• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.4
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• pp.73-80
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• 2010

The grounding impedance is not lowered by expanding the dimension of the grounding electrode, and the length of grounding electrode which shows the minimum value of the grounding impedance for each condition of frequency and soil characteristics is existent, and it is defined as Critical Length. In this paper, a new distributed parameter circuit model considering the condition of the multi-layered soil structures was proposed, and the grounding impedance and critical length of the vertical grounding electrode were analyzed by using the newly proposed simulation model and the MATLAB program. As a consequence, it was found that the effect of the soil structure on the frequency-dependent grounding impedance and critical length of the vertical grounding electrode is significant. It is desirable to consider the soil structure in optimal design of the grounding system.

• Journal of Magnetics
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• v.13 no.2
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• pp.65-69
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• 2008

The magneto impedance (MI) behaviors of patterned $Co_{30}Fe_{34}Ni_{36}$ microwire were investigated with respect to its shape variation. After preparing $Co_{30}Fe_{34}Ni_{36}$ microwires using electrodeposition and photolithography methods, impedance measurements were conducted to compare the MI ratios of the devices with different aspect ratios. As a result, the anisotropy field and transverse permeability were found to be strongly affected by the aspect ratio of the device. The external field value at the maximum impedance and maximum sensitivity of the device was found to increase with increasing device width, which was attributed to the increased transverse anisotropy with decreasing aspect ratio. While an increase in the thickness also contributed to an increase in the MI ratio, a variation in the thickness not only increased the anisotropic field, but the variation in the MI ratio was as also affected by the skin effect. Conversely, the MI ratios of the present devices were hardly affected by variations in the length. Considering the typical aspect ratios of our devices, it was expected that the length effect would emerge when the aspect ratio was reduced to less than 10. Nevertheless, our results show that for the practical application of MI devices, the MI characteristics can be optimized by tailoring the aspect ratio of the devices.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.18-28
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• 2001

The present study investigates flow dynamics between two dimensional compliant plates under sinusoidal flow conditions in order to understand influence of wall motion, impedance phase angle (time delay between pressure and flow waveforms), and non-Newtonian fluid on wall shear stress using computational fluid dynamics. The results showed that wall motion induced additional terms in the streamwise velocity profile and the pressure gradient. These additional terms due to wall motion reduced the amplitude of wall shear stress and also changed the mean wall shear stress. The trend of the changes was very different depending on the impedance phase angle. As the impedance phase angle was changed to more negative values, the mean wall shear stress decreased while the amplitude of wall shear stress increased. As the phase angle was reduced from 0°to -90°under $\pm$4% wall motion, the mean wall shear stress decreased by 12% and the amplitude of wall shear stress increased by 9%. Therefore, for hypertensive patients who have large negative phase angles, the ratio of amplitude and mean of the wall shear stress is raised resulting in a more vulnerable state to atherosclerosis according to the low and oscillatory shear stress theory. We also found that non-Newtonian characteristics of the blood protect atherosclerosis by decreasing the oscillatory shear index.

• The Journal of the Acoustical Society of Korea
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• v.20 no.3
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• pp.76-82
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• 2001

Most fluid machines can be considered as periodic noise sources when operated under constant conditions, which allows for a frequency domain representation of the source and the associated acoustic field In the duct. In such a representation, the source is characterized by frequency-dependent values of both strength and impedance. Although knowledge of these values can be gained by either experimentation or by modeling, one-port acoustic characteristics of an in-duct source with high flow velocity, high temperature, and high sound level can be measured only by the multiload method using an overdetermined set of open pipes with different lengths as applied loads. However, the problem is that negative source resistances have been often measured. This paper reviews the possible causes of the problem, with reference to experimental and theoretical results, in an attempt to clarify the issue. A new interpretation is given for the violation of basic assumptions and the defect in the algorithm of multiload method. The major cause and mechanism of the problem is due to the violation of time invariance assumption of the source and the load impedance can seriously affect the final measured result of source impedance.

• Journal of the Korean Electrochemical Society
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• v.11 no.1
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• pp.33-36
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• 2008

In the present study, impedance spectrometry has been used for predicting State-of-Charge (SoC) of gel type, Valve Regulated Lead Acid (VRLA), battery. The impedance measurements of VRLA battery (2V/1.2 Ah) at various SoC were made over the frequency range from 100kHz to 10mHz with an amplitude 10 mV. The impedance parameters have been evaluated by the analysis of the data using an equivalent circuit and a complex non-linear least squares (CNLS) fitting method. The charge transfer resistance values and double layer capacitance values of the positive electrode were higher than those of the negative electrode. The gel resistance values increased with decreasing in SoC. This indicates that the gel resistance is an important parameter for predicting SoC of VRLA battery.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.9
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• pp.1019-1024
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• 2012

In this paper, a UWB antenna using a SIR(Step Impedance Resonator) that eliminate signal interference at 5 GHz WLAN as the first rejection band and adjust the second rejection band is proposed. Unlike the unit impedance resonator, the second harmonic of SIR is decided according to step impedance. Therefore, To adjust the second rejection band, SIR is applied to UWB antenna. Also, the equivalent circuit of the antenna at first rejection band is presented and the equivalent modeling values of the SIR and the coupling value is obtained. The proposed antenna is satisfied to cover full UWB band with return losses less than -10 dB and has band rejection characteristic in 5 GHz WLAN band. The radiation patterns show +y directivity characteristics in H-plane and the group delay variations are within 1.0 ns.

• Transactions on Electrical and Electronic Materials
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• v.6 no.5
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• pp.238-242
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• 2005

The Pt counter electrode of a dye-sensitized solar cell (DSSC) plays a role in helping redox reaction of iodine ions in electrolyte, also, transferring electrons into electrolyte. In this case, it is expected that characteristics of Pt electrodes strongly depend on fabrication process and its surface condition. In this study, Pt electrodes were prepared by a electro-deposition and a RF magnetron sputtering. Electrochemical behavior of Pt electrodes was compared using cyclic-voltammetry and impedance spectroscopy. Surface morphology of Pt electrodes was investigated by FE-SEM and AFM. I-V characteristics of DSSC were measured and discussed in association with the surface properties of counter electrode. As a result, electrochemical properties of electro-deposited Pt electrode were superior to that of sputtered Pt electrode. This is likely that enlarged area of surface in electro-deposited Pt electrode in comparison with the case of sputtered Pt electrode playa role in enhancing such electrochemical properties.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.1
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• pp.7-11
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• 2004

In this paper, the wideband microstrip patch antennas for the Personal communications Service (PCS : 1750∼1870 MHz) and International Mobile Telecommunications-2000 (IMT-2000 : 1920∼2170 MHz) dual band are studied. Experimental and simulation results on the dual band antenna are presented. Simulation results are in good agreement with measurements. The experimental and simulation results confirm the wideband characteristics of the antenna. The studied antenna satisfied the wideband characteristics that are required characteristics for above 420 MHz impedance bandwidth for the PCS and IMT-2000 dual band antenna. In this paper, through the designing of a dual band antenna, we have presented the availability for PCS ＆ IMT-2000 base station antenna. An impedance bandwidth of 33% (VSWR<1.5, 650 GHz) and a maximum gain of 7dB can be achieved. The radiation pattern is stable across the passband.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.6
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• pp.964-973
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• 2008

In this study, a short-wavelength coplanar-type transmission line employing periodic ground structure (PGS) was developed for application to miniaturized on-chip passive component on Si Radio Frequency Integrated Circuit (RFIC). The transmission line employing PGS showed shorter wavelength and lower characteristic impedance than conventional coplanar-type transmission line. The wavelength of the transmission line employing PGS structure was 57 % of the conventional coplanar-type transmission line on Si substrate. Using the theoretical analysis. basic characteristics of the transmission line employing PGS (e.g., bandwidth. loss, impedance, and resonance characteristics) were also investigated in order to evaluate its suitability for application to a development of miniaturized passive on-chip components on silicon RFIC. According to the results. the bandwidth of the transmission line employing PGS was more than 895 GHz as long as T is less than 20${\mu}m$, and the resonance characteristic was observed in 1239 GHz, which indicates that the PPGM structure is a promising candidate for application to a development of miniaturized on-chip passive components on Si RFIC.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.8
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• pp.718-725
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• 2004

If a wall separates the bounded and unbounded spaces, then the wall’s role in transporting the acoustic characteristics of the two spaces is not well defined. In this paper, we attempted to see how the acoustic characteristics of two spaces are really affected by the spatial characteristics of the wall. In order to understand coupling mechanism, we choose a finite space and a semi-infinite space separated by the flexible or rigid wall and an opening. A volume interaction can be occurred in structure boundary and a pressure Interaction can be happened in the opening boundary. For its simplicity, without loosing generality, we use rather simplified rectangle model instead of generally shaped model. The source impedance is presented to the various types of boundaries. The distributions of pressure and active intensity are also presented at the cavity- and structure-dominated modes. The resulting modification, shifts of modal frequencies and changing of standing wave patterns to satisfy both coupled boundary conditions and governing equations, are presented.