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Optical Fiber Sensors for Aircraft Structural Health Monitoring.

García I, Zubia J, Durana G, Aldabaldetreku G, Illarramendi MA, Villatoro J - Sensors (Basel) (2015)

Bottom Line: Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors.Several practical applications for structures and engines we have been working on are reported in this article.With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.

View Article: PubMed Central - PubMed

Affiliation: Department of Communications Engineering, E.T.S.I. of Bilbao, University of the Basque Country UPV/EHU, Alda. Urquijo s/n Bilbao 48013, Spain. iker.garciae@ehu.eus.

ABSTRACT
Aircraft structures require periodic and scheduled inspection and maintenance operations due to their special operating conditions and the principles of design employed to develop them. Therefore, structural health monitoring has a great potential to reduce the costs related to these operations. Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors. Several practical applications for structures and engines we have been working on are reported in this article. Fiber Bragg gratings have been analyzed in detail, because they have proved to constitute the most promising technology in this field, and two different alternatives for strain measurements are also described. With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.

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LPG concept and working principle.
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sensors-15-15494-f011: LPG concept and working principle.

Mentions: In this section we present the use of long period gratings in microstructured POFs (mPOFs) as an option to measure strain in aircraft structures instead of FBGs. mPOFs are the counterpart version of the photonic crystal fibers using polymer fibers instead of glass fibers. In the mPOFs a pattern of air channels along the POF guides the light and confers unique properties to the fiber [56]. Among these properties, the single-mode and polarization-maintaining behavior, combined with the intrinsic flexibility and ease of connection of the POF are particularly interesting for sensing purposes. In order to obtain an LPG in an mPOF, a periodic modification of the cladding structure of the mPOF is written along the direction of light propagation [57], so that the core mode is coupled to cladding modes, which are rapidly attenuated, resulting in depressions in the transmission spectrum at wavelengths where the Equation (9) is satisfied [58]: (9)mλ=(ncore(λ)−ncl(λ))ΛLPG where m is the order of the interaction, ncore and ncl are the effective indices of the core and the cladding, and ΛLPG is the period of the grating. Unlike FBGs, this period is much larger than the wavelength of the light propagating along the mPOF, so LPGs are easier to fabricate. In the case of LPGs, the length of the structure is in the order of 30 mm, whereas the grating period range is typically from 100 µm to 1 mm [59]. The LPG causes the coupling between the core-guided mode and the forward-propagating cladding modes at certain wavelengths, which causes “notches” in its transmission spectrum. The working principle of the LPG is depicted in Figure 11.


Optical Fiber Sensors for Aircraft Structural Health Monitoring.

García I, Zubia J, Durana G, Aldabaldetreku G, Illarramendi MA, Villatoro J - Sensors (Basel) (2015)

LPG concept and working principle.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4541841&req=5

sensors-15-15494-f011: LPG concept and working principle.
Mentions: In this section we present the use of long period gratings in microstructured POFs (mPOFs) as an option to measure strain in aircraft structures instead of FBGs. mPOFs are the counterpart version of the photonic crystal fibers using polymer fibers instead of glass fibers. In the mPOFs a pattern of air channels along the POF guides the light and confers unique properties to the fiber [56]. Among these properties, the single-mode and polarization-maintaining behavior, combined with the intrinsic flexibility and ease of connection of the POF are particularly interesting for sensing purposes. In order to obtain an LPG in an mPOF, a periodic modification of the cladding structure of the mPOF is written along the direction of light propagation [57], so that the core mode is coupled to cladding modes, which are rapidly attenuated, resulting in depressions in the transmission spectrum at wavelengths where the Equation (9) is satisfied [58]: (9)mλ=(ncore(λ)−ncl(λ))ΛLPG where m is the order of the interaction, ncore and ncl are the effective indices of the core and the cladding, and ΛLPG is the period of the grating. Unlike FBGs, this period is much larger than the wavelength of the light propagating along the mPOF, so LPGs are easier to fabricate. In the case of LPGs, the length of the structure is in the order of 30 mm, whereas the grating period range is typically from 100 µm to 1 mm [59]. The LPG causes the coupling between the core-guided mode and the forward-propagating cladding modes at certain wavelengths, which causes “notches” in its transmission spectrum. The working principle of the LPG is depicted in Figure 11.

Bottom Line: Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors.Several practical applications for structures and engines we have been working on are reported in this article.With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.

View Article: PubMed Central - PubMed

Affiliation: Department of Communications Engineering, E.T.S.I. of Bilbao, University of the Basque Country UPV/EHU, Alda. Urquijo s/n Bilbao 48013, Spain. iker.garciae@ehu.eus.

ABSTRACT
Aircraft structures require periodic and scheduled inspection and maintenance operations due to their special operating conditions and the principles of design employed to develop them. Therefore, structural health monitoring has a great potential to reduce the costs related to these operations. Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors. Several practical applications for structures and engines we have been working on are reported in this article. Fiber Bragg gratings have been analyzed in detail, because they have proved to constitute the most promising technology in this field, and two different alternatives for strain measurements are also described. With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.

No MeSH data available.


Related in: MedlinePlus