A Microscale Differential Capacitive Direct Wall-Shear-Stress Sensor

This paper presents the development of a floating-element-based capacitively sensed direct wall-shear-stress sensor intended for measurements in a turbulent boundary layer. The design principle is presented, followed by details of the fabrication, packaging, and characterization process. The sensor is designed with an asymmetric comb finger structure and metalized electrodes. The fabrication process uses deep reactive ion etching on a silicon-on-insulator wafer, resulting in a simple two-mask fabrication process. The sensor is dynamically characterized with acoustically generated Stokes layer excitation. At a bias voltage of 10 V, the sensor exhibits a linear dynamic sensitivity of 7.66 mV/Pa up to the testing limit of 1.9 Pa, a flat frequency response with resonance at 6.2 kHz, and a pressure rejection of 64 dB. The sensor has a noise floor of 14.9 μPa/√(Hz) at 1 kHz and a dynamic range >;102 dB. The sensor outperforms previous sensors by nearly two orders of magnitude in noise floor and an order of magnitude in dynamic range.