Thermal and Mechanical Analyses of Fiber Bragg Gratings-Embedded Polymer Diaphragms

This letter presents the development and thermal and mechanical considerations of sensing elements using different diaphragm materials which are embedded in optical fiber Bragg gratings (FBGs). Diaphragms made of polyurethane, polydimethylsiloxane (PDMS) and nitrile rubber were fabricated, and all of them with embedded FBGs. Tensile tests were performed in each material, showing the lower Young's modulus of the PDMS (0.8 MPa), which is orders of magnitude lower than the ones of polyurethane (2.0 MPa) and nitrile rubber (362.2 MPa). Moreover, the highest strain limit was obtained in the PDMS diaphragm (24.5%). These results indicated the potential for higher pressure sensitivity of the PDMS, which was confirmed in the pressure characterization tests (pressure sensitivity of 1.4 nm/kPa). In addition, temperature tests indicated a higher sensitivity of the nitrile rubber, which presented a sensitivity of 49.8 pm/°C. Considering applications in which there are simultaneous variation of pressure and temperature, the nitrile presented a cross-sensitivity of 0.01 nm kPa −1 °C −1 which is the lowest among the materials tested, indicating the possibility of obtaining the mitigation of temperature influence in the pressure response. It is also worth noting that the highest measurement range was obtained in the nitrile rubber diaphragm with linear responses in the range of pressures up to 3 kPa.