Electroacoustic Device

Abstract

Electroacoustic device (5) for generating at least one acoustic wave (Fv,Vx), the device comprising a piezoelectric substrate (10) and first (15) and second (20) groups of electrodes (60,65,70,75) arranged on the substrate, each electrode of the first and second groups comprising a track (80.sub.a-f,85.sub.a-f,90.sub.a-d,95.sub.a-d), the tracks (90.sub.a-d,95.sub.a-d) of the electrodes of the first group spiralling around a same spiral axis (Z) along a first winding direction (W.sub.1), and the tracks (80.sub.a-f,85.sub.a-f) of the electrodes of the second group spiralling around said spiral axis along a second winding direction (W.sub.2) opposite to the first winding direction.

Claims

1-16. (canceled)

17. An electroacoustic device for generating an acoustic wave, comprising: a piezoelectric substrate; first electrodes arranged on the substrate, each first electrode comprising first tracks; and second electrodes arranged on the substrate, each second electrode comprising second tracks, wherein, the first tracks spiral around a spiral axis in a first winding direction, and the second tracks spiral around the spiral axis in a second winding direction opposite to the first winding direction.

18. The device of claim 17, wherein the first electrodes each comprise a first contact brush arranged on the substrate and connected to corresponding first tracks.

19. The device of claim 18, each first contact brush is electrically connected to one of the second tracks.

20. The device of claim 18, wherein the second electrodes each comprise a second contact brush arranged on the substrate and connected to corresponding second tracks.

21. The device of claim 20, wherein the first tracks are arranged remotely from the second contact brushes.

22. The device of claim 20, wherein the second tracks extend from the second contact brushes to corresponding ones of the first tracks.

23. The device of claim 20, the wherein: one of the second tracks is partially superimposed on one of the first contact brushes; and/or one of the first tracks is partially superimposed on one of the second contact brushes.

24. The device of claim 17, wherein the acoustic wave is a swirling surface acoustic wave propagating in the substrate.

25. The device of claim 24, further comprising a support acoustically coupled with the substrate, the device being further configured such that the swirling surface acoustic wave is transmitted to the support and propagates in the support as an acoustic vortex.

26. The device of claim 17, wherein: the acoustic wave is a focused acoustic vortex propagating in the substrate; or the device comprises a support acoustically coupled with the substrate, the acoustic wave being a focused acoustic vortex that propagates in the support; or the acoustic wave is a focused acoustic vortex that propagates in a fluid medium acoustically coupled with the device.

27. A process for manipulating an object embedded in a fluid medium, the process comprising: generating an acoustic vortex or a focused acoustic vortex using a device of claim 17; propagating the acoustic vortex or the focused acoustic vortex in the fluid medium to create a radiation pressure to entrap the object; and manipulating the object by displacement of the first and second electrodes relatively to the fluid medium.

28. The process of claim 27, wherein the manipulating the object comprises: rotating the object; and/or translating the object.

29. A process comprising: generating an acoustic vortex or a focused acoustic vortex using a device of claim 17; and propagating the acoustic vortex or the focused acoustic vortex in a fluid medium to generate a vortical flow of the fluid medium.

30. The process of claim 27, wherein the generating an acoustic vortex or a focused acoustic vortex comprises electrically supplying: a first master signal to a first one of the first electrodes; a first slave signal to a second one of the first electrodes; a second master signal to a first one of the second electrodes; and a second slave signal to a second one of the second electrodes.

31. The process of claim 30, wherein the amplitude of the first master signal and/or of the first slave signal is different from an amplitude of the second master signal and/or of the second slave signal.

32. The process of claim 27, wherein: the first electrodes and the second electrodes at least partially define respective first and second wave transducers having different resonance frequencies; and the generating an acoustic vortex or a focused acoustic vortex comprises supplying master and slave electric signals adapted for exciting the first and second wave transducers with a frequency ranging between the resonance frequencies of the first and second wave transducers.

Description

[0181] The invention can be better understood from a reading of the detailed description that follows, with reference to exemplary and non-limiting embodiments thereof, and by the examination of the appended drawing, in which:

[0182] FIG. 1 illustrates, from a front view along the spiral axis, of a portion of a first example of a device according to the invention;

[0183] FIG. 2 is a cross section view of the electroacoustic device illustrated on FIG. 1;

[0184] FIG. 3 illustrates some other features of the tracks of the electrodes of the example illustrated on FIG. 1;

[0185] FIGS. 4 and 5 show the evolution with time t of the amplitude A of master and slave signals supplied to electrodes of the first and second groups of the device illustrated on FIG. 1, according to some examples of implementation;

[0186] FIG. 6 illustrates the evolution of the radial step between consecutive tracks of electrodes of the first and second group, depending on the radial distance r.sub.d to the spiral axis, according to a second example of device of the invention;

[0187] FIG. 7 is a cross section view of the second example of electroacoustic device;

[0188] FIG. 8 is a front view of another example of device;

[0189] FIG. 9 is a cross section view in a plane containing the spiral axis of the device illustrated on FIG. 8;

[0190] FIG. 10 is a front view of another example of the device;

[0191] FIG. 11 illustrates the definition of reference points for expressing equations (i) to (x), and

[0192] FIG. 12 illustrates a method implemented to define the specific shape of a hot electrode for generating a focalized ultrasonic wave according to the second specific embodiment of the invention.

[0193] In the drawing, the respective proportions and sizes of the different elements are not always respected for sake of clarity.

[0194] FIG. 1 illustrates an electroacoustic device 5 according to the invention.

[0195] The device comprises a substrate 10 and first 15 and second 20 groups of electrodes arranged on a face of the substrate.

[0196] The substrate comprises a part 25 made of a piezoelectric material and a dielectric layer 30 made of silica which contacts and overlaps the part. It is shaped as a plate parallel to a plane defined by directions X and Y. The substrate has for instance a thickness e.sub.s equal to 120 μm, and presents an upper face 35 and a lower face 40. It is for instance made of LiBNO.sub.3 Y-cut at 35°. The two groups of electrodes are provided on the upper face of the substrate. In a variant, they can be arranged on opposite faces of the substrate.

[0197] The first group of electrodes and the substrate defines a first wave transducer 45 and the second group of electrodes and the substrate defines a second wave transducer 50.

[0198] Each electrode 60, 65, 70, 75 of the first and second groups comprises several tracks 80.sub.a-f, 85.sub.a-f, 90.sub.a-d, 95.sub.a-d. Each track spirals around a same spiral axis Z which is normal to the plate.

[0199] The tracks 90, 95 of the electrodes of the first group spiral around a same spiral axis Z along a first winding direction, as indicated by curved arrow W.sub.1, and the tracks 80, 85 of the electrodes 60,65 of the second group spiralling around said spiral axis along a second winding direction, as indicated by curved arrow W.sub.2, which is opposite to the first winding direction W.sub.1. The tracks 90, 95 of the electrodes of the first group spiral in an anti-clockwise direction whereas the tracks 80, 85 of the electrodes of the second group spiral in a clockwise direction. The spiral axis Z is perpendicular to the substrate upper face which supports the first and second groups of electrodes.

[0200] The tracks 90,95 of the electrodes 70,75 of the first group are provided radially inner from the tracks 80, 85 of the electrodes 60, 65 of the second group.

[0201] As illustrated on FIG. 3, each track has a width w.sub.d, measured along a radial direction r.sub.d, which is less, for instance at least 10 times less, even at least 100 times less, than the length of the track, the length being measured along the first, respectively second winding direction.

[0202] The first group consists in first 70 and second 75 electrodes, each comprising one contact brush 100, 105 and four tracks 90.sub.a-d, 95.sub.a-d, and the second group consists in two electrodes 60, 65, each comprising two contact brushes 110, 115 and six tracks 80.sub.a-f, 85.sub.a-f. Such a number of tracks is nevertheless not limitative and can be adapted depending on the desired shape of the wave front to generate.

[0203] Each track of each electrode of the first and second group extends around the spiral axis with an angle greater than 300°, from the contact brush it is in contact with.

[0204] The tracks of the first electrode and the tracks of the second electrode of the first group, respectively the second group, are arranged in an alternating manner, radially from the spiral axis.

[0205] The tracks of the electrodes of the first group are at a distance of the contact brushes of the electrodes of the second group and vice-versa. Moreover, the tracks of the first electrode of the first group are at a distance from the tracks of the second electrode of the first group, and the tracks of the first electrode of the second group are at a distance from the tracks of the second electrode of the second group.

[0206] In addition, each of the four contact brushes is connected to a power supply apparatus 120 which is aimed at providing to every electrode a specific electric signal, at it will be explained in more detail here below. In the example of FIG. 1, the radial step Δ.sub.r between two consecutive tracks of each of the electrodes of the first and second group is constant, and the device is adapted to generate a SSAW. As it observed on FIG. 3, the radial step is defined by the radial distance between the radially inner edge of a coil or of a track and the radially inner edge of the consecutive coil of track.

[0207] Moreover, as observed on FIG. 2, the device comprises a support 130 which is acoustically coupled to the substrate. The electrodes are arranged between the support and the substrate. The support is acoustically coupled to the piezoelectric part by means of a layer of a coupling medium 135, for instance optical adhesive NOA61 of Portland Product.

[0208] The device further comprises a base 132 disposed on the upper face of the support. The base is a plate made of borosilicate glass of thickness e.sub.a of 150 μm. It can be moved in at least two directions transverse to the spiral axis. An interface liquid 133 of thickness less than 10 μm is provided between the base and the support, such as to acoustically couple the base with the support and such that the base can be displaced relatively to the support without damaging the support.

[0209] A sound absorber 140 made for instance of PDMS is provided on the base, which defines a cavity 145 containing a fluid medium 150, preferably a liquid medium. An object 155 is embedded in the fluid medium.

[0210] When the electrodes of both the first and second groups are electrically supplied, a SSAW is generated by the device and propagates at the surface of the substrate. It is transmitted in the bulk of support, but the swirling SAW degenerates at the interface between the substrate and the support in an acoustic vortex or in a degenerated acoustic vortex propagating in the bulk of the support and in the liquid medium, as illustrated by arrow Vx.

[0211] The radiation pressure associated with the vortex concentrates in a volume represented by the dashed square 168, which is located perpendicularly to the substrate and substantially aligned with the spiral axis Z.

[0212] The object 155, when located in the vicinity of said volume represented by the dashed square 168, also named “3D trap”, if having a size comparable to the wavelength of the swirling SAW, is submitted to attraction forces which aims at entrapping said object in the 3D trap.

[0213] By displacing the base relatively to the support, the object can be brought close to the spiral axis. It can then be manipulated and notably be entrapped along the spiral axis.

[0214] In a variant, the tracks of the electrodes can be disposed on a face of the substrate which is opposite to the face regarding the support. The swirling wave can be either a Lamb wave or a bulk wave.

[0215] In order to control the rotation of the object, and notably to prevent the object from any rotation, the device illustrated on FIGS. 1 and 2 is electrically supplied by the power supply apparatus 120.

[0216] Power supplying can be performed in the following ways.

[0217] The power supply apparatus can deliver one of the electrodes of the first group, respectively of the second group, with a master electric signal and the other electrode of the first group, respectively of the second group, with a slave electric signal which is out of phase with the master electric signal.

[0218] Preferably, the amplitudes of the master electric signal and of the slave electric signal supplied to the first group of electrodes, respectively to the second group of electrodes, are equal. Preferably, the frequencies of the master electric signal and of the slave electric signal supplied to the first group of electrodes, respectively to the second group of electrodes, are equal.

[0219] In a first implementation of the device, as illustrated on FIG. 4, the amplitude A of the master electric signal 160, respectively to the slave electric signal 165, supplied to the first group of electrodes is different from the amplitude A of the master electric signal 170, respectively to the slave electric signal 175, supplied to the second group of electrodes.

[0220] In a second example of implementation of the device, the frequency of the master electric signal, respectively of the slave electric signal, supplied to the first group of electrodes is different from the frequency of the master electric signal, respectively of the slave electric signal, supplied to the second group of electrodes.

[0221] In a third example of implementation, the frequency of the master electric signal, respectively of the slave electric signal, supplied to the first group of electrodes and the frequency of the master electric signal, respectively of the slave electric signal, supplied to the second group of electrodes are both ranging between the resonance frequency of the first wave transducer 45 and the resonance frequency of the second wave transducer 50. By appropriately tuning said signal frequencies, the user of the device can modulate the relative effect of both first and second wave transducers.

[0222] Preferably, the frequencies of the master and slave electric signals supplied to the first and second group of electrodes are equal. Preferably, the amplitudes of the master and slave electric signals supplied to the first and second group of electrodes are equal.

[0223] A man skilled in the art knows how to determine the resonance frequency of a wave transducer, either by computation or by appropriate measurement techniques.

[0224] Having wave transducers presenting both different resonant frequencies can be achieved notably by the radial step between two consecutives tracks of one of the electrodes of the first group, or the radial step between two consecutive coils of the track of one of the electrodes of the first group, being different from the radial step between two consecutives tracks of one of the electrodes of the second group, or the radial step between two consecutive coils of the track of one of the electrodes of the second group.

[0225] In a fourth example of implementation, the master and slave signals supplied to the first, respectively second, group of electrodes can be provided as wave packet. Notably, as illustrated on FIG. 5, when master Pm1 and slave Ps1 wave packets are supplied to the corresponding electrodes of the first group, the electrodes of the second group are off, no electric signal being supplied to them. The supply of the electric signal can be alternating between supplying the first group of electrodes with wave packets, the electrodes of the second group being off, then followed by supplying the second group with master Pm.sub.2 and slave Ps.sub.2 wave packets, and the electrodes of the first group being off, and so on. Notably, wave packets can be supplied to the second group of electrodes as soon as the supply of wave packets to the first group of electrodes to the first packet has ended, and vice versa, as illustrated on FIG. 5.

[0226] In particular, the duration Δt.sub.1, respectively Δt.sub.2 between supplying two consecutive wave packets to the first, respectively second group of electrodes, can be lower than the hydrodynamic reaction time of the object. The hydrodynamic reaction time can be easily determined by a skilled worker from the size of the object and the viscosity of the fluid medium which embeds the object.

[0227] Notably, the sum Δt.sub.1+Δt.sub.2 of the duration of the wave packet supplied to the first group of electrodes and of the duration of the wave packet supplied to the second group of electrodes is lower than the hydrodynamic reaction time of the object.

[0228] The example illustrated on FIG. 1 is notably characterized by consecutive tracks of the electrodes of the first, respectively second, group being separated by a constant radial step. In a variant illustrated on FIGS. 6 and 7, the tracks of the electrodes of the first, respectively second, group are arranged on the substrate such that the radial step Δr.sub.1, respectively Δr.sub.2 between two successive tracks decreases radially from the spiral axis, along a radial direction r.sub.d.

[0229] Furthermore, and notably in order to supply the device according to the third example of implementation described here above, the radial decrease α.sub.1, α.sub.2 of the radial step can be different between the two groups of electrodes. The tracks of the first and second groups of electrodes each draw a line along a polar coordinate R(θ), being obtained by solving the equation (i) described here above.

[0230] In the example of FIG. 7, the first and second groups each comprise two hot electrodes 60, 65, 70, 75 provided on the face of the device which faces the support. The hot electrodes of each group are supplied with out of phase electric signals.

[0231] Furthermore, the device comprises a ground electrode 190, arranged on the lower face 40 of the substrate. The ground electrode is connected to a ground socket of the power supply apparatus. It overlaps both the first and second grounds electrodes.

[0232] When powering the hot electrodes (not represented for clarity reasons), the first and second wave transducers are deformed by volume ultrasonic waves propagating substantially along a direction parallel to the spiral axis, in the piezoelectric substrate.

[0233] The wave transducers transmit the volume ultrasonic waves to the bulk of the support wherein they define a focalized ultrasonic vortex Fv which focal locus (wherein the acoustic intensity is the lowest) is located in the cavity 145. By displacing the base relatively to the support, the object can be brought close to the focal locus. It can then be manipulated and notably be entrapped along the spiral axis.

[0234] The device illustrated on FIG. 8 differs from the device illustrated on FIG. 1 by the fact that the tracks of the electrodes of the first and second groups are interdigitated the one with another.

[0235] Notably, a group of two tracks of different polarity of the second group of electrodes are arranged radially between two different groups of tracks of different polarity of the first group of electrodes and vice versa. In this embodiment, the rings intensity of the two counter rotating vortices synthesized by the first and second group of electrodes can be more similar, which is desirable when equilibrating the master electrical signals to control the speed of rotation of the object.

[0236] The arrangement on the substrate of the contact brushes 100, 105 and tracks 90, 95 of the electrodes of the first group prevents any continuous extension of the contact brushes 110, 115 of the electrodes of the second group along a substantially radial direction such as to connect the corresponding tracks.

[0237] As it can be observed on FIG. 9, the contact brush 110 of one of the electrodes of the second group is provided on a face of the piezoelectric part 25. Two portions 190.sub.a-b of the contact brush are provided on top of the dielectric layer 30 from either side of one track 95 of the electrode 75 of the first group. The two portions 190.sub.a-b are connected with respective tracks 80 of the electrode 60 of the second group. The two portions 190.sub.a-b are connected the one with the other by a buried portion 200 which follows a track defined by a tunnel 205 formed in the dielectric layer. The buried portion is provided at a distance from one track of the first electrode, by a portion of the dielectric layer.

[0238] The manufacture of the buried portion of the dielectric layer can be performed by selective etching of the silica dielectric layer followed by deposition of an alloy or a metal such as to form the respective portions of the contact brush.

[0239] FIG. 10 shows another example of the device 5 according to the invention. It comprises first and second groups of electrodes.

[0240] The first 15 group of electrodes is arranged radially inner to the second group 20 of electrodes.

[0241] The first group of electrodes comprise two electrodes 90, 95 each consisting in a single track comprising five coils. The second group of electrodes comprises two electrodes 80, 85 each comprising a single track comprising seven coils. Each electrode of the second group of electrodes comprises a single track and a contact brush 110, 115, the track being connected to the contact brush by one its end 205, 210. Further, the track of each electrode of the second group is connected by its opposite end 215, 220 to the track of one of the electrodes of the first group.

[0242] Thus, the track of one of the electrodes of the first group and the track of one of the electrodes of the second group are connected together to the contact brush of the electrode of the second group and the track of the other electrode of the first group and the track of the other electrode of the second group are connected together to the contact brush of the electrode of the first group.

[0243] Thus, when a current is supplied to an electrode of the second group through the corresponding contact brush, it is also supplied to the corresponding electrode of the first group.

[0244] In addition, the width w.sub.d1 of the track of each electrode of the first group is different from the width w.sub.d2 of the track of the corresponding electrode of the second group to which the electrode of the first group is connected. Providing tracks of electrodes of first and second groups having different widths results in first and second wave transducers presenting different reasoning frequencies.

[0245] By selecting an appropriate frequency of the electric master and slave signals supplied to the first and second groups of electrodes, the rotation of the object which is submitted to the acoustic wave generated by the device can be controlled, and notably prevented.

[0246] FIG. 11 illustrates the location of a Cartesian coordinate system for defining a spherical vortex such as for instance defined by equation (x), which focal locus is referred by point 2 and intercepts the plane, referred by n=0, on which the electrodes are provided, for instance being the upper face 35 of the piezoelectric part.

[0247] FIG. 12 aims at illustrating the resolution of equations (i) to (vii), in the case the vortex Fv propagates in the support from the hot track towards the focal locus 2 over a distance z.sup.(N) along axis Z. The vortex Fv comprises 3D lines along which the phase is constant, named equi-phase lines. For instance, along an equi-phase line 99, the phase of the vortex is the same at points 250a to 250c. The projection, along the line 260 that joins the focal locus 2 and points 250a to 250c, of equi-phase line is a plane line which is set by parameter R(θ) expressed from the center C on the surface where the tracks are provided. In other words, the intersection of the phase of the focalized ultrasonic vortex onto the plane where the hot track has to be provided yields the drawing of the hot track. This is for instance mathematically expressed by the set of equations (i) to (viii). By forming at least one hot track drawing said line R(θ), an ultrasonic vortex focalizing at focal point 2 can be generated.

[0248] As it appears throughout the present description, the device according to the invention improves the efficiency of manipulating an object embedded in a fluid medium, by controlling its rotation when the object is entrapped. It further improves the selectivity, when manipulating a specific object among a population of objects.

[0249] Of course, the invention is not limited to the specific embodiments detailed in the present description.