U.S. patent application number 11/304909 was filed with the patent office on 2007-06-21 for piezoelectric pump.
Invention is credited to James Sproat Green.
Application Number | 20070140875 11/304909 |
Document ID | / |
Family ID | 38173716 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070140875 |
Kind Code |
A1 |
Green; James Sproat |
June 21, 2007 |
Piezoelectric pump
Abstract
A method, apparatus and system for a piezoelectric pump wherein
the piezoelectric elements is made from a fluid retention material
that contains voids that are used to transport fluid from one
element of the piezoelectric material to the next in a sequential
fashion. The pump can include the use of a secondary fluid that is
made to act upon the primary fluid through a piston or
membrane.
Inventors: |
Green; James Sproat;
(Allentown, PA) |
Correspondence
Address: |
Jonathan E. Grant
2107 HOUNDS RUN PLACE
Silver Spring
MD
20906
US
|
Family ID: |
38173716 |
Appl. No.: |
11/304909 |
Filed: |
December 16, 2005 |
Current U.S.
Class: |
417/413.2 |
Current CPC
Class: |
F04B 43/0081 20130101;
F04B 19/006 20130101; F04B 43/12 20130101 |
Class at
Publication: |
417/413.2 |
International
Class: |
F04B 17/00 20060101
F04B017/00 |
Claims
1. A piezoelectric pump for providing a new pumping capability for
fluids, said pump comprising: a) at least one piezoelectric element
comprising a piezoelectric material comprising a fluid retention
material having voids contained therein; b) at least one fluid
channel or allowing for the passage of fluid therethrough; c) an
electronic control comprising means for electrically activating the
piezoelectric element; and d) a housing for containing the
assembled piezoelectric element and said fluid channel.
2) The piezoelectric pump in accordance with claim 1, wherein said
at least one piezoelectric element further comprises: a. electrodes
attached on each of two sides of each of said at least one
piezoelectric element; and b. insulation material attached on an
outside portion of said electrodes, said insulation positioned away
from the piezoelectric element.
3) The piezoelectric pump in accordance with claim 2, wherein a)
said electrodes are mounted on two opposing sides of the
piezoelectric elements; and b) insulating elements are mounted
adjacent the electrodes to insulate each electrode from the
adjacent said piezoelectric element and electrode pair.
4) The piezoelectric pump in accordance with claim 3, further
comprising an electronic control system attached to the
electrodes.
5) The piezoelectric pump in accordance with claim 4 wherein the
electronic control system actuates piezoelectric elements in a
sequential fashion.
6) A piezoelectric pump for moving fluid used to operate a piston
or membrane, said piezoelectric pump comprising: a) at least one
piezoelectric element comprised of material having fluid retention
properties, said material having voids therein; b) at least one
channel for the passage of fluid therethrough; c) an electronic
control means for electrically activating the piezoelectric
element; d) a housing for containing the assembled piezoelectric
element and fluid channel; and e) at least one piston or membrane
upon which a first fluid from the piezoelectric element acts on
said piston to move a second fluid.
7) A piezoelectric element, said piezoelectric element comprising:
a) a piezoelectric material comprising a fluid retention material
having voids contained therein.
8) The piezoelectric element in accordance with claim 7, wherein
the element comprises a ring mounted around the piezoelectric
material so as to constrict motion, thereby enhancing the
dimensional movement of the piezoelectric element.
14) A method of pumping fluids from a first location to a second
location, the method comprising: applying a charge to at least one
piezoelectric pump, said at least one piezoelectric pump
comprising: a) a plurality of piezoelectric elements comprising
fluid retention properties and voids therein; b) a sequence of
fluid channels for the passage of fluid through said plurality of
piezoelectric elements; c) an electronic control means for
electrically activating the plurality of said piezoelectric
elements; and d) a housing for containing the assembled plurality
of piezoelectric elements and said sequence of fluid channels;
wherein said voids of said plurality of piezoelectric elements
contract and expand in a sequence to retain and discharge fluid
therefrom so as to move the fluid through the sequence of said
fluid channels.
Description
FIELD OF THE DISCLOSURE
[0001] This disclosure pertains to the field of piezoelectric
pumps, and, in particular, nonmagnetic piezoelectric pumps which
may be implanted inside a living body without causing a later
magnetic interaction problem for Magnetic Resonance Imaging (MRI)
problem for MRI scans.
BACKGROUND OF THE DISCLOSURE
[0002] Piezoelectric materials and their various applications have
been known in the art for a number of years and their use as a
pumping mechanism for fluids are well established. The
piezoelectric effect includes the application of a potential
electrical difference across a piezo-material, such as a crystal,
resulting in the material undergoing a change in size. In one
example, each of the elements of a stack of piezoelectric elements
deforms with two dimensional extension, accompanied by a thickness
deformation that results in the mechanical motion used to move a
piston type structure, the piston being used in a conventional
manner to move a fluid to be pumped.
[0003] The construction of such a piezoelectric pump may be formed
by placing the stack of piezoelectric elements on the mechanical
piston and electrically activating the elements to cause the piston
to move in the desired manner. Other forms of piezoelectric pumps
include various mechanical displacement means wherein the
mechanical motion is provided by the electrically excited
piezoelectric elements that are connected to various types of
mechanical displacement devices.
[0004] One form of a mechanical pump for fluids is known as a
"finger" pump, and includes a series of finger-like elements that
perform a rhythmic, wave-like motion along a flexible tube with the
motion causing the fluid in the tube to be moved from one end of
the tube to the other. This "finger" pump can be constructed using
piezoelectric elements as the "fingers." The use of a varying
electric field applied to the piezoelectric elements, causes a
rhythmic motion used to transport the fluid in the tube.
[0005] Over the years, there have been a number of developments in
the area of piezoelectric pumps.
[0006] U.S. Pat. No. 5,192,197, issued to Culp, discloses a
piezoelectric pump in which a plurality of piezoelectric elements,
noted as waveplates, are resonated electrically by a multiplicity
of electrical phases and used to create traveling waves. The
waveplates are arranged to touch at the wave crests with the fluid
in the volumes between the wave crests carried along with the
rhythmic motion of the waves. It is noted that this pump can be
used to move fluids in either direction by changing the electric
phases to change the direction of the rhythmic motion of the
fingers.
[0007] U.S. Pat. No. 6,004,115, issued to da Costa, discloses a
compressor for refrigeration system wherein a plurality of pistons
comprised of piezoelectric material arranged within a hermetic
shell are caused to compress in adjacent pairs such that fluid
contained in the spaces between the tops of the pistons and the
shell moves from one adjacent piston pair to the next until the
fluid is moved from the entrance of the shell to the exit portion
of the shell. Each of the pistons contract relative to the shell
when in a second energizing condition so as to provide the space
between the tops of the piston and the shell. When in the first
energizing condition, the piston tops occupy the space to the top
of the shell, forcing the fluid to move to an open space. An
electrical energizing system is used to impart electrical signals
to the piezoelectric pistons in a selective fashion to establish
the pattern of first and second energizing conditions, and so cause
the displacement of the fluid from the entrance to the exit of the
compressor.
[0008] U.S. Pat. No. 4,808,084, issued to Tsubouchi et al,
discloses an apparatus for transferring small amount of fluid and
which includes at least three vibration pumps arranged serially,
with a fluid transfer pipe between each of the vibration pumps. The
pumps themselves are comprised of piezoelectric elements that are
caused to vibrate via an electrical signal control system, the
signals applied to each of the adjacent pumps operated at a
predetermined phase difference.
[0009] U.S. Pat. No. 3,418,980, issued to Benson, discloses a fuel
injector-ignition system wherein a stack of piezoelectric elements
are energized in such a fashion so as to cause the stack to deform
axially and move a plunger attached thereto, the axial movement of
the plunger used to draw fuel into an annular chamber.
[0010] U.S. Pat. No. 5,338,164, issued to Sutton, et al. discloses
a positive displacement pump wherein a plurality of chambers in a
stack have diaphragms therein, the diaphragms having an
electro-deformable material associated with each of the diaphragms.
The arrangement of the pump features stacks of chambers having a
common diaphragm between adjacent chambers such that when a
diaphragm is deformed to increase the volume of one chamber, the
adjacent chamber is simultaneously decreased in volume. Thus, a
pumping action is achieved in the pump.
[0011] As noted above, the use of piezoelectric elements for use in
various ways to move fluid from one location to another is known.
However, a piezoelectric material having voids contained within the
body of the material moving fluid by changing shape or size (e.g.
similar to a sponge) has not been proposed.
SUMMARY OF THE DISCLOSURE
[0012] In the present disclosure, a piezoelectric material can be
made porous to absorb fluids. When the absorbent piezoelectric
material is electrically stimulated, the piezoelectric material
changes shape and either draws in or expels any nearby fluid in a
fashion similar to a sponge. A linear arrangement of such absorbing
piezoelectric devices would allow fluid to be passed along from one
element to the next in a bucket brigade fashion.
[0013] In another embodiment of the disclosure, a secondary fluid
can be made to flow into and out of the piezoelectric elements by
the aforementioned action. Specifically, the secondary fluid acts
upon the wall of structure that contains the primary fluid,
creating a pulsating action vis a vis a primary fluid which in turn
moves the fluid through the pump.
[0014] In yet another embodiment of the disclosure, the
piezoelectric elements can be made to act upon a mechanical piston
either directly or via the secondary fluid which moves the primary
fluid. In another embodiment the fluid of the piezoelectric pump
may act upon a fluid filled membrane to move the fluids
therein.
[0015] In one embodiment of the disclosure, a piezoelectric pump
allowing for fluid flow has been developed for use in micro-fluid
delivery systems. A sequential arrangement of piezoelectric
elements is disclosed, with each element of the sequential
arrangement being expandable due to electric excitation applied to
their individual electrodes. Removal of the electrical voltage from
the piezoelectric elements results in the return of the elements to
their original size and shape. Concomitantly (or subsequently) a
change in the size of the contained voids occurs, resulting in the
release of the fluid contained within those voids. Fluid can thus
be made to flow sequentially, from one piezoelectric element to the
adjacent element. The construction of the piezoelectric elements is
comprised of a material that is of a slightly elastic, or
sponge-like form that expands when electrical voltage is applied
thereto, and which contracts when the voltage is removed. Voids
formed during construction of the pump can be used as a fluid
transport pathway or channel either directly, or by the use of a
secondary fluid that is caused to act upon tube or mechanical
piston to move a primary fluid.
[0016] In an alternative embodiment of the disclosure, each element
of the sequential arrangement can contract due to electric
excitation applied to their individual electrodes. Removal of the
electrical voltage from the piezoelectric elements results in the
return of the elements to their original size and shape.
Concomitantly (or subsequently) an increase in the size of the
contained voids occurs, resulting in the absorption of the fluid.
Fluid can thus be made to flow sequentially, from one piezoelectric
element to the adjacent element. The construction of the
piezoelectric elements is comprised of a material that is of a
flexible, or sponge-like form that contracts when electrical
voltage is applied thereto, and which expands when the voltage is
removed. Voids formed during construction of the pump can be used
as a fluid transport pathway or channel either directly, or by the
use of a secondary fluid that is caused to act upon tube or
mechanical piston to move a primary fluid.
BRIEF DESCRIPTION OF THE FIGURES
[0017] FIG. 1 is a schematic view of a piezoelectric element;
[0018] FIG. 2 is a schematic view of a series arrangement of
piezoelectric elements used in a pump;
[0019] FIG. 3 is a schematic view of an alternate embodiment of the
arrangement of piezoelectric elements used in a pump;
[0020] FIG. 4 is a schematic view of an embodiment of a
piezoelectric element of the present disclosure;
[0021] FIGS. 5 thru 7 are drawings of an additional embodiment of
the construction of a pump using the piezoelectric elements;
[0022] FIG. 8 is an overhead view of the stressing of a polymer
film for the formation of the piezoelectric elements;
[0023] FIG. 9 is a sideview of a stack of polymer films showing
voids acting as channels.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0024] Referring to FIG. 1, a fundamental building block of the
present disclosure comprises a body, which may take many forms but
is preferably a sheet or film of piezoelectric material 101. In the
case of a ceramic or porous polymer or plastic structure, the
piezoelectric material body may be a block. Electrodes 102 and 104
are mounted on either side of and in contact with the body 101.
Insulation elements 103 and 105 insulate the respective electrodes
102 and 104 of each body from similar adjacent assemblies.
[0025] An electric charge passing from or between electrode 102 to
104 excites or energizes the piezoelectric material, therein
causing the voids in the body to change their volume. A fluid that
is in contact with the piezoelectric body will be drawn into the
voids as they increase in volume or the fluid will be expelled as
the voids decrease in volume.
[0026] The expansion or contraction of the piezoelectric body (upon
application of an electric charge) will depend in large part on the
types and designs of the material being used. For example, and as
shown in FIG. 9, a plastic material may have voids 160 between
adjacent sheets 161 of polymer film. The application of a charge
may in fact cause the plastic to align itself in such a way as to
eliminate these voids, or, with some plastics, the application of a
charge may cause the plastics to change their shape so as to
increase the size of said voids. Materials which may be used
include a variety of polymer films, including but not limited to
polyvinylidene fluoride (such as PVDF or PVF2), polyparaxyline, and
polypyrrole(Ppy).
[0027] Additionally, certain inorganic materials may be used,
including but limited to barium titanate (BaTiO.sub.3), lead
zirconate (PZT), lead titanate, and quartz (SiO.sub.2b).
[0028] A stack of layered elements are shown in FIG. 2, starting
with insulation element 203, followed by one electrode 202, the
piezoelectric block 201, the other electrode 204, and finally the
other insulation element 205. Sets of four or more such stacks may
be built upon layers with each layer referred to by the letters
`A`, `B`, `C`, and `D`. This ABCD sequence may be repeated multiple
times with all of the respective electrodes of the layers of a
given letter designation being interconnected with their
counterparts of the same letter designation. This cyclic repetition
is maintained for each additional stack or set of stacks. The above
designed stack assembly, which for example, may be in the form a
wafer, will have one or more holes or channels 206 passing through
from an inlet channel to a separate outlet, such that a given
channel, or sequence of channels, will pass through all of the
stacks. Configurations other than wafer stacks are also
anticipated, including rolled configuration shown in FIG. 7.These
channels may be formed as the wafers are fabricated or as they are
assembled.
[0029] Fabrication methods would include the casting of the
piezoelectric material or the laying up of sheets of piezoelectric
material separately formed as printed deposits, or sheets of either
ceramic or polymer piezoelectric material.
[0030] Channels may be a sequence of voids which develop as a part
of the process of forming the specific material such as would be
obtained, for example, in the use of porous ceramics. The channels
may also be formed as included voids which develop as a part of the
geometry or shaping of the material. A lost wax or other process
may be utilized to obtain such voids. Finally, the channels may be
added later in the fabrication process either before or after the
wafers have been assembled by any of the available means of
drilling or machining holes; including mechanical cutting, laser
burning, or any other technique known to those skilled in the art.
Regardless of how the channels are formed, there is no reason to
assume that the channels must be round holes. A variety of channel
shapes can be used to allow the fluid to be pumped by the
piezoelectric stacks from one side to the other.
[0031] Alternatively, the piezoelectric elements can be stacked
such that each body of each piezoelectric element is positioned
next to the body of the next "stacked" piezoelectric element as
shown in FIG. 3. Hence, as the fluid held in the body of
piezoelectric element "A" is released, it will be passed directly
through and taken up by the body of piezoelectric element "B," and
so forth.
[0032] While a sequence of four stacks is used in this description,
other combinations of stacks are possible. The electrical signals
used to operate the stacks may be a digital sequence of a traveling
wave of two or more ON states followed by two or more OFF states.
Such a traveling wave may be generated by a walking ring circuit.
The electrical signals may, alternatively, be linear in the form of
pairs of sine-like waves with the peristaltic action thus obtained
propelling the fluid in the channel in the direction of the
progressing waves or the electrical signals may be a mixed digital
approximation of linear signals.
[0033] The design of the channels should be such as to permit a
high percentage change in volume from the most fully charged state
to the least fully charged state. In one embodiment of the
disclosure, channels have an effective high aspect ratio in cross
section to the flow path, which would maximize restricting the
material expansion of the piezoelectric material into the channel.
The effective extreme width of such a channel would permit the
increase of volume flow, while the narrowness of the alternate
dimension would effectively increase the peristaltic efficiency of
the pump. In situations where the pump may interact chemically or
electrically with the pumped fluid or the surrounding environment,
a thin isolating shield may be included in the channel and exterior
pump design.
[0034] A preferred, but not exclusive, construction form of the
piezoelectric elements is shown in FIG. 4. Disc 401 of the
piezoelectric material is constrained by a rigid structure 402. The
sponge-style pump may be surrounded and contained by a more-or-less
rigid ring, cylinder, or other structure that would force any
physical dimensional changes to take place within the material and
hence into the void spaces. For use within a human or animal body,
this structure may be made of, but not limited to, a non-ferrous
material, such as titanium in order to avoid later difficulties in
the use of MRIs
[0035] Several means may be used to create and/or control voids in
the piezoelectric material during the fabrication process and could
include the addition of a substance to produce small bubbles or
voids. Additionally, a filler material could be added to the
piezoelectric material which could later be removed by either
melting (a lost-wax variant) or dissolved by a solvent or the
like.
[0036] As there is the possibility that the materials used to make
the piezoelectric elements could contaminate the fluid to be
pumped, the voids of the elements can be coated with a substance
that precludes contamination with the material of the elements, or,
as described above, a transport means can include a secondary fluid
transported in the voids of the piezoelectric elements, with that
secondary fluid acting upon either a tube containing the fluid to
be pumped, or upon a mechanical contrivance, such as a piston pump
or the like.
[0037] Another method for fabricating a piezoelectric pump is shown
in FIG. 5 and includes a strip or ribbon of plastic insulator 501
having a single conductor 502 plated or otherwise attached to its
bottom surface and four or more conductors 503 plated or otherwise
attached to its upper surface. The conductors on the upper surface
are substantially parallel to each other and run along the length
of the insulator. The insulating ribbon substrate may be corrugated
or rippled perpendicular to its length as a means of relieving
stress on the attached conductors and as a means for providing flow
channels. FIG. 6. is a cross section of the piezoelectric pump that
includes a showing of the piezoelectric material 601 placed on top
of the electrodes A, B, C, and D.
[0038] As shown in FIG. 7, a paste or putty-like form of
piezoelectric material 701 is thinly applied to and along each of
the multiple conductors 702 on the upper surface. A separating
insulating material 703 may be applied between each strip of
piezoelectric material if necessary or desirable to isolate them
electrically. The ribbon and piezoelectric material are rolled-up
along its length to form a spiral cylinder before the materials are
cured. Separate wires are attached to each of the five or more
conductors and a suitable covering material is placed over the
cylinder. The wire attached to what was the bottom electrode will
be referred to as the common wire and will be the common path for
each of the individual piezoelectric actuators. The wires to the
individual piezoelectric actuators are attached to their respective
walking ring electrical circuit sources.
[0039] The flow channels(s) in the pump may be via voids in the
piezoelectric material or via spaces created between the
piezoelectric material and the substrate, or both. Such spaces can
be created by ripples in either the substrate or in the
piezoelectric material by a controlled combination of unfilled
corrugations or ripples and the careful use of piezoelectric
material that only moderately adheres to the substrate. These same
spaces could also be created using a lost-wax technique whereby the
spaces are initially filled with a low melting-point wax that
prevents the piezoelectric material from occupying the space. The
wax is later melted and removed to create the channels.
[0040] A sheet of polymeric material such as polyvinylidene
fluoride (PVDF or PVF2) will acquire piezoelectric properties when
it is drawn, stretched or otherwise stressed while being subjected
to a strong electrical polarization field. Later, when excited by
an electric charge the sheet will tend to change its dimensionality
along the lines of stress.
[0041] In an alternative embodiment, and as shown in FIG. 8, a
sheet of polymeric material such as PVDF is preferably passed
between two geared wheels while under tension and while being
subjected to a strong electrical polarization field. The sheet will
acquire piezoelectric properties and a rippled or corrugated
surface, especially along the portions of the sheet that is
stressed the most.
[0042] As multiple copies of these piezoelectric sheets are stacked
together the rippled or corrugated surfaces will form voids or
hollow cells between the layers. Later, as these layers receive a
change in electrical charge, the piezoelectric surface will change
its dimensions with the result that the voids will be reduced and a
portion of their liquid contents, if present, will be ejected.
[0043] As shown in FIG. 8, a PVDF sheet may be physically stressed
between either pins or blades while being subjected to a strong
electrical charge. The outer edge of the pins or blades move at
more-or-less the same rate and in the same direction as the PVDF
sheet that moves between them. It should be noted that heat may
also be used to stress the polymer.
[0044] FIG. 9 shows a portion of stack of PVDF sheets with some
resultant voids between them. A sequence of these stacks would be
used to form the pump.
[0045] While presently preferred embodiments have been described
above, various other modifications and adaptations of the instant
invention can be made by those persons skilled in the art without
departing from either the spirit of the invention or the scope of
the appended claims.
* * * * *