A Flush-Mounted Dual-Axis Wall Shear Stress Sensor

This paper presents the fabrication, packaging, and calibration of a flush-mounted, dual-axis, differential capacitive wall shear stress sensor. The two-mask fabrication process produces a 7-mm die with a 2-mm by 2-mm floating element supported by eight, compliant crab-leg tethers. Taking advantage of backside wire bonds, the hydraulically smooth package is suitable for wind tunnel testing and is designed to have a resonant frequency of 3.7 kHz. Initial dynamic calibration data are presented using both single-ended and fully-differential electronics, with sensitivities as high as 80 mV/Pa and minimum detectable wall shear stress values as low as 10 μPa/Hz
^1/2
, resulting in dynamic ranges near 135 dB.