FIELD OF THE DISCLOSURE
- BACKGROUND OF THE DISCLOSURE
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.
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.
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.
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.
Over the years, there have been a number of developments in the area of piezoelectric pumps.
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.
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.
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.
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.
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.
- SUMMARY OF THE DISCLOSURE
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.
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.
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.
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.
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.
- BRIEF DESCRIPTION OF THE FIGURES
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.
FIG. 1 is a schematic view of a piezoelectric element;
FIG. 2 is a schematic view of a series arrangement of piezoelectric elements used in a pump;
FIG. 3 is a schematic view of an alternate embodiment of the arrangement of piezoelectric elements used in a pump;
FIG. 4 is a schematic view of an embodiment of a piezoelectric element of the present disclosure;
FIGS. 5 thru 7 are drawings of an additional embodiment of the construction of a pump using the piezoelectric elements;
FIG. 8 is an overhead view of the stressing of a polymer film for the formation of the piezoelectric elements;
- DETAILED DESCRIPTION OF THE DISCLOSURE
FIG. 9 is a sideview of a stack of polymer films showing voids acting as channels.
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.
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.
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).
Additionally, certain inorganic materials may be used, including but limited to barium titanate (BaTiO3), lead zirconate (PZT), lead titanate, and quartz (SiO2b).
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.