optical fibre sensors for environmental monitoring at lhc and slhc experiments

XXIII International Symposium on Nuclear Electronics & ComputingBulgaria, Varna, 12-19 September, 2011

Optical fibre sensors for environmental monitoring at LHC and SLHC experiments - Paolo Petagna (CERN)1/24

Optical fibre sensors for environmental monitoring at LHC and SLHC experiments

•Fibre Optical Sensors (FOS) applications

•Fibre Bragg Grating FOS (FBG) specificities

•First FBG applications in HEP: T and e measurements in CMS

•New R&D line: FBG as Relative Humidity sensors

•Polyimide coated FBG as RH sensors: experimental results

N. Beni (ATOMKI / CERN); G. Breglio (Federico II / Optosmart); S. Buontempo (INFN Napoli /

CERN); M. Consales (Sannio); A. Cusano (Sannio / Optosmart); A. Cutolo (Sannio /

Optosmart); M. Giordano (CNR Napoli / Optosmart); P. Petagna (CERN); Z. Skillasi (ATOMKI / CERN)



•Multipoint distributed sensor through fibre grating

Concept of Fibre Optical Sensor (FOS)

LTh

DTh Dco

Dclad

L1

L2

-0.5 0 0.50

0.5

1

LTh = 125m

Unperturbed FBG

-B [nm]

Ref

lect

ivity

External medium

Sensitive layer

Single-mode optical fiber

Pout=k·RFilm·Pin

• k is a constant• RFilm is the film reflectance

ΔRfilm=f ( ΔεFilm , ΔdFilm , Δεext)• εFilm is the complex dielectric constant of the film• dFilm is the film thickness• εext is the external medium dielectric constant

•Single point sensor through fibre tip coating



Main advantages of FOS technology

For a large number of environmental monitoring and industrial applications fiber-optic sensor technology now offers several advantages for significant metrological improvement through:

• Immunity to electromagnetic interference• Lightweight• Possibility to work in hard environments• Intrinsic Radiation Hardness• High sensitivity, versatility and bandwidth• Simple multiplexing• Absence of electronic circuitry in the measurement area

This technology is suitable for remote measurements and it is, by definition, compatible with the fiber-optic communication networks



FOS fields of application

Measured parameters: StrainTemperatureVibrationRefractive indexChemical detectionHumidityElectric and Magnetic field

Integration with: Metal oxide particle layers

Nanoporous Polymers

Carbon nanotubes

1 e

0.1 C°Up to 1 MHz10-5

< 1 ppm< 1%

Bandgap engineering

Microstructuration

Tapering

Application to: Structural health monitoringDamage detectionAeronautic monitoringGeodetical monitoringEnviromental monitoringAcoustic monitoringRailways monitoring

Photonic devices

Micro-structured Fiber Gratings

Tapered Fiber

Hollow core optical fiber

Micro resonators

Long period Fiber Gratings



Examples of “industrial” applications

Undercarriage 1 Undercarriage 2 (engine compartment)

Undercarriage 3

Smart RailwaysSmart Railways

Undercarriage 1

Undercarriage 2

Undercarriage 3Undercarriage 1

Undercarriage 2

Undercarriage 3

A Single FBG element can A Single FBG element can provide useful information provide useful information about:about:- occupation state,- train velocity,- acceleration,- weighing in motion,- axle counting

APPLICATION TO :

ADVANCED CONFIGURATIONS :

Water Monitoring

HYDROCARBONS AND AMMONIA

Limit of Detection: <1 ppm

H2 Detection at -160 °C

CRYOGENIC H2

Limit of Detection: <1 %

Air Pollution MonitoringVAPORS (VOCs)

Limit of Detection: <0.5 ppm

GAS (NO2)

Limit of Detection:0.1 ppm

Near fieldchemo- optic sensors

Hollow- core Fiber filledwith CarbonNanotubes

Microlenses on taperedoptical fibers

• Low cost fabrication

•Spheres diameters: 50-300 μm

Fiber core

Near Field Intensity

Layer Topography

Hollow-core Optical Fiber end

face

Guiding Properties Modifications

Web-like Carbon NanotubesDeposition

MICRO AND NANOPHOTONICS FOR CHEMICAL SENSING

Sphere diameter: 90 μm

Modal Analysis Tests on a Composite Aircraft Model WingModal Analysis Tests on a Composite Aircraft Model Wing

NN°°4 4 FBGsFBGs Embedded within Spar, Parallel Embedded within Spar, Parallel to Wingto Wing’’s Axiss Axis

NN°°4 Uni 4 Uni –– AxialAxial AccelerometersAccelerometers BondedBondedtoto WingWing’’s s SurfaceSurface

29 Excitation Points for 29 Excitation Points for Experimental MeasuresExperimental Measures

20 40 60 80 100 120 140

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

Excitation Point Position [cm]

Arb

itrar

y U

nits

[ A

. U. ]

II Dispalcement Bending Shape

Experimental Data Interpolating Polynomial

20 40 60 80 100 120 140

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

Excitation Point Position [cm]

Arb

itrar

y U

nits

[ A

. U. ]

II Strain Bending Mode Shape

Experimental Data Interpolating Polynomial

AccelerometerAccelerometer FBG OutputFBG OutputSimulationSimulation



Fibre Bragg Grating FOS

Reflected signal

Transmitted signal

Cladding

CoreSource LED

effB n2 Where:• neff is the effective refractive index of the fibre• is the grating pitch • B is the reflected Bragg wavelength

Any strain or temperature perturbation experienced by the FBG results in a Bragg wavelength shift

TSS TB e e

1,2,…n

1

2,…n

1/2neff



Why FBG Sensors?



First use of FBG sensors in HEP: CMS

~ 100 T or e sensors placed in the following areas in CMS:– HF region negative side (Raiser and Castor table)– Tracker bulkhead on both sides (10-10 sensor)– Experimental Cavern (60) (in January 2011)

(in 2009)

Aim:• demonstrate feasibility• follow mechanical changes

induced by magnetic field (HF-)

• Monitor the T distribution in front of the Tracker

• (2011) monitor the cavern environment

In the last two years the CMS experiment at LHC accepted to pioneer the application of FOS (FBG) to an HEP experiment



e measurement during 2011 magnet ramp-up

Near side Far side



T distribution in front of the Tracker

Z-

Z+

One year record of temperature measured by FBG follows the activity of Tracker and provide information on the thermal mapping of the critical area between the TK and the EE



Additional FBG to map T in the cavern

19.6 19.6 19.5

18.7 --- 19.2 19.2 18.7

19.319.820.019.619.2

19.9

19.1 19.5 20.0 20.1 19.8

19.119.921.720.3

Z+Z-

19.5 19.7 19.4

19.2 19.2 --- 19.2 19.3

---19.219.920.019.8

19.8

19.5 19.6 19.8 19.2 18.9

19.219.921.820.3

Z-Z+

Additional 60 FBG T sensors has been installed in the experimental cavern in January 2011 :

- 23 sensors on wall near side- 3 sensors on ceiling +Z side- 23 sensors on wall far side- 8 sensors on shaft far side- 3 sensors on ceiling -Z side

Some HOURS of work to install all of them!

In the figures a snapshot of the T distribution on the rack balconies is shown



A curiosity about T distribution in the shaft

16.4

16.4

16.6

16.9

16.8

17.1

17.5

18.6Shaft plug closed

Shaft FBGs are installed

Daily temperature peak of the top sensor appearing when shaft plug is open (every day a bit later than the previous one): effect of direct sunlight discriminated

surface

cavern



Humidity sensing issues in HEP Trackers

HUMIDITY SENSOR SPECIFICATIONS FOR HEP TRACKING DETECTORS

• Low mass• Small dimensions

• Insensitivity to magnetic field• Operation at temperature down to -40 ˚C• Response to the full range [0, 100]% RH

• Reduced number of wires needed • Radiation resistance to doses up to 1 MGy

HIH 4000 series by Honeywell

• Small• Inexpencive

• 3 wires for each measuring point• Accuracy of 3,5%RH• Response time 15s

• Minimum operation temperature -40°C• Not radiation resistant!!!

CURRENTLY AT CERN (typical)



•Almost all miniaturized humidity sensors presently available on the market are electronic sensors (mainly capacitive-based, followed by resistive-based).

•Despite all efforts, these sensors still fail to provide a complete set of favourable characteristics, e.g., good linearity, high sensitivity, low uncertainty, low hysteresis and rapid response time.

•For an application in HEP detectors, one should add to this the sensitivity to electro-magnetic noise pick-up, the suitability for multi-point distributed measurements and the resistance to ionizing radiations.

Motivations for R&D on new RH sensors

Nowadays – although important requirements on environmental control exist, in particular for Trackers – there is no miniaturized humidity

sensor on the market well suited for HEP detector applications



FBG as relative humidity sensor

• Bare FBG is insensitive to humidity.• Use of sensitive material as coating of the FBG to induce a mechanical effect.• Hygroscopic polymers swell upon adsorption of water molecules.

Sensing principleAbsorbtion of

moisture by the polymeric coating

Expansion of the coating (“swelling”)

Strain induced on the FBG

Bragg wavelength

shift

%)(%),( RHfTSRHTf TTB

Realization of humidity sensor by coating the gratings with a suited polymer.

POLYIMIDE COATING

FBG2RH SENSOR

FBG1T- SENSOR

Temperature compensation is needed



Starting point: polyimide coating

2002 2005

• Relative humidity range limited to 10 – 90 % RH• Temperature range limited to 10 ÷ 65 °C• Completely unexplored effect of ionizing

radiations



RH testing / calibration facility @ CERNTest section

Thermally controlled liner

Salt solution container (if needed)

External air circulation(dry + saturated air mixer)

Closed loop circulation(salt solution in box)

Chilled mirror

Ranges:0% ≤ RH ≤ 100%

-20 °C ≤ T ≤ +30 °C

Insulated confinement



Optoelectronic interrogation system



Custom fabricated polyimide coated FBG

•Naked FBG outsourced under strict specifications•In-house multiple dip coating + oven curing cycles with PI2525 HD Microsystem Pyralin

Family 1 (thin): coating thickness = 8 m Family 2 (thick): coating thickness = 17 m



Low temperature & humidity properties

0 10 20 30 40 50 60 70 80 90 100

1529,9

1530,0

1530,1

1530,2

1530,3 T=20°C T=0 °C T= -15°C

nm

RH(%)

T

0 10 20 30 40 50 60 70 80 90 100

1569,4

1569,5

1569,6

1569,7

1569,8

1569,9 T= 20°C T= 0°C T= -15°C

(nm

)

RH (%)

T

Family 1 (thin): coating thickness = 8 m(typical)

Family 2 (thick): coating thickness = 17 m(typical)

SRH=0.42 pm/%RH±7,.%

ST=9.54 pm/°C±0.9%Temperature sensitivity:

Humidity sensitivity:SRH=2.09 pm/%RH±19.6%

ST=10.08 pm/°C±12.4%Temperature sensitivity:

Humidity sensitivity:

NOTE:

Time response very (too?) slow at T < 0 C



First ionizing irradiation dose: 10 kGy

0 5000 10000 15000 20000-30

-20

-10

0

10

20

30

40

50

RH

(%)

t(sec)

HIH pre-irradiation HIH post-irradiation

1568 1568.5 1569 1569.5 1570 1570.5 1571 1571.5 1572 1572.5

-45

-40

-35

-30

-25

-20

-15

-10

[nm]

Am

plitu

de [d

Bm

]

Spectrum

S10 at T=20°C pre irradiationS10 at T=20°C post irradiation

1527 1528 1529 1530 1531 1532 1533 1534-70

-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

[nm]

Am

plitu

de [d

Bm

]

Spectrum

S2 at T=20°C pre irradiation S2 at T=20°C post irradiation

Family 1 (thin): coating thickness = 8 m Family 2 (thick): coating thickness = 17 m

Perfect peak invariance after first irradiation

Note: Honeywell HIH 4000 dies (no signal) after 10 kGy ionizing irradiation dose



Further irradiation level: 50 kGyT = 20 C: before and after irradiation T = 0 C: before and after irradiation

g-irradiation tests up to 50 kGy* show good radiation resistance and suggest no further variation after the first level (possibility of applying a “pre-stress”)

* latest data at 100 kGy confirm the observation



More technical details and results?

“Relative Humidity Monitoring by Polyimide-Coated Fiber Bragg Grating Sensors for High-Energy Physics Applications”

Accepted to IEEE Sensors 2011 (Limerick-Ireland)



Further developments

• Continue irradiation studies up to 1 MGy• Perform tests at intermediate T (accurate T dependence estimate)• Accurate measurement of response time in function of T• Develop reliable packaging for field operation

• Study different kind of polymeric coatings (epoxies?)• Feasibility of different gratings for direct humidity reading

(LPG)

• Create a real network among all FOS developments suited for HEP (Full scale cryogenic thermometers, Magnetic field measurement, Dosimeters, CFRP and

Silicon –embedded strain measurement,…) Resubmission of the FOS4HEP MC ITN proposal

ONGOING

2012

FUTURE



(RESERVE SLIDES FOLLOW)

THANK YOU FOR YOUR ATTENTION!



RESERVE: e and T discrimination in FBG



RESERVE: FBG interrogation

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