GB757490A - Improvements in or relating to electric cables and wave-guides - Google Patents

Abstract

757,490. Waveguides. HYDE, G. A. M. March 2, 1954 [March 14, 1953], No. 7102/53. Class 40 (8). A composite electrical medium for the propagation of electromagnetic waves consists of conducting and dielectric elements arranged to be anisotropic in conductivity so that the medium has a greater conductivity along its length than in a direction perpendicular to its length the electrical constants of the constituents being so chosen that the permeance of the medium is substantially equal to the quotient of its permittence in the direction of its length divided by the square of the conductance in the direction of its length. The permeance and permittance are the so-called permeability and permittivity of the M.K.S. system and are referred to one meter cube of material. The Specification contains a detailed mathematical analysis of the invention and figures are given for the attenuation of a typical cable of which the dimensions and relevant electrical constants are given. The composite anisotropic medium may be placed within a medium having the same impedance and velocity of propagation as the anisotropic medium. The cable may consist of a central dielectric core 4 of e.g. polythene upon which is evaporated a film 3 of bismuth of about 100 Angstroms thickness. A suitable conducting coating may also be obtained by spraying or dipping with a paint mixture containing colloidal graphite, although such a coating will be much thicker than 100 Angstroms. In order to fulfil the necessary criteria as regards permeance and permittance the conductive layer is arranged to have a resistance of <SP>30</SP>/ #2À3 ohms per every a/2 cms. of its length where a is the radius of the core 4 and 2.3 is taken as the dielectric constant of polythene. The conductive layer is surrounded by a layer 2 of material having the same dielectric constant as the core 4 the layer having an outer radius b such that 2 loge b/a = 1. The outer layer 2 is surrounded by a sheath 1 of conductive material. The Specification also gives the relative dimensions of a waveguide according to the invention having several similar conductive layers separated by layers of dielectric of much greater thickness. It is shown also that the same results can be achieved with conductive layers which are of substantial thickness compared to the dielectric layers and an example, with relative dimensions, of such a cable is given in the Specification. Specification 715,359 is referred to.