• 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.

• Geomechanics and Engineering
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• v.2 no.2
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• pp.89-106
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• 2010

Sliding within the dam foundation is one of the key failure modes of a gravity dam. A two-dimensional (2-D) physical model test has been conducted to study the sliding failure of a concrete gravity dam under overloading conditions. This model dam was instrumented with strain rosettes, linear variable displacement transformers (LVDTs), and embedded fiber Bragg grating (FBG) sensing bars. The surface and internal displacements of the dam structure and the strain distributions on the dam body were measured with high accuracy. The setup of the model with instrumentation is described and the monitoring data are presented and analyzed in this paper. The deformation process and failure mechanism of dam sliding within the rock foundation are investigated based on the test results. It is found that the horizontal displacements at the toe and heel indicate the dam stability condition. During overloading, the cracking zone in the foundation can be simplified as a triangle with gradually increased height and vertex angle.

• Smart Structures and Systems
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• v.5 no.4
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• pp.345-355
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• 2009

This article describes the development of a fiber optic accelerometer based on Fiber Bragg Gratings (FBG). The accelerometer utilizes the stiffness of the optical fiber and a lumped mass in the design. Acceleration is measured by the FBG in response to the vibration of the fiber optic mass system. The wavelength shift of FBG is proportional to the change in acceleration, and the gauge factor pertains to the shift in wavelength as a function of acceleration. Low frequency version of the accelerometer was developed for applications in monitoring bridges. The accelerometer was first evaluated in laboratory settings and then employed in a demonstration project for condition assessment of a bridge. Laboratory experiments involved evaluation of the sensitivity and resolution of measurements under a series of low frequency low amplitude conditions. The main feature of this accelerometer is single channel multiplexing capability rendering the system highly practical for application in condition assessment of bridges. This feature of the accelerometer was evaluated by using the system during ambient vibration tests of a bridge. The Frequency Domain Decomposition method was employed to identify the mode shapes and natural frequencies of the bridge. Results were compared with the data acquired from the conventional accelerometers.

• Journal of Power System Engineering
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• v.16 no.6
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• pp.86-91
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• 2012

A multi purpose environmental monitoring system has been developed as a commercially available standard using the techniques which are FBG(Fiber Bragg Grating), Hetero-core spliced fiber optic sensor and etc, for the purposes of monitoring large scaled structures and preserving natural environments. The monitoring system has been tested and evaluated in a possible outdoor condition in view of the full scaled operation at actual sites to be monitored. Additionally, the developed systems in the previous works conveniently provided us with various options of sensor modules intended for monitoring such physical quantities as displacement, distortion, pressure, binary states, and liquid adhesion. In this paper, we extend the previous results to a water leakage detection problem and develop a sensing system as a result. By the experimental study, it is verified that multi-point leakage detection is possible using single line optical fiber.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.4
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• pp.18-23
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• 2007

This paper presents a transmissive dispersion compensator based on tilted chirped fiber Bragg grating pairs which happen mode coupling between core mode and cladding mode. And, as a result of simulation, the phase matching condition and optimum tilted angle to maximize the mode-coupling in the dispersion compensator are shown and the dispersion slope and bandwidth in the proposed dispersion compensator is respectively 3,068ps/nm and 0.45nm.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.2113-2116
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• 2007

In this study, transmission and reflection of multi-directional random waves propagating over multi-arrayed submerged breakwaters are investigated using eigenfunction expansion method. The numerical analysis on the wave energy reflection of submerged breakwaters with various crown widths is carried out. Strong wave reflection is occurred at the Bragg reflection condition of the peak frequency. When relative heights and crown widths of breakwaters are equal to 0.6 and 0.4h, respectively, more than 25% of wave energy is reflected to off shore.

• Journal of the Optical Society of Korea
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• v.19 no.6
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• pp.575-585
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• 2015

Magnetic field in magnetic bearings is the physical medium to realize magnetic levitation, the distribution of the magnetic field determines the operating performance of magnetic bearings. In this paper, a thin-slice Fiber Bragg Grating-Giant Magnetostrictive Material magnetic sensor used for the air gap of magnetic bearings was proposed and tested in the condition of dynamic magnetic field. The static property of the sensor was calibrated and a polynomial curve was fitted to describe the performance of the sensor. Measurement of dynamic magnetic field with different frequencies in magnetic bearings was implemented. Comparing with the finite element simulations, the results showed the DC component of the magnetic field was detected by the sensor and error was less than 5.87%.

• Korean Journal of Optics and Photonics
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• v.15 no.5
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• pp.469-474
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• 2004

We have fabricated and designed wavelength-tunable sampled grating distributed Bragg reflector laser diodes(SGDBR-LD) by using, for the first time, planar buried heterostructures(PBH). The diodes have low threshold current values and high-performance of laser operation. Growth condition using metal organic chemical vapor deposition(MOCVD) was optimized for the formation of a good butt-coupling at the interface. A maximum output power of the fabricated device was 20 mW under 200 mA continuous wave(CW) operation at $25^{\circ}C$. Average threshold current and voltage were 12 mA and 0.8 V, approximately. This output power is higher than those of ridge waveguide(RWG) and buried ridge stripe(BRS) structures by amounts of 9 mW and 13 mW, respectively. We obtained a tuning range of 44.4nm which is well matched with the target value of our design. The side mode suppression ratio of more than 35 dB was obtained for the whole tuning range. Optical output power variation was less than 5 dB, which is 4 dB smaller than that of RWG structures.

• Composites Research
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• v.15 no.3
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• pp.30-38
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• 2002

Fiber Bragg grating(FBG) like other optical fiber sensors also has the merit of embedding capability. To increase their actual value related to embedding capability, this paper reported the reliability and signal characteristics of FBGS embedded in composite laminates. The microphotographs of embedded optical fibers visualized the embedding environments of stripped optical fibers and coated optical fibers. Based on these microphotographs and cure monitoring performed using FBGs, we could understand that the main cause breaking the unique Bragg condition of low-birefrigence FBG were residual stress artier curing and reported the stale of stress/strain of optical fiber quantitatively. The cure monitoring also showed the history of splitting peak of a stripped FBG along cure processing. In addition, we could obtain a transverse insensitive grating(TIG) with ease by recoating a stripped FBG. TIG has good advantage for real-time signal processing.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.12
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• pp.1195-1200
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• 2007

Torque of a rotating shaft has been mostly measured by strain gages combined with either a slip ring or telemetry. However, these methods have severe inherent problems like low S/N ratio, high cost, limited number of channels and difficult installation. In this paper, a new method using FBG(fiber bragg grating) sensors and a rotary optical coupler for online non-contact torque monitoring is suggested. FBG sensor can measure both strain and temperature, and has much batter characteristics than those of a strain gage. A rotary optical coupler is a optical connecting device between a rotating shaft and stationary side without any physical contact. It has been devised for transmitting light between a rotating optical fiber and a stationary optical fiber. The proposed method uses this rotary optical coupler to connect FBG sensors on the rotating shaft to instruments at stationary side. And a reference FBG sensor is also applied to compensate the insertion loss change of the rotary optical coupler due to rotation. Three FBG sensors have been fabricated in a single optical fiber. Two FBG sensors are attached on the shaft surface to measure torque and one sensor is installed at the shaft center to compensate the insertion loss change. The torque of a rotating shaft has been successfully measured by the suggested method proving its superior performance potential.