WO2013190507A2

WO2013190507A2 - Micropump

Info

Publication number: WO2013190507A2
Application number: PCT/IB2013/055094
Authority: WO
Inventors: Gabor Kosa; Ori EHRENBERG
Original assignee: Ramot At Tel Aviv University Ltd
Priority date: 2012-06-21
Filing date: 2013-06-21
Publication date: 2013-12-27
Also published as: US20150322932A1; WO2013190507A3; EP2888480A2

Abstract

A micropump for pumping a fluid, the pump comprising: a tube formed from a piezoelectric material and having inner and outer surfaces; a plurality of electrodes electrifiable to generate vibrations in the tube; and at least one voltage source that applies voltages to the electrodes to generate a displacement traveling wave that propagates along the tube and causes fluid in the tube to flow through the tube.

Description

MICROPUMP

RELATED APPLICATIONS

[0001] The present application claims the benefit under 35 U.S.C. 119(e) of U.S.

Provisional Applications 61/662,370 filed on June 21, 2012 the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

[0001] Embodiments of the invention relate to micropumps for pumping small volumes of fluid.

BACKGROUND

[0002] Micro-pumps that are operable to convey small volumes of fluids are finding an increasingly varied range of applications that include by way of example, pumping fluids in chemical and medical assay systems, dispensing ink in ink jet printers, delivering lubricants to moving machine parts, pumping coolants in integrated circuits, feeding fuel cells, and dosing medications. In the various functions for which they are used micro-pumps may be required to convey volumes of fluid at volumetric flow rates that range from pl/m (picoliters/minute = 10^" ^ liters/m) to tens of ml/m (milliliters/minute).

[0003] As material science and engineering technologies become more sophisticated and capable, many of the devices and components with which micropumps may be used are being made smaller and miniaturized. To deliver fluids to the devices, and control fluid flow in the devices, it can be advantageous for given fluid volumetric flow rates that are required by the devices to be provided by smaller micropumps.

[0004] A convenient parameter that may be used as a measure of a micropump' s capacity to deliver fluid relative to its size is a volumetric flow rate that the micropump provides relative to a planform area of the micropump. The planform area of a micropump is an area of a largest cross section of a volume of the micropump in which the micropump increases pressure of a fluid that it pumps. For convenience of presentation, a ratio of the pumping capacity of a micropump in units of volumetric flow per unit time divided by its planform area may be referred to as a "specific pumping capacity" of the micropump.

SUMMARY

[0005] An aspect of an embodiment of the invention relates to providing a micropump having a relatively large specific pumping capacity, that is, a relatively small size for a fluid volumetric flow rate that the micropump provides. [0006] In an embodiment of the invention, the micropump comprises a tube, hereinafter also referred to as a "pumping tube", formed from a piezoelectric material. The pumping tube has a configuration of excitation electrodes and a power supply connected to the electrodes controllable to electrify the electrodes with time varying voltages to generate a displacement traveling wave that propagates from a first end of the pumping tube to a second end of the pumping tube. In accordance with an embodiment of the invention, a displacement generated by the traveling wave at a given location along the pumping tube is a displacement substantially without distortion of a cross section of the pumping tube at the given location, relative to, and in a direction perpendicular to, an axis of the pumping tube. The axis of the pumping tube, which may also be referred to as an axis of the micropump, is an axis that passes through centroids of cross sections of the pumping tube when the pumping tube is not electrified by the power supply. The displacement traveling wave transports liquid in the pumping tube in a direction of propagation of the traveling wave, from the first end of the pumping tube to the second end of the pumping tube.

[0007] In an embodiment of the invention the traveling displacement wave may be represented by a function of the form Δχ = A sin[k(z+Ut)], where propagation of the traveling wave is assumed to be along the z-axis of a Cartesian coordinate system that is coincident with the pumping tube axis, and displacement "Δχ" of the pumping tube cross section from the z-axis is assumed to be only along the x-axis of the coordinate system. The parameter "k" is a wave number of the traveling wave, and the coefficient "U" of time "t" is a propagation velocity of the traveling wave. Depending on electrification of the electrodes comprised in the pumping tube, U may be positive or negative, and fluid transport in the pumping tube may be in either direction along the tube.

[0008] Optionally, the pumping tube has a substantially circular cross section having substantially same inner radius and a same outer radius at each point along the micropump axis. In an embodiment of the invention the micropump has a substantially square, or rectangular cross section, of same dimensions at each point along the micropump axis.

[0010] In an embodiment of the invention, a micropump may be configured having a stationary housing that forms a lumen, hereinafter a "pumping lumen", through which fluid pumped by the micropump flows. The micropump, hereinafter also referred to as a beam drive micropump, comprises at least one "pumping" beam that protrudes into the pumping lumen and may be excited to vibrate and pump a fluid through the pumping lumen. One end, a "fixed end" of the pumping beam is anchored to the housing so that it is stationary relative to the housing. A second end, a "free end" of the pumping beam is free to exhibit vibratory motion in the pumping lumen. The pumping beam comprises at least one layer of a piezoelectric material and electrodes that may be electrified to generate a traveling wave that propagates along the beam and causes vibratory displacements of material in the beam having a component along a direction perpendicular to the beam length. The vibratory displacements generate flow of fluid through the pumping volume in a direction of propagation of the traveling wave

[0011] There is therefore provided in accordance with an embodiment of the invention, a micropump for pumping a fluid, the pump comprising: a tube formed from a piezoelectric material and having inner and outer surfaces; a plurality of electrodes electrifiable to generate vibrations in the tube; and at least one voltage source that electrifies the electrodes to generate a displacement traveling wave that propagates along the tube and causes fluid in the tube to flow through the tube. Optionally, the tube has a circular inner cross section. Optionally, the tube has a rectangular inner cross section. Optionally, the tube has a square inner cross section.

[0012] In an embodiment, the inner cross section is characterized by a maximum dimension less than or equal to about 5 mm. In an embodiment, the inner cross section is characterized by a maximum dimension less than or equal to about 3 mm. In an embodiment, the inner cross section is characterized by a maximum dimension less than or equal to about 1 mm.

[0013] The tube, in an embodiment, may have a length less than or equal to about 30 mm. The tube may have a length less than or equal to about 15 mm. The tube may have a length less than or equal to about 5 mm.

[0014] The tube may have a wall thickness less than or equal to about 0.2 mm. Optionally, the wall thickness is about equal to 0.1 mm.

[0015] In an embodiment of the invention, the plurality of electrodes comprises a plurality of outer electrodes formed on the outer surface and an inner electrode covering substantially all the inner surface of the tube. Optionally, the outer electrodes comprise first and second linear arrays of outer electrodes respectively located on different portions of the outer surface. Optionally, the first and second linear arrays are substantially mirror images of each other. Each of the first and second linear arrays may comprise at least three outer electrodes. Optionally, a first electrode of the at least three electrodes in each linear array extends along the tube for a distance equal to about 0.19L, where L is equal to a length of the tube from a region at a first end of the tube at which the tube exhibits a node when the electrodes are electrified to generate the traveling wave to a region of a second end of the tube at which the tube exhibits an antinode when the electrodes are electrified to generate the traveling wave. Optionally, a second electrode of the at least three electrodes in each linear array extends along the tube from about where the first electrode ends at about 0.19L to about 0.85L. The third electrode of the at least three electrodes in each linear array optionally extends along the tube from about where the second electrode ends at about 0.85L to about the region of the second end of the tube.

[0016] In an embodiment of the invention, the voltage source electrifies the first, second, and third electrodes of the first and second linear arrays with harmonic voltages having a same frequency. Optionally, a phase difference between the harmonic voltage applied to the first electrode in each array and the second electrode in each array is equal to about 192°. Optionally, a phase difference between the harmonic voltage applied to the first electrode in each array and the third electrode in each array is equal to about 100°. In an embodiment of the invention, the harmonic voltages applied to homologous electrodes in the first and second arrays are 180° out of phase.

[0017] There is further provided in accordance with an embodiment of the invention a micropump for pumping a fluid, the micropump comprising: a housing having a lumen through which fluid pumped by the micropump flows and first and second flow ports through which fluid pumped by the micropump enters or exits the lumen; at least one beam comprising at least one layer of piezoelectric material and having a first fixed end fixed to the housing and a second free end free to exhibit vibratory motion located in the lumen; a plurality of electrodes electrifiable to generate a displacement traveling wave in each of the at least one beam that propagates along the beam and causes fluid that enters the lumen to flow through and exit the lumen. Optionally, the at least one beam comprises one beam.

[0018] In an embodiment, the at least one beam comprises two beams. Optionally, the beams are parallel to each other. Optionally, the beams are mirror images of each other. In an embodiment the lumen has a rectangular cross section. In an embodiment the lumen has a circular cross section.

[0019] In the discussion unless otherwise stated, adjectives, such as "substantially" and "about", modifying a condition or relationship characteristic of a feature or features of an embodiment of the invention, are understood to mean that the condition or characteristic is defined to within tolerances that are acceptable for operation of the embodiment for an application for which it is intended.

[0020] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF FIGURES

[0021] Non-limiting examples of embodiments of the invention are described below with reference to figures attached hereto that are listed following this paragraph. Identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are chosen for convenience and clarity of presentation and are not necessarily shown to scale.

[0022] Figs. 1A and IB schematically show a cross section and a perspective view respectively of a micropump before being electrified to pump a fluid, in accordance with an embodiment of the invention;

[0023] Figs. 2A and 2B schematically show a cross section and a perspective view respectively of the micropump shown in Figs. 1A and IB operating to pump a fluid in accordance with an embodiment of the invention;

[0024] Fig. 3 A schematically shows a graph of values for fluid velocity of a fluid pumped by a simulated micropump as a function of electrode configurations of the micropump, in accordance with an embodiment of the invention;

[0025] Fig. 3B schematically shows a graph of values for volumetric fluid flow provided by a simulated micropump as a function dimensions of the micropump pumping tube, in accordance with an embodiment of the invention;

[0026] Fig. 4 schematically shows a perspective view of a micropump comprising a pumping tube having a rectangular cross section, in accordance with an embodiment of the invention;

[0027] Fig. 5 shows a graph of simulated values for specific pumping capacity of a micropump as a function of planform area having configuration similar to that of the micropump shown in

Fig. 4, in accordance with an embodiment of the invention;

[0028] Fig. 6A-6C schematically shows a beam drive micropump in accordance with an embodiment of the invention;

[0029] Fig. 6D shows a graph of pumping rate of the beam drive micropump shown in Figs.

6A-6C as a function of frequency of harmonic voltage that electrifies pumping beams in the beam drive micropump; and [0030] Fig. 7 schematically shows a beam drive micropump comprising a single pumping beam, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

[0031] Figs. 1A and IB schematically show cross section and perspective views respectively of a micropump 20, coupled to a panel 60 of a reservoir (not shown) containing a fluid that the micropump is controlled to pump, in accordance with an embodiment of the invention.

[0032] Micropump 20 comprises a pumping tube 22 formed from a piezoelectric material that has a first end 23, a second end 24, an outer surface 25, an inner surface 26, and an axis 27, which is assumed to be coincident with the z-axis of a Cartesian coordinate system 70. The coordinate system has its origin at the first end of the pumping tube. Optionally, pumping tube 20 has a circular cross section having same inner and outer radii at each location along the pumping tube's length.

[0033] In an embodiment of the invention, first end 23 is tightly held so that it is substantially spatially fixed and immobile, and second end 24 is loosely held so that it may move. By way of example, in Fig. 1A pumping tube 20 may be secured to panel 60 at first end 23 of the pumping tube so that end 23 does not move relative to the panel. Second end 24 may be seated in an aperture (not shown) having a radius slightly larger than the outer radius of pumping tube 22 so that the second end may vibrate freely within the aperture.

[0034] Inner surface 26 (Fig. 1 A) is covered substantially completely by a common electrode 30.

Outer surface 25 is covered by a first set of "top" excitation electrodes 31-T, 32-T, and 33-T, and a second set of "bottom" excitation electrodes 31-B, 32-B, and 33-B. Bottom excitation electrodes 31-B, 32-B, and 33-B, may be mirror images of top sector excitation electrodes 31-T, 32-T, and 33-T respectively. Optionally, each excitation electrode has an angular extent close to about 180°.

[0035] For a total length "L" of pumping tube 22, top and bottom excitation electrodes 31-T and 31-B extend from about first end 23 of pumping tube 22, to a distance equal to about cqL from the first end. Electrodes 32-T and 32-B extend along the pumping tube from a distance equal to about a L from first end 23 to a distance equal to about from the first end.

Electrodes 33-T and 33-B extend from about a distance CC2L from the first end to about second end 24 of the pumping tube. The extents of the excitation electrodes along pumping tube 22 are indicated in Fig. 1A.

[0036] In an embodiment of the invention, a power supply 40, schematically shown in Fig. IB, is connected to and controllable to electrify excitation electrodes 31-T, 31-B, 32-T, 32-B, 33-T, and 33-B relative to common electrode 30 with time varying voltages V31-T, V31-B, V32-T, V32-B, V33-T, and V33-B respectively. The voltages and excitation electrodes may be configured to generate substantially rigid, non-distorting displacements of the cross section of pumping tube 22 perpendicular to the z-axis of coordinate system 70 that propagate as a displacement traveling wave selectively in either direction along the z-axis. In an embodiment of the invention the displacement traveling wave is a harmonic wave substantially dominated by a single frequency.

[0037] Let the displacements be assumed to lie only along the x-axis of coordinate system 70 and be represented by "Δχ". Then a displacement of the cross section of pumping tube 22 at time t and location z generated by electrification of excitation electrodes 31-T, 33-B may be described by an expression Δχ = A sin[k(z+Ut)]. The coefficient, U, of time t is a propagation velocity of the displacement traveling wave. The traveling wave generates fluid flow of a fluid in pumping tube 22 at velocity "Vf", in a direction of propagation of the traveling wave. Vf is an average velocity of flow of the fluid in the pumping tube. A value for Vf may be estimated from a velocity field of fluid flow in pumping tube 22 determined from a solution of Stokes equations that may be used to model fluid flow in the pumping tube. In Figs 1A and IB and figures that follow, power supply 40 is assumed to excite micropump 20 to generate a traveling wave Δχ = A sin[k(z+Ut)] in pumping tube 22 that pumps a fluid optionally a liquid, such as water, in a direction from end 23 to end 24 of the pumping tube and out from the reservoir to which micropump 20 is connected at panel 60.

[0038] In an embodiment of the invention, to excite the displacement traveling wave, time varying voltages V31-T, V32-T, V33-T vary harmonically at substantially a same angular frequency, kU. Optionally, V32-T is equal to about 1.67xV31-T and V33-T is equal to about 1.47xV31-T. Optionally, relative to phase of voltage V31-T, voltages V32-T and V33-T have phases substantially equal to 192° and 100° respectively. Voltages V31-B, V32-B, and V33-B are 180 ⁰ out of phase with voltages V31-T, V32-T, and V33-T respectively.

[0039] In an embodiment of the invention for which pumping tube 22 has inner and outer radii equal to about 0.77 mm and 1.09 mm and length about 20 mm, a simulation indicates that for a magnitude of voltages V31-T, ... V33-B equal to about twenty volts, micropump 20 may pump a liquid such as water at a rate of about 3 pl/m. In the simulation the piezoelectric pumping tube was assumed to be formed from a material having density p = to 7,500 kg/m^, a Young's modulus Y = 66xl0l0 /m^ a dielectric constant dy i = -173 pN/m and an electro-mechanical coefficient k^i = 0.41. For an excitation voltage of about 250 volts the pumping tube traveling wave has an amplitude of about 8 μιη, which generates a liquid flow velocity equal to about 4.5 mm/s and a flow rate of about 1 μΐ/m.

[0040] It is noted that operating voltage of a micropump in accordance with an embodiment of the invention may be lowered by forming the micropump pumping tube from a plurality of layers of piezoelectric material interleaved with electrodes. By way of example, a pumping tube may be formed by producing two optionally mirror image semicircular cylindrical layered bodies and bonding the bodies together to form a pumping tube having a circular cross section.

[0041] A simulation for another micropump in accordance with an embodiment of the invention for a micropump comprising a pumping tube 22 having an outer radius of about 2.5 mm and length 25 mm indicated that the micropump could be operated to pump a fluid at a volumetric flow rate of about 100 μΐ/m.

[0042] Fig. 2A shows a schematic cross section of micropump 20 having electrodes 31-T, 33-B electrified by power supply 40 to generate the traveling wave that propagates from end 23 to end 24 of pumping tube 22 and pumps fluid out of the reservoir bounded by panel 60. A block arrow 81 schematically represents entry of fluid into micropump 20 from the reservoir and a block arrow 82 schematically represents fluid exiting the micropump. Fig. 2B schematically shows a perspective view of micropump 20 pumping fluid out of the reservoir bounded by panel 60.

[0043] The volumetric fluid flow provided by a micropump in accordance with an embodiment of the invention is not only a function of excitation voltages V31-T, ... V33-B, but is a relatively complex function of structural parameters of pumping tube 22. Fig. 3A shows a three dimensional graph of fluid velocity Vf in m/s simulated for different values of cq and <¾· Fig. 3B shows a three dimensional graph of values for volumetric flow rate in μΐ/m for a pumping tube having wall thickness equal to 0.1 mm, cq equal to about 0.19, and <¾ equal to about 0.85, as a function of pumping tube length and inner radius. The pumping tube was assumed excited by excitation voltages having amplitudes equal to about 250 volts. The graph indicates that a pumping tube having a 3 mm inner radius and length of about 10mm may be controlled to pump a fluid at about 300 μΐ/m. The micropump may have a specific pumping capacity equal to about 10 cm/m (centimeters per minute) and a ratio of pumping volume in μΐ/m to volume of the pump in mm^ equal to about 1.

[0044] It is noted that whereas in Figs. 1A - 3B and the discussion above, a micropump in accordance with an embodiment of the invention comprises a total of six excitation electrodes and a common electrode, practice of the invention is not limited to six excitation electrodes. To provide a desired displacement traveling wave, more or less than six excitation electrodes may be used. Generally, more excitation electrodes enable increased fidelity in generating a desired traveling waveform.

[0045] Whereas Figs. 1A - 3B and the discussion above relate to a micropump comprising a pumping tube having a circular cross section, a micropump in accordance with an embodiment of the invention is not limited to pumping tubes having a circular cross section. By way of example, Fig. 4 schematically shows a micropump 100 having a pumping tube 122 having a rectangular cross section. Pumping tube 122 comprises "top" and "bottom" piezoelectric strips 122-T and 122-B mounted to optionally non-piezoelectric side walls 123. The pumping tube has a common electrode 130 and excitation electrodes 131-T, 132-T, 133-T on top piezoelectric strip 122-T and mirror image excitation electrodes 131-B, 132-B, 133-B on bottom piezoelectric strip 122-B. The lengths and locations of the excitation electrodes on piezoelectric strips 122-T and 122-B are similar to the length and locations of homologous excitation electrodes on pumping tube 22.

[0046] Simulations for micropumps in accordance with an embodiment of the invention, having configurations similar to that show in Fig. 4 indicate that such micropumps may be configured to provide relatively large fluid flow rates per unit volume of the pump, and very large specific pumping capacities, which increase substantially linearly with maximum cross section area of the pumping tube. For example, a micropump 100 having a rectangular cross section 4.6 mm in height along the x-axis direction and width 2 mm along the y-axis direction may have a specific pumping capacity equal to about 700 μΐ/m per mm^ and a volumetric fluid flow rates per unit volume equal to about 140 μΐ/m per mm^. Fig. 5 schematically shows a graph of specific pumping capacity as a function of planform area, which exhibits linear increase of specific pumping capacity with cross section area.

[0047] In the above description of micropumps in accordance with embodiments of the invention a micropump pumping tube as a whole, whether configured having a round, square, or other shape cross section, was described as exhibiting harmonic undulation. In an embodiment of the invention, a micropump may be configured having a stationary housing that forms a lumen, hereinafter a "pumping lumen", through which fluid pumped by the micropump flows. The micropump comprises at least one "pumping" beam that protrudes into the pumping lumen and may be excited to vibrate and pump a fluid through the pumping lumen. One end, a "fixed end" of the pumping beam is anchored to the housing so that it is stationary relative to the housing. A second end, a "free end" of the pumping beam is free to exhibit vibratory motion in the pumping lumen. The pumping beam comprises at least one layer of a piezoelectric material and electrodes that may be electrified to generate a traveling wave that propagates along the beam and causes vibratory displacements of material in the beam having a component along a direction perpendicular to the beam length. The vibratory displacements generate flow of fluid through the pumping volume in a direction of propagation of the traveling wave.

[0048] Figs. 6A schematically shows a perspective, exploded view of a beam drive micropump 320 optionally comprising two pumping beams 340 having fixed and free ends 341 and 342 respectively, in accordance with an embodiment of the invention. Fig. 6B schematically shows a cross section of beam drive micropump 320 after assembly, along a plane A-A indicated in Fig. 6A.

[0049] Beam drive micropump 320 optionally comprises a housing block 360 and top and bottom, optionally mirror image, housing panels 362. Housing block 360 is formed having a cavity 364 that is open on a top surface 365 of the housing block and on a bottom surface indicated by a reference numeral 366 but not shown in the figure. Pumping beams 340 are mounted in cavity 364 with fixed ends 341 anchored to housing block 360, optionally by T-clamps 370, each T-clamp 370 comprising a mounting block 371 and an anchor stem 372. To anchor fixed ends 341 to housing block 360, the T-clamp mounting blocks 371 are fixed, for example by binding, welding, or using small screws, to top and bottom surfaces 365 and 366 so that anchor stems 372 press the fixed ends 341 of the pumping beams to anvil shelves 367 shown in Fig. 6B. Housing panels 362 are comprise protuberances 363 having hollows 369 (Fig. 6B, 6C) configured to accommodate T-clamp mounting blocks 371 when the T-clamps and housing panels are assembled to housing block 360, as schematically shown on Figs. 6B and 6C.

[0050] Top surface 365 of housing block 360 is optionally formed having a gasket groove 368 for receiving a sealing gasket, optionally an o-ring. Bottom surface 366 is optionally a mirror image of top surface 365 and is formed having a gasket groove that is a mirror image of gasket groove 368 formed in top surface 365. Top and bottom panels 362 may be mounted to top and bottom surfaces 365 and 366 to lock sealing gaskets, not shown, into gasket grooves 368 and seal cavity 364 of housing block 360 to form a pumping lumen of beam micropump 320. The pumping lumen is referred to by the same reference numeral, "364", used to refer to cavity 364 in Fig. 6A. Fluid pumped by beam drive micropump 320 may enter and exit pumping lumen 364 via flow ports 381 and 382. Optionally the flow ports are configured to be coupled to flow tubes (not shown).

[0051] In an embodiment of the invention, each pumping beam 340 comprises a strip 343 of piezoelectric material optionally having a rectangular cross section perpendicular to the beam length and having a large common electrode 344 on one side of the strip, and three excitation electrodes 345, 346, and 347 on the other side of the strip. Optionally, the large common electrodes 344of the pumping beams 340 face each other. Excitation electrode 345 comprised in a pumping beam 340 extends from about fixed end 341 of the pumping beam, to a distance equal to about cqL from the fixed end (see Fig. 6B). Excitation electrode 346 extends along the pumping beam from a distance equal to about ai L from fixed end 341 to a distance equal to about CC2L from the fixed end. Excitation electrode 347 extends from about a distance CC2L from the fixed end to about free end 342 of the pumping beam. The extents of the excitation electrodes along pumping tube 22 are indicated in Fig. 6B.

[0052] In an embodiment of the invention, excitation electrodes 345, 346, and 346 in each pumping beam 340 are electrified relative to common electrode 344 to generate a travelling displacement wave that propagates along the pumping beam and pumps fluid through pumping lumen 364 in a direction of propagation of the traveling wave. Electrification of the excitation electrodes may be provided by any suitable power supply (not shown) connected to excitation electrodes 345-347 and common electrode 344 by suitable conducting traces (not shown) formed on or in the pumping beam. Optionally, the conducting traces are electrically connected to contact pads (not shown) formed on a contact platform 349 at the fixed end 341 of pumping beam 340.

[0053] In an embodiment of the invention the traveling displacement wave may be represented by a function of the form Δχ = A sin[k(z+Ut)] . In the expression for the traveling displacement wave propagation is along a z-axis schematically shown in Figs. 6B and 6C and displacement Δχ is along an x-axis indicated in the figures. Fig. 6C schematically shows pumping beams excited to vibrate and pump a fluid through pumping lumen 364 in a direction indicated by block arrows 380. [0054] By way of a numerical example, a beam drive micropump in accordance with an embodiment of the invention may comprise a pumping beam 340 formed from lead zirconate titanate PZT having a density equal to about 7,400 kg/m^, piezoelectric coefficient dy i equal to about -320xl0^"1 , _and elastic modulus equal to about 60 xl0^"9 N/m^. The pumping beam may have length L (Fig. 6B) equal to about 30 mm, width equal to about 2.5 mm and thickness equal to about 0.71 mm. In an embodiment of the invention cq L = 0.19L and = 0.85L. Optionally, the pumping beams are positioned in a pumping lumen having length, width, and height equal to respectively to about 32 mm, about 4 mm and about 5 mm.

[0055] A beam drive micropump having the specifications listed above was operated to pump water by electrifying excitation electrodes 345, 346 and 347 with harmonic driving voltages having amplitudes equal to about 45 V and respective phases equal to 0°, 192° and 68°. The volume flow rate of water provided by the beam drive micropump as a function of frequency of the harmonic driving voltage is given in a graph 390 shown in Fig. 6D. The pump provided a maximum flow rate at a frequency of the driving voltage equal to about 2500 Hz.

[0056] As noted above, a beam drive micropump in accordance with an embodiment of the invention is not limited to having two pumping beams and may have more or less than two pumping beams. For example, a beam drive micropump in accordance with an embodiment of the invention may comprise three pumping beams optionally similar to pumping beams 340 having lengths parallel to a same z-axis, with adjacent pumping beams rotated with respect to each other about the z-axis by 120°. Or a beam drive micropump in accordance with an embodiment of the invention may comprise four pumping beams having lengths parallel to a same z-axis, with adjacent pumping beams rotated with respect to each other about the z-axis by

90°.

[0057] Fig. 7 schematically shows a cross section of a beam drive micropump 400 comprising a single pumping beam 402, in accordance with an embodiment of the invention. Pumping beam 402 has a fixed end 403 that is optionally clamped in place by two T-clamps 404. In an embodiment of the invention the two T-clamps clamp fixed end 403 of pumping beam 402 between them. Optionally, each T-clamp is formed having a channel 406 that provides for free flow of fluid into or out of pumping lumen 364 via a flow port 381. Fig. 7 schematically shows beam drive micropump 320 electrified to exhibit travelling displacement waves that pump fluid from right to left in the figure in a direction indicated by block arrows 420. [0058] It is noted that whereas beam drive micropump 320 and 400 are described as having a pumping lumen 364 formed by fixing housing panels 362 to a housing block 360, and that the pumping lumen may be assumed from Fig. 6A as having a square or rectangular cross section, beam drive micropumps in accordance with embodiment of the invention are not limited to such assemblies and configurations of pumping lumens.

[0059] For example, one or more pumping beams, optionally similar to pumping beams 340, may have their respective fixed ends mounted to a circular bung, which may be press fit to seal a first end of a cylindrical tube having a pumping lumen in which the bung positions the pumping beams. The pumping beam bung may have a through hole optionally formed at its center to allow influx and efflux of fluid into and out of the pumping lumen. A second end of the cylindrical tube may be "stoppered" by another bung having a through hole optionally formed at the center of the bung to accommodate fluid flow through the pumping lumen.

[0060] In the description and claims of the present application, each of the verbs, "comprise" "include" and "have", and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of components, elements or parts of the subject or subjects of the verb.

[0061] Descriptions of embodiments of the invention in the present application are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments utilize only some of the features or possible combinations of the features. Variations of embodiments of the invention that are described, and embodiments of the invention comprising different combinations of features noted in the described embodiments, will occur to persons of the art. The scope of the invention is limited only by the claims.

Claims

1. A micropump for pumping a fluid, the pump comprising:

a tube formed from a piezoelectric material and having inner and outer surfaces;

a plurality of electrodes electrifiable to generate vibrations in the tube; and

at least one voltage source that electrifies the electrodes to generate a displacement traveling wave that propagates along the tube and causes fluid in the tube to flow through the tube.

2. A micropump according to claim 1 wherein the tube has a circular inner cross section.

3. A micropump according to claim 1 wherein the tube has a rectangular inner cross section.

4. A micropump according to claim 1 wherein the tube has a square inner cross section.

5. A micropump according to any of claims 2-4 wherein the inner cross section is characterized by a maximum dimension less than or equal to about 5 mm.

6. A micropump according to any of claims 2-4 wherein the inner cross section is characterized by a maximum dimension less than or equal to about 3 mm.

7. A micropump according to any of claims 2-4 wherein the inner cross section is characterized by a maximum dimension less than or equal to about 1 mm.

8. A micropump according to any of the preceding claims wherein the tube has a length less than or equal to about 30 mm.

9. A micropump according to claim 8 wherein the tube has a length less than or equal to about 15 mm.

10. A micropump according to claim 9 wherein the tube has a length less than or equal to about 5 mm.

11. A micropump according to any of the preceding claims wherein the tube has a wall thickness is less than or equal to about 0.2 mm.

12. A micropump according to claim 11 wherein the wall thickness is about equal to 0.1 mm.

13. A micropump according to any of the preceding claims wherein the plurality of electrodes comprises a plurality of outer electrodes formed on the outer surface and an inner electrode covering substantially all the inner surface of the tube.

14. A micropump according to claim 13 wherein the outer electrodes comprise first and second linear arrays of outer electrodes respectively located on different portions of the outer surface.

15. A micropump according to claim 14 wherein the first and second linear arrays are substantially mirror images of each other.

16. A micropump according to claim 15 wherein each of the first and second linear arrays comprises at least three outer electrodes.

17. A micropump according to claim 16 wherein a first electrode of the at least three electrodes in each linear array extends along the tube for a distance equal to about 0.19L, where L is equal to a length of the tube from a region at a first end of the tube at which the tube exhibits a node when the electrodes are electrified to generate the traveling wave to a region of a second end of the tube at which the tube exhibits an antinode when the electrodes are electrified to generate the traveling wave.

18. A micropump according to claim 17 wherein a second electrode of the at least three electrodes in each linear array extends along the tube from about where the first electrode ends at about 0.19L to about 0.85L.

19. A micropump according to claim 18 wherein the third electrode of the at least three electrodes in each linear array extends along the tube from about where the second electrode ends at about 0.85L to about the region of the second end of the tube.

20. A micropump according to claim 19 wherein the voltage source electrifies the first, second, and third electrodes of the first and second linear arrays with harmonic voltages having a same frequency.

21. A micropump according to claim 20 wherein a phase difference between the harmonic voltage applied to the first electrode in each array and the second electrode in each array is equal to about 192°.

22. A micropump according to claim 21 wherein a phase difference between the harmonic voltage applied to the first electrode in each array and the third electrode in each array is equal to about 100°.

23. A micropump according to any of claims 20-22 wherein the harmonic voltages applied to homologous electrodes in the first and second arrays are 180° out of phase.

24. A micropump for pumping a fluid, the micropump comprising:

a housing having a lumen through which fluid pumped by the micropump flows and first and second flow ports through which fluid pumped by the micropump enters or exits the lumen; at least one beam comprising at least one layer of piezoelectric material and having a first fixed end fixed to the housing and a second free end free to exhibit vibratory motion located in the lumen; and

a plurality of electrodes electrifiable to generate a displacement traveling wave in each of the at least one beam that propagates along the beam and causes fluid that enters the lumen to flow through and exit the lumen.

25. A micropump according to claim 24 wherein the at least one beam comprises one beam.

26. A micropump according to claim 24 wherein the at least one beam comprises two beams.

27. A micropump according to claim 26 wherein the beams are parallel to each other.

A micropump according to claim 27 wherein the beams are mirror images of each other.

29. A micropump according to any of claims 24-28 wherein the lumen has a rectangular cross section.

30. A micropump according to any of claims 24-28 wherein the lumen has a circular cross section.