• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.374-379
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• 2013

Helmholtz resonators have high transmission loss in a narrow band at the resonance frequency. The transmission loss characteristics of resonators at high sound pressure levels can change due to variations of the impedance as a result of nonlinear behavior. Different sound pressure levels are applied to each resonator when resonators were arranged along the path. Therefore, impedance variation due to incident sound pressure level should be considered in order to predict the transmission loss.

• Proceedings of the KIEE Conference
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• summer
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• pp.369-371
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• 2004

With the proliferation of nonlinear loads, high neutral harmonic currents in three-phase four-wire distribution system have been observed. It has been. known that the ground impedance has an effect on the neutral currents of a system which operates with harmonics present. On-site measurements of harmonic currents and voltages according to the fell-of-potential method under case study system were made and the ground impedance modeling using the pattern search method for the harmonic analysis was developed. The ground impedance model obtained by the proposed method was compared with the frequency characteristics by field tests and has shown appropriate results, and would be applicable to evaluate the harmonic and transient response characteristics of the ground system.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.11
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• pp.67-78
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• 2005

In this paper, impedance characteristics of overhead medium-voltage (MV) power line for power line communication (PLC) is analyzed. For analysis, a two-port equivalent network model of MV power lines is derived. By applying the equivalent model and basic transmission line theory, input impedance at the signal induction part is calculated. And also calculated input impedance of power line itself that the medium voltage coupler and coaxial cable effect are removed. For verification, impedance of power lines is measured at a test field for an MV PLC. The results show that impedance of MV power line itself is between $200\;{\Omega}\;and\;300\;{\Omega}$ and converges to a half of their characteristic impedance with increasing frequency. And also measured data is very similar to calculated data.

• The Journal of the Acoustical Society of Korea
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• v.37 no.1
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• pp.46-52
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• 2018

The piezoelectric single crystals used in piezoelectric transformers have a problem that power transfer capacity is comparatively low due to their high input impedance. In this study, we suggest a method to improve the power transfer capacity by reducing the high input impedance of the piezoelectric single crystal vibrator by connecting a capacitance increasing circuit to the electrical terminals of the piezoelectric single crystal vibrator where the circuit is a GIC (Generalized Impedance Converter) circuit using operational amplifiers. The result of measuring driving characteristics after applying the designed capacitance increasing circuit to the $128^{\circ}$ rotated Y-cut $LiNbO_3$ crystal vibrator confirmed that the input impedance decreased by 25 %, electromechanical coupling factor increased by 30 %, and the power transfer capacity increased by about 17 to 30 times in voltage conversion characteristics.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1999.12a
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• pp.340-345
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• 1999

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.240-243
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• 2005

This paper presents the transient behaviors of grounding system impedance against lighting impulse currents. The dynamic characteristics of the deeply driven ground rod and grounding grid subjected to the impulse current with various rise time were investigated. It was found that the transient ground impedance strongly depends on the configuration and size of grounding electrodes and the shapes of impulse currents, and the inductance of grounding electrodes has a significant affect on the transient ground impedance of grounding system in the short time domain.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.5
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• pp.393-399
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• 2011

An empirical formula proposed by Petersson and Plunt(PP's formula) and finite element analysis for impedance calculation of ship equipment foundations are investigated by comparing the analysis results with those of experimental results. The PP's formula well estimates resonant frequency of the foundations and impedance level except around the resonant region although the impedance level around the resonant frequency is heavily dependent upon the assumed loss factor. The results show that the PP's formula and finite element models can be complementarily used to estimate the impedance characteristics of various types of foundation of ships in design stage.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.12
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• pp.1264-1268
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• 2003

In this paper, we have designed the duplexer using non-radiative dielectric(NRD) guide in millimeter wave band. The designed duplexer is composed of two stepped-impedance filters and T-junction. Stepped-impedance filters we designed with an equivalent circuit model of evanescent waveguide and the T-junction is optimized to minimize return loss of -20 dB or more. The characteristics of duplexer show good agreements with the expected results.

• Journal of electromagnetic engineering and science
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• v.11 no.2
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• pp.91-96
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• 2011

In this paper, we propose a microstrip bandpass filter using stepped-impedance coupled-line hairpin resonators. The stepped-impedance coupled-line hairpin resonator has extended harmonic suppression in comparison with a conventional hairpin resonator due to transmission zero and the movement of harmonic frequencies resulting from the stepped-impedance characteristic. A high-pass type impedance/admittance inverter is employed in order to improve the lower frequency skirt characteristics of the passband. A 4-pole bandpass filter is designed and fabricated at 1.8 GHz. The measured results show the excellent attenuation performance at the stopband which is greater than 30 dB up to 10 GHz.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.5
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• pp.253-257
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• 2004

In order to analyze the frequency dependance of ground impedance in grounding grids for lightning and surge protection, a novel method for measuring the ground impedance as a function of frequency were experimentally investigated. The experiments were carried out in rectangular grounding grids with $6{\times}8$ conductors of 22 $mm^2$ buried at a depth of 0.5 m. The test current was injected by the variable frequency inverter whose frequency is linearly controlled for the established period in the range of 5∼500 KHz. The amplitude and phase of ground impedance were calculated from the waveforms of the test current and ground potential rise measured by the band-pass filter tuned in a specific frequency. The frequency dependence of ground impedance was mainly caused by the inductive current flowing through grounding conductors over the frequency of 100 KHz. The proposed measurement method of ground impedance would be applicable to evaluate the transient response characteristics in lightning protection grounding systems.