EP1432530B1 - Device and method for producing high-pressure ultrasonic pulses - Google Patents

Device and method for producing high-pressure ultrasonic pulses Download PDF

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Publication number
EP1432530B1
EP1432530B1 EP02793156A EP02793156A EP1432530B1 EP 1432530 B1 EP1432530 B1 EP 1432530B1 EP 02793156 A EP02793156 A EP 02793156A EP 02793156 A EP02793156 A EP 02793156A EP 1432530 B1 EP1432530 B1 EP 1432530B1
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Prior art keywords
electric field
application
transducer
polarisation
sub
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German (de)
French (fr)
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EP1432530A1 (en
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Dominique Cathignol
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Institut National de la Sante et de la Recherche Medicale INSERM
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Institut National de la Sante et de la Recherche Medicale INSERM
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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
    • B06B1/0207—Driving circuits
    • B06B1/0215—Driving circuits for generating pulses, e.g. bursts of oscillations, envelopes

Definitions

  • the present invention relates to the technical field of generation ultrasonic pulses of very high intensity, that is to say of the order of several hundreds of bars, even thousands.
  • the present invention relates to applications particularly in the field of non-destructive testing of a material or structure, or in the medical field (Lithotripsy, tissue destruction by cavitation etc).
  • Ultrasonic pulses are produced in a coupling medium, using of a source having a piezoelectric transducer which, when a voltage is applied to it, produces an acoustic wave which is usually focused to achieve high pressures.
  • a source having a piezoelectric transducer which, when a voltage is applied to it, produces an acoustic wave which is usually focused to achieve high pressures.
  • antenna gain the relation between the pressure at the focus and the pressure at the surface of the transducer.
  • Such an antenna gain is a function of the frequency transmitted, as well as the opening, that is to say the ratio between the focal length and the diameter of the transducer.
  • the generation of a pressure wave of 1000 bars in the focus of a lithotripter can be obtained with a cup-shaped source, whose diameter is approximately 45 cm and whose pressure on the surface is about 10 bars, with a frequency of 400 kHz.
  • the device for producing sound pulses described by this patent can not be used in practice in an application including lithotripsy.
  • the waveform produced by such a device does not respect the constraints associated with an acoustic shock wave.
  • the prestress applied to the transducer leads to the generation of a relaxation wave of substantially value equal to that of the compression wave generated subsequently. This wave of relaxation induces cavitation, which impairs the good propagation of the compression wave following.
  • the prestress applied to the transducer inevitably leads to his depolarization.
  • the object of the invention is therefore to remedy the disadvantages of the state of the technique by proposing a device adapted to produce pulses high-pressure ultrasound, without creating a prior relaxation wave and designed to avoid depolarizing the piezoelectric transducer while being realized so simple.
  • the means ensure the application of a voltage progressive with a rise time to create an opposite electric field in the sense of polarization, during a period of application less than that leading to the depolarization of the piezoelectric ultrasonic transducer.
  • Another object of the invention is to propose a production device ultrasound pulses of high pressure adapted to prevent depolarization of the transducer which, in particular, has a high amplitude polarization likely to gradually lead to depolarization.
  • the device for generating pulses ultrasound system comprises means for applying a voltage ensuring the application of a transient electric field during a application time greater than or equal to the duration of application of the electric field of opposite to the direction of polarization to allow the possible repolarization of the ultrasonic transducer.
  • Figs. 1 to 3 are various schematic views of an ultrasonic pulse generating device according to the invention, according to different operating positions.
  • Fig. 4 is a timing diagram for illustrating the operating principle of the device according to the invention.
  • the device for producing high pressure ultrasonic pulses comprises an ultrasonic transducer 2 , of piezoelectric type, forming a source of production of an acoustic wave in a coupling medium.
  • This transducer 2 comprises electrodes 3 , parallel to each other and connected to means 4 for applying a voltage.
  • the transducer 2 is not described more precisely because its constitution is well known to those skilled in the art.
  • the ultrasonic transducer 2 may comprise, as active element for generating an acoustic wave, any type of piezoelectric material, such as piezo-ceramic, piezo-composite, piezoelectric polymer.
  • the transducer 2 has a polarization whose direction is represented by the arrow f 1 , in a direction which is perpendicular to the electrodes 3 .
  • the transducer 2 thus operates in compression / extension mode, insofar as the polarization direction, peculiar to the piezoelectric material, is parallel to the electric field created by the electrodes 3 when an electrical voltage is applied to its terminals. .
  • the deformation of the piezoelectric material of the transducer is essentially in a direction parallel to the electric field.
  • the means 4 ensure the application of an electrical prestress to the transducer 2, prior to the production of an ultrasonic wave of high pressure.
  • the means 4 are controlled to apply a progressive electrical voltage to the electrodes 3 of the transducer 2, so as to create, in the piezoelectric material, an electric field represented by an arrow f 2 , in a direction opposite to the direction of polarization f 1 , in order to gradually compress the transducer 2.
  • the progressive electrical voltage applied to the electrodes 3 is such that the transducer 2 is subjected to an electric field of direction f 2 opposite to the polarization, so that the transducer 2 compresses gradually.
  • the transducer 2 is compressed gradually because it is recalled that the pressure generated is proportional to the rate of change (derivative) of the voltage.
  • the control voltage V 2 of duration T leads to the application on the electrodes 3 of the transducer, of a progressive electrical voltage with a rise time t 2m , represented by the corresponding part of the voltage V 4 .
  • the means 4 ensure the application of an electric voltage V 3 for creating, in the piezoelectric material, a transient electric field in the same direction as that of the polarization.
  • V 3 an electric voltage
  • the transducer 2 is subjected to an electric field, represented by the arrow f 3 , in the same direction as that f 1 of polarization.
  • the transducer 2 undergoes, from the previous state, an extension, so that it emits a compression wave 5 into the coupling medium.
  • the object of the invention is a simple method for ensuring the emission of an ultrasonic wave 5 by progressively compressing the transducer 2 by applying to it, via a voltage progressive electric, an electric field of direction opposite to the direction of polarization of the transducer, then an electric field of the same direction as that of polarization which leads to its extension.
  • the transducer 2 was initially compressed before being elongated, it can be considered that the transducer 2 is little removed from its initial state, as illustrated in FIG. 1.
  • the transducer 2 undergoes an elongation sufficiently weak not to break.
  • progressively pre-stressing the transducer 2 does not lead to the appearance of an expansion wave that can hinder the propagation of the compression wave.
  • the means 4 ensure the application of an electrical voltage allowing the application of an electric field of direction f 2 opposite to the direction of polarization f 1 during a duration of application T less than that leading to the depolarization of the piezoelectric transducer 2 ( FIG 4 ).
  • the duration of application T of this progressive electrical voltage ensuring the application of an electric field of direction opposite to the direction of polarization is greater than 10 ⁇ s and is preferably of the order of 100 ⁇ s.
  • the application of a progressive voltage for a limited time makes it possible to preload the transducer 2 progressively without depolarizing it.
  • the means 4 ensure the application of an electrical voltage V 3 to create the transient electric field of the same direction f 3 as that f 1 of the polarization, during a time of application t 3 between 1 ⁇ s and 1 s and, preferably, of the order of 100 ms.
  • the application time t 3 of the transient electric field is greater than or equal to the duration of application T of the electric field of opposite direction f 2 in polarization direction f 1 to allow the repolarization of the ultrasonic transducer piezoelectric 2 , in the event that a minimal depolarization would have appeared, especially in the particular case of polarization of the transducer 2 with a high amplitude.
  • the voltage V 3 generating the compression wave gradually returns to its initial value (0 volts) to allow the repolarization of the transducer.
  • the means 4 ensure the application of an electrical voltage V 3 ensuring the application of a transient electric field of the same direction f 3 as that f 1 of the polarization during a rise time t 3m between 0.1 and 20 ⁇ s and preferably between 1 and 10 ⁇ s in the case of lithotripsy.
  • the third chronogram of fig. 4 shows the shape of the electrical voltage V 4 across the transducer 2.
  • the progressive electrical voltage ensuring the application of an electric field of direction f 2 opposite to the direction of polarization f 1 , has a rise time t 2m greater than the rise time t 3m of the transient electric field, so as to minimize the influence of a parasitic wave, namely relaxation.
  • this rise time t 2m is greater than at least ten times the rise time t 3m of the transient electric field.
  • the object of the invention thus makes it possible to have a production device an ultrasonic wave of high pressure.
  • a maximum pressure 35 bars (before deterioration) for a transducer not implementing the object of the invention.
  • the application means 4 of the electrical voltages across the electrodes can be made in any suitable manner by one or two generators for example.
  • the transducer may receive any shape, such as a cup-shaped embodiment.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Transducers For Ultrasonic Waves (AREA)
  • Apparatuses For Generation Of Mechanical Vibrations (AREA)
  • Surgical Instruments (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
  • Electrophonic Musical Instruments (AREA)
  • Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
  • Ultra Sonic Daignosis Equipment (AREA)

Abstract

A device for producing high pressure ultrasound pulses. The device includes an ultrasound source having a piezoelectric transducer provided with electrodes and presenting polarization in a given direction (f<SUB>1</SUB>). An electrical voltage is applied to the electrodes to emit an ultrasound wave and to apply an electric field in a direction (f<SUB>2</SUB>) opposite to the polarization direction (f<SUB>1</SUB>) in order to compress the ultrasound transducer. A transient electric field having the same direction (f<SUB>3</SUB>) as the polarization direction (f<SUB>1</SUB>) is then applied so as to cause a compression ultrasound wave to be emitted in the coupling medium.

Description

La présente invention concerne le domaine technique de la génération d'impulsions ultrasonores de très forte intensité, c'est-à-dire de l'ordre de plusieurs centaines de bars, voire du millier.The present invention relates to the technical field of generation ultrasonic pulses of very high intensity, that is to say of the order of several hundreds of bars, even thousands.

La présente invention concerne des applications notamment dans le domaine du contrôle non destructif d'un matériau ou d'une structure, ou dans le domaine médical (lithotritie, destruction tissulaire par cavitation .....).The present invention relates to applications particularly in the field of non-destructive testing of a material or structure, or in the medical field (Lithotripsy, tissue destruction by cavitation .....).

Les impulsions ultrasonores sont produites dans un milieu de couplage, à l'aide d'une source comportant un transducteur de type piézo-électrique qui, lorsqu'une tension électrique lui est appliquée, produit une onde acoustique qui est généralement focalisée en vue d'atteindre des pressions élevées. A cet égard, il est à noter que le rapport qui existe entre la pression au foyer et la pression à la surface du transducteur est appelé gain d'antenne. Un tel gain d'antenne est fonction de la fréquence émise, ainsi que de l'ouverture, c'est-à-dire du rapport entre la distance focale et le diamètre du transducteur. A titre illustratif, la génération d'une onde de pression de 1 000 bars au foyer d'un lithotriteur peut être obtenue avec une source en forme de coupelle, dont le diamètre est de 45 cm approximativement et dont la pression à la surface est de 10 bars environ, avec une fréquence de 400 kHz.Ultrasonic pulses are produced in a coupling medium, using of a source having a piezoelectric transducer which, when a voltage is applied to it, produces an acoustic wave which is usually focused to achieve high pressures. In this respect, it should be noted that the relation between the pressure at the focus and the pressure at the surface of the transducer is called antenna gain. Such an antenna gain is a function of the frequency transmitted, as well as the opening, that is to say the ratio between the focal length and the diameter of the transducer. As an illustration, the generation of a pressure wave of 1000 bars in the focus of a lithotripter can be obtained with a cup-shaped source, whose diameter is approximately 45 cm and whose pressure on the surface is about 10 bars, with a frequency of 400 kHz.

Il doit donc être constaté qu'une telle source de production d'impulsions ultrasonores présente un encombrement important ne permettant pas la réalisation de dispositifs portables ou semi-portables. La réduction de la taille d'une telle source passe par l'augmentation de la pression surfacique au niveau de la coupelle d'émission.It must therefore be noted that such a source of pulse generation ultrasound has a large footprint that does not allow the realization of portable or semi-portable devices. Reducing the size of such a source goes through the increase of the surface pressure at the level of the cup resignation.

Pour tenter d'atteindre cet objectif, l'art antérieur a proposé d'utiliser des matériaux de types composites, appelés piézo-composites, permettant d'augmenter la pression surfacique par un facteur de 1,5 à 2 environ, comparativement aux matériaux classiques piézo-céramiques. En effet, ce type de matériau, vibrant essentiellement en épaisseur, génère des modes latéraux dont l'amplitude est plus faible que dans le cas des matériaux piézo-céramiques classiques. Ce gain, quoique intéressant, s'avère encore insuffisant. In an attempt to achieve this objective, the prior art has proposed using Composite materials, called piezo-composites, to increase the surface pressure by a factor of about 1.5 to 2, compared with classical piezo-ceramic materials. Indeed, this type of material, vibrating essentially in thickness, generates lateral modes whose amplitude is more weak as in the case of conventional piezo-ceramic materials. This gain, though interesting, is still insufficient.

Dans la thèse de Doctorat présentée par Luc CHOFFLET à l'Université Paris VIII sur "L'étude de l'optimisation des transducteurs ultrasonores et des structures multi-piézo-électriques empilées", il a été montré qu'il était possible d'augmenter la pression surfacique en assemblant deux transducteurs sous la forme d'un sandwich. En effet, du point de vue théorique, le gain est proportionnel au nombre de couches de l'empilement. Cependant, des études pratiques ont montré que le gain est en réalité plus faible, du fait que le transducteur frontal reçoit toute la contrainte entraínant la rupture de l'élément situé le plus en avant. Par ailleurs, si la réalisation d'un transducteur de type à empilement est déjà complexe pour un transducteur plan, elle devient extrêmement délicate lorsqu'il s'agit de réaliser une coupelle mettant en oeuvre ce principe.In the doctoral thesis presented by Luc CHOFFLET at the University Paris VIII on "The study of the optimization of ultrasonic transducers and stacked multi-piezoelectric structures ", it has been shown that it is possible to increase the surface pressure by assembling two transducers in the form a sandwich. Indeed, from the theoretical point of view, the gain is proportional to the number of layers of the stack. However, practical studies have shown that the gain is actually lower, because the front-end transducer receives the entire constraint causing the rupture of the most forward element. Moreover, if making a stack-type transducer is already complex for a plane transducer, it becomes extremely delicate when it comes to achieving a cup implementing this principle.

Dans l'état de la technique, il est aussi connu des transducteurs de type TONPILZ (champignon acoustique) conçus principalement pour générer une onde monochromatique, utilisable notamment pour les sonars de pêche ou de l'armée. Les brevets FR 2 640 455 et FR 2 728 755 décrivent diverses variantes de réalisation d'une contrainte mécanique effectuée sur le matériau piézo-électrique, afin de générer des pressions élevées.In the state of the art, it is also known of type transducers TONPILZ (acoustic mushroom) designed mainly to generate a wave monochromatic, usable especially for fishing sonar or army. The patents FR 2 640 455 and FR 2 728 755 describe various variant embodiments. mechanical stress on the piezoelectric material, in order to generate high pressures.

Il doit être constaté que le serrage du matériau piézo-électrique du transducteur diminue de façon drastique la fréquence de résonance de l'ensemble. Ainsi, un tel transducteur fonctionne uniquement à une fréquence de résonance de quelques dizaines de kHz au maximum, de sorte que leur application se trouve limitée aux sonars. Par ailleurs, dans la mesure où le transducteur est formé d'un empilement de couches, une telle source permet de transmettre uniquement la fréquence pour laquelle l'ensemble des couches rentre en résonance, ce qui ne permet pas de transmettre une impulsion de pression présentant un large spectre de fréquence et donc une impulsion courte. De plus, la réalisation d'un transducteur mettant en oeuvre un empilement de couches n'est pas simple à réaliser.It must be noted that the tightening of the piezoelectric material of the transducer drastically decreases the resonant frequency of the set. So, such a transducer works only at a resonant frequency of a few tens of kHz maximum, so that their application is limited to sonars. Moreover, insofar as the transducer is formed of a stack of layers, such a source can transmit only the frequency for which all the layers come into resonance, which makes it impossible to transmit a pressure pulse having a broad frequency spectrum and so a short pulse. Moreover, the realization of a transducer a stack of layers is not easy to achieve.

Dans l'état de la technique, il est connu également par le brevet US 5 549 110 un dispositif de production d'impulsions sonores comportant un transducteur de type piézo-céramique muni d'électrodes raccordées à des moyens d'application d'une tension électrique sur lesdites électrodes. Selon une variante de réalisation, ces moyens d'application d'une tension électrique assurent l'application d'un champ électrique de sens opposé au sens de polarisation du transducteur et ensuite, l'application d'un champ électrique transitoire de même sens que celui de la polarisation afin d'obtenir l'émission d'une onde sonore.In the state of the art, it is also known from US Pat. No. 5,549,110 a device for producing sound pulses comprising a transducer of the type piezo-ceramic having electrodes connected to means for applying a voltage on said electrodes. According to an alternative embodiment, these means for applying an electrical voltage ensure the application of a field opposite direction to the direction of polarization of the transducer and then, the application of a transient electric field with the same meaning as polarization in order to obtain the emission of a sound wave.

La mise en oeuvre d'une précontrainte électrique sur le transducteur piézo-électrique permet d'éviter les problèmes inhérents à l'application d'une précontrainte mécanique. Par ailleurs, dans la mesure où le transducteur est préalablement comprimé avant d'être soumis à une extension pour créer une onde ultrasonore de forte pression, il n'apparaít aucun allongement susceptible de le rompre.The implementation of an electrical prestress on the transducer piezoelectric avoids the problems inherent in the application of a mechanical prestressing. Moreover, since the transducer is previously compressed before being subjected to an extension to create a wave ultrasonic pressure, it appears no elongation likely to to break up.

Toutefois, le dispositif de production d'impulsions sonores décrit par ce brevet ne peut pas être utilisé en pratique dans une application notamment de lithotritie. En effet, la forme d'onde produite par un tel dispositif ne respecte pas les contraintes associées à une onde acoustique de choc. En particulier, la précontrainte appliquée au transducteur conduit à la génération d'une onde de détente de valeur sensiblement égale à celle de l'onde de compression générée par la suite. Cette onde de détente entraíne de la cavitation, ce qui nuit à la bonne propagation de l'onde de compression qui suit. De plus, la précontrainte appliquée au transducteur conduit inévitablement à sa dépolarisation.However, the device for producing sound pulses described by this patent can not be used in practice in an application including lithotripsy. In Indeed, the waveform produced by such a device does not respect the constraints associated with an acoustic shock wave. In particular, the prestress applied to the transducer leads to the generation of a relaxation wave of substantially value equal to that of the compression wave generated subsequently. This wave of relaxation induces cavitation, which impairs the good propagation of the compression wave following. In addition, the prestress applied to the transducer inevitably leads to his depolarization.

L'objet de l'invention vise donc à remédier aux inconvénients de l'état de la technique en proposant un dispositif adapté pour produire des impulsions ultrasonores de forte pression, sans créer une onde de détente préalable et conçu pour éviter de dépolariser le transducteur piézo-électrique tout en étant réalisé de façon simple.The object of the invention is therefore to remedy the disadvantages of the state of the technique by proposing a device adapted to produce pulses high-pressure ultrasound, without creating a prior relaxation wave and designed to avoid depolarizing the piezoelectric transducer while being realized so simple.

Pour atteindre un tel objectif, le dispositif de production d'impulsions ultrasonores de forte pression conforme à l'invention comporte :

  • une source ultrasonore comportant un transducteur de type piézo-électrique muni d'électrodes et présentant un sens de polarisation dans une direction donnée,
  • et des moyens d'application d'une tension électrique sur les électrodes du transducteur ultrasonore, assurant pour obtenir l'émission d'une onde ultrasonore :
    • l'application d'un champ électrique de sens opposé au sens de polarisation, afin de comprimer le transducteur ultrasonore,
    • puis l'application d'un champ électrique transitoire de même sens que celui de la polarisation, de manière à obtenir l'émission d'une onde ultrasonore de compression dans le milieu de couplage.
To achieve such an objective, the device for producing high pressure ultrasonic pulses according to the invention comprises:
  • an ultrasonic source comprising a piezoelectric type transducer provided with electrodes and having a direction of polarization in a given direction,
  • and means for applying an electrical voltage to the electrodes of the ultrasonic transducer, ensuring to obtain the emission of an ultrasonic wave:
    • the application of an electric field of direction opposite to the direction of polarization, in order to compress the ultrasonic transducer,
    • then the application of a transient electric field in the same direction as that of the polarization, so as to obtain the emission of an ultrasonic wave compression in the coupling medium.

Selon l'invention, les moyens assurent l'application d'une tension électrique progressive avec un temps de montée pour créer un champ électrique de sens opposé au sens de polarisation, pendant une durée d'application inférieure à celle conduisant à la dépolarisation du transducteur ultrasonore piézo-électrique.According to the invention, the means ensure the application of a voltage progressive with a rise time to create an opposite electric field in the sense of polarization, during a period of application less than that leading to the depolarization of the piezoelectric ultrasonic transducer.

Un autre objet de l'invention est de proposer un dispositif de production d'impulsions ultrasonores de forte pression adapté pour éviter la dépolarisation du transducteur qui, en particulier, présente une polarisation de forte amplitude susceptible d'entraíner progressivement sa dépolarisation.Another object of the invention is to propose a production device ultrasound pulses of high pressure adapted to prevent depolarization of the transducer which, in particular, has a high amplitude polarization likely to gradually lead to depolarization.

Pour atteindre un tel objectif, le dispositif de production d'impulsions ultrasonores, conforme à l'invention, comporte des moyens d'application d'une tension électrique assurant l'application d'un champ électrique transitoire pendant un temps d'application supérieur ou égal à la durée d'application du champ électrique de sens opposé au sens de polarisation pour permettre la repolarisation éventuelle du transducteur ultrasonore.To achieve such an objective, the device for generating pulses ultrasound system, according to the invention, comprises means for applying a voltage ensuring the application of a transient electric field during a application time greater than or equal to the duration of application of the electric field of opposite to the direction of polarization to allow the possible repolarization of the ultrasonic transducer.

Diverses autres caractéristiques ressortent de la description faite ci-dessous en référence aux dessins annexés qui montrent, à titre d'exemples non limitatifs, des formes de réalisation et de mise en oeuvre de l'objet de l'invention.Various other features are apparent from the description given below in reference to the accompanying drawings which show, by way of non-limiting examples, embodiments and implementation of the subject of the invention.

Les fig. 1 à 3 sont diverses vues schématiques d'un dispositif de production d'impulsions ultrasonores conforme à l'invention, selon différentes positions caractéristiques de fonctionnement. Figs. 1 to 3 are various schematic views of an ultrasonic pulse generating device according to the invention, according to different operating positions.

La fig. 4 est un chronogramme permettant d'illustrer le principe de fonctionnement du dispositif selon l'invention. Fig. 4 is a timing diagram for illustrating the operating principle of the device according to the invention.

Tel que cela apparaít plus précisément à la fig. 1, le dispositif de production d'impulsions ultrasonores de forte pression, représenté sous la référence générale 1, comporte un transducteur ultrasonore 2, de type piézo-électrique, formant une source de production d'une onde acoustique dans un milieu de couplage. Ce transducteur 2 comporte des électrodes 3, parallèles entre elles et reliées à des moyens 4 d'application d'une tension électrique. As it appears more precisely in FIG. 1 , the device for producing high pressure ultrasonic pulses, represented under the general reference 1 , comprises an ultrasonic transducer 2 , of piezoelectric type, forming a source of production of an acoustic wave in a coupling medium. This transducer 2 comprises electrodes 3 , parallel to each other and connected to means 4 for applying a voltage.

Le transducteur 2 n'est pas décrit plus précisément car sa constitution est bien connue de l'homme du métier. De plus, le transducteur ultrasonore 2 peut comporter, en tant qu'élément actif de génération d'une onde acoustique, tout type de matériau piézo-électrique, tel que piézo-céramique, piézo-composite, polymère piézo-électrique.The transducer 2 is not described more precisely because its constitution is well known to those skilled in the art. In addition, the ultrasonic transducer 2 may comprise, as active element for generating an acoustic wave, any type of piezoelectric material, such as piezo-ceramic, piezo-composite, piezoelectric polymer.

D'une manière connue, le transducteur 2 présente une polarisation dont le sens est représenté par la flèche f1 , dans une direction qui est perpendiculaire aux électrodes 3. Le transducteur 2 fonctionne ainsi en mode compression/extension, dans la mesure où la direction de polarisation, propre au matériau piézo-électrique, est parallèle au champ électrique créé par les électrodes 3 lors de l'application d'une tension électrique à ses bornes. La déformation du matériau piézo-électrique du transducteur se fait essentiellement dans une direction parallèle au champ électrique.In known manner, the transducer 2 has a polarization whose direction is represented by the arrow f 1 , in a direction which is perpendicular to the electrodes 3 . The transducer 2 thus operates in compression / extension mode, insofar as the polarization direction, peculiar to the piezoelectric material, is parallel to the electric field created by the electrodes 3 when an electrical voltage is applied to its terminals. . The deformation of the piezoelectric material of the transducer is essentially in a direction parallel to the electric field.

Conformément à l'invention, les moyens 4 assurent l'application d'une précontrainte électrique au transducteur 2, préalablement à la production d'une onde ultrasonore de forte pression. Tel qu'illustré à la fig. 2, les moyens 4 sont commandés pour appliquer une tension électrique progressive sur les électrodes 3 du transducteur 2, de manière à créer, dans le matériau piézo-électrique, un champ électrique représenté par une flèche f2, selon un sens opposé au sens de polarisation f1 , afin de comprimer progressivement le transducteur 2. Ainsi, tel que cela ressort clairement de la fig. 2 en comparaison avec la fig. 1, la tension électrique progressive appliquée sur les électrodes 3, est telle que le transducteur 2 est soumis à un champ électrique de sens f2 opposé à la polarisation, de sorte que le transducteur 2 se comprime progressivement. En effet, le transducteur 2 est comprimé progressivement car il est rappelé que la pression générée est proportionnelle à la vitesse de variation (dérivée) de la tension. Tel que cela ressort de la Fig. 4, la tension de commande V2 de durée T conduit à l'application sur les électrodes 3 du transducteur, d'une tension électrique progressive avec un temps de montée t2m , représentée par la partie correspondante de la tension V4 .According to the invention, the means 4 ensure the application of an electrical prestress to the transducer 2, prior to the production of an ultrasonic wave of high pressure. As shown in fig. 2 , the means 4 are controlled to apply a progressive electrical voltage to the electrodes 3 of the transducer 2, so as to create, in the piezoelectric material, an electric field represented by an arrow f 2 , in a direction opposite to the direction of polarization f 1 , in order to gradually compress the transducer 2. Thus, as is clear from FIG. 2 in comparison with FIG. 1, the progressive electrical voltage applied to the electrodes 3 is such that the transducer 2 is subjected to an electric field of direction f 2 opposite to the polarization, so that the transducer 2 compresses gradually. Indeed, the transducer 2 is compressed gradually because it is recalled that the pressure generated is proportional to the rate of change (derivative) of the voltage. As can be seen from FIG. 4 , the control voltage V 2 of duration T leads to the application on the electrodes 3 of the transducer, of a progressive electrical voltage with a rise time t 2m , represented by the corresponding part of the voltage V 4 .

Ensuite, les moyens 4 assurent l'application d'une tension électrique V3 permettant de créer, dans le matériau piézo-électrique, un champ électrique transitoire de même sens que celui de la polarisation. Ainsi, tel que cela apparaít plus précisément à la fig. 3, le transducteur 2 est soumis à un champ électrique, représenté par la flèche f3 , de même sens que celui f1 de polarisation. Le transducteur 2 subit, à partir de l'état précédent, une extension, de sorte qu'il émet une onde de compression 5 dans le milieu de couplage.Then, the means 4 ensure the application of an electric voltage V 3 for creating, in the piezoelectric material, a transient electric field in the same direction as that of the polarization. Thus, as it appears more precisely in FIG. 3 , the transducer 2 is subjected to an electric field, represented by the arrow f 3 , in the same direction as that f 1 of polarization. The transducer 2 undergoes, from the previous state, an extension, so that it emits a compression wave 5 into the coupling medium.

Tel que cela ressort de la description qui précède, l'objet de l'invention est un procédé simple pour assurer l'émission d'une onde ultrasonore 5 en comprimant progressivement le transducteur 2 en lui appliquant, par l'intermédiaire d'une tension électrique progressive, un champ électrique de sens opposé au sens de polarisation du transducteur, puis un champ électrique de même sens que celui de polarisation qui conduit à son extension. Dans la mesure où le transducteur 2 était initialement comprimé avant d'être allongé, il peut être considéré que le transducteur 2 s'éloigne peu de son état initial, tel qu'il est illustré à la fig. 1. Le transducteur 2 subit un allongement suffisamment faible pour ne pas se rompre. Par ailleurs, le fait de précontraindre progressivement le transducteur 2 ne conduit pas à l'apparition d'une onde de détente susceptible de gêner la propagation de l'onde de compression.As is apparent from the foregoing description, the object of the invention is a simple method for ensuring the emission of an ultrasonic wave 5 by progressively compressing the transducer 2 by applying to it, via a voltage progressive electric, an electric field of direction opposite to the direction of polarization of the transducer, then an electric field of the same direction as that of polarization which leads to its extension. Insofar as the transducer 2 was initially compressed before being elongated, it can be considered that the transducer 2 is little removed from its initial state, as illustrated in FIG. 1. The transducer 2 undergoes an elongation sufficiently weak not to break. Moreover, progressively pre-stressing the transducer 2 does not lead to the appearance of an expansion wave that can hinder the propagation of the compression wave.

Selon une caractéristique de l'invention, les moyens 4 assurent l'application d'une tension électrique permettant l'application d'un champ électrique de sens f2 opposé au sens de polarisation f1 pendant une durée d'application T inférieure à celle conduisant à la dépolarisation du transducteur piézo-électrique 2 (fig. 4). Par exemple, la durée d'application T de cette tension électrique progressive assurant l'application d'un champ électrique de sens opposé au sens de polarisation est supérieure à 10 µs et est, de préférence, de l'ordre de 100 µs. Ainsi, l'application d'une tension progressive pendant un temps limité permet de précontraindre le transducteur 2 progressivement sans le dépolariser.According to one characteristic of the invention, the means 4 ensure the application of an electrical voltage allowing the application of an electric field of direction f 2 opposite to the direction of polarization f 1 during a duration of application T less than that leading to the depolarization of the piezoelectric transducer 2 ( FIG 4 ). For example, the duration of application T of this progressive electrical voltage ensuring the application of an electric field of direction opposite to the direction of polarization is greater than 10 μs and is preferably of the order of 100 μs. Thus, the application of a progressive voltage for a limited time makes it possible to preload the transducer 2 progressively without depolarizing it.

Selon une caractéristique préférée de réalisation, les moyens 4 assurent l'application d'une tension électrique V3 pour créer le champ électrique transitoire de même sens f3 que celui f1 de la polarisation, pendant un temps d'application t3 compris entre 1 µs et 1 s et, de préférence, de l'ordre de 100 ms.According to a preferred embodiment, the means 4 ensure the application of an electrical voltage V 3 to create the transient electric field of the same direction f 3 as that f 1 of the polarization, during a time of application t 3 between 1 μs and 1 s and, preferably, of the order of 100 ms.

Selon une caractéristique préférée de réalisation, le temps d'application t3 du champ électrique transitoire est supérieur ou égal à la durée d'application T du champ électrique de sens opposé f2 au sens f1 de polarisation pour permettre la repolarisation du transducteur ultrasonore piézo-électrique 2, dans le cas éventuel où une dépolarisation minime serait apparue, notamment dans le cas particulier de polarisation du transducteur 2 avec une forte amplitude. Tel que cela apparaít à la Fig. 4, la tension électrique V3 générant l'onde de compression retourne progressivement à sa valeur initiale (0 Volt) afin de permettre la repolarisation du transducteur.According to a preferred characteristic embodiment, the application time t 3 of the transient electric field is greater than or equal to the duration of application T of the electric field of opposite direction f 2 in polarization direction f 1 to allow the repolarization of the ultrasonic transducer piezoelectric 2 , in the event that a minimal depolarization would have appeared, especially in the particular case of polarization of the transducer 2 with a high amplitude. As it appears in FIG. 4, the voltage V 3 generating the compression wave gradually returns to its initial value (0 volts) to allow the repolarization of the transducer.

Selon une autre caractéristique préférée de réalisation, les moyens 4 assurent l'application d'une tension électrique V3 assurant l'application d'un champ électrique transitoire de même sens f3 que celui f1 de la polarisation, pendant un temps de montée t3m compris entre 0,1 et 20 µs et, de préférence, compris entre 1 et 10 µs dans le cas de la lithotritie.According to another preferred embodiment, the means 4 ensure the application of an electrical voltage V 3 ensuring the application of a transient electric field of the same direction f 3 as that f 1 of the polarization during a rise time t 3m between 0.1 and 20 μs and preferably between 1 and 10 μs in the case of lithotripsy.

Le troisième chronogramme de la fig. 4 montre la forme de la tension électrique V4 aux bornes du transducteur 2. Selon une caractéristique préférée de réalisation, la tension électrique progressive assurant l'application d'un champ électrique de sens f2 opposé au sens de polarisation f1 , présente un temps de montée t2m supérieur au temps de montée t3m du champ électrique transitoire, de manière à minimiser l'influence d'une onde parasite, à savoir de détente. Selon une variante préférée de réalisation, ce temps de montée t2m est supérieur à au moins dix fois le temps de montée t3m du champ électrique transitoire.The third chronogram of fig. 4 shows the shape of the electrical voltage V 4 across the transducer 2. According to a preferred embodiment, the progressive electrical voltage ensuring the application of an electric field of direction f 2 opposite to the direction of polarization f 1 , has a rise time t 2m greater than the rise time t 3m of the transient electric field, so as to minimize the influence of a parasitic wave, namely relaxation. According to a preferred embodiment, this rise time t 2m is greater than at least ten times the rise time t 3m of the transient electric field.

L'objet de l'invention permet ainsi de disposer d'un dispositif de production d'une onde ultrasonore de forte pression. Ainsi, il a été obtenu une pression maximale de 35 bars (avant détérioration) pour un transducteur ne mettant pas en oeuvre l'objet de l'invention. Avec un transducteur auquel était appliquée une précontrainte électrique, il a pu être obtenu une pression maximale de 60 bars.The object of the invention thus makes it possible to have a production device an ultrasonic wave of high pressure. Thus, it was obtained a maximum pressure 35 bars (before deterioration) for a transducer not implementing the object of the invention. With a transducer to which preload was applied electric, it could be obtained a maximum pressure of 60 bar.

Bien entendu, les moyens d'application 4 des tensions électriques aux bornes des électrodes peuvent être réalisés de toute manière appropriée par un ou deux générateurs par exemple. De plus, le transducteur peut recevoir une forme quelconque, telle qu'une réalisation en forme de coupelle.Of course, the application means 4 of the electrical voltages across the electrodes can be made in any suitable manner by one or two generators for example. In addition, the transducer may receive any shape, such as a cup-shaped embodiment.

L'invention n'est pas limitée aux exemples décrits et représentés car diverses modifications peuvent y être apportées sans sortir de son cadre.The invention is not limited to the examples described and shown because various changes can be made without departing from its scope.

L'invention est définie par les revendications suivantes.The invention is defined by the following claims.

Claims (7)

  1. Method for producing high pressure ultrasonic pulses comprising:
    an ultrasound source comprising a transducer (2) of piezoelectric type provided with electrodes (3) and having a given direction (f1) of polarisation,
    and means (4) for applying an electric voltage to the electrodes (3) of the ultrasound transducer (2) which, to obtain the emission of an ultrasonic wave, ensure
    the application of an electric field of direction (f2) opposite to the direction (f1) of polarisation, so as to compress the ultrasound transducer (2),
    then the application of a transient electric field of same direction (f3) as that of polarisation (f1) so as to obtain the emission of an ultrasonic compression wave in the coupling medium,
    characterized in that means (4) ensure the application of an electric voltage with a rise time (t2m) to create an electric field of direction (f2) opposite to the direction (f1) of polarisation, during an application time (T) that is shorter than that leading to depolarisation of the piezoelectric ultrasound transducer.
  2. Device for producing high pressure ultrasonic pulses as in claim 1, characterized in that the application time (T) of an electric voltage ensuring the application of an electric field of direction (f2) opposite to the direction (f1) of polarisation is longer than 10 µs and is preferably in the order of 100 µs.
  3. Device for producing high pressure ultrasonic pulses as in claim 1 or 2, characterized in that the means (4) for applying an electric voltage (V3) ensure the application of a transient electric field in the same direction (f3) as that (f1) of polarisation for an application time (t3) of between 1 µs and 1 s and preferably in the order of 100 ms.
  4. Device for producing high pressure ultrasonic pulses as in claims 1 to 3, characterized in that the means (4) for applying an electric voltage (V3) ensure the application of a transient electric field in the same direction (f3) as that (f1) of polarisation for a rise time (t3m) of between 0.1 and 20 µs.
  5. Device for producing high pressure ultrasonic pulses as in claims 1 or 2 and 4 characterized in that the progressive electric voltage ensuring the application of an electric field of direction (f2) opposite to direction (f1) of polarisation has a rise time (t2m) that is greater than the rise time (t3m) of the transient electric field.
  6. Device for producing high pressure ultrasonic pulses as in claim 5, characterized in that the rise time (t2m) is greater than at least ten times the rise time (t3m) of the transient electric field.
  7. Device for producing high pressure ultrasonic pulses. as in any of claims 1 to 6 characterized in that the application time (t3) of the transient electric field is equal to or greater than the application time (T) of the electric field of direction (f2) opposite to the direction (f1) of polarisation, to enable optional repolarisation of the ultrasound transducer (2).
EP02793156A 2001-10-04 2002-10-04 Device and method for producing high-pressure ultrasonic pulses Expired - Lifetime EP1432530B1 (en)

Applications Claiming Priority (3)

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FR0112774 2001-10-04
FR0112774A FR2830468B1 (en) 2001-10-04 2001-10-04 DEVICE AND METHOD FOR PRODUCING HIGH PRESSURE ULTRASONIC PULSES
PCT/FR2002/003390 WO2003028904A1 (en) 2001-10-04 2002-10-04 Device and method for producing high-pressure ultrasonic pulses

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US20040254506A1 (en) 2004-12-16
JP5280761B2 (en) 2013-09-04
DE60203922D1 (en) 2005-06-02
IL161254A0 (en) 2004-09-27
EP1432530A1 (en) 2004-06-30
CN1326634C (en) 2007-07-18
ATE294028T1 (en) 2005-05-15
US7264597B2 (en) 2007-09-04
FR2830468B1 (en) 2004-02-20
JP2005503921A (en) 2005-02-10
IL161254A (en) 2007-12-03
JP2009022012A (en) 2009-01-29
FR2830468A1 (en) 2003-04-11

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