A highly flexible sensing skin with embedded polymer optical fibre Bragg gratings is characterised The response to
pressure and strain compare favourably to a similar skin instrumented with silica fibre Bragg grating sensors.
In this paper, we report on the strain and pressure testing of highly flexible skins embedded with Bragg grating sensors
recorded in either silica or polymer optical fibre. The photonic skins, with a size of 10cm x 10cm and thickness of 1mm,
were fabricated by embedding the polymer fibre or silica fibre containing Bragg gratings in Sylgard 184 from Dow
Corning. Pressure sensing was studied using a cylindrical metal post placed on an array of points across the skin. The
polymer fibre grating exhibits approximately 10 times the pressure sensitivity of the silica fibre and responds to the post
even when it is placed a few centimetres away from the sensing fibre. Although the intrinsic strain sensitivities of
gratings in the two fibre types are very similar, when embedded in the skin the polymer grating displayed a strain
sensitivity approximately 45 times greater than the silica device, which also suffered from considerable hysteresis. The
polymer grating displayed a near linear response over wavelength shifts of 9nm for 1% strain. The difference in
behaviour we attribute to the much greater Young's modulus of the silica fibre (70 GPa) compared to the polymer fibre
(3 GPa).
Water is a common impurity of jet fuel, and can exist in three forms: dissolved in the fuel, as a suspension and as a
distinct layer at the bottom of the fuel tank. Water cannot practically be eliminated from fuel but must be kept to a
minimum as large quantities can cause engine problems, particularly when frozen, and the interface between water and
fuel acts as a breeding ground for biological contaminants. The quantities of dissolved or suspended water are quite
small, ranging from about 10 ppm to 150 ppm. This makes the measurement task difficult and there is currently a lack of
a convenient, electrically passive system for water-in-fuel monitoring; instead the airlines rely on colorimetric spot tests
or simply draining liquid from the bottom of fuel tanks. For all these reason, people have explored different ways to
detect water in fuel1,2,3, however all these approaches have problems, e.g. they may not be electrically passive or they
may be sensitive to the refractive index of the fuel. In this paper, we present a simple, direct and sensitive approach
involving the use of a polymer optical fibre Bragg grating to detect water in fuel. The principle is that poly(methyl
methacrylate) (PMMA) can absorb moisture from its surroundings (up to 2% at 23 °C)4, leading to both a swelling of the
material and an increase in refractive index with a consequent increase in the Bragg wavelength of a grating inscribed in
the material5.
We present an optical bend sensor based on a Bragg grating written in an eccentric core polymer optical fibre. The
grating wavelength shifts are studied as a function of bend curvature and fibre orientation and the device exhibits strong
fibre orientation dependence, wide bend curvature range of ± 22.7 m-1 and high bend sensitivity of 63 pm/m-1, which is
80 times higher than the reported sensor based on an offset-FBG in standard single mode silica fibre.
Fibre Bragg gratings (FBGs) in polymer optical fibres (POFs) have been used to measure the strain in a woven textile.
FBGs in both POFs and silica optical fibres were attached to a woven textile specimen, and their performance
characterised. It was demonstrated that the POF FBGs provide improved strain transfer coefficients and reduce local
structural reinforcement compared to silica FBGs and therefore make a more suitable proposition for textile monitoring.
We describe our recent progress in polymer fibre Bragg grating technology, including the writing of the first FBGs in
TOPAS cyclic olefin copolymer, enhancements to photosensitivity brought about by dopants and studies on grating
annealing.
We report on the temperature response of FBGs recorded in pure PMMA and TOPAS holey fibres. The gratings are fabricated for operational use at near IR wavelengths, using a phase mask and a CW He-Cd laser operating at 325nm. The room temperature grating response is non-linear and characterized by quadratic behaviour for temperatures from room temperature to the glass transition temperature, and this permanent change is affected by the thermal history of the gratings. We also report the first FBG inscription in microstructured polymer optical fibres fabricated from TOPAS. This material is fully polymerized and has very low moisture absorption, leading to very good fibre drawing properties. Furthermore, although TOPAS is chemically inert and bio-molecules do not readily bind to its surface, treatment with Antraquinon and subsequent UV activation allows sensing molecules to be deposited in well defined spatial locations. When combined with grating technology this provides considerable potential for label-free bio-sensing.
We report on the temperature response of FBGs recorded in pure PMMA and TOPAS holey fibers. The gratings are
fabricated for operational use at near IR wavelengths, using a phase mask and a cw He-Cd laser operating at 325nm. The
room temperature grating response is non-linear and characterized by quadratic behavior for temperatures from room
temperature to the glass transition temperature, and this permanent change is affected by the thermal history of the
gratings. We also report the first FBG inscription in microstructured polymer optical fibers fabricated from TOPAS. This
material is fully polymerized and has very low moisture absorption, leading to very good fiber drawing properties.
Furthermore, although TOPAS is chemically inert and bio-molecules do not readily bind to its surface, treatment with
Antraquinon and subsequent UV activation allows sensing molecules to be deposited in well defined spatial locations.
When combined with grating technology this provides considerable potential for label-free bio-sensing.
We present measurements on the non-linear temperature response of fibre Bragg gratings recorded in pure and
trans-4-stilbenemethanol-doped polymethyl methacrylate (PMMA) holey fibres.
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