Rotating Microsensors With Non-Linear Feedback

The need for instruments that detect and quantify small amounts of chemical and biological agents has spurred the development of micro-scale and nano-scale resonators. Most of these sensors are variations of vibrating cantilever beams and rely on resonant frequency shifts to quantify added mass. While very sensitive in vacuum or low viscosity environments, these types of sensors suffer performance degradation in viscous fluids, where damping is significantly increased. This paper presents a unique sensor architecture consisting of an immersed micro-plate designed to vibrate rotationally about an axis as fluid flows past it in a micro-channel. The idea behind this design is that some of the energy in the incoming flow can be harvested due to fluid-structure interaction, thereby reducing the effective damping. Only a small outside energy input is then required to obtain sustained, large amplitude vibrations. We show how sensitivity vector techniques applied to such a device can provide an alternate means of effectively detecting small mass variations. A method of optimizing the feedback control in order to maximize sensitivity using a spline-based force surface spanning the state space is also presented.