Michael O. Muller

High-Density Micromachined Acoustic Ejector Array For Micro Propulsion

This paper reports a high-density (23 units/cm2) all-silicon micromachined acoustic ejector array utilizing Helmholtz resonators coupled with an acoustic ejector for the generation of high-speed micro-jets needed in applications such as micro propulsion, jet cooling, and pumping. The ejector array has been fabricated by using a novel 3D MEMS technology. The ejector (∼1.6mmm×1.6mm×1mm) produces an air jet with a velocity higher than 0.65 m/sec measured by hot-wire anemometry at a distance of 560 µm from the ejector hole when driven electrostatically at a frequency of ∼70kHz. Flow entrainment and jet visualization are also demonstrated.

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.

Acoustically Generated Micromachined Jet Arrays for Micropropulsion Applications

Theory, manufacturing and experimental results of acoustically generated micromachined jet arrays for micropropulsion applications are presented. A reduced order theoretical analysis is found to be an accurate performance predictor. Scaling laws derived from the theory suggest the performance benefits derived by reducing the geometric size of the resonators, specifically the application of MEMS technologies. A novel manufacturing method is employed to construct the devices, incorporating an electrostatically actuated membrane to drive the acoustic jets. Experimental results of the MEMS devices demonstrate a structurally sound design, and a performance commensurate with expectations.Copyright