Home > Jobs & theses > PhD Thesis : Nicolas LINZE, Sept. 30; 2013; 10:30 (UMONS)

PhD Thesis : Nicolas LINZE, Sept. 30; 2013; 10:30 (UMONS)

Thursday 19 September 2013, by Alexandra Peereboom

We are pleased to invite you to the PhD thesis defense of Ir Nicolas LINZE on September 30, 2013 at 10:30.

The title of the thesis is : “Development of optical fiber vibration sensors based on light polarization properties

Location :
UMONS, Faculté Polytechnique
Rue de Houdain 9
7000 Mons

Room: Auditoire 23 (2nd floor)

Summary :
Development of optical fiber vibration sensors based on light polarization properties
Nicolas Linze

Electromagnetism and Telecommunication Department, Boulevard Dolez 31, 7000 Mons, Belgium

The thesis consisted in developing point, quasi-distributed and distributed vibration sensors, using the light polarization properties. Such sensors are of great importance as vibrations are a health and ageing indicator of civil structures and industrial machines, thereby providing the detection of internal modifications. Compared to mechanical vibration sensors, in particular accelerometers, which have long been studied and used, optical fiber sensors have some very interesting advantages. First, with optical fibers it is possible to measure the vibration properties (frequencies and amplitudes) in a quasi-distributed or distributed way, i.e. in several points along the fiber or continuously along the fiber. This kind of measurements is difficult, if not impossible with conventional sensors as they consist of point sensors. Secondly, contrary to optical fibers, the conventional sensors cannot be used in harsh environments such as nuclear plants or electromagnetic-disturbed environments.
In our optical fiber vibration sensors, the light polarization state is used as the sensitive parameter. One of its main advantages of using this parameter is its high sensitivity to vibrations. Its working principle is as follows: a vibration has for effect to modify the birefringence properties in the fiber and in turn, the light polarization state. In our case, this modification is generated by crushing the fiber and is obtained by using a home-made mechanical transducer. Using a polarizer transforms the light polarization state modification into a power variation, which, after an electrical conversion, is easily measurable on an oscilloscope as a voltage variation.
Different sensors have been developed. A point sensor, made up of one transducer and measuring the vibrations at one position, has first been conceived. This sensor can measure high-level accelerations (14 g) with limited distortions and with a high sensitivity.
A quasi-distributed sensor, measuring the vibration at different positions and thus composed of several transducers, has then been developed. This sensor can recover the frequency spectrum of vibrations applied at different sensing positions. The quasi-distributed nature of this system is obtained by using a wavelength-multiplexing configuration.
Another quasi-distributed system, based on the Rayleigh backscattering process, has then been developed. Such a system is particularly interesting because the number of sensors (measurement points) can here be very high. The developed sensor can measure vibrations applied at different positions and with different frequency components.
During this thesis, an international collaboration allowed to use the mechanical transducers in a different kind of vibration sensor, thereby extending the range of potential applications.
These different vibration sensors can be potentially used in the monitoring civil structures (bridges, buildings…).

An intrusion sensor has finally been conceived. Based on a low-cost configuration, this sensor allows to detect reliably intrusions inducing a minimal 1.5 cm displacement. This kind of sensor opens another range of possible applications (security of private properties, integrity of nuclear plants…).