[0001] This invention relates to the mounting of sonic devices by which term is meant a
transducer for the transmission and/or reception of sound energy.
[0002] Particularly for underwater installations a number of such devices are often formed
as an array, and it is therefore necessary accurately to locate each sonic device
relative to other sonic devices of the array. Hitherto such arrays have been held
and located by a form of mechanical structure which generally comprises a metallic
block or stave. Such a stave is generally produced by machining, from the solid, the
appropriate apertures for each sonic device and location means has to be provided
to provide the required support, for example, of a resilient nature, for each device
at its nodal point, in its respective aperture in the stave, whilst mechanically de-coupling.
it from every other device. Such constructions are relatively complex in design, expensive
to manufacture, and unnecessarily heavy. These considerations also introduce complexities
in--the mechanical structure which may impair the acoustic performance of the elements
of the array.
[0003] An object of the present invention therefore is to provide ways of mounting and locating
one sonic device, or a number of sonic devices, e.g. to form an array, without having
a complex supporting construction, but at the same time providing for optimum performance
of each device once mounted and located.
[0004] According to one aspect of the present invention at least one sonic device is mounted
and located in a block of acoustically-opaque foamed plastics materials, with the
sensitive head or heads left uncovered by the plastics material.
[0005] The foamed plastics material used for the formation of the block may vary according
to requirements, but it may specifically be BIBBITHANE ISOFOAM 510 prepared and cured
in accordance with the manufacturers' instructions.
[0006] The foamed plastics material may have closed cells which are filled with gas generated
during foaming. This feature is found to improve the mechanical decoupling of one
sonic device from each other device of the array, by virtue of the gas within the
foam itself, which makes the material acoustically opaque.
[0007] According to another aspect of the present invention in a method of mounting a sonic
device or an array of sonic devices the, or each, sonic device is located within a
mould, preferably by its sensitive- head, and a body of foamed plastics material is
moulded around it.
[0008] Whilst it is envisaged that in most cases an array of sonic devices will be located
within a single block of foamed plastics material, in certain circumstances, it may
be appropriate for each sonic device to be located in an individual foamed plastics
block, and for such blocks then to be assembled into an array.
[0009] The block with its sonic device or devices is preferably mounted in a sealed casing
to protect it against sea water, for example. A space between a wall of the casing
and the heads of the devices may be filled with an acoustic coupling material.
[0010] The invention may be carried into practice in various ways, but one specific embodiment
will now be described by way of example with reference to the accompanying drawings,
in which:-
Figure 1 diagrammatically illustrates a completed moulding tool;
Figure 2 is a diagrammatic sectional end elevation through the tool of Figure 1 taken
on the line 2-2 of Figure 3;
Figure 3 is a plan view of the tool of Figure 1;
Figure 4 is a diagrammatic perspective view of a completed array of sonic devices
produced in accordance with the present invention;
Figure 5 is a transverse cross-section of one end of an array of the type shown in
Figure 4, assembled in an acrylic casing, and
Figure 6 is a longitudinal cross-section of one end of the assembly of Figure 5.
[0011] Figure 1 illustrates a typical moulding tool 10 employed with the present invention
and having a base 10A, end walls 10B and 10C, and side walls 10D and 10
E, the latter having a recess 10F between them and defining a ledge 10G (see Figure
2) which forms the top of the mould.
[0012] As shown in the cross-section of Figure 2, within the mould a single longitudinal
cavity 10H is formed within which an array of sonic devices 11 can be located, the
array comprising two longitudinal rows of spaced devices. The location of the sonic
devices within the mould is accurately carried out firstly by locating the sensitive
heads 24 of the devices in locating recesses 10J of the base 10A. Thereafter, and
before the remainder of the mould 10B, C, D, E, G is assembled, appropriate wiring
of the devices takes place. Each sonic device is coated with an appropriate releasing
agent in order that the foamed plastics material to be moulded will not stick to it,
since this would affect the vibration of the device. The end walls and side walls
are then placed in position, the latter abutting one another in a vertical plane 40
following which a set of holding pins 12 are projected down through the ledge 10G
to engage the top ends of the sonic devices. Each pair of pins 12 is connected to
one of a series of horizontal bars 14 (one is shown in Figure 3), each of which, in
turn, is connected to a pair of further supports 16 projecting upwardly therefrom.
[0013] In this way, the sonic devices are accurately located and secured wtihin the mould
cavity 10H prior to a moulding operation, during which foamed plastics
'material is either poured, or injected, into the cavity via one or more injecting
sprues or holes 18 formed in the ledge 10G as shown in Figure 3. Preferably, the choice
of foam, e.g. BIBBITHANE ISOFOAM 510, is such that the injection, and curing can take
place at room temperature. During curing, the holes 18 may be sealed. If the foamed
plastics material requires heat- curing this can- be carried out in an oven. The resulting
foam block 22 is shown diagrammatically in Figure 4. It provides a lightweight structure
in which all of the array of sonic devices are effectively encapsulated, although,
as shown in Figure 4, the element heads 24 of the array of devices are left proud
of the block and uncovered by the foam.
[0014] The foam moulding operation is such that the foam is formed with closed cells containing
gas generated during moulding.
[0015] The resulting closed gas-filled cavity foam is rigid enough to provide an effective
mounting for the devices, and to give protection against shocks. In addition, the
gas-filled foam has acoustic opacity to prevent acoustic coupling between devices.
[0016] The end walls 10B and 10C are preferably provided with circular recesses (not shown)
so that the end product has integral disc-like protuberances 20.
[0017] The resultant block of foamed plastics material with the array of sonic devices embedded
therein is now mounted in the manner shown in Figures 5 and 6 in a casing 30 of acrylic
material. The casing comprises a longitudinal tube having end caps 32 of the form
shown in Figure 6. It will be seen from Figures 5 and 6 that the casing 30 in the
region of the heads 24 of the sonic devices is spaced from these heads. This space
34 is filled with an acoustic coupling medium 35, which may, for example, be a semi-liquid,
petroleum jelly, lanolin, silicon oil, a melted solid, or a rubber. The choice of
medium depends on the intended use of the completed array. Thus, it may have a similar
acoustic refractive index to that of the sea water within which it is intended to
operate.
[0018] The end caps 32 locate the protuberances 20 of the foamed plastics material in order
to provide secure location for the array within the casing 30. Between the end caps
32 and the tube of the casing suitable O-ring seals 36 are provided so that there
is a sealed casing between the foam of the block 22 and the sea water in which it
is to operate.
1. A sonic device (11) mounted and located in a block (22) of acoustically-opaque
foamed plastics material, with the sensitive head (24) of the device left uncovered
by the plastics material.
. 2. A sonic array comprising a plurality.of spaced sonic devices (11) which are located
with respect to one another by being mounted in a common block (22) of acoustically-opaque
foamed plastics material, with the sensitive heads (24) of the devices left uncovered
by the plastics material.
3. A device or devices as claimed in Claim 1 or Claim 2 in which electrical leads
or. other interconnections from the device or devices are encapsulated' in the block
of foamed plastics material.
4. A device or devices as claimed in any preceding claim in which the cells of the
foamed plastics material, are closed cells and are gas filled.
5. A device or devices as claimed in any preceding claim, in which the foamed plastics
material is rigid enough to provide an effective mounting and to give protection against
shocks.
6. A sonic device or an array of sonic devices as claimed in any preceding claim,
in which the block is mounted in an outer casing (30, 32) sealed (at 36) against the
entry of water.
7. A device or an array as claimed in Claim 6 in which a wall portion of the outer
casing is spaced from the block (22) in the region of the operative head or heads
(24), and the space in that region is filled with an acoustic coupling medium (35).
8. A device or an array as claimed in Claim 7 in which the acoustic coupling medium
is a liquid, a semi-liquid, a jelly, lanolin, silicon oil, or a rubber.
9. A method of mounting a sonic device (11) or an array of sonic devices comprising
locating the or each sonic device within a mould (10), and forming a foamed plastics
material body (22) in the mould, to constitute a mounting for the device or devices.
10. A method as claimed in Claim 9 in which the,' or each sonic device is located
in the mould by its sensitive head or face (24), so that that head is not covered
by the foamed material.