• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.309-312
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• 2004

본 연구에서는 매미가 소형이면서도 광대역의 소리를 낼 수 있는 원리가 무엇인지를 파악하고 이중 음향 발생 장치 제작에 적용할 수 있는 요소를 도출하였다. 매미의 발음기관에서 가장 중요한 부분은 복부 공명실과 진동판이다. 복부 공명실은 위상 반전형 인클로져 시스템으로 모델링 할 수 있으며, 진동판은 돔 형태의 박판으로 볼 수 있다. 근육에서 발생된 입력 신호는 진동판의 곡면에 의해 판에 좌굴을 일으켜 높은 음압의 소리를 발생시킨다. 발생된 소리는 복부를 통해 위상이 반전되어 특정 대역이 강조된다. 진동판의 가장 큰 특징은 곡면구조에 의한 비선형적인 출력이며 이를 통하여 가진 주파수와 상이한 주파수 성분들을 효과적으로 발생시키게 된다. 이러한 구조를 음향 발생장치로 활용하기 위하여 단순한 곡면판의 기하학적 파라미터 변화에 따른 출력 변화 경향을 관찰 하였으며, 이러한 원리를 활용한 음향 발생장치를 구성하였다.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.6
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• pp.44-49
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• 2007

It is well known that the acoustic cavity inside the tire-wheel assembly contributes to vehicle interior noise. In this paper, we have performed acoustic and structural modal testings to investigate the influences of the acoustic cavity resonance on structural vibration characteristics for the tire in free-suspension and for the loaded tire. The testings have given us some findings, which are reported in this paper.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.11 no.2
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• pp.133-141
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• 2017

The hybrid acoustic sensor for implantable hearing aid has the structure in which a sound pressure based acoustic sensor (ECM) and a vibration based acceleration sensor are combined. This sensor combines the low frequency sensitivity of an acoustic sensor with the high frequency sensitivity of an acceleration sensor, allowing the acquisition of a wide range of sound from low to high frequency. In this paper, an acceleration sensor for use in a hybrid acoustic sensor has been proposed. The acceleration sensor captures the vibration of the tympanic membrane generated by the acoustic signal. The size of the proposed acceleration sensor was determined to diameter of 3.2 mm considering the anatomical structure of the tympanic membrane and the standard of ECM. In order to make the hybrid acoustic sensor have high sensitivity and wide bandwidth characteristics, the aim of the resonance frequency of the acceleration sensor is to be generated at about 3.5 kHz. The membrane of the acceleration sensor derives geometric structure through mathematical model and finite element analysis. Based on the analysis results, the membrane was implemented through a chemical etching process. In order to verify the frequency characteristics of the implemented membrane, vibration measurement experiment using external force was performed. The experiment results showed mechanical resonance of the membrane occurred at 3.4 kHz. Therefore, it is considered that the proposed acceleration sensor can be utilized for a hybrid acoustic sensor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.371.2-371
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• 2002

자동차 및 유체기계의 흡기계나 배기계에 사용되는 소음기의 음향 성능은 전달손실로 기계성능은 배압으로 표현된다. 유체가 흐르는 관 사이의 임피던스 부정합을 이용하는 반사형 소음기의 경우, 내부 유로에 천공을 주어 음향 감쇠를 시키거나 유동을 안정시키는 경우가 많다. 본 연구에서는 동심관형 공명기의 내부 관에 존재하는 천공의 분포양상이 공명기 내부의 유동장에 어떤 영향을 미치며, 그 유동장의 변화에 따라서 소음기의 성능에 어떠한 영향을 미치게 되는지를 고찰하였다. (중략)

• Journal of KSNVE
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• v.1 no.1
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• pp.29-38
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• 1991

The performance of silencer system is controlled by the geometrical parameters such as the relative location of inlet and outlet ports, size of main chamber, and cross sectional geometry of inlet-outlet ports and main chamber of silencer. In addition to these parameters, the presence of mean flow and temperature gradient along the silencer also affects the acoustic characteristics of silencer system. Due to the complexity of silencer, it is not straight forward to design the appropriate silencer system. In this paper, a design methodology based on an oustic analysis of silencer system is proposed ; low frequency and high frequency tuning method.

• Journal of KSNVE
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• v.8 no.5
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• pp.914-921
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• 1998

Combusion instability due to thermoacoustic feedback in a ducted combustor usually excites severe noise and vibration, which could lead to result in the failure of the system or environmental dispute. In the present study, an active noise control(ANC) method with an adaptive algotithm is hired to suppress instability which has very discrete behavior in the frequency domain. Especially a feedback system is composed to evade hot environment of the combustor, and as a preliminary, the performance and stability of the controller is chekced by simulating the real situation with harmonic waves. Application to the real combustor showed serious reductions in sound pressure level by 20∼30 dB. It was also shown that the selected control system was very stable and effective.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.33 no.3
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• pp.183-188
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• 1997

A method for designing a broadband transducer was investigated experimentally. Control of the resonance frequency of a Piezoelectric circular transducer with two pairs of electrodes was achieved by varying the inductance of external coil connected across the terminal of one pair of electrodes of transducer. The conductance curves of transducer in water were obtained as a function of the inductance value in mH of the coil used in the tuning. As the tuning inductance is increased in value, the resonance frequency is reduced toward the fundamental frequency of 50 kHz. This interesting result suggest that it is possible to produce a continuously tunable transducer covering a frequency range between 61.3 kHz and 121.7 kHz by varying the inductance value of external coil from 2.7 mH to 15.0 mH. One of other problems in the design and construction of such broadband transducer is the transducer efficiency, but this will be the subject of our future work.

• Journal of Digital Convergence
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• v.13 no.12
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• pp.187-192
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• 2015

If the software is developed to analyze the speech disorder, the application of various converged areas will be very high. This paper implements the user-friendly program based on CART(Classification and regression trees) analysis to distinguish between normal and pathological voices utilizing combination of the acoustical and HOS(Higher-order statistics) parameters. It means convergence between medical information and signal processing. Then the acoustical parameters are Jitter(%) and Shimmer(%). The proposed HOS parameters are means and variances of skewness(MOS and VOS) and kurtosis(MOK and VOK). Database consist of 53 normal and 173 pathological voices distributed by Kay Elemetrics. When the acoustical and proposed parameters together are used to generate the decision tree, the average accuracy is 83.11%. Finally, we developed a program with more user-friendly interface and frameworks.

• The Journal of the Acoustical Society of Korea
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• v.30 no.4
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• pp.223-230
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• 2011

Korean bell is hung with some air gap between the bell bottom and the ground. In addition, it has a peculiar acoustic element, so called resonance cavity below the bell. A proper design of the air gap and cavity size dramatically amplifies the bell sound by resonance effect. Bell interior cavity, air gap and resonance cavity consist of an acoustic cavity system. When the acoustic cavity frequency coincides with the natural frequency of the bell body, the frequency component is significantly amplified. On the Sacred Bell of the Great King Seongdeok, this study proposes a resonance condition of the cavity system considering air gap effect for the first time. With the exact dimension of the bell, boundary element analysis is performed using SYSNOISE. Finally, this study reveals how the temperature in season influences the resonance condition and proposes a concept of variable type resonance cavity. By using the variable type resonance cavity, the cavity size is controlled on site and exact resonance is available regardless of temperature difference in season.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.34 no.1
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• pp.74-84
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• 1998

A doubly resonant ultrasonic transducer has been designed as an attempt to increase the bandwidth of underwater transducers. The dual resonance conditions were accomplished by attaching a single acoustic matching layer on the front face of a Tonpilz transducer consisted of an aluminum head, a piezoelectric ring, a brass tail and a prestress bolt. A modified Mason's model was used for the performance analysis and the design of transducers, and the constructed transducers were tested experimentally and numerically by changing the impedances and thicknesses of the head, tail and matching layers in the water tank. Two distinct resonance peaks in the transmitting voltage response(TVR) of a developed transducer were observed at 34.3 and 40.4 kHz, respectively, with the difference frequency of 6.1kHz and the center frequency of 37.2kHz. The values of TVR at these frequencies were 136.5 dB re $1\;\muPa/V$ at 34.3 kHz and 136.8 dB re $1\;\muPa/V$ at 40.4 kHz, respectively. Reasonable agreement between the experimental results and the numerical results was achieved. From this result, it is expected that the generation of the distinct resonances at any two desired frequencies can be achieved through the proper choice of the matching layer to provide the impedance transformation between the transducer and the medium.