PUMP ACTUATED BY PIEZOELECTRIC TRANSDUCERS

Abstract

Pump (1) intended to pump a fluid between an inlet and an outlet, including: a first annular piezoelectric transducer (11) extending around a central axis (A) and including a first electrode (12);a first resonator (10) connected to the first piezoelectric transducer and extending around the central axis, the first resonator becoming thinner toward the central axis and being deformed by the effect of polarisation of the first piezoelectric transducer;a control unit (30) configured to polarise the first electrode at a polarisation voltage;the first resonator defines a cavity (2) extending around the central axis and configured to receive the fluid;the pump includes at least one channel (4) discharging into the cavity;deformation of the resonator is produced because of the effect of the polarisation of the first piezoelectric transducer, locally and temporarily reducing the thickness of the cavity.

Description

TECHNICAL FIELD

The technical field of the invention is a pump configured to be actuated by a piezoelectric transducer.

PRIOR ART

Most pumps employ moving parts, which can generate a problem of reliability, wear and limited compactness. In the health field peristaltic pumps are routinely used. However, the repeated crushing of a tube, which drives the movement of the liquid, can lead to premature wear of the tube.

The patent application WO2013/41700 describes a pump that can be implanted, is not a peristaltic pump, and is actuated piezoelectrically. The sleeve at the centre of a resonator is subjected to bending because of the effect of rotary deformation of the resonator generated by piezoelectric transducers activated at an ultrasound frequency. The bending of the sleeve generates a pumping effect, which leads to the expulsion of the fluid. Reducing the cross section of the resonator in the vicinity of or along the sleeve enables amplification of the vibrations propagating to the sleeve. Such a pump is effective. However, it has been found that the sleeve is subjected to repeated bending, which can lead to wear. Also, the pump is intended to be coupled to a fluidic circuit. Control of the flowrate depends on the amplitude of vibration of the sleeve, which must be slaved to the mechanical load of the fluidic circuit, which is not easy.

A pump that is as compact as possible and preferably as flat as possible is looked for.

In particular, the search is for the pumping principle, the frequency and the amplitude of the ultrasound vibration of pumping to be less dependent on the mechanical coupling of the pump with the fluidic circuit.

Another objective is to design a pump enabling pumping to be effected with a controlled flowrate and with optimised energy expenditure and that can be particularly compact.

STATEMENT OF INVENTION

A first object of the invention is a pump intended to pump a fluid between an inlet and an outlet, including:

• • a first annular piezoelectric transducer extending around a central axis and including 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 becoming thinner toward the central axis, the first resonator being configured to be deformed when the first piezoelectric transducer is polarized;
  • a control unit configured to polarise the first electrode at a polarisation voltage modulated with a modulation frequency greater than 20 kHz;wherein:
  • the first resonator defines a cavity extending around the central axis and configured to receive the fluid, the cavity thickness extending along the central axis;
  • the pump includes a first sleeve connected to the first resonator discharging at the centre of the cavity and forming the pump inlet;
  • the pump includes at least one channel discharging from the cavity, the channel extending along the first resonator about an axis perpendicular to the central axis, the channel forming the outlet of the pump;
  • so that when the first piezoelectric transducer is polarized, a deformation of the resonator occurs locally and transiently reduces the thickness of the cavity, the deformation propagating around the central axis and leading to a propulsion of a fluid admitted into the cavity around the central axis, the propulsion inducing a suction effect at the centre of the cavity facing the inlet.

According to one possibility, the first transducer includes at least two distinct angular portions configured to be deformed differently by the effect of the polarisation applied to the first electrode so as to generate deformation of the first resonator propagating around the central axis.

According to one possibility, the first electrode is segmented to form n angular sectors, n being an integer greater than 2, the control unit being configured to polarise two angular sectors of the first electrode by respective voltages phase either shifted by a phase-shift less than or equal to

$\frac{2\pi }{n},$

or time-shifted by a time-shift less than or equal to

$\frac{2\pi }{n}.$

According to one possibility, the first piezoelectric material includes at least two different portions in which the electric dipolar moment is oriented oppositely.

According to one possibility, the first resonator faces a support forming a bottom of the cavity, the cavity extending between the first resonator and the bottom.

In accordance with one possibility the first sleeve is coaxial with the central axis.

In accordance with one possibility the pump includes:

• • a second annular piezoelectric transducer extending around the central axis and including 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 becoming thinner toward the central axis, the second resonator being configured to be deformed when the second piezoelectric transducer is polarized;
  • the second resonator extending facing the first deformable solid material;
  • the cavity extending between the first resonator and the second resonator.

In accordance with one possibility the second transducer includes at least two distinct angular portions configured to be deformed successively by the effect of the polarisation applied to each second electrode so as to generate deformation of the second resonator, the deformation propagating around the central axis.

In accordance with one possibility the second electrode is segmented to form n angular sectors, n being greater than or equal to 2, the control unit being configured to polarise two angular sectors of the second electrode by respective voltages phase-shifted by

$\frac{2\pi }{n},$

or time-shifted by a time-shift

$\frac{2\pi }{n}.$

According to one possibility, the second piezoelectric material includes at least two different portions in which the electric dipolar moment is oriented oppositely. In accordance with one possibility

• • the first electrode is segmented to form angular sectors symmetrical about a first axis of symmetry and activated in phase opposition;
  • the second electrode is segmented to form angular sectors symmetrical about a second axis of symmetry and activated in phase opposition;
  • the first axis of symmetry is orthogonal to the second axis of symmetry.

The pump may include a second sleeve connected to the second resonator and discharging at the centre of the cavity.

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

The modulation frequency may be greater than 100 kHz.

In accordance with one possibility:

• • the first electrode is segmented to form n angular sectors, n being greater than or equal to 2;
  • the control unit is configured to send a polarisation signal to each angular sector in succession;
  • the pump includes 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 polarisation signals.

The thickness of the cavity is preferably less than 1 mm.

According to one possibility, the control unit is configured to polarise the first electrode by a frequency-domain polarisation signal by carrying out a frequency sweep at a finite number of successive discrete frequencies.

According to one possibility, the internal surface of the cavity includes at least one hydrophobic part.

A second object of the invention is a peristaltic pump configured to pump a liquid along a capillary, pumping resulting from successively compressing the capillary in a pumping direction, the pump including:

• • a first annular piezoelectric transducer extending around a central axis and configured to be polarised 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 becoming thinner toward the central axis, the first deformable solid material forming a first resonator configured to be deformed when the first piezoelectric transducer is polarized;
  • a control unit configured to polarise the first electrode using a polarisation voltage modulated at a modulation frequency greater than 20 kHz;wherein:
  • the capillary is disposed against the resonator, around the central axis;
  • deformation of the first resonator occurs because when the first electrode is polarized, the deformation propagating around the central axis and leading to the compression of the capillary filled with a liquid around the central axis, the propulsion inducing a suction effect at the centre of the cavity, facing the inlet.

The capillary may extend around the sleeve, forming a plurality of turns, so that the turns are successively deformed along the sleeve.

The first resonator may include a surface, in particular a plane surface, forming a support. The capillary may be disposed against the support so that the capillary is subjected to progressive deformation resulting from the deformation of the first resonator. The capillary may form a turn around the central axis so that because of the effect of the deformation of the resonator the turn is deformed by a deformation turning around the central axis.

The pump may include two resonators disposed one against the other. The capillary may be disposed in a space between the two resonators, around the central axis, so that the capillary is subjected to 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 because of the effect of the deformation of the first and second resonators the turn is deformed by a deformation turning around the central axis.

The invention will be better understood after reading the description of embodiments given in the remainder of the description with reference to the figures listed below.

FIGURES

FIGS. 1A to 1E depict a first embodiment of the invention.

FIGS. 2A and 2B depict a second embodiment of the invention.

FIG. 3 depicts frequency sweeping.

FIG. 4A represents segmentation of an electrode forming angular sectors.

FIG. 4B shows a control time sequence of the electrode described with reference to FIG. 4A.

FIGS. 5A and 5B show one embodiment of a peristaltic pump.

FIGS. 6A, 6B and 6C shows another embodiment of a peristaltic pump.

FIG. 7 depicts a variant of the pump described with reference to FIGS. 6A to 6C.

DESCRIPTION OF PARTICULAR EMBODIMENTS

FIGS. 1A to 1E depict a first embodiment of a pump according to the invention. Here this is a pump including:

• • a first annular piezoelectric transducer 11 extending around the central axis Δ including a first layer 13 of a piezoelectric material between at least one first electrode 12 and one first counter-electrode 14;
  • 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 about the central axis Δ;
  • a second annular piezoelectric transducer 21 around the central axis Δ including a first layer 23 of a piezoelectric material between at least one second electrode 22 and one second counter-electrode 24;
  • 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 about the central axis Δ.

The first resonator 10 and the second resonator 20 are annular around the central axis Δ. They become thinner toward the latter. Thus their thickness as defined parallel to the central axis Δ decreases as a function of the distance from the central axis Δ. The thinning enables the amplitude of the vibrations propagating in each resonator to be increased.

Each resonator extends from a plane portion to an end formed by a cylindrical sleeve 3₁, 3₂ described hereinafter. The plane portion enables mechanical coupling with a piezoelectric transducer.

The outside radius R of each resonator as defined around the central axis Δ can extend 50 mm or more. The plane portion of each resonator extends beyond a first radius R₁ less than the previously defined radius R. Before the first radius R₁ is reached each resonator has a portion becoming thinner in the direction of the central axis Δ. The first radius R₁ is for example equal to 50% of the outside radius R of the resonator.

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 represented here the first resonator and the second resonator are symmetrical with respect to 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 linked to friction or to surface tension. The minimum thickness can 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 onboard a mobile system, for example a vehicle or a robot, subject to jolting.

Surface conditions enabling reduction of the static forces are described hereinafter.

The first resonator extends as far as a first cylindrical sleeve 3₁ coaxial with the central axis Δ and discharging into the cavity 2. The diameter of the sleeve 3₁ is between approximately 0.2 mm and 2 mm and preferably close to 1 mm. The first sleeve 3₁ can be formed by an extension of the first resonator. The first sleeve 3₁ is open so as to form a first inlet 1_i of the pump. The radius of the first sleeve forms an inside radius of the first resonator 10.

The pump can include a second cylindrical sleeve 3₂ coaxial with the central axis Δ and discharging into the cavity 2. The diameter of the sleeve 3₂ may be equal to the diameter of the first sleeve 3₁. The second sleeve 3₂ may be formed by an extension of the second deformable resonator. The second sleeve 3₂ may be open so as to form a second inlet 1′_i of the pump.

Each sleeve and the cavity are sized so that the flow of the liquid inside them is subjected to capillary forces that are greater than gravity forces. Thus in the absence of activation of each resonator the liquid is held immobile in each sleeve and in the cavity 2 by the action of the capillary forces. This enables a pump to be produced with no moving parts, limiting the risk of leaks.

The cavity 2 is defined in a radial direction perpendicular to the central axis Δ by a rib 5 connecting the first resonator 10 to the second resonator 20.

The internal wall of the cavity is preferably coated with a hydrophobic material. The presence of the hydrophobic coating can facilitate minimising friction forces and surface tension forces at the interface between the fluid and the material on or in which the ultrasound waves propagate so as to facilitate division of this fluid. Combined with ultrasound vibration, an hydrophobic coating enables the liquid to be broken down into microdroplets, or liquid fractions, which increases liquid's mobility. This minimizes the pumping force around the central axis by the centrifugal effect, as described hereinafter. The internal wall of each sleeve may be coated with a hydrophilic material. The height of each sleeve along the central axis is approximately 2 or 3 mm. This enables a particularly flat pump to be produced.

More generally, the internal surface of the cavity is advantageously hydrophobic either following functionalisation of the parts of each resonator defining the cavity or by an appropriate structure of the latter, for example groove type texturing, or formation of microchannels.

Generally speaking, the design of the pump aims to optimise the surfaces along which energy is transmitted to the fluid: the design aims to distribute the fluid along the internal surfaces of the cavity, which are preferably rendered hydrophobic. The geometrical configuration used, whereby the fluid is moved in a cavity with a high surface-to-volume ratio, favours the movement 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 essentially surface configuration minimises the energy to be imparted to the fluid. This enables prevention of transmission of surplus energy to a large volume of fluid, inducing a risk of cavitation.

Note that this is a counter-intuitive configuration because the usual practice is to push a thick volume. When the fluid is distributed in a thin film an effect of creeping of the fluid on the internal wall of the cavity is obtained.

The radius of the cavity perpendicular to the axis Δ is greater than the radius of the sleeve or of each sleeve. The radius of the cavity is preferably at least two times to ten times greater than the diameter of the sleeve or of each sleeve.

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.

Each deformable solid material forming the first and second resonators may be a metal (titanium, stainless steel, aluminium or aluminium alloy, brass or other copper-based alloy, or nickel-based alloy), an inorganic material (glass), an organic material (PEEK), alumina, without this limiting the choice of other materials not included in this non-exhaustive list.

Each layer of piezoelectric material may be formed of a PZT (lead zirconate titanate) type material, in particular a Ferroperm PZ26, PZ27, PZ46 or PZ29 material. The coefficients d33 and d31 which take account of 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:

• • 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 the coefficient d31 quantifying the response of the piezoelectric material in a direction perpendicular to the direction of the applied electric field.

The pump includes a control unit 30 connected to the first electrode 12 and to the second electrode 22 and to apply a frequency-modulated polarisation voltage. The modulation frequency depends on the dimensions of and the 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 these cases the modulation frequency is an ultrasound frequency so as to avoid generation of audible sound.

The counter-electrodes 14, 24 may be left at a floating potential or connected to a fixed potential, for example to earth.

According to one possibility the first and/or second electrode may be annular. In this case the first transducer and the second transducer are segmented to form angular sectors so as to obtain between two adjacent angular sectors opposite electric dipolar moments. Each angular sector may subtend an angle close to

$\frac{2\pi }{M},$

where M is the number of different angular sectors in the transducer.

According to one possibility the first transducer and the second transducer are annular and the first and/or second electrode is or are segmented to form angular sectors subtending an angle of

$\frac{2\pi }{N}$

where N is the number of angular sectors. According to one possibility each angular sector may extend a few degrees less than

$\frac{2\pi }{N}$

so as to favour electrical insulation between two adjacent sectors of the electrode. The control unit 30 is configured to apply a phase-shift or a delay to the polarisation voltage between two adjacent sectors 12₁, 12₂ equal to

$\frac{2\pi }{N}$

where N corresponds to the number of sectors of the first electrode. The same applies to t e second electrode, which may be segmented to form adjacent sectors 22₁, 22₂.

When the polarisation voltage is sinusoidal

$\frac{2\pi }{N}$

corresponds to a phase-shift. When the polarisation voltage is pulsed the phase-shift

$\frac{2\pi }{N}$

corresponds to a time delay T/N with respect to a characteristic time that is the main period T of resonance of the actuator. When the polarisation voltage is pulsed it is usual but not necessary for each pulse to be of crenellated shape with a duration less than or equal to a quarter of the resonance period T of the resonator.

In FIGS. 1B and 1C there has been represented a first possible arrangement of the pump. In this example:

• • The first piezoelectric transducer includes a first portion 13₁ and a second portion 13₂ forming two angular half-sectors and having respective permanent electric dipolar moments oriented in opposite directions: M=2. The electric dipolar moments are denoted −P and +P. The first piezoelectric transducer 13 is polarised by a non-segmented annular first electrode 11 at 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 includes a first portion 23₁ and a second portion 23₂ forming two angular half-sectors having respective permanent electric dipolar moments −P and +P oriented in opposite directions: M=2. The second piezoelectric transducer 23 is polarised by a second annular non-segmented electrode 22 at the voltage Vsin(wt). The second piezoelectric transducer is segmented along an axis Y parallel to the median plane PM perpendicular to the axis X.

The angle

$\frac{\pi }{2}$

between the axes X and Y segmenting the transducers 13, 23 combined with the phase-shift

$\frac{\pi }{2}$

of the polarisation voltages of the first and second electrodes leads to a rotation of the compression of the cavity by quadrants of angle π/2 at the polarisation frequency. Thus under the effect of the respective polarisations of the first electrode combined with the spatial segmentation of the electric moments of the first and second piezoelectric transducers the resonators 10 and 20 deform periodically, each deformation leading to rotating compression of the cavity 2 with a maximum deformation located within the radius R1.

The deformation of the cavity 2 turns around the central axis Δ due to the polarization voltages phase-shifted relative to one another. The compression of the cavity, propagating in a circular manner, leads to centrifuging of the liquid. This results in a reduced pressure forming at the level of the central part of the cavity 2, facing the sleeves. This favours the suction of a fluid, either a liquid or a gas, into the cavity via one of the sleeves. The opposite sleeve can enable the entry of a complementary fluid. In this case the pump enables mixing of a main fluid and the complementary fluid. Alternatively one of the sleeves enables the intake of a liquid while the opposite sleeve may admit a gas that is then mixed with the pumped liquid. It may for example be oxygen to meet a liquid's oxygenation requirements.

When two fluids are mixed, a first fluid can be supplied over a short period of time, while a second fluid can be supplied, via the second sleeve, over a longer period of time.

The device's ability to pump gas enables the cavity 2 to be completely emptied. When gas is pumped, it also dries the inner surface of the cavity.

After use, cavity 2 can be cleaned and/or sanitized with liquid cleansers or antiseptics. It can then be dried when gas is pumped. The pumping of gas induces a drying-inducing gas sweep. Drying is accelerated when the cavity's inner wall is hydrophobic. It is therefore advantageous for the pump to be able to pump either liquid or gas.

Centrifuging tends to press the pump's liquid against the contour 5 of the cavity. The liquid can be discharged through channel 4. Preferably, the surface of the channel is hydrophilically treated, which makes it easier for the liquid to enter the channel and then be discharged.

Another configuration of the transducer is shown in FIGS. 1D and 1E. In these figures the first and second transducers are annular. Each transducer has the same electric dipolar moment all around the ring. Rotating deformation of the cavity is achieved by segmenting the first electrode 12 and the second electrode 22 forming two sectors 12₁, 12₂ and two sectors 22₁, 22₂, respectively. The first and second electrodes are segmented along the axis X and the axis Y respectively. The respective sectors of the first and second electrodes, which face one another, are polarised by voltages phase-shifted by

$\frac{\pi }{2}.$

As in the previous case, this induces a rotating deformation of the cavity at an ultrasound frequency leading to centrifuging of the liquid and a pumping effect by formation of a reduced pressure at the centre of the cavity.

In the configuration described with reference to FIG. 1A one of the sleeves may be closed. The closure of the sleeve may be removable so as to allow access via the sleeve for cleaning or for functionalising the surfaces of the resonator defining the cavity. This functionalisation may involve applying a hydrophobic coating to the internal surfaces of the cavity and a hydrophilic coating at the level of the inlet sleeve or the outlet channel.

FIGS. 2A to 2B show another embodiment in which only one resonator 10 is used. The resonator 10 is as described with reference to FIG. 1A.

Each first electrode is obtained by segmentation of a first annular electrode 12 forming angular sectors 12₁, 12₂, 12₃, 12₄ subtending an angle of

$\frac{\pi }{2}.$

In the example represented in FIGS. 2A and 2B each angular sector extends over

$\frac{\pi }{2}$

steradians. Two diametrically opposed sectors 12₁, 12₃ are polarised by a voltage Vsin(wt) phase-shifted

$\frac{\pi }{2}$

relative to the other two diametrically opposed sectors 12₂, 12₄.

The transducer 13 is divided into two half-rings the electric moments of which are opposite so that the sectors 12₁, 12₂ polarise the half-ring of electric dipolar moment-P, the other two sectors 12₃, 12₄ polarising the half-ring of opposite electric dipolar moment.

The cavity 2 extends between the resonator 10 and a support 6 forming a bottom. A rib 5 connects the resonator 10 to the support 6. When the bottom is made of duralumin aluminium alloy the thickness of the bottom for a frequency of 100 kHz may be 0.5 mm and its diameter 7 mm.

Under the effect of deformation of the resonator 10 turning about the central axis and given the polarisations as described and the structure of the piezoelectric transducer, the cavity 2 is deformed by a deformation wave rotating around the central axis during which the resonator presses toward the bottom 6. This results in centrifuging of the liquid leading to a reduced pressure at the centre of the cavity 2 facing the sleeve and evacuation of the pumped liquid via the channel 4 extending between the resonator and the bottom 6 perpendicularly to the central axis.

The configurations described with reference to FIGS. 1A and 2A may include a plurality of outlet channels 4, which enables distribution of the pumped liquid in various orientations around the central axis.

Whatever the configuration the sleeve or sleeves is or are preferably arranged at a vibration node of each resonator, which enables connection with low damping losses with the fluidic circuit connected to the sleeves. The height of the sleeve may be adjusted accordingly. It is preferable for the sleeve and the resonator to which it is connected to be formed in the same piece, the sleeve extending the resonator: thus the sleeve 3₁ described with reference to FIG. 1A forms part of the resonator 10, forming one end thereof. The sleeve 3₂ forms part of the resonator 20, forming one end thereof. In the FIG. 2A example the sleeve 3 is an extension of the resonator 10.

Whatever the configurations described with reference to FIGS. 1A and 2A the cavity 2 extends with a greater diameter than the sleeve so as to be able to enable the centrifuging effect leading to a sufficiently reduced pressure facing the sleeve to aspirate the liquid present in the sleeve. Aspiration is favoured when the internal surface of the sleeve is hydrophilic. Centrifuging is favoured when the internal surface of the cavity is hydrophobic.

Whatever the configurations, the piezoelectric transducers have a small 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 maximises the electric field, which may be of the order of 300 V/mm. This increases the mechanical stress, the latter being directly proportional to the electric field.

Whatever the configuration the peak-to-peak polarisation voltage may vary for example by a few volts to a few hundred volts, the voltage affecting the amplitude of the out-of-plane deformation components of the resonator which itself acts on the volume of fluid centrifuged and therefore on the pumping pressure.

The configurations described with reference to FIGS. 1A and 2A can be particularly compact: the outside diameter of each piezoelectric transducer is preferably less than 10 mm and the inside diameter can be 5 mm. Smaller outside diameters, for example 7 mm, can be envisaged. The dimensions can be determined analytically, in particular for simple geometries, or by digital simulation.

The configurations described with reference to FIGS. 1A and 2A lead to a predominance of surface effects over volume effects: at zero centrifuging speed the gravity forces are weaker than the surface effects and the liquid conforms to the surface effects. Energising the fluid by application of ultrasound waves reduces the wettability of the liquid, which tends to become organised in the form of spherical microdroplets of smaller size. This leads to weaker overall cohesion. This modifies the spatial distribution of the surface forces. When the liquid is caused to move by the rotating ultrasound wave, because of its viscosity, the adhesion to the surface is reduced. Beyond a certain angular speed the inertia induced by the ultrasound wave generate a pumping effect by creation of a central depression and a peripheral overpressure. In the static regime the liquid therefore tends to adhere to the internal wall of the cavity. The rotating ultrasound wave generates through shear an overall movement of the fluid that is the origin of the pumping effect. The pumping effect is obtained while the energy introduced is less than an energy threshold generating nebulisation of the liquid. This is advantageous because nebulisation can generate aggressive mechanical effects on the walls.

The resonant frequency of the resonators can vary. In order to take into account possible drift of the resonant frequency the control unit can be configured to apply frequency sweeping. FIG. 3 represents the modulus of the Fourier transform of one of the excitation signals when it consists of a succession of a finite number of sinusoidal periods of standardised amplitude 1 and frequencies increasing incrementally. In this example frequency sweeping was carried out between 195 kHz and 202 kHz with frequency increments of 3%. The frequency sweeping makes it possible to cross the optimum frequency, allowing for the variability affecting the pumps, and in particular the manufacturing processes: adhesives, fixing systems. The pumped fluid may also influence the resonant frequency because it leads to a variation of the mechanical impedance of the system through its viscosity and its movement in the pump or its temperature.

For example the resonant frequency of the resonators may be 200 kHz under nominal operating conditions. However, the resonant frequency can vary in a predetermined spectral interval as a function of the operating conditions, the latter including the nature and the composition of the fluid, its homogeneity, its possible multiphase composition, temperature, the quantity of fluid inside the cavity or the viscosity of the fluid. The spectral interval 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 the spectral sweep in the predetermined spectral interval. The excitation signal is therefore formed of a succession of an integer number of sinusoidal periods between the minimum frequency 195 kHz and the maximum frequency 203 kHz in accordance with a predetermined frequency increment. When several phase-shifted excitation signals are successively applied to different angular sectors of an electrode, the excitation signals are at the same frequency, enabling the pumped fluid to rotate.

The frequency sweeping makes it possible to address the optimum frequency, regardless of the operating conditions, provided that it is within the predetermined limits. The excitation frequency of the pump is not continuously centred on the optimum resonant frequency but reaches the optimum frequency on each sweep.

Frequency sweeping is repeated periodically. The time interval separating two consecutive frequency sweeps can be adjusted to enable continuous pumping (zero time interval) or cyclic pumping, during which an excitation cyclic ratio is taken into account that corresponds to the duration of the frequency sweep over the duration of the time interval between two consecutive frequency sweeps.

In accordance with one possibility when an electric transducer is coupled to a plurality of segmented electrodes the excitation electric potential of each electrode, referred to here as the polarisation potential, varies in the form of pulses that are sent successively to the electrodes in a predetermined rotation direction. Each sector is polarised with a delay

$\frac{2\pi }{N}T$

relative to the preceding electrode, where T is the period necessary for addressing all of the sectors, and the duration of this polarisation is at most equal to

$\frac{2\pi }{N}T.$

It may be shorter.

To be able to excite the pump while remaining slaved to the optimum excitation frequency of the device it is possible to extract useful information from a sector between two polarisations so as to effect an analysis of the functioning of the pump. To this end the pump includes a monitoring unit 31 connected to each electrode programmed to effect an analysis of control signals generated by a sector between two successive polarisations. The control signal generated by the sector may be considered as an image of the functioning of the pump. This enables information to be obtained on the vibration of the resonator, which can vary as a function of the functioning of the pump or of a filling level.

The control signal generated by the sector may be connected to a low-impedance input LZ or a high-impedance input HZ of the control unit. A connection to a low-impedance input LZ has the disadvantages of sampling charges of the piezoelectric transducer, which reduces the efficacy of actuation with the aid of another electrode. The use of such low-impedance connection enables monitoring of the resonant frequency of the “series” equivalent electric model type, on the basis of the charges collected. A connection to a high-impedance input HZ preserves the efficacy of actuation to the detriment of increased complexity of the analysis. The use of such high-impedance connection enables monitoring of the resonant frequency of “parallel” equivalent electric model type on the basis of a measured voltage. A low-impedance and/or high-impedance analysis of the signal may be chosen.

In FIG. 4A there has been represented an electrode 12 comprising angular sectors 12₁, 12₁, 12₄, 12₄ subtending an angle

$\frac{\pi }{2}.$

In FIG. 4B there have been diagrammatically represented 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:

• • polarised by an actuating 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
  • not used.

In FIG. 4B there have been represented, from top to bottom, the successive connections during the period T of each connector 12₁, 12₂, 12₃ and 12₄. The use of a control signal enables observation of the functioning of the pump.

This makes it possible for example to monitor a resonant frequency. In fact sampling the voltage (high-impedance measurement) or the electric charge (low-impedance measurement) that appears in a sector takes account of the electrical impedance of the sector. Regardless of the measurement, the resonant frequency depends on temperature and the fluid charge conditions. The control signal enables estimation of an electrical impedance at the level of the angular sector. The latter varies as a function of temperature and the fluid charge conditions. The control signal therefore enables slaving of the resonant frequency by maintaining the voltage (measured in high-impedance mode) or the electric charge (measured in low-impedance mode, oscilloscope) at a certain setpoint value. Furthermore the fact of carrying out a frequency sweep makes it possible to reconstruct a transfer function of the actuator in real time on each sweep with precise identification of the optimum electro-mechanical coupling frequency corresponding to the minimum impedance of the sector.

FIGS. 5A to 7 depict various embodiments of a pump functioning in a peristaltic mode.

In FIG. 5A there has been represented a pump including:

• • a first annular piezoelectric transducer 11 extending around a central axis Δ as described with reference to FIG. 1A;
  • a deformable solid material 10 extending around the central axis Δ which because of the action of the first piezoelectric transducer 11 forms a resonator;
  • the resonator 10 forms a disk around the central axis Δ; it becomes thinner toward the latter; its thickness as defined parallel to the central axis Δ therefore decreases as a function of the distance from the central axis; the resonator 10 includes a plane portion surrounding a thinner portion, the latter being centred around a sleeve 3;
  • a second annular piezoelectric transducer 21 also connected to the resonator 10 and extending around the central axis Δ symmetrically to the first piezoelectric transducer.

The radius R of the resonator as defined around the central axis may extend up to 50 mm. In the example represented here the resonator has a constant thickness exterior portion beyond a first radius R₁ less than the radius R defined above. Before reaching the first radius R1_i the resonator has a portion becoming thinner in the direction of the central axis Δ. The first radius R₁ is for example equal to 50% of the radius R of the resonator.

The pump includes a cylindrical sleeve 3 coaxial with the central axis formed by an extension of the first resonator. The diameter of the sleeve 3 may be of the order of 1 mm. The sleeve and the resonator form one and the same part as described with reference to FIGS. 1A and 2A. The base of the sleeve is a vibration node while it vibrates by a movement of tilting or bending and its end is chosen to define a vibration antinode of the resonator 10.

Under the effect of cyclic activation of the first piezoelectric transducer 11 and the second piezoelectric transducer 21 the sleeve undergo a deformation, forming a bending wave unfolding along the axis of the sleeve, at a resonant frequency that corresponds to the activation frequency of the first and second electrodes. The amplitude of the bending is preferably greater than 1 μm.

The pump includes a capillary 8 fixedly wound around the sleeve 3 and preferably tightened around the latter over a portion that is close to its end where the amplitude of the tilting is high. The capillary preferably includes a plurality of turns pressed against the external surface of the sleeve.

FIG. 5B is a view in section of the sleeve 3 showing a few preferably joined turns of the capillary 8 pressed against the sleeve. Because of 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 leads to progress of the fluid in the capillary. Peristaltic type pumping is thus achieved with no rotatable moving parts. The bending creates a rotating periodic mechanical stress applied to the turns, some of the turns being periodically compressed while the diametrically opposite turns are periodically tensioned.

This type of pump can be very compact, the diameter being less than 10 mm, the maximum thickness of the resonator being 0.5 mm. The resonator may be made of metal or plastic. The capillary may be made of silicone. Only one turn around the sleeve may be used, but operation is more effective with a plurality of turns.

FIGS. 6A and 6B show another peristaltic pump configuration. The pump includes a resonator 10 as described with reference to FIG. 5A. The resonator is connected to an annular piezoelectric transducer 11 as described above. The resonator extends between a base 10_b and a plane support face 10_a. The capillary 8 is disposed on a plane portion of the plane support face. The thickness of the resonator is reduced by moving the base toward the plane support face.

FIG. 6A shows segmentation of the first electrode 12 into four angular sectors subtending an angle of

$\frac{\pi }{2}.$

As in the preceding embodiments the transducer is configured to generate a deformation of the resonator that turns about the central axis at an ultrasound frequency.

The pump includes a capillary 8 pressed against the plane face of the resonator by means of a clamping ring 9 at the level of a vibration antinode. The antinode is such that the out-of-plane deformation is at all times positive over a semicircle passing through the maximum of the vibration antinode and negative on the other semicircle. In FIG. 6C shows the absolute value of the amplitude of the out-of-plane vibration (Y abscissa) relative to the plane 10a as a function of a coordinate along a radial axis (X axis). A first vibration node lies at the level of a zone in which the transducer is held against the resonator. A second vibration node is situated at the centre of the resonator at the level of 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.

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 that enables pumping by the peristaltic effect. Depending on the direction of rotation of the deformation pumping can be effected in two opposite directions.

FIG. 7 represents an embodiment based on a similar principle to that of the pump described with reference to FIGS. 6A to 6C. A capillary 8 is disposed between a first resonator 10 as described with reference to FIGS. 6A and 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.

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 adapted to generate compression of the capillary 8 that turns about the central axis Δ. This leads to peristaltic pumping. The pumping direction depends on the direction of the rotation of the deformation.

Each resonator may have 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 level of inertial compression of the capillary can be from a few volts to a few hundred volts peak-to-peak.

Claims

1. A pump configured to pump a fluid between an inlet and an outlet, including: a first annular piezoelectric transducer extending around a central axis and including 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 becoming thinner toward the central axis, the first resonator being configured to be deformed when the first piezoelectric transducer is polarised;a control unit configured to polarise the first electrode at a polarisation voltage modulated with a modulation frequency greater than 20 kHz;

2. The pump according to claim 1, wherein the first transducer includes at least two distinct angular portions configured to be deformed differently under the effect of the polarisation applied to the first electrode so as to generate deformation of the first resonator propagating around the central axis.

3. The pump according to claim 2, wherein the first electrode is segmented to form n angular sectors, n being greater than 2, the control unit being configured to polarise two angular sectors of the first electrode by respective voltages phase-shifted by a phase-shift less than or equal to

4. The pump according to claim 2, wherein the first piezoelectric material includes at least two different portions in which the electric dipolar moment is oriented oppositely.

5. The pump according to claim 1, wherein the first resonator faces a support forming a bottom of the cavity, the cavity extending between the first resonator and the bottom.

6. The pump according to claim 1, wherein the first sleeve is coaxial with the central axis.

7. The pump according to claim 1, wherein: a second annular piezoelectric transducer extends around the central axis and including a second electrode connected to the control unit;a second resonator is connected to the second piezoelectric transducer and extends around the central axis, the second resonator being formed of a deformable solid, the second resonator becoming thinner toward the central axis, the second resonator being configured to be deformed when the second piezoelectric transducer is polarised;the second resonator extends facing the first deformable solid material;the cavity extends between the first resonator and the second resonator.

8. The pump according to claim 1, wherein the second transducer includes at least two distinct angular portions configured to be deformed successively by the effect of the polarisation applied to each second electrode so as to generate deformation of the second resonator, so that the deformation of the second resonator propagates around the central axis.

9. The pump according to claim 8, wherein the second electrode is segmented to form n angular sectors, n being greater than or equal to 2, the control unit being configured to polarise two angular sectors of the second electrode by two voltages phase-shifted by

10. The pump according to claim 8, wherein the second piezoelectric material includes at least two different portions in which the electric dipolar moment is oriented oppositely.

11. The pump according to claim 10, wherein: the first electrode is segmented to form angular sectors symmetrical about a first axis of symmetry and activated in phase opposition;the second electrode is segmented to form angular sectors symmetrical about a second axis of symmetry and activated in phase opposition;the first axis of symmetry is orthogonal to the second axis of symmetry.

12. The pump according to claim 8, including a second sleeve connected to the second resonator and discharging at the centre of the cavity.

13. The pump according to claim 8, wherein the second sleeve is coaxial with the central axis of the cavity.

14. The pump according to claim 1, wherein the modulation frequency is greater than 100 kHz.

15. The pump according to claim 1, wherein: the first electrode is segmented to form n angular sectors, n being greater than or equal to 2;the control unit is configured to send a polarisation signal to each angular sector in succession;the pump includes 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 polarisation signals.

16. The pump according to claim 1, wherein the thickness of the cavity is less than 1 mm.

17. The pump according to claim 1, wherein the control unit is configured to polarise the first electrode by a frequency-domain polarisation signal by carrying out a frequency sweep at a finite number of successive discrete frequencies.

18. The Pump according to claim 1, wherein the internal surface of the cavity includes at least one hydrophobic part.