• International Journal of Concrete Structures and Materials
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• v.8 no.4
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• pp.289-299
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• 2014

Alkali-activated slag concretes are being extensively researched because of its potential sustainability-related benefits. For such concretes to be implemented in large scale concrete applications such as infrastructural and building elements, it is essential to understand its early and long-term performance characteristics vis-a'-vis conventional ordinary portland cement (OPC) based concretes. This paper presents a comprehensive study of the property and performance features including early-age isothermal calorimetric response, compressive strength development with time, microstructural features such as the pore volume and representative pore size, and accelerated chloride transport resistance of OPC and alkali-activated binder systems. Slag mixtures activated using sodium silicate solution ($SiO_2$-to-$Na_2O$ ratio or $M_s$ of 1-2) to provide a total alkalinity of 0.05 ($Na_2O$-to-binder ratio) are compared with OPC mixtures with and without partial cement replacement with Class F fly ash (20 % by mass) or silica fume (6 % by mass). Major similarities are noted between these binder systems for: (1) calorimetric response with respect to the presence of features even though the locations and peaks vary based on $M_s$, (2) compressive strength and its development, (3) total porosity and pore size, and (4) rapid chloride permeability and non-steady state migration coefficients. Moreover, electrical impedance based circuit models are used to bring out the microstructural features (resistance of the connected pores, and capacitances of the solid phase and pore-solid interface) that are similar in conventional OPC and alkali-activated slag concretes. This study thus demonstrates that performance-equivalent alkali-activated slag systems that are more sustainable from energy and environmental standpoints can be proportioned.

• Korean Journal of Materials Research
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• v.10 no.6
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• pp.430-436
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• 2000

In this paper, we have studied the effect of constituent ratio NiO, CuO and doped with B-Bi-Zn on proper-ties(microstructure, density, shrinkage, permeability as a function of frequency, etc.) of hexagonal-ferrite for high fre- quency chip-inductor material about several GHz. The permeability were analyzed by impedance analyzer(100 kHz∼ 40 MHz) and network analyzed(30 MHz∼3 GHz). As a result of the characteristics. the B-Bi-Zn glass ceramic was used to lower the sintering temperature for additive as function of frequency from 100kHz to 1.8 GHz showed con-stant tends. The maximum imaginary value of complex permeability was observed near the resonance frequency of 2 GHz.

• Applied Chemistry for Engineering
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• v.16 no.4
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• pp.507-512
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• 2005

When carbon electrode is used as an anode in Li ion battery, passivation film forms on the electrode surface during the initial charge process due to so called Solid-Electrolyte Interphase (SEI). The passivation film formed by solvent decomposition during the initial charge process affects charge/discharge capacity. In this paper, 1 M $LiPF_6,EC:DEC$ (1 : 1, volume ratio) electrolyte with $Li_2CO_3$, at various temperatures, the electrochemical characteristics of passivation film formed on Kawasaki Mesophase Fine Carbon electrode surface were investigated by using chronopotentiometry, cyclic voltammetry, and impedance spectroscopy. Experimental observations indicated that as solvent decomposition occurred, the decomposition voltage was strongly dependent on ionic conductivity, which was low in the process at low temperature. The impedance of passivation film formed during the initial charge process, were dependent on the temperature.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.39 no.6
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• pp.9-19
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• 2002

An NAC(Natural Admittance Control) system design is presented for interaction controller that achieves high-performance and guarantees stability. The NAC can be classified as a particular flavor of impedance control similar to control schemes that have velocity compensator and force compensator. The NAC significantly improves the response characteristics when Coulomb friction is presented in One-link Robot System and guarantees stability when robot contacts with environment. Pragmatic rules for NAC synthesis are derived. It shows method to choose a target impedance for realizable force compensator. Important parameters are found experimentally. It is demonstrated, by the experimental result, that NAC algorithm is successful in rejecting Coulomb friction through velocity compensator and guarantees stability through force compensator. We implement an experimental set-up consisting of environment-generated one-link robot system and DSP system for controller development. We apply the natural admittance controller to the One-link robot system, and show the good performance on desired force control in case of contacting with arbitrary environment.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.38 no.3
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• pp.47-54
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• 2001

This study is to analyze the impedance response in human body by acoustic stimulation on acupoints and contrast parte; for objectification of the meridian substance. It is to verify meridian pathway and channel theory or bio-energy in body. This paper proposes to make an hypothesis about the underground water theory. The meridian has not tube or pipe line type channel but bio-energy flow along the channel similar to flowing pattern of underground water in body. It was analyzed the current characteristic or impedance response after acoustic stimulation by sound wave of 5 specific tones. The response characteristics of current stimulation are measured by the average current magnitude and variation ratio or meridian. The current variation ratio or Live Meridian(gung) 33.2%, Heart Meridian(sang) 30.7% Kidney Meridian (gak) 33.1%, Spleen Meridian(chi) 33.9%, Lung Meridian (wo) 30.7% are to be compared to contrast parts (non-acupoint and meridian). In experimental results, meridian is discrimination to non-meridian, and 5 vital meridians have a reciprocal relationship with sound wave of 5 specific tones.

• IEIE Transactions on Smart Processing and Computing
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• v.3 no.3
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• pp.153-159
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• 2014

As the number of treatments in the therapeutic ultrasound field targeted at fat tissue increase, the performance of the equipment should be evaluated for safety using a fat phantom. In this study, a fat phantom was fabricated using olive oil and a tissue-mimicking material (TMM) phantom. To evaluate the acoustic properties of the TMM phantom according to the changes in the olive oil, the composition ratio of a liquid mixture of olive oil with a surfactant was adjusted from 5-20% in 5% steps. The acoustic properties of the phantom were evaluated using the sound velocity, attenuation coefficient, density, and acoustic impedance. The experimental results showed that the sound velocity decreased with increasing amount of olive oil but the other acoustic properties did not change. In addition, the phantom using an olive-oil mixture with a 15% composition ratio was most similar to the acoustic characteristics of fat tissue with a sound velocity of 1477.35 m/s, an attenuation coefficient of 0.514 dB/MHz-cm, a density of $1.07g/cm^3$, and an acoustic impedance of 1.575 MRayl. These experimental results are expected contribute to the accuracy of the results using a TMM phantom and will be useful for the therapeutic ultrasound field targeted at subcutaneous fat tissue.

• Journal of the Korean Electrochemical Society
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• v.13 no.2
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• pp.138-144
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• 2010

In order to investigate the electrochemical propertied of titanium electrode for electrolysis, manganese oxide was electrodeposited on surface of mesh titanium by pulse voltammetry. The morphological changes and impedance results of manganese oxide electrodeposited electrode were analyzed by SEM and EDX. The size of electrodeposited manganese oxide on mesh titanium was increased with first cycle pulse time increase, and approximately 100 non-uniform manganese oxide was grown at 10 ms pulse polarization time. Charge transfer resistance($R_{ct}$) of near the overpotential was analyzed by EIS measurement and the feasibility of prepared electrode was evaluated by the overpotential calculated from Tafel plots.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.4
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• pp.542-550
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• 2001

In this paper, a channel combiner is designed to combine two adjacent digital TV channels without interference to transmit these channels with one broadband antenna. A constant impedance type combiner, consisting of two identical bandpass filters and two identical 3 dB power combiners, is chosen as a channel combiner. The bandpass filter used in the channel combiner also suppresses out-of-band signal caused by digital transmitter's non-linearity. H-plane type bandpass filters and branch-line fewer combiners are adopted in the design. The simulated results of the designed bandpass filter and power combiner show excellent agreement with the theoretical results. Finally, a channel combiner is designed by combining filters with rover combiners and the characteristics are simulated. It is shown that the designed channel combiner shows excellent performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.9
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• pp.1070-1076
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• 2007

In this paper, we study the characteristics of dual band microstrip antenna with the wedge-shaped radiation patch added the slot using air substrate. Wedge-shaped patch antenna with air substrate is avoided the large probe reactance associated with a thick substrate owing to the use of short probe and good impedance matching over a wide frequency range can be obtained. Slot on the antenna radiator varies the reactance component according to the employed frequency and affect the resonance freaqency of the antenna, therefore the antenna can resonate at the dual band(cellular and PCS band). The slot length and position have an effect on the bandwidth and input impedance of the antenna are optimized by simulation. From the experiment results for the fabricated antenna, -10 dB of $S_{11}$ is content with the allocated bandwidth of Cellular and PCS system and - 15 dB of cross polarization level. From the results of this paper, it has been confirmed that the proposed antenna can be used as the base station antenna fur Cellular and PCS band.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.1
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• pp.63-69
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• 2000

The high-$T_c$ Superconducting (HTS) antenna which consists of "H" type resonator has the benefits for the miniaturization of antenna in comparison with the microstrip antenna of the similar dimension. To fabricate the "H" type antenna, HTS $YBa_2Cu_3O_{7-x}$ (YBCO) thin films were deposited on MgO substrates using rf-magnetron sputtering. Standard etching processes were performed for the patterning of the "H" type antenna. For comparison between normal conducting antennas and superconducting antennas, the gold antennas with the same dimension were also fabricated. An aperture coupling was used for impedance matching between $50{\Omega}$ feed line and HTS radiating patch. The diverse experimental results were reported in terms of the resonant frequency, the return loss and the characteristics impedance. The "H" type superconducting antenna showed the performance of 1.36 in SWR, 24% in efficiency, and 14.6 dB in the return loss superior of the normal conducting counterpart.