Development of a sapphire optical pressure sensor for high-temperature applications

This paper presents the fabrication, packaging, and characterization of a sapphire optical pressure sensor for high-temperature applications. Currently available instrumentation poses significant limitations on the ability to achieve real-time, continuous measurements in high-temperature environments such as those encountered in industrial gas turbines and high-speed aircraft. The fiber-optic lever design utilizes the deflection of a circular platinum-coated sapphire diaphragm to modulate the light reflected back to a single send/receive sapphire optical fiber. The 7 mm diameter, 50 mu m thick diaphragm is attached using a novel thermocompression bonding process based on spark plasma sintering technology. Bonds using platinum as an intermediate layer are achieved at a temperature of 1200 degrees C with a hold time of 5 min. Initial characterization of the bond interface using a simple tensile test indicates a bond strength in excess of 12 MPa. Analysis of the buckled diaphragm after bonding is also presented. The packaged sensor enables continuous operation up to 900 degrees C. Room-temperature characterization reveals a first resonance of 18.2 kHz, a flat-band sensitivity of -130 dB re 1 V/Pa (0.32 mu V/Pa) from 4-20 kHz, a minimum detectable pressure of 3.8 Pa, and a linear response up to 169 dB at 1.9 kHz.