Composite sonar transducer for operation as a low frequency unde

Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type

Patent

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Details

367158, 310337, H04R 1700

Patent

active

048782076

DESCRIPTION:

BRIEF SUMMARY
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 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 related to the frequency at which the operation is required, and the object 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 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 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 a push-pull manner.
In this way a relatively large unit can be constructed in 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 fibers, which may either be formed of KEVLAR or piano wire or other suitable tensile material, are 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 diameter of tensioning elements, it is possible to maintain the integrity of the structure at a very high drive level.
The low frequency behavior is effected by the low mass and high compliance of the structure.
The tensioning fibers are anchored in a rigid end structure which then acts as a nodal support for the device.
The ceramic members are elements which expand in the upper direction as the lower contracts and vice-versa and thus form a structure formed of isotropic piezo materials which can readily be applied and can exert the necessary forces 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 meant as example only and are 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 to the invention,
FIG. 4 is an enlarged sectional perspective view of the device showing the pre-stressing fibers and indicating the motions by the arrows,
FIG. 5 is a sectional elevation of a modification showing 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 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 spring section interposed between the support and end member and 8C showing how a compliant spring may be

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