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EP 0 057 506 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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02.01.1986 Bulletin 1986/01 |
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Date of filing: 12.01.1982 |
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Ultrasonic transducers
Ultraschallwandler
Transducteurs ultrasonores
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Designated Contracting States: |
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DE FR IT |
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Priority: |
27.01.1981 GB 8102354
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Date of publication of application: |
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11.08.1982 Bulletin 1982/32 |
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Applicant: UNITED KINGDOM ATOMIC ENERGY AUTHORITY |
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London SW1Y 4QP (GB) |
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Inventors: |
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- 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)
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(74) |
Representative: Wood, Paul Austin |
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Patents Department,
AEA Technology plc,
329 Harwell Didcot, Oxfordshire OX11 0RA Didcot, Oxfordshire OX11 0RA (GB) |
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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).
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[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.
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.
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.
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.

