• The Journal of the Acoustical Society of Korea
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• v.18 no.1
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• pp.25-31
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• 1999

This paper proposes a new wide-band beamforming algorithm which has Gaussian weighting at nested linear array for acoustic measurement. The beamforming is performed one-shot by using all sensors simultaneously, not octave-by-octave. Gaussian weighting of frequency-dependent function is applied to each sensor before time-delay compensation so as to control the frequency receiving band of each sensor. As the results of the simulations, it is confirmed that the proposed algorithm can form the one-shot beams having uniform directivity index and also it can be applied to the broad-band acoustic measurement.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.10
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• pp.987-995
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• 2009

As an experimental technique to analyze the far-field characteristics of underwater cylindrical array sensors, cylindrical acoustic holography is studied. Inside an laboratory water tank, far-field directivity patterns as well as near-field source images are reconstructed from the measured hologram by hydrophone array. Approximate equation for far-field directivity estimation is derived based on stationary phase method. The simulation and experiment show well usefulness of the proposed method in application of underwater array sensors.

• Journal of Environmental Impact Assessment
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• v.16 no.1
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• pp.99-105
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• 2007

Since 1990s, the railway noise has been researched and developed in our nation. First of all, what's causing the noise and how to eliminate the cause of the noise must be found out. Secondly, cutting off the propagation path of the noise from the noise source to the receiving points. In this study the characteristics of prediction formula for the assessment of railway noise used in some nations including Korea were investigated. In order to develop the prediction formula of the railway noise, the noise radiated from railway vehicle, rails and sleepers, characteristics of noise barrier, velocity of train, ground effects, roughness should be analyzed and predicted. Especially, on the basis of acoustics, the characteristics of source are applied to acoustic power and directivity information.

• Journal of Korean Library and Information Science Society
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• v.32 no.3
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• pp.91-115
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• 2001

Today academic libraries have to show that they are using given resources for right purpose and in the best way. In order to reach this goal, academic libraries should develop the effective evaluation model. And carefully selected and used, performance measures or evaluation indicators are the most important tool the Library has to ensure goals and objectives are being accomplished. The purpose of this study is to understand a theoretical foundation for evaluation indicators of academic libraries, that is, its diverse(various) meanings and directivity.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.705-710
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• 2010

Bender element is made of connecting two piezoelectric elements which have different polarities from each other, and is a kind of sensors which can be used either way as a source making elastic wave or a receiver. Elastic waves generated by stimulating the bender elements can be decomposed to P-wave and S-wave propagation. Numerical and expeimental studies are conducted, and results show that multiple measurements are recommended to determine wave arrivals from the received signals.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.111-116
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• 2009

As an experimental technique to analyze the far-field characteristics of underwater cylindrical array sensors, cylindrical acoustic holography is studied. Inside an laboratory water tank, far-field directivity patterns as well as near-field source images are reconstructed from the measured hologram by hydrophone array. Approximate equation for far-field directivity estimation is derived based on stationary phase method. The simulation and experiment show well usefulness of the proposed method in application of underwater array sensors.

• Journal of Ship and Ocean Technology
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• v.4 no.1
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• pp.28-36
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• 2000

Numerical simulation based on the superposition of ring waves generated by the linear periodic source distributions for the plunger type wave maker was accomplished. The characteristics of directional spreading function were investigated. Mirror images are also introduced to consider reflections of side-wall together with the reflection coefficient to account for the imperfect reflection from the real side wall in the long experimental towing tank. Unexpected spurious waves, resulting from the combined effect of finite breadth of segmented wave maker, wavelength and main wave maker, wavelength and main wave propagating direction, were observed in the line source method and also in the analysis of the directivity. The influence of spurious waves to the directional spreading function was also investigated.

• Journal of KSNVE
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• v.8 no.4
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• pp.603-608
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• 1998

In order to obtain basic data for the prediction of railway noise propagation, the noise radiation characteristics (source position, radiation directivity, etc) of trains were measured by using the sound intensity method. The measurements were performed at a side of railway by setting an intensity-probe array. As the measurement results, it was found that rolling noise due to interaction between wheel and rail and motor noise radiation from the lower part of train are dominant. The location of main sound sources can be described as being at the height of 0.1m in the center line of track, and the radiation directivity in the cross section of actually running trains are presented as a dipole source.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.2
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• pp.50-55
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• 2012

Fabry-Perot (FP) resonator antennas with scan capabilities are described in this paper. The proposed antennas, excited by a thinned array, not only achieve higher directivities but also improve suppression of sidelobes relative to that of the thin array alone. Compared to the conventional microstrip patch array, the directivity enhancement and suppression of sidelobe level were achieved by increase of the aperture size of the proposed Fabry-Perot resonator antenna.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1714-1716
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• 2002

Optical fiber sensor is a subject which has been attracted considerable attention in recent year. Especially, it is being developed for the detection and location of partial discharge in oil-filled transformers. In this paper, we propose and experimentally demonstrate directivity and sensitivity of a hollow cylindrical mandrel sensor. The sound source is a PZT actuator of hollow cylinder type. Several layers of the fiber laminated around the mandrel surface and experiments were performed on three axis modes. The experimental results can be applied to analyze detected signals optimally.