• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.5
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• pp.667-672
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• 2013

In this paper, we propose a multi-impedance changes localization method of on-voltage underground power cable using the wavelet transform based time-frequency domain reflectometry (WTFDR). To localize the impedance change in on-voltage power cable, the TFDR is the most suitable among reflectometries because the inductive coupler is used to inject the reference signal to the live cable. At this time, the actual on-voltage power cable has multi-impedance changes such as the automatic section switches and the auto load transfer switches. However, when the multi-impedance changes are generated in the close range, the conventional TFDR has the cross term interference problem because of the nonlinear characteristics of the Wigner-Ville distribution. To solve the problem, the wavelet transform (WT) is used because it has the linearity. That is, using WTFDR, the cross term interference is not generated in multi-impedance changes due to the linearity of the WT. To confirm the effectiveness and accuracy of the proposed method, the actual experiments are carried out for the on-voltage underground power cable.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.1
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• pp.47-51
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• 2000

To make a practical application of a micro-strain sensors with ultrahigh sensitivity, a strain on electrical properties of micro-patterned amorphous (Fe\ulcornerco\ulcorner)\ulcornerSi\ulcornerB\ulcorner films had influenced on the impedance over frequency range from 1 MHz to 1 GHz. Reflecting excellent magnetomachanical couping properties of films, high frequency impedance was subject to change sensitively by a strain : a change in impe-dance of 39% was observed at 200 MHz applied a strain of 224$\times$10\ulcorner. To determine a optimum shape of micro-patterned films, film impedance was analyzed by virtue of its constitutive components of resis-tance and reactance. Result was shown that reduction of the resistance term(hence increase of resultant reactance term) of impedance is more effective for enhancing the strain sensitivity of films at relatively low frequency range.

• Journal of Biomedical Engineering Research
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• v.9 no.1
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• pp.109-116
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• 1988

In this paper, principles of impedance tenchinque and relationship between stroke volume and impedance change were theoretically explained. An impedance cardiograph was designed and constructed. Its reproducibility was verified by experiment. Until now, the peak point of dZ/dt waveform, first derivative of impedance change(${\Delta}$Z) , has been detected by software technique requiring considerable time to process. However in this paper its peak point was found using hardware for saving processing time. Useful cardiac parameters such as stroke volume and contractility of cardiac muscle were measured noninvasively. The reproducibility of the instrument was measured to be better(less than 10%) than that of clinical standard method such as thermodilution (more than 30%). Hence impedance cardiography was found to be better techique for monitoring stroke volume and myocardial contractility for pre and post operation, and pharmacological studies.

• Journal of the Korean institute of surface engineering
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• v.50 no.5
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• pp.405-410
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• 2017

In order to study current-voltage-luminance and impedance characteristics according to elapsed time, a blue fluorescent OLED was fabricated. The current density and luminance gradually decreased in accordance with elapsed time and did not emit light after 480 hours, and the threshold voltage increased as time elapsed. The Cole-Cole plot was a semicircular shape of a very large size at 2 V of the applied voltage below the threshold voltage, and the maximum value of the real number impedance did not change greatly from 9314.5 to $9902.2{\Omega}$ as time elapsed. Applied voltages 4, 6, and 8 V above the threshold voltage showed a large change in the real number impedance value at the semicircle end to 9,678.2, 9,826, $9,535.4{\Omega}$ according to the elapsed time from 2,222.5, 183.7, $48.2{\Omega}$ immediately after fabricating the device. By increasing the applied voltage beyond the threshold voltage just after device fabrication, the energy difference between the device and the organic layer was overcome and the current flowed, the maximum value of the real number impedance sharply decreased. As time passed, current did not flow through the element even at high applied voltage due to degradation of the element, and even when the applied voltage was higher than the threshold voltage, it showed an impedance value such as applied voltage equal to or less than the threshold voltage. As a result, it can be learned that the change in the impedance with elapsed time reflects the characteristics due to the degradation of the OLED and can predict the characteristics and lifetime of the OLED.

• International Journal of Advanced Culture Technology
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• v.10 no.3
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• pp.281-286
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• 2022

In this study, design of an intuitive internal resistance diagnostic device is to diagnose the residual capacity and aging of the battery regardless of the model and the internal protocol of the waste battery through the method of measuring the internal resistance of a waste battery. In this paper, charging and discharging were continuously performed with 2A charging and 5A discharging in order to secure data on impedance changes that may occur in the charging and discharging process of various methods. As a result of the final experiment, it was confirmed that the impedance change occurred during charging and discharging, and the amount of change increased as the charging/discharging C-rate increased. In addition, it was confirmed that the waste battery aged or abnormal cell had a large change in the impedance value.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.7
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• pp.1339-1342
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• 2007

In this study, we determined the optimum electrode pair for measuring the abdominal pressure using bio-impedance method and compared with conventional methods. Because impedance changes differ from a weight, a height, contractile force, volume of muscle and blood other or whatever of individuals, it was quantified using values of impedance change, correlation coefficient and SNR. Our results showed the optimum electrode pair (1, 9) which could detect impedance changes due to an increase of the intensity of the abdominal pressure. The correlation coefficient and quadratic function between the RMS values of EMG and the impedance changes were 0.87 and $y=0.0014x^2+0.0620x+0.6958$, respectively. It demonstrated that the abdominal pressure could be measured noninvasively and simply using bio-impedance method. We propose that this optimum electrode configuration would be useful for future studies involving the convenient measurement of abdominal pressure by ambulatory urodynamics monitoring study.

• Journal of the Korean Ceramic Society
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• v.43 no.3 s.286
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• pp.156-161
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• 2006

Impedance spectroscopy was applied to the initial hydration of calcium phosphate bone cements in order to investigate the electrical/dielectric properties. Hydration or equivalently setting was monitored as a function of the amount of water and initial powder characteristics. Higher amounts of water produced more open microstructures, leading to higher conductivity and enhanced dielectric constant. The effects of the initial characteristics in the powder were investigated using bone cement powder prepared with and without granulation. Granulated powder exhibited a significant change in resistance and produced a higher dielectric constant than those of conventional powder. Through a simplified modeling, the effects of thickness in reaction products and pore sizes were estimated by the frequency-dependent impedance measurements. Furthermore, impedance spectroscopy was proven to be a highly reliable tool for evaluating the continuous change in pore structure occurring in calcium phosphate bone cements.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.1
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• pp.102-107
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• 2010

Dye-sensitized solar cell (DSC) has been expected to be an alternative to the conventional silicon solar cell due to simple manufacturing process and low fabrication casts. In order to improve productivity of DSC, we attempted to optimize the required time of the adsorption process. According to the change in the adsorption time from 1 to 24h, We analyzed the output characteristics and the change of internal impedance. As a result, The outputs of DSC were continuously increased until 12h of the adsorption time and remained the same after that. Also, We reconfirmed this result that 12h was optimum adsorption by the analysis of the electrochemical impedance spectroscope because the internal impedance was similar to the output.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.8
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• pp.668-674
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• 2004

The possibility of global noise reduction by the sound power control through selection of distribution and impedance of absorptive materials is discussed. It is necessary to investigate the relation between the global sound energy in the field and the total sound power radiated by sources. In the previous work,$^{(1.2)}$ the authors presented a useful design method to change boundary condition that can be useful to reduce noise in acoustically small enclosures. Changing boundary condition Is related to not only enclosure’s geometrical shape but also acoustical treatment on walls for example, attaching of impedance patches (ex: absorptive material). In many practical situations, we often meet situation to change acoustical treatment on walls. The possibility of total acoustic potential energy(globa1 noise) reduction by acoustic source power control is examined in an acoustically small cavity Using acoustic energy balance equation, the relation between global noise control performance and absorptive material’s arrangement/impedance is deduced. Numerical simulation is performed to interpret its physical meaning in terms of absorbent’s distribution and impedance.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.718-723
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• 2017

In this paper, Analytical study is carried out on the impedance characteristics of the globe control valve, which is mainly used for thrust control in liquid rockets, according to the effective area at low frequency perturbation. The impedance tends to increase according to effective area and the cause of impedance characteristic change through flow field visualization is investigated. In the future, the information on the change in the impedance characteristics of the control valve can be used to obtain the impedance of the supply system and it can be utilized to predict pogo phenomenon as well as design accumulator and orifice to reduce the pogo phenomenon.