FR2681495A1 - OPTICAL FIBER TRANSDUCER FOR USE IN THE CONSTITUTION OF A GROUP OF HYDROPHONES. - Google Patents

Abstract

A large-area hydrophone is described using an optical fiber as the detecting medium, the hydrophone consisting of four small coils (4) of fiber (4A) joined together in series, each coil being wound on a mandrel and the whole assembly. the whole being encapsulated in a suitable material (6), for example polyurethane.

Description

The present invention relates to transducers (e.g.

  hydrophones) and relates more particularly to

  fiber optic transducers, which are part of a group.

  Large hydrophone groups are needed

  sit large numbers of separate transducers.

  Large range hydrophones are currently used

  or are offered for sonar systems, for which

  large, filled openings are required which require good rejection

  tion at high acoustic wave numbers for elimination of

flow noise.

  Fiber optic transducers for use

  read in hydrophones are revealed for example in British patent application No. 2 126 820 A, having the same applicant as La

this request.

  The invention aims to produce a transducer element which

  can be used in a grouping While the British document

  pic 2 126 820 A mainly deals with the case of multi-

  the invention aims to produce an element which can be used

  read in any system, whether multiplexed or not.

  The invention provides a transducer comprising several coils of optical fiber optically connected so as to form a single path for the light and encapsulated together inside.

of solid material.

  It offers a transducer element offering a rejection

  improved at high acoustic wave numbers.

  The following description, intended as an illustration of

  the invention aims to give a better understanding of its par-

  features and benefits; it is based on the accompanying drawings, in which: FIG. 1 shows a known transducer element;

  FIG. 2 shows a grouping of transducer elements

  teurs; Figure 3 shows a first transducer element according to the invention; and Figure 4 shows a second transducer element according to the invention. In FIG. 1, a known type of optical fiber pressure sensor element is shown. This comprises a reel of optical fiber 1 encapsulated with a wrapping material 2, for example an epoxy resin If the sensor must be incorporated in a group of hydrophones, we can add

  an additional amount of encapsulating material to insert

  pitch the spool so that it is "off" and form a square 3 of square shape Optical signals can enter the spool along the free end 1 A of the optical fiber 1, and exit the spool according to the free end l B of the optical fiber 1 As is well known, such a sensor operates on the basis of variations in sound pressure modifying the optical path length of the optical fiber and therefore varying the

  time it takes for light to pass through the coil.

  Such a sensor element can be produced by winding the optical fiber on a mandrel, then removing the mandrel and

  encapsulating the coil in epoxy resin.

  While we can form a group of hydrophones using several of these sensor elements linked in series optically, it gives poor rejection for the numbers

high acoustic wave.

  A typical grouping of sensor elements 3 of the type

  hydrophone is shown in Figure 2, where we see that more

  several sensor elements 3 are towed by a ship 14 on a floating cable 15 To reduce the load exerted on the cable 15, the hydrophones 3 are constructed so that they float in a balanced manner The cable 15 carries an optical fiber cable which links all the coils 1 while fixing the sensor elements 3 to the

  ship 14 We understood that it was possible to improve the rejection

  tion of the flow noise by a pressure sensor element by replacing the single coil with several co-planar coils more

  small, as shown in Figure 3.

  Four coils are arranged in a coplanar group

  nary having their axes of symmetry 4 E parallel and forming a single sensor element The coils 4 are arranged in a square assembly lying in a plane perpendicular to their axes of symmetry 4 E Each coil 4 consists of a wound optical fiber 4 A which is encapsulated using an epoxy resin 4 B Naturally, one could use, in place of the epoxy resin, other suitable encapsulation materials. The four coils 4 are all connected to a connection box 5 by the

  free ends of their respective 4 A wound optical fibers.

  The free end 4 C of one of the coiled optical fibers 4 A located in one of the coils 4 plays the role of the optical input of the sensor element, and the free end 4 D of the optical fiber wound 4 A located in another of the coils 4 plays the role of

  The optical output of the sensor element.

  The four coils 4, the connection box 5 and the

  the free ends of the fibers are all encapsulated in a material

  appropriate line 6 so as to form a square-shaped square 7.

  The ends of the inlet 4 C and outlet 4 D fibers are each covered by a shielding layer 8 serving to protect them, and the ends 8 A of this shielding 8 are also

  encapsulated by the elastomeric material 6.

  The connection box 5 contains couplers allowing

  both to link the four coils 4 in series optically in series and allows any stress exerted on the pane 6 to be relaxed without placing stress on the optical fibers 4 A thanks to the possibility of a relative movement of the fibers 4 A and of a

  reflective connection as described in the British application

  pic 2 126 820 A Alternatively, the reflective connection could be placed outside the structure shown. It has also been understood that another method of improving the rejection of flow noise would consist in replacing the single coil by several parallel coils, as shown

in figure 4.

  The four coils 10 are all formed by a single optical fiber 10 C which connects them according to a single optical structure and has a first free end 10 D forming an optical input line and a second free end 10 E forming an optical output line , these two free ends 10 D and 10 E being protected by shielded sheaths 11 The coils 10 and the sheath 11 are encapsulated in a material 12 compatible with the point

  acoustically, so as to form a square 13 of square shape

  rée. Whereas, in The two examples, four

  coils, it would be possible to use any other number.

  The coils of Example 4 can be formed by winding

  an optical fiber on a single mandrel, then cutting the man-

  drin so as to produce four separate coils linked by a

single fiber.

  The use or non-use of a gearbox

  cording is an option whose desirability depends on the application for which the hydrophone is to be used, so that the example in Figure 4 could use separate coils connected by a junction box, in the same way as the example of FIG. 3 could be formed by a single continuous fiber formed by winding an optical fiber on a

mandrel, as above described.

  In this case, the chucks could be left at

  inside the coils and be encapsulated with it.

  The systems shown are of the transmission type with separate input and output fibers, but the invention could equally well be applied to systems of the reflection type having

  a single fiber for entry and exit.

  In all cases, the encapsulation material forming the square tiles 13 must have an internal stiffness making it possible to ensure that all the resonance frequencies of the structure are outside the working band of the hydrophone system. Of course, those skilled in the art will be able to imagine,

  from the device whose description has just been given to

  title merely illustrative and not limiting, various

  variants and modifications not departing from the scope of the invention.

Claims (5)

  1 Transducer characterized in that it comprises more   several coils (4; 10) of optical fiber (4 A; 10 C) linked optically so as to form a single path for the light   and encapsulated together with a solid material (6; 12).   2 transducer according to claim 1, characterized in that the coils are cylindrical and have parallel axes of symmetry.   3 transducer according to claim I or 2, character-   risé in that the coils (4) are arranged so as to form a group lying in a plane perpendicular to their axes of symmetry.   4 transducer according to claim 1 or 2, character-   laughed in that the coils (10) are arranged so that their   axes of symmetry are coplanar.   Transducer according to any one of the claims   1 to 4, where there are four transducers.   6 Transducer according to any one of the claims.   1 to 5, characterized in that all the coils are formed   and linked by a single continuous optical fiber.