FR2651082A1 - LARGE TRANSMITTER-SUBMARINE BAND - Google Patents

Abstract

The transmitter comprises a first electro-acoustic transducer 1 in the form of a hollow circular cylinder, and a second electro-acoustic transducer 2 in the form of a sphere, of radius r at most equal to the radius R of the cylinder, and centered on the axis 12 of it. The distance D between the cylinder and the sphere is of the order of magnitude of the radius R of the cylinder. Each transducer 1, 2 is excited by an independent noise generator. The two noise generators are comparable but decorrelated. The emitter thus obtained produces, in an underwater environment, acoustic radiation having, in a wide frequency band, the spectral characteristics of noise. Such a transmitter can in particular be used as a decoy to deceive underwater acoustic wave detectors.

Description

The present invention relates to a transmitter intended to produce, in

  underwater environment, an acoustic radiation having the spectral characteristics of a noise, and comprising at least one electroacoustic transducer and at least one noise generator for exciting said transducer. Such emitters are used as decoys to deceive underwater acoustic wave detectors for determining the position of a tactical submarine, for example. They can also be used for

  calibration and sonar testing.

  Transmitters of the type defined above are already known, equipped with a single transducer, for example having the

  shape of a hollow cylinder, or the shape of a sphere.

  Such a transducer has the disadvantage of having a limited bandwidth. As a result, the radiation produced by the transmitter is also of limited spectrum, which

  affects its performance as a decoy, for example.

  Indeed, a decoy is all the more effective as it covers

a broad spectrum.

  To obtain a broad-spectrum transmitter, it is conceivable to use a set of several identical transducers of increasing size, each of them being responsible for covering a portion of the total spectrum to be covered. It is thus possible to use a set of several cylinders, or a set of several spheres. However, this leads to solutions that are cumbersome and difficult to implement, because of the number of transducers to be used, and because of their arrangement, which must avoid possible interactions and which must take into account the problems posed by the cables.

bringing the excitation signals.

  The present invention aims to overcome the above disadvantages by providing a transmitter covering a spectrum

2651O82

  2 - wide, and which remains relatively compact, that is to say

including a reasonable volume.

  For this purpose, it relates to an emitter of the type defined above, characterized in that it comprises a first transducer in the form of a hollow circular cylinder and a second transducer in the form of a sphere, of radius at most equal to the radius of said cylinder, centered on the axis of said cylinder, the distance between said cylinder and said sphere being at least of the order of magnitude of the radius of said

cylinder.

  In the transmitter of the invention, the cylindrical transducer covers the lower part of the total spectrum to be covered, while the spherical transducer covers the upper part. In addition, the appearance of the spectrum radiated by the cylinder and that of the spectrum radiated by the sphere are connected well. This makes it possible to easily obtain a total spectrum of decreasing general frequency depending on the frequency, which is well suited for use in underwater acoustics. In addition, the sphere and the cylinder having the same axis, the radiation pattern retains a symmetry of revolution. Finally, and surprisingly, the Applicant has found that the interactions between the two transducers remain tolerable over most of the spectrum since the distance between the two transducers is at least of the order of magnitude of the radius.

of the cylinder.

  Advantageously, the transmitter comprises a first noise generator for exciting said first transducer, and a second noise generator for exciting said second transducer, said first and second generators being decorrelated. In this case, interference in the overlapping frequency band is avoided. Indeed, given the fact that the spectra of each transducte: rs do not have abrupt flanks, it is necessary that they overlap, at least partially, to avoid a trough at the border between the two spectrums. However, if the two transducers are excited by means of a single noise generator, interference phenomena can occur in the overlapping frequency band, which is troublesome in some applications because they give rise to

  radiation cancellations in certain directions.

  The use of two decorrelated generators avoids these phenomena, because the instantaneous radiations of the two transducers are independent. In this case, they can not interfere with each other to add or cancel their effects, even if, by. elsewhere, both

generators are identical.

  Advantageously, the transmitter comprises a layer of acoustic radiation absorbing material, arranged

  between said first and said second transducers.

  In this case, the proximity phenomena related to the residual interaction between the two transducers are attenuated.

  for the lowest frequencies of the spectrum.

  According to one characteristic of the invention, the transmitter comprises first means for supporting said first transducer by its base opposite said second transducer and second means for supporting said second transducer by its pole closest to said first transducer, said second support means comprising a rod extending through said first

  transducer, and along its axis.

  Such an arrangement makes it possible in particular to adjust, in addition to the problem of the mechanical support of the transducers, that of the passage of the cables for supplying the excitation signals. Indeed, they can be arranged in the supports, without disturbing the perfect symmetry of revolution of the whole.

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  According to another characteristic of the invention, said first transducer is of height substantially equal to its radius, and said radius of said second transducer is

  just below said radius of said first transducer.

  The term "just below" means here that the ratio between the radius of the second transducer, that is to say the sphere, and that of the first transducer, that is to say the cylinder, is the order of 0.7 to 1. In this case, the spectrum covered by the decoy reaches several octaves, with a good connection of the upper part and the lower part. The present invention will be better understood on reading

  the following description of the preferred embodiment

  of the transmitter of the invention, with reference to the accompanying drawings, in which: - Figure 1 is a simplified view of the transmitter of the invention, and - Figure 2 shows an electrical block diagram of

the transmitter of the invention.

  Referring firstly to Figure 1, a broadband transmitter for underwater environment, here an active lure,

is now described.

  In a known manner, this decoy is intended to produce an acoustic radiation having the spectral characteristics of a noise. Here the covered spectrum extends over a few octaves and its rate is substantially decreasing as a function of the frequency, that is to say that the amplitude of the low frequency components is substantially higher than the amplitude of the components of

high frequency.

  The acoustic radiation is produced by two electroacoustic transducers 1 and 2, e cited by two noise generators contained in a housing 3, which

  supports both transducers 1 and 2.

  The housing 3 is here a circular cylinder of axis 12,

  arranged vertically in Figure 1.

  The first transducer I is in the shape of a hollow circular cylinder of radius R, with axis 12 also. One of its bases, in this case its lower base 14 in Figure 1, is supported by a spacer 13, here polyvinyl chloride, secured to the upper base, in the figure

1, of the housing 3.

  The first transducer 1 has here a height H substantially equal to its radius R. In known manner, the first transducer i comprises a ring of piezoelectric material, here and for example of a material of the type marketed by VERNITRON under the reference PZT 4 that is, titanate lead zirconate. Still in known manner, the cylindrical outer surface of the crown is coated with a metal layer forming a first electrode. The same is true for the cylindrical inner surface, which thus forms a second electrode. In normal operation, the first transducer 1 is immersed, and the water enters the cylinder, which transforms the excitation signal applied to it via the

  two electrodes in underwater acoustic radiation.

  The second transducer 2 is in the form of a sphere of radius E, centered on the axis 12, on the opposite side to that of the base 14. The radius r of the sphere is here just smaller than the radius P of the hollow cylinder, the ratio _ / R worth here

substantially 0.95.

* -. - 2651082

  A rod 23, vertical in FIG. 1, supports the second transducer 2 by its pale closest to the first transducer 1, in this case its lower pole 24 in FIG. 1. The rod 23 extends along of the axis 12, through the hollow cylinder of the first transducer 1, to the housing 3, which it is secured. The distance D between the hollow cylinder and the sphere, more precisely here the distance between the pale 24 and the upper base, in FIG. 1, of the hollow cylinder, is of the order of magnitude of the

radius R of the hollow cylinder.

  In known manner, the sphere of the second transducer 2 is hollow, and here made of the same material as the hollow cylinder of the first transducer 1. The outer surface of the sphere, and its inner surface are metallized. The outer and inner metallizations form the two electrodes. In normal operation, the second transducer 2 is immersed, but the water does not penetrate inside the sphere, which transforms into underwater acoustic radiation the excitation signal applied to it via the two electrodes . A layer 21 of acoustic radiation absorbing material, for example an absorbent foam, may optionally be disposed between the first 1 and the second transducer 2. The layer 21 is represented in

dotted in Figure 1.

  Referring now to FIG. 2, the electrical diagram

lure is now described.

  A first channel comprises, in cascade, a noise generator 10, a filtering and correction circuit 15, an amplifier 16, and an adaptation circuit 17. The output 39 of the matching circuit 17 is connected to the electrodes of the

first transducer 1.

  Similarly, a second chain, similar to the first chain, comprises, in cascade, a noise generator 20, a filtering and correction circuit 25, an amplifier 26, and an adaptation circuit 27. The output of FIG. adaptation circuit 27 is connected to the electrodes of the second transducer 2. In known manner, the matching circuits 17 and 27 are provided to perform the impedance matching between the transducers 1 and 2 and the amplifiers 16 and 26, respectively . Thus, the best possible transfer of power between the output of the amplifiers 16 is assured.

  and 26 and the input of the transducers 1 and 2.

  The circuits 15 and 25 for filtering and correction have the particular function of ensuring that, at any frequency, the amplitude of the emitted radiation is in accordance with what is desired. The circuits 15 and 25 correct, including in particular the irregularities in the frequency response of the amplifiers 16 and 26, in that of the matching circuits 17 and 27, and in that of the transducers i and 2. The two noise generators 10 and here are identical, but they are decorrelated. As a result, they deliver signals whose spectra are statistically identical,

  but whose instantaneous values are independent.

  The cables which make it possible to bring the excitation signals from the output of the circuits 17 and 27 to the transducers 1 and 2 are respectively disposed in the spacer 13 which supports the first transducer 1, and in the rod 23 which supports the second transducer 2, of

  way & do not disturb acoustic radiation.

  The decoy which has just been described produces, when immersed, a broad-spectrum acoustic radiation, the upper part of the spectrum being radiated by the sphere of the second transducer, and the lower part being radiated by the hollow cylinder. of the first transducer. Given the relative dimensions of the radius r of the sphere and the radius R of the hollow cylinder, the connection of the spectra is satisfactory. Because the noise generators 10 and 20 are decorrelated, there is no risk of interference in the border area. Similarly, the layer 21 avoids proximity phenomena at low frequency. Spectrum

  covered thus reaches several octaves.

  Naturally, it is within the abilities of those skilled in the art to determine the dimension of the radius r so that the upper boundary of the emitted spectrum has a determined value, then to determine the dimensions of the radius R, the height H and the distance D, which flow from it. Thus, the spectrum covered by the decoy, of a few octaves, can be arranged where it is desirable in the sound and ultra-sonorous soundtrack, which ranges from a few kilohertz to a few tens of kilohertz. Obviously, it is not imperative to choose the ratio r / R equal to the value 0.95 which has been given above as an advantageous example. In practice, we can choose other values. Thus, if the radius R is increased by keeping the radius r constant, the covered spectrum will widen towards the low frequencies, but there is a risk of a hollow in the connection zone between the two transducers. This can be tolerated or not depending on whether the amplitude of the radiation at

  transmitting in the connection band is critical or not.

  Naturally, in a practical case, a person skilled in the art is able to determine the optimum value of the ratio rE / R, which must however remain less than or equal to 1 so as to ensure that the upper part of the spectrum remains radiated by the sphere, and greater than substantially 0.7 to avoid a too large hollow in the connection area. -9

Claims (6)

claims   Transmitter for producing, in a submarine environment, acoustic radiation having the spectral characteristics of a noise, and comprising at least one electro-acoustic transducer (1,2) and at least one generator (10,20) of noise for exciting said transducer (1,2), transmitter characterized in that it comprises a first transducer (1) in the form of a hollow circular cylinder and a second transducer (2) in the form of a sphere, of radius (r) at more equal to the radius (R) of said cylinder, centered on the axis (12) of said cylinder, the distance (D) between said cylinder and said sphere being at least   the order of magnitude of the radius (R) of said cylinder.   The transmitter according to claim 1, comprising a first noise generator (10) for exciting said first transducer (1), and a second noise generator (20) for exciting said second transducer (2), said   first (10) and second (20) generators being decorrelated.   3. Emitter according to one of claims 1 or 2,   comprising a layer (21) of acoustic radiation absorbing material disposed between said first (1)   and said second (2) transducers.   Transmitter according to one of Claims 1 and 3,   comprising first means (3,13) for supporting said first transducer (1) with its base (14) opposite said second transducer (2) and second means (3,23) for supporting said second transducer (2) with its blade (24) closest to said first transducer (1), said second support means (3,23) comprising a rod (23) extending through said first transducer (1), and the along its axis (12).   5. Emitter according to one of claims 1 to 4, in   wherein said first transducer (1) is of height (H) substantially equal to its radius (R), and said radius (_) of said second transducer (2) is just lower than said   radius (R) of said first transducer (1).   Emitter according to one of Claims 1 to 5, in   wherein said first and second transducers (1,2) are made of a piezoelectric material, of the titanate type lead zirconate.