Patent Application
20130105195
The present invention relates generally to communications systems and, more particularly, to conductors and cables for communications systems that exhibit enhanced conductivity.
A variety of communications cables are well known in the art. Many such communications cables are designed to carry high frequency signals such as, for example, signals with center frequencies of 100 MHz or more. Two types of communications cables are primarily used to carry such high frequency signals, namely (1) communications cables that include metal conductive wires and (2) fiber optic communications cables.
A variety of different conductive wire-based communications cables are known in the art, with two of the most widely used being coaxial cables and twisted pair cables. Typically, the conductive wires used in both coaxial and twisted pair cables use pure copper wires or wires formed of copper alloys, as copper is highly conductive and relatively inexpensive (e.g., as compared to silver which is more conductive but far more expensive). In order to reduce the weight or expense of a communications cable, in some cases copper or copper alloys may be plated onto the outside of another lighter and/or cheaper metal wire such as, for example, aluminum.
As a demand for communications systems that operate at higher frequencies and/or data rates increases, a need exists for communications cables that support these higher data rates without prohibitive increases in the expense, size and/or weight of the communications cables.
Pursuant to embodiments of the present invention, conductors for communications cables are provided that may exhibit significantly enhanced conductivity at high frequencies. These conductors are formed by welding or otherwise bonding a thin, elongated metal sheet such as a metal tape onto an outside surface of an elongated metal wire so that the metal tape at least partially surrounds the elongated metal wire. The thin metal tape may include a large number of carbon nanotubes either embedded therein and/or plated onto the metal tape.
As is known to those of skill in the art, carbon nanotubes are structural bodies formed of carbon atoms that have a generally cylindrical shape. The diameter of the cylindrical structure may be on the order of, for example, a few nanometers to a few hundred nanometers, while the length of the cylindrical structure may be much larger such as, for example, thousands or millions of times the diameter (e.g., tens or hundreds of microns). Carbon nanotubes may exhibit unique electrical properties, including conductivity along the length of the carbon nanotube that may be 1000 times greater than copper for the same area. Carbon nanotubes are commercially available in large quantities from a variety of sources including, for example, Mitsui & Co., Ltd. (Tokyo, Japan) and Bayer AG (Leverkusen, Germany). Carbon nanotubes may be plated in order to maintain conductivity even in the presence of imperfect internal lattice structures. The term carbon nanotubes as used herein is inclusive of such plated carbon nanotubes.
For high frequency communications, nearly all of the energy of an electrical signal will travel on or about the surface of an electrical conductor due to a phenomena known as the “skin effect” that is caused by eddy currents that are generated by the alternating current characteristic of the high frequency signal. As high frequency electrical signals flow primarily in only a small portion of a metal conductor, the effective resistance of the conductor may be significantly increased since nearly all of the current must flow through a small portion of the conductor.
Pursuant to embodiments of the present invention, conductors for high frequency communications signals are provided that include a metal core that has a carbon nanotube enhanced metal sheet (e.g., a metal tape) bonded to the outer surface of the metal core. In some embodiments, the metal core may comprise a copper wire, a copper alloy wire, a copper plated wire or a copper alloy plated wire. The metal sheet may be a thin copper or copper alloy tape that has the carbon nanotubes embedded therein and/or deposited thereon. In some embodiments, the metal sheet may comprise two separate metal tapes, the first of which is bonded along the longitudinal length of the top half of the copper/copper alloy wire core, while the second metal tape is bonded along the longitudinal length of the bottom half of the copper/copper alloy wire core so that the two tapes may substantially or completely surround the copper/copper alloy wire core. The metal core may also be hollow to reduce material usage.
In some embodiments, the metal sheet/tape may be manufactured so that the carbon nanotubes have enhanced alignment along at least one direction (i.e., the carbon nanotubes have a preference to generally align to be parallel to the x-axis, but may be randomly aligned with respect to the y-axis and the z-axis). In some embodiments, the carbon nanotubes may have enhanced alignment along two directions so that the carbon nanotubes have a preference to generally align along the axis of the wire core. Techniques for aligning carbon nanotubes are known in the art and hence will not be discussed further herein. The metal tape(s) may be welded to the exterior of the wire core by, for example, bringing the carbon nanotube containing metal tape and the wire core together while heating the metal tape and the wire core to a temperature that is sufficient to at least partially melt a surface of the metal tape and an outer surface of the wire core so that the two materials coalesce to have a common crystallographic structure.
The above-described conductors may exhibit substantially improved conduction of high frequency communications signals. As noted above, the high frequency signal will tend to congregate on the outer surface of the conductor. By providing carbon nanotubes to an appropriate depth (e.g., 260 microinches) along the outer surface of the conductor, substantially improved conductivity may be achieved at high frequencies (e.g. 100 MHz). Even very thin depths (e.g. 100 microinches) along the surface of the conductor may substantially improve conductivity at higher frequencies (e.g. 700 MHz). Moreover, by processing the metal sheet/tape so that the carbon nanotubes have a preference to be aligned along the axial direction of the conductor, the conductivity may be further enhanced.
Methods of plating metal wires for communications cables are already known in the art. For example, copper plated aluminum wires are used in certain communications cables in order to take advantage of the lower cost and/or weight of aluminum as compared to copper. The copper (or a copper alloy) is typically plated onto the aluminum wire core using a welding process whereby a molten copper coating is applied to an aluminum wire core that is likewise heated to a temperature at which the aluminum on the surface starts to melt so that the copper and aluminum coalesce. This method or similar methods may be used to weld the carbon nanotube containing metal sheet to partially or completely surround an outside surface of a metal wire core. Moreover, since both the metal wire core and the carbon nanotube containing metal sheet may use copper or a copper alloy as the base metal, a very strong weld may be achieved between the wire core and the metal sheet.
As shown in
The metal sheet 30 may comprise, for example, a thin metal tape that is formed of, for example, copper or a copper alloy. The metal sheet 30 may be bent into a circular shape so as to surround (or, alternatively, partially surround) the outer surface of the metal wire core 20. In such embodiments, the ends of the metal sheet 30 may be welded together to provide metal sheet 30 having an annular cross-section. As illustrated in the callout 32 of
The conductors according to embodiments of the present invention may be used in a variety of communications cables, specifically including coaxial cables.
As shown in
As noted above, in some embodiments (and particularly in embodiments that use larger gauge wires for the central conductor), the central conductor 52 may have a hollow central region. In such embodiments, the central conductor 52 may appear identical (except in diameter) to the outer conductor 58 depicted in
The conductors according to embodiments of the present invention may also be used in twisted pair communications cables such as the so-called “Ethernet” cables that are commonly used in local area networks and various other applications.
As shown in
While the present invention is described above with reference to drawings that illustrate preferred embodiments thereof, it will be appreciated that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Instead, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
In the drawings, the size of lines and elements may be exaggerated for clarity. It will also be understood that when an element is referred to as being “coupled” to another element, it can be coupled directly to the other element, or intervening elements may also be present. In contrast, when an element is referred to as being “directly coupled” to another element, there are no intervening elements present. Likewise, it will be understood that when an element is referred to as being “connected” or “attached” to another element, it can be directly connected or attached to the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly connected” or “directly attached” to another element, there are no intervening elements present.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
In the drawings and specification, there have been disclosed typical embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.
| Number | Date | Country | |
|---|---|---|---|
| 61476825 | Apr 2011 | US |
