Loading of flextensional transducer shells

Details Loading of flextensional transducer shells Loading of flextensional transducer shells

1992-12-03

1994-08-16

Hall, Carl E.

Metal working

Piezoelectric device making

29450, 310337, 367165, H01L 4122

Patent

active

053374614

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to apparatus and method for use in the manufacture of flextensional sonar transducers and in particular to a method for extending the major axis of flexural shells therefor to allow insertion of piezoelectric elements.
2. Discussion of Prior Art
Commonly, flextensional sonar transducers comprise one more stacks of ceramic piezo-electric elements held in compression along the major axis of an elliptical flexural shell made of filament-wound glass, carbon fibres or metal. In operation, electrical signals applied to the piezo-electric elements produce contractions and extensions along the major axis of the flexural shell. These in turn produce larger transverse flexing movements along the minor axis. In use, hydrostatic pressure on the external wall of the elliptical flexural shell reduces the pressure on the transducer stacks along the major axis. Thus, in order to prevent movement the stacks are assembled in the elliptical shell such that a pre-stress is applied along the length of the stacks. This pre-stress is designed to overcome hydrostatic pressure effects corresponding to the maximum pressure depth of the flextensional transducer.
Conventionally during manufacture of flextensional transducers the elliptical shell is made by first winding a resin-coated filament around a mandrel and then the piezo-electric drive elements are inserted along the major axis of the elliptical shell by applying a compressive force on the minor axis of the shell by means of two flat parallel plates to cause an extension along the major axis. The ceramic drive (piezo-electric elements) together with pre-tensioning wedges are then inserted and finally the compressive force on the minor axis is removed.
A major drawback associated with this method has been the occurrence of interlaminar shearing in the composite shell during the compressive stage of ceramic drive assembly. Conventional shell loading has proved particularly unreliable for deep water transducers, requiring large shell compression.


SUMMARY OF THE INVENTION

The object of the invention is to provide apparatus and method for improving the assembly of piezo-electric drive stack(s) within the elliptical flexural shell of a flextensional transducer. The invention provides:
a method of assembling one or more piezo-electric drive stacks along the major axis of the elliptical flexural shell of a flextensional transducer comprising the steps of: shell so as to extend the major axis of the shell;
Preferably the method includes the further steps of placing the shell within an enclosure; with fluid; and be applied to the outer surface of the shell.
Preferably the fluid is water.
Advantageously an elliptical seal provided with serrations therearound is sealed to each end of the shell.
In a preferred arrangement of the method the enclosure is assembled around the shell by means of the following steps: locating first and second enclosure endplates against respective elliptical seals for a shell end, at least one of the end plates being provided with an elliptical aperture; providing a cylindrical third enclosure member for pressure-tight assembly between the two end plates so as to form an enclosure defined by the inner surface of the third member, the two end plates and the outer surface of the shell.


BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanying Drawings of which:
FIG. 1 illustrates a known method for assembling piezo-electric drive stacks in the elliptical shell of a flextensional transducer;
FIG. 2 illustrates a method, according to the present invention, utilising isostatic pressure on the outer surface of the elliptical shell; and
FIG. 3 shows a perspective view, part cut away, of a hydrostatic press for carrying out the assembly of the flextensional transducer.


DETAILED DISCUSSION OF PREFERRED EMBODIMENTS

As shown in FIG. 1, a filament-wound elliptical flexural shell 10 for a flextensional transducer is conventionally compressed b

REFERENCES:
patent: 4731764 (1988-03-01), Ponchaud
patent: 4941202 (1990-07-01), Upton
patent: 4970706 (1990-11-01), Tocquet et al.

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