• Journal of Electrochemical Science and Technology
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• v.15 no.2
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• pp.242-252
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• 2024

To date, methods used to assess the interfacial transition zone (ITZ), which represents the boundary between the aggregate and paste inside concretes, have primarily relied on destructive tests, and non-destructive tests has received little attention until recently. This study assessed the interfaces of concretes with lightweight aggregates based on electrochemical impedance spectroscopy (EIS) for high-strength concretes and examined the possibility of estimating the compressive strength of concretes through non-destructive testing using EIS. The experimental results revealed that the impedance of the hardened cement increased with increasing compressive strength and aggregate density. In particular, when the results of impedance measurement were displayed as a Nyquist plot, the intercept of the x-axis depicting the effective conductivity was proportional to the compressive strength. Furthermore, an equivalent circuit was selected to interpret the correlation between cement aggregates and impedance. Consequently, the compressive strength was found to increase with the value of the resistances of the electrolyte filled in continuous pores in the cement aggregate. And, the pores formed in the ITZ affect this value. The resistance at the ITZ for different aggregates was also obtained, and it was found that the resistance was consistent with the results predicted by SEM images of the ITZ and correlated with the strength of the concretes. The proposed method can be used as a way to easily determine the strength of cement according to differences in aggregate.

• Journal of electromagnetic engineering and science
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• v.10 no.1
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• pp.1-5
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• 2010

A spurious suppressed bandpass filter is proposed and discussed using the stepped impedance resonator(SIR) on a substrate-integrated waveguide(SIW) structure with a double-layer substrate. The second resonance of the fundamental $TE_{10}$ mode can be controlled by adjusting the electrical length and impedance ratio of each SIR. The spurious suppressed SIW bandpass filter shows the measurement results of the insertion loss of 3.98 dB and return loss of less than 11.58 dB at the center frequency of 12 GHz. Also, the second spurious frequency is improved to about $1.5f_0$ compared with $1.33f_0$.

• The Journal of Korea Robotics Society
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• v.12 no.3
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• pp.356-364
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• 2017

This paper presents a force control based on the observer without taking any force or torque measurement from the robot which allows realizing more stable and robust human robot interaction for the developed multi-functional upper limb rehabilitation robot. The robot has four functional training modes which can be classified by the human robot interaction types: passive, active, assistive, and resistive mode. The proposed observer consists of internal disturbance observer and external force observer for distinctive performance evaluation. Since four training modes can be quantitatively identified as impedance variation, position-based impedance control with feedback and feedforward controller was applied to the assistive training mode. The results showed that the proposed sensorless observer estimated cleaner and more accurate force compared to the force sensor and the impedance controller embedded with the proposed observer completed the assistive training mode safely and properly.

• Journal of the Korean Society for Nondestructive Testing
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• v.11 no.1
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• pp.38-43
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• 1991

The relationship between eddy current response and case hardening depth has been studied on SM40C(KS D-3752) and SCM440(KS D-3711) steels which were surface hardened by high frequency induction hardening. The results obtained in this study were as follows ; 1) Case hardening depth was successfully measured by observing the eddy current impedance changes of each steel. The impedance decreased linearly with increasing case hardening depth. 2) For large impedance gradient between the hardened surface and core metal, the eddy current response was more sensitive to case hardening depth than for low impedance gradient.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1140-1153
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• 2018

The harmonic impedance characteristic of a traction power supply system (TPSS) is necessary for taking actions to suppress the high-order harmonic resonances caused by AC electric locomotives. This paper proposes a controllable harmonic generating method (CHGM) for measuring the TPSS harmonic impedance by injecting harmonic disturbances of different frequencies and amplitudes into the TPSS. This method applies phase shifted pulse-width modulation (PSPWM) and ensures that the undesired sideband harmonics can be negligible while the desired harmonic is both controllable and adjustable. Multiple harmonics can be emitted at the same time. The implementation of the method is also presented. Simulations are carried out to validate the performance of the proposed method. Finally, experimental results on a 5 H-bridge converters platform verified the effectiveness and feasibility of the proposed method.

• Proceedings of the KIEE Conference
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• 2006.11a
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• pp.405-407
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• 2006

The power system analysis based on the accurate impedance of the individual underground cable, which is the inter connected to a large power system, is required. A study on calculation method of impedance allowable current for underground cables. furthermore, various methods of bonding and earthing the sheath have been used for the purpose of eliminating or reducing the sheath losses. the effectes of bonding and earthing must be includied in impedances. therefore, the subject of predicting thermal performance of soil and cable systems has been received increasing attension. for these problems, this paper describes a general formulation of impedance that is based on the effect of crossbonding and earthing of the sheath on the 66kV, 132kV and 220kV underground cable systems. also the work is presented, for calculating the temperature rise of power cable and soil.

• Transactions of the Korean hydrogen and new energy society
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• v.20 no.4
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• pp.283-290
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• 2009

This study focuses on the performance characteristics of polymer electrolyte membrane fuel cell (PEMFC) using the AC impedance technique. The experiment was carried out to investigate the optimal operating conditions of PEMFC such as cell temperature, flow rate, humidified temperature and back-pressure. The fuel cell performance was analyzed by DC electronic-loader with constant voltage mode and expressed by voltage-current density. Additionally, AC impedance was measured to analysis of ohmic and activation loss and expressed by Nyquist plot. The results showed that the cell performance increased with increase of cell temperature, air flow rate, humidified temperature and backpressure. Also, the activation loss decreased as the increase of cell temperature, air flow rate, humidified temperature and backpressure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.106-109
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• 2008

In this paper, impedance of the chiller foundation for ships is studied by using FEM and prediction is compared to measurements. Small and medium weight hammer are used to cover high and low frequency ranges in impedance measurements. Comparison shows that measurement and prediction is in good agreement in which coherence is higher than 0.98 for the frequency ranges of 40-50 Hz to 1600 -2000 Hz.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1629-1632
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• 2008

Rapid, real-time detection of pathogenic microorganisms is an emerging and quickly evolving field of research, especially with regard to microorganisms that pose a major threat to public health. Herein, a new method that uses bioimpedance and solid culture medium for the real-time detection of microorganisms is introduced. We fabricated a new impedimetric biosensor by integrating solid media and two plane electrodes attached on two facing sides of an acryl well. During bioelectrical impedance analysis, the solid medium showed the characteristics of a homogenous conductive material. In a real-time impedance measurement, our solid-medium biosensor could monitor bacterial growth in situ with a detection time of ${\sim}4$ hrs. Our data indicate that the solid-medium biosensor is useful for detecting airborne microorganisms, thereby providing a new analytical tool for impedance microbiology.

• Biomolecules & Therapeutics
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• v.19 no.1
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• pp.109-117
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• 2011

In this work, we have investigated the effect of polyoxyethylene alkyl ester nonionic surfactants on percutaneous permeation enhancement of a model drug, ketoprofen. We also investigated the mechanism involved in the enhancement using impedance and solubility measurement. Three groups of nonionic surfactants with different ethylene oxide content were studied. The permeation results showed that all surfactants enhanced the percutaneous absorption, irrespective of the molecular weight. The permeation results from PEG-45 monostearate (PEGMS45) were rather unexpected. Impedance and solubility results indicate that the mechanism involved in the enhancement of permeation by PEG-10 monooleate (PEGMO10) and PEGMS45 is rather different. The results from PEGMS45 suggest that it could be a potential candidate as a skin penetration enhancer with high molecular weight, which may poses less skin irritation and systemic side effect than the smaller surfactant molecules. Overall, this work provided some useful information on percutaneous transport enhancement and the mechanistic insights involved in skin permeation for these nonionic surfactants.