Technical paper

Microsystem Technologies

, Volume 11, Issue 12, pp 1292-1300

First online:

Electrostatically driven synthetic microjet arrays as a propulsion method for micro flight

Part II: microfabrication and initial characterization
  • Babak A. ParvizAffiliated withDepartment of Electrical Engineering, University of Washington Email author 
  • , Khalil NajafiAffiliated withDepartment of Electrical Engineering and Computer Science, Center for Wireless Integrated Micro Systems, University of Michigan
  • , Michael O. MullerAffiliated withAerospace Engineering Department, University of Michigan
  • , Luis P. BernalAffiliated withAerospace Engineering Department, University of Michigan
  • , Peter D. WashabaughAffiliated withAerospace Engineering Department, University of Michigan

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access


A propulsion system based on acoustic streaming generated by Helmholtz resonators is presented. High frequency (>60 kHz) electrostatically driven micromachined Helmholtz resonators constitute the basic unit of the system. Microjets produced at the exit of these resonators can be combined to form a distributed propulsion system. A high yield (>85%) fabrication process is introduced for fabrication of individual as well as arrays of resonators. The fabrication results for ten different designs are presented. About 1000 resonators of similar design cover the surface of a 4-in. wafer, effectively converting it to a distributed propulsion system. A number of characterization methods such as monitoring the harmonics of the drive current, laser interferometry, hot-wire anemometry, acoustic spectrum measurement and video particle imaging are used to determine the structural and fluidic behavior of different resonator designs. Collapse and recovery times of the diaphragm in the electrostatic actuator of the resonator are characterized and reduced to less than 10 μs by optimizing the perforation design. The occurrence of acoustic streaming in the micron-scale is verified via video particle imaging. The jet streams produced with pulse drive at low frequencies (~1 kHz) are spatially profiled and jet velocities exceeding 1 m/s are measured at the exit of the resonators. It has been verified that the resonance frequencies of the device at 50 and 175 kHz can be closely predicted by modeling.