US 3284562 A
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Nov. 8, 1966 F. STEBLETON FLEXIBLE ELECTRICAL CONDUCTOR Filed Feb. 8, 1965 COMPRESSED CONDUCTIVE PARTICLES ELASTOMERIC INSULATION INVENTOR LEO F. STEBLETON BY im/m/hm ATTORNEY United States Patent 3,284,562 FLEXIBLE ELECTRICAL CONDUCTOR Leo F. Stebleton, Midland, Mich., assignor to Dow Corning Corporation, Midland, Mich., a corporation of Michigan Filed Feb. 8, 1965, Ser. No. 430,953 3 Claims. (Cl. 174--110) The present invention relates to insulated electrical conductors and more particularly to electrical conductors for use under conditions of frequent flexing, and to methods of making such conductors.
Insulated electrical conductors in use today are generally made of strands of solid electrically conductive material such as copper or other metals, surrounded by an electrically insulating jacket. For use under conditions where the conductor is frequently flexed it is known to form the conductor in the shape of a coil or in a zigzag pattern to allow for flexure. In cases where frequent conditions of flexure occur, however, the solid conductor frequently breaks due to fatigue. In particular applications such as, for example, in electrical conductors used with stimulation equipment for heart muscles in the medical field, wherein the conductor may be permanently embedded in the human body, an open circuit can be disastrous.
It is an object of the present invention to provide an insulated electrical conductor which is incapable of being broken by flexure.
A further object is the provision of an electrical conductor suitable for use within a living body.
Other objects and attendant advantages of the invention will become apparent from the following description thereof. Briefly, the present invention consists of a hollow tube of silicone rubber, or the like, in which a quantity of freely flowable particles of electrically conducting material are held under compression and therefore in intimate contact with one another.
In the accompanying drawings:
FIG. 1 is a view in perspective of a segment of insulated electrical conductor made in accordance with the present invention, and
FIG. 2 is a diagramamtic end view of the conductor of FIG. v1 illustrating the forces applied to the conductive material.
Referring now to the drawings wherein like reference characters designate like parts in both views, there is shown in FIG. 1 a tube 11 of electrically insulating material of an elastomeric nature. Silicone rubber has been found to be an ideal material since it is a good electrical insulator and is chemically inert within a living body, as is well known in the art. Held within the tube 11 is a quantity of freely flow-able electrically conducting particles 12. Silver, in ball form, rather than flake form, is a preferred material, although other good electrical conductors capable of formation into freely flowing par-ticles may be used.
In manufacture, the tube is first expanded in diameter. With silicone rubber this may be done simply by use of a slowly evaporating solvent, such as Stoddard solvent. When the tube has been expanded, the finely granular conductor is poured into tube and the tube is then shrunk. In the case wherein Stoddard solvent has been used for expansion, shrinking may be accomplished simply by heating to dry the solvent out of the tube. As an alternative to using solvent for expansion of the tube, the tube may be inflated with air and while being held in its inflated condition the conductor is poured into the tube.
Upon shrinking of the tube, the conductive particles are held in compression by the elastomeric nature of the tube due to the attempted reduction in diameter. As shown in FIG. 2, the compressive forces, indicated by the arrows 13, exerted due to the elastomeric nature of the tube 11, hold the particles in intimate contact with one another, thereby insuring good electrical contact throughout. In use, as the conductor is flexed the particles may shift in position due to their freely flowable nature, but intimate electrical connection between particles is never lost. Thereby a high electrical conductivity is retained in a conductor which is not subject to breakage.
Obviously, modifications and variations of the invention will become apparent to those skilled in the art. Accordingly, it is to be understood that, within the scope of the appended claims, the invention may be practiced, otherwise than as specifically described.
That which is claimed is:
1. An insulated electrical conductor comprising:
a multiplicity of free flowing electrically conductive particles positioned in a plurality of layers, and
a tube of electrically insulating elastomeric material enclosing said particles and holding said particles in compression.
2. An insulated electrical conductor as defined in claim 1 wherein said tube is silicone rubber.
3. An insulated electrical conductor as defined in claim 2, wherein said electrically conductive particles are ballshaped particles of silver.
References Cited by the Examiner UNITED STATES PATENTS 450,734 4/1891 Bunker 174119 2,249,091 6/1937 Robinson et al. 174-152 X "2,577,466 12/1951 Jones 156-85 X 2,739,616 3/1956 Duff. 3,185,182 5/1965 Waddell et al. 156-294 X FOREIGN PATENTS 167,3 87 12/ 1950 Austria.
LEWIS H. MYERS, Primary Examiner.
LARAMIE E. ASKIN, Examiner.
H. HUBERFELD, Assistant Examiner.
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