The present invention provides a shielding that uses conductive particles in high concentrations to reduce or eliminate internal and external cable cross talk as well as other EMI/RF from sources outside of the cable. Combinations of conductive particles can be mixed or layered to “tune” the frequency bandwidth at which shielding is effective.
A conventional communication cable typically includes a number of insulated conductors that are twisted together in pairs and surrounded by an outer jacket. Crosstalk or interference often occurs because of electromagnetic coupling between the twisted pairs within the cable or other components in the cable, thereby degrading the cable's electrical performance. Also, as networks become more complex and have a need for higher bandwidth cabling, reduction of cable-to-cable crosstalk (alien crosstalk) becomes increasingly important.
Shielding layers are often used to reduce crosstalk. Conventional shielding layers for communication cables typically include a continuous solid conductive material that is wrapped around the cable's core of twisted wire pairs to isolate electromagnetic radiation from the core and also protect the core from outside interference. The conductive materials that can be used in this arrangement, however, are limited to those specific conductive foils that can be readily vacuum deposited onto flat substrates. Other shielding applications rely on materials that highly absorb and dissipate interference. Shielding formed of such materials, however, are not advantageous in high performance communication cables.
To achieve the higher performance needed for high speed applications, like 40 Gb/s Ethernet cabling, the performance attributes of return loss, insertion loss, internal and external crosstalk must be improved over the conventional 10 Gb/s cabling, and those performance characteristics need to be maintained across a much wider band width. Return loss is a function of the impedance of the individual cable pairs swept across the desired frequency range. The impedance is a function of the size of the conductors in the wire pair, the thickness of the insulation around the conductors in the wire pair, the dielectric constants of the insulations and the distance of the wire pair to the shield. Insertion loss is a measure of the signal attenuation along the cable. Thick foils (typically ranging from 0.0003 to 0.0030 inches in thickness) that are made from aluminum and copper are often employed in conventional cabling to abate return loss and insertion loss. Although thicker foils within the cabling may provide sufficient isolation to control crosstalk, such conventional foils tend to be rigid. Also, during processing, the conventional foils tend to crinkle and crease which changes the impedance along the cable and thus adversely affects return loss. Uniform shielding through the length of the cable enables a more controllable and predictable return loss and impedance. That is because return loss is a measured loss of signal reflected back from the cable due to impedance mis-matching of the device and cable. Also, shield deformation in processing and installation reduces overall return loss performance across the frequency range.
While the conventional shielding materials may reduce the internal cable crosstalk and other EMI from sources outside the pair, such materials do not typically improve return loss, particularly in high speed applications. Moreover, conventional shielding materials have limited application, that is the materials are limited to being applied to only a polymer layer, such as a polyester-backing layer. Therefore, a need exists for a shielding that can be applied to any layer or substrate material while also improving flame and smoke performance even in high performance applications.
Accordingly, the present invention provides a shielding for a cable component that comprises a non-conductive base material and a plurality of conductive particles suspended in the base material. The conductive particles may be at least one of substantially the same size, the same shape, the same conductive material, different sizes, different shapes, or different conductive materials, such that selection of the conductive particles tunes the frequency bandwidth for effective shielding.
The present invention also provides a shielding for a cable component that comprises a non-conductive base substrate and a plurality of conductive particles disposed on an outer surface of the base substrate. The conductive particles may be at least one of substantially the same size, the same shape, the same conductive material, different sizes, different shapes, or different conductive materials, such that selection of the conductive particles tunes the frequency bandwidth for effective shielding.
The present invention also provides a cable that comprises a plurality of twisted insulated wire pairs and a shielding surrounding at least one of said wire pairs. The shielding includes a base material that is being non-conductive. A plurality of conductive particles may be suspended in the base material. The conductive particles are at least one of substantially the same size, substantially the same shape, the same conductive material, different sizes, different shapes, or different conductive materials, such that selection of the conductive particles tunes the frequency bandwidth for effective shielding.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
Referring to
This tuning can be done because different particles, such as copper, aluminum, zinc, nickel and silver, have varying permeability constants at specific frequencies. In addition, these permeability constants vary differently across various frequency ranges or bandwidth. Particle concentration may also contribute to tuning of the frequency bandwidth by varying the mixture proportions as well as the density of particles through which an electromagnetic wave must propagate. The particles preferably make up about 60%-99% of the shielding. Mixing particles for tuning may refer to more than one type of particle, based on elemental type, size or shape, combined together in a well dispersed manner and in which each type of particle maintains its inherent characteristics on a local or micro scale; however, exhibit inherent characteristics from all of the combined particles on a general scale. Local conductivity refers to conductivity of a small scale region on the order of particle sizes used (e.g. measured in ohm/mm or ohm/mil); whereas, general conductivity refers to conductivity of an area larger than the local conductivity, typically measured in ohm/m or ohm/ft on the maximum allowable installed length of cable per the industry standard requirements. By reducing local conductivity, the localized shielding area becomes more resistive and absorbs more of the interfering energy from outside the shielding layer therefore improving the overall shielding. However, increasing general conductivity of the shielding layer decreases the longitudinal impedance of the shielding layer and causes the signal traveling along the pair or other signal carrying element surrounded by the shielding layer to be less attenuated at higher frequencies, typically greater than 500 MHz.
Alternatively, mixing for tuning may refer to more than one type of particle, based on elemental type, size or shape; combined in distinct regions of like particles in which each type of particle maintains its inherent characteristics on a local scale. This means that the particles are not elementally changed when they are present in the mixture. Every particle type, size, shape and concentration has a specific frequency bandwidth at which it effectively shields to a varying degree across this bandwidth. Thus by increasing the concentration of a specific particle in the shielding, the shielding effectiveness can be increased until a limiting concentration is reached. In addition, multiple layers of each specific mixture could be used to increase shielding.
In another example, using smaller particles for tuning allows tighter particle packing, in other words less empty space between particles. This can have the effect of increasing local conductivity. Whereas if high aspect ratio particles are used, general conductivity could increase. Local conductivity is dependent on the coverage area of the particles that exhibit metal like characteristics. Particle size and shape effect local conductivity as smaller particles are able to pack closer together and form a continuous sheet. Particles with a characteristic dimension less than 50 microns are generally considered in this group; however it is highly dependent on the application method if they are able to be placed in close contact. General conductivity is dependent on particle-to-particle contact as larger or high aspect ratio particles are more likely to touch and overlap, but tend to leave larger gaps between the particles. For example, if long rod shaped particles were laid out, there is likely to be conductivity down the length of the shield showing general conductivity; however, if conductivity was measured at a random spot on a small scale, there is a chance that no particles will be touched and exhibit zero local conductivity. This leads to gaps in the shield which would allow the ingress and egress of electromagnetic interference. It would also allow the use of different sized materials to independently adjust or tune the effects that the shield would have on a cable's length-dependant electrical characteristics, such as insertion loss from its cross-sectional-dependant electrical characteristics, such return loss, impedance, near end crosstalk as seen in
By using conductive particles according to the exemplary embodiments of the invention, that are suspended in non-conductive inks or adhesives, for example, the shielding of the present invention may be applied to any substrate or layer material while improving flame and smoke performance over the traditional polyester backing. The shielding of the present invention also has minimal impact on data cable electrical characteristics while still providing adequate shielding.
The shielding of the exemplary embodiments of the present invention may be applied to cable components, such as wire pairs 1000 (
The amount of particles used can also be decreased if sintering (heating) is used to either increase percent of shielded area or decrease the volume resistivity of the bulk particles once applied. Particle sintering effectively amalgamates the individual particles into a continuous grouping by starting to melt the particles together. By making the particles more continuous, the overall resistance of the particles can be reduced as the shortest path between two particles is reduced. Particle concentration could also remain high and sintering techniques could be applied to even further increase shielding effectiveness. Another way of achieving the same effect is to apply the conductive particles with a thermal application. In this type of system, the conductive particles are heated and applied to the substrate, effectively already semi-sintered together.
While particular embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims. For example, the conductive particles of the above exemplary embodiments may have any cross-sectional shape, and are not limited to the shapes described herein. Moreover, the shielding of the exemplary embodiments may be applied to any component of a cable.
This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. Nos. 61/389,984 and 61/393,631, filed on Oct. 5, 2010 and Oct. 15, 2011, respectively, and both entitled Shielding For Communication Cables Using Conductive Particles, the subject matter of each of which is herein incorporated by reference.
Number | Date | Country | |
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61393631 | Oct 2010 | US | |
61389984 | Oct 2010 | US |