Operation and testing of electrostatic microactuators and micromachined sound detectors for active control of high speed flows

The operation and testing of a combined microactuator/microsensor system for use in a high speed jet are presented. Electrostatic actuators have been fabricated using a bulk-silicon dissolved-wafer process, and are more than 12 μm in thickness to achieve a large stiffness in the z-direction. The “micro” actuators resonate at a frequency of 5 kHz/14 kHz and an amplitude of >70 μm peak-peak, generate significant disturbances into the “macro” scale jet flow, and survive operation at speeds of >210 m/s. An array of micromachined sound detectors for the detection of onset of jet screech has also been fabricated. The detectors use stress compensated PECVD silicon nitride/oxide membranes together with monocrystalline ion-implanted p⁺⁺ silicon piezoresistors to achieve high sensitivity. They have a static sensitivity of 1.1 μV/V·Pa with a 2% nonlinearity over an operating pressure range of 10 kPa