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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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The Journal of the Acoustical Society of Korea
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Journal DOI :
The Acoustical Society of Korea
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Volume & Issues
Volume 33, Issue 6 - Nov 2014
Volume 33, Issue 5 - Sep 2014
Volume 33, Issue 4 - Jul 2014
Volume 33, Issue 3 - May 2014
Volume 33, Issue 2 - Mar 2014
Volume 33, Issue 1 - Jan 2014
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Long-Range Sound Transmission Characteristics in Shallow-Water Channel with Thermocline
Byun, Sung-Hoon ; Kim, Sea-Moon ; Lim, Yong-Kon ;
The Journal of the Acoustical Society of Korea, volume 33, issue 5, 2014, Pages 273~281
DOI : 10.7776/ASK.2014.33.5.273
This paper analyzes the effect of a thermocline on the long-range acoustic signal propagation using the experimental data acquired in the shallow water near Jeju island. Temperature and salinity measurement data in Korea Oceanographic Data Center (KODC) show that the seasonal thermocline exists near Jeju island, and, under the thermocline, the bottom loss property strongly affects the long-range propagation of acoustic signal along the down-ward refractive paths. We estimate the bottom loss under the thermocline using experiment data obtained near Jeju island in May, 2013. The result shows that the estimated bottom losses are below 3 dB and the higher level signal is received at the deeper receiver depths. This shows that the acoustic trapping under the thermocline can be a viable long-range signal transmission channel in the shallow water with a thermocline.
Numerical Analysis of the Backscattering Amplitude for a Partially Buried Cylinder on a Flat Interface Using Method of Moments
Baik, Kyungmin ; Marston, Philip L. ;
The Journal of the Acoustical Society of Korea, volume 33, issue 5, 2014, Pages 282~290
DOI : 10.7776/ASK.2014.33.5.282
Though there have been advances in the numerical analysis of the acoustic scattering by smooth objects, numerical analysis of the acoustic scattering by the objects that are partially exposed on the interface are still rare. In determining the backscattering amplitude by a partially buried cylinder on a seabed, reverberation by the interface changes the feature of the scattering form function. Current study adopted the Method of moments (MoM) to provide the numerical analysis on the backscattering amplitude for a partially buried cylinder on a flat interface. Suggested numerical analysis showed the good agreements with the measurements and the analytic solution obtained by the Kirchhoff approximation. Numerical analysis described in the current study can be applied to the backscattering problem of any shape of the objects partially imbedded on a seabed by combining the reverberation from the seabed with the scattered wave from the objects.
Tissue Mimicking Phantom for Visualization of Temperature Elevation Caused by Ultrasound
Jung, Ji-Hee ; Kim, Jung-Soon ; Ha, Kang-Lyeol ; Kim, Moo-Joon ; Cao, Yonggang ;
The Journal of the Acoustical Society of Korea, volume 33, issue 5, 2014, Pages 291~299
DOI : 10.7776/ASK.2014.33.5.291
To probe the temperature elevation effect caused by ultrasound, a tissue mimicking phantom was newly suggested. A carrageenan gel was adopted to realize not only the required transparency for visualization but also acoustic characteristics similar to human tissue. To visualize the temperature elevation inside phantom, thermochromic film with a critical temperature of discoloration was introduced. Acoustic characteristics of the tissue mimicking phantom were examined when the concentrations of carrageenan and sucrose changed. As the results, the attenuation coefficient of the phantom could be controlled in the range of 0.44~0.49 dB/cm/MHz, and the acoustic impedance in the range of 1.52~1.77 Mrayls. We could control the acoustic characteristics of the phantom by different concentration of carrageenan and sucrose, and it was possible to examine the temperature elevation caused by ultrasound in the phantom. The suggested method was verified by noninvasively visualizing the temperature elevation due to planar and focused ultrasound using the fabricated phantom.
Fabrication and Evaluation of High Frequency Ultrasound Receive Transducers for Intravascular Photoacoustic Imaging
Lee, Jun-Su ; Chang, Jin Ho ;
The Journal of the Acoustical Society of Korea, volume 33, issue 5, 2014, Pages 300~308
DOI : 10.7776/ASK.2014.33.5.300
Photoacoustic imaging is a useful tool for the diagnosis of atherosclerosis because it is capable of providing anatomical and pathological information at the same time. A photoacoustic signal detector is a pivotal element to achieve high spatial resolution, so that it should have broadband spectrum with a high center frequency. Since a photoacoustic imaging probe is directly inserted into blood vessel to diagnose atherosclerosis, the total size of the photoacoustic signal detector should be less than 1 mm. The main purpose of this paper is to demonstrate that PVDF can be used as an active material for the photoacoustic signal detector with a high frequency and broadband characteristic. The photoacoustic signal detector developed in this study was a single element ultrasound transducer with an aperture of
and the total size of 1 mm. In the design stage, the natural focal depth was adjusted for an effective focal area to cover the region of interest, i.e., 1~5 mm in depth. This was because geometrical focusing could not be used due to the small aperture. Through a pulse-echo test, it was ascertained that the developed photoacoustic signal detector has the -6 dB bandwidth ranging between 40.1 and 112.8 MHz and the center frequency of 76.83 MHz.
Novel Variable Step-Size Gradient Adaptive Lattice Algorithm for Active Noise Control
Lee, Keunsang ; Kim, Seong-Woo ; Im, Jaepoong ; Seo, Young-Soo ; Park, Youngcheol ;
The Journal of the Acoustical Society of Korea, volume 33, issue 5, 2014, Pages 309~315
DOI : 10.7776/ASK.2014.33.5.309
In this paper, a novel variable step-size filtered-x gradient adaptive lattice (NVSS-FxGAL) algorithm for active noise control system is proposed. The gradient adaptive lattice (GAL) algorithm is capable of controlling the narrow band noise effectively. The GAL algorithm can achieve both fast convergence rate and low steady-state level using the variable step-size. However, it suffers from the convergence performance for varying signal characteristic since the global variable step-size is equally applied to all lattice stages. Therefore, the proposed algorithm guarantees the stable and consistency convergence performance by using the local variable step-size for the suitable each lattice stage. Simulation results confirm that the proposed algorithm can obtain the fast convergence rate and low steady-state level compared to the conventional algorithms.
Analysis of the Acoustic Performance of Classrooms in Korea
Park, Chan-Jae ; Ryu, Da-Jung ; Kyoung, Ju-Young ; Haan, Chan-Hoon ;
The Journal of the Acoustical Society of Korea, volume 33, issue 5, 2014, Pages 316~325
DOI : 10.7776/ASK.2014.33.5.316
The basic unit of school is a classroom and the aural environment of the classrooms is essential factor for education purposes. Therefore, many efforts have been undertaken for enhancing the acoustical performance of the classrooms in many countries. As a result, acoustic criteria including reverberation time and background noise level have been established in US and UK for school classrooms depending on the usage and size of the rooms. However, in Korea, there has been little researches concerning the room acoustical investigations of the classrooms. The present study investigates the current situation of the aural environment of the 15 classrooms in Korea including elementary, middle and high schools. The acoustic criteria measured include RT,
, STI, SNR and background noise level. As the results, it was found that the background noise levels of the schools adjacent to roads exceed the US and UK standard of 35 dB(A). Also, most schools have so low SNR that they may be interfered by noise, which may affect speech transmission. It was also revealed that some schools have longer RT than the US standard of 0.6 s, but they all have high speech intelligibility.
A Novel Covariance Matrix Estimation Method for MVDR Beamforming In Audio-Visual Communication Systems
You, Gyeong-Kuk ; Yang, Jae-Mo ; Lee, Jinkyu ; Kang, Hong-Goo ;
The Journal of the Acoustical Society of Korea, volume 33, issue 5, 2014, Pages 326~334
DOI : 10.7776/ASK.2014.33.5.326
This paper proposes a novel covariance matrix estimation scheme for minimum variance distortionless response (MVDR) beamforming. By accurately tracking direction-of-sound source arrival (DoA) information using audio-visual sensors, the covariance matrix is efficiently estimated by adopting a variable forgetting factor. The variable forgetting factor is determined by considering signal-to-interference ratio (SIR). Experimental results verify that the performance of the proposed method is superior to that of the conventional one in terms of interference/noise reduction and speech distortion.
A New Sign Subband Adaptive Filter with Improved Convergence Rate
Lee, Eun Jong ; Chung, Ik Joo ;
The Journal of the Acoustical Society of Korea, volume 33, issue 5, 2014, Pages 335~340
DOI : 10.7776/ASK.2014.33.5.335
In this paper, we propose a new sign subband adaptive filter to improve the convergence rate of the conventional sign subband adaptive filter which has been proposed to deal with colored input signal under the environment with impulsive noise. The existing sign subband adaptive filter does not increase the convergence speed by increasing the number of subband because each subband input signal is normalized by
of all of the subband input signals. We devised a new sign subband adaptive filter that normalizes each subband input signal with
of each subband input signal and increases the convergence rate by increasing the number of subband. We carried out a performance comparison of the proposed algorithm with the existing sign subband adaptive filter using a system identification model. It is shown that the proposed algorithm has faster convergence rate than the existing sign subband adaptive filter.
An Energy-Efficient Clustering Scheme in Underwater Acoustic Sensor Networks
Lee, Jae-Hun ; Seo, Bo-Min ; Cho, Ho-Shin ;
The Journal of the Acoustical Society of Korea, volume 33, issue 5, 2014, Pages 341~350
DOI : 10.7776/ASK.2014.33.5.341
In this paper, an energy efficient clustering scheme using self organization method is proposed. The proposed scheme selects a cluster head considering not only the number of neighbor nodes but also the residual battery amount. In addition, the network life time is extended by re-selecting the cluster heads only in case the current cluster head`s residual energy falls down below a certain threshold level. Accordingly, the energy consumption is evenly distributed over the entire network nodes. The cluster head delivers the collected data from member nodes to a Sink node in a way of multi-hop relaying. In order to evaluate the proposed scheme, we run computer simulation in terms of the total residual amount of battery, the number of alive nodes after a certain amount of time, the accumulated energy cost for network configuration, and the deviation of energy consumption of all nodes, comparing with LEACH which is one of the most popular network clustering schemes. Numerical results show that the proposed scheme has twice network life-time of LEACH scheme and has much more evenly distributed energy consumption over the entire network.