| 摘要 |
An electric cable for conveying signals, the cable having a diameter of less than 2 mm and comprising at one conductor in an insulating sheath, the sheath having a dielectric constant epsilon of less than 1.7. To achieve this, the sheath is made of PTFE and it includes at least one continuous cell. Fabrication is preferably by performing the following operations: compressing a lubricant-impregnated PTFE powder in a converging chamber arranged in an extrusion die and around a guide for guiding said at least one conductor, the impregnated PTFE powder thus being thrust towards an extrusion orifice to form an extrudate; causing said extrudate to pass from said orifice along an extrusion passage inside the die, in which it is shaped around the conductor(s), and of inside section that corresponds to the outline desired for the sheath; passing said extrudate around at least one solid bar presenting, at least over a distance within the extrusion passage, the same section as said cell and thereby preventing the extrudate from occupying the section that is to be occupied by said cell, the cell(s) being formed from the downstream end surface(s) of the bar(s) and extending downstream therefrom; extracting the lubricant by evaporation; and sintering the resulting assembly so as to stabilize the material of the sheath.
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