• Journal of KSNVE
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• v.9 no.3
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• pp.565-569
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• 1999

Recently, fiber optic hydrophone is a subject which has attracted as a underwater acoustic sensor. In this study, Finite element modeling of fiber optic hydrophone for hollow cylindrical mandrel was performed and the acoustic sensitivity was calculated to estimate the performance of single element fiber optic hydrophone. And acoustic sensitivity was measured in acoustic water tank to verify the result of simulation. The result of FE analysis and experiment is -126 dB re rad/$\mu$ Pa and -128 dB re rad/$\mu$ Pa respectively.

• Journal of KSNVE
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• v.9 no.6
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• pp.1152-1156
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• 1999

In this study, a fiber optic air-backed mandrel hydrophone has been constructed and performance of acoustic signal detection has been measured. The hydrophone is based on a Mach-Zehnder interferometer with 35 m of sensing fiber. The sensitivity is measured up to -128 dB re rad/$\mu$ Pa in range from 1.4 kHz to5 kHz. A system with this design of hydrophone may be applied to detect low frequency underwater acoustic signals.

• Journal of Sensor Science and Technology
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• v.8 no.2
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• pp.102-107
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• 1999

In this paper, to develop the fiber optic hydrophone for the use of low frequency applications, two channels TDM(Time Division Multiplexing) fiber-optic hydrophone array was fabricated and their acoustic charateristics were investigated in the acoustic water tank. A fiber length of the order of 150m is wounded at the hollow cylinder type aluminum mandrel and the fundamental natural frequency of the mandrel maintained above 10kHz. An unbalanced interferometer (discrete Mach-Zehnder type) was used. Sound detection performance is tested in the underwater tank with 3kHz continuous sound source. Finally, it is shown that two channels TDM fiber-optic hydrophone array can detect 3kHz sound stably. This results can also applicable for the development of multi-channel fiber optic hydrophone array.

• The Journal of the Acoustical Society of Korea
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• v.20 no.7
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• pp.89-93
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• 2001

In recent years Fiber optic hydrophone systems have been the focus of much attention in the sonar world. For sonar arrays, a fiber optic approach offers the major benefit of passive multiplexing of large numbers of hydrophones without underwater electronics. This paper describes recent development work covering array construction, opto-electronics development, hydrohpone design and sea trials. And the development of an interferometric mult-channel fiber optic hydrophone system which uses time division multiplexing capable of driving in excess of 32 channel is described. For this, a 12 channel time division multiplexing array has been constructed, and the performance of this system is demonstrated by sea trial.

• The Journal of the Acoustical Society of Korea
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• v.21 no.1E
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• pp.25-30
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• 2002

We report on the development of a fiber optic hydrophone consists of a sensing Michelson interferometer and a compensating Mach-Zehnder interferometer for optical path length compensation. The double interferometer configuration has the following advantages: the hydrophone can be made more small; a laser source with a relatively short coherence length can be used; and the compensating interferometer can be located near the signal processing electronics, far away from the sensing interferometer and noise introduced by reference arm can be greatly reduced. The performance of the hydrophone is evaluated experimentally by immersing the sensing interferometer in a water tank to detect underwater acoustic signals generated by an acoustic wave projector. Experimental results show that over the frequency range of 1 to 4 kHz, the hydrophone has an almost flat response with an average normalized sensitivity of -302 dB re 1/ μ Pa.

• Journal of KSNVE
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• v.7 no.6
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• pp.931-936
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• 1997

Optical fiber sensor is a subject which has been attracted considerable attention in recent years. Detection of sound pressure with optical fibers positioned in the arms of a Mach-Zehnder interferometer is presented in this paper. A fiber length of the order of 150m is wounded is made by hollow cylinder type. To increase the sound signal 3${\times}3$ directional coupler is used. Fiber optic hydrophone is the underwater tank with 2kHz sound source. Finally, it is shown that the fiber optic hydeophone can stably detec 2kHz sound.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.617-621
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• 1998

Optical sensing techniques have been associated with high sensitivity and precise measurements and attracted considerable attention in recent years. In this paper, two channels TDM(Time Division Multiplexing) fiber-optic hydrophone array for the underwater applications was fabricated and their acoustic characteristics were investigated by using the acoustic water tank. A fiber length of the order of 100m is wounded at the hollow cylinder type aluminum mandrel. An unbalanced interferometer (discrete Mach-Zehnder type) was used. Sound detection performance is tested in the underwater tank with 2kHz continuous sound source. Finally, it is shown that two channels TDM(Time Division Multiplexing) fiber-optic hydrophone array can detect 2kHz sound stably.

• Journal of KSNVE
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• v.6 no.4
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• pp.475-479
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• 1996

Recently, fiber optic hydrophone is a subject which has attracted as a underwater acoustic sensor. In this paper, a length of optical fiber is bonded to an end-capped hollow cylinder of some elastic material, e. g. aluminum and glass-pyres. The normalized sensitivity is derived according to the direction of polarization. Derived sensitivity equations are simulated for two different mandrel materials. The results are also compared to the McMahon's results which calculated for an average Pockel coefficient. Based on the numerical simulation normalized sensitivity is propotional to the inner to outer diameter ratio.

• Journal of Sensor Science and Technology
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• v.9 no.4
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• pp.281-287
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• 2000

For the improvement of frequency characteristics of FBG(Fiber Bragg Grating) hydrophone sensor, we can detected the frequency ranging to 1.4KHz and acoustic directivity by the development of newly designed diaphragm and united type of FBG.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.286-290
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• 1996

수중 음향센서로서 최근에 많이 연구되고 있는 광섬유 하이드로폰(fiber optic hydrophone)의 성능을 예측하기 위하여 광섬유의 편광특성(polarization)에 따른 정규화 감도식 (normalized sensitivity)을 유도하였다. 본 연구에서 사용된 하이드로폰은 광섬유가 끝단이 막힌 중공 원통형 맨드럴(mandrel)에 감긴 구조이며 음압이 하이드로폰에 작용할 때 응력 관계식을 이용하여 정규화 감도식을 유도하였으며 유도된 감도식을 맨드럴의 내외경비에 따라 특성을 수치해석하였다. 균일한 재질의 광섬유에서 맨드럴의 내외경비의 값이 클수록 그리고 맨드럴의 탄성계수의 값이 작을수록 감도가 증가함을 관찰 하였다.