Characterization of a sapphire optical wall shear stress sensor for high-temperature applications – AIAA Jan 2016

This paper presents the development and initial experimental characterization of the first sapphire micromachined wall shear stress sensor for high-temperature applications utilizing geometric moire optical transduction. The microelectromechanical systems (MEMS) sensor utilizes a folded tether floating element structure to extend the operating range of the sensor. Picosecond pulsed laser micromachining is employed to pattern mechanical structures in sapphire, and a four-channel alumina fiber array with sapphire optical fibers is used to interrogate the moire fringe. Platinum thin-film gratings and a stainless steel package enable a theoretical maximum operating temperature in excess of 800C. Calibration of the sensor system in differential mode demonstrates a dynamic shear stress sensitivity of 76.8 uV/Pa at 1.128 kHz, sensor resonance of 3.5 kHz, pressure rejection ratio of 75 dB, minimum detectable shear stress of 4.6 mPa at 1.128 kHz for a 1 Hz bin, and an experimentally verified dynamic range of 52 dB.

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