Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a "barrel-stave" projector
which efficiently generates high power un~erwater spund at low
frequencies. The projector is also of small size, of light
weight, and is capable of being produced at a low manufacturing
cost.
It is known to construct underwater acoustic transducers
using a flextensional concept such as that discussed in applied
acoustics (3)~1970) Page 117 in an article by L.H. Royster
entitled "The Flextensional Concept: A New Approach to the Design
Of Underwater Acoustic Transducers". A transducer of this type
consists of a ceramic piezoelectric, or piezo-magnetic driver,
a mechanical shell and an internal and external fluid medium. The
shell is slit lengthwise forming curved beams or staves. The name
"flextensional" implies that the flexural vibration of the curved
stave i5 driven by the extensional vibration of the piezoelectric,
or piezo-magnetic, driver. The volume velocity of the vibrating
stave is much greater than that available from the driver, and the
resonance frequency is much lower.
However, such a known transducer is quite e~pensive to
manufacture and not very amenable to mass production. Moreover,
disassembly of the transducer for repair or for any other reason
risks its complete destruction. There are various configurations
produced utilizing the flextensional concept, and with some of
these configurations, the hydrostatic pressure due to submergence
; tends to generate tensile stresses in the ceramic driver, which
itself is very weak in tension.
In the present invention, the vibrating staves curve
inwardly rather than the conventional outwardly. The ceramic
driver that is utilized is a stack of rings coupled to stiff, flat
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end plates to which the staves are at-tached. The end plates are
preferably polygonal and, after assembly, the outer surface of
each of the staves could be machined so that the finished
projector is of round cross-section between -the end plates. This
shape allows for the easy application of a tubular rubber boot for
sealing purposes, such as waterproofing. If preferred, the
driver and the end plates can be open to the medium (with suitable
sealing) so that electrical and support cables can pass through
the driver. This allows for a very compact unit.
The invention will now be described with reference to
the accompanying drawings in which:
Figures lA and lB show two perspective views of a
preferred embodiment of the barrel-stave projector of this
invention without a rubber boot, with Figure lB having some of the
staves removed to show the inner construction;
Figure 2 is a cross-sectional view along a longitudinal
axis of Figure 1 with a rubber boot in place and without the upper
and lower end caps of Figure l;
Figure 3 is a plan view of the projector of Figure 2;
Figures 4A and 4B are cross-sectioned elevational and
plan views of a ceramic stack piezo-electric driver for the
projector, with the electrical connections shown schematically;
and
Figures 5A, 5B and 5C are side elevational, front
elevational, and plan views of a single stave of the projector of
Figure 1.
Referring to the drawings and in particular Figures lA
and lB, the "barrel-stave" projector consists of a driver 1
manufactured from piezo-electric ceramic; an enclosure around the
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driver 1 which consists of staves 2, and two polygonal end plates
3. The end plates are shown specifically as being octagonal in
this embodiment. The staves 2 are secured -to the end plates 3
with an adhesive, one suitable adhesive being epoxy resin, and
bolts ~, retained in threaded holes 4a in the end plates. The
bolts have countersunk heads which recess into suitable
countersunk holes in the staves so that the heads do not protrude
above the general immediate surface level of the staves. Between
adjacen-t staves there are gaps 5 which permits the staves to
vibrate freely in flexure. If it is wished to close off the
inside of the driver 1, end caps 6 and 7 can be used to cover
openings in end plates 3. The end caps can be of any suitable
design, being ~ade to fit partly within each opening within the
end plates, or being large enough to surround the opening. They
may be sealed with O-rings or bonded to the end plates if
disassembly is not a requirement. A single bolt (not shown)
through the center of the driver can alternatively be utilized for
pulling the end caps towards each other for sealing purposes.
~ote that no electrical wires or connections have been shown in
Figures lA and B, but such wires could be passed through one of
the end caps through a sealing grommet.
Referring to Figures 2 and 3, the end plates 3 having
openings 3a are clamped together across the ceramic driver 1 by
relatively small bolts 10 which mainly serve as an assembly aid to
provide ruggedness when handling during assembly. The end plates
will normally be bonded to the ends of the ceramic driver 1. ~o
electrical connections are shown in these Figures. Referring to
Figure 3, the outer surface of the staves is machined to form a
circular cross-s~ction throughout the length of the staves, and
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gaps ll between the staves at the end regions only are filled with
a potting plaskic such as epoxy. A tubular rubber boot 8 is
fit-ted over the stave section of the projector to prevent the
external acoustic fluid from entering the space 9 between the
staves and the driver 1. A light coating of ethylene glycol or
other suitable liquid is wiped onto the staves before the boot is
placed thereon, so that the boot ~ will be in good acoustical
contact with the staves. The enhanced vibration amplitude of the
staves is thus transformed into an enhanced volume velocity in the
external acoustic fluid.
The projector of Figure 2 and 3 is a free flooding
design, the interior of the driver 1 being open to the surrounding
medium. Therefore a sealing coating will be required on the inner
surface of the driver. If the surrounding medium is to be water,
a suitable waterproofing coating would be applied to the inner
surface of the driver. Alternatively, if the projector of Figure
2 is not to be free flooding, a pair of simple end caps can be
utilized such as those shown in Figures lA and lB.
The driver l is shown in more detail in Figures 4A and
4B is comprised of rings 12 of piezo-electric ceramic which will
typically be a lead zirconate-titante material, each ring being
plated on its flat surfaces with conductive electrodes and axially
poled to render it piezo-electrically active. The rings 12 are
bonded together by epoxy, or another suitable adhesive, in a
cylindrical stack and connected electrically in parallel, by wire
conductors 13 and 14. Short pins 15 are soldered or conductively
cemented into notches 16 in the rings 12 and conductors 13 and 14
are then soldered to these pins. There are other methods of
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connecting the conductors to ~he rings, the
method shown being only one of the preferred ways. The wiriny
harness is potted within a plastic 17, the plastic preferably
being epoxy. This potting of the harness prevents the connections
from suffering from fatigue failure which could be caused by the
severe vibration conditions under which the driver operates. If
-the driver is to be free-flooded with water, the potting must be
thicker than required if the driver is not to be free-flooded, and
the potting should extend around the whole of the inner surface of
the driver. The conductor 13 leads to the "high" side of an
electrical cable 18, and conductor 14 leads to the "low" side,
which is common to the metal parts of the projector. Therefore in
the structure shown, connection to the "low" electrode of the
upper ring of the driver can be made via the metal structure.
A single stave is shown in Figures 5A, 5B and 5C in its,
as installed, shape. Countersunk holes 19 accommodate the heads
of the bolts 4 and the outer surface of the staves is rounded to
present a circular cross-section finished body.
This invention is restricted only by the scope of the
claims which follow.
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