US 20070140875 A1
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.
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
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
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
5) The piezoelectric pump in accordance with
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
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.
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.
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.
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.
FIGS. 5 thru 7 are drawings of an additional embodiment of the construction of a pump using the piezoelectric elements;
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
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
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
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
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
As shown in
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
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
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.