• Journal of the Korean Chemical Society
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• v.56 no.2
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• pp.201-206
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• 2012

The anticorrosive effect of 3-Hydroxyflavone (3HF) in combination with quarternary ammonium bromide and iodide salts (QAB and QAI) for aluminium corrosion in NaOH medium was studied at the temperature range of 303K-323K using weight loss study, potentiodynamic polarization study and impedance spectroscopic measurements. The results revealed that the inhibition efficiency increases with the inhibitor concentration and it further increases on the addition of quarternary ammonium bromide and iodide salts. The enhanced inhibition efficiency of the inhibitor in the presence of quarternary ammonium salts may be due to synergistic effect. The adsorption process of 3HF on the aluminium surface obeys Langmuir's adsorption isotherm. The mechanism of adsorption is further supported by Scanning Electron Microscopic study (SEM).

• Journal of the Korean Chemical Society
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• v.56 no.2
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• pp.264-273
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• 2012

Five derivatives of phenylthiourea namely: 1-(4-methoxyphenyl)-3-phenylthiourea (1), 1-(4-methylphenyl)-3- phenylthiourea (2), 1-(4-bromophenyl)-3-phenylthiourea (3), 1-(4-chlorophenyl)-3-phenylthiourea (4) and 1-phenylthiourea (5) have been evaluated as new inhibitors for the corrosion of carbon steel in 2 M HCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Potentiodynamic polarization measurements showed that these derivatives are mixed-type inhibitors. The inhibition efficiency was found to increase with inhibitor concentration and decreases with rise in temperature. The thermodynamic parameters of adsorption and activation were determined and discussed. Nyquist plots showed depressed semicircles with their centre below real axis. The adsorption process of studied derivatives on carbon steel surface obeys Temkin adsorption isotherm. The synergistic effect of these derivatives and some anions is discussed from the viewpoint of adsorption models. The electrochemical results are in good agreement with the calculated quantum chemical HOMO and LUMO energies of the tested molecules.

• Corrosion Science and Technology
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• v.10 no.3
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• pp.95-100
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• 2011

Protective coatings play an important role in the protection of metallic structures against corrosive environment. The main function of anticorrosive coating is to prevent the materials from corrosive agents, such as water, oxygen and ions. In the study, the corrosion protection properties of urethane and epoxy coating systems were evaluated using EIS methods exposed to the corrosion acceleration test such as Norsok M501, Prohesion and hygrothermal cyclic test. AFM analysis of the coating systems was carried out to monitor the change of roughness of coatings. Urethane coating system was more stable than the epoxy coating under given cyclic conditions. Water uptake into the urethane coatings was less than that into the epoxy coating. The urethane coating system showed better corrosion protection than epoxy coating system based on the changes of the impedance modulus at low frequency region with exposure time. Consequently, the corrosion protection properties of the epoxy and urethane coatings was well correspond with their surface roughness changes and water uptakes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.6
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• pp.2734-2747
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• 2018

In this study, a novel fractal ring antenna with a compact size of $24{\times}9{\times}0.8mm^3$ was configured using three iterations. Low profile, circular polarization, and measured operating bands (4.5-6.5 GHz) meet specifications of the upper band used in Wi-Fi and WiMAX applications. The antenna featured, stable radiation properties, especially gain and efficiency, in the notched band (92%). In deep, the antenna impedance, reflection coefficients, surface current distribution and circular polarization for the three iterations had been studied to improve the process of antenna design and its radiation characteristics.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.6
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• pp.622-634
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• 2003

This paper is concerned with a computational method for recovering a crack shape of steam generator tubes of nuclear plants. Problems on the shape identification are discussed arising in the characterization of a structural defect in a conductor using data of eddy current inspection. A surface defect on the generator tube ran be detected as a probe impedance trajectory by scanning a pancake type coil. First, a mathematical model of the inspection process is derived from the Maxwell's equation. Second, the input and output relation is given by the approximate model by virtue of the hybrid use of the finite element and boundary element method. In that model, the crack shape is characterized by the unknown coefficients of the B-spline function which approximates the crack shape geometry. Finally, a parameter estimation technique is proposed for recovering the crack shape using data from the probe coil. The computational experiments were successfully tested with the laboratory data.

• Journal of electromagnetic engineering and science
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• v.12 no.1
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• pp.37-44
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• 2012

This paper describes a compact and novel wireless vital sign sensor at 2.4 GHz that can detect heartbeat and respiration signals. The oscillator circuit incorporates a planar resonator, which functions as a series feedback element as well as a near-field radiator. The periodic movement of a human body during aerobic exercise could cause an input impedance variation of the radiator within near-field range. This variation results in a corresponding change in the oscillation frequency and this change has been utilized for the sensing of human vital signs. In addition, a surface acoustic wave (SAW) filter and power detector have been used to increase the system sensitivity and to transform the frequency variation into a voltage waveform. The experimental results show that the proposed sensor placed 20 mm away from a human body can detect the vital signs very accurately.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.498-501
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• 2006

When an object or objects, rigid or flexible, presents in incident sound field, the sound wave is scattered. This, we call, is scattered sound field. It, of course, depends on the amplitude and the direction of the incident sound field as well as the geometry and the surface impedance of the scatterer(object). This paper addresses the way to measure scattered sound field by using arbitrary incident sound wave. This means that the method can decompose the scattered field from measured sound field with respect to any magnitudes and directions of incident plane-waves.

• The Korean Journal of Ceramics
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• v.7 no.1
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• pp.6-10
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• 2001

Ultrafine $(CeO_2)_{0.9}(Gd_2O_3)_{0.1}$ solid solution powders synthesized by the glycine-nitrate process, with specific surface areas of $19-23\;\textrm{m}^2$/g were sintered at $1500^{\circ}C$ for various sintering times and then their electrical characteristics were investigated using AC impedance and four-point probe measurements. The electrical resistivity of the sintered $(CeO_2)_{0.9}(Gd_2O_3)_{0.1}$ bodies showed the minimum value at the sintering time of 10 hrs. The minimum total resistivity of the $(CeO_2)_{0.9}(Gd_2O_3)_{0.1}$ bodies sintered at $1500^{\circ}C$ for 10 hrs seems to result from the lowest activation energy for the electrical resistivity by the combination between the activation energies for the resistivities at the grain interior and grain boundary.

• Journal of Electrical Engineering and Technology
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• v.4 no.2
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• pp.277-281
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• 2009

The complex resonant frequency problem of a superconductor patch is formulated in terms of an integral equation which is the kernel of a dyadic Green's function. To include the effect of the superconductivity of the microstrip patch, the surface complex impedance of the superconductor film is introduced using the two fluids model of Gorter and Casimir. The Galerkin procedure is used in the resolution of the electric field integral equation. Numerical results concerning the effect of the operating temperature of a superconductor patch on the characteristics of the antenna are presented.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.6
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• pp.509-516
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• 2008

Multi-layer circuit card for semiconductor inspection was fabricated by LTCC technology. After a proper impedance design without electrical interference, ceramic tapes with the composition of $CaO-Al_2O_3-SiO_2-B_2O_3$ glass and $Al_2O_3$ were prepared. The electrode with silver paste printed on the tape. Printed ceramic sheets were then laminated and sintered. Densities and dielectric properties were measured. The microstructure, fracture surface of the region of via and matching state of substrate-electrode were observed. The durability of plated outside electrode were examined by hardness and scratch test.