Low frequency vibration measurements in a composite material using embedded polarimetric sensor are presented in this
paper. A glass fiber reinforced composite material sample is fabricated with two different polarimetric sensor types
embedded in it. The two types of polarimetric sensors embedded are based on polarization maintaining photonic crystal fiber
(PM-PCF) and Panda fiber. The vibration frequencies and amplitudes are measured using the embedded polarimetric sensors
and the results from both sensor types are compared. Analysis of the limitations of Panda fiber based vibration measurements
over PM-PCF is carried out and the results are presented. It is found that for high amplitude vibration measurements, PMPCF
based sensors offer a wider linear range and are more suitable than Panda fiber based polarimetric fiber sensors. It is
envisaged that the results from the studies will provide important information to end-users for selecting an appropriate sensor
for vibration measurements in composite materials.
A demodulation scheme is presented for a hybrid sensing system based on a polarimetric fiber sensor and a fiber Bragg
grating (FBG) for composite structural health monitoring (SHM). The demodulation module is comprised of a Thin Film
Filter Wavelength Division Demultiplexer (TFF WDM- Demux) and an Electro-optic (EO) modulator. Unlike
"laboratory-use" demodulation systems which typically do not need a compact form factor, the proposed miniaturized
demodulation system is compact, lightweight and has low power consumption. The bandpass responses of the TFF
WDM- Demux are designed to match the peak reflected wavelengths of the FBGs so that the differential wavelength
information can be converted to intensity variations recorded by the array of detectors connected to the output channels
of the TFF WDM- Demux. In the polarimetric sensor demodulation section of the system, an electrical control voltage is
applied to the electro-optic modulator in order to shift the polarimetric sensor output to the maximum sensitive linear
response region. Two types of polarimetric fiber sensors are used; a Panda fiber and a polarization maintaining photonic
crystal fiber. The polarimetric strain sensors provide the average strain and temperature information, while the fiber
Bragg grating sensors give localized strain information. The demodulation system uniquely allows for the multiple
outputs of FBG and polarimetric sensors to be converted to a common optical intensity domain, for strain and
temperature measurements.
The design of a polyimide film packaged hybrid fiber sensor for simultaneous strain and temperature measurement is
presented. This hybrid sensor operates in the intensity domain by converting the polarization and wavelength information
from a polarization maintaining photonic crystal fiber (PM-PCF) sensor and fiber Bragg grating sensor (FBG)
respectively into intensity variations. The strain sensitivity of a polarimetric sensor for various lengths of the PM-PCF is
studied. The effective strain sensitivity of the FBG sensing system is adjusted to match that of the polarimetric sensor by
varying the slope of the edge filter. The packaging aspects of the hybrid fiber sensor are also presented in this paper.
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