• Korean Journal of Optics and Photonics
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• v.31 no.1
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• pp.13-19
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• 2020

To measure underwater acoustics using a fiber-optic Sagnac interferometric sensor, the sensitivities of ring-type probes are investigated by theoretical and experimental studies. A ring-type probe was fabricated by packaging a single-mode fiber wound around an acrylate cylinder of diameter 5 cm with epoxy bond. The probes were prepared as A-type, which was packaged with 46.84 m of sensing optical fiber, and B-type, which was packaged with 112.22 m of sensing fiber. The underwater acoustic test was performed at frequencies of 50, 70, and 90 kHz, and over a range of acoustic pressure of 20-100 Pa, to study the sensitivity. A commercial acoustic generator was located 1 m from the acoustic sensor, such as the ring-type probe or a commercial acoustic sensor. From the experimental test, the acoustic sensitivity of the ring-type probe had different values due to acoustic frequencies, unlike the theoretical prediction. Therefore, the experimental sensitivities were averaged for comparison to the theoretical values. These averaged sensitivities are 25.48 × 10^-5 rad/Pa for the A-type probe and 60.79 × 10^-5 rad/Pa for the B-type probe. The correction coefficient of Young's modulus c was determined to be 0.35.

• Current Optics and Photonics
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• v.2 no.3
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• pp.250-260
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• 2018

A pressure wave created by the photoacoustic effect is affected by the medium and by laser parameters. The effect of these parameters on the generated pressure wave can be seen by solving the photoacoustic wave equation. These solutions which are examined in the time domain and the frequency domain should be considered by researchers in acoustic sensor design. In particular, frequency domain analysis contains significant information for designing the sensor. The most important part of this information is the determination of the operating frequency of the sensor. In this work, the laser parameters to excite the medium, and the acoustic signal parameters created by the medium are analyzed. For the first time, we have obtained solutions for situations which have no frequency domain solutions in the literature. The main focal point in this work is that the frequency domain solutions of the acoustic wave equation are performed and the effects of the frequency analysis of the related parameters are shown comparatively from the viewpoint of using them in acoustic sensor designs.

• Smart Structures and Systems
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• v.18 no.3
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• pp.471-484
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• 2016

Optical fiber sensors have been proven that they have the potential to detect high-frequency ultrasonic signals, in structural health monitoring field which generally refers to acoustic emission signals from active structural damages and guided waves excited by ultrasonic actuators and propagating in waveguide. In this work, the sensing properties of optical fiber sensors based on Mach-Zehnder interferometer were investigated in the metal plate. Analytical formulas were conducted first to explore the parameters affecting its sensing performances. Due to the simple and definable frequency component, the Lamb wave excited by the piezoelectric wafer was employed to study the sensitivity of the proposed optical fiber sensors with respect to the frequency, rather than the acoustic emission signals. In the experiments, according to above investigations, spiral shape optical fiber sensors with different size were selected to increase their sensitivity. Lamb waves were excited by a circular piezoelectric wafer, while another piezoelectric wafer was used to compare their voltage responses. Furthermore, by changing the excitation frequency, the tuning frequency characteristic of the proposed optical fiber sensor was also investigated experimentally.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1983.10a
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• pp.44-47
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• 1983

Through intensity modulation induced by micro bending of an optical fiber, a sensor detects the pressure and frequency of acoustic wave has been implemented. Axial slots on the cylinder suface with a period of 5.5 mm induce efficient microbending of the fiber, and a rubber sleeve covering the fiber enhances the fiber. Compared with a conventional hydrophone, it has a low minimum detectable pressure and can detect acoustic wave in 100Hz - 2KHz range.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.10
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• pp.256-263
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• 2014

We have designed and made three kinds of FBG(Fiber Bragg Grating) Acoustic Transducer using Hopper type WDM on the use of recently developed FBG in Korea. The newly designed three kinds of FBG Acoustic Transducer using Hopper type WDM have an excellent merit of practical use with simple structure of sensors arm as well as the merit with existing fiber sensors. It was possible to detect sound waves in the range of 10 Hz to 18 kHz through the newly designed three kinds of FBG Acoustic Transducer and also, possible to detect its signal within the maximum range of 8.6 m by the use of most suitable resonance condition of the transducer. Especially, we can expect the utilization of low-frequency signal detection instead of existing acoustic sensor in the environment of electric noise and inferior condition. Furthermore, they can be developed as the high-sensibility and multi-point signal detection system through the sensor array system.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1563-1565
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• 2000

This paper presents the preliminary results on the application of optical fiber sensor(OFS) for the diagnosis of degradation in the transformer oil. An OFS system using a Mach-Zehnder interferometry technique was built to detect attenuation of acoustic signal produced by discharging. With increasing the number of discharging in the insulation oil, the attenuation of acoustic signal became greater. A strong correlation between electrical and acoustic signal intensities from discharge generated in the transformer oil was confirmed by the results reported here.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.1
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• pp.57-61
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• 2008

A tensile-strain measurement method is proposed based on Depolarized Guided Acoustic-wave Brillouin Scattering (DGAWBS). The effect of tensile-strain applied to an optical fiber is investigated experimentally, observing that the resonance spectrum increases the measurement accuracy of DGAWBS at the TR25 mode. This paper presents a simple structure as tensile-strain sensor using two analyzers after sensing fiber.

• Smart Structures and Systems
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• v.1 no.1
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• pp.63-82
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• 2005

This paper introduces a technology for robust and low maintenance cost sensor network capable to detect accelerations below a micro-g in a wide frequency bandwidth (above 1,000 Hz). Sensor networks with such performance are critical for navigation, seismology, acoustic sensing, and for the health monitoring of civil structures. The approach is based on the fabrication of an array of high sensitivity accelerometers, each utilizing Fabry-Perot cavity with wavelength-dependent reflectivity to allow embedded optical detection and serialization. The unique feature of the approach is that no local power source is required for each individual sensor. Instead one global light source is used, providing an input optical signal which propagates through an optical fiber network from sensor-to-sensor. The information from each sensor is embedded onto the transmitted light as an intrinsic wavelength division multiplexed signal. This optical "rainbow" of data is then assessed providing real-time sensing information from each sensor node in the network. This paper introduces the Fabry-Perot based accelerometer and examines its critical features, including the effects of imperfections and resolution estimates. It then presents serialization techniques for the creation of systems of arrayed sensors and examines the effects of serialization on sensor response. Finally, a fabrication process is proposed to create test structures for the critical components of the device, which are dynamically characterized.

• The Journal of the Acoustical Society of Korea
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• v.9 no.2
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• pp.91-99
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• 1990

• Proceedings of the Acoustical Society of Korea Conference
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• 1987.11a
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• pp.20-23
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• 1987