• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.5
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• pp.443-449
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• 2007

The structural and thermal stability of $Li[Co_{0.1}Ni_{0.15}Li_{0.2}Mn_{0.55}]O_2$ electrode during cycling process was studied. The sample was prepared by simple combustion method. Although there were irreversible changes on the initial cycle, O3 stacking for $Li[Co_{0.1}Ni_{0.15}Li_{0.2}Mn_{0.55}]O_2$ structure was retained during the first and subsequent cycling process. Impedance of the test cell was decreased after the first charge-discharge process, which would be of benefit to intercalation and deintercalation of lithium ion on subsequent cycling. As expected, cycling test for 75 times increased impedance of the cell a little, instead, thermal stability of $Li[Co_{0.1}Ni_{0.15}Li_{0.2}Mn_{0.55}]O_2$ was improved. Moreover, based on DSC analysis, the initial exothermic peak was shifted to high temperature range and the amount of heat was also decreased after cycling test, which displayed that thermal stability was not deteriorated during cycling.

• Journal of Advanced Navigation Technology
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• v.21 no.3
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• pp.287-293
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• 2017

This paper describes an unequal Bagley divider using uniform transmission lines with adjustment electrical lengths between output ports. To obtain an arbitrary dividing ratio of Bagley divider, we have only adjusted the electrical lengths of the transmission line between output ports. All the transmission lines have the same characteristic impedance value. This design method does not require an impedance transformer for port matching. For verification, we simulated and fabricated a 3-way, 1:2:1 and 5-way, 2:3:4:3:2 ratio Bagley divider with an operating frequency of 2 GHz. The experimental results are in agreement with the simulated results.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.2
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• pp.236-241
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• 2004

New electrolytes of cubic L $a_2$M $o_2$-x Nbx $O_{9-}$$\delta$/(x=0, 0.05, 0.1, 0.2) were fabricated by a solid-state reaction method and their sintered densities were approximately 93％ of theoretical density. X-ray diffraction analysis and microstructure observation for the sintered specimens were performed. The at complex impedance were measured at 34$0^{\circ}C$ to 93$0^{\circ}C$ in air and fitted with a Solatron ZView program. Their impedance spectra showed big difference below and over the phase transition temperature (58$0^{\circ}C$). The electrical conductivity of L $a_2$M $o_2$ $O_{9}$ was 1.36${\times}$10$^{-2}$ S$cm^{-1}$ / at 817$^{\circ}C$. Comparing to undoped L $a_2$M $o_2$ $O_{9}$ , Nb-doped specimen showed the increase of electrical conductivity due to the aliovalent doping effect..

• Smart Structures and Systems
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• v.6 no.7
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• pp.851-866
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• 2010

This paper presents a new concept of using PZT (lead zircornate titanate) transducers as a non-destructive testing (NDT) tool for evaluating quality of concrete. Detection of defects in concrete is very important in order to check the integrity of concrete structures. The electro-mechanical impedance (EMI) response of PZT transducers bonded onto a concrete specimen can be used for evaluating local condition of the specimen. Measurements are carried out by electrically exciting the bonded PZT transducers at high frequency range and taking response measurements of the transducers. In this study, the compression test results showed that concrete specimens without sufficient compaction are likely to fall below the desired strength. In addition, the strength of concrete was greatly reduced as the voids in concrete were increased. It was found that the root mean square deviation (RMSD) values yielded between the EMI signatures for concrete specimens in dry and saturated states showed good agreement with the specimens' compressive strength and permeable voids. A quality metric was introduced for predicting the quality of concrete based on the dry-saturated state of concrete specimens. The simplicity of the method and the current development towards low cost and portable impedance measuring system, offer an advantage over other NDE methods for evaluating concrete quality.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.8
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• pp.41-46
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• 2008

This paper conducts the research on the variation in the characteristics of the resonance and impedance of the metallic parallel plates due to the replacement of the normal dielectric substrate by the metamaterial. The ENG(${\epsilon}<0$), MNG(${\mu}<0}$) and DNG(${\epsilon},{\mu}<0$) types of metamaterial as well as the DPS(Double Positive) material are taken into consideration a full-wave modal analysis method known for accurate computation, as the SRR-kind of Lorentz model for permittivity and metal wire-periodic array-kind of Drude model for permeability, and the behaviors of parallel plates' resonance mode and impedance are observed. Based upon the observation, the design guidelines for the substrate can be addressed regrading how to suppress the parallel plates' spurious resonance modes that degrade the quality of the electronic equipment.

• Geomechanics and Engineering
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• v.12 no.1
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• pp.161-183
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• 2017

This paper investigates the damage identification of the concrete pile element through axial wave propagation technique using computational and experimental studies. Now-a-days, concrete pile foundations are often common in all engineering structures and their safety is significant for preventing the failure. Damage detection and estimation in a sub-structure is challenging as the visual picture of the sub-structure and its condition is not well known and the state of the structure or foundation can be inferred only through its static and dynamic response. The concept of wave propagation involves dynamic impedance and whenever a wave encounters a changing impedance (due to loss of stiffness), a reflecting wave is generated with the total strain energy forked as reflected as well as refracted portions. Among many frequency domain methods, the Spectral Finite Element method (SFEM) has been found suitable for analysis of wave propagation in real engineering structures as the formulation is based on dynamic equilibrium under harmonic steady state excitation. The feasibility of the axial wave propagation technique is studied through numerical simulations using Elementary rod theory and higher order Love rod theory under SFEM and ABAQUS dynamic explicit analysis with experimental validation exercise. Towards simulating the damage scenario in a pile element, dis-continuity (impedance mismatch) is induced by varying its cross-sectional area along its length. Both experimental and computational investigations are performed under pulse-echo and pitch-catch configuration methods. Analytical and experimental results are in good agreement.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2785-2790
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• 2007

This study presents an impedance method of in-vitro characterization of the thrombotic potential of whole blood. Whole blood samples of 0.2 cc were put into a micro-cell with embedded three electrodes immediately after venepuncture at $37^{\circ}C$. Anti-coagulated blood samples were also collected for hematocrit and blood viscosity analyses. The rate of change of electron flow was measured, which indicates the inverse of the thrombotic potential. A sudden decrease in the rate of change of electron flow was observed at a time equal to approximately 110 seconds. This sudden decrease was significantly delayed in anti-coagulated samples. After the sudden decrease, the rate continued to decrease, reaching a minimum value in unadulterated samples while the change in the rate in the anti-coagulated ones was found rather moderate. Based on these preliminary findings, the present method may be of used as a new tool for the diagnosis of the thrombotic potential of whole blood.

• Journal of IKEEE
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• v.16 no.3
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• pp.211-216
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• 2012

In the phase boundary estimation problem, the estimation performance depends on the initial guess. However, there is no information on the number of bubbles and those positions for the initial guess in real flows. Therefore, it is very important to set appropriate initial guesses from prior information. In this paper, in order to set initial guesses for estimating the phase boundaries in two-phase flows, first, unknown resistivity distribution was estimated using the difference reconstruction method. After that, an adaptive threshold value was automatically computed using intermodes method. Based on this value, the number of bubbles and the initial position were determined. The numerical experiments have been performed to evaluate the estimation performance of the proposed method.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.2
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• pp.137-143
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• 2015

This paper presents the intra capacitance modeling based on the winding method and section bobbin for CM choke capable of EMI attenuation of broad bands from lower to higher frequency bands and high frequency type common-mode choke capable of EMI attenuation of high frequency band used in the EMI Block of LED-TV SMPS. The case of high frequency type CM choke can be explained by the parasitic capacitance of three types of CM choke. The winding method of section bobbin type is smaller than the others. The first resonant frequency of the proposed CM choke tends to increase as the parasitic capacitance becomes small and its impedance characteristics improved performance as the first resonant frequency increases. The CM chokes of the proposed section bobbin type shows that in the future, the method may have practical use in LED/LCD-TV SMPS and in several applications, such as LED lighting, adapters, and so on.

• Journal of Power Electronics
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• v.17 no.1
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• pp.305-313
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• 2017

A novel interference isolation method is proposed by using several designed coils in capacitive power transfer systems as isolation impedances. For each designed coil, its stray parameters such as the inter-turn capacitance, coil resistance and capacitance between the coil and the core, etc. are taken into account. An equivalent circuit model of the designed coil is established. According to this equivalent circuit, the impedance characteristic of the coil is calculated. In addition, the maximum impedance point and the corresponding excitation frequency of the coil are obtained. Based on this analysis, six designed coils are adopted to isolate the interference from power delivery. The proposed method is verified through experiments with a power carrier frequency of 1MHz and a data carrier frequency of 8.7MHz. The power and data are transferred parrallelly with a data carrier attenuation lower than -5dB and a power attenuation on the sensing resistor higher than -45dB.