Carbon nanotube wall shear stress sensors

Continued miniaturization of fluid flow devices demands ever smaller sensors. We have developed a miniature, capacitive, wall shear stress sensor made from vertically aligned carbon nanotube arrays grown from photolithographically patterned catalyst. The components that mechanically respond to flow and convert that signal to an electrical response measure 50 by 60 by 200 cubic microns and can measure wall shear stress in the range of 0.1 to 7 Pa. Sensor stiffness and response to deformation are characterized by atomic force microscopy while sensor deflection in flow is visualized by optical microscopy. Capacitance response to wall shear stress is further characterized through calibration in a flow channel. The results reveal a diverse range of ways the sensor can respond to flow, which could be leveraged to tune sensitivity or operating range for specific target applications. The design furthers efforts to miniaturize drag-based flow sensors, with applications in microfluidic systems, autonomous micro aerial vehicle control, and experiments resolving microscopic flow features.