WO1991003808A1 - Absorbant acoustic material and anechoic coating using same - Google Patents

Absorbant acoustic material and anechoic coating using same Download PDF

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Publication number
WO1991003808A1
WO1991003808A1 PCT/FR1990/000642 FR9000642W WO9103808A1 WO 1991003808 A1 WO1991003808 A1 WO 1991003808A1 FR 9000642 W FR9000642 W FR 9000642W WO 9103808 A1 WO9103808 A1 WO 9103808A1
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WIPO (PCT)
Prior art keywords
polymer
crystallites
amorphous phase
conductive
anechoic
Prior art date
Application number
PCT/FR1990/000642
Other languages
French (fr)
Inventor
Olivier Lacour
Original Assignee
Thomson-Csf
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Filing date
Publication date
Application filed by Thomson-Csf filed Critical Thomson-Csf
Publication of WO1991003808A1 publication Critical patent/WO1991003808A1/en

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Classifications

    • 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
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/162—Selection of materials
    • G10K11/165—Particles in a matrix

Definitions

  • the present invention relates to materials which allow the absorption of acoustic waves, more particularly the sounds propagating in the underwater environment. It also relates to anechoic coatings manufactured using such a material and which make it possible to eliminate, or at least to reduce very strongly, the echoes returned by objects provided with such a coating.
  • an anechoic coating used in underwater acoustics depends essentially on the absorption of the acoustic waves in this material and on its acoustic impedance relative to that of water. So that the incident wave can be absorbed by the material, it must penetrate it. If therefore the acoustic impedance thereof is too different from that of water, a large part of the incident wave is reflected on the interface separating the water from the coating, which gives rise to an echo which is all the stronger as the reflection is greater.
  • piezoelectric crystals or ceramics which have a high coupling coefficient as the electroactive element of anechoic materials
  • an absorbent material is obtained whose density is important because the density of these crystals or of these ceramics is itself high.
  • the acoustic impedance of the anechoic material is then very different from that of water, which limits the effectiveness of the coating as a result of the reflection due to the difference in acoustic impedances.
  • the material finally obtained is of a consistency such that it is difficult to work.
  • the invention provides a material.
  • FIG. 1 a schematic section of a known piezoelectric polymer
  • FIG. 2 a schematic section of a piezoelectric polymer according to the invention.
  • a piezoelectric polymer is not a homogeneous product, but that it consists of two phases, as shown very schematically in Figure 1: an amorphous phase 10 and a crystalline phase formed of a multitude of small criteria 11 scattered in the amorphous phase.
  • the crystallites have been represented by spheres when in fact they have a geometry of platelets. Only the crystallites exhibit piezoelectric effects schematized by the arrows in the figure while the amorphous phase is electrically inert. It is therefore possible to assimilate a piezoelectric polymer to a composite formed by a dispersion of crystallites in an amorphous matrix.
  • this structure is formed spontaneously during the polymerization of the material and there is therefore no problem concerning the distribution of the crystallites, since these form directly within the mass of the product.
  • the amorphous phase 20 in which the crystallites are dispersed is made conductive.
  • the electrical voltages developed by the crystallites under the action of mechanical forces, for example from propagation of an acoustic wave inside the mass of the material give rise to currents which circulate in the amorphous phase and dissipate the energy by Joule effect inside this phase. Since the action of the acoustic waves is located at the microscopic level of each crystallite, the current coming from a crystallite will dissipate the corresponding energy around this crystallite and there will therefore be no macroscopic level compensation for the microscopic effects thus obtained . There is therefore no need according to the invention to carry out a polarization of the material which can thus be used in a massive manner without constraint on the thickness.
  • the polymer or at least its amor ⁇ phe phase, conductive.
  • the simplest consists of incorporating carbon powder into the mass of the polymer, for example by means of a roller calender when the material is at a stage where it is still relatively pasty without being completely liquid. At this stage the crystallites are still solid and the carbon powder will only disperse in the mass of the amorphous phase which is much more liquid.
  • Another solution consists in incorporating into the basic polymer an intrinsically conductive polymer such as for example doped polypyrrole.
  • This preparation will advantageously be carried out at the liquid level before the polymerization of the assembly, so as to have a completely homogeneous product.
  • the crystallites themselves will be conductive in addition to the amorphous phase, which does not present any drawback. Since there is no need to polarize the material, it can be used in different ways to obtain an anechoic coating.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
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  • Compositions Of Macromolecular Compounds (AREA)

Abstract

The invention relates to anechoic coatings for protection against acoustic waves. Said invention consists in the production of this type of material using a non-polarised piezoelectric polymer containing an amorphous phase (20) in which crystallites (21) with the same composition as the amorphous phase are dispersed. The amorphous phase, at least, is made conductive, either by incorporating carbon powder, or by means of an intrinsically conductive polymer. The proportion of crystallites is, preferably, brought by heat treatment to a value at least equal to 80 %. The invention makes it possible to produce an anechoic covering by simple coating.

Description

Matériau absorbant acoustique et revêtement anéchoïque utilisant un tel matériau Acoustic absorbent material and anechoic coating using such material
La présente invention se rapporte aux matériaux qui per¬ mettent d'absorber les ondes acoustiques, plus particulièrement les sons se propageant dans le milieu sous-marin. Elle concerne également les revêtements anéchoïques fabriqués à l'aide d'un tel matériau et qui permettent d'éliminer, ou tout au moins de diminuer très fortement, les échos renvoyés par les objets munis d'un tel revêtement.The present invention relates to materials which allow the absorption of acoustic waves, more particularly the sounds propagating in the underwater environment. It also relates to anechoic coatings manufactured using such a material and which make it possible to eliminate, or at least to reduce very strongly, the echoes returned by objects provided with such a coating.
Il est connu de fabriquer un matériau absorbant les ondes acoustiques en dispersant dans une matrice viscoélastique, formée par exemple d'un polymère, des inclusions se présentant sous la forme de particules d'un matériau dur, généralement un métal tel que le plomb ou le tungstène . L'énergie élastique des ondes acoustiques est alors dissipée par frottement visqueux dans la matrice . Les inclusions augmentant la densité, et donc l'impédance acoustique du matériau, il est également connu d'abaisser cette impédance acoustique pour se rapprocher de celle de l'eau, en dispersant également dans la matrice des microsphères creuses, par exemple en verre, dont la densité est considérablement inférieure à 1. II est aussi connu du brevet américain 4 628 490 de rempla¬ cer ces inclusions métalliques par des inclusions faites d'un matériau piézoélectrique tel que de la céramique piézoélectrique en grains fins. La matrice est rendue conductrice par incorporation de poudre de graphite. Sous l'effet d'une onde acoustique les inclusions piézoélectriques engendrent des tensions électriques qui produisent des courants dans la matrice. L'énergie acoustique se dissipe donc partiellement par effet Joule. Elle se dissipe également par diffraction et frottement visqueux selon le mécanisme décrit plus haut, et au total l'absorption est meilleure que dans le cas d'une poudre métallique . On sait que l'efficacité d'un revêtement anéchoïque utili¬ sé en acoustique sous -marine dépend essentiellement de l'absorp¬ tion des ondes acoustiques dans ce matériau et de son impédance acoustique par rapport à celle de l'eau. Pour que l'onde incidente puisse être absorbée par le matériau, il faut qu'elle y pénètre. Si donc l'impédance acousti¬ que de celui-ci est trop différente de celle de l'eau, une grande partie de l'onde incidente est réfléchie sur l'interface séparant l'eau du revêtement, ce qui donne naissance à un écho qui est d'autant plus fort que la réflexion est plus grande.It is known to manufacture a material absorbing acoustic waves by dispersing in a viscoelastic matrix, formed for example of a polymer, inclusions appearing in the form of particles of a hard material, generally a metal such as lead or tungsten. The elastic energy of the acoustic waves is then dissipated by viscous friction in the matrix. As inclusions increase the density, and therefore the acoustic impedance of the material, it is also known to lower this acoustic impedance to approach that of water, by also dispersing in the matrix hollow microspheres, for example glass, whose density is considerably less than 1. It is also known from US Pat. No. 4,628,490 to replace these metallic inclusions with inclusions made of a piezoelectric material such as fine grain piezoelectric ceramic. The matrix is made conductive by incorporating graphite powder. Under the effect of an acoustic wave the piezoelectric inclusions generate electrical voltages which produce currents in the matrix. The acoustic energy therefore partially dissipates by the Joule effect. It also dissipates by diffraction and viscous friction according to the mechanism described above, and overall the absorption is better than in the case of a metal powder. It is known that the effectiveness of an anechoic coating used in underwater acoustics depends essentially on the absorption of the acoustic waves in this material and on its acoustic impedance relative to that of water. So that the incident wave can be absorbed by the material, it must penetrate it. If therefore the acoustic impedance thereof is too different from that of water, a large part of the incident wave is reflected on the interface separating the water from the coating, which gives rise to an echo which is all the stronger as the reflection is greater.
Il faut également que la plus grande partie de l'onde qui a pénétré le matériau soit absorbée de manière à ce qu'elle ne ressorte pas dans l'eau, soit après réflexion sur l'interface séparant le matériau absorbant du support du revêtement anéchoïque soit après diffusion au sein de ce matériau.It is also necessary that the major part of the wave which has penetrated the material is absorbed so that it does not stand out in the water, or after reflection on the interface separating the absorbent material from the support of the anechoic coating. either after diffusion within this material.
Or l'efficacité des matériaux anéchoïques utilisant l'ef¬ fet piézoélectrique est étroitement liée au coefficient de cou¬ plage électromécanique de l'élément électroactif, puisque cette grandeur est proportionnelle à la quantité d'énergie mécanique transformée en énergie électrique.However, the efficiency of anechoic materials using the piezoelectric effect is closely linked to the electromechanical cou¬ coefficient coefficient of the electroactive element, since this quantity is proportional to the amount of mechanical energy transformed into electrical energy.
Si on utilise des cristaux ou des céramiques piézoélectriques qui possèdent un fort coefficient de couplage comme élément électroactif des matériaux anéchoïques, on obtient un matériau absorbant dont la densité est importante parce que la densité de ces cristaux ou de ces céramiques est elle-même grande. L'impédance acoustique du matériau anéchoïque est alors très différente de celle de l'eau ce qui limite l'efficacité du revêtement par suite de la réflexion due à la différence des impédances acoustiques. On ne peut pas espérer réduire cet effet indésirable en diminuant la proportion de matériaux piézoélectriques, parce que l'absorption est maximale pour une concentration volumique en inclusions voisine de 50%, et qu'elle chute rapidement lorsque cette proportion diminue. Avec une telle proportion d'inclusions il est encore plus difficile que dans la technique plus classique où l'on utilise des poudres métalliques, d'obtenir un mélange homogène. En outre le matériau finalement obtenu est d'une consistance telle qu'il se travaille malaisément.If piezoelectric crystals or ceramics are used which have a high coupling coefficient as the electroactive element of anechoic materials, an absorbent material is obtained whose density is important because the density of these crystals or of these ceramics is itself high. The acoustic impedance of the anechoic material is then very different from that of water, which limits the effectiveness of the coating as a result of the reflection due to the difference in acoustic impedances. One cannot hope to reduce this undesirable effect by decreasing the proportion of piezoelectric materials, because the absorption is maximum for a volume concentration in inclusions close to 50%, and that it falls quickly when this proportion decreases. With such a proportion of inclusions it is even more difficult than in the more conventional technique where metallic powders are used, to obtain a homogeneous mixture. In addition, the material finally obtained is of a consistency such that it is difficult to work.
Pour pallier ces inconvénients, l'invention propose un matériau .To overcome these drawbacks, the invention provides a material.
D'autres particularités et avantages de l'invention appa¬ raîtront clairement dans la description suivante présentée à titre d'exemple non limitatif en regard des figures annexées qui représentent :Other features and advantages of the invention will become apparent from the following description presented by way of nonlimiting example with reference to the appended figures which represent:
- la figure 1 une coupe schématique d'un polymère piézoélectrique connu ; et- Figure 1 a schematic section of a known piezoelectric polymer; and
- la figure 2 une coupe schématique d'un polymère piézoélectrique selon l'invention.- Figure 2 a schematic section of a piezoelectric polymer according to the invention.
On sait qu'un polymère piézoélectrique n'est pas un pro¬ duit homogène, mais qu'il est constitué de deux phases, comme représenté de manière très schématique sur la figure 1 : une phase amorphe 10 et une phase cristalline formée d'une multitude de petits critaUites 11 dispersés dans la phase amorphe . Pour la simplicité de la figure, on a représenté les cristallites par des sphères alors qu'en fait ils possèdent une géométrie de plaquettes. Seuls les cristallites présentent des effets piézo¬ électriques schématisés par les flèches sur la figure alors que la phase amorphe est inerte électriquement. On peut donc assimi¬ ler un polymère piézoélectrique à un composite formé d'une dis¬ persion de cristallites dans une matrice amorphe. Toutefois, à l'inverse des dispersions obtenues par mélange de deux produits distincts, cette structure se constitue spontanément lors de la polymérisation du matériau et il n'y a donc aucun problème concernant la répartition des cristallites, puisque ceux-ci se forment directement au sein de la masse du produit.We know that a piezoelectric polymer is not a homogeneous product, but that it consists of two phases, as shown very schematically in Figure 1: an amorphous phase 10 and a crystalline phase formed of a multitude of small criteria 11 scattered in the amorphous phase. For the simplicity of the figure, the crystallites have been represented by spheres when in fact they have a geometry of platelets. Only the crystallites exhibit piezoelectric effects schematized by the arrows in the figure while the amorphous phase is electrically inert. It is therefore possible to assimilate a piezoelectric polymer to a composite formed by a dispersion of crystallites in an amorphous matrix. However, unlike dispersions obtained by mixing two separate products, this structure is formed spontaneously during the polymerization of the material and there is therefore no problem concerning the distribution of the crystallites, since these form directly within the mass of the product.
On sait que le coefficient de couplage, désigné par k.,.. , d'un copolymère piézoélectrique est assez faible. Par exemple pour un copolymère P(VF2/TrFE) il est inférieur à 0, 12. Or des expérimentations récentes ont permis de mesurer directement le coefficient de couplage des cristallites et de constater qu'il est beaucoup plus fort que celui du mélange cristallite/phase amorphe . Il peut atteindre par exemple pour ce même copolymère 0,5 à 20°.It is known that the coupling coefficient, designated by k., .., of a piezoelectric copolymer is quite low. For example, for a copolymer P (VF 2 / TrFE) it is less than 0.12. Recent experiments have made it possible to directly measure the coupling coefficient of the crystallites and to note that it is much stronger than that of the crystallite / amorphous phase mixture. For this same copolymer, it can reach, for example, 0.5 to 20 °.
On est par ailleurs arrivé à augmenter dans des propor¬ tions considérables le pourcentage cristallite/phase amorphe par rapport au pourcentage obtenu de manière spontanée lors de la polymérisation du produit. Pour cela, selon une technique con- nue, on soumet le matériau à des cycles thermiques répétés afin d'obtenir des recristallisations successives à l'issue desquel¬ les on peut arriver à un pourcentage de cristallites voisin de 80%. Un matériau massif tel que représenté sur la figure 1 ne présente pas de manière macroscopique des propriétés piézo- électriques, puisque la répartition aléatoire de l'orientation des cristallites conduit à ce que les tensions électriques déve¬ loppées par ceux-ci sous l'effet des contraintes extérieures se neutralisent les unes les autres. C'est la raison pour laquelle dans l'utilisation habituelle de ce genre de matériau on est conduit à leur faire subir un traitement à la fois mécanique et électrique, par exemple un laminage conduit simultanément avec l'application d'une tension électrique. On peut orienter ainsi les cristallites tous dans la même direction pour obtenir une polarisation telle que le produit final présente des propriétés piézoélectriques macroscopiques . En fait les contraintes des différents procédés utilisés amènent à obtenir le matériau sous forme de films relativement minces. Il faut ensuite veiller, lorsque l'on utilise ces films, à ne pas détruire la polarisation ainsi obtenue, ce qui entraîne d'autres difficultés de mise en oeuvre.We have also managed to increase in considerable proportions the crystallite / amorphous phase percentage compared to the percentage obtained spontaneously during the polymerization of the product. For this, according to a known technique, the material is subjected to repeated thermal cycles in order to obtain successive recrystallizations at the end of which it is possible to arrive at a percentage of crystallites close to 80%. A solid material as shown in FIG. 1 does not macroscopically exhibit piezoelectric properties, since the random distribution of the orientation of the crystallites leads to the fact that the electrical voltages developed by them under the effect external constraints neutralize each other. This is the reason why in the usual use of this kind of material we are led to subject them to a treatment that is both mechanical and electrical, for example a rolling conducted simultaneously with the application of an electrical voltage. We can thus orient the crystallites all in the same direction to obtain a polarization such that the final product has macroscopic piezoelectric properties. In fact, the constraints of the various methods used lead to the material being obtained in the form of relatively thin films. Care must then be taken, when using these films, not to destroy the polarization thus obtained, which leads to other difficulties of implementation.
Selon l'invention, telle que représentée très schématique- ment sur la figure 2, on rend conducteur au moins la phase amorphe 20 dans laquelle sont dispersés les cristallites 21. Ainsi les tensions électriques développées par les cristallites sous l'action des forces mécaniques, provenant par exemple de la propagation d'une onde acoustique à l'intérieur de la masse du matériau, donnent naissance à des courants qui circulent dans la phase amorphe et dissipent l'énergie par effet Joule à l'inté¬ rieur de cette phase. Puisque l'action des ondes acoustiques se situe au niveau microscopique de chaque cristallite , le courant provenant d'un cristallite va dissiper l'énergie correspondante autour de ce cristallite et il n'y aura donc pas au niveau macroscopique compensation des effets microscopiques ainsi obtenus . Il n'y a donc pas besoin selon l'invention de procéder à une polarisation du matériau qui peut ainsi être utilisé de manière massive sans contrainte sur l'épaisseur.According to the invention, as shown very schematically in FIG. 2, at least the amorphous phase 20 in which the crystallites are dispersed is made conductive. Thus the electrical voltages developed by the crystallites under the action of mechanical forces, for example from propagation of an acoustic wave inside the mass of the material, give rise to currents which circulate in the amorphous phase and dissipate the energy by Joule effect inside this phase. Since the action of the acoustic waves is located at the microscopic level of each crystallite, the current coming from a crystallite will dissipate the corresponding energy around this crystallite and there will therefore be no macroscopic level compensation for the microscopic effects thus obtained . There is therefore no need according to the invention to carry out a polarization of the material which can thus be used in a massive manner without constraint on the thickness.
Pour rendre le polymère, ou tout au moins sa phase amor¬ phe, conducteur, on peut utiliser divers procédés . Le plus sim- pie consiste à incorporer de la poudre de carbone dans la masse du polymère, au moyen par exemple d'une calandreuse à rouleau lorsque le matériau se trouve à un stade où il est encore relati¬ vement pâteux sans être carrément liquide. A ce stade les cristallites sont encore solides et la poudre de carbone ne se dispersera que dans la masse de la phase amorphe qui elle est beaucoup plus liquide.Various methods can be used to make the polymer, or at least its amor¬ phe phase, conductive. The simplest consists of incorporating carbon powder into the mass of the polymer, for example by means of a roller calender when the material is at a stage where it is still relatively pasty without being completely liquid. At this stage the crystallites are still solid and the carbon powder will only disperse in the mass of the amorphous phase which is much more liquid.
Une autre solution consiste à incorporer dans le polymère de base un polymère Intrinsèquement conducteur tel que par exemple le polypyrrole dopé. Cette préparation s'effectuera avantageusement au niveau liquide avant la polymérisation de l'ensemble, de manière à avoir un produit tout à fait homogène . Dans ces conditions les cristallites eux-mêmes seront conduc¬ teurs en plus de la phase amorphe, ce qui ne présente aucun inconvénient . Comme il n'y a pas besoin de polariser le matériau on peut l'utiliser de différentes manières pour obtenir un revêtement anéchoïque .Another solution consists in incorporating into the basic polymer an intrinsically conductive polymer such as for example doped polypyrrole. This preparation will advantageously be carried out at the liquid level before the polymerization of the assembly, so as to have a completely homogeneous product. Under these conditions, the crystallites themselves will be conductive in addition to the amorphous phase, which does not present any drawback. Since there is no need to polarize the material, it can be used in different ways to obtain an anechoic coating.
On peut ainsi à la fin de la phase d'élaboration, lorsqu'il est encore relativement liquide, le couler sous diffé- rentes formes, par exemple en plaques ou dans des moules ayant la forme de la surface à revêtir, ou encore sous une forme mas¬ sive dans laquelle on taillera des pièces de dimensions adéquates . Une autre méthode consiste, toujours lorsque le matériau est à l'état relativement liquide ou pâteux, à enduire la sur¬ face à traiter, par exemple la coque d'un bateau, pour obtenir l'épaisseur voulue. Cette induction peut se faire par différen¬ tes méthodes, par exemple au rouleau ou avec un pistolet prévu pour les matières pâteuses. On constate ainsi que la mise en oeuvre du matériau selon l'invention est extrêmement aisée. It is thus possible at the end of the preparation phase, when it is still relatively liquid, to pour it in different forms, for example in plates or in molds having the shape of the surface to be coated, or in a mas¬ sive form in which we will cut parts of adequate dimensions. Another method consists, always when the material is in a relatively liquid or pasty state, of coating the surface to be treated, for example the hull of a boat, in order to obtain the desired thickness. This induction can be done by different methods, for example using a roller or with a spray gun intended for pasty materials. It can thus be seen that the use of the material according to the invention is extremely easy.

Claims

REVENDICATIONS
1. Matériau absorbant acoustique, comprenant une matrice viscoélastique conductrice et des particules piézoélectriques dispersées dans cette matrice, caractérisé en ce que la matrice est formée d'un polymère en phase amorphe (20) et que lesdites particules sont formées de cristallites (21) de ce dit polymère.1. Sound absorbing material, comprising a conductive viscoelastic matrix and piezoelectric particles dispersed in this matrix, characterized in that the matrix is formed from a polymer in amorphous phase (20) and that said particles are formed from crystallites (21) of this said polymer.
2. Matériau selon la revendication 1, caractérisé en ce que les cristallites sont également conducteurs .2. Material according to claim 1, characterized in that the crystallites are also conductive.
3. Matériau selon l'une quelconque des revendications 1 et3. Material according to any one of claims 1 and
2, caractérisé en ce que la proportion de cristallites est au moins égale à 80%.2, characterized in that the proportion of crystallites is at least equal to 80%.
4. Matériau selon l'une quelconque des revendications 1 à4. Material according to any one of claims 1 to
3, caractérisé en ce que le polymère est un copolymère P(VF2/TrFE) .3, characterized in that the polymer is a copolymer P (VF 2 / TrFE).
5. Matériau selon l'une quelconque des revendications 1 à 4, caractérisé en ce que le polymère est rendu conducteur par incorporation d'une poudre conductrice.5. Material according to any one of claims 1 to 4, characterized in that the polymer is made conductive by incorporation of a conductive powder.
6. Matériau selon l'une quelconque des revendications 1 à6. Material according to any one of claims 1 to
4, caractérisé en ce que le polymère est rendu conducteur par incorporation d'un polymère intrinsèquement conducteur. 4, characterized in that the polymer is made conductive by incorporating an intrinsically conductive polymer.
7. Matériau selon la revendication 6, caractérisé en ce que le polymère est un copolymère dont une composante est ledit polymère intrinsèquement conducteur.7. Material according to claim 6, characterized in that the polymer is a copolymer, a component of which is said intrinsically conductive polymer.
8. Revêtement anéchoïque, caractérisé en ce qu'il est formé d'une couche massive d'un matériau selon l'une quelconque des revendications 1 à 7. 8. Anechoic coating, characterized in that it is formed of a solid layer of a material according to any one of claims 1 to 7.
PCT/FR1990/000642 1989-09-08 1990-09-04 Absorbant acoustic material and anechoic coating using same WO1991003808A1 (en)

Applications Claiming Priority (2)

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FR89/11748 1989-09-08
FR8911748A FR2651690A1 (en) 1989-09-08 1989-09-08 ACOUSTIC ABSORBENT MATERIAL AND ANECHOIC COATING USING SUCH MATERIAL.

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Cited By (2)

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Publication number Priority date Publication date Assignee Title
WO1997007496A1 (en) * 1995-08-16 1997-02-27 Poiesis Research, Inc. Acoustic absorption and damping material with piezoelectric energy dissipation
US20040095848A1 (en) * 2002-11-19 2004-05-20 Honeywell International Inc. Transducers coated with anechoic material for use in down hole communications

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JP2002069424A (en) 2000-08-31 2002-03-08 Masao Sumita Organic hybrid-based vibration damping material, its manufacturing method and vibration damping improving agent used for the same

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US3515910A (en) * 1968-11-12 1970-06-02 Us Navy Acoustic absorbing material
DE3431776A1 (en) * 1983-08-30 1985-03-14 Murata Manufacturing Co., Ltd., Nagaokakyo, Kyoto VIBRATION-INSULATING OBJECT
US4628490A (en) * 1985-12-24 1986-12-09 The United States Of America As Represented By The Secretary Of The Navy Wideband sonar energy absorber

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Publication number Priority date Publication date Assignee Title
US3515910A (en) * 1968-11-12 1970-06-02 Us Navy Acoustic absorbing material
DE3431776A1 (en) * 1983-08-30 1985-03-14 Murata Manufacturing Co., Ltd., Nagaokakyo, Kyoto VIBRATION-INSULATING OBJECT
US4628490A (en) * 1985-12-24 1986-12-09 The United States Of America As Represented By The Secretary Of The Navy Wideband sonar energy absorber

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997007496A1 (en) * 1995-08-16 1997-02-27 Poiesis Research, Inc. Acoustic absorption and damping material with piezoelectric energy dissipation
US20040095848A1 (en) * 2002-11-19 2004-05-20 Honeywell International Inc. Transducers coated with anechoic material for use in down hole communications
US7061830B2 (en) * 2002-11-19 2006-06-13 Honeywell International Inc. Transducers coated with anechoic material for use in down hole communications

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FR2651690A1 (en) 1991-03-15

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