• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.686_687
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• 2009

The traceability maintenance system for the AC voltage and current has been developed at the frequency range of 20 Hz to 100 Hz without using any compensation technique which is used at thermal converter (TC) ac-dc transfer system at low frequencies. The system uses a digital voltmeter (DVM) as a data acquisition system of the input waveform and stored data in memory. The developed algorithm acquires and processes the sampling data to calculate the root mean square (rms) value of the input voltage of DVM which operates at DC 10 V range for better accuracy. The best uncertainty of the AC voltage measurements is $3 {\mu}V/V$ within the frequency range. The best uncertainty of the AC current measurements is better than the $5 {\mu}A/A$ and mainly depend on the current to voltage converter, ac-dc current shunt or Current Transformer (CT), used for the measurement

• Proceedings of the Optical Society of Korea Conference
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• 1990.02a
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• pp.136-140
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• 1990

A hybrid wideband amplifier having bandwidth from 5MHz to 2000MHz with a gain of 10db$\pm$3dB is designed and implemented by using a lossy matched network and GaAs FET. The implemented amplifier circuit operates as a capacitor-resistor(C-R) coupled amplifier circuit in the low frequency range (below 800 MHz) in which {{{{ LEFT $\mid$ S_{21 } RIGHT $\mid$ }} for the GaAs FET is constant. It also operates as a lossless impedance matching circuit in the microwave frequency range in which S21 for the GaAs FET has a slope of approximately -6dB/octave. Using this configuration technique, Two stage GaAs FET amplifier implemented is measured to 10dB gain within a 3dB fluctuation over the frequency band from 5 to 2000MHz.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.8
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• pp.651-657
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• 2003

A new mechanical-electrical hybrid passive damping treatment is proposed to improve the performance of structural vibration control. The proposed hybrid passive damping system consists of a constrained layer damping treatment and a shunt circuit. In a passive mechanical constrained layer damping, a viscoelastic material damping layer is used to control the structural vibration modes in high frequency range. The passive electrical damping is designed for targeting the nitration amplitude in the low frequency range. The governing equations of motion are derived through the Hamilton's principle. The obtained mathematical model Is validated experimentally. The presented theoretical and experimental techniques provide invaluable tools for controlling the multiple modes of a vibrating structure over a wide frequency band.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.4
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• pp.216-222
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• 2002

Brake Moan is a laud and strong noise occurring at any vehicle speed over 2 mph as a low frequency in below 600Hz. In this study, we targeted to shift the unstable mode that causes the brake moan from the moats frequency range to sufficiently higher frequency range to avoid the moan phenomenon. We simulated the finite element model and found out the nodes in which the brake moan occurs the most and we regarded the boundary and its relationship between the brake pad and the rotor as a spring coefficient k. With the binary set of the spring coefficient k, we finally used genetic algorithm (GA) to get the optimal topology of the brake pad and its shape to avoid the brake moan. The final result remarkably shows that genetic algorithm can be used in topology optimization procedures requiring complex eigenvalue problems.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.2
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• pp.198-201
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• 2014

The phase frequency detector (PFD) is one of the most important building blocks of a phase locked Loop (PLL). Due to blind-zone problem, the detection range of the PFD is low. The blind zone of a PFD directly depends upon the reset time of the PFD and the pre-charge time of the internal nodes of the PFD. Taking these two parameters into consideration, a PFD is designed to achieve a small blind zone closer to the limit imposed by process-voltage-temperature variations. In this paper an enhanced architecture is proposed for dynamic logic PFD to minimize the blind-zone problem. The techniques used are inverter sizing, transistor reordering and use of pre-charge transistors. The PFD is implemented in 180 nm technology with supply voltage of 1.8 V.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.718-721
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• 2005

The purpose of the study is to evaluate the usage of microtremor in estimation of subsurface structure and ground response to ground motion. Ground motion amplification based on site condition of an area is an important parameter for dynamic design. Microtremor cover the characteristics in a low frequency range, while forced vibrations cover them in a high-frequency range. Microtremor consider ground characteristics and offer transfer function in area. To determine the dominant frequency, the passive microtremor measurement is performed and to determine the transfer function of test site, active microtremor measurement is performed. Microtremor measurement in the site is compared with theoretical transfer function calculated from the known structures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.627-632
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• 2002

The paper considers acoustic analysis of the shock absorbing muffler within a rotary compressor. The internal space of the compressor is modelled as a combination of cavities and pipes. A simple one-dimensional impedance approach is used fur the acoustic analysis in the low frequency range, with ignoring the effects of gas flow and temperature gradients that are closely related to power efficiency of the compressor. Using the similarity between the vibration isolator and the shock absorbing muffler, the source strength transmissibility is newly proposed as a performance measure of the muffler and its validity is supported by power analysis. Some Important muffler design rules obtained are; (1) a muffler cavity and its opening throat should be used as a pair, (2) a long thin throat is desirable for high frequency noise isolation, (3) a large muffler cavity should be used with care since it shortens the working frequency range of the muffler. The rules were applied to redesign a compressor muffler currently in use, and a significant improvement was achieved by simply attaching a throat to the outlet holes of the muffler.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.669-674
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• 1997

A sound field in a reverberation room is analyzed by using numerical methods and the SPL distributions are compared to the measurements. In numerical predictions, the BEM is employed in the low frequency range, while sound ray tracing method is used for the high frequency range. In the BEM analysis, the surfaces of the empty reverberation room are assumed as rigid boundaries and the damping coefficients are estimated from the measured absorption coefficient. The comparisons with measurements for 100Hz shows good agreement. In the sound ray tracing analysis, the predicted energy decay are in excellent agreements with theoretical results. It is shown that the energy absorption by air damping plays an important role as frequency becomes higher.

• Proceedings of the KIEE Conference
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• 1998.07f
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• pp.1947-1950
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• 1998

GTO inverter used for traction motor drives includes harmonics in the output current and torque by the limitation of switching frequency. However, the hybrid PWM method, using SPWM in low frequency range and SHE PWM in upper frequency range, can be obtained the relative less harmonic characteristic. The transient reaction, which the magnetic flux and the torque is altered and instantly the large current is flowed, may be produced at the mode change. This paper presents the techniques which can reduce the transient reactions produced in the gear changing of inverter fed traction motor drives operating in the hybrid PWM. The results are verified by the simulations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.362-367
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• 2003

A new mechanical-electrical hybrid passive dam ping treatment is proposed to improve the performance of structural vibration control. The proposed hybrid passive damping system consists of a constrained layer damping treatment and a shunt circuit. In a passive mechanical constrained layer damping, a viscoelastic material damping layer is used to control the structural vibration modes in high frequency range. The passive electrical damping is designed for targeting the vibration amplitude in the low frequency range. The governing equations of motion are derived through the Hamilton's principle. The obtained mathematical model is validated experimentally. The presented theoretical and experimental techniques provide invaluable tools for controlling the multiple modes of a vibrating structure over a wide frequency band.