Note: Descriptions are shown in the official language in which they were submitted.
,' CA 02232992 2006-04-05
X3970-59
Electrode
TECHNICAL FIELD
The present invention relates to the technique of achieving a large area of
contact
and a good connection between a conductive electrode and the electrolyte which
is
in contact with the electrode. The electrolyte could for instance be in the
form of
either salt water or fresh water. Such an electrode with water as electrolyte
can be
used for measuring purposes or as a part of an antenna construction. With this
large area of contact, very small changes in electrical fields can be
measured,
whereby the electrode can be used for instance for measuring of water-
currents.
BACKGROUND OF THE INVENTION
For detecting changes in the electrical field under water, pairs of different
kinds of
electrodes, made of zinc, graphite, silver/silver chloride etc., have
previously been
used. They have all had their benefits and drawbacks, such as silver/silver
chloride
electrodes having high sensitivity but at high costs, zinc electrodes having a
low
price but beingvmechanically o~ electrically instable, and graphite electrodes
which
are difficult to manufacture according to defined specifications without
discarding.
Large active areas have required large physical dimensions and have, in connec-
tion with graphite electrodes, caused irreproducible properties conditioned by
small
chemical or morphological variations. Consequently, there are big problems
with the
previously available techniques.
PURPOSE OF THE INVENTION
The purpose of the invention is to solve these problems by accomplishing an
elec-
trode based on bundles of carbon fibres which are connected to a desired
conduc-
tor, and a method for manufacturing this electrode. A further purpose of the
inven-
tion is to accomplish an underwater electrode having much better performance
characteristics than previously available underwater electrodes. Furthermore,
the
purpose of the invention is to accomplish an antenna mainly for underwater mea-
surements.
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la
SUMMARY OF THE INVENTION
In accordance with one aspect of the present
invention, there is provided an electrode having a contact
surface that is able to contact an electrolyte, wherein the
contact surface includes a plurality of carbon fibres, with
at least one of their two ends gathered together and
electrically connected to a signal conductor through end
surfaces of the carbon fibres.
In accordance with a second aspect of the present
invention, there is provided a method for the manufacture of
an electrode, wherein a bundle of carbon fibres is wound
into a carbon fibre skein, after which the carbon fibre
skein is gathered together at a connection area where it is
bound together to form a connecting stud, the connecting
stud is treated to make the end surfaces of all the carbon
fibres gathered together in the connecting stud appear, and
the carbon fibre end surfaces thereafter are connected to a
signal conductor.
In accordance with a third aspect of the present
invention, there is provided an antenna comprising
electrically connected electrodes, each electrode having a
contact surface that is able to contact an electrolyte,
wherein the contact surface of each electrode with the
electrolyte includes a plurality of carbon fibres with at
least one of their two ends gathered together and
electrically connected to a signal conductor through end
surfaces of the carbon fibres.
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WO 97/12419 PCT/SE96/01202
2
An electrode according to the invention is provided with tufts or bundles of
carbon
fibres which have been cleaned along the fibre surtaces to get a good
electrical
contact with surrounding water, and which, furthermore, have been gathered to-
gether at one end and connected to an electrical conductor.
Such a manufactured electrode constitutes, together with an electrode of the
same
kind, a pair of electrodes which has turned out to have good antenna
properties in
water. Furthermore, it is comparatively easy to manufacture. As the electrode
is
made by carbon fibres, which have a homogenous chemical structure all along
the
fibres, an electrode having reproducible properties is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a step in the manufacture of a device according to the
invention.
Figure 2 shows a further step in the manufacture of a device according to
the invention.
Figure 3 shows a cross-sectional view according to fig. 1.
Figure 4 shows a first embodiment of the invention.
Figure 5 shows a second embodiment of the invention.
Figure 6 shows an antenna according to the invention.
DESCRIPTION OF THE INVENTION
An electrode according to the invention is produced by winding a bundle of
carbon
fibres into a carbon fibre skein 2, which is then gathered together at a
connection
area where the carbon fibres are bound together to form a connecting stud 5,
which
is then treated so that the end surfaces 6 will appear of all the carbon
fibres gath-
ered together in the connecting stud 5, after which the carbon fibres are
connected
to a signal conductor 8 through their end surtaces 6.
The electrode according to the invention is suitably produced, see fig. 1, by
winding
carbon fibres 1, in form of a bundle of generally 6000 carbon fibres,
approximately
50 turns around two end poles 3,4 with an intermediate distance of about half
a
meter, into a skein 2. These chosen values of the number of carbon fibres, the
number of turns and the distance, will result in an electrode having
approximately
600 000 carbon fibre ends for connection to a signal conducting cable. With
these
values, the area of contact with the electrolyte will be fully 3 m2.
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3
The oblong skein 2 of fibres is loosened carefully and is fixed in the middle
thereof,
for instance with a piece of shrinkage hose. After cutting in the middle of
the piece
of shrinkage hose, the ends of the two carbon fibre bundles fitted with hose
are em-
bedded in epoxy plastic in vacuum so that a connecting stud 5 is formed, see
fig. 2,
which after curing is shaped by means of grinding tools. The connecting stud 5
is
grinded until all the end surfaces 6 of the carbon fibres appear in the
grinding sur-
face, see fig. 3. On these carbon fibre end surtaces a metallic coating is
applied,
see fig. 4, which forms a connecting plate 7 for connection of a signal
conducting
cable 8. After the connection, the connection place is embedded in epoxy
plastic to
form a protective cover 9 for shielding the contact surfaces from water
influence.
Thereafter, the epoxy coating which the fibres have been given during their
manu-
facture is cleaned off from the fibre surfaces. This coating has generally
been ap-
plied to improve the wetting properthes of the fibres and their ability of
binding to an
epoxy matrix, and it constitutes a layer having insulating properties. Through
the
cleaning, the fibres, and thereby also the electrode, have been adapted for
use in
electro-chemical applications. The cleaning is carried out in a normal way
with dif-
ferent solvents, for instance with acetone, alcohol and water in tuns. Between
the
different steps in the manufacturing process it is checked that none of the
individu-
als differs in various aspects from empirically obtained set values, to make
sure that
the different individuals in a manufacturing process are as equal as possible
regard-
ing for instance electric resistance, length etc.
The manufacturing process is finished by cutting open the loop-shaped carbon
fibre
tufts 10, if a brush-like appearance with a lot of fibre ends sticking out in
the water
is desired, see fig. 4. Otherwise the carbon fibres are remained in loop-
shape, see
fig. 5, so that an attachment is possible in both ends, whereby a similar
utilisation in
water is possible independent of the spatial orientation of the attachment.
Final as-
sembling with mounting ears 11 for mechanical fixation and with a water
permeable
flow protection around the fibres is done in the easiest way, after which
final testing
and verification of the individuals, i.e. each electrode, is done in
laboratory.
Another possible method of manufacturing is to form the connecting stud 5 at
first,
by making an embedment at the middle part of the carbon fibre skein 2, after
which
the connecting stud 5 is bisected and the carbon fibre end surfaces 6 of each
bi-
secting surface are connected to a signal conductor 8 in the way mentioned
above.
The connection place is then embedded and the fibres are cleaned in accordance
with what is mentioned above.
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4
With the present type of electrode a large active area of an inert kind with
small
external physical dimensions and an extremely high reproducibility and
mechanical
durability is combined in a new way with a for the purpose simplifiable
manufactur-
ing technique. Two electrodes can also be combined to form a reliable and cost
ef-
fective antenna 12, see fig. 6, for detecting variations in the electrical
field under
water.
Possible utilisations could be scientific measurements of the geological E-
field,
measurement of sea-heave and water-currents, detection and measurement of ship
movements, or signal transmission between water vessels or divers with limited
range of voice messages .