• Proceedings of the KOSOMBE Conference
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• v.1991 no.11
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• pp.98-100
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• 1991

We studied the characteristics of the compound electrode and found that the compound electrode provides the four-electrode method in a compact form. We developed a new method of measuring the skin impedance using simple electrodes at low frequencies. At high frequencies where the effect of internal tissue impedance is not negligible, we used the compensation method using compound electrodes since they measure the voltage right under the skin. At 50 kHz, we measured the real part of the skin impedance of less than $80\;{\Omega}$ on the thorax.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1997.10a
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• pp.311-314
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• 1997

This paper presents recognition of high impedance fault patterns based of chaotic features using the Radial Basis Function Network(RBFN). The chaos attractor is reconstructed from the fault current data for pattern recognition. The RBFN successfully classifies the three kinds of fault pattems and one normal pattem.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.11
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• pp.1059-1066
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• 2011

The micro-perforated panel absorber(MPPA) is one of promising noise control elements because of its applicability to extreme environments where general porous materials cannot be used. Since the MPPA is inherently non-porous sound absorber, it can be a good candidate of acoustic protection system of a space launcher. The overall sound pressure level inside payload fairings of commercial launch vehicles is so high(around 140 dB OASPL) that the conventional linear impedance model cannot be directly applied to the design of the acoustic protection systems. In this paper an acoustic impedance models of a micro-perforated panel absorber at high sound pressure environment were reviewed and the use of the impedance on the practical design of MPPAs was addressed. The variation of absorption characteristics of MPPA was discussed according to the design parameters, e.g., perforation ratio, the minute hole diameter, the thickness of MPP and the incident sound pressure level.

• Journal of Advanced Navigation Technology
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• v.17 no.2
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• pp.202-207
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• 2013

In this paper, a high dividing ratio unequal power divider using parallel connection transmission line is presented. Because a very low impedance transmission line can't implement a microstrip technology, this can fabricate a parallel connection transmission line with high impedance. When we design a high dividing ratio divider, we need the very low impedance line. The parallel connection transmission line could be implemented to obtain a low impedance line characteristic. To validity this approach, we are implemented a 10:1 unequal divider at center frequency 1 GHz. The performances of power divider agree with simulation results.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.1
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• pp.81-90
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• 2015

This paper investigates the droop control-based real and reactive power load sharing with a virtual inductor when the line impedance between inverter and Point of Common Coupling (PCC) is partly and unequally resistive in high-capacity systems. In this paper, the virtual inductor method is applied to parallel inverter systems with resistive and inductive line impedance. Reactive power sharing error has been improved by applying droop control after considering each line impedance voltage drop. However, in high capacity parallel systems with large output current, the reference output voltage, which is the output of droop controller, becomes lower than the rated value because of the high voltage drop from virtual inductance. Hence, line impedance voltage drop has been added to the droop equation so that parallel inverters operate within the range of rated output voltage. Additionally, the virtual inductor value has been selected via small signal modeling to analyze stability in transient conditions. Finally, the proposed droop method has been verified by MATLAB and PSIM simulation.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.3
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• pp.339-353
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• 2014

A straightforward method for optimal determining of a high frequency inductor's parasitic capacitance is presented. The proposed estimation method is based on measuring the inductor's impedance samples over a limited frequency range bordering on the resonance point considering k-dB deviation from the maximum impedance. An optimized solution to k could be obtained by minimizing the root mean squared error between the measured and the estimated impedance values. The model used to provide the estimations is a parallel RLC circuit valid at resonance frequency which will be transferred to the real model considering the mentioned interval of frequencies. A straightforward algorithm is suggested and programmed using MATLAB which does not require a wide knowledge of design parameters and could be implemented using a spectrum analyzer. The inputs are the measured impedance samples as a function of frequency along with the diameter of the conductors. The suggested algorithm practically provides the estimated parameters of a real inductance model at different frequencies, with or without design information. The suggested work is different from designing a high frequency inductor; it is rather concentration of determining the parameters of an available real inductor that could be easily done by a recipe provided to a technician.

• Journal of the Korean Institute of Telematics and Electronics
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• v.5 no.1
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• pp.13-25
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• 1968

A detailed analysis of the transistor wide-band feedback amplifiers using the hybrid-$\pi$ equivalent circuit has been made. It is considered both for the low freqnency and for the high frequency. The expressions of the gain, bandwidth. input impedance and output impedance have been presented. It is shown that a series feedback amplifier should be driven from the voltage source and should drive into the low resistance load, and a shunt feedback amplifier should be driven from the current source and should drive into the high resistance load. It is also shown that these stages can be coupled without use of the buffer stage or coupling transformer.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.239_240
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• 2009

This paper presents the brief analytical study on 돋 effects of higher impedance transformer(HIT) to reduce distribution system fault current. With the increase of source and load capacity of power system, fault current of D/L is much more increased and, conventional protection equipment-such as sectionalizer and recloser, have to be replaced higher switching capacity. However, this replacements needs a lot of budget to utility. Increase of transformer impedance is can be a countermeasure in practical basis. This paper compares the voltage and fault current magnitude of both cases -%Zt=20% and %Zt2=33.3%(transformer capacity is 75/100MVA). The simulation results show that the steady state voltage of HIT is dropped 5~6% more in peak load, and fault current was decreased about 5kA by high impedance on transformer.

• Journal of Electrical Engineering and Technology
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• v.4 no.4
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• pp.531-537
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• 2009

Lightning has a broad frequency spectrum from DC to a few MHz. Consequently, the high frequency performance of grounding systems for protection against lightning should be evaluated, with the distributed parameter circuit model in a uniform soil being used to simulate grounding impedances. This paper proposes a simulation method which applies the distributed parameter circuit model for the frequency-dependent impedance of vertically driven ground rods by considering multi-layered soil structures where ground rods are buried. The Matlab program was used to calculate the frequency-dependent ground impedances for two ground rods of different lengths. As a result, an increase of the length of ground rod is not always followed by a decrease of grounding impedance, at least at a high frequency. The results obtained using the newly proposed simulation method considering multi-layered soil structures are in good agreement with the measured results.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.1-6
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• 2007

Two impedance imaging systems of multi-frequency electrical impedance tomography (MFEIT) and magnetic resonance electrical impedance tomography (MREIT) are described. MFEIT utilizes boundary measurements of current-voltage data at multiple frequencies to reconstruct cross-sectional images of a complex conductivity distribution (${\sigma}+i{\omega}{\varepsilon}$) inside the human body. The inverse problem in MFEIT is ill-posed due to the nonlinearity and low sensitivity between the boundary measurement and the complex conductivity. In MFEIT, we therefore focus on time- and frequency-difference imaging with a low spatial resolution and high temporal resolution. Multi-frequency time- and frequency-difference images in the frequency range of 10 Hz to 500 kHz are presented. In MREIT, we use an MRI scanner to measure an internal distribution of induced magnetic flux density subject to an injection current. This internal information enables us to reconstruct cross-sectional images of an internal conductivity distribution with a high spatial resolution. Conductivity image of a postmortem canine brain is presented and it shows a clear contrast between gray and white matters. Clinical applications for imaging the brain, breast, thorax, abdomen, and others are briefly discussed.