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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
The Journal of the Acoustical Society of Korea
Journal Basic Information
Journal DOI :
The Acoustical Society of Korea
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Volume & Issues
Volume 8, Issue 5 - Oct 1989
Volume 8, Issue 4 - Aug 1989
Volume 8, Issue 1 - Feb 1989
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Design and Construction of Hexgonal Ring-type Transducers for Ultrasonic Hyperthermia
Cho, Young-Hwan ; Sung, Koeng-Mo ;
The Journal of the Acoustical Society of Korea, volume 8, issue 4, 1989, Pages 5~12
In the clinical application of ultrasonic hyperthermia, selective heating of tumor is essential and thus precise control of ultrasonic intensity in both tumor and normal tissue is needed. In this paper, a hexagonal array transducer for ultrasonic hyperthermia is designed and manufactured of which focal point and focal region can be ocntrolled by the digital phase control circuit proposed by authors. Profiles of the focussed ultrasound beam in water and those of temperature in phantom were determined. The experimental and computed results are in good agreement.
Communication Under the Shallow Water Using an Equalizer
Yoon, Byung-Woo ; Shin, Yoon-Ki ; Sung, Koeng-Mo ;
The Journal of the Acoustical Society of Korea, volume 8, issue 4, 1989, Pages 13~22
Underwater channels can be regarded as time-varying systems in view of the acoustical characteristics due to the fact that the characteristics of the channel are affected by the environmental and geometrical conditions. Especially in shallow water case, the surface and bottom conduct as a waveguide so echo effect due tu the multipath reflections are severe. Therefore in shallow water communications, it is very important to equalize the transmitted signals distorted by the underwater channels with time-varying multipath fading. In this paper an equalizer system which employs the frequency domain adaptive filter to equalize the channels using inverse modeling technique is introduced.
The Construction of Ultrasonic Hologram and the Image Reconstruction Using Computer
Jang, Seong-Hwan ; Go, Dae-Sik ; Jeon, Gye-Seok ;
The Journal of the Acoustical Society of Korea, volume 8, issue 4, 1989, Pages 23~28
In this paper, the construction of ultrasonic hologram and the image reconstruction using computer have been studied, and it has been compared with optical reconstruction. The ultrasonic hologram has been constructed using c-scanning method
and the image of the object has been reconstructed by computer using Rayleigh -Sommerfeld formula and DFT algorithm. In this experiment, the holography system has been builted with the transducer of 5MHz center frequency and 5cm focal length, and the mechanical c-scanning system. It has been shown that the reconstructed image using computer for aluminum plane with the 'S' shaped defect has been displayed image of high quality.
Detection of Underwater Target Using Adaptive Filter
Oh, Jong-Taik ; Kwon, Sung-Jai ; Park, Song-Bai ;
The Journal of the Acoustical Society of Korea, volume 8, issue 4, 1989, Pages 29~38
Detection of an underwater target by acoustic wave raises various difficulties due to unpredictable noise interference which originates from clutter, reverberation, and variations of medium characteristics with time and location. The SNR and the range resolution of conventional SONAR systems using a matched filter are generally poor, since the latter is optimum only in the additive white noise case. Furthermore, it cannot compensate for variations of the detection level which are responsible for the resultant detection errors. In this paper, the unpredictable interferences are compensated for by using an adaptive filter. It recursively estimates the channel impulse response based on the received echo signal. In the low noise environments, the estimated impulse response is close to the true one, providing a good range resolution, and a matched filter is used subsequently for the purpose of detection. It is shown through computer simulation that good performance can be achieved via the two steps of filtering. Also, the detection level remains unchanged without any additional provisions. Finally, we present the characteristics of the employed adaptive filter parameters.
A Modeling of an Ultrasonic Transmission Imaging System
Gwon, Yeong-Bin ;
The Journal of the Acoustical Society of Korea, volume 8, issue 4, 1989, Pages 39~43
In this paper, the concept of ultrasonic transmission imaging system with crossed -arrays is Introduced. The crossed-array system is simulated by angular spectrum method In the operating frequency of 12MHz. A theoritical development of a system transfer function matrix 1M is presented. Using this matrix, a priori knowledge on the physical properties of the system is understood. It proves to be a block Toeplitz matrix with Toeplitz entries. Using the Inversion procedure, the spatial degradations of the measured image can be removed.
On Estimating the Incident Angles of Wide Band Signals in Low SNR Environment
Jo, Jeong-Gwon ; Hwang, Yeong-Su ; Cha, Il-Hwan ; Yun, Dae-Hui ;
The Journal of the Acoustical Society of Korea, volume 8, issue 4, 1989, Pages 44~52
The UCERSS (Unit Circle Eigendecomposition Rational Signal Subspace) algorithm has extended MUSIC (MUltiple Signal Classification ) by using eigendecomposition on the unit circle in order to estimate incident angles of multiple wide band signals. The purpose of this thesis is to further extend the UCERSS to be able to estimate the direction of arrivals of multiple wide band signals in very low SNR . The wide band ESPRIT (Estimation of Signal Parameter via Rotational Invariance Technique) uses covariance difference matrices to reduce noise components. In this paper the wide band ESPRIT which combines the ideas of UCERSS and ESPRIT Is proposed. Computer simulation results Indicate that the performances of the proposed approaches are superior to those of the UCERSS in very low SNR.
Separation of Heart Sounds and Lung Sounds Using Adaptive Lattice Wiener Filter
Lee, Sang-Hun ; Kim, Geun-Seop ; Lee, Jin ; Hong, Wan-Hui ; Kim, Seong-Hwan ;
The Journal of the Acoustical Society of Korea, volume 8, issue 4, 1989, Pages 53~59
A new proposed method can separate heart sounds and lung sounds by the realization of adaptive noise canceler using adaptive lattice Wiener filter in contrast to adaptive transversal LMS filter and high pass filter as before. Lung sounds and ECG signal are detected for this purpose, and especially the second heart sounds are reduced by finding T wave location with a T wave seeking algorithm. As a result, for heart sounds reduction It was found that adaptive transversal LMS filter required 100-200's orders, 75-100's orders In adaptive transversal MLMS filter, and only 10-20's orders in adaptive lattice Wiener filter. Adaptive filtering technique has shown greater accuracy than high pass filtering without loss of low frequency component.
The Local Path Constraint for the Recognition of Speech
Ann, Tae-Ock ; Kim, Soon-Hyob ;
The Journal of the Acoustical Society of Korea, volume 8, issue 4, 1989, Pages 60~64
In this paper, an local path constraint Is proposed in order to increase the speech recognition rate. An input speech signal is analyzed by autocorrelation and LPC coefficient as parameters. The local path constraint of the proposed type was compared with the conventional five types. The speechs used in this search are the subway stops, and the 130 words pronounced 10 times for the different 13 words consisting of 11 characters of syllable by 2 male and 1 female are tested. As a result, we proved that this proposed type is the most optimal type and the recognition rate of
is obtained .
Speaker Identification Based on Vowel Classification and Vector Quantization
Lim, Chang-Heon ; Lee, Hwang-Soo ; Un, Chong-Kwan ;
The Journal of the Acoustical Society of Korea, volume 8, issue 4, 1989, Pages 65~73
In this paper, we propose a text-independent speaker identification algorithm based on VQ(vector quantization) and vowel classification, and its performance is studied and compared with that of a conventional speaker identification algorithm using VQ. The proposed speaker identification algorithm is composed of three processes: vowel segmentation, vowel recognition and average distortion calculation. The vowel segmentation is performed automatlcally using RMS energy, BTR(Back-to-Total cavity volume Ratio)and SFBR(Signed Front-to-Back maximum area Ratio) extracted from input speech signal. If the Input speech signal Is noisy, particularity when the SNR is around 20dB, the proposed speaker identification algorithm performs better than the reference speaker identification algorithm when the correct vowel segmentation is done. The same result is obtained when we use the noisy telephone speech signal as an input, too.
A Study on the Speech Packetized Coding by Zero Bit Reduction of 1'st Order Differences
Shin, Dong-Jin ; Lim, Un-Cheon ; Bae, Myung-Jin ; Ann, Sou-Guil ;
The Journal of the Acoustical Society of Korea, volume 8, issue 4, 1989, Pages 74~82
In this paper, we have studied on the methodologies of implementation and the performance evaluations about the real-time packetized coding of multi-channel speech signals. Our suggested coding algorithm is very, simple and it has majorly the data handling operations rather than the numerical calculations. And it gives about
of compression ratio with less than the conventional codings. Nevertheless, using this algorithm, we can save the memories for the speech signal and we can raise the efficiency of the channel transmission. Especially because of its simplicity of algorithm, we can easily obtain the merits of the multi-channel operations.