• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 추계학술대회 논문집 학회본부
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• pp.205-208
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• 1994

The purpose of this study is to research and develop solid polymer electrolyte(SPE) for Li secondary battery. PEO-$LiClO_4$ electrolyte with plasticizer is very unstable. Passivation phenomena in polymer electrolyte cell was described by the SPL model. The time dependance of the impedance indicates that a passivation layer grows rapidly on the Li surface. However, the growing of passivation layer on the Li surface can be restrained by addition of zeolite to the PEO electrolyte. It suggested that addition of zeoliteto to the PEO-$LiClO_4$ electrolyte effectively controls the formation of a passivation layer on Li electrode.

• 한국소음진동공학회논문집
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• 제24권1호
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• pp.62-68
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• 2014

Recently, MRI(magnetic resonance imager) scanner is continually used for medical diagnosis and many biomedical researches. When it operates, however, intense noise is generated. The SPL(sound pressure level) of the noise approaches 130 dB especially in 3 T(Tesla) MRI. Meanwhile, more than 3 T MRI scanners have been developed to get higher-resolution images, so louder noise is expected in the future. The intense noise makes patients feel nervous and uncomfortable. Moreover, it could possibly cause hearing loss to patient in extreme cases. For this reason, some active noise control systems have been researched. One of them used feedback Filtered-X LMS(FXLMS) algorithm which is able to control only narrowband noises and possible to diverge in severe case. In this paper, we determine the property of MRI noise. Using the property, we applied a method of open-loop and adaptive control for reducing MRI noise at target point inside bore. We verified performance of the method with computer simulation and preliminary experiment. The results demonstrate that the method can effectively reduce MRI noise at target point.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.493-496
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• 2005

With the growth in electronics and the remarkable advance in wireless communication technology, mobile devices, such as mobile phones and PDAs are incessantly improved in their diverse functional performance. Lighter weight and smaller size has been gradually accomplished by recent circuit integration technology resulting in rapid growth in the number of mobile phone subscribers. Driven by customer demand, recent mobile devices are fully capable of realizing a variety of dazzling multimedia effects powered by electro-acoustic parts that have become one of the generic components. However, this paper also presents an oval micro-speaker, that is expected to show an excellent performance within limited space of mobile phone, and its performance design has been suggested as well. Finally, a statistical approach to achieve high characteristic and performance is suggested by Taguchi method to identify a certain relationship between a mobile phone and a micro-speaker.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.497-502
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• 2005

In mobile phones of multimedia era, microspeakers of high quality sound are essential parts to generate human voice in speaker phone and MP3 song player. In this paper, two types of microspeakers, outer permanent magnet (PM) and combined PM type, are analyzed using electromagnetic, mechanical, acoustical and their coupling analysis. For performance comparison, voice coil diameter is chosen as a design parameter to change excitation position and magnet volume for both types. For combined PM type, sound pressure level (SPL) is improved due to increased PM volume compared to outer PM type. Also, with the decreased voice coil diameter for combined PM type, the 1st resonant mode of the diaphragm is more efficiently excited due to concentrative excitation, resulting in lower and broader frequency range. Therefore, it can be said that the combined PM type microspeakers are more advantageous for high performance microspeaker which are essential for multimedia era.

• 한국소음진동공학회논문집
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• 제16권6호
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• pp.593-601
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• 2006

In many fire emergencies, the auditory fire alarm signals are very important to save the occupant's life. But as the sound insulation of building elements has been improved, it is more difficult for occupant to recognize the fire alarm signals when the audible fire alarm worked. This is the first study to show the sound attenuation of audible fire alarm device in apartments. We measured and analyzed the sound attenuation level in seven units. The result showed that it was not sufficient to detect the sound from the fire alarm device in bedrooms. Whether the fire alarm device worked or not, the differences of sound level in bedrooms were below 1$\sim$10 dBA. To give the minimum sound level 60 dBA in bedrooms, the proper sound levels from alarm device installed in livingrooms were suggested using computer simulation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.1067-1071
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• 2004

In this paper, the characteristic of the regenerative pump is reviewed by the measurement and the analysis. The dominant noise sources are harmonic components of the rotating impeller frequency. The acoustic characteristics and the noise source position at the dump are identified. In order to reduce the high-level peak noise, the interior flow of the pump chamber is analyzed by CFD (Computational Fluid Dynamics). Acoustic pressure is calculated with Ffowscs Williams and Hawkings equation. As the result of the analysis new design of the pump chamber is recommended. The recommended pump is compared with original pump by evaluating the RMS value of a interior static pressure and the sound pressure level. The new pump chamber recommended by analysis results is proved by a process of the measurement. The overall SPL of a recommended pump is reduced about 3 dBA.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.253-256
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• 2004

Acoustical noise at low frequency range (below 500Hz) of refrigerator result from fans which are inside of the refrigerator. In generally to evaluate and apply to refrigerator it is recommended that acoustical noise and fluidic performance of the fan were measured simultaneously. To do that twin-room type anechoic wind tunnel was needed. But constructing twin room type anechoic wind tunnel was very expensive and estimation of small refrigerator fan performance was not easy. So in this paper we composed anechoic fan tester. A successful noise and performance measurement was performed using the anechoic fan tester. Existing 22 kinds of refrigerator fan were investigated and mapped into one database. Refrigerator duct pressure resistance were measured and reflected into the fan database to find out appropriate fan. Through the application of fan database, the refrigerator became less noise compared to current one and these data shows what is the best way to reduce fan noise.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.763-766
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• 2004

Recently, various acoustic artifacts that contains speaker have been produced such as cellular phone. Speaker consists of diaphragm generating sound and coil vibrating diaphragm. Generally, good speaker means that it has a wide frequency range, high output power rate to input power and flat sound pressure level in specified frequency range. Acoustic characteristic was estimated through the experiment and computer simulation, or sound power was controlled with acoustic sensitivity in a natural frequency range fer last decade. However, the flatness of sound pressure level has not been considered to enhance the sound quality of a speaker. Tn this study, a method for speaker design is proposed for a good acoustic characteristic, which is flatness of SPL(sound pressure level) and wideness between the first and second natural frequency. SYSNOISE is used fer acoustic analysis and ANSYS is used for harmonic response analysis and modal analysis. Optimization for acoustic characteristics of a speaker diaphragm is performed using ModelCenter. All analyses are done within a frequency domain. And we confirm that the experimental and computational simulations have similar trend.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.612-621
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• 2008

For the purpose of improving accuracy in jet noise prediction and investigating its generation mechanism, high subsonic jets were computed by using compressible Large Eddy Simulation(LES), wherein the inflow forcing or disturbance added in the inflow shear layer was incorporated. The far-field Sound Pressure Levels(SPL) as well as the flow field resulted in good agreement with available experimental data by applying only the high azimuthal modes among the inflow forcing parameters. We found that this result was due to an important role of the inflow forcing upon breaking down the axiymmetric vortices that caused high amplitude velocity and pressure fluctuations. In order to examine generation mechanism of the dominant noise component, wavelet transformation was introduced to reveal the presence of a well-organized structure of pressure fluctuations that originated mainly from vortex motions near the end of the jet potential core. This structure took a train of alternately positive and negative wavelet-transformed pressure regions along the jet distance, spreading towards the downstream with advection and propagation. It was concluded that this structure and its dynamic motion are the reason why a high subsonic jet produces the dominant noise with a particular downstream directivity.

• 대한조선학회논문집
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• 제38권3호
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• pp.23-30
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• 2001

고속 프로펠러들의 단면 및 기하학적 형상변화에 대한 캐비테이션 및 소음특성 연구가 새로운 실험장치를 이용하여 KRISO의 캐비테이션 터널에서 실험적으로 연구되었다. 대형 고속선형 프로펠러에 대한 날개단면, 부하분포 및 전개면적비 변화에 대한 일련의 캐비테이션 소음시험이 수행되었으며, 이런 실험결과로부터 캐비테이션 형태 및 프로펠러 형상에 대한 소음성능이 분석되었다. 새로운 실험장치를 이용하여 얻은 소음결과는 실선추정 및 고부하 저소음 추진기 설계에 유용한 자료로 활용될 수 있다.