Capacitive Wall Shear Stress Sensors Based on Carbon Nanotube Pillars
Abstract
Miniature fluid flow sensors are being integrated in autonomous air and water vehicles, microfluidic devices, medical equipment, and intelligent systems. This work presents a wall shear stress sensor that has a 50 µm by 60 µm footprint, 200 µm height, sensitivity of 0.05–1 fF/Pa and range up to ±8 Pa. The sensor consists of two carbon nanotube pillars and produces a capacitance change in response to deformation in flow. Sensor elasticity and touch sensitivity were quantified by atomic force microscopy. Sensing element deformation was confirmed via optical microscopy. Capacitance response was established by calibration in channel flow. Sensor operating range widens when the thinner pillar was downstream since greater deflection did not cause pillar contact. Some sensors responded differently to flow due to pillar twisting or a dominant Bernoulli effect. Potential topics for future work include liquid flow sensing, external circuitry integration, and fabrication tuning.