Broad band electromagnetic wave absorbers designed with nano-metal films

In the thirties of the last century it was shown that nano-metal films have a frequency independent absorption in the far infrared regime and below. Moreover, the absorption A of these films is 0.5 and at the same time both reflection R and transmission T are 0.25, complying with the relation A + R + T = 1 at a sheet resistance Z(square) of 60 pi Omega. The latter property of nano-metal films was shown by Woltersdorff in 1934. Multiple reflections between such films allow the design of low reflecting large scale absorbers for the wave length range from far infrared to low frequency radio waves. Experimental data of the novel absorber device measured in the GHz frequency range are presented. The electrical nano-metal film properties are also useful for applications in IR-photonics and IR-communication systems. The article presents a brief review of the historical studies on free carrier electromagnetic wave absorption and on novel applications. (c) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim