Ultra low noise fiber optic acoustic sensor for underwater applications
Author
Bilek, Şaban
Advisor
Özbay, Ekmel
Date
2015-08Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
Fiber optic sensor have many advantages over the conventional sensor technologies
such as electromangnetic compatibility, light weight,
exible geometric design,
sensing signal at a remote point and no electrical signal at the signal detection
point, easy sensor multiplexing,compatibility to fiber optic communication.
Experimental studies have been available for underwater acoustic sensor with using
fiber optics. In this thesis mandrel type interferometric fiber optic acoustic
sensor design is analyzed in terms of noise performance characteristics and design
parameters' contribution to noise performance is evaluated.
Acoustic signals create phase change at the fiber optic acoustic probe and
phase change is detected by using an interferometer. Experimental setup is used
to emulate the design of the sensor and different components are used to evaluate
the effect on the noise performance. Phase generated carrier method is evaluated
for phase detection method.
Finally noise measurement is done with a experimental setup emulating the
design. Noise level is measured around -100 db re rad/VpHz and responsivity of
the sensor(-140 dB re rad/VHzPa) is used to convert noise unit to pressure units
and 40 dB re uPa=VpHz noise level in terms of pressure is obtained. This level of
noise
oor is close to sea sate 0 (SS0) noise level of the ocean. Sea state 0 is the
state where there is no wind, wave or shipping traffic. This state is the lowest
possible ambient noise available in the ocean and it is quite rare to find such state
of the ocean. Therefore self noise of the designed fiber optic acoustic sensor is
not the limiting factor for acoustic signal detection. Any signal over the ambient
noise of the ocean can be detected using the designed fiber optic acoustic sensor.