Method and apparatus for reducing acoustic noise in a synthetic jet

Abstract

A synthetic jet includes a first backer structure and a first actuator coupled to the first backer structure to form a first composite unit. The synthetic jet also includes a second backer structure, and a second actuator coupled to the second backer structure to form a second composite unit. A wall member is coupled to and positioned between the first and second backer structures to form a cavity. The first composite unit has an orifice formed therethrough and the orifice is fluidically coupled to the cavity and fluidically coupled to an environment external to the cavity.

What is claimed is: 
     
       1. A method of fabricating a synthetic jet comprising:
 attaching two plates to a wall to encircle form a volume; 
 coupling a first micromechanical device to one of the two plates to form a first unitary member; 
 coupling a second micromechanical device to the other of the two plates to form a second unitary member; 
 penetratingforming an orifice through both the first micromechanical device and the plate coupled thereto to fluidically couple the volume to a gasfluid outside the volume; and 
 coupling a first controller to the first unitary member, wherein the first controller is configured to operate the first unitary member at a first frequency and to operate the second unitary member at a second frequency that is different from the first frequency. 
 
     
     
       2. The method of  claim 1  further comprising attaching a shim to the second unitary member. 
     
     
       3. The method of  claim 2  wherein attaching the shim to the second unitary member comprises attaching the shim to the second unitary member via one of a thermoset adhesive, and a solder material. 
     
     
       4. The method of  claim 1  wherein at least one of the micromechanical devices is a monomorph piezoelectric device. 
     
     
       5. The method of  claim 1  wherein at least one of the micromechanical devices is a bimorph piezoelectric device. 
     
     
       6. A system for cooling a device comprising:
 a synthetic jet comprising:
 a first plate; 
 a first actuator coupled to the first plate; 
 a second plate; 
 a second actuator coupled to the second plate; 
 a wall member coupled to and positioned between the first and second plates to form a cavity; and 
 wherein the first plate and the first actuator have an orifice penetrating therethrough, the orifice fluidically coupled to the cavity and fluidically coupled to an environment external to the cavity; and 
 
 at least one control system configured to drive the first and second actuators at electrical frequencies that are different from one another such that a jet expels from the orifice. 
 
     
     
       7. The system of  claim 6  wherein the at least one control system includes a first control system to drive the first actuator and a second control system to drive the second actuator. 
     
     
       8. The system of  claim 7  wherein the electrical frequencies provided to the first and second actuators are out-of-phase with one another. 
     
     
       9. The system of  claim 7  wherein the electrical frequencies are below 100 Hz or above 20 kHz. 
     
     
       10. The system of  claim 6  further comprising attaching a shim to the first actuator. 
     
     
       11. The system of  claim 10  wherein the shim is positioned between the first actuator and the one of the first plate. 
     
     
       12. The system of  claim 6  wherein at least one of the first and second actuators is one of a monomorph and a bimorph piezoelectric device. 
     
     
       13. The system of  claim 6  wherein at least one of the first and second actuators is a hydraulic, a pneumatic, a magnetic material, an electrostatic material, and an ultrasonic material. 
     
     
       14. The system of claim 6 further comprising a second synthetic jet; and
 wherein the at least one control system operates the synthetic jets out of phase with one another.   
     
     
       15. A synthetic jet comprising:
 two plates attached to a wall to form a volume;   a first micromechanical device coupled to one of the two plates;   a second micromechanical device coupled to the other of the two plates; and   a control system to operate the first micromechanical device at a frequency out of phase from that of the second micromechanical device; and   wherein the first micromechanical device and the plate coupled thereto have an orifice formed therethrough.   
     
     
       16. The synthetic jet of claim 15 further comprising a shim attached to one of the two plates. 
     
     
       17. The synthetic jet of claim 15 wherein the second micromechanical device and the plate coupled thereto have an orifice formed therethrough to fluidically couple the volume to a fluid outside the volume. 
     
     
       18. The synthetic jet of claim 15 wherein the two plates are comprised of at least one of a metal, a polymer, a plastic, a glass, and a ceramic. 
     
     
       19. The synthetic jet of claim 15 wherein the first and second micromechanical devices are composed of different materials. 
     
     
       20. The synthetic jet of claim 15 wherein the two plates comprise materials selected to de-tune a plurality of natural frequencies of the synthetic jet by separating a band gap therebetween. 
     
     
       21. A synthetic jet assembly comprising:
 a first synthetic jet comprising:
 a first plurality of plates coupled to a first wall to form a first volume, at least one of the first plurality of plates having an orifice formed therethrough; and 
 a first piezoelectric actuator coupled to a plate of the first plurality of plates; 
   a second synthetic jet comprising:
 a second plurality of plates coupled to a second wall to form a second volume, at least one of the second plurality of plates having an orifice formed therethrough; and 
 a second piezoelectric actuator coupled to a plate of the second plurality of plates; and 
   wherein the first piezoelectric actuator is operated at a first frequency; and   wherein the second piezoelectric actuator is operated at a second frequency that is out-of-phase with the first frequency.   
     
     
       22. The synthetic jet assembly of claim 21 wherein at least one of the first and second synthetic jets further comprises a shim. 
     
     
       23. The synthetic jet assembly of claim 21 wherein at least one of first and second synthetic jets comprises a plurality of piezoelectric actuators.