Flow measurement via novel Fiber Bragg Grating optical sensor

Somerville, Matthew
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University of Delaware
A novel fiber optic sensor was designed and developed for the measurement of fluid flow. The sensor was specifically designed to measure flow within small channels such as those found in many biomedical applications without any metal parts (i.e. MRI compatible). At the heart of the device was a Fiber Bragg Grating (FBG). The FBG is an optical device that is very sensitive to axial strain. Specific mounts were designed to fit over the FBG and convert the pressure field, produced by the flow, into an axial stain that is then sensed optically by the FBG. Several different sets of mounts were designed, fabricated via 3D printing and tested experimentally. The mounts were developed to test two types of flow measurement. One set was a flexure mount designed to convert the radial compressive forces of a pressure wave into axial strain. The other set was a flow restriction disc paired with a fixed point on the fiber. The interaction of the flow with the disc would create a tensile force on the fiber and generate a proportional signal. The sensor was tested against theoretical values by measuring reflected wavelength values against known axial strains. The sensor was also tested in a closed loop system that generated forces similar to those found within the human body. Conclusions based on experimental results were; (1) the FBG with the flexure mount was found to be sensitive and reliable in biological settings, (2) the FBG with the flow restriction disc was not able to generate consistent results to be considered useable.