Z. Sipus - Moderna Fizika i Primena u Elektrotehnici-P3

8/9/2019 Z. Sipus - Moderna Fizika i Primena u Elektrotehnici-P3

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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


2/14

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


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:


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


Sensor with vibrating

fiber cantilever(pictures taken withmicroscope):



4/14

1

23 mm

245 mm

+aser diode 1556nm

Isolator 1556nm

Coupler 1556nm

Sensor

!etector diode

1556nm

Fiber cantile"er

7)IF 8259


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


21

Measurement ofsensor response:

Optical sensor

Electromehancal sensor


We are considering sensor realization as an integrated 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;


7/14

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


8/14

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


9/14

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)


Siemens optical temperature sensors for power generators

and power lines (based on Bragg grating)


Question:How to make an optical sensor systemwith a reasonable price?


10/14

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!


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


Difference betweenFBG responsesis NOT sensitiveon enviromentalchanges!


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


Practical problems

Due to presence ofnoise there is an errorin determining theBragg wavelength.


12/14

Convolution method for noise reduction :


*

=

Convolution method for noise reduction :


*

=

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


Final testing dynamic sensor response on change of temperature:

heating of sensor


Example: Distributed Optical Sensors

Fire alarm systems in tunnels

sensing optical fiber

#onitoring

*>ample = monitoring of tunnels


13/14

$'!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

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Z. Sipus - Moderna Fizika i Primena u Elektrotehnici-P3