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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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Identification of the Sectional Distribution of Sound Source in a Wide Duct
Heo, Yong-Ho ; Ih, Jeong-Guon ;
The Journal of the Acoustical Society of Korea, volume 33, issue 2, 2014, Pages 87~93
DOI : 10.7776/ASK.2014.33.2.087
If one identifies the detailed distribution of pressure and axial velocity at a source plane, the position and strength of major noise sources can be known, and the propagation characteristics in axial direction can be well understood to be used for the low noise design. Conventional techniques are usually limited in considering the constant source characteristics specified on the whole source surface; then, the source activity cannot be known in detail. In this work, a method to estimate the pressure and velocity field distribution on the source surface with high spatial resolution is studied. The matrix formulation including the evanescent modes is given, and the nearfield measurement method is proposed. Validation experiment is conducted on a wide duct system, at which a part of the source plane is excited by an acoustic driver in the absence of airflow. Increasing the number of evanescent modes, the prediction of pressure spectrum becomes further precise, and it has less than -25 dB error with 26 converged evanescent modes within the Helmholtz number range of interest. By using the converged modal amplitudes, the source parameter distribution is restored, and the position of the driver is clearly identified at kR = 1. By applying the regularization technique to the restored result, the unphysical minor peaks at the source plane can be effectively suppressed with the filtering of the over-estimated pure radial modes.
Study on the Wideband Tonpilz Transducer with a Cavity-Type Head Mass
Kim, Hyunki ; Lim, Youngsub ; Roh, Yongrae ;
The Journal of the Acoustical Society of Korea, volume 33, issue 2, 2014, Pages 94~101
DOI : 10.7776/ASK.2014.33.2.094
In this work, we present an underwater acoustic transducer with a cavity-type head mass to achieve a wide frequency bandwidth. We analyzed the effects of design variables on the transducer characteristics, and optimized the structure of the Tonpilz transducer based on the analysis results. Further, validity of the design was verified by manufacturing a prototype of the transducer and measuring its properties. The designed transducer had a far wider -6 dB fractional bandwidth which is 131 % than that of a single mode transducer, and the measured results were confirmed to be in good agreement with the analysis results.
Effect of a Bonding Layer between Electrodes on the Performance of a λ/4-Mode PVDF Ultrasound Transducer
Cao, Yonggang ; Ha, Kanglyeol ; Kim, Moojoon ; Kim, Jungsoon ;
The Journal of the Acoustical Society of Korea, volume 33, issue 2, 2014, Pages 102~110
DOI : 10.7776/ASK.2014.33.2.102
The effect of a bonding layer on the performance of a quarter-wave (
) mode PVDF ultrasound transducer having not only a piezoelectric layer but also a non-piezoelectric layer between two electrodes was analyzed. The equivalent circuit of a transmission line model by Kikuchi et al.[Sound of IEICE, 55-A, 331-338 (1981)] was introduced for the analysis. The validity of the model was confirmed by comparison with a KLM model for three postulated adhesion cases of a
thick piezoelectric PVDF film to a copper (Cu) backer. The pulse-echo responses of five PVDF transducers, each fabricated with a different thickness (
) of the bonding layer, were measured and the results were compared with those by simulation. The two results were in good agreement with each other and it was noted that the effect of the bonding layer on the performance of the transducer could be analyzed by the Kikuchi model. In detail, the
bonding layer decreased the center frequency and the bandwidth by about 19.7 % and 25.0 %, respectively, and increased the insertion loss by 57.2 %.
An Experimental Analysis of the Structure-Borne Noise Reduction on Electrical Equipment
Lee, Seong-Hyun ; Seo, Yun-Ho ; Kim, Won-Hyoung ; Choi, Young-Cheol ;
The Journal of the Acoustical Society of Korea, volume 33, issue 2, 2014, Pages 111~117
DOI : 10.7776/ASK.2014.33.2.111
In this paper, the structure-borne noise reduction on electrical equipment is discussed by the experimental analysis. The water cooling system in electrical equipment is the only noise source, so the mock-up was made to measure noise characteristics. Effects of power supply, stiffness, isolation of noise source and natural frequency determined by resilient mounts are investigated using the mock-up. The console prototype was made referring to noise reduction technique by the mock-up. The structure-borne noise level of a console prototype was measured and some experiments to reduce the noise was undertaken. The
harmonics of operating frequency of cooling fans causes highest structure-borne noise levels. The control of operating speeds of several DC cooling fan groups was tried. Also types and installation layouts of resilient mounts were investigated. To reduce structure-borne noise, followings can be applied: increase of stiffness, isolation of source, decrease of natural frequency of mount, combination of operating speed of fans, selection of mounts, and so on.
Regeneration of the Retarded Time Vector for Enhancing the Precision of Acoustic Pyrometry
Kim, Tae-Kyoon ; Ih, Jeong-Guon ;
The Journal of the Acoustical Society of Korea, volume 33, issue 2, 2014, Pages 118~125
DOI : 10.7776/ASK.2014.33.2.118
An approximation of speed of sound in the measurement plane is essential for the inverse estimation of temperature. To this end, an inverse problem relating the measured retarded time data in between set of sensors and actuators array located on the wall is formulated. The involved transfer matrix and its coefficient vectors approximate speed of sound of the measurement plane by using the radial basis function with finite number of interpolation points deployed inside the target field. Then, the temperature field can be reconstructed by using spatial interpolation technique, which can achieve high spatial resolution with proper number of interpolation points. A large number of retarded time data of acoustic paths in between sensors and arrays are needed to obtain accurate reconstruction result. However, the shortage of interpolation points due to practical limitations can cause the decrease of spatial resolution and deterioration of the reconstruction result. In this works, a regeneration for obtaining the additional retarded time data for an arbitrary acoustic path is suggested to overcome the shortage of interpolation points. By applying the regeneration technique, many interpolation points can be deployed inside the field by increasing the number of retarded time data. As a simulation example, two rectangular duct sections having arbitrary temperature distribution are reconstructed by two different data set: measured data only, combination of measured and regenerated data. The result shows a decrease in reconstruction error by 15 % by combining the original and regenerated retarded time data.
Improvement of RFID Tag Anti-Collision Algorithm Based on the Dynamic Framed Slotted ALOHA
Park, Nho-Kyung ; Yun, Hyoung-Kie ; Moon, Dai-Tchul ;
The Journal of the Acoustical Society of Korea, volume 33, issue 2, 2014, Pages 126~132
DOI : 10.7776/ASK.2014.33.2.126
In this paper, a DFSA (Dynamic Framed Slotted ALOHA) based anti-collision algorithm is described and a performance improved algorithm of DFSA and FSA is proposed. The proposed method makes use of expected values and has merits in operation speed by estimating closest value of the number of tags on a single operation. The algorithm compares and analyses number of empty slots and collide slots in accordance with the number of tags, which enables estimation of actual number of tags. we simulated the proposed algorithm and compared it with conventional methods. Results show that our method needs average 18.8 rounds to identify all tags. In case of less than 1000 tags, an average of 18.2 rounds is necessary and an average of 19.2 rounds is needed to identify all tags for more than 1000 tags. The proposed algorithm improves processing speed by 3.1 % comparing to DFSA with cancellation strategy, 10.1 % comparing to DFSA, 37.5 % comparing to FSA(Framed Slotted ALOHA).
Playout Scheduling Method Based on Adaptive Jitter Estimation for Enhancing VoIP Speech Quality
Ryu, Sang-Hyeon ; Kim, Hyoung-Gook ;
The Journal of the Acoustical Society of Korea, volume 33, issue 2, 2014, Pages 133~138
DOI : 10.7776/ASK.2014.33.2.133
Packet arrival-delay variation, so-called 'jitter' is one of the main factors that degrade the quality of voice in mobile devices at the Voice over Internet Protocol (VoIP). To resolve this issue, a playout scheduling based on adaptive jitter estimation for enhancing VoIP speech quality is proposed. The proposed algorithm copes with the effect of transmission jitter by expanding or compressing each packet according to the predicted network delay and variations. Additionally, the active network jitter estimation incorporates rapid detection of delay spikes and reacts to changes in network conditions. The experimental results have shown that the proposed algorithm delivers high voice quality in unstable network environment.
A Single Channel Voice Activity Detection for Noisy Environments Using Wavelet Packet Decomposition and Teager Energy
Koo, Boneung ;
The Journal of the Acoustical Society of Korea, volume 33, issue 2, 2014, Pages 139~145
DOI : 10.7776/ASK.2014.33.2.139
In this paper, a feature parameter is obtained by applying the Teager energy to the WPD(Wavelet Packet Decomposition) coefficients. The threshold value is obtained based on means and standard deviations of nonspeech frames. Experimental results by using TIMIT speech and NOISEX-92 noise databases show that the proposed algorithm is superior to the typical VAD algorithm. The ROC(Receiver Operating Characteristics) curves are used to compare performance of VAD's for SNR values of ranging from 10 to -10 dB.
An Improved Frequency Modeling Corresponding to the Location of the Anjok of the Gayageum
Kwon, Sundeok ; Cho, Sangjin ;
The Journal of the Acoustical Society of Korea, volume 33, issue 2, 2014, Pages 146~151
DOI : 10.7776/ASK.2014.33.2.146
This paper analyzes the previous Anjok model of the Gayageum and describes a method to improve the frequency modeling based on previous model. In the previous work, relation between the fundamental frequency and Anjok's location on the body is assumed as an exponential function and these frequencies are integrated by a first-order leaky integrator. Finally, a parameter of the formula to calculate the fundamental frequency is obtained by applying integrated frequencies to the linear regression. This model shows 2.5 Hz absolute deviation on average and has maximum error 7.75 Hz for the low fundamental frequencies. In order to overcome this problem, this paper proposes that the Anjok's locations are grouped according to the rate of error increase and linear regression is applied to each group. To find the optimal parameter, the RMSE(Root Mean Square Error) between measured and calculated fundamental frequencies is used. The proposed model shows substantial reduction in errors, especially maximum three times.