• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2003.10a
• /
• pp.556-565
• /
• 2003

Light losses in optical fibers are investigated by a fiber optic OTDR (Optical Time Domain Reflectometry) sensor system to develop fiber optic probes for structural displacement measurement. The displacement sensitivity was determined by the measurements of fiber-bending loss according to the gage length changes of the displacement sensor. The fiber optic displacement probe was manufactured to verify the feasibility of the structural displacement measurement.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2005.03a
• /
• pp.1361-1368
• /
• 2005

In this paper, the theoretical method of measuring the tunnel convergence and underground displacement, the objective indices of assessing safety for tunnel construction, using the fiber optic sensor is studied by developing the program to automatically measure them. The model test of Con'c beam is conducted to evaluate reliability of the fiber optic sensor. Furthermore, using the RS232 communication protocol as well as Visual C# and Visual C++, the programming tools, the program was developed to detect automatically the measured value of the fiber optic sensor, calculate the tunnel convergence and underground displacement, predict the deformed shape of the tunnel, and evaluate loosening zone due to the tunnel excavation.

• Journal of Sensor Science and Technology
• /
• v.14 no.3
• /
• pp.169-179
• /
• 2005

A multiplexed bend loss type single-mode fiber-optic sensor system was prepared to measure the displacement of several cm of the civil engineering structures such as many bridges, tunnels and various buildings. This bend loss type fiber-optic sensor used the signal difference between two reflection signals due to various bend losses generating at a pair of optical connectors by using OTDR (optical time domain reflectometer) for measuring displacements. And the experiments were conducted for showing the measurement feasibility on the range of 10 cm, and the multiplexing experiments were also performed to measure the displacements of 5 measuring positions of an object by setting these 5 fiber-optic sensors on a single mode fiber simultaneously.

• Korean Journal of Optics and Photonics
• /
• v.15 no.5
• /
• pp.415-422
• /
• 2004

We propose and present a new multiplexed bend loss type single-mode fiber-optic sensor system for displacement measurement in order to measure the displacement of several mm of civil engineering structures such as bridges and buildings. We make a bend loss type fiber-optic sensor for measuring displacements using the signal difference between two reflection signals due to various bend losses generating at a pair of optical connectors by using the optical time domain reflectometer. And we fabricate a multiplexed bend loss type fiber-optic sensor detecting linear displacements of 4 measuring positions of an object by setting these new 4 fiber-optic sensors on a single mode fiber simultaneously. We find that the multiplexed fiber-optics displacement sensor has linearity of 0.9942, maximum displacement of 6 mm, and accuracy of 6% for 4 measuring points.

• Journal of Sensor Science and Technology
• /
• v.14 no.5
• /
• pp.302-307
• /
• 2005

Precision displacement of less than a few nm resolution was measured in real-time using fiber optic EFPI sensor. The novel method for real-time processing of analyzing EFPI output signal was developed and verified. Linearity in the mean values of interferometric light intensity among adjacent fringes was shown and verified the sinusoidal approximation algorithm that estimates past and coming fringe values. Real-time signal processing program was developed and the intensity signal of the EFPI sensor was transformed to the phase shift with this program. The resolution below $0.36{\sim}8.6$ nm in the displacement range of $0{\sim}300{\mu}m$ was obtained. The nano-positioner with a piezoelectric actuator and the EFPI sensor system was designed and tested. The positioner successfully reached to the desired destination within 1 nm accuracy.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.25 no.5
• /
• pp.350-355
• /
• 2005

The probes of fiber optic OTDR (Optical Time Domain Reflectometry) sensor was developed to measure displacements of social infrastructures. This probe was simply constructed with two conventional optical fiber connectors, and a fiber bending part, which transforms displacement to optical loss. When the displacement was affected on the bending loss part, the reflected light intensity of one optical connector was changed. The displacement was determined from this reflected light intensity change of the connector. fiber optic OTDR displacement sensor was developed as the multiplexed type of one fiber line with 5 sensor probes. Multiplexing operation was tested by these 5 sensor probes.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2003.10a
• /
• pp.154-157
• /
• 2003

Precision displacement of less than a few nm resolution was measured in real-time using fiber optic EFPI sensor. The novel method for real-time processing of analyzing EFPI output signal was developed and verified. Linearity in the mean values of interferometric light intensity among adjacent fringes was shown, and the sinusoidal approximation algorithm that estimates past and coming fringe values was verified through the linearity. Real-time signal processing program was developed, and the intensity signal of the EFPI sensor was transformed to the phase shift with this program. The resolution below 0.4 ~ 10 nm in the displacement range of $0 ~ 300\mu\textrm{m}$ was obtained by reducing the photodetector noise using low-pass filter and signal averaging. The nano-translation stage with a Piezo-electric actuator and the EFPI sensor system was designed and tested. This stage successfully reached to the desired destination in $15\mu\textrm{m}$ range within 1 nm accuracy.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.478-481
• /
• 1995

This paper presents the system demonstrator for an optical fiber sensor system developed as a technological evaluator suitable for generic sensric sensing applications. The new type of fiber-optic sensor employed a diaphragm displacement transforms pressure into optical intensity. Form this sensing technique, we can know the variation of source intensity, the loss of a optical fiber, and the reflectivity of the diaphragm surface. Experimental results are applied to the low-pressure transducer suitable for measuring miniature pressure.

• Transactions of The Korea Fluid Power Systems Society
• /
• v.7 no.2
• /
• pp.1-6
• /
• 2010

A new type fiber optic sensing system has been developed as a commercially available standard using the technique of hetero-core spliced fiber optic sensor, for the purposes of monitoring large scaled structures, preserving natural environments and measuring physical phenomenons. The sensing 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 system in this work conveniently provides us with various options of sensor modules intended to measure such physical quantities as displacement, distortion, pressure, binary states and liquid adhesion. The experiment study has been performed to examine the performance to a pseudo-cracking experiment in the outdoor situation, and to clarify temperature influences to the system in terms of the coupling of optical connectors and the OTDR stability. It has been verified that the sensing system is robust to the temperature change ranging from the general condition to the hard condition. Especially, in this study, the specification and performances of the pressure sensor have been demonstrated to show the capability of inspecting various physical quantities.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.31 no.4
• /
• pp.374-381
• /
• 2011

It has been doing to research on novel techniques for structural health monitoring by applying various sensor techniques to measure the deflection in mechanical and civil structures. Several electric-based displacement sensors have many difficulties for using them because of EMI (Electro-Magnetic Interference) noise of many lead-wires when they are installed to many points in the structures. In this paper, it is proposed an affordable intensity-based fiber optic sensor to measure small displacement solving the problems of conventional sensors. In detail, the sensor head was designed on the basis of the principle of bending loss and a basic experiment was performed to obtain the sensitivity, the linearity and the stroke of the sensor. Moreover, a prototype was designed and manufactured to be easily installed to a structure and a real-time control software was also successfully developed to drive the fiber optic sensor system.