• The Journal of the Acoustical Society of Korea
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• v.27 no.4
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• pp.178-182
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• 2008

In measurements of the vibration of structures underwater with a laser Doppler vibrometer, the surface vibration is measured by means of detecting the phase change of the laser beam due to the structural vibration. The laser beam passes through the sound field radiated from the vibrating structures underwater. It experiences an additional phase change due to the change in refractive index in the radiated sound field. This phase change due to the sound field may cause the error in surface vibration measurements. In this paper, this phase change due to the radiated sound filed has been analyzed. The numerical simulation has been peformed to evaluate the phase change in sound field radiated from an infinite cylindrical structure vibrating underwater.

• The Journal of the Acoustical Society of Korea
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• v.25 no.1
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• pp.1-6
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• 2006

The Possibility of using acoustic impedance as an input Parameter for computation of underwater acoustic field in shallow waters was investigated. Analysis of the acoustic reflection from the ocean bottom with shear wave effect showed that acoustic impedances below the critical grazing angle have nearly angle-independent property and could be approximated with a single value of near-grazing impedance $Z_0$. Computations of the Propagation loss based on the concept of 'effective depth' indicate that near-grazing bottom acoustic impedances could be used as an input parameter for simulation of the acoustic fields in shallow waters.

• The Journal of the Acoustical Society of Korea
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• v.12 no.6
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• pp.45-52
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• 1993

1986년 미국 음향학회 수중음향학술분과 특별회기중에 제안된 표준쐐기형 매질내의 음장을 계산하기 위하여 영상모델이 사용되었다. 음장의 계산 결과는 왕복결합모드무델과 음선모델에 의한 계산 결과들과 비교되었다. 영상모델은 그 특성에 의한 제한점을 갖고 있으나, 표준 쐐기형 매질의 음장 계산에 사용될 수 있고, 기존의 수치모델과는 달리 개인용 컴퓨터로써 쐐기형 매질의 음장 계산이 가능하기 때문에 음파 전파 현상분석 등의 연구에 유용하게 사용될 수 있다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.407-408
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• 2014

본 논문은 3차원 수중방사패턴 예측을 위하여 수중구조물의 표면진동장을 이용하여 3 차원 원음장 패턴을 예측한 뒤 수중구조물의 근접음장 계측데이터를 활용하여 산출된 원음장 음향파워를 이용하여 산출된 원음장 패턴의 음압크기를 보정하였고 이를 실험데이터와 비교 분석한 논문이다.

• The Journal of the Acoustical Society of Korea
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• v.20 no.5
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• pp.76-82
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• 2001

Because the biological tissue with inhomogeneous acoustic properties does not keep a particular shape, the measurement of propagation characteristics of ultrasonic fields by the conventional scanning method with a miniature hydrophone is difficult. In this study, a two-dimensional may hydrophone was fabricated using the PVDF (Polyvinylidene fluoride) piezo-electric film and a ultrasonic field measurement system with it was established. For the acoustic field produced by a circular plan transducer with center frequency of 2.25㎒ and 13㎜ in diameter, it was possible to make a fairly accurate field measurement using the hydrophone system. The attenuation coefficients at 2.25 ㎒ for biological tissues were 0.7∼1.3 dB/cm(average; 1.0 dB/cm) in bovine liver, 1.0∼1.8 dB/cm (average; 1.6 dB/cm) in pig liver, 0.9∼2,9 dB/cm(average: 2.1 dB/cm) in bovine muscles, 1.7∼3.3 dB/cm (average; 2.5 dB/cm) in pig muscles.

• Journal of Sensor Science and Technology
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• v.10 no.5
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• pp.320-328
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• 2001

Two-dimensional array hydrophones with $8{\times}8$ elements were designed and fabricated using the PVDF(Polyvinylidene fluoride) piezoelectric film, and the method and system for ultrasonic field measurement in several MHz $\sim$ tens of MHz band using the hydrophones was established. The characteristics of frequency response relating to the backing materials were analyzed with the Mason equivalent circuit for design, and the accuracy of ultrasonic field measurement relating to the sizes and kerfs of piezoelectric elements was discussed. Good results of the measurement of ultrasonic field formed by a circular plane transducer of 2.25MHz in water were obtained by the system with the array hydrophones.

• The Journal of the Acoustical Society of Korea
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• v.16 no.5
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• pp.105-111
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• 1997

Before application of the angular spectrum method to calculate acoustic fields in stratified water, its efficiencies and errors were analyzed by using a virtual boundary in homogeneous water. As the results, it was confirmed that the angular spectrum method was able to calculate an acoustic field rapidly though some errors due to the limitation of reference field size and number of data in FFT ware included. A modified method combined the angular spectrum with Lommel's approximation, which was newly proposed in this paper, was useful to reduce the errors.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.397-400
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• 2004

소음원 또는 방사음장을 가시화하기 위하여 소음원을 둘러싸는 한 면에서의 음압측정을 통해 임의의 3차원 공간상의 음향 물리량을 예측하는 음향 홀로그래피 방법이 사용되고 있으며 이때 반사파가 존재하지 않는 기본 가정을 만족해야 한다. 반사파가 존재하는 경우에는 반사파를 보정하거나 또는 반사파의 음장이 미치는 영향이 무시할 만큼 작다고 가정하여 음장 예측이 가능하게 된다. 최근 해양연구원에서는 음향 홀로그래피 방법을 이용하여 수중음장을 가시화하는 시스템을 개발하였으며 시스템 검증을 위해 무향수조 내 단순음원을 이용하여 음장예측을 수행하였다. 무향수조 표면에는 흡음처리가 되지 않아 표면 반사파가 존재하나 해석 결과 반사파의 영향이 작은 경우에는 반사파를 무시하고 음장해석의 수행이 가능함을 확인하였다.

• The Journal of the Acoustical Society of Korea
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• v.24 no.3
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• pp.166-170
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• 2005

This paper describes the experimental study for the position estimation method of underwater sound source using the Nearfield Acoustic Holography. The result confirms that it can be used in the identification of underwater noise sources. The sound sources in the experimental work consists of 2 spherical projectors and the near-Held sound pressure is measured in the hologram plane. From the cross-power spectra of the measured data, the complex sound pressures on the hologram plane is derived and its spatial transformation gives sound fields in a source region. The obtained sound fields in a source region showed that the position of each sound source and their relative source strength are exactly estimated. In conclusion, this technique can be applied for estimation of each source position and its relative strength contribution for the underwater multiple sound sources.

• The Journal of the Acoustical Society of Korea
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• v.16 no.3
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• pp.45-50
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• 1997

Four different wedge angle absorptive tiles were designed and made, and the magnitudes of the reflected acoustic fields by the wedge shaped underwater sound absorptive tiles were measured. The minimum magnitude was found at the angle of 30$^{\circ}$ and the maximum of it was found at the wedge angle of 120$^{\circ}$ from measured the reflected acoustic fields at the front sides of the tiles. The fact that as wedge angle of the absorptive tile increases, the reflection coefficient is increasing is verified. The measured reflected acoustic fields were not dependent on the frequency in the range of 10kHz~30kHz used in this experiment for the same wedge angle tile. The measured reflected acoustic fields at the back sides of the tiles show that they are independent from both type of the absorptive tiles and the frequencies used in the experiments. The measured values and the computed values by the numerical model for the reflected acoustic fields of the wedge shaped absorptive tiles are fairly well comparable with one another.