Capacitive shear stress sensor with DC sensing capability for fluid flow measurements
MetadataShow full item record
In this work, the design, simulation, fabrication, and characterization of a shear stress sensor based on a differential capacitive sensing scheme are presented. The sensor is an adaptation of previous generations that utilized piezoelectric sensing techniques. The present generation of the device replaces the piezoelectric with a dielectric film, converting the sensing mechanism of the device from piezoelectric to capacitive. The motivation for this adaptation is to create a shear stress sensor capable of sensing static shear stresses, such as those generated by a constant flow across a surface. The sensors consist of an array of unit sensing cells, each of which contains three electrodes: two resting on the substrate, and a third resting on top of the dielectric, between the bottom electrodes. This configuration creates a resting capacitance between the top electrode and either bottom electrode that varies when the top surface of the device experiences shear stress and thus deflection of the top electrode. The departure from the resting capacitance is monitored by applying a sinusoidal signal to the bottom electrode, and observing the change in amplitude of the signal at the top electrode as the surface shears. The device is first modeled analytically and numerically to estimate the sensitivity for the device, which is used as the figure of merit in evaluation of these shear sensors. Sensitivity is defined in this context as the change in capacitance per Pascal [ΔC/Pa]. The fabrication and testing of the device are described, through which a measurement of the sensitivity of the sensors is obtained and found to be in agreement with the predicted sensitivity via simulation.