U.S. patent application number 10/323035 was filed with the patent office on 2004-06-24 for passive membrane microvalves.
Invention is credited to Christie, Andrew, Dai, Xunhu, Xie, Chenggang.
Application Number | 20040120836 10/323035 |
Document ID | / |
Family ID | 32593093 |
Filed Date | 2004-06-24 |
United States Patent
Application |
20040120836 |
Kind Code |
A1 |
Dai, Xunhu ; et al. |
June 24, 2004 |
Passive membrane microvalves
Abstract
An exemplary device and method for microfluidic transport is
disclosed as providing inter alia a valve membrane sheet (400), an
inlet channel (140) and an outlet channel (150). The valve membrane
sheet effectively confines transport of fluid from the inlet
channel to the outlet channel where fluid may be purged. The valve
membrane sheet also generally provides means for preventing or
otherwise substantially decreasing the incidence of purged fluid
re-entering the inlet channel. Accordingly, the reduction of
backflow generally tends to enhance overall pumping performance and
efficiency. Disclosed features and specifications may be variously
controlled, adapted or otherwise optionally modified to improve
micropump operation in any microfluidic application. Exemplary
embodiments of the present invention representatively provide for
substantially self-priming micropumps that may be readily
integrated with, for example, existing portable LTCC technologies
for the improvement of device package form factors, weights and
other manufacturing and/or device performance metrics.
Inventors: |
Dai, Xunhu; (Gilbert,
AZ) ; Christie, Andrew; (Vancouver, CA) ; Xie,
Chenggang; (Phoenix, AZ) |
Correspondence
Address: |
MOTOROLA, INC.
CORPORATE LAW DEPARTMENT - #56-238
3102 NORTH 56TH STREET
PHOENIX
AZ
85018
US
|
Family ID: |
32593093 |
Appl. No.: |
10/323035 |
Filed: |
December 18, 2002 |
Current U.S.
Class: |
417/413.2 |
Current CPC
Class: |
F16K 2099/008 20130101;
F04B 43/046 20130101; F16K 99/0057 20130101; F16K 99/0001 20130101;
F15C 5/00 20130101; F16K 99/0048 20130101; F16K 2099/0094 20130101;
F16K 99/0015 20130101; F04B 53/106 20130101 |
Class at
Publication: |
417/413.2 |
International
Class: |
F04B 017/00 |
Claims
We claim:
1. A passive membrane valve for use with a microfluidic pump, said
valve comprising: a valve membrane sheet, an inlet channel and an
outlet channel; said inlet channel suitably adapted to receive
fluid for transport across said valve membrane sheet; said valve
membrane sheet comprising an opening region and a valve seating
region; said valve membrane sheet effectively confining transport
of fluid from said inlet channel to said outlet channel where fluid
may be purged; said valve membrane sheet comprising passive means
for substantially restricting backflow of purged fluid back into
said inlet channel wherein said valve seating region seats against
a sealing element.
2. The passive membrane valve of claim 1, wherein said means for
restricting the backflow of purged fluid further comprises: means
for effectively unseating at least a portion of said valve membrane
sheet from said sealing element when the direction of fluid
pressure tends to flow fluid in a direction away from said inlet
channel across said valve membrane sheet toward said outlet
channel; and means for effectively seating said valve membrane
sheet against said sealing element when the direction of fluid
pressure tends to flow fluid in a direction away from said outlet
channel across said valve membrane toward said inlet channel.
3. The passive membrane valve of claim 2, wherein said sealing
element comprises a printed ring.
4. The passive membrane valve of claim 3, wherein said printed ring
comprises at least one of glass, silicone, silicone-based rubber,
rubber and polymer.
5. The passive membrane valve of claim 2, wherein said valve
membrane sheet comprises at least one of an inorganic material, an
organic material, a metal, a metal alloy, silicone, silicone-based
rubber, rubber and polymer.
6. The passive membrane valve of claim 2, further comprising means
for retaining said valve membrane sheet between said inlet channel
and said outlet channel.
7. The passive membrane valve of claim 2, wherein said valve
membrane sheet effectively confines transport of fluid from said
inlet channel to said outlet channel by means of peripheral slits
oriented normal to the direction of fluid transport.
8. The passive membrane valve of claim 7, wherein said peripheral
slits comprise said opening region.
9. A microfluidic pumping system, comprising a passive membrane
valve according to claim 1 and at least one of a pump actuator and
a piezoelectric actuator.
10. The microfluidic pumping system of claim 9, wherein said means
for restricting the backflow of purged fluid comprises: means for
effectively unseating at least a portion of said valve membrane
sheet from said sealing element when the direction of fluid
pressure tends to flow fluid in a direction away from said inlet
channel across said valve membrane sheet toward said outlet
channel; and means for effectively seating said valve membrane
sheet against said sealing element when the direction of fluid
pressure tends to flow fluid in a direction away from said outlet
channel across said valve membrane sheet toward said inlet
channel.
11. The microfluidic pumping system of claim 9, further comprising
means for retaining said valve membrane sheet within a microfluidic
channel.
12. The microfluidic pumping system of claim 9, wherein said pump
actuator comprises at least one of a unimorphic piezoelectric
element and a bimorphic piezoelectric element.
13. The microfluidic pumping system of claim 9, further comprising
a plurality of microfluidic pumps in fluidic communication with
each other.
14. The microfluidic pumping system of claim 13, wherein said
fluidic communication of said microfluidic pumps comprises at least
one of a series configuration and a parallel configuration.
15. A multilayer micropump device, comprising a substrate, the
passive membrane valve according to claim 1, a pump actuator and a
pumping cavity.
16. The multilayer micropump of claim 15, wherein said substrate
comprises at least one of ceramic, metal, glass, polymer and
wood.
17. The multilayer micropump of claim 15, wherein said means for
restricting the backflow of purged fluid comprises means for
effectively seating said valve membrane sheet against said sealing
element when the direction of fluid pressure tends to flow fluid in
a direction away from said outlet channel across said valve
membrane sheet toward said inlet channel.
18. The multilayer micropump of claim 15, wherein said pump
actuator comprises at least one of a unimorphic piezoelectric
element and a bimorphic piezoelectric element.
19. A method of fabricating the multilayer micropump device of
claim 15, comprising: providing a plurality of substrate layers;
forming into said plurality of substrate layers a transport conduit
and a cavity, said transport conduit and said cavity in
microfluidic communication to define a fluid transport path and a
pumping cavity respectively; placing within said fluid transport
path a passive membrane valve according to claim 1; and laminating
each of the plurality of substrate layers to form a substantially
monolithic micropump device.
20. The method of claim 19, wherein said substrate layers comprise
at least one of ceramic, metal, glass, polymer and wood.
21. The method of claim 20, wherein said step of providing ceramic
layers further comprises the step of providing a plurality of green
sheets comprised of a ceramic material dispersed in an organic
binder.
22. The method of claim 21, wherein the step of forming said
channel and said cavity in said plurality of ceramic layers
comprises at least one of mechanically punching and laser drilling
into each ceramic layer.
23. The method of claim 22, further comprising the step of
sintering said ceramic layers to form said monolithic package.
24. The method of claim 23, further comprising the step of
providing a pumping actuator element on a surface of said
monolithic package, said pumping actuator suitably adapted to exert
a pumping force as a result of application of a voltage to the
monolithic micropump package.
25. The method claim 23, further comprising the step of providing a
pumping actuator element embedded in said monolithic package, said
pumping actuator suitably adapted to exert a pumping force as a
result of application of a voltage to the monolithic micropump
package.
Description
FIELD OF INVENTION
[0001] The present invention relates to micropumps, and more
particularly, in one representative and exemplary embodiment, to
piezoelectrically actuated micropumps having passive membrane
valves for improved performance and efficiency in microfluidic
applications.
BACKGROUND
[0002] Development of microfluidic technology has generally been
driven by parallel ontological advancements in the commercial
electronics industry with an ever-increasing demand for
sophisticated devices having reduced part counts, weights, form
factors and power consumption while improving or otherwise
maintaining overall device performance. In particular, advancement
of microfluidic technology has met with some success in the areas
of packaging and the development of novel architectures directed to
achieving many of these aims at relatively low fabrication
cost.
[0003] The development of microfluidic systems, based on for
example, multilayer laminate substrates with highly integrated
functionality, have been of particular interest. Monolithic
substrates formed from laminated ceramic have been generally shown
to provide structures that are relatively inert or otherwise stable
to most chemical reactions as well as tolerant to high
temperatures. Additionally, monolithic substrates typically provide
for miniaturization of device components, thereby improving circuit
and/or fluidic channel integration density. Potential applications
for integrated microfluidic devices include, for example, fluidic
management of a variety of microsystems for life science and
portable fuel cell applications. One representative application
includes the use of ceramic materials to form micro-channels and/or
cavities within a ceramic structure to define, for example, a
monolithic micropump device.
[0004] Conventional pumps and pumping designs have been used in
several applications; however, many of these are generally too
cumbersome and complex for application with microfluidic systems.
For example, existing designs typically employ numerous discrete
components externally assembled or otherwise connected together
with plumbing and/or component hardware to produce ad hoc pumping
systems. Accordingly, conventional pump designs have generally not
been regarded as suitable for integration with portable ceramic
packages, microfluidic technologies or in various applications
requiring, for example, reduced form factor, weight or other
desired performance and/or fabrication process metrics. Moreover,
previous attempts with integrating microfluidic pumps in monolithic
substrates have met with considerable difficulties in producing
reliable fluidic connections and/or hermetic seals capable of
withstanding manufacturing processes and/or operational stress
while maintaining or otherwise reducing production cost.
Accordingly, despite the efforts of prior art pump designs to
miniaturize and more densely integrate components for use in
microfluidic systems, there remains a need for micropumps having
high aspect ratio integrated valves suitably adapted for
incorporation with, for example, a monolithic package.
SUMMARY OF THE INVENTION
[0005] In various representative aspects, the present invention
provides a system and method for fluid transport in microfluidic
systems. A representative design is disclosed as comprising a fluid
inlet cavity, a fluid outlet cavity, a passive membrane valve
disposed substantially between each of the cavities, and means for
moving fluid through the device. An integrated micropump, in
accordance with one embodiment of the present invention, may be
formed utilizing multilayer ceramic technology in which passive
membrane valves are integrated into a ceramic structure; however,
the disclosed system and method may be readily and more generally
adapted for use in any fluid transport system. For example, the
present invention may embody a device and/or method for providing
integrated pumping and/or valving systems for use in fuel cell fuel
delivery and/or partitioning applications.
[0006] One representative advantage of the present invention would
allow for improved process control and manufacturing of integrated
micropump systems at substantially lower cost. Additional
advantages of the present invention will be set forth in the
Detailed Description which follows and may be obvious from the
Detailed Description or may be learned by practice of exemplary
embodiments of the invention. Still other advantages of the
invention may be realized by means of any of the instrumentalities,
methods or combinations particularly pointed out in the Claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Representative elements, operational features, applications
and/or advantages of the present invention reside inter alia in the
details of construction and operation as more fully hereafter
depicted, described and claimed--reference being made to the
accompanying drawings forming a part hereof, wherein like numerals
refer to like parts throughout. Other elements, operational
features, applications and/or advantages will become apparent to
skilled artisans in light of certain exemplary embodiments recited
in the detailed description, wherein:
[0008] FIG. 1 representatively depicts a cross-section, elevation
view of a micropump device package in accordance with one
embodiment of the present invention;
[0009] FIG. 2 representatively illustrates a cross-section,
elevation view of the micropump device package of FIG. 1 during an
intake stroke in accordance with one operational embodiment of the
present invention;
[0010] FIG. 3 representatively illustrates a cross-section,
elevation view of the micropump device package of FIG. 1 during an
output stroke in accordance with another operational embodiment of
the present invention;
[0011] FIG. 4 representatively illustrates a valve membrane sheet
in accordance with one exemplary embodiment of the present
invention;
[0012] FIG. 5 representatively illustrates a valve membrane sheet
in accordance with another exemplary embodiment of the present
invention;
[0013] FIG. 6 representatively illustrates a valve membrane sheet
in accordance with still another exemplary embodiment of the
present invention; and
[0014] FIG. 7 representatively illustrates a valve membrane sheet
in accordance with yet another exemplary embodiment of the present
invention.
[0015] Those skilled in the art will appreciate that elements in
the Figures are illustrated for simplicity and clarity and have not
necessarily been drawn to scale. For example, the dimensions of
some of the elements in the Figures may be exaggerated relative to
other elements to help improve understanding of various embodiments
of the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0016] The following descriptions are of exemplary embodiments of
the invention and the inventors' conceptions of the best mode and
are not intended to limit the scope, applicability or configuration
of the invention in any way. Rather, the following description is
intended to provide convenient illustrations for implementing
various embodiments of the invention. As will become apparent,
changes may be made in the function and/or arrangement of any of
the elements described in the disclosed exemplary embodiments
without departing from the spirit and scope of the invention.
[0017] Various representative implementations of the present
invention may be applied to any system and/or method for fluid
transport. As used herein, the terms "fluid", "fluidic" and/or any
contextual, variational or combinative referent thereof, are
generally intended to include anything that may be regarded as at
least being susceptible to characterization as generally referring
to a gas, a liquid, a plasma and/or any matter, substance or
combination of compounds substantially not in a solid or otherwise
effectively immobile condensed phase. As used herein, the terms
"inlet" and "outlet" are generally not used interchangeably. For
example, "inlet" may generally be understood to comprise any
dross-sectional area or component feature of a device, the flux
through which tends to translate fluid from a volume element
substantially external to the device to a volume element
substantially internal to the device; whereas "outlet" may be
generally understood as referring to any cross-sectional area or
component feature of a device, the flux through which tends to
translate fluid from a volume element substantially internal to the
device to a volume element substantially external to the device. On
the other hand, as used herein, the terms "liquid" and "gas" may
generally be used interchangeably and may also be understood to
comprise, in generic application, any fluid and/or any
translationally mobile phase of matter. As used herein, the term
"purged", as well as any contextual or combinative referent or
variant thereof, is generally intended to include any method,
technique or process for moving a volume element of fluid through
the outlet of a device so as to dispose or otherwise positionally
locate the "purged" volume element external to the device.
Additionally, as used herein, the terms "valve" and "valving", as
well as any contextual or combinative referents or variants
thereof, are generally intended to include any method, technique,
process, apparatus, device and/or system suitably adapted to
control, affect or otherwise parameterize fluid flow scalar
quantities (e.g., volume, density, viscosity, etc.) and/or fluid
flow vector quantities (i.e., direction, velocity, acceleration,
jerk, etc.). Additionally, as used herein, the terms "pump" and
"pumping", or any contextual or combinative referents or variants
thereof, are generally intended to include any method, technique,
process, apparatus, device and/or system suitably adapted to flow
or otherwise translate a fluid volume element from a first location
to a second location.
[0018] A detailed description of an exemplary application, namely a
system and method for pumping a fluid in an integrated microfluidic
package is provided as a specific enabling disclosure that may be
readily generalized by skilled artisans to any application of the
disclosed system and method for microfluidic transport in
accordance with various embodiments of the present invention.
Moreover, skilled artisans will appreciate that the principles of
the present invention may be employed to ascertain and/or realize
any number of other benefits associated with fluid transport such
as, but not limited to: improvement of pumping efficiency;
reduction of device weight; reduction of device form factor;
improved sample loading in microfluidic assays; improvement in
sample throughput; sample multiplexing and/or parallel sample
processing; integration with micro-array techniques and/or systems;
microfluidic sample transport; pumping of fuel and/or fuel
components in a fuel cell system and/or device; and any other
applications now known or hereafter developed or otherwise
described in the art.
[0019] In one representative application, in accordance with an
exemplary embodiment of the present invention, a passive membrane
valve 400, as generally depicted in FIG. 4, is disclosed for
application with a microfluidic pump. Membrane valve 400 generally
comprises opening regions 410 for providing a path for fluid
transport across the valve membrane. In one representative
application, in accordance with an exemplary embodiment of the
present invention, a laminar micropump system, as generally
depicted in FIG. 1 is disclosed. The system generally includes at
least one substantially flexible or otherwise at least partially
deformable material comprising a valve membrane sheet 130, 160. A
piezoelectric membrane 120 is anchored to one surface of substrate
100 via anchoring element 110. Membrane sheets 130, 160 generally
form a substantially hermetic seal when sealed against seating
element 170. In one embodiment, seating element 170 may comprise a
glass ring or other substantially annular feature demonstrating
relatively low surface roughness. The disclosed valving system, in
certain representative embodiments, may include features to control
the effective magnitude of cross-sectional area presented for fluid
acceptance in order to at least partially control or otherwise
parameterize fluid flux through said inlet opening 140 and/or
outlet opening 150. For example, inlet opening 140 and/or outlet
opening 150 may comprise a taper, a flare, a constriction, a
plurality of corrugations, a bend, a pinch, an oblique plane of
fluid acceptance (e.g., wherein inlet opening 140 and/or outlet
opening 150 facial alignment generally may be other than normal to
the instantaneous vector of fluid flow) or such other means,
features and/or methods now known, subsequently developed or
otherwise hereafter described in the art.
[0020] The operation of membrane valves 130, 160 generally provide
passive means for substantially preventing or otherwise controlling
or restricting the backflow of purged outlet fluid into inter alia
the pumping chamber. For example, outlet membrane valve 160
generally permits fluid flow when the flow vector (i.e., the
direction of fluid pressure; also termed the "fluid transport
gradient") corresponds to translation of fluid volume elements away
from inlet opening 140 through fluidic channels toward outlet
opening 150. Additionally, outlet flapper valve 160, in accordance
with representative aspects of the present invention, conjunctively
provides for effective prevention of fluid flow to outlet opening
150 when the instantaneous fluid transport gradient corresponds to
translation of fluid volume elements away from outlet opening 150
through fluidic channels toward inlet opening 140 (i.e.,
"backflow"). In an alternative exemplary embodiment, the pumping
chamber may further or alternatively comprise a mixing chamber, a
reservoir chamber, a reaction chamber and/or a fuel reformer
chamber (in the case of application of the present invention, for
example, to fuel cell systems).
[0021] One exemplary implementation of the present invention may be
manufactured from the substrate representatively illustrated in
FIG. 1, wherein a laminar substrate 100 is provided for the
fabrication of a piezo-driven micropump. Outlet opening 150 is
suitably configured to provide a path for fluid transport to the
pumping chamber. Fluidic channels provide fluidic communication
between the inlet opening 140 and outlet opening 150. Skilled
artisans, however, will appreciate that other channel
configurations and/or circuit geometries may be employed in order
to define inter alia various fluidic transport paths, for example,
in a laminar substrate in accordance with various other embodiments
of the present invention.
[0022] Skilled artisans will appreciate that the term "passive", as
it may refer to valving devices and/or function, generally connotes
the ability of a valve and/or valve device feature so
characterized, to actuate the operation of restriction,
constriction and/or dilation of fluid inlet acceptance and/or fluid
outlet purging in effective correspondence to the forces nominally
inherent to the translation of fluid volume elements through the
valve device. That is to say, when the fluid flow is in a first
direction, the fluidic forces operate to actuate the valve into a
first conformation (e.g., substantially open); and, when the fluid
flow is in a second direction (i.e., for a binary valve, generally
given as the "opposite direction"), the fluidic forces operate to
actuate the valve into a second conformation (e.g., substantially
closed).
[0023] In various exemplary embodiments, passive membrane valves
130, 160 may be fabricated from silicone, silicone-based rubber,
rubber, metal, metal alloy, polymer or such other materials whether
now known or subsequently discovered or otherwise hereafter
described in the art. In an exemplary application, the membrane
valves may comprise a silicone-based rubber material. Additionally,
passive membrane valves 130, 160 may optionally comprise means for
attachment, such as, for example, an extension tab having a
substantially annular retaining ring for securing or otherwise at
least partially immobilizing membrane valve 130, 160 within device
package substrate 100. Various other attachment means and/or
packaging features for retaining, localizing or otherwise disposing
check valves known in the art may be used as well. For example, the
following retaining means may be conjunctively, alternatively or
sequentially employed: adhesives, organic epoxies, a mechanical
anchor, press-fit clips, solder, clamps, seals, adaptors and/or
such other retention, connection or attachment devices, means
and/or methods, whether now known or otherwise hereafter described
in the art.
[0024] FIG. 2 generally depicts two passive membrane valves 230,
160 disposed within an exemplary monolithic package substrate 100
during the intake pumping stroke. During the intake stroke,
actuator element 220 distends away from the substrate surface so as
to generally enlarge the volume of the pumping chamber. Also during
the intake stroke, inlet valve membrane sheet 230 distends away and
unseats from the glass sealing ring seating element beneath the
membrane sheet. FIG. 3 generally depicts two passive membrane
valves 130, 320 disposed within an exemplary monolithic package
substrate 100 during the output pumping stroke. During the output
stroke, actuator element 320 distends toward the substrate surface
so as to generally decrease the volume of the pumping chamber. Also
during the output stroke, output valve membrane sheet 360 distends
away and unseats from the glass sealing ring seating element
beneath the membrane sheet. In one representative embodiment, pump
actuator may comprise a piezoelectric micropump element. In an
exemplary embodiment, piezoelectric element 220 may be secured to
the package substrate 100 by, for example, solder 110. Accordingly,
substrate 100 may comprise solder-wettable features that are
generally provided to permit secure solder attachment of
piezoelectric element 220 and/or a cover. Various other means for
attaching piezoelectric element 220 and/or a cover may include, for
example: epoxy, adhesive and/or such other attachment means and/or
methods whether now known or hereafter described in the art. In yet
another exemplary embodiment of the present invention,
piezoelectric element 220 may alternatively be integrated within
the package substrate; for example, between ceramic layers in a
position substantially internal to the device as the package is
built up.
[0025] As electric current is supplied to the package,
piezoelectric element 120 operates as a deformable diaphragm
membrane whose deformation (i.e., "stroke volume") causes
oscillating over- and under-pressures in the pump chamber. The pump
chamber, in an exemplary embodiment, may be bounded by, for
example, two passive membrane valves 130, 160. The pump actuation
mechanism 120 need not be limited to piezoelectric actuation, but
may alternatively, sequentially or conjunctively be driven by
electrostatic or thermopneumatic actuation or such other means
and/or methods now known, subsequently derived or otherwise
hereafter described in the art.
[0026] During the movement of the diaphragm element (i.e.,
piezoelectric element 120) in a direction which tends to enlarge
the pump chamber volume, an under-pressure is generated in the pump
chamber causing fluid to flow through inlet channel 140 in a flow
direction which causes inlet passive membrane valve 230 to distend
toward piezoelectric element 220 thereby permitting fluid to flow
through membrane valve 230 to enter into the pump chamber. Since
the fluid transport gradient during the under-pressure stroke is
anti-parallel to the fluid flow acceptance conformation of outlet
passive membrane valve 160, membrane valve 160 seals against
seating element 170 so as to at least partial reduce the occurrence
of fluid disposed in outlet channel 150 re-entering into the pump
chamber (i.e., backflow). Accordingly, this component of the pump
cycle is termed the "supply mode" or the "supply stroke".
[0027] In the alternate and next phase of the stroke cycle, the
movement of the diaphragm element 320 in a direction which tends to
reduce the pump chamber volume causes an over-pressure to be
generated in the pump chamber, thereby flowing fluid through outlet
opening 150 as a result of fluid flowing out of the pump chamber in
a flow direction which causes outlet membrane valve 360 to distend
away from diaphragm element 320 thereby permitting fluid to flow
through outlet membrane valve 360 to outlet channel 150. Since the
fluid transport gradient during the over-pressure stroke is
anti-parallel to the fluid flow acceptance conformation of inlet
membrane valve 130, membrane valve 130 seals against the
corresponding seating element so as to at least partial reduce the
occurrence of fluid disposed in the pump chamber from back-flowing
into the inlet channel 140. Accordingly, this component of the pump
cycle is termed the "pumping mode" or the "delivery stroke".
[0028] The volume of the pump chamber upon relaxation of the
actuation diaphragm is known as the dead volume V.sub.0 and the
volume the actuation membrane deflects during a pump cycle
generally defines the stroke volume .DELTA.V. The ratio between the
stroke volume and dead volume may be used to express the
compression ratio E. Due in part to the relatively small stroke of
micro-actuators and the relatively large dead volume, the
compression ratio 1 = V V 0
[0029] is usually relatively small.
[0030] The pressure cycles (i.e., "pressure waves") generated from
the actuation supply and pump modes typically operate to
alternately switch the passive membrane valves. In the limit of the
pump chamber being filled with an ideally incompressible fluid, the
pressure waves would ideally propagate from the actuation diaphragm
to the valves with no net pressure loss--in which case, the
compression ratio is generally not regarded as an important metric
of pump performance and/or efficiency. However, where the fluid
medium is not ideally incompressible, there exists a
compressibility factor .kappa.>0 which may be employed to
characterize the tendency of a real fluid to dampen the propagation
of the actuation pressure wave .DELTA.p. If the pressure change
.DELTA.p falls below a certain value p' (e.g., the threshold
pressure differential for actuation of a valve), the pump generally
will not properly operate. Accordingly, a minimum condition for
operation of any micropump may be expressed as
.vertline..DELTA.p.vertline..gtoreq..vertline.p'51 .
[0031] Given the compressibility .kappa. of a liquid, the pressure
change .DELTA.p may be calculated (if the volume change .DELTA.V
induced by the actuator is known) in accordance with the equation
V.sub.0 +.DELTA.V=V.sub.0(1-.kappa..DELTA.p). If this expression is
substituted into those previously presented, the compressibility
ratio .epsilon. for liquid micropumps may be expressed as
.epsilon..sub.liquid.gtoreq..kappa.- .vertline.p'.vertline..
Accordingly, a threshold valve actuation pressure p' of 1 kPa in
combination with the compression ratio for water .kappa..sub.water
(5*10.sup.-9 m.sup.2/N) would yield a minimum compression ratio
.epsilon..sub.water of 5*10.sub.-6. In this case, where the stroke
volume .DELTA.V is assumed to be 50 nl, the dead volume V.sub.0
generally may not exceed 10 ml. Skilled artisans, however, will
appreciate that the preceding example will generally only hold true
where the pump chamber is completely filled with liquid and no
degassing and/or bubble occlusion occurs during micropump operation
and therefore provides a first-order approximation for the
determination of operational parameters and/or design
specifications.
[0032] In the case of a gas pump, assuming an ideal gas having an
adiabatic coefficient of .gamma.(1.4 for air), at atmospheric
pressure p.sub.0 and an actuation pressure wave of magnitude
.DELTA.p, the following expression may be obtained:
p.sub.0V.sub.0.sup..gamma.=(p.sub.0-
+.DELTA.p)(V.sub.0+.DELTA.V).sup..gamma.
[0033] Accordingly, it may be shown that the criterion for the
compression ratio of a gas micropump may be similarly derived as 2
gas ( p 0 p 0 - p ' ) 1 - 1
[0034] and, in the case of isothermal state transitions, the
adiabatic coefficient .gamma. may be taken as equal to unity. For
the device previously presented for the micropumping of water
(e.g., p'=1 kPa and .DELTA.V=50 nl), the dead volume V.sub.0 for
the same system adapted for the micropumping of air must generally
not exceed 5 .mu.l.
[0035] In conventional micropump operation, gas bubbles may often
remain in the pump chamber during the priming procedure and/or the
liquid may even volatized in response to temperature changes during
operation. In these cases, the expression for the compression ratio
of a liquid
.epsilon..sub.liquid.gtoreq..kappa..vertline.p'.vertline. will no
longer hold true since the compressibility of the gas bubble is
generally much larger than the compressibility of the liquid.
Depending on the volume of the gas bubble, the actuation pressure
wave will be dampened in an amount that may be calculated if the
volume of the gas bubble is substituted for the dead volume in the
appropriate equation presented vide supra. If the gas bubble volume
becomes so large that the actuation pressure wave falls below the
threshold valve actuation pressure, the micropump will fail.
Consequently, in the limit of the entire pump chamber volume being
filled with a gas, the operational design criteria for liquid
self-priming pumps converges to the design criteria for those of
gas micropumps.
[0036] Additionally, in practical applications, the design criteria
may even need to be more stringent to account for higher-order
fluid dynamics. For example, self-priming liquid micropumps must
typically suck the liquid meniscus from the inlet 140 into the pump
chamber, thereby increasing the threshold critical pressure p' in
parity with the surface tension of the meniscus at the juncture
between and/or within, for example, the microfluidic channels and
the microfluidic valves. Those skilled in the art will recognize
that other fluid dynamics and/or parametric contributions may
require consideration in the determination of optimal operational
specifications for a micropump in accordance with the present
invention as they may be employed in a variety of practical
applications and/or operating environments. The same shall be
regarded as within the scope and ambit of the present
invention.
[0037] Skilled artisans will appreciate that various other
configurations or geometries for slit opening regions 410 may be
defined in membrane valve sheet 400 so as to produce substantially
the same result in accordance with other representative embodiments
of the present invention. Opening regions may comprise symmetric
patterns, asymmetric patterns, polygonal geometries 510, slits 610
and/or fanciful or parametric designs 710 as generally depicted,
for example, in membrane valve sheets 500, 600, 700 corresponding
to FIGS. 5, 6 and 7 respectively.
[0038] In accordance with various operational embodiments of the
present invention, very low frequency actuation of the micropump
was able to achieve flow rates in excess of 1.5 mL/min. Skilled
artisans will appreciate that low frequency operation generally
corresponds to low power consumption. Additionally, when driven
with a sinusoidal signal, near silent operation was observed.
[0039] In the foregoing specification, the invention has been
described with reference to specific exemplary embodiments;
however, it will be appreciated that various modifications and
changes may be made without departing from the scope of the present
invention as set forth in the claims below. The specification and
figures are to be regarded in an illustrative manner, rather than a
restrictive one and all such modifications are intended to be
included within the scope of the present invention. Accordingly,
the scope of the invention should be determined by the claims
appended hereto and their legal equivalents rather than by merely
the examples described above. For example, the steps recited in any
method or process claims may be executed in any order and are not
limited to the specific order presented in the claims.
Additionally, the components and/or elements recited in any
apparatus claims may be assembled or otherwise operationally
configured in a variety of permutations to produce substantially
the same result as the present invention and are accordingly not
limited to the specific configuration recited in the claims.
[0040] Benefits, other advantages and solutions to problems have
been described above with regard to particular embodiments;
however, any benefit, advantage, solution to problems or any
element that may cause any particular benefit, advantage or
solution to occur or to become more pronounced are not to be
construed as critical, required or essential features or components
of any or all the claims.
[0041] As used herein, the terms "comprises", "comprising", or any
variation thereof, are intended to reference a non-exclusive
inclusion, such that a process, method, article, composition or
apparatus that comprises a list of elements does not include only
those elements recited, but may also include other elements not
expressly listed or inherent to such process, method, article,
composition or apparatus. Other combinations and/or modifications
of the above-described structures, arrangements, applications,
proportions, elements, materials or components used in the practice
of the present invention, in addition to those not specifically
recited, may be varied or otherwise particularly adapted by those
skilled in the art to specific environments, manufacturing
specifications, design parameters or other operating requirements
without departing from the general principles of the same.
* * * * *