• The Journal of the Acoustical Society of Korea
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• 제21권1E호
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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.

• 전기전자학회논문지
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• 제11권2호
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• pp.77-82
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• 2007

본 논문에서는 광섬유 표면 플라즈몬 공명 센서를 이용하여 스트레인 및 온도 변화에 따른 센서를 제시하였다. 광섬유 센서의 구조는 광섬유의 클래딩 일부를 제거하여 크롬, 은, 금을 증착한 다층 박막 구조를 모델로 하였고, dip 파장의 변화가 선형성을 보임으로써 효율적인 센서로의 활용 가능성을 보이고자 한다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.517-522
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• 2000

In the past few years, the nondestructive inspection technology has greatly developed due to the increased necessity to gain a complete understanding of the bridge behavior. Especially, the deformations of bridges contain a lot of informations about its health state. By measuring these deformations it is possible to analyze the loading and aging behavior of the structure. However, the current methods (such as LVDT, dial gage, optical displacement tranceducer, etc) are often of changeable application on site and have the limitations of installation. In this paper, the classical beam theory was reviewed and the deflections of structure are estimated using measured strain which is easy to acquire. The applicability of this algorithm is verified by a preliminary steel beam test and two types of concrete beam tests. Also fiber optic sensors as well as resistive strain gages were installed in the concrete beams to establish the applicability of fiber optic sensors in the field of civil engineering.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 C
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• pp.1715-1717
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• 2001

The partial-discharge(PD) is accompanied by physical and chemical phenomena, such as heat, light, noise gas, chemical transformation, electric current, and electromagnetic radiation. The PD can be detected by measuring one of these changes. Although some techniques are employed in this purpose, several obstacles interfere with an on-line measurement. Now, a fiber-optic sensor for detecting ultrasonics is suggested for the on line measurement system with high accuracy. This paper describes the basic principles fiber-optic sensor for ultrasonic measurement.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 추계학술발표대회 논문집
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• pp.154-157
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• 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.

• 한국철도학회논문집
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• 제9권4호
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• pp.467-472
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• 2006

This paper deals with the applicability of long-gauge deformation fiber optic sensors (FOS) to prestressed concrete structures. A main motivation is the desire to monitor the deflection of the railway bridges without intervenes of the signal intensity fluctuations. A 25 m long, 1.8 m deep PSC girder was fabricated compositely with 22 cm thick reinforced concrete deck. Two pairs of 3 m long-gauge sensors are attached to the prestressed concrete girder with parallel topology. Using the relationship between curvature and vortical deflection and the quadratic regression of curvatures at the discrete point, it is possible to extrapolate the deflection curve of the girder. The estimated deflection based on the developed method is compared with the results using conventional strain gauges and LVDTS. It has been demonstrated that the proposed instrumentation technique is capable of estimating the vertical deflection and neutral axis position of the prestressed concrete girder up to weak nonlinear region.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 춘계학술대회 논문집
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• pp.109-114
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• 2005

Fiber optic sensors hold a great potential for structural monitoring due to their stability and durability. This paper deals with the applicability of long-gage deformation fiber optic sensors to prestressed concrete structures. Two sets of 3 m long-gage sensors are attached to the prestressed concrete girder with parallel topology. Using the quadratic regression of measured deformations over the length of sensors it is possible to extrapolate the deflection of the girder. The static response based on the developed method is compared with the results using conventional strain gages and LVDTs.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1987년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 16-17 Oct. 1987
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• pp.528-532
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• 1987

Closed-loop fiber-optic gyroscope with linear scale factor for a wide dynamic range is demonstrated using a gating process and two-harmonic phase modulation, of which the second harmonic is obtained by a frequency doubler. Also the effects of the second harmonic and duty cycle of gating signal on the linearity of scale factor are estimated theoretically and compared with the measured data. The experimental results show the best linearity of scale factor is about 0.5% within the rotation rate 90.deg./sec. The closed-loop fiber-optic gyroscope with gated two-harmonic phase modulation can be used in the application demanding less sensitive performance and modest scale factor linearity.

• 제어로봇시스템학회논문지
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• 제20권4호
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• pp.437-442
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• 2014

Due to electrical cross-coupling between modulation voltage and photodetector output in a closed-loop fiber optic gyro, deadzone inevitably occurs. In this paper, deadzone error by cross-coupling effect was analyzed and the overcoming method was suggested. Simulation and measurement results show the main reason for deadzone is mainly related to electrical cross-coupling, and it can be effectively reduced by square-wave dithering method.

• 센서학회지
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• 제9권6호
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• pp.416-423
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• 2000

Sagnac 간섭계를 이용한 광섬유 음향 센서에서 음향 신호를 간단하면서도 효과적으로 복조할 수 있는 이중위상 천이 신호처리 기법을 제안하고 실험을 통하여 그 특성을 검증하였다. 이 기법을 사용하여 기존의 ${\pi}/2$ 위상 바이어스 복조 방식이 갖는 동적 범위의 이론적 한계를 근본적으로 제거하였다. 이 기법은 고주파의 위상 변조를 하지 않으므로 간단한 전자 회로만으로도 음향 신호의 복조가 가능하다. 또한 디지털 신호처리에 적합하며 다른 간섭계에도 적용이 가능하다.