Monitoring of Acoustic Emissions Using a Fiber Bragg ...
Transcript of Monitoring of Acoustic Emissions Using a Fiber Bragg ...
![Page 1: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/1.jpg)
Center for Quality Engineering and Failure Prevention
Monitoring of Acoustic Emissions Using a Fiber Bragg Grating Dynamic
Strain Sensing System
Department of Mechanical Engineering / Center for Quality Engineering and Failure Prevention
Northwestern University Evanston, IL 60208
Brad Regez, Yan-Jin Zhu, Yinian Zhu, Oluwaseyi Balogun, and Sridhar Krishnaswamy
AEWG, Denver, Colorado, May 18, 2011. Acknowledgement: ONR, NSF, CCITT
![Page 2: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/2.jpg)
Center for Quality Engineering and Failure Prevention
Goal: Develop a network of high-frequency strain sensors with the following requirements:
• Always ready to detect and locate impact and other transient signals; • Adaptive to detect dynamic strains (ultrasound-induced) in the presence of large quasi-static strains (structural deformation-induced) or thermal drift; • Multiplexable for large sensor arrays.
Technology: Optical Fiber Bragg Grating (FBG) Sensors and Multiplexed Two-Wave Mixing (MTWM) in adaptive photorefractive crystals.
Dynamic Strain Monitoring System - requirements -
![Page 3: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/3.jpg)
Center for Quality Engineering and Failure Prevention
Talk Outline
• Fiber Bragg-Grating sensors as dynamic strain sensors • Current methods of demodulation
• Two Wave Mixing demodulator system • frequency response • sensitivity • cross-talk
•Applications: •acoustic emission
![Page 4: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/4.jpg)
Center for Quality Engineering and Failure Prevention
Talk Outline
• Fiber Bragg-Grating sensors as dynamic strain sensors • Current methods of demodulation
• Two Wave Mixing demodulator system • frequency response • sensitivity • cross-talk
•Applications: •acoustic emission
![Page 5: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/5.jpg)
Center for Quality Engineering and Failure Prevention
Fiber Bragg Grating Sensors
Strain or temperature signal is spectrally encoded in the reflected / transmitted light from an FBG sensor.
1µε 1.2pm 1oC 13pm
Ref: A.Othonos, and K.Kalli, “Fiber Bragg Gratings,” Artech House, Boston. (1999)
• Bragg-gratings are refractive-index gratings in the optical fiber. • They are very easy to fabricate. • They are local sensors • Several sensors can be readily multiplexed. • Useful as temperature, strain sensors. • Can be used for dynamic strain sensing
![Page 6: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/6.jpg)
Center for Quality Engineering and Failure Prevention
Demodulation Scheme
Readiness Adaptivity Multiplexability
CCD Spectrometer / AWG
Always No Demodulator for each sensor
Tunable Filter Intermittent – Scanned
Feedback Filter for each sensor
Tunable Source Intermittent – Scanned
Feedback yes
Interferometric Always Feedback Demodulator for each sensor
MTWM system Always Self Single demodulator
Current Approaches for Spectral Shift Demodulation
![Page 7: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/7.jpg)
Center for Quality Engineering and Failure Prevention
Talk Outline
• Fiber Bragg-Grating sensors as dynamic strain sensors • Current methods of demodulation
• Two Wave Mixing demodulator system • frequency response • sensitivity • cross-talk
•Applications: •acoustic emission
![Page 8: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/8.jpg)
Center for Quality Engineering and Failure Prevention
Pump
Signal
Transmitted Signal +
Diffracted Pump
In a nutshell: • PRC’s act as “novelty filters” • Output only “sees” sudden variations in the input • what is new is dictated by the PRC response time
Principle: • Pump + Signal create a refractive index grating in the PRC • Pump and signal beams diffract off the index grating • Diffracted pump is a replication of the quasistatic signal beam • Dynamic changes in the signal beam are not tracked by the PRC • The transmitted signal beam effectively interferes with the diffracted pump beam and only dynamic changes in the signal beam are observed.
Ref: Yi Qiao, Yi Zhou, and Sridhar Krishnaswamy, (July 2006), “Adaptive two-wave mixing wavelength demodulation of Fiber Bragg Grating dynamic strain sensors”, Applied Optics, vol. 45, No. 21, pp 5132-5142.
Two Wave Mixing Interferometry in Photorefractive Crystals
![Page 9: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/9.jpg)
Center for Quality Engineering and Failure Prevention
TWM Interferometer for Spectral Demodulation
• Bragg-sensor signal at λB split into two legs with optical path difference OPD ‘d’ • The two-beams are mixed in a PRC to create a grating. • Path-mismatch causes a phase difference between the two legs of:
• Quasistatic drift in λB compensated for by creation of new grating in PRC • Dynamic changes in λB cause instantaneous phase shift at the PRC output.
2
2( ) ( )B nB
dt tπ λ ϕλ
∆Φ = − ∆ +
Fiber Coupler Fiber Bragg Grating Sensor Broadband Laser Source
Optical Fiber Amplifier PRC
Fiber Coupler
![Page 10: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/10.jpg)
Center for Quality Engineering and Failure Prevention
Multiplexability
• A single TWM spectral demodulator can be used to demodulate multiple FBG sensors simultaneously by wavelength multiplexing.
• The different channels are separated after the PRC by band-drop filters.
Circulator
ASEBroadband Optical Amplifier
1 by 2Coupler
Collimator
Collimator
PRC
DC field 6kV/cm
InP:Fe
λ/2
λ/2
Freespace to
fibercoupler
Photodetector
Photodetector
1548nm
1552nm
Band drop filters
Photodetector
Photodetector
1560nm
1556nm
1536nm 1540nm 1544nm 1548nm
Optical Analyzer
bandsplittertransmission band
1537-1543nm
FBG reflection0.1nm
1540nm 1548nm
bandsplitterreflection band
<1537nm & >1543nm
![Page 11: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/11.jpg)
Center for Quality Engineering and Failure Prevention
4.0 4.5 5.0 5.5 6.0 6.5Time(ms)
20 kHz
2 kHz
5 kHz
10 kHz
Signal
Amplit
ude(a.u
.)
Ch4
Ch3
Ch2
Ch1
-0.04-0.020.000.020.04
-0.04-0.020.000.020.04
-0.04-0.020.000.020.04
-0.04-0.020.000.020.04
0 5000 10000 15000 20000 25000
0.00.20.40.60.81.0
Frequency (Hz)
ch
1
0.00.20.40.60.81.0
ch
2
0.00.20.40.60.81.0
ch
3
0.00.20.40.60.81.0
ch
4
Time response Frequency response
Multiplexed 4-channel TWM spectral demodulator - crosstalk
• 20 kHz, 10kHz, 5 kHz and 2 kHz 5με strains were applied onto the four FBG sensors respectively.
• No detectable cross-talk
![Page 12: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/12.jpg)
Center for Quality Engineering and Failure Prevention
Talk Outline
• Fiber Bragg-Grating sensors as dynamic strain sensors • Current methods of demodulation
• Two Wave Mixing demodulator system • frequency response • sensitivity • cross-talk
•Applications: •acoustic emission
![Page 13: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/13.jpg)
Center for Quality Engineering and Failure Prevention
TWM System NWU Prototype
![Page 14: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/14.jpg)
Center for Quality Engineering and Failure Prevention
Pencil Lead Break AE Data FBG vs. PZT
450 500 550 600 650 700 750 800 850 900 950
-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.21.4
FBG Response PZT Response
Relat
ive A
mpl
itude
Time (µs)
Source to Receiver Distance: 2 cm
450 500 550 600 650 700 750 800 850 900 950-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
FBG Response PZT Response
Relat
ive A
mpl
itude
Time (µs)
Source to Receiver Distance: 3 cm
450 500 550 600 650 700 750 800 850-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
FBG Response PZT Response
Rela
tive
Ampl
itude
Time (µs)
Source to Receiver Distance: 4 cm
450 500 550 600 650 700 750 800 850 900 950-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
FBG Response PZT Response
Relat
ive A
mpl
itude
Time (µs)
Source to Receiver Distance: 5 cm
Pencil Break
Experimental Setup
![Page 15: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/15.jpg)
Center for Quality Engineering and Failure Prevention
TWM Spectral Demodulation - Pencil Lead Break AE Monitoring -
Fmax = 210kHz
Time (µs)
Freq
uenc
y (k
Hz)
900 1000 1100 1200 1300 1400 1500
-10
-5
0
5
10
15
20
Rela
tive
Ampl
itude
Time (µs)
Time – Frequency Transform Experimental Waveform
![Page 16: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/16.jpg)
Center for Quality Engineering and Failure Prevention
• Tyfo SEH-51 Composite – Tyfo S Epoxy – Uni-directional Glass/Aramid
custom weave [0/90]
• Composite Gross Laminate Properties: – σu =575 MPa, ε=2.2%, E=26.1 GPa – Laminate Thickness: 1.3mm
Collaborative work between NU & Harbin Institute of Technology (Li Hui)
Glass Fiber Composite Coupon
![Page 17: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/17.jpg)
Center for Quality Engineering and Failure Prevention
Continuous AE – Matrix Damage
487.72 487.74 487.76 487.78 487.80.17
0.18
0.19
0.2
0.21
Time (s)
Am
plitu
de (v
)
487.744 487.746 487.748 487.75
0.18
0.185
0.19
0.195
0.2
0.205
Time (s)
Am
plitu
de (
v)
![Page 18: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/18.jpg)
Center for Quality Engineering and Failure Prevention
Burst AE – Fiber Damage
511.38 511.39 511.4 511.41 511.42
0.16
0.17
0.18
0.19
0.2
0.21
0.22
0.23
Time (s)Am
plitud
e (v)
![Page 19: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/19.jpg)
Center for Quality Engineering and Failure Prevention
FBG Sensors Disadvantages / Advantages Over Piezoelectric Based Sensors
DISADVANTAGES • Systems are more expensive than piezoelectric based systems • FBG sensors are less sensitive than piezoelectric sensors
ADVANTAGES • Smaller footprint • Immune to electromagnetic signals or noise • Minimum signal loss since cables are replaced by a fiber optic • Exhibit long term stability • Can be mounted underwater in needed • Can be embedded within the structure • Can be used in high temperature applications.
![Page 20: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/20.jpg)
Center for Quality Engineering and Failure Prevention
Conclusions TWM Wavelength demodulation demonstrated:
1. Always On: Wavelength demodulation induced by transient events is demonstrated.
2. Adaptive: The TWM wavelength demodulator is demonstrated to have adaptivity to quasistatic drift (both strains and temperature).
3. Frequency response: High pass – no upper limit from TWM.
4. Multiplexability: Little detectable cross-talk.
![Page 21: Monitoring of Acoustic Emissions Using a Fiber Bragg ...](https://reader035.fdocuments.in/reader035/viewer/2022071614/615805dfe623cc2ce23dd385/html5/thumbnails/21.jpg)
Center for Quality Engineering and Failure Prevention
Monitoring of Acoustic Emissions Using a Fiber Bragg Grating Dynamic
Strain Sensing System
Department of Mechanical Engineering / Center for Quality Engineering and Failure Prevention
Northwestern University Evanston, IL 60208
Brad Regez, Yan-Jin Zhu, Yinian Zhu, Oluwaseyi Balogun, and Sridhar Krishnaswamy
AEWG, Denver, Colorado, May 18, 2011. Acknowledgement: ONR, NSF, CCITT
Thank You!