Pressure Sensor Arrays and Microactuators for Fluid Mechanics Research

摘要

A combined microactuator/microsensor system has been developed using siliconmicromachining techniques for use in high speed jets and control of screech in these jets. The 14 microns-thick electrostatic microactuator was fabricated and tested at the exit of a supersonic axisymmetric jet for the introduction of perturbations into the convectively unstable supersonic shear layer. It can be forced into mechanical resonance at frequencies of 5/14 kHz at an amplitude of greater then 70 microns, thus generating significant disturbances into the macro scale jet flow, and survive operation at speeds of >210 m/s. These microactuators have survived hundreds of experiments in the harsh jet environment, and their performance matches or exceeds that of other macro actuators. 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 uV/VPa with a 2% nonlinearity over a pressure range of 10kPa. A chip has been fabricated that supports an array of microactuators and sound detectors. Ongoing investigations are aimed at developing a technique to modify, and ultimately control, the feedback loop responsible for the creation of screech.