A COMPOSITE SONAR TRANSDUCER FOR OPERATION AS A LOW FREQUENCY UNDERWATER ACOUSTIC SOURCE

Abstract: A low frequency sonar transducer comprising a head (1) having first and second stacks of piezo ceramic elements (2, 3) in two spaced apart planes between common nodal end supports (7, 8), the stacks being oppositely polarised to act in push-pull action with one stack expanding and the other contracting to cause the head (1) to bow. The transducer is pre-stressed with fibres (6) to prevent fracture.

Description: A COMPOSITE SONAR TRANSDUCER FOR OPERATION AS A LOW . FREQUENCY UNDERWATER ACOUSTIC SOURCE This invention relates to a composite sonar transducer for operation as a low frequency underwater acoustic source. Sonar transducers are already well known and usually comprise a head which is coupled to a ceramic driving assembly such 5. as piezo-electric members so that motion of the head which is in contact with the ocean either transmits a signal outward or receives a signal translated by the piezo-electric assembly. Problems are encountered in these units when related to the frequency at which the operation is required and the object 10. - of the present invention is to provide a unit which can operate at a relatively low frequency at relatively high efficiency. The present invention operates on the basis of deforming a head which may act in the nature of a diaphragm so that while 15. selected edges of the head can be stabily supported the head itself distorts under action of the drive to form the transducer The invention comprises ceramic elements stacked along two separate planes and arranged so that when properly driven by the ceramic composite elements the head is bowed to provide 20. the necessary transmission. Thus when the ceramic elements form stacks along at least two planes in the head and are correctly driven they act in push-pull. In this way a relatively large unit can be constructed in 25. which stacks of the ceramic elements are arranged in groups spaced apart and adapted to be driven in opposite direction in a push-pull manner so that as one group expands the other group contracts to bow the assembly. To prevent fracture of the ceramic modules when it is driven into tension, tensile fibres, which may either be formed of KEVLAR or piano wire or other suitable tensile material, are 5. included in the structure to load the ceramics to avoid this fracture, the whole structure thus being pre-stressed with such tensile members so that, for instance, the ceramic can see a compressive force of about 3.5 - 4 MPa by controlling the compliance of the tensioning section, that is number and 10. diameter of tensioning elements, it is possible to maintain the integrity of the structure at a very high drive level. The low frequency behaviour is effected by the low mass and high compliance of the structure. The tensioning fibres are anchored in a rigid end structure 15. which then acts as a nodal support for the device. The ceramic members are elements which expand in the 33 direction as the lower contracts and vice-versa and thus form a structure formed of iso ropic p±&zσ—materials which can readily be applied and can exert the necessary forces 20. to cause the head so formed to bow. In order, however, that the invention may be fully understood, embodiments thereof will now be described with reference to the accompanying drawings. Embodiments of the invention are shown, but it is to be understood that these are examplary 25. only and not limiting. In the drawings:- FIG. 1 shows a composite element of the type used in forming the head in the invention, FIG. 2 shows at A the element when not electrically energized, at B when energized in push-pull by applying opposite polarities to the two adjacent assemblies, and at C the action when the polarities are reversed, FIG. 3 is a perspective view of a typical structure according 5. to the invention, FIG. 4 is an enlarged sectional perspective view of the device showing the pre-stressing fibres and indicating the motions by the arrows, FIG. 5 is a sectional elevation of a modification showing 10. centrally positioned stressing members, FIG. 6 shows a suggested clamping device to obtain the correct tension on the tensioning members, FIG. 7 is a schematic side elevation showing the unit supported between rigid end members and showing how the head 15. bows, FIG. 8 shows at A, B and C different methods of supporting the end members of the assembly from the supports by nodal support means, 8A showing a rod which acts as a pivot between the support and end member of the assembly, 8B showing a 20. spring section interposed between the support and end member and 8C showing how a compliant spring may be used as the nodal support means, and FIG. 9 shows a composite using printed circuit boards in the active composite structure. 25. Referring first to FIGS. 1, 2 and 3, the active composite transducer structure comprises a head 1 having two stacks of polarised ceramic elements 2 and 3 mounted on a support 4 to form an elemental cell 5 as shown in FIG. 1, a series of such cells 5 being stacked in- two planes to form a compound planar array comprising the ceramic elements 2 and 3 as shown in FIG. 2A. In FIG. 2B and C are shown respectively low bowing of the head 1 in the opposite direction occurs when the stacks 5. 2,3 of ceramic elements are electrically oppositely energized. In FIG. 3 is shown how a stack of 2 or 3 of ceramic trans¬ ducer elements can be supported by tensioning member 6 whereby to prevent overdrive showing end members 7 and 8 10. to which the tensioning members 6 are anchored. FIG. 4 shows the motion of the composite structure, the arrows 9 and 10 indicating the opposite motion at the two parts of the composite structure, the arrows 11 showing the signal transmitting movement of the composite structure when 15. driven by a signal, this figure showing the composite fragmented at one end. The dimensions shown in FIGS. 1 and 3 are examplary only. FIG. 5 shows a transverse section of the composite structure showing the tensioning members 6 disposed between the stacks 20. of ceramic elements 2 and 3. FIG. 6 shows a method of anchoring the tensioning members 6, this comprising apertured screw elements 12 having tapered portions 13 formed to be compressed on to the tension member 6 and arranged to encircle the tensioning members 25. and lock same to the end members 7 and 8 after applying the required tension. Other tensioning devices could be used. FIG. 7 is a schematic view showing the mode of operation of the transducer, the stacks of ceramic elements 2 and 3 and supports 4 forming the transducer head 1 which is carried 30. by rigid support members 14. The end members 7 and 8 of the transducer may be supported from the support members 14 by any nodal supports 15 which allow the bowing movement of the head 1 referred to, and in FIG. 8A is shown how a pivot rod 16 can engage in 5. grooves 17 formed respectively in the support member 14 and the end members 7 and 8 to form the nodal support. In FIG. 8B a spring section 18 forms the nodal support while in FIG. 8C a compliant spring 19 forms the nodal support 15. FIG. 9 illustrates how the supports 4 can be in the form of 10. printed circuit boards 4A, this f cilitating electrical circuitry. It will be appreciated, as stated earlier herein, that constructional details can be varied within the spirit of the invention, the invention relating to a push-pull 15. assembly adapted for low frequency-active sonar transducers in which the transducer is actuated by bowing a head formed by an assembly of ceramics under electrical activation, using tensioning means to prevent fracture of the ceramics by overdrive. 20. The system of transmitting low frequency sonar signals accord¬ ing to this invention consists in energizing a transducer head 1 comprising first and second stacks 2,3 of piezo ceramic elements arranged in two spaced apart planes between common nodal end supports, arranging the elements of the 25. first stack 2 to be polarised in a selected direction, arranging the elements of the second stack to be polarised in the opposite direction, and passing an electrical signal through both stacks to cause a push-pull action on the two stacks 2,3 which one expanding as the other contracts to 30. bow the transducer head 1 signal-wise.

Claims: THE CLAIMS DEFINING THE INVENTION ARE .AS FOLLOWS:- 1. A composite sonar transducer for operation as a low frequency underwater acoustic source in which the transducer comprises a head (1) having piezo-ceramic elements carried by support means and arranged to be energizable characterized 5. by stacks (2,3) of piezo-ceramic elements arranged along at least two separated planes in the said head and arranged to be energized in push-pull. 2. A composite sonar transducer for operation as a low frequency underwater acoustic source according to Claim 1 10. further characterized in that the head (1) is formed of an active composite structure comprising first and second- stacks (2,3) of piezo-ceramic elements arranged in generally planar form and positioned adjacent to each other, said elements of said first stack (2) being positioned in the 15. same polar orientation and said elements of the said second stack (3) being also in the same polar orientation, but of opposite orientation to the said first stack (2), and nodal supports (16) for the ends of the said stacks (2,3) whereby the said stacks cause the head to bow when 20. energized. 3. A composite sonar transducer for operation as a low frequency underwater acoustic source as defined in Claim 2 characterized in that the said transducer is arranged as a transmitter, and by means to apply an electrical signal to the ends of the said stacks (2,3) whereby at any time 25. to drive one stack to expand and the other to contract. 4. A composite sonar transducer for operation as a low frequency underwater acoustic source according to Claim 1, 2 or 3 characterized by arranging the stacks (2,3) of piezo-ceramic elements on supports (4) to form elemental 30. cells (5), and positioning an array of the said elemental cells (5) between the supports (4) to form a transducer head. 5. A composite sonar transducer for operation as a low frequency underwater acoustic source according to Claim 4 characterized by tension members (6) extending through the head (1) and anchored in end members (7,8) disposed 5. at the ends of the stacks (2,3) of the elemental cells (5), said end members (7,8) engaging nodal supports (15) whereby to support cells (5) . 6. A composite sonar transducer for operation as a low frequency underwater acoustic source according to Claim 4 10. or 5 characterized in that the said tension members (6) extend through the stacks (2,3) of piezo-ceramic elements. 7. A composite sonar transducer for operation as a low frequency underwater acoustic source according to Claim 4 or 5 characterized in that the said tension members (6) 15. extend through a space between the stacks (2,3) of the piezo-ceramic elements. 8. A composite sonar transducer for operation as a low frequency underwater acoustic source according to Claim 2 characterized in that the piezo-ceramic elements of the 20. stacks (2,3) comprise cells (5) each containing a plurality of piezo-ceramic elements on a support, a series of the said cells (5) being arranged in planar relationship and held between end members (7,8) carried by supports 14 through nodal supports (15) disposed between the end members (7,8) 25. and the supports (14). 9. A composite sonar transducer for operation as a low frequency underwater acoustic source according to any one of preceding Claims 4, 5 and 8 characterized in that the supports (4) of the elemental cells (5) are printed circuit boards. 10.: The system of transmitting low frequency sonar signals which consists in energizing a transducer head (1) characterised by arranging first and second stacks (2,3) of piezo-ceramic elements in two spaced apart planes between 5. common nodal end supports, arranging the elements of the first stack (2) to be polarised in a selected direction, arranging the elements of the second stack to be polarised in the opposite direction, and passing an electrical signal through both stacks to cause the push-pull action on the 10. two stacks (2,3) with one expanding as the other contracts to bow the transducer head (1) signal-wise. 11. The system of claim 10 characterised by arranging the piezo-ceramic stacks (2,3) to each comprise a cell consisting of a pair of spaced apart piezo-ceramic members 15. mounted on a support (4) about a central plane. 12. The system of claim 11 wherein the said support (4) is a printed circuit board (4A) , the said printed circuit boards (4A) being constructed to transmit the electric signal through the said stacks (2,3) . 20. 13. T e system of Claim 11 or 12 characterised by tensioning members (6) extending through the said cells (5) and anchored in end members (7,8) to restrict excessive expansion of the said piezo-ceramic members of the cells (5) . 14. The system of claim 13 characterised by applying a 25. selected tensioning to the tension members (6) and then locking the tensioning members (6) to the said end members (7,8).

Inventors: BEDWELL IAN ROSS, JANDERA ZDENEK, BEDWELL, IAN, ROSS, JANDERA, ZDENEK
Applicants: PLESSEY AUSTRALIA, PLESSEY AUSTRALIA PTY. LIMITED
Application year: 1987
Main classification: H04R17
IPC codes: B06B1, G01S7, H04R1