GB750692A - Improvements in or relating to electrical conductors - Google Patents

Abstract

750,692. Waveguides. WESTERN ELECTRIC CO., Inc. June 27, 1952 [June 29, 1951; June 29, 1951; June 29, 1951; June 29, 1951; June 29, 1951; June 29, 1951], No. 16231/52. Class 40 (8). [Also in Group XXXVI] A waveguide or artificial line for use at frequencies up to and including the megacycle range comprises one or more stacks or assemblies of elongated conducting members insulated from each other and having a thickness which is less than the skin depth of a solid conductor of the same material, the insulating material or the conductors or both being of magnetic material. The skin depth # is given by where f is the frequency in cycles/sec., Á is the permeability of the conductor in henries/metre and # is its conductivity in mhos/metre. The cable of Figs. 1 and 2 comprises an outer shield 19, a central core 11 of either metal or dielectric, an inner conductor 12 formed of a large number of layers 13 of magnetic conducting material spaced by laminations 14 of magnetic insulating material, e.g. a ferrite, and an outer conductor 15 constructed in the same manner as the inner conductor. The space between the conductors is filled with an insulator 18 which may be either magnetic or non-magnetic. The dielectric constant # 1 farads per metre and the permeability Á 1 henries per metre of the insulating material 18 are chosen to satisfy the relation where t is the thickness of the magnetic insulating laminµ in meters, # 2 is their dielectric constant and Á 2 their permeability; h is the thickness of the magnetic conducting laminµ and Á their permeability. It is shown in the Specification that an optimum value of h/t may be chosen such that, with appropriate choice of insulator 18 in accordance with the above equation, the electromagnetic wave is propagated at a certain velocity appropriate to the average dielectric constant multiplied by the average permeability of the composite conductors and that under these conditions deep penetration of the currents into the composite conductors is obtained. A value h/t = 2 is preferred. The effect of the magnetic material is to increase the total magnetic flux and decrease the current density, thus increasing the impedance and decreasing the attenuation of the line. If the space between the conductors is completely filled with laminµ (instead of the insulator 18) the conditions set forth above are fulfilled. Figs. 3 and 4 (not shown) illustrate a transmission line constructed in accordance with this principle. The conducting laminµ may be replaced by filaments 33, Fig. 5, whose diameter is comparable with the thickness of the laminae. They are embedded within a magnetic insulating material 34 and surrounded by a shield 31. In any of the above constructions either the conducting or the insulating layers or filaments, but not both, may be formed of a non-magnetic material. In a modification (Figs. 8-11, not shown) the conductors are formed of laminations of conducting material spaced by laminations of magnetic material, which need not be a good conductor, and laminations of insulating material. The insulating and magnetic layers are preferably of equal thickness and half the thickness of the conducting layer. The same principle may be applied to the line of Fig. 5, some of the conducting filaments 33 being replaced by filaments of magnetic material which need not be a conductor. In a further embodiment, Fig. 16, the dielectric member 218 between the inner and outer conductors 212, 215 is made of foamed plastic and has embedded in it one or more ferro magnetic members 220 in the form of longitudinal tapes. A single tape with a longitudinal seam may be used or a number of tapes may be disposed spirally within the dielectric. The magnetic member may take the form of a cylinder of ferrite. In a further modification (Fig. 19a, not shown) two layers of magnetic tape separated by dielectric are used. The tapes are situated in a neutral plane, i.e. a region where Ez is zero, and are thin compared with the skin depth # defined above. Instead of using magnetic tapes the same result may be achieved by mixing ferrite powder with the foamed resin of the dielectric member 218. The coaxial cable of Fig. 24 comprises an inner conductor 311, which may be either solid or tubular, an outer conductor 312 and a stack 313 of alternate thin laminations of magnetic and insulating material. The stack 313 may be held in position by dielectric spacers 316 or by a solid layer of foamed resin. The outer conductor 312 is surrounded by ferromagnetic and copper cylinders 317, 318. The stack 313 may be situated in a neutral plane, e.g. in a position where Ez is zero. The laminated constructions of the invention may also be used to form the walls of waveguides. Specifications 715,359 and 750 693, [Group XXXVI], are referred to.