Performance of ultrasonic electrostatic resonators for use in micro propulsion

High speed micro-jets produced by acoustic streaming can be used for micro propulsion in miniature airborne vehicles. A wafer-level technology was developed to fabricate hundreds of resonators to form these jets on a 4-inch silicon wafer. In this paper, modeling and full characterization of these jets is presented. The performance of electrostatic resonators was tested by laser interferometry, video particle imaging and hot-wire anemometry. The occurrence of non-linear streaming phenomenon and jet formation was verified by particle imaging. The effect of various design parameters such as throat size and perforation geometry on jet performance was investigated and an optimum experimental design was identified. Jet velocities as high as 1 m/s were measured and by spatial investigation of the velocity field, the micro jet stream along and away from the centerline was measured and profiled. A coupled equivalent circuit that models the electrostatic drive and acoustic streaming is developed and shown to closely match experimental results.