Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 2013/041437 PCT/EP2012/067935
Support module for an underwater antenna
The invention relates to a support module of the type,
an acoustic underwater antenna as well as a method for
attaching a support module.
In water acoustic technology, direction finding
systems with a towed antenna towed by a watercraft are
generally used as a receiver for water acoustic
signals, said direction finding systems when not in
use being wound onto a drum which is fixed on board.
Such towed antennas have a significant length in order
to detect and locate targets over long distances.
A towed antenna constructed from a plurality of
mechanically and electrically connected sections is
disclosed in DE 69 429 586 T2, said towed antenna
having a plurality of hydrophone carriers for
fastening the hydrophones in the towed antenna. To
this end, the hydrophone carriers are pulled into an
antenna sheath configured as a resilient tube which is
filled with a filling agent in order to adjust the
density of the towed antenna substantially to the
density of the seawater.
The hydrophone carriers are arranged spaced apart from
one another in the longitudinal direction in the towed
antenna, and thus form a skeleton structure which
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absorbs the forces which act on the towed antenna and
passes a central traction cable through said carriers.
The transducers of a towed antenna which are generally
used have a separate transducer element, in particular
a hydrophone, and are pressure-sensitive in all
directions, whereby in each case a spherical
directional characteristic is produced. By means of a
direction generator, the received signals of the
transducers are combined to form group signals, the
directional characteristics thereof being oriented in
different directions, laterally relative to the towed
antenna. Thus correct focusing of the directional
characteristic may be achieved transversely to the
longitudinal direction of the towed antenna, but the
sensitivity in the radial direction is the same. As a
result, it is not possible to carry out a right-left
differentiation of a detected target.
Clear direction-finding results may be achieved, for
example, by a transducer consisting of three
transducer elements, the transducer elements being
arranged at the same radial spacing to the
longitudinal axis and offset relative to one another
by the same circumferential angle. The received
signals of two of the three transducer elements are
received with a time delay to form a received signal
of the transducer. Directional characteristics of the
towed antenna are formed by means of such received
signals of all transducers, the main receiving
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directions thereof in each case being oriented to one
side. Combining the received signals of three
individual transducer elements of a transducer by
using such signal technology is set forth in DE 31 51
028 C2.
Due to the measured time delays between all three
pairs of transducer elements, the left-right ambiguity
may be resolved, irrespective of the rotation of the
towed antenna. This method, however, requires
relatively large spacings between the transducer
elements in order to maintain measurable time delays.
Acoustic towed antennas are also used in seismic
marine research. US 5 867 451 reveals a marine seismic
cable assembly comprising a cable, hydrophone
housings, a buoyant filler and an outer protective
jacket, the cable comprising a load-bearing fibre
bundle, data transmitting wires, electrical power
conductors, optical fibres and a protective sheath.
The hydrophone housings are arranged individually
spaced apart around the cable.
Moreover, US 3 675 193 reveals a seismic hydrophone
streamer which is formed by using hydrophones
consisting of cylindrical crystal segments, the
crystal segments being arranged with their axis
transversely to the axis of the streamer cable. A
fastening means is provided, said fastening means
being fastened from the outside to a central traction
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cable and supporting the crystal parallel to the axis
of the traction cable.
The object of the invention, therefore, is to improve
the acoustic properties of the towed antenna, with a
diameter thereof which is as small as possible.
The invention solves this object by the features of a
support module for an acoustic underwater antenna, by
an underwater antenna and by the features of a
corresponding method for fastening a support module.
The invention provides the advantage of a symmetrical
construction of the transducer being provided by a
specific design of the support module, by which good
acoustic properties may be achieved in spite of the
reduction of the spacing between the transducer
elements. To this end, the support module comprises a
shaped piece which is composed of at least two parts
and serves for accommodating the transducer elements
which are combined to form a transducer.
A central axial opening in the shaped piece permits a
traction cable of the towed antenna to be passed
through, said traction cable distributing the tensile
stress via the antenna.
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A releasable connection is preferably located between
the parts of the shaped piece for opening the support
module in order to attach said support module to the
traction cable and for closing the support module
after being positioned on the traction cable.
By means of the support module according to the
invention, acoustic problems which are caused by
asymmetrical support shapes are avoided. As a result,
the spacings between the transducer elements may be
advantageously reduced as, with such a symmetrical
construction of the support module, said transducer
elements have substantially improved acoustic
properties.
Moreover, the support module has an electronic
assembly assigned to the transducer, for signal
processing of the received signals of the transducer
elements. Preferably, the electronic assembly is
arranged radially around the shaped piece, so that the
support module not only serves for mechanical
stabilisation of the towed antenna and for receiving
the transducer elements but also for retaining
electronic components. By such an arrangement of the
electronic assembly on the support module, the
spacings between the transducers of the towed antenna
may be advantageously minimised as no additional
shaped pieces are required for receiving the required
electronics. A spacing which is able to be minimised
between the transducers has the advantage that the
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receiving frequency of the towed antenna may be
shifted to higher frequencies.
According to a preferred embodiment of the invention,
the electronic assembly is configured as flat boards,
in particular as printed circuit boards, which are
directly populated with electronic components assigned
to the transducers. Moreover, the printed circuit
boards are connected to a flexible strip containing
conductors. This advantageously permits the space-
saving arrangement radially around the shaped piece.
In a further preferred embodiment of the invention, at
least three transducer elements are arranged on the
shaped piece, offset relative to one another by the
same circumferential angle and in each case having the
same transverse spacing relative to the longitudinal
axis of the support module. Preferably, each
transducer element is attached to a part of the shaped
piece, the parts of the shaped piece being releasably
connected together. Such a transducer arrangement, in
which at least three transducer elements are combined,
results in the advantage of being able to make a
right-left differentiation of a detected target.
In a further embodiment of the invention, the
transducer elements are resiliently attached to the
shaped piece. Such a resilient attachment has the
advantage of the decoupling of structure-borne sound
which improves the acoustic properties of the antenna.
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According to a further preferred embodiment of the
invention, the shaped piece is constructed from a core
piece and individual elements for receiving one
respective transducer element. A releasable connection
exists between the individual elements and the core
piece. Preferably, the individual elements are of
identical construction so that the transducer elements
of a set and/or of a transducer have the same acoustic
properties due to the same environment. This
releasable connection has the advantage that the
shaped piece may be opened by releasing at least one
individual element and thus may be positioned on a
traction cable.
According to a further preferred embodiment of the
invention, the support module has spacers between the
core piece and the individual elements. Said spacers
provide the advantage of producing an intermediate
space in which the transducer elements may be
positioned when attaching the individual elements to
the core piece.
In a further embodiment of the invention, the core
piece has a cover for closing the axial opening, the
cover being able to be fastened to the core piece. The
cover is preferably attached to the core piece over
the length thereof so as to prevent in an advantageous
manner the traction cable from slipping out of the
core piece.
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In a further embodiment of the invention, the support
module has a module housing. Preferably, said module
housing is made up of housing halves, in particular
two half-shells. It has the advantage of protecting
the shaped piece, in particular the core piece with
the electronic assembly attached thereto, from
mechanical stress.
In a further preferred embodiment of the invention,
the support module has one or more hook and loop
strips for holding the module housing together. This
construction has the advantage that an acoustic
decoupling of the support module from the sheath wall
of the antenna is produced by means of the hook and
loop strips, whereby the acoustic properties of the
antenna are improved.
According to a further embodiment of the invention,
the support module has a base carrier which is
configured in order to fasten the support module to
the traction cable. To this end, the base carrier is
initially screwed tightly to the traction cable and
then adhesively bonded thereto. The fastening of the
support module to the traction cable by means of a
base carrier has the advantage that easy replacement
of a support module is possible for the purpose of
maintenance operations. The support module is fixed by
at least one screw to the base carrier to prevent
twisting.
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In a further preferred embodiment of the invention,
the support module comprises recesses in the axial
opening of the shaped piece. This has the advantage of
also being able to guide power supply lines and signal
lines of the transducer elements through the support
module, in addition to the traction cable of the towed
antenna.
Moreover, the invention comprises an acoustic
underwater antenna, in particular a towed antenna, a
tubular outer casing and a traction cable in the
longitudinal direction on which at least one support
module, described above, is arranged. Preferably, the
support modules are configured to be substantially
cylindrical and have an external diameter which is
slightly smaller than the internal diameter of the
outer casing of the underwater antenna. This has the
advantage that the support modules may be pulled into
the tubular outer sleeve and thus provide the
cylindrical shape to the towed antenna.
In a further alternative embodiment of the invention,
the acoustic underwater antenna has an arrangement of
support modules, described above, and empty modules in
the longitudinal direction of the underwater antenna.
In this case, the empty module simply consists of a
shaped piece without transducer elements and
preferably serves for shaping and stabilising the
antenna if larger transducer spacings are required in
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the longitudinal direction for the antenna
construction. Moreover, the use of empty modules has
the advantage of avoiding deformation of the tube when
the antenna is wound onto a drum.
A further alternative embodiment of the invention
reveals a method for attaching the support module to
the traction cable of the towed antenna. To this end,
the support module is firstly opened by releasing the
connections between the individual parts of the shaped
piece, which required for opening, in order to
position said support module on the traction cable or
on a base carrier connected to the traction cable.
After fixing the support module to the traction cable,
the support module is subsequently closed by
connecting the individual parts of the shaped piece.
Further advantageous embodiments of the invention are
revealed from the sub-claims and from the exemplary
embodiments explained with reference to the
accompanying drawings, in which:
Fig. 1 shows a watercraft with a towed antenna
being towed thereby,
Fig. 2 shows a side view of a support module
according to the invention,
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Fig. 3 shows a plan view of a support module
according to the invention without the view
of individual elements of the shaped piece,
Fig. 4 shows a plan view of a support module
according to the invention,
Fig. 5 shows a plan view of an electronic sub-
assembly positioned in the sheet plane and
Fig. 6 shows a support module according to the
invention in a perspective view.
Fig. 1 shows a towed antenna 4 being towed by a
watercraft 2. In this case, the watercraft 2 may be a
surface water vessel or an underwater vessel, such as
for example a submarine.
The towed antenna 4 is retrieved and removed from the
water by means of a drum 6 located on board the
watercraft 2. The towed antenna 4 has a towing cable
8, two damping modules 10, 12 as well as an acoustic
part 14 located therebetween. The damping modules 10,
12 in this case serve for the mechanical decoupling of
vibrations of the acoustic part 14. A towing brake 16
is also located at the end of the towed antenna 4,
said towing brake, when towed, ensuring a certain
degree of tensile stress on the towed antenna 4
counter to the towing direction.
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The support modules are located at freely selectable
intervals in the towed antenna 4. Said support modules
serve for the dimensional stability of the towed
antenna 4 as well as for accommodating the transducer
elements and electronic sub-assemblies.
Moreover, a traction cable and signal lines for the
received signals of the transducer elements are passed
through the towed antenna 4, the support modules being
attached in an axially undisplaceable manner to said
traction cable. For protection against seawater, the
support modules are pulled into a resilient tubular
outer sleeve having tensile strength. To facilitate
the process, the support modules have to this end an
external diameter which is slightly smaller than the
internal diameter of the outer sleeve of the towed
antenna 4. The tube thus produced is preferably filled
with oil or a gel in order to ensure the buoyancy of
the antenna.
Fig. 2 shows a schematic view of a support module
according to the invention in a side view. The support
module 20 has a substantially cylindrical shaped piece
consisting of a plurality of parts, said parts being
releasably connected together. A core piece 22
primarily serves for shaping and receiving an
electronic assembly 24 which is arranged radially
around the core piece 22. Preferably, the shaped
pieces are manufactured from synthetic, technically
applicable plastics material, in particular polyamide.
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Via spacers 26, three individual elements 28 of
identical construction are connected to the core piece
22, a releasable connection being formed by means of
screws 30. This exemplary embodiment shows the
attachment of the three individual elements 28 on one
side of the core piece 22. The invention is, however,
not limited to such a construction. Instead, a
symmetrical construction of the support module 20 is
also possible. In particular, such a construction has
individual elements 28 arranged on both sides of the
core piece 22, said individual elements being
releasably connected via spacers 26 to the core piece
22.
A transducer element 32 is resiliently fastened to
each individual element 28 in order to decouple said
transducer element from the support module 20 of the
stresses caused by vibrations, for example. The
vibrations which are produced when the antenna 4 is
towed through the water are thus not transmitted to
the transducer element 32 from the shaped piece
connected via the traction cable.
In this exemplary embodiment, the transducer elements
32 have a spherical shape. The invention is, however,
not limited to such piezoceramic spheres. Instead, a
series of piezoelectric ceramics of different shapes,
piezoelectric polymers and fibre-optic transducers may
be used as transducer elements 32.
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Fig. 3 shows a plan view of a support module according
to the invention but without a view of the individual
elements. The transducer elements 32 are combined in
the known manner to form a set and/or a transducer,
the cabling of the transducer elements 32, also called
signal lines, as well as the power supply lines, being
guided through the support module 20 via recesses 36
in a central axial opening 38. The central axial
opening 38 is arranged centrally in the core piece 22
and serves to position the shaped piece on the
traction cable of the towed antenna. As the traction
cable, the power supply lines and the signal lines are
able to be installed in the interior of the support
module 20, a symmetrical construction of the support
module 20 is advantageously produced.
Fig. 4 shows a plan view of a support module according
to the invention. The individual elements 28 are
illustrated in this schematic view.
As also clearly indicated in Fig. 3, it is also
indicated in Fig. 4 that the core piece 22 is enclosed
by a cylindrical module housing 40. Preferably, said
module housing 40 is made up of two half-shells.
To this end, the core piece 22 has a greater diameter
on the outer faces so that the module housing 40 is
fastened in the recess thus produced in the centre of
the core piece 22 and thus fixed in the longitudinal
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direction. Preferably, the module housing 40 is welded
to the shaped piece, for example by ultrasonic
welding, and held together by hook and loop strips,
the hook and loop strips additionally serving for
acoustic decoupling from the tubular wall.
Moreover, the module housing 40 serves as protection
from mechanical stress for the electronic sub-
assemblies 24 located thereunder, for example when the
towed antenna 4 is wound onto the drum 6.
Fig. 5 shows an electronic assembly placed in the
sheet plane. The electronic assembly 24 is configured
as flat boards, in particular as printed circuit
boards 44, which are directly populated with
electronic components assigned to the transducers but
not shown in more detail here. In the exemplary
embodiment described, three populated printed circuit
boards 44 are provided, said printed circuit boards
being connected together via a flexible strip 46
containing conductors. As a result, the electronic
assembly 24 may be arranged radially around the core
piece 22. Such a printed circuit board arrangement
advantageously provides a greater surface area for the
electronic components to be used.
Fig. 6 shows a support module according to the
invention in a perspective view. For mounting the
underwater antenna according to the invention, a
plurality of the above-described support modules 20
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are attached to the traction cable. To this end, the
necessary screws 30 on the individual elements 28 are
released for opening the shaped piece.
For attaching the support module 20 to the traction
cable, the support module 20 has a base carrier, not
shown further here. Said base carrier is initially
tightly screwed to the traction cable and then
adhesively bonded thereto.
The base carrier also has a cylindrical shape and is
slightly longer than the entire shaped piece of the
support module 20. The substantially circular cross
section of a central part of the base carrier
corresponds approximately to the cross section of the
axial opening 38 of the core piece 22 without the
recesses 36 for passing through the power supply lines
and signal lines.
As a result, the open shaped piece of the support
module 20 may be placed on the base carrier in an
axially undisplaceable manner and secured against
twisting by means of a screw.
The shaped piece is now closed, by the individual
elements 28 being fastened via the spacers 26 to the
core piece 22. The transducer elements 32 which are
fastened to the individual elements 28 thus gain a
symmetrical construction relative to their
surroundings.
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The associated lines are guided in the recesses 36 of
the axial opening 38 through the core piece 22.
A cover is then pushed over the longitudinal side of
the core piece 22 in recesses provided therefor and
fastened thereto in order to secure the core piece 22
from slipping down off the traction cable or the base
carrier fastened to the traction cable.
Subsequently, the printed circuit boards 44 of the
electronic assembly 24 are arranged around the core
piece 22 and fastened, in particular screwed.
Preferably, an electronic assembly 24 is assigned to
each transducer, a transducer being produced by one or
more transducer elements 32.
Finally, the module housing 40 is closed by placing
the two housing halves on top of one another, the
module housing 40 being fitted between the two outer
regions where the core piece 22 has a slightly greater
diameter. Additionally, the housing halves are held
together by hook and loop strips. This results in an
acoustic decoupling from the tube, whereby the
acoustic properties of the antenna are improved.
The maximum operating frequency in which the towed
antenna 4 operates is provided by the spacing between
the transducers. So that the towed antenna 4 is able
to cover a frequency range, the towed antenna 4 has
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regions with a variable number of transducers. Where
the spacings between the transducers have to be
larger, empty modules are arranged between the support
modules 20 in the longitudinal direction of the towed
antenna 4. Such empty modules have no transducer
elements 32 and serve to avoid deformation of the
tubular sleeve, for example when wound onto the drum
6.
When using towed antennas 4 of long length, it is
advantageous to keep the diameter of the towed antenna
4 as small as possible. This means, however, in an
arrangement as described above of three transducer
elements 32 for a right-left differentiation, that the
relative spacing between the transducer elements 32
has to be reduced. A smaller spacing between the
transducer elements 32, however, requires a specific
design of the support module 20 as provided by the
invention. By the symmetrical design of the support
module 20 according to the invention it is possible to
reduce the diameter of the towed antenna 4 whilst the
good acoustic properties of the underwater antenna are
kept the same.
All of the features cited in the above description of
the figures, in the claims and in the introduction to
the description are able to be used individually and
in any combination with one another. The disclosure of
the invention is thus not limited to the combination
of features described and/or claimed. On the contrary,
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all combinations of features should be considered as
disclosed.
