• The Journal of the Acoustical Society of Korea
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• v.10 no.3
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• pp.13-18
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• 1991

In this study, the analysis technique of fracture stress using the reflection coefficient of SAW reflected from a brittle solid with surface crack has been studied. Fracture stress of brittle solid with surface crack has been obtained by the function of the critical stress intensity factor and the maximum normalized stress intensity factor of the crack in the body. And the maximum normalized stress intensity factor of a surface crack can be inferred from a measurement of reflection coefficient of SAW. In experiment, the surface cracks ranging from 0.5mm to 0.9mm in crack depth has been made at the center of each Pyrex disc, and the SAW wedge transducer has been set up for the pitch-catch mode. It has been compared the theoretical values of the fracture stress calculated from the reflection coefficient of SAW with the values of the fracture stress measured from UTM.

• The Journal of the Acoustical Society of Korea
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• v.19 no.5
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• pp.41-45
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• 2000

The effective elastic constants of a single-crystal superlattice film have been determined by two methods based on the velocities of surface acoustic waves (SAW). One method uses formulas to calculate the effective elastic constants of a superlattice from the known elastic constants of the constituent layers. The calculated effective elastic constants are tested by comparing the corresponding SAW velocities calculated for thin-film/substrate systems with the corresponding SAW velocities measured by line-focus acoustic microscopy (LFAM). The other method determines the effective elastic constants of the superlattices by inverting the SAW velocity dispersion data measured by LFAM. The results of both methods applied to a TiN/NbN superlattice film are in good agreement.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.273-276
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• 2000

본 연구에서는 무반향 수조의 내벽 흡음 물질로 사용되는 무반향 타일을 쐐기형으로 제작하여 쐐기의 꼭지 각 변화에 따른 음향학적인 특성을 고찰하였다. 실험에서 사용된 쐐기형 무반향 타일의 크기는 $40{\cal}cm{\times}38.5{\cal}cm$ 이며, 타일을 구성하는 각 쐐기의 길이는 $2.75{\cal}cm$로 고정하고 각각 쐐기의 꼭지각이 $30^\circ$ 와 $60^\circ$ 인 타일을 제작하였다. 수중에서 쐐기가 없는 무반향 시료와 쐐기형 무반향 타일에 음파를 수직 입사하여 반사계수를 측정하였으며, 쐐기의 유무와 무반향 타일을 구성하는 쐐기의 꼭지각 변화에 따른 반사 및 흡음 특성을 고찰하였다. 음향특성 임피던스가 $2.14\times10^6$ Pa$\cdot$s/m인 쐐기형 무반향 타일을 25kHz 에서 100kHz의 주파수 영역의 음파를 입사했을 애 쐐기의 꼭지각이 $30^\circ$ 일 때 $60^\circ$보다 압력반사계수가 작고, 반사손실이 증가함을 알 수 있었으며, 그 결과로써 본 실험에서 사용된 $30^\circ$의 쐐기 꼭지각을 갖는 무반향 타일이 내벽 흡음 물질로서 성능이 더 좋다는 것을 확인하였다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06c
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• pp.103-106
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• 1998

본 논문에서는 음성인식 시스템의 인식 정도의 향상을 위해서 동적 특징으로서 K-L(Karhanen-Loeve)계수를 이용하여 음소모델을 구성하는 방법을 제안하고, 음소, 단어, 숫자음 인식 실험을 통하여 그 유효성을 검토하였다. 인식 실험을 위한 음성자료는 한국 전자통신 연구소에서 채록한 445단어와 국어정보공학연구소에서 채록한 4연속 숫자음을 사용하였으며, K-L계수 동적 특징의 유효성을 확인하기 위해 정적 특징으로서 멜-켑스트럼과 동적 특징으로서 K-L계수 및 회귀계수를 추출한 후 음소, 단어, 숫자음 인식 실험을 수행하였다. 인식의 기본 단위로는 48개의 유사음소단위(Phoneme Likely Unite ; PLUs)를 음소모델로 사용하였으며, 단어와 숫자음 인식을 위해서는 유한상태 오토마타(Finite State Automata; FSA)에 의한 구문제어를 통한 OPDP(One Pass Dynamic Programming)법을 이용하였다. 인식 실험 결과, 음소인식에 있어서는 정적특징인 멜-켑스트럼을 사용한 경우 39.8%, K-L 동적 계수를 사용한 경우가 52.4%로 12.6%의 향상된 인식률을 얻었다. 또한, 멜-켑스트럼과 회수계수를 사용한 경우 60.1%, K-L계수와 회귀계수를 결합한 경우에 있어서도 60.4%로 높은 인식률은 얻었다. 이 결과를 단어인식에 확장하여 인식 실험을 수행한 결과, 기존의 멜-켑스트럼 계수를 사용한 경우 65.5%, K-L계수를 사용한 경우 75.8%로 10.3% 향상된 인식률을 얻었으며, 멜-켑스트럼과 회귀계수를 결합한 경우 91.2%, K-L계수와 회귀계수를 결합한 경우 91.4%의 높은 인식률을 보였다. 도한, 4연속 숫자음에 적용한 경우에 있어서도 멜-켑스트럼을 사용한 경우 67.5%, K-L계수를 사용한 경우 75.3%로 7.8%의 향상된 인식률을 보였으며 K-L계수와 회귀계수를 결합한 경우에서도 비교적 높은 인식률을 보여 숫자음에 대해서도 K-L계수의 유효성을 확인할 수 있었다.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.5
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• pp.979-986
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• 2018

This paper deals with acoustic echo cancellation using blind signal separation method. This method does not degrade the echo cancellation performance even during double-talk. In the closed echo environment, the mixing model of acoustic signals is multi-channel, so the convolutive blind signal separation method is applied and the mixing coefficients are calculated by using the feedback model without directly calculating the separation coefficients for signal separation. The coefficient update is performed by iterative calculations based on the second-order statistical properties, thus estimates the near-end speech. A number of simulations have been performed to verify the performance of the proposed blind signal separation method. The simulation results show that the acoustic echo canceller using this method operates safely regardless of the presence of double-talk, and the PESQ is improved by 0.6 point compared with the general adaptive FIR filter structure.

• The Journal of the Acoustical Society of Korea
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• v.21 no.5
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• pp.494-502
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• 2002

In this paper, the Low Rank Approximation (LRA) method to suppress the interference of signals from temporal fluctuations is applied. The reverberation signals and temporally fluctuating signals are separated from the measured data using the Ink. The Singular value decomposition (SVD) method is applied to extract the low rank and the temporally stable reverberation was extracted using the LRA. The reverberation suppression is performed on the LRA residual value obtained by removing the approximate reverberation signals. In overall, the method can be applied to the suppression of reververation in active sonar system as well as to the modeling of reverberation.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.195-204
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• 2006

A linear acoustic analysis has been performed to elucidate damping characteristics of acoustic cavities in a liquid rocket combustor. Results have shown that resonant frequencies of acoustic cavity obtained by classical theoretic approach and by the present linear analysis are somewhat different with each other. This difference is attributed to the limitation of the simplified classical theory. To quantify the damping characteristics, acoustic impedance has been introduced and resultant absorption coefficient and conductance have been evaluated. Satisfactory agreement has been achieved with previous experiment. Finally the design procedure for an optimal tuning of acoustic cavity has been established.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.890-895
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• 2002

The equivalent electroacoustic circuit approach has been conventionally used for estimating the absorption coefficient of a single layer perforated plate system. When the single layer system is extended to the multiple layer ones, however, it is found that an analogy error has been involved in the equivalent electroacoustic parallel circuit approach proposed by previous investigators. The analogy error is demonstrated by the corrected equivalent electroacoustic circuit approach in this study.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.387.2-387
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• 2002

The equivalent electroacoustic circuit approach has been conventionally used for estimating the absorption coefficient of a single layer perforated plate system. When the single layer system is extended to the multiple layer ones, however, it is found that an analogy error has been involved in the equivalent electroacoustic parallel circuit approach proposed by previous researchers. The analogy error is demonstrated by the corrected equivalent electroacoustir circuit approach proposed en this study.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.618-621
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• 2014

This research is to review the possibility of reducing the noise radiated from the tube exit by controling the sound reflection coefficient at the inclined exit. The sound reflection coefficient at the inclined exit of flanged tube was measured by both transfer function method and standing wave ratio method. Accuracy on the sound reflection coefficient measured by transfer function method was verified through comparison with sound reflection coefficient measured by standing ratio method. The flanged tube had lower sound reflection coefficient than the tube which have no flange. Also the sound reflection coefficient was decreased in accordance with increasing the inclined angle of unflanged tube.