EP3014606A2

EP3014606A2 - Ultrasound transducer

Info

Publication number: EP3014606A2
Application number: EP14735537.4A
Authority: EP
Inventors: Bernard Sartre; Jean-François SAILLANT
Original assignee: Areva NP SAS
Current assignee: Areva NP SAS
Priority date: 2013-06-27
Filing date: 2014-06-27
Publication date: 2016-05-04
Anticipated expiration: 2034-06-27
Also published as: WO2014207215A3; FR3007926A1; JP6449866B2; WO2014207215A2; FR3007926B1; CN105612575A; US20170323626A1; KR20160057355A; JP2016523493A; EP3014606B1; KR102214167B1; US10242656B2; CA2916582C; CN105612575B; CA2916582A1

Abstract

The ultrasound transducer (1) according to the invention comprises at least one emitter (3) made from a piezoelectric material, having first and second emitting surfaces (7, 9) opposite one another provided to emit first and second ultrasound beams. The transducer comprises at least first and second mirrors (11, 13) placed across from the first and second emitting surfaces (7, 9), respectively, and configured so as to return the first and second ultrasound beams (F1, F2) by forming a reflected beam (FR) with a predetermined shape.

Description

Ultrasonic transducer

The invention generally relates to ultrasonic transducers.

More specifically, the invention relates to an ultrasonic transducer comprising at least one emitter made of a material for converting an electrical signal into an ultrasonic wave, having first and second emitter surfaces opposite to each other designed to emit first and second second ultrasound beams.

Such a transducer is known from EP 0 147 070, which describes that one of the two emitting surfaces is covered with a damping material, also known as backing, used to damp the vibration of the material constituting the transmitter and to trapping the acoustic energy emitted by the rear surface of the transmitter, so that it does not disturb the useful beam emitted by the front surface.

Such a transducer has a relatively high production cost because it implements a large number of different materials. Moreover, only a part of the acoustic energy produced by the vibration of the transmitter is used, the other part being dissipated in the damper.

In this context, the invention aims to provide an ultrasound transducer which is less expensive and more efficient in terms of energy conversion.

To this end, the invention relates to an ultrasonic transducer of the aforementioned type, characterized in that it comprises at least first and second mirrors placed respectively facing first and second emitting surfaces and shaped so as to return the first and second second ultrasonic beams forming a reflected beam of predetermined shape.

Thus, the ultrasonic beams emitted by the two opposite emitting surfaces are used, so that for a given electrical power supplying the emitter, the energy of the beam produced by the ultrasonic transducer is significantly higher.

Since all of the acoustic energy emitted by the transmitter is concentrated in the reflected ultrasound beam, it is possible to obtain a better sensitivity of the ultrasound transducer for the same electrical energy supplied to the transmitter.

Furthermore, it is no longer necessary to provide a backing against one of the two emitting surfaces, so that the design of the ultrasound transducer is considerably simplified. The manufacture of the transducer is thus simpler, and its cost is reduced.

The reproducibility of the sensors is improved. This means that the performance of one sensor to another is more uniform. Indeed, in the state of the art, the bonding of the backing on the rear surface of the transmitter is an operation delicate. Depending on the quality of the bonding, the properties of the transducer are affected.

The transducer of the invention is well suited for operation in a severe environment. It has a favorable temperature behavior, because it no longer has several bulky layers stacked on top of each other as in the state of the art. The risks of failure of the transducer following the stresses caused by the differential expansion of the materials are reduced.

The transducer has a good ability to withstand the pressure, since the backing is eliminated. The backing is generally made of an elastomeric material, and therefore has a moderate resistance to pressure.

The transducer is well suited for operation under irradiation. Indeed, it is possible to achieve it entirely without elastomeric material. In the state of the art, the backing is made of an elastomeric material.

The transmitter is typically a piezoelectric crystal. Alternatively, the emitter is an electrostrictive material, or magnetostrictive, or any other material adapted to convert an electrical signal into an ultrasonic wave.

Transmitter is here understood to mean the active element of the transducer whose function is to convert electrical energy into mechanical energy. This active element is reversible. It is able to emit ultrasonic waves, but also to receive ultrasonic waves and convert them into an electrical signal. In other words, the transducer may operate at certain times as an ultrasound generator, and at other times as an ultrasonic receiver, in a collector mode.

Advantageously, the transducer comprises a housing to which the transmitter is attached.

The housing has two reflective surfaces defining the first and second mirrors, or the first and second mirrors are attached to the housing.

In the first case, the design of the transducer is simplified, since it is the housing itself which constitutes the mirrors, these being not additional patches.

The housing is for example a stainless steel part. Alternatively, the housing is of another metal alloy or ceramic. The material in any case is chosen to have a high acoustic impedance, that is to say a high coefficient of reflection with water. Alternatively, it is chosen so as to have high sound propagation speeds, so that for a given mirror angle, the critical angle of the longitudinal wave and that of the transverse wave are exceeded (law of Snell). For example, in the case of a stainless steel mirror and a water propagation medium, the two critical angles are approximately 15 ° and 28 ° respectively. In this case, no volume wave can be transmitted in a mirror beyond 28 °. .

The first and second ultrasonic beams are reflected directly on the first and second mirrors.

Alternatively, the first and second mirrors are reported on the housing. In this case, the mirrors are made of stainless steel or of another metal alloy or ceramic, and have either a high acoustic impedance or a high sound propagation speed, as described above.

Advantageously, the housing has a slot in which the transmitter is engaged, the slot having a substantially identical section to that of the transmitter.

Thus, the transmitter is held in position relative to the housing through a portion of said transmitter, which is locked in the slot. Said portion of the transmitter is directly applied against the peripheral edge of the slot. The transmitter is glued to the slot or engaged in force or pinched in the slot. Alternatively, a protective layer is interposed between said portion and the peripheral edge of the slot.

Advantageously, the housing is made of material or comprises two half-housings enclosing the emitter between them.

Each half-casing defines one of the first and second mirrors, where the first mirror is attached to one of the two half-casings and the second mirror is attached to the other of the two half-casings.

Thus, the housing is particularly economical. When it has two half-boxes, the mounting of the transmitter is simplified.

The slot is formed in the mass of the housing when it came from material. In a variant, it is delimited between the two half-housings.

Advantageously, the transducer is immersed in an environment, the first and second emitting surfaces being arranged with respect to the housing so that the first and second ultrasonic beams propagate from the first and second emitting surfaces to the first and second through the surrounding environment or through a material constituting the housing.

In the first case, the transducer is well suited for use where the reflected beam is transmitted from the ambient to the room in which the ultrasonic wave is transmitted. The ambient medium is, for example, water or another liquid or gaseous fluid.

In the second case, the transducer is well adapted to send the reflected beam directly into the room in which it is desired to transmit the ultrasonic wave, without transmission through the ambient environment. The first and second surfaces transmitter transmitters are then pressed against wave input surfaces of the housing. Wave output surfaces of the housing are pressed against the workpiece in which the ultrasonic wave is transmitted, directly or indirectly. The first and second mirrors, the entrance surfaces and the exit surfaces are arranged so that the first and second ultrasonic beams entering the housing through the entrance surfaces are reflected by the first and second mirrors to the surfaces. Release. The reflected beam leaves the housing through the exit surfaces and enters the room in which the ultrasonic wave is transmitted.

The housing can then be made of material or comprises two half-housings enclosing the emitting faces, each half-housing defining one of the first and second mirrors.

Advantageously, the transducer comprises electrical wires that can be connected to a voltage source, and an organ that pinches the electrical wires against the transmitter so as to fix the electrical wires to the solderless transmitter.

In other words, because none of the two opposite surfaces of the transmitter is covered by a backing, it is possible to put the electrical wires in contact with the transmitter. This makes it easier to manufacture the transducer, since it is no longer necessary to solder the electrical wires to the transmitter.

Advantageously The attachment is carried out for example using a clamp. This clamp has two arms, biased against two surfaces of the transmitter opposite to each other. The electrical wires are pinched between the arms and the transmitter. For example, the transducer comprises two electrical wires, one of the electrical wires being clamped against one of the surfaces, and the other electrical wire being pinched against the opposite surface.

Alternatively, these electrical son are welded, contacted or fixed by any other means.

Typically, the transmitter comprises an active part defining the first and second emitter surfaces and a portion connected to the electrical wires, the portion of the emitter engaged in the slot being located between the active part and the connecting part.

Advantageously, the transducer comprises a protective layer covering the first and second emitter surfaces. Such a protective layer makes it possible to protect the piezoelectric material. Indeed, the transmitter is arranged so that it forms a projection relative to the housing, and may therefore be damaged by shocks. The use of a protective layer reduces this risk. Typically, the protective layer covers the entire outer surface of the transmitter, with the exception of areas on which are pinched or connected the electrical son. The protective layer is an elastomeric material, or a metallic material or a ceramic. For example, for a transducer for the control of a nuclear reactor vessel, the selected material has an acoustic impedance and a thickness for optimal transmission of acoustic energy.

According to a first embodiment, the first and second ultrasound beams have first and second propagation directions from the first and second emitter surfaces, the first and second mirrors being planar and having first and second normal forming an included angle. between 30 ° and 60 ° with respect to the first and second propagation directions.

Preferably, the angle is between 40 ° and 50 °, and is typically 45 °. The first and second mirrors are rotated to reflect the first and second ultrasonic beams in the same direction corresponding to the central axis of the reflected beam. When the angle is 45 °, the reflected beam is a straight beam, with a plane wavefront.

Typically, the first and second propagation directions from the emitting surfaces are aligned and opposite to one another. The first and second mirrors form an angle of 90 ° to each other. Alternatively, the first and second emitter surfaces are not strictly parallel to each other and form between them a non-zero angle, for example a few degrees.

According to a second embodiment, the first and second mirrors are concave towards the first and second emitter surfaces. Such an arrangement makes it possible to generate a concentric wavefront, and thus a focused reflected beam.

According to a third embodiment, the first and second mirrors are convex towards the first and second emitter surfaces. Such an arrangement makes it possible to generate a diverging wave front, and therefore a very open beam.

The transmitter can have any kind of shape.

Advantageously, the emitter is a plate, the first and second emitter surfaces being two large parallel faces of the plate opposite to each other.

In this case, the emitting surfaces are typically plane.

Alternatively, the emitter is a cylinder or a tube of axis coincident with that of the mirror, the emitting surfaces being one or more diametrically opposite surfaces of revolution.

Typically, the cylinder or tube is circular in section perpendicular to its central axis. Alternatively, the cylinder or tube has an oval section, elliptical or any other shape. Typically, the first and second emitter surfaces together cover the entire periphery of the emitter. Each emitting surface has the shape of a half-cylinder.

In this case, the first and second mirrors together define a frustoconical surface, of the same axis as the emitter.

According to another aspect of the invention, the transducer comprises at least one sensor provided for measuring the shape and the intensity of the ultrasonic waves, arranged in one of the first and second mirrors.

Because the sensor is arranged in one of the first and second mirrors, it can measure the shape or intensity of the waves generated by the transducer without disturbing the ultrasonic beam.

Indeed, in known applications, such a sensor is placed at a distance from the transducer, in the ultrasonic beam generated by it. The sensor thus disturbs this ultrasonic beam. It can not be placed permanently in this beam.

The sensor, for underwater applications, is known as a hydrophone.

The transducer may comprise a single sensor arranged in one of the two mirrors. Alternatively, it may have a sensor in each of the two mirrors, or several sensors arranged at several points of each of the two mirrors.

Advantageously, the first and second mirrors have first and second reflective surfaces, the sensor comprising a level head with one of the first and second reflective surfaces.

Thus, the presence of the sensor does not create reliefs on the reflective surfaces, and does not disturb the reflection of ultrasonic beams.

The sensors are typically small in size with respect to the surface of the first and second mirrors. Their heads are placed in channels opening at the reflective surfaces formed in the first and second mirrors. They have an outer surface that is in continuity with the first or second reflective surface.

Typically, the sensor head is a piezoelectric material. It is electrically connected to a device for recording and analyzing the electrical voltage from the piezoelectric crystal.

Alternatively, the sensor comprises a thin layer of a material for converting an ultrasonic wave into an electrical voltage, for example a piezoelectric material, covering one of the first and second mirrors.

This thin layer typically covers the entire surface of the first or second mirror. The sensor then comprises a plurality of electrodes, each connected at one point of the thin layer, which allows controlling several areas of the beam. Each electrode is connected to a device for recording and analyzing the electrical voltage emitted by the converter material.

Other characteristics and advantages of the invention will emerge from the detailed description which is given below, by way of indication and in no way limiting, with reference to the appended figures, among which:

FIG. 1 is a simplified schematic representation of a transducer according to the invention,

FIG. 2 is a view similar to that of FIG. 1, showing alternative embodiments of the invention;

FIG. 3 and FIG. 4 are views similar to that of FIG. 1, showing shape variants for the mirrors of the transducer; and

- Figures 5 and 6 are views similar to that of Figure 2, illustrating another aspect of the invention; and

FIGS. 7 and 8 are views similar to that of FIG. 1, showing still other alternative embodiments of the invention.

The ultrasound transducer 1 shown in FIG. 1 is intended to be used in a fluid, for example underwater. It is intended for example for the inspection of the pressurized water reactor vessel during shutdowns. It can also be permanently mounted on the pressurized water reactor vessel for temperature and / or flow rate measurements. It can still be used for the inspection of internal equipment in reactors where the coolant is sodium, or to perform physical measurements (temperature, flow) on these same reactors. It can also be used in the medical or therapeutic field, for marine SONARs, as a position or metrology sensor in all kinds of applications, or for cleaning parts.

The transducer 1, as visible in FIG. 1, comprises a transmitter 3 made of a material making it possible to convert an electrical voltage into an ultrasonic wave and a case 5.

The transmitter 3 has first and second emitting surfaces 7, 9 opposite to each other, designed to emit first and second ultrasonic beams F1 and F2.

The housing 5 defines first and second mirrors January 1, 13, placed respectively facing first and second emitter surfaces 7, 9. The first and second mirrors 11, 13 are shaped to return the first and second ultrasonic beams forming a reflected FR beam having a predetermined shape.

The housing 5 is made of stainless steel. It has a slot 15 in which the transmitter 3 is engaged.

The two mirrors 1 1 and 13 are formed on a front face of the housing 5. It delimits together a recessed area 17 on this front face. More precisely, the first and second mirrors 11 and 13 are two plane surfaces converging towards one another. As shown in Figure 1, the slot 3 defines the bottom of the recessed area, the first and second mirrors converging towards the slot. The slot is open both on the side of the front face of the mirror and the side of the rear face 19 of the housing, this rear face 19 being opposite to the front face 17. In the example shown, the first and second mirrors 1 1 and 13 form an angle of 90 ° relative to each other.

The forward direction here corresponds to the direction of propagation of the reflected beam. The rear direction is the opposite of the forward direction.

In the example shown in FIG. 1, the emitter 3 is a piezoelectric crystal thin plate. It has an intermediate portion 21 engaged in the slot 15, a front portion 23 protruding forwards out of the slot 15, a rear portion 25 projecting out of the slot 15, rearwardly. The transmitter 3 has first and second large faces 27, 29, opposite to each other. The zones of the first and second major faces 27, 29 delimiting the front portion 23 of the emitter constitute the first and second emitting surfaces 7 and 9. The first and second emitter surfaces 7 and 9 therefore form an angle of 45 ° with the first and second mirrors 1 1 and 13.

The transmitter 3 is fixed to the housing 5 by shape cooperation between the portion 21 and the slot 15 or by bonding the portion 21 inside the slot 15.

The operation of the ultrasonic transducer is as follows.

The first and second emitting surfaces 7, 9 emit first and second ultrasonic beams F1 and F2 propagating in first and second directions of propagation. The first and second propagation directions are substantially perpendicular to the surfaces 7 and 9. They form an angle of 45 ° with respect to the normals of the first and second mirrors 11 and 13. The first and second ultrasonic beams are reflected on the first and second and second mirrors 11 and 13 and form a reflected beam FR. The first and second ultrasonic beams are reflected at 90 °, in the sense that the direction of propagation of the reflected beam is at 90 ° of the first and second directions of propagation, as shown by the arrows in FIG. An alternative embodiment of the invention will now be described with reference to FIG. 2. Only the points by which this variant embodiment differs from that of FIG. 1 will be detailed below.

As can be seen in FIG. 2, the transducer comprises a protective layer 31 covering the emitter. The protective layer is made of an elastomeric material. It covers the first and second emitting surfaces 7 and 9. It also covers the two large faces 27 and 29, in their near totality. In particular, the layer 31 is interposed between the intermediate portion 21 and the edge of the slot 15. In contrast, the layer 31 does not cover a rear edge 32 of the transmitter 3.

Furthermore, the transducer 1 comprises electrical son 33, 35, connected to a voltage source not shown. The electrical wires 33 and 35 are respectively plated against the first and second large faces 27, 29 of the transmitter 3, at the rear edge 32. As that is not covered by the protective layer 31, it is possible to thus make an electrical contact between the son 33 and 35 and the transmitter. The son 33 and 35 are held in position by a not shown clamp. They are not soldered to the transmitter.

The rear portion 25 of the transmitter is housed in a cavity 37 formed in the housing 5. This part, as well as the connections between the electric wires 33 and 35 and the rear edge 32, are thus protected from external aggression. The housing 5 has an orifice 39, placing the cavity 37 in communication with the outside. The electrical wires 33 and 35 leave the housing via the orifice 39.

The casing 5 comprises two half-casings 40 gripping the emitter 3 between them. Each half-casing 40 defines one of the first and second mirrors 1 1, 13. The slot 15 is delimited between the two half-casings 40. The half-casings 40 are attached to each other by any suitable means: screws, welding points, etc.

Figures 3 and 4 show two embodiments of the invention, in which the mirrors 1 1 and 13 are not planar.

In FIG. 3, the mirrors 11 and 13 are concave towards the first and second emitter surfaces 7 and 9. The concavity is calculated so that the reflected beam has a concentric wavefront. The reflected beam FR is then focused on a point P, located at a distance towards the front of the transmitter.

In FIG. 4, the first and second mirrors 11 and 13 are convex toward the first and second emitter surfaces 7 and 9. The first and second mirrors 11 and 13 are arranged so that the reflected beam has a diverging wavefront .

A second aspect of the invention will now be detailed, with reference to FIGS. 5 and 6. Only the points by which the transducers of FIGS. 5 and 6 differ those of Figures 2 and 1 respectively will be detailed below. The identical elements or providing the same function in Figures 2 and 1 in Figures 5 and 6 will be designated by the same references.

In the exemplary embodiments of FIGS. 5 and 6, the transducer 1 comprises at least one sensor 41 designed to measure the shape or the intensity of the ultrasonic waves. This sensor 41 is arranged in one of the first and second mirrors.

In the example of FIG. 5, the transducer comprises two identical sensors 41, arranged one in the first mirror 11 and the other in the second mirror 13.

The housing 5 has two channels 43, opening on one side in the cavity 37 and the other at the first and second reflecting surfaces 45 and 47 of the first and second mirrors. Each sensor 41 comprises a head 49 made of a piezoelectric crystal, engaged in the channel 43. The head 49 reaches flush with the first or second reflecting surface. The sensor, is more precisely the head 49 of the sensor, is therefore level with the first or the second reflective surface. The head 49 has a free surface 51 which is in continuity with the reflecting surface 45 or 47.

Each sensor 41 also comprises at least one electrical line (not shown) electrically connected to the head 49. This line travels the channel 43, opens into the cavity 47 and leaves the housing through the orifice 39. It is connected for example to a computer.

In the variant embodiment of FIG. 6, each sensor 41 comprises a thin layer 51 of a piezoelectric crystal, covering the first or the second mirror 11, 13. Each sensor 41 also comprises a plurality of electrodes 53 electrically connected to different points of the thin layer 51. These electrodes 53 are connected by electric wires to a computer. The thin layer 51 covers the entire reflecting surface 45, 47 of the first and second mirrors. It is thus possible to control the shape of the ultrasonic signal emitted by different areas of the mirror.

An alternative embodiment of the invention will now be described with reference to FIG. 7. Only the points by which this variant embodiment differs from that of FIG. 1 will be detailed below.

In the variant embodiment of FIG. 1, the transducer 1 is designed to be immersed in an ambient medium such as water. The first and second emitting surfaces 7, 9 are arranged with respect to the housing 5 so that the first and second ultrasonic beams F1, F2 propagate from the first and second emitting surfaces 7, 9 to the first and second mirrors 11 , 13 through the ambient environment. The reflected beam FR is transmitted by the ambient medium to the room in which the ultrasonic wave is transmitted.

In the variant embodiment of FIG. 7, the transducer 1 is adapted to send the reflected beam FR directly into the room in which the ultrasonic wave is transmitted 55, without transmission through the ambient medium.

For this purpose, the first and second emitting surfaces 7, 9 are arranged with respect to the housing 5 so that the first and second ultrasonic beams F1, F2 propagate from the first and second emitting surfaces 7, 9 to the first and second second mirrors 11, 13 through a material constituting the housing 5.

The first and second emitter surfaces 7, 9 of the emitter 3 are then pressed against wave input surfaces 57 of the housing. In the example shown, these input surfaces 57 delimit the slot 15 in which the transmitter 3 is engaged. Wave output surfaces 59 of the housing 5 are pressed against the part in which the ultrasonic wave is transmitted. In the example shown, the outlet surfaces 59 are pressed directly against the part 55. In a variant shown in Figure 8, a shoe 61 is interposed between the outlet surfaces 59 and the part 55. The shoe allows for example to adjust the propagation direction of the ultrasonic beam in the room in which the ultrasonic wave is transmitted.

Alternatively, the housing 5 and the shoe 61 are integral and constitute a single piece. The mirrors are a little longer (they extend beyond the end point of the transmitter) and directly incorporate the angle to deflect the ultrasonic beam in the room (below the critical angle).

The first and second mirrors 11, 13, the input surfaces 57 and the exit surfaces 59 are arranged so that the first and second ultrasound beams F1, F2 entering the housing 5 through the input surfaces 57 are reflected by the first and second mirrors January 1, 13 to the outlet surfaces 59. The reflected beam FR propagates inside the housing 5, leaves the housing 5 by the exit surfaces 59, and enters the room to in which the ultrasonic wave is transmitted 55.

Claims

1. Ultrasonic transducer (1) comprising at least one emitter (3) of a material for converting an electrical signal into an ultrasonic wave, having first and second emitter surfaces (7, 9) opposite to each other provided for emitting first and second ultrasonic beams (F1, F2);

characterized in that it comprises at least first and second mirrors (1 1, 13) respectively facing first and second emitter surfaces (7, 9) and shaped so as to return the first and second ultrasonic beams ( F1, F2) by forming a reflected beam (FR) of predetermined shape.

2. Transducer according to claim 1, characterized in that it comprises a housing (5) to which the transmitter (3) is fixed.

3. Transducer according to claim 2, characterized in that the housing (5) has two reflecting surfaces (45, 47) defining the first and second mirrors (1 1, 13), or the first and second mirrors (1 1, 13 ) are reported on the housing or (5).

4. Transducer according to claim 2 or 3, characterized in that the housing (5) has a slot (15) in which is engaged the transmitter (3), the slot (15) having a section substantially identical to that of the transmitter (3).

5. Transducer according to any one of claims 2 to 4, characterized in that the housing (5) is integral or comprises two half-housings (40) enclosing the emitter (3) between them.

6. Transducer according to claim 5, characterized in that each half-housing (40) defines one of the first and second mirrors (1 1, 13), or the first mirror (10) is attached to one of the two half housings (40) and the second mirror (13) is attached to the other of the two half-housings (40).

7. Transducer according to any one of claims 2 to 6, characterized in that the transducer (1) is immersed in an environment, the first and second emitter surfaces (7, 9) being arranged relative to the housing (5) for the first and second ultrasonic beams (F1, F2) to propagate from the first and second emitter surfaces (7, 9) to the first and second mirrors (11, 13) through the ambient medium or through a material constituting the housing (5).

8. Transducer according to any one of the preceding claims, characterized in that it comprises electrical son (33, 35) may be connected to a voltage source, and an organ pinching the electrical son (33, 35) against the transmitter (3) so as to fix the electrical wires (33, 35) to the transmitter (3) without welding.

9. Transducer according to any one of the preceding claims, characterized in that it comprises a protective layer (31) covering the first and second emitter surfaces (7, 9).

Transducer according to one of the preceding claims, characterized in that the first and second ultrasonic beams (F1, F2) have first and second directions of propagation from the first and second emitter surfaces (7, 9). the first and second mirrors (11, 13) being planar and having normal first and second angles of 30 ° to 60 ° with respect to the first and second propagation directions.

1 1. Transducer according to any one of claims 1 to 9, characterized in that the first and second mirrors (1 1, 13) are concave towards the first and second emitter surfaces (7, 9).

12. Transducer according to any one of claims 1 to 9, characterized in that the first and second mirrors (1 1, 13) are convex to the first and second emitter surfaces (7, 9).

13. Transducer according to any one of the preceding claims, characterized in that the transmitter (3) is a plate, the first and second emitter surfaces (7, 9) being two large faces of the plate opposite each other. 'other.

14. Transducer according to any one of the preceding claims, characterized in that the transmitter (3) is a cylinder or a radially polarized tube, the first and second emitter surfaces (7, 9) being two diametrically opposite radial surfaces.

15. Transducer according to any one of the preceding claims, characterized in that it comprises at least one sensor (41) provided for measuring the shape of the ultrasonic waves, arranged in one of the first and second mirrors (1 1, 13 ).

16. Transducer according to claim 15, characterized in that the first and second mirrors (1 1, 13) have first and second reflective surfaces (45, 47), the sensor (41) being level with one of the first and second reflective surfaces (46, 47).

17. Transducer according to claim 15 or 16, characterized in that the sensor

(41) comprises a head (49) of a piezoelectric crystal.

18. Transducer according to claim 15, characterized in that the sensor (41) comprises a thin layer (51) of a material for converting an ultrasonic wave into an electrical signal, for example a piezoelectric crystal, covering one of the first and second mirrors (1 1, 13).