A capacitance-based whisker-like artificial sensor for fluid motion sensing

The ability to navigate a fluid environment using only hydrodynamic information without visual or acoustic cues represents a technical challenge with broad utility for numerous commercial, military, and scientific purposes. Here we report the successful design, numerical modeling, fabrication, and experimental characterization of a novel, capacitance-based whisker-like artificial sensor for measuring fluid motion speed and direction. Inspired by seal vibrissae, our design features a rigid artificial whisker mounted on a novel cone-in-cone parallel-plate capacitor base, separated into four distinct quadrants, and covered by a polydimethylsiloxane (PDMS) membrane. The PDMS membrane creates the necessary damping and restoring forces, and the base divisions enable us to discriminate fluid direction. Numerical modeling of the system predicted capacitive output signals within a 1 pF range for flows ranging from 0 - 1.0 m/s. Experimental testing, however, using a custom-built force rig successfully demonstrated the sensor's ability to produce a reliable signal with a 3 pF range for the same flows. The testing showed the sensor's ability to discriminate flow-induced forces for both steady and oscillatory conditions with millinewton-level precision, and signal output from each of the four quadrants allowed us to extrapolate flow direction as well. Finally, the sensor was subjected to the same range of steady flows in our laboratory's water tunnel and produced nearly identical capacitance changes as a function of flow speed compared to the force rig testing.