• Journal of Sensor Science and Technology
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• v.9 no.2
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• pp.96-105
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• 2000

Fiber optic TR-EFPI(total reflected extrtinsic Fabry-Perot interferometric) sensor was developed to measure the strain of structures, such as building, bridge, aircraft, etc. It has been difficult to distinguish the increase and decrease of the strain from the conventional fiber optic EFPI sensor because their signals only have a sinusoidal wave pattern related to the change of strain. Also, the absolute strain could not be measured by the simple fiber optic EFPI sensor. In this study, in order to measure the magnitude of strain with the direction of strain, the fiber optic sensor was simply constructed with the total reflected EFPI sensor probe. This probe was manufactured with a single mode fiber and a mirror coated fiber in a silica glass capillary tube. The output signal of this fiber optic TR-EFPT sensor can give the information about the magnitude and the direction of strain. The loading-unloading test was performed by the universal testing machine with alluminum beam specimen to compare the strain from fiber optic TR-EFPI sensor with the value from electrical strain gauge. In the result of this experiment. the strain from fiber optic TR-EFPI sensor had a good agreement with the values from the electrical strain gauge.

• Composites Research
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• v.31 no.6
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• pp.429-434
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• 2018

We investigate strain transmissions of a surface bonded distributed optical fiber sensor considering strain variation according to positions. We first derive a strain transmission ratio depending on a wavelength of a strain distribution of the host structure from an analysis model. The strain transmission ratio is compared with numerical results obtained from the finite element method using ABAQUS. We find that the analytical results agree well with the numerical results. The strain transmission ratio is a function of a wavelength, i.e. the strain transmission ratio decreases (increases) as the wavelength of the host strain decreases (increases). Therefore, if an arbitrary strain distribution containing various wavelengths is given to a host structure, a distorted strain distribution will be observed in the distributed optical fiber sensor compare to that of the host structure, because each wavelength shows different strain transmission ratio. The strain transmission ratio derived in this study will be useful for accurately identifying the host strain distribution based on the signal of a distributed optical fiber sensor.

• Korean Journal of Optics and Photonics
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• v.12 no.4
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• pp.294-299
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• 2001

Recently great efforts and investment have been made in order to develop a structural health monitoring technology using fiber optic sensors. Therefore, in this study, we have focused on the development of a fiber optic BOTDA (Brillouin Optical Time Domain Analysis) sensor system in order to measure strains distributed on large structures by an optical fiber. The fiber optic BOTDA sensor was constructed simply, with only two electro-optic modulators. The results of strain measurement tests of an optical fiber showed that the strain can be determined accurately from the Brillouin frequency shift measurement on the strain induced range of 10 m in the total fiber length of 4.8 kIn using 200 averaged signals. Also, the strain sensitivity of Samsung single mode fiber was 4.81 MHz/O.Ol % under the test. test.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.30-35
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• 2003

In this paper, the transverse strain was measured using polarization maintaining fiber Bragg grating(PMFBG) sensor. PMFBG sensor was fabricated using phase mask and Excidmer laser. The reflected wavelength of PMFBG sensor had dual peaks due to intrinsic birefringence. To find the polarization axes, peak sensitivity was measured under compression test. The signal characteristics of PMFBG sensor were also examined in embedding condition. The embedded PMFBG sensor in epoxy block was loaded for the transverse strain measurement, The wavelength-swept fiber laser(WSFL) was used to construct the PMFBG sensor system. Experiments showed that the PMFBG sensor could successfully measure the transverse strain.

• Journal of Sensor Science and Technology
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• v.10 no.6
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• pp.304-309
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• 2001

A Fiber optic strain sensor for the measurement of the internal strain of a concrete specimen was developed. This sensor was a 11 mm Fiber-optic Fabry-Perot interferometer attached inside a stainless steel pipe of 2 mm diameter. The fabricated strain sensors were embedded in a reinforced concrete structure of $100{\times}100{\times}500\;mm^3$ size and were measured the internal strain of a concrete structure when the external pressure was applied to the structure. For a field application, the strain sensors were attached on the bottom of a real bridge and dynamic loading test were executed. In the test, they showed good sensitivity as a deformation sensor and capability of remote monitoring.

• Composites Research
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• v.16 no.3
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• pp.58-67
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• 2003

To perform the realtime strain and fracture monitoring of the smart composite structures, two optical fiber sensor systems are proposed. The two types of the coherent sources were used for fracture signal detection - EDFA with FBG and EDFA with Fabry-Perot filter. These sources were coupled to EFPI sensors imbedded in composite specimens. To understand the characteristics of matrix crack signals, at first, we performed tensile tests using surface attached PZT sensors by changing the thickness and width of the specimens. This paper describes the implementation of time-frequency analysis such as short time Fourier transform (STFT) and wavelet transform (WT) for the quantitative evaluation of fracture signals. The experimental result shows the distinctive signal features in frequency domain due to the different specimen shapes. And, from the test of tensile load monitoring using optical fiber sensor systems, measured strain agreed with the value of electric strain gage and the fracture detection system could detect the moment of damage with high sensitivity to recognize the onset of micro-crack fracture signal.

• Composites Research
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• v.14 no.6
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• pp.32-37
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• 2001

It is known that recoating or protection with glass-tube can prevent FBG sensor from being affected by birefringence. However, the effect on the strain transfer of such treatment has not been verified yet. Three types (uncoated, recoated and glass-tube protection) of FBG sensors are fabricated to verify the effect on the strain transfer of each treatment. The strain from each sensor embedded into a graphite/epoxy composite specimen was compared with that of ESG attached on the surface through the tensile test. And the signal characteristics of each sensor were also compared using the tensile test of a tapered aluminum specimen which was under the state of strain gradient.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.254-255
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• 2000

광섬유 전반사형 외부 패브리-패로(TR-EFPI total reflected extrinsic Fabry-Perot inteferometric) 센서를 개발하여 외부 물리량의 변화 크기와 방향을 간편하게 알아낼 수 있도록 하였다. 이 TR-EFPI 센서 탐촉자는 한 개의 단일모드 광섬유와 한 개의 거울도금 광섬유를 모세 유리관 안에 고정하여 공기간극을 형성함에 의하여 만들어진다. 또한 외부 물리량은 변형률을 측정할 수 있도록 알루미늄 시험편의 표면에 부착하고 만능시험기를 사용하여 하중을 증감시키면서 변형률의 변화를 측정하도록 하였다. (중략)

• Journal of Sensor Science and Technology
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• v.10 no.1
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• pp.16-23
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• 2001

Comparing with general optical fiber sensors performing localized measurement, distributed optical fiber sensors can measure along an optical fiber, and they have large measuring range. The surface-mounting method with epoxy adhesive is general in attaching optical fiber sensors to structures, This is also appliable to the structural integrity monitoring with Brillouin-scattering distributed optical fiber sensors. In this paper, Brillouin-scattering distributed optical fiber sensors, which are attached to the surface of a structure with epoxy adhesive, was verified with the finite element method. From the analysis results of strain transfer through the structure, optical fiber coating, cladding and core, the strain transfer rates were calculated. And the influence of the epoxy free-end was also studied.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.199-202
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• 2011

플로팅구조물은 열악한 해양환경상태에 있기 때문에 구조물응답에 대한 실시간 모니터링 기술을 적용하여 구조안전성을 확보해야 한다. 특히 기존의 전기 저항식 스트레인 게이지 단점을 극복한 광섬유 센서를 이용하여 실시간 모니터링 시스템 개발에 관한 연구가 필요하다. 본 논문에서는 플로팅구조물의 축소 모델에 광섬유 센서 중 하나인 FBG센서를 부착하고 실험용 수조에 설치하여 광학 스펙트럼 분석기를 통해 중심파장을 측정한 후 변형률을 계산하였다. 또한 유한요소 모델을 유한요소 해석 프로그램인 ABAQUS를 사용하여 모델링하고 유한요소 해석을 통해 변형률을 출력하고 실험결과와 해석 결과를 비교하여 광섬유 센서를 이용한 플로팅구조물의 실시간 모니터링을 위한 기초자료를 제공하고자 한다.