Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (54) (entfernen)
Sprache
- Englisch (47)
- Deutsch (5)
- Mehrsprachig (1)
- Polnisch (1)
Schlagworte
Organisationseinheit der BAM
The potential impact of optical fiber sensors embedded into medical textiles for the monitoring of respiratory movements in a magnetic resonance imaging environment is presented. We report on three different designs, all textile based: a macrobending sensor, a Bragg grating sensor, and a time reflectometry sensor. In all three cases, the sensing principle is based on the measure of the elongation of the abdominal circumference during breathing movements. We demonstrate that the three sensors can successfully sense textile elongations between 0% and 3%, while maintaining the stretching properties of the textile substrates for a good comfort of the patients.
We present the latest advances in distributed strain measurement in perfluorinated polymer optical fibres (POFs) using backscatter techniques. Compared to previously introduced poly(methyl methacrylate) POFs, the measurement length can be extended to more than 500 m at improved spatial resolution of a few centimetres. It is shown that strain in a perfluorinated POF can be measured up to 100%. In parallel to these investigations, the incoherent optical frequency domain reflectometry (OFDR) technique is introduced to detect strained fibre sections and to measure distributed length change along the fibre with sub-millimetre resolution by applying a cross-correlation algorithm to the backscatter signal. The overall superior performance of the OFDR technique compared to the optical time domain reflectometry in terms of accuracy, dynamic range, spatial resolution and measurement speed is presented. The proposed sensor system is a promising technique for use in structural health monitoring applications where the precise detection of high strain is required.
The radiation-induced Bragg wavelength shift (BWS) was measured with type I gratings made of 12 fibers with very different composition, i.e., of fibers with an extremely different radiation-induced attenuation. With two of the fibers fabrication parameters like laser intensity, hydrogen loading, and annealing conditions after grating inscription were varied. With another fiber type I and type II gratings were made by a completely different process. With gratings made under identical conditions of the 12 fibers the radiation-induced BWS only varied by about a factor of three. Varying the fabrication parameters led to BWS differences up to nearly a factor of ten.
Polymer optical fiber (POF) sensors have the unique ability to measure high strain distributed along the fiber up to 40% using the optical time-domain reflectometry (OTDR) technique. Both, standard PMMA fibers and perfluorinated (PF) graded-index (GI) POF are introduced and evaluated in potential use and applicability. Further, distributed length change measurement based on cross-correlation analysis of the characteristic fiber signature of PF POF is introduced. We conclude the advances in distributed POF strain sensors technology with respect to application in structural health monitoring. Special focus is on the sensor integration into technical textiles for health monitoring of geotechnical structures and masonry structures. Measurement results of sensor-equipped textiles in different model tests are presented, displacement of soil and cracks in retrofitted masonry structures are detected and evaluated.
We present, to our knowledge for the first time, the possibility of measuring the backscatter signal of perfluorinated polymer optical fibers (POF) using an incoherent optical frequency domain reflectometry (OFDR) technique. The OFDR setup is described and it is shown that the dynamic range and measurement speed are superior to standard OTDR systems. It is shown for the first time that distributed detection of strain in POF is possible using the OFDR technique.
We have measured for the first time the shift of the Bragg wavelength and other parameters of fibre Bragg gratings (FBGs) exposed to radiation at different wavelengths up to a dose of 100 kGy. The results show that the FBG sensitivity to radiation increases from 820 nm to 1516 nm so that FBGs with higher Bragg wavelength, e.g. 1.55 µm, are good candidates for high dose radiation sensing: no saturation was observed up to 100 kGy and the measured wavelength shift was fairly independent on the radiation dose rate.