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 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;   penetrating an orifice through both the first micromechanical device and the plate coupled thereto to fluidically couple the volume to a gas 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. A synthetic jet comprising:
 a first plate;   a second plate;   a wall coupled to the first plate and the second plate to form a volume; and   an actuator coupled to one of the first plate and the second plate;   wherein at least one of the first plate and the second plate has an orifice formed therein that fluidically couples the volume to an external environment; and   wherein the first plate and the second plate comprise materials selected to de-tune a plurality of natural frequencies of the synthetic jet by separating a band gap therebetween.    
     
     
       15. The synthetic jet of claim 14 wherein the band gap is in the hundreds of Hertz. 
     
     
       16. The synthetic jet of claim 15 wherein the band gap is in the thousands of Hertz. 
     
     
       17. The synthetic jet of claim 14 wherein the plurality of natural frequencies comprises a peak Helmholtz frequency and a peak structural resonant frequency. 
     
     
       18. The synthetic jet of claim 17 wherein the peak Helmholtz frequency of the synthetic jet is greater than the peak structural resonant frequency of the synthetic jet. 
     
     
       19. The synthetic jet of claim 18 wherein at least one of the first plate and the second plate comprise at least one of a plastic and a polymer. 
     
     
       20. The synthetic jet of claim 17 wherein the peak Helmholtz frequency of the synthetic jet is less than the peak structural resonant frequency of the synthetic jet. 
     
     
       21. The synthetic jet of claim 20 wherein at least one of the first plate and the second plate comprise at least one of a metal and a ceramic. 
     
     
       22. The synthetic jet of claim 14 further comprising a second actuator coupled to the second plate; and
 wherein the actuator is coupled to the first plate.   
     
     
       23. The synthetic jet of claim 14 wherein the orifice extends through both the actuator and the one of the first plate and the second plate. 
     
     
       24. The synthetic jet of claim 14 further comprising a shim coupled to one of the first plate and the second plate, wherein the shim further separates the band gap between the plurality of natural frequencies. 
     
     
       25. 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; and   a second micromechanical device coupled to the other of the two plates;   wherein the first micromechanical device and the plate coupled thereto have an orifice formed therethrough; and   wherein the two plates comprise materials selected to separate a peak acoustic frequency and a peak structural frequency of the synthetic jet by a band gap therebetween.   
     
     
       26. The synthetic jet of claim 25 further comprising a shim attached to one of the two plates, wherein the shim further separates the band gap between the peak acoustic frequency and the peak structural frequency. 
     
     
       27. The synthetic jet of claim 25 wherein the two plates comprise at least one of a plastic and a polymer, such that the peak acoustic resonant frequency is above the peak structural resonant frequency. 
     
     
       28. The synthetic jet of claim 25 wherein the two plates comprise at least one of a metal and a ceramic, such that the peak acoustic resonant frequency is below the peak structural resonant frequency. 
     
     
       29. A system for cooling a device comprising:
 a first 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; and 
 a wall member coupled to and positioned between the first plate and the second plate to form a cavity; 
 wherein the first plate and the first actuator have an orifice therethrough, the orifice fluidically coupled to the cavity and fluidically coupled to an environment external to the cavity; and 
 wherein the first plate and the second plate comprise materials selected to de-tune a plurality of natural frequencies of the synthetic jet by separating a band gap therebetween; and 
 a control system configured to operate the first actuator and the second actuator of the first synthetic jet. 
   
     
     
       30. The system of claim 29 wherein the plurality of natural frequencies comprises a peak acoustic resonant frequency and a peak structural resonant frequency. 
     
     
       31. The system of claim 30 wherein at least one of the first plate and the second plate comprises at least one of a plastic and a polymer, such that the peak acoustic resonant frequency is greater than the peak structural resonant frequency. 
     
     
       32. The system of claim 30 wherein at least one of the first plate and the second plate comprise at least one of a metal and a ceramic, such that the peak acoustic resonant frequency is less than the peak structural resonant frequency. 
     
     
       33. The system of claim 29 further comprising a second synthetic jet, wherein the control system operates the first synthetic jet out of phase with the second synthetic jet.