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Erscheinungsjahr
- 2011 (11) (entfernen)
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- Beitrag zu einem Tagungsband (11) (entfernen)
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- Englisch (11)
Schlagworte
- BOFDA (2)
- BOTDA (2)
- Brillouin sensor (2)
- Distributed sensor (2)
- Dynamic sensor (2)
- Heart rate sensor (2)
- Long period grating (LPG) (2)
- Macrobending sensor (2)
- Microstructured polymer optical fibre (mPOF) (2)
- OFDR (2)
Technical textiles with embedded distributed fiber optic sensors have been developed for the purposes of structural health monitoring in geotechnical and civil engineering. The distributed fiber optic sensors are based on Brillouin Scattering in silica optical fibers and OTDR in polymer optical fibers. Such “smart” technical textiles can be used for reinforcement of geotechnical and masonry structures and the embedded fiber optic sensors can provide information about the condition of the structures and detect the presence of any damages and destructions in real time.
Thus, structural health monitoring of critical geotechnical and civil infrastructures can be realized. The paper highlights the results achieved in this innovative field in the framework of several German and European projects.
We present the status of our work on a tube shaped 3D deformation sensor based on continuously distributed fiber optic sensing. A sensor tube of very large diameter is used to ensure high sensitivity while the transportability and applicability are still comfortable due to our application strategy. The setup is designed to use different measurement techniques in the applied optical fibers including Brillouin based measurements and interferometric optical frequency domain measurements using an OBR 4400 from Luna Technologies.
We studied Brillouin gain spectrum characteristics in dispersion-shifted fibers having compound GeO2-doping compositions in the fiber core to realize simultaneous measurement of distributed strain and temperature. Due to various dopant concentration alongside the radius of tested nonzero dispersion-shifted fibers several multiple Brillouin scattering resonances were observed in the stimulated Brillouin spectra arose through backscattering on higher acoustic modes which propagated along the fiber axis. As a result of the varying acoustic velocities, the Brillouin resonance peaks featured different temperature coefficients which can be used to accomplish the simultaneous measurement of fiber strain and temperature. We presented our first measurement results for NZDS Fujikura and LEAF Corning fiber and discussed the superior sensory suitability of the former fiber types.
For long-range measurements in geotechnical and industrial applications, distributed optical fiber sensors have become a tool of increasing importance throughout the past decade.
Classic deformation monitoring (performed by strain gauges etc.) and temperature monitoring (Pt100 and alike) deliver data from fixed, single spots of a structure; quasidistributed measurements (fiber bragg gratings) provide a Chain of discrete measurement points along a limited sensing length. In contrast, an opticai fiber connected to a device for distributed strain and temperature sensing (DTSS) will provide a continuous profile of strain and temperature - spatially resolved down to less than 1 m - over a ränge of several tens of kilometers.
In DTSS measurements, the nonlinear opticai effect of stimulated Brillouin Scattering (SBS) is employed: two light waves with a stable, tunable frequency offset are injected into opposite ends of the sensing fiber, where they will form a beat pattem, at which parts of the light will be scattered. By matching the frequency offset of the light waves to the propagation of acoustic fluctuation in the opticai fiber, a power transfer from one light wave to the other can be measured; since the acoustic propagation directly shifts with train and temperature of the fiber, these two quantities can be measured by tuning the light waves’ frequency offset.
We investigated the capabilities of long period gratings (LPG) in single-mode microstructured polymer optical fibre (mPOF) for humidity sensing. For that mPOF LPGs were exposed to different humidity levels
at a constant temperature of 30°C in a climate chamber. During the long term tests, which took up several weeks, the humidity was changed in several steps while mPOF LPG wavelength and fibre attenuation were measured.
We also measured the water uptake of mPOF in environment with different relative humidity.
This paper reports on a fibre optic sensor for heart rate measurement which is developed within the framework of the FP7 EU project i-Protect. Goal is integration of the sensor into personal protective equipment Two different sensor prototypes based on polymer optical fibre (POF) were developed. One is based on long period gratings in microstrutured POF and the other one is based on macrobending effects in POF.
We investigated to our knowledge for the first time the capabilities of long period gratings (LPG) in single-mode microstructured polymer optical fibre (mPOF) as real-time gamma dosimeter. The fibre is made from polymethyl methacrylate (PMMA) with a polycarbonate jacket. We measured the radiation-induced wavelength shift of the mPOF LPG loss feature wavelength and the radiation-induced attenuation of a mPOF for
different wavelength between 600 nm and 800 nm for gamma radiation with an energy distribution between 6 keV and 18 keV.
This paper reports on a fiber optic sensor for heart rate measurements. The sensor will be integrated into personal protective equipment within the framework of the FP7 EU project i-Protect. Two different sensor prototypes were developed. One is based on fiber Bragg gratings in silica fiber and the other one is based on macrobending effects in polymer optical fiber.
A novel quasi-distributed long-gauge fiber optic strain sensor system for dynamic measurement
(2011)
We present a novel technique based on incoherent optical frequency domain reflectometry (OFDR) to measure length changes quasi-distributed between reflection points in optical fibres. The technique enables length changes to be measured with a resolution better than 1 µm and allows for static and dynamic measurement capabilities up to 2 kHz. We demonstrate that dynamic measurements of multiple fibre sections can be conducted independently from each other with high precision. Due to the precise and dynamic measurement capabilities, the proposed sensor system is expected to open new fields of application, especially in the structural-health-monitoring sector. Possible applications are discussed in the paper.
A dynamic and quasi-distributed sensor principle for simultaneous measurement of length changes and optical power changes between reflection points in an optical fiber is presented. The technique is based on the incoherent optical frequency domain reflectometry (I-OFDR). Length change resolutions < 1 µm and measurement repetition rates up to 2 kHz can be achieved using standard single-mode and multi-mode optical fibers. Simultaneous length change and refractive index measurement as well as field test results showing the deformation of a masonry building under seismic load are presented. Promising fields of application for this technique are the structural health monitoring sector and chemical process control.