use of a surface temperature bestaendigen titanium containing zirconium, aluminum, niobium and tantalum for hitzebeanspruchte gegenstaende and procedures for verguetung alloy

摘要

879,489. Radio wave absorbers. McMILLAN, E. B. May 12, 1959 [June 24, 1958], No. 16267/59. Class 40(7) A radio wave absorber comprises alternate layers of solid dielectric 32, 34 and lossy material 33 backed by a reflecting layer 31, e.g. the wall of a test chamber, and having a dielectric layer at the surface on which the waves impinge, the dielectric layers being of equal electrical thickness. The dielectric constants of the different dielectric layers are preferably equal and in this case the dielectric layers are of equal physical thickness. The dielectric layers may be formed of honeycomb or foamed material such as expanded polystrene or polyurethane and the dielectric constant can be controlled by the deposition of metallic particles within the cells. The lossy layers may comprise thin sheets of paper or cloth impregnated with a semiconductor such as carbon, e.g. "Aquadag" (Registered Trade Mark). An absorber comprising a single lossy layer such as shown in Fig. 3 may be formed by painting a graphite layer on the back of a first sheet of dielectric foam, glueing a second sheet of dielectric foam to the back of the graphite layer and painting one exposed surface of the dielectric sheets with aluminium paint. For an absorber comprising f lossy layers and #+1 dielectric layers it is shown mathematically that the thickness d and dielectric constant # of the dielectric layers and the surface conductivity Y S of the lossy layers can be selected so that the reflection co-efficient 1r1, Fig. 4A, is zero at #+1 resonance frequencies and that by making the values of the dielectric constants sufficiently small the value of 1r1 between the resonance frequencies may be so reduced as to produce satisfactory absorption over a wide frequency band. When the dielectric layers are of equal thickness and dielectric constant, the surface conductivity Y S of the lossy layers increases in the direction from the front of the absorber towards the reflecting layer, Fig. 8 (not shown), the overall thickness of the absorber increases with the number of layers but approaches a limit of half the wavelength of the longest wavelength to be absorbed, Fig. 9B (not shown), and the dielectric constant # decreases with the number of layers, Fig. 9A (not shown). In the examples considered it is assumed that the dielectrics are loss free but it is stated that some electrical loss may be included in the dielectric material.