Optical fibre sensors have a number of advantages over conventional electrical strain gauges. The most significant advantages are that they:
- are immune to electromagnetic fields
- have the ability to take many measurement points along a single fibre - greatly improving the ease at which sensors can be multiplexed
- can be embedded within or bonded to structures without the risk of de-bonding during operation
Several different optical sensing techniques have found their way into the marketplace but fibre Bragg gratings (FBGs) are commercially one of the most successful. The applications areas are very wide - covering wind turbine performance monitoring, oil and gas exploration, bridge and tunnel monitoring, other structural monitoring, marine defence and health.
Optical sensing technology of this type can be used to:
- Monitor strain and temperature throughout a composite structure - allowing operators to monitor in-service stresses and optimise servicing schedules according to work done rather than miles flown
- Detect cracks in composite structures
- Monitor vibrations
- Measure high resolution temperature or strain profiles of key parts
- Measure wear on test components
- Check critical design parameters during the design phase and understand how the structure will operate full size
- Monitor temperatures up to at least 600oC
- Interferometric sensors allow very high precision monitoring of pressure and other sensor designs can be used for flow monitoring, level detection or proximity alarms
The group has five UV laser inscription systems, each of which is optimised for the manufacture of different fibre Bragg grating types. Extensive laboratory and cleanroom facilities allow devices to be made in optical fibres and planar waveguides. Researchers use commercially available single mode silica fibres, multi-core and D-shaped fibres and also fabricate their own polymer fibre. In addition, the group has extensive test and measurement equipment for device characterisation and environmental test facilities for lifetime and performance studies.
The group has worked on a number of important collaborative programmes in this area that were undertaken with UK and European partners. This includes the following DTI LINK / TSB programmes (partners shown in brackets): GIFTS (BNR, GEC Marconi, Exitech, BAE Systems, Hull University and Cambridge University), MAST (Pendennis Shipyard, Carbospars and BAE Systems), SHODOS (Bookham Technology, BICC, GEC Marconi, Kent University, Taywood Engineering and Tarmac Ltd), EMPIRE (Deutsch, BAE Systems and Indigo Photonics), LASEWAVE (Exitech and Indigo Photonics), ROADS (Sensa, National Grid, BP and Southampton University), CONSTRUCT (Airbus, BAE Systems, Insensys, Deutsch, Aston University, Messier-Dowty, Ultra Electronics SCS, Ultra Electronics), and INTEGRATED WING (led by Airbus).
- I. Bennion, J. A. R. Williams,L. Zhang,K. Sugden,N. J. Doran Uv-written in-fibre Bragg gratings Optical and Quantum Electronics February 1996, Volume 28, Issue 2, pp 93-135
- L Zhang, W Zhang, I Bennion, ‘In-fibre grating optic sensors’, in Fibre Optic Sensors, ed. F T S Yu & S Yin, CRC Press, 1st edition 2002, 2nd edition 2008, ISBN 978-1-4200-5365-4