Classifications

• • 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
  • G10K9/121—Flextensional transducers

Definitions

• the present invention relates to acoustic transducers of the flexural type capable of being submerged to a significant depth without suffering damage and always operating correctly. It applies to the emission and / or reception of acoustic or ultrasonic acoustic waves in fluid environments such as the submarine space.
• Known flextensor transducers are generally composed of a flexible, watertight shell with a cylindrical side wall of elliptical cross section, vibrated by one or more pillars or bars of piezoelectric ceramic cells. Each pillar is kept in compression between the opposite parts furthest from the side wall. In emission, an alternating electric field is applied in the longitudinal direction of each pillar and the resulting movement, which takes place along the longitudinal axis of each pillar, is transmitted, amplified, to the surrounding liquid medium, the amplitude of this movement being maximum in the plane generated by the minor axes of the ellipses formed by each cross section.
• a compression preload of the piezoelectric cells of each pillar is necessary to avoid breakage of the ceramic when the pillars are stressed in extension.
• this prestressing is supplied directly by the shell when the pillars are assembled.
• the housings provided in the shell for the pillars have, before assembly, shorter lengths than those of the pillars.
• To set up the pillars it suffices to apply two opposite external forces to the facing parts closest to the wall lateral to compress the shell at this point and cause by elastic deformation thereof a just sufficient increase in the length of the housings to allow the installation of the pillars.
• the prestressing force is applied when the action of the two external forces is suppressed.
• the pillars then remain compressed in their housings between the parts of the inner lateral wall of the shell in contact with their ends.
• This embodiment requires, in order to obtain correct operation of the transducers at a determined depth, to give the amplitude of the two external forces a value greater than that which is normally exerted by the hydrostatic pressure at this depth.
• This has the disadvantage of limiting the use of these types of transducers to the depths for which the prestressing force of the pillar can still be ensured, to avoid breakage of the ceramic constituting the piezoelectric cells.
• the prestressing force of each pillar can be obtained by means of a rod passing through each pillar along its longitudinal axis, the ends of the rod being held by bolting to the shell.
• the hydrostatic pressure exerts, via the shell, a tensile force on each pillar which causes, when it is too strong, a rupture of the ceramic making up the piezoelectric cells.
• the stacking of the piezoelectric cells can be carried out along a prestressing rod which is not fixed by its ends to shell.
• the stack is maintained by two rails so as not to be subjected, as in the embodiment described above, to a tensile force directed along the longitudinal axis of the pillar.
• the immersion of the transducer is such that one or two sides of the pillars are no longer in contact with the shell, the transducer can no longer function properly.
• the invention proposes a flexural tensor acoustic transducer for deep immersion, comprising a hollow shell of oblong section and an electroacoustic motor intended to excite this shell along the major axis of this section, mainly characterized in that it further comprises viscoelastic means making it possible to absorb without presenting appreciable mechanical resistance the forces exerted by the hull on the engine under the effect of deformations originating from immersion, and having a significant stiffness at the operating frequencies of the engine to communicate to the hull the vibrations of this engine with good efficiency.
• FIG. 1 a sectional view of a transducer according to a first embodiment of the invention
• Figure 2 a characteristic diagram of the material making up the part 104 of Figure 1
• - Figure 3 a sectional view of a second embodiment
• Figure 1 a sectional view of a type 4 flexuring transducer according to the classification established by ROYSTER in the journal JASA N ° 38, 1965 p. 879 to 880.
• This -transducteur includes a shell of elliptical section 101 in which is inserted a piezoelectric motor 102 placed along the major axis of the ellipse and which is supported by its two ends on the interior faces of the shell to make it vibrate, under the influence of an electric voltage, along an axis OX parallel to this major axis. Under this influence the whole shell begins to vibrate and the amplitude of the movement is maximum along an OY axis parallel to the minor axis of the ellipse.
• the shell deforms by flattening along an axis 0Y, and therefore widening along the axis 0X since the interior 103 does not communicate with the outside and therefore contains only 1 air at atmospheric pressure.
• This enlargement tends to draw on the motor 102, formed of a stack of piezoelectric ceramics. As these do not support the traction forces, they risk breaking in dynamics.
• a part 104 formed of a viscoelastic material whose static stiffness is low and the dynamic stiffness is high is inserted, substantially in the middle of the motor 102.
• two intermediate steel plates 105 and 106 have also been inserted between this viscoelastic part and the ceramics making up the motor, but this arrangement is not essential.
• the dimensions of the viscoelastic part and of the metal plates are shown to be substantially equal to those of the ceramic plates forming the motor, but the exact dimensioning will be chosen according to the characteristics of the materials used.
• the material used having a difference in compliance, or stiffness, between the low frequencies which correspond to static stresses and the high
• OR - f Q _ is the resonance frequency before the seals are put in place.
• Various materials make it possible to manufacture such a seal.
• a typical characteristic for selecting these materials is that they have a glass transition at room temperature in the frequency range considered.
• a polyurethane can be used as material, of which the stiffness modulus G expressed in N / m 2 and the loss factor tg ⁇ as a function of the frequency in Hz has shown in FIG. 2.
• the transition is obtained for a frequency substantially equal to 10 ⁇ 2 Hz, that is to say for stresses on the material moving very slowly (period 100 seconds typically corresponding to the progressive crushing of the shell of the flexor when it is immersed more and more deeply).
• the value G Q of the module at this transition is then substantially equal to 4.10 N / m.
• the viscoelastic material can be placed in many other places and there is shown in FIG. 3 a second embodiment in which a seal 304 is inserted between the shell 301 and the motor 302.
• This motor 302 comprises a stack of ceramics subjected to a prestressing using a rod 311 which crosses the stack right through. Clamping nuts 312 are screwed to the ends of the rod to compress the ceramics via a metal support piece
• the viscoelastic seal 304 is formed by two plates inserted on either side between the shell and the part 313. In this configuration, this seal works in bending while in the previous embodiment it worked in compression, but the result is the same .
• the other end of the flexuring transducer of FIG. 3 may be identical to the end shown in this figure, or else the motor may be directly fixed to the hull.
• the realization comprising only one joint on one side is easier to manufacture but this joint is subjected to larger deformations, which are not always desirable.
• a class 4 flextensor transducer whose depth is equal to 10 cm long and whose attachment is in accordance with Figure 3 to both ends of this engine.
• the shell therefore has 4 flat seals 10 cm long (2 on each side).
• Typical characteristics of such a transducer are for example:
• the transducer will be manufactured by thickening this shell at the connection with the motor. The dynamic stiffness is then worth
• the invention also extends to other types of flexors, such as those of class 2 or 5.
• the viscoelastic filter 404 has the form of a ring placed between the motor 402, itself in the form of a ring, and the shell 401 which is in the form of two domes assembled by their circumferences.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Multimedia (AREA)
• General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)
• Vibration Prevention Devices (AREA)
• Transducers For Ultrasonic Waves (AREA)
• Apparatuses For Generation Of Mechanical Vibrations (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=9409057

Family Applications (1)

Country Status (6)

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Family Cites Families (6)

• 1991
  • 1991-01-25 FR FR9100860A patent/FR2672179B1/fr not_active Expired - Fee Related
• 1992
  • 1992-01-14 DE DE69212806T patent/DE69212806T2/de not_active Expired - Fee Related
  • 1992-01-14 CA CA002101053A patent/CA2101053C/fr not_active Expired - Fee Related
  • 1992-01-14 US US08/090,142 patent/US5431058A/en not_active Expired - Fee Related
  • 1992-01-14 EP EP92903815A patent/EP0568592B1/de not_active Expired - Lifetime
  • 1992-01-14 WO PCT/FR1992/000025 patent/WO1992013338A1/fr active IP Right Grant

Non-Patent Citations (1)

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