U.S. patent application number 14/410083 was filed with the patent office on 2015-11-12 for micropump.
The applicant listed for this patent is Ramot at Tel-Aviv University Ltd.. Invention is credited to Ori EHRENBERG, Gabor KOSA.
Application Number | 20150322932 14/410083 |
Document ID | / |
Family ID | 49769627 |
Filed Date | 2015-11-12 |
United States Patent
Application |
20150322932 |
Kind Code |
A1 |
KOSA; Gabor ; et
al. |
November 12, 2015 |
MICROPUMP
Abstract
A micropump for pumping a fluid, the pump comprising: a tube
formed from a piezoelectric material and having inner and outer
surfaces; a plurality of electrodes electrifiable to generate
vibrations in the tube; and at least one voltage source that
applies voltages to the electrodes to generate a displacement
traveling wave that propagates along the tube and causes fluid in
the tube to flow through the tube.
Inventors: |
KOSA; Gabor; (Modiin,
IL) ; EHRENBERG; Ori; (Tel Aviv, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ramot at Tel-Aviv University Ltd. |
Tel Aviv |
|
IL |
|
|
Family ID: |
49769627 |
Appl. No.: |
14/410083 |
Filed: |
June 21, 2013 |
PCT Filed: |
June 21, 2013 |
PCT NO: |
PCT/IB2013/055094 |
371 Date: |
December 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61662370 |
Jun 21, 2012 |
|
|
|
Current U.S.
Class: |
417/413.2 |
Current CPC
Class: |
F04B 43/046 20130101;
F04B 43/14 20130101; F04B 19/006 20130101 |
International
Class: |
F04B 19/00 20060101
F04B019/00; F04B 43/04 20060101 F04B043/04 |
Claims
1. A micropump for pumping a fluid, the pump comprising: a tube
formed from a piezoelectric material and having inner and outer
surfaces; a plurality of electrodes comprising first and second
linear arrays of outer electrodes respectively located on different
portions of the outer surface, the plurality of electrodes being
electrifiable to generate vibrations in the tube; and at least one
voltage source that electrifies the electrodes to generate a
displacement traveling wave that propagates along the tube and
causes fluid in the tube to flow through the tube.
2-7. (canceled)
8. A micropump according to claim 1 wherein the tube has a length
less than or equal to about 30 mm.
9. A micropump according to claim 8 wherein the tube has a length
less than or equal to about 15 mm.
10. (canceled)
11. A micropump according to claim 1 wherein the tube has a wall
thickness that is less than or equal to about 0.2 mm.
12. A micropump according to claim 11 wherein the wall thickness is
about equal to 0.1 mm.
13. A micropump according to claim 1 wherein the plurality of
electrodes comprises an inner electrode covering substantially all
the inner surface of the tube.
14. (canceled)
15. A micropump according to claim 1 wherein the first and second
linear arrays are substantially mirror images of each other.
16. A micropump according to claim 15 wherein each of the first and
second linear arrays comprises at least three outer electrodes.
17. A micropump according to claim 16 wherein a first electrode of
the at least three electrodes in each linear array extends along
the tube for a distance equal to about 0.19L, where L is equal to a
length of the tube from a region at a first end of the tube at
which the tube exhibits a node when the electrodes are electrified
to generate the traveling wave to a region of a second end of the
tube at which the tube exhibits an antinode when the electrodes are
electrified to generate the traveling wave.
18. A micropump according to claim 17 wherein a second electrode of
the at least three electrodes in each linear array extends along
the tube from about where the first electrode ends at about 0.19L
to about 0.85L.
19. A micropump according to claim 18 wherein the third electrode
of the at least three electrodes in each linear array extends along
the tube from about where the second electrode ends at about 0.85L
to about the region of the second end of the tube.
20. A micropump according to claim 19 wherein the voltage source
electrifies the first, second, and third electrodes of the first
and second linear arrays with harmonic voltages having a same
frequency.
21. A micropump according to claim 20 wherein a phase difference
between the harmonic voltage applied to the first electrode in each
array and the second electrode in each array is equal to about
192.degree..
22. A micropump according to claim 21 wherein a phase difference
between the harmonic voltage applied to the first electrode in each
array and the third electrode in each array is equal to about
100.degree..
23. A micropump according to claim 20 wherein the harmonic voltages
applied to homologous electrodes in the first and second arrays are
180.degree. out of phase.
24. A micropump for pumping a fluid, the micropump comprising: a
housing having a lumen through which fluid pumped by the micropump
flows and first and second flow ports through which fluid pumped by
the micropump enters or exits the lumen; at least one beam
comprising at least one layer of piezoelectric material and having
a first fixed end fixed to the housing and a second free end free
to exhibit vibratory motion located in the lumen; and a plurality
of electrodes electrifiable to generate a displacement traveling
wave in each of the at least one beam that propagates along the
beam and causes fluid that enters the lumen to flow through and
exit the lumen.
25. A micropump according to claim 24 wherein the at least one beam
comprises one beam.
26. A micropump according to claim 24 wherein the at least one beam
comprises two beams.
27. A micropump according to claim 26 wherein the beams are
parallel to each other.
28. A micropump according to claim 27 wherein the beams are mirror
images of each other.
29-30. (canceled)
Description
RELATED APPLICATIONS
[0001] The present application claims the benefit under 35 U.S.C.
119(e) of U.S. Provisional Applications 61/662,370 filed on Jun.
21, 2012 the disclosure of which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] Embodiments of the invention relate to micropumps for
pumping small volumes of fluid.
BACKGROUND
[0003] Micro-pumps that are operable to convey small volumes of
fluids are finding an increasingly varied range of applications
that include by way of example, pumping fluids in chemical and
medical assay systems, dispensing ink in ink jet printers,
delivering lubricants to moving machine parts, pumping coolants in
integrated circuits, feeding fuel cells, and dosing medications. In
the various functions for which they are used micro-pumps may be
required to convey volumes of fluid at volumetric flow rates that
range from pl/m (picoliters/minute=10.sup.-12 liters/m) to tens of
ml/m (milliliters/minute).
[0004] As material science and engineering technologies become more
sophisticated and capable, many of the devices and components with
which micropumps may be used are being made smaller and
miniaturized. To deliver fluids to the devices, and control fluid
flow in the devices, it can be advantageous for given fluid
volumetric flow rates that are required by the devices to be
provided by smaller micropumps.
[0005] A convenient parameter that may be used as a measure of a
micropump's capacity to deliver fluid relative to its size is a
volumetric flow rate that the micropump provides relative to a
planform area of the micropump. The planform area of a micropump is
an area of a largest cross section of a volume of the micropump in
which the micropump increases pressure of a fluid that it pumps.
For convenience of presentation, a ratio of the pumping capacity of
a micropump in units of volumetric flow per unit time divided by
its planform area may be referred to as a "specific pumping
capacity" of the micropump.
SUMMARY
[0006] An aspect of an embodiment of the invention relates to
providing a micropump having a relatively large specific pumping
capacity, that is, a relatively small size for a fluid volumetric
flow rate that the micropump provides.
[0007] In an embodiment of the invention, the micropump comprises a
tube, hereinafter also referred to as a "pumping tube", formed from
a piezoelectric material. The pumping tube has a configuration of
excitation electrodes and a power supply connected to the
electrodes controllable to electrify the electrodes with time
varying voltages to generate a displacement traveling wave that
propagates from a first end of the pumping tube to a second end of
the pumping tube. In accordance with an embodiment of the
invention, a displacement generated by the traveling wave at a
given location along the pumping tube is a displacement
substantially without distortion of a cross section of the pumping
tube at the given location, relative to, and in a direction
perpendicular to, an axis of the pumping tube. The axis of the
pumping tube, which may also be referred to as an axis of the
micropump, is an axis that passes through centroids of cross
sections of the pumping tube when the pumping tube is not
electrified by the power supply. The displacement traveling wave
transports liquid in the pumping tube in a direction of propagation
of the traveling wave, from the first end of the pumping tube to
the second end of the pumping tube.
[0008] In an embodiment of the invention the traveling displacement
wave may be represented by a function of the form .DELTA.x=A sin
[k(z+Ut)], where propagation of the traveling wave is assumed to be
along the z-axis of a Cartesian coordinate system that is
coincident with the pumping tube axis, and displacement ".DELTA.x"
of the pumping tube cross section from the z-axis is assumed to be
only along the x-axis of the coordinate system. The parameter "k"
is a wave number of the traveling wave, and the coefficient "U" of
time "t" is a propagation velocity of the traveling wave. Depending
on electrification of the electrodes comprised in the pumping tube,
U may be positive or negative, and fluid transport in the pumping
tube may be in either direction along the tube.
[0009] Optionally, the pumping tube has a substantially circular
cross section having substantially same inner radius and a same
outer radius at each point along the micropump axis. In an
embodiment of the invention the micropump has a substantially
square, or rectangular cross section, of same dimensions at each
point along the micropump axis.
[0010] In an embodiment of the invention, a micropump may be
configured having a stationary housing that forms a lumen,
hereinafter a "pumping lumen", through which fluid pumped by the
micropump flows. The micropump, hereinafter also referred to as a
beam drive micropump, comprises at least one "pumping" beam that
protrudes into the pumping lumen and may be excited to vibrate and
pump a fluid through the pumping lumen. One end, a "fixed end" of
the pumping beam is anchored to the housing so that it is
stationary relative to the housing. A second end, a "free end" of
the pumping beam is free to exhibit vibratory motion in the pumping
lumen. The pumping beam comprises at least one layer of a
piezoelectric material and electrodes that may be electrified to
generate a traveling wave that propagates along the beam and causes
vibratory displacements of material in the beam having a component
along a direction perpendicular to the beam length. The vibratory
displacements generate flow of fluid through the pumping volume in
a direction of propagation of the traveling wave
[0011] There is therefore provided in accordance with an embodiment
of the invention, a micropump for pumping a fluid, the pump
comprising: a tube formed from a piezoelectric material and having
inner and outer surfaces; a plurality of electrodes electrifiable
to generate vibrations in the tube; and at least one voltage source
that electrifies the electrodes to generate a displacement
traveling wave that propagates along the tube and causes fluid in
the tube to flow through the tube. Optionally, the tube has a
circular inner cross section. Optionally, the tube has a
rectangular inner cross section. Optionally, the tube has a square
inner cross section.
[0012] In an embodiment, the inner cross section is characterized
by a maximum dimension less than or equal to about 5 mm. In an
embodiment, the inner cross section is characterized by a maximum
dimension less than or equal to about 3 mm. In an embodiment, the
inner cross section is characterized by a maximum dimension less
than or equal to about 1 mm.
[0013] The tube, in an embodiment, may have a length less than or
equal to about 30 mm. The tube may have a length less than or equal
to about 15 mm. The tube may have a length less than or equal to
about 5 mm.
[0014] The tube may have a wall thickness less than or equal to
about 0.2 mm. Optionally, the wall thickness is about equal to 0.1
mm.
[0015] In an embodiment of the invention, the plurality of
electrodes comprises a plurality of outer electrodes formed on the
outer surface and an inner electrode covering substantially all the
inner surface of the tube. Optionally, the outer electrodes
comprise first and second linear arrays of outer electrodes
respectively located on different portions of the outer surface.
Optionally, the first and second linear arrays are substantially
mirror images of each other. Each of the first and second linear
arrays may comprise at least three outer electrodes. Optionally, a
first electrode of the at least three electrodes in each linear
array extends along the tube for a distance equal to about 0.19L,
where L is equal to a length of the tube from a region at a first
end of the tube at which the tube exhibits a node when the
electrodes are electrified to generate the traveling wave to a
region of a second end of the tube at which the tube exhibits an
antinode when the electrodes are electrified to generate the
traveling wave. Optionally, a second electrode of the at least
three electrodes in each linear array extends along the tube from
about where the first electrode ends at about 0.19L to about 0.85L.
The third electrode of the at least three electrodes in each linear
array optionally extends along the tube from about where the second
electrode ends at about 0.85L to about the region of the second end
of the tube.
[0016] In an embodiment of the invention, the voltage source
electrifies the first, second, and third electrodes of the first
and second linear arrays with harmonic voltages having a same
frequency. Optionally, a phase difference between the harmonic
voltage applied to the first electrode in each array and the second
electrode in each array is equal to about 192.degree.. Optionally,
a phase difference between the harmonic voltage applied to the
first electrode in each array and the third electrode in each array
is equal to about 100.degree.. In an embodiment of the invention,
the harmonic voltages applied to homologous electrodes in the first
and second arrays are 180.degree. out of phase.
[0017] There is further provided in accordance with an embodiment
of the invention a micropump for pumping a fluid, the micropump
comprising: a housing having a lumen through which fluid pumped by
the micropump flows and first and second flow ports through which
fluid pumped by the micropump enters or exits the lumen; at least
one beam comprising at least one layer of piezoelectric material
and having a first fixed end fixed to the housing and a second free
end free to exhibit vibratory motion located in the lumen; a
plurality of electrodes electrifiable to generate a displacement
traveling wave in each of the at least one beam that propagates
along the beam and causes fluid that enters the lumen to flow
through and exit the lumen. Optionally, the at least one beam
comprises one beam.
[0018] In an embodiment, the at least one beam comprises two beams.
Optionally, the beams are parallel to each other. Optionally, the
beams are mirror images of each other. In an embodiment the lumen
has a rectangular cross section. In an embodiment the lumen has a
circular cross section.
[0019] In the discussion unless otherwise stated, adjectives, such
as "substantially" and "about", modifying a condition or
relationship characteristic of a feature or features of an
embodiment of the invention, are understood to mean that the
condition or characteristic is defined to within tolerances that
are acceptable for operation of the embodiment for an application
for which it is intended.
[0020] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used to limit the scope of the claimed
subject matter.
BRIEF DESCRIPTION OF FIGURES
[0021] Non-limiting examples of embodiments of the invention are
described below with reference to figures attached hereto that are
listed following this paragraph. Identical structures, elements or
parts that appear in more than one figure are generally labeled
with a same numeral in all the figures in which they appear.
Dimensions of components and features shown in the figures are
chosen for convenience and clarity of presentation and are not
necessarily shown to scale.
[0022] FIGS. 1A and 1B schematically show a cross section and a
perspective view respectively of a micropump before being
electrified to pump a fluid, in accordance with an embodiment of
the invention;
[0023] FIGS. 2A and 2B schematically show a cross section and a
perspective view respectively of the micropump shown in FIGS. 1A
and 1B operating to pump a fluid in accordance with an embodiment
of the invention;
[0024] FIG. 3A schematically shows a graph of values for fluid
velocity of a fluid pumped by a simulated micropump as a function
of electrode configurations of the micropump, in accordance with an
embodiment of the invention;
[0025] FIG. 3B schematically shows a graph of values for volumetric
fluid flow provided by a simulated micropump as a function
dimensions of the micropump pumping tube, in accordance with an
embodiment of the invention;
[0026] FIG. 4 schematically shows a perspective view of a micropump
comprising a pumping tube having a rectangular cross section, in
accordance with an embodiment of the invention;
[0027] FIG. 5 shows a graph of simulated values for specific
pumping capacity of a micropump as a function of planform area
having configuration similar to that of the micropump shown in FIG.
4, in accordance with an embodiment of the invention;
[0028] FIG. 6A-6C schematically shows a beam drive micropump in
accordance with an embodiment of the invention;
[0029] FIG. 6D shows a graph of pumping rate of the beam drive
micropump shown in FIGS. 6A-6C as a function of frequency of
harmonic voltage that electrifies pumping beams in the beam drive
micropump; and
[0030] FIG. 7 schematically shows a beam drive micropump comprising
a single pumping beam, in accordance with an embodiment of the
invention.
DETAILED DESCRIPTION
[0031] FIGS. 1A and 1B schematically show cross section and
perspective views respectively of a micropump 20, coupled to a
panel 60 of a reservoir (not shown) containing a fluid that the
micropump is controlled to pump, in accordance with an embodiment
of the invention.
[0032] Micropump 20 comprises a pumping tube 22 formed from a
piezoelectric material that has a first end 23, a second end 24, an
outer surface 25, an inner surface 26, and an axis 27, which is
assumed to be coincident with the z-axis of a Cartesian coordinate
system 70. The coordinate system has its origin at the first end of
the pumping tube. Optionally, pumping tube 20 has a circular cross
section having same inner and outer radii at each location along
the pumping tube's length.
[0033] In an embodiment of the invention, first end 23 is tightly
held so that it is substantially spatially fixed and immobile, and
second end 24 is loosely held so that it may move. By way of
example, in FIG. 1A pumping tube 20 may be secured to panel 60 at
first end 23 of the pumping tube so that end 23 does not move
relative to the panel. Second end 24 may be seated in an aperture
(not shown) having a radius slightly larger than the outer radius
of pumping tube 22 so that the second end may vibrate freely within
the aperture.
[0034] Inner surface 26 (FIG. 1A) is covered substantially
completely by a common electrode 30. Outer surface 25 is covered by
a first set of "top" excitation electrodes 31-T, 32-T, and 33-T,
and a second set of "bottom" excitation electrodes 31-B, 32-B, and
33-B. Bottom excitation electrodes 31-B, 32-B, and 33-B, may be
mirror images of top sector excitation electrodes 31-T, 32-T, and
33-T respectively. Optionally, each excitation electrode has an
angular extent close to about 180.degree..
[0035] For a total length "L" of pumping tube 22, top and bottom
excitation electrodes 31-T and 31-B extend from about first end 23
of pumping tube 22, to a distance equal to about .alpha..sub.1L
from the first end. Electrodes 32-T and 32-B extend along the
pumping tube from a distance equal to about a.sub.1L from first end
23 to a distance equal to about .alpha..sub.2L from the first end.
Electrodes 33-T and 33-B extend from about a distance
.alpha..sub.2L from the first end to about second end 24 of the
pumping tube. The extents of the excitation electrodes along
pumping tube 22 are indicated in FIG. 1A.
[0036] In an embodiment of the invention, a power supply 40,
schematically shown in FIG. 1B, is connected to and controllable to
electrify excitation electrodes 31-T, 31-B, 32-T, 32-B, 33-T, and
33-B relative to common electrode 30 with time varying voltages
V31-T, V31-B, V32-T, V32-B, V33-T, and V33-B respectively. The
voltages and excitation electrodes may be configured to generate
substantially rigid, non-distorting displacements of the cross
section of pumping tube 22 perpendicular to the z-axis of
coordinate system 70 that propagate as a displacement traveling
wave selectively in either direction along the z-axis. In an
embodiment of the invention the displacement traveling wave is a
harmonic wave substantially dominated by a single frequency.
[0037] Let the displacements be assumed to lie only along the
x-axis of coordinate system 70 and be represented by ".DELTA.x".
Then a displacement of the cross section of pumping tube 22 at time
t and location z generated by electrification of excitation
electrodes 31-T, . . . , 33-B may be described by an expression
.DELTA.x=A sin [k(z+Ut)]. The coefficient, U, of time t is a
propagation velocity of the displacement traveling wave. The
traveling wave generates fluid flow of a fluid in pumping tube 22
at velocity "V.sub.f", in a direction of propagation of the
traveling wave. V.sub.f is an average velocity of flow of the fluid
in the pumping tube. A value for V.sub.f may be estimated from a
velocity field of fluid flow in pumping tube 22 determined from a
solution of Stokes equations that may be used to model fluid flow
in the pumping tube. In FIGS. 1A and 1B and figures that follow,
power supply 40 is assumed to excite micropump 20 to generate a
traveling wave .DELTA.x=A sin [k(z+Ut)] in pumping tube 22 that
pumps a fluid optionally a liquid, such as water, in a direction
from end 23 to end 24 of the pumping tube and out from the
reservoir to which micropump 20 is connected at panel 60.
[0038] In an embodiment of the invention, to excite the
displacement traveling wave, time varying voltages V31-T, V32-T,
V33-T vary harmonically at substantially a same angular frequency,
kU. Optionally, V32-T is equal to about 1.67.times.V31-T and V33-T
is equal to about 1.47.times.V31-T. Optionally, relative to phase
of voltage V31-T, voltages V32-T and V33-T have phases
substantially equal to 192.degree. and 100.degree. respectively.
Voltages V31-B, V32-B, and V33-B are 180.degree. out of phase with
voltages V31-T, V32-T, and V33-T respectively.
[0039] In an embodiment of the invention for which pumping tube 22
has inner and outer radii equal to about 0.77 mm and 1.09 mm and
length about 20 mm, a simulation indicates that for a magnitude of
voltages V31-T, . . . V33-B equal to about twenty volts, micropump
20 may pump a liquid such as water at a rate of about 3 pl/m. In
the simulation the piezoelectric pumping tube was assumed to be
formed from a material having density .rho.=to 7,500 kg/m.sup.3, a
Young's modulus Y=66.times.10.sup.10 N/m.sup.2 a dielectric
constant d.sub.31=-173 pN/m and an electro-mechanical coefficient
k.sub.31=0.41. For an excitation voltage of about 250 volts the
pumping tube traveling wave has an amplitude of about 8 .mu.m,
which generates a liquid flow velocity equal to about 4.5 mm/s and
a flow rate of about 1 .mu.l/m.
[0040] It is noted that operating voltage of a micropump in
accordance with an embodiment of the invention may be lowered by
forming the micropump pumping tube from a plurality of layers of
piezoelectric material interleaved with electrodes. By way of
example, a pumping tube may be formed by producing two optionally
mirror image semicircular cylindrical layered bodies and bonding
the bodies together to form a pumping tube having a circular cross
section.
[0041] A simulation for another micropump in accordance with an
embodiment of the invention for a micropump comprising a pumping
tube 22 having an outer radius of about 2.5 mm and length 25 mm
indicated that the micropump could be operated to pump a fluid at a
volumetric flow rate of about 100 .mu.l/m.
[0042] FIG. 2A shows a schematic cross section of micropump 20
having electrodes 31-T, . . . , 33-B electrified by power supply 40
to generate the traveling wave that propagates from end 23 to end
24 of pumping tube 22 and pumps fluid out of the reservoir bounded
by panel 60. A block arrow 81 schematically represents entry of
fluid into micropump 20 from the reservoir and a block arrow 82
schematically represents fluid exiting the micropump. FIG. 2B
schematically shows a perspective view of micropump 20 pumping
fluid out of the reservoir bounded by panel 60.
[0043] The volumetric fluid flow provided by a micropump in
accordance with an embodiment of the invention is not only a
function of excitation voltages V31-T, . . . V33-B, but is a
relatively complex function of structural parameters of pumping
tube 22. FIG. 3A shows a three dimensional graph of fluid velocity
V.sub.f in m/s simulated for different values of .alpha..sub.1 and
.alpha..sub.2. FIG. 3B shows a three dimensional graph of values
for volumetric flow rate in .mu.l/m for a pumping tube having wall
thickness equal to 0.1 mm, .alpha..sub.1 equal to about 0.19, and
.alpha..sub.2 equal to about 0.85, as a function of pumping tube
length and inner radius. The pumping tube was assumed excited by
excitation voltages having amplitudes equal to about 250 volts. The
graph indicates that a pumping tube having a 3 mm inner radius and
length of about 10 mm may be controlled to pump a fluid at about
300 .mu.l/m. The micropump may have a specific pumping capacity
equal to about 10 cm/m (centimeters per minute) and a ratio of
pumping volume in .mu.l/m to volume of the pump in mm.sup.3 equal
to about 1.
[0044] It is noted that whereas in FIGS. 1A-3B and the discussion
above, a micropump in accordance with an embodiment of the
invention comprises a total of six excitation electrodes and a
common electrode, practice of the invention is not limited to six
excitation electrodes. To provide a desired displacement traveling
wave, more or less than six excitation electrodes may be used.
Generally, more excitation electrodes enable increased fidelity in
generating a desired traveling waveform.
[0045] Whereas FIGS. 1A-3B and the discussion above relate to a
micropump comprising a pumping tube having a circular cross
section, a micropump in accordance with an embodiment of the
invention is not limited to pumping tubes having a circular cross
section. By way of example, FIG. 4 schematically shows a micropump
100 having a pumping tube 122 having a rectangular cross section.
Pumping tube 122 comprises "top" and "bottom" piezoelectric strips
122-T and 122-B mounted to optionally non-piezoelectric side walls
123. The pumping tube has a common electrode 130 and excitation
electrodes 131-T, 132-T, 133-T on top piezoelectric strip 122-T and
mirror image excitation electrodes 131-B, 132-B, 133-B on bottom
piezoelectric strip 122-B. The lengths and locations of the
excitation electrodes on piezoelectric strips 122-T and 122-B are
similar to the length and locations of homologous excitation
electrodes on pumping tube 22.
[0046] Simulations for micropumps in accordance with an embodiment
of the invention, having configurations similar to that show in
FIG. 4 indicate that such micropumps may be configured to provide
relatively large fluid flow rates per unit volume of the pump, and
very large specific pumping capacities, which increase
substantially linearly with maximum cross section area of the
pumping tube. For example, a micropump 100 having a rectangular
cross section 4.6 mm in height along the x-axis direction and width
2 mm along the y-axis direction may have a specific pumping
capacity equal to about 700 .mu.l/m per mm.sup.2 and a volumetric
fluid flow rates per unit volume equal to about 140 .mu.l/m per
mm.sup.3. FIG. 5 schematically shows a graph of specific pumping
capacity as a function of planform area, which exhibits linear
increase of specific pumping capacity with cross section area.
[0047] In the above description of micropumps in accordance with
embodiments of the invention a micropump pumping tube as a whole,
whether configured having a round, square, or other shape cross
section, was described as exhibiting harmonic undulation. In an
embodiment of the invention, a micropump may be configured having a
stationary housing that forms a lumen, hereinafter a "pumping
lumen", through which fluid pumped by the micropump flows. The
micropump comprises at least one "pumping" beam that protrudes into
the pumping lumen and may be excited to vibrate and pump a fluid
through the pumping lumen. One end, a "fixed end" of the pumping
beam is anchored to the housing so that it is stationary relative
to the housing. A second end, a "free end" of the pumping beam is
free to exhibit vibratory motion in the pumping lumen. The pumping
beam comprises at least one layer of a piezoelectric material and
electrodes that may be electrified to generate a traveling wave
that propagates along the beam and causes vibratory displacements
of material in the beam having a component along a direction
perpendicular to the beam length. The vibratory displacements
generate flow of fluid through the pumping volume in a direction of
propagation of the traveling wave.
[0048] FIG. 6A schematically shows a perspective, exploded view of
a beam drive micropump 320 optionally comprising two pumping beams
340 having fixed and free ends 341 and 342 respectively, in
accordance with an embodiment of the invention. FIG. 6B
schematically shows a cross section of beam drive micropump 320
after assembly, along a plane A-A indicated in FIG. 6A.
[0049] Beam drive micropump 320 optionally comprises a housing
block 360 and top and bottom, optionally mirror image, housing
panels 362. Housing block 360 is formed having a cavity 364 that is
open on a top surface 365 of the housing block and on a bottom
surface indicated by a reference numeral 366 but not shown in the
figure. Pumping beams 340 are mounted in cavity 364 with fixed ends
341 anchored to housing block 360, optionally by T-clamps 370, each
T-clamp 370 comprising a mounting block 371 and an anchor stem 372.
To anchor fixed ends 341 to housing block 360, the T-clamp mounting
blocks 371 are fixed, for example by binding, welding, or using
small screws, to top and bottom surfaces 365 and 366 so that anchor
stems 372 press the fixed ends 341 of the pumping beams to anvil
shelves 367 shown in FIG. 6B. Housing panels 362 are comprise
protuberances 363 having hollows 369 (FIG. 6B, 6C) configured to
accommodate T-clamp mounting blocks 371 when the T-clamps and
housing panels are assembled to housing block 360, as schematically
shown on FIGS. 6B and 6C.
[0050] Top surface 365 of housing block 360 is optionally formed
having a gasket groove 368 for receiving a sealing gasket,
optionally an o-ring. Bottom surface 366 is optionally a mirror
image of top surface 365 and is formed having a gasket groove that
is a mirror image of gasket groove 368 formed in top surface 365.
Top and bottom panels 362 may be mounted to top and bottom surfaces
365 and 366 to lock sealing gaskets, not shown, into gasket grooves
368 and seal cavity 364 of housing block 360 to form a pumping
lumen of beam micropump 320. The pumping lumen is referred to by
the same reference numeral, "364", used to refer to cavity 364 in
FIG. 6A. Fluid pumped by beam drive micropump 320 may enter and
exit pumping lumen 364 via flow ports 381 and 382. Optionally the
flow ports are configured to be coupled to flow tubes (not
shown).
[0051] In an embodiment of the invention, each pumping beam 340
comprises a strip 343 of piezoelectric material optionally having a
rectangular cross section perpendicular to the beam length and
having a large common electrode 344 on one side of the strip, and
three excitation electrodes 345, 346, and 347 on the other side of
the strip. Optionally, the large common electrodes 344 of the
pumping beams 340 face each other. Excitation electrode 345
comprised in a pumping beam 340 extends from about fixed end 341 of
the pumping beam, to a distance equal to about .alpha..sub.1L from
the fixed end (see FIG. 6B). Excitation electrode 346 extends along
the pumping beam from a distance equal to about a.sub.1L from fixed
end 341 to a distance equal to about .alpha..sub.2L from the fixed
end. Excitation electrode 347 extends from about a distance
.alpha..sub.2L from the fixed end to about free end 342 of the
pumping beam. The extents of the excitation electrodes along
pumping tube 22 are indicated in FIG. 6B.
[0052] In an embodiment of the invention, excitation electrodes
345, 346, and 346 in each pumping beam 340 are electrified relative
to common electrode 344 to generate a travelling displacement wave
that propagates along the pumping beam and pumps fluid through
pumping lumen 364 in a direction of propagation of the traveling
wave. Electrification of the excitation electrodes may be provided
by any suitable power supply (not shown) connected to excitation
electrodes 345-347 and common electrode 344 by suitable conducting
traces (not shown) formed on or in the pumping beam. Optionally,
the conducting traces are electrically connected to contact pads
(not shown) formed on a contact platform 349 at the fixed end 341
of pumping beam 340.
[0053] In an embodiment of the invention the traveling displacement
wave may be represented by a function of the form .DELTA.x=A sin
[k(z+Ut)]. In the expression for the traveling displacement wave
propagation is along a z-axis schematically shown in FIGS. 6B and
6C and displacement .DELTA.x is along an x-axis indicated in the
figures. FIG. 6C schematically shows pumping beams excited to
vibrate and pump a fluid through pumping lumen 364 in a direction
indicated by block arrows 380.
[0054] By way of a numerical example, a beam drive micropump in
accordance with an embodiment of the invention may comprise a
pumping beam 340 formed from lead zirconate titanate PZT having a
density equal to about 7,400 kg/m.sup.3, piezoelectric coefficient
d.sub.31 equal to about -320.times.10.sup.-12, and elastic modulus
equal to about 60.times.10.sup.-9 N/m.sup.2. The pumping beam may
have length L (FIG. 6B) equal to about 30 mm, width equal to about
2.5 mm and thickness equal to about 0.71 mm. In an embodiment of
the invention .alpha..sub.1L=0.19L and .alpha..sub.2L=0.85L.
Optionally, the pumping beams are positioned in a pumping lumen
having length, width, and height equal to respectively to about 32
mm, about 4 mm and about 5 mm.
[0055] A beam drive micropump having the specifications listed
above was operated to pump water by electrifying excitation
electrodes 345, 346 and 347 with harmonic driving voltages having
amplitudes equal to about 45 V and respective phases equal to
0.degree., 192.degree. and 68.degree.. The volume flow rate of
water provided by the beam drive micropump as a function of
frequency of the harmonic driving voltage is given in a graph 390
shown in FIG. 6D. The pump provided a maximum flow rate at a
frequency of the driving voltage equal to about 2500 Hz.
[0056] As noted above, a beam drive micropump in accordance with an
embodiment of the invention is not limited to having two pumping
beams and may have more or less than two pumping beams. For
example, a beam drive micropump in accordance with an embodiment of
the invention may comprise three pumping beams optionally similar
to pumping beams 340 having lengths parallel to a same z-axis, with
adjacent pumping beams rotated with respect to each other about the
z-axis by 120.degree.. Or a beam drive micropump in accordance with
an embodiment of the invention may comprise four pumping beams
having lengths parallel to a same z-axis, with adjacent pumping
beams rotated with respect to each other about the z-axis by
90.degree..
[0057] FIG. 7 schematically shows a cross section of a beam drive
micropump 400 comprising a single pumping beam 402, in accordance
with an embodiment of the invention. Pumping beam 402 has a fixed
end 403 that is optionally clamped in place by two T-clamps 404. In
an embodiment of the invention the two T-clamps clamp fixed end 403
of pumping beam 402 between them. Optionally, each T-clamp is
formed having a channel 406 that provides for free flow of fluid
into or out of pumping lumen 364 via a flow port 381. FIG. 7
schematically shows beam drive micropump 320 electrified to exhibit
travelling displacement waves that pump fluid from right to left in
the figure in a direction indicated by block arrows 420.
[0058] It is noted that whereas beam drive micropump 320 and 400
are described as having a pumping lumen 364 formed by fixing
housing panels 362 to a housing block 360, and that the pumping
lumen may be assumed from FIG. 6A as having a square or rectangular
cross section, beam drive micropumps in accordance with embodiment
of the invention are not limited to such assemblies and
configurations of pumping lumens.
[0059] For example, one or more pumping beams, optionally similar
to pumping beams 340, may have their respective fixed ends mounted
to a circular bung, which may be press fit to seal a first end of a
cylindrical tube having a pumping lumen in which the bung positions
the pumping beams. The pumping beam bung may have a through hole
optionally formed at its center to allow influx and efflux of fluid
into and out of the pumping lumen. A second end of the cylindrical
tube may be "stoppered" by another bung having a through hole
optionally formed at the center of the bung to accommodate fluid
flow through the pumping lumen.
[0060] In the description and claims of the present application,
each of the verbs, "comprise" "include" and "have", and conjugates
thereof, are used to indicate that the object or objects of the
verb are not necessarily a complete listing of components, elements
or parts of the subject or subjects of the verb.
[0061] Descriptions of embodiments of the invention in the present
application are provided by way of example and are not intended to
limit the scope of the invention. The described embodiments
comprise different features, not all of which are required in all
embodiments of the invention. Some embodiments utilize only some of
the features or possible combinations of the features. Variations
of embodiments of the invention that are described, and embodiments
of the invention comprising different combinations of features
noted in the described embodiments, will occur to persons of the
art. The scope of the invention is limited only by the claims.
* * * * *