EP0100711A2 - Half wave transducer using an active piezo-electric polymer element - Google Patents

Half wave transducer using an active piezo-electric polymer element Download PDF

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Publication number
EP0100711A2
EP0100711A2 EP83401485A EP83401485A EP0100711A2 EP 0100711 A2 EP0100711 A2 EP 0100711A2 EP 83401485 A EP83401485 A EP 83401485A EP 83401485 A EP83401485 A EP 83401485A EP 0100711 A2 EP0100711 A2 EP 0100711A2
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EP
European Patent Office
Prior art keywords
sheet
piezoelectric polymer
transducer according
polymer material
transducer
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EP83401485A
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German (de)
French (fr)
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EP0100711A3 (en
Inventor
Hoang Giang Nguyen
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Thales SA
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Thomson CSF SA
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • B06B1/0688—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction with foil-type piezoelectric elements, e.g. PVDF
    • B06B1/0692—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction with foil-type piezoelectric elements, e.g. PVDF with a continuous electrode on one side and a plurality of electrodes on the other side
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S310/00—Electrical generator or motor structure
    • Y10S310/80—Piezoelectric polymers, e.g. PVDF

Definitions

  • the present invention relates to transducers of the half-wave type using as active element a sheet of piezoelectric polymer such as polyvinylidene fluoride.
  • Piezoelectric polymer materials offer the advantage of having an acoustic impedance of the same order of magnitude as that of the propagation media. These materials also lend themselves to easy implementation, because they can be molded, thermoformed and take advantage of their flexibility. On the other hand, these materials have relatively weak piezoelectric properties compared for example to those of piezoelectric ceramics and they pose technological problems in particular as regards the poor adhesion of the metal layers intended to materialize the electrodes of a transducer.
  • the half-wave operation makes it possible to approach more perfect reflection of the waves towards the external face of the transducer, since the medium charging the rear face of the transducer has an acoustic impedance typically equal to that of air , that is to say practically zero.
  • a non-dissipative medium does not constitute an appropriate support for depositing electrodes there and it is necessary to turn to another means to resolve the problem posed, that is to say the lack of adhesion of metal deposits on piezoelectric polymers.
  • Half-wave or full-wave configurations are more efficient with regard to bandwidth and sensitivity. They are usually constituted by a piezoelectric polymer sheet whose external face is coupled to the biological medium via a quarter-wave layer of impedance adapter and whose internal face is directly related to the air contained inside. a housing or with a similar medium with low impedance, for example a polymer foam. The distance between the external and internal faces is entirely occupied by the active material, the thickness of which most often corresponds to half a wavelength of the central operating frequency.
  • the invention suggests making the vibrating structure by combining several layers, one of which, active, provides the transducer effect, the others simply playing the role of electrode support.
  • These electrode-carrying layers are integral with the active layer, so that there is a laminated vibrating structure remaining half-wave as a whole although partially active.
  • the layers fixed by bonding on the active layer can have their electrodes in contact with the active layer, the problem of adhesion is resolved by keeping a small spacing of the electrodes and a perfect reflection of the waves at the rear face of the structure. composite, which is in direct relation with a reflective medium of very low acoustic impedance.
  • the subject of the invention is a half-wave type transducer with an active element of piezoelectric polymer comprising at least two electrodes framing a sheet of piezoelectric polymer material mounted on a support; said transducer having an external radiating face intended to be coupled to a medium having an acoustic impedance of the same order as that of said piezoelectric polymer material and an internal face in direct relation inside said support with a reflective medium of acoustic impedance very substantially lower, characterized in that at least the electrode situated on the side of said reflecting medium is formed on a sheet-shaped substrate integral with said sheet of material piezoelectric polymer; the free face of said substrate constituting said internal face.
  • the simplest comprises a single pair of electrodes defining a transducer with a single emissive surface; the other is provided with two sets of electrodes making it possible to define several elementary radiating zones arranged in a network.
  • These electromechanical transducers can be used reversibly either to emit acoustic waves in a medium from an external radiating face coupled to this medium, or to convert incident acoustic radiation from the same medium into electrical voltages.
  • the propagation medium considered is generally a biological medium comparable to a volume of water and, where appropriate, this medium is coupled to the external face of the transducer by a pocket of water.
  • the invention is not limited to the case of coupling with a biological medium, because it applies to any medium whose acoustic impedance is of the same order of magnitude as that of the active or passive materials constituting the vibrating structure .
  • Full-wave operation is similar to half-wave operation, since one of the faces carrying the electrodes is still free to vibrate and to reflect the waves towards the other face.
  • the transducers produced starting from a sheet coated on its two electrode faces the height H to be considered is of course the thickness of the sheet, while the width L is simply deduced from the width of the electrodes.
  • the volume framed by two electrodes represents within a sheet, the elementary volume mentioned above and such volumes can be delimited by electrodes in network to form an alignment of radiating sources.
  • the decoupling between elementary vibratory volumes does not require the presence of special cuts such as notches made in the piezoelectric material.
  • Polystyrene used as a quarter wave transformer is a material used to adapt the impedance of polyvinylidene fluoride to that of water.
  • Polyethylene terephthalate has an acoustic impedance close to that of polyvinylidene fluoride and it constitutes a suitable substrate for metallic deposits having good adhesion.
  • FIG. 1 an isometric view can be seen of an electromechanical transducer produced in accordance with the invention.
  • This transducer comprises a base 1 comprising a central recess 2.
  • a thin sheet 3 of polyethylene terephthalate is bonded by its periphery to the base 1.
  • Deposits of electrodes 4, 5, 7 and 8 are made on the upper face of the sheet 3.
  • These deposits form in the middle of sheet 3 a network of parallel conductive strips which overhang the recess 2.
  • These conductive strips are covered by a sheet 6 of piezoelectric polymer, for example polyvinylidene fluoride.
  • the sheet 6 is bonded to the sheet 3 and carries on its upper face a counter-electrode 9 which cooperates with each of the conductive strips in a network so as to delimit elementary volumes of piezoelectric polymer which represent elementary radiating sources.
  • the electrodes 4, 5, 7 and 8 are extended on the sheet 3 outside the rectangular area covered by the sheet 6, to allow more spaced connections for the application of excitation voltages between the common counter electrode 9 and the arrayed electrodes which extend along the interface between the sheet 6 and the sheet 3.
  • the system of axes 0, x i , x 2 , x 3 is located in the space which overhangs the radiating face of the transducer here constituted by the counter-electrode 9. This space is generally occupied by a propagation medium 12 having the acoustic impedance of the water.
  • FIG. 2 is a partial sectional view of the electromechanical transducer of Figure 1. It can be seen that the sheet 3 which is made of a passive polymer material, is fixed to the base 1 by a peripheral adhesive seal 10 and carries the conductive strips 4, 5, 8 and 7 which act as rear electrodes for the piezoelectric polymer sheet 6. A glue joint 11 secures these two sheets 3 and 6 in the part which overhangs the recess 2. Thus a vibrating structure mixed active and passive of total thickness h l + h 2 is interposed between the propagation medium 12 and the medium which fills the recess 2. The half-wave or full-wave operation of the arrangement of FIG.
  • the parameter h 2 / h 1 is plotted on the abscissa and the central operating frequency f R on the ordinate.
  • the measurement of the transducer conversion losses was also plotted on the ordinate on a decibel scale.
  • Curves 13, 14 and 15 relate to the half-wave operating mode, while curves 16, 17 and 18 in phantom relate to the full-wave operating mode.
  • Curve 13 shows that the central operating frequency of the transducer decreases with increasing the thickness of the sheet 3, which serves as a support for the electrodes. This effect is quite predictable, since the half-wave operation of the vibrating structure links the operating frequency to the choice of the thicknesses h l and h 2 taking into account the propagation speeds in the media 3 and 6 which make up this structure.
  • the vibrations originating in the active sheet 6 undergo little reflection when they enter the sheet 3 because the impedances of the two juxtaposed media are advantageously chosen close to one another. On the other hand, the vibrations undergo an almost perfect reflection at the level of the lower face of the sheet 3 from where they are returned towards the medium 12 in order to obtain maximum radiation.
  • the curve 15 which represents the conversion losses shows that the addition of the sheet 3 makes it possible to keep low losses not exceeding 15 dB for a thickness h 2 reaching 200 smokes
  • the curve 14 can be read on the frequency scale and gives the AF bandwidth of the transducer in absolute value. We see that this bandwidth varies little since it remains between 1, 2 and 0.8 MHz. The presence of the sheet 3 therefore makes it possible to obtain a good conversion yield and a good resolution while bringing a clear advantage as regards the production of metal deposits having good adhesion.
  • the curves in phantom which relate to the operation in whole wave indicate characteristics in general less favorable.
  • the curve 17 gives the operating frequency which is higher, since an entire wave must be established between the end faces of the vibrating structure.
  • Curve 18 gives the value of the conversion losses which are generally higher than in half-wave operation. However, when the thickness of the sheet 3 is of the same order as that of the sheet 6, it can be seen that the conversion loss is practically as low as with the sheet 6 alone in half-wave operation. The curve 16 which gives the bandwidth shows that it can be as good, or even better than with the half-wave operating mode.
  • the sheet 3 although it is passive, perfectly solves the problem of the adhesion of the electrodes 4, 5, 7, 8 while retaining the good operating qualities of the transducer both in sensitivity only in resolution.
  • FIG. 4 an alternative embodiment can be seen in which the electrode 9 is surmounted by a quarter wave layer 19 made of polystyrene which performs the impedance matching between the propagation medium 12 and the piezoelectric polymer material 6.
  • This impedance matching increases the relative bandwidth at 5 MHz which goes from 26% to 32% and the layer 19 can serve as a support for the deposition of the electrode 9 before being bonded to the polymer sheet 6 piezoelectric.
  • a metal deposit adheres much better on supports made of organic material having a carbon oxygen double bond and much less well on piezoelectric polymer materials such as polyvinylidene fluoride PVF 2 or PVF - TRFE copolymers.
  • the recess 2 in the base 1 can be completely or partially filled with a porous material of low density having an acoustic impedance low enough to ensure high reflectivity at the level of the lower face of the sheet 3.
  • the proposed technique consists in adding a layer of non-piezoelectric polymer whose acoustic impedance is close to that of the piezoelectric polymer and whose thickness varies between 3.04 and 0.5 wavelength.
  • the layers can be bonded using epoxy resin, preferably placing the electrodes against the faces of the piezoelectric polymer sheet.
  • FIG. 5 we can see a single probe transducer which differs from the transducer in FIG. 4 by the shape of a spherical cap given to its radiating face. This shape can be obtained by pressing all of the sheets 3, 6, 19 in a preform. The solidification of the adhesive can take place during the preforming operation, in order to ensure the conservation of the deformations imposed by the preform. It is also possible to bond together preformed parts separately by thermoforming.
  • the monoprobe device of FIG. 5 has the symmetry of revolution around the axis 22 and F is the center of curvature of the radiating face, the emitted E wave can be focused at point F.
  • FIG. 6 an alternative embodiment of the device in FIG. 4 can be seen, which consists in providing on each side of the active sheet 6 sheets 3 and 20 made of passive materials having an acoustic impedance close to the acoustic impedance of the active material of the sheet 6.
  • the vibrating structure obtained by bonding the sheets 20, 6 and 3 can function in half-wave or in whole wave between a quarter-wave adapter layer 19 and a medium with low impedance such as air filling the recess 2 of the base 1.
  • the acoustic impedance of the quarter adapter layer wave is chosen close to the geometric mean of the acoustic impedances of the propagation medium and of the active sheet 6.
  • transducer implements a radiating face of cylindrical shape having as its axis the line 21.
  • the radiation is focused in a plane perpendicular to the line 21.
  • the transducer comprises a network of sources.
  • Each source is a part of vibrating structure delimited by an active portion of the sheet 6 comprised between the counter-electrode 9 and an electrode 4, 5, 7 or 8.
  • the electrodes 4, 5, 7, 8 suitably delayed, the acoustic radiation can be made to converge at a point F on line 21.
  • the network arrangements of FIGS. 1 and 7 can be produced on a sheet of polyethylene terephthalate measuring 12.5 cm in length and 3.5 cm in width.
  • the central network of parallel conductive strips can occupy a rectangular range of 4 cm in length and 1.4 cm in width.
  • the network of conductive strips may have a width of 125 l um and a pitch of 250 smoke Such networking arrangement may operate at 3 MHz.
  • the electrodes are photo-etched or deposited through a mask on the sheet 3 of polyethylene terephthalate, after which a sheet 6 of polyvinylidene fluoride measuring 4 cm in length and 1.4 cm in width is brought back into the central part.
  • the assembly After bonding of the sheet 6 provided with its metallization 9 on the sheet 3 and after bonding of an adapter blade 19 of polystyrene on the electrode 9, the assembly is mounted on a base 1 in the form of a frame so that all of the active surface overhangs a central recess of the base 1.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Transducers For Ultrasonic Waves (AREA)
  • Ultra Sonic Daignosis Equipment (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

Abstract

L'invention se rapporte aux transducteurs électromécaniques de type demi-onde dans lesquels l'élément actif est une feuille de polymère piézoélectrique (6) encadrée par des électrodes (9, 4, 5, 7, 8). L'invention a pour objet un transducteur dans lequel la structure vibrante comporte, faisant corps avec la feuille active de polymère piézoélectrique (6), au moins une feuille passive (3) servant de support aux électrodes (4, 5, 7, 8). L'invention s'applique notamment à l'excitation et à la détection de rayonnements ultrasonores dans les tissus biologiques.The invention relates to electromechanical transducers of the half-wave type in which the active element is a sheet of piezoelectric polymer (6) framed by electrodes (9, 4, 5, 7, 8). The invention relates to a transducer in which the vibrating structure comprises, integral with the active sheet of piezoelectric polymer (6), at least one passive sheet (3) serving to support the electrodes (4, 5, 7, 8) . The invention is particularly applicable to the excitation and detection of ultrasonic radiation in biological tissues.

Description

La présente invention se rapporte aux transducteurs du type demi-onde utilisant comme élément actif une feuille de polymère piézoélectrique tel que le polyfluorure de vinylidène.The present invention relates to transducers of the half-wave type using as active element a sheet of piezoelectric polymer such as polyvinylidene fluoride.

Ces transducteurs reçoivent des applications intéressantes dans le domaine du diagnostic médical par examen d'images tomo-échographique. Les matériaux polymères piézoélectriques offrent J'avantage de présenter une impédance acoustique du même ordre de grandeur que celle des milieux de propagation. Ces matériaux se prêtent également à une mise en oeuvre facile, car on peut les mouler, les thermoformer et mettre à profit leur souplesse. Par contre, ces matériaux ont des propriétés piézoélectriques relativement faibles comparées par exemple à celles des céramiques piézoélectriques et ils posent des problèmes technologiques notamment en ce qui concerne l'adhérence médiocre des couches métalliques destinées à matérialiser les électrodes d'un transducteur. Lorsqu'on dépose de l'aluminium, du nickel, du chrome ou de l'or par évaporation sous vide sur une feuille de polyfluorure de vinylidène, on rencontre des difficultés pour réaliser certaines configurations d'électrodes un tant soit peu étendues ou correspondant à un dessin compliqué. Lorsqu'on dispose d'un milieu réflecteur à très haute impédance acoustique jouxtant la face arrière d'une feuille de polymère piézoélectrique, on effectue les dépôts d'électrodes sur ce milieu à condition qu'il soit isolant et qu'il permette une meilleure adhérence. Cependant, les transducteurs réalisés selon ce principe fonctionnent en quart d'onde et l'on constate que les pertes de conversion, la résolution en profondeur et la bande passante sont moins bonnes qu'avec une configuration fonctionnant en demi-onde ou en onde entière. Le fonctionnement en demi-onde permet en effet d'approcher d'avantage d'une réflexion parfaite des ondes vers la face externe du transducteur, car le milieu chargeant la face arrière du transducteur présente une impédance acoustique typiquement égale à celle de l'air, c'est-à-dire pratiquement nulle. En contrepartie, un tel milieu non dissipatif ne constitue pas un support approprié pour y déposer des électrodes et il faut se tourner vers un autre moyen pour résoudre le problème posé, c'est-à-dire le manque d'adhérence des dépôts métalliques sur les polymères piézoélectriques.These transducers receive interesting applications in the field of medical diagnosis by examination of tomo-echographic images. Piezoelectric polymer materials offer the advantage of having an acoustic impedance of the same order of magnitude as that of the propagation media. These materials also lend themselves to easy implementation, because they can be molded, thermoformed and take advantage of their flexibility. On the other hand, these materials have relatively weak piezoelectric properties compared for example to those of piezoelectric ceramics and they pose technological problems in particular as regards the poor adhesion of the metal layers intended to materialize the electrodes of a transducer. When depositing aluminum, nickel, chromium or gold by evaporation under vacuum on a sheet of polyvinylidene fluoride, one encounters difficulties in achieving certain configurations of electrodes which are somewhat extensive or corresponding to a complicated drawing. When there is a reflective medium with very high acoustic impedance adjoining the rear face of a piezoelectric polymer sheet, the electrodes are deposited on this medium provided that it is insulating and that it allows better grip. However, the transducers produced according to this principle operate in quarter wave and it is found that the conversion losses, the depth resolution and the bandwidth are less good than with a configuration operating in half-wave or in whole wave. . The half-wave operation makes it possible to approach more perfect reflection of the waves towards the external face of the transducer, since the medium charging the rear face of the transducer has an acoustic impedance typically equal to that of air , that is to say practically zero. In return, such a non-dissipative medium does not constitute an appropriate support for depositing electrodes there and it is necessary to turn to another means to resolve the problem posed, that is to say the lack of adhesion of metal deposits on piezoelectric polymers.

Les configurations de type demi-onde ou onde entière s'avèrent plus performantes en ce qui concerne la bande passante et la sensibilité. Elles sont habituellement constituées par une feuille de polymère piézoélectrique dont la face externe est couplée au milieu biologique via une couche quart d'onde adaptatrice d'impédance et dont la face interne est directement en relation avec l'air contenu à l'intérieur d'un boîtier ou avec un milieu similaire à faible impédance, une mousse de polymère par exemple. L'inter- distance entre faces externe et interne est entièrement occupée par le matériau actif dont l'épaisseur correspond le plus souvent à une demi longueur d'onde de la fréquence centrale de fonctionnement.Half-wave or full-wave configurations are more efficient with regard to bandwidth and sensitivity. They are usually constituted by a piezoelectric polymer sheet whose external face is coupled to the biological medium via a quarter-wave layer of impedance adapter and whose internal face is directly related to the air contained inside. a housing or with a similar medium with low impedance, for example a polymer foam. The distance between the external and internal faces is entirely occupied by the active material, the thickness of which most often corresponds to half a wavelength of the central operating frequency.

En conservant le principe de l'excitation en demi-onde ou en onde entière, l'invention suggère de réaliser la structure vibrante par la réunion de plusieurs couches dont l'une, active, fournit l'effet transducteur, les autres jouant simplement le rôle de support d'électrodes. Ces couches porte- électrodes font corps avec la couche active, de sorte qu'on dispose d'une structure vibrante stratifiée restant demi-onde dans son ensemble bien que partiellement active. Comme les couches fixées par collage sur la couche active peuvent avoir leurs électrodes en contact avec la couche active, le problème d'adhérence est résolu en conservant un faible écartement des électrodes et une réflexion parfaite des ondes au niveau de la face arrière de la structure composite, laquelle est en relation directe avec un milieu réflecteur de très faible impédance acoustique.By retaining the principle of half-wave or full-wave excitation, the invention suggests making the vibrating structure by combining several layers, one of which, active, provides the transducer effect, the others simply playing the role of electrode support. These electrode-carrying layers are integral with the active layer, so that there is a laminated vibrating structure remaining half-wave as a whole although partially active. As the layers fixed by bonding on the active layer can have their electrodes in contact with the active layer, the problem of adhesion is resolved by keeping a small spacing of the electrodes and a perfect reflection of the waves at the rear face of the structure. composite, which is in direct relation with a reflective medium of very low acoustic impedance.

L'invention a pour objet un transducteur de type demi-onde à élément actif en polymère piézoélectrique comprenant au moins deux électrodes encadrant une feuille de matériau polymère piézoélectrique montée sur un support ; ledit transducteur ayant une face rayonnante externe destinée à être couplée à un milieu présentant une impédance acoustique du même ordre que celle dudit matériau polymère piézoélectrique et une face interne en relation directe à l'intérieur dudit support avec un milieu réflecteur d'impédance acoustique très sensiblement inférieure, caractérisé en ce que, au moins l'électrode située du côté dudit milieu réflecteur est formée sur un substrat en forme de feuille faisant corps avec ladite feuille de matériau polymère piézoélectrique ; la face libre dudit substrat constituant ladite face interne.The subject of the invention is a half-wave type transducer with an active element of piezoelectric polymer comprising at least two electrodes framing a sheet of piezoelectric polymer material mounted on a support; said transducer having an external radiating face intended to be coupled to a medium having an acoustic impedance of the same order as that of said piezoelectric polymer material and an internal face in direct relation inside said support with a reflective medium of acoustic impedance very substantially lower, characterized in that at least the electrode situated on the side of said reflecting medium is formed on a sheet-shaped substrate integral with said sheet of material piezoelectric polymer; the free face of said substrate constituting said internal face.

L'invention sera mieux comprise au moyen de la description ci-après et des figures annexées parmi lesquelles :

  • La figure 1 est une vue isométrique d'un transducteur en réseau selon l'invention.
  • La figure 2 est une coupe partielle du transducteur illustré sur la figure 1.
  • La figure 3 est une figure explicative.
  • La figure 4 est une première variante de réalisation du transducteur selon l'invention.
  • La figure 5 est une seconde variante de réalisation du transducteur selon l'invention.
  • La figure 6 est une troisième variante de réalisation du transducteur selon l'invention.
  • La figure 7 est une vue isométrique partielle d'une quatrième variante de réalisation du transducteur selon l'invention.
The invention will be better understood by means of the description below and the appended figures among which:
  • Figure 1 is an isometric view of a network transducer according to the invention.
  • FIG. 2 is a partial section of the transducer illustrated in FIG. 1.
  • Figure 3 is an explanatory figure.
  • Figure 4 is a first alternative embodiment of the transducer according to the invention.
  • Figure 5 is a second alternative embodiment of the transducer according to the invention.
  • Figure 6 is a third alternative embodiment of the transducer according to the invention.
  • Figure 7 is a partial isometric view of a fourth alternative embodiment of the transducer according to the invention.

Dans la description qui va suivre, on abordera successivement deux types de configurations de transducteurs. La plus simple comporte une seule paire d'électrodes définissant un transducteur à surface émissive unique ; l'autre est munie de deux jeux d'électrodes permettant de définir plusieurs zones rayonnantes élémentaires agencées en réseau. Ces transducteurs électromécaniques sont utilisables de façon réversible soit pour émettre des ondes acoustiques dans un milieu à partir d'une face rayonnante externe couplée à ce milieu, soit pour convertir en tensions électriques des rayonnements acoustiques incidents provenant du même milieu. Le milieu de propagation considéré est en général un milieu biologique assimilable à un volume d'eau et, le cas échéant, ce milieu est couplé à la face externe du transducteur par une poche d'eau. Bien entendu, l'invention n'est pas limitée au cas du couplage avec un milieu biologique, car elle s'applique à tout milieu dont l'impédance acoustique est du même ordre de grandeur que celle des matériaux actifs ou passifs constituant la structure vibrante.In the description which follows, two types of transducer configurations will be approached successively. The simplest comprises a single pair of electrodes defining a transducer with a single emissive surface; the other is provided with two sets of electrodes making it possible to define several elementary radiating zones arranged in a network. These electromechanical transducers can be used reversibly either to emit acoustic waves in a medium from an external radiating face coupled to this medium, or to convert incident acoustic radiation from the same medium into electrical voltages. The propagation medium considered is generally a biological medium comparable to a volume of water and, where appropriate, this medium is coupled to the external face of the transducer by a pocket of water. Of course, the invention is not limited to the case of coupling with a biological medium, because it applies to any medium whose acoustic impedance is of the same order of magnitude as that of the active or passive materials constituting the vibrating structure .

L'étude des modes vibratoires en volume d'un résonateur élémentaire constitué par un bloc de hauteur H et de largeur L en matériau élastique piézoélectriquement actif montre, qu'équipé d'électrodes de largeur L distantes de H, ce bloc peut vibrer selon la direction de la normale aux électrodes, mais aussi dans des directions parallèles à celles-ci. Lorsque le rapport L/H est supérieur à trois, le mode d'épaisseur tend à se produire à une fréquence pour laquelle la longueur d'onde X dans le matériau est égale à deux fois la hauteur H, ce qui définit un fonctionnement en demi-onde. Si le rapport L/H est inférieur à l'unité, on constate que la fréquence de fonctionnement peut être inférieur à celle calculée à partir de l'expression H = X /2, néanmoins on reste en présence d'un fonctionnement demi-onde qui se caractérise par la vibration libre de l'une des faces portant les électrodes.The study of the vibratory modes in volume of an elementary resonator constituted by a block of height H and width L in elastic material piezoelectrically active shows, that equipped with electrodes of width L distant from H, this block can vibrate according to the direction of the normal to the electrodes, but also in directions parallel to these. When the L / H ratio is greater than three, the thickness mode tends to occur at a frequency for which the wavelength X in the material is equal to twice the height H, which defines an operation in half -wave. If the L / H ratio is less than unity, we note that the operating frequency can be lower than that calculated from the expression H = X / 2, nevertheless we remain in the presence of half-wave operation which is characterized by the free vibration of one of the faces carrying the electrodes.

Le fonctionnement en onde entière est similaire au fonctionnement demi-onde, car l'une des faces portant les électrodes est encore libre de vibrer et de réfléchir les ondes vers l'autre face. Dans la pratique, les transducteurs réalisés en partant d'une feuille revêtue sur ses deux faces d'électrodes, la hauteur H à considérer est bien entendu l'épaisseur de la feuille, alors que la largeur L est tout simplement déduite de la largeur des électrodes. Ainsi, le volume encadré par deux électrodes représente au sein d'une feuille, le volume élémentaire mentionné ci-dessus et de tels volumes peuvent être délimités par des électrodes en réseau pour former un alignement de sources rayonnantes. Dans le cas d'une structure de transducteur en polymère piézoélectrique, le découplage entre volumes vibratoires élémentaires ne nécessite pas la présence de découpes particulières telles que des entailles pratiquées dans le matériau piézoélectrique. Ceci est dû au fait que les matériaux polymères piézoélectriques polarisés selon la normale x3 aux électrodes portées par les deux faces de la feuille, ont un coefficient piézoélectrique d33 nettement supérieur aux coefficients piézoélectriques d31 et d32 qui correspondent aux vibrations selon les axes xl et x2.Full-wave operation is similar to half-wave operation, since one of the faces carrying the electrodes is still free to vibrate and to reflect the waves towards the other face. In practice, the transducers produced starting from a sheet coated on its two electrode faces, the height H to be considered is of course the thickness of the sheet, while the width L is simply deduced from the width of the electrodes. Thus, the volume framed by two electrodes represents within a sheet, the elementary volume mentioned above and such volumes can be delimited by electrodes in network to form an alignment of radiating sources. In the case of a piezoelectric polymer transducer structure, the decoupling between elementary vibratory volumes does not require the presence of special cuts such as notches made in the piezoelectric material. This is due to the fact that the piezoelectric polymer materials polarized according to the normal x 3 to the electrodes carried by the two faces of the sheet, have a piezoelectric coefficient d 33 significantly higher than the piezoelectric coefficients d 31 and d 32 which correspond to the vibrations along the axes. x l and x 2 .

Avant d'entamer la description détaillée des figures, il est utile de rappeler les valeurs d'impédance acoustique de quelques matériaux mis en oeuvre dans les transducteurs et des milieux qui encadrent ces matériaux.

Figure imgb0001
Before starting the detailed description of the figures, it is useful to recall the acoustic impedance values of some materials used in the transducers and of the media which surround these materials.
Figure imgb0001

On voit que l'impédance acoustique de l'air est négligeable par rapport à celle des autres matériaux qui figurent dans ce tableau. Le polystyrène utilisé comme transformateur quart d'onde est un matériau permettant d'adapter l'impédance du polyfluorure de vinylidène à celle de l'eau. Le polyéthylène téréphtalate présente une impédance acoustique proche de celle du polyfluorure de vinylidène et il constitue un substrat approprié pour des dépôts métalliques présentant une bonne adhérence.We see that the acoustic impedance of the air is negligible compared to that of the other materials which appear in this table. Polystyrene used as a quarter wave transformer is a material used to adapt the impedance of polyvinylidene fluoride to that of water. Polyethylene terephthalate has an acoustic impedance close to that of polyvinylidene fluoride and it constitutes a suitable substrate for metallic deposits having good adhesion.

Sur la figure 1, on peut voir une vue isométrique d'un transducteur électromécanique réalisé conformément à l'invention. Ce transducteur comporte une embase 1 comportant un évidement central 2. Une feuille mince 3 de polyéthylène téréphtalate est collée par son pourtour sur l'embase 1. Des dépôts d'électrodes 4, 5, 7 et 8 sont effectués sur la face supérieure de la feuille 3. Ces dépôts forment au milieu de la feuille 3 un réseau de bandes conductrices parallèles qui surplombent l'évidement 2. Ces bandes conductrices sont recouvertes par une feuille 6 de polymère piézoélectrique, par exemple du polyfluorure de vinylidène. La feuille 6 est collée à la feuille 3 et porte sur sa face supérieure une contre-électrode 9 qui coopère avec chacune des bandes conductrices en réseau de façon à délimiter des volumes élémentaires de polymère piézoélectrique qui représentent des sources rayonnantes élémentaires.In FIG. 1, an isometric view can be seen of an electromechanical transducer produced in accordance with the invention. This transducer comprises a base 1 comprising a central recess 2. A thin sheet 3 of polyethylene terephthalate is bonded by its periphery to the base 1. Deposits of electrodes 4, 5, 7 and 8 are made on the upper face of the sheet 3. These deposits form in the middle of sheet 3 a network of parallel conductive strips which overhang the recess 2. These conductive strips are covered by a sheet 6 of piezoelectric polymer, for example polyvinylidene fluoride. The sheet 6 is bonded to the sheet 3 and carries on its upper face a counter-electrode 9 which cooperates with each of the conductive strips in a network so as to delimit elementary volumes of piezoelectric polymer which represent elementary radiating sources.

Comme le montre la figure 1, les dépôts d'électrodes 4, 5, 7 et 8 se prolongent sur la feuille 3 à l'extérieur de la zone rectangulaire recouverte par la feuille 6, afin de permettre des connexions plus espacées pour l'application de tensions d'excitation entre la contre-électrode commune 9 et les électrodes en réseaux qui s'étendent selon l'interface entre la feuille 6 et la feuille 3. Le système d'axes 0, xi, x2, x3 se situe dans l'espace qui surplombe la face rayonnante du transducteur ici constituée par la contre-électrode 9. Cet espace est en général occupé par un milieu de propagation 12 ayant l'impédance acoustique de l'eau.As shown in Figure 1, the electrodes 4, 5, 7 and 8 are extended on the sheet 3 outside the rectangular area covered by the sheet 6, to allow more spaced connections for the application of excitation voltages between the common counter electrode 9 and the arrayed electrodes which extend along the interface between the sheet 6 and the sheet 3. The system of axes 0, x i , x 2 , x 3 is located in the space which overhangs the radiating face of the transducer here constituted by the counter-electrode 9. This space is generally occupied by a propagation medium 12 having the acoustic impedance of the water.

La figure 2 est une vue en coupe partielle du transducteur électromécanique de la figure 1. On voit que la feuille 3 qui est faite d'un matériau polymère passif, est fixée sur l'embase 1 par un joint de colle périphérique 10 et porte les bandes conductrices 4, 5, 8 et 7 qui font office d'électrodes arrière pour la feuille de polymère piézoélectrique 6. Un joint de colle 11 solidarise ces deux feuilles 3 et 6 dans la partie qui surplombe l'évidement 2. Ainsi une structure vibrante mixte active et passive d'épaisseur totale hl + h2 se trouve intercalée entre le milieu de propagation 12 et le milieu qui remplit l'évidement 2. Le fonctionnement en demi-onde ou en onde entière de la disposition de la figure 2 a été expérimenté en utilisant une feuille 6 de polyfluorure de vinylidène d'épaisseur hl = 220 /um. Le milieu 12 était constitué par de l'eau et le milieu de remplissage de l'évidement 2 était de l'air. Une feuille 3 de polyéthylène théréphtalate dont l'épaisseur h2 variait entre 0 à 200 jum a permis de dresser les courbes de la figure 3. Les électrodes 4, 5, 7 et 8 avaient une largeur supérieure à l'épaisseur hl de la feuille 6, afin que la fréquence centrale de fonctionnement corresponde assez exactement au fonctionnement demi-onde ou onde entière.Figure 2 is a partial sectional view of the electromechanical transducer of Figure 1. It can be seen that the sheet 3 which is made of a passive polymer material, is fixed to the base 1 by a peripheral adhesive seal 10 and carries the conductive strips 4, 5, 8 and 7 which act as rear electrodes for the piezoelectric polymer sheet 6. A glue joint 11 secures these two sheets 3 and 6 in the part which overhangs the recess 2. Thus a vibrating structure mixed active and passive of total thickness h l + h 2 is interposed between the propagation medium 12 and the medium which fills the recess 2. The half-wave or full-wave operation of the arrangement of FIG. 2 a was tested using a sheet 6 of polyvinylidene fluoride of thickness h l = 220 / μm. The medium 12 consisted of water and the filling medium of the recess 2 was air. 3 a sheet of polyethylene terephthalate whose thickness h 2 ranged from 0 to 200 j um allowed to draw the curves of Figure 3. The electrodes 4, 5, 7 and 8 had a width greater than the thickness h of the sheet 6, so that the central operating frequency corresponds fairly exactly to the half-wave or whole wave operation.

Sur la figure 3, on a porté en abscisse le paramètre h2/h1 et en ordonnée la fréquence centrale de fonctionnement fR. On a également porté en ordonnée sur une échelle en décibel la mesure des pertes de conversion du transducteur. Les courbes 13, 14 et 15 se rapportent au mode de fonctionnement en demi-onde, tandis que les courbes 16, 17 et 18 en trait mixte se rapportent au mode de fonctionnement en onde entière.In FIG. 3, the parameter h 2 / h 1 is plotted on the abscissa and the central operating frequency f R on the ordinate. The measurement of the transducer conversion losses was also plotted on the ordinate on a decibel scale. Curves 13, 14 and 15 relate to the half-wave operating mode, while curves 16, 17 and 18 in phantom relate to the full-wave operating mode.

La courbe 13 montre que la fréquence centrale de fonctionnement du transducteur diminue lorsqu'on augmente l'épaisseur de la feuille 3, qui sert de support aux électrodes. Cet effet est tout à fait prévisible, puisque le fonctionnement demi-onde de la structure vibrante lie la fréquence de fonctionnement au choix des épaisseurs hl et h2 compte tenu des vitesses de propagation dans les milieux 3 et 6 qui composent cette structure. Les vibrations prenant naissance dans la feuille active 6 subissent peu de réflexion lorsqu'elles pénètrent dans la feuille 3 car les impédances des deux milieux juxtaposés sont avantageusement choisies proches l'une de l'autre. Par contre, les vibrations subissent une réflexion quasi parfaite au niveau de la face inférieure de la feuille 3 d'où elles sont renvoyées vers le milieu 12 afin d'obtenir un rayonnement maximal. La courbe 15 qui représente les pertes de conversion montre que l'adjonction de la feuille 3 permet de conserver de faibles pertes n'excédant pas 15 dB pour une épaisseur h2 atteignant 200 fume La courbe 14 se lit sur l'échelle des fréquences et donne en valeur absolue la bande passante AF de transducteur. On voit que cette bande passante varie peu puisqu'elle reste comprise entre 1, 2 et 0,8 MHz. La présence de la feuille 3 permet donc d'obtenir un bon rendement de conversion et une bonne résolution tout en apportant un net avantage en ce qui concerne la réalisation de dépôts métalliques ayant une bonne adhérence. Les courbes en trait mixte qui concernent le fonctionnement en onde entière indiquent des caractéristiques en général moins favorables. La courbe 17 donne la fréquence de fonctionnement qui est plus élevée, puisqu'une onde entière doit s'établir entre les faces extrêmes de la structure vibrante. La courbe 18 donne la valeur des pertes de conversion qui sont en général plus fortes qu'en fonctionnement demi-onde. Cependant, lorsque l'épaisseur de la feuille 3 est du même ordre que celle de la feuille 6, on voit que la perte de conversion est pratiquement aussi faible qu'avec la feuille 6 seule en fonctionnement demi-onde. La courbe 16 qui donne la bande passante montre que celle-ci peut être aussi bonne, voire meilleure qu'avec le mode de fonctionnement en demi-onde.Curve 13 shows that the central operating frequency of the transducer decreases with increasing the thickness of the sheet 3, which serves as a support for the electrodes. This effect is quite predictable, since the half-wave operation of the vibrating structure links the operating frequency to the choice of the thicknesses h l and h 2 taking into account the propagation speeds in the media 3 and 6 which make up this structure. The vibrations originating in the active sheet 6 undergo little reflection when they enter the sheet 3 because the impedances of the two juxtaposed media are advantageously chosen close to one another. On the other hand, the vibrations undergo an almost perfect reflection at the level of the lower face of the sheet 3 from where they are returned towards the medium 12 in order to obtain maximum radiation. The curve 15 which represents the conversion losses shows that the addition of the sheet 3 makes it possible to keep low losses not exceeding 15 dB for a thickness h 2 reaching 200 smokes The curve 14 can be read on the frequency scale and gives the AF bandwidth of the transducer in absolute value. We see that this bandwidth varies little since it remains between 1, 2 and 0.8 MHz. The presence of the sheet 3 therefore makes it possible to obtain a good conversion yield and a good resolution while bringing a clear advantage as regards the production of metal deposits having good adhesion. The curves in phantom which relate to the operation in whole wave indicate characteristics in general less favorable. The curve 17 gives the operating frequency which is higher, since an entire wave must be established between the end faces of the vibrating structure. Curve 18 gives the value of the conversion losses which are generally higher than in half-wave operation. However, when the thickness of the sheet 3 is of the same order as that of the sheet 6, it can be seen that the conversion loss is practically as low as with the sheet 6 alone in half-wave operation. The curve 16 which gives the bandwidth shows that it can be as good, or even better than with the half-wave operating mode.

D'après ce qui précède, on voit que la feuille 3, bien qu'elle soit passive, résoud parfaitement le problème de l'adhérence des électrodes 4, 5, 7, 8 tout en conservant bonnes les qualités de fonctionnement du transducteur tant en sensibilité qu'en résolution.From the above, it can be seen that the sheet 3, although it is passive, perfectly solves the problem of the adhesion of the electrodes 4, 5, 7, 8 while retaining the good operating qualities of the transducer both in sensitivity only in resolution.

Sur la figure 4, on peut voir une variante de réalisation dans laquelle l'électrode 9 est surmontée d'une couche quart d'onde 19 en polystyrène qui réalise l'adaptation d'impédance entre le milieu de propagation 12 et le matériau polymère piézoélectrique 6. Cette adaptation d'impédance augmente la bande passante relative à 5 MHz qui passe de 26 % à 32 % et la couche 19 peut servir de support pour le dépôt de l'électrode 9 avant d'être collée sur la feuille 6 de polymère piézoélectrique.In FIG. 4, an alternative embodiment can be seen in which the electrode 9 is surmounted by a quarter wave layer 19 made of polystyrene which performs the impedance matching between the propagation medium 12 and the piezoelectric polymer material 6. This impedance matching increases the relative bandwidth at 5 MHz which goes from 26% to 32% and the layer 19 can serve as a support for the deposition of the electrode 9 before being bonded to the polymer sheet 6 piezoelectric.

En général, un dépôt métallique adhère beaucoup mieux sur les supports en matériau organique ayant une double liaison carbone oxygène et beaucoup moins bien sur les matériaux polymères piézoélectriques tels que le polyfluorure de vinylidène PVF2 ou les copolymères PVF - TRFE.In general, a metal deposit adheres much better on supports made of organic material having a carbon oxygen double bond and much less well on piezoelectric polymer materials such as polyvinylidene fluoride PVF 2 or PVF - TRFE copolymers.

Sur la figure 4, on peut voir que l'évidement 2 de l'embase 1 peut être rempli complètement ou partiellement par un matériau poreux à faible densité ayant une impédance acoustique assez faible pour assurer une forte réflectivité au niveau de la face inférieure de la feuille 3.In FIG. 4, it can be seen that the recess 2 in the base 1 can be completely or partially filled with a porous material of low density having an acoustic impedance low enough to ensure high reflectivity at the level of the lower face of the sheet 3.

Pour résumer, on voit que la technique proposée consiste à additionner une couche de polymère non piézoélectrique dont l'impédance acoustique est proche de celle du polymère piézoélectrique et dont l'épaisseur varie entre 3,04 et 0,5 longueur d'onde. Le collage des couches peut se faire au moyen de résine époxy en placant de préférence les électrodes contre les faces de la feuille de polymère piézoélectrique.To summarize, we see that the proposed technique consists in adding a layer of non-piezoelectric polymer whose acoustic impedance is close to that of the piezoelectric polymer and whose thickness varies between 3.04 and 0.5 wavelength. The layers can be bonded using epoxy resin, preferably placing the electrodes against the faces of the piezoelectric polymer sheet.

Dans les figures qui précèdent, on a décrit un transducteur monosonde et un transducteur en réseau ayant des surfaces rayonnantes planes.In the foregoing figures, a single probe transducer and an array transducer having planar radiating surfaces have been described.

Sur la figure 5, on peut voir un transducteur monosonde qui diffère du transducteur de la figure 4 par la forme en calotte sphérique donnée à sa face rayonnante. Cette forme peut être obtenue en pressant l'ensemble des feuilles 3, 6, 19 dans une préforme. La solidification de la colle peut avoir lieu pendant l'opération de préformage, afin d'assurer la conservation des déformations imposées par la préforme. On peut également coller entre elles des pièces préformées séparément par thermoformage. Lorsque le dispositif monosonde de la figure 5 présente la symétrie de révolution autour de l'axe 22 et que F est le centre de courbure de la face rayonnante, l'onde E émise peut être focalisée au point F.In FIG. 5, we can see a single probe transducer which differs from the transducer in FIG. 4 by the shape of a spherical cap given to its radiating face. This shape can be obtained by pressing all of the sheets 3, 6, 19 in a preform. The solidification of the adhesive can take place during the preforming operation, in order to ensure the conservation of the deformations imposed by the preform. It is also possible to bond together preformed parts separately by thermoforming. When the monoprobe device of FIG. 5 has the symmetry of revolution around the axis 22 and F is the center of curvature of the radiating face, the emitted E wave can be focused at point F.

Sur la figure 6, on peut voir une variante de réalisation du dispositif de la figure 4 qui consiste à prévoir de chaque côté de la feuille active 6 des feuilles 3 et 20 faites de matériaux passifs ayant une impédance acoustique proche de l'impédance acoustique du matériau actif de la feuille 6. La structure vibrante obtenue par collage des feuilles 20, 6 et 3 peut fonctionner en demi-onde ou en onde entière entre une couche adaptatrice quart d'onde 19 et un milieu à basse impédance tel que l'air emplissant l'évidement 2 de l'embase 1. L'impédance acoustique de la couche adaptatrice quart d'onde est choisie proche de la moyenne géométrique des impédances acoustiques du milieu de propagation et de la feuille active 6.In FIG. 6, an alternative embodiment of the device in FIG. 4 can be seen, which consists in providing on each side of the active sheet 6 sheets 3 and 20 made of passive materials having an acoustic impedance close to the acoustic impedance of the active material of the sheet 6. The vibrating structure obtained by bonding the sheets 20, 6 and 3 can function in half-wave or in whole wave between a quarter-wave adapter layer 19 and a medium with low impedance such as air filling the recess 2 of the base 1. The acoustic impedance of the quarter adapter layer wave is chosen close to the geometric mean of the acoustic impedances of the propagation medium and of the active sheet 6.

Sur la figure 7, on peut voir une autre variante de transducteur selon l'invention. Cette variante met en oeuvre une face rayonnante de forme cylindrique ayant pour axe la ligne 21. Ainsi, le rayonnement est focalisé dans un plan perpendiculaire à la ligne 21. Pour qu'il soit focalisable dans un plan contenant la ligne 21, le transducteur comporte un réseau de sources. Chaque source est une partie de structure vibrante délimitée par une portion active de la feuille 6 comprise entre la contre-électrode 9 et une électrode 4, 5, 7 ou 8. En appliquant aux électrodes 4, 5, 7, 8 des tensions électriques convenablement retardées, on peut faire converger le rayonnement acoustique en un point F de la ligne 21.In FIG. 7, we can see another variant of transducer according to the invention. This variant implements a radiating face of cylindrical shape having as its axis the line 21. Thus, the radiation is focused in a plane perpendicular to the line 21. So that it can be focused in a plane containing the line 21, the transducer comprises a network of sources. Each source is a part of vibrating structure delimited by an active portion of the sheet 6 comprised between the counter-electrode 9 and an electrode 4, 5, 7 or 8. By applying electric voltages to the electrodes 4, 5, 7, 8 suitably delayed, the acoustic radiation can be made to converge at a point F on line 21.

A titre d'exemple de réalisation, non limitatif, les agencements en réseaux des figures 1 et 7 peuvent être réalisés sur une feuille de polyéthylène téréphtalate mesurant 12,5 cm de longueur et 3,5 cm de largeur. Le réseau central de bandes conductrices parallèles peut occuper une plage rectangulaire de 4 cm de longueur et de 1,4 cm de largeur. Les bandes conductrices du réseau peuvent avoir une largeur de 125 lum et un pas de 250 fume Un tel agencement en réseau peut fonctionner à 3 MHz. Dans ce cas, les électrodes sont photogravées ou déposées à travers un masque sur la feuille 3 de polyéthylène téréphtalate, après quoi on rapporte dans la partie centrale une feuille 6 de polyfluorure de vinylidène mesurant 4 cm de longueur et 1,4 cm de largeur. Après collage de la feuille 6 munie de sa métallisation 9 sur la feuille 3 et après collage d'une lame adaptatrice 19 en polystyrène sur l'électrode 9, l'ensemble est monté sur une embase 1 en forme de cadre de façon que toute la surface active surplombe un évidement central de l'embase 1.By way of non-limiting exemplary embodiment, the network arrangements of FIGS. 1 and 7 can be produced on a sheet of polyethylene terephthalate measuring 12.5 cm in length and 3.5 cm in width. The central network of parallel conductive strips can occupy a rectangular range of 4 cm in length and 1.4 cm in width. The network of conductive strips may have a width of 125 l um and a pitch of 250 smoke Such networking arrangement may operate at 3 MHz. In this case, the electrodes are photo-etched or deposited through a mask on the sheet 3 of polyethylene terephthalate, after which a sheet 6 of polyvinylidene fluoride measuring 4 cm in length and 1.4 cm in width is brought back into the central part. After bonding of the sheet 6 provided with its metallization 9 on the sheet 3 and after bonding of an adapter blade 19 of polystyrene on the electrode 9, the assembly is mounted on a base 1 in the form of a frame so that all of the active surface overhangs a central recess of the base 1.

Claims (13)

1. Transducteur du type demi-onde à élément actif en polymère piézoélectrique comprenant au moins deux électrodes (4, 9) encadrant une feuille de matériau polymère piézoélectrique (6) montée sur un support (1) ; ledit transducteur ayant une face rayonnante externe destinée à être couplée à un milieu (12) présentant une impédance acoustique du même ordre que celle dudit matériau polymère piézoélectrique (6) et une face interne en relation directe à l'intérieur (2) dudit support (1) avec un milieu réflecteur d'impédance acoustique très sensiblement inférieure, caractérisé en ce que, au moins l'électrode (4) située du côté dudit milieu réflecteur est formée sur un substrat (3) en forme de feuille faisant corps avec ladite feuille de matériau polymère piézoélectrique (6) ; la face libre dudit substrat (3) constituant ladite face interne.1. Transducer of the half-wave type with active element in piezoelectric polymer comprising at least two electrodes (4, 9) framing a sheet of piezoelectric polymer material (6) mounted on a support (1); said transducer having an external radiating face intended to be coupled to a medium (12) having an acoustic impedance of the same order as that of said piezoelectric polymer material (6) and an internal face in direct relation to the interior (2) of said support ( 1) with a very substantially lower acoustic impedance reflecting medium, characterized in that at least the electrode (4) located on the side of said reflecting medium is formed on a sheet-shaped substrate (3) integral with said sheet piezoelectric polymer material (6); the free face of said substrate (3) constituting said internal face. 2. Transducteur selon la revendication 1, caractérisé en ce que l'électrode (9) opposée à ladite électrode (4) est disposée sur l'une des faces de ladite feuille de matériau polymère piézoélectrique (6).2. Transducer according to claim 1, characterized in that the electrode (9) opposite to said electrode (4) is arranged on one of the faces of said sheet of piezoelectric polymer material (6). 3. Transducteur selon la revendication 1, caractérisé en ce que l'électrode (9) opposée à ladite électrode (4) est formée sur un autre substrat (19, 20) en forme de feuille faisant corps avec ladite feuille de matériau polymère piézoélectrique (6).3. Transducer according to claim 1, characterized in that the electrode (9) opposite to said electrode (4) is formed on another sheet-shaped substrate (19, 20) integral with said sheet of piezoelectric polymer material ( 6). 4. Transducteur selon l'une quelconque des revendications 1 à 3, caractérisé en ce qu'il comporte un jeu d'électrodes (4, 5, 7, 8) et une contre-électrode (9) encadrant ladite feuille de matériau polymère piézoélectrique (6).4. Transducer according to any one of claims 1 to 3, characterized in that it comprises a set of electrodes (4, 5, 7, 8) and a counter-electrode (9) framing said sheet of piezoelectric polymer material (6). 5. Transducteur selon l'une quelconque des revendications 1 à 4, caractérisé en ce que lesdites électrodes sont en contact avec ladite feuille de matériau polymère piézoélectrique (6).5. Transducer according to any one of claims 1 to 4, characterized in that said electrodes are in contact with said sheet of piezoelectric polymer material (6). 6. Transducteur selon l'une quelconque des revendications 1 à 5, caractérisé en ce que l'impédance acoustique dudit substrat (3, 20) est proche de l'impédance acoustique de ladite feuille de matériau polymère piézoélectrique (6).6. Transducer according to any one of claims 1 to 5, characterized in that the acoustic impedance of said substrate (3, 20) is close to the acoustic impedance of said sheet of piezoelectric polymer material (6). 7. Transducteur selon l'une quelconque des revendications 1 à 6, caractérisé en ce que ladite face rayonnante est plane.7. A transducer according to any one of claims 1 to 6, characterized in that said radiating face is planar. 8. Transducteur selon l'une quelconque des revendications 1 à 6, caractérisé en ce que ladite face rayonnante comporte au moins une section incurvée.8. Transducer according to any one of claims 1 to 6, characterized in that said radiating face comprises at least one curved section. 9. Transducteur selon l'une quelconque des revendications 1 à 8, caractérisé en ce que ladite feuille de matériau polymère piézoélectrique (6) recouvre une partie centrale dudit substrat (3) surplombant un évidement (2) dudit support (1) ; la partie non recouverte dudit substrat (3) étant fixée audit support (1).9. A transducer according to any one of claims 1 to 8, characterized in that said sheet of piezoelectric polymer material (6) covers a central part of said substrate (3) overhanging a recess (2) of said support (1); the uncovered part of said substrate (3) being fixed to said support (1). 10. Transducteur selon la revendication 9, caractérisé en ce que lesdites électrodes (4, 5, 7, 8) comportent des prolongements dans la partie dudit substrat (3) non recouverte par ladite feuille de matériau polymère piézoélectrique (6).10. A transducer according to claim 9, characterized in that said electrodes (4, 5, 7, 8) have extensions in the part of said substrate (3) not covered by said sheet of piezoelectric polymer material (6). 11. Transducteur selon l'une quelconque des revendications 1 à 10, caractérisé en ce qu'il comporte un élément quart d'onde adaptateur d'impédance (19).11. Transducer according to any one of claims 1 to 10, characterized in that it comprises a quarter wave element impedance adapter (19). 12. Transducteur selon la revendication 11, caractérisé en ce que ledit élément (19) est une feuille de polystyrène ; ledit matériau polymère piézoélectrique (6) étant du polyfluorure de vinylidène.12. A transducer according to claim 11, characterized in that said element (19) is a sheet of polystyrene; said piezoelectric polymer material (6) being polyvinylidene fluoride. 13. Transducteur selon l'une quelconque des revendications 1 à 12, caractérisé en ce que ledit substrat (3, 20) est fait de polyéthylène téréphtalate.13. Transducer according to any one of claims 1 to 12, characterized in that said substrate (3, 20) is made of polyethylene terephthalate.
EP83401485A 1982-07-30 1983-07-19 Half wave transducer using an active piezo-electric polymer element Withdrawn EP0100711A3 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8213357 1982-07-30
FR8213357A FR2531298B1 (en) 1982-07-30 1982-07-30 HALF-WAVE TYPE TRANSDUCER WITH PIEZOELECTRIC POLYMER ELEMENT

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EP0100711A2 true EP0100711A2 (en) 1984-02-15
EP0100711A3 EP0100711A3 (en) 1984-11-14

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EP (1) EP0100711A3 (en)
FR (1) FR2531298B1 (en)

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Also Published As

Publication number Publication date
US4473769A (en) 1984-09-25
FR2531298B1 (en) 1986-06-27
FR2531298A1 (en) 1984-02-03
EP0100711A3 (en) 1984-11-14

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