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Fibre Optic Sensing at Extreme Temperatures
Fibre Optic Sensing at Extreme Temperatures
Wolfgang Ecke
Institute of Photonic Technology - IPHT Jena, Germany
Wolfgang Ecke
Institute of Photonic Technology - IPHT Jena, Germany
Outline:
• What makes fibre-optic sensors an attractive sensor solution
• Spectrally encoded fibre Bragg grating (FBG) sensor technology
• Application examples of technical relevance
• Sensors for extreme low and high temperatures
• Technical and economical outlook
Jena – the Optics Valley in Germany> Science City 2009 <
Jena – the Optics Valley in Germany> Science City 2009 <
History: 1846 Carl Zeiss (engineer), Ernst Abbe (physicist) → optics company ZEISSOtto Schott (chemist) → technical glass works SCHOTT
Present: Zeiss, Jenoptik, j-fiber + more than 50 SMEs→ 8000 people in optics + photonics industries
Science Campus: IPHT Jena + 9 Research & University Institutes→ 2000 people in R+D on OPTO-BIO-NANO technologies
JENA
IPHT Jena / GermanyIPHT Jena / Germany
Fibre OpticsOptical fibres, micro-optics, optical micro-systems
Laser TechnologyMaterials processing, diagnostics
Micro SystemsBio-technical micro-systems, spectroscopy
Cryo-ElectronicsCryo-electronic devices, HTSC
Institution for applied research and development
240 employees (110 scientists)
Cooperation with industry and universities
Application orientation
JENA
General Structure of Fibre Optic Sensor Systems
General Structure of Fibre Optic Sensor Systems
a) Intrinsic sensor – light modulation inside fibre
b) Extrinsic sensor – light modulation outside optical fibre
c) Hybrid sensor – fibre optic signal transmission + electrical sensor
1. Measurand modulates light (intensity, wavelength, ..)
⇔ 2. Signal transmission via optical fibre
⇔ 3. Signal processing unit
3.1. 2.
Fibre Sensor ConfigurationsFibre Sensor Configurations
Single-point sensor
Multi-point (quasi-distributed) sensor
Sensing element
Fibre
Multiple sensing points
Distributed sensor
Continuous sensing elementGraphs: Alexis Mendez
Advantages of Fibre Optic SensorsAdvantages of Fibre Optic Sensors
Immunity against, i.e., applicable in- Electro-magnetic fields, high voltage, lightning- Explosive or chemically aggressive + corrosive media
⇒ Oil, Gas, Energy, Transportation
Light-weight, miniaturised, flexible, low thermal conductivity, temperature-resistant material (silica, ..)
⇒ High and Low Temperatures
Low-loss, non-interfering signal transmission, no safety risk ⇒ Remote Sensing
Multiplexing capability ⇒ Sensor Networks ⇒ Structure Monitoring
Embedding in composite materials ⇒ Smart Structures
Optical Fibre Sensor TechnologiesOptical Fibre Sensor Technologies
Preform and fibre development
active laser fibre
photo-sensitive fibre
micro-structured fibre
...
Fibre Bragg grating sensor inscriptionexcimer & fs laser; phase mask & interferometric pattern; DTG®
in silica, sapphire, active doped laser fibre, ..
Sensor-specific coatings
Photo: R. Wehking/IPHT
Photo: R. Wehking/IPHT
Photo: R. Wehking/IPHT
Photo: R. Wehking/IPHT
Inscription Technology for Fibre-Optic Bragg Grating (FBG) Sensors
Inscription Technology for Fibre-Optic Bragg Grating (FBG) Sensors
Beam splitter
FBG inscription site(interference fringe pattern)
UV Excimer laser single-pulse shots
UV Talbot interferometer
Sensor specific primary coatinge.g., hard coating for strain transfer: Ormocer, Polyimide, ...
Silica based preform material, Ge doped for high photo-sensitivity
FBG inscription immediately at fibre drawing tower: Stable & reversible at strain ≥ 5% !
Preform oven
Marker
Structure of Fibre Bragg Gratings (FBG)Structure of Fibre Bragg Gratings (FBG)
Grating period Λ ∼ 250..500 nm
Fibre core Diameter 5..10 μm
Refractive index
Optical single-mode fibreSensor diameter 125 μm
ΔnFBG sensor length 1..8 mm
Graph: DaimlerChrysler
Excimer laser illumination inscribes a refractive index modulation in the core of optical fibre (periodic fringe pattern of refractive index = Bragg grating)
Bragg reflection at specific wavelength: λB = 2 neff ΛSensor for temperature, strain, chemicals: λB ∼ T, ε, nA, ..
FBG = optical equivalent to resistive strain gages
FBG Sensors and Sensor ArraysFBG Sensors and Sensor Arrays
Spectrum of sensor array:
Optical fibre with inscribed Bragg grating:
(diffraction pattern)
Fibre drawing tower for single pulse laser Bragg grating inscription
Strain measurement:Range ± 0.3 .. ± 5 %Repeatablity 0.5 με, accuracy 15 με
Temperature measurement :Range -270 .. +250°C ( .. +900, .. +1800°C)Repeatability 0.05 K, accuracy 1 K
810 830 850 870
0
20
Refle
ctiv
ity
[%]
Wavelength [nm]
10
3 μm
Fibre-Optic Sensors –Obstacles and BarriersFibre-Optic Sensors –Obstacles and Barriers
Today, FOS are still not cost-effective in competition with mass production electrical sensors.
Unfamiliarity with FOS technology, old habits, not immediately trusted by users (broader education required in fibre optics).
Fibre-optic sensors must fit a need: technically, economically, legally.
Fibre-optic sensors apply in niches, where other sensors fail, i.e., in processes without established measuring technique.
Source: Brian Culshaw, Univ. of Strathclyde
Application Fields of FBG Sensor Systems for Structural Health Monitoring
Application Fields of FBG Sensor Systems for Structural Health Monitoring
Aerospace structures
Hydrogen monitoring
Wind turbine rotor blades
Railway interfaces - to contact lines and rails
Temperature and vibration in electrical generators
Temperature and vibration in energy andaircraft turbines
Rock-bolts in coal mining
ESA/Kayser-ThredePhoto: ESA
NASAKayser-Threde
Enercon/Jenoptik
DaimlerChrysler
Siemens
Siemens
SiemensKayser-Threde
MTU Aero Engines GESO Jena, GFZ Potsdam
Superconductive magnets
MPI Plasma Physics
Siemens Gas Turbine W501
Application Fields for FBG Sensors –Specific Advantages
Application Fields for FBG Sensors –Specific Advantages
Strain & temperature measurement, structural health monitoring Aerospace
Aircraft structures (intrinsic FOS for embedment in composites, light weight)Spacecraft (no safety objections, EMC)Aerostate (electrical insulation, lightning safe)
Energy industry (electrical insulation, EMC) Power generators, transformers, switchesWind power stations (embedment, lightning safe)
TransportationRailway overhead contact lines, Railway pantographs (electrical insulation)
Geo-technical & civil engineeringcoal mining, petrol & gas exploration (explosion-proof, remote sensor)Rock-bolts / anchors
Opto-chemical monitoring, using evanescent interactionPetrol industry
Refractive index measurements (explosion-proof, on-line monitoring) Biochemistry, biochemical adsorbates, SPR (reversible, laser annealing)Chemicals, via specific transducer overlays (multi-sensor network, explosion-proof)
Large Scale FBG Sensor Application for Seismic Exploration (Optoplan Trondheim)Large Scale FBG Sensor Application for
Seismic Exploration (Optoplan Trondheim)
Sensor installation inEkofisk field
Application scheme: Seismic deep sea exploration
Source:www.wavefield-inseis.com/pdfs/Optowave_web_Oct08.pdf
Enhancing Railway Safety: Impact Monitoring at Interface Contact Line/Current Collector
Enhancing Railway Safety: Impact Monitoring at Interface Contact Line/Current Collector
Embedded Strain Sensors
Current Collector
Monitoring of force impacts immediately inside ofhigh-voltage current collector
Benefit:- Maintenance on demand - Enhanced availability at reduced cost
Detection of ill-positioned contact clamp
EU funded projects 'SMITS' & 'Catiemon'
Photo: Deutsche Bahn
Graph: Morganite
Application Example in Energy Sector: Condition Monitoring of Power Generators
Application Example in Energy Sector: Condition Monitoring of Power Generators
Temperature measurement immediately on electrical conductors:
Vibration monitoring on stator windings:
Stator bars with integrated FBG temperature sensors
external short-circuit
Partner:
Willsch M., Theune N.M., Bosselmann T., Ecke W., Latka I., Höfer B., "Distributed Dynamic Strain Measurement in Power Generators Using a Novel Fast FBG Interrogation System", Proc. of 16th International OFS Conference, IEICE Japan, ISBN 4-89114-036-4, pp. 294-297 (2003)
Theune N.M., Kaufmann M., Kaiser J., Willsch M., Bosselmann T., Krämmer P., "Fiber Bragg Gratings for the Measurement of Direct Copper Temperature of Stator Coil and Bushing Inside Large Electrical Generators" Proc. of SPIE, Vol. 4185 (OFS-14), pp. 202-205 (2000)
Photo: Siemens AG Photo: Siemens AG
FBG Sensors in Wind TurbinesFBG Sensors in Wind Turbines
Partners:
Bending load monitoring of blades in world's largest wind turbine E112 (4,5 MW, blade length 53 m)
6 FBG strain sensor pads on opposite positions of wind blade ⇒ temperature independent monitoring of bending load
400 mm length strain sensor pads
FBG-SPU
WLAN
Schroeder K., Ecke W., Apitz J., Lembke E., Lenschow G.Fibre Bragg Grating Sensor System Monitors Operational Load in a Wind Turbine Rotor BladeMeasurement Science and Technology, Vol. 17, pp. 1167-1172 (2006)
Photo: Enercon
Smart Structures in Aircrafts –Composites with Integrated 'Nervous System'
Smart Structures in Aircrafts –Composites with Integrated 'Nervous System'
Graph: DaimlerChrysler / EADS-Airbus
Carbon Fibre Reinforced Polymerwith embedded fibre-optic Bragg grating sensor
100μm
Once a vision – now already reality:
Cross-section of a test structure for novel adaptive aircraft wing
Fatigue test at Airbus test centre Hamburg/Finkenwerder
Source: DaimlerChrysler / EADS-Airbus
FBG vs. Resistive Strain Gauges (RSG) in Aircraft Applications
FBG vs. Resistive Strain Gauges (RSG) in Aircraft Applications
Surface mounted RSGsEmbedded FBG sensors
RSGs with heavy weight electrical cables
CFRP aircraft wing fatigue test: 1 year complete lifetime simulation20 FBG strain sensors over full test: strain results correspond to resistive strain gauges
Project partners/Source: DaimlerChrysler / EADS-Airbus
0 50 100 150 200 250-1400 -
-1200 -
-1000 -
-800 - FEM modelRSGFBG
Stra
in [μm
/m]
Sensor positionN.M. Trutzel, K. Wauer, D. Betz,L. Staudigel, O. Krumpholz, H.-C. Mühlmann, T. Müller, W. Gleine "Smart Sensing of Aviation Structures with Fiber-optic Bragg Grating Sensors" Proc. of SPIE, Vol. 3986, pp. 134-143 (2000)
Fibre-Optic Structural Health Monitoringfor Space Applications
Fibre-Optic Structural Health Monitoringfor Space Applications
Crew return vehicle X38:
Sensor pads:2 strain sensors+ 1 temperature sensor
0 5 10 15 20 25838
844
845
846
847
848
849-0.36nm=-560με
1.27nm =2000με
elongated sensorcompressed sensortemperature sensor
Bra
gg W
avel
engt
h [n
m]
Time [min]
SPU box(NASA standard)
Test Measurement
Partners:
Source: NASA
Source: NASA
Ecke W., Latka I., Willsch R., Reutlinger A., Graue R. , "Fibre Optic Sensor Network for Spacecraft Health Monitoring ", Measurement Science Technology, Vol. 12, pp. 974-980 (2001)
The Low Temperature Extreme: Strain Monitoring in Superconducting Magnets
The Low Temperature Extreme: Strain Monitoring in Superconducting Magnets
Potential application fields:Super-conductive materialSuper-conductive drivesMagnet-resonance tomographMagnetic levitation transportNuclear accelerator, fusion reactor
Increasing need to monitor cryogenic devices in science and technique:- High-temperature superconducting ceramics = mechanically unstable, brittle material- high mechanical loads, strong magnetic fields
Source: Oswald
Source: MPI Plasma Physics Source: MPI Plasma Physics
Source: Japan Railway
Source: IHI Marine United
Advantage: Minimum Temperature Cross Sensitivity at 4..40 K:
Advantage: Minimum Temperature Cross Sensitivity at 4..40 K:
0 10 20 30 40
846,90
846,92
846,94
Temperature [K]
Bra
gg W
avel
engt
h [n
m]
FBG on steel
FBG on quartz10 με
0 10 20 30 40348,8
349,0
349,2
349,4
on Quartz
Res
istiv
ity [O
hm]
Temperature [K]
on Steel500 με
Fibre Bragg Grating Resistive Strain Gauge
Experimental results within temperature range 4.2 .. 40 K (operation range of super-conductive magnets)
Comparison of FBG with resistive strain gauges:
Kondo effect ∂εapp/∂T ≈ 150 με/K
Thermo-optic effect + expansion ∂εapp/∂T ≈ 0.05 με/K
Latka I., Ecke W., Höfer B., Habisreuther T., Willsch R.Fiber-optic Bragg gratings as magnetic field-insensitive strain sensors for the surveillance of cryogenic devicesCryogenics Vol. 49, pp. 490-496, doi:10.1016/j.cryogenics.2009.07.002 (2009)
-6 -4 -2 0 2 4 6
-1
0
1
App
aren
t Stra
in [µ
ε]
Magnetic Inductance [T]
FBG Strain Sensor with Minimum Magnetic Field Sensitivity at 4..40 K:
FBG Strain Sensor with Minimum Magnetic Field Sensitivity at 4..40 K:
∂εapp/∂B = 40 με/T
Comparison: Fibre Bragg Grating / Resistive Strain Gage
Magneto-optic effect Δneff(B) causes apparent strain εapp, maximum for circular polarisation:
Model calculation: Δneff = V · λ/2π · B∂εapp/∂B = Δneff/n/(1-p)/B = 0.4 με/T
Experimental result:
∂εapp/∂B ≈ 0.1 με/T
Magneto-resistance causes high apparent strain εapp :
Source: P. L. Walstrom, Cryogenics Vol. 20, pp. 509-512 (1980)
Strain Monitoring of Superconducting Materials and Components
Strain Monitoring of Superconducting Materials and Components
Fibre-optic vacuum feed-through
Results for melt-textured YBCO, e.g., coefficients of thermal elongation:
300 K: αab = 10·10-6 /K; αc = 16·10-6 /K 30 K: αab = 2.1·10-6 /K; αc = 3.9·10-6 /K
Latka I., Ecke W., Höfer B., Habisreuther T., "Fiber Bragg grating based measurement of elastic properties at cryogenic temperatures",SPIE Symposium "Optics East", Proc. of SPIE, Vol. 6770 (2007)
Nuclear Fusion Experiment Stellarator Wendelstein 7-XNuclear Fusion Experiment Stellarator Wendelstein 7-X
50 super-conductive magnet coils for plasma confinement
Monitoring task:
Strain and position monitoring of super-conductive magnets • during cooling at T = 300 .. 4.2 K• at different magnetic fields
Partner: Max Planck Institute for Plasma Physics, Germany
4Helium
Neutron
Deuterium
Tritium
Source: MPI Plasma Physics
Source: MPI Plasma Physics
Actual Progress with New Chances for FBG Sensor Applications
Actual Progress with New Chances for FBG Sensor Applications
Busch M., Ecke W., Latka I., Fischer D., Willsch R., Bartelt H.Inscription and characterisation of Bragg gratings in single-crystal sapphire optical fibres for high-temperature sensor applicationsMeas. Sci. Technol. Vol. 20, 115301, http://dx.doi.org/10.1088/0957-0233/20/11/115301 (2009)
Silica glass based conventional FBG sensors- diameter 125 μm, down to Ø ∼ 30 μm- embedding without structure- "Type II" FBG sensors –270 ..+900 °C
Silica glass based "Draw Tower Gratings" (DTG®)- high mechanical strain loads ε ~ ± 6%- hard strain transducer coatings (OrMoCer coating) –270 ..+250 °C- high-temperature coatings: metals, oxides, carbides, ..
Special fibre materials: sapphire fibre for very high temperature- Thermal stability 1800 °C, and probably more- Temperature & strain sensing at extremely high temperatures
Medium Temperature Range: Monitoring Vane Temperature in Natural Gas TurbinesMedium Temperature Range: Monitoring
Vane Temperature in Natural Gas Turbines
0 200 400 600 8001535
1540
1545
1550
Bra
gg W
avel
engt
h [n
m]
Temperature [°C]
Draw Tower Type II FBG
Temperature characteristic
Partner: Siemens AG
Applications:natural gas combustion turbine
for 200 MW power generationhigh-temperature fuel cells
Silica based "Type II" FBG sensors
Temperature monitoring inside turbine vane
Temperature range up to 800°C
Photo: Siemens AG
Photo: Siemens AG
Bartelt H., Schuster K., Unger S., Chojetzki Ch., Rothhardt M., Latka I., "Single-pulse fiber Bragg gratings and specific coatings for use at elevated temperatures", Applied Optics, Vol. 46, Issue 17, pp. 3417-3424 (2007)
Combustion Monitoring in Gas Turbines: Sapphire Optical Fibres for T > 1700°C
1520 1540 1560 15800
250500750
1000125015001750
Tem
pera
ture
[°C
]
Bragg wavelength [nm]
ΔλB/ΔT = 25..35 pm/K
fibre embedded in brazing alloy
Graph: Siemens AG
Sapphire optical fibre- Diameter 100 μm; single crystal drawn from laser melt- Bragg grating inscription by high-energy fs laser pulses
Temperature stability - at least 1750°C (limit of first tests)- Probably up to 1900°C (melting point ~ 2050°C)- Sensor potential for several measurands:
- temperature- strain/vibrations at high temperature- gases (fluorescence monitoring)
First Sapphire Fibre Sensor Tests in European R&D Project 'HEATTOP'
First Sapphire Fibre Sensor Tests in European R&D Project 'HEATTOP'
Industrial Partners: Siemens, Volvo, RollsRoyceTerm of 4 years: 2007 – 2010Target: Demonstration of fibre-optic high-temperature sensor feasibility
Sensor Test Sites in a Siemens Test Combustion Rig (Left) and in an Operational Siemens Engine (Scheme)
Distributed temperature monitoring: housing, combustion chamber, vanes
Hot spot detection in front vane rows
Graph: Siemens AG Photo: Siemens AG
More Sapphire Fibre Based High-Temperature Sensor Configurations
More Sapphire Fibre Based High-Temperature Sensor Configurations
Fabry-Perot interferometer:
Black-body radiometer:
Shift of intensity in emission spectrum ~ temperature
Shift of minimum in reflected spectrum ~ temperature
750 800 850 9000,0
0,2
0,4
0,6
0,8
T = 20 °C
T = 600 °C
Ref
lect
ivity
Wavelength [nm]
Cavity
Pt layer
8 mm
Steel armed casing Ø 0.7 mm
More Fibre-Optic Sensors in Metallurgy: DC Magneto-Optic Ultra-High Current Sensors
More Fibre-Optic Sensors in Metallurgy: DC Magneto-Optic Ultra-High Current Sensors
High-stability interferometric magneto-optic current sensor
Source: Asea Brown Boveri
More Fibre-Optic Sensors: Distributed Long Range Strain and Temperature Monitoring
More Fibre-Optic Sensors: Distributed Long Range Strain and Temperature Monitoring
FF
εT1
Sensor Interrogator Unit
Distributed Sensor0 m
10 m 1 km
10 km
50 kmT2
Brillouin and Raman Backscattering Sensor Systems for monitoring integrity and leakage of dams, pipelines, other civil structures.
Source: D. Inaudi
Total Fibre Optic Sensor MarketTotal Fibre Optic Sensor Market
Multiplexed and distributed fibre sensor systems:
FBG sensors, Raman, Brillouin backscattering
Single point sensors
Source: David A. Krohn, Light Wave Venture, LLC
Percentage of total sensor market:1% 3%
Forecast for 2014: 370% of 2009(Technical market research report “Fibre-Optic Sensors” IAS002D, BCC Research)
Fibre Bragg Grating Sensors: Major Milestones of Technology Evolution
Fibre Bragg Grating Sensors: Major Milestones of Technology Evolution
1978 - Discovery of photosensitivity in optical fibres — K. O. Hill
1987 - UV side-writing technique — Meltz, Morey & Glenn
Mask writing technique — Snitzer & Hill
1993 - Hydrogen loading photo-sensitisation — Lemaire
Long period gratings — Vengasarkar
1995 - Commercial FBG production — 3M, Bragg Photonics, Innovative Fibers
First commercial FBG interrogator — ElectroPhotonics
1997 - Initial work on down-hole P/T sensors — ABB, Cidra
2000 - Advanced FBG instrumentation — Micron Optics and many others
2003 - Commercial reel-to-reel FBG arrays — LxSix, Sabeus
2006 - Commercial high reliability Draw Tower Gratings® – FBGS Technologies
2009 - Bragg gratings in sapphire fibres for very high temperatures – IPHT Jena
Data source (1978 .. 2003): Alexis Mendez
Application Sectors of FBG Sensors –World-Wide Average
Application Sectors of FBG Sensors –World-Wide Average
Data source: Alexis Mendez
26% Civil Infrastructure
25% Oil & Gas 18% Aerospace
9% Nuclear
6% Medical4% Process
4% Electric4% Automotive
4% Chemical
Chances for Fibre-Optic Sensing
Fibre-optic sensors have unique advantages for structural health monitoring:- best choice for monitoring in strong electro-magnetic fields- supports light weight/high efficiency, especially of Renewables
After ~30 years of R&D, FBG sensors and sensor systems are available in production scale now; they are gaining popularity and a worldwide increasing market – and they have their potential by far not yet realised.
Actual applications are focussed on oil/gas wells, energy production, aerospace, and also on seismic/intrusion monitoring, geo-technique, civil structures.
New fibre materials extend applications into extreme temperatures: from cryogenic superconductors up to gas turbines and metallurgical processes close to 2000°C
See actual progress at International Optical Fibre Sensor Conference series, since 1980; OFS-20, Edinburgh, October 2009: http://www.ofs20.org
OFS-21 will be held in Ottawa, May 2011: http://www.ofs21.com