A Sapphire Based Fiber Optic Dynamic Pressure Sensor for Harsh Environments: Fabrication and Characterization

Abstract

This paper describes the modeling, fabrication, and characterization of a proof-ofconcept dynamic pressure sensor utilizing sapphire materials for the harsh environments of gas turbine engines. The harsh environment makes conventional instrumentation unsuitable for time-resolved, continuous, direct measurements. High temperature sensing is enabled by the use of sapphire materials due to a high melting point and corrosion resistance. The availability of commercial sapphire substrates and optical fibers provides a direct path for optical sapphire sensors with a matched coefficient of thermal expansion. The dynamic pressure sensor uses a fiber optic lever transduction mechanism with a remote photodiode optical readout allowing for isolation of the electronics from the harsh environment. A circular diaphragm is formed by joining two sapphire substrates using an alumina-based high temperature epoxy. The first substrate is 50 μm thick sapphire with a sputtered titanium/platinum reflective surface. The second substrate is a 1 mm thick sapphire substrate that has been machined to form a circular back cavity. Presented along with the sensor fabrication are a systems level dynamic model and a dc exploration of the performance of the fiber optic lever transduction. Finally, initial dynamic characterization of the frequency response function and linearity are presented with a resulting sensitivity of -113 dB re 1 V/Pa.