(19)
(11) EP 0 057 506 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Mention of the grant of the patent:
02.01.1986 Bulletin 1986/01

(21) Application number: 82300147.4

(22) Date of filing: 12.01.1982
(51) International Patent Classification (IPC)4B06B 3/00, G10K 11/36, G10K 15/00

(54)

Ultrasonic transducers

Ultraschallwandler

Transducteurs ultrasonores


(84) Designated Contracting States:
DE FR IT

(30) Priority: 27.01.1981 GB 8102354

(43) Date of publication of application:
11.08.1982 Bulletin 1982/32

(71) Applicant: UNITED KINGDOM ATOMIC ENERGY AUTHORITY
London SW1Y 4QP (GB)

(72) Inventors:
  • Gillespie, Arthur Blackley
    Abingdon Oxfordshire (GB)
  • Watkins, Roger David
    Wantage Oxfordshire (GB)
  • Deighton, Michael Oliver
    Goring Heath Oxfordshire (GB)
  • Pike, Roger Barrie
    Newbury Berkshire (GB)
  • Scott-Kestin, Colin Basil
    Reading Berkshire (GB)

(74) Representative: Wood, Paul Austin 
Patents Department, AEA Technology plc, 329 Harwell
Didcot, Oxfordshire OX11 0RA
Didcot, Oxfordshire OX11 0RA (GB)


(56) References cited: : 
   
       
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] The present invention relates to ultrasonic transducers for producing or receiving compression waves in fluids.

    [0002] If one face of a strip or plate carrying a surface acoustic wave is immersed in a fluid, then over a distance of several wavelengths of the surface acoustic wave (10-15 if the strip is made of stainless steel) the surface acoustic wave in the strip is progressively converted into a compression wave in the fluid which travels at an angle 8 to the normal to the strip given by the relation



    [0003] The reverse phenomenon also occurs. That is, if a compression wave in a fluid impinges at the appropriate angle on the surface of a strip or plate immersed in the fluid, it will be mode converted into a surface acoustic wave in the strip.

    [0004] The term surface acoustic wave describes an acoustic wave which involves the displacement of the surface region of a body in which the wave is travelling over a depth of the same order of magnitude as the wavelength of the wave. Thus forthe purposes of this specification, Lamb waves are to be considered as surface acoustic waves in which the wavelength of the waves is comparable with the thickness of the body in which they are travelling.

    [0005] According to the present invention there is provided an ultrasonic transducer for generating or receiving compression waves in a fluid, comprising an elongated metal body which terminates in an active surface, means for exciting or responding to Lamb waves and other surface acoustic waves in the elongated metal body, characterised in that there is provided means for acoustically isolating all but the active surface of the body from a fluid in which the compression waves are to be generated or from which they are to be received.

    [0006] According to the invention in one aspect, the elongated body is disposed within an enclosed chamber at least a portion of one wall of which is constituted by the active surface of the body and said means for acoustically isolating all but the active surface of the body from a fluid in which the compression waves are to be generated, or from which they are to be received, is constituted by means for preventing the passage of surface acoustic waves along the surfaces of the chamber other than the active surface.

    [0007] According to the invention in another aspect, the elongated metal body is a metal strip and the means for acoustically isolating all but the active surface of the body from a fluid in which the compression waves are to be generated or from which they are to be received comprises a sleeve surrounding the metal strip and arranged to leave a portion of the metal strip exposed to form the active surface, the sleeve being attached to the metal strip in a liquid-tight fashion so as to prevent the access of fluid to the inside of the sleeve and means for preventing physical and acoustic contact between the inactive portion of the metal strip and the sleeve.

    [0008] The invention will now be described, by way of example, with reference to the accompanying drawings in which:

    Figure 1 is a diagrammatic representation of a transducer embodying the invention.

    Figure 2 shows two views of another embodiment of the invention.



    [0009] Referring to Figure 1 of the drawings, a transducer 1 for the generation or reception of compression waves in a liquid 2 in which the transducer 1 is immersed consists of a stainless steel box 3 which is closed by means of top and bottom plates which are not apparent in the figure. The major part 4' of one wall 4, of the box 3 is constituted by one limb 5 of a u-shaped stainless steel strip 6. Attached to the free end 7 of the strip 6 is a piezo electric or electromagnetic acoustic generator 8 of surface acoustic waves in the strip 6 in response to electrical signals applied via leads 9. Piezo electric generation would normally be used whereever possible, but electromagnetic/acoustic generation has distinct advantages if the transducer is to be located in a hostile liquid, e.g. radioactive or at a high temperature. As is usual in the art, the generator 8 also will respond to surface acoustic waves in the strip 6 to generate electrical signals, thus enabling the transducer 1 to be used in either generating or receiving modes. The top and bottom plates of the box 3 and the leads 9 have seals associated with them so that no liquid can penetrate into the inside of the box 3. The surfaces of the box 3, with the exception of the part 4' of the wall 4 are treated so as to render them incapable of transmitting coherently surface acoustic waves. A suitable way of doing this is by roughening or breaking up the smooth surface. Surface acoustic waves produced by the generator 8 and travelling in the metal strip 6 will only appear at the outer surface 4" of the part 4' of the wall 4' of the box 3, which therefore forms an active surface. As has been explained, such surface acoustic waves will be mode converted into a beam 10 of compression waves in the liquid 2 travelling at an angle cr to the normal to the active surface 4". Conversely, compression waves in the liquid 2 which impinge on the active surface 4" at the same angle will be converted into surface acoustic waves which will travel along the strip 6 to the generator 8, there to be converted into electrical signals.

    [0010] Figure 2 shows an alternative form of transducer in which the surface acoustic wave generator/receiver is positioned outside the liquid in which compression waves are to be generated. Referring to Figure 2, a piezoelectric crystal 21 is arranged to generate surface acoustic waves in a stainless steel strip 22. One way of doing this, shown in Figure 2 is to use a comb type coupler 27 between the crystal and the metal strip. The strip 22 is surrounded by a sleeve 23 which extends to the bottom of the strip 22 on one side, but terminates somewhat short of the bottom on the other side so as to leave a portion of the strip 22 exposed to form an active surface 24. The sleeve 23 is welded to the strip 22 around the periphery of the active surface 24 so as to isolate the remainder of the strip 22 from a liquid 25 in which a compression wave is to be generated. The strip 22 is maintained in a central position in the sleeve 23 by means of a support 26 which makes infrequent contact only with the acoustically quiescent edges of the strip 22. This could be in the form of a specially shaped coil spring, 26, as shown in Figure 2. As in the previous embodiment surface acoustic waves travelling down the strip 22 are mode converted at the acoustic surface 24 into a beam of compression waves 28 in the liquid 25, and vice versa.


    Claims

    1. An ultrasonic transducer -for generating or receiving compression waves in a fluid, comprising an elongated metal body which terminates in an active surface, means for exciting or responding to Lamb waves and other surface acoustic waves in the elongated metal body, characterised in that there is provided means (23, 26, 1) for acoustically isolating all but the active surface (4", 24) of the body (6, 22) from a fluid in which the compression waves are to be generated or from which they are to be received.
     
    2. An ultrasonic transducer according to Claim 1, wherein said elongated body is disposed within an enclosed chamber (1) at least a portion of one wall (4) of which is constituted by the active surface of the body, and wherein said means for acoustically isolating all but the active surface (4") of the body from a fluid in which the compression waves are to be generated, or from which they are to be received, is constituted by means for preventing the passage of surface acoustic waves along the surfaces of the chamber (1) other than the active surface (4").
     
    3. An ultrasonic transducer according to Claim 1, wherein the elongated metal body is a metal strip (22) and the means for acoustically isolating all but the active surface (24) of the body from a fluid in which the compression waves are to be generated or from which they are to be received comprises a sleeve (23) surrounding the metal strip (22) and arranged to leave a portion of the metal strip (22) exposed to form the active surface (24), the sleeve (23) being attached to the metal strip (22) in a liquid-tight fashion so as to prevent the access of fluid to the inside of the sleeve (23) and means (26) for preventing physical and acoustic contact between the inactive portion of the metal strip (22) and the sleeve (23).
     
    4. An ultrasonic transducer according to any of Claims 1 to 3, wherein the means for generating and responding to the said surface acoustic waves comprises a piezo-electric device (8, 21, 27) so shaped and positioned on the elongated metal body (6, 22) as to generate the said surface acoustic waves in the elongated metal body, (6, 22) in response to an exciting stimulus.
     
    5. An ultrasonic transducer according to Claim 4, wherein the piezoelectric device comprises a lamina (21) of piezoelectric material and a coupler (27), the coupler (27) having a plane surface to which the piezoelectric lamina (21) is bonded and an opposite surface having a plurality of regularly spaced slots therein to provide a plurality of regularly spaced contacting surfaces.
     
    6. An ultrasonic transducer according to any of Claims 1 to 3, wherein the means for generating and responding to the said surface acoustic waves in the elongated metal body utilises electromagnetic forces to generate the said surface acoustic waves.
     


    Ansprüche

    1. Ultraschallwandler zum Erzeugen oder zum Empfangen von Druckwellen in einer Flüssigkeit, mit einem länglichen Metallteil, welches in einer aktiven Fläche endet, mit einer Einrichtung zum Anregen oder zum Ansprechen auf Lamb-Wellen und andere akustiche Oberflächenwellen in dem länglichen Metallteil, dadurch gekennzeichnet, daß Mittel (23, 26, 1) zur akustischen Isolation aller Flächenabschnitte ausgenommen der aktiven Fläche (4", 24) des Metallteiles. (6, 22) gegenüber einer Flüssigkeit, in der Druckwellen erzeugt werden sollen oder von welcher Druckwellen empfangen werden sollen, vorgesehen sind.
     
    2. Ultraschallwandler nach Anspruch 1, dadurch gekennzeichnet, daß das längliche Teil in einer umschlossenen Kammer (1) angeordnet ist, von der wenigstens ein Teil einer Wand (4) von der aktiven Fläche des länglichen Teiles gebildet ist, und daß die Mittel für die akustische Isolation aller Flächenabschnitte, mit Ausnahme der aktiven Fläche (4") des länglichen Teiles gegenüber einer Flüssigkeit, in welcher Druckwellen erzeugt werden sollen oder von welcher Druckwellen empfangen werden sollen, derart ausgebildet sind, daß ein Hindurchtreten akustischer Oberflächenwellen entlang der Flächen der Kammern (1), ausgenommen der aktiven Fläche (4") verhindert wird.
     
    3. Ultraschallwandler nach Anspruch 1, dadurch gekennzeichnet, daß das längliche Metallteil aus einem Metallstreifen (22) besteht, und daß die Mittel für die akustische Isolation der Flächen des Teiles, ausgenommen der aktiven Fläche (24) gegenüber einer Flüssigkeit, in welcher Druckwellen erzeugt werden sollen oder von welcher Druckwellen empfangen werden sollen, aus einer Hülse (23) bestehen, welche den Metallstreifen (22) umgibt und so angeordnet ist, daß ein Abschnitt des Metallstreifens (22) zur Bildung der aktiven Fläche (24) freiliegt bzw. freigelassen ist, daß die Hülse (23) flüssigkeitsdicht an dem Metallstreifen (22) befestigt ist, um den Zutritt eines Mediums zur Innenseite der Hülse (23) zu verhindern, und daß Mittel (26) vorgesehen sind, um einen physikalischen und akustischen Kontakt zwischen dem nicht aktiven Abschnitt des Metallstreifens (22) und der Hülse (23) zu verhindern.
     
    4. Ultraschallwandler nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß die Einrichtung zum Erzeugen akustischer Oberflächenwellen oder zum Ansprechen auf akustische Oberflächenwellen eine piezoelektrische Vorrichtung (8, 21, 27) umfaßt, die so gestaltet und auf dem länglichen Metallteil (6, 22) angeordnet ist, daß die akustischen Oberflächenwellen in dem länglichen Metallteil (6, 22) abhängig von einer Anregung erzeugt werden.
     
    5. Ultraschallwandler nach Anspruch 4, dadurch gekennzeichnet, daß die piezoelektrische Vorrichtung ein Laminat (21) aus einem piezoelektrischen Material und einen Koppler (27) umfaßt, daß der Koppler (27) eine ebene Oberfläche aufweist, an welcher das piezoelektrische Laminat (21) befestigt bzw. gebunden ist, und eine gegenüberliegende Fläche aufweist, die mehrer in regulärem Abstand angeordnete Schlizte enthält, um dadurch mehrere Berührungsflächen mit regulärem Abstand vorzusehen.
     
    6. Ultraschallwandler nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß die Vorrichtung zum Erzeugen akustischer Oberflächenwellen und zum Ansprechen auf akustische Oberflächenwellen in dem länglichen Metallteil elektromagnetische Kräfte verwendet, um die akustischen Oberflächenwellen zu erzeugen.
     


    Revendications

    1. Transducteur ultrasonore destiné à créer ou à recevoir des ondes de compression dans un fluide, comprenant un corps métallique allongé qui aboutit à une surface active, un dispositif d'excitation d'ondes de Lamb ou d'autres ondes acoustiques de surface dans le corps metallique allongé ou sensible à de telles ondes, caractérisé en ce qu'il comporte un dispositif (23, 26, 1) destiné à isoler acoustiquement la totalité du corps (10, 22) sauf sa surface active (4", 24) par rapport à un fluide dans lequel les ondes de compression doivent être créées ou à partir duquel elles doivent être reçues.
     
    2. Transducteur ultrasonore selon la revendication 1, dans lequel le corps allongé est disposé dans une chambre fermée (1) dont une partie ou moins paroid (4) est constitutée par la surface active du corps, et dans lequel le dispositif d'isolement acoustique de la totalité du corps sauf de la surface active (4"), par rapport à un fluide dans lequel les ondes de compression doivent être créées ou à partir duquel elles doivent être reçues, est constitué par un dispositif destiné à empêcher le passage des ondes acoustiques de surface le long des surfaces de la chambre (1) autres que la surface active (4").
     
    3. Transducteur ultrasonore selon la revendication 1, dans lequel le corps métallique allongé est une bande métallique (22) et le dispositif d'isolement acoustique de la totalité du corps sauf de la surface active (24), par rapport à un fluide dans lequel les ondes de compression doivent être créées ou à partir duquel elles doivent être reçues, comporte un manchon (23) entourant la bande métallique (22) et disposé afin qu'il laisse exposée une partie de la bande métallique (22) afin qu'elle forme la surface active (24), le manchon (23) étant fixé à la bande métallique (22) d'une manière étanche au liquide afin que le liquide n'ait pas accès à l'intérieur du manchon (23), et un dispositif (26) destiné à empêcher le contact physique et acoustique entre la partie inactive de la bande métallique (22) et le manchon (23).
     
    4. Transducteur ultrasonore selon l'une quelconque des revendications 1 à 3, dans lequel le dispositif générateur des ondes acoustiques (8, 21, 27) dont la configuration et la position sur le corps métallique allongé (6, 22) sont telles que les. ondes acoustiques de surface sont créées dans le corps métallique allongé (6, 22) à la suite d'un stimulus excitateur.
     
    5. Transducteur ultrasonore selon la revendication 4, dans lequel le dispositif piézoélectrique comporte une couche (21) d'un matériau piézoélectrique et un coupleur (27), ce dernier ayant une surface plane à laquelle la couche piézoélectrique (21) est collée et une surface opposée ayant plusieurs fentes régulièrement espacées à l'intérieur, destinées à former plusieurs surfaces de contact qui sont régulièrement espacées.
     
    6. Transducteur ultrasonore selon l'une quelconque des revendications 1 à 3, dans lequel le dispositif générateur des ondes acoustiques de surface et sensible à ces ondes, dans le corps métallique allongé, utilise des forces électromagnétiques pour la création desdites ondes acoustiques de surface.
     




    Drawing