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Moderna fizikaModerna fizikai primjene u elektrotehnicii primjene u elektrotehnici
ZvonimirZvonimir ipuipu
Sadraj
2
Uvod u svjetlovodne sustave
Nove vrste svjetlovoda
Optiki svjetlovodni senzori
How to monitora civil structurelike this bridge?
Classical technology
Classical monitoringtechnology:
Classical electrical sensors
- electro-mechanicalsensors
- UTP lines
- power lines andconsumption meter
Problems:- limited length
- noise
Classical technology
Monitoringand
control
Fiber-optic monitoringtechnology:
- long sensing distances
- no additional powerlines needed
sensing optical fiber
Fiber optic technology
Embeddedcomputer
up to 20km
Publicnetwork
Office inZagreb
Final goal - Remote sensor system
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Introduction
Fiber optic sensor system:
Laser
source
Opticalsensor
Detector
Signal
processing
+ display
unit
Fiber
OS
+
OD
+
ESP.G&D
The same structure as for the optical communication system!
Classical or fiber optic technology?
Classical technology is mature and cheap. New fiber optic technology is still more expensive
(the prices of optical components are constantlyfalling down).
However, with fiber optic technology one can obtainsensors sytems that are possible to built only withoptical technology.
Basic principle of fiber sensors
Extrinsic fiber sensor
Optical fiber carry a light beam to and from a black box. The black box modulates the light beam in response to
an environment effect.
Environmental
signal
Input fiber
Output
fiberOptical sensor
Basic principle of fiber sensors
Intrinsic fiber sensor
The light beam is modulated inside the fiber in responseto an environment effect.
Environmental
signalOptical fiber
Distributed spatial distribution of the measurement locations:
Quasi-distributed spatial distribution of the measurementlocations:
Basic principle of fiber sensors
optoelectronicunit
optical channel & transducer
V o (I) I V i (I)
optoelectronicunit
optical channel & transducer
V o (n)V i (n=1)V i (n=0)
V i (n=k)
hy fiber-optic sensors?
Advantages of fiber-optic technology:
Light weight and small size
Inherent immunity against electromagnetic fields and high-voltages
Safety & environmental benefits
No fero-resonances, no open secondary circuits, no distancepower supply
The distance to the measuring point can be great(in kilometers).
A large number of sensors can be integrated using multiplexingand interrogation techniques in the photonic domain.
High accuracy over wide dynamic range
Wide bandwidth from DC to THz
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!e"elopment process
Which magnitudeto be measured?
Which technologywould be suitable?
Which modulationtechnique?Methodology for
denominatingoptical sensors
What should the opticaltransducer device be like?
How should the variablebe determined spatially?
Example:Intensity Modulated Fiber Optic Sensors
Intensity #odulated Fiber $ptic Sensors
Basic structures:
Reflection type Source: broadband Fiber: multimode is better Pout is proportional to L Used as distance, vibration or pressure sensors
Transmission type Similar to a movable reflector Used as strain,vibration or distance sensors
movingmirror
fiberPoutPin
L
PoutPin
L
%IBR&'I() FIB*RC&('I+*%*R
MIRROR
,R$'*C'I%*
$.SI()
VIBRATING FIBERCANTILEVER
HOLDERPROTECTIVE
HOUSING
Sensor with vibratingfiber cantilever:
$ptomehanical "ibration sensor
#easured
"ibrations
Sensor response !etector
/ distance bet0een fiber cantile"er andmirro0ed fiber cantile"er
= 35m = 0
$ptomehanical "ibration sensor
Sensor with vibrating
fiber cantilever(pictures taken withmicroscope):
$ptomehanical "ibration sensor
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1
23 mm
245 mm
+aser diode 1556nm
Isolator 1556nm
Coupler 1556nm
Sensor
!etector diode
1556nm
Fiber cantile"er
7)IF 8259
$ptomehanical "ibration sensor
Detection scheme: System with referent DC signal. Spectrum and amplitude of vibrations is determined using FFT
Digital signalprocessing
A/D converterLow-pass filter
Detector
A/D converter
Low-noiseamplifier
Microcontroller Cortex M3 (LPC1769)
Band-passfilter
$ptomehanical "ibration sensor
21
Measurement ofsensor response:
Optical sensor
Electromehancal sensor
$ptomehanical "ibration sensor
We are considering sensor realization as an integrated sensor:
$ptomehanical "ibration sensor
Input waveguide
Etched silicon
Cantilever beam Seismic mass
Output waveguide
The basic principle behind the active pedestrian protectionsystem is the cladding surface treatment of the fiber:
,olymer optical fiber 7,$F9 sensors
Example: Active pedestrian protection system with lifting hood(pedestrian protection has to be provided for every new car from 2007):
,olymer optical fiber 7,$F9 sensors
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#acrobend:microbend fiber optic sensors
Macrobending - introducing losses since at somepoint of the curvature the energy cannot travel athigher speed than the speed of light in the medium
Microbending - coupling to higher order modes whichare highly attenuated by the optical fiber.
Macrobending Microbending
#easurement of the macrobend losses
Measurement setup:
Measured macrobend losses:(measurements: Niko Duki)
#icrobend fiber optic sensors
Pressure-sensitive optical cable (Herga Ltd.)
#icrobend fiber optic sensors
Schematic of application of fiber optic intruderdetector system buried in ground.
Fiber optic intruder detector system
Multimode fiber electromagnetic field is a superposition of fielddistributions of all guided modes. The result has a form of a speckle pattern:
#odes in the multimode fiber
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If the fiber is vibrating, the speckle pattern is changing:
#odes in the multimode fiberStructural "ibration sensor - measured results
7"ibrations are present9
Nthtime step
(N +1)thtime step
Difference pattern
Structural "ibration sensor - measured results
7"ibrations are not present9
Nthtime step
(N +1)thtime step
Difference pattern
SAMPLEAND HOLD SAMPLEAND HOLD
SUBTRACTION
SIGNALPROCESSING
CCD CAMERA
n n-1
Structural "ibration sensor
Idea to measure vibrations one needs to measurechanges in the speckle pattern!
,eriodical "ibrations 7;
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Spectral analysis (FFT) of measured result Iout
:
,eriodical "ibrations 7;
Sensor system - the wavelength of the reflected waveis measured at receiver.
The period of the Bragg grating depends on strain,temperature, etc. Therefore, by measuring thewavelength of reflected wave one can determinethe measurand.
BBSFBG
spectrumanalyzer
physicalmeasurand
Fiber Bragg )rating sensor 7FB)9
FB) as a strain and temperature sensor
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FB) as a strain sensor
For a longitudinal strain of , the correspondingwavelength shift BS will be:
where is the photoelastic coefficient of the fiber.
Strain sensitivities of FBG sensors (Rao et al.)
= )1(BBS
Wavelength(m)
Strainsensitivity(pm -1)
0.83 0.64
1.3 1
1.55 1.2
FB) as a strain sensor
Measuring strain sensitivity
FB) as a temperature sensor
For a temperature change of T, the correspondingwavelength shift BT will be:
where is the thermo-optic coefficient.
Temperature sensitivities of FBG sensors (Rao et al.)
TBBT += )1(
Wavelength(m) Temperaturesensitivity(pm/C)
0.83 6.8
1.3 10
1.55 13
Measuring temperature sensitivity
FB) as a temperature sensor
Dependency on temperaturewith applied strain 4 m/mm:
[ ]TBBS
++
=
)1()1(
Strain andtemperaturedependency
Temperaturedependency
FB) as a strain and temperature sensor
Temperature only
Temperature & strain
System for controling strainof the steel rope:
Measurement of strain:
Strain measurement in reinforced concrete structures
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Implementation incivil engineering: Bridges Tunnels Roads Dams Harbor structures Smart Buildings
Implementation of FB) optical sensors Implementation of FB) optical sensors
Pont Canal, Belgium
SOFO sensors, EPFL (CH)
Traffic Monitoring: Speed monitoring Weight sensing Future Vehicle classification,
weight in motion Combined with video cameras
could allow specificvehicle identification
(Photos and graphs from Blue Road Research,Traffic Monitoring Using Fiber Optic Grating Sensorson the I84 Freeway & Future uses in WIM. www.bluerr.com
Implementation of FB) optical sensors
Siemens optical dynamic strain sensors for power generators
(based on Bragg grating)
Implementation of FB) optical sensors
Siemens optical temperature sensors for power generators
and power lines (based on Bragg grating)
Implementation of FB) optical sensors
Question:How to make an optical sensor systemwith a reasonable price?
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If the price is not important (the most expensivecomponent is the spectrum analyser):
BBSFBG
spectrumanalyzer
physicalmeasurand
*>ample FB) sensor system
Filter f()
Detector Vsen()
x
FBG
Simple FB) sensor system
Problems: only one FBG sensor, limited accuracy.
BBS
Goals: up to 16 sensors in one fiber large accuracy reasonable price.
Detector
FBG1BBS
FBG2 FBG3 FBG4
Tunablefilter
Signal processingLP filter
Dither
+o0-cost FB) sensor system FB) sensor system = de"elopment at F*R
Advantages of digital electronics: Simple way of generating arbitrary wave shape (for tunable filter) Two step procedure for determining the Bragg wavelength Simple way of noise reduction (based on digital signal processing).
Digital signalprocessing
D/A converterOperational
amplifier
Detector
FBG1BBS
FBG2 FBG3 FBG4
Tunablefilter
A/D converterLow-noiseamplifier
Microcontroller Cortex M3 (LPC1769)
FB) sensor system = de"elopment at F*R
Proof-of-concept prototypedeveloped by
Ana Pogajec Marko prem Alan Vovk Ivan Drai-egrt Marko Bosiljevac Tin Komljenovi Dubravko Babi Zvonimir ipu
0 500 1000 1500 2000 2500 3000 35000
0.5
1
1.5
2
2.5
3
3.5
Vrijeme [uzorci]
Napon[V]
FB) sensor system 0ith tunable filter
Duration of one measurement cycle: 10 ms.
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1.364 1.366 1.368 1.37 1.372 1.374
x 105
0
0.5
1
1.5
2
2.5
3
Maks. naponReetke 2
Broj mjerenja
Napon(V)
Maks. naponReetke 1
Maks. naponReetke 3
Napon na filtru
Napon iz optikog
mjeraa snage
FB) sensor system 0ith tunable filter FB) sensor system 0ith tunable filter
30 40 50 60 70 80 90 100
0.8
1
1.2
1.4
1.6
1.8
2
Temperatura [oC]
Upravljakinaponn
apromjenjivomf
iltru[V]
FBG1
FBG2
FBG3
Practical problems
Tunable filter isextremely sensitiveon enviromentalchanges!
FB) sensor system 0ith tunable filter
30 40 50 60 70 80 90 1000.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Temperatura [oC]
Razlikanaponanapromjen
jivomf
iltruzadvijereetke[V]
Razlika tree i druge reetkeRazlika druge i prve reetkeRazlika tree i prve reetke
30 40 50 60 70 80 90 1000.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Temperatura [oC]
Razlikanaponanapromjen
jivomf
iltruzadvijereetke[V]
Razlika tree i druge reetkeRazlika druge i prve reetkeRazlika tree i prve reetke
FB) sensor system 0ith tunable filter
Difference betweenFBG responsesis NOT sensitiveon enviromentalchanges!
FB) sensor system 0ith tunable filter
Practical problems:
Due to presence ofnoise there is an errorin determining theBragg wavelength.
0 50 100 150 20030
35
40
45
50
55
60
65
70
Vrijeme [uzorci]
Temperatura[oC]
Elektriki izmjereno
FBG3 je referentna
FBG1 je referentna
FB) sensor system 0ith tunable filter
Practical problems
Due to presence ofnoise there is an errorin determining theBragg wavelength.
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Convolution method for noise reduction :
FB) sensor system 0ith tunable filter
*
=
Convolution method for noise reduction :
FB) sensor system 0ith tunable filter
*
=
Cyclic averaging of last Nsamples:
0 10 20 30 40 5022
23
24
25
26
27
28
29
30
31
32
Vrijeme [uzorci]
Temperatura[oC]
Optiki senzor - bez usrednjavanja
Optiki senzor - usrednjeno
Elektrini senzor
FB) sensor system 0ith tunable filter
Final testing dynamic sensor response on change of temperature:
heating of sensor
FB) sensor system 0ith tunable filter
Example: Distributed Optical Sensors
Fire alarm systems in tunnels
sensing optical fiber
#onitoring
*>ample = monitoring of tunnels
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$'!R- Instrument for monitoring fiber net0or@s
OTDR - Optical Time Domain Reflectometer In principle, OTDR is optical radar. The test pulse is launched into the fiber, and the return
signal is due to Rayleigh backscattering (scattering from microscopic
fluctuations in material density)
reflections
From pulse delay time one can determine the distanceof event.
$'!R - bloc@ diagram
laser
Rayleigh bac@scatter
pulser
beam splitteroptical pulse
detectortrigger pulse
fiber
oscilloscope
'ypical $'!R trace
A8
Raman scattering
When photons are scattered from an atom or molecule, mostphotons are elastically scattered (Rayleigh scattering), and suchscattered photons have the same energy (frequency) as theincident photons.
A small fraction of the scattered photons has different frequency,usually lower than the incident photons:
13h 32h
virtual energy state(3)
(2)
basic energy state (1)
AA
Raman scattering
Incident photons produce an oscillating polarization in themolecules, exciting them to a virtual energy state. TheRaman interaction leads to two possible outcomes: the material absorbs energy and the emitted photon has a
lower energy than the absorbed photon. This outcome islabeled Stokes Raman scattering.
the material loses energy and the emitted photon has ahigher energy than the absorbed photon. This outcome islabeled anti-Stokes Raman scattering.
13h 32h(3)
(2)
(1)
13h 32h
(3)
(2)
(1)
Raman $'!R
= based on non-linear spontaneous Raman scattering4'he ratio of anti-Sto@es intensity to Sto@es intensity
Raman scattering spectrum
Raman $'!R
anti-StokesStokes
I
a-ss
=
kT
h
I
I
s
sa
s
sa
exp
4
4
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System diagram for Raman $'!R
Raman $'!R
laser
Raman bac@scatter
pulser
0a"elength
selecti"e coupler
optical pulse
detector
6
trigger
pulse
fiber
oscilloscope
detector
6-
'ypical temperature "ersus distance display
Raman $'!R
Final goal - Remote sensor system
powerlines
powergenerators
bridgesInterrogation
unit
Interrogationunit
Interrogationunit
Public
netw
ork