FR2733838A1 - SUBMARINE ACOUSTIC TRANSMITTER - Google Patents

Abstract

The invention relates to an underwater acoustic transmitter. In this transmitter comprising a hollow towed body (10) attached to a cable (12) and containing a transmitting antenna (16) formed of several electroacoustic transducers (17) arranged so as to emit acoustic signals on both sides of the longitudinal axis (19) of the body (10), the transducers (17) are superimposed, and acoustic reflectors (20) are associated with these transducers at a certain radial distance laterally in the body (10) being located to the left and to the right of the longitudinal axis (19). Application in particular to towed submarine sonar systems.

Description

The invention relates to a sub-acoustic transmitter

  marine for a sonar towing system, comprising a hollow towed body, attached to a towing cable and preferably having stabilizing elements, and a transmitting antenna integrated into the towed body and consisting of a plurality of electroacoustic transducers, which are spaced from each other and have an omnidirectional characteristic, which antenna is shaped and controlled so that it transmits acoustic emission signals separately on both sides of the axis

  length of the towed body, which coincides with the direc-

towing.

  Such sonar towing systems, which consist of a towed submarine transmitter and a towed antenna in the form of a hose and equipped with a hydrophone (known as "Towed").

  Array ", ie towed together) as a receiver

  for this reason are designated as two-carrier sonar towing systems, one for the transmitting part and the other for the receiving part of the

  sonar, are used for sub-tracking tasks.

  marine. Since the transmission transducers have

  As an omnidirectional characteristic, the emission signal is therefore emitted in both transverse directions with respect to the towing direction, the receiver can in general determine, only from the received echo signals, the direction of tracking and the distance to a target, but without additional provisions, no indication can be obtained

  the fact that the target is located on the port or starboard side.

  This is why it has already been proposed to arrange and control the transmitter antenna of the acoustic transmitter

  submarine so that it alternately emits an im-

  transmission pulse exclusively to the right (starboard) and then an emission pulse exclusively on the left (port), the transmission frequency of emission pulses transmitted to starboard and port may still be

  different. So, on the basis of the amplitude and eventual

  the frequency of the echo signals received, the reception

  is able to distinguish whether the target triggering the

  echo signals are located to starboard or port.

  An emission antenna used for this purpose

  carries two electroacoustic transducers, which are

  placed at the transverse distance of λ / 4 symmetrically with respect to the longitudinal axis of the towed body (λ = length

  waveform of the transmission signal). For the issuing of an impulse

  acoustic transmission on either starboard or port side, the two transduc-

  transmitters are supplied with an electrical transmit signal, in which case in the case of the "starboard" transmit direction, the starboard transducer is controlled by a shifted X / 4 transmit signal and, in the case of the "starboard" transmit direction, the case of the direction of emission "port", the electroacoustic transducer located at the port is controlled with a

  emission signal out of phase of λ / 4. To get a focus

  vertically, one can also superimpose vertically on

  each transducer of other identical transducers.

  Since there are always two additional transducers

  are identical, a transmitting antenna having a direction

  sufficiently good vertical space contains a multiplicity of transducers and electronic components, which are necessary for the control of the transducers, which

  rapidly increases the costs of manufacturing

  underwater sound transmitter.

  The object of the invention is to create an underwater acoustic transmitter having emission directions

  left / right and a vertical directivity sufficient

  of the transmitting antenna, which uses only a minimum number of electroacoustic transducers and

  therefore involves relative manufacturing costs

  low and has a low tow weight.

  The problem is solved according to the invention in an underwater acoustic transmitter of the type indicated above, thanks to the fact that the transducers are arranged exclusively vertically above each other, an acoustic reflector is associated with each transducer -

  the acoustic reflectors are arranged laterally.

  in the towed body at a certain distance from

  of the associated transducer so that

  acoustic reflectors associated with successful transducers

  cessives are alternately left and right

  of the longitudinal axis of the towed body.

  The underwater acoustic transmitter according to the invention

  has the advantage that each

  half of the transducers emit from one side and the other half from the transducers on the other side

  towing direction of the acoustic transmitters under

  sailors. However, due to the presence of acoustic reflectors, an acoustic pressure is radiated in

  each direction of transmission, as if all transmissions

  issuers participated in the issuing operation.

  Compared to the acoustic transmitters described above, having a right / left emission device, for a

  same sound pressure radiation and the same

  vertical directivity, only the me-

  electroacoustic transducers is required.

  This means significant savings in terms of manufacturing costs and contributes to a significant reduction in weight, due to the reduction, which is related to the reduction in the number of transducers,

  necessary components for the control of the transducers.

  According to another preferred embodiment of the invention, the radial distance of the acoustic reflector

  relative to the associated transducer is approximately equal

  at A / 2, in the case where the acoustic reflector is made with a strong acoustic reflecting power, and

  is approximately equal to λ / 4 in the case where the reflection

  acoustic transducer is made with low acoustic reflectance, λ being the wavelength of the signal

  resignation. Since in the case of a wall

  sound acoustic reflection, the acoustic pressure of the reflecting wave has the same absolute value and

  the same sign as the acoustic pressure of the incident wave

  dente and that, in the case of a wall performing a weak acoustic reflection, the acoustic pressure of the reflecting wave has the same absolute value as the acoustic pressure of the incident waves, but the opposite sign, in both cases we obtain a superposition in phase of the acoustic signal delivered by the transducer and the acoustic signal reflected by the acoustic reflector,

  so that the acoustic amplitude emitted by the transduc-

  in the transmission direction is doubled.

  In accordance with a preferred embodiment

  of the invention, the vertical distance of the transducers

  is between approximately A / 4 and X / 2, where A is the wavelength of the transmit signal. For such a distance, the transducers associated with a transmission direction respectively provide a good directivity

  of the transmitting antenna, which corresponds approximately

  to the vertical directivity of the antenna

  transmitters uniformly equipped with transducers.

  According to a preferred embodiment of the invention, for a corresponding configuration of the towed body, the acoustic reflectors are formed directly on the inner wall of the hull of the towed body or are formed by the hull itself of the towed body, when the wall structure of this shell is shaped correspondingly. The surface elements, which are respectively opposed to the acoustic reflector, of the shell of the towed body are transparent from the point

  acoustically, that is to say that they possess a

  wall dance, which corresponds to the characteristic impedance

tick of the middle, namely water.

  According to another characteristic of the invention, a separation layer producing a good acoustic reflection is arranged between the transducers which are

  superimposed at a certain vertical distance.

  According to another characteristic of the invention, the front faces of the two external transducers in the transmitting antenna are covered respectively by a same layer producing a good acoustic reflection and which

  is located at the same distance from the frontal surface

  transducers, as the separation layers. We

  will then understand that the layers covering the frontier faces

  Both transducers are of the same nature.

  According to another characteristic of the invention,

  the acoustic reflectors are formed on the inner wall

  the hull of the towed body or in the hull itself.

  even. According to another characteristic of the invention, the transducers used are transducers

broadband ring.

  Other features and advantages of the pre-

  invention will emerge from the description given below.

  after making reference to the accompanying drawings, on

  which: - Figure 1 shows a perspective view of an underwater acoustic transmitter; FIG. 2 represents a simplified longitudinal section of the underwater acoustic transmitter of FIG. 1; and - Figure 3 shows a section taken following

line III-III in Figure 2.

  The underwater acoustic transmitter, which is

  diagrammatically in the perspective view of FIG. 1, has, in known manner, a hollow towed body comprising a dimensionally stable shell 101, which is formed in such a way as to promote the flow and is fixed by means of a hook of towing 11 in the form of fork to a pulling cable 12. The pulling cable 12 is fixed, on board a ship not shown here, to a winch, by means of which the underwater acoustic transmitter can be mounted on board and can be handed back to

  the water. In transmission operation, the acoustic transmitter

  tick is pulled by the traction cable 12 behind the boat, the towing direction being characterized by the arrow 13 in Figures 1 and 3. To maintain the vertical position, shown in Figure 1, the body of the acoustic transmitter during the towing operation, on the one hand the towing hook 11 is hinged in an articulated manner on both sides of the towed body 10, the hinge pins being oriented transversely with respect to the towing direction 13, and on the other hand the towed body 10 is equipped with stabilizing elements 14, 15. The stabilizing elements 14, 15 can also be arranged in the form of an adjustment unit of

  depth, which allows the depth of the trailer to be

  sound transmitter, within certain limits.

  The longitudinal axis of the towed body 10 is designated by the reference 19 which coincides with the towing direction

13 of the towed body 10.

  In the hollow towed body 10 filled with water is integrated a transmitting antenna 16, which consists of several, here four, electroacoustic transducers 17

  superimposed vertically at a distance from each other.

  Each transducer 17 has an omnidirectional characteristic

  -directional. The axes, designated 18, superimposed transducers 17 are reciprocally aligned. The power supply of the transmitting antenna 16 and the transmission of signals to the boat are effected by means of an underwater electrical cable 23 which extends inside the towing cable 12 Each transducer 17 is associated with an acoustic reflector 20, which is arranged at a

  some radial distance laterally in the tow body

  10. The layout is such that the acoustic reflectors

  20 associated with successive transducers 17 are

  alternatively left and right of the longitudinal axis

  tudinal 19 of the towed body 10. Each acoustic reflector

  tick 20 is made in order to achieve a good

  acoustic reflection or low acoustic reflection.

  A good acoustic reflection is obtained by means of a laminated structure of the acoustic reflector 20, in which a layer of foam is placed between two metal sheets. The sheet metal should have such a mass per unit area (M), that w.M times is equal to the characteristic acoustic impedance p.c of water. A low acoustic reflection is obtained in the case of a laminated structure of the reflector 20, which is constituted by a foam facing the transducer 17, and a steel sheet or a metal sheet. The distance between the acoustic reflector 20 and the center of the transducer 17

  is chosen equal to λ / 2 in the case of an acoustic reflector

  tick performing a good acoustic reflection and X / 4 in the case of a acoustic reflector 20 performing a low acoustic reflection, A being the wavelength of the transmission signal, which is combined with the emission frequency f and

  at the speed of sound c in water, by the relation A = c / f.

  The reciprocal vertical distance of the transducers 17 is

between A / 4 and A / 2.

  As is schematically indicated in FIG. 2, while this is not shown in FIG. 1 in order to preserve its clarity, between the transducers 17 superimposed at a certain vertical distance are arranged respective separation layers 21 that perform a good reflection. acoustic. The end faces of the two outer transducers 17, that is to say the highest transducer 17 and the lowest transducer 17, are

  covered respectively by the same layer 22, which is

  reads a good acoustic reflection. The distance of these layers 22 from the front face of the outermost transducers 17 is chosen equal to the distance of the

  separation layers 21 with respect to each of the transducers

17 neighbors.

  The acoustic reflectors 20 are attached to the hull (101) of the towed body 10 (Figure 1). As shown in FIG. 3, for an adequate form of

  towed body 10, the reflectors are preferably

  directly on the inner wall of the hull 101 of the

  10. However, thanks to a strati-

  of the hull 101 of the towed body 10 in the zone of the reflectors, the acoustic reflector 20 may be

  also formed of parts of the hull 101 of the tow body

  only 10 himself. If the hull 101 of the towed body 10 is not constructed so as to be generally acoustically transparent, the wall elements of the hull 101, which are located vis-à-vis the reflectors

  20, in a manner related to the longitudinal axis

  19 of the towed body 10, must be arranged so that their wall impedance is equal to

  the characteristic impedance of the medium, formed by water.

  This window called transmission window 102 is marked on

  Figure 3 by lines formed dashes.

  As electroacoustic transducers 17, wide ring transducers are preferably used.

  gang. The electrical control of the transducers 17 is effected

  so that the transducers 17, whose acoustic reflectors 20 are located on the same side of the longitudinal axis 19 of the towed body 10, are powered

  simultaneously with an electrical transmission signal.

  The transmitting antenna 16, which preferably works in the low frequency range, therefore transmits

  acoustic signals only in a direction

  transverse to the longitudinal axis 19. In the following emission interval, the other transducers

  17, the associated acoustic reflectors 20 are dis-

  placed on the other side of the longitudinal axis 19 of the towed body 10, are triggered so as to emit acoustic emission signals. The transmitting antenna transmits

  then in the opposite direction transversely

  port to the longitudinal axis 19 of the towed body 10 or by

  report to towing direction 13.

Claims (7)

  1. Underwater acoustic transmitter for a sonar towing system, comprising a towed body   recess (10), attached to a towing cable (12) and   preferably carrying stabilizing elements (14, 15), and a transmitting antenna (16) integrated in the towed body (10) and consisting of a plurality of electroacoustic transducers (17), which are spaced apart from each other.   others and have an omnidirectional   an antenna which is shaped and controlled so that it transmits acoustic emission signals separately on both sides of the longitudinal axis (19) of the towed body (10) which coincides with the towing direction (13) , characterized in that the transducers (17) are arranged exclusively vertically above each other, an acoustic reflector (20) is associated with each transducer (17) and the acoustic reflectors (20) are arranged laterally in each other. the towed body (10) at a certain radial distance from the associated transducer (17)   such that acoustic reflectors (20)   successive transducers (17) are arranged alternately to the left and to the right of the longitudinal axis. (19) of the towed body (10).   Acoustic transmitter according to claim 1, characterized in that the radial distance of the acoustic reflector (20) from the associated transducer (17)   is approximately equal to λ / 2, in the case where the reflection   acoustic transmitter (20) is realized with a reflective   acoustically strong, and is approximately equal to λ / 4 in the case where the acoustic reflector (20) is made with a low acoustic reflectance, λ being the   wavelength of the transmission signal.   Acoustic transmitter according to claim 1 or 2, characterized in that the vertical distance of the transducers (17) is approximately between λ / 4   and λ / 2, λ being the wavelength of the transmit signal.   4. Acoustic transmitter according to any one of   Claims 1 to 3, characterized in that a layer of   separation (21) providing a good acoustic reflection is arranged between the transducers (17) which are super-   at a certain vertical distance.   Acoustic transmitter according to Claim 4,   characterized in that the front faces of the two trans-   external conductors (17) in the transmitting antenna (16) are respectively covered by a same layer (22) producing a good acoustic reflection and which is located at the same distance from the associated frontal surface of the   transducers, only the separation layers (21).   6. Acoustic transmitter according to any one of   Claims 1 to 5, characterized in that the reflectors   acoustic (20) are formed on the inner wall of the hull (101) of the towed body (20) or in the hull (101) itself. 7. Acoustic transmitter according to any one of   Claims 1 to 6, characterized in that   transducers (17), ring-shaped transducers broadband.