EP0524371B1 - Transducteur à sonar - Google Patents

Transducteur à sonar Download PDF

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Publication number
EP0524371B1
EP0524371B1 EP19920104886 EP92104886A EP0524371B1 EP 0524371 B1 EP0524371 B1 EP 0524371B1 EP 19920104886 EP19920104886 EP 19920104886 EP 92104886 A EP92104886 A EP 92104886A EP 0524371 B1 EP0524371 B1 EP 0524371B1
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EP
European Patent Office
Prior art keywords
bar
free
flexure
nodal
end sections
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EP19920104886
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German (de)
English (en)
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EP0524371A1 (fr
Inventor
James W. Fitzgerald
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KILDARE Corp
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KILDARE CORP
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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K9/00—Devices in which sound is produced by vibrating a diaphragm or analogous element, e.g. fog horns, vehicle hooters or buzzers
    • G10K9/12—Devices in which sound is produced by vibrating a diaphragm or analogous element, e.g. fog horns, vehicle hooters or buzzers electrically operated
    • 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
    • B06B1/0603—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 piezoelectric bender, e.g. bimorph

Definitions

  • the invention relates to underwater electroacoustic transducers, and more particularly to improvements in flexural-bar type acoustic sources for use in sonar systems.
  • the present invention is concerned with improvements in the design of a modified "free-free" flexure bar transducer element, a vibratile element that thereafter sometimes is called “FLEXBAR" to distinguish it from the common "bender-bar” sonar projector element.
  • the extensive prior art has evolved three principal mounting designs for bender-bars: viz: (1) the pin-hinge; (2) the flange-hinge; and (3) the leaf-hinge. To some degree all three design approaches can be made to yield end bending moments that are small, but none of these can achieve the other requirement of end deflections being small, without adding excessive mass to the mounts.
  • US-A 3 704 385 describes a piezoelectric transducer assembly comprising a flat disk of piezoelectric material held by bosses formed on a pair of mounting chips located at both sides of said disk. The bosses contact the element along its node line so that it may vibrate in an unrestrained manner.
  • the patent describes the disadvantage that as the portion of the disk on one side of the node line vibrates in one direction, the portion of the disk on the other side of the node line always vibrates in an opposite direction so that the compression and rarefaction waves created on opposite sides of the node line tend to destructively interfere with each other and essentially cancel out the acoustical output.
  • acoustical delay means are provided in the form of air vents or acoustical ports in the path of the rarefaction waves which phase delay means time-delay the compression wave by one-half wave length before this wave combines with the compression wave.
  • This phase compensation requires additional air vents or acoustical restrictions and operates only at one particular frequency where the phase delay is just half of the wave length of the generated ultrasonic frequency.
  • the conventional wisdom of the sonar community has been that, "The free-free bar is free of external applied forces or reaction forces ... such a bar has no useful applications as an underwater transducer". (R. S. Woollett, The Flexural Bar Transducer , 1986, p. 203). This viewpoint presumeably has its origins in the fact that, unmodified, the free-free flexure bar radiates as an acoustic dipole with the concomitant poor radiation loading.
  • the present invention relates to a method and means for modifying the free-free bar so that it radiates as a monopole, with greatly improved radiation loading. At the same time, the modified free-free bar retains the unique properties of being (a) nodally mounted and (b) dynamically balanced.
  • the modified free-free bar has substantially zero mechanical reaction on its mounts, and exhibits essentially no structure-borne vibration.
  • This object is achieved by the invention as characterized in the independent claims.
  • This invention prevents acoustic radiation from said outer portions which would be out of phase with said acoustic radiation from said central portion; and thus allowing the said underwater acoustic transducer to radiate acoustic energy into the water essentially as a monopol, rather than a dipole.
  • Fig. 1 depicts an ideal elastic uniform free-free bar 1 excited by some means so as to vibrate freely in its lowest, fundamental flexure mode. Under this condition two nodes 2 develop, which represent points (or lines) of no vibration. The section of the bar between the nodal points vibrates in opposite phase to the outer sections; i.e. when the center section is flexing upward, the outer sections are flexing downward, and vice versa. Since no external forces are acting on the bar, the total momentum (both translational and rotational) must be zero; and this leads to the requirement that the total momentum of the center section must be equal (and of opposite phase) to the sum of the total momentum of end sections.
  • the free-free bar can be hung from its nodal points 2 by threads 3 from overhead supports 4; then, when the bar is excited in high amplitude vibrations at its fundamental frequency, the threads experience no vibratory reaction forces, and are subjected only to the static force corresponding to the weight of the bar.
  • Fig. 2 shows a schematic representation of a free-free bar as an underwater acoustic source.
  • the free-free bar 1 is mounted on its nodal points 2 by means of suitable mounting brackets 5 in an appropriate housing 6.
  • An acoustically transparent rubber window 7 is bonded to the radiating surface of the bar and to the housing so as to form a water-tight seal, while at the same time allowing the bar to vibrate relatively freely.
  • Air which may be at the same pressure as the water, depending on the depth, fills the interior of the housing, resulting in acoustic radiation into the water only.
  • the free-free bar transducer radiates as a dipole, since the center section is vibrating 180° out of phase with the outer sections.
  • the center section of the bar moves up, it increases the water pressure as indicated by the symbol ⁇ ; while at the same time the outer sections move down, decreasing the adjacent water pressure, as indicated by the symbol ⁇ .
  • the reverse takes place on the succeeding portion of the vibration, when the center section is moving down and the outer sections are moving up.
  • Much of the kinetic energy of the vibrating bar is wasted by hydrodynamically sloshing water back and forth between the adjacent zones. Such behavior interferes with the primary compressional acoustic waves and results in the poor acoustic radiation loading characteristic of a dipole source.
  • the free-free bar can be further modified by shortening the "bent" end section and increasing their cross-section and mass so as to maintain the same total inertia about the nodal points.
  • This further modified free-free bar will still vibrate at the same fundamental resonant frequency as the original free-free bar, and with the same locations of nodal points.
  • Such a flexure bar is designated a "FLEXBAR”.
  • Fig. 4 is a schematic representation of a FLEXBAR, as an underwater acoustic source.
  • the FLEXBAR 9 is mounted on its nodal points 2 by suitable mounting brackets 5 in an appropriate housing 10.
  • a combination cover-window 11 is bonded to the radiating surface of the FLEXBAR so as to form a water-tight seal.
  • the end-section masses have clearance from the cover plate in those areas 12 beyond the nodal points so that the FLEXBAR can vibrate freely.
  • the interior of the housing is air-filled so that the FLEXBAR radiates only into the water.
  • the center section between nodes is the only section of the FLEXBAR that is acoustically coupled to the water.
  • the out-of-phase modified end sections vibrate entirely in the air-filled housing and are effectively decoupled from the water. This results in the desired monopole radiation, while at the same time the FLEXBAR is nodally mounted and essentially dynamically balanced.
  • the FLEXBAR exhibits excellent radiaton characteristics and virtually no reaction forces on the mountings and mechanical coupling to the housing.
  • the preferred embodiment of the invention is an electroacoustic underwater transducer element that is basically a piezoceramic "free-free” flexure bar, but modified so as to radiate as a "monopole” rather than as a “dipole", and retaining the unique properties of being nodally mounted and dynamically balanced.
  • One of the important consequences is the fact that the reaction forces on the modified flexure bar mountings and the concomitant structure-borne vibrations, are virtually eliminated.
  • FIG. 5 A preferred embodiment of the FLEXBAR is shown in Fig. 5. It is of trilaminar construction; the center lamina of which is a metal bar 13 of generally rectangular cross-section, with a relatively thin center web 14 and enlarged ends 15. Electrical insulation 16 and 17 line the inner sections of the metal bar, forming a top and bottom opening. Two outer laminae 18-A and 18-B consisting of a plurality of piezoceramic blocks with suitable electrodes 19 and assembled with appropriate polarity, are placed in the top and bottom openings. The whole assembly, including the metal bar 13, the insulation 16 and 17, and the piezoceramic blocks 18-A and 18-B are consolidated into a solid composite bar by means of an electrically insulating cement.
  • Metal-clad plastic plates 30 are cemented to the top and bottom of the bar to enhance its shock resistance. Finally, electrical conductors 20 leading from the piezoceramic blocks are entirely imbedded in high dielectric strength cement in order to avoid electrical breakdown and corona discharge under the high drive voltages.
  • Fig. 6-A and Fig. 6-B Three different configurations of mechanical bias blocks were found useful in applying precompression bias to the piezoceramic blocks.
  • the first of these methods is biased on the use of wedges as shown in Fig. 6-A and Fig. 6-B.
  • pairs of wedges 31 and 32 are inserted, top and bottom, at one end of the metal bar 13 between the piezoceramic stacks 18-A and 18-B and both of the shoulders of the enlarged bar end section 15.
  • Electrical insulating pads 17 between the wedge-pairs 31 and 32 and the piezoceramic stacks 18-A and 18-B insulate the stacks from the bar ground potential.
  • Each wedge has one parallel face and one inclined face and all inclined faces have the same incline angle.
  • the wedge-pairs are assembled with the inclined faces mated. More-or-less equal, inward forces are applied along the main axis of the wedge-pairs (at right angle to the main bar axis), forcing the piezoceramic stacks against the shoulders of the enlarged bar end section 15 at the opposite end of the metal bar. This results in tension stress in the bar center web 14 and compression stress in the piezoceramic stacks 18-A and 18-B.
  • the amount of precompressional stress in the piezoceramic stack can be controlled by the incline angle of the wedges, the force applied to the wedges, the cross-sectional area of the center web and the tension modulus of the material of the center web.
  • the piezoceramic stacks 18-A and 18-B are preassembled with their insulation 16 and 17 cemented in place.
  • the cement is then applied between the center web 14 and the insulating plates 16.
  • the stacks 18-A and 18-B are then placed on the bar and put into compression.
  • the cement joint between the web 14 and the insulating plates 16 is allowed to set up with the stacks under compression, thus avoiding an unwanted shear stress in this cement joint.
  • the protruding end of the wedges can then be cut off along the dotted lines 33.
  • FIG. 7 An alternative means for applying precompression is shown in the sectional sketch of Fig. 7.
  • a pair of mechanical bias blocks 34 with tapered holes drilled into each end of the block pair are inserted between the piezoceramic stack 18 (with end insulating pad 17) and the shoulder of the enlarged end section 15 of the bar.
  • the blocks are forced apart by driving two taper-pins 35 into the tapered holes, resulting in precompression of the piezoceramic stack (and tension in the bar center web).
  • the tapered holes in the blocks 36 are threaded and tapered, threaded plugs 37 are screwed into the blocks, forcing them apart and, thus, precompressing the piezoceramic stack.
  • the protruding ends of the taper-pins or threaded-plugs can be removed after the inner cement joints have fully set-up.
  • the FLEXBAR shown in Fig. 5 can be set into flexural vibration by applying an alternating electrical voltage to the terminals 21-A and 21-B. Since the piezoceramic stacks 18-A and 18-B are oppositely polarized, one-half cycle of the resulting alternating current causes the upper stack to expand and the lower stack to contract; and in the next half of the cycle the opposite occurs. This results in the bar being driven in flexural vibration at the frequency of the applied alternating current.
  • the amplitude of vibration is a maximum at the resonant frequency (lowest mode) of the FLEXBAR, which is given by the approximate formular: where:
  • Fig. 10 shows a typical measured relative (rms) displacement, in decibels, of the center of the FLEXBAR of Fig. 9-B as a function of frequency.
  • the bar was measured in air and exhibited resonance at the design frequency.
  • the high mechanical Qm ⁇ 130 indicates that the bar has very low internal mechanical losses.
  • Fig. 11 shows the measured relative displacement along the same FLEXBAR driven at its resonant frequency. The nodes are well defined and some 60 db below the center deflection.
  • Fig. 12 shows the measured total impedance vs. frequency of the same FLEXBAR with a typical resonance-antiresonance at ⁇ 1 KHz.
  • the next higher mode at ⁇ 2.75 KHz is nearly suppressed, but discernable, and the third mode at ⁇ 5.4 KHz, is also discernable. Above 10 KHz the bar breaks up into a number of complex resonant modes.
  • the effect is relatively small for such a wide range of frequencies representing approximately ⁇ 12,7 mm ( ⁇ 0.5 inches) from the location for the design frequency. Since the nodal mounting pins 24 of Fig. 5 are decoupled from the vibrating FLEXBAR by means of the compliant rubber sleeve 25, the small movement of the nodal point location has little effect on the performance of the bar.
  • the total added mass is approximately 1200 g, or 600 g on each end. As can be seen from Fig. 14, this wide range of added mass has negligible effect on the electromechanical coupling coefficient of the FLEXBAR.
  • a FLEXBAR sonar transducer is comprised of one or more FLEXBARs, nodally mounted in a suitable water-tight housing, and acoustically coupled to the water through a sound-transparent rubber window.
  • Fig. 15 is a schematic sketch showing the principal parts comprising such a transducer: the cover plate 38 has a bonded sound-transparent rubber window 39 with bolt holes 40; an ensemble of FLEXBARs 41 with nodal mounting pins 42; and a flanged housing 43 with an electrical cable 44.
  • FLEXDUCER In order to distinguish such a FLEXBAR transducer from one comprised of bender-bar elements, it is named it a "FLEXDUCER", and this terminology will be used throughout the rest of this specification.
  • Fig. 16-A, Fig. 16-B, and Fig. 16-C are, respectively, the top-view, the end-view, and the side-view of a FLEXDUCER module comprised of 5 FLEXBARs of the design shown in Fig. 9-B having element performance characteristics delinated above.
  • Fig. 17-A, Fig. 17-B, and Fig. 17-C are, respectively, the top-view, the side-view, and the end-view of sectional sketches showing certain design details of the FLEXDUCER construction.
  • the FLEXBARs 41 are mounted by means of their rubber covered nodal pins 42 to mounting lugs 46 rigidly attached (actually cast) to the cover plate 38.
  • Fig. 18 shows a conventional equivalent circuit, that represents the response of the FLEXDUCER; the circuit components being defined as follows:
  • Fig. 20 shows the maximum acoustic power output as a function of the number of modules in a rectangular array. The transition from the stress-limited to the field-limited output occurs at approximately 6 modules. For 40 modules, the FLEXDUCER array would be capable of 100 KW of acoustic power output. The mechanical Qm drops from ⁇ 3.5 for a single module to ⁇ 35 for the full array of 40 modules due to the increase in radiation loading.
  • the FLEXBAR module has an average transmissibility of -60 dB over a whole octave from 700 - 1,400 Hz; i.e. the amplitude of vibration of the housing is only 0.1% of that of the FLEXBAR.
  • the transmissibility of the bender-bar module is on the average, only -14 dB; i.e. the amplitude of vibration of the housing is 20% of that for the bender-bar.
  • the significance of this difference becomes clear if one considers a large, high-power array capable of an acoustic output of 0.5 megawatts.
  • the back radiation from the FLEXDUCER array would only be of the order of 0.5 acoustic watts; while the bender-bar array would have back radiation of ⁇ 20,000 watts.
  • the FLEXBAR is comprised of two piezoceramic plates 47 with electrodes 48 on the main faces, and the polarization vector P essentially perpendicular to the principal axis of the bar.
  • V alternating voltage
  • V alternating voltage
  • E electric field vector
  • the electric field because of the electromechanical coupling, causes an expansion strain +S in the upper plate and a contraction strain -S in the lower plate, both strains being parallel to the main axis of the bar.
  • the mechanical strains are reversed and the FLEXBAR is driven into flexural vibration.
  • the electromechanical coupling coefficient is typically k31 ⁇ 0.30.
  • the electromechanical driving elements are two stacks 49 of piezoceramic blocks 50 consolidated with an appropriate cement (e.g. epoxy), and with electrodes 51 so oriented that the electric field E and the mechanical strain S are in the same direction and parallel to the main axis of the bar, as shown.
  • an appropriate cement e.g. epoxy
  • the electromechanical coupling coefficient is higher, typically k33 ⁇ 0.60.
  • the electromechanical driving elements are two piezoceramic plates 52 with striped-electrodes 53 fused to the ceramic in regularly spaced bands, the plates are polarized parallel to the longitudinal axis of the bar, but in alternating directions as shown.
  • the mechanical strain S and the electric field E are also substantially in the same direction and parallel to the main axis of the bar.
  • the electromechanical coupling coefficient is less than that of the second configuration, being typically k sp ⁇ 0.45.
  • FLEXBAR One of the unique features of a FLEXBAR is the fact that it can be mechanically tuned by varying the amount of the total moment of inertia of the end portions of the bar beyond the nodal lines, symbolically designated as M2 in the equivalent circuit of Fig. 18.
  • Three means of achieving this have been devised ; viz,: (1) by varying the amount of the added-mass end pieces; (2) by varying the position of a portion of the added-mass end pieces; and (3) by a combination of both (1) and (2).
  • These means for mechanical tuning apply equally well to piezoceramic FLEXBARs and FLEXBARs driven by other means (e.g. electrodynamic drive, variable reluctance drive, etc.).
  • the mass M2 can be reduced by simply drilling holes 54 in the added-mass end pieces as shown in Fig. 25-A; or it can be increased by filling the holes with a high density material such as lead 55 as shown in Fig. 25-B.
  • Another way of varying the mass M2 is shown in Fig. 25-C, where plates 56 are added or removed from the added-mass end pieces. Reducing the added-mass, of course, increases the resonant frequency of the bar; and increasing the added-mass reduces the resonant frequency.
  • the second means for mechanically tuning a FLEXBAR does not vary the added-mass, but rather moves the centers-of-mass of the end pieces away from, or toward the nodal points. This varies the total moment of inertia (linear plus rotational) of the end-pieces, and changes the resonant frequency accordingly.
  • slotted plates 57 are bolted in their extreme outward position, which lowers the resonant frequency.
  • the slotted plates 57 are in their extreme inward position, resulting in a higher resonant frequency. Intermediate positions result in intermediate resonant frequencies.
  • Fig. 26-C Another way of varying the moment of inertia of the end-pieces, and thus changing the resonant frequency, is shown in Fig. 26-C.
  • threaded tuning-slugs 58 located in the added-masses 59 can be moved outward to lower the frequency, or inward to raise the frequency.
  • the tuning slugs can be locked into position by means of locknuts 60 or set screws 61.
  • the percentage change in frequency can be increased by filling the tuning-slugs with a higher density material such as lead.
  • the resonant frequency of a FLEXBAR can be varied by means of a combination of the above procedures.
  • FIG. 27-C An alternate to this method is shown in Fig. 27-C.
  • integral tabs 69 at the nodal points extend out from the bar 63 and are encased in a compliant elastomer sheath 66.
  • the vibration isolation of the nodal pins or nodal tabs, by means of compliant members, is an important feature of the "fixed-nodal mounting" since subsequent mechanical tuning and radiation loading can result in small movement of the nodal locations determined from experimental measurements of FLEXBAR vibrations in air.
  • the compliant mounting accommodates to this change.
  • the second means for nodal mounting of FLEXBARs is called the "auto-nodal mounting" and is shown in section view of Fig. 28.
  • a flange 70 completely surrounds the FLEXBAR 63 which is encased in a compliant elastomer 71 serving as a sonar window and 72 serving as a compliant mount.
  • the elastomer is bonded to both the flange and to the bar so that the FLEXBAR is essentially "floating" in elastomer.
  • the ends of the bar are recessed with an intervening air space so that their vibration is decoupled from the flange. Under these conditions, the FLEXBAR automatically determines its own nodal location corresponding to a particular radiation loading.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Mechanical Engineering (AREA)
  • Transducers For Ultrasonic Waves (AREA)

Claims (27)

  1. Transducteur acoustique sous-marin comprenant :
    a) une barre de flexion libre à ses deux extrémités (9 ; 13, 14, 15 ; 41 ; 63),
    b) un moyen (18, 19, 20 ; 44 ; 47, 48 ; 49, 50, 51 ; 52, 53) pour entraîner électromécaniquement ladite barre en vibration par flexion sur une bande de fréquences ayant comme fréquence centrale, une fréquence correspondant pratiquement au mode de flexion en liberté aux deux extrémités le plus bas de ladite barre,
    c) des moyens (2, 5 ; 24 à 27 ; 42 ; 68, 70) pour monter ladite barre de flexion pratiquement sur les deux lignes nodales (2, 27) caractéristiques dudit mode de vibration de flexion à deux extrémités libres le plus bas de ladite barre,
    d) des éléments en élastomère (66, 67, 72) isolant partiellement lesdits moyens de montages (68) vis-à-vis de la vibration de ladite barre de flexion (63),
    e) un moyen (38, 42, 45, 46) pour fixer ladite barre de flexion et ces dits montages nodaux dans un logement étanche à l'eau rempli de gaz (6, 43) de manière telle que la barre de flexion peut vibrer librement sur ses montages nodaux sans pratiquement de couplages mécaniques avec lesdits montages ou ledit logement,
    f) un moyen (39) pour coupler mécano-acoustiquement avec l'eau seulement la partie centrale (9) de la surface extérieure de ladite barre (9 ; 13 à 15 ; 41 ; 63) se trouvant entre lesdites deux lignes nodales (2, 27) de sorte que lorsqu'elle est entraînée électro-mécaniquement en vibration par flexion, ladite barre de flexion rayonnera de l'énergie acoustique dans l'eau à partir de ladite partie centrale (9),
    g) un moyen pour permettre aux autres parties extérieures (8A, 8B ; 22) de ladite barre de flexion, se trouvant à l'extérieur des deux lignes nodales de vibrer librement dans l'intérieur rempli de gaz dudit logement (6, 43) sans couplage mécano-acoustique avec l'eau.
  2. Transducteur selon la revendication 1, caractérisé en ce qu'il comprend une pluralité (41) de dites barres de flexion à deux extrémités libres.
  3. Transducteur selon la revendication 1 ou 2, caractérisé en ce que la barre de flexion à deux extrémités libres comprend deux sections d'extrémité modifiées (8A, 8B ; 22) se trouvant à l'extérieur des lignes nodales (2, 27) de ladite barre de flexion, qui sont rigidement fixées à la partie centrale de ladite barre et s'étendent pratiquement à angle droit par rapport à et sur le côté opposé à la surface de rayonnement centrale de ladite barre de flexion, où lesdites sections d'extrémité devraient procurer pratiquement la même inertie totale, à la fois en translation et en rotation, prise autour des lignes nodales que celle qui serait assurée par des sections d'extrémité uniformes se prolongeant à l'extérieur des lignes nodales et parallèles à la surface de rayonnement centrale de la barre de flexion à deux extrémités libres.
  4. Transducteur selon la revendication 3, caractérisé en ce que lesdites sections d'extrémité modifiées comportent une partie (12) de leurs surfaces qui est contiguë à la surface de rayonnement centrale (9) évidée de façon à éviter une interférence de vibration avec une plaque de couverture de transducteur (38).
  5. Elément vibrant, approprié pour utilisation dans un transducteur selon l'une quelconque des revendications précédentes, comprenant :
    a) une barre de flexion à deux extrémités libres (9 ; 13, 14, 15 ; 41; 63),
    b) un moyen (18, 19, 20 ; 44 ; 47, 48 ; 49, 50, 51 ; 52, 53) pour entraîner électro-mécaniquement ladite barre en vibration par flexion sur une bande de fréquences ayant comme fréquence centrale, une fréquence correspondant pratiquement au mode de vibration par flexion à deux extrémités libres le plus bas de ladite barre,
    c) des moyens pour monter ladite barre de flexion pratiquement aux deux lignes nodales caractéristiques dudit mode de vibration de flexion à deux extrémités libres le plus bas de ladite barre,
    d) des éléments en élastomère (66, 67, 72) isolant partiellement lesdits moyens de montages des vibrations de ladite barre de flexion,
    e) deux sections d'extrémité modifiées (8A, 8B ; 22) se trouvant à l'extérieur des lignes nodales (2, 27) de ladite barre de flexion qui sont rigidement fixées à la partie centrale (9) de ladite barre et s'étendent pratiquement à angle droit par rapport à et sur le même côté de la partie centrale de ladite barre, où lesdites sections d'extrémité (8A, 8B ; 22) devraient procurer pratiquement la même inertie totale, à la fois en translation et en rotation, prise autour des lignes nodales, que celle qui devrait être assurée par des sections d'extrémité uniformes se prolongeant à l'extérieur des lignes nodales et parallèles à la partie centrale de ladite barre de flexion à deux extrémités libres.
  6. Elément vibrant selon la revendication 5, caractérisé par un moyen (54 à 61) pour modifier la masse desdites sections d'extrémité modifiées (8A, 8B ; 22, 59) de façon à changer la fréquence correspondant sensiblement au mode de vibration de flexion à deux extrémités libres le plus bas de ladite barre.
  7. Elément vibrant selon la revendication 5, caractérisé par un moyen (54 à 61) pour changer le moment d'inertie pris autour des lignes nodales (2, 27) desdites sections d'extrémité modifiées (8A, 8B ; 22, 59) de façon à changer la fréquence correspondant sensiblement au mode de vibration de flexion à deux extrémités libres le plus bas de ladite barre.
  8. Elément vibrant approprié pour montage dans un logement de transducteur acoustique sous-marin, en particulier transducteur selon l'une quelconque des revendications 1 à 4, comprenant :
    a) une barre de flexion à deux extrémités libres (63) ayant deux sections d'extrémité modifiées (8A, 8B, 22) se trouvant à l'extérieur des deux lignes nodales (2, 27) caractéristiques du mode de vibration à la flexion à deux extrémités libres le plus bas de ladite barre, lesdites sections d'extrémité étant fixées de manière rigide à la partie centrale (9) de ladite barre de flexion et s'étendant pratiquement à angle droit par rapport à et dans la même direction à partir de la partie centrale de ladite barre, où lesdites sections d'extrémité devraient procurer pratiquement la même inertie totale, à la fois en translation et en rotation, prise autour des lignes nodales, que celle qui devrait être assurée par des sections d'extrémité uniformes se prolongeant à l'extérieur des lignes nodales d'une barre de flexion uniforme non modifiée à deux extrémités libres,
    b) un moyen (18, 19, 20 ; 44 ; 47, 48 ; 49, 50, 51 ; 52, 53) pour entraîner électro-mécaniquement ladite barre en vibration à la flexion sur une bande de fréquences ayant comme fréquence centrale, une fréquence correspondant pratiquement au mode de vibration à la flexion à deux extrémités libres le plus bas de ladite barre,
    c) des couches d'élastomère adaptées (72) entre chaque côté de ladite barre de flexion (68) et des structures de montage parallèles correspondantes (70) fixées audit logement de transducteur, de manière telle que ladite barre est suspendue dans ledit matériau élastomère adapté (71, 72) et lorsqu'entraîné et pratiquement libre de vibrer en flexion, trouvant ses propres lignes nodales sans tenir compte des changements de l'inertie totale desdites sections d'extrémité, ou des changements dans la charge de rayonnement,
    d) un moyen (71) pour couplage acoustique à l'eau, seulement la face centrale de ladite barre se trouvant entre les lignes nodales et opposée à la direction desdites sections d'extrémité modifiées, laissant l'autre face de ladite barre et ses dites sections d'extrémité découplées de l'eau et libres de vibrer dans l'intérieur rempli d'air dudit logement du transducteur (43).
  9. Dispositif selon l'une quelconque des revendications 1 à 8, caractérisé en ce que le moyen pour entraîner électro-mécaniquement ladite barre (9 ; 13, 14, 15 ; 41 ; 63) en vibration en flexion est un moyen piézoélectrique.
  10. Dispositif selon la revendication 9 caractérisé en ce que le moyen piézoélectrique est un moyen de la classe des piézocéramiques polarisées.
  11. Dispositif selon la revendication 9 ou 10 caractérisé en ce que le moyen piézoélectrique comprend deux plaques de piézocéramique (47) munies d'électrodes (48) sur les faces principales desdits plaques, tandis que le vecteur de polarisation s'étend essentiellement perpendiculaire à l'axe principal de la barre.
  12. Dispositif selon la revendication 9 ou 10 caractérisé en ce que le moyen piézoélectrique comprend au moins deux empilages (49) de blocs de piézocéramique (50) avec des électrodes (51) orientées de sorte que le champ électrique entre les électrodes et la contrainte mécanique soient dans la même direction et parallèles à l'axe principal de la barre.
  13. Dispositif selon la revendication 9 ou 10 caractérisé en ce que le moyen piézoélectrique comprend au moins deux plaques de piézocéramique (52) avec des électrodes en forme de bande (53) en bandes régulièrement espacées, les plaques sont polarisées parallèlement à l'axe longitudinal de la barre, mais dans des directions alternées.
  14. Dispositif selon l'une quelconque des revendications 1 à 8, caractérisé en ce que le moyen pour entraîner électro-mécaniquement ladite barre en vibration en flexion est un moyen magnétostrictif.
  15. Dispositif selon l'une quelconque des revendications 1 à 8, caractérisé en ce que le moyen pour entraîner électro-mécaniquement ladite barre en vibration en flexion est un moyen électrodynamique magnétique.
  16. Dispositif selon l'une quelconque des revendications 1 à 8, caractérisé en ce que le moyen pour entraîner électro-mécaniquement ladite barre en vibration en flexion est un moyen magnétique à réluctance variable.
  17. Dispositif selon la revendication 10, caractérisé par un moyen (28 ; 31, 32 ; 34, 35 ; 36, 37) pour soumettre la piézocéramique polarisée (18, 18A, 18B) à une sollicitation mécanique de précompression pratiquement permanente pendant la fabrication dudit élément vibrant.
  18. Dispositif selon la revendication 17, caractérisé en ce qu'un paire de coins coniques (31, 32) sont les moyens pour obtenir ladite sollicitation mécanique.
  19. Dispositif selon la revendication 17, caractérisé en ce qu'un paire de broches coniques (35) et de blocs d'adaptation (34) sont les moyens pour obtenir ladite sollicitation mécanique.
  20. Dispositif selon la revendication 17, caractérisé en ce qu'un paire de boutons filetés (37) et de blocs d'adaptation (36) sont les moyens pour obtenir ladite sollicitation mécanique.
  21. Dispositif selon l'une quelconques des revendications précédentes, caractérisé par un moyen pour accorder mécaniquement la barre.
  22. Dispositif selon la revendication 21, caractérisé en ce que la masse des pièces d'extrémité (22) de la barre peut être modifiée.
  23. Dispositif selon la revendication 21, caractérisé par un moyen pour changer la position du centre de masse des pièces d'extrémité (22).
  24. Dispositif selon l'une quelconques des revendications précédentes, caractérisé en ce que la barre (63) à chaque emplacement nodal (64) comporte un trou pour recevoir une broche de montage nodal (65) et une gaine d'élastomère adaptée (66) et une rondelle élastomère adaptée (67) est insérée entre la barre et le montage.
  25. Dispositif selon l'une quelconques des revendications 1 à 23, caractérisé en ce qu'à chaque point nodal (64) de la barre (63), une languette intégrale (69) s'étend à l'extérieur de la barre et est enfermée dans une gaine d'élastomère adaptée (66) qui, en même temps que la rondelle d'élastomère adaptée (67), isole la barre du montage (68).
  26. Dispositif selon l'une quelconques des revendications 1 à 23, caractérisé en ce qu'un rebord (70) entoure totalement la barre (63) qui est enfermée dans un élastomère (72), de sorte que l'élastomère soit collé à la fois au rebord et à la barre et la barre est essentiellement flottante sur l'élastomère.
  27. Dispositif selon la revendication 26, caractérisé en ce que les extrémités de la barre sont évidées avec un espace d'air se trouvant entre elles pour découplage de celles-ci vis-à-vis du rebord.
EP19920104886 1991-07-25 1992-03-20 Transducteur à sonar Expired - Lifetime EP0524371B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US73606491A 1991-07-25 1991-07-25
US736064 1991-07-25

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EP0524371B1 true EP0524371B1 (fr) 1994-09-21

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6322532B1 (en) 1998-06-24 2001-11-27 3M Innovative Properties Company Sonophoresis method and apparatus

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ES2938849T3 (es) * 2014-07-11 2023-04-17 Microtech Medical Technologies Ltd Transductor de múltiples celdas

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3704385A (en) * 1971-03-02 1972-11-28 Delta Products Inc Piezoelectric transducer assembly with phase shifting accoustical parts

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6322532B1 (en) 1998-06-24 2001-11-27 3M Innovative Properties Company Sonophoresis method and apparatus

Also Published As

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DK0524371T3 (da) 1995-02-20
DE69200439D1 (de) 1994-10-27
EP0524371A1 (fr) 1993-01-27
DE69200439T2 (de) 1995-03-16

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