• The Journal of the Acoustical Society of Korea
• /
• v.14 no.6
• /
• pp.62-67
• /
• 1995

In this paper, the features extraction of reflected ultrasonic signals from various type of defects existing in Al metal has been studied by digital signal processing. Since the reflected signals from various type of the defects are ambiguous in features distinction from effects of noise, Wiener filtering using AR (auto-regressive) technique and least-absolute-values norm method has been used in features extraction and comparison of signals. In this experiment, three types of the defect in aluminum specimen have been considered: a flat cut, an angular cut, a circular hole. And the reflected signal have been measured by pulse-echo methods. In the result of digital signal processing of the reflected signal, it has been found that the features extraction method have been effective for classification of the reflected signals from various defects.

• Proceedings of the Acoustical Society of Korea Conference
• /
• autumn
• /
• pp.293-296
• /
• 2001

1990년대 중반 이후 우리나라 초등학교 교실은 열린교육과 다양성을 추구하는 새로운 열린교실을 표방하고 진행되고 있다. 또한 건축설계에 있어서도 과거의 종합 표준설계에 의하지 않고 각 학교마다 별도의 건축설계에 따라 지어지고 있다. 본 논문의 목적은 현재의 초등학교 교서의 차음환경을 조사하고 새로이 지어진 교사의 교실과 열린교실의 실내 음환경을 조사하여 현재 상황을 분석평가하고 이에 대한 대안을 제시하고자 하는 것이다. 이를 위하여 건축시공연대가 다른 초등학교 3개 학교를 선택하여 단위교실에서의 실내음향인자(RT60, C80, D50, RASTI)와 인접교실과의 차음성능(TL)을 측정하였다. 또한 해당교실의 학생과 교사에 대하여 설문조사를 실시하였다. 각 측정은 외부와 복도에 인접한 창문의 개폐여부와 실내의 위치별로 이루어 졌다. 실험결과, 열린교육에 따라 가변적 교실의 구성은 기존의 교실보다 차음성능이 평균$5\sim6dB$ 낮은 것으로 나타났다. 또한 신축교사의 RASTI값(0.73)이 10년 이상 된 학교(0.70)나 열린교실(0.64)보다 높은 것으로 나타났다. 음성명료도(D50) 역시 일반 신축교사가 열린교실 보다 높게 나타났다. 이것은 실의 기밀과 내부바닥의 마감자재로 비롯되었으며 최근의 열린교실은 음의 차음과 실내명료도에서 열악한 것으로 결론되었다.

• The Journal of the Acoustical Society of Korea
• /
• v.20 no.5
• /
• pp.54-60
• /
• 2001

This paper investigates the equivalent circuit analysis method for the multi-functional device in mobile telephones, which works both as a buzzer and a vibrator in a single unit form. With a representative multi-functional device, we construct the corresponding equivalent circuits for the buzzer mode and the vibrator mode of the device, respectively, and analyze the performance of each of the modes. For proper construction of the circuit, we analyze the structure and operation mechanism of the device, and develop a computer simulation tool to simulate the behavior of the device. Validity of the analysis method is verified through comparison of the analysis results with experimental measurement results, which shows good agreement between the two sets of data.

• The Journal of the Acoustical Society of Korea
• /
• v.20 no.5
• /
• pp.61-68
• /
• 2001

In this paper, an analytical method and a difference approximation method to calculate the gradient of an objective function have been applied to the directivity optimization in an adaptive ultrasonic transducer which is combined with a point source array and an optimization algorithm (DFP method). To compare these two methods, quasi-ideal .beam with a beam width and direction specified are chosen as the desired directivity. As the numerical results, the difference approximation method shows better suppressive capacity of side lobe level, good stability in the convergence processing, faster convergence speed and excellent adaptability compared with the analytical method.

• The Journal of the Acoustical Society of Korea
• /
• v.22 no.1
• /
• pp.23-27
• /
• 2003

Recently attempts to we the syllable as the recognition unit to enhance performance in continuous speech recognition hate been reported. However, syllables are worse in their trainability than phones and the former have a disadvantage in that contort-dependent modeling is difficult across the syllable boundary since the number of models is much larger for syllables than for phones. In this paper, we propose a method to enhance the trainability for the syllables in Korean and phoneme-context dependent syllable modeling across the syllable boundary. An experiment in which the proposed method is applied to word recognition shows average 46.23% error reduction in comparison with the common syllable modeling. The right phone dependent syllable model showed 16.7% error reduction compared with a triphone model.

• The Journal of the Acoustical Society of Korea
• /
• v.19 no.3
• /
• pp.92-99
• /
• 2000

In this paper, theoretical acoustic sensitivity was derived to describe acousto-optic transduction property of the mandrel type fiber optic acoustic sensor with respect to external acoustic field. The acoustic sensitivity was analyzed in relation to both material properties and geometrical influence factors of the constitutional parts of the sensor, analytically. Validity of the theoretical results were verified through comparison with the finite element analysis results. The variation trends of the sensitivity of the sensor in relation to the studied parameters showed good agreement for the two analysis methods. According to the results, it is considered more economical to design the basic structure of the sensor with the analytic equations developed in this paper, and then to carry out further detailed analysis with the finite element method for specific points of design interest.

• The Journal of the Acoustical Society of Korea
• /
• v.13 no.1E
• /
• pp.25-36
• /
• 1994

A problem of making a neural network learning self-adaptive to the training set supplied is addressed in this paper. This arises from the aspect in choice of an adequate stepsize for the update of the current weigh vectors according to the training pairs. Related issues in this attempt are raised and fundamentals in neural network learning are introduced. In comparison to the most popular back-propagation scheme, the usefulness and superiority of the proposed weight update algorithm are illustrated by examing the identification of unknown nonlinear systems only from measurements.

• The Journal of the Acoustical Society of Korea
• /
• v.21 no.7
• /
• pp.592-599
• /
• 2002

In this study, an ultrasonic transducer was designed with a commercial finite element analysis (FEA) code, PZFlex, and fabricated based on the design. The transducer has the dimension and shape suitable for abdomen diagnosis working at 5 ㎒ and consists of 128 piezoelectric elements disposed in a convex linear array form. The transducer is composed of two impedance matching layers, one backing layer, and kerfs placed between the piezoelectric elements. Validity of the design with the FEA was illustrated through experimental characterization of a sample transducer. Comparison with the design results by equivalent circuit analysis method was also made to check the superiority of the FEA design.

• The Journal of the Acoustical Society of Korea
• /
• v.24 no.8
• /
• pp.447-453
• /
• 2005

Laboratory measurements were performed in a uni-algae medium Cochlodinium polykrikoides (Phytoplankton, dinoflagellates) using an Underwater Ultrasound $(5\~15\;MHz)$ to study Characteristics of Acoustic Backscattering of Harmful algae. In an effort to detect the harmful algal scatterers with population density of less than 300 cells/ml that corresponds to the precaution stage of red tide, backscattered signals from various scatterer-density samples were obtained and analyzed. Correlations between volume backscattering strength (Sv) and population density (cells/ml) of scatterers in the medium have been investigated. Comparison of Volume Backscattering Strengths calculated with the fluid-sphere model [1] and the measured values showed an agreement.

• The Journal of the Acoustical Society of Korea
• /
• v.36 no.1
• /
• pp.64-69
• /
• 2017

In this paper, we propose a single-channel speech enhancement method based on restoration of both spectral amplitudes and phases for PTT (Push-To-Talk) communication. The proposed method combines the spectral amplitude and phase enhancement to provide high-quality speech unlike other single-channel speech enhancement methods which only use spectral amplitudes. We carried out side-by-side comparison experiment in various non-stationary noise environments in order to evaluate the performance of the proposed method. The experimental results show that the proposed method provides high quality speech better than other methods under different noise conditions.