Development of Fiber Bragg Grating based Transducers

摘要

Some issues pertaining to the design and development of practical fiber Bragg grating (FBG) based transducers are addressed. In general, FBG sensors are attached to sensing elements by two methods, as (i) surface-mounted FBG and (ii) embedded FBG. For the surface-mounted case, the investigation of strain gradient induced spectral broadening in FBG attached-based transducer has been conducted. Because Bragg spectral broadenign can have adverse effects on the sensor interrogation, a circular diaphragm pressure transducer is used as an example. We derive anaytical closed form results for describing measurandinduced strain gradients in circular geometry transducers. In addition, Bragg spectral broadenign analysis by use of Tmatrix calculation is also conducted to validate some of the experimental results. For the embedded case, the investigation of strain transfer between FBG and host transducers has been conducted. Therefore, a transducer, made by aluminum epoxy with embedded FBG material, subjected to transverse load is used as an example, where FBGs are subjected to lateral expansion of the host epoxy. A shear-lag analysis with incorporation of the experimental result was given. Finally, the three FBG normal strain estimations (one longitudinal and two transverses) are all verified by finite element approach.