GB1060830A - Improvements in materials with electromagnetic wave reflection properties - Google Patents

Abstract

1,060,830. Tuned absorbing means for radio waves. ELTO G.m.b.H. May 10, 1955 [May 10, 1954], No. 13578/55. Heading H4A. A layer for absorbing radio waves having a thickness which is an odd number of quarter wavelength is made of a material such that where 8E and #Á are the factors of dielectric and magnetic losses, A in the area, and Á and E are the permeability and dielectric constant. Preferably a lattice of regular form is provided on the surface exposed to radation to provide a three dimensional surface with rectangular square, or circular protrusions to reduce reflection from the front face. The layers of material may be provided with wire meshes, metal layers or foils applied by spraying or rolling, so that flexible layers of absorbing material are produced in the form of matting. A radar camouflage for 3 cm. waves may comprise three layers: (1) 80 gm. of material containing 65 gm. of an isocyanate compound dissolved in ethyl acetate and 16 gm. of a polyester mixture containing adipic acid, 1,2,4-butanetriol, and butyleneglycol; (2) 2448 gm. of a similar mixture containing in addition 680 gm. of barium sulphate and 68 gm. of carbon black; (3) 957 gm. of a mixture similar to the first layer and containing in addition 348 gm. of iron with an average grain size of 3 Á and 29 gm. of carbon black. Each layer must be dried before the application of the next layer to prevent intermingling. The quantities stated cover 1 square metre of area and give a coating 1À1 mm. thick, and the layer is effective against radiation from 2À3 to 3À5 cm. in wavelength.