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
  • B06B1/0633—Cylindrical array
• • 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
  • B06B1/0611—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 in a pile
  • B06B1/0618—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 in a pile of piezo- and non-piezoelectric elements, e.g. 'Tonpilz'
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
  • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
  • H04R1/40—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers
  • H04R1/403—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers loud-speakers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/44—Special adaptations for subaqueous use, e.g. for hydrophone
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R17/00—Piezoelectric transducers; Electrostrictive transducers

Definitions

• the present invention relates to an electro-acoustic transducer for underwater acoustic communication or even underwater acoustic tomography. More specifically, the invention relates to a submersible electro-acoustic transducer operating in the low frequency domain (less than 1 kHz) compatible with large immersion depths (greater than 3000 m.) And having a large autonomy. The invention also relates to a method of generating acoustic waves at low frequency and wide bandwidth.
• An electro-acoustic transducer is used for transmitting and / or receiving acoustic pressure waves.
• an acoustic transducer transforms an electric potential difference into an acoustic pressure wave, and vice versa into a reception mode.
• a transducer has a frequency bandwidth and has a so-called central frequency which corresponds to the middle of the bandwidth.
• Underwater acoustic communications over distances of more than ten kilometers require the use of low-frequency acoustic sources (below 1 kHz) to achieve long-range and broadband objectives (bandwidth greater than 10 % of the central frequency) and allow sufficient data rates.
• the sparkers are acoustic spark gaps whose coding of the transmitted wave is not possible
• the piezoelectric rings are systems composed of one or more metal rings on the inner wall of which are arranged radially several piezoelectric motors. When the piezoelectric motors are excited, the rings are vibrated. These rings thus fulfill the role of pavilion or vibrating wall. However, the implementation of piezoelectric ring systems remains difficult and their repeatability is insufficient.
• a Janus-Helmhotz type transducer also called a double Tonpilz, is based on the use of a stack of piezo electric motors forming a piezoelectric motor.
• a Janus-Helmholtz transducer comprises two piezo-acoustic motors aligned along the same axis and fixed on a central contermasse, each piezo-acoustic motor being connected to a horn by a prestressing rod. The two flags are thus located at opposite ends on the axis of the device and symmetrical with respect to a plane transverse to the axis.
• a Janus-Helmholtz transducer generally comprises a non-resonant rigid cylindrical casing which delimits a fluid cavity located between the inner wall of the casing and the rear faces of the casings.
• a Janus-Helmholtz transducer makes it possible to work at lower acoustic frequencies (from 150 Hz to 20 kHz) than a Tonpilz transducer (frequency greater than 1 kHz).
• a Janus-Helmholtz transducer generates a longitudinal acoustic resonance mode along an emission direction along the axis of the transducer. In the rest of this document, we call this resonance mode longitudinal resonance mode.
• Janus-Helmholtz transducers have low frequency limitations ( ⁇ 1 kHz). In particular, the resonant frequency being inversely proportional to the volume of the cavity, a low frequency Janus-Helmholtz transducer poses congestion constraints.
• a piezo-acoustic resonator is generally placed in a sealed protective housing.
• the outer face of the flag is in direct contact with the immersion medium or placed behind an acoustically transparent membrane.
• the inner cavity of the housing is filled with either air or a fluid chosen to have a good acoustic impedance without loss, that is to say without breaking impedance with water.
• the fluid used is usually an oil.
• the cavity is filled with air
• the acoustic coupling between the transducer and the immersion medium is through the outer face of the flag.
• the acoustic coupling between the transducer and the immersion medium is through the horn through the oil and the housing.
• the immersed transducer transforms the vibration wave of the resonator into an acoustic pressure wave propagating in the immersion medium.
• electro-acoustic transducers including a gas-filled sealed casing, but the casing must be strong enough to withstand the pressures of immersion in the liquid, which considerably increases the weight of the transducer when the immersion depth is important.
• electro-acoustic transducers including a pneumatic compensation system to compensate for the hydrostatic pressure forces on the housing and to increase the resistance to external pressure in deep immersion.
• pneumatic compensation systems are limited to immersion depths of less than 3000 m.
• One of the aims of the invention is to provide an autonomous underwater acoustic communication system for emitting acoustic waves of great depth of immersion and low frequency.
• Another object of the invention is to provide a method for generating acoustic waves at low frequency and wide bandwidth.
• the technical problem is to reduce the resonance frequency of a Janus-Helmhotz-type submersible electro-acoustic transducer without increasing the dimensions and the weight of the transducer to ensure high electroacoustic performance and autonomy at great depth of immersion.
• the object of the present invention is to overcome the disadvantages of prior devices and more particularly relates to a submersible electro-acoustic transducer in an immersion fluid for underwater acoustic communication, said transducer comprising two horns, a counterweight, two electric motors acoustic, placed on either side of the counterweight, said motors being aligned along an axis of symmetry, the opposite ends of said motors being respectively connected to a horn, the assembly consisting of said electroacoustic motors, said counter and said flags being able to generate a longitudinal electro-acoustic resonance mode.
• said transducer comprises a rigid and hollow cylindrical piece extending around said counterweight, said cylindrical piece having an axis coincident with the axis of symmetry of the transducer, the inside of said cylindrical piece forming a fluid cavity capable of to be filled by said immersion fluid, said electro-acoustic motors and said cylindrical piece being dimensioned so that said fluid cavity forms an acoustic coupling between said longitudinal electro-acoustic resonance mode of said transducer and a circumferential resonance mode of said cylindrical piece when said fluid cavity is filled with said immersion fluid.
• said cylindrical piece is fixed to said counterweight by suspension means capable of acoustically decoupling said cylindrical piece of said counterweight.
• said cylindrical piece is made of metallic material or of composite material capable of producing a circumferential type of acoustic vibration mode.
• said transducer is capable of providing an acoustic frequency acoustic emission source of less than 10000 Hz and having a bandwidth greater than 10% of the central acoustic frequency. According to a preferred embodiment of the invention, said transducer is able to provide an acoustic frequency acoustic emission source of less than 1000 Hz and having a bandwidth greater than 10% of the central acoustic frequency.
• Said cylindrical piece has an annular section
• Said fluid cavity is filled with water
• the difference in frequency between the longitudinal resonance mode of the piezoelectric stack and the circumferential mode of the cylindrical part is less than or equal to approximately 10% of the central frequency of the transducer.
• the invention also relates to a method for emitting low frequency acoustic waves in an immersion fluid comprising the following steps:
• the invention will find a particularly advantageous application in submarine acoustic communication systems.
• Another application of the transducer of the invention relates to underwater acoustic tomography.
• the present invention also relates to the features which will emerge in the course of the description which follows and which will have to be considered individually or in all their technically possible combinations.
• FIG. 1 shows a sectional view of an electro-acoustic transducer according to one embodiment of the invention.
• the transducer of FIG. 1 is an electro-acoustic transducer enabling underwater acoustic communication by resonant coupling between a piezoelectric stack and a cylindrical piece of annular section of axis coinciding with the piezoelectric stack.
• the cylindrical piece is circumferential resonance, this resonance mode is also called the breathing mode.
• Figure 1 shows schematically a sectional view of a transducer comprising two piezoelectric motors (1a, 1b) aligned along a longitudinal axis (6).
• the piezoelectric motors are fixed on either side of a central counterweight (4).
• the opposite ends of the two motors (1a, 1b) are respectively fixed to a horn (3a, 3b).
• the assembly consisting of piezoelectric motors (1a, 1b), counterweight (4) and flags (3a, 3b) is maintained prestressed by rods, called prestressing, which can be either external or internal to the pillar axial.
• the transducer further comprises a cylindrical piece (5), preferably of annular section, hollow and coaxial with the longitudinal axis (6).
• the cylindrical piece (5) is arranged around the counterweight (4) and preferably centered on the plane of symmetry of the transducer.
• the length of the cylindrical part (5) is less than the total length of the piezoelectric stack and countermass, or even less than the distance between the two flags (3a, 3b).
• the outside diameter of the cylindrical piece (5) is substantially equal to the outside diameter of the flags.
• the thickness of the cylindrical piece is typically of the order of one centimeter.
• the walls of the cylindrical part are preferably solid, the cylindrical part (5) having two openings at its two opposite ends.
• the dimensions of the hollow cylindrical part (5) are such that it delimits a fluid internal cavity (7).
• the fluid cavity (7) is open to the outside through the openings at both ends so that when the transducer is immersed the volume of the cavity (7) is filled by the immersion fluid (8), for example seawater.
• the components of the transducer are permanently in equipressure with respect to the hydrostatic pressure immersion medium, regardless of immersion depth.
• the structure of the transducer allows it to withstand high hydrostatic pressures associated with large depths of immersion, without requiring a pneumatic compensation system.
• the physical parameters of the cylindrical piece (5) are determined so that it is able to generate a circumferential acoustic resonance mode.
• the first circumferential resonance mode is determined by the following formula:
• F r represents the resonance frequency
• S r the radial flexibility
• p the density of the material and has the mean radius.
• the application of this formula typically gives for a 1 m diameter aluminum disc a resonance frequency close to 1500 Hz.
• the excitation of the circumferential resonance mode of the cylindrical part (5) is done by the electrical excitation of a piezoelectric resonator (1 a, 1 b) via an acoustic coupling of the fluid cavity (7).
• the electro-acoustic transducer constitutes a source of low frequency ( ⁇ 1000 Hz) wideband acoustic emission based on the coupling of two resonators.
• the first resonator is the mass-spring type piezoelectric resonator, whose fundamental mode is longitudinal, called expansion-compression.
• the second resonator is a resonator formed of the cylindrical piece (5) having a circumferential or radial resonance mode.
• the longitudinal resonance mode and the circumferential resonance mode are coupled via the fluid cavity (7) consisting of the seawater of the surrounding medium.
• the coupling is achieved via the fluid cavity (7) contained within the cylindrical piece (5).
• the longitudinal resonance mode of the piezoelectric stack is sized to be near frequency in the circumferential mode of the annular piece to allow efficient coupling between the two resonances.
• the radial part may be metal or composite material (such as carbon fiber / epoxy) and is secured to the piezoelectric stack by central counterweight.
• the radial piece is connected to the central counterweight by suspension means forming an acoustic decoupler.
• the suspension means are made by suspension blocks (or block silence), for example in the form of rubber washers.
• the suspension means are not shown in Figure 1, to illustrate the acoustic decoupling between the counterweight (4) and the cylindrical part (5). Moreover, the suspension means are not sealed and do not obstruct the open fluid cavity.
• the mechanical structure of the transducer allows its use at great depth of immersion (greater than 3000 m).
• the transducer has no internal fluid portion filled with air or oil.
• the transducer of the invention thus has great robustness.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Mechanical Engineering (AREA)
• Transducers For Ultrasonic Waves (AREA)
• Piezo-Electric Transducers For Audible Bands (AREA)
• Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

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• 2011
  • 2011-02-01 FR FR1150771A patent/FR2971112B1/fr active Active
• 2012
  • 2012-01-31 CN CN201280011032.0A patent/CN103492090B/zh active Active
  • 2012-01-31 WO PCT/FR2012/050212 patent/WO2012104549A2/fr not_active Ceased
  • 2012-01-31 US US13/982,587 patent/US9387514B2/en active Active
  • 2012-01-31 JP JP2013552247A patent/JP5852138B2/ja active Active
  • 2012-01-31 EP EP12707834.3A patent/EP2670536B1/fr active Active

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