Low Reflection Absorbers for Electromagnetic Waves (Reflexionsarme Absorber Fuer Elektromagnetische Wellen).

摘要

Low reflecting absorbers for electromagnetic waves in the range of m- and cm- wavelengths are used in research - for example, for coating the walls of test rooms and in radar technique. The major aspect of the development of absorbers is the elimination of reflections which under vertical incidence of waves on plane surfaces occur at almost all dissipative materials. This reduction of reflections may be attained in different ways: by a continual transition from free space into the absorbing material, by using resonance arrangements, or with the help of certain absorbing substances with uniform, spatial distribution. Wedge-, pyramid-, and rib-absorbers; foil-, layer-, dipole-, slit-, and loop-absorbers; absorbers with low density material and epsilon = micron-absorbers: These various absorbers resulting from the three basic principles of reduction of reflections are treated with respect to the dependence of their reflection coefficients on frequency, angle of incidence, and direction of polarization and finally the thickness of the arrangement. Numerous theoretical and experimental data indicate the most favorable design and the range of application of the individual absorbers. In addition to the statements put forward for absorbers for electromagnetic waves short remarks are made concerning the corresponding absorbers for air - or water-borne sound, which are physically closely related to the electromagnetic absorbers and have in part been prototypes for the latter. Finally test methods for low reflection absorbers (measurement in the free field and in the echo chamber) and their application in electromagnetically oanechoic rooms are discussed.