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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
Editor in Chief :
Volume & Issues
Volume 29, Issue 8 - Nov 2010
Volume 29, Issue 7 - Oct 2010
Volume 29, Issue 6 - Aug 2010
Volume 29, Issue 5 - Jul 2010
Volume 29, Issue 4 - May 2010
Volume 29, Issue 3 - Apr 2010
Volume 29, Issue 2 - Feb 2010
Volume 29, Issue 1 - Jan 2010
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Influences of the Defective Piezo-Elements of a Medical Ultrasonic Probe on Transient Acoustic Fields and B-Mode Images
Choi, Kwang-Yoon ; Ha, Kang-Lyeol ; Kim, Moo-Joon ; Kim, Jung-Soon ; Yang, Jeong-Hwa ; Kang, Gwan-Suk ; Choi, Min-Joo ;
The Journal of the Acoustical Society of Korea, volume 29, issue 8, 2010, Pages 476~482
The ultrasonic transient fields and B-mode images of a point target which were simulated for a medical ultrasonic probe with a few defective piezo-elements were compared with those for a normal probe. The present study considered a 3.5 MHz linear array probe whose acoustic beam was formed by the 64 active elements of total 192 elements. The results showed that the maximum amplitude and -3 dB width of the acoustic fields by main-lobes decreased linearly as the defective element number increased from one to four. However, the depths of foci remained almost unchanged, and the pressure differences between main-lobes and side-lobes tended to decrease due to rise in pressures in side-lobes. Such changes in ultrasonic fields affected the B-mode images of point targets. So the artifacts were formed in the right and left side of the target, and the lateral spatial resolutions were decreased while the axial resolution was almost the same.
Detection of a Crack on a Plate by IDT Type Lamb Wave Sensors
Kim, Jun-Ho ; Roh, Yong-Rae ;
The Journal of the Acoustical Society of Korea, volume 29, issue 8, 2010, Pages 483~490
In this paper, an Inter-Digital Transducer (IDT) type Lamb wave sensor is proposed to estimate the geometry and number of cracks on a plate structure, and its validity is checked through experiments. This IDT type sensor is more readily controllable than conventional patch type piezoelectric sensors to modify its operation frequency and directionality by altering its finger patterns. In this work, omni-directional annular IDT and highly directional rectangular IDT sensors are designed and fabricated. The IDT sensors are used to diagnose the length, number and orientation of cracks on an aluminum plate by measuring the amplitude and time of flight of Lamb waves. The results are analyzed to discuss the efficacy of the IDT sensors.
Thermoacoustic Power Generation by a Spiral Heater in the Rijke Tube
Kwon, Young-Pil ;
The Journal of the Acoustical Society of Korea, volume 29, issue 8, 2010, Pages 491~496
Thermoacoustic power generation by a spiral heater in the Rijke tube was analyzed numerically. In the analysis, variables were normalized by the angular frequency of the sound and the thermal diffusivity of the air. The effect of the heater wire diameter d, the spacing between wires P-d, and the air-current velocity
, upon the power generation was obtained and discussed. When the spacing is broad enough, the normalized velocity is
and the diameter is
for the maximum power generation. With decrease of the spacing, however, the power generation increases more than 5 times and becomes maximum around
. And the velocity
for the maximum power generation is almost independent of the wire spacing.
Evaluation of Noise Reduction Performance of HVAC System for Ships
Kim, Sang-Ryul ; kim, Hyun-Sil ; Kim, Jae-Seung ; Kim, Bong-Ki ; Lee, Sung-Hyun ;
The Journal of the Acoustical Society of Korea, volume 29, issue 8, 2010, Pages 497~503
In this paper, evaluation of noise reduction performance of HVAC system for ships by means of HVAC mock-up system is presented. Test is done for six different types of HVAC elements including room unit, silencer, etc. It is found that when diameter of silencer is small and air flow is large, flow noise degrades insertion loss. However, as diameter of silencer becomes larger, the effect of flow noise becomes smaller, and insertion loss up to 25 dB is measured. It is observed that insertion loss of diffuser type room unit is usually between zero and 10 dB, whereas that of the nozzle type room unit can be down to - 15 dB. In addition, it is shown that changing duct arrangement can reduce cabin noise by up to 2 dB, and providing same air flow to each room unit is crucial for generating less noise.
Contrast Improvement in Diagnostic Ultrasound Strain Imaging Using Globally Uniform Stretching
Kwon, Sung-Jae ; Jeong, Mok-Kun ;
The Journal of the Acoustical Society of Korea, volume 29, issue 8, 2010, Pages 504~508
In conventional diagnostic ultrasound strain imaging, when displaying strain image on a monitor, human visual characteristics are utilized such that hard regions are displayed as dark and soft regions are displayed as bright. Thus, hard regions representing tumor or cancer are displayed as dark, decreasing the contrast inside the lesion. Because the lesion area is stiff and thus displayed as dark, a method of inverting the image brightness and thereby increasing the contrast in the lesion for better diagnostic purposes is proposed wherein a postcompression signal is extended in the time domain by a factor corresponding to the reciprocal of the amount of the applied compression using a technique termed globally uniform stretching. Experiments were carried out to verify the proposed method on an ultrasound elasticity phantom with radio-frequency data acquired from a diagnostic ultrasound clinical scanner. It is found that the new method improves the contrast-to-noise ratio by a factor of up to about 1.8 compared to a conventional strain imaging method that employs a reversed gray color map without globally uniform stretching.
Mono-To-Stereo Blind Upmix Using Non-Negative Matrix Factorization and Decorrelator
Choi, Keun-Woo ; Chon, Sang-Bae ; Lee, Seok-Jin ; Sung, Koeng-Mo ;
The Journal of the Acoustical Society of Korea, volume 29, issue 8, 2010, Pages 509~515
This paper presents a new method for upmixing mono signal to stereo signal with guaranteeing high stereophonic image quality (SIQ) and large apparent source width (ASW). The proposed method consists of analysis phase and synthesis phase. In analysis phase, a mono signal is first decomposed into multiple sound sources by the use of high-rank nonnegative matrix factorization. Then the multiple sources are clustered into two groups based on tonality criterion. In synthesis phase, one group is directly fed into left and right channels while the other group is decorrelated before being fed into each channel. Subjective tests reveals that the proposed method gives listener high SIQ and large ASW with minimizing timbral distortions.