Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-04-03
2002-06-11
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S330000, C310S334000, C310S337000
Reexamination Certificate
active
06404106
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a pressure tolerant transducer for transforming energy from one form to another, for example for transforming electrical energy into acoustic energy or vice versa.
BACKGROUND OF THE INVENTION
Transducers, for example acoustic transducers, are well known in the prior art.
In a published international patent application no. WO 98/53924, there is disclosed a flexural plate sound transducer comprising a housing having an open central volume, a flexural plate attached around an inner surface of the housing and extending across the central volume, at least one piezoelectric element attached to a surface of the flexural plate. A mechanical hinge is formed near an outer periphery of the flexural plate and extends around the flexural plate. The mechanical hinge is formed such as to cause the flexural plate to move in a substantially piston-like manner when the piezoelectric element is energised. In the published application, the flexural plate and its associated at least one piezoelectric element are of uniform thickness except in the region where the hinge is formed.
In a published European application EP 0 264 557 A2, there is described a piezo-ceramic sound transducer comprising a metal membrane onto which is bonded in a central region thereof a piezo-ceramic slice. The membrane includes a support ring at a peripheral region thereof, and also a concentric ring-form compliant grove in the membrane between the slice and the support ring. The membrane is of uniform thickness even in the grove.
In a U.S. Pat. No. 5,724,315, there is described an omni-directional ultrasonic microprobe hydrophone. The hydrophone comprises two sensing elements where each element is composed of lead zirconate titanate and includes a plurality of columnar voids. In the hydrophone, the elements are bonded to an associated substrate material in the form of a backing plate. The voids are located in the hydrophone between the backing plate and the elements, the voids forming compressible cavities.
The inventors have appreciated that transducer structures known in the art often experience difficulties coping with relatively elevated environmental pressures applied thereto. Thus, the inventors have developed an alternative transducer exhibiting enhanced resilience to elevated environmental pressure, for example as experienced at a depth in the order of 200 m in aquatic environments.
SUMMARY OF THE INVENTION
The present invention seeks to provide a transducer incorporating a plate structure which is so constructed that it provides a workably low resonant frequency and which is capable of operating under extreme conditions, for example at large depths underwater in the order of 200 m.
According to a first aspect of the present invention, there is provided a transducer comprising a layer of active material, a backing plate having first and second major surfaces, to the first surface of which is affixed a layer of active material, and a region adjacent to the second major surface into which region the backing plate can be deflected, the region being substantially isolated from any external pressure incident on the layer of active material, wherein the backing plate and/or layer of active material is of a non-uniform thickness.
The invention provides the advantage that the transducer is capable of being used in applications where the transducer is exposed to relatively high external pressures.
One specific usage is where hydrostatic pressure is encountered when the transducer is used underwater. Thus, a transducer of the invention which acts in use to transform electrical energy into acoustic energy may be utilised as a ‘projector’ in a sonar system where the acoustic energy is broadcast into water. Alternatively, or in addition to, the transducer of the invention may be utilised as a hydrophone in a sonar system where it acts to transform acoustic energy into electrical energy.
Other applications envisaged for the transducer include diver-to-diver, ship-to-diver and ship-to-ship communications systems, and ships in these contexts should be understood to include ‘submarines’.
The transducer with which the present invention is concerned is of the type which includes a plate structure comprising a backing plate to at least one side, namely a major surface, of which an active material is applied. In the context of the present invention, an active material is defined as:
(a) a polarised or unpolarised material, such as lead-zirconate titanate, lead titanate, barium titanate, lead metaniobate, lead magnesium niobate/lead titanate (typically either ceramic or single crystalline) or nickel;
(b) a piezo-electric material, such as crystalline quartz; or
(c) a magnetostrictive material, such as Terfenol-D.
When the transducer is in use, the active material is deformed by the application of energy in one form and converts that energy into a different form. Thus, in one type of transducer for example, an alternating potential is applied to the two major surfaces of the active material plate via metal electrodes. Such excitation produces an alternating electrical field across the thickness of the active material plate. In response to this field, the plate attempts to expand or contract in the direction of its plane, that is radially in the case of a disc-shaped plate. The backing plate, to which the active material plate is bonded, constrains most of the said strain at or near the bond line. The side of the active material plate remote from the bond line, however, remains reasonably free to expand and contract. The composite plate therefore undergoes periodic flexure. In the case of an underwater projector, this movement is communicated to the surrounding water, and the energy is propagated away as sound.
In transducers where an active material plate is bonded to each side of a backing plate, the electrical field will be applied to each active material plate in such a phase relation so that the active plates flex in opposite directions, thereby reinforcing each other's action.
Because of its flexural action, such a transducer is sometimes referred to as a ‘bender’.
The invention provides an improved plate structure which overcomes problems associated with conventional prior art plate structures.
In this regard
FIG. 1A
shows a section through one face of a prior art plate structure, and
FIG. 1B
is a plan view of the plate structure of FIG.
1
A.
The plate structure
1
comprises a backing plate
10
which is flat and of uniform thickness. The backing plate
10
is generally symmetrical; the plate
10
is shown as circular but other shapes are possible. Attached to at least one side of the backing plate
10
is a layer
11
of the active material, for example a polarised electrostrictive material. The layer
11
as shown itself takes the form of a circular plate which is flat and of uniform thickness and which is attached to the backing plate
12
by suitable attachment means
13
.
As shown, the layer
11
is of such a size that there is an annular area
12
of the backing plate
10
adjacent the outer circumference thereof which is free of active material, although such an area does not necessarily have to be provided.
It is further known to have layers, for example in plate form, of the active material on both sides of the backing plate; such a configuration is described in a published international application WO 98/53924.
The backing plate
10
may be supported on a support structure which can take various forms as shown below.
Further and as illustrated in
FIG. 2
it is known to utilise two plate structures of a type illustrated in
FIG. 1
in a transducer. In
FIG. 2
the two structures
1
are separated by an annular support element
20
which is affixed at or near the outer circumference of the backing plate(s)
10
to support and separate the two plate structures. The space between the plate structures can be filled with a gas (for example air) or liquid.
Such a prior art structure will, when used underwater, experience hydrostatic pressure from the water, wh
Dale Philip John
Doble Michael James
Smith Grant
Walden John Robert
Budd Mark O.
Crowell & Moring LLP
Thales Underwater Systems Limited
LandOfFree
Pressure tolerant transducer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pressure tolerant transducer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pressure tolerant transducer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2950359