U.S. patent number RE46,003 [Application Number 14/469,699] was granted by the patent office on 2016-05-17 for method and apparatus for reducing acoustic noise in a synthetic jet.
This patent grant is currently assigned to General Electric Company. The grantee listed for this patent is General Electric Company. Invention is credited to Mehmet Arik, Charles Erklin Seeley, Yogen Vishwas Utturkar, Stanton Earl Weaver.
United States Patent |
RE46,003 |
Arik , et al. |
May 17, 2016 |
**Please see images for:
( Certificate of Correction ) ** |
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.
Inventors: |
Arik; Mehmet (Uskudar Istanbul,
TR), Weaver; Stanton Earl (Broadalbin, NY),
Seeley; Charles Erklin (Niskayuna, NY), Utturkar; Yogen
Vishwas (Niskayuna, NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
41723600 |
Appl.
No.: |
14/469,699 |
Filed: |
August 27, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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14013834 |
Aug 29, 2013 |
|
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Reissue of: |
12198240 |
Aug 26, 2008 |
8006917 |
Aug 30, 2011 |
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Reissue of: |
12198240 |
Aug 26, 2008 |
8006917 |
Aug 30, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
23/467 (20130101); F15D 1/00 (20130101); B05B
17/0607 (20130101); H01L 2924/00 (20130101); H01L
2924/0002 (20130101); H01L 2924/09701 (20130101); F28F
13/02 (20130101); Y10T 29/494 (20150115); H01L
2924/0002 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
B05B
1/08 (20060101); F15D 1/00 (20060101); H01L
23/467 (20060101); F28F 13/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Arik, "An investigation into feasibility of impingement heat
transfer and acoustic abatement of meso scale synthetic jets,"
Applied Thermal Engineering, 2007, vol. 27, pp. 1483-1494. cited by
applicant .
Utturkar et al., "An Experimental and Computational Heat Transfer
Study of Pulsating Jets," Journal of Heat Transfer, Jun. 2008, vol.
130. cited by applicant .
Garg et al., "Meso Scale Pulsating Jets for Electronics Cooling",
Dec. 2005. cited by applicant.
|
Primary Examiner: Kaufman; Joseph
Attorney, Agent or Firm: Ziolkowski Patent Solutions Group,
SC Testa; Jean K.
Claims
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..].
.Iadd.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. .Iaddend.
.Iadd.15. The synthetic jet of claim 14 wherein the band gap is in
the hundreds of Hertz..Iaddend.
.Iadd.16. The synthetic jet of claim 15 wherein the band gap is in
the thousands of Hertz..Iaddend.
.Iadd.17. The synthetic jet of claim 14 wherein the plurality of
natural frequencies comprises a peak Helmholtz frequency and a peak
structural resonant frequency..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.30. The system of claim 29 wherein the plurality of natural
frequencies comprises a peak acoustic resonant frequency and a peak
structural resonant frequency..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
.Iadd.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..Iaddend.
Description
BACKGROUND OF THE INVENTION
The invention relates generally to synthetic jets and, more
particularly, to a method and apparatus of acoustic noise reduction
therein.
A synthetic jet may influence the flow over a surface to control
flow, as in, for example, separation from an airfoil, or to enhance
convection on a surface. A typical synthetic jet actuator includes
a housing defining an internal chamber, and an orifice is present
in a wall of the housing. The actuator further includes a mechanism
in or about the housing for periodically changing the volume within
the internal chamber so that a series of fluid vortices are
generated and projected in an external environment out from the
orifice of the housing. Various volume changing mechanisms include,
for example, a piston positioned in the jet housing to move so that
gas or fluid is moved in and out of the orifice during
reciprocation of the piston and a flexible diaphragm as a wall of
the housing. The flexible diaphragm is typically actuated by a
piezoelectric actuator or other appropriate means.
Typically, a control system is utilized to create time-harmonic
motion of the diaphragm. As the diaphragm moves into the chamber,
decreasing the chamber volume, fluid is ejected from the chamber
through the orifice. As the fluid passes through the orifice, the
flow separates at the sharp edges of the orifice and creates vortex
sheets which roll up into vortices. These vortices move away from
the edges of the orifice under their own self-induced velocity. As
the diaphragm moves outward with respect to the chamber, increasing
the chamber volume, ambient fluid is drawn from large distances
from the orifice into the chamber. Because the exiting vortices get
connected away from the edges of the orifice, they are not affected
by the ambient fluid being entrained into the chamber. Thus, as the
vortices travel away from the orifice, they synthesize a jet of
fluid, thus called a "synthetic jet," through entrainment of the
ambient fluid.
A synthetic jet may be used for thermal management of tight spaces
where electronics may be housed and where space for the electronics
is a premium. Typically, wireless communication devices such as
cellular phones, pagers, two-way radios, and the like, have much of
their heat generated in integrated circuit (i.e. IC) packages that
are positioned in such tight spaces. Because of the limited space
and limited natural convection therein, the heat generated is
typically conducted into printed circuit boards and then
transferred to the housing interior walls via conduction,
convection, and radiative processes. The heat is then typically
conducted through the housing walls and to the surrounding ambient
environment. The process is typically limited because of the
limited opportunity for convection cooling within the housing and
over the printed circuit boards. The low thermal conductivity of
the fiberglass epoxy resin-based printed circuit boards can lead to
high thermal resistance between the heat source and the ambient
environment. And, with the advent of smaller enclosures, higher
digital clock speeds, greater numbers of power-emitting devices,
higher power-density components, and increased expectations for
reliability, thermal management issues present an increasing
challenge in microelectronics applications.
To improve the heat transfer path, micro/meso scale devices such as
synthetic jets have been proposed as a possible replacement for or
augmentation of natural convection in microelectronics devices.
Applications may include impingement of a fluid in and around the
electronics and printed circuit boards. However, a synthetic jet
typically has two natural frequencies at which the synthetic jet
yields superior cooling performance. These natural frequencies
include the structural resonant frequency and the acoustic
resonance (Helmholtz) frequency. The structural resonant frequency
is caused at the natural frequency of the structure of the
synthetic jet, which consists typically of the synthetic jet plates
acting as a mass and the elastomeric wall acting as a spring. The
acoustic resonance frequency is characterized by the acoustic
resonance of air mass flowing in and out of the synthetic jet
orifice. The effect is due to the air in the synthetic jet volume
acting as a spring and the air in the orifice acting as a mass. The
acoustic resonance is expectedly accompanied by a loud tonal noise
and a determined vibrational mode if the two modes are not
separated from one another in the frequency domain. Thus, the
process of operating a synthetic jet typically results in a loud
noise that may limit or preclude its use in cooling and other
applications.
Therefore, it would be desirable to design an apparatus and method
for reducing acoustic noise in a synthetic jet while not
compromising performance thereof.
BRIEF DESCRIPTION OF THE INVENTION
Embodiments of the invention provide a method and apparatus that
overcome the aforementioned drawbacks. Embodiments of the invention
are directed method and apparatus for reducing acoustic noise in a
synthetic jet while not compromising performance thereof.
According to one aspect of the invention, 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 there through and the orifice is
fluidically coupled to the cavity and fluidically coupled to an
environment external to the cavity.
In accordance with another aspect of the invention, a method of
fabricating a synthetic jet includes attaching two plates to a wall
to encircle a volume and coupling a first micromechanical device to
one of the two plates to form a first unitary member. The method
also includes coupling a second micromechanical device to the other
of the two plates to form a second unitary member and penetrating
an orifice through the first unitary member to fluidically couple
the volume to a gas outside the volume.
Yet another aspect of the invention includes a system for cooling a
device that includes a synthetic jet. The synthetic jet includes 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 and second
plates to form a cavity. The first plate and the first actuator
have an orifice penetrating therethrough, and the orifice is
fluidically coupled to the cavity and fluidically coupled to an
environment external to the cavity. The system includes at least
one control system configured to drive the first and second
actuators at an electrical frequency such that a jet expels from
the orifice.
Various other features and advantages will be made apparent from
the following detailed description and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings illustrate one preferred embodiment presently
contemplated for carrying out the invention.
In the drawings:
FIG. 1 is a schematic cross-sectional side view of a prior art zero
net mass flux synthetic jet actuator with a control system.
FIG. 2 is a schematic cross-sectional side view of the synthetic
jet actuator of FIG. 1 depicting the jet as the control system
causes the diaphragm to travel inward, toward the orifice.
FIG. 3 is a schematic cross-sectional side view of the synthetic
jet actuator of FIG. 1 depicting the jet as the control system
causes the diaphragm to travel outward, away from the orifice.
FIG. 4 is an illustration of a cross-section of a synthetic
jet.
FIGS. 5 and 6 illustrate performance curves for a synthetic jet
having both a structural mode and a Helmholtz mode.
FIG. 7 is an illustration of a cross-section of a synthetic jet
according to an embodiment of the invention.
FIG. 8 is an illustration of a cross-section of a synthetic jet
according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Embodiments of the invention relate to a piezoelectric motive
device and methods of making and using a piezoelectric motive
device to reduce the acoustic noise emitting therefrom. The
operating environment is described with respect to a thermal
management system for enhancing convection in cooling of
electronics. However, it will be appreciated by those skilled in
the art that embodiments of the invention are equally applicable
for use with other synthetic jet applications. For instance,
synthetic jets have been routinely used for stand-point flow
control, thrust vectoring of jets, triggering turbulence in
boundary layers, and other heat transfer applications. Heat
transfer applications may include direct impingement of vortex
dipoles on heated surfaces and employing synthetic jets to enhance
the performance of existing cooling circuits. Thus, although
embodiments of the invention are described with respect to cooling
of electronics, they are equally applicable to systems and
applications using synthetic jets for other purposes.
Referring to FIGS. 1-3, a synthetic jet 10 as known in the art, and
the operation thereof, is shown. The synthetic jet 10 includes a
housing 11 defining and enclosing an internal chamber 14. The
housing 11 and chamber 14 can take virtually any geometric
configuration, but for purposes of discussion and understanding,
the housing 11 is shown in cross-section in FIG. 1 to have a rigid
side wall 12, a rigid front wall 13, and a rear diaphragm 18 that
is flexible to an extent to permit movement of the diaphragm 18
inwardly and outwardly relative to the chamber 14. The front wall
13 has an orifice 16 of any geometric shape. The orifice
diametrically opposes the rear diaphragm 18 and connects the
internal chamber 14 to an external environment having ambient fluid
39.
The flexible diaphragm 18 may be controlled to move by any suitable
control system 24. For example, the diaphragm 18 may be equipped
with a metal layer, and a metal electrode may be disposed adjacent
to but spaced from the metal layer so that the diaphragm 18 can be
moved via an electrical bias imposed between the electrode and the
metal layer. Moreover, the generation of the electrical bias can be
controlled by any suitable device, for example but not limited to,
a computer, logic processor, or signal generator. The control
system 24 can cause the diaphragm 18 to move periodically, or
modulate in time-harmonic motion, and force fluid in and out of the
orifice 16. Alternatively, a piezoelectric actuator could be
attached to the diaphragm 18. The control system would, in that
case, cause the piezoelectric actuator to vibrate and thereby move
the diaphragm 18 in time-harmonic motion.
The operation of the synthetic jet 10 is described with reference
to FIGS. 2 and 3. FIG. 2 depicts the synthetic jet 10 as the
diaphragm 18 is controlled to move inward into the chamber 14, as
depicted by arrow 26. The chamber 14 has its volume decreased and
fluid is ejected through the orifice 16. As the fluid exits the
chamber 14 through the orifice 16, the flow separates at sharp
orifice edges 30 and creates vortex sheets 32 which roll into
vortices 34 and begin to move away from the orifice edges 30 in the
direction indicated by arrow 36.
FIG. 3 depicts the synthetic jet 10 as the diaphragm 18 is
controlled to move outward with respect to the chamber 14, as
depicted by arrow 38. The chamber 14 has its volume increased and
ambient fluid 39 rushes into the chamber 14 as depicted by the set
of arrows 40. The diaphragm 18 is controlled by the control system
24 so that when the diaphragm 18 moves away from the chamber 14,
the vortices 34 are already removed from the orifice edges 30 and
thus are not affected by the ambient fluid 39 being drawn into the
chamber 14. Meanwhile, a jet of ambient fluid 39 is synthesized by
the vortices 34 creating strong entrainment of ambient fluid drawn
from large distances away from the orifice 16.
FIG. 4 illustrates a cross-section of one embodiment of a synthetic
jet 50 known in the art. Synthetic jet 50 includes first and second
plates 52, 54 separated by a wall 56. A cavity 58 having a gas or
fluid 59 therein is encircled by first and second plates 52, 54 and
wall 56. A piezoelectric motive device 60 is coupled to second
plate 54 and is controlled by a control system 62. An orifice 64 is
positioned in first plate 52. During operation, control system 62
causes actuator 60 to move periodically in a time-harmonic motion,
thus forcing fluid 59 in and out of cavity 58 through orifice 64,
causing a jet 66 to emit therefrom.
FIG. 5 shows a plot 200 of frequencies for synthetic jet 50 of FIG.
4. As illustrated, synthetic jet 50 has two natural frequencies: a
peak structural resonant frequency illustrated at 202 and a peak
Helmholtz frequency illustrated at 204. The peak structural
resonant frequency 202 is caused at the natural frequency of the
structure of the synthetic jet 50, which typically includes the
synthetic jet plates 52, 54 acting as a mass and the wall 56 acting
as a spring. The peak Helmholtz frequency 204 is characterized by
acoustic resonance of air mass in and out of the orifice 64 of the
synthetic jet 50. The Helmholtz frequency 204 occurs as a result of
the air in the synthetic jet volume acting as a spring and may be
accompanied by a loud tonal noise and a determined vibrational
mode. A narrow separation 206 between the two frequencies 202, 204,
of less than a .[.few.]. hundred Hz, may lead to the accompaniment
of a loud tonal noise while still providing superior cooling. This
tends to preclude its use in cooling and other applications.
The acoustic noise may be reduced in a structure wherein the peak
structural resonant frequency 202 and the peak Helmholtz frequency
204 are separated from one another by an appreciable band gap of,
for instance, a few .Iadd.hundred .Iaddend.Hz to a few kHz, or
more. The band gap leads to low-noise cooling by enabling operation
of the jet 50 at the structural resonant frequency 202, which gets
de-tuned from the acoustically active frequency range. FIG. 6 shows
a plot 210 of frequencies where the peak structural resonant
frequency 212 and the peak Helmholtz frequency 214 are separated
from one another such that noise is reduced by operating the jet 50
at a low resonant frequency. A separation 216 represents the
separation between the two peaks 212, 214 and results in a
separation of two frequencies of a few hundred Hz or more. While
the peak Helmholtz frequency 214 is shown in FIG. 6 as having a
frequency greater than the peak structural resonant frequency 212,
noise reduction in a synthetic jet may be equally achieved in a
device having an adequate separation where the peak Helmholtz
frequency 214 is less than the peak structural resonant frequency
212. The amount of separation may be a few hundred Hz or more,
depending on the device structural design and the noise
requirements thereof.
FIG. 7 illustrates a cross-section of a synthetic jet 300 according
to an embodiment of the invention. Synthetic jet 300 includes a
wall 302 and first and second backer plates 304, 306. The plates
304, 306 are coupled to wall 302 to enclose a cavity 308. A first
actuator 310 is coupled to the first plate 304 to form a first
unitary member or composite unit or structure 311. A second
actuator 312 is coupled to the second plate 306 to form a second
unitary member or composite unit or structure 314. An orifice 313
passes through both plate 304 and actuator 310 of first composite
311 and fluidly couples cavity 308 to an exterior volume 309.
Orifice 313 may be centrally positioned in composite 311 or may
instead be placed in other locations of composite 311. According to
an embodiment of the invention, an additional orifice 316 may be
positioned in second composite 314. Furthermore, it is contemplated
that one or both composites 311, 314 may have one or multiple
orifices therein, depending on the application and the desired
location(s) of the jets emitting therefrom.
In one embodiment, actuators 310, 312 are piezoelectric motive
(piezomotive) devices that may be actuated by application of a
rapidly alternating voltage that causes the piezomotive devices to
rapidly expand and contract. A pair of control systems 318, 320 are
coupled to piezomotive actuators 310, 312, respectively, and
provide rapidly alternating voltages to the piezomotive actuators
310, 312. Piezomotive actuators 310, 312 may be monomorph or
bimorph devices. In a monomorph embodiment, piezomotive actuators
310, 312 may be coupled to plates 304, 306 formed from materials
including metal, plastic, glass, or ceramic. In a bimorph
embodiment, one or both piezomotive actuators 310, 312 may be
bimorph actuators coupled to plates 304, 306 formed from
piezoelectric materials. In an alternate embodiment, the bimorph
may include single actuators 310, 312, and plates 304, 306 are the
second actuators, thus in this embodiment the composites 311, 314
may themselves make up the bimorph.
The actuation of piezomotive actuators 310, 312 coupled to
respective backer plates 304, 306, causes a rapid flexing of the
composites 311, 314, which causes a volume change in cavity 308
that causes an interchange of gas or other fluid between cavity 308
and exterior volume 309. For example, when the volume of cavity 308
decreases, a jet 322 of gas emits from cavity 308 through orifice
313 and into exterior volume 309. An increase in the volume of
cavity 308 causes gas from exterior volume 309 to flow into cavity
308 through orifice 313. Likewise, in an embodiment having multiple
orifices, such as orifice 313 and orifice 316, actuation of
piezomotive actuators 310, 312 causes jets 322, 324 to emit from
both orifices 313, 316 when the volume of cavity 308 decreases.
In an embodiment of the invention, actuators 310, 312 may include
devices other than piezoelectric motive devices, such as hydraulic,
pneumatic, magnetic materials, electrostatic materials, and
ultrasonic materials. Thus, in such embodiments, control systems
318, 320 are configured to activate respective actuators 310, 312
in corresponding fashion. That is, for an electrostatic material,
controllers 318, 320 may be configured to provide a rapidly
alternating electrostatic voltage to actuators 310, 312 in order to
activate and flex composites 311, 314. Such additional materials
may themselves be configured in monomorph and bimorph
arrangements.
In order to reduce acoustic noise emission from the jet 300, the
peak structural frequency and the peak Helmholtz frequency may be
separated by proper selection of materials and material
combinations, and appropriate dimensioning. In one embodiment, the
materials and dimensions are selected in order to cause the peak
structural frequency to be below the peak Helmholtz frequency, and
in another embodiment the materials and dimensions are selected in
order to cause the peak structural frequency to be above the peak
Helmholtz frequency. Optimal acoustic noise reduction may be
obtained by separating the two peak frequencies by a few hundred Hz
or more.
As discussed above, plates 304, 306 may be formed from metal,
plastic, glass, and ceramic. Likewise, wall 302 may be formed from
a metal, plastic, glass, and ceramic. Suitable metals include
materials such as nickel, aluminum, copper, and molybdenum, or
alloys such as stainless steel, brass, bronze, and the like.
Suitable polymers and plastics include thermoplastics such as
polyolefins, polycarbonate, thermosets, epoxies, urethanes,
acrylics, silicones, polyimides, and photoresist-capable materials,
and other resilient plastics. Suitable ceramics include titanates
(such as lanthanum titanate, bismuth titanate, and lead zirconate
titanate) and molybdates. Furthermore, various other components of
the synthetic jet 300 may be formed from metal as well.
Thus, for an embodiment having the peak Helmholtz frequency below
the peak structural frequency, in order to increase the separation
between the two frequencies, the structure of synthetic jet 300 may
be stiffened using, for instance, metals and alloys thereof or
ceramics for the plates 304, 306. The separation may be enhanced
by, for instance, increasing the thickness-to-diameter ratio of the
components as well.
Similarly, for a design having the peak Helmholtz frequency above
the peak structural frequency, in order to increase the separation
between the two frequencies, compliance or pliability may be added
to the structure of synthetic jet 300 to decrease the peak
structural frequency using, for instance, plastics and polymers for
the plates 304, 306. The separation may be enhanced by, for
instance, decreasing the thickness-to-diameter ratio of the
components as well.
The synthetic jet components may be adhered together or otherwise
attached to one another using adhesives, solders, and the like. In
one embodiment, a thermoset adhesive or an electrically conductive
adhesive is employed to bond actuators 310, 312 to plates 304, 306
to form first and second composite structures 311, 314. In the case
of an electrically conductive adhesive, an adhesive may be filled
with an electrically conductive filler such as silver, gold, and
the like, in order to attach lead wires (not shown) to the
synthetic jet. Suitable adhesives may have hardnesses in the range
of Shore A hardness of 100 or less and may include silicones,
polyurethanes, thermoplastic rubbers, and the like, such that an
operating temperature of 120.degree. or greater may be
achieved.
FIG. 8 illustrates a synthetic jet 400 according to another
embodiment of the invention. Synthetic jet 400 includes a wall 402
and first and second backer plates 404, 406. The plates 404, 406
are coupled with wall 402 to enclose a cavity 408. A first actuator
410 is coupled to the first plate 404 to form a first composite
411, and a second actuator 412 is coupled to the second plate 406
to form a second composite 414.
As discussed above with respect to FIG. 7, the peak structural
frequency and the peak Helmholtz frequency of synthetic jet 400 may
be separated by proper selection of materials and material
combinations of its components. In addition, an additional backer
structure or shim 415 is positioned in second composite 414 between
and coupled to the second backer plate 406 and the second actuator
412 to add further separation between the peak structural frequency
and the peak Helmholtz frequency. Shim 415 may be made of material
that is appropriately selected to increase separation between the
structural and Helmholtz modes, as described above. Orifice 413 and
orifice 416 (shown in phantom) are configured to pass through the
respective composites 411, 414 and may be centrally or
non-centrally positioned. Orifices 413, 416 are configured to emit
jets 422, 424, upon activation of actuators 410, 412 via respective
control systems 418, 420. It is contemplated that one or both
composites 411, 414 may have multiple orifices therein, depending
on the application and the desired location(s) of the jets emitting
therefrom. Additionally, while not illustrated, a shim may also be
positioned as part of the first composite 411.
As with the embodiment illustrated in FIG. 7, the actuators 410,
412 may be piezoelectric motive devices, and may include either
monomorph or bimorph configurations. Thus, either or both actuators
410, 412 may be bimorph devices, or each actuator 410, 412 may
include single actuators, and respective backer plates 404, 406, or
shim 415 in the case of composite 414, may be configured as
actuators, and each composite 411, 414 may be configured as
bimorphs. Likewise, actuators 410, 412 may include materials other
than piezoelectric motive devices and respective controllers 418,
420. Components may be adhered via adhesives or solder as described
with respect to the embodiment described regarding FIG. 7.
To further reduce the noise thereof, multiple synthetic jets,
according to the embodiments described herein, may be each operated
with frequencies that are out of phase with one another. In other
words, a first synthetic jet may have an actuator therein that is
operated at a first frequency, and a second synthetic jet may have
an actuator therein that are operated at a second frequency that is
out-of-phase with the first frequency, thus producing an overall
reduced noise compared to operation of both in-phase with one
another.
Additionally, embodiments of the synthetic jets described herein
may be configured to be circular, oval, square, rectangular, or
other shapes, depending on the application and the space available
for mounting the synthetic jets. Likewise, the orifices themselves
may include square, circular, oblong, and other shapes depending on
the application.
According to one embodiment of the invention, 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.
In accordance with another embodiment of the invention, a method of
fabricating a synthetic jet includes attaching two plates to a wall
to encircle a volume and coupling a first micromechanical device to
one of the two plates to form a first unitary member. The method
also includes coupling a second micromechanical device to the other
of the two plates to form a second unitary member and penetrating
an orifice through the first unitary member to fluidically couple
the volume to a gas outside the volume.
Yet another embodiment of the invention includes a system for
cooling a device that includes a synthetic jet. The synthetic jet
includes 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 and second plates to form a cavity. The first plate and the
first actuator have an orifice penetrating therethrough, and the
orifice is fluidically coupled to the cavity and fluidically
coupled to an environment external to the cavity. The system
includes at least one control system configured to drive the first
and second actuators at an electrical frequency such that a jet
expels from the orifice.
The invention has been described in terms of the preferred
embodiment, and it is recognized that equivalents, alternatives,
and modifications, aside from those expressly stated, are possible
and within the scope of the appending claims.
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