• The Journal of the Acoustical Society of Korea
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• v.18 no.4
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• pp.3-10
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• 1999

Investigations of temperature differences between both cnds of thermoacoustic exchanger generated by acoustic heat transport have been carried out as a function of the position of TAC(Thermo-Acoustic Couple)[1] in a 68-cm-long duct. Fixed with the electric power at 50W, measurements were compared with the theory changing the frequency from 150Hz to 300Hz with 10Hz step. The frequency-position dependent distribution of temperature difference corresponding to the Q-values was obtained with the numerical simulation. Through this distribution, the optimum position of the thermoacoustic exchanger and the optimum driving frequency can be determined.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.04a
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• pp.195-200
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• 1994

과학문명의 발달은 지구환경에 미치는 영향이 서로 달라도 환경파괴라는 대가를 치르면서 발전하여 왔다. 환경문제는 수질오염, 대기오염, 폐기물 및 소음진동이 있다. 이중에서 소음진동과 관련된 환경문제는 도시가 커지고 기계문명이 발달하면서 심각성은 더해가고 있다. 환경소음중 주거생활에 직접적으로 영향을 미치는 교통소음, 공장소음에 대하여 일반적인 성분을 파악하였다. 조사시 소음레벨보다는 주파수 분석에 의한 특성을 중시하였으며, 주파수 분석 결과에 따라 저주파 대역 및 고주파 대역으로 분류하였다. 음향블럭은 시멘트 블럭을 가공하여 제작한 것으로 일정한 크기의 홈이 있다. 음향블럭의 음향특성은 이 홈에 따라 달라지는 것이 일반적인 특성인데 본 연구에서는 동일한 음향블럭에 대하여 설치방법 및 흡음재 사용에 따라 달라지는 음향 특성에 대하여 실험결과와 적용방법을 제시하였다.

• The Journal of the Acoustical Society of Korea
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• v.39 no.5
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• pp.400-405
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• 2020

To analyze the flow distribution formed by multiple acoustic sources, the distribution of acoustic streaming speed caused by an ultrasonic transducer composed of two identical piezoelectric vibrators was examined for various angles between the sound sources. In order to measure the distribution of the speed along the acoustic axis of the transducer, a simple measurement method using a droplet indicator having density similar to that of water is suggested. The simulation results calculated by a numerical method and experimental results showed a similar tendency, and the change of flow speed distribution with the intersection angle between acoustic beams radiated from two acoustic sources was analyzed.

• Journal of the Korea Organic Resources Recycling Association
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• v.12 no.4
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• pp.121-129
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• 2004

Anaerobic digestion is the most common process for sewage sludge stabilization and has benefits of VS reduction and biogas production. Many pretreatment methods have been studied to improve hydrolysis rate because the rate of sewage sludge degradation is slow in anaerobic digestion. This study mainly focused upon the effects on disintegration of sewage sludge by ultrasonic pretreatment according to the variation of acoustic density and duration of sonication time. In this study, acoustic density has been changed as follows : 33W/L, 70W/L, 88W/L, 139W/L in case of 40 kHz with the test time changes of 10min, 20min, 25min, 30min and 40min. In the comparison of $SCOD_{Cr}/TCOD_{Cr}$ variation for excess sludge and mixed sludge disintegration, the rates of $SCOD_{Cr}/TCOD_{Cr}$ have been increased in the condition of denser acoustic density and longer sonication time with acoustic frequency of 40kHz. The pH of the excess sewage sludge and mixed sewage sludge has been decreased in the condition of denser acoustic density and longer sonication time with acoustic frequency of 40kHz.

• Water for future
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• v.53 no.12
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• pp.58-63
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• 2020

• The Journal of the Acoustical Society of Korea
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• v.33 no.5
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• pp.291-299
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• 2014

To probe the temperature elevation effect caused by ultrasound, a tissue mimicking phantom was newly suggested. A carrageenan gel was adopted to realize not only the required transparency for visualization but also acoustic characteristics similar to human tissue. To visualize the temperature elevation inside phantom, thermochromic film with a critical temperature of discoloration was introduced. Acoustic characteristics of the tissue mimicking phantom were examined when the concentrations of carrageenan and sucrose changed. As the results, the attenuation coefficient of the phantom could be controlled in the range of 0.44~0.49 dB/cm/MHz, and the acoustic impedance in the range of 1.52~1.77 Mrayls. We could control the acoustic characteristics of the phantom by different concentration of carrageenan and sucrose, and it was possible to examine the temperature elevation caused by ultrasound in the phantom. The suggested method was verified by noninvasively visualizing the temperature elevation due to planar and focused ultrasound using the fabricated phantom.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.257-260
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• 1999

본 연구에서는 압전형 쇄석기에 의한 충격파 조사시에 초점위치 및 파쇄정도에 따른 파쇄대상물의 진동과 그 때 들려오는 방사음과의 관계에 대하여 검토해 본 시뮬레이션 결과를 제시한다. 아울러 동일한 실험을 파쇄가능한 대상물에 시행하여 진동과 파쇄효율과의 관계에 대해서도 실험적으로 검토한다. 최종적으로 압전형 쇄석기로 충격파를 대상물에 조사할 때, 충격시의 방사음과 대상물의 진동 및 그것에 따른 파쇄효율의 전체적인 상관성에 대하여 고찰한다.

• The Journal of the Acoustical Society of Korea
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• v.17 no.6
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• pp.23-28
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• 1998

고분자 압전 필름인 PVDF를 이용하여 단일막과 이층막의 초음파 변환기를 제작하 여 임펄스 응답특성을 이론식에서 계산하여 실험적으로 확인하여 보았다. 또한 RF 펄스를 이용하여 초음파 변환기의 다층막에 따른 주파수 특성을 조사하였다. 그 결과 임펄스 응답 특성은 이론식과 잘 일치하였으며, 단일막의 변환기가 이층막에 비하여 지속시간이 짧은 펄 스를 나타내었다. RF펄스에 대한 주파수특성은 이층막의 변환기가 단일막에 비하여 광대역 의 특성을 나타냄을 알 수 있었다.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.6
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• pp.103-109
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• 2017

An increase in acoustic energy in a combustion chamber coupled with heat fluctuations from flame results in the occurrence of combustion instability. The assessment of combustion stability requires the prediction of acoustic energy variation by understanding the acoustical characteristics of flow boundaries in a combustion chamber. The present paper discusses about the characteristics of acoustic impedances at boundaries in terms of Strouhal number and summarizes theoretical analyses on the acoustic characteristics of injector-head-like configurations. Also, the details of the two-microphone measurement technique have been presented.

• The Journal of the Acoustical Society of Korea
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• v.25 no.3
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• pp.101-106
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• 2006

In this study, the impedance behavior of micro-speaker had been investigated as a function of hole area existing on the grille. In order to theoretically study the change of acoustical property due to the different total hole area, the holes were treated as a short open pipe system, such as an orifice. This theoretical result was in an excellent agreement with the experimental one. In detail, the acoustic impedance to be caused by the hole could be greatly increased with the decrease of hole area. Therefore, it can be concluded that the acoustic property of micro-speaker could be greatly changed by increasing the acoustic impedance of hole with reducing hole area.