Fibre Optic Sensing at Extreme Temperatures

Fibre Optic Sensing at Extreme Temperatures

Wolfgang Ecke

Institute of Photonic Technology - IPHT Jena, Germany

wolfgang.ecke@ipht-jena.de

Wolfgang Ecke

Institute of Photonic Technology - IPHT Jena, Germany

wolfgang.ecke@ipht-jena.de

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