Piezoresistive MEMS Underwater Shear Stress Sensors

We report on the design and performance of underwater piezoresistive floating-element shear stress sensors for direct dynamic measurements. Our design utilizes sidewall-implanted piezoresistors to measure lateral force and infer shear stress, and traditional top-implanted piezoresistors to detect normal forces and pressure transients. A gravity-driven flume was used to test the sensors. FEMLAB simulation and microscale Particle Image Velocimetry experiments were used to characterize the flow disturbance over different gap sizes. The results show no detectable disturbance of the flow over the range of sensor gap sizes evaluated (5-20 µ m).