• Journal of KSNVE
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• v.6 no.4
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• pp.513-519
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• 1996

This paper is concerned with the bubble sound at the accumulator which is generated by the difference of the high pressure side and the low pressure side in the cycle of the refrigerator. The causes of the bubble sound generation are verified by the visualized test of the operating refrigerant flow at the accumulator and the measurements of the temperature and pressure. Two cases were tested, one with the accumulator has a orifice and the other with the accumulator hasn't a orifice. So that, it is presented the comparison of the bubble sound levels and spectrums in each cases. To predict the bubble sizes when they are generated, the linearized equation driven by Strasberg is used.

• Current Optics and Photonics
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• v.1 no.6
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• pp.637-641
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• 2017

We present dielectric constant measurements of thin films using THz metamaterials fabricated on a quartz substrate. The resonance shifts of the metamaterials exhibit saturation behavior with increasing film thickness. The saturation frequency shift varies with the real part of the dielectric constant, from which the numerical expression for the particular metamaterial design was extracted. We first performed finite-difference time-domain simulations to find an explicit relationship between the saturated frequency shift and the dielectric constant of a thin film, which was confirmed by the experimental results from conventional techniques. In particular, the quartz substrate enables us to determine their values more accurately, because of its low substrate index. As a result, we extracted the dielectric constants of various films whose values have not been addressed previously without precise control of the film thickness.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1823-1828
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• 2000

Power transformers, air-intakes, stacks in a combined thermal power plant are the main noise sources. Power transformer noise among them has being get a target of public complaint due to 480Hz component of its pure tone. The source is mainly magnetostrictive vibration of the transformer core. The first countermeasures was installing sound barrier on the front of transformer. However, 500Hz, center of the frequency is not reduced. This paper includes the measurements of noise level at the near resident apartment, the identification of noise transfer and the countermeasures for noise sources. Cavity resonance type of noise reduction devices was installed on enclosuring wall of transformers. As a result, the noise level from transformer is reduced about 3dB.

• Journal of the Korean Ceramic Society
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• v.48 no.6
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• pp.577-583
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• 2011

Stabilized biocompatible superparamagnetic iron oxide nanoparticles (SPIONs) were prepared by controlled coprecipitation method for hyperthermia application. ESR measurements determined that all of the interactions in the individual SPIONs (1 nm and 11 nm) were antiferromagnetic in nature because the ions contributed to the magnetization with a range of magnetic moments. In-situ monitoring of the temperature increment was performed, showing that the microwave absorption rate of the SPIONs was dispersed in an appropriate host media (polar or non-polar solvents) during microwave irradiation. Microwave absorption energy rates and heat loss of SPIONs in solvent were calculated by non-linear data fitting with an energy balance equation. The microwave absorption rates of SPIONs dispersed in solvent linearly increases when the concentration of SPIONs increases, implying that the microwave absorption rate can be tunable by changing the concentration of SPIONs.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.4
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• pp.84-91
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• 1994

A compact electron cyclotron resonance(ECR) plasma system composed of a microwave generator and a magnet coil was fabricated. A Langmuir single probe was used to investigate the plasma characteristics of the system through I-V measurements. The performance of the compact ECR plasma system was tested for the case of silicon etching reaction with $CF_{4}/O_{2}$(30%) mixed gas. Electron density and etch rate increased to maximum values and then decreased with increasing argon gas pressure, but electron temperature changed in the opposite way. The electron density and the electron temperature of argon gas plasma were 0.85${\times}~5.5{\times}10^{10}cm^{-3}$ and 4.5~6.0 eV, respectively, in the pressure range from $3{\times}10^{4}$ to 0.05Torr. The etch rate reached a maximum value at the position of 2.5cm from the bottom of plasma cavity. Etch rate uniformity was $\pm$6% across 6cm wafer. Anisotropic index was 0.75 at 1.5${\times}10^{-4}$Torr.

• Proceedings of the KSMRM Conference
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• 2003.10a
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• pp.22-22
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• 2003

The purpose of this study was to compare the detection rate of brain metastasis according to size of nodule between 1.5T and 3.0T MRI 대상 및 방법： We reviewed 44 patients with primary tumors and clinical symptoms suggesting brain metastasis. After administration of double dose gadolinium-DTPA, MR imaging was performed with 3D SPGR sequence by 3.0T MRI and then with T1 SE sequence by 1.5T MRI. Consequently, comparison was done in 1.5T T1 SE sequence and 3.0T 3D SPGR sequence. With use of the signal intensity (SI) measurements in the metastatic nodules and adjacent tissue, metastatic nodule-to-adjacent tissue SI ratio were calculated. In each patient, the number of metastatic lesions detected in 1.5T and 3.0T, and their size were assessed qualitatively by three blinded readers.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.6
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• pp.790-796
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• 2010

This paper designed the horn of half-wave needed for Ultrasonic meta) welding. The horn has to be designed and manufactured accurately, because measurements such as the shape, length, mass and etc. have effects on the resonant frequency and the vibration mode. Designed horn of half-wave has the feature of 40,000Hz of nature frequency, and maximizes vibration range in the Tip by resonance in the frequency of ultrasonic wave machine. In this study, we calculated and analyzed the natural frequency to find the optimal design of the horn that amplified the amplitude about double by the modal analysis and harmonic analysis using ANSYS. And we did FFT analysis of the manufactured horn.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.384-389
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• 2011

The vibration of a LP turbine casing may cause the problems of power generation and the life of its facility. In this study, we carried out on-site measurements of a LP Turbine in order to find the cause of the vibration and conducted experimental and numerical modal analysis of the turbine with its support frame. The measurement and the modal analysis show that the natural frequency of the turbine becomes close to 60 Hz due to the subsidence of the support. The elimination of the subsidence by shimming between the turbine and the support frame gave rise to the reduction of the vibration of the LP turbine case.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.303-303
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• 2011

Orderings and electronic structures of organic molecules on metal substrates have been studied due to possible applications in electronic devices. In molecular systems, delocalized pi-electrons play important roles in the adsorption behaviors and electronic structures. We studied the adsorption and electronic structures of Co-Porphyrin molecules on Au(111) using scanning tunneling microscopy (STM) and spectroscopy (STS) at low temperature. Molecules form closely packed two-dimensional islands on Au(111) surface with two different types, having different shape evolutions in our energy-dependent STM observations. The Kondo resonance state, occurred by spin exchange interaction between the Co center atom and conduction electrons in the metal substrate, was observed in one type, while it was absent in the other type in scanning tunneling spectroscopy measurements. Possible origins of two molecular shapes will be discussed.

• Journal of electromagnetic engineering and science
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• v.2 no.2
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• pp.68-74
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• 2002

In this paper, a pre-layout design approach for high-speed microprocessor is proposed. For multilayer PCB stark up configuration as well as selection and placement of decoupling capacitors, an effective solution for reducing SSN and EMI is obtained by modeling and simulation of complete power distribution system. The system model includes VRM, decoupling capacitors, multiple power and ground planes for core voltage, vias, as well as microprocessor. Finally, the simulation results are verified by measurements data.