Piezoelectric pump

Abstract

Pump (1) intended to pump a fluid between an inlet and an outlet, comprising: an annular piezoelectric transducer (11) extending around a central axis (Δ) and comprising an electrode (12); a resonator (10) connected to the piezoelectric transducer (11) and extending around the central axis (Δ), the resonator thinning towards the central axis (Δ) and deforming under the effect of a polarization of the piezoelectric transducer (11); and a control unit (30) configured to polarize the electrode according to a polarization voltage. The resonator (10) delimits a cavity (2) extending around the central axis (Δ) and configured to receive the fluid. The pump also comprises at least one channel (4) opening out from the cavity (2).Under the effect of the polarization of the piezoelectric transducer (11), a deformation of the resonator (10) occurs, locally and transiently reducing the thickness of the cavity, around the central axis (Δ), the propulsion inducing a suction effect at the center of the cavity (2), facing the intake.

Description

DOMAINE TECHNIQUE

[0001] The technical field of the invention is a pump configured to be actuated by a piezoelectric transducer. ART ANTERIEUR

[0002] Most pumps use moving parts, which can lead to reliability issues, wear, and limited compactness. Peristaltic pumps are commonly used in healthcare. However, repeated squeezing of a hose, which causes fluid to move, can lead to premature hose wear.

[0003] Patent application WO2013 / 41700 describes a pump, which may be implantable, non-peristaltic, with piezoelectric actuation. A sleeve, arranged at the center of a resonator, undergoes bending, under the effect of a rotating deformation of the resonator, generated by piezoelectric transducers activated according to an ultrasonic frequency. The bending of the sleeve generates a pumping effect, which causes the expulsion of the fluid. A reduction in the cross-section of the resonator, in the vicinity of the sleeve or along it, makes it possible to amplify the vibrations propagating to the sleeve. Such a pump is effective. However, it has been found that the sleeve undergoes repeated bending, which can lead to wear. Furthermore, the pump is intended to be coupled to a fluid circuit. Controlling the flow rate depends on the vibration amplitude of the sleeve, which must be controlled by the mechanical load of the fluid circuit, which is not easy.

[0004] We are looking for a pump that is as compact as possible, and preferably as flat as possible.

[0005] In particular, the aim is to make the pumping principle, the frequency and the amplitude of the ultrasonic pumping vibration less dependent on the mechanical coupling of the pump with the fluid circuit.

[0006] Another objective is to design a pump that can pump at a controlled flow rate, with optimized energy expenditure, and that can be particularly compact. EXPOSE DE L'INVENTION

[0007] A first object of the invention is a pump, intended to pump a fluid between an inlet and an outlet, comprising: a first annular piezoelectric transducer, extending around a central axis, and comprising a first electrode; a first resonator, connected to the first piezoelectric transducer, and extending around the central axis, the first resonator being formed of a deformable solid material thinning towards the central axis, the first resonator being configured to deform under the effect of a polarization of the first piezoelectric transducer; a control unit, configured to polarize the first electrode according to a polarization voltage, modulated according to a modulation frequency greater than 20 KHz; the pump being characterized in that: the first resonator delimits a cavity, extending around the central axis, and configured to receive the fluid, the cavity extending, along the central axis, according to a thickness; the pump comprises a first sleeve, connected to the first resonator, opening at the center of the cavity, forming the inlet of the pump; the pump comprises at least one channel, opening from the cavity, the channel extending, along the first resonator, around an axis perpendicular to the central axis, the channel forming the discharge of the pump; such that under the effect of the polarization of the first piezoelectric transducer, a deformation of the resonator occurs, locally and transiently reducing the thickness of the cavity, the deformation propagating around the central axis, and causing a propulsion of a fluid, admitted into the cavity, around the central axis, the propulsion inducing a suction effect at the center of the cavity, facing the inlet.

[0008] According to one possibility, the first transducer comprises at least two distinct angular portions configured to deform differently, under the effect of the polarization applied to the first electrode, so as to generate a deformation of the first resonator propagating around the central axis.

[0009] According to one possibility, the first electrode is segmented into n angular sectors, n being greater than 2, the control unit being configured to polarize two angular sectors of the first electrode respectively by two phase-shifted voltages with a phase shift less than or equal to 2 π n or temporally shifted by an offset less than or equal to 2 π n .

[0010] According to one possibility, the first piezoelectric material comprises at least two different portions, in which the electric dipole moment is oriented oppositely. According to one possibility, the first resonator is arranged facing a support, forming a bottom of the cavity, the cavity extending between the first resonator and the bottom.

[0011] According to one possibility, the first sleeve is coaxial with the central axis.

[0012] According to one possibility, the pump includes a second annular piezoelectric transducer, extending around the central axis, and comprising a second electrode, connected to the control unit; a second resonator, connected to the second piezoelectric transducer, and extending around the central axis, the second resonator being formed of a deformable solid, the second resonator thinning towards the central axis, the second resonator being configured to deform under the effect of a polarization of the second piezoelectric transducer; the second resonator extends opposite the first deformable solid material; the cavity extends between the first resonator and the second resonator.

[0013] According to one possibility, the second transducer comprises at least two distinct angular portions configured to deform successively, under the effect of the polarization applied to each second electrode, so as to generate a deformation of the second resonator, the deformation propagating around the central axis.

[0014] According to one possibility, the second electrode is segmented into n angular sectors, n being greater than or equal to 2, the control unit being configured to polarize two angular sectors of the second electrode respectively by two voltages shifted by a phase shift of 2 π n or temporally shifted by a shift of 2 π n .

[0015] According to one possibility, the second piezoelectric material comprises at least two different portions, in which the electric dipole moment is oriented in opposite directions. According to one possibility: the first electrode is segmented into symmetrical angular sectors, with respect to a first axis of symmetry, and activated in phase opposition; the second electrode is segmented into symmetrical angular sectors, with respect to a second axis of symmetry, and activated in phase opposition; the first axis of symmetry is orthogonal to the second axis of symmetry.

[0016] The pump may include a second sleeve, connected to the second resonator, and opening into the center of the cavity.

[0017] The second sleeve may be coaxial with the central axis of the cavity.

[0018] The modulation frequency can be higher than 100 KHz.

[0019] According to one possibility: the first electrode is segmented into n angular sectors, nbeing greater than or equal to 2, the control unit is configured to address a polarization signal successively to each angular sector; the pump comprises a control unit, connected to at least one angular sector of the first electrode, the control unit being configured to detect a control signal between two successive polarization signals.

[0020] Preferably, the thickness of the cavity is less than 1 mm.

[0021] According to one possibility, the control unit is configured to bias the first electrode according to a frequency bias signal, by performing a frequency sweep according to a finite number of successive discrete frequencies.

[0022] According to one possibility, the internal surface of the cavity comprises at least one hydrophobic part.

[0023] A second object of the invention is a peristaltic pump, intended to pump a liquid along a capillary, the pumping resulting from a compression of the capillary exerted successively, in a pumping direction, the pump comprising: a first annular piezoelectric transducer, extending around a central axis, and configured to be polarized by a first electrode; a first deformable solid material, connected to the first piezoelectric transducer, and extending around the central axis, the first deformable solid material thinning towards the central axis, the first deformable solid material forming a first resonator configured to deform under the effect of a polarization of the piezoelectric transducer; a control unit, configured to polarize the first electrode according to a polarization voltage, modulated according to a modulation frequency greater than 20 KHz; the pump being characterized in that: the capillary is arranged against the resonator, around the central axis; so that under the effect of the polarization of the first electrode, a deformation of the first resonator occurs, the deformation propagating around the central axis, and causing the compression of the capillary filled with a liquid around the central axis, the propulsion inducing a suction effect in the center of the cavity, facing the intake.

[0024] The capillary can extend around the sleeve, forming several turns, so that each turn is successively deformed, along the sleeve.

[0025] The first resonator may comprise a surface, in particular a flat surface, forming a support. The capillary may be arranged against the support, such that the capillary undergoes a progressive deformation resulting from the deformation of the first resonator. The capillary may form a turn around the central axis, such that under the effect of the deformation of the resonator, the turn is deformed by a deformation rotating around the central axis.

[0026] The pump may comprise two resonators, arranged one against the other; The capillary may be arranged in a space between the two resonators, around the central axis, so that the capillary undergoes a progressive deformation resulting from the deformation of the first resonator and the second resonator. The capillary may form a turn around the central axis, so that under the effect of the deformation of the first and second resonators, the turn is deformed by a deformation rotating around the central axis.

[0027] The invention will be better understood by reading the description of the exemplary embodiments presented in the remainder of the description, in conjunction with the figures listed below. FIGURES

[0028] THE figures 1A à 1E describe a first embodiment of the invention. The figures 2A et 2B describe a second embodiment of the invention. The figure 3 illustrates a frequency sweep. The figure 4A represents a segmentation of an electrode into angular sectors. The figure 4B shows a time sequence of electrode control described in connection with the figure 4A . THE figures 5A et 5B show one embodiment of a peristaltic pump. The figures 6A, 6B et 6C show another embodiment of a peristaltic pump. The figure 7 illustrates a variant of the pump described in connection with the figures 6A à 6C . EXPOSE DE MODES DE REALISATION PARTICULIERS

[0029] THE figures 1A à 1E describe a first embodiment of a pump according to the invention. This is a pump comprising: a first annular piezoelectric transducer 11, extending around a central axis Δ comprising a first layer of a piezoelectric material 13 between at least a first electrode 12 and a first counter electrode 14 on the other hand. a first deformable solid material 10, extending around the central axis Δ, which, under the action of the first piezoelectric transducer 11, forms a first resonator. The first resonator 10 is symmetrical with respect to the central axis Δ. a second annular piezoelectric transducer 21, around the central axis Δ, comprising a first layer of a piezoelectric material 23 between at least a second electrode 22 and a second counter electrode 24 on the other hand. a second deformable solid material 20, extending around the central axis Δ, which, under the action of the second piezoelectric transducer 21, forms a second resonator. The second resonator is symmetrical with respect to the central axis Δ.

[0030] The first resonator 10 and the second resonator 20 are annular, around the central axis Δ. They thin towards the latter. Thus, their thickness, defined parallel to the central axis Δ, decreases as a function of the distance from the central axis Δ. The thinning makes it possible to increase the amplitude of the vibrations propagating in each resonator.

[0031] Each resonator extends from a planar portion to an end formed by a cylindrical sleeve 3 1 , 3 2 described below. The planar portion allows mechanical coupling with a piezoelectric transducer.

[0032] The outer radius R of each resonator, defined around the central axis Δ, can extend up to 50 mm, or more. The flat portion of each resonator extends beyond a first radius R 1 , less than the previously defined outer radius R . Below the first radius R 1 , each resonator has a portion that tapers towards the central axis Δ. The first radius R 1 is for example equal to 50% of the outer radius R of the resonator.

[0033] The first resonator 10 is assembled facing the second resonator 20. A cylindrical cavity 2 extends between the first resonator 10 and the second resonator 20. The thickness of the cavity, parallel to the central axis, is preferably less than 2 mm and is for example of the order of 1 mm. In the example shown, the first resonator and the second resonator are symmetrical along a median plane PM perpendicular to the central axis Δ. The minimum thickness depends on the pumping force to be deployed to overcome so-called static forces opposing the movement of the fluid, for example forces related to friction or surface tension. The minimum thickness may also depend on the operating conditions of the pump, for example movements to which the pump is subjected, for example when the pump is implanted in a living body or when the pump is embedded in a mobile system, for example a vehicle or a robot, subject to jerks.

[0034] Surface conditions that reduce static forces are described below.

[0035] The first resonator extends to a first sleeve 3 1 , cylindrical, coaxial with the central axis Δ, and opening into the cavity 2. The diameter of the sleeve 3 1 is between approximately 0.2 mm and 2 mm and preferably close to 1 mm. The first sleeve 3 1 can be formed by an extension of the first resonator. The first sleeve 3 1 is open, so as to form a first inlet 1 i of the pump. The radius of the first sleeve forms an internal radius of the first resonator 10.

[0036] The pump may comprise a second sleeve 3 2 , cylindrical, coaxial with the central axis Δ, opening into the cavity 2. The diameter of the sleeve 3 2 may be identical to the diameter of the first sleeve 3 1 . The second sleeve 3 2 may be formed by an extension of the second deformable resonator. The second sleeve 3 2 may be open, so as to form a second inlet 1' i of the pump.

[0037] Each sleeve and cavity are sized so that the flow of liquid inside them is subject to capillary forces that are greater than gravity. Thus, in the absence of activation of each resonator, the liquid is kept stationary, in each sleeve and in cavity 2, by the action of capillary forces. This makes it possible to form a pump without moving parts, limiting the risk of leakage.

[0038] The cavity 2 is delimited, in a radial direction, perpendicular to the central axis Δ, by a rib 5, the latter connecting the first resonator 10 to the second resonator 20.

[0039] Preferably, the inner wall of the cavity is coated with a hydrophobic material. The presence of the hydrophobic material can facilitate the minimization of frictional forces and surface tension forces at the interface between the fluid and the material on or in which the ultrasonic waves propagate, so as to facilitate the fractionation of this fluid. Combined with ultrasonic vibrations, a hydrophobic coating allows a fractionation of the liquid into microdroplets, or liquid fractions, which increases the mobility of the liquid. This minimizes the pumping force. Around the central axis, by centrifugation effect, as described later. The inner wall of each sleeve can be coated with a hydrophilic material. The height of each sleeve, along the central axis, is approximately 2 or 3 mm. This makes it possible to form a particularly flat pump.

[0040] More generally, the internal surface of the cavity is advantageously hydrophobic either following functionalization of the parts of each resonator delimiting the cavity, or by appropriate structuring of the latter, for example a grooving type texturing or a formation of microchannels.

[0041] Generally speaking, the pump design aims to optimize the surfaces along which energy is transmitted to the fluid: the design aims to distribute the fluid along the internal surfaces of the cavity, the latter preferably being made hydrophobic. The geometric configuration used, according to which the fluid is displaced in a cavity with a high surface area to volume ratio, favors the displacement of the fluid along the surface of the resonator. To this end, the diameter of the cavity is greater than its thickness, and preferably at least 5 or 10 times greater than its thickness. This configuration, essentially surface-based, minimizes the energy to be supplied to the fluid. This avoids transmitting excess energy to a large volume of fluid, inducing a risk of cavitation.

[0042] Note that this is a counterintuitive configuration, as the usual practice is to push a thick volume. When the fluid is distributed in a thin film, we obtain a creeping effect of the fluid on the internal wall of the cavity.

[0043] The radius of the cavity, perpendicular to the Δ axis, is greater than the radius of the sleeve or each sleeve. The radius of the cavity is preferably at least twice to 10 times greater than the diameter of the sleeve or each sleeve.

[0044] A channel 4, extending between the first resonator 10 and the second resonator 20, opens into the cavity 2. The channel 4 extends in the radial direction, perpendicular to the central axis Δ. The channel 4 forms an outlet 1 o of the pump 1.

[0045] Each deformable solid material, forming the first and second resonator can be of the metal type (titanium, stainless steel, aluminum or aluminum alloy, brass, or other copper-based alloy, or nickel-based alloy), inorganic material (glass), organic material (PEEK), alumina without limitation of choice of other materials outside this non-exhaustive list.

[0046] Each layer of piezoelectric material may be formed from a PZT (Lead Zirconate Titanate) type material, in particular the references PZ26, PZ27, PZ46 and PZ29 from Ferroperm. Preferably, the coefficients d33 and d31, which account for the coefficient of the deformation observed for an applied electric field (also perceived as a density of charges collected for an applied stress), are respectively: of at least 200 pC / N and preferably above 570 pC / N for the coefficient d33 quantifying the response of the piezoelectric material in a direction parallel to the direction of the applied electric field. less than -50 pC / N and preferably of the order of -240 pC / N. for d31, which quantifies the response of the piezoelectric material in a direction perpendicular to the direction of the applied electric field.

[0047] The pump comprises a control unit 30, connected to the first electrode 12 and to the second electrode 22, and allowing a frequency-modulated bias voltage to be applied to them. The modulation frequency depends on the size and material forming each resonator. When the diameter of each resonator is 50 mm, the modulation frequency may be approximately 25 kHz. When the diameter of each resonator is 25 mm, the modulation frequency may be approximately 50 kHz. When the diameter of each resonator is 13 mm, the modulation frequency may be approximately 100 kHz. In all cases, the modulation frequency is ultrasonic, so as to avoid generation of an audible sound.

[0048] The counter electrodes 14, 24 can be left at a floating potential or connected to a fixed potential, for example a ground.

[0049] According to one possibility, the first and / or the second electrode can be annular. In this case, the first transducer and the second transducer are segmented, into angular sectors, so as to present, between two adjacent angular sectors, opposite electric dipole moments. Each angular sector can extend according to an angular value pocket of 2 π M , Or M denotes the number of different angular sectors of the transducer.

[0050] According to one possibility, the first transducer and the second transducer are annular and the first and / or the second electrode is segmented according to angular sectors of 2 π N , where N denotes the number of angular sectors. According to one possibility, each angular sector can extend by a value a few degrees less than 2 π N ,so as to promote isolation between two adjacent sectors of the electrode. The control unit 30 is configured to apply a phase shift or a delay of the polarization voltage between two adjacent sectors 12 1 , 12 2 of 2 π N , Or N corresponds to the numbers of the sectors of the first electrode. The same is true for the second electrode, which can be segmented into adjacent sectors 22 1 , 22 2 . When the polarization voltage is sinusoidal, 2 π N corresponds to a phase shift. When the polarization voltage is impulse, 2 π N phase shift corresponds to a time delay T N with respect to a characteristic time which is the main resonance period T of the actuator. When the bias voltage is pulsed, it is usual, but not necessary, for each pulse to be in the form of a square wave, with a duration less than or equal to a quarter of the resonance period T of the resonator.

[0051] On the figures 1B et 1C , a first possibility of arrangement of the pump has been represented. In this example: the first piezoelectric transducer comprises a first portion 13 1 and a second portion 13 2 , forming two angular half-sectors, and respectively having permanent electric dipole moments oriented in opposite directions: M = 2. The electric dipole moments are denoted -P and +P. The first piezoelectric transducer 13 is polarized by a first annular, non-segmented electrode 11, according to the voltage Vcos(wt). The first piezoelectric transducer is segmented along an axis X parallel to the median plane PM. The second piezoelectric transducer 23 comprises a first portion 23 1 and a second portion 23 2 , forming two angular half-sectors, and respectively having permanent electric dipole moments -P and +P oriented in opposite directions: M= 2. The second piezoelectric transducer 23 is polarized by a second annular, non-segmented electrode 22, according to the voltage Vsin(wt). The second piezoelectric transducer is segmented along a Y axis parallel to the median plane PM, perpendicular to the X axis.

[0052] The angle of π 2 between the X and Y axes, segmenting the transducers 13, 23, combined with the phase shift of π 2 bias voltages of the first and second electrodes, causes rotation of the cavity compression by angle dials π 2 , at the polarization frequency. Thus, under the effect of the respective polarizations of the first electrode and the second electrode, combined with the spatial segmentation of the electrical moments of the first and second piezoelectric transducers, the resonators 10 and 20 deform periodically, each deformation causing a rotating compression of the cavity 2 with a maximum of the deformation located inside the radius R1.

[0053] The deformation of cavity 2 rotates around the central axis Δ, due to the polarization voltages being out of phase with each other. The compression of the cavity, propagating in a circular manner, causes centrifugation of the liquid. This results in a depression forming at the central part of cavity 2, facing the sleeves. This promotes the admission of a fluid, liquid or gas into the cavity, through one of the sleeves. The opposite sleeve can allow the admission of a complementary fluid. In this case, the pump can mix the fluid and the complementary fluid. Alternatively, one of the sleeves allows the admission of a liquid while the opposite sleeve can admit a gas, which then mixes with the pumped liquid. This can, for example, be oxygen, to meet the oxygenation needs of a liquid.

[0054] When two fluids are mixed, a first fluid can be supplied, through the first sleeve, for a short time while a second fluid can be supplied, through the second sleeve, for a longer time.

[0055] The device's ability to pump gas allows for complete emptying of the cavity. This also allows the internal wall of the cavity to dry when gas is pumped.

[0056] After use, cavity 2 can be cleaned and / or sanitized with liquid cleaning or antiseptic liquids. It can then be dried when gas is pumped. The pumping of gas induces a gas flush, which leads to drying. Drying is accelerated when the inner wall of the cavity is hydrophobic.

[0057] It is therefore advantageous that the pump can pump either liquid or gas.

[0058] Centrifugation tends to press the pumped liquid against the contour 5 of the cavity. The liquid can be evacuated through channel 4. Preferably the surface of the channel is hydrophilic, which facilitates the admission of the liquid into the channel, then its evacuation.

[0059] Another transducer configuration is shown in the figures 1D et 1E . In these figures, the first and second transducers are annular. Each transducer has, all around the ring, the same electric dipole moment. The rotating deformation of the cavity is obtained by segmenting the first electrode 12 and the second electrode 22 respectively into two sectors 12 1 , 12 2 and two sectors 22 1 , 22 2 . The first and second electrodes are respectively segmented along the X axis and the Y axis. The respective sectors of the first and second electrodes, which face each other, are polarized by phase-shifted voltages of π 2 . As in the previous case, this induces a rotating deformation of the cavity, at an ultrasonic frequency, causing the centrifugation of the liquid, and a pumping effect by forming a depression in the center of the cavity.

[0060] In the configuration described in connection with the figure 1A , one of the sleeves can be closed. The closure of the sleeve can be removable, so as to allow access, through the sleeve, for cleaning, or to functionalize the surfaces of the resonator delimiting the cavity. The functionalization can consist of applying a hydrophobic coating on the internal surfaces of the cavity, and hydrophilic at the level of the inlet sleeve or the exhaust channel.

[0061] THE figures 2A à 2B describe another embodiment in which a single resonator 10 is used. The resonator 10 is as described in connection with the figure 1A .

[0062] Each first electrode is obtained by segmenting a first annular electrode 12, forming angular sectors 12 1 , 12 2 , 12 3 , 12 4 extending according to an angular movement of π 2 . In the example shown on the figures 2A et 2B , each angular sector extends according to π 2 steradians. Two diametrically opposed sectors 12 1 12 3 are polarized by a voltage Vsin(wt) out of phase with π 2 compared to the other two diametrically opposed sectors 12 2 12 4.

[0063] The transducer 13 is divided into two half-rings whose electric moments are opposite, so that the sectors 12 1 , 12 2 polarize the half-ring with electric dipole moment -P, the other two sectors 12 3 , 12 4 polarizing the half-ring with opposite electric dipole moment.

[0064] The cavity 2 extends between the resonator 10 and a support 6, forming a bottom. A rib 5 allows the connection between the resonator 10 and the support 6. When the bottom is made of duralumin aluminum alloy, for a frequency of 100 kHz, the thickness of the bottom can be 0.5 mm, and its diameter 7 mm.

[0065] Under the effect of a deformation of the resonator 10, rotating around the central axis, taking into account the polarizations described and the structure of the piezoelectric transducer, the cavity 2 is deformed by a rotating deformation wave, around the central axis, during which the resonator presses towards the bottom 6. This results in a centrifugation of the liquid, causing a depression in the center of the cavity 2, facing the sleeve 3, as well as an evacuation of the pumped liquid through the channel 4, extending between the resonator and the bottom 6, perpendicular to the central axis.

[0066] The configurations described in connection with the figures 1A And 2Amay have several discharge channels 4, which allows distribution of the pumped liquid in different orientations, around the central axis.

[0067] Regardless of the configurations, the sleeve, or sleeves, are preferably arranged at a vibration node of each resonator, which allows a connection with little damping loss with the fluid circuit connected to the sleeves. The height of the sleeve can be adjusted accordingly. It is preferable that the sleeve and the resonator to which it is connected are formed from a single piece, the sleeve extending the resonator: thus, the sleeve 3 1 described in connection with the figure 1A is part of the resonator 10, and forms one end thereof. The sleeve 3 2 is part of the resonator 20, and forms one end thereof. In the example given on the figure 2A , sleeve 3 extends resonator 10.

[0068] Whatever the configurations described in the figures 1A And 2A , the cavity 2 extends along a diameter larger than the sleeve, so as to be able to allow a centrifugation effect, resulting in sufficient depression, facing the sleeve, to cause suction of the liquid present in the sleeve. Suction is favored when the internal surface of the sleeve is hydrophilic. Centrifugation is favored when the internal surface of the cavity is hydrophobic.

[0069] Whatever the configurations, piezoelectric transducers have a low thickness, typically between 0.05 mm and 5 mm, preferably 0.5 mm for a radius R of 25 mm and 0.2 mm for a radius R less than 10 mm, which maximizes the electric field, the latter being able to be of the order of 300 V / mm. This makes it possible to increase the mechanical stress, this being directly proportional to the electric field.

[0070] Whatever the configurations, the peak / peak bias voltage can vary for example from a few volts to several hundred volts, the voltage playing on the amplitude of the out-of-plane deformation component of the resonator which itself plays on the volume of centrifuged fluid and therefore on the pumping pressure.

[0071] The configurations described in connection with the figures 1A And 2A can be particularly compact: the external diameter of each piezoelectric transducer is preferably less than 10 mm, the internal diameter can be 5 mm. Shorter external diameters, for example 7 mm, are possible. The dimensions can be determined analytically, particularly for simple geometries, or by numerical simulation.

[0072] The configurations described in connection with the figures 1A And 2Alead to a predominance of surface effects over volume effects: At zero centrifugation speed, the forces of gravity are weaker than the surface effects and the liquid conforms to the surface effects. By energizing the fluid by applying ultrasonic waves, the wettability of the liquid is reduced, which tends to organize into smaller spherical microdroplets. This leads to lower overall cohesion. The spatial distribution of surface forces is modified. When the liquid is set in motion, due to its viscosity, by the rotating ultrasonic wave, adhesion to the surface is reduced. Beyond a certain angular speed, the inertial effects induced by the ultrasonic wave generate a pumping effect by creating a central depression and a peripheral overpressure. Thus, in static conditions, the liquid tends to adhere to the internal wall of the cavity.The rotating ultrasonic wave generates, by shearing, an overall movement of the fluid is created, which is the origin of the pumping effect. The pumping effect is obtained while the energy supplied is below an energy threshold generating a nebulization of the liquid. This is advantageous because a nebulization can cause aggressive mechanical effects on the walls.

[0073] The resonant frequency of the resonators can vary. In order to take into account a possible drift of the resonant frequency, the control unit can be configured to apply a frequency sweep. figure 3 represents the modulus of the Fourier transform of one of the excitation signals, when it is made up of a succession of a finite number of sinusoidal periods with amplitude normalized to 1 and at frequencies increasing in frequency increments. In this example, a frequency sweep was carried out between 195 kHz and 202 kHz in 3% frequency increments. The frequency sweep allows the optimal frequency to be crossed, taking into account the variability affecting pumps, and in particular manufacturing processes: bonding, fixing systems. The pumped fluid can also have an influence on the resonance frequency, because it causes a variation in the mechanical impedance of the system, through its viscosity as well as through its movement in the pump or its temperature.

[0074] For example, the resonant frequency of the resonators may be 200 kHz under nominal operating conditions. However, the resonant frequency may vary, within a predetermined spectral range, depending on the operating conditions, the latter including the nature and composition of the fluid, its homogeneity, its possible multiphase composition, the temperature, the quantity of fluid inside the cavity, or the viscosity of the fluid. The spectral range may vary between a minimum resonant frequency, for example 195 kHz, and a maximum resonant frequency, for example 203 kHz. The control unit is configured to apply an excitation signal by performing a spectral sweep in the predetermined spectral range. The excitation signal is thus formed from a succession of an integer number of sinusoidal periods between the minimum frequency 195 kHz and the maximum frequency 203 kHz, according to a predetermined frequency increment.When several out-of-phase excitation signals are successively applied to different angular sectors of an electrode, the excitation signals are at the same frequency, which allows rotation of the pumped fluid.

[0075] Frequency sweeping allows the resonant frequency to be addressed regardless of operating conditions, provided they are within predetermined limits. The pump excitation frequency is not continuously centered on the optimum resonant frequency, but reaches the optimum frequency during each sweep.

[0076] The frequency sweep is renewed periodically. The time interval separating two consecutive frequency sweeps can be adjusted to allow continuous pumping (zero time interval) or cyclic pumping, during which an excitation duty cycle is taken into account, corresponding to the duration of the frequency sweep over the duration of the time interval between two consecutive frequency sweeps.

[0077] According to one possibility, when an electrical transducer is coupled to several segmented electrodes, the electrical excitation potential of each electrode, which is here called polarization, varies in the form of square waves, which are successively addressed to the electrodes, in a predetermined direction of rotation. If T is the period necessary to address all the sectors, each sector is polarized with a delay of 2 π N T compared to the previous electrode and the duration of this polarization is at most equal to 2 π N T . It can be shorter

[0078] To be able to excite the pump while remaining controlled by the optimal excitation frequency of the device, it is possible to extract useful information from a sector, between two polarizations so as to carry out an analysis of the operation of the pump. For this, the pump comprises a control unit 31, connected to each electrode, and programmed to carry out an analysis of control signals generated by a sector between two successive polarizations. The control signal generated by the sector can be considered as an image of the operation of the pump. This makes it possible to obtain information on the vibration of the resonator, the latter being able to vary according to the operation of the pump or a filling level.

[0079] The mains-generated control signal can be connected to a low-impedance LZ input or a high-impedance HZ input of the control unit. A connection to a low-impedance LZ input has the disadvantage of drawing charges from the piezoelectric transducer, which reduces the efficiency of actuation using another electrode. Using such a low-impedance connection allows for resonant frequency monitoring using a “series” equivalent electrical model, based on collected charges. Connecting to a high-impedance HZ input preserves actuation efficiency, at the expense of increased analysis complexity. Using such a high-impedance connection allows for resonant frequency monitoring using a “parallel” equivalent electrical model, based on a measured voltage. One can choose to perform low-impedance and / or high-impedance signal analysis.

[0080] On the figure 4A , an electrode 12 is shown arranged in angular sectors 12 1 , 12 1 , 12 4 , 12 4 of angle π 2 . On the figure 4B , we have schematized a connection of each angular sector during a measurement period T. The measurement period is segmented into four time sequences (x-axis), during which each sector is: either polarized with an actuation signal V; or connected to a low impedance input LZ of the control unit; or connected to a high impedance input HZ of the control unit; or unused.

[0081] On the figure 4B , we have represented, from top to bottom, the successive connections, during the period T, of each sector 12 1 , 12 2 , 12 3 and 12 4 .

[0082] The use of a control signal allows observation of the pump's operation. This allows, for example, monitoring a resonance frequency. Indeed, sampling the voltage (measurement in high impedance) or the electrical load (measurement in low impedance) that appears in a sector reflects the electrical impedance of the sector. Whatever the measurement, the resonance frequency depends on the temperature and the fluid load conditions. The control signal makes it possible to estimate an electrical impedance at the angular sector. The latter varies according to the temperature and the fluid load conditions. The control signal thus makes it possible to control the resonance frequency, by maintaining the voltage (measured in high impedance mode) or the measured electrical load (measured in low impedance mode, oscilloscope) at a certain setpoint value.In addition, performing a frequency sweep makes it possible to reconstruct an actuator transfer function in real time at each sweep with precise identification of the optimal electromechanical coupling frequency corresponding to the minimum impedance of the sector.

[0083] THE figures 5A à 7 illustrate different embodiments of a pump operating in a peristaltic mode.

[0084] On the figure 5A , a pump is shown, comprising: a first annular piezoelectric transducer 11, extending around a central axis Δ as described in connection with the figure 1A . a deformable solid material 10, extending around the central axis Δ, which, under the action of the first piezoelectric transducer 11, forms a resonator. The resonator 10 forms a disk around the central axis Δ. It thins towards the latter. Thus, its thickness, defined parallel to the central axis Δ, decreases as a function of the distance from the central axis. The resonator 10 comprises a flat portion surrounding a thinned portion, the latter being centered around a sleeve 3. a second annular piezoelectric transducer 21, also connected to the resonator 10, and extending around a central axis Δ symmetrical to the first piezoelectric transducer.

[0085] The radius R of the resonator, defined around the central axis, can extend up to 50 mm. In the example shown, the resonator has an outer portion of constant thickness, beyond a first radius R 1 , less than the radius R previously defined. Below the first R1 i , the resonator has a portion thinning in the direction of the central axis Δ. The first radius R 1 is for example equal to 50% of the radius R of the resonator.

[0086] The pump comprises a sleeve 3, cylindrical, coaxial with the central axis, formed by an extension of the first resonator. The diameter of the sleeve 3 can be of the order of 1 mm. The sleeve and the resonator form a single part, as described in connection with the figures 1A And 2A The foot of the sleeve is a vibration node as it vibrates by a rocking or bending motion and its end is chosen to define a vibration antinode of the resonator 10.

[0087] Under the effect of a cyclic activation of the first piezoelectric transducer 11 and the second piezoelectric transducer 21, the sleeve can undergo a deformation forming a bending wave unfolding along the axis of the sleeve, according to a resonance frequency which corresponds to the activation frequency of the first and second electrodes. The amplitude of the bending is preferably greater than 1 µm.

[0088] The pump comprises a capillary 8, wound fixedly around the sleeve 3, and preferably clamped around the latter on a portion which is close to its end, where the amplitude of the tilting is high. The capillary preferably comprises several turns, pressed against the external surface of the sleeve.

[0089] There figure 5B is a sectional view of the sleeve 3, showing a few turns of the capillary 8, preferably contiguous, applied against the sleeve. Under the effect of the bending of the sleeve, and its propagation along the central axis Δ, each turn of the capillary is progressively deformed, which causes the liquid to progress in the capillary. This results in peristaltic pumping, without any rotating moving parts. The bending creates a periodic rotating mechanical stress applied to the turns, a part of the turns being periodically compressed while the diametrically opposite part being periodically stretched.

[0090] This type of pump can be very compact, with a diameter of less than 10 mm and a maximum resonator thickness of 0.5 mm. The resonator can be made of metal or plastic. The capillary can be made of silicone. Only one coil can be provided around the sleeve, but operation is more efficient with multiple coils.

[0091] THE figures 6A et 6B show another configuration of a peristaltic pump. The pump includes a resonator 10 as described in connection with the figure 5A . The resonator is connected to an annular piezoelectric transducer 11, as previously described. The resonator extends between a base 10 b and a flat support face 10 a . The capillary 8 is arranged on a flat portion of the flat support face. The reduction in the thickness of the resonator is obtained by moving the base closer to the flat support face.

[0092] There figure 6A shows a segmentation of the first electrode 12 into 4 angular sectors, of angle π 2 . As in previous embodiments, the transducer is configured to cause a deformation of the resonator which rotates about the central axis, according to an ultrasonic frequency.

[0093] The pump comprises a capillary 8, pressed against the flat face of the resonator, using a clamping ring 9, at the level of a vibration antinode. The antinode is such that the out-of-plane deformation is at each instant positive on a semicircle passing through the maximum of the vibration antinode and negative on the other semicircle. On the figure 6C , the absolute value of the amplitude of the out-of-plane vibration (y-axis) relative to the plane 10a is represented as a function of a coordinate along a radial axis (x-axis). A first vibration node extends at the level of an area in which the transducer is held against the resonator. A second vibration node is located at the center of the resonator at the base of the sleeve. The height of the sleeve makes it possible to define the radial position of the vibration antinode, between the first vibration node and the second vibration node.

[0094] The capillary 8 forms at least one turn around the central axis. Under the effect of the rotating deformation of the resonator, the capillary 8 undergoes rotating compression, which allows pumping to be carried out by peristaltic effect. Depending on the direction of rotation of the deformation, pumping can be carried out in two opposite directions.

[0095] There figure 7 represents an embodiment based on a principle similar to that governing the pump described in connection with the figures 6A à 6C . A capillary 8 is arranged between a first resonator 10, as described in connection with the figures 6A et 6C , and a second resonator 20. The second resonator 20 is symmetrical to the first resonator with respect to a median plane PM perpendicular to the central axis Δ.

[0096] The first resonator 10 is coupled to a first piezoelectric transducer 11. The second resonator 20 is coupled to a second piezoelectric transducer 21. Each piezoelectric transducer is arranged to cause compression of the capillary 8, rotating around the central axis Δ. This results in peristaltic pumping. The pumping direction depends on the direction of rotation of the deformation.

[0097] Each resonator can extend to a diameter of 50 mm, and a thickness of 3.8 mm, the resonant frequency being 26.6 kHz. The smaller the diameter, the higher the resonant frequency. For a diameter of 25 mm, the resonant frequency is of the order of 50 kHz. For a diameter of 13 mm, the resonant frequency is of the order of 100 kHz. The excitation voltage that defines the inertial compression level of the capillary can range from a few volts to several hundred volts peak-peak.

Claims

1. Pump (1), intended to pump a fluid between an inlet and an outlet, comprising: - a first annular piezoelectric transducer (11), extending around a central axis (Δ), and comprising a first electrode (12); - a first resonator (10), connected to the first piezoelectric transducer, and extending around the central axis, the first resonator being formed of a deformable solid material thinning towards the central axis, the first resonator being configured to deform under the effect of a polarization of the first piezoelectric transducer; - a control unit (30), configured to polarize the first electrode according to a polarization voltage, modulated according to a modulation frequency greater than 20 KHz; the pump being characterized in that: - the first resonator delimits a cavity (2), extending around the central axis, and configured to receive the fluid, the cavity extending, along the central axis, according to a thickness; - the pump comprises a first sleeve (31), connected to the first resonator, opening at the center of the cavity, forming the inlet of the pump; - the pump comprises at least one channel (4), opening from the cavity, the channel extending, along the first resonator, around an axis perpendicular to the central axis, the channel forming the discharge of the pump; - so that under the effect of the polarization of the first piezoelectric transducer, a deformation of the resonator occurs, locally and transiently reducing the thickness of the cavity, the deformation propagating around the central axis, and causing a propulsion of a fluid, admitted into the cavity, around the central axis, the propulsion inducing a suction effect in the center of the cavity, facing the admission.

2. Pump according to claim 1, in which the first transducer comprises at least two distinct angular portions configured to deform differently, under the effect of the polarization applied to the first electrode, so as to generate a deformation of the first resonator propagating around the central axis.

3. Pump according to claim 2, in which the first electrode is segmented into n angular sectors (121, 122), n being greater than 2, the control unit being configured to polarize two angular sectors of the first electrode respectively by two phase-shifted voltages with a phase shift less than or equal to 2 π n or temporally shifted by a time shift less than or equal to 2 π n .

4. Pump according to any one of claims 2 or 3, in which the first piezoelectric material comprises at least two different portions (131, 132), in which the electric dipole moment is oriented in opposite directions.

5. Pump according to any one of the preceding claims, in which the first resonator (10) is arranged facing a support (6), forming a bottom of the cavity, the cavity extending between the first resonator and the bottom.

6. Pump according to any one of the preceding claims, comprising - a second annular piezoelectric transducer (21), extending around the central axis, and comprising a second electrode (22), connected to the control unit; - a second resonator, connected to the second piezoelectric transducer, and extending around the central axis, the second resonator being formed of a deformable solid, the second resonator thinning towards the central axis, the second resonator being configured to deform under the effect of a polarization of the second piezoelectric transducer; - the second resonator extends opposite the first deformable solid material; - the cavity extends between the first resonator and the second resonator.

7. Pump according to any one of the preceding claims, in which the second transducer comprises at least two distinct angular portions configured to deform successively, under the effect of the polarization applied to each second electrode, so as to generate a deformation of the second resonator, the deformation propagating around the central axis.

8. Pump according to claim 8, in which the second electrode is segmented into n angular sectors (221, 222), n being greater than or equal to 2, the control unit being configured to polarize two angular sectors of the second electrode respectively by two phase-shifted voltages of 2 π n .

9. Pump according to any one of claims 8 to 9, in which the second piezoelectric material comprises at least two different portions (231, 232), in which the electric dipole moment is oriented in opposite directions.

10. Pump according to claim 10, in which: - the first electrode is segmented into symmetrical angular sectors, relative to a first axis of symmetry, and activated in phase opposition; - the second electrode is segmented into symmetrical angular sectors, relative to a second axis of symmetry, and activated in phase opposition; - the first axis of symmetry is orthogonal to the second axis of symmetry.

11. Pump according to any one of claims 8 to 11, comprising a second sleeve (32), connected to the second resonator, and opening into the center of the cavity.

12. Pump according to any one of the preceding claims, in which: - the first electrode is segmented into n angular sectors, nbeing greater than or equal to 2, - the control unit is configured to address a polarization signal successively to each angular sector; - the pump comprises a control unit, connected to at least one angular sector of the first electrode, the control unit being configured to detect a control signal between two successive polarization signals.

13. Pump according to any one of the preceding claims, in which the thickness of the cavity is less than 1 mm.

14. Pump according to any one of the preceding claims, in which the control unit is configured to polarize the first electrode according to a frequency polarization signal, by performing a frequency sweep according to a finite number of successive discrete frequencies.

15. Pump according to any one of the preceding claims, in which the internal surface of the cavity comprises at least one hydrophobic part.

Images