Vibrating device comprising embedded mechanical reflectors for defining an active plate mode propagation area and mobile apparatus comprising the device

Abstract

A vibrating device comprises: a first support configured to be deformed having a surface defined in a plane in directions X and Y; at least one actuator configured to generate plate modes propagated in the first support; the first support comprising: at least one defect with respect to the propagation of the plate modes; the defect being of geometrical nature or corresponding to a structural heterogeneity; comprising: a second support; at least one embedded mechanical reflector secured to the first support and in contact with the first support, configured to immobilize the first support in at least one direction Z at right angles to the directions X and Y, the mechanical reflector being secured to the second support and; the embedded mechanical reflector being configured to isolate a so-called active zone belonging to the surface defined in a plane in directions X and Y in which the plate modes are propagated, the active zone excluding the defect; the actuator being situated in the active region.

Claims

1. A vibrating device comprising: a first support configured to be deformed having a surface defined in a plane in directions X and Y, said first support comprising at least one defect with respect to the propagation of the plate modes, said defect being of geometrical nature or corresponding to a structural heterogeneity; at least one actuator configured to generate plate modes being propagated in said first support; a second support; at least one embedded mechanical reflector in contact with said first support, the at least one embedded mechanical reflector is secured to said first support such that the first support is immobilized in at least one direction Z at right angles to said directions X and Y, said mechanical reflector being secured to said second support, wherein said embedded mechanical reflector being configured to isolate an active zone belonging to said surface defined in a plane in directions X and Y in which the plate modes are propagated, said active zone excluding said defect, said actuator being situated in said active zone, said embedded mechanical reflector is in contact on at least a first surface with the first support and on at least a second surface with the second support, the first and second surfaces of the embedded mechanical reflector are elongated, and the first support including a bottom surface defined in a plane in directions X and Y and the second support including a top surface defined in a plane in directions X and Y that faces the bottom surface of the first support, the embedded mechanical reflector being secured to each of the bottom surface of the first support and the top surface of the second support.

2. The vibrating device as claimed in claim 1, wherein the first support comprises defects, the device comprising a set of embedded mechanical reflectors configured to define said active zone, excluding said defects.

3. The vibrating device as claimed in claim 1, wherein the first support comprises defects, the device comprising a set of embedded mechanical reflectors configured to define several active zones, excluding said defects.

4. The vibrating device as claimed in one of claim 1, wherein said first support comprises, at the periphery, roundings, said device comprising at least one pair of embedded mechanical reflectors configured to define said active zone, excluding said roundings.

5. The vibrating device as claimed in one of claim 1, comprising a set of actuators.

6. The vibrating device as claimed in claim 5, wherein the actuators are distributed linearly in the directions X and/or Y.

7. The vibrating device as claimed in claim 1, comprising at least one or more actuators positioned on the surface of said first support, opposite that facing said second support.

8. The vibrating device as claimed in claim 1, comprising at least one or more actuators positioned on the surface of said first support, facing said second support.

9. The vibrating device as claimed in claim 1, wherein the embedded mechanical reflector comprises elementary discrete elements separated from one another by a distance such that it makes it possible to isolate said defect from said active zone.

10. The vibrating device as claimed in claim 1, wherein said first support is a plate.

11. The vibrating device as claimed in claim 1, wherein the second support is a casing in which the first support is positioned.

12. The vibrating device as claimed in claim 1, wherein: the first support comprises at least one embedment region; the second support comprises at least one protuberance capable of cooperating with said embedment region to immobilize it in the direction Z and render the protuberance secured to the first support, the protuberance and the embedment region defining said embedded mechanical reflector.

13. The vibrating device as claimed in claim 1, comprising at least one glue element, locally gluing the first support to the second support and defining said embedded mechanical reflector.

14. The vibrating device as claimed in claim 1, comprising a haptic face plate with at least one defect.

15. The vibrating device as claimed in claim 14, wherein the haptic face plate has a rectangular geometry with rounded corners.

16. The vibrating device as claimed in claim 14, wherein the haptic face plate has a diagonal of between 10 cm and 12 cm and embedded mechanical reflectors having a width of between 2 mm and 10 mm.

17. The vibrating device as claimed in claim 15, comprising two columns of mechanical reflectors, of which one is positioned at an end of the face plate, at a rounding limit.

18. The vibrating device as claimed in claim 14, wherein the haptic face plate has at least one transparent part.

19. A mobile unit comprising a device as claimed in claim 1.

20. The mobile unit as claimed in claim 19, wherein it is a cell phone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood and other advantages will become apparent on reading the following description given in a nonlimiting manner and from the attached figures in which:

(2) FIGS. 1a and 1b schematically represent a vibrating device of the present invention comprising at least one embedded mechanical reflector;

(3) FIGS. 2a and 2b illustrate an antisymmetrical Lamb mode on a rectangular plate;

(4) FIG. 3 schematically represents an example of a first support comprising a plate with rounded ends and comprising a pair of acoustic reflectors;

(5) FIG. 4 illustrates the absolute value of the amplitude of the antinodes of a Lamb mode with 14 antinodes of a Lumia 920 screen made of Dragontrail glass as a function of the position on for four different types of embedments;

(6) FIG. 5 schematically represents a Lumia 920 face plate that can be used in an example of a first support of a device of the invention and comprising roundings and a material defect corresponding to a hole for placing a loudspeaker;

(7) FIG. 6 illustrates the amplitude of a Lamb mode as a function of the position on X, obtained on a plate with rounded corners of Lumia 920 type with embedded mechanical reflector or without: called free, for a mode with 13 antinodes;

(8) FIG. 7 illustrates the amplitude of a Lamb mode as a function of the position on Y, obtained on a plate with rounded corners of Lumia 920 type, and for three observations at three points of the plate;

(9) FIG. 8 schematically represents a cell phone screen with two rows of actuators and two rows of embedded mechanical reflectors;

(10) FIGS. 9a and 9b respectively illustrate the amplitude and the deviation in the direction Y, obtained as a function of the dimension in the direction X of the embedment for a mode with 11 antinodes obtained in the case of the screen illustrated in FIG. 8;

(11) FIGS. 10a and 10b illustrate the amplitude and the deviation on Y as a function of the width of the embedment for a mode with 11 antinodes obtained in the case of the screen illustrated in FIG. 8, with an embedded mechanical reflector placed at the rounding limit of the first support;

(12) FIG. 11 schematically represents a Lumia 920 screen with a visible zone, the actuators and two series of discretized embedded mechanical reflectors;

(13) FIGS. 12a and 12b illustrate the amplitude and the deviation on Y as a function of the number of attachment points, with constant dimension in the direction X of embedment;

(14) FIG. 13 schematically represents a Lumia 920 screen with embedment on the hole of the loudspeaker;

(15) FIG. 14 illustrates a device comprising rows of embedded mechanical reflectors with a wave considered having a propagation in the direction Y;

(16) FIG. 15 illustrates any plate geometry that can be used in the present invention and comprising two orthogonal series of embedded mechanical reflectors;

(17) FIG. 16 illustrates a first embodiment of the invention comprising embedded reflectors produced by gluing;

(18) FIG. 17 illustrates a second mode of integration of a plate with embedded reflectors produced by snap-fitting.

DETAILED DESCRIPTION

(19) Generally, the present invention relates to a device comprising at least one embedded mechanical reflector making it possible to ensure a suitable plate mode propagation on the surface of a support. FIG. 1a thus schematically represents a first support 1 comprising a surface S defined in a plane X,Y defined by the directions X and Y (or axes X and Y) orthogonal in an orthonormal reference frame (X,Y,Z) with at least one defect in the context of the present invention. In the case represented, this is an outline defect: for example a partially rounded and non-rectangular periphery. The support 1 thus comprises at least one actuator 2 capable of generating plate modes referenced Os, of Lamb wave type, and at least one embedded mechanical reflector 3, making it possible to define a so-called active surface Sa, isolated from the non-rectilinear outline part, where the propagation of the plate modes is produced so as to be able to be correctly used. The first support 1 is secured to a second support 4, making it possible to locally immobilize, on the axis Z, the secured region constituting the embedded mechanical reflector, as schematically represented in FIG. 1b, the shadings schematically represent the embedded mechanical reflector function (it should be noted that the actuator can be either on the face opposite the reflector, or on the same face).

(20) Thus, it is proposed to mitigate the presence of defects with respect to the propagation of plate modes in a device using them by introducing at least one embedded mechanical reflector.

(21) The applicants explain hereinbelow the approach adopted used to design such a device. Generally, the devices using the propagation of Lamb wave propagation mode type plate mode, can comprise a plate typically of rectangular geometry.

(22) Starting from this type of geometry, the applicants studied an antisymmetrical Lamb mode A.sub.0, obtained by using piezoelectric actuators shrewdly placed on a plate having a surface area of 4030 mm.sup.2 (with a thickness of 725 m), as shown in FIG. 2a (3D view obtained from a finite elements simulation, method known by the acronym FEM, standing for Finite Element Method, under the Coventor commercial software and seen in cross section), highlighting the number of antinodes corresponding to energy maxima and nodes corresponding to a null displacement upon the vibration. In FIG. 2b, which illustrates more specifically the vibration mode sought, for example an antisymmetrical Lamb mode, here on the rectangular plate, the mode exhibits, for example, 8 antinodes Vi separated by nodes Ni.

(23) The applicants search for how to conserve the desired vibration mode, for example the antisymmetrical Lamb standing mode A.sub.0 presented in FIGS. 2a and 2b, in a non-rectangular plate.

(24) The example studied is a rectangular plate with rounded corners, but the invention can be extended to other types of non-rectangular plate geometries, possibly exhibiting any geometry in the plane (X,Y).

(25) In a plate with rounded edges, the same vibration mode could not be generated with thin layer actuators, even by working on the positioning of the actuators, because of the interferences provoked by the roundings.

(26) This is why the applicants turn to the use of acoustic reflectors making it possible to draw a parallel with those developed for SAWs. FIG. 3 schematically represents a plan view of an example of a plate 1 with rounded ends and comprising a pair of reflectors R.sub.1 and R.sub.2.

(27) When these reflectors are shrewdly placed as explained later in the present description, it is possible, by FEM simulations, to determine the dimension (w.sub.m) corresponding to the dimension in the direction Y, the dimension (l.sub.m) corresponding to the dimension in the direction X and the thickness of the reflector (t.sub.m) corresponding to the dimension in the direction Z, as well as the appropriate properties (density) of the material used. The properties making it possible to obtain the desired Lamb mode, on the plate with rounded corners, are given in the table below which represents the dimensioning of the reflectors that make it possible to obtain the Lamb mode on the plate with rounded corners considered, for example a plate of Dragontrail glass from the company Asahi Glass (800 m thick).

(28) Two types of plates were simulated, corresponding to different radii of curvature of the roundings (concrete cases of existing cell phone face plates were simulated).

(29) It can be noted that the thicknesses t.sub.m and/or the densities needed are very significant and difficult to access physically, requiring a solution other than that using known acoustic wave reflectors to be sought.

(30) TABLE-US-00001 Param- iPhone 5 Lumia 920 eter (dimensions = 4 inches) (dimensions = 4.5 inches) (mm) 25 kHz (13) 33 kHz (15) 27 kHz (14) 35 kHz (16) Position 2 5 4.5 3.5 on x l.sub.m 4 2-3 2 2.5 w.sub.m 45 35-45 66 55-60 t.sub.m 2-100 30-400 2-100 2 .sub.m <10 000 200 000 max <1 000

(31) That is why, starting from this observation, the applicants turned to another solution and propose a vibrating device using at least one mechanical reflector, instead of a conventional acoustic reflector, making it possible, in addition to the acoustic reflection of the wave which ensures the desired mode in a non-rectangular plate, to maintain the propagation properties as in a plate of rectangular configuration.

(32) The present invention thus proposes a solution in which mechanical embedments are used as reflectors with respect to mechanical waves.

(33) FIG. 4, taken from FEM simulation with the commercial simulation tool ANSYS, provides the absolute value of the amplitude of the antinodes of a mode with 14 antinodes of a Lumia 920 screen made of Dragontrail glass also called face plate (800 m thick) as a function of the position on X for four different types of embedments, the curve C.sub.4X relates to an immobilization in the direction X, the curve C.sub.4Y relates to an immobilization in the direction Y, the curve C.sub.4Z relates to an immobilization in the direction Z and the curve C.sub.4XYZ relates to an immobilization in all three directions X, Y and Z. This figure shows that, in the case of a rectangular plate with rounded corners (dimensions of a Lumia 920 screen, 4.5 inch diagonal (or 11.43 cm), Dragontrail glass thickness 800 m), embedded mechanical reflectors making it possible to restore the desired Lamb mode. Also, it emerges from all of these curves that the necessary embedment is only like an immobilization of the face plate in the direction Z, that is to say an immobilization preventing the face plate from being displaced in this off-plane direction.

(34) To also dimension embedded mechanical reflectors of other types of non-rectangular plates, the applicants studied non-rectangular plates having dimensions deriving from existing smartphones, this methodology being able to be used also to dimension embedded mechanical reflectors of other types of non-rectangular plates.

(35) In detail, the applicants thus studied a plate with rounded corners corresponding to the dimensions of a face plate of a Lumia 920 (4.5 inches for this existing smartphone) (by implementing the invention in this face plate) and represented in FIG. 5, i.e. a first support 11 comprising a transparent screen E, at the periphery of which are arranged two embedded mechanical reflectors 31.sub.1 and 31.sub.2 and a loudspeaker HP.

(36) This plate thus comprises outline defects (rounded corners) and material defects (hole left at the loudspeaker position), the mechanical reflectors being positioned to exploit the maximum of space of the plate, that is to say by defining an active surface that is as large as possible by locking the roundings of the outline.

(37) For that, the following methodology is applied:

(38) the modelling of the geometry of the vibrating plate is produced, on which two beads of embedded mechanical reflectors are positioned;

(39) a modal analysis is initiated under the commercial FEM software (ANSYS) to identify the frequency of the mode sought;

(40) according to the FEM model, the piezoelectric actuators are positioned on vibration antinodes, dependent on the frequency of the mode retained (the methodology for optimizing the positioning of the actuators is known to those skilled in the art);

(41) a harmonic simulation is then carried out, or a series of harmonic simulations, in order to best position the embedded mechanical reflectors, the position of the actuators evolving therefrom. In effect, after having determined the position of the embedded mechanical reflector or reflectors making it possible to delimit the active surface, the actuator or actuators then have to be positioned on this active surface.

(42) FIG. 6 illustrates the amplitude of a Lamb mode as a function of the position on X, obtained on a plate with rounded corners of Lumia 920 type without an embedded mechanical reflector: so-called free configuration (curve C.sub.6A) or with embedded mechanical reflector (curve C.sub.6B), for a mode with 13 antinodes.

(43) FIG. 7 illustrates the amplitude of a Lamb mode as a function of the position on y in the direction Y, obtained on a plate with rounded corners of Lumia 920 type, and for three observations at three points of the plate: at the left end, at the right end and at the center (in the direction X). The curve C.sub.7A relates to a free configuration taken at the left end, the curve C.sub.7B relates to a free configuration taken at the center, the curve C.sub.7C relates to a free configuration taken at the right end. The curve C.sub.7D relates to a configuration with embedded mechanical reflector taken at the left end, the curve C.sub.7E relates to a configuration with embedded mechanical reflector taken at the center, the curve C.sub.7F relates to a configuration with embedded mechanical reflector taken at the right end.

(44) These figures show that, with embedded mechanical reflectors, it becomes possible to restore, on a rectangular plate with rounded corners, a Lamb mode such as that obtained on a rectangular plate, namely: a subset of vibration antinodes and nodes in the direction X and little modulation in the direction Y.

(45) The applicants have thus proven that embedded mechanical reflectors make it possible to overcome disturbances caused by the presence of defects such as rounded corners but also defects of material heterogeneity (in the present case, a hole left at the point of the loudspeaker), and thus conserve a desired vibration mode in a non-rectangular plate, by having delimited a defect-free active surface where the actuators are positioned.

(46) In order to define design rules, the applicants studied the impact of the width (l.sub.m) for example that of the embedded mechanical reflector on the right in FIG. 5, on the uniformity of the modes on an 800 m substrate of Dragontrail glass and for a geometry corresponding to the IPhone 5 (4-inch dimensions). The width of the reflectors corresponds to the dimension of the reflectors in the direction X. The configuration studied is that illustrated in FIG. 8 having on a first support 12, a pair of embedded mechanical reflectors 32.sub.1 and 32.sub.2 and two columns of actuators 22.sub.1 and 22.sub.2. A loudspeaker HP hole is positioned juxtaposed at the level of an embedded mechanical reflector, the mechanical reflector on the right is positioned at the end of the face plate, but widthwise, it more or less blocks the outline roundings (each reflector prevents the wave from seeing the defect which is located behind so, in a way, a reflector is therefore needed for each defect).

(47) For that, it is possible to vary the dimension in the direction X, of said embedded mechanical reflector on the right 32.sub.2, and observe the modes obtained. In each case, the optimal position of the actuators must be found. FIGS. 9a and 9b respectively illustrate the amplitude and the deviation in the direction Y, obtained as a function of the dimension in the direction X, of the embedment for a mode with 11 antinodes (curve C.sub.9a: configuration taken at the left end, curve.sub.9b: configuration taken at the center and curve C.sub.9c: configuration taken at the right end).

(48) It appears that embedments of larger dimension in the direction X allow for a better uniformity of the mode on the plate, thus for a greater amplitude at the center of the face plate. However it does not seem useful to exceed a dimension in the direction X of approximately 10-11 mm (in this precise case) because, generally, the optimal dimension in the direction X of the reflectors depends on the wavelength.

(49) In effect, the roundings have less impact in these ranges.

(50) The applicants also analyzed the influence of the dimension in the direction X of the embedment and the influence of its position on the face plate.

(51) The same system as that previously described was modelled, with the embedded mechanical reflector on the right placed at the limit of the roundings, and by varying its dimension in the direction X. In this way, the roundings must no longer intervene in the vibration, this approach makes it possible to determine whether the dimension in the direction X of the embedded mechanical reflector intervenes in the amplitude, the frequency or the uniformity. The results are presented in FIGS. 10a and 10b, which also illustrate the amplitude and the deviation in the direction Y as a function of the dimension in the direction X of the embedment for a mode with 11 antinodes. (curve C.sub.10a: configuration taken at the left end, curve.sub.10b: configuration taken at the center and curve C.sub.10c: configuration taken at the right end).

(52) It appears that the amplitude and the uniformity are not modified by the dimension in the direction X of the embedded mechanical reflector as long as this width remains sufficient (approximately 2 mm). For a dimension on the axis X of the embedded mechanical reflector below this value, a significant deformation of the portion of face plate situated after the embedment appears linked to a loss of energy. This is reflected in a loss of uniformity of the order of 40%.

(53) It thus appears that an embedded mechanical reflector having a dimension in the direction X at least equal to 2 mm makes it possible to optimize the amplitude and the uniformity of the mode on the face plate.

(54) The applicants thus sought to determine the optimal positon, in the two directions X and Y, of the embedded mechanical reflector. On the right, it was shown that it is possible to position the embedded mechanical reflector at the end of the face plate, to retain a maximum of available space. The applicants thus sought to determine whether the embedded mechanical reflector has to cover all the dimension on the axis Y of the face plate, and whether it can be positioned at the level of the loudspeaker hole. For that, studies of implementation of the invention on a Lumia 920 screen with a thickness of 800 m were carried out.

(55) Initially, the position on the axis Y of the embedded mechanical reflectors was studied. For simplicity, two columns of identical embedded mechanical reflectors were taken into consideration respectively made up of reflectors 33.sub.1i and 33.sub.2j. The first column is positioned just after the hole of the loudspeaker HP. The second column is positioned at the end of the face plate. This is shown in FIG. 11 which illustrates a first support configuration that can be used in a device of the invention and comprising a visible zone E and two series of actuators 23.sub.1 and 23.sub.2. The number of embedded mechanical reflectors is modified, these embedded mechanical reflectors covering half of the width of the face plate. It appears that the amplitude increases with the number of embedded mechanical reflectors. It is not essential to have a single embedded mechanical reflector over all the dimension on the axis Y of the face plate. It is nevertheless suitable to have embedded mechanical reflectors sufficiently close to one another to retain the effect counted on. FIGS. 12a and 12b illustrate the amplitude and the deviation on y in the direction Y as a function of the number of embedded mechanical reflectors, with dimension in the direction X of embedment constant (curve C.sub.12a: configuration taken at the left end, curve C.sub.12b: configuration taken at the center and curve C.sub.12c: configuration taken at the right end).

(56) With a sufficient number of embedded mechanical reflectors, the performance levels obtained are satisfactory. In effect, for a given dimension on the axis Y, the increase in the number of reflectors makes it possible to reduce the free space between reflectors.

(57) According to a variant of the invention illustrated in FIG. 13, it is also possible to position the loudspeaker HP at the level of one of the embedded mechanical reflectors 34.sub.1.

(58) To sum up, an example of an efficient vibrating device according to the present invention, intended to be able to be incorporated in smartphones, can comprise, on a 4 to 4.5 inch face plate, equipped with a loudspeaker hole:

(59) two columns of embedded mechanical reflectors making it possible to immobilize the plate in the direction Z;

(60) one of the columns can be positioned at the end of the face plate;

(61) the dimension on the axis X of the embedded mechanical reflectors lying between approximately 2 mm and less than approximately 10 mm;

(62) the two columns of embedded mechanical reflectors being discretized, with embedded mechanical reflectors separated by a distance less than 5.5 mm.

(63) Configurations were described previously in which the embedded reflectors are positioned parallel to the small sides of a rectangular face plate with rounded corners. This principle can be extended for a positioning of the reflectors parallel to the long sides of such a plate as shown in FIG. 14 which illustrates a device comprising a plate 15, columns of actuators not represented being able to be arranged parallel or orthogonal to the reflectors 35.sub.1 and 35.sub.2, the wave considered Os having a propagation in the direction Y. In effect, according to the excitation frequency, even actuators positioned in the direction Y, i.e. orthogonally to the position of the embedded mechanical reflectors, can generate a wave whose wave front is at right angles to said embedded mechanical reflectors.

(64) Generally, the present invention can relate to any plate geometry, such as that illustrated in FIG. 15. To delimit the active surface Sa, two series of reflectors are respectively arranged on the axis X: reflectors 36.sub.1 and 36.sub.2 and on the axis Y: reflectors 36.sub.3 and 36.sub.4. To optimize the positioning of the reflectors, the study methodology described previously can be used according to the wave considered, the position of the actuators, etc.

(65) Example of Application to Haptic Face Plates

(66) A haptic face plate operates by an air blade effect, created on the surface of the face plate by the vibration thereof. This vibration is provoked by piezoelectric actuators glued or deposited and etched on the plate. For a good haptic effect, it is necessary to obtain a vibration amplitude of approximately 1 m in the Lamb mode A.sub.0. The applicants have proven the possibility of obtaining a haptic feel by using thin layer actuators in PZT, a material that is particularly advantageous and sought after in applications for smartphones which have rounded corners as schematically presented previously throughout the description.

First Exemplary Embodiment

(67) The embodiments can depend on the application targeted. In many cases, like that of haptics, producing an embedded mechanical reflector ensuring at least an immobilization in the direction Z is easy to implement through fixing a plate ensuring the first support in synergy with a casing secured to said first support.

(68) The embedded mechanical reflector must prevent the movement of the plate in the direction Z. It can for example be ensured by gluing the casing with the resonant plate. The glued region at the level of said plate constituting the embedded mechanical reflector.

(69) The bead of glue has dimensions on x, y (in the plane) dimensioned like those described previously so as to produce an embedded mechanical reflector with the desired dimensions.

(70) The thickness of glue can also be set according to the material used. The glue can be an epoxy glue, a UV glue or any other suitable glue. This configuration is illustrated in FIG. 16 and highlights: a first support 17; two actuators 27.sub.1 and 27.sub.2 (it should be noted that the actuators can preferentially be on the same side as the reflectors, and they can also be on both sides of the first support); two embedded mechanical reflectors 37.sub.1 and 37.sub.2 produced by beads of glue; a second support 47.

Second Exemplary Embodiment

(71) According to this second example, the embedded mechanical reflector consists of a snap-fitting of the face plate onto the casing. In this case, the vibrating face plate is machined by laser, ion machining or any other suitable method so as to partially etch the face plate in the embedment zones provided by the dimensioning step and thus define the cavities.

(72) This etching can have a depth ranging from a few micrometers to several hundreds of micrometers. Opposite, the casing has pins, produced at the same time in the same material as that of the casing, or produced subsequently and possibly in a material other than that of the casing. The dimensions on the axes X and Y of the pins are set by the dimensions of the opposite cavities (and by design rules for the insertion of the pins to induce the fixing thereof at the face plate level). The height of the pins is matched to the depth of the cover. Upon assembly of the casing and of the vibrating face plate, the pins are inserted and immobilized in the cavities of the face plate so as to immobilize the movement of the plate in the direction Z. This configuration is illustrated in FIG. 17 which highlights: a first support 18; two actuators 28.sub.1 and 28.sub.2: in this example the actuators can equally be situated on the opposite face of the second support (and/or on the other face); two embedded mechanical reflectors 38.sub.1 and 38.sub.2 produced by pins capable of cooperating with etchings produced at the level of the plate 18; a second support 48 corresponding to the casing in which the face plate is positioned.

(73) It should be noted that the configuration of the actuators is given purely as an example in the form of two columns, but many other configurations can be envisaged: a single column of actuators, actuators not arranged in columns but positioned along the long side of the face plate, etc.