Patent GB-715359-A (GB)
Title: Improvements in or relating to electrical conductors
IPC: H01B3/08
Filed: 1952-02-29
Abstract: 715,359. Transmission lines. WESTERN ELECTRIC CO., Inc. Feb. 29, 1952 [March 7, 1951], No. 5363/52. Class 40 (8). [Also in Groups XXXVI and XL(c)] Losses due to skin effect are reduced at frequencies within the megacycle range by utilizing a conductor consisting of an assembly of spaced elongated conductive elements insulated from each other and extending parallel to the direction of flow of current, the elements having a transverse dimension which is small compared to the "skin-depth" of a corresponding solid conductor. The skin depth is the distance at which the current or field penetrating into a solid conductor decreases by one neper, i.e. is reduced by a factor <SP>1</SP>/ e  =.3679.... The invention may be applied to co-axial cables, wave-guides, antennae, coils, parallel cables or to single composite conductors. Fig. 7b shows the invention applied to a co-axial line, the inner and outer conductors of which are made up of alternate laminations of metal 66 and dielectric material 67 separated by a body of dielectric material 63 whose dielectric constant is made equal to # 1  (1+w/t) where # 1  is the dielectric constant of the material 67 and W and t are respectively the thicknesses of the metal layers 66 and dielectric layers 67. Under these conditions the electromagnetic wave propagates in the conductor at a certain critical velocity at which penetration into the conductor is much greater than the penetration into a solid conductor of the same dimensions. In other words, the skin-depth is effectively increased. The core 64 of the inner conductor may be of either metal or dielectric and the outer conductor may be surrounded by a metallic sheath 65. Modifications are described in which the outer or the inner conductor comprises a conventional solid conductor, the other conductor being of the laminated construction of the invention. In a further modification the dielectric 63 is replaced by an air-space or is composed of laminae according to the invention. Fig. 10 shows a waveguide in which two opposite walls 81, 82 are of laminated construction, the other walls 85, 86 being of conductive material. Instead of being in the form of laminae the conductive elements may be in the form of filaments having a diameter which is small compared with the skin depth. In the two-conductor line of Fig. 12 the filaments 101 are embedded in a body of dielectric 103 which may be surrounded by a conductive sheath. The filamented conductor 131 of Fig. 15 is in the form of a coil embedded in a body of dielectric 132. The co-axial lines of the invention may be joined to a conventional dielectric-filled co-axial line 201 in the manner shown in Fig. 23. Where the inner member 64 is of dielectric material, the inner conductor 202 of the line 201 is flared out at its end to make contact with the conductive laminae 66. Where the laminae 66, 67 occupy the whole space between the inner member 64 and the outer sheath 65, the dielectric constant of the material 203 is made equal to the average dielectric constant of the laminated conductor. Specification 616,109, [Group XXXVI], is referred to.