US 3769532 A
A device for attachment of electroacoustic transducers in casings immersed under water and effecting mechanical decoupling through flexible or deformable portions such as rubber or elastomer rings between the vibrating parts and their support.
Description (OCR text may contain errors)
te States Patent 1 1 Tocquet et a1. 1 1 Oct. 30, 1973  MECHANICAL DECOUPLING DEVICE FOR 3,539,980 11/1970 Massa, Jr. 340/10 X C M N o ELECTROACOUSTIC 2,917,642 12/1959 Wright et aL... 310/91 X 3,328,610 6/1967 Jacke et al 310/9.1 X TRANSDUCERS 3,337,844 8/1967 Baltakis SID/9.1 x [76} inventors: Bernard Tocquet, Sanary; Marcel 3,031,591 4/1962 y e! Personnic Toulon both of France Straube X 3,546,497 12/1970 Craster 310/9.1 X  Filed: Nov. 8, 1971 3,321,189 5/1967 Scarpa 310/91 X  Appl. No.: 196,344
Primary Examiner-J. D. Miller Assistant Examiner-Mark O. Budd  Foreign Application Pnority Data Attorney-Eric H. Waters et a1.
Nov. 6, 1970 France 7039959  11.8. CI. 310/89, 310/9.l, 340/10  ABSTRACT  Int. Cl. H04r 17/00  Field of Search 310/8 2 8 3 8 7 A device for attachment of electroacoustlc transduc- 0/9 ers in casings immersed under water and effecting me- I chanical decoupling through flexible or deformable  References Cited portions such as rubber or elastomer rings between UNITED STATES PATENTS the vibrating parts and their support. 3,474,403 10/1969 Massa et a1. 340/10 6 Claims, 7 Drawing Figures N fl J i //////1H/// //l W 11 f i I T T\ H, i m Z/c w? i; do '0, ,2 3
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DF0/?M/4770A/ paw/02E 7/45 UFmm) MECHANICAL DECOUPLING DEVICE FOR ATTACHMENT T ELECTROACOUSTIC TRANSDUCERS BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to electroacoustic transducers and specifically to the support of a vibration generator thereof in a support casing.
2. Description of the Prior Art Conventional electroacoustic transducers are provided with a stack of piezoelectric ceramic plates forming a generator, and the generator is mounted in a casing adapted for use in underwater acoustic operations. The generator is mounted in the casing or onto the frame of an antenna by means of an attachment which must serve to decouple the generator subjected to sustained vibrations and its support casing. Two constructions of such attachment are currently in use; the first being a wholly flexible attachment by means of an O- ring member and the second being a rigid attachment to the casing at the vibration node by means of an electrode intercalated between the piezoelectric ceramic plates.
These constructions do not satisfactorily meet the necessary requirements. A wholly flexible attachment is possible only for transducers subject to low ambient pressures and therefore not immersed to great depths in a body of water. Moreover, such attachment does not provide protection against impact, implosions or explosions, and to attain such protection it becomes necessary to use additional devices which greatly lower the efficiency.
A rigid attachment at the nodal point is used to a large extent and this partly resolves these latter problems but it down not provide satisfactory decoupling. In fact, it is not always possible to mount the support electrode precisely at the nodal point, if only because the electrode is of a certain thickness. Moreover, the position of the nodal plane itself is not permanent and it varies in relation to the frequency. This makes the attachment of the transducers for a very large pass band a delicate operation.
The difficulties presented by both these arrangements usually result in a deterioration of the electroacoustic efficiency which is all the more pronounced the wider the transducer band and the greater the depth of immersion.
SUMMARY OF THE INVENTION An object of the present invention is to provide a system for attaching an electroacoustic transducer either in its sealed casing or directly to an antenna frame to remedy the above deficiencies and additionally to increase electroacoustic efficiency.
The invention comtemplates as an attachment means a mechanical part termed an electrode support, comprising two rigid portions, one integral with the stack of piezoelectric plates, and constituting one of the electrodes, and the other integral with the casing or more generally with the transducer support. Between these two portions is a connection having a high mechanical impedance allowing slight relative movements of the portions of the order of -100 millimeters under the force of hydrostatic pressure at maximum depths of the order of 50 to 100 kilonewtons for a diameter of several centimeters. Further, when the assembly has to withstand impact, explosions or implosions, stop means are arranged for limiting displacement of the portion integral with the piezoelectric stack.
In the course of construction, the connecting element of high mechanical impedance is mounted close to the nodal plane, under various working conditions, thus assuring optimal acoustic decoupling of the piezoelectric stack relative to the support.
The aforesaid mechanical attachment is constructed in terms of the conditions of manufacture, use and environment in order to attain suitable impedance and mechanical properties.
Such mechanical attachment can be made of one or more metal or hard plastic rings in which two or more deep grooves are machined in planes perpendicular to the axis of the rings, leaving between them only a thin partition of material having the desired flexibility to provide the required relative movement between the two rigid portions located on both sides of the grooves. The elastic connection between the two rigid portions can also be obtained by one or more discs of the same material or of different materials respectively secured, as by cementing or welding, at their inner and outer peripheries to the respective portions to be connected.
The attachment can also be constituted of two or more stiff or rigid rings nesting into each other with a predetermined clearance and assembled by means of a rubber or elastomer ring fixedly attached, by cementing or preferably by hot vulcanization under pressure, to the opposite faces of the two attachment rings.
One of the attachment rings is made integral with the piezoelectric stack with which it forms one of the electrodes, by precast cementing with the whole of the transducer.
The other attachment ring is rigidly attached to the sealed casing which serves as a housing for the transducer, or to the antenna frame. The connection between the two rings is obtained by the rubber or elastomer ring.
The mechanical clearance between thesetwo attachment parts when they are nested into each other is calculated so as to meet the following requirements: the friction between the two parts must be zero or negligible; the clearance between the parts must not allow the rubber or elastomer to seep out by creepage under the action of the forces due to the surrounding hydrostatic pressure exerted on the electrode through the outside vibrating surface of the transducer.
The size, shape and characteristics of the rubber or elastomer ring joining the two parts are selected so as to obtain the required high mechanical impedance.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal section through a transducer equipped with an electrode support according to the invention,
FIG. 2 is a sectional view of the support by itself,
FIG. 2a is an enlarged sectional view of a modified ring used in the support,
FIG. 2b shows another modified ring,
FIG. 3 is a graphical representation of deformation of the support with respect to applied force,
FIG. 4 is a sectional view of another embodiment of an electrode support, and
FIG. 5 is a graphical representation similar to FIG. 3, for the support of FIG. 4.
DETAILED DESCRIPTION Referring to FIG. 1, herein is illustrated an embodiment of a transducer with an electrode support I! adapted for use as a small size electroacoustic transducer in underwater operations at which the maximum hydrostatic force on the electrode is 32,000 newtons.
The transducer comprises a conventional stack of piezoelectric ceramic plates P assembled as a unit on shaft 8 and sewing as one of the electrodes. A counterweight W is assembled with the unit and the assembly is mounted in a metal casing C by the electrode support I-! constructed in accordance with the invention. The casing C is contained within an airtight enclosure E carrying an acoustic element F as is conventional.
The electrode support I-I comprises an inner member 1 made of an aluminum alloy and fixedly secured to the stack by an adhesive or the like. The support I-I further comprises an outer member 2 made of steel. The outer member 2 is threaded externally and is screwed into the casing C of the transducer. A very compact unit is thus obtained. The inner and outer members I and 2 are joined together by a ring 3 which is fixedly secured at its opposite faces respectively to members l and 2. The ring 3 is secured to the members 1 and 2 by adhesives, or preferably by hot vulcanization under pressure. The ring 3 is made of an elastomer substance such as Neoprene having a Shore hardness of 50 on scale A, after the vulcanization at high temperature and intense pressure. The inner and outer members are interfitted with minimal clearance of less than 0.5 mm and offer little or no frictional resistance to their relative longitudinal displacement.
FIG. 3 graphically illustrates the relative movement of the inner and outer members 1 and 2 as a function of the applied force. Up to forces of 50,000 newtons, such relative movement is very low and linear in relation to the applied force, even after a considerable number of cycles.
Th electroacoustic performance of the transducer using this attachment arrangement of the electrode holder shows the efficiency to be improved by more than percent as compared to identical transducers equipped with the standard attachment.
FlG. 2a shows a modification of the ring of the support and in FIG. 2a the ring 3a is formed with inner and outer grooves 31 and 32 respectively in a plane perpendicular to the axis of the ring 30 to define a thin wall of material 33 providing the requisite flexibility. The ring 311 can be made of metal or hard plastic material.
FIG. 2b shows another modification of the ring and herein the ring 3b is composed of a plurality of juxtaposed discs 41, with clearances therebetween, of the same or different materials and respectively secured, e.g., by cementing or welding, at their inner and outer peripheries to the inner and outer members I and 2.
A second embodiment of the electrode support is illustrated in FIG. 4 and is adapted for a decoupling electrode of a transducer on which forces up to 90,000 newtons may be applied. This embodiment provides for impact resistance limiting the displacement of the inner member of the electrode support under the effect of separation forces.
In the embodiment of FIG. 4, the inner member 1' is made of aluminum alloy as is also the outer member 2'. The ring 3' is made of Neoprene and has a Shore hardness of 60 on Scale A after vulcanization under normal conditions of temperature and pressure. The transducer is attached to the casing by two screws engaged in threaded bores 5 in member 2'. A circlip 6 is engaged within the outer member 2' for limiting relative displacement between members I and 2' in one direction. The members I and 2' are formed with opposed respective shoulders 7a and 7b which limit relative movement of members 1' and 2' in the opposite direction. Thus, protection is provided against excessive relative displacement or implosion forces.
FIG. 5 shows graphically the relative displacement of members 1 and 2' with respect to applied force. The displacement is low and perfectly linear with respect to force up to 100,000 newtons.
What is claimed is:
1. In an electroacoustic transducer adapted for immersion in a body of water to a considerable depth and having firstly a vibration assembly formed by a stack of piezoelectric elements alternating with electrodes and having a nodal plane and means for transmitting vibration to the surrounding water and secondly a leak proof casing, said vibration assembly and said casing being bodies of revolution around the same, center line; the provision of means for supporting said stack within said casing, said means comprising an inside ring fastened to said stack close to said nodal plane; an external ring fastened to said casing, said external and internal rings being of substantially equal thickness and facing each other, each comprising two portions of different diameters interjoined along a face perpendicular to said center line and nesting within one another parallel to said center line with very close clearance between the external face of the inside ring and the internal face of the external ring, said faces of each of the two rings perpendicular to the said center line and facing one another being spaced from one another at a particular distance so that the external surface of the inside ring and the internal surface of the external ring define a housing therebetween; and an elastic coupling means located in said housing, said elastic coupling means having a high mechanical impedance and being able to resist the stresses due to high hydrostatic pressure.
2. A support means as claimed in claim 16 wherein said elastic coupling means comprises an elastic plate located in said housing, said plate having opposite faces which are perpendicular to said center-line, said faces being adhesively secured to said faces of the two rings which are perpendicular to the said center line and facing one another.
3. A support means as claimed in claim 1 wherein said elastic coupling means comprises plates of elastic material of equal dimensions, stacked in said housing and fastened circumferentially internally and externally respectively to the external periphery of the said inside ring and to the internal periphery of the said external ring defining the housing.
4. A support means as claimed in claim l comprising stop means for restricting the relative movement of the inside ring and of the external ring to prevent implosion of said elastic coupling means.
5. A support means as claimed in claim Al wherein said stop means comprises firstly, a clip engaged in a slot provided in said casing to limit the movements of the inside ring parallel to the center line in one direction and secondly a shoulder located on the external ring and facing a shoulder on the inside ring to limit the movements of said rings parallel to the axis in opposite directions.
6. A support means as claimed in claim 5 wherein said inside and external rings each have a second surmeasured along the axis of the transducer is less than the distance measured in the same direction separating the faces which define the housing in which said ealstic face perpendicular to the center of each, the second 5 cmpling means is mounted-