EP0462037B1 - Underwater electro-acoustic transducer - Google Patents

Description

The present invention relates to a submerged electro-acoustic transducer and to a method of manufacturing this electro-acoustic transducer.

Electro-acoustic transducers are commonly used, in particular to emit signals intended for communications and underwater detection.

The most commonly used electro-acoustic transducers include a motor, or active part, which generally consists of a stack of piezoelectric ceramic alternating with electrodes, the assembly forming a cylinder of elongated shape; under the action of a tension applied to ceramics, they deform; the ceramics are arranged and wired in such a way that their deformations are added, which means that longitudinal contraction and expansion movements of the stack of piezoelectric ceramics are obtained. This stack is linked at one of its two longitudinal ends to a generally metallic support piece, serving as a support, often called a counter-support piece or counter-mass, which is kept substantially stationary relative to the transducer housing; the stack is linked at its other end to another mass, sometimes called the pavilion, which vibrates along the longitudinal axis of the stack, due to the movements of the latter, resulting from the tension applied to the ceramics.

This flag is in contact with the desired propagation medium, generally water, in general by means of an elastic coating which seals the transmitter.

The evolution of techniques and technologies in this field has led to the production of several types of relatively standard mechanical assemblies for these electro-acoustic transducers, particularly the following three types.

The electro-acoustic transducers of the "TONPILZ" type include the basic mechanical assembly, briefly described above, which includes a counter-mass fixed in a cylindrical case by means of suspensions limiting the movements of the sealed case with respect to this counter-mass, a stack of ceramics piezoelectric which vibrates a pavilion.

The stack is axially prestressed along its longitudinal axis, by means generally constituted by a rod screwed into the roof, which passes through the stack, which is blocked in the counter-mass by a nut and which is tensioned.

The "JANUS" type electro-acoustic transducers correspond substantially to two "TONPILZ" type electro-acoustic transducers, having a common counter-mass and whose stacks vibrate in phase opposition.

Electro-acoustic transducers of the "FLEXTENSIONAL" type use a principle of prestressing and diffusion of vibrations in the somewhat different propagation medium: in this type of electro-acoustic transducers, for example the "FLEXTENSIONAL" of class 4, the housing consists of a shell, generally made of epoxy glass composite, of cylindrical shape with elliptical section; this shell of elliptical section is, due to its elasticity, capable of flattening and rounding; in this shell, symmetrically with respect to a central core extending along the axis of the cylindrical shell, one or more pairs of stacks of piezoelectric ceramics, which rest at one end on metal inserts which extend parallel to the central core, which metal inserts are supported inside the shell, in the vicinity of the end of the major axis of the ellipse defining the shell section. EP-A-0 367 681 describes such a transducer.

The assembly consisting of the stacks and the central counter-mass is introduced into the shell, the latter being prestressed by pinching, along the minor axis of the ellipse; when the assembly is in place inside the shell, the prestress is released, the long axis of the ellipse shortens, which prestresses the assembly, along the longitudinal axis of the stacks.

Although the most commonly used transducer elements consist of stacks of piezoelectric ceramics, these stacks of ceramics can, in certain cases, be replaced by magnetostrictive transducers; these transducers mainly comprise an elongated bar, constructed of a material generally mainly consisting of rare earths, which can vibrate by contracting and expanding along its axis longitudinal, under the effect of a magnetic field created by a coil which surrounds this bar.

Current uses of these electro-acoustic transducers mean that we are looking for ways to increase the power of these electro-acoustic transducers and to transmit at increasingly low frequencies.

In the case of electro-acoustic transducers constructed with stacks of piezoelectric ceramics, it is known that the power is substantially proportional to the volume of ceramic placed in the electro-acoustic transducer, the lower limit of the frequencies likely to be emitted being linked at the natural frequency in longitudinal compression of the stack of ceramics; in order to produce a high power electro-acoustic transducer capable of emitting the lowest possible frequencies, we are therefore led to produce a stack forming a cylinder of great height.

This principle obviously comes up against technological and above all economic limits; it is then often necessary to produce a plurality of electro-acoustic transducers which are assembled as an antenna, also called an array, which complicates the mechanical assembly of the assembly, the electrical wiring and increases the cost.

The problem posed is therefore to provide electro-acoustic transducers capable of being submerged, and their manufacturing process, allowing, without appreciable increase in the size of the electro-acoustic transducer, to provide increased power and / or capable of transmit at relatively low frequencies.

According to the invention, a solution to the problem posed is to provide an electro-acoustic transducer comprising in a housing, at least a first support part, or pavilion, and at least a second support part, or counter-mass, comprising at least two transducer elements of elongated shape along a longitudinal axis of said transducer, comprising at least one prestressing rod along said longitudinal axis, between said first and second bearing parts of said transducer elements, such that said transducer elements are arranged side by side side, and / or constitute coaxial cylinders having for axis said longitudinal axis, and can vibrate in phase, and such that it comprises at least one part or assembly, rigid, mobile intermediate, which is mounted or stacked, interposed between said transducer elements, mechanically in series with said transducer elements, so that said rigid intermediate piece can be prestressed by said rod, simultaneously with said transducer elements, and so that said rigid intermediate piece is capable of vibrating in phase with said transducer elements.

Advantageously, an electro-acoustic transducer according to the invention comprises at least two transducer elements of elongated shape along a longitudinal axis, located between a first and a second support piece, prestressed along said longitudinal axis by a prestressing device, which tends to bring said support pieces closer together, which transducer elements each have two longitudinal, parallel, planar ends, which transducer elements are parallel, arranged side by side, and operate in phase, the assembly being contained in a housing, and only a first end of a first of said transducer elements is pressed against said first support piece, and only a first end of a second of said transducer elements is pressed against said second support piece, and said transducer comprises a rigid intermediate assembly which is sandwiched between said first and second transducer elements, which has two parallel faces which bear respectively on the second ends of said transducer elements and which is capable of being prestressed simultaneously with said first and second transducer elements, along said longitudinal axis by said prestressing device; each of said transducer elements can be constituted either by at least one magnetostrictive bar, or by at least one stack of piezoelectric ceramics, alternating with electrodes forming a cylinder of elongated shape.

In an electro-acoustic transducer according to the invention, longitudinal clearances are respectively provided between said rigid intermediate assembly and said first and second support pieces, so that during relative displacements between said support pieces due to the forces developed by said transducer elements and to the forces due to said prestressing device, the contacts between said rigid intermediate assembly and said support parts, are avoided.

Advantageously, in an electro-acoustic transducer according to the invention, said rigid intermediate assembly consists of a single rigid metal part, which can for example consist of a substantially cylindrical part, having an axis, parallel to said longitudinal axis, terminated at one end by a bottom which comprises one of said two parallel faces, which is supported on the second end of a first of said transducer elements, and at its other end, by an external flange which comprises the other of said two parallel faces, which rests on the second end of the second of said transducer elements.

In a preferred embodiment, said intermediate assembly comprises at least two rigid intermediate parts and at least one intermediate transducer element which is interposed between said two rigid intermediate parts and arranged mechanically in series therewith.

In preferred embodiments of electro-acoustic transducers according to the invention, said prestressing device comprises one or more rods, which are fixed respectively by each of their two ends to each of said support pieces, or to an intermediate piece, in particular for application to "TONPILZ" and "JANUS" type assemblies, or else is constituted by said case which is deformable, in particular for application to "FLEXTENSIONAL" type assemblies.

In a particular embodiment according to the invention, the cross sections of the active parts of said first and second transducer elements are substantially equal.

A solution to the problem posed is also to provide a method of manufacturing electro-acoustic transducers of the type comprising at least one transducer element of elongated shape, prestressed axially between two support pieces, characterized in that it is mounted between said pieces support, a first transducer element of elongated shape, having only one first end pressed against one of the two support pieces and a second transducer element of elongated shape, having only one first end pressed against the other support piece, which transducer elements are parallel and arranged side by side and operate in phase, interposed between these two transducer elements an intermediate piece which bears on the second ends of said transducer elements, and the two transducer elements and said intermediate piece which transmits the longitudinal forces between the two transducer elements are axially prestressed between the two bearing pieces.

The advantages provided by the electro-acoustic transducers according to the invention are numerous.

In fact, it is possible, for example, in an electro-acoustic transducer according to the invention, to nest a second stack of ceramics in the form of a crown, which substantially surrounds the first stack, the two stacks having the same height and the active elements having substantially the same section, and an electro-acoustic transducer is thus obtained, the power of which will be substantially doubled compared to known electro-acoustic transducers of the same size, which include that said first stack, since the volume of ceramics is doubled; at the same time, the equivalent length of the fictitious stack thus produced by the two nested stacks is doubled; therefore, the resonant frequency of the nested stack according to the invention, being approximately, inversely proportional to the square root of the length, will therefore be reduced by 40% compared to the known electro-acoustic transducer of the same size.

Furthermore, the assembly according to the invention can be used so as to nest more than two stacks, without significantly increasing the size of the transducer, which makes it possible to achieve even higher performance in low power and / or frequency.

The reliability of the assemblies composed of electro-acoustic transducers according to the invention is significantly improved, and the cost of these assemblies is markedly reduced.

The electro-acoustic transducers according to the invention can be constructed both with piezoelectric ceramic transducers and with magnetostrictive bars.

The numerous advantages and characteristics of the invention will appear clearly in the appended figures which represent, without any limiting character, embodiments of electro-acoustic transducers according to the invention and their manufacturing process.

FIG. 1 represents a cross-sectional view, on a reduced scale, of an embodiment of electro-acoustic transducer according to the invention, in an assembly of the "TONPILZ" type.

FIG. 2 represents a cross-sectional view, on a reduced scale, of another embodiment.

FIG. 3 represents a cross-sectional view, on a reduced scale, of an embodiment of electro-acoustic transducer according to the invention, in an assembly of the "JANUS" type.

FIG. 4 represents a cross-sectional view, on a reduced scale, of an embodiment of electro-acoustic transducer according to the invention, in an assembly of the "FLEXTENSIONAL" type.

FIG. 5 represents a cross-sectional view, on a reduced scale, of an embodiment of electro-acoustic transducer according to the invention, in a “TONPILZ” type assembly fitted with magnetostrictive transducer elements.

FIG. 6 is a section on VI-VI of FIG. 5.

According to Figure 1, there is shown an electro-acoustic transducer according to the invention which is equipped with two transducer elements made of piezoelectric ceramics, in an assembly of the "TONPILZ" type.

In a known manner, the electro-acoustic transducer comprises in this type of mounting, a metal housing 3, a counterweight 2, a horn 1, a prestressing rod 4 and a locking nut 5.

It can be seen that said housing 3 is closed at one end by a cover 13, in leaktight manner thanks to a seal 14.

Said counter-mass which constitutes a support piece is mounted inside said housing by means of suspension devices 11 which bear on an internal shoulder of said housing, and by means of a suspension nut 12 ; said counterweight is kept centered in said housing by means of a centering ring 21;

On said cover 13 is mounted a waterproof connector 18 linked to an electric cable 19 which supplies the electric energy necessary for the supply of said piezoelectric ceramics.

An insulating disc 16 is mounted between said housing and said cover and delimits therewith a cavity 15 in which are housed the electrical wires which provide the connection between said connector and said transducer elements.

Said pavilion 1 which constitutes a second support part is generally provided with an elastic coating 17, which can be vulcanized on said pavilion, and which is tightened on one end of said housing by clamps 20, thus ensuring the tightness of said transducer electro-acoustic.

We see that in known manner, said electro-acoustic transducer comprises a first stack of piezoelectric ceramics 6 in the form of discs alternating with electrodes 10, so as to constitute a first cylinder elongated along a longitudinal axis xx1, which in this mode of realization is confused with the axis of said electro-acoustic transducer.

Said prestressing rod is anchored in said pavilion by screwing one of its threaded ends into a tapped hole machined in said pavilion.

It can be seen that, in accordance with the invention, said electro-acoustic transducers comprises a second stack of piezoelectric ceramics 7 in the form of a crown alternating with electrodes 10, so as to constitute a second cylinder elongated along said axis xx1, and that said electro-acoustic transducer comprises a rigid intermediate piece 8, which is interposed between said first and second stacks of piezoelectric ceramics, said rigid intermediate piece 8 constituting said rigid intermediate assembly in this embodiment according to the invention.

In known electro-acoustic transducers, said stacks are supported by one of their longitudinal ends on one of said support pieces (horn) and by their other longitudinal end on the other support piece, (counter-mass). In an electro-acoustic transducer according to the invention, only a first end of a first of said transducer elements is pressed against a first support piece, only a first end of a second of said transducer elements is pressed against a second piece of support, and the transducer comprises a rigid intermediate assembly which is interposed between said first and second transducer elements, which comprises two parallel faces which bear respectively on the second ends of said transducer elements, and which is capable of being prestressed simultaneously with said first and second transducer elements, along said longitudinal axis (xx1) by said prestressing device.

More specifically, in this particular embodiment according to the invention, the bearing face 1A of said pavilion 1 is opposite the first bearing face A of said first stack of ceramics 6, the second bearing face B of said first stack is facing the first bearing face 81, located on the bottom of said rigid intermediate piece 8, the second bearing face 82 located on the outer flange of said rigid intermediate piece 8 is facing the first face d 'support C of said second ceramic stack 7, the second support face D of said second ceramic stack 7 is opposite the support face 2A located on said counter-mass.

When mounting said electro-acoustic transducer according to the invention, said prestressing rod is screwed and blocked on said pavilion, said first stack is made to slide around said rod which comes into contact with said pavilion, it is made to slide around said rod and around said first set of ceramics 6, said rigid intermediate piece which comes into contact with said first stack by its face 81, said second stack of ceramics 7 which comes into contact with said rod is made to slide around said rod and said rigid intermediate piece flange of said rigid intermediate part by its bearing face C, and finally sliding around said rod and said stack said counterweight which comes into contact by its face 2A with the face D of said second stack.

Said counter-mass is then maintained and a pull is exerted on said rod, along its longitudinal axis and in a direction opposite to said roof; said traction therefore tends to bring said pavilion towards the counter-mass, and by means of said bearing faces opposite one another, said traction generates a compression preload along said axis xx1 of said first stack between said faces of support 1A, 81 respectively of said flag and of said intermediate rigid piece, said traction generates a compression preload along said axis xx1 of said second stack between said bearing faces 82, 2A respectively of said rigid intermediate piece and said counter-mass, said traction generates tensile preload along said axis xx1 of said intermediate piece rigid.

In known manner, then screwing, without stopping said pulling, said nut 5 on the second threaded end of said rod until it comes into contact with said counter-mass and then releasing said pulling, the nut now all prestressed.

The assembly thus formed can then be mounted in said housing, and the final mounting operations carried out.

It is clear that a very good quality of parallelism must be obtained between the bearing faces of these parts, particularly between said bearing faces 81 and 82 of said rigid intermediate part.

It can be seen that in an electro-acoustic transducer according to the invention a clearance 9A, along said longitudinal axis xx1 must be provided between said counterweight 2 and said rigid intermediate piece 8. On the other hand a clearance 9B must be provided between said intermediate piece 8 and said pavilion 1, so that during vibration movements of said pavilion and said rigid intermediate piece, under the action of the contraction and expansion movements of said first and second stacks, the contacts between said rigid intermediate piece, said flag and said counter-mass are avoided. The value of these clearances will preferably be of the order of a few millimeters.

In this document, in the expressions - rigid intermediate assembly - and - rigid intermediate part -, the rigidity in question is the longitudinal rigidity of said part or of said assembly, that is to say the rigidity with respect to tensile or compressive forces, along said longitudinal axis xx1; it is obvious that moreover the rigidity - we will then speak of stiffness - of said intermediate piece or of said intermediate assembly, along all other axes not parallel to xx1, must be sufficient in order to guarantee good mechanical strength; said longitudinal rigidity of said intermediate piece or of said intermediate assembly will in the majority of cases be significantly greater than the longitudinal rigidity of said first and second stacks.

It should be noted that said rod 4, said first stack, said intermediate piece and said second stack are preferably sheathed by insulating sleeves 40, substantially cylindrical; these sleeves serve in fact to provide electrical insulation between these different parts; they also make it possible to minimize the friction which could occur between these parts, due to their relative vibratory movements.

Passages (not shown) are of course provided in these different parts which allow the routing of the electrical wires (not shown) from said cavity 15 to said electrodes of said stacks.

It is clear that the electrical wiring of said first and second stack is such that the respective longitudinal vibrations of said stacks add up at each instant, which means that the amplitudes are added, and therefore that the power of said electro-acoustic transducers is substantially equal to the sum of the powers of said first and second stacks.

It can be seen in the figure that, in a known manner, said electro-acoustic transducer comprises clearances 22, 23 which correspond respectively to spaces formed between said housing and said roof on the one hand, and between said housing and said counter-mass of on the other hand, which spaces are generally filled with gas.

In Figure 2, there is shown a cross section of another embodiment of an electro-acoustic transducer according to the invention, in an assembly of the type "TONPILZ".

The functional elements identical to those of FIG. 1 are identified by the same numbers.

It can be seen in the figure, that in this particular embodiment according to the invention, said pavilion is in contact by a bearing face 1A with a first end A of said first stack of ceramics 6 in the form of discs, that said first stack is in contact by its second end B with the face 81 of said rigid intermediate assembly, said rigid intermediate assembly being supported by a face 82 on the first bearing face C of a second stack of ceramics 7, which may be in the form crown; nevertheless given the relatively large diameter of this crown, said ceramics 7 could advantageously be in the form of crown sectors, in order for example to obtain a section of the active parts - of ceramics - of said second stack substantially equal to the section of said first stack. These choices of shape and size are made according to the performance requested from the transducer.

It can be seen in this figure, that in accordance with the invention, said rigid intermediate assembly which transmits the prestressing forces in compression exerted by said rod 4 between said first and second stack, consists of the assembly of five rigid intermediate parts 8, and four intermediate stacks 8A, 8B, 8C, 8D, of piezoelectric ceramics, which can be in the form of crowns or sectors.

According to the invention, said first and second stacks and said intermediate stacks are connected so that the vibrational movements of said stacks are in phase.

It can be seen that said intermediate parts are cylindrical in shape, having for their axis said longitudinal axis xx1, and each provided at one end with an internal flange and at the other end with an external flange, which flanges are each provided with a bearing face, the two bearing faces of each of said rigid intermediate parts being parallel, and perpendicular to said longitudinal axis xx1.

Games 9A are provided between each rigid intermediate piece which are liable to vibrate and said counter-mass, as well as clearances between each rigid intermediate piece and said pavilion.

It can be seen that, in accordance with the invention, the prestressing exerted by said rod which tends to bring said pavilion closer to said counter-mass, generates a compression preload in said first and second stacks and said intermediate stacks 8A, 8B, 8C, 8D , and generates a tensile stress in said rigid intermediate parts.

In Figure 3, there is shown a cross-sectional view of an embodiment of an electro-acoustic transducer according to the invention, in an assembly of the "JANUS" type.

We see in this figure, that in a known manner in this type of electro-acoustic transducer mounting, the housing 3 generally cylindrical with longitudinal axis xx1, is not sealed; inside said housing are arranged symmetrically with respect to the transverse axis yy1, cutting said electro-acoustic transducer in its middle, two pavilions 1, connected by a preloading rod 4, provided at each end with a thread on which are screwed two locking nuts 5, which are supported on said pavilions; are also arranged inside said housing and symmetrically with respect to said axis yy1, two first stacks of ceramics 6, two rigid intermediate pieces 8, and two second stack of ceramics 7.

In this type of assembly, the central counterweight 2 is generally of reduced size and mass compared to the assemblies of FIGS. 1 and 2, and said rod 4 tends to bring said pavilions closer to one another, likewise that it tends to bring the first two stacks of ceramics 6 together, the two rigid intermediate pieces from one another, and the second second stacks of ceramics 7 from each other.

Note that in this embodiment, the rod 4 passes through the counter-mass, but is not rigidly linked to the latter.

The counter-mass, which may be in the form of a disc, has two parallel bearing faces 2A.

It can be seen in the figure that, in accordance with the invention, each of the pavilions is supported by at least part of its face 1A on the first end of a first stack of piezoelectric ceramics 6, which may be in the form of disc, which first stack is supported by its second end on a first support face 81, located on the bottom of a rigid intermediate piece 8, which can be bell-shaped, which is provided at its second end with a second bearing face 82, which is parallel to said first bearing face 81, which rigid intermediate piece is supported by said face 82 on the first end of a second stack of piezoelectric ceramics 7, which s presses at its second end on a support face 2A of said central counterweight.

We see that this type of assembly called "JANUS" consists essentially of two "TONPILZ" assemblies as described in FIGS. 1 and 2, which would be placed symmetrically with respect to a transverse axis yy1, and which would have a common counter-mass.

In the type of assembly illustrated in FIG. 3, said stacks of piezoelectric ceramics are vibrated in phase located on the same side of said transverse axis yy1, and said stacks of piezoelectric ceramics are vibrated with a phase offset by 180 ° located on the other side of said transverse axis yy1.

It can be seen in the figure that, in a known manner in this type of mounting, the elastic coating 17 which covers said pavilions 1, also surrounds said stacks of piezoelectric ceramics.

In this type of assembly, the assembly consisting of said pavilions, said stacks and said counter-mass, coated with said elastic coating 17, is introduced into said housing and immobilized therein by parts 24 and 25 - generally in the form of tubes - and flanges.

It can also be seen that the cavity 15 allowing the feed wires of said ceramics to travel from them to the feed connector is located inside said counter-mass.

In a known manner, this type of assembly comprises baffles 23, generally made of cellular material, which substantially fill the space between said elastic coating and the walls of said housing.

In Figure 4, there is shown a cross-sectional view on a reduced scale of an embodiment of an electro-acoustic transducer according to the invention, in an assembly of the "FLEXTENSIONAL" type.

The type of assembly shown is more particularly that called "FLEXTENSIONAL" class 4.

In this type of mounting, the housing of said electro-acoustic transducer is constituted by a shell 28, generally made of epoxy glass composite, which has the shape of a cylinder with an axis perpendicular to the plane of FIG. 4, of elliptical section, the small of which axis is carried by the transverse axis yy1 and the major axis is carried by the longitudinal axis xx1.

Said support pieces are usually constituted in this assembly by a central core 27 and two inserts 26, which extend along an axis perpendicular to the plane of the figure; on either side of said transverse axis yy1, are usually, and in a known manner, arranged stacks of ceramics, of elongated shape, which are supported at one of their ends on one of said inserts, preferably by means of a slide 41 and a wedge 29, and at their other end on said core; the prestressing is carried out in this type of assembly by the shell itself, which, during assembly, is pinched along its transverse axis yy1, so that the assembly constituted by said slides and shims, said stacks and said core, then the pinch is released, which tends to release said cylindrical shell along said longitudinal axis xx1 and thus prestress said ceramic stacks.

We see in the figure that according to the invention, there is interposed on each side of said core, between a first stack of ceramics 6 and a second stack of ceramics 7, which is parallel to said first stack, a rigid intermediate piece 8, which transmits the prestress between said first and second stack.

It can be seen that an elastic sealing coating 17 is provided, which surrounds said shell.

The general mode of operation of these electro-acoustic transducers is substantially identical to that of the assembly of FIG. 3, except for the principle of prestressing by the shell explained above, and the principle of transmission of vibrations to the propagation medium. In the assembly of FIG. 4, in fact, said shell of elliptical section is used as an amplifier of vibratory movements of the inserts caused by said stacks; in fact, said vibratory movements of the inserts along the longitudinal axis xx1, cause vibratory movements of greater amplitude, parts of the shell which extend on either side of these inserts, which movements are transmitted to the outside environment of propagation.

In Figure 5, there is shown a cross-sectional view of an embodiment of an electro-acoustic transducer according to the invention, in an assembly of the "TONPILZ" type equipped with magnetostrictive transducer elements.

In FIG. 6, a section along VI-VI of FIG. 5 is shown.

In these figures, said transducer elements consist of magnetostrictive bars 29, which are liable to vibrate along their longitudinal axis parallel to the axis xx1, under the effect of the magnetic field produced by the coils 30.

The bars if killed on the same circle of axis xx1 are magnetically linked together by magnetic rings 31 which are not shown in FIG. 6.

In these figures, it can be seen that a first transducer element is constituted by four first bars located outside the rigid intermediate piece 8; which four first bars are supported by a first of their respective ends on the support face 1A of the pavilion 1 by means of a crown 31, and by their second end and by means of a crown 31 on the first bearing face of said rigid intermediate piece which is constituted in this embodiment by four legs 83.

We see that a second transducer element is constituted by four second bars located inside the rigid intermediate piece 8, which four second bars are supported by a first of their end and by means of a crown 31 respectively. on the bearing face 2A of the counterweight 2 and by their second end and / or by means of a second ring 31 on the second bearing face of said rigid intermediate piece 8, which is formed by the bottom 84, which is itself crossed by the prestressing rod 4.

It can be seen in FIG. 6 that said rigid intermediate piece comprises in its central tubular part, a crown section which advantageously follows the outline of the coils 30 of said first four bars on its periphery, and whose internal profile follows the outline of the coils 30 of said four second bars.

The technical field of the invention is that of immersed electro-acoustic transducers.

Claims (10)

1. Electro-acoustic transducer enclosed in a case (3) and containing at least one first supporting component (1) and at least one second supporting component (2), containing at least two transducer units (6, 7) of elongated shape along a longitudinal axis (xx1) of said transducer, containing at least one pre-stressed rod (4) along said longitudinal axis (xx1) of said transducer units between said first and second supporting components, characterized in that said transducer units are arranged side by side and can vibrate in phase, and in that it contains at least one rigid intermediate unit (8) which is fitted in between said transducer units, in series with said transducer units.
2. Transducer according to claim 1, characterized in that said transducer units each have two longitudinal flat parallel ends (A, B, C, D), and in that only the first end (A) of the first of said transducer units (6) is in contact with the first said supporting component (1), and in that only the first end (D) of the second of said transducer units (7) is in contact with said second supporting component (2), and in that said rigid intermediate unit (8) has two parallel faces (81, 82) with are in contact respectively with the second ends (B, C) of said transducer units (6, 7).
3. Electro-acoustic transducer according to any one of claims 1 to 2, characterized in that each of said transducer units (6, 7) is made up of at least one magnetostrictive bar.
4. Electro-acoustic transducer according to any one of claims 1 to 2, characterized in that said transducer units (6, 7) are each made up of at least one stack of piezo-electric ceramics, alternating with electrodes (10), forming an elongated cylinder.
5. Electro-acoustic transducer according to any one of claims 1 to 4, characterized in that longitudinal gaps (9A, 9B) are respectively allowed for between said rigid intermediate unit (8) and said first and second supporting components (1, 2), such that during relative displacements between said supporting components due to forces developed by said transducer units (6, 7) and to the forces due to said pre-stressing device, contacts between said rigid intermediate unit and said supporting components are avoided.
6. Electro-acoustic transducer according to any one of claims 1 to 5, characterized in that said rigid intermediate unit (8) is made up of a single rigid piece of metal.
7. Electro-acoustic transducer according to any one of claims 1 to 5, characterized in that said intermediate unit is made up of at least two rigid intermediate components (8) and at least one intermediate transducer unit (8A, 8B, 8C, 8D) which is interposed between said two rigid intermediate components (8).
8. Electro-acoustic transducer according to any one of claims 6 to 7, characterized in that said rigid component (8) is made up of a part that is almost cylindrical, with its axis parallel to said longitudinal axis (xx1), finishing at one end by a base (84) which contains one of said two parallel faces, which is in contact with the second end of said first transducer unit, and having at its other end an external collar which contains the other one of said two parallel faces, which is in contact with the second end of the second of said transducer units.
9. Electro-acoustic transducer according to any one of claims 1 to 8, characterized in that the transverse sections of the active parts of said first and second transducer units (6, 7) are roughly equal.
10. Manufacturing process for electro-acoustic transducers of the type containing at least one transducer unit of elongated shape, pre-stressed axially between two supporting components, characterized in that a first transducer unit of elongated shape, having only its first end in contact with one of the two supporting components and a second transducer unit of elongated shape, having only its first end in contact with the other supporting component, are fitted between said supporting components, said transducer units being parallel and side-by-side and functioning in phase, and in that an intermediate component which is in contact with both ends of said transducer units is interposed between these two transducer units, and in that the two transducer units and said intermediate component, which transmits the longitudinal forces between the two transducer units, are pre-stressed axially between the two supporting components.

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