EP0378021A1 - Signal receiver insensitive to static pressure variations - Google Patents

Signal receiver insensitive to static pressure variations Download PDF

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Publication number
EP0378021A1
EP0378021A1 EP89403518A EP89403518A EP0378021A1 EP 0378021 A1 EP0378021 A1 EP 0378021A1 EP 89403518 A EP89403518 A EP 89403518A EP 89403518 A EP89403518 A EP 89403518A EP 0378021 A1 EP0378021 A1 EP 0378021A1
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EP
European Patent Office
Prior art keywords
sensor according
pressure sensor
volume
pressure
absorbent material
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EP89403518A
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German (de)
French (fr)
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EP0378021B1 (en
Inventor
Claude Beauducel
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IFP Energies Nouvelles IFPEN
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IFP Energies Nouvelles IFPEN
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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
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • B06B1/0644—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element
    • B06B1/0662—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element with an electrode on the sensitive surface
    • B06B1/0681—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element with an electrode on the sensitive surface and a damping structure
    • B06B1/0685—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element with an electrode on the sensitive surface and a damping structure on the back only of piezoelectric elements

Definitions

  • the present invention relates to a signal sensor insensitive to variations in the static pressure prevailing in the medium in which it is arranged.
  • Such a signal sensor can be used in any environment where acoustic signals are measured and in particular in water.
  • a hydrophone comprising two circular plates. At least one of the two plates has a flexible central part against which is fixed a sensitive element consisting of a piezoelectric ceramic disc associated with an electrode on each of its two opposite planar faces.
  • the peripheral part of the two plates is reinforced and rigid.
  • the two plates are applied one against the other and delimit an interior cavity filled with air. Variations in the seismic signals to be measured distort each flexible central part.
  • Each sensitive element works in flexion, which gives it a high sensitivity.
  • the static pressure which increases with the depth of immersion, for example, causes each flexible plate to flex towards the inside of the housing.
  • the device is designed so that the possible deformation of the flexible plates under the effect of static pressure remains reversible.
  • the spacing of the two plates is chosen for example so that they come into abutment against one another before their deformation becomes irreversible.
  • Such a hydrophone is suitable for a determined range of depths.
  • the French patent 1,556,971 also discloses a hydrophone comprising a sensitive element fixed to a flexible thin plate, which is subject to a rigid body.
  • This includes two interior cavities filled with air communicating through a capillary channel.
  • a first cavity is separated from the external environment by a flexible membrane.
  • the outside of the flexible plate is exposed to the pressure to be measured.
  • the pressure prevailing in the second cavity is applied to its inner face.
  • the variations in the external pressure are transmitted into the first cavity by deformation of the flexible membrane.
  • the capillary channel acting as a low-pass filter, prevents the transmission of dynamic variations in the pressure to be measured in the second cavity, on the inside of the thin plate. Dynamic pressure variations can therefore be measured.
  • the range of depths where the hydrophone can operate is significantly increased.
  • the limits are essentially fixed by the capacity of the membrane to compensate by its deformation, the variations of the external static pressure.
  • the filtering effect of the dynamic variations provided by the capillary depends on its length. If you are trying to widen the passband of such a hydrophone as much as possible towards low frequencies, use a very long capillary. In practice this solution is hardly compatible with the construction of very small hydrophones as is used in large numbers for the construction of seismic flutes for example.
  • the sensor according to the invention makes it possible to avoid the above-mentioned drawbacks.
  • It comprises at least one flexible plate, a sensitive element fixed to this plate and filtering means for subtracting one of the faces of said plate from dynamic variations in the pressure of the medium. It is characterized in that the filtering means comprise a volume of a substantially incompressible absorbent material suitable for transmitting to this face the variations in the static pressure of the medium.
  • the volume of substantially incompressible absorbent material is contained, for example, in a box open to the medium.
  • the volume of substantially incompressible absorbent material is produced for example from fibers produced in a rigid material from a so-called syntactic substance, balls of solid material (glass for example) coated in a binder or immersed in a liquid.
  • the senor according to the invention comprises at least a pair of flexible plates each provided with a sensitive element, and a volume of a substantially incompressible absorbent material to subtract one face of each of the plates from the dynamic variations of the pressure in the middle.
  • the two flexible plates are for example walls of a common housing containing the volume of damping material and provided with openings, this housing being able to comprise a screened portion and to be filled for example with glass beads.
  • the senor according to the invention can also be produced by applying at least one flexible plate provided with its sensitive element, against a face of said block.
  • the senor according to the invention can resist possible compression. This makes it possible to use relatively fragile piezoelectric ceramics but having a high electro-acoustic efficiency, bonded to very thin and very flexible plates.
  • the construction is made simpler because the absorbent material is in equi-pressure with the external medium and even in certain cases, is impregnated with this very medium. .
  • the difficulties that could be encountered in sealing the interior environment of the sensor housing are here eliminated.
  • Each sensor comprises (fig. 1) one or more sensitive elements 1 each consisting for example of a disc 2 produced in one piezoelectric material on the opposite faces of which are bonded two conductive films 3, 4 constituting the collecting electrodes. Electrical conductors 5 allow the electrodes to be connected to an adapter amplifier (not shown) as is well known.
  • the senor comprises for example at least one sensitive element 1 applied against a thin and flexible circular plate 6 provided with an annular flange 7.
  • This flange plate 6, 7 is crimped on one end of a rigid tubular sleeve 8.
  • the opposite end of the sleeve is closed by a plate 9 provided with openings, a grid for example.
  • the openings put the inside of the sleeve 8 in communication with the outside environment.
  • the inside of the sleeve is filled with a damping material 10 chosen for its ability to filter dynamic variations in the external pressure up to very low frequencies.
  • a fibrous material such as a fiberglass or textile wick.
  • this fibrous material permeates the fluid where the pressure sensor is immersed.
  • the static pressure of the fluid is therefore exerted on the two sides of the plate 6 supporting the sensitive element 1.
  • Due to the filtering effected by the damping material 10, the dynamic variations in the fluid pressure are exerted only by one single side of the flexible plate.
  • the sensitive element 1 can therefore pick up the vibrations thereof and translate them into an electrical signal.
  • the senor comprises two sensitive elements 1 associated respectively with two identical plates 6, 7 covering the opposite ends of a sleeve 8 whose side wall is crossed by numerous orifices 11.
  • the interior of the sleeve 8 is filled with a similar damping material, a fibrous substance or even a porous substance capable of being impregnated with the fluid penetrating into the sleeve through the openings 11.
  • this damping material has the effect of removing the inner faces of the two plates 6, 7 at the static pressure of the medium.
  • the two sensitive elements are electrically interconnected (by conductors not shown) as is well known for achieving electrical compensation for accelerations.
  • the two flexible rim plates 6, 7 cover the ends of a sleeve made up of a portion of screened tube 12.
  • the interior is filled with a fibrous or porous damping material such as previously or even particles or glass beads 13 a few millimeters in diameter.
  • a binder 14 such as an epoxy resin.
  • the acoustic impedance of glass is very different from that of bonding resin. Because of the high density of beads it contains and therefore of glass / epoxy interfaces, the composite material has the effect of absorbing the variable acoustic waves on the side of the internal face of the plates 6, 7. The variations in external static pressure are however transmitted to the internal faces of these same plates 6, 7.
  • the sensor is able to operate whatever the static pressure of the external medium.
  • the balls or grains can be produced generally from any solid material whose acoustic impedance is different from that of the interstitial material.
  • the interstitial substance between the balls can be replaced by the fluid where the sensor is placed.
  • the damping material has sufficient cohesion to be cut into a block 15.
  • Each support plate 6, 7 is pressed directly against one face of the block 15 so that its inner face is removed from the dynamic pressure variations which are absorbed by the material.
  • Sensors can be included in a marine seismic flute 16.
  • This generally comprises a flexible sheath 17 of great length filled with oil or kerosene for example at all along which are distributed a large number of pressure sensors 18. Due to the openings made in each sleeve 8, the damping material when it is fibrous or porous, is impregnated with the liquid filling the flute 16. The variations in the external pressure, which they are static or dynamic, are transmitted to the internal liquid through the sheath 17. But here again only the dynamic variations of the pressure are measured by each sensitive element.
  • the fluid where the sensor is placed can be used as interstitial fluid (case of glass beads) or as impregnation fluid (case of porous or fibrous materials).
  • the fluid can be water if the sensor is used as such as a hydrophone. It is noted however that the damping effect of the acoustic signals is better when the liquid is viscous. This is the case of the liquid generally filling the seismic streamers.
  • This fluid can in this case be chosen according to its physical properties to constitute, with the damping medium, an optimal acoustic absorbent.
  • boxes made of a sintered material which has the property of being transparent to variations in static pressure .
  • a suitable material can be obtained, for example, by strongly compressing small beads. Its granularity depends on the size of these.
  • a sintered material casing also has the effect of attenuating variations in dynamic pressure. It can be used alone or in combination with an acoustic absorbent such as those previously defined, to absorb dynamic variations which could be transmitted inside.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
  • Measuring Fluid Pressure (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
  • Geophysics And Detection Of Objects (AREA)
  • Transducers For Ultrasonic Waves (AREA)

Abstract

The signal receiver is provided with a system which automatically compensates for any variations in the static pressure in the environment in which it is placed. <??>It consists of one or two units each consisting of a sensitive piezoelectric element (1) pressed against one face of a flexible plate (6). The other face of the plate is shielded from the variations in the dynamic pressure to be measured by a material (10) which absorbs the vibrations but is flexible enough to transmit any variation in the ambient static pressure. This material (10), which may be a porous foam or a fibrous substance impregnated with fluid, fills a tubular sleeve (8) provided with apertures (11). <??>Application, for example, to the production of hydrophones which can be used over a large range of depths under water. <IMAGE>

Description

La présente invention a pour objet un capteur de signaux insensible aux variations de la pression statique régnant dans le milieu où il est disposé.The present invention relates to a signal sensor insensitive to variations in the static pressure prevailing in the medium in which it is arranged.

Un tel capteur de signaux peut être utilisé dans tout milieu où l'on fait des mesures de signaux acoustiques et notamment dans l'eau.Such a signal sensor can be used in any environment where acoustic signals are measured and in particular in water.

Il convient par exemple, en océanographie, pour effectuer des opérations de détection sous-marine ou encore pour constituer des dispositifs de réception multi-capteurs convenant pour des opérations de prospection sismique marine.It is suitable for example, in oceanography, to carry out underwater detection operations or also to constitute multi-sensor reception devices suitable for marine seismic prospecting operations.

Par le brevet français no 2 122 675, on connait un hydrophone comprenant deux plaques circulaires. L'une au moins des deux plaques comporte une partie centrale flexible contre laquelle est fixé un élément sensible constitué d'un disque en céramique piézo-électrique associé à une électrode sur chacune de ses deux faces planes opposées. La partie périphérique des deux plaques est renforcée et rigide. Les deux plaques sont appliquées l'une contre l'autre et délimitent une cavité intérieure remplie d'air. Les variations des signaux sismiques à mesurer déforment chaque partie centrale flexible. Chaque élément sensible fonctionne en flexion, ce qui lui donne une sensibilité élevée. La pression statique qui augmente avec la profondeur d'immersion par exemple, a pour effet de faire fléchir chaque plaque flexible vers l'intérieur du boîtier. Le dispositif est conçu pour que la déformation possible des plaque flexibles sous l'effet de la pression statique reste réversible. A cet effet, l'écartement des deux plaques est choisi par exemple pour qu'elles viennent en butée l'une contre l'autre avant que leur déformation ne devienne irréversible.By the French patent No. 2,122,675 discloses a hydrophone comprising two circular plates. At least one of the two plates has a flexible central part against which is fixed a sensitive element consisting of a piezoelectric ceramic disc associated with an electrode on each of its two opposite planar faces. The peripheral part of the two plates is reinforced and rigid. The two plates are applied one against the other and delimit an interior cavity filled with air. Variations in the seismic signals to be measured distort each flexible central part. Each sensitive element works in flexion, which gives it a high sensitivity. The static pressure which increases with the depth of immersion, for example, causes each flexible plate to flex towards the inside of the housing. The device is designed so that the possible deformation of the flexible plates under the effect of static pressure remains reversible. For this purpose, the spacing of the two plates is chosen for example so that they come into abutment against one another before their deformation becomes irreversible.

Un tel hydrophone convient pour une gamme de profondeurs déterminée.Such a hydrophone is suitable for a determined range of depths.

En rendant les deux plaques opposées plus épaisses, on peut élargir la gamme de profondeur où l'hydrophone fonctionne mais c'est au détriment de sa sensibilité. Il faut noter aussi que la capacité électrique de chaque élément sensible fonctionnant en flexion varie avec la flêche de la déformation. La réponse de l'hydrophone change donc avec la profondeur.By making the two opposite plates thicker, we can widen the depth range where the hydrophone works, but this is to the detriment of its sensitivity. It should also be noted that the electrical capacity of each sensitive element operating in flexion varies with the arrow of the deformation. The hydrophone's response therefore changes with depth.

Par le brevet français 1 556 971, on connait aussi un hydrophone comportant un élément sensible fixé à une plaque mince flexible, laquelle est assujettie à un corps rigide. Celui-ci comprend deux cavités intérieures remplies d'air communiquant par un canal capillaire. Une première cavité est séparée du milieu extérieur par une membrane flexible. La face extérieure de la plaque flexible est exposée à la pression à mesurer. Sur sa face intérieure s'applique la pression régnant dans la seconde cavité. Les variations de la pression extérieure sont transmises dans la première cavité par déformation de la membrane flexible. Mais le canal capillaire agissant comme un filtre passe-bas, empêche la transmission des variations dynamiques de la pression à mesurer dans la seconde cavité, du côté intérieur de la plaque mince. Les variations de pression dynamiques peuvent donc être mesurées.The French patent 1,556,971 also discloses a hydrophone comprising a sensitive element fixed to a flexible thin plate, which is subject to a rigid body. This includes two interior cavities filled with air communicating through a capillary channel. A first cavity is separated from the external environment by a flexible membrane. The outside of the flexible plate is exposed to the pressure to be measured. The pressure prevailing in the second cavity is applied to its inner face. The variations in the external pressure are transmitted into the first cavity by deformation of the flexible membrane. However, the capillary channel, acting as a low-pass filter, prevents the transmission of dynamic variations in the pressure to be measured in the second cavity, on the inside of the thin plate. Dynamic pressure variations can therefore be measured.

Avec un tel agencement, la gamme de profondeurs où l'hydrophone peut fonctionner est accrue notablement. Les limites sont fixées essentiellement par la capacité de la membrane à compenser par sa déformation, les variations de la pression statique extérieure. On peut noter aussi que l'effet de filtrage des variations dynamiques procuré par le capillaire, dépend de sa longueur. Si l'on cherche à élargir le plus possible vers les basses fréquences la bande passante d'un tel hydrophone, il faut employer un capillaire très long. Dans la pratique cette solution est difficilement compatible avec la construction d'hydrophones très petits comme on en emploie en grand nombre pour la construction des flûtes sismiques par exemple.With such an arrangement, the range of depths where the hydrophone can operate is significantly increased. The limits are essentially fixed by the capacity of the membrane to compensate by its deformation, the variations of the external static pressure. It can also be noted that the filtering effect of the dynamic variations provided by the capillary depends on its length. If you are trying to widen the passband of such a hydrophone as much as possible towards low frequencies, use a very long capillary. In practice this solution is hardly compatible with the construction of very small hydrophones as is used in large numbers for the construction of seismic flutes for example.

Le capteur selon l'invention permet d'éviter les inconvénients ci-dessus mentionnés.The sensor according to the invention makes it possible to avoid the above-mentioned drawbacks.

Il comporte au moins une plaque flexible, un élément sensible fixé à cette plaque et des moyens de filtrage pour soustraire une des faces de ladite plaque aux variations dynamiques de la pression du milieu. Il est caractérisé en ce que les moyens de filtrage comportent un volume d'un matériau absorbant sensiblement incompressible adapté à transmettre à cette face les variations de la pression statique du milieu.It comprises at least one flexible plate, a sensitive element fixed to this plate and filtering means for subtracting one of the faces of said plate from dynamic variations in the pressure of the medium. It is characterized in that the filtering means comprise a volume of a substantially incompressible absorbent material suitable for transmitting to this face the variations in the static pressure of the medium.

Le volume de matériau absorbant sensiblement incompressible est contenu par exemple dans un boîtier ouvert sur le milieu.The volume of substantially incompressible absorbent material is contained, for example, in a box open to the medium.

Le volume de matériau absorbant sensiblement incompressible est réalisé par exemple à partir de fibres réalisées dans un matériau rigide à partird'une substance dite syntactique, de billes en matière solide (du verre par exemple) enrobées dans un liant ou baignant dans un liquide.The volume of substantially incompressible absorbent material is produced for example from fibers produced in a rigid material from a so-called syntactic substance, balls of solid material (glass for example) coated in a binder or immersed in a liquid.

Suivant un mode de réalisation, le capteur selon l'invention comporte au moins une paire de plaques flexibles munies chacune d'un élément sensible, et un volume d'un matériau absorbant sensiblement incompressible pour soustraire une face de chacune des plaques aux variations dynamiques de la pression dans le milieu.According to one embodiment, the sensor according to the invention comprises at least a pair of flexible plates each provided with a sensitive element, and a volume of a substantially incompressible absorbent material to subtract one face of each of the plates from the dynamic variations of the pressure in the middle.

Les deux plaques flexibles sont par exemple des parois d'un boîtier commun contenant le volume de matériau amortisseur et pourvu d'ouvertures, ce boîtier pouvant comporter une partie grillagée et être remplie par exemple de billes de verre.The two flexible plates are for example walls of a common housing containing the volume of damping material and provided with openings, this housing being able to comprise a screened portion and to be filled for example with glass beads.

Lorsque le matériau amortisseur est suffisamment cohérent pour être découpé en blocs, on peut aussi réaliser le capteur selon l'invention en appliquant au moins une plaque flexible munie de son élément sensible, contre une face dudit bloc.When the damping material is sufficiently coherent to be cut into blocks, the sensor according to the invention can also be produced by applying at least one flexible plate provided with its sensitive element, against a face of said block.

Le volume de matériau absorbant sensiblement incompressible, qu'il soit solide ou imprégné de liquide, étant adapté à transmettre tout changement de la pression statique du milieu, les deux face opposées de chaque plaque flexible sont donc soumises à des forces égales. Les effets néfastes et/ou les limitations apportés aux capteurs antérieurs par l'augmentation de la pression statique du milieu, sont ici totalement supprimés.The volume of substantially incompressible absorbent material, whether solid or impregnated with liquid, being adapted to transmit any change in the static pressure of the medium, the two opposite faces of each flexible plate are therefore subjected to equal forces. The harmful effects and / or the limitations brought to previous sensors by the increase in the static pressure of the medium, are here completely eliminated.

Le matériau absorbant utilisé étant sensiblement incompressible, le capteur selon l'invention peut résister à une éventuelle compression. Ceci rend possible l'emploi de céramiques piézo-électriques relativement fragiles mais possédant un rendement électro-acoustique élevé, collées sur des plaques très minces et très flexibles.The absorbent material used being substantially incompressible, the sensor according to the invention can resist possible compression. This makes it possible to use relatively fragile piezoelectric ceramics but having a high electro-acoustic efficiency, bonded to very thin and very flexible plates.

Quel que soit le mode de réalisation choisi pour réaliser le capteur selon l'invention, la construction est rendue plus simple du fait que le matériau absorbant est en équi-pression avec le milieu extérieur et même dans certains cas, est imprégné de ce milieu même. Les difficultés que l'on pouvait rencontrer pour isoler de façon étanche le milieu intérieur au boîtier du capteur, sont ici éliminées.Whatever the embodiment chosen for producing the sensor according to the invention, the construction is made simpler because the absorbent material is in equi-pressure with the external medium and even in certain cases, is impregnated with this very medium. . The difficulties that could be encountered in sealing the interior environment of the sensor housing are here eliminated.

La construction d'un boîtier pourvu d'ouvertures et par exemple d'une partie grillagée et remplie de matériau absorbant est très facile à réaliser. On peut donc obtenir à moindre coût un capteur très sensible et de petites dimensions.The construction of a housing provided with openings and for example of a mesh part and filled with absorbent material is very easy to carry out. It is therefore possible to obtain a very sensitive and small sensor at low cost.

D'autres caractéristiques et avantages du capteur selon l'invention apparaîtront à la lecture de la description de modes de réalisation donnés à titre d'exemple non limitatifs, en se référant aux dessins annexés où :

  • - la figure 1 montre la constitution d'un élément sensible;
  • - la figure 2 montre un premier mode de réalisation du capteur avec une seule plaque flexible;
  • - la figure 3 montre un second mode de réalisation du capteur avec deux plaques flexibles;
  • - la figure 4 montre une variante du mode de réalisation précédent;
  • - la figure 5 montre un troisième mode de réalisation du capteur selon l'invention, et
  • - la figure 6 montre une utilisation du capteur à l'intérieur d'une flûte sismique.
Other characteristics and advantages of the sensor according to the invention will appear on reading the description of embodiments given by way of nonlimiting example, with reference to the accompanying drawings in which:
  • - Figure 1 shows the constitution of a sensitive element;
  • - Figure 2 shows a first embodiment of the sensor with a single flexible plate;
  • - Figure 3 shows a second embodiment of the sensor with two flexible plates;
  • - Figure 4 shows a variant of the previous embodiment;
  • FIG. 5 shows a third embodiment of the sensor according to the invention, and
  • - Figure 6 shows a use of the sensor inside a seismic streamer.

Chaque capteur comporte (fig. 1) un ou plusieurs éléments sensibles 1 constitués chacun par exemple d'un disque 2 réalisé en un matériau piézo-électrique sur les faces opposées duquel sont collés deux films conducteurs 3, 4 constituant les électrodes collectrices. Des conducteurs électriques 5 permettent de relier les électrodes à un amplificateur adaptateur (non représenté) comme il est bien connu.Each sensor comprises (fig. 1) one or more sensitive elements 1 each consisting for example of a disc 2 produced in one piezoelectric material on the opposite faces of which are bonded two conductive films 3, 4 constituting the collecting electrodes. Electrical conductors 5 allow the electrodes to be connected to an adapter amplifier (not shown) as is well known.

Suivant le mode de réalisation de la figure 2, le capteur comporte par exemple au moins un élément sensible 1 appliqué contre une plaque circulaire 6 mince et flexible pourvue d'un rebord annulaire 7. Cette plaque à rebord 6, 7 est sertie sur une extrémité d'un manchon tubulaire rigide 8. L'extrémité opposée du manchon est fermée par une plaque 9 pourvue d'ouvertures, une grille par exemple. Les ouvertures mettent l'intérieur du manchon 8 en communication avec le milieu extérieur. On remplit l'intérieur du manchon avec un matériau amortisseur 10 choisi pour sa capacité à filtrer les variations dynamiques de la pression extérieure jusqu'à des fréquences très basses.According to the embodiment of FIG. 2, the sensor comprises for example at least one sensitive element 1 applied against a thin and flexible circular plate 6 provided with an annular flange 7. This flange plate 6, 7 is crimped on one end of a rigid tubular sleeve 8. The opposite end of the sleeve is closed by a plate 9 provided with openings, a grid for example. The openings put the inside of the sleeve 8 in communication with the outside environment. The inside of the sleeve is filled with a damping material 10 chosen for its ability to filter dynamic variations in the external pressure up to very low frequencies.

Différents matériaux peuvent convenir. On choisit par exemple un matériau fibreux tel qu'une mêche en fibre de verre ou en textile. En opération, ce matériau fibreux s'imprègne du fluide où le capteur de pression est plongé. La pression statique du fluide s'exerce donc des deux côtés de la plaque 6 supportant l'élément sensible 1. En raison du filtrage opéré par le matériau amortisseur 10, les variations dynamiques de la pression de fluide ne s'exercent que d'un seul côté de la plaque flexible. L'élément sensible 1 peut donc capter les vibrations de celle-ci et les traduire en un signal électrique.Different materials may be suitable. For example, a fibrous material is chosen such as a fiberglass or textile wick. In operation, this fibrous material permeates the fluid where the pressure sensor is immersed. The static pressure of the fluid is therefore exerted on the two sides of the plate 6 supporting the sensitive element 1. Due to the filtering effected by the damping material 10, the dynamic variations in the fluid pressure are exerted only by one single side of the flexible plate. The sensitive element 1 can therefore pick up the vibrations thereof and translate them into an electrical signal.

Dans le mode de réalisation de la figure 3, le capteur comporte deux éléments sensibles 1 associés respectivement à deux plaques identiques 6, 7 coiffant les extrémités opposées d'un manchon 8 dont la paroi latérale est traversée par de nombreux orifices 11. L'intérieur du manchon 8 est rempli d'un matériau amortisseur analogue, une subtance fibreuse ou bien encore une substance poreuse susceptible de s'imprégner du fluide pénétrant dans le manchon par les ouvertures 11. De la même façon ce matériau amortisseur a pour effet de soustraire les faces intérieures des deux plaques 6, 7 à la pression statique du milieu. Les deux éléments sensibles sont interconnectés électriquement (par des conducteurs non représentés) comme il est bien connu pour réaliser une compensation électrique des accélérations.In the embodiment of FIG. 3, the sensor comprises two sensitive elements 1 associated respectively with two identical plates 6, 7 covering the opposite ends of a sleeve 8 whose side wall is crossed by numerous orifices 11. The interior of the sleeve 8 is filled with a similar damping material, a fibrous substance or even a porous substance capable of being impregnated with the fluid penetrating into the sleeve through the openings 11. In the same way this damping material has the effect of removing the inner faces of the two plates 6, 7 at the static pressure of the medium. The two sensitive elements are electrically interconnected (by conductors not shown) as is well known for achieving electrical compensation for accelerations.

On peut encore utiliser comme matériau amortisseur une substance composite du type dit syntactique.It is also possible to use as a damping material a composite substance of the so-called syntactic type.

Suivant le mode de réalisation de la figure 4, les deux plaques flexibles à rebord 6, 7 coiffent les extrémités d'un manchon constitué d'une portion de tube grillagé 12. L'intérieur est rempli d'un matériau amortisseur fibreux ou poreux comme précédemment ou bien encore de particules ou billes de verre 13 de quelques millimètres de diamètre. Ces billes peuvent être prises dans un liant 14 tel qu'une résine époxy. L'impédance acoustique du verre est très différente de celle de la résine de liage. En raison de la densité élevée de billes qu'il contient et donc d'interfaces verre/époxy, le matériau composite a pour effet d'absorber les ondes acoustiques variables du côté de la face intérieure des plaques 6, 7. Les variations de la pression statique extérieure sont cependant transmises aux faces internes de ces mêmes plaques 6, 7. Avec ce mode de réalisation aussi, le capteur est apte à fonctionner quelle que soit la pression statique du milieu extérieur. Les billes ou grains peuvent être réalisés d'une façon générale à partir de toute matière solide dont l'impédance acoustique est différente de celle du matériau intersticiel.According to the embodiment of FIG. 4, the two flexible rim plates 6, 7 cover the ends of a sleeve made up of a portion of screened tube 12. The interior is filled with a fibrous or porous damping material such as previously or even particles or glass beads 13 a few millimeters in diameter. These balls can be taken in a binder 14 such as an epoxy resin. The acoustic impedance of glass is very different from that of bonding resin. Because of the high density of beads it contains and therefore of glass / epoxy interfaces, the composite material has the effect of absorbing the variable acoustic waves on the side of the internal face of the plates 6, 7. The variations in external static pressure are however transmitted to the internal faces of these same plates 6, 7. With this embodiment also, the sensor is able to operate whatever the static pressure of the external medium. The balls or grains can be produced generally from any solid material whose acoustic impedance is different from that of the interstitial material.

Suivant une variante, la substance intersticielle entre les billes peut être remplacée par le fluide où le capteur est placé.According to a variant, the interstitial substance between the balls can be replaced by the fluid where the sensor is placed.

Dans le mode de réalisation de la figure 5, le matériau amortisseur a une cohésion suffisante pour être découpé en un bloc 15. Chaque plaque-support 6, 7 est plaquée directement contre une face du bloc 15 de manière que sa face intérieure soit soustraite aux variations de pression dynamiques qui sont absorbées par le matériau.In the embodiment of FIG. 5, the damping material has sufficient cohesion to be cut into a block 15. Each support plate 6, 7 is pressed directly against one face of the block 15 so that its inner face is removed from the dynamic pressure variations which are absorbed by the material.

Des capteurs, selon l'un des modes de réalisation des figures 2 à 5, peuvent être inclus dans une flûte sismique marine 16. Celle-ci comporte généralement une gaine souple 17 de grande longueur remplie d'huile ou de kérosène par exemple tout au long de laquelle sont répartis un grand nombre de capteurs de pression 18. Du fait des ouvertures pratiquées dans chaque manchon 8, le matériau amortisseur quand il est fibreux ou poreux, s'imprègne du liquide remplissant la flûte 16. Les variations de la pression extérieure, qu'elles soient statiques ou dynamiques, sont transmises au liquide intérieur au travers de la gaine 17. Mais là encore seules les variations dynamiques de la pression sont mesurées par chaque élément sensible.Sensors, according to one of the embodiments of FIGS. 2 to 5, can be included in a marine seismic flute 16. This generally comprises a flexible sheath 17 of great length filled with oil or kerosene for example at all along which are distributed a large number of pressure sensors 18. Due to the openings made in each sleeve 8, the damping material when it is fibrous or porous, is impregnated with the liquid filling the flute 16. The variations in the external pressure, which they are static or dynamic, are transmitted to the internal liquid through the sheath 17. But here again only the dynamic variations of the pressure are measured by each sensitive element.

Dans les différents modes de réalisation décrits, le fluide où le capteur est placé peut être utilisé comme fluide intersticiel (cas des billes de verre) ou comme fluide d'imprégnation (cas des matériaux poreux ou fibreux). Le fluide peut être de l'eau si le capteur est utilisé tel quel comme hydrophone. On note cependant que l'effet d'amortissement des signaux acoustiques est meilleur quand le liquide est visqueux. C'est le cas du liquide remplissant généralement les flûtes sismiques.In the various embodiments described, the fluid where the sensor is placed can be used as interstitial fluid (case of glass beads) or as impregnation fluid (case of porous or fibrous materials). The fluid can be water if the sensor is used as such as a hydrophone. It is noted however that the damping effect of the acoustic signals is better when the liquid is viscous. This is the case of the liquid generally filling the seismic streamers.

On ne sortirait pas du cadre de l'invention en isolant le boîtier du capteur du milieu extérieur. Le fluide à l'intérieur de celui-ci est alors maintenu en équi-pression statique avec le milieu extérieur par des moyens d'équilibrage. Ce fluide peut dans ce cas être choisi en fonction de ses propriétés physiques pour constituer avec le milieu amortisseur un absorbant acoustique optimal.It would not go beyond the scope of the invention to isolate the sensor housing from the outside environment. The fluid inside the latter is then maintained in static equi-pressure with the external medium by balancing means. This fluid can in this case be chosen according to its physical properties to constitute, with the damping medium, an optimal acoustic absorbent.

On ne sortirait pas non plus du cadre de l'invention en remplaçant les boîtiers pourvus d'ouvertures représentés aux figures 2 à 4 par exemple, par des boîtiers réalisés en un matériau fritté qui a la propriété d'être transparent aux variations de pression statique. Un matériau convenable peut être obtenu par exemple en comprimant ensemble fortement des petites billes. Sa granulosité dépend de la taille de celles-ci. Dans certains cas et dans certaines bandes de fréquence au moins, un boîtier en matériau fritté a aussi pour effet d'atténuer les variations de pression dynamique. Il peut être utilisé seul ou en combinaison avec un absorbant acoustique tel que ceux précédemment définis, pour absorber les variations dynamiques qui pourraient se transmettre à l'intérieur.It would also not go beyond the scope of the invention to replace the boxes provided with openings shown in FIGS. 2 to 4 for example, by boxes made of a sintered material which has the property of being transparent to variations in static pressure . A suitable material can be obtained, for example, by strongly compressing small beads. Its granularity depends on the size of these. In certain cases and in at least certain frequency bands, a sintered material casing also has the effect of attenuating variations in dynamic pressure. It can be used alone or in combination with an acoustic absorbent such as those previously defined, to absorb dynamic variations which could be transmitted inside.

Claims (14)

1. - Capteur de signaux insensible aux variations de la pression statique régnant dans un milieu où il est placé, comportant au moins une plaque (6, 7) dont la partie centrale est flexible, un élément sensible (1) en forme de disque fixé contre une première face de ladite plaque et des moyens de filtrage pour soustraire la face opposée de chaque plaque aux variations dynamiques de la pression du milieu, caractérisé en ce que les moyens de filtrage comportent un volume (10) d'un matériau absorbant sensiblement incompressible adapté à transmettre à ladite face opposée les variations de la pression statique du milieu.1. - Signal sensor insensitive to variations in the static pressure prevailing in a medium in which it is placed, comprising at least one plate (6, 7) whose central part is flexible, a sensitive element (1) in the form of a fixed disc against a first face of said plate and filtering means for subtracting the opposite face of each plate from dynamic variations in the pressure of the medium, characterized in that the filtering means comprise a volume (10) of a substantially incompressible absorbent material adapted to transmit to said opposite face variations in the static pressure of the medium. 2. - Capteur de pression selon la revendication 1, caractérisé en ce que le volume (10) de matériau absorbant sensiblement incompressible est contenu dans un boîtier rigide (8, 12) ouvert sur ledit milieu.2. - Pressure sensor according to claim 1, characterized in that the volume (10) of substantially incompressible absorbent material is contained in a rigid housing (8, 12) open on said medium. 3. - Capteur de pression selon la revendication 1 ou 2, caractérisé en ce que le volume (10) de matériau absorbant sensiblement incompressible est réalisé à partir de fibres réalisées dans un matériau rigide.3. - Pressure sensor according to claim 1 or 2, characterized in that the volume (10) of substantially incompressible absorbent material is made from fibers made of a rigid material. 4. - Capteur de pression selon la revendication 1 ou 2, caractérisé en ce que le volume (10) de matériau absorbant sensiblement incompressible est réalisé à partir d'une substance poreuse.4. - Pressure sensor according to claim 1 or 2, characterized in that the volume (10) of substantially incompressible absorbent material is made from a porous substance. 5. - Capteur de pression selon la revendication 1 ou 2, caractérisé en ce que le volume de matériau absorbant sensiblement incompressible est réalisé à partir d'une substance syntactique.5. - Pressure sensor according to claim 1 or 2, characterized in that the volume of substantially incompressible absorbent material is made from a syntactic substance. 6. - Capteur de pression selon la revendication 5, caractérisé en ce que le volume de matériau absorbant sensiblement incompressible est réalisé à partir de particules (13) d'une substance solide associée à un matériau intersticiel.6. - Pressure sensor according to claim 5, characterized in that the volume of substantially incompressible absorbent material is produced from particles (13) of a solid substance associated with an interstitial material. 7. - Capteur de pression selon la revendication 1, caractérisé en ce qu'il comporte au moins une paire de plaques flexibles (6, 7) pourvues chacune d'un élément sensible (1) et un volume de matériau absorbant sensiblement incompressible pour soustraire la face opposée de chacune des plaques (6, 7) aux variations dynamiques de la pression dans le milieu.7. - pressure sensor according to claim 1, characterized in that it comprises at least one pair of plates hoses (6, 7) each provided with a sensitive element (1) and a volume of absorbent material which is substantially incompressible to subtract the opposite face of each of the plates (6, 7) from dynamic variations in the pressure in the medium. 8. - Capteur de pression selon la revendication 7, caractérisé en ce que les deux plaques flexibles (6, 7) sont des parois d'un boîtier commun (8, 12) contenant ledit volume de matériau absorbant sensiblement incompressible et pourvu d'ouvertures.8. - pressure sensor according to claim 7, characterized in that the two flexible plates (6, 7) are walls of a common housing (8, 12) containing said volume of absorbent material substantially incompressible and provided with openings . 9. - Capteur de pression selon la revendication 8, caractérisé en ce que le boîtier commun comporte au moins une partie grillagée (17).9. - pressure sensor according to claim 8, characterized in that the common housing comprises at least one screen portion (17). 10. - Capteur de pression selon la revendication 7, caractérisé en ce que ledit boîtier (12) est rempli de particules (13) en matière solide noyées dans un liquide.10. - Pressure sensor according to claim 7, characterized in that said housing (12) is filled with particles (13) of solid material embedded in a liquid. 11. - Capteur de pression selon la revendication 1 ou 7, caractérisé en ce que le volume de matériau absorbant sensiblement incompressible est un bloc (15) en équi-pression avec la pression statique du milieu, chaque plaque étant disposée contre une face dudit bloc.11. - Pressure sensor according to claim 1 or 7, characterized in that the volume of substantially incompressible absorbent material is a block (15) in equi-pressure with the static pressure of the medium, each plate being disposed against one face of said block . 12. - Capteur de pression selon la revendication 11, caractérisé en ce que ledit bloc est réalisé en noyant des particules de verre dans un matériau d'enrobage.12. - Pressure sensor according to claim 11, characterized in that said block is made by embedding glass particles in a coating material. 13. - Capteur de pression selon la revendication 1, caractérisé en ce que les moyens de filtrage comportent un boîtier réalisé en un matériau fritté.13. - Pressure sensor according to claim 1, characterized in that the filtering means comprise a housing made of a sintered material. 14. - Capteur de pression selon la revendication 2, caractérisé en ce que le boitier rigide est disposé à l'intérieur d'une flûte sismique.14. - Pressure sensor according to claim 2, characterized in that the rigid case is arranged inside a seismic flute.
EP89403518A 1988-12-23 1989-12-15 Signal receiver insensitive to static pressure variations Expired - Lifetime EP0378021B1 (en)

Applications Claiming Priority (2)

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FR8817205 1988-12-23
FR8817205A FR2641155B1 (en) 1988-12-23 1988-12-23

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EP (1) EP0378021B1 (en)
JP (1) JPH02224598A (en)
CN (1) CN1019444B (en)
CA (1) CA2006565A1 (en)
DE (1) DE68902311T2 (en)
FR (1) FR2641155B1 (en)
NO (1) NO174490C (en)

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Also Published As

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FR2641155A1 (en) 1990-06-29
CN1019444B (en) 1992-12-09
US4996675A (en) 1991-02-26
NO174490C (en) 1994-05-11
EP0378021B1 (en) 1992-07-29
CN1043845A (en) 1990-07-11
CA2006565A1 (en) 1990-06-23
NO174490B (en) 1994-01-31
FR2641155B1 (en) 1994-06-03
NO895169D0 (en) 1989-12-21
DE68902311D1 (en) 1992-09-03
JPH02224598A (en) 1990-09-06
NO895169L (en) 1990-06-25
DE68902311T2 (en) 1993-02-18

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