ELECTRODE

Abstract: An electrode having a contact surface with the electrolyte consisting of a number of carbon fibers (1), and a method for the manufacture of an electrode where a number of carbon fibers (1) are wound into a carbon fibre skein (2) whereupon the skein (2) is gathered together at a connection area and embedded to form a connecting stud (5), which is then treated so that the end surfaces (6) appear of all the carbon fibres gathered together in the connecting stud (5), after which the carbon fibre end surfaces (6) are connected to a signal conductor (8). And an antenna (12) comprising electrically connected electrodes where the contact surface of each electrode with the electrolyte consists of a number of carbon fibres (1).

Description: 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 being mechanically or 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 moφhological 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. SUMMARY OF THE INVENTION With the present type of electrode a large active area of an inert kind with small extemal 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 . 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 surfaces 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 properties 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 turns. 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. 6 8. Method according to claim 7, characterized in that the carbon fibres used for the manufacturing of the electrode have an epoxy coating which is finally cleaned off from the fibre surfaces by means of different solvents. 9. Antenna comprising electrically or in other way connected electrodes, char¬ acterized in that the contact surface of each electrode with the electrolyte consists of a number of carbon fibres (1).

Claims: Claims: 1. Electrode, characterized in that its contact surface with the electrolyte consists of a number of carbon fibres (1), which in at least one of their two ends are gathered together and electrically connected to a signal conductor (8) through the end surfaces (6) of the carbon fibres. 2. Electrode according to claim 1, characterized in that the carbon fibres in both of their ends are gathered together and electrically connected to a signal conductor (8). 3. Method for the manufacture of an electrode, characterized in that a bundle of carbon fibres is wound into a carbon fibre skein (2), after which the car¬ bon fibre skein (2) is gathered together at a connection area where it is bound to- gether to form a connecting stud (5), that the connecting stud (5) is treated to make the end surfaces (6) appear of all the carbon fibres gathered together in the con¬ necting stud (5), and that the carbon fibre end surfaces (6) thereafter are connected to a signal conductor (8). 4. Method according to claim 3, characterized in that the connecting stud (5) is formed by making an embedment of the carbon fibre skein (2) at the connec¬ tion area, and that the connecting stud (5) thereafter is bisected whereupon the carbon fibre end surfaces (6) of each bisecting surface are connected to the signal conductor (8). 5. Method according to claim 3, characterized in that the carbon fibre skein (2) is cut in the connection area whereupon thereby obtained end piece is embedded, and that the connecting stud (5) formed by the embedment is grinded until all the end surfaces (6) of the carbon fibres appear in the grinding surface. 6. Method according to one of claim 3-5, characterized in that the signal conductor (8) is connected to the carbon fibre end surfaces (6) through a metallic coating (7) which is applied on the carbon fibre end surfaces. 7. Method according to claim 6, characterized in that the connecting stud (5), the carbon fibre end surfaces (6), the metallic coating (7) and a part of the sig¬ nal conductor (8) are embedded in a polymeric substance to form a protective cover (9).

Inventors: BRAGE ANDERS, BRAGE, ANDERS
Applicants: BRAGE ANDERS, FOERSVARETS FORSKNINGSANSTALT, BRAGE, ANDERS
Application year: 1996
Main classification: H01R3
IPC codes: G01R29, G01V3, H01R3