• Corrosion Science and Technology
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• v.4 no.6
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• pp.217-221
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• 2005

In the present investigation, holographic interferometry was utilized for the first time to monitor in situ the thickness of the oxide film of aluminium samples during anodization processes in boric acid solutions. The anodization process (oxidation) of the aluminium samples was carried out by the technique of the electrochemical impedance spectroscopy(EIS), in different concentrations of boric acid (0.5-5.0% $H_3BO_3$) at room temperature. In the mean time, the real-time holographic interferometry was used to measure the thickness of anodized (oxide) film of the aluminium samples in solutions. Consequently, holographic interferometry is found very useful for surface finish industries especially for monitoring the early stage of anodization processes of metals, in which the thickness of the anodized film of the aluminium samples can be determined without any physical contact. In addition, measurements of electrochemical values such as the alternating current (A.C) impedance(Z), the double layer capacitance($C_{dl}$), and the polarization resistance(Rp) of anodized films of aluminium samples in boric acid solutions were made by the electrochemical impedance spectroscopy(EIS). Attempts to measure electrochemical values of Z, Cdl, and Rp were not possible by holographic interferometry in boric acid especially in low concentrations of the acid. This is because of the high rate of evolutions of interferometric fringes during the anodization process of the aluminium samples in boric acid, which made measurements of Z, Cdl, and Rp are difficult.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.3
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• pp.528-531
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• 1994

Digitalization in electronic system is required the capacitor which have a large capacitance with small size, low impedance at high frequency, and high reliability. The fabrication and its properties of aluminum solid electrolytic capacitor are investigated. Employing conduction polymer film such as, polypyrrole as solid electroylte, solid type aluminum electrolytic capacitors were made. The surface of insulationg oxide is covered with conducting polymer layer prepared by chemical oxidative polymerization. Thereafter this conducting layer is covered with conducting polymer prepared by electrochemical polymerization. The dielectric properties of these capacitors were also measured and discussed. Regarding on frequency characteristics of the trial made capacitor, impedance and ESR at high frequency is lower than those of the stacked type film capacitor. It is alo confirmed that temperature coefficient of capacitance and dissipation factor of the capacitor are lower than those of film capacitor and liquid type aluminum electrolytic capacitor.

• Corrosion Science and Technology
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• v.16 no.6
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• pp.298-304
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• 2017

Coil spring steels from the automobile suspension part after field exposure for 10 years and those after anti-corrosion validation test in proving ground of 5,000 ~ 10,000 km were examined for corrosion damages. Partial loss of paint, accumulation of corrosion product, and cracking of paint and superficial material were observed. The surface and subsurface region of spring steels had compressive residual stress and high hardness by shot peening. The surface hardness values of the specimens were 620 ~ 670 Hv. They were 60 ~ 80 Hv higher than those of the samples taken from the middle part of the spring. The maximum compressive stress was -916 ~ -1208 MPa measured at depth of about $100{\mu}m$. Electrochemical impedance spectroscopy showed that the resistances of charge transfer and the paint layer of the spring steels ranged from several tens to millions ${\Omega}{\cdot}cm^2$. The resistance of the field samples was much higher than that of the proving ground samples used in this study, implying that the proving ground test condition would be more corrosive than the field environment.

• Korean Journal of Metals and Materials
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• v.49 no.4
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• pp.329-333
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• 2011

To develop wide-band noise absorbers with a special design for low-frequency performance, this study proposes a tin oxide (Sn-O) thin films as the noise absorbing materials in a microstrip line. Sn-O thin films were deposited on polyimide film substrates by reactive sputtering of the Sn target under flowing $O_{2}$ gas, exhibiting a wide variation of surface resistance (in the range of $10^{0}-10^{5}{\Omega}$) depending on the oxygen partial pressure during deposition. The microstrip line with characteristic impedance of $50\Omega$ was used for the measurement of noise absorption by the Sn-O films. The reflection parameter $(S_{11})$ increased with a decrease of surface resistance due to an impedance mismatch at the boundary between the film and the microstrip line. Meanwhile, the transmission parameter $(S_{21})$ diminished with a decrease of surface resistance resulting from an Ohmic loss of the Sn-O films. The maximum noise absorption predicted at an optimum surface resistance of the Sn-O films was about $150{\Omega}$. For this film, greater power absorption is predicted in the lower frequency region (about 70% at 1 GHz) than in conventional magnetic sheets of high magnetic loss, indicating that Ohmic loss is the predominant loss parameter for the conduction noise absorption in the low frequency band.

• Journal of the Korean institute of surface engineering
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• v.56 no.4
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• pp.250-258
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• 2023

Ceramic oxide layer was formed on the surface of high silicon aluminum alloy by using PEO (plasma electrolytic oxidation) process. The microstructure of the oxide layer was analyzed using scanning electron microscopy (SEM) and x-ray diffraction patterns (XRD). The high silicon aluminum alloy prior to PEO process consists of Al, Si and Al₂Cu phases in XRD analysis, whereas Al₂Cu phase selectively disappeared after PEO treatment. Considerable decrease of relative intensity in most of peaks in XRD results of the high silicon aluminum alloy treated by PEO process was observed. It may be attributed to the formation of amorphous phases after PEO treatment. The corrosion behavior of the high silicon aluminum alloy treated by PEO process was investigated using electrochemical impedance spectroscopy (EIS) and other electrochemical techniques (i.e., open circuit potential and polarization curve). Electroanalytical studies indicated that the high silicon aluminum alloy treated by PEO process shows greater corrosion resistance than that untreated by PEO process.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.9
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• pp.453-458
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• 2001

This paper presents a new vector control algorithm of the surface mounted permanent magnet motor (SMPMM) without any rotational tranceducer. Originally, SMPMM does not have any magnetic saliency in structure, but it has a little magnetic saliency due to the saturation by the flux of the permanent magnet. Moreover, it varies according to the load conditions and the control performance of schematics using the saliency can be easily degraded. To prevent it and to improve the performance of the proposed algorithm, the saliency of a SMPMM under various load conditions is analyzed. In the proposed algorithm, the saliency or the impedance difference related to the saliency is utilized in order to estimate the position and speed of the rotor. And the high frequency signal is injected into the motor to measure the impedance difference and also to enhance the control performance of the system. The experimental results verify the performance of the proposed sensorless algorithm.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.4
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• pp.139-143
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• 2005

For application of carbon nano-tube (CNT) as a counter electrode materials of dye-sensitized solar cell (DSSC), the electrochemical behavior of CNT electrode was studied, employing cyclic-voltammetry (C-V) and impedance spectroscopy. Fabrication of CNT-paste and formation of CNT-counter electrode for characteristic measurement have been carried out using ball-milling and doctor blade process, respectively. Unit cell for measurements was assembled using Pt electrode, CNT electrode, and iodine-embedded electrolyte. Field emission-scanning electron microscopy (FE-SEM) was used for structural investigation of CNT powder and electrode. Sheet resistance of electrode was measured with 4-point probe method. Electrochemical properties of electrode, C-V and impedance spectrum, were studied, employing potentiogalvanostat (EG&G 273A) and lock in amplifier (EG&G 5210). As a results, the sheet resistance of CNT electrode is almost similar to that of F-doped SnO2 (FTO) coated glass substrate as approximately 10 ohm/sq. From C-V and impedance spectroscopy measurements, it was found that CNT electrode has high reaction rate and low interface reaction resistance between CNT surface and electrolyte. These results provides that CNT electrode were superior to that of conventional Pt electrode. Particularly, the reaction rate in the CNT electrode is about thrice high than Pt electrode. Therefore. CNT electrode is to be good candidate material for counter electrode in DSSC.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.135-138
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• 2005

On the basis of theoretical studies on the effect of the cylinders attached to semi-infinite screens, the effect of the tangential sound power-transport along the cylindrical top section of noise barriers is studied. Four types of acoustical mechanism between the surface of the cylinder and the adjacent air particles are investigated, namely Z $\rightarrow$ $\infty$, Z $\rightarrow$ pc, Z $\rightarrow$ 0 and actively controlled surface sound field. In active control case the sound power parallel to the surface of the attached cylinder is minimized by means of a secondary sound field, which is generated from a part of the attached cylinder. In each case the change in the acoustical shadow zone was shown and compared. The numerical study shows the possibility of deflecting the incident sound by minimizing the acoustical surface impedance of the upper sections.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.4
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• pp.267-271
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• 2011

The insulating characteristics and temperature rise behaviors of porcelain suspension insulators were investigated. The testing insulators had used in the distribution systems normally and were sampled. Firstly, leakage current was measured and its impedance was calculated. The leakage current of good insulators is 0.2 mA and its impedance is 66 $M{\Omega}$. The worse insulators have lower impedance and the insulators having below 15 $M{\Omega}$ take place flashover at the high frequency voltage flashover test. Secondly, the temperature rise characteristics were analyzed depending on leakage current and its impedance. Surface temperature of insulators was measured for 30 minutes and until its saturation after voltage was applied. The temperature rise of insulators having 15 $M{\Omega}$ is about $14.5^{\circ}C$ above the ambient temperature. Lastly, the heating behaviors of 3 insulators in a string was analyzed. Any insulator in the string does not generate heat so far as it has at least one sound insulator. On the other hand, all the insulators in the string are bad if the string have any heating insulator.

• Korean Journal of Materials Research
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• v.13 no.4
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• pp.259-265
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• 2003

For the aim of thin microwave absorbers used in mobile telecommunication frequency band, this study proposed a high permittivity dielectrics(λ/4 spacer) coated with ITO thin films of 377 $\Omega$/sq(impedance transformer). High frequency dielectric properties of ferroelectric ceramics, electrical properties of ITO thin films and microwave absorbing properties of ITO/dielectrics were investigated. Ferroelectric materials including $BaTiO_3$(BT), 0.9Pb($Mg_{1}$3/Nb$_{2}$3/)$O_3$-0.1 $PbTiO_3$(PMN-PT), 0.8 Pb (Mg$_{1}$3/$Nb_{2}$3/)$O_3$-0.2 Pb($Zn_{1}$3$_Nb{2}$3/)$O_3$(PMN-PZN) were prepared by ceramic processing for high permittivity dielectrics,. The ferroelectric materials show high dielectric constant and dielectric loss in the microwave frequency range. The microwave absorbance (at 2 ㎓) of BT, 0.9PMN-0.1PT, and 0.8PMN-0.2PZN were found to be 60%(at a thickness of 3.5 mm), 20% (2.5 mm), and 30% (2.5 mm), respectively. By coating the ITO thin films on the ferroelectric substrates with λ/4 thickness, the microwave absorbance is greatly improved. Particularly, when the surface resistance of ITO films is closed of 377 $\Omega$/sq, the reflection loss is reduced to -20 ㏈(99% absorbance). This is attributed to the wave impedance matching controlled by ITO thin films at a given thickness of high permittivity dielectrics of λ/4 (3.5 mm for BT, 2.5 mm for PMN-PT and PMN-PZN at 2 ㎓). It is, therefore, successfully proposed that the ITO/ferroelectric materials with controlled surface resistance and high dielectric constant can be useful as a thin microwave absorbers in mobile telecommunication frequency band.