| The utility of synthetic jet actuators has been demonstrated in a number of application areas including flow control, thermal management of integrated circuits, and micromixing. Micromachined synthetic jets (microjets) are particularly attractive for these applications since batch microfabrication facilitates the integration of large numbers of synthetic jets into addressable arrays that can individually addressed and phased as needed. Most importantly, micromachining techniques can be used to fabricate microjet modulator arrays which when operated at the synthetic jet frequency, can create localized areas of positive, zero, or negative synthetic jet exit velocity, a unique effect which has not been achieved with an un-modulated synthetic jet.; Procedures were developed for the fabrication of individual microjet array elements, non-addressable and addressable microjet arrays, and prototype microjet modulator arrays. Using these procedures, a pneumatically actuated micromachined synthetic jet modulator array was fabricated and tested. The DC and transient operating characteristics of the pneumatic microjet modulator array were measured by using a miniature pitot tube connected to a differential pressure sensor. A mathematical model of the streamwise exit velocity of the modulated synthetic jet flow was also developed, and when compared to experimental measurements, was found to be in close agreement. Operation of the pneumatic microjet modulator array at the 20Hz synthetic jet frequency was found to permit continuous variation of the streamwise orifice exit velocity from positive to negative values by variation of the relative phase of the modulation and synthetic jet generation signals. In this manner phase modulation of the synthetic jet flow using a micromachined modulator array could create airflow sources and airflow sinks. Finally, the unique capabilities advantages of microjet modulator arrays were demonstrated in a sample application in which a pneumatic microjet modulator array was operated as an air pump by operating one orifice as a pump inlet (an airflow sink) and another as the pump outlet (an airflow source). |
