Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
1997-09-09
2001-01-30
Kincaid, Kristine (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C174S028000
Reexamination Certificate
active
06180877
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a conductor protected against electromagnetic interference.
2. Description of the Prior Art
Conductors or cables for transmission of electrical power or electrical signals can carry electromagnetic interference that can damage the equipment (transmitter and/or receiver) to which the cable or conductor is connected.
The interference can be of many different kinds with varying frequencies and amplitudes.
The most meaningful example is lightning which consists in electrical energy of great amplitude and extending over a wide frequency spectrum. Also, the intensification of telecommunications is increasing stray electromagnetic fields. These fields are produced by various sources such as radio and television transmitters, telephone communications or radar transmissions. The interference can also originate from the electrical power distribution network. It may also be in the form of intentional jamming.
Whatever the source of the pollution, the stray fields are often detected by the cables acting as receive antennas.
Various types of protection have routinely been used until now to combat such interference. An outer conductor forming a Faraday cage is commonly employed to protect cables against external radiated interference. Apparatus and equipment is protected against interference carried by a cable or a conductor by means of a filter at the input of the apparatus or equipment, the filter incorporating inductors, capacitors and diodes. The most frequently employed form of lightning protection is a lightning arrester or surge arrester, or a varistor shunting the conductor to be protected. A varistor is a component having an electrical resistance which is greatly reduced if the electric field exceeds a particular threshold; in this case, the interference is shunted to ground.
A cable having a dielectric material with a non-linear characteristic or a threshold characteristic between the core and the outer conductor has also been proposed.
All these protection means or devices are relatively complex, bulky and costly. Moreover, the threshold of the non-linear materials that can be used is generally too high to protect electronic equipment.
The invention remedies these drawbacks.
SUMMARY OF THE INVENTION
The invention consists in a device for transmitting electrical energy or electrical signals comprising a core, an outer conductor and a threshold characteristic dielectric material between said core and said outer conductor, wherein said dielectric material comprises, at least in part, a material that is insulative if the electric field is below a particular threshold and conductive when the electric field exceeds this threshold, so as to prevent the transmission of signals for which the electric field is above said threshold, and the configuration of said core and/or of said outer conductor is such that the external electric field threshold from which said material becomes conductive is significantly less than the intrinsic triggering threshold of said material.
The “spike effect”, i.e. the local increase in the electric field in the vicinity of a conductive surface having a small radius of curvature, is preferably used to achieve this result. The factor by which the breakdown threshold is divided is between 10 and 100, for example.
This greatly facilitates the choice of the threshold characteristic material.
In one example of use of the spike effect mentioned above, the core and/or the outer conductor have corrugations with a small radius of curvature. In other words, in cross-section on a plane passing through its axis, the core has ribs. It is the radius of curvature of each corrugation that determines the factor by which the threshold is divided. If two corrugations join at an edge, the latter can contribute to the spike effect, despite its greater distance from the outer conductor. As an alternative, the core has spiral edges, like a screwthread.
In another example, the core has a polygonal cross-section. The vertices of the polygon are the edges that generate the spike effect.
In this latter embodiment, it is preferable to provide a plurality of successive sections in the longitudinal direction that are identical to each other but offset by a particular angle about the longitudinal axis, so as to homogenize the distribution of the “spikes”, i.e. the places where the electric field is locally increased. For example, if the cross-section is a polygon with n sides, each of which subtends an angle steel at the center of 360°
, the angular offset between two prismatic (or polygonal cross-section cylindrical) sections will advantageously be equal to 360°/2n.
The threshold characteristic material is disposed between the core and the conductor either alone or in combination with at least one other dielectric material.
The conductor constitutes, for example, a connector between a conventional cable and equipment for receiving and/or transmitting signals transmitted by the cable.
In another application, the threshold characteristic material constitutes at least one separator member between the core and the outer conductor of a cable for transmitting power or electrical signals.
The threshold characteristic material is preferably an organic material such as a conductive polymer or a zwitterion. By “conductive” polymer is meant a polymer which, whilst being insulative under normal conditions, nevertheless has a conductivity higher than that of a conventional insulator. For example, a conventional insulator such as polyethylene has a conductivity of 10
−15
S/cm whereas a conductive polymer such as polyaniline has a conductivity of 10
−10
S/cm.
Other features and advantages of the invention will emerge from the description of some embodiments of the invention given with reference to the accompanying drawings.
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E. Costamagna et al, “Characteristic Impedances of Coaxial Structures of Various Cross Section by Conformal Mapping”,IEEE Transactions on Microwave Theory and Techniques, vol. 39, No. 6 Jun. 1, 1991 pp. 1040-1043.
8099 IEEE Transactions on Microwave Theory and Techniques, Jun. 1991, pp. 1-4.
Braut Jean-Louis
Cottevieille Denis
Lamesch St{acute over (e)}phane
Le Mehaute Alain
Kincaid Kristine
Mayo III William H.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Thomson-CSF Communications
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