University of Limerick - Politecnico di Torino - presentation for Optical Metrology 2013, Munich - FBG paper.

1. High-Frequency Optical Fiber Microphone for
Condition-Based Maintenance (CBM) Application
[Optical Metrology, 2013]
Daniele Tosi
University of Limerick, Optical Fibre Sensors Research Centre
Massimo Olivero, Guido Perrone, Alberto Vallan
Politecnico di Torino, Dept. of Electronics and Telecommunications

2. Fiber optic microphone
High-frequency optical fiber microphone for condition-based maintenance application
Performance
➡ , n , <n sensing resolutionμε ε ε
➡ Long-haul sensing
Miniature size
➡ Miniature size ( 125 m + coating)∅ μ
➡ Lightweight, versatile coating
Distribution
➡ Time+wavelength multiplexing
➡ Quasi-distributed
Total immunity
➡ Totally EMI compatible
➡ Fire-safe, passive device

3. Fiber Bragg grating (FBG)
High-frequency optical fiber microphone for condition-based maintenance application
•Information encoded in
FBG optical spectrum
•Linear dependance on
strain and temperature
•1.08 pm/με (10.2 pm/K)
•High-speed interrogation
•Information encoded in
FBG optical spectrum
•Linear dependance on
strain and temperature
•1.08 pm/με (10.2 pm/K)
•High-speed interrogation
Reflected Bragg wavelength shifts linearly with variation of
tensile strain and temperature

4. High-speed interrogation
High-frequency optical fiber microphone for condition-based maintenance application
High speed, no scanning elements
Short range, high sensitivity
Sensitive to backreflection noise

5. Signal processing
High-frequency optical fiber microphone for condition-based maintenance application
Adaptive filtering
•Mitigates the effect
of backreflection
laser noise
•Applied in pre-
training conditions
Frequency estimat.
•Operate in low
SNR, well below
-35 dB
•Computational
complexity increase
High sensitivity, 0.1 n≲ ε
No real-time detection

6. FBG multiplexing
High-frequency optical fiber microphone for condition-based maintenance application
...
...
...
.
.
.
.
.
.
FBG matrix
channel 1
channel 2
channel N
.
.
.
wavel. Wwavel. 2wavel. 1

7. Architecture
High-frequency optical fiber microphone for condition-based maintenance application
Switch
Laser array
Laser
controller
Photodiode
...
...
...
.
.
.
.
.
.
FBG matrix
.
.
.

8. Prototype
High-frequency optical fiber microphone for condition-based maintenance application
Laser(s)
Detector
Switch 1x2Circulator
TEC/LDC
Fiber outputDAQ output
DAQ 5kS/s

9. Frequency response
High-frequency optical fiber microphone for condition-based maintenance application

10. Voice detection
High-frequency optical fiber microphone for condition-based maintenance application
Intelligibility + peak reproduction

11. CBM Condition-Based Maintenance
High-frequency optical fiber microphone for condition-based maintenance application

12. CBM Condition-Based Maintenance
High-frequency optical fiber microphone for condition-based maintenance application

13. CBM Condition-Based Maintenance
High-frequency optical fiber microphone for condition-based maintenance application
EMI-prone environment
Critical location placement
Noisy environment
Network structure
Long process time

14. CBM model
High-frequency optical fiber microphone for condition-based maintenance application
Ahmadi, H. and Mollazade, K., "Bearing fault diagnosis of a mine stone crasher by
vibration condition monitoring technique," Res. J. Appl. Sci. Eng. Technol. 1 (2009).
Sound = f(shape) +
+ f(rotation/contact) +
+ f(damage)
Warning signal (fm)

15. CBM model
High-frequency optical fiber microphone for condition-based maintenance application
Ahmadi, H. and Mollazade, K., "Bearing fault diagnosis of a mine stone crasher by
vibration condition monitoring technique," Res. J. Appl. Sci. Eng. Technol. 1 (2009).

16. CBM model
High-frequency optical fiber microphone for condition-based maintenance application
Ahmadi, H. and Mollazade, K., "Bearing fault diagnosis of a mine stone crasher by
vibration condition monitoring technique," Res. J. Appl. Sci. Eng. Technol. 1 (2009).
Useful region

17. Future work
High-frequency optical fiber microphone for condition-based maintenance application
FBGs
Shaker
CFC
(4 layer)