| Abstract |
The use of oak barrels for wine aging is a widespread technique due to the physical
properties of oak wood. The oak barrel is an active, interactive container that
releases aromatic compounds and tannin when wet, while allowing oxygen to
penetrate and largely determines the characteristics of the produced wine.
However, the release of aromatic compounds from oak, is limited resulting to the
need for replacement of the barrel after prolonged use. Currently, the common
practice of wine makers in the assessment of the condition of oak barrels is empirical
and thus subjective.
The release of compounds from the wood into the wine takes place due to the
wetting of the wood, therefore the detection of the wetting condition in real time
could give useful information about the condition of the barrel. A sensor able to
accurately detect the wetting condition of an oak barrel in situ, would help to both
reduce unnecessary costs and quantify the wine aging process. In order for the
sensor to be functional in a restrictive environment such as a winery, it must be
portable as well as have miniature size and weight, so that the disturbance in the
barrel due to its placement is minimal. It must also have the ability of multiple uses
(without reduction of its efficiency), have high efficiency and wide dynamic range.
Optical fiber sensors are ideal for this application because they meet all of the above
requirements. Additional advantages of such sensors are their low cost, fast
response and durability.
The two methods considered for the development of humidity sensors are Tilted
Optical Fiber Bragg Gratings (TOFBG) and Fabry-Pérot cavities and relay on changes
in the refractive index of hydroscopic materials under varying humidity. Specifically,
in the first sensor, we coated the area surface of the TOFBG with agarose solution
while for the second sensor, we formed a cavity of photo-polymerizable resin at the
fiber end face. Different levels of ambient humidity, induce changes in the refractive
index of the gel/resin thus altering the spectroscopic signature of the developed
sensors.
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