• 교육시설
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• 제11권1호
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• pp.5-14
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• 2004

Since 1990s in Korea, elementary school classrooms have been designed toward open education system in pursuit of variety of educational purpose. Also, the architectural designs of schools have been acomplished for individual school not based on the standard design code. The present paper aims to investigate the acoustic environment of existing classrooms and to compare the sound insulation capacity between the ordinary classrooms and the newly built classrooms for open education. The current acoustical situation of elementary classrooms was analyzed using field measurements and questionnaire survey. In order to this, Three elementary schools were selected which were built in 1978, 1996 and 2000 respectively. Room acoustical parameters including Reverberation time(RT), Definition(D50), Speech Intelligibility(RASTI), Transmission loss(TL) and STC were measured in a classroom in each elementary school classroom. Each measurement was undertaken with the windows and doors being open or closed. As the result, it was found that the transmission loss between rooms in open classrooms is, $5{\sim}6dB$ in average, inferior than the ordinary classrooms. The RASTI of 0.70 was measured in newly built classrooms which is better than old classrooms(0.70) and open classrooms(0.73). This was shown as same in the speech definition measurements. This results from the condition of sealing and airtightness of classrooms and floor materials. The results denote that open classrooms have poor acoustic condition in sound insulation and speech intelligibility.

• 한국연소학회지
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• 제19권1호
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• pp.29-38
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• 2014

This paper described an experimental investigations of combustion instability mode in a lean premixed dual swirl combustor for micro-gasturbine system. When such the instability occurs, a strong coupling between pressure oscillations and unsteady heat release excites a self-sustained acoustic wave which results in a loud, annoyed sound and may also lead a structural damage to the combustion chamber. The detailed period of flame behavior and heat release in combustion instability mode have been examined with high speed OH and CH-PLIF system and $CH^*$ chemiluminescence measurement, flame tomography with operated at 10 kHz and 6 kHz each. Experiment results suggest that unstable flame behavior has a specific frequency with 200 Hz and this frequency is accords with about 1/2 sub-harmonic of combustor resonance frequency, not fundamental frequency. This is very interesting phenomenon that have not reported yet from other previous works. Therefore, when a thermo-acoustic instability with Rayleigh criterion occurs, the fact that the period of heat release and flame behavior are different each other was proposed for the first time through this work.

• 전기학회논문지
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• 제64권9호
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• pp.1330-1336
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• 2015

It is necessary to study on acoustic and vibratory response of a MEMS resonant accelerometer before applying to military applications. In this paper, we analyze why the resonant accelerometer reacts to an acoustic wave and a high frequency vibration. And we describe experimental results on acoustic and vibratory response of the accelerometer. The accelerometer consists of a proof mass and a dual ended tuning fork. It is a differential resonant accelerometer with arranging a pair of accelerometers. The mode shape was analyzed to find out the input mode frequency by using a FEM simulation. Some experiments regarding the acoustic noise was carried out by using a tweeter and a microphone in the anechoic room. Results showed that the accelerometer reacted to the acoustic wave and vibration which had the input mode frequency as we had expected. We showed experimentally not only that the susceptibility of the accelerometer to an acoustic wave was 70 dB but also that the effectiveness of applying an acoustic absorber and a metal case was 20 dB, respectively. Also, we could minimize the vibratory response property of the accelerometer by installing a IMU with a silicone rubber mount pad.

• 한국음향학회지
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• 제38권5호
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• pp.558-567
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• 2019

스피치, 국악, 뮤지컬, 대중음악과 콘서트까지 다양한 장르의 공연이 이루어지는 방송용 다목적 홀의 경우 공연에 필요한 전기, 건축 음향적 요구 조건이 다양하다. 하지만 실제 음향 환경 가변을 위한 효율적인 운용 방법은 많지 않다. 본 연구는 무대 반사판의 설치 유 무와 전기 음향 사용 조건하에서 배너의 가변에 따른 홀의 음향 환경 변화를 살펴보았다. 그 결과 벽체 면적의 15 %에 해당하는 배너를 설치한 실제 측정에서 잔향 시간(Reverberation Time, $T_{30}$)은 최대 0.12 s, 초기감쇠시간(Early Decay Time, EDT)은 0.15 s, 음악 명료도(Clarity, $C_{80}$)는 0.76 dB, 음성 명료도(Definition, $D_{50}$)는 6.43 % 변하였다. 배너의 면적을 확장시킨 컴퓨터 시뮬레이션을 통해 전체 벽체 면적의 40 %에 해당하는 배너를 설치할 경우 잔향 시간은 0.11 s에서 최대 0.55 s까지 가변되는 것을 확인했다.

• 한국광학회:학술대회논문집
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• 한국광학회 2009년도 동계학술발표회 논문집
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• pp.435-436
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• 2009

LNG 선박에 설치된 대용량 탱크의 누출을 검사하는 방법으로 $NH_3$를 사용하고 있다. 본 논문에서는 광음향효과를 이용하여 $NH_3$의 흡수선을 조사하였고, 이를 이용하여 $NH_3$의 농도를 측정하는 방법을 실험하였다.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1998년도 학술발표대회 논문집 제17권 1호
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• pp.239-242
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• 1998

A new real time sound field visualization technique is introduced in this study using PIV(Particle Imaging Velocimetry) technique. Small particles of which density is small enough to follow up the air flow are used for sound visualization. When the driving frequency is in the vicinity of the resonance frequency of the simplified 2-dimensional muffler system, an acoustic streaming is shown and of which velocity distribution is obtained through PIV technique. It is experimentally proved that the present technique is able to visualize and quantify the sound field's energy flow.

• Journal of information and communication convergence engineering
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• 제3권3호
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• pp.137-141
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• 2005

The paper presents some methods to improve characteristics of film bulk acoustic resonator (FBAR) devices. The FBAR devices were fabricated on Bragg reflectors. Thermal treatments were done by sintering and/or annealing processes. The measurement showed a considerable improvement of return loss $(S_{11})$ and quality factor $(Q_{s/p}).$ These thermal treatment techniques seem very promising for enhancing FBAR resonance performance.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.308-314
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• 2011

The research which sees, the parameters inputs and acoustic measurement result in simulation error most on a large scale concreteness of 3D models which affect number of effective surface. Therefore DATA of above the comparison which will listen, analyzed and investigated.

• 소음진동
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• 제9권6호
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• pp.1152-1156
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• 1999

In this study, a fiber optic air-backed mandrel hydrophone has been constructed and performance of acoustic signal detection has been measured. The hydrophone is based on a Mach-Zehnder interferometer with 35 m of sensing fiber. The sensitivity is measured up to -128 dB re rad/$\mu$ Pa in range from 1.4 kHz to5 kHz. A system with this design of hydrophone may be applied to detect low frequency underwater acoustic signals.

• 비파괴검사학회지
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• 제23권2호
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• pp.116-124
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• 2003