WO2025202040A1 - Device for forming droplets - Google Patents

Abstract

The present description relates to a device (30) for forming droplets (20) of a liquid material comprising a pipe (31) extending along an axis, the pipe (31) being filled with a gas or a gas mixture and having an inlet opening (32) intended to receive a block or a droplet of the liquid material, the device (30) for forming droplets (20) further comprising at least one electro-acoustic transducer (40) configured to emit first ultrasonic waves in the gas or the gas mixture contained in the pipe (31) towards the block or the droplet of the liquid material, resulting in the formation or the displacement of the droplet (20) of the liquid material.

Description

DESCRIPTION

TITLE: Droplet forming device

This patent application claims priority from French patent application FR2403206 which will be considered as an integral part of this description.

Technical field

[0001] The present description relates generally to a droplet forming device.

Prior art

[0002] An example of a droplet-forming device corresponds to a printing nozzle for a printer, for example for a 3D printer or for an inkjet printer, which makes it possible to deliver a droplet of a liquid material to be printed onto a support. The printing nozzle is filled with the liquid material to be printed and a droplet of the liquid material is ejected through an outlet orifice of the printing nozzle. Current printing heads group together several tens to several thousand of these nozzles which can be controlled, and therefore generate droplets, independently of each other within the same printing head. Some printing heads allow the creation of droplets of different materials.

[0003] A disadvantage of such a droplet forming device is that the properties of the droplet, including the viscosity of the material to be printed, the dimensions of the droplet and the direction of expulsion of the droplet, depend in particular on the shape of the printing nozzle outlet orifice and the shape of the printing nozzle near the outlet orifice. The design of the printing nozzle can thus be complex. Another disadvantage is that, once the printing nozzle has been designed, it can be difficult to vary certain properties of the droplet, including the direction of droplet expulsion, during operation of the printing nozzle

[0004] Another disadvantage is that, once the printing nozzle is designed, it may be difficult to vary the viscosity of the material beyond a certain range predefined when designing the printing nozzle.

[0005] Another disadvantage lies in the fact that the print heads are highly dimensionally constrained because they must be able to accommodate a large number of these electromechanical expulsion and droplet generation nozzles.

Summary of the invention

[0006] One embodiment overcomes all or part of the drawbacks of known droplet forming devices.

[0007] One embodiment provides a device for forming droplets of a liquid material comprising a conduit extending along an axis, the conduit being filled with a gas or gas mixture and having an inlet opening for receiving a block or droplet of the liquid material, the droplet forming device further comprising at least one electroacoustic transducer configured to emit first ultrasonic waves into the gas or gas mixture contained in the conduit to the block or droplet of the liquid material, resulting in the formation or displacement of the droplet of the liquid material.

[0008] According to one embodiment, the device comprises electro-acoustic transducers resting on a first plane inclined relative to said axis and configured to emit the first ultrasonic waves into the gas or mixture gaseous content in the pipe to the block or drop of liquid material.

[ 0009 ] According to one embodiment, the first plane is orthogonal to said axis.

[0010] According to one embodiment, the device comprises at least a first pair of electroacoustic transducers symmetrical with respect to said axis.

[0011] According to one embodiment, the device further comprises a second pair of electroacoustic transducers symmetrical with respect to said axis.

[0012] According to one embodiment, the device further comprises an electronic circuit for controlling said at least one electro-acoustic transducer.

[0013] According to one embodiment, the electronic circuit is configured to control the electroacoustic transducers so that the superposition of the first ultrasonic waves forms a standing acoustic wave in the pipe.

[0014] According to one embodiment, the electronic control circuit is configured to control said at least one electro-acoustic transducer to deform the block of liquid material under the action of acoustic radiation forces.

[0015] According to one embodiment, the electronic control circuit is configured to control said at least one electro-acoustic transducer to provide the first ultrasonic waves in a first phase and to control said at least one electro-acoustic transducer to pick up second ultrasonic waves in a second phase.

[0016] According to one embodiment, the device comprises additional electro-acoustic transducers resting on a second plane parallel to the first plane. [0017] According to one embodiment, the electroacoustic transducer is a capacitive micromachined ultrasonic transducer, or a piezoelectric micromachined ultrasonic transducer, or a transducer comprising at least one layer of a piezoelectric material.

[0018] One embodiment provides a 3D printer comprising a droplet forming device as defined above, a reservoir of the liquid material to be printed, and a device for transferring the block of liquid material from the reservoir to the droplet forming device.

Brief description of the drawings

[0019] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0020] Figure 1A, Figure 1B, and Figure 1C are schematic side views with partial section of embodiments of a system 10 for supplying droplets of a liquid material;

[0021] Figure 2A, Figure 2B and Figure 3 are partial, schematic perspective views of embodiments of a droplet forming device of the system of Figure 1A;

[0022] Figure 4, Figure 5 and Figure 6 are each a partial and schematic perspective view of an embodiment of an electro-acoustic transducer of the droplet forming device of Figure 2A, 2B or 3;

[0023] Figure 7 represents a curve of evolution as a function of time of a control signal of a transducer electroacoustics of the droplet forming device of Figure 2A, 2B or 3;

[0024] Figure 8, Figure 9, Figure 10, and Figure 11 each represent, in the left part, a curve of evolution as a function of time of a control signal of an electro-acoustic transducer of the droplet formation device of Figure 2A, 2B or 3 and, in the right part, the spectrum of the control signal represented in the left part for different embodiments of control of the electro-acoustic transducer;

[0025] Figure 12 represents a curve of the evolution of the pressure of an ultrasonic wave supplied by an electro-acoustic transducer;

[0026] Figure 13, Figure 14, Figure 15, and Figure 16 illustrate examples of standing acoustic waves;

[0027] Figure 17 and Figure 19 are partial schematic top sectional views of the droplet forming device of Figure 2A or 2B illustrating the locations of standing acoustic wave nodes and Figures 18 and 20 are perspective views of pressure evolution curves in perpendicular planes for the standing acoustic waves of the devices of Figures 17 and 19 respectively;

[0028] Figure 21 and Figure 22 illustrate other examples of standing acoustic waves;

[0029] Figure 23 is a partial, schematic, top sectional view of the droplet forming device of Figure 2A or 2B illustrating the node locations of a standing acoustic wave;

[0030] Figure 24A, Figure 24B, Figure 24C, and Figure 24D are partial and schematic sectional views, of the droplet forming device of Figure 2A, 2B or 3 at successive steps of an embodiment of a method of operating the droplet forming device;

[0031] Figure 25A, Figure 25B, Figure 25C, and Figure 25D are partial, schematic sectional views of the droplet forming device of Figure 2A, 2B, or 3 in successive steps of another embodiment of a method of operating the droplet forming device;

[0032] Figure 26 is a partial and schematic sectional view of the droplet forming device of Figure 2A, 2B or 3 at successive stages of a variant of the method of operation of the droplet forming device;

[0033] Figure 27 is a partial, schematic perspective view of another embodiment of the droplet forming device of the system of Figure 1A;

[0034] Figure 28 is a schematic, partial, sectional view of the droplet forming device of Figure 27 illustrating the node locations of a standing acoustic wave;

[0035] Figure 29 is a partial, schematic, sectional view of the droplet forming device of Figure 2A, 2B or 3 at a step of another embodiment of a method of operating the droplet forming device; and

[0036] Figure 30 is a partial, schematic, sectional view of the droplet forming device of Figure 2A, 2B or 3 at a step of another embodiment of a method of operating the droplet forming device. Description of the embodiments

[0037] The same elements have been designated by the same references in the different figures. In particular, the structural and/or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0038] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the electro-acoustic transducer control circuits are well known to those skilled in the art and are not described in detail.

[0039] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0040] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures in a normal position of use.

[0041] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%. In addition, Here, the terms "insulator" and "conductor" are considered to mean "electrically insulating" and "electrically conducting" respectively. Furthermore, the "average diameter" of a surface is the diameter of a disk having the same area as the surface.

[0042] Figure 1A is a partial and schematic side view of an embodiment of a system 10 for supplying droplets 20 of a liquid material to be deposited on a support 22 or on a portion of an already printed part. The system 10 corresponds for example to a 3D printer.

[0043] The system 10 comprises a reservoir 12 of the liquid material, a device 30 for forming the droplets 20, and a device 14 for transferring the liquid material from the reservoir 12 to the device 30 for forming the droplets 20. The transfer device 14 may be of any type. The transfer device 14 may comprise an actuator, for example piezoelectric.

[0044] The device 30 for forming the droplets 20 has an inlet opening 32 at one end and an outlet opening 33 at the opposite end. The conduit 31 delimits an internal volume 34 open to the inlet opening 32 and to the outlet opening 33. The conduit 31 comprises an internal wall 35 on the side of the internal volume 34 and an external wall 36 on the side opposite the internal wall 35. According to one embodiment, the internal volume 34 is filled with air. Alternatively, a gas or a mixture of gases, other than air, is provided in the internal volume 34.

[0045] The device 30 further comprises electro-acoustic transducers 40 configured for the generation of ultrasonic waves in the internal volume 34 of the pipe 31, two electro-acoustic transducers 40 being shown as an example in FIG. 1A. The device 30 further comprises a control circuit 41 for the electro-acoustic transducers acoustics 40. The control circuit 41 may correspond to an application-specific integrated circuit. The control circuit 41 is configured to transmit a control signal S to each electro-acoustic transducer 40. The control circuit 41 may be located near the electro-acoustic transducers 40 or may be remote from the electro-acoustic transducers 40.

[0046] According to one embodiment, the system 10 comprises a device 60 for recovering liquid material located on the side of the outlet opening 33. The device 60 comprises a receptacle 61 crossed by a through opening 62 located in the extension of the outlet opening 33 but of dimensions smaller than the dimensions of the outlet opening 33. The outlet opening 33 allows the passage of the droplets 20 while the liquid material which flows along the internal wall 35 of the pipe 31 and escapes through the outlet opening 33 is recovered on the receptacle

61. The device 60 may further comprise a mechanism, not shown, for returning the recovered liquid material to the reservoir 12.

[0047] Figure 1B is a partial and schematic side view of a variant of the system 10 of Figure 1A in which the reservoir 12 comprises a first sub-reservoir 12A of a first liquid material and a second sub-reservoir 12B of a second liquid material. The transfer device 14 is then adapted to transfer the first liquid material from the sub-reservoir 12A and the second liquid material from the sub-reservoir 12B to the device 30 for forming the droplets 20.

[0048] Figure IC is a partial and schematic side view of a variant of the system 10 of Figure 1A in which the system 10 comprises several devices 30 for forming the droplets 20 connected to the reservoir 12. [0049] According to one embodiment, the liquid material is a solution (which is a homogeneous mixture resulting from the dissolution of one or more solutes in a solvent) or a dispersion (which is a heterogeneous mixture in which one or more phases are finely mixed with another without being dissolved therein). According to one embodiment, the liquid material is an ink, that is to say a liquid loaded with particles or nanoparticles allowing it to be functionalized (pigmentation, electrical, mechanical, rheological, piezoelectric, ferroelectric, pyroelectric, thermoelectric, photoresistive properties, etc.). According to one embodiment, the liquid material is suitable for the production by 3D printing of a semiconductor, conductive, or insulating region. According to one embodiment, the fluid material is used for the manufacture of an electronic device. According to one embodiment, the fluid material comprises one or more p-type semiconductor compounds, in particular one or more p-type organic semiconductor compounds, one or more n-type semiconductor compounds, in particular n-type organic semiconductor compounds, one or more conductive materials, and/or one or more insulating materials, and/or one or more dielectric materials. According to one embodiment, the fluid material contains conductive or functionalizing fillers.

[0050] Figures 2A, 2B and 3 are partial and schematic perspective views of embodiments of the droplet forming device 30 of the droplet supply system 10 of Figure 1A. In the embodiments illustrated in Figures 1, 2 and 3, each electroacoustic transducer 40 rests on the outer wall 36 of the conduit 31. According to another embodiment not shown, each electroacoustic transducer 40 rests on the inner wall 35 of the conduit 31 in the internal volume 34 of the pipe 31 and in direct physical contact with the gas or gas mixture present in the internal volume 34. According to another embodiment not shown, each electro-acoustic transducer 40 is integrated in the pipe 31, in direct physical contact with the gas or gas mixture present in the internal volume 34, or without direct physical contact with the gas or gas mixture present in the internal volume 34.

[0051] The conduit 31 has, for example, a circular, oval, or polygonal shape in top view, for example square, rectangular, or hexagonal. The dimensions of the conduit 31 depend on the intended application. According to one embodiment, the average diameter of the conduit 31 is between 1 mm and 45 mm. According to one embodiment, the conduit 31 extends at least locally along an axis A and the electro-acoustic transducers 40 rest on a plane perpendicular to the axis A. According to one embodiment, the device 30 comprises a first pair of electro-acoustic transducers 40 arranged symmetrically with respect to the axis A and a second pair of electro-acoustic transducers 40 arranged symmetrically with respect to the axis A.

[0052] In the embodiment illustrated in Figure 2A, the pipe 31 has a square shape in top view, the external wall 36 of the pipe comprising four substantially flat faces 37 opposite each other in pairs, and the device 30 comprises an electro-acoustic transducer 40 having the general shape of a rectangular parallelepiped on each face 37 of the pipe 31.

[0053] In the embodiment illustrated in Figure 2B, two of the walls 37 are used as reflectors and then only one device 40 is required per direction for ensure the operation of the system by creating the standing wave.

[0054] In the embodiment illustrated in Figure 3, the pipe 31 has a circular shape with axis A in top view, and the device 30 comprises four electroacoustic transducers 40 distributed regularly around the axis A on the external wall 36 of the pipe 31, each electroacoustic transducer 40 having the general shape of an annular sector.

[0055] Each electro-acoustic transducer 40 converts the electrical signal S into ultrasound. The electro-acoustic transducer 40 is for example made of a plate of monocrystalline or polycrystalline piezoelectric material, for example PZT (Lead-Zirconia Titanate) whose thickness varies when a voltage is applied to it. The electro-acoustic transducer 40 is for example a micro-electromechanical system (or MEMS), which uses micro-electronics production technologies. This micro-electromechanical system is for example made of a deformable membrane suspended above a cavity. The deformable membrane is for example moved by capacitive effect using an electrode fixed to the membrane and an electrode separated by the cavity. This type of transducer is known by the acronym CMUT for Capacitive Micro-machined Ultrasonic Transducer. The deformable membrane is for example moved by piezoelectric effect using a layer of piezoelectric material with two electrodes attached to the membrane. This type of transducer is known by the acronym PMUT for Piezoelectric Micro-machined Ultrasonic Transducer. The electro-acoustic transducer 40 is for example a magnetostrictive transducer made of a material that slightly changes size when exposed to a magnetic field. Depending on the type of the acoustic transducer 40, the control signal S transmitted by the control circuit 41 to the electro-acoustic transducer 40 may correspond to a voltage, a current, or an electrical charge.

[0056] Figure 4 is a perspective view, partial and schematic, of an embodiment of the electro-acoustic transducer 40 of the piezoelectric type. The electro-acoustic transducer 40 comprises a pellet 43 of a piezoelectric material between two electrodes 44 and 45. The pellet 43 and each electrode 44, 45 has for example in top view a circular, oval, or polygonal shape, for example square, rectangular, or hexagonal. The average diameter of the pellet 43 in top view is for example between 1 μm and 10 mm. The thickness of the pellet 43 is for example between 1 μm and 1 mm. The signal S can correspond to a variable voltage applied between the two electrodes 44 and 45, which causes the deformation of the pellet 43, in particular a variation in its thickness, and the generation of ultrasonic waves.

[0057] Figure 5 is a partial and schematic sectional view of an embodiment of the electro-acoustic transducer 40 of the CMUT type. The electroacoustic transducer 40 comprises an electrode 46 fixed relative to the conduit 31 and an electrode 47 movable relative to the fixed electrode 46, and for example separated from the electrode 46 by a gap 48 filled with air, or vacuum, or any other gas. Although not shown in Figure 5, the electrode 47 may be made up of several layers, for example a first insulating layer, for example made of silicon oxide, and a second conductive layer, for example made of gold. Each electrode 46, 47 has for example in top view a circular, oval, or polygonal shape, for example square, rectangular, or hexagonal. The average diameter of each electrode 46, 47 in top view is for example between 0.1 pm and 40 mm, preferably between 1 pm and 200 pm. The thickness of the gap 48 is for example between 5 nm and 2 mm. The signal S can correspond to a variable voltage applied between the two electrodes 46 and 47, which causes the displacement of the mobile electrode 47 relative to the fixed electrode 46 and the generation of ultrasonic waves.

[0058] Figure 6 is a partial and schematic sectional view of an embodiment of the electro-acoustic transducer 40 of the PMUT type. The electroacoustic transducer 40 comprises a deformable membrane 49 mounted on the pipe 31 and forming, with the pipe 31, a gap 48 for example filled with air, vacuum, or any other gas. A pellet 43 of a piezoelectric material between two electrodes 44 and 45 is fixed to the membrane 49. The signal S can correspond to a variable voltage applied between the two electrodes 44 and 45, which causes the deformation of the pellet 43, which in turn causes the displacement of the membrane 49 and the generation of ultrasonic waves.

[0059] According to one embodiment, the device 30 comprises electro-acoustic transducers 40 of different types, that is to say for which the generation of ultrasonic waves is obtained according to different technologies, for example at least one electro-acoustic transducer 40 of PMUT type and one electro-acoustic transducer 40 of CMUT type.

[0060] Each electro-acoustic transducer 40 is controlled to transmit and receive ultrasonic waves. As described in more detail below, the electro-acoustic transducers 40 can be controlled so that the ultrasonic waves transmitted by the electro-acoustic transducers 40 lead to the formation of a wave stationary acoustics in the cavity 34 and/or the application of an acoustic radiation force on the droplet 20.

[0061] According to one embodiment, the frequency of the ultrasonic waves emitted by each electroacoustic transducer 40 is between 25 kHz and 1 GHz.

[0062] According to one embodiment, the device 30 comprises at least two electro-acoustic transducers 40 which, in operation, emit ultrasonic waves in different frequency ranges.

[0063] According to one embodiment, each electro-acoustic transducer 40 is controlled by the control circuit 41 to emit one or more bursts of ultrasonic waves. The duration of each burst of ultrasonic waves may be between 1 ns and 100 ms. In each burst of ultrasonic waves, the wavelength of the ultrasonic waves may be substantially constant or may be variable.

[0064] According to one embodiment, the electroacoustic transducer 40 is adapted to provide ultrasonic waves in different frequency bands. According to one embodiment, the frequencies of the ultrasonic waves in a first burst of ultrasonic waves may be in a first frequency band and the frequencies of the ultrasonic waves in a second burst of ultrasonic waves may be in a second frequency band different from the first frequency band. According to one embodiment, the electroacoustic transducer 40 is adapted to simultaneously provide in the same burst ultrasonic waves in a first frequency band and in a second frequency band different from the first frequency band. [0065] According to one embodiment, a burst of ultrasonic waves can be composed of multiple frequencies which evolve continuously or discontinuously, regularly or irregularly during the time of an excitation burst.

[0066] Figure 7 represents a curve of evolution as a function of time t of the control signal S of the electro-acoustic transducer 40 making it possible to obtain a burst of ultrasonic waves corresponding to a pseudoperiodic signal modulated in frequency around a carrier frequency and also modulated in amplitude by an envelope whose variations are slow compared to the oscillations of the phase, such a signal also being called Chirp.

[0067] According to one embodiment, the control signal S corresponds to a periodic waveform, for example a sinusoidal signal, an oscillating signal of increasing or decreasing frequency, a signal with multiple frequencies, etc.

[0068] Figure 8, Figure 9, Figure 10, and Figure 11 each represent, on the left side, a curve of evolution as a function of time t of the control signal S of the electro-acoustic transducer 40 and, on the right side, the amplitude M of the spectrum as a function of the frequency F of the control signal S represented on the left side for different embodiments of control of the electro-acoustic transducer 40. A control signal S with a slow variation of its amplitude such as that represented in Figure 7 and Figure 10 has a spectrum whose harmonics at the central frequency are strongly attenuated in comparison with a control signal S whose envelope would have rapid variations as is the case of the signals represented in Figures 8 and 9.

[0069] Figure 12 represents a curve of evolution as a function of time of the pressure P of an ultrasonic wave provided by the electroacoustic transducer 40 according to an embodiment in which the electroacoustic transducer 40 is controlled to provide successive bursts of ultrasonic waves of different amplitudes.

[0070] In operation, the electroacoustic transducers 40 emit ultrasonic acoustic waves into the internal volume 34 which are superimposed.

[0071] According to one embodiment, the electro-acoustic transducers 40 are controlled by the control circuit 41 so that the ultrasonic acoustic waves that they emit and which are superimposed in the internal volume 34 form a standing acoustic wave in the internal volume 34.

[0072] Figure 13, Figure 14, Figure 15, and Figure 16 illustrate examples of standing acoustic waves 50 and each represent curves of evolution of the pressure P, in arbitrary units, in the internal volume 34 along a straight line connecting points A and B located on the internal wall 35 of the pipe 31. The distance between points A and B is called D. The wavelength of the standing acoustic wave is called, which is also equal to the wavelength of the ultrasonic waves emitted by the electro-acoustic transducers 40. In Figure 13, several curves of evolution of the pressure P are represented at different times while in Figures 14 to 16, only the two evolution curves corresponding to the maximum and minimum pressure P are represented. In Figure 13, the wavelength of the standing acoustic wave is equal to twice the distance D. In Figure 14, the wavelength X of the standing acoustic wave is equal to 3/2 times the distance D. In Figure 15, the wavelength X of the standing acoustic wave is equal to 5/2 times the distance D. In Figure 16, the length wave length of the standing acoustic wave is equal to 9/2 times the distance D. On the straight line connecting points A and B, we can observe locations, called nodes N, at which the pressure P is substantially constant over time, and locations, called antinodes V, at which the variation of pressure P over time is maximum. Each node N is located between two adjacent antinodes V. In particular, in Figure 13, we observe two antinodes V and one node N. In Figure

14, we observe three N nodes and four V antinodes. In figure

In Figure 15, we observe five N nodes and six V antinodes. In Figure 16, we observe nine N nodes and ten V antinodes. The position of the N node or N nodes can be precisely controlled.

[0073] According to one embodiment, the frequency of the ultrasonic waves emitted by each electroacoustic transducer 40 is between 17 KHz and 510 MHz when the dimension D is between 1 pm and 10 cm. For example, the frequency of the ultrasonic waves is of the order of 0.17 MHz when the dimension D is of the order of 1 mm to obtain a standing acoustic wave 50 having a single node N as shown in FIG. 13. The following table indicates examples of the frequency F of the ultrasonic waves emitted by each electroacoustic transducer 40 as a function of the desired number of nodes N of the standing wave and the distance D [Table 1]

[0074] According to one embodiment, the electro-acoustic transducers 40 are controlled by the control circuit 41 so that the ultrasonic acoustic waves that they emit and which are superimposed in the internal volume 34 form a standing acoustic wave in the internal volume 34 comprising nodes distributed substantially along a plane.

[0075] Figure 17 and Figure 19 are partial and schematic top sectional views of the droplet forming device 30 of Figure 2A or 2B illustrating the locations of standing acoustic wave nodes 50 in two configurations. Figure 18 is a perspective view showing pressure evolution curves of a standing wave in two perpendicular planes for the configuration of Figure 17 and Figure 20 is a perspective view showing standing waves in different planes for the configuration of Figure 19 in a first set of nine parallel planes and a second set of nine planes parallel and perpendicular to the planes of the first set.

[0076] In Figures 17 and 18, the standing acoustic wave comprises a single node N located substantially in the center of the pipe 31. In Figures 19 and 20, the standing acoustic wave comprises 81 nodes N distributed substantially in rows and columns along a plane. [0077] In the examples of standing waves described previously in relation to figures 13 to 22, the maximum amplitudes of the ultrasonic waves provided by the electroacoustic transducers 40 are substantially equal. According to one embodiment, the positions of the nodes N can be modified when the maximum amplitudes of the ultrasonic waves emitted by the two electroacoustic transducers 40 on two opposite faces 37 are not equal and/or when a different phase term is applied to the electroacoustic transducers 40.

[0078] In the embodiments described previously in relation to figures 13 to 20, the nodes N of the standing wave are distributed regularly in a plane of the internal volume 34. As a variant, the standing waves can be generated with a distribution of the nodes N different from a regular distribution.

[0079] Figure 21 is a figure similar to Figure 13 and illustrates two standing waves 50_l and 50_2 both having a single node NI and N_2. The standing waves 50_l and 50_l have the same frequency. For the standing wave 50_l, which corresponds to the standing wave 50 of Figure 13, the maximum amplitudes of the pressure P at points A and B are substantially equal so that the node NI is substantially halfway between points A and B. For the standing wave 50_2, the maximum amplitude of the pressure P at point A is greater than the maximum amplitude of the pressure P at point B so that the node N2 is closer to point B than to point A.

[0080] Figure 22 is a figure similar to Figure 14 and illustrates a standing wave 50 having three nodes N. The standing wave 50 is obtained by supplying ultrasonic waves at point A and point B of the same frequency but out of phase with each other. [0081] In the embodiments described above, a single electro-acoustic transducer 40 is present on each face 37 of the pipe 31. As a variant, the droplet-forming device 30 of the droplet-delivery system 10 of FIG. 1A may comprise two or more electro-acoustic transducers 40 on at least one face 37 of the pipe 31. According to one embodiment, the electro-acoustic transducers 40 may be located in the same plane inclined relative to the axis of the pipe 31, for example perpendicular to the axis of the pipe 31, which means that the geometric centers of the electro-acoustic transducers 40 are located in the same plane inclined relative to the axis of the pipe 31, for example perpendicular to the axis of the pipe 31. Advantageously, when the electro-acoustic transducers 40 are controlled for the formation of a standing acoustic wave, the greater number of electroacoustic transducers 40 allows for greater flexibility in positioning the nodes N of the standing acoustic wave.

[0082] Figure 23 is a figure similar to Figure 19 of another embodiment of the droplet forming device 30 of the droplet supply system 10 of Figure 1A. The device 30 illustrated in Figure 23 comprises all of the elements of the droplet forming device 30 illustrated in Figure 19 with the difference that it comprises several electro-acoustic transducers 40 on each face 37 of the pipe 31. Each of the transducers 40 can be driven by a signal that is different in amplitude, phase or frequency. Figure 23 illustrates a standing wave comprising 81 nodes N that are not distributed regularly in a plane. [0083] Figure 24A, Figure 24B, Figure 24C, and Figure 24D are partial and schematic sectional views of the droplet forming device 30 of Figure 2A, 2B or 3 at successive steps of an embodiment of a method of operating the device 30.

[0084] Figure 24A is a sectional view of the device 30 after the introduction of a block 21 of the liquid material through the inlet opening 32 of the device 30. The block 21 is supplied to the droplet-forming device 30 by the transfer device 14, not shown in Figure 24A. The transfer device 14 can project the block 21 into the inlet opening 32 of the device 30 with a given initial velocity. The electro-acoustic transducers 40 are controlled by the control circuit 41 to provide a standing acoustic wave 50 in the internal volume 34 comprising a node N, for example substantially in the center of the pipe 31, and antinodes V around the node N.

[0085] Figure 24B is a sectional view of the device 30 when the block 21 arrives on the standing acoustic wave 50. The pressure variations at the antinodes V of the standing acoustic wave 50 tend to force the liquid material out of the locations of the antinodes V towards the node N of the standing acoustic wave 50.

[0086] Figure 24C is a sectional view of the device 30 after the formation of a droplet 20 at the node N of the standing acoustic wave 50.

[0087] Figure 24D is a sectional view of the device 30 after the droplet 20 has continued its path in the pipe 31 to the outlet opening 33 under the action of gravity. Figure 24D also partially shows the device 60 for recovering liquid material located on the side of the outlet opening 33. The device 60 makes it possible to recover excess material liquid or any droplets 20 that may have formed incorrectly.

[0088] The position of the droplet 20 relative to the outlet orifice 33 can advantageously be precisely controlled. Furthermore, this position can advantageously be modified during use of the device 30 by modifying the standing acoustic wave 50. Furthermore, the droplet 20 may advantageously not be in mechanical contact with the walls of the conduit 31 when it exits through the outlet orifice 33.

[0089] According to one embodiment, the block 21 already corresponds to a droplet of the fluid material. In this case, the droplet formation device 30 makes it possible to move the incident droplet 21 to a given position.

[0090] The embodiments described previously in relation to Figures 24A to 24D relate to the treatment of a single droplet 20. However, the droplet forming device 30 may be used for the simultaneous treatment of several droplets by the generation of a standing acoustic wave and/or acoustic radiation forces.

[0091] Figure 25A, Figure 25B, Figure 25C, and Figure 25D are partial and schematic sectional views of the droplet forming device 30 of Figure 2A, 2B or 3 at successive steps of an embodiment of a method of operating the device 30.

[0092] Figure 25A is a sectional view of the device 30 after the introduction of a block 21 of the liquid material through the inlet opening 32 of the device 30. The block 21 is supplied to the droplet-forming device 30 by the transfer device 14, not shown in Figure 15. The transfer device 14 can project the block 21 into the inlet opening 32 of the device 30 with a given initial speed. The electro-acoustic transducers 40 are controlled by the control circuit 41 to provide a standing acoustic wave 50 in the internal volume 34 comprising nodes N, for example substantially distributed along a plane, and antinodes V between the nodes N.

[0093] Figure 25B is a sectional view of the device 30 when the block 21 arrives in the standing acoustic wave 50. The pressure variations at the antinodes V of the standing acoustic wave 50 tend to expel the liquid material at the locations of the antinodes V. The block 21 thus tends to divide into droplets located substantially at the locations of the nodes N of the standing acoustic wave 50.

[0094] Figure 25C is a sectional view of the device 30 after the division of the block 21 into droplets 20 at the nodes N of the standing acoustic wave 50.

[0095] Figure 25D is a sectional view of the device 30 after the droplets 20 continue their path in the conduit 31 to the outlet opening 33 under the action of gravity.

[0096] Several droplets 20 may advantageously be supplied simultaneously by the droplet forming device 30. The positions of the droplets 20 relative to the outlet orifice 33 may advantageously be precisely controlled. Furthermore, the droplets 20 may advantageously not be in mechanical contact with the walls of the conduit 31 when they exit through the outlet orifice 33. Furthermore, the number of droplets 20 supplied simultaneously may advantageously be varied during use of the device 30 by varying the standing acoustic wave 50. [0097] Figures 24A to 24D, 25A to 25D, and 26 are schematic sectional views illustrating embodiments of methods of operating the droplet forming device 30 which can be implemented with a droplet forming device 30 having an axially rotationally symmetrical structure as for the device illustrated in Figure 3 or with a droplet forming device 30 having a planarly symmetrical structure as for the device illustrated in Figure 2A or 2B, and more generally with a droplet forming device 30 not having symmetry.

[0098] Figures 24A to 24D, 25A to 25D, and 26 are schematic sectional views illustrating embodiments of methods of operating the droplet forming device 30 which can be implemented with a droplet forming device 30 having an axially rotationally symmetrical structure as for the device illustrated in Figure 3 or with a droplet forming device 30 having a planarly symmetrical structure as for the device illustrated in Figure 2A or 2B, and more generally with a droplet forming device 30 not having symmetry.

[0099] In the embodiments described above, all the electro-acoustic transducers 40 of the droplet-forming device 30 20 are located in the same plane inclined relative to the axis A of the pipe 31, for example perpendicular to the axis A of the pipe 31, which means that the geometric centers of the electro-acoustic transducers 40 are located in the same plane inclined relative to the axis A of the pipe 31, for example perpendicular to the axis A of the pipe 31. However, the droplet-forming device 30 20 may comprise electro-acoustic transducers 40 which are located in different planes perpendicular to the axis A, which means that the geometric centers of the electroacoustic transducers 40 are located in different planes perpendicular to the axis A. This allows in particular the formation in the cavity of a standing ultrasonic wave having nodes in different planes perpendicular to the axis A. This also allows the application of an acoustic radiation force on the droplet, possibly variable throughout the movement of the droplet 20 over at least part of its path in the cavity 34.

[0100] Figure 27 is a partial, schematic perspective view of another embodiment of the droplet forming device 30 of the droplet delivery system 10 of Figure 1A. The device 30 illustrated in Figure 27 comprises all of the elements of the droplet-forming device 30 illustrated in Figure 2A or 2B with the difference that it comprises several electroacoustic transducers 40 on each face 37 of the pipe 31 located in different planes inclined relative to the axis A, for example perpendicular to the axis A, which means that the geometric centers of the electroacoustic transducers 40 are located in different planes inclined relative to the axis A, for example perpendicular to the axis A. According to one embodiment, the control circuit connected to the electroacoustic transducers 40 resting on the same face 37 makes it possible to apply a specific control signal to each electroacoustic transducer 40 resting on the same face 37. According to one embodiment, the same control signals can be transmitted to a group of electroacoustic transducers 40 resting on the same face 37 or on several different faces 37. In Figure 27 on each face 37, the electro-acoustic transducers 40 are arranged in rows and columns to form a matrix of electro-acoustic transducers 40. [0101] According to one embodiment, the device 30 for forming droplets 20 of FIG. 27 is used to form standing acoustic waves whose nodes are located on several planes substantially perpendicular to the axis A. According to another embodiment, the transducers 40 resting on a face 37 of the device are individually driven by control signals out of phase with each other and can provide acoustic waves having amplitudes which are used jointly to form a standing acoustic wave with a distribution of non-rectilinear nodes in the cavity 34.

[0102] Figure 28 is a partial and schematic sectional view of an embodiment of droplet formation 20 comprising electroacoustic transducers 40 located in different planes inclined relative to the axis A, for example perpendicular to the axis A, which means that the geometric centers of the electroacoustic transducers 40 are located in different planes inclined relative to the axis A, for example perpendicular to the axis A, and illustrates a standing wave comprising nodes N which are not distributed regularly along the axis A of the pipe 31. This can make it possible, for example, to conduct the drops in a direction not parallel to the axis A, or to make sorts of funnels.

[0103] According to one embodiment, the electro-acoustic transducers 40 are controlled so that the standing acoustic wave evolves as a function of time. According to one embodiment, the electro-acoustic transducers 40 are controlled to obtain different or similar successive standing acoustic waves along the delta axis. According to one embodiment, the electro-acoustic transducers 40 are controlled to apply a radiation force to the droplet having a component perpendicular to axis A, in different planes perpendicular to axis A.

[0104] According to one embodiment, the control signals provided to the transducers 40 can be adapted so as to focus ultrasonic waves towards the droplet 20 during its movement in the cavity 34.

[0105] According to one embodiment, the control of the electro-acoustic transducers 40 can be modified over time as a function of at least one measurement signal. In amplitude, phase and frequency. In particular, the amplitude, frequency and/or phase of the ultrasonic waves emitted by the electro-acoustic transducers 40 can be modified over time as a function of at least one measurement signal. The measurement signal can be provided by a real-time detection system for the positioning of the droplet 20. According to one embodiment, the detection system can be an optical system or an acoustic system. According to one embodiment, the electro-acoustic transducers 40 can be part of the detection system.

[0106] Figure 29 is a partial and schematic sectional view of the droplet forming device 30 of Figure 2A, 2B or 3 at a step of another embodiment of a method of operating the droplet forming device.

[0107] According to one embodiment, the electro-acoustic transducers 40 are controlled by the control circuit 41 to emit ultrasonic waves 51 which propagate in the internal volume 34 of the pipe 31 to the droplet 20 without however forming standing waves in the internal volume. The ultrasonic waves 51 exert acoustic radiation forces which act on the droplet 20 of liquid material during the path of the droplet 20 in the pipe 31. The acoustic radiation forces are mechanical forces whose amplitude depends in particular on the acoustic absorption capacity of the liquid material of the droplet 20 and on the difference in acoustic impedance between the liquid material and the air at the interface. In particular, the acoustic radiation forces which act on the droplet 20 of liquid material can cause the droplet 20 to split into several droplets 20, and can, if necessary, deflect the droplet 20 from its trajectory along the axis A by applying to the droplet a force oriented along an axis perpendicular to the axis A, or apply a rotation to the droplet 20, which has the effect of changing the trajectory of the droplet 20 and/or better containing its shape up to the substrate 22, not shown in FIG. 29.

[0108] In the embodiment illustrated in Figure 29, two electro-acoustic transducers 40 are shown. However, when the forces exerted on the block 21 are essentially acoustic radiation forces, the droplet-forming device 30 comprising a single electro-acoustic transducer 40 can be used, in particular by providing that the wall 33 opposite the single electro-acoustic transducer 40 is absorbent for ultrasonic waves.

[0109] Figure 30 is a partial and schematic sectional view of an alternative embodiment of the device 30 for forming droplets 20 shown in Figure 29. According to this alternative, at least one of the electroacoustic transducers 40 is further adapted to operate as an ultrasonic wave sensor 52, and is adapted to provide the control circuit 41 with a signal S' representative of the ultrasonic waves 52 captured. The control circuit 41 is then further adapted to carry out processing of the signal S'. ultrasonic waves 52 captured by the electroacoustic transducer 40 may come from reflections of the ultrasonic waves 51 emitted by one of the electroacoustic transducers 40 towards the droplet 20 or may correspond to ultrasonic waves 51 emitted by one of the electroacoustic transducers 40 having passed through the droplet 20.

[0110] According to one embodiment, at least one of the electro-acoustic transducers 40 is used alternately as an ultrasonic wave generator and as an ultrasonic wave sensor. During a control phase in which the electro-acoustic transducer 40 is used as an ultrasonic wave generator, the control circuit 41 transmits the control signal S to the electro-acoustic transducer 40 for the emission of the ultrasonic waves 51 and, during a measurement phase during which the electro-acoustic transducer 40 is used as an ultrasonic wave sensor, the control circuit 41 receives the signal S' transmitted by the electro-acoustic transducer 40 following the reception of the ultrasonic waves 52 by the electro-acoustic transducer 40.

[0111] According to one embodiment, the control circuit 41 is adapted to analyze the signal S' provided by the electro-acoustic transducer 40 during a measurement phase to modify the signal S provided during a subsequent control phase provided to at least one of the electro-acoustic transducers 40. According to one embodiment, the control circuit 41 is adapted to determine the evolution of properties of the droplet 20, for example the position of the droplet 20, by implementing a time-of-flight method by determining the propagation time of the ultrasonic waves 51 from the electro-acoustic transducer 40 to the droplet 20 and the propagation time of the reflected ultrasonic waves 52 on the droplet 20 to the electro-acoustic transducer 40. According to one embodiment, the control circuit 41 is adapted to determine the evolution of properties of the droplet 20, for example the position of the droplet 20 and/or its volume, by an analysis of the resonance of the interior volume 34 or by an analysis of the resonance of the droplet 20 by determining the spectrum of the reflected ultrasonic waves 52 on the droplet 20 and/or of the reflected ultrasonic waves 52 having passed through the droplet 20. The modification of the signal S comprises for example the increase in the intensity of the emitted ultrasonic waves 51, the decrease in the intensity of the emitted ultrasonic waves 51, or the stopping of the emission of the ultrasonic waves 51.

[0112] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art.

[0113] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art based on the functional indications given above.

Claims

1. Device (30) for forming droplets (20) of a liquid material comprising a conduit (31) extending along an axis (A), the conduit (31) being filled with a gas or a gas mixture and having an inlet opening (32) intended to receive a block (21) or a droplet of the liquid material, the device (30) for forming droplets (20) further comprising electro-acoustic transducers (40) configured to emit first ultrasonic waves (51) into the gas or the gas mixture contained in the conduit (31) up to the block (21) or the droplet of the liquid material, the superposition of the first ultrasonic waves (50) forming a standing acoustic wave (50) in the conduit (31), which results in the formation or displacement of the droplet (20) of the liquid material. 2. Device according to claim 1, comprising electro-acoustic transducers (40) located in a first plane inclined relative to said axis (A) and configured to emit the first ultrasonic waves (51) into the gas or gas mixture contained in the pipe (31) up to the block (21) or the drop (20) of liquid material. 3. Device according to claim 1 or 2, in which the first plane is orthogonal to said axis (A). 4. Device according to claim 2 or 3, comprising at least a first pair of electro-acoustic transducers (40) symmetrical with respect to said axis (A). 5. Device according to claim 4, further comprising a second pair of electro-acoustic transducers (40) symmetrical with respect to said axis (A). 6. Device according to any one of claims 1 to 5, further comprising an electronic circuit (41) for controlling said at least one electro-acoustic transducer (40). 7. Device according to claim 6 in its attachment to claim 2, in which the electronic circuit (41) is configured to control the electro-acoustic transducers (40) so that the superposition of the first ultrasonic waves (50) forms a standing acoustic wave (50) in the pipe (31). 8. Device according to claim 6, wherein the electronic control circuit (41) is configured to control said at least one electro-acoustic transducer (40) to deform the block (21) of liquid material under the action of acoustic radiation forces. 9. Device according to claim 6, wherein the electronic control circuit (41) is configured to control said at least one electro-acoustic transducer (40) to provide the first ultrasonic waves (51) in a first phase and to control said at least one electro-acoustic transducer (40) to pick up second ultrasonic waves (51, 52) in a second phase. 10. Device according to any one of claims 2 to 5, comprising additional electro-acoustic transducers (40) located in a second plane parallel to the first plane. 11. Device according to any one of claims 1 to 10, wherein the electro-acoustic transducer (40) is a capacitive micromachined ultrasonic transducer, or a piezoelectric micromachined ultrasonic transducer, or a transducer comprising at least one layer of a piezoelectric material (43). 12. 3D printer comprising a device (30) for forming droplets (20) according to any one of claims 1 to 11, a reservoir (12) of the liquid material to be printed (30), and a device (14) for transferring the block (21) of liquid material from the reservoir (12) to the device (30) for forming droplets.