EP0114764B1 - Vorrichtung zur Reflexion von akustischen Wellen - Google Patents

Vorrichtung zur Reflexion von akustischen Wellen Download PDF

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Publication number
EP0114764B1
EP0114764B1 EP19840400076 EP84400076A EP0114764B1 EP 0114764 B1 EP0114764 B1 EP 0114764B1 EP 19840400076 EP19840400076 EP 19840400076 EP 84400076 A EP84400076 A EP 84400076A EP 0114764 B1 EP0114764 B1 EP 0114764B1
Authority
EP
European Patent Office
Prior art keywords
wall
rigid
rigid wall
volume
closing element
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP19840400076
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English (en)
French (fr)
Other versions
EP0114764A2 (de
EP0114764A3 (en
Inventor
Bernard Fromont
René Reynier
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thales SA
Original Assignee
Thomson CSF SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomson CSF SA filed Critical Thomson CSF SA
Publication of EP0114764A2 publication Critical patent/EP0114764A2/de
Publication of EP0114764A3 publication Critical patent/EP0114764A3/fr
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Publication of EP0114764B1 publication Critical patent/EP0114764B1/de
Expired legal-status Critical Current

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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/18—Methods or devices for transmitting, conducting or directing sound
    • G10K11/20—Reflecting arrangements
    • G10K11/205—Reflecting arrangements for underwater use

Definitions

  • the present invention relates to devices for reflecting acoustic waves propagating in a fluid such as water.
  • the reflection of acoustic waves according to an interface separating two media of impedances Z 1 and Z 2 is linked to a ratio Z 1 / Z 2 different from unity.
  • Z 2 must be very different from Z 1
  • acoustic wave reflectors “hard” reflectors whose acoustic impedance Z 2 is greater than the impedance Z 1 of water and "soft” reflectors whose acoustic impedance Z 2 is less than the impedance Z 1 of water.
  • the invention relates more particularly to devices with an acoustic wave reflector interface of the "soft" type.
  • reflectors are known, the structure of which is made of a flexible and waterproof envelope which contains two rigid plates enclosing an airy structure made of metal wires.
  • These reflectors have the drawback of losing their deformability too quickly when they have to withstand a significant hydrostatic pressure which is encountered at immersion depths of a few tens of meters.
  • the reflective interface risks losing its shape and can change position relative to the transducers mounted nearby, so that the expected phase shifts are modified.
  • wave reflection structures employing a foam reflective cushion which have the same drawbacks.
  • the foam used has a density lower than that of water and consists of gaseous cells delimited by a matrix of viscoelastic material of the elastomer type. This foam withstands hydrostatic pressure well and retains good reflective properties.
  • the main object of the invention is a device for reflecting acoustic waves according to an interface separating a volume of viscoelastic material with gaseous cells from a material permeable to said acoustic waves used to isolate this volume from the external fluid medium of higher density, in which said volume is applied against a rigid wall made of said permeable material; said wall being carried by a rigid support; a flexible closing element cooperating with said rigid wall to ensure the tightness of said device while transmitting to said volume the external hydrostatic pressure, in order to prevent the deformation and the change of position of the interface whose shape is imposed by said wall rigid.
  • FIG 1 we see a device for reflecting acoustic waves where the normal incidence is represented by the arrow X'X.
  • This device which rests on a support 26, _complement for example a volume 20 of foam with gas cells made of a viscoelastic material having a density half less than that of water.
  • the viscoelastic material advantageously consists of polyurethane, synthetic rubber, polyvinyl chloride, or ethylene vinyl acetate (EVA).
  • the reflection device of FIG. 1 comprises, upstream of the reflective interface 24, a rigid wall 21 comprising a flange 28.
  • This wall which follows the shape of an open housing is permeable to acoustic waves while serving as a sealing means vis-à-vis the external fluid.
  • the wall 21 is made of a material transparent to incident acoustic waves such as an organic synthetic material.
  • the open case 21 can for example be made up of an assembly of glass fibers impregnated with polyester resin. After polymerization, a resistant and light shell is obtained. It is also possible to use for the housing 21 a material of acoustic impedance markedly greater than poCo, for example metal, but the thickness must satisfy certain conditions for transmission of the incident acoustic waves.
  • the housing 21 When the housing 21 is metallic, its wall thickness will be between a few tenths of a millimeter and a few millimeters.
  • the housing 21 imposes on the face 24 of the foam 20 a precise shape which must not change under the action of hydrostatic pressure.
  • the external face 29 of the reflection device opposite to the external face 27 of the wall 21 is covered by a flexible envelope 30, for example made of elastomeric material a few millimeters thick. This closing element completes the sealing of the device while effectively transmitting, via the foam 20, the hydrostatic pressure which is thus also applied to the two faces of the wall of the rigid housing 21.
  • the envelope 30 can overflow so as to cover the rim (28) of the housing 21 to which it is fixed by means of an adhesive 23, participating in the sealing of the assembly.
  • the envelope 30 can cover the entire reflective device of the flexible closing element which undergoes all the deformations which result from the crushing of the foam by hydrostatic pressure, but the presence of gaseous cells prevents compaction which would modify undesirably the acoustic impedance used to efficiently reflect the incident acoustic waves.
  • the face 29 of the reflector according to the invention is provided with studs 25, for example made of elastomeric material, situated on the edges. These studs form a spacer and allow good fixing on the support 26. They thus allow the hydrostatic pressure to be exerted on the face 29 of the reflector.
  • FIG. 2 illustrates the behavior of a soft reflector device, the internal environment of which would be enclosed in a completely rigid envelope 101.
  • the deformation under the action of the external hydrostatic pressure of the two rigid elements 27 and 29 gives rise to the deformed parts 270 and 290 shown in dotted lines by exaggerating the deformation.
  • the wall elements 28 can also deform.
  • a hydrophone 100 is shown which receives acoustic waves in particular from the reflector assembly 101.
  • the deformation of the face 270 is the cause of the path difference such that the difference A illustrated in FIG. 2 modifies the phase of the reflected wave.
  • the curvature of the structure changes due to the deformation, which can influence the trajectory of the reflected acoustic waves.
  • the undesirable deformations of the device of FIG. 2 result from the differences in external and internal hydrostatic pressures.
  • Figure 3 shows the device of Figure 1 subjected to external hydrostatic pressure.
  • the hydrostatic pressure symbolized by the arrows 32 is exerted in particular on the faces 27 and 29 of the reflector.
  • the casing 30 fully transmits the pressure to the viscoelastic foam 20, which transmits it entirely to the rigid casing 21.
  • the pressures exerted on its two main faces being the same, the casing does not deform when the hydrostatic pressure varies.
  • the foam 20 of thickness d is crushed.
  • the thickness d 3 is chosen so that is weak compared to ⁇ 1 c 1 , at the lowest frequency that we want to reflect with the reflector.
  • d e is the reduced thickness of the foam 20 at the maximum depth for which the device according to the invention is intended, so that the thickness d must be chosen accordingly.
  • FIG. 4 illustrates an alternative embodiment of the device according to the invention where the rigid wall 21 is a simple plate fixed directly to the structure 26 by means of a support forming a mounting frame 110. Openings 112 are provided in the frame 110 , so that the external hydrostatic pressure can act on the face 29 of the device.
  • the face 29 belongs to a flexible closing element which envelops the foam 20 and which is sealed against the wall 21.
  • a soft reflector device can be provided for example with a sheet of piezoelectric material 31 placed between electrodes to perform the transducer function on transmission or reception. This variant is illustrated in FIG. 5.
  • the reflector devices described above are particularly well suited to the production of passive listening antennas which include one or more hydrophones.
  • the hydrophones are located opposite a reflecting surface composed of a set of devices as described above.
  • the shortest distance separating each hydrophone from the reflecting surface is advantageously equal to ⁇ / 4 where ⁇ is the wavelength corresponding to the central frequency of the hydrophone listening band.
  • FIG. 6 illustrates an example of arrangement of the reflectors 41 and hydrophones 40, in a passive listening antenna using a surface cylindrical reflector.
  • the reflectors 41 have an elementary reflecting surface of square shape and the hydrophones 40 are located directly above the center of symmetry of each elementary surface.
  • the reflectors 41 are held contiguously on a base by means of stirrups 42 held by tie rods 43, for example made of steel.
  • Figure 7 is a sectional view of the device of Figure 6.
  • the base 26 of the antenna being for example cylindrical
  • the reflectors 41 are curved to match the structure and are held contiguously by means of stirrups 42 retained by steel ties 43 on the base 26.
  • Holes 45 allow the water to exert hydrostatic pressure on the faces 29 of the reflector devices according to the invention.
  • FIG. 8 illustrates an example of an arrangement similar to that of FIG. 6, but where the reflectors 41 are triangular. It is obvious that other arrangements of reflectors and hydrophones can be adopted.

Claims (11)

1. Vorrichtung zum Reflektieren akustischer Wellen an einer Grenzschicht (24), die ein Volumen aus viskoelastischem Material (20) mit gasgefüllten Zellen gegen eine starre Wand (21) aus einem für die akustischen Wellen durchlässigen Material abgrenzt, wobei diese Wand der Isolierung des Volumens gegen das äußere Fluidmilieu mit höherer Dichte dient und von einem starren Träger (26) getragen wird, dadurch gekennzeichnet, daß sie außerdem ein nachgiebiges Verschlußelement (30) aufweist, das mit der starren Wand in Hinblick auf die Dichtheit der Vorrichtung zusammenwirkt und zugleich dem Volumen den äußeren hydrostatischen Druck mitteilt, um die Verformung und die Lageveränderung der Grenzschicht (24) zu verhindern, deren Form durch die starre Wand (21) vorgegeben ist.
2. Vorrichtung nach Anspruch 1, dadurch gekennzeichnet, daß die Wand (21) einen hochstehenden Rand (28) besitzt und somit eine offene Dose bildet.
3. Vorrichtung nach einem beliebigen der Ansprüche 1 oder 2, dadurch gekennzeichnet, daß das verformbare viskoelastische Material (20) ein viskoelastischer Schaum aus Kautschuk, Polyvinylchlorid, Polyäthylen oder Äthylen-Vinylacetat (EVA) ist.
4. Vorrichtung nach einem beliebigen der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß das nachgiebige Verschlußelement (30) eine Membran aus einem Elastomermaterial ist.
5. Vorrichtung nach einem beliebigen der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß das Verschlußelement (30) die Vorrichtung vollständig umgibt.
6. Vorrichtung nach einem beliebigen der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß die starre Wand (21) aus Metall ist.
7. Vorrichtung nach einem beliebigen der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß die starre Wand (21) aus einem organischen Kunststoff ist.
8. Vorrichtung nach einem beliebigen der Ansprüche 1 bis 7, dadurch gekennzeichnet, daß die äußere Oberfläche (29) des Verschlußelements (30) über-Abstandsstücke (25) mit dem Träger (26) verbunden ist, so daß Meereswasser an diese äußere Oberfläche (29) gelangen kann.
9. Vorrichtung nach einem beliebigen der Ansprüche 1 bis 8, dadurch gekennzeichnet, daß die akustische Impedanz pro Flächeneinheit des Fluids bei der niedrigsten Frequenz der zu reflektierenden akustischen Welle größer als die akustische Impedanz ist, die vom Volumen aus viskoeleastischem Schaum mit gasgefüllten Zellen manifestiert wird.
10. Vorrichtung nach einem beliebigen der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß sie ein piezoelektrisches Transduktorelement (31) aufweist, das an die starre Wand (21) angrenzt.
11. Passive Lauschantenne, dadurch gekennzeichnet, daß sie mindestens eine Vorrichtung nach einem der vorherigen Ansprüche enthält.
EP19840400076 1983-01-19 1984-01-13 Vorrichtung zur Reflexion von akustischen Wellen Expired EP0114764B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8300753A FR2539541B1 (fr) 1983-01-19 1983-01-19 Dispositif a interface reflectrice d'ondes acoustiques
FR8300753 1983-01-19

Publications (3)

Publication Number Publication Date
EP0114764A2 EP0114764A2 (de) 1984-08-01
EP0114764A3 EP0114764A3 (en) 1984-08-22
EP0114764B1 true EP0114764B1 (de) 1987-09-02

Family

ID=9285062

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19840400076 Expired EP0114764B1 (de) 1983-01-19 1984-01-13 Vorrichtung zur Reflexion von akustischen Wellen

Country Status (6)

Country Link
EP (1) EP0114764B1 (de)
AU (1) AU2355484A (de)
CA (1) CA1239693A (de)
DE (1) DE3465809D1 (de)
ES (1) ES8503449A1 (de)
FR (1) FR2539541B1 (de)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2204217B (en) * 1987-05-02 1990-05-23 Gec Avionics Acoustic reflector
EP0328931A3 (de) * 1988-02-18 1991-07-31 The B.F. Goodrich Company Schallwand mit federnden Röhren
FR2656720B1 (fr) * 1989-12-29 1992-03-20 Thomson Csf Reflecteur d'ondes acoustiques pouvant fonctionner sous une forte immersion.
FR2674717B1 (fr) * 1991-03-29 1993-05-14 Thomson Csf Antenne acoustique basse frequence directive.
FR2720590B1 (fr) * 1994-05-31 1996-06-28 Thomson Csf Antenne acoustique passive absorbante.

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2811216A (en) * 1954-04-28 1957-10-29 Harris Transducer Corp Acoustic baffle construction
US2884084A (en) * 1954-10-28 1959-04-28 Sussman Harry Acoustic panel
DE1815684A1 (de) * 1968-12-19 1970-06-25 Krupp Gmbh Reflektor fuer Wasserschall
FR2240813B1 (de) * 1973-08-16 1976-04-30 France Etat

Also Published As

Publication number Publication date
EP0114764A2 (de) 1984-08-01
DE3465809D1 (en) 1987-10-08
EP0114764A3 (en) 1984-08-22
FR2539541A1 (fr) 1984-07-20
AU2355484A (en) 1984-07-26
CA1239693A (en) 1988-07-26
ES528948A0 (es) 1985-02-16
FR2539541B1 (fr) 1986-09-19
ES8503449A1 (es) 1985-02-16

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