In this work, we demonstrated the possibility realize a continuous measurement of liquid level based on light diffusing fibers (LDFs). The sensor consists of two parallel LDFs coupled together. The illuminating fiber is connected to a laser diode. The light scattered into the liquid is then coupled, always by the scattering, to the detection fiber and delivered to a detector. By setting a working wavelength that is strongly absorbed by the liquid, the power coupled between the fibers depends on liquid level.
The sensor is made by a polymeric beam of Polyvinyl chloride (PVC), on which two LDF (3M Fibrance) with a diffusion length of 1m have been glued side by side at a distance of 1.5mm. The fiber has a core diameter of 170 μm, a low-index polymeric cladding with a diameter of 230 μm, and loose tube PVC jacket with an outer diameter of 900 μm.
As light source a 1550nm fiber coupled laser diode is used. At this wavelength, water, employed as the test liquid, exhibits a strong absorption (=1210 m-1). A high sensitivity photodetector connected to a data acquisition module (DAQ) is used for measuring the detection fiber output power at different liquid levels
The optical coupling phenomena between the fibers could be modelled by coupled power equations. Co-propagation and counter-propagation coupling configurations have been analyzed and experimentally validated.
The measurements results are in good agreement with the theory, and demonstrate that both configurations could be used for liquid level sensing. The counter-propagation configuration exhibits a nonlinear response as function of the liquid level, while the co-propagation coupling configuration response is linear simplifying the calibration procedure. In the co-propagation configuration, the resolution ranges from ±8mm at low liquid level up to ±2mm at high liquid level over a 1m length measurement range.
The response of natural stratification to electromagnetic wave has received much attention in last decades, due to its
crucial role played in the remote sensing arena. In this context, when the superficial structure of the Earth, whose
formation is inherently layered, is concerned, the most general scheme that can be adopted includes the characterization
of layered random media. Moreover, a key issue in remote sensing of Earth and other Planets is to reveal the content
under the surface illuminated by the sensors. For such a purpose, a quantitative mathematical analysis of wave
propagation in three-dimensional layered rough media is fundamental in understanding intriguing scattering phenomena
in such structures, especially in the perspective of remote sensing applications. Recently, a systematic formulation has
been introduced to deal with the analysis of a layered structure with an arbitrary number of rough interfaces. Specifically,
the results of the Boundary Perturbation Theory (BPT) lead to polarimetric, formally symmetric and physical revealing
closed form analytical solutions. The comprehensive scattering model based on the BPT methodologically permits to
analyze the bi-static scattering patterns of 3D multilayered rough media. The aim of this paper is to systematically show
how polarimetric models obtainable in powerful BPT framework can be successfully applied to several situations of
interest, emphasizing its wide relevance in the remote sensing applications scenario. In particular, a proper
characterization of the relevant interfacial roughness is adopted resorting to the fractal geometry; numerical examples are
then presented with reference to representative of several situations of interest.
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