Classifications

• • 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
  • B06B1/0607—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 multiple elements
  • B06B1/0622—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 multiple elements on one surface
  • B06B1/0629—Square array

Definitions

• the present invention relates to the field of sonar antennas, in particular those intended to be carried on a sub-ma ⁇ n vehicle to constitute an attached head of this vehicle. It more particularly relates to a sonar antenna capable of operating in different frequency bands
• a sonar antenna generally consists of a large number of transducers Each transducer, for example of reception, consists of an element for converting the pressure energy which propagates in the liquid medium, into electrical energy which can be processed by electronic means
• the transducers are placed next to each other on an acoustically transparent material ensuring the transfer of energy, they are also mechanically fixed so more or less complex on a support capable of withstanding the pressure forces
• patent FR 2603761 which describes a sonar antenna constituting the attached head of an underwater vehicle, which antenna comprises a core which is a rigid syntactic foam block, resistant to hydrostatic immersion pressure, which block has housings in ch none of which is placed an electroacoustic transducer, the outer face of which is flush with the outer face of said block the hull of the machine and means of attachment against the external face of the front end of the hull of the machine
• the sub-manna antennas can be exclusively passive
• the antenna has an optimal operating frequency which is characterized by the fact that the sampling of the sensitive surface, or in other words the number of transducers per unit of surface, is well suited and for the active antennas, which each transducer can transform electric energy into mechanical energy with the best efficiency so-called "broadband" active antennas have led to the design, by more or less complex means, of transducers whose efficiency is maintained at a level sufficient for a frequency excursion of the order of 30% of the optimal frequency.
• the dimension of the transducer horn which constitutes the coupling between the medium and the energy transformer material, this dimension fixing the surface sampling and on the other hand the dimensions of the component parts of the transducers, which set the optimal operating frequency.
• GB patent 2077552 describes a sonar antenna which can be used to search for schools of fish or sand and which comprises transducers emitting at two frequencies Vj and V2, 55 kHz and 130 kHz respectively, the size of the flag of each transducer being substantially equal to half the wavelength ⁇ -
• the efficiency drops notably when the transducers operate at the frequency V2
• such an antenna cannot be used in a torpedo seeker due to its very low directivity
• the present invention aims in particular to remedy these drawbacks by proposing a sonar antenna having a high efficiency in multiple frequency bands Vj y 2 reconciling for these multiple frequency bands optimal spatial sampling while retaining the transmission function on several bands frequencies
• a sonar antenna according to the invention comprises identical transducers and having at least two sensitivity peaks vj and V2 and is characterized in that the dimension of the horn of these transducers is between 0.35 and 0.65 times the wavelength ⁇ 2 corresponding to the higher of the frequencies v-
• the matrix of transducers constituting the antenna can thus be as follows
• tapped bores are produced in a plate made of a material suitable for making pavilions, for example aluminum, according to a square matrix, the distance separating two consecutive bores being substantially equal to half the length d ⁇ 2 wave
• said plate is covered by a layer of acoustically transparent material.
• this material can be rubber deposited by vulcanization so as to ensure perfect adhesion.
• This coating is intended to constitute the waterproof envelope of the antenna at the level of the torpedo head,
• grooves are made in the longitudinal direction and in the transverse direction of the plate so as to constitute a mosaic of pavilions of square or rectangular shape whose axes correspond to those of the tapped bores and whose length of the sides is substantially equal to half the wavelength ⁇ 2
• a prestressing rod at least one of the ends of which is threaded, is screwed into each of the threaded bores of the plate - in a fifth step, a piezoelectric motor then a countermass having an axial bore and sized for able to operate at the two frequencies Vi and V2 are fixed to each of the prestressing rods, each transducer then being constituted
• a sonar antenna comprising at least two transducers of the type comprising a prestressing rod, a piezoelectric motor, a horn and a countermass, characterized in that the horns are constituted by a plate comprising grooves in order to delimit them , this plate being covered with an acoustically transparent material
• a method for its implementation consists, when the transducers operate at a frequency lower than the highest frequency from which the flags transducers have been dimensioned to electrically group several transducers so that, for this frequency, the equivalent characteristic dimension of the pavilions of this group of transducers is between 0.35 and 0.65 times the corresponding wavelength
• FIG. 1 shows a conventional transducer as well as a conventional implantation of the transducers in an antenna
• FIG. 2 shows a transducer and an installation according to the invention
• FIG. 3 illustrates various stages in the production of an antenna according to the invention
• FIG. 4 shows a simplified diagram of a torpedo head comprising an antenna
• FIG. 5 shows a diagram of the method of grouping the transducers
• a transducer according to the state of the art II is dimensioned so as to be able to operate at one or more frequencies and comprises an element 101 of energy conversion, a flag 102 and a countermass 103, the assembly being secured by a prestressing rod not shown
• FIG. 1 b is represented a conventional implantation of the transducers in an antenna 100
• FIG. 2 is shown an antenna 50 according to an embodiment of the invention.
• the transducers 60 are identical and dimensioned, in a known manner, for example using simulation software, so as to transmit at a first frequency v «
• can be chosen equal to 15 kHz and
• ⁇ > 2 correspond to a frequency of the order of 45kHz They include an element
• the characteristic dimension of the pavilion ie the diameter s 'it has the shape of a flattened cylinder or the length of one side if it has the shape of a rectangular parallelepiped with a square base, is chosen according to the wavelength ⁇ 2 corresponding to the frequency V2 In this exemplary embodiment, this dimension is chosen to be equal to half of this wavelength ⁇ 2
• the transducers constituting the antenna 50 according to a method which comprises the following two steps
• a plate of material intended to constitute the pavilions is secured to an acoustically transparent coating
• this plate is cut, but not the covering so as to form a matrix of juxtaposed pavilions
• the antenna manufacturing process can thus be as follows In a first step, tapped bores are produced in a plate made of a material suitable for forming pavilions, for example aluminum, according to a square matrix, the distance separating two consecutive bores being substantially equal to half the wavelength ⁇ 2
• said plate is covered by a layer of acoustically transparent material.
• this material can be rubber deposited by vulcanization so as to ensure perfect adhesion.
• This coating is intended to constitute the waterproof envelope of the antenna at the torpedo head
• grooves are made in the longitudinal direction and in the transverse direction of the plate so as to constitute a mosaic of pavilions of square shape whose axes correspond to those of the tapped bores and whose length of the sides is substantially equal to half the wavelength ⁇ 2 These grooves are produced by a milling operation
• a preload rod at least one of the ends of which is threaded, is screwed into each of the threaded bores of the plate.
• FIGS. 3a to 3d Another method of manufacturing the transducers 60 of the antenna 50 could be, as illustrated in FIGS. 3a to 3d, the following
• bores 64 having a countersink 65, are produced in a plate 66 made of a material adapted to constitute pavilions, for example aluminum, according to a square matrix, the distance separating two 64 consecutive bores being substantially equal to half the wavelength ⁇ 2.
• a prestressing rod 67 having a head 68 at one of its ends is fixed, by gluing in each of the bores 64, the head 65 resting on the counterbore 65 of the plate 66 so as to touch the part superior 66 of the latter,
• a third step the upper surface 69 of the plate 66 is covered by a layer 70 of acoustically transparent material, for example rubber deposited by vulcanization so as to ensure perfect adhesion
• grooves 71 are made in the direction longitudinal and transversely of the plate, but not of the covering, so as to constitute a mosaic of independent pavilions 62 of square shape whose axes correspond to those of the tapped bores 64 and whose length of the sides is substantially equal to half of the wavelength ⁇ 2
• These grooves 71 are produced by a milling operation
• FIG. 4 is a diagram in section of a sonar antenna according to the invention on board a torpedo comprising a hollow shell 1
• the shell of the machine comprises, at its front end, a part 2 intended to support the antenna It is of frustoconical shape and has an axial bore 3 It is covered, from the periphery to the bore with a material 7 able to dampen vibrations of the machine in operation such as, for example, an elastomer with a high damping coefficient, the thickness of which is variable and such that the section is substantially perpendicular to the axis of the machine
• a head 4 which has the general shape of a flattened warhead and whose external surface 70 has been secured to the plate 66 intended to constitute the mosaic of transducers, by vulcanization
• Head 4 constitutes a sonar antenna intended to perform transmission and reception functions of acoustic waves
• a core 5 which can be a block of syntactic foam which has sufficient mechanical strength to withstand the hydrostatic pressure and which has an acoustic impedance different from that of the shell and the transducers and a density less than 1
• This core 5 comprises a flat front face in which blind housings 6 are reserved intended to receive the array of Tonpilz type transducers the components of which have been described above and the electrodes of which are connected to an electrical connector 12
• the blind housings 6 are connected to an axial cavity by holes in the core 5 inside which pass conductors connected to the electrodes and to the connector 12 which is fixed, for example to a multiconductor cable, to the electronic equipment located at the interior of the craft
• the head further comprises an envelope 7, for example of acoustically transparent material such as that which is fixed to the covering of the pavilions
• the head is then fixed in a known manner, such as that described in patent FR2603761, to the shell by means of a centering and fixing piece 14
• Sizing of the transducer pavilions allows optimal functioning of the antenna at all frequencies. Indeed, to obtain a correct surface sampling both at the frequency v-
• the number of transducers per group is of the order of magnitude of the ratio ( ⁇ 1 / ⁇ 2) 2 or 9 in this embodiment of the invention
• the transducer can be dimensioned to operate at more than two frequencies, the dimension of the pavilions being always dimensioned with respect to the highest operating frequency and the operation.
• transducers carried out by group of transducers the number of which depends on the operating frequency
• the number of transducers per group is chosen so that for the frequency considered the characteristic dimension of the pavilion of these transducers either between approximately 0.35 and 0.65 times the corresponding wavelength and the number of transducers per group is chosen from the values 4, 9, 16 or n ⁇ . n being an integer

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• 1995
  • 1995-09-28 FR FR9511371A patent/FR2739522B1/fr not_active Expired - Fee Related
• 1996
  • 1996-09-26 WO PCT/FR1996/001504 patent/WO1997011789A1/fr active IP Right Grant
  • 1996-09-26 AU AU71356/96A patent/AU700895B2/en not_active Ceased
  • 1996-09-26 US US08/836,613 patent/US5898642A/en not_active Expired - Lifetime
  • 1996-09-26 EP EP96932657A patent/EP0794841B1/de not_active Expired - Lifetime
  • 1996-09-26 DE DE69602579T patent/DE69602579T2/de not_active Expired - Fee Related

Non-Patent Citations (1)

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