a p-type Si(100) substrate using a mixture gases of the bis-trimethylsilyl-methane (BTMSM) and oxygen by an inductively coupled plasma chemical vapor deposition (ICPCYD). High density plasma of about $~10^{12}\textrm{cm}^{-3}$ is obtained at low pressure (<400 mTorr) with rf power of about 300W in ICPCVD where the BTMSM and $O_2$ gases are fully dissociated. Fourier transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS) spectra show that the film has $Si-CH_3$ and OH-related bonds. The void within films is formed due to $Si-CH_3$ and OH-related bonds after annealing at $500^{\circ}C$ for the as-deposition samples. The lowest relative dielectric constant of annealed film at $500^{\circ}C$ is about 2.1.